Pyrometallurgical options for recycling spent lithium-ion batteries A comprehensive review.pdf

Journal of Power Sources 491 (2021) 229622
Available online 14 February 2021
0378-7753/© 2021 Elsevier B.V. All rights reserved.
Pyrometallurgical options for recycling spent lithium-ion batteries: A
comprehensive review
Brian Makuza a,b
, Qinghua Tian a,b
, Xueyi Guo a,b
, Kinnor Chattopadhyay c
, Dawei Yu a,b,*
a
School of Metallurgy and Environment, Central South University, Changsha 410083, China
b
National and Regional Joint Engineering Research Center of Nonferrous Metal Resource Recycling, Changsha 410083, China
c
Department of Materials Science and Engineering, Faculty of Applied Science and Engineering, University of Toronto, Toronto, Ontario, M5S 3E4, Canada
H I G H L I G H T S G R A P H I C A L A B S T R A C T
• Current status on pyrometallurgical
recycling of Li-ion batteries is presented.
• The industrial pyrometallurgical recy
cling processes are reviewed.
• The influence of legislation on recycling
is summarized.
• This review provides a rundown of lim
itations that will help to do further
research.
A R T I C L E I N F O
Keywords:
Spent LIB
Pyrometallurgy
Thermal treatment
Industrial recycling
Legislation
A B S T R A C T
Lithium-ion batteries (LIBs) have attracted increasing attention for electrical energy storage applications in
recent years due to their excellent electrochemical performance. The unprecedented growth trajectory in lithium-
ion battery manufacturing perpetuated by the inception of electric vehicles (EV) results in a vast amount of spent
LIBs reaching their end of life (EOL). From the perspective of resource circulation, procurement, and sustain
ability with an insight into the circular economy, an effective recycling system must be developed to recycle the
spent LIBs. This paper provides a comprehensive overview of the current status of pyrometallurgical options for
recycling spent LIBs. In particular, this study summarizes the thermal pretreatment methods used to recover the
active cathode material and then discusses the developed extractive pyrometallurgical options for recycling spent
LIBs. A summary is presented on some recent examples of laboratory and industrial-scale recycling processes to
demonstrate the practical applications of pyrometallurgical options for recycling. Finally, the review sheds light
on the battery recycling legislation, and challenges and future outlook for recycling LIBs are also discussed.
1. Introduction
The lithium-ion battery (LIB) is the leapfrog technology for powering
portable electrical devices and robust utilities such as drivetrains. LIB is
one of the most prominent success stories of modern battery electro
chemistry in the last two decades since its advent by Sony in 1990 [1–3].
LIBs offer some of the best options for electrical energy storage for
high-energy and high-power applications such as transportation and
* Corresponding author. School of Metallurgy and Environment, Central South University, Changsha 410083, China.
E-mail address: dawei.yu@csu.edu.cn (D. Yu).
Contents lists available at ScienceDirect
Journal of Power Sources
journal homepage: www.elsevier.com/locate/jpowsour
https://doi.org/10.1016/j.jpowsour.2021.229622
Received 23 November 2020; Received in revised form 11 January 2021; Accepted 4 February 2021

2
stationary storage, as illustrated in Fig. 1, because of its high electro
chemical performance, which translates to high volumetric energy
density, high operating cell voltage, and high theoretical capacity [2,
4–6].
The ongoing transition towards a new energy system has caused an
ever-growing demand for LIBs. From statistics released by the European
Union (EU) [9], the growth in electric vehicles is to be around 50–200
million in 2028 from 4 million in 2018. Electric vehicle manufacturing is
expected to reach 900 million electric cars by 2048 [9]. This unprece
dented growth results in a vast amount of spent LIBs being discarded off.
The LIB cell has a short life span of just around 1–3 years [10] because of
technical drawbacks relating to cycling, elevated temperature, and rate
performance [11], which exacerbates the massive generation of spent
LIBs. Forecast depicts that about 11 million metric tonnes of spent LIBs
are to be discarded by 2030 [12,13]. The recycling rate in the European
Union is staggering, and only a meager 5% was recycled in 2010 [14,
15], considering this projected demand surge in battery consumption.
LIB recycling has been a global research hotspot since its advent because
of the complex nature of battery chemistry [16], and it is always
changing in a bid to reconfigure battery storage sustainability [17,18].
Lithium and cobalt mining has been associated historically with
different forms of institutional risk, such as political risks, security risks,
conflicting land use, uncertain mineral rights, unethical mining prac
tices, scanty supply, and uneven distribution over the earth’s crust.
These factors create instability in the supply and prices of these metals
[19]. The concentration of the valuable metals from spent LIBs is also
much higher than that from primary natural ores [19,20], and the sep
aration is much easier to attain than that from the primary resource
[21]. Moreover, cathode resynthesis from metallurgical recycling is less
energy-intensive [22] and is associated with emission reductions [23]
compared to cathode synthesis from virgin materials. Optimizing
resource recovery of these metals for reuse by improving LIB recycling
helps make these metals remain a viable source over the long run and
lower the overall cost of battery storage [24,25]. Apart from recycling
valuable metals back into circulation to resolve the sustainability gap,
LIBs contain a significant amount of toxic chemicals [26]. The envi
ronmental impacts arising from spent LIBs include global warming,
ecotoxicity, resource depletion, and human health impacts. When dis
charged, these chemicals percolate into the ground leading to ecotox
icity and water pollution in the ecosystems. Thus the LIBs cannot be
disposed of anyhow and require a proper waste disposal system. Burning
was a previous option to dispose of batteries, but it releases harmful
gases [27]. Similarly, when the battery cell vents, the gases released
react with the atmosphere, producing a flammable mixture, and the
electrolyte can react with water releasing harmful gases like hydrogen
fluoride (HF) [17]. Continuous development in the recycling of LIBs is
indispensable to guarantee environmental protection.
Pyrometallurgy, hydrometallurgy, or a combination of the processes
is widely adopted to recycle spent LIBs [28,29]. Hydrometallurgy en
compasses pretreatment to recover the cathode materials followed by
leaching and subsequent purification and recovery techniques such as
selective precipitation, ion exchange, and solvent extraction to extract
the valuable metals [15]. Some hydrometallurgical processes have
drawbacks of relatively long leaching time and low leaching efficiency
due to the high valence state of the active cathode material and a strong
binding force of the organic binders [11]. Moreover, the vast con
sumption of concentrated acid and reductants [15,27,30] and the mul
tiple process steps generate significant effluent [28,29], which can
exacerbate secondary pollution from the discharge of acidic wastewater
and gas during the leaching processes. Li is also dispersed amongst these
separation and refining stages, leading to low lithium recovery [17,30,
31]. Alternatively, pyrometallurgical treatments can be used to extract
and purify metals [17]. The pyrometallurgical recycling options possess
the advantages of a high rate of chemical reactions, allowing large
treatment capacity [32,33], being relatively flexible in the feed material,
simple operation, and the dross has negligible environmental impacts
[27]. Moreover, pyrometallurgical recycling is a relatively mature and
dominant recycling process [34]. Continuous research and development
Fig. 1. Emerging applications demanding lithium-ion batteries, such as the aerospace industry, power transmission, consumer electronics, hybrid electric vehicles, as
well as renewable energy industry [7,8]; Copyright 2020, reproduced with permission from Elsevier.
B. Makuza et al.

3
are still required to enable more efficient extraction and separation of
valuable metals from the spent LIBs. Thus, pyrometallurgical recycling is
focused for review in this paper.
Depending on the pyrometallurgical options chosen for recycling,
the battery material can undergo pretreatment to recover the active
cathode material for further recycling or be fed directly into the furnace
as in the smelting process. The thermal pretreatment methods for
recovering the active cathode material are incineration, calcination, and
pyrolysis, and the enriched metal fraction is processed using roasting or
smelting processes. Toxic gas emissions from pyrometallurgical pro
cesses used to be a technical hurdle. However, continuous advancements
in pyrometallurgy have resulted in integrated off-gas treatment mech
anisms such as the one incorporated by Umicore that result in no volatile
organic fraction, complete dust removal, and low volume of gas evolu
tion [35]. With the advent of recent developments in pyrometallurgical
recycling, it has been possible to recover the high-value metals from
spent LIBs in an environmentally benign manner and with high recovery
rates [11]. These pyrometallurgical recycling techniques have gained
extensive applications at the industrial scale, e.g.,
Ultra-high-temperature smelting-technology (UHT) of Umicore.,
Belgium [32], Roasting− smelting process of Glencore (Xstrata).,
Switzerland [32], High temperature melting recovery (HTMR) process
of Inmetco., USA, Calcination process of Sony-Sumitomo., Japan [15],
and Accurec., Germany [18].
Various types of review work have been conducted in the field of
lithium-ion battery recycling; however, most of these review articles
have been restricted to the advances in hydrometallurgical recycling
options despite pyrometallurgical recycling being a dominant and
mature process. A standalone review on pyrometallurgical recycling has
been done by Assefi et al. [16], and the review encompasses brief de
scriptions on Li-ion, Ni–Cd, and Ni–MH recycling. Moreover, some
important reviews have been published by Lv et al. [17], Zheng et al.
[27], Zhang et al. [36], and Liu et al. [37], although few attempts have
been made to critically assess pyrometallurgical recycling options. To
the best of our knowledge, the documented reviews gave a broad
overview of the smelting process, and the other pyrometallurgical
recycling options (pyrolysis, incineration, calcination, roasting, micro
wave reduction, etc.) were not explained.
Therefore, an in-depth review of existing pyrometallurgical options
for recycling spent lithium-ion batteries is essentially necessitated in
order to create a common framework of knowledge in this emerging
research area. Herein we provide a synthesis of the most recent
advanced available pyrometallurgical options for recycling lithium-ion
batteries and new insights for the guidance and concept for the char
acterization (incineration, pyrolysis, calcination, roasting, smelting,
etc.) of pyrometallurgical LIB recycling options not previously presented
in the literature that collectively add to our comprehension. Moreover,
the advancements, limitations, advantages, and potential for scaling up
to the industrial scale of these processes are also described. Section 2
describes the structure of the lithium-ion battery as it affects the recy
cling mechanism. Section 3 summarizes and compares the currently
developed pyrometallurgical recycling options, including the thermal
pretreatment methods used to recover the enriched metal fraction for
recycling and the extractive pyrometallurgical options. Section 4 re
views the mechanisms available for refining pyrometallurgical products
for the recovery of pure materials. Section 5 discusses the pyrometal
lurgical recycling processes at an industrial scale and gives a rundown of
the legislation governing battery recycling. The final section outlines the
challenges of the current pyrometallurgical recycling technologies, and
the prospects for future research and development are also put forward.
2. Construction of Li-ion battery
2.1. History of Li-ion battery
LIB is one of the most prominent success stories of modern battery
electrochemistry in the last two decades since its advent by Sony in 1990
[1–3]. The Li metal element was initially discovered by Arfwedson [36]
in 1817 in the Swedish mine petalite ore (LiAlSi4O10) [37]. The metal
was named lithium after Arfwedson along with Berzelius [38] gave the
alkaline material the name “lithion/lithina,” from the Greek word λιθoς
(transliterated as lithos, signifying “stone”) [36]. Willian T. Brande
achieved Li metal isolation from its salts in 1821 by electrolysis of
lithium oxide, a process used by the chemist Sir Humphry Davy to isolate
the alkali metals potassium and sodium [37]. The electrochemical
properties of Li were investigated by Gilbert N. Lewis a year afterward,
and it was immediately realized that Li could serve well as a battery
cathode [37]. Excellent electrochemical properties of Li such as low
atomic number (3), least density (0.53 g/cm3), high specific capacity
(3860 mAh/g), and very low standard reduction potential (Li+/Li
couple − 3.05 V vs. SHE) made the metal suitable for high density and
high voltage battery cells. William S. Harris conducted studies on
non-aqueous electrolytes in 1958 since water and air had to be avoided
when using Li because of its reactive nature [39]. During this study, the
formation of a passivation layer capable of preventing a direct chemical
reaction between the electrolyte and Li while still allowing for ionic
transport across it was observed [37,39]. This observation led to the
exploration of the stability of LIBs and the surge of interest in the
commercialization of primary LIBs. Continuous R & D about the inter
calation of Li metal in various materials gave birth to rechargeable
secondary LIBs [37].
2.2. Structure of Li-ion battery
Five principal components makeup a LIB cell, and these components
are all recyclable and have the possibility for reuse [12]. The compo
nents consist of an anode, cathode, electrolyte, separator, and current
collector, as illustrated in Fig. 2 [18,19,23]. Most lithium-ion batteries
share standard components in terms of electrolyte, separators, and
casing, and what differentiates them is the type of lithiated metal oxide
used for the cathode [40].
The cathode (+) is an aluminum metallic conductive foil covered
with an electrochemically intercalated active material [2,24]. The anode
(− ) comprises a copper foil coated with graphite. The choice of carbon
for anode material is due to its abundant availability, low cost, high
coulombic efficiency, and long cycle life [10,42]. The electrolyte is
present to make the battery conductive by promoting the movement of
ions from the cathode to the anode when charging and in reverse when
discharging [43]. Electrolyte for LIB can be in the form of polymer
electrolyte [44], colloidal electrolyte [45], liquid electrolyte, and
ceramic electrolyte [46]. Excellent choice of electrolyte is imperative as
it is correlated with the cycle efficiency, operating temperature range,
specific capacity, and safety concerns [47]. The separator partitions the
anode and cathode and blocks the electrons from traveling freely in the
cell.
Moreover, the separator acts as a fuse in a LIB and prevents a short
circuit between the anode and cathode. The convectional separator is
typically made from polypropylene (PP) or polyethylene (PE). The
current collector material for the anode and cathode is different. The
choice for copper for the anode current collector is because it is one of
the few metals that do not intercalate Li at low voltages. The current
collectors are linked to the electrode by an adhesive polymeric binder,
and polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE) is
the material typically used for the binder [24,42]. The binder material
should have good mechanical and chemical strength to bind the cells
effectively [17].
3. Pyrometallurgical recycling options
Pyrometallurgy uses elevated temperatures to recover valuable
metals [42,47] and purify them through physical and chemical trans
formations [17,48]. At lower temperatures, the reactions involve phase
B. Makuza et al.

