Supplementary Information
Amorphous iron phosphate: Potential host for various charge carrier ions
Vinod Mathew1, Sungjin Kim1, Jungwon Kang1, Jihyeon Gim1, Jinju Song1, Joseph Paul Baboo1,
Wangeun Park1, Docheon Ahn2, Junhee Han3, Lin Gu4, Yuesheng Wang4, Yong-Sheng Hu4,
Yang-Kook Sun5 and Jaekook Kim1*
1
Department of Materials Science and Engineering, Chonnam National University, Gwangju
500-757, South Korea.
2
Beamline Research Division, Pohang Accelerator Laboratory, Pohang 790-784, South Korea.
3
4
Department of Materials Science and Engineering, KAIST, Daejon 305-701, South Korea.
Key Laboratory for Renewable Energy, Beijing National Laboratory for Condensed Matter
Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100-190, China.
5
Department of Energy Engineering, Hanyang University, Seoul 133-791, South Korea
*
Correspondence: Professor Jaekook Kim, Laboratory for Energy Materials Synthesis,
Department of Materials Science and Engineering, Chonnam National University, 300 Yong
bong dong, Buk-gu, Gwangju 500-757, South Korea
E-mail: jaekook@chonnam.ac.kr Tel: +82-62-530-1703. Fax: +82-62-530-1699.
1
*
* trigonal FePO4
700 oC
*
* ** *
*
* *
Intensity (a.u)
*
**
*

250 C
As prepared
10
20
30
40
50

Cu K2( )
60
70
80
Figure S1: X Ray Diffraction (XRD) characterization results. The XRD patterns obtained for
the prepared FePO4 samples under various conditions. Amorphous halo patterns are observed for
the as-prepared and vacuum-annealed (250 C) samples around the scanning angle, 2 = 25°. In
order to empirically assess the constituent phases of the amorphous samples, the XRD pattern
was recorded for the as-prepared sample annealed at 700 °C in air. The resulting pattern reveals
sharp diffraction peaks well-indexed to trigonal FePO4.
2
102
Exo Up
0
100
Weight (%)
-4
96
9 wt%
94
-6
92
-8
-10
1.7 wt%
90
88
100
200
300
500
400
600
Heat flow (mW)
-2
98
700
-12
800
o
Temperature ( C)
Figure S2: Thermo-gravimetric (TG) and Differential scanning calorimetry (DSC) studies.
The TG-DSC plot recorded for the as-prepared amorphous FePO4 under nitrogen atmosphere at
an heating rate of 3 C/min. The major weight loss of 9 wt% that correspond to 0.83 mol of H2O
is observed in the temperature range of 30 – 250 C whereas a negligible weight loss ( 1.7 wt%)
occurs in the range 250 – 500 C. The chemical composition of the as-prepared sample is thus
FePO41H2O. The three exothermic peaks at 506, 516 and 527 C with no appreciable weight
loss are associated with the amorphous to crystalline phase transition of FePO4. These
exothermic effects possibly indicate the three-step structural transformation of the FePO
framework.1
3
Absorption (%)
0
2
4
Experimental data
Fit data
3+
6
1 QS (Fe )
EQS = 0.88 mm/s
I.S. = 0.29 mm/s
Ratio = 100.00 %
8
-10
-5
0
Velocity (mm/s)
5
10
Figure S3: Mossbauer spectroscopy studies: Mossbauer spectrum obtained for the vacuum
annealed a-FePO4 at ambient temperature conditions (25 C).
4
200 nm
Figure S4. Scanning electron microscopy (SEM) characterization. SEM image reveals that
amorphous FePO4 is comprised of secondary aggregates formed from primary particles of sizes
ranging between 20 and 50 nm.
5
4
dVp/dlogd
3
2
1
-1
Volume (cm3g STP)
p
600
400
0
0
50
100
150
200
Pore diameter (nm)
200
Adsorption
Desorption
0
0.0
0.2
0.4
0.6
0.8
1.0
P/PO
Figure S5. Nitrogen adsorption studies. A type-IV isotherm plot with an H1 hysteresis loop at
relative pressure (p/p0)  0.8 – 1.0 is observed in the N2 adsorption/desorption plot and pore-size
distribution plot (inset) reveals the presence of mesopores in the amorphous FePO4. It is
anticipated that such amorphous electrodes with pore-like features can serve as prospective hosts with
competent guest-ion insertion capabilities for energy storage applications as batteries.
