Effect of excess Li+in solution on LiFePO4preparation via wet chemical method

Article abstract of DOI:10.1016/j.jallcom.2016.07.029

Olivine structure LiFePO₄has attracted much attention as a promising cathode material for lithium ion batteries, and many approaches have been developed to produce electrochemically active LiFePO₄at low cost. Here lithium iron phosphate (LiFePO₄) was prepared via co-precipitation method by using FeSO₄·7H₂O, LiOH·H₂O, and o-H₃PO₄as the raw materials. The effects of Li:Fe:P molar ratios and solution pH value on the synthesis of LiFePO₄were studied. The results illustrated that besides of the pH value parameter which was reported in many other previous researches, excess Li⁺in the solution was another essential condition for pure LiFePO₄preparation. It suggested that excessive LiOH was not only a pH regulator, but also a precipitation promoter. Maintaining a certain excess Li⁺ion in solution was an efficient measure to avoid the formation of impurities.

Full text of DOI:10.1016/j.jallcom.2016.07.029

Journal of Alloys and Compounds 688 (2016) 386e391
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: http://www.elsevier.com/locate/jalcom
Effect of excess Liþ in solution on LiFePO4 preparation via wet
chemical method
,
, *
Lihua He a b, Zhongwei Zhao b
a Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084, PR China
b School of Metallurgy and Environment, Central South University, Changsha, Hunan 410083, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Olivine structure LiFePO4 has attracted much attention as a promising cathode material for lithium ion
batteries, and many approaches have been developed to produce electrochemically active LiFePO4 at low
cost. Here lithium iron phosphate (LiFePO4) was prepared via co-precipitation method by using FeS-
O4$7H2O, LiOH$H2O, and o-H3PO4 as the raw materials. The effects of Li:Fe:P molar ratios and solution pH
value on the synthesis of LiFePO4 were studied. The results illustrated that besides of the pH value
parameter which was reported in many other previous researches, excess Liþ in the solution was another
essential condition for pure LiFePO4 preparation. It suggested that excessive LiOH was not only a pH
regulator, but also a precipitation promoter. Maintaining a certain excess Liþ ion in solution was an
efficient measure to avoid the formation of impurities.
Received 25 April 2016
Received in revised form
21 June 2016
Accepted 3 July 2016
Available online 5 July 2016
Keywords:
Lithium iron phosphate
Lithium ion battery
Wet chemical method
Excess Liþ
© 2016 Elsevier B.V. All rights reserved.
Impurity
1. Introduction
particle size mini-mization [5], and customizing particle mor-
phologies [7] have been undertaken.
In recent years, lithium ion battery has become the basis of the
huge market for cellular phones and lap top computers, and these
mobile communication markets continues to grow at a rapid rate.
Even so, intensive efforts are still under way to further improve the
technology. The main target of the effort is not only the electric
automobile industry by achieving higher energy and higher power,
but also the chemical energy storage, which are becoming
increasingly important for future environmentally friendly soci-
eties, by using rechargeable lithium-ion batteries. Since the pio-
neering work of Goodenough in 1997 [1], lithium iron phosphate
(LiFePO4) was found to be a particularly attractive cathode material
for lithium-ion batteries due to its low cost, nontoxic, high lithium
intercalation voltage, high theoretical specific capacity and greater
thermal stability [2,3]. Nevertheless, it has suffered with its
inherent low electronic conductivity and low lithium diffusion ki-
netics, which seriously prevent it from being used on a large-scale.
Up to now, progressive efforts to eliminate this obstacle by carbon
coating on the particle surface [4], developing composites via
mixing conductive materials [5], aliovalent cation substitution [6],
Conventionally, LiFePO4 powders are prepared by solid-state
synthesis with their associated repeated grinding and a long
period of high temperature operations. However, this approach has
some conspicuous disadvantages such as large particle size, broad
particle size distribution, and impurities. In contrast, wet chemical
preparation routes, such as hydrothermal [8,9], solvothermal
[10,11], sol-gel [12,13], emulsion-drying [14,15] and co-
precipitation [16,17] have an indisputable advantage over solid-
state reactions in achieving better homogeneity and mixing the
starting compounds on the molecular level. Generally, for the wet
chemical routes of LiFePO4 synthesis, it is commonly believed that
intermediate precipitates, i.e. Fe3(PO4)2$8H2O and Li3PO4, will be
yielded in the initial preparation stage [17,18], and LiFePO4 will be
formed after the following heat treating as equation (1).