4
transitions and structural changes, while at higher temperatures,
chemical reactions are involved to a greater extent [49]. The energy
required to carry out the process is provided by the exothermic reaction
of the material, combustion, and or electrical energy. Pyrometallurgical
techniques depend on several factors, with the most prominent being
temperature, processing time, types of purge gas, and flux addition.
In this paper, battery recycling comprises virtually four main process
groups, and these are further subdivided into unit operations. The main
process groups for pyrometallurgical recycling are discharging,
dismantling, pretreatment, and extractive metallurgy, as illustrated in
Fig. 3.
3.1. Thermal pretreatment methods
Current trends in the recycling of spent lithium-ion batteries aim to
use thermal pretreatment methods to disintegrate the battery module
and separate the battery into enriched metal fractions that can be
reclaimed by extractive metallurgy [33,42]. The LIB is the most critical
battery type to transport, handle, and recycle due to the presence of
reactive and high energy metals and flammable electrolyte [50]. Ther
mal pretreatment offers a controlled deactivation and safe decomposi
tion of the combustible organic component of the LIB [51,52].
Moreover, thermal pretreatment can be used to discharge the LIB [19].
LIB discharge is vital before disassembly to guarantee stabilization and
security as the energy content in the battery can cause adverse chemical
reactions [53]. If the anode and cathode of the LIB get into contact, they
can short-circuit, leading to self-ignition, spontaneous combustion, or
toxic gas emission [16,26].
Depending on the temperature employed, thermal treatment can
serve multiple purposes. For instance, the organic binder decomposes at
around 350 ◦
C [27,35], while other organic components such as
conductive carbon and acetylene black decompose above 600 ◦
C [27].
Fig. 2. Schematic drawing showing the components of a lithium-ion battery [41]; Copyright 2015, Reproduced with permission from Royal Society of Chemistry.
Fig. 3. Schematic drawing showing lithium-ion battery recycling stages.
B. Makuza et al.

5
Thermal treatment is one of the effective ways to remove the organic
binder material. The force of bonding between the binder and active
cathode material is removed by thermal decomposition of the binder at
high temperatures, and the cathode material can be easily separated by
sieving and so on [27]. Thermal pretreatment has found extensive ap
plications both at a laboratory and industrial-scale, and its common
purpose is to remove carbon and organic components [54].
Complete removal of carbon is imperative as the carbon would
absorb lithium ions during the subsequent leaching process leading to a
lower Li leaching efficiency [55]. The organic binders in the LIB have a
strong binding force with the active cathode material as they are ad
hesive, and this affects the recovery rate as some cathode powders
remain attached to the Al foils. The organic components cause problems
in leaching and solid-liquid separation. The separation of the active
cathode material from the Al foils using chemicals is challenging as the
binder material has excellent chemical stability and good mechanical
strength [20]. In cases where the cathode remains coated with the
electrolyte, this affects secondary processes like froth flotation as the
hydrophobicity differences between the anode and cathode becomes
insignificant [4]. Mechanical pretreatment has also been adopted to
remove the binder, and according to Zhang et al. [4] after comminution
and size classification, Ni, Co, Mn, and Li were mainly concentrated in
the size fraction passing 0.2 mm, while Cu and Al foil reported to the
+1.44 mm size fraction. However, some metals were distributed in the
size fraction greater than 0.2 mm because of the action of the binder, as
the metals were still attached to the Al foil even after liberation [4].
Moreover, communition releases toxic gases, and it also results in loss of
cathode powder as it adheres to non-metallic powder produced in the
crushing process [4,20].
3.1.1. Incineration pretreatment
Incineration process involves burning the carbon and binder at
higher temperatures in air or oxygen [53]. Plastic covers and all organic
compounds get incinerated. Incineration has been an effective method
to reduce the volume of municipal solid waste (MSW) [56]. The selec
tion of an optimum temperature range for incineration can be beneficial
for the subsequent extraction of Li and Co [53]. Incineration of LiCoO2 at
700 ◦
C for 60 min resulted in an improvement in Co and Li recovery rate
as reported by Petranikova et al. [55] as well as Slovaca [54] due to the
carbothermic reduction and carbon removal [19]. The lithium recovery
rate in the leaching process increased after complete carbon removal as
the carbon would act as an absorbent for Li salts [55].
Furthermore, the carbon and organic compounds present in the spent
LIBs are hydrophobic and create problems in the subsequent solid
− liquid separation processes. However, a further increase in the incin
eration temperature limits Co recovery as Al foils melt and cover the
LiCoO2 particles [57]. To curb the problems emanating from the melting
of the Al current collector, Hanisch et al. [58] devised the Adhesion
Neutralization Via Incineration and Impact Liberation (ANVIL) method
to enhance separation of the current collectors from the active cathode
material. The ANVIL process utilizes a moderate temperature of 500 ◦
C
to decompose the PVDF, followed by subsequent separation using an
air-jet separator to separate the coating powder from current collector
foils [58].
Although incineration and pyrolysis are similar methods in that they
all involve thermochemical conversion, they are different processes;
according to Bridgwater [57], the notable difference between inciner
ation and pyrolysis is that pyrolysis is the thermal treatment in the
absence of air or oxygen, and incineration involves burning in the
presence of air or oxygen. Incineration involves mostly exothermic re
actions, whereas pyrolysis involves endothermic reactions. Moreover,
possible energy recovery from incineration is in the form of steam,
which can be used for generators, and pyrolysis yields storable energy
that can be used later [57]. Also, to note is the distinction between
incineration and roasting in the field of waste lithium-ion battery
recycling. Incineration is conducted as a pretreatment method, and it
mostly refers to the burning of the spent LIBs in an oxygen-bearing
environment to get rid of carbon-containing material and organic
components, as this can be a problem in the subsequent refining stage
[53]. In contrast, reduction roasting is a processing route that uses a
reducing agent such as coal, coke, or carbon to reduce the active cathode
material to a low valence state [59].
3.1.2. Pyrolysis pretreatment
Pyrolysis is the process of heating the battery material above its
decomposition temperature in an oxygen-free environment to facilitate
the thermal decomposition of organic compounds into low molecular
weight products, which can be used as fuel or chemical feedstock [20,
60]. Pyrolysis also finds application in deactivating batteries with any
residual electrical energy [52]. Pyrolysis takes advantage of the thermal
instability of the organic compounds. It is often carried out in an inert
atmosphere or under vacuum condition because lithium is highly reac
tive with moisture and air and to eliminate the possibility of adverse
chemical reactions [61]. Heating the material under vacuum condition
lowers the decomposition temperature for the by-product and thus im
proves processing efficiency [20]. Pyrolysis also enables the electrolyte
to be recovered by condensation [62].
The active cathode material can withstand the pyrolysis temperature
and remains as a solid residue, which is then further processed during
the subsequent recycling steps [21]. The low molecular weight products
(volatile products) are transferred from the reactor to the gas collector
by vacuum pump [10]. A condenser condenses the volatiles on leaving
the reactor. A gas collector system employing a vacuum pump extracts
the non-condensable gases [20]. The Al foil becomes crisp under py
rolysis and is easy to fall off from the cathode. Sun and Qiu [20] devised
a novel method to separate cathode materials utilizing vacuum pyrolysis
and was able to peel Al foils from the cathode. The operating conditions
were a pyrolysis temperature of 600 ◦
C, a residual gas pressure of 1.0
kPa, and a vacuum evaporation time of 30 min. A high recovery yield of
over 99% of Co and Li was achieved after acid leaching using 2 M sul
furic acid leaching solution at 80 ◦
C and a solid/liquid ratio of 50 g/L for
60 min [4,10].
Advancements in metallurgy have seen microwave-assisted pyrolysis
being used as a pretreatment method. In convectional pyrolysis, heating
is provided directly to the material, whereas in microwave-assisted py
rolysis, heating is provided indirectly by microwaves depending on the
material dielectric properties [60]. The heating mechanism of
microwave-assisted pyrolysis offers several advantages: high metal
selectivity, high heating rates, easy power control, uniform heating, and
increased degradation kinetics [60].
3.2. Extractive pyrometallurgical process for recycling LIBs
The extractive pyrometallurgical options employed for recycling
spent lithium-ion batteries are roasting/calcination and smelting. These
processes are further classified in terms of the extraction mechanisms
used, and the atmosphere the processing is carried out in, as illustrated
in Fig. 4 [4,11,15,20,26,30–32,55,60,63–69].
3.2.1. Roasting/calcination
Roasting is an exothermic process that encompasses gas-solid re
actions at elevated temperatures. Pretreatment of the battery material is
done before roasting to obtain the cathode material [47], and carbo
thermic reduction (CTR) roasting is used to process the recovered active
cathode material. In this process, the active cathode material is heated
with a reducing agent such as carbon, charcoal, or coke, leaving carbon
residue and a mixture of alloys/intermediate compounds (impure met
als/oxides) for further refining [59]. The lithiated metal oxide is reduced
to a low valence state, which is beneficial in subsequent leaching as it
eliminates the need for the use of reductants as with the convectional
hydrometallurgical process. Moreover, carbothermic reduction (CTR)
promotes the destruction of oxygen octahedrons in the lithiated metal
B. Makuza et al.