6
250
-1
4
200
Discharge Capacity
Charge Capacity
150
50
100
Coulombic efficiency
50
0
+
Potential vs. Li/Li (V)
5
100
0
10
20 30 40
Cycle Number
0
50
Coulombic efficiency (%)
Specific Capacity (mAhg )
6
3
2
st
1 cycle 5th cycle
1
0
50
100
-1
Specific Capacity (mAhg )
150
200
Figure S6. Electrochemical profile of a-FePO4 versus lithium. The initial five
discharge/charge curves of amorphous FePO4 cathode within the voltage window of 4.2-1.6 V
versus Li0 at a current density of 20 mAg-1. The active material loading is 2.5 mgcm-2. The cycle
performance is provided in the inset. The a-FePO4 cathode registered an initial discharge capacity of
180 mAhg-1. The cycle performance (inset) indicates steady capacity retentions with high Coulombic
efficiencies until 50 electrochemical cycles.
7
5
-1
1000 mAg
-1
260 mAg
-1
60 mAg
+
Potential vs. Li/Li (V)
4
3
2
-1
40 mAg
-1
2000 mAg
-1
500 mAg
-1
120 mAg
1
0
50
100
-1
Capacity (mAhg )
150
Figure S7. Rate performance of amorphous FePO4 versus lithium. The discharge/charge
curves of a-FePO4 electrode at various C-rates within the voltage window of 4.2-1.6 V versus Li0.
The active material loading is 2.5 mg/cm2. The discharge capacities attain values of 87 and 56 mAhg-1
at 1000 and 2000 mAg-1 current densities respectively.
8
Figure S8. Ex-situ HRTEM studies. The ex-situ SAED pattern of the FePO4 cathode recovered
after one complete K-insertion cycle.
9
Fe
K
P
O
Figure S9. Energy Dispersive X-ray (EDX) characterization. Elemental mapping images of
Fe, K, P and O for the ex-situ electrode sample recovered from the potassium cell after 2
discharge cycles and the corresponding Energy Dispersive X-ray (EDX) results of the area under
study obtained using a using FEI Tecnai F20 instrument operating at 200 kV accelerating voltage.
The spatial EDX mapping reveals a uniform distribution of the K element through the entire
sample area under study.
10
2.0
-2
Current (mAcm )
1.5
1.0
0.5
0.0
-0.5
1
st
cycle
nd
2 cycle
-1.0
-1.5
0.0
0.5
1.0
1.5
2.0
2+
Potential vs. Zn/Zn (V)
Figure S10. Cyclic Voltammetry studies of amorphous FePO4 versus zinc. The initial two
CV curves recorded for the Zn/FePO4 cell within the 0 - 2 V potential window at a sweep rate of
0.5 mVs-1. The electrolyte used was 1 mol l-1 ZnSO4. The cathodic peak ( 1.05 V) and the
11
corresponding anodic peak ( 1.25 V) suggest possible Zn-insertion/de-insertion in amorphous
FePO4.
4
2.5
a
b
2.0
3+
Potential vs. Al/Al (V)
-2
Current (mA cm )
2
0
st
1 cycle
nd
2 cycle
1.5
1.0
-2
0.5
-4
0.0
0.0
0.5
1.0
1.5
3+
Potential vs Al/Al (V)
2.0
2.5
0
25
50
75
100
-1
Capacity (mAh/g )
125
Figure S11. Cyclic voltammetry and electrochemical studies. (a) The initial two CV curves
recorded for the Al/FePO4 test cell within the potential window of 0 – 2.5 V at a sweep rate of 1
mVs-1. The counter and reference electrode was metallic aluminum and the electrolyte used was
a mixture of 1-Ethyl-3-methylimidazolium chloride (EMIC) and AlCl3 in the ratio 1:1.1
respectively. (b) The initial discharge profile of the amorphous FePO4 cathode evaluated within
the potential window of 1.6 – 0.1 V versus aluminum under a current density of 5 mAg-1 at room
temperature.
12
150
References
1.
Scaccia, S., Carewska, M., Bartolomeo, A. D. & Prosini, P. P. Thermoanalytical
investigation of iron phosphate obtained by spontaneous precipitation from aqueous
solutions. Thermochim. Acta. 383, 145-152 (2002).
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