Electronic Supplementary Material (ESI) for Journal of Materials Chemistry
This journal is © The Royal Society of Chemistry 2012
Crystal chemistry of Na insertion/deinsertion in
FePO4/NaFePO4
Montse Casas-Cabanas,*a Vladimir Roddatis, a Damien Saurel, a Pierre Kubiak, a Javier
Carretero-González,a Verónica Palomares, b Paula Serras, b Teófilo Rojo a,b
CIC energiGUNE, Parque Tecnológico de Álava. Albert Einstein 48, 01510 Miñano, Álava, Spain. Tel: +34 945 297 108; E-mail:
[email protected]
a
b
Departamento de Química Inorgánica, Facultad de Ciencia y Tecnología, Universidad del País Vasco UPV/EHU, Apdo. 644, 48080
Bilbao, Spain.
Experimental information
C-FePO4 materials were prepared by chemical delithiation of a commercially available carbon
coated LiFePO4 (Advanced Lithium Electrochemistry Co.). The chemical oxidation was
performed by stirring a mixture of pristine LiFePO4 using NO2BF4 (Sigma-Aldrich) as oxidizing
agent in acetonitrile (Sigma-Aldrich) at room temperature. The reaction was carried out in a
glove box under argon atmosphere (02 and H2O ppm ≤ 5). After the reaction was completed
the mixture was vacuum filtered and the delithiated collected powder washed with
acetonitrile twice and dried under vacuum at 80 °C overnight. The obtained FePO4 powder was
chemically sodiated with NaI (Sigma-Aldrich) in acetonitrile under reflux in argon atmosphere.
The structure and microstructure of the electrode/active materials have been characterized by
X-ray diffraction with a Bruker D8 Advance diffractometer and electron diffraction with a FEI
Tecnai G2 electron microscope. The composition of the intermediate sample was determined
by EDX analysis using a Quanta 250FEG SEM operated at 30kV and equipped with an Apollo 10
SSD EDX detector. The Na/Fe ratio was found to be 0.73 and the 2Na/(Fe+P) ratio 0.72.
Electrochemical measurements were performed in 2-electrode configuration using swagelok
type electrochemical cells. The composition of the laminated electrode was: 80 % wt. active
material; 10 % wt. binder (PVDF P-5130,Solvay) and 10% carbon black (Super C65,Timcal) with
an average loading of 3mg cm-2. High purity metallic sodium was used as the counter
electrode and NaClO4 1M in EC/PC 50-50 wt% mixture as the electrolyte. The cells were
galvanostatically cycled in a voltage window of 2-4V vs Na+/Na.
Electronic Supplementary Material (ESI) for Journal of Materials Chemistry
This journal is © The Royal Society of Chemistry 2012
Figure 1: Electron diffraction patterns of Na1-xFePO4 sample corresponding to an a3bc unit cell
a) [100] zone axis and b) [001] zone axis.
Electronic Supplementary Material (ESI) for Journal of Materials Chemistry
This journal is © The Royal Society of Chemistry 2012
x Na exchanged
Capacity (mA h g -1 )
0.0
Potential vs. Na/Na + (V)
4.0
3.5
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
140
120
100
80
Charge
Discharge
60
40
20
0
1
2
3
4
5
6
7
8
cycle
3.0
2.5
2.0
1
2
4 5 6
3
n cycle
1.5
0
20
40
60
80
100
120
140
-1
Capacity (mA h g )
x Na exchanged
0.0
0.4
0.6
0.8
1.0
1.2
C-FePO4
4.0
Potential vs. Na (V)
0.2
1st and 2nd discharges
1st Charge
C/20, 50°C
Na anode, NaClO4 in EC/PC
3.5
3.0
2nd
2.5
1st
2.0
0
50
100
150
200
-1
Capacity (mA h g)
Figure 2: Galvanostatic Na+ insertion into FePO4 at