6
oxide crystal structures, promoting the reduction to occur, as illustrated
in Fig. 5 [70]. As the O octahedrons collapse, Li and Co easily escape,
promoting the reaction to progress further [70]. When carbon is used as
a reducing agent, the reduction of metals can be performed as a double
redox reaction at relatively low temperatures [65].
During CTR, carbon does not directly reduce the active cathode
material, but it is a combination of coupling reactions [70]. Instead, the
active cathode material decomposes first, followed by the
oxidation-reduction reactions of graphite and the decomposed binary
metal oxides [70]. In the case of LiCoO2, the overall reaction for the
roasting process should follow equation (1) [70]. However, the
elementary equations for the CTR process are depicted in order as re
actions (2–7) [65,70]. Carbon as reductant reduces the lowly soluble
Co3+
to Co2+
in LCO and Mn4+
/Mn3+
in LMO, thus increasing the
leaching efficiency and extraction rate of valuable metals in the active
cathode material [71].
4LiCoO2 + 3C → 2Li2CO3 + 4Co + CO2 (1)
(i) Decomposition of lithium cobalt oxide
4LiCoO2 → 2Li2O + 4CoO + O2(g) (2)
(ii) Carbothermic reduction of cobalt oxide by carbon and carbon
monoxide
2CoO + C → 2Co + CO2(g) (3)
CoO + CO(g) → Co + CO2(g) (4)
(iii) Complete and incomplete combustion of carbon
C + O2 → CO2(g) (5)
Fig. 4. A brief data review of published work on pyrometallurgical options for recycling Li-ion batteries.
Fig. 5. A schematic of the mechanism of coupling reaction and collapsing model in carbothermic reduction roasting [70]; Copyright 2018, Reproduced with
permission from Elsevier.
B. Makuza et al.

7
2C + O2(g) → 2CO(g) (6)
CTR method relies on applying two carbon oxidation reactions
equations (5) and (6), and the ease of reduction for a particular metal
oxide depends on the affinity of that metal for the oxide lattice, a
property characterized by the standard free energy of formation for the
oxide [69]. When the oxidation of carbon is incorporated in these con
siderations, then it becomes clear that reaction (5) is favored at tem
peratures lower than 650 ◦
C, whereas reaction (6) is expected to
dominate at higher temperatures (Boudouard reaction). Thus, stronger
reducing conditions are produced at higher reaction temperatures, while
lower temperatures favor less reductive conditions and slower kinetics
[72]. These important characteristics can be attributed to entropy ef
fects, i.e., since reaction (5) only incurs a small volume change, the
entropy change is negligible. In contrast, reaction (6) involves an in
crease in volume and, therefore, in entropy. This property implies that
carbon can theoretically reduce any oxide when a high enough tem
perature is reached [72]. Moreover, the extent of reduction will also
depend on the amount of carbon available to reduce the metal oxide. If
the graphite (carbon) content is not enough to effect complete reduction,
then the roasting products will be intermediate oxides instead of metal
alloys.
(iii) Formation of lithium carbonate
Li2O + CO2 → Li2CO3 (7)
Similarly, the same CTR mechanism has been reported in other
active cathode materials, typically LiNi1/3Co1/3Mn1/3O2 [11], LiNiO2,
and LiMn2O4, which follow the same route of thermal decomposition
followed by oxidation-reduction reactions of graphite and the decom
posed metal oxides, and the elementary equations are listed below;
12LiNi1/3Co1/3Mn1/3O2 → 6Li2O + 4NiO + 4CoO + 4MnO2 + O2(g) (8)
(iv) Decomposition of lithium nickel oxide
4 LiNiO2 = 2 Li2O + 4NiO + O2(g) (9)
(v) Carbothermic reduction of lithium nickel oxide
4LiNiO2 + C = 2Li2O + 4NiO + CO2(g) (10)
2 LiNiO2 + 3 C = Li2O + 2 Ni + 3 CO(g) (11)
4LiNiO2 + 3 C = 2 Li2CO3 + 4 Ni + CO2(g) (12)
(vi) Carbothermic reduction of nickel oxide by carbon and carbon
monoxide
2NiO + C = 2 Ni + CO2(g) (13)
NiO + C = Ni + CO(g) (14)
NiO + CO(g) = Ni + CO2(g) (15)
(i) Decomposition of lithium manganese oxide
3LiMn2O4 = 3LiMnO2 + Mn3O4 + O2(g) (16)
4 LiMn2O4 = 8 MnO + 2 Li2O + 3O2(g) (17)
4 LiMnO2 = 4 MnO + 2 Li2O + O2(g) (18)
(ii) Carbothermic reduction of manganese oxides by carbon and
carbon monoxide
Mn3O4 + C = 3MnO + CO(g) (19)
Mn3O4 + CO(g) = 3MnO + CO2(g) (20)
Liu and Xiao [11] conducted carbothermic reduction roasting of
NMC cathode material at a roasting temperature of 650 ◦
C, roasting time
of 30 min, and a carbon dosage of 10% of raw material input. The
roasted products were Li2CO3, MnO, Ni, and Co, as depicted in equation
(21). Evaporative crystallization was used to recover the Li2CO3 from
the leachate, while the insoluble fraction underwent acid leaching. High
recovery rates were obtained for Ni, Mn, and Co, which were 98.68%,
98.08%, and 93.33%, respectively [11].
12LiNi1/3 Co1/3 Mn1/3 O2 + 7C → 6Li2CO3 +4Ni + 4Co + 4MnO + CO2
(g) (21)
Li et al. [65] roasted a mixture of LiCoO2 (LCO) and graphite under a
nitrogen atmosphere for 30 min at 1000 ◦
C. The residue after roasting
consists of graphite, Co, and Li2CO3, and it was subjected to water
leaching. The recovery rate of Li, Co, and graphite after wet magnetic
separation is 98.93%, 95.72%, and 91.05%, respectively [65]. In sub
sequent research, the feasibility of recycling LMO cathode material
utilizing the roasting mechanism was confirmed. LMO battery material
was roasted for 45 min at a roasting temperature of 800 ◦
C. The LMO
active material was reduced by the graphite contained in the mixture to
Li2CO3 and MnO. Subsequent water leaching and mechanical separation
recovered 99.13% Li, and the filter residue was calcined to remove
carbon, and Mn3O4 with a purity of 95.11% was attained [73]. Apart
from carbothermic reduction playing a rampant role in recycling LIBs,
oxidizing roasting has also been adopted to recycle LiFePO4 batteries,
and the oxidative roasting process is presented as equation (22) [33,74].
Effective temperature control is imperative during oxidative roasting. At
higher temperatures (>650 ◦
C), oxidizing roasting has notable effects on
the separation of LPF from the Al current collectors owing to the release
of fluorine-containing gases such as HF, which enhances corrosion [33].
Moreover, this high-temperature results in the decrease of Fe recovery in
the subsequent acid leaching process due to the massive formation of
Fe2O3, which can not be effectively leached out [33].
6LiFePO4 + 3O2 = 2Li3Fe(PO4)3 + 2Fe2O3 (22)
3.2.1.1. Salt-assisted roasting. Recent advances in pyrometallurgy have
seen a transition from carbothermic reduction roasting to salt assisted
reduction roasting since the formation of Li2CO3 in carbothermic
reduction roasting results in lower Li leaching efficiency as the solubility
of Li2CO3 is low (13.3 g/L, 20 ◦
C [75]). The low solubility of Li2CO3
results in excessive energy requirements for evaporative crystallization
[31]. Besides, salt-assisted roasting can potentially increase recycling
efficiency, reduce acid consumption, and toxic gas emissions by pro
ducing readily water-soluble salts. Also, some salts have low melting
points coupled with high solubility and high volatility [63]. The core
concept behind salt assisted roasting is to convert the different metal
elements into water-soluble products, and it has proved to be an effec
tive method to separate the metals in the lithium transition metal oxides
[15].
Depending on the reagent used, salt assisted roasting processes can
be categorized as chlorination, sulfation, and nitration roasting. Chlo
rination roasting involves heating the cathode with a chlorination agent
such as HCl(g), NH4Cl, NaCl, or Cl2(g) to produce readily soluble metal
chlorides (solubility 832 g/L, 20 ◦
C [75]) [63]. Sulfation agents such as
SO2(g), MgSO4, NH4SO4, NaHSO4⋅H2O, or Na2SO4 have been used to
produce readily soluble Li2SO4 in sulfation roasting (solubility 257 g/L,
20 ◦
C [76]) [15,68]. The SO3 partial pressure can be controlled to
recover Li selectively [77]. H2SO4 has also been adopted as a sulfation
agent in LIB recycling, and it has proved to be cleaner and more envi
ronmentally benign than other additives [68,78]. The LIB active cathode
material is first mixed with H2SO4 at ambient temperature, and this
results in a partial structure breakdown of the active cathode material to
divalent in different degrees to form sulfates. Exposure of the blend of
H2SO4 and cathode material to high-temperatures results in the
B. Makuza et al.

