Poster presented and Poster Award at the 5th Australia-China Conference on Science, Technology and Education and the 5th Australia-China Symposium for Material Science (July 2015)

1. 800 1000 1200 1400 1600 1800 2000
Intensity(a.u.)
Raman Shift (cm-1
)
Simple and environmental friendly preparation of LiFePO4/C for
lithium ion batteries with effective industrial scale-up potential
Katja Kretschmer1, Shuangqiang Chen1, Yufei Zhao1, Dawei Su1,2, Bing Sun1 and
Guoxiu Wang1*
1Centre for Clean Energy Technology, University of Technology, Sydney, NSW 2007, Australia http://www.cleanenergy.uts.edu.au
2Institute for Superconducting & Electronic Materials, University of Wollongong, Wollongong, NSW 2522, Australia
2.08 nm
2.39 nm
2.50 nm
24h
350 °C 10h
700°C 10h
Iron
precursor
Phosphate
precursor
Lithium
precursor
Carbon
precursor
Pre-sintered
precursor
LiFePO4
interconnected
in 3D carbon
network
• Precursor materials ball milled for 24h in ethanol followed by decomposition at 350
Experimental
Materials preparation
X-ray diffraction (XRD, Siemens D5000), field emission scanning electron microscopy
(SEM, Zeiss Supra 55VP), transmission electron microscopy (HRTEM, FEGTEM 3000
JEOL) and Raman (Renishaw, inVia Raman Microscope) were used to characterize the
prepared materials.
Introduction
Carbon-coated LiFePO4 is prepared in a sequence of simple and easily up scalable
steps via ball milling and solid-state reaction using Starch as carbon source. The
generated morphology appears to be very uniform and the particles are well dispersed.
This uniformity can be attributed to the initiated particle growth during decomposition
and subsequently growth restriction achieved by effective carbon wrapping. The
secondary particle size is between 50-200nm. XRD analysis and electrochemical testing
indicate the significant impact of the applied amount of Starch for the final product,
which so far implies that 10wt% Starch added to the Li/FePO4 precursor is the maximum
content to avoid impurities.
a) b)
c) d)
e) f)
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
*
**
LiFePO4
2 theta (degree)
Fe2
P
*
15wt%
20wt%
18.5wt%
5wt%
10wt%
8wt%
Results and Discussion
Fig. 1: (a) XRD patterns of LiFePO4/C prepared with 5 – 20 wt% added carbon source (soluble starch); (b) Raman
spectrum of LiFePO4/C prepared with 5 wt% carbon source (soluble starch)
Fig. 1 (a) shows that depending on the amount of added carbon precursor conductivity
enhancing impurities (Fe2P) can be detected. Fig. 1 (b) shows the presence of a rather
amorphous carbon component in the LiFePO4/C composite prepared with 5 wt% carbon
precursor.
Characterization and morphology
Fig. 2: SEM images of LiFePO4/C prepared with 5 – 20 wt% added carbon source (soluble starch);
(a) 5 wt%, (b) 8 wt%, (c) 10 wt%, (d) 15 wt%, (e) 18.5 wt% and (f) 20 wt%
Fig. 2 (a) shows uniformly dispersed grape-like particles of 100-200 nm size wrapped in
a thin 3D carbon network. Fig 2 (b) - (f) shows the influence of the added carbon
precursor on morphology and agglomeration.
a) b)
Conclusion
Carbon-coated LiFePO4 cathode materials are successfully prepared by ball milling and
solid-state reaction using starch as carbon source and only environmental friendly iron,
lithium and phosphate precursors. This method can generate uniformly carbon coated
grape-like nanoparticles, which are very favourable for Li+ transport and tap density of
the final product. Even though Fe2P phases are beneficial for reducing over-potential,
the capacity reduction caused by the high carbon content is disproportionate to justify
adding more than 10 wt% carbon source. Adding 5 wt% carbon source combined with
environmental friendly iron, lithium and phosphate precursor materials appears to be a
suitable and efficient approach to generate large amounts of high performance
LiFePO4/C cathode materials.
