Layered composite for high energy density cathode material

1. Effect of ZnO Treatment on
0.5Li2MnO3.0.5LiNi0.5Mn0.5O2
Monday, May 5, 2012 , Seattle
WashingtonECS Seattle
Department of Physics and Institute for Functional Nanomaterials, University of
Puerto Rico, San Juan, PR 00931-3343, USA.
Gurpreet Singh ,Arun Kumar, R. Thomas and R.S. Katiyar ,A.Manivannam

2. Outline
Introduction & Motivation
Rechargeable battery and applications
Cathode material selection
Experimental details
Powder synthesis, coin cell construction.
Structural and electrochemical
characterization
Results & Discussion
XRD, SEM, Raman spec. for process
optimization.
CV and cycleability
Rate capability
Summary and conclusion
Outlook
Outline

3. Li-ion batteries are among the best battery systems in terms of energy
density (W-h/kg & W-h/L). This makes them very attractive for hybrid
automobiles & portable electronics.
Before coming to working principle of rechargeable battery, let’s see
why Li is so important
Why Li(ion) batteries?
 It is lighter (3rd
in periodic table)
 Most electropositive
Contributes positively towards
higher energy density

4. Li-ion Battery & Cathode Materials Considerations
Schematic of Rechargeable Li Battery
Li ion shuttles between anode and
cathode
During charge Li ion move from
cathode to anode
During discharge Li gets intercalated
into cathode
X Li + + x e - + Li yM X Liy+x MX
Charge
Discharge
X Li + + x e - + Li yM X Liy+x MX
Charge
Discharge
∆G= -nFE
For maximum (+ve) E, cathode has to be highly oxidizing and anode has to be highly reducing
Cathode –Intercalation compound
Anode - Li metal (Li battery) not
safe
or another intercalation compound (Li
ion battery)

5. Energy density (Wh) = Capacity (Ah) × Voltage (V)
Large work function (highly oxidizing)
+ maximize cell voltage.
 Insertion/extraction of a large amount of lithium
+ maximize the capacity.
High cell capacity + high cell voltage = high energy density
 Reversible lithium insertion/extraction process.
+ make it rechargeable
 No structural changes
+This prolongs the lifetime of the electrode.
 Good electronic and Li+
ionic conductivities.
+ improves the rate capability
 Chemically stable over the entire voltage range
+ No reaction with the electrolyte.
 Inexpensive, environmentally benign and lightweight.
+safe, friendly, portability
Cathode: Material requirements

6. LiCoO2
is still the only commercialized cathode material
+ Excellent electrochemical properties.
-relatively expensive and toxic
-only 50% of the theoretical capacity practically utilized.
- exhibit three phase transitions during the Li
extraction and insertion ( from the CV )
- The cation disorder of Ni ions
- Layered rhombohedral structure to pristine LiNiO2
Current status of cathode material
Pros and cons with LiMnO2
Higher discharge capacity (~200 mAh/g), LiNiO2
considered for replacing LiCoO2.
layers of Mn-O edge-sharing octahedra
Li+
Partial substitution of nickel with other elements that leads to a
reduction in the amount of Ni in the Li-type sites can be expected to
improve the structural and electrochemical properties of lithium nickelate
form the basis of the present work
Substitution of Ni ion with trivalent M cation (M= Mn & Co)

7. Stirring @5 0°C
PH of solution adjusted 8 by NH40H
Light green color precipitatesLight green color precipitates
Dried over night , Li2CO3 mixed thoroughly in agate mortar pestleDried over night , Li2CO3 mixed thoroughly in agate mortar pestle
Synthesis of 0.5Li2MnO3.0.5LiNi0.5Mn0.5O2
raw materials (MnSO4.H2O,NiSO4.H2OCO3O4, Li2CO3 1 M aqueous solution of
NaHCO3 in a 500 ml flask
Pellets were claimed at 950 C for 12 h and quenched in liquid
nitrogen .
The resulting 0.5Li2MnO3.0.5LiNi0.5Mn0.5O2 powered was
gray