8
combination of the released Li+
from the unstable layered structure with
the SO2
4- in the transition metal sulfate to form Li2SO4 [78]. By effective
control of the amount of H2SO4 addition in sulfation roasting, sulfur
produced in the process can be recycled as SO4
2−
instead of SOx emission,
thereby curbing secondary pollution [78]. The sulfation roasting
mechanism employing H2SO4 can be further extended to other active
cathode material by controlling the appropriate conversion tempera
ture. Using H2SO4 as the sulfation agent, Lin et al. [68] obtained 99.3%
selective lithium recovery and 98.7% Co3O4 [68]. Nitration roasting
involves heating the cathode with a nitration agent to produce readily
soluble LiNO3, and it has a high solubility (622.7 g/L, 35 ◦
C [79]). Peng
et al. [31] used nitration roasting to recover a high-grade LiNO3 at a
roasting temperature of 250 ◦
C for 60 min, as described by reactions
(23–28) [31]. Owing to the complexity of the reactions between HNO3
and the various components present in the spent LIB, the reactions be
tween nitric acid and waste LIBs components were simplified as outlined
in equations 23–28, where Ni, Co, Mn were assumed to exist as LiNiO2,
LiCoO2, and LiMnO2, and the other metals were assumed to be in
elementary forms [31]. However, in the case of composite electrodes,
other complex reactions are possible due to the dissolution of the binder
or cathode during the nitration process.
According to Peng et al. [31], Li2CO3 was attained after the
carbonation of the filtrate with Na2CO3 to synthesize Li2CO3. The
leaching efficiency was up to 93% for Li, and the leaching rate of Co, Ni,
Cu, was 92.9% [31]. It should be noted that in nitration roasting, the
nitrous gases produced from the nitration roasting process can poten
tially be converted into nitric acid by oxidizing agents, catalysts, or
pressurized adsorption [31].
LiCoO2 + 4HNO3 → LiNO3 + Co(NO3)2 + NO(g) + O2(g) +H2O(g) (23)
LiNiO2 + 4HNO3 → LiNO3 + Ni(NO3)2 + NO(g) + O2(g) +H2O(g) (24)
LiMnO2 + 4HNO3 → LiNO3 + Mn(NO3)2 + NO(g) + O2(g) + 2H2O(g) (25)
Fe + 4HNO3 → Fe(NO3)3 +NO(g)+ 2H2O(g) (26)
Al + 4HNO3 → Al(NO3)3 +NO(g) + 2H2O (27)
1.5Cu + 4HNO3 → 1.5Cu(NO3)2 +NO(g) + 2H2O (28)
3.2.1.2. Microwave-assisted carbothermic reduction. Continuous
research and development in pyrometallurgy have seen microwave-
assisted carbothermic reduction being employed to recycle spent LIBs.
The battery material can be subjected to a carbothermic reduction in a
microwave furnace [64]. The conventional methods often result in
relatively long reaction time [80], as the heat transfer through the ma
terial bed takes time. Carbon, which is present in LIBs, is an active
absorber of microwaves, and the absorption of microwave energy by the
carbon particles, raises the temperature, allowing carbothermic reduc
tion to take place effectively [64]. Continuous research should be done
concerning microwave-assisted carbothermic reduction.
3.2.2. Smelting
Smelting is another effective pyrometallurgical option for recovering
high-value metals from spent LIBs. In the smelting process, the battery
material is heated above its melting point to facilitate the separation of
the metals in the liquid phase by reduction and subsequent formation of
immiscible molten layers [81]. The process allows the recycling of
various end-of-life (EOL) LIBs based on different chemistries. Moreover,
it also eliminates the need for a prior passivation step, and the battery
cells and modules can be directly fed into the furnace [77]. In this
process, the unsorted and untreated spent batteries are fed directly into a
high-temperature furnace [30,34]. Smelting is carried out in two phases,
(i) firstly, the material is heated at a lower temperature to evaporate the
electrolyte and avoid burst as intensive heating would cause the battery
to explode due to overpressure caused by the sudden evaporation of the
electrolyte [34], (ii) the material is then heated at a high temperature to
melt the feeds [82]. All the organic material is burnt out, providing
energy for the smelting process [42,83]. Carbon and Al, which are
present in the LIB, act as reductants in the reduction smelting approach,
and the reduction reactions are depicted by equations 29–31 [32]. The
reduction of the cathode material is conducted in a blast or electric
furnace in the presence of flux to produce molten metal (alloy), gases,
and slag [77]. Flux addition assists in melting the battery material to a
low melting slag phase [47], and it chemically reacts with the unwanted
impurities resulting in the formation of slag [59]. Cu retains its metallic
form during the reduction process while the Al from the current col
lector is slagged as Al2O3 [47]. Although Al cannot be recovered, the
reaction produces a large amount of energy, and this decreases the en
ergy requirements [32,34].
2LiCoO2+2Al → Li2O+2Co + Al2O3 (29)
2LiCoNiO2+3C → Li2O + 2Co+2Ni+3CO(g) (30)
2LiCoNiO2+2Al → 2Li2O+24Co+2Ni+Al2O3 (31)
After the reduction smelting process has been completed, the tran
sition metals are preferentially concentrated into a molten alloy phase,
reporting to the bottom of the furnace and enter the molten metal pool.
The valuable metals are then further recovered from the alloy by hy
drometallurgical processes [42,83]. In contrast, lithium oxide is not
reduced and is reported to the slag fraction [47]. The smelting process
faces a challenge of intensive energy requirement, and it is much more
economical for batteries with high Co and Ni, and not the recent Mn
spinel oxides or LiFePO4, as Li and Mn are lost in the slag [83].
Reduction smelting is prevalent for industrial-scale applications because
of its simple operation and high productivity [73,84].
3.2.2.1. Smelting slag system design. Slag system design is vital for a
successful smelting operation [34]. The most commonly used slag sys
tem is CaO–SiO2–Al2O3, in which SiO2, along with CaO, is chosen as a
slag former, while Al2O3 in slag mainly comes from the spent LIBs [32].
The choice of SiO2 and CaO is attributed to its effective temperature
control and fluidity of the slag phase [47]. The principle is to oxidize the
metals with low economic value as much as possible so that they report
to the slag and suppress the oxidation of valuable target metals so that
they report to the alloy phase [85]. The oxygen affinity for Fe and Co is
similar, which makes the oxidation reactions coincide [86]. The oxida
tion degree is controlled to make a portion of the Fe report to the alloy
phase and the majority to the slag phase. A high content of Al2O3 in the
slag phase results in a slag system with high viscosity and melting point,
which causes the alloy droplets to be physically entrained in the slag
phase during the separation of the slag and metal layers, causing metal
loss [85]. New smelting methods have been devised, encompassing
multi-stage slag separation to curb challenges faced in single-stage slag
smelting [85].
The conventional CaO–SiO2–Al2O3 slag system design does not
recover Li and Mn as they report to the slag. Recovery of the Li is made
by salt assisted roasting to convert the insoluble Li in the slag to water-
soluble Li, which is neither economical nor energy-efficient [67]. Recent
progress has seen MnO–SiO2–Al2O3 being adopted as a slag system
because it results in the potential subsequent recovery of Li and Mn [32].
Guoxing et al. [32] adopted the MnO–SiO2–Al2O3 slag system and ob
tained a Co–Ni–Cu–Fe alloy, and lithium-containing manganese-rich
slag was produced, and with subsequent leaching of the slag, the re
covery rates for Li and Mn were 94.85% and 79.86%, respectively [32,
34].
3.3. Recovery concept of less economic metals
Research and development in recycling are ongoing to recover all
B. Makuza et al.

9
components in the LIB with minimum losses. Pyrometallurgical recy
cling of LIBs has been reported in facilities that are not designed for
recycling LIBs, which also renders economic advantages [87].
3.3.1. Advancements for recycling low cobalt content batteries – (Cu
smelter)
The research interest in the previous years was centered on cobalt
recovery, and most industrial recycling facilities also target Co recovery
because of its high economic value. New developments propose the
recycling of low cobalt content LIBs such as LiMnO2 (LMO) and LiFePO4
(LFP) in a copper smelter [88]. The LIBs are fed as secondary feed in
addition to the copper-bearing feed, slag formers, and reducing agents.
When spent LMO and LFP batteries are used as feed into the Cu smelter,
the production rate of blister Cu is increased by more than 20% while
hazardous waste is being recycled [88]. However, this depends on the
relative amount of the Cu present in the reference furnace charge and
the spent LIBs. The carbon and Al present in the LIBs compensate for the
fuel and reducing agents. Moreover, the organic components in the LIB
also compensate for the fuel as they have a high calorific value. By
adjusting the flux addition, particularly SiO2, the produced slag should
meet the slag requirements of SiO2>0.5%, Fe < 2.5%, and Al2O3< 10%.
The Co battery content must be <3% to attain a slag fraction with a Co
content <0.1% to cater to environmental concerns [88].
3.3.2. Advancements for recycling lithium - (EcoBatRec recycling process)
EcoBatRec process is a patented thermal treatment process that of
fers an alternative to conventional recycling routes, and it is centered on
lithium recovery. The objective of the EcoBatRec process is to achieve
the 50% mass recycling stipulated by the EU directive using robust and
flexible technology, at a lower recycling cost, and producing high-
quality end products with minimal emissions [89]. A schematic of the
EcoBatRec recycling process is illustrated in Fig. 6.
The LIB undergoes sorting, removal of the packing material, and
dismantling to the module level to produce several raw material streams
with a positive value, and this reduces the mass flow by 50% [89]. After
disassembling, the battery modules are subjected to pyrolysis to cause
thermal deactivation, discharge of the batteries [89], safe removal of
fluorine and halogens, and evaporation of the organic component [90].
Any possible harmful gases produced during pyrolysis are treated using
a condenser unit and gas treatment mechanism. The pyrolysis product
undergoes comminution, and mechanical classification separates the
active cathode material from the aluminum, copper, and steel. A com
bination of mechanical and thermal pretreatment in the EcoBatRec
process enables the recovery of entirely all battery components. The
enriched metal fraction is subjected to carbothermic reduction at
1400 ◦
C for 120 min in a vacuum induction furnace [66,89]. Knowledge
of the vapor pressure of Li and accompanying elements is imperative
when recovering Li from the powder by volatilization. An increase in
temperature is associated with an increase in volatilization rate, and this
enables selective volatilization [89]. The material is then subjected to
direct vacuum evaporation to recover metallic Li by distillation, and
selective entraining gas evaporation recovers lithium oxide [89,90]. A
steam jet was directed via a riser to the condenser to effect condensation.
Lithium vapor that exits the furnace via the riser was oxidized to LiO2
under the action of the baffle plate mounted above the riser [89].
4. Subsequent extraction and refining of valuable metals
4.1. Leaching processes
Leaching is a key process in the refining stage, and it aims at con
verting the pyrometallurgy products into metal ions in an aqueous so
lution for subsequent separation and recovery [9,11]. The main factors
affecting the extent of conversion for pyrometallurgy also affect leaching
efficiency. The roasting temperature [91], roasting time, and coke
dosage are correlated with the leaching efficiency. An increase in all
Fig. 6. EcoBatRec recycling process [89]; Copyright 2015 reproduced with permission from John Wiley & Sons.
B. Makuza et al.

10
these factors will increase the leaching rate up to a point a plateau is
reached where further increase in these parameters will bear no effect
[11,15,30], as depicted in Fig. 7.
After leaching, the leached metals are recovered from the solution by
a series of processes in sequence, such as selective precipitation, solvent
extraction, ion exchange, or electrolytic deposition [71,92]. Using the
precipitation method, it is sometimes challenging to extract a single ion
from the solution because of the pH range overlap. For instance, the
overlap between stable areas of Ni(OH)2 and Co(OH)2 is so large that
Co2+
and Ni2+
are prone to be coprecipitated via neutralization reaction.
A possible approach to curb this is to transform the Co2+
to Co3+
as the
stable area of Co(OH)3 and Ni2+
has a small overlap gap [17]. Joulié
et al. [93] used selective precipitation with NaClO as the oxidant to
extract Co and Ni from the leaching solution of NCA battery material. In
the case of Mn presence in the system, the Mn2+
would be oxidized to
Mn4+
at pH 2, forming MnO2 or hydroxide precipitate [93]. Recovered
metallic salts can undergo thermal treatment to produce crystalline
metal oxides (e.g., Co3O4), which can be used for resynthesis of the
cathode material [71].
Solvent extraction is a liquid-liquid extraction method that utilizes
the different relative solubilities of compounds in immiscible liquids to
separate them from each other [45]. Several groups have reported the
successful use of PC-88A, D2EHPA, Cyanex 272, or Cyanex 302 as
extractants in solvent extraction. Junmin et al. [94] extracted Co2+
by
Cyanex272 and Cu2+
by AcorgaM5640, and the recovery efficiencies of
Co and Cu were 97% and 98%, respectively [94].
Ion exchange is where the leached solution is passed through a bed of
resin with a high affinity for specific ions, and the affinity is usually
limited to either cations or anions. Compared with the chemical pre
cipitation method and solvent extraction method, this method is more
selective for metal ions and is suitable for separating and recovering
target metal ions with a small content from a solution with a large
number of other ions [95]. Jia et al. [95] utilized this method to recycle
cobalt in the spent LIBs. The results show that: using TP207 resin, a pH
of 2.5 and 10 circulation cycles, the extraction rate of Cu ions can reach
97.44%, and the recovery rate of cobalt ions can reach 90.20%, and the
product obtained after treatment can be utilized for resynthesis of
cathode material. This method is relatively simple to operate and has the
potential to scale up to large-industrial applications [95].
Electrowinning is a widely adopted technique for plating metallic
nickel, cobalt, or electrolytic manganese dioxide (EMD). Electro
chemical deposition obtains the highest purity products compared to
other refining techniques since it does not require any addition of
chemicals; hence it avoids contamination [10]. Moreover, electrowin
ning enables selective deposition of Cu on the cathode without losing
other metal ions (Mn, Co, and Li) due to its positive potential (E0 = +
0.337 V). Also, Mn (E0 = − 1.18 V) and Co (E0 = − 0.28 V) can also be
separated electrolytically due to the huge difference in reduction po
tentials, whereas Li (E0 = − 3.045 V) will not deposit electrolytically
from aqueous solution due to its negative potential [96]. It produces
high-grade cobalt, although it has intensive energy requirements [92].
In the electrowinning process, a low pH promotes the evolution of H2(g)
as the standard reduction potential of Co (E0 = − 0.28 V) is lower than
the potential for the evolution of H2. The cathode material must exhibit a
high overpotential over H2 to avoid the progression of this side reaction.
Lupi et al. [97] used aluminum and stainless steel as the cathode ma
terial to provide a relatively high hydrogen overpotential, and the
choice of these materials was due to their relatively low cost and easy
recovery of the metallic Co deposit [97].
Salting-out method is a new refining method in which the leaching
solution is supersaturated by salt addition to precipitate out some ele
ments and enable recovery of target metals [10]. It has been found that
when (NH4)2SO4 saturated solution and anhydrous alcohol are added in
HCl(aq) leaching solution, the Co2+
separates in the form of precipitate
(NH4)2Co(SO4)2. The exhalation rate and mass fraction of cobalt reach
92–94% under optimal conditions [10].
Fig.
7.
a)
Influence
of
roasting
temperature
on
the
leaching
efficiency
of
target
metals
(roasting
time
=
30
min,
coke
dosage
=
20%)
b)
Influence
of
roasting
time
on
the
leaching
efficiency
of
target
metals
(roasting
temperature
=
650
◦
C,
coke
dosage
=
10%)
c)
Influence
of
coke
dosage
on
the
leaching
efficiency
of
target
metals
(roasting
temperature
=
650
◦
C,
roasting
time
=
30
min)
[11];
Copyright
2018,
Reproduced
with
permission
from
Springer
Nature.
B. Makuza et al.