Fe3ðPO4Þ2$8H2O þ Li3PO4¼ 3 LiFePO4þ8H2O
(1)
According to equation (1), it can be seen obviously that
obtaining an equimolar ratio of Fe3(PO4)2$8H2O(s) and Li3PO4(s) is a
basic prerequisite for preparing pure LiFePO4. Even so, sometimes it
is still difficult to avoid the formation of impurities such as Li3PO4
[19,20], Fe3(PO4)2 [19] and Fe2O3 [21e23] due to the complex
physical chemistry properties of the solution system. In general,
inactive impurities will decrease the specific capacity of the
* Corresponding author.
E-mail address: zhaozw@csu.edu.cn (Z. Zhao).
http://dx.doi.org/10.1016/j.jallcom.2016.07.029
0925-8388/© 2016 Elsevier B.V. All rights reserved.

L. He, Z. Zhao / Journal of Alloys and Compounds 688 (2016) 386e391
387
solution also played an important role for the formation of LiFePO4
via precipitation method. Therefore, in order to validate this theory
predicts, this work concerned with synthesis of LiFePO4 by co-
precipitation, and the emphasis focused on the effects of molar
ratio Li:Fe:P and solution pH on LiFePO4 preparation. Furthermore,
the precipitation process of the LiOH-FeSO4-H3PO4-H2SO4-H2O
system was also studied, aiming at a better understanding of the
precipitation characteristics.
2. Experimental
LiFePO4 powders were synthesized via co-precipitation method,
followed by sintering at 700 ꢁC by using the FeSO4$7H2O(A.R.
China), LiOH$H2O(A.R., China), and o-H3PO4 (A.R., China) as the
starting materials. The co-precipitation process was carried out in a
250 ml three-necked flask equipping with a magnetic stirrer, a
thermometer and a pH electrode. Firstly, in order to avoid oxidation
of Fe2þ to Fe3þ, the reactants FeSO4$7H2O, o-H3PO4 and proper
ascorbic acid were premixed in the three-necked flask containing
100 ml of deionized water. LiOH was also dissolved with 50 ml of
deionized water and then added to the previously prepared solu-
tion of FeSO4$7H2O and o-H3PO4. The whole processes were carried
out under nitrogen atmo-sphere, and the pH value of the solutions
was adjusted by 0.1 mol Lꢀ1 NH3$H2O and/or 0.1 mol Lꢀ1 H2SO4.
After stirring at room temperature for 2 h, the precipitates were
collected by filtration and washed several times with deionized
water and alcohol, respectively. The resulting precipitates were
mixed with a certain amount of glucose solution. Then the slurry
was dried at 60 ꢁC for 8 h in a vacuum oven, and subsequently
calcined at 400 ꢁC for 4 h and then sintered at 700 ꢁC for 10 h in
nitrogen atmosphere.
Fig. 1. XRD patterns of precursors which were synthesized under the conditions of
LiOH 0.3 mol Lꢀ1, Li:Fe:P molar ratio1:1:1 and labeled as a, b, c, and d, according to
different pH values 5.2, 7.3, 8.7, and 10.2, respectively.
material and cause a lower the energy density. It is well known that
the formation of impurity phases closely linked to the preparation
process of the samples. For example, Liu et al. [24]reported that
LiFePO4 just have been prepared by hydrothermal method at pH
value from 6.3 to 9.04, but not at pH value 5.4 and 11.04. Coinci-
dentally, Lee and coworkers’ [25] research showed that pure
LiFePO4 was synthesized at pH value 6.5 and 9.22; LiFePO4, iron
oxide and Li3PO4 coexisted at pH value 10.62; and a mix of iron
oxide (Fe3O4) and lithium phosphate (Li3PO4) was obtained at pH
value 14.32.
X-ray diffraction (XRD) profiles of the sample were measured
with TTR-III (Cu Ka
radiation, Rigaku Corporation) at a speed of 4ꢁ/
Besides the pH value parameter, in our previous thermodynamic
min. The particle morphology was observed by SEM (JXAꢀ8800R,
study [26], we found that the molar ration of Liþ:Fe2þ:PO43ꢀ in
JEOL Ltd.).