8. J.R. Dahn, et al., electrochem. Act.,38 (1993) 1179
Schematic of CR2032 coin cell
Working electrode (cathode)
Active powder – 80 wt%
Carbon black – 10 wt%
PVDF binder – 10 wt%
Current collector- Al
Electrolyte
LiPF6 – 1M
EC : DMC- 1:1
Anode
Li foil
Powder Preparation:
Structural Characterization:
X-ray diffraction,
Raman spectroscopy
Electrochemical Characterization:
Cyclic voltammetry, Charge discharge and rate -
capability
Coin cell assembled in our group
Experiment: coin cell fabrication

9. Phase Check : X-ray Diffraction
20 40 60 80


Intensity(a.u)
2θ (Degrees)
(a) Pristine LLNMO
(b) ZnO Treated LLNMO
- Al

(003)
(101)
(006)
(012)
(104)
(015)
(107)
(018)
(110)
(113)
(a)
(b)
(020)C2/m
(110)C2/m
(021)C2/m
(-111)C2/m
(116)
(021)
(0012)
(024)
(0111)(205)
• Major peaks are indexed to R-3m
• Peaks Between 20 – 30 are presence
of monoclinic LiMnO3 phase with
space group of C2/m.
• Clear splitting of (006) and (012)
along with (018) and (110) is
observed, showing formation of well
crystalline layered structure
• No change in XRD pattern before and
after ZnO treatment shows no major
effect of ZnO on the crystal structure

10. Phase Check: Raman Spectroscopy
200 300 400 500 600 700 800
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
Intensity(A.U)
Wavenumber (cm-1)
(a) Pristine LLNMO
(b) ZnO Treated LLNMO
(b)
(a)
• Three major Raman active modes have
been observed at 420,467 and 590 cm-1
for both pristine LLNMO and ZnO
treated LLNMO
• Literature shows that 424 cm-1
corresponds to the presence of
Li2MnO3 in composite structure .
• Raman spectroscopy results are in
accordance with X-ray diffraction,
showing the presence of Li2MnO3
short range ordering in the crystal
structure
• ZnO treatment does not lead to any
change in the local structure

11. Morphology Check
(a)
(b)
(c)
• Before the synthesis of the material, target was to
make highly dense spherical agglomerates of the
primary particles.
• More precise control over the precipitate
formation conditions might lead to even better
spherical morphology
• Primary particle size : 0.5 – 1 µm
• Spherical agglomerates : 5 - 10 µm
(a) Dried metal carbonates obtained after precipitation
(b) Pristine LLNMO
(c) ZnO treated LLNMO showing the agglomerates of
primary particles

12. Presence of Zinc : EDS
(a)
(b)
Presence of Zn has been confirmed by EDS
Pristine LLNMO
ZnO Treated LLNMO

13. Presence of Zn and Oxidation states
check : XPS
630 640 650 660 670
4000
6000
8000
10000
12000
(ii)
(i)
Counts/s
Binding Energy (eV)
Prisitne LNMO
ZnO Treated LNMO
642.5 eV (Mn+4)(a)
840 850 860 870 880 890
1600
1800
2000
2200
2400
2600
(ii)
(i)
Counts/s
Binding Energy (eV)
Pristine LNMO
ZnO Treated LNMO
855.0 eV (Ni+2)(b)
1000 1010 1020 1030 1040 1050
6500
7000
7500
8000
8500
9000
9500
10000
(ii)
Binding Energy (eV)
Counts/s
Pristine LNMO
ZnO Treated LNMO
1021.5 eV (Zn2+)(C)
(i)
Mn is observed to be present +4 oxidation state
Ni is observed to be present +2 oxidation state
Zn is observed to be present +2 oxidation state
in sample treated with ZnO