11
4.2. Cathode regeneration
Current trends in the recycling of spent LIBs aim towards a transition
from traditional separation and extraction technologies, e.g., solvent
extraction, selective precipitation, and ion-exchange, as they are
sometimes not economically justifiable to be applied at industrial scale
due to their significant drawbacks, e.g., high chemical reagent con
sumption, complicated recycling routes, and high waste emission [62].
Direct regeneration of the cathode material from the leachate has been
introduced to shorten the processing route, avoid the problems in
separating metal ions from each other, reduce secondary pollution, and
enhance the recycling efficiencies of valuable metals [98]. Direct
regeneration of the cathode material using hydrometallurgical tech
niques such as sol-gel and coprecipitation methods requires extensive
monitoring of the temperature, pH, flow rate, and agitation, making it
unfavorable in extending to industrial scale [99]. Thus, a need arises to
develop facile, time-efficient, and cost-effective regeneration methods,
and high-temperature synthesis methods such as spray pyrolysis have
been developed to curb some of these shortcomings [100,101]. The
other high-temperature synthesis methods in place are calcination and
sintering [62], microwave heating [102], and combustion synthesis
[103]. However, these methods can not directly regenerate the active
cathode material from the leaching solution, as in the case with spray
pyrolysis [100].
4.2.1. Spray pyrolysis
Spray pyrolysis is an aerosol pyrometallurgical technique used to
synthesize the cathode material directly from the leachate, and it offers
an effective method for the fabrication of the cathode material [98].
Spray pyrolysis is an important technique in the fabrication of ultrafine
powders, and the method is based on the continuous generation of a
stream of droplets from a solution containing colloidal particles.
Numerous methods can be used for the generation of droplets, and these
include the use of a peristaltic pump or ultrasonic transduction [103]. In
this process, the generation of droplets is a crucial step because the
droplets act as the nucleation centers of the particles where dense and
pure well-crystallized particles will eventually evolve. The properties of
the powders regenerated by spray pyrolysis have a small particle size,
narrow size distribution, and large surface area coupled with high pu
rity, and all these properties are desirable for attaining cathode material
with an excellent electrochemical performance [103].
Spray pyrolysis typically starts with spraying (or pumping) of the
solution of mixed precursors into a pyrolysis furnace at a temperature
range of 400–600 ◦
C in the form of droplets by a carrier gas. The
collected precursor powder is calcined at 700–800 ◦
C. Unlike other
synthesis methods, it provides advantages of fast processing time, cost-
effectiveness, and ease of scalability [98,100]. Furthermore, the inten
sive heat from the flame serves annealing purposes to the cathode ma
terial and eliminates the need for post-deposition heat treatment [104].
As reported by Zheng et al. [98] and Ajayi et al. [100], spray
pyrolysis-assisted resynthesis resulted in regenerated NMC cathode
material, which exhibits similar characteristics to the commercial LIBs
in terms of cycle life and capacity [98,100]. According to Ajayi et al.
[100], the initial discharge capacity of the regenerated
LiNi0⋅2Mn0⋅6Co0⋅2O2 active cathode material was 258mAh/g at a current
of 10mAh/g [100].
4.2.2. Solid-state reaction
Solid-state sintering is a conventional method that has been used to
regenerate the active cathode material by subjecting it to extreme
pressure and temperature conditions [103]. The process typically starts
with the homogenous mixing of the precursors in a ball mill or other
mixing techniques. Afterward, the mixed powders are subjected to heat
treatment in two stages; (i) the first step is a pre-calcination step
(250–350 ◦
C) to decompose precursors and remove the gases, (ii) the
next step is final calcination at relatively high temperature (400–800 ◦
C)
to attain stability and purer phase material [103]. Moreover, the first
calcination step is responsible for the structure of the material
(morphology related), while the second calcination step stabilizes the
structure. The powder material might also not get heat homogeneously
in the first calcination step. Control of calcination temperature is
imperative as it has a rampant effect on the particle growth (particle
size), structure, and discharge capacity of the regenerated active cath
ode material [103]. Solid-state sintering is a relatively simple and easy
technique to adopt at an industrial scale due to the low equipment
requirement, and the reaction can be easily controlled [105]. However,
the requirement for multi-stage grinding and calcination leads to the
formation of non-uniform and larger particles, which results in lower
electrochemical performance [103,105].
Tang et al. [26] regenerated LiCoO2 by calcinating the solid CoO
residue obtained from the water leaching process. The CoO was calcined
in a muffle furnace in the air for 30 min at 750 ◦
C to convert it into Co3O4
[26]. Afterward, Li2CO3 was calcined with the obtained Co3O4 to
regenerate the LiCoO2 active cathode material. The processing condi
tions were a Li/Co ratio of 1.05, a heating rate of 2 ◦
C/min, and a sin
tering temperature of 850 ◦
C for 13 h. The regenerated LiCoO2 exhibited
a discharge capacity of over 125 mAh/g at 5C coupled with high
coulombic efficiency close to 100%. Moreover, the capacity retention
rate of the regenerated LCO cathode material exceeded 93% [26].
4.2.3. Carbothermic reduction (CTR)
CTR method stands out as a simple, versatile, and cost-effective
regeneration method that can be scaled to industrial applications [72,
106]. The carbothermic reduction method (CTR) has been extensively
used for the synthesis of LiFePO4 batteries. Synthesis of LFP using
solid-state synthesis has not been economically favorable at the indus
trial scale as it encompasses multi-stage preparative strategies and the
use of expensive Fe2+
precursor compounds, typically Iron(II) oxalate
(FeC2O4⋅2H2O) or Iron (II) acetate (Fe(OOCH3)2), which exacerbates the
regeneration costs [72]. CTR method relies on applying two carbon
oxidation reactions (reactions 5–6), and it has been used extensively in
the metallurgy industry. Inexpensive and readily available Fe2O3 has
been used in the CTR process as a precursor source, and FePO4, Fe3O4
has been equally successful as alternative schemes [72]. Liu et al. [107]
regenerated LiFePO4/C utilizing the CTR method by milling Li2CO3,
FePO4⋅4H2O, and acetylene black (AB) at a molar ratio of 1:2:4 for 24 h
[107]. The resultant mixture was calcined at 750 ◦
C for 15 h in a tube
furnace as depicted in equation (32);
Li2CO3 + 2FePO4 + 2C = 2LiFePO4 + 3CO (32)
The regenerated LiFePO4/C had an initial discharge capacity of
133mAh/g and showed good capacity retention of 128 mAh/g at the end
of the 20th cycle [107]. Besides the CTR method, LiFePO4 batteries can
also be regenerated using doping mechanisms, which confers perfor
mance improvement advantages [108].
Despite the CTR synthesis method finding wide application for
LiFePO4 cathode material regeneration, the method has been adopted to
regenerate other active cathode material. For instance, LiMnO2 [109,
110], Li2S [111,112], and Li4Ti5O12 [113] have been regenerated by the
CTR method. Zhao et al. [109] and Zhou et al. [110] reported the suc
cessful preparation of LiMnO2 nanorod by in situ CTR process. Accord
ing to Zhao et al. [109], MnO2 was employed as the precursor in the CTR
process, and it was obtained by the thermal decomposition of potassium
permanganate. Potassium permanganate was dissolved in 65 ml UPW,
and the solution was subjected to continuous stirring and drop size
addition of ethanol for 30 min [109]. The resultant precipitate was
heated for 90 min at 350 ◦
C to obtain the MnO2 nanorods. Multi-stage
heating, as in the solid-state reaction synthesis, was adopted for the
synthesis of LiMnO2. Firstly LiOH⋅H2O, MnO2, and glucose in the mole
ratio 5:4:2 after grinding were heated for 2 h at 300 ◦
C under argon
protection. Finally, the obtained powder was further sintered for 10 h at
B. Makuza et al.