Fig. 2. SEM images of the precursors prepared at various pH values: (a)- 5.2, (b)-7.3, (c)-8.7, and (d)-10.2, respectively.

388
L. He, Z. Zhao / Journal of Alloys and Compounds 688 (2016) 386e391
Fig. 5. XRD patterns of LiFePO4 samples synthesized under the conditions of 25 ꢁC,
LiOH 0.3 mol Lꢀ1, and molar ratio Li:Fe:P ¼ 1:1:3 (pH values: a-5.1, b-7.3, c-9.1, and d-
11.3,
-Fe (PO ) ; -Fe2O3; -Li2CO3).
3 4 2
7
▫
⋄
Fig. 3. XRD patterns of LiFePO4 which were labeled as a, b, c, and d, according to
different pH values 5.2, 7.3, 8.7, and 10.2 sintered at 700 ꢁC, respectively. (Symbols:
-
7
JCPDS 49-1087 > Graftonite Fe3(PO4)2; -JCPDS 39-0341 > Sarcopside Fe3(PO4)2).
⋄
700 ꢁC in N2 atmosphere for 10 h by using the precursors in Fig. 2 as
raw materials were shown in Fig. 3. From the X-ray diffraction re-
sults, it can be seen that the peaks of the samples synthesized at
pH ¼ 5.2 can be indexed as a well-crystallized Fe3(PO4)2 phase, and
the space group of the Fe3(PO4)2 transformed from P21/c (Graf-
tonite-type [27], JCPDS No. 40-1087) to P21/a space group (Sar-
copside-type [28,29], JCPDS No.39-0341) with the pH value
increasing from 5.2 to 7.3. For the phase transformation of
Fe3(PO4)2, it can be attributed to the different crystal form of
Fe3(PO4)2$nH2O precursor. At neutral and slightly basic solution,
vivianite Fe3(PO4)2$8H2O(Space group C 2/m) is a stable solid phase
in FeSO4ꢀH3PO4ꢀH2O system. While it will convert to phospho-
ferrite Fe3(PO4)2$3H2O (Space group Pbna) in an acid environment,
which possesses a large domain of stability [30]. Furthermore, with
the pH value increasing to 10.2, the X-ray diffraction peaks (020),
(011), (131) belonging to LiFePO4 appeared, and yet containing large
amounts of Fe3(PO4)2 impurity. The results seemed to contradict
with the general view that pure LiFePO4 can be synthesized at
neutral or slightly basic conditions [26,31,32].
3. Results
Fig. 1 showed the X-ray diffraction profiles of precipitates syn-
thesized under the conditions of 25 ꢁC, LiOH concentration
0.3 mol Lꢀ1, Li: Fe: P molar ratio 1:1:1, pH values 5.2e10.2, drying
temperature 60 ꢁC for 8 h in a vacuum oven. It can be seen that at
acid conditions, just a single phase of Fe3(PO4)2$8H2O(JCPDS 30-
0662) was obtained from the precursor solution. With the pH value
increasing from 5.2 to 10.2, the diffraction intensities of (110), (020),
(200), (130) peaks belonging to Fe3(PO4)2$8H2O became weaker. In
contrast, diffraction intensities of the (020), (101), (021) peaks of
Li3PO4 phase (JCPDS 15-0760), were generated and became
stronger.
Fig. 2 showed the SEM images of the precursors yielded at
various pH values. Obviously, the particle morphology changed
along with the pH values. At pH ¼ 5.2, the precursor was charac-
terized by thin layers, arranged in alternating and overlapping
planes, spreading out radially as a flower corolla (Fig. 2a). With the
pH values increasing, the particle was still like a flower corolla, but
its “leaves” changed from the “thin layers” to a thicker strips (at pH
7.3, Fig. 2b), and then turned into fusiformis-plate-like crystals (at
pH 8.7, Fig. 2c). When the pH value was 10.2, the particles became
randomly shaped(Fig. 2d).
