1
Supplementary Information
Advanced electrochemical performance of hybrid nanocomposites based on
LiFePO4 and lithium salt doped polyaniline
Oleg Yu. Posudievsky,* Olga A. Kozarenko, Vyacheslav S. Dyadyun,
Vyacheslav G. Koshechko, Vitaly D. Pokhodenko
L.V. Pisarzhevsky Institute of Physical Chemistry of the National Academy of Sciences Ukraine,
31 prospekt Nauki, Kyiv 03028, Ukraine; Tel/Fax: +38 044 525 6672; E-mail:
posol@inphyschem-nas.kiev.ua
Preparation of LFP/PAni5 nanocomposite.
LiFePO4/PAni5 (LFP/PAni5) nanocomposite was prepared by mechanochemical
treatment of a dry mixture of 2 g of LiFePO4 (MTI, USA), 0.142 g of anilinium chloride and
0.125 g of ammonium persulfate using a planetary ball mill Pulverisette 6 (Fritsch) at rotation
rate of 300 rpm for 1 h. in an argon atmosphere. The prepared product was washed with ethanol
and water. Then it was treated by 3% aqueous ammonium hydroxide to dedope the polyaniline,
separated by filtration and dried in vacuum at 60 C. The content of the polymer in the
nanocomposite was 5%.
Mechanochemical treatment of LFP.
Mechanochemical treatment of LiFePO4 was performed under conditions similar to those
used for preparation of LFP/EB nanocomposites. 2g of LFP was milled using the planetary ball
mill at a rotation rate of 300 rpm for 1h. in an argon atmosphere. The product, LFPmt, was
separated by dry sieving and used for further studies.
Electrochemical performance of LFP/PAni5 and LFPmt.
Cyclability of the initial LFP and LFP/PAni5 nanocomposite, containing the same
amount of the polymer as its LFP/EB5 analogue, are shown in Fig. S1a. It follows from the
presented data that LFP/PAni5 nanocomposite prepared by the mechanochemical polymerization
2
is characterized by a sufficiently lower specific capacity and worse cyclability in comparison
with the initial LFP (Fig. S1a).
4.4
(a)
(b)
-1
Discharge capacity (mAh g )
200
+
Potential (V vs. Li/Li )
160
120
80
LFP
LFP/PAni5
40
4.0
3.6
3.2
2.8
LFP
LFP/PAni5
2.4
0
0
2
4
6
8 10 12 14 16 18 20
Cycle number
0
20 40 60 80 100 120 140 160 180
-1
Discharge capacity (mAh g )
Figure S1. Cyclability (a) and discharge chronopotentiograms (3d cycle) (b) of the initial LFP
and LFP/PAni5 nanocomposite (discharge rate of С/10).
It is known that the electrochemical performance of LFP, its specific capacity in
particular, is very sensitive to the appearance of defects connected with increase of the oxidation
degree of Fe2+ ions up to Fe3+ [32, 33]. So, it could be supposed that the relatively worse
characteristics of LFP/PAni5 are connected with partial oxidation of iron ions in LFP due to
usage of ammonium persulfate during the mechanochemical polymerization of anilinium
chloride and/or the consequence of the post-synthesis treatment of the nanocomposite by
ammonium hydroxide for dedoping of PAni. The discharge curve, presented in Fig. S1b, show
the feasibility of this supposition, because the form of the chronopotentiogram of LFP/PAni5 is
typical for the over-oxidized samples of LFP [33].
)
180
(b)
160
1
120
-1
140
120
2
100
100
80
60
0
5
10
15
Cycle number
20
Capacity (mAh g
140
25
(c)
160
-1
)
160
Capacity (mAh g
-1
Discharge capacity (mAh g
180
(a)
)
180
1
2
80
60
C/10 С/8 С/5 С/3
Discharge rate
1С
2С
140
120
100
1
2
80
60
40
С/10 С/8 С/5 С/3
Discharge rate
1С
2С
Figure S2. Cyclability (charge/discharge rate of C/5) (a), discharge rate dependence of
the discharge capacity at the fixed charge rate of C/10 (b) and equal rates of charge and
discharge (c) for the initial LFP (1) and LFPmt (2).
One of the reasons for the deterioration of the electrochemical properties of LFP after
mechanochemical treatment could be the appearance of various defects in its structure, which, as
known [S1, S2], adversely affect its electrochemical performance (Fig. S2). So, the fact of the
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advanced electrochemical performance of the LFP/EB nanocomposites could be due to the
ability of the polymer to be a "shock absorber" at mechanical impacts during the
mechnochemical treatment, which minimizes their negative effect on the structure of LFP.
Table S1. Parameters used for fitting impedance spectra of LFP.
Parameter
Re, Ω cm2
4.0
3.4
6.2
6.1
Q, sn/( Ω cm2) 4.7E-5 5.05E-5
ZCPEdl
n
0.75
0.74
Rсt, Ω cm2
51.3
55.4
Q, sn/( Ω cm2)
–
0.007
n
–
0.83
Rgb, Ω cm2
–
20.9
RW, Ω cm2
26.9
–
ω0, rad/sec
0.14
–
n
0.45
–
–
0.04
–
0.47
1.8E-4
1.0E-4
ZCPEgb
ZW
Potential, V
ZCPEdiff Q, sn/( Ω cm2)
n
χ2
Table S2. Parameters used for fitting impedance spectra of LFP/EB15.
Parameter
Re, Ω cm2
Potential, V
4.0
3.4
4.0
4.1
ZCPEEB Q, sn/( Ω cm2) 7.57E-5 1.58E-4
n
0.73
0.655
4
ZW
REB, Ω cm2
14.4
24.1
Cdl, F/cm2
2.5E-5
1.9E-5
Rct, Ω cm2
17.3
23.9
RW, Ω cm2
65.84
–
ω0, rad/sec
2.44
–
n
0.34
–
–
0.034
–
0.27
1.9E-4
9.6E-5
ZCPEdiff Q, sn/( Ω cm2)
n
χ2
References
[S1]
Yuan L-X, Wang Z-H, Zhang W-X, Hu X-L, Chen J-T, Huang Y-H, Goodenough JB
(2011) Development and challenges of LiFePO4 cathode material for lithium-ion
batteries. Energy Environ Sci 4:269–284
[S2]
Wang J, Sun X (2012) Understanding and recent development of carbon coating on
LiFePO4 cathode materials for lithium-ion batteries. Energy Environ Sci 5:5163–5185