12
750 ◦
C to obtain LiMnO2 cathode [109]. The regenerated LiMnO2
exhibited a maximum discharge capacity of 227.5 mAh/g and 7.4%
capacity fading after 40 cycles. Furthermore, carbothermic reduction of
the Li2SO4 selectively recovered from sulfation roasting has been
documented to regenerate Li2S–C composite [111].
4.2.4. Molten salt synthesis (MSS)
Continuous research has seen molten salt synthesis being adopted as
a regeneration method for LIB active cathode material. The molten-salt
method has proved to be a versatile and simple method for preparing
highly crystalline pure and mixed oxides [6,114,115] with tailored
physical and electrochemical properties and controlled morphology
[114]. Under controlled conditions, nanocrystalline phases can also be
attained [6]. In molten media, reactions are usually controlled by
chemical equilibria and proceed much faster than diffusion controlled
solid-state reactions [116]. The MSS method is a “one-pot” technique
that eliminates the need for mechanical mixing or multi-stage grinding
and heating of reagents. Salt flux is used to form the product at the
required temperature, and it can be recovered and reused after filtration
and evaporation of the water, thus offering energy and reagent savings
[116]. The MSS method has also been adopted to curb capacity fading
on charge-discharge cycling in the active cathode material typically for
LiCoO2, which has been ascribed to be due to crystal structure transi
tions taking place in Li1− xCoO2 as a function of x following Li
de-intercalation (charge) and discharge [6]. However, recently, MSS
method has been adopted to regenerate various active cathode materials
including LiMn2O4, Li(Ni2/3Mn1/3)O2 [117], Li(Co0⋅7Ni0.3)O2, and Li
(Ni0⋅7Co0.3)O2 [118], and the underlying mechanism was explored
[116]. Reddy et al. [115] regenerated Li(Ni1/3Co1/3Mn1/3)O2 using high
purity LiNO3–LiCl salts in the mole ratio 0.88:0.12 (eutectic mixture)
and Ni(NO3)2⋅6H2O, Co(NO3)2⋅6H2O and Mn(NO3)2⋅4H2O [115]. The
mole ratio of transition metal nitrates and eutectic was fixed at 1:4. After
homogenous mixing, the reactants were heated in air at a heating rate of
3 ◦
C/min in the temperature range of 750–950 ◦
C in a box furnace. After
the heating time was elapsed, the product was cooled to ambient tem
perature. The calcine was soaked for 8 h, washed thoroughly with
distilled water, filtered and the powder (filter residue) was dried in air
oven at 150 ◦
C for 24 h [115]. As reported by Reddy et al. [100] the
synthesized NCM active cathode material performed well with a
reversible capacity of 125–145 (±5) mAh/g on the fifth cycle and
illustrated hardly any noticeable capacity fade up to 50 cycles. In similar
work, LCO synthesized using molten salt of KCl or KNO3 or LiNO3–LiCl
eutectic depicted stable capacity and good cyclability [116].
4.2.5. Combustion synthesis
In the combustion synthesis process, the obtained metal salts from
the recycling process are mixed with urea/nitrates/acid and heated
directly to the ignition temperature [105,119,120]. The exothermic heat
of the reaction synthesizes the active cathode material [105]. As the fuel
starts to burn, the temperature dramatically increases, and nucleation
rapidly accelerates, producing high-performance nanomaterials as the
final product [121]. This method has the potential to scale up to in
dustrial scale as it involves entirely thermal reactions in the air without
any requirements for grinding, pulverization, particle morphology
control, and particle size control of reactants as well as products [121].
The method confers the advantages of fast heating rates, low cost, simple
equipment setup, and requires no external energy [105,121]. Carbon
has also been adopted recently to replace the urea in combustion syn
thesis. Organic molecules (as a carbon source) can also be dissolved
together with other precursors providing the carbon layer on the particle
surface [120]. The carbon layer on the particle surface is produced by
burning the organic material during the calcination step [122]. In this
regard, the particle size and shape, crystal structure, phase, and the
specific surface area can be controlled by the amount and type of organic
molecules added [120,122]. For instance, Gan et al. [123] used carbon
to synthesize LiCoO2. Co3O4 and Li2CO3 at a molar ratio of 1:1.05 were
homogeneously mixed in a planetary ball mill and further ground with
carbon at a molar ratio of carbon: Co = 5. The mixture was then ignited
and heated at 800 ◦
C for 2 h. The synthesized LiCoO2 exhibited an initial
discharge capacity of 148 mAh/g with capacity retention greater than
97% after 10 cycles [123].
A non-exhaustive review of published laboratory work on pyromet
allurgical options for recycling spent lithium-ion batteries is summa
rized in Table 1.
5. Li-ion battery recycling at an industrial scale
5.1. Pyrometallurgical industrial recycling processes
Pyrometallurgical treatment of the spent LIBs is predominant at the
industrial scale as it is a mature process with relatively simple operation
and high productivity [34,47]. The economic prospects of the vast
amount of LIBs reaching their end of life have attracted a lot of industrial
LIB recycling companies [124], and it is seeing new entrants such as
Valdi (Emerat) with much higher recycling capacity (20 000 tonnes per
annum) [125]. The industrial battery recycling process encompasses
pyrometallurgy and subsequent refining steps to enhance the purity of
the recovered product, as illustrated in Fig. 8.
Pyrometallurgical recycling at the industrial scale follows multiple
recycling process paths, as described in Table 2.
The recycling processes are sometimes designed for recycling specific
types of batteries. However, there are some cases in which batteries can
be recycled together with other types of material. For most companies,
LIB recycling is an expansion of their Ni–Cd and or Ni-MH recycling
facilities; hence they can treat all types of batteries, e.g., the Glencore-
Xstrata process recycles LIBs, Ni–Cd, and Ni-MH [128].
5.1.1. Umicore Val’eastm battery recycling process
Umicore recycles spent batteries by an ultra-high temperature (UHT)
smelting technology [129,130]. The UHT smelting technology can treat
all types and size fractions of LIBs. It is a controlled smelting reduction
process in a vertical shaft furnace [35]. Battery pretreatment is optional
as the batteries are fed directly into the shaft furnace, eliminating the
need for hazardous and costly pretreatment [30,82,131]. In this process,
dismantling to module-level is only conducted to batteries that exceed
the size requirements for material handling [124,132]. The battery
scraps should contain between 30 and 50% Co as the economic effi
ciency of the process is strongly dependent on the price and content of
Co in the battery. The vertical shaft furnace is divided into three parti
tions, which are preheating, pyrolysis, and smelting zones. The first step
is the preparation of the furnace charge consisting of the LIBs, slag
formers, sand (SiO2), limestone (CaCO3), and coke (C). The prepared
batch is fed into the preheating zone [82,124]. The temperature of the
preheating zone is maintained below 300 ◦
C to evaporate the electrolyte
without the risk of explosions [1]. The temperature of the pyrolysis zone
is up to 700 ◦
C to completely decompose the organic components. The
organic components are used as fuel, thereby compensating the fuel
requirements, and it also decreases the greenhouse gas (GHG) emission
by eliminating the need for waste landfill of any residue that would have
emitted greenhouse gases while decomposing [131]. Smelting of the
batch commences in the third zone, and by injecting oxygen via tuyeres
into the furnace, temperatures of 1200–1450◦
C can be reached [124].
Umicore Val’eastm process produces three output streams: (i) an
alloy comprising of Cu, Fe, Ni, and Co, which is scheduled for a down
stream hydrometallurgical process. The recovered alloy is leached with
hydrochloric acid, and the leached metals are extracted by solvent
extraction. The recovered products are Cu, Fe, CoCl2, and Ni(OH)2 [18],
(ii) a slag fraction comprising of Al, Si, Li, Ca, and Mn [124], (iii) clean
gas stream after gas treatment [131]. The alloy and slag fraction can be
tapped out and granulated. A significant proportion of Li is lost in the
dust, and the Li in the slag fractions requires complex hydrometallur
gical processes to recover it [30]. The CoCl2 is used to synthesize
B. Makuza et al.

13
Table 1
A brief review of published laboratory work on pyrometallurgical recycling options.
Pyrometallurgy
Technique
Cathode
material
Additive Pretreatment Thermal
treatment
condition
Separated material Secondary process Recovery rate Ref
Reduction Roasting LiNiMnCoO2 Carbon – 650 ◦
C,
30 min
Li2CO3, Co, Ni, NiO,
MnO, CO2(g)
Water and acid
leaching (H2SO4)
93.67% Li, 93.33%
Ni, 98.08% Co and
98.68% Mn
[11]
Sulfation Roasting LiCoO2 SO2(g) – 700 ◦
C,
120 min
Li2SO4, Li2Co(SO4)2,
CoO, O2(g),
Water leaching 99.5% Li, 17.4%
Co
[15]
Sulfation
Roasting
LiNiMnCoO2 Na2SO4 NaCl submersion,
Manual
dismantling,
Calcination
750 ◦
C,
90 min
Li2SO4, MnO, NiO,
CoO, CuO2,
Water leaching 85.43% Li,
efficiencies of Ni,
Co, and Mn were
84.93%
[30]
Nitration Roasting LiCoO2 HNO3 Mechanical
pretreatment
250 ◦
C,
60 min
LiNO3, Co(NO3)2,
NO(g), O2(g), H2O(g)
Water leaching 93% Li,
efficiencies of Co,
Ni, Cu were 92.9%
[31]
Vacuum pyrolysis LiCoO2 Carbon NaCl discharging,
Manual
dismantling,
Vacuum pyrolysis
600 ◦
C, Co, CoO, Li2CO3, CO2
(g)
Water leaching 93% Li, 99% Co [26]
Plasma Spray
Pyrolysis
LiNiMnCoO2 – NaOH dissolution 600 ◦
C, Regenerated
LiNiMnCoO2
[98]
Chlorination
calcination
LiCoO2 NH4Cl Discharging,
Manual
dismantling,
NaOH dissolution
350 ◦
C for 20
min
LiCl, CoCl2, H2O(g),
Cl(g), N2(g), NH3(g)
Water leaching 99.18% Li, 99.3%
Co
[63]
Microwave
Carbothermic
Reduction
LiNiMnCoO2 Carbon NaCl discharge,
Manual
dismantling,
comminution
(900 ◦
C) 500
W,
30 min
– Acid leaching (HCl(aq)) 99.68% Li, 97.65%
Ni, 97.85% Co, and
96.73% Mn
[64]
Carbothermic
Reduction
Smelting
LiCoNiO2 Cu slag (slag
former)
– 1450 ◦
C for
30 min
Co, Ni, Cu, and Fe
Alloy and slag FeO,
SiO2, Al2O3, CaO,
MgO
Manual separation of
slag & alloy
Comminution
98.83% Co,
98.39% Ni and
93.57% Cu
[32]
Reduction Smelting LiNiMnCoO2 Pyrolusite slag
former, SiO2,
CaO
Roasting at 800 ◦
C
for 120 min to
remove carbon
1475 ◦
C,
30 min
Co–Ni–Cu–Fe alloy
and lithium-
containing
manganese-rich slag
Manual separation,
comminution, acid
leaching (sulfuric
acid)
79.86% Li, 94.85%
Mn
[69]
Oxygen-free
roasting
LiCoO2 Carbon – 1000 ◦
C,
30 min
Li2CO3, Co Wet magnetic
separation
95.72% Co,
98.93% Li
[65]
Fig. 8. Lithium-ion battery industrial recycling process flow chart [126].
B. Makuza et al.