To this confusion, it can be explained by using the solubility
product principle. For Li3PO4, its dissolution reaction can be
expressed as equation (2), with its solubility product constant
Ksp1 ¼3.2 ꢂ 10ꢀ9, which is much larger than that of Fe3(PO4)2$8H2O
(Ksp2 ¼ 1.0 ꢂ 10ꢀ36, Eq. (3)). Under acid conditions, phosphate is
mainly existed in the form of H3PO4 and/or H2POꢀ4 . For example, at
The XRD patterns of the LiFePO4 samples which were sintered at
Fig. 4. Photographs of various precursors prepared at pH values: a-5.1, b-7.3, c-9.1, and d-11.3, respectively (LiOH concentration 0.3 mol Lꢀ1, Li:Fe:P molar ratio 1:1:3).

L. He, Z. Zhao / Journal of Alloys and Compounds 688 (2016) 386e391
389
Fe3ðPO4Þ2$8H2O ¼ 3Fe2þþ2PO43ꢀþ8H2O; Ksp2
h
i h
i
3
2
¼ Fe2þ PO43ꢀ ¼ 1:0 ꢂ 10ꢀ36
(3)
As we know from the above discussion and Eq. (1), obtaining
equimolar ratio of Fe3(PO4)2$8H2O(s) and Li3PO4(s) is a basic pre-
requisite for preparing pure LiFePO4 via co-precipitation method. In
order to obtain pure LiFePO4 product, the key is to improve the
precipitation rate of Li3PO4 which will react with Fe3(PO4)2$8H2O to
form LiFePO4 in the subsequent heat treatment. One of the mea-
sures is to increase the PO34ꢀ concentration to ensure that Liþ ions
can be precipitated completely.
The photographs of the precipitation prepared at the conditions
of LiOH concentration 0.3 mol Lꢀ1, Li:Fe:P molar ratio 1:1:3 at
various pH values were shown in Fig. 4. The results revealed that
the color of the precursors changed from grayish (pH ¼ 5.1), to
darkolivegreen (pH ¼ 7.3), to dark green (pH ¼ 9.1), and then to
brick red(pH ¼ 11.3) after washing. It proved the existence of
Fe(OH)2 in the basic reaction solution, and it was easily oxidized to
Fe(OH)3 during the washing procedure. Furthermore, the Xꢀray
diffraction profiles of precursors sintered at 700 ꢁC were shown in
Fig. 5. The results indicated that a mixture of Sarcopside-type of
Fe3(PO4)2 and LiFePO4 was obtained at pH 5.1e7.3. With the pH
values increasing, diffraction intensity of the impurity Fe3(PO4)2
phase were becoming weaker, pure and well-crystallized LiFePO4
was obtained at pH ¼ 9.1. However, a mixture of Fe2O3, Li3PO4 and
LiFePO4 was obtained at strong basic conditions (pH ¼ 11.3). It can
be attributed to the hydrolysis of FeSO4$7H2O to Fe(OH)2 or
Fe(OH)3 at high pH, and the hydroxides Fe(OH)2 and Fe(OH)3 are
easily converted to Fe2O3 or Fe3O4. Obviously, the XRD results were
consistent with that of the photographs results listed in Fig. 4.
Nevertheless, pure and single phase of LiFePO4 powders just
was prepared at a narrow pH range after adopting the measure of
increasing the H3PO4 concentration. Actually, taking the equation
(2) into consideration, it can be observed that increasing the Liþ
Fig. 6. XRD patterns of LiFePO4 as-prepared under conditions of LiOH 0.9 mol Lꢀ1, and
Li:Fe:P 3:1:1(pH values: (a)- 4.5, (b)-6.7, (c)- 8.9, and (d)-10.6; -Fe (PO ) ;
-Fe2O3; -Li2CO3).
¼
7
3
4 2
▫
⋄
pH 5.0, H2POꢀ4 is estimated dominant with 99.23% molar occupancy
while only 7.9 ꢂ 10ꢀ8% of phosphate is in the form of PO34ꢀ
(calculated from dissociation equilibrium of phosphoric acid:
Ka1 ¼7.5 ꢂ 10ꢀ3, Ka2 ¼ 6.2 ꢂ 10ꢀ8, Ka3 ¼ 4.8 ꢂ 10ꢀ13). Therefore, the
amount of PO34ꢀ in the solution is insufficient for the precipitation
of Li3PO4, but sufficient for Fe3(PO4)2$8H2O precipitation.
h
i h
i
3
Li3PO4¼ 3LiþþPO43ꢀ
;
Ksp1 ¼ Liþ PO43ꢀ ¼ 3:2 ꢂ 10ꢀ9 (2)
Fig. 7. SEM images of LiFePO4 samples prepared at different pH values: (a)- 4.5, (b)-6.7, (c)- 8.9, and (d)-10.6.