14. Differential Capacity vs Voltage
2.0 2.5 3.0 3.5 4.0 4.5 5.0
-400
-200
0
200
400
600
800
1000
1200
dQ/dV
Voltage (V)
1st
1st
20th
20th
(a)
2.0 2.5 3.0 3.5 4.0 4.5 5.0
-400
-200
0
200
400
600
800
1000
1200
1400
(b) 1st
1st
20th
20th
dQ/dV
Voltage (V)
• From the differential capacity plots it has
been observed that there is no
distinguishable peak below 3.5 V in the
first cycle discharge curve.
• Major peak has been observed between
4.25 and 3.5 V in the first cycle
differential discharge curve.
• Continuous cycling shows very
pronounced peak appearing in between 3.5
– 3.0 V in both charging as well as
discharging cycle, which interns show the
effective reversible intercalation of the
lithium ions in the host MnO2 structure and
activation of the inactive component.
(a) Pristine LLNMO
(b) ZnO treated LLNMO

15. Galvanostatic Charge/Discharge
0 50 100 150 200 250
2.0
2.5
3.0
3.5
4.0
4.5
5.0
15
th
Voltage(V)
Capacity (mAh/g)
1
st
20
th
(a)
2
nd
5
th
10
th
0 5 10 15 20 25
0
50
100
150
200
250
Charge Capacity
Discharge Capacity
Coulombic Efficiency
Cycle Index (N)
Capacity(mAh/g)
(b)
0
20
40
60
80
100
CoulombicEfficiency(%)
0 50 100 150 200 250
2.0
2.5
3.0
3.5
4.0
4.5
5.0
Voltage(V)
Capacity (mAh/g)
(a)
15
th
1
st
20th
2
nd
5
th
10
th
0 5 10 15 20
0
50
100
150
200
250
Charge Capacity
Discharge Capacity
Coulombic Efficiency
Cycle Index (N)
Capacity(mAh/g)
(b)
0
20
40
60
80
100
CoulombicEfficiency(%)
Pristine LLNMO ZnO Treated LLNMO
Faster activation in case of ZnO treated samples has been observed compared to pristine
Rate
of
charging
and
discharging
is C/20

16. Rate Performance
0 5 10 15 20
0
40
80
120
160
200
240
DischargeCapacity(mAh/g)
Cycle Index (N)
LLNMO
ZnO Treated LLNMO
C/20
C/10
C/5
1C
C/20
• Materials were fully activated
before rate performance
check
• Charging rate was fixed at
C/20
• Discharging rate is given in
Figure
• Discharging rate was reverted
back to C/20 after net 40
cycles and it has been
observed that discharge
capacity also reverts back to
initial value
Net 40 cycle data : 20 Cycles were used to
fully activate the samples at C/20

17. Electrochemical Impedance Study
Zw
RctRsl
CPE CPE
Csl Cct
Cint
Re
Nyquest plots were fitted using above
shown model
Refined parameters
Pristine LLNMO ZnO Treated LLNMO
Before
Charge
Full
Charge
Full
Dischar
ge
Before
Charge
Full
Charge
Full
Dischar
ge
Re (ohm) 5.388 5.532 5.091 7.8 5.99 3.77
Rct (ohm) 379.1 85.97 254.8 309.9 166.1 213
Rsl (ohm) 31.53 210.8 299.8 28.1 3250.1 186.3

18. Conclusions
• Better electrochemical performance of the ZnO treated composite layered-layered
0.5Li2MnO3-0.5LiMn0.5Ni0.5O2 cathode material synthesised by carbonate based co-
precipiation method.
• Coagulation of the primary particles resulted in spherical agglomerates.
• ZnO treated LLNMO had the following benefits compared to pristine LLMNO: (i) faster
activation, (ii) high charge/discharge capacity, (iii) high columbic efficiency and (iv)
improved rate performance.
• Lower charge transfer resistance value in case of the ZnO treated sample enhances the
electrochemical performance of ZnO treated LLMNO compared to pristine sample.
• We have not examined the possible ZnF2 formation in our current system, but such
a study may be of interest to test the battery life. Further work on optimization of
the ZnO content for achieving the best electrochemical property, understanding of
possible formation of ZnF2 and the underlying reaction mechanisms in achieving the
improved electrochemical performance towards stability are underway.