14
battery-grade LiCoO2 [34]. The Umicore Val’eastm process has an in
tegrated off-gas treatment system, which results in no volatile organic
fraction, complete dust removal, and low volume gas [35]. The tem
perature of the gases as they exit the furnace is around 450 ◦
C, and they
are subjected to cooling and filtering in a post-combustion chamber [18,
124]. By injecting water vapor in the chamber, the formation of dioxins
and furans is inhibited as halogens do not recombine with organic
compounds. The exhaust gas in the pyrolysis zone is recirculated to the
preheating zone, and this increases the furnace temperature, thus
decreasing energy requirements and also helps to evaporate the elec
trolyte [18]. A plasma torch is used to treat the waste gases at a tem
perature of 1150 ◦
C to avoid their condensation, and ZnO, Ca, or Na can
be added to capture volatile components, and halogens evolved from
electrolyte and binder evaporation [34,82,133]. Umicore has an annual
operating capacity of 7000 metric tonnes [131], and the process requires
5000 MJ of energy for the smelter and gas treatment system to treat one
tonne of batteries [29,129]. The transition from LCO to NMC cathode
material would render this process vulnerable.
5.1.2. Glencore (Xstrata) battery recycling process
Glencore utilizes a combination of pyrometallurgical and hydro
metallurgical processes to recycle spent LIBs as a secondary feedstock
[34,87]. The LIBs form a very small proportion of the total production,
but they are a niche market for Glencore, and it intends to increase the
capacity [134]. The total annual recycling capacity for spent LIBs is
7000 tonnes [18] compared to 550 000 tonnes of Cu and Ni [134].
Glencore works hand in hand with battery collectors, and it requires that
the batteries be pretreated to deactivate them and dismantle them into
individual battery cells or battery packs with 6–12 cells, which is due to
the input size limitations of the rotary kiln [134]. The LIBs are processed
by either directly feeding them to a converter or a rotary kiln. The
temperature in the molten metal bath is 1300 ◦
C. The organic compo
nents are burnt off, and the off-gas is treated using afterburners to ensure
no dioxins are released. The cobalt and steel casings from the recycling
process are introduced into the converter for further processing [134].
The matte phase undergoes a subsequent hydrometallurgical refining
process to recover Co. In this process, only the Co, Ni, and Cu are of
interest. The remaining fractions are consumed in the process to provide
heat, utilized as a reductant, or is slagged [87]. The process was not
initially designed to treat LIBs; hence the Li is lost in slag [34].
5.1.3. Accurec battery recycling process
The Accurec recycling process employs mechanical pretreatment,
pyrometallurgy, and hydrometallurgy to recycle all types of LIBs. The
battery cells are opened, and organic components (electrolyte, plastics,
binders) are removed entirely by pyrolysis [87]. The pyrolysis temper
ature is maintained below 250 ◦
C and does not change the state of the
metal contents [35,47,87]. Thermal pretreatment in the Accurec process
offers the advantage of controlled deactivation and safe destruction of
combustible organic material, eliminating the risk of fluorine com
pounds being released into the atmosphere or electrolyte reacting with
the atmosphere during mechanical pretreatment [51]. LIB consists of
approximately 30%wt of carbon with respect to overall battery weight,
and the vacuum thermal treatment process reduces the carbon content
to about 15%wt [87]. Moreover, the battery cells are discharged during
this vacuum thermal pretreatment process as the electrolyte evaporates
[124]. The electrolyte is condensed in a condenser system, and the
condensate composition is ~10% ethylene carbonate and ~71% ethyl
methyl carbonate, but it is nearly impractical to reuse it as it contains
decomposition products [87]. Recovery of the condensate can be made
in a separate process with a recovery rate of up to 80% [87].
The deactivated cells undergo comminution in a hammer mill, and
four separate size fractions are obtained by mechanical classification.
Depending on the physical properties of the treated material, separation
can be made by magnetic separation, air separation, zig-zag classier, or
vibrating screen. The obtained fractions are an enriched metal fraction
containing cathode material, current collectors (foils), Al, and Fe–Ni
fraction [47]. The target metals Co, Mn, Li, are concentrated in the size
fraction passing 0.2 mm, and the binder material is added to the fine
fraction to agglomerate the particles to the pellets to enhance better
handling and charging into the furnace [87]. The pellets are treated in a
carbothermic reduction process at a temperature of 800 ◦
C, producing a
Co alloy, and Li is lost in the flue dust and slag. The Li in slag can be
recovered by subsequent hydrometallurgical processes [124]. The
characteristics of the Accurec process are safe recycling as no carcino
genic powders are produced during the process [50].
5.1.4. INMETCO battery recycling process
The International Metals Reclamation Company (INMETCO) oper
ates an industrial scale pyrometallurgical facility for recycling spent
LIBs. The LIBs are fed as secondary feedstock in the High-Temperature
Melting Recovery (HTMR) process [135]. The HTMR process was
initially designed to treat steel manufacturing waste (furnace dust,
Table 2
Industrial pyrometallurgical recycling paths [127].
Steps Pretreatment Extractive
pyrometallurgy
Energy
requirement
Recovered
fraction
Lost fraction Advantages
1,2,
3, 4
Sorting,
+Dismantling,
+Pyrolysis (rotary kiln)
+Mechanical separation
– High Ni, Co, Cu, Fe,
Mn, Li (Black
mass)
Electrolyte
Binder, graphite
Complete removal of carbon and
organic components, which increases
leaching efficiency.
Possibility to recover electrolyte by
condensation.
Possibility to recover Mn, Li, Fe, and
Al.
1, 2,
3
Sorting,
+Dismantling,
+Thermal treatment
EAF & converter High Ni, Co, Cu Organic components,
ignoble metals, and Li is
slagged
Complete removal of carbon and
organic components, which increases
leaching efficiency.
1, 4 Dismantling Smelting in a
shaft furnace
Medium Ni, Co, Cu, Fe, Carbon, organic
components, Ignoble metals
are slagged
Organic components can be burnt out
to compensate for energy
requirements, and it also decreases
GHG emissions
4 Dismantling done to batteries that
do not meet the size specifications
of the material handling system
Direct Smelting in
EAF
High Ni, Co, Cu No recovery of Li, Al,
electrolyte, graphite,
plastics, Ignoble metals are
slagged
Eliminates the need for costly and
hazardous pretreatment.
Organic components can be burnt out
to compensate for energy
requirements, and it also decreases
GHG emissions
All products undergo hydrometallurgical refining to extract pure metals.
B. Makuza et al.

15
electric fumes, mill scale, swarf) [135]. The recycling steps in the HTMR
process include mechanical pretreatment, reduction, melting, and
casting. The feed to the furnace is prepared by opening the battery,
dismantling, draining the electrolyte, followed by shredding the battery.
The other solid components are blended, and a carbon-based reductant
is added. The mixture is pelletized, and during the pelletizing stage,
liquid waste, which contains cadmium and nickel, is added. The pellets
are combined with the shredded batteries and fed into the rotary hearth
furnace. The HTMR process is carried out in the rotary hearth furnace at
a temperature of 1260 ◦
C for 20 min [136]. The organic components and
carbon are burnt or utilized as reductants in the carbothermic reduction
of the active cathode material [34,87]. The off-gas from the rotary
hearth furnace is scrubbed, and the scrub solution is sent to a wastewater
treatment facility, from which treated water is recycled back to the
process [136]. A submerged electric arc furnace (SEAF) is used to refine
the reduced molten material from the hearth furnace by smelting. The
INMETCO process is a direct reduced iron (DRI) process, and it only
recovers Co, Ni, and Fe in the form of an iron-based alloy [18,87]. The
alloy is tapped from the furnace and fed to a casting step [136]. The
ignoble metals, including Li, are slagged as the INMETCO process is not
a LIB dedicated recycling process. The annual operating capacity of the
facility is 6000 tonnes [18].
5.1.5. JX Nippon Mining & metals battery recycling process
JX Nippon Mining and Metals operates an industrial scale pyro-
hydrometallurgical facility for recycling spent LIBs. The initial design
for the plant was to treat waste cathode material from the manufacturing
plant, but as the competition became inevitable for waste cathode ma
terial, the facility made adjustments to process spent LIBs [137]. The
lithium-ion batteries are fed in a stationary furnace and incinerated to
recover the active cathode material and separate it from the casing,
connectors, and wires. Incineration evaporates and burns out the
organic electrolyte, and fluorine is recovered by precipitation. The
clinker is shredded and undergoes mechanical classification on a screen.
The fine material, which is composed mainly of cathode material, un
dergoes leaching, solvent extraction, and electrowinning to recover
electrolytic Ni and electrolytic Co as main products, and lithium and
manganese carbonate as by-products [137]. The coarse fraction and
residue of the fine fraction from hydrometallurgical processing are
smelted to recover refined copper. The plant has an annual operating
capacity of 5000 tonnes [125,133].
5.1.6. Sony-Sumitomo battery recycling process
The Sony-Sumitomo process is a pyrometallurgical recovery route
developed by Sony and Sumitomo Mining Metals Company (SMM). In
the process, untreated LIBs are fed into the furnace and calcined at
1000 ◦
C [29,132,138]. The inflammable components like plastics,
electrolyte, and all other organic components are burnt off, producing
energy for the process [17,35]. Moreover, Li is lost as flue dust together
with the organic components. A scrubber is used to remove the vapor
ized gases from the flue dust [29]. After calcination, the calcine is
crushed and screened [139]. Magnetic separation separates the metallic
residue, which consists of Al, Fe, and Cu. The remaining fraction is a
powder containing primarily the active cathode material and carbon,
and it undergoes subsequent hydrometallurgical processing to recover
CoCl2 [35]. The main product of this recycling process is a high-grade
CoO [47], which can be utilized to regenerate LiCoO2 cathode mate
rial [18]. This approach is primarily meant to recover cobalt, which
comes as a drawback as other metals are lost. Sony-Sumitomo has an
annual operating capacity of 150 tonnes, and the process requires 992
MJ of energy to incinerate one tonne of organic material [138].
Recent progress by Sony-Sumitomo is the development of the first
practical pyrometallurgical technique in Japan to recover copper and a
hydrometallurgy technique to recover nickel. The process is a combi
nation of the nickel hydrometallurgical refining process (Niihama Nickel
Refinery) and copper pyrometallurgical refining process (Toyo Smelter).
These advancements will enhance value realization from recycling spent
LIBs and resource sustainability [34].
Table 3 gives a non-exhaustive data review of some of the pyro
metallurgical recycling methods applied at an industrial scale.
5.2. Battery recycling legislation
Lithium-ion batteries have deleterious effects on the environment
and require an effective collection and disposal management system.
The low recycling rates for spent LIBs can also be attributed to inade
quate collection systems exacerbated by deficient recycling regulations
[17]. An excellent collection system is imperative as industrial recycling
facilities for treating waste Li-ion batteries require a constant feed
supply.
5.2.1. China policy and regulatory framework
China ranks top in terms of battery recycling capacity because the
recycling efforts in China are supported by the economic value of
recycled materials and legislative pressure [143]. Furthermore, China
dominates the LIB manufacturing industry, and hence the recovered
material has a ready market. Moreover, the explosive growth in the
electric vehicle market in China sets the country as the largest electric
vehicle market. This demand surge is supported vigorously by govern
ment incentive schemes to address climate change and energy shortage
[144]. According to China Automotive Technology and Research Center
(CATRC), the volume of scrapped EV batteries in China was projected to
reach 120 000–170 000 tons by 2020 [144]. The Ministry of Ecology and
Environment for the People’s Republic of China has enacted laws and
technology standards to curb the growing pressure on environmental
impacts emanating from LIB disposal [145]. Battery manufacture,
collection, and recycling must conform to national standards. Since
2001, battery disposal regulations were passed [143], and they were a
small aspect under Municipal Solid Waste (MSW) disposal regulations.
Since then, continuous adjustments have been made up to now, and
lithium-ion battery recycling standards are now a standalone standard
[17]. However, much emphasis is placed on lead-acid batteries, as
depicted in Table 4. Table 4 gives a review of the GB Standards and Laws
about battery recycling in China. China’s legal framework for waste
management also incorporates the 3R’s, which are reclaim, reuse/r
efurbish, and recycle with an insight into the circular economy to
optimize material life span and reduce life cycle impacts [73,77]. The
batteries containing 80–85% energy are reused for stationary energy
storage as it requires less energy density [146].
Apart from legislation, government subsidy (incentives) also confers
a significant benefit in battery recycling. The battery recycling com
panies have different battery recycling strategies depending on the
impact of the recycling scale on costs [144]. When the benefit from
recycling is low to moderate, partial recycling arises. The government of
China has been giving subsidies for battery recycling to enable
comprehensive battery recycling [144]. Apart from recycling subsidies,
recycling companies also request gate fees as the spent batteries cannot
be landfilled, and these gate fees form an integral part of the business
model [40]. The disposal fees for batteries with less cobalt content in the
EU are double that of batteries with higher cobalt content. A high cobalt
content battery is anecdotally pegged at 2.50 €/kg, whereas a low cobalt
content battery is 5.00 €/kg [40,90]. As new entrants enter the battery
recycling market, the battery selective pressure and gate fees are likely
to drop [40].
Outside China, legislation is also immense concerning battery
disposal, e.g., Directive 2012/19/EU [147] and Restriction of Hazardous
Substances (RoHS) regards spent LIBs as hazardous waste and prohibits
its incineration [8]. The EU directive calls for 50% mass recycling and
does not regard energy recovery as recycling [40,147].
5.2.2. Forecast of pyrometallurgical recycling in China
The pyrometallurgical recycling process is dominant in the EU, and
B. Makuza et al.