390
L. He, Z. Zhao / Journal of Alloys and Compounds 688 (2016) 386e391
Scheme 1. The process of chemical reaction in co-precipitation synthesis.
concentration may be more efficient. For example, when the Liþ
concentration increase 10 times, the product value of
[Liþ]3 ꢂ [PO34ꢀ] will increase by an exponent of three, i.e. 1000
times, which is much bigger comparing with the case of increasing
the concentration of H3PO4 (10 times). So when the concentration
product of Liþ and PO43ꢀ becomes above the critical value of Ksp1, the
reaction (2) is balanced to keep equilibrium by encouraging the
reaction from the right to the left side, and then accelerate the
Li3PO4 precipitation.
surface was rough (Fig. 7c).
4. Discussion
In the prior literature, researches synthesized LiFePO4 via co-
precipitation route or other solution chemistry method
constantly emphasised that pure LiFePO4 only can be prepared at
neutral or slightly basic conditions. Therefore, the molar ratio of the
starting materials which contain Li, Fe, P resources was always to be
LiOH:Fe2þ:H3PO4 ¼ 3:1:1. Under this conditions, triple amount of
LiOH can react with H3PO4 completely, obtaining a neutral or
slightly basic solution with the pH value 7e9. During this process,
excess-LiOH was generally reckoned as a pH adjuster.
In fact, this is not entirely true. From the three comparison ex-
periments illustrated in Figs. 3, 5 and 6, we can see that it was hard
for us to synthesize pure LiFePO4 product by using the stoichio-
metric starting materials of FeSO4$7H2O, LiOH$H2O and o-H3PO4
(Li:Fe:P ¼ 1:1:1) at pH 4e10, and the situation was similar in the
case of Li:Fe:P ¼ 1:1:3. However, pure and well-crystallized LiFePO4
particles can be prepared at the Li:Fe:P molar ratio 3:1:1 and pH
7e9.
According to the results of the XRD, the obtained product is
different under different pH and Li: Fe: P molar ratio conditions.
Therefore, we can roughly calculate the chemical reaction process
according to the results of the XRD. In this work, the precipitation
processes were based on the LiOHeFeSO4eH3PO4eH2O system.
Fe3(PO4)2$8H2O was prepared as the first intermediate precipitate
by adding LiOH to an aqueous solution of FeSO4 and H3PO4
(3 < pH < 6). When an excess of LiOH was introduced to the
equilibration solution of Fe3(PO4)2$8H2O precipitate with an
enough amount of free ions of Liþ and PO43ꢀ, the second interme-
diate Li3PO4 precipitated in the form of small particles on the sur-
face of the pre-formed Fe3(PO4)2$8H2O particles at neutral or
slightly basic conditions (6 < pH < 10). The chemical reaction can be
generally written as equation (4), with the processes being shown
in Scheme 1.
Fig. 6 showed the XRD patterns of particles obtained after the
LiOH concentration being improved from 0.3 mol Lꢀ1 to 0.9 mol Lꢀ1
,
with the molar ratio Li:Fe:P ¼ 3:1:1. The results demonstrated that
both LiFePO4 and Fe3(PO4)2 were discovered at pH 4.5. In addition,
the impurities Fe2O3 and Li3CO3 were yielded under strong basic
solution (Fig. 6d). Remarkably, a single phase and well-crystallized
LiFePO4 sample was obtained at pH 7e9 (Fig. 6b and c), indicating
an efficient improvement on Li3PO4 precipitation via maintaining
an excess of LiOH in the solution. Furthermore, the SEM images of
the samples was displayed Fig. 7, with diamond-shaped particles
being those of LiFePO4. It can be seen that the particle morphology
changed depending on the solution pH values. At pH ¼ 4.5, the
morphology of the particles was random-irregular, no diamond-
shaped one was discovered (Fig. 7a). It could be attributed to
mixed crystal phenomenon by LiFePO4 and Fe3(PO4)2, i.e. in the
sintering process, the intermediates Fe3(PO4)2$8H2O and Li3PO4
will react with each other to form LiFePO4 phase, and the excess
Fe3(PO4)2$8H2O will dehydrate to generate Fe3(PO4)2. Because
LiFePO4 and Fe3(PO4)2 have different crystalline structures, and
both of them can be regarded as an impurity for each other. So it is
easy to occur a crystal form blending and inhibit the growth and
formation of LiFePO4 and Fe3(PO4)2 crystals, resulting a random-
irregular morphology of the particles. With the pH value
increasing to 6.7, the morphology of the samples became diamond-
shaped, and the surface of the particles was smooth, indicating a
good crystallization (Fig. 7b). In the case of pH ¼ 8.9, the
morphology still kept a diamond shape, but by contrast the particle

L. He, Z. Zhao / Journal of Alloys and Compounds 688 (2016) 386e391
391
Sintering at 700oC
Excess LiOHð6 < pH < 10Þ
LiOHð3 < pH < 6Þ
Fe ðPO Þ $8H OY
Fe ðPO Þ $8H OYþLi PO Y
LiFePO Y
4
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ!