Acknowledgment
This original research was proudly supported by Commonwealth of Australia through the
Automotive Australia 2020 Cooperative Research Centre (AutoCRC).
Fig. 3: TEM images of LiFePO4/C prepared with 5 wt% added carbon source (soluble starch) confirming a well
interconnected particle cluster and a uniform distributed carbon coating
Fig. 3 confirms the crystallinity of the obtained material as well as the presence of a
conductivity enhancing, very uniform and thin carbon wrapping of 2 - 3 nm thickness.
The thermal decomposition and carbonization behaviour of starch is very favourable for
the generation of a uniform and thin carbon layer.
Materials characterization
Electrochemical testing
The working electrodes were prepared by mixing 80 % as-prepared LiFePO4/C with 10
% carbon black and 10 % poly(vinyl difluoride) (PVDF, Sigma-Aldrich) in N-Methyl-2-
pyrrolidone (NMP, Sigma-Aldrich). The obtained dispersion was carefully pasted onto
aluminium foil. The working electrodes were assembled to standard CR2032-type coin
cells.
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170
2.0
2.5
3.0
3.5
4.0
4.5
5wt%
8wt%
10wt%
18.5wt%
20wt%
Voltage(V)
Capacity (mAh/g)
10 20 30 40 50 60 70 80 90 100
3.30
3.35
3.40
3.45
3.50
3.55
95.5mV 79.3mV
Electrochemical performance
Fig. 4: (a) Charge-discharge profile of LiFePO4/C prepared with 5 - 20wt% added carbon source (soluble starch); (b)
differential capacity analysis ; (c) cycling performance of LiFePO4/C prepared with 5 wt% added carbon source (soluble
starch) and (d) rate performance of LiFePO4/C prepared with 5 wt% added carbon source (soluble starch)
The reversible capacity of LiFePO4/C prepared with 5 – 10 wt% added carbon source
~148 mAh g-1 whereas the samples prepared with >10 wt% added carbon source only
reach ~128 mAh g-1 at 0.2 C. A reduction in over-potential can be observed
corresponding to the presence of Fe2P impurities., as shown in Fig 4 (a). The differential
capacity analysis in Fig. 4 (b) confirms the observation of the voltage gaps. The samples
with a high Fe2P content show smaller voltage gaps in combination with reduced peak
heights, which is consistent with decreased capacity shown in Fig. 4 (a). The cycling
performance test revealed the high stability of LiFePO4/C for 100 cycles. As shown in
Fig. 4 (c), the material prepared with 5 wt% added carbon source maintained 94 % of the
initial capacity of 140 mAh g-1 after 100 cycles at 1 C. The rate performance test,
displayed in Fig. 4 (d), shows a very good capacity retention and appropriate rate
capability.
0 10 20 30 40 50 60 70 80 90 100
0
20
40
60
80
100
120
140
160
Capacity(mAh/g)
Cycle
5 wt% Starch
1C
0 5 10 15 20 25 30 35 40 45
100
110
120
130
140
150
160
170
Capacity(mAh/g)
Cycle
5 wt% Starch
2 C
1 C
0.5 C
0.2 C
a)
c)
d)
2.0 2.5 3.0 3.5 4.0
-5000
-4000
-3000
-2000
-1000
0
1000
2000
3000
4000
5000
6000
dQ/dV(mAhg-1
V-1
)
Voltage (V)
3.35 3.40 3.45 3.50 3.55
-6000
-4000
-2000
0
2000
4000
6000
dQ/dV(mAhg-1
V-1
)
Voltage (V)
20 wt% 87.4 mV
18.5 wt% 96.6 mV
8 wt% 95.2 mV
5 wt% 103.0 mV
10 wt% 105.4 mV
b)