Journal
of
Power
Sources
491
(2021)
229622
16
Table 3
Outline of industrial pyrometallurgical battery recycling technologies.
Company Country Capacity
(t/year)
Battery type
processed
Pretreatment Pyrometallurgy Post-treatment Products Secondary
Products
Losses Ref
Valdi (Eramet) France 20 000 LIB and
other
batteries
– (not reported) – FeNi/FeMn alloy – – [125]
Umicore Belgium 7000 LIB, Ni–Cd,
Ni-MH
No pretreatment
Only dismantling for large
batteries
Smelting
Shaft furnace
Leaching, solvent
extraction
CoCl2, Co, Ni, Cu,
Fe
Slag (Al, Si, Ca,
Fe, Li, Mn, REE)
Electrolyte, plastics,
graphite
[17,18,
131]
Xstrata
(Glencore)
Switzerland 7000 All LIB
chemistry
No pretreatment Conditioning (rotary kiln) and
introducing into a Co–Ni
winning process (EAF)
Hydrometallurgy alloy (Co–Ni–Cu) Li slagged and
ignoble metals
No recovery of Li, Al,
electrolyte, graphite,
plastics
[17,87]
Inmetco USA 6000 LIB, Ni–Cd,
Ni-MH
Sorting Calcination (rotary hearth
furnace), smelting EAF
Iron casting alloy (Co–Ni–Fe) Li slag Organic material
used as chemical
reagent
[17,
140]
Accurec Germany 6000 All LIB
chemistry
Sorting, Dismantling
Milling, separation,
agglomeration, filtration
Vacuum thermal treatment,
reduction
Acid leaching Li2CO3
Co-Alloy
Metallic alloy Electrolyte,
polymers,
graphite
[18,50,
51]
JX Nippon
Mining and
Metals
Japan 5000 – Incineration, comminution Smelting Selective precipitation,
electrowinning
Li2CO3, Ni,
MnCO3, Co
– Electrolyte, [125,
133,
137]
Dowa Japan, 1000 All LIB – Co, Ni, Mn [128,
133],
[141]
SNAM France 300 – Crushing
Pyrolysis
Magnetic separation
(not reported) – Black mass (Cu,
Ni, Co)
– – [17]
Sumitomo Japan 150 LIB (LiCoO2) Sorting, dismantling Calcination Acid leaching,
hydrometallurgy
CoO Co–Ni–Fe alloy
Cu, Al, Fe
Electrolyte, plastics,
Li, Ni, graphite
[15,16,
33]
G & P Batteries UK, 145 LIB – (not reported) (not reported) – – – [40,
133]
LithoRec Germany 100 – Manual disassembly, Two-
stage crushing, two-stage air
classification
Drying, Calcination Leaching Li2CO3 Al–Cu, plastic
fractions
Electrolyte [18]
GRS Batteries Germany – LiMnO2 – Vacuum distillation – Co, Ni, Cu,
FeNi and FeMn
– – [40]
Battery
resources
Germany – – Discharging, shredding,
magnetic separation,
sieving, DMS
Sintering Leaching by NaOH,
H2O2, H2SO4, Na2CO3
LI2CO3, metal
oxides
Al–Cu, plastic
fractions
Electrolyte [40]
Onto USA – LIB Discharge, dismantling,
shredding, sieving, DMS,
(Not reported) Leaching purification,
dissolution
Refurbished cell
cathode powder
Ferrous & non-
ferrous metals
Binder, graphite [17,18]
Nickelhütte Aue
GmbH
Germany – LIB, Ni-MH – Smelting (not reported) Co, Ni, Cu matte – – [128,
142]
B.
Makuza
et
al.

17
the EU has sufficient pyrometallurgical recycling capacity for LIBs for
2020 [148], with companies such as Valdi Emerat having an annual
recycling capacity of 20 000 tonnes per annum of LIBs [125]. However,
hydrometallurgical processes are primarily deployed for LIB recycling in
China [12,34], although the future of LIB recycling in China is likely to
transition due to continuous R & D in pyrometallurgical recycling.
Among the most extensive battery recycling companies in China are
Hunan Brunp (HP) and Green eco manufacture (GEM), with annual
battery and scrap recycling capacities of 100 000 and 30 000 tonnes,
respectively. Although the recycling capacity is not low, the amount of
recycled battery scrap is far from the projected demand surge, and the
design capacity is not reached. Regardless of the recycling processes
being centered on hydrometallurgy, the facilities also incorporate
high-temperature processes. For instance, the active cathode material in
the Huna Brunp processes is recovered by the pyrolysis/wet method
[128]. Moreover, the large processing capacity in the process also stems
from the Ni–Fe alloy produced by the pyrometallurgical processes,
mainly in the recycling of waste Ni-MH batteries [149].
Hydrometallurgical processes had been developed further as pyro
metallurgy could not recover Li [150]; however, this is no longer the
case. Moreover, it was characterized by too high temperatures, coupled
with toxic gas emission, and it was centered on recovering the
high-value metal Co while the other valuable metals were slagged. These
conditions made the processes not favorable mostly for China, which
already had a high carbon footprint, and the large number of batteries
employed in the electric buses and EVs used LiFePO4 active cathode
material [151]. However, the pyrometallurgical recycling facilities
employed in Europe now have an integrated off-gas treatment system
and capabilities to recover multiple raw material streams.
It is worth mentioning that companies such as Retriev have already
transitioned from the hydrometallurgical recycling route, despite the
adoption of the traditional hydrometallurgical route by multiple leading
companies in China [150]. Consequently, the massive number of LIBs to
be discarded and the projected demand for heavy metals for LIB cathode
manufacture is likely to cause pyrometallurgical recycling options to be
developed further in China. Pyrometallurgical recycling will enhance
production efficiency due to faster recycling steps by eliminating the
need for costly, time-intensive, and hazardous pretreatment such as
discharging and dismantling [41]. Moreover, the automated disman
tling process is complicated and likely to deter production as the battery
designs are not standard, and the use of different bonding mechanisms,
fixtures, and adhesives complicates the process [77].
6. Summary, challenges, and future outlook
A growing market for LIBs in the consumer and automotive industry
has led to an inevitable amount of batteries reaching their end of life.
Battery recycling is indispensable in order to resolve the battery disposal
concerns, guarantee environmental protection, resolve the sustainability
gap, and ensure a constant supply chain of critical materials like cobalt
and nickel. Pyrometallurgical recycling is a dominant and mature pro
cess because of its short reaction time, high productivity, and ease of
scaling up [47]. The main pyrometallurgical options for recycling spent
lithium-ion batteries are pyrolysis, incineration, roasting, and smelting.
Continuous research and development (R & D) in pyrometallurgical
recycling will enable battery recycling companies to cope with the
inevitable increase in spent LIBs. Ongoing R & D will foster the effective
implementation of an economically more feasible circular economy
value chain for the batteries. The paper presents the following as a
rundown of the challenges and future outlook for pyrometallurgical
options for recycling spent LIBs.
1. The economic prospects of the industrial battery recycling facilities
vary with battery chemistry, and a strong research focus has been
placed on Co recovery, which has a volatile price. The developments
in the field of LIB are highly dynamic, and the individual battery
components are always changing. Most processes consider LiCoO2 as
the cathode material, which is no longer the ideal case on the com
mercial side [130]. Substitution of Co with other metals will threaten
the economic efficiency of the recycling process and also render the
recycling technology obsolete. It is imperative to devise low-cost and
flexible recycling facilities that can recover a broad spectrum of
critical components to maintain an effective long-run battery
industry.
2. Most of the traditional industrial pyrometallurgical processes cannot
recover lithium [1]. Although Li is not listed as a critical raw material
like Co, its scarcity and uneven distribution over the earth’s crust
make it a mineral of societal interest [152]. It would be advanta
geous if the process technology can recover Li from both the lithiated
metal oxide and the electrolyte. The industrial recycling processes
are fully aligned for the recovery of valuable metals Co, Ni, and Cu
[90], and this leads to a low recycling efficiency as other materials
are not recovered. For instance, the recycling efficiency for Xstrata
and Umicore in 2015 was <30%, which is less than the stipulated
50% mass recovery by the Directive 2012/19/EU [90].
3. Pyrometallurgy is capital intensive in part due to high energy re
quirements and complicated off-gas treatment mechanisms.
Research is still required to develop a resource-efficient recycling
system with low off-gas production and chemistry [127], which can
substantiate growth. Pyrometallurgical recycling option with mild
processing conditions (salt assisted carbothermic reduction) has
been explored as an alternative to the traditional recycling options
employing intermediate temperature (<1000 ◦
C) and mild hydro
metallurgical conditions (alkali or acid-free). The methods have
proven to be promising, although the mechanisms of physical and
chemical changes during the recycling process need to be explored
further.
4. A precarious legal framework is in place for recycling lithium-ion
batteries as regulation is much centered on lead-acid battery,
which has a recycling rate of ~98% [13]. The weak policy formu
lation results in poor collection and recycling systems, and this has
dire consequences on pyrometallurgy processes as they require a
Table 4
Data review of the GB Standards and Laws about battery recycling in China
[145].
Year Standard number Standard
2001 GB 18484-2001 Pollution control standard for hazardous wastes
incineration
2006 HJ/T 238-2006 Technical requirement for environmental labeling
products-Rechargeable batteries
2007 HJ 348－2007 Environmental protection technical specifications for
disassembly of end-of-life vehicles
2008 HJ 447-2008 Cleaner production standard - Lead-acid battery
industry
2008 GB/T 22424-
2008
Technical requirements and treatment of lead-acid
battery for telecommunication
2008 GB/T22425-
2008
The recycling and treatment of lithium-ion battery for
telecommunication
2009 HJ 510－2009 Cleaner production standard - Waste lead-acid battery
recycling
2009 HJ 519－2009 Technical specifications of pollution control for the
treatment of lead-acid battery
2013 GB 30484-2013 Emission standard of pollutants for the battery
industry
2017 GB/T 33598-
2017
Recycling of traction battery used in an electric vehicle
-Dismantling specification
2019 GB/T 37281-
2019
The technical specification for recycling waste lead-
acid battery
2020 GB/T
38698.1–2020
Recycling of traction battery used in an electric
vehicle-Management specification - Part 1：Packing
and transporting
2020 GB/T
34015.2–2020
Recycling of traction battery used in an electric
vehicle-Echelon use - Part2：Removing requirements
2020 GB/T
33598.2–2020
Recycling of traction battery used in an electric vehicle
- Recycling-Part 2：Materials recycling requirements
B. Makuza et al.

Pyrometallurgical options for recycling spent lithium-ion batteries A comprehensive review.pdf

Pyrometallurgical options for recycling spent lithium-ion batteries A comprehensive review.pdf

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Pyrometallurgical options for recycling spent lithium-ion batteries A comprehensive review.pdf

Similar to Pyrometallurgical options for recycling spent lithium-ion batteries A comprehensive review.pdf (20)

Recently uploaded

Recently uploaded (20)

Pyrometallurgical options for recycling spent lithium-ion batteries A comprehensive review.pdf