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ!
3
4
2
3
4
2
3
4
2
2
FeSO4 þ H3PO4
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ!
(4)
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Actually, the experimental research results in this paper were
consistent with the thermodynamic analysis of LiFePO4 precipita-
tion in our previous study [26], i.e., excess-Liþ was one of the
essential conditions for LiFePO4 preparation by co-precipitation
method, and it was not only a pH adjuster, but also a “precipita-
tion promoter”.
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synthesis of olivine LiFePO4/C composite and its electrochemical properties as
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5. Conclusions
This work explored the effect of Li:Fe:P molar ratio and pH value
on the synthesis of LiFePO4 via co-precipitation method. At molar
ratio Li:Fe:P ¼ 1:1:1, Fe3(PO4)2 was the main phase of the prepared
samples, and no pure LiFePO4 was obtained during the whole
experimental pH values range. By increasing the molar ratio Li:Fe:P
to 1:1:3, pure LiFePO4 was synthesized at a narrow pH range (pH
value was about 9.0). Especially when the molar ratio of Li:Fe:P
adjusted to 3:1:1, pure LiFePO4 samples were prepared at a wider
pH range (pH vales 6.7e8.9). The results illustrated that excess-Liþ
in solution was an essential condition for pure LiFePO4 preparation
at neutral or slightly basic conditions, and excess-LiOH was not only
a pH adjuster, but also a precipitation promoter for intermediate
precipitate Li3PO4.
[18] M.-H. Lee, J.-Y. Kim, H.-K. Song, A hollow sphere secondary structure of
LiFePO4 nanoparticles, Chem. Commun. 46 (2010) 6795e6797.
[19] K. Dokko, S. Koizumi, H. Nakano, K. Kanamura, Particle morphology, crystal
orientation, and electrochemical reactivity of LiFePO4 synthesized by the
hydrothermal method at 443 K, J. Mater. Chem. 17 (2007) 4803e4810.
[20] Y. Denis, K. Donoue, T. Kadohata, T. Murata, S. Matsuta, S. Fujitani, Impurities
in LiFePO4 and their influence on material characteristics, J. Electrochem. Soc.
155 (2008) A526eA530.
€
[21] G. Arnold, J. Garche, R. Hemmer, S. Strobele, C. Vogler, M. Wohlfahrt-Mehrens,
Fine-particle lithium iron phosphate LiFePO4 synthesized by a new low-cost
aqueous precipitation technique, J. Power Sources 119 (2003) 247e251.
[22] K. Park, J. Son, H. Chung, S. Kim, C. Lee, H. Kim, Synthesis of LiFePO4 by co-
Acknowledgements
This work was supported by Science and Technology Bureau of
Changsha City (Grant No. 328 K1205034-11) and Hunan Provincial
Innovation Foundation for Postgraduate (1105-71380100001).
precipitation and microwave heating, Electrochem. Commun.
5 (2003)
839e842.
[23] A.A. Salah, A. Mauger, K. Zaghib, J. Goodenough, N. Ravet, M. Gauthier,
F. Gendron, C. Julien, Reduction Fe3þ of impurities in LiFePO4 from pyrolysis of
organic precursor used for carbon deposition, J. Electrochem. Soc. 153 (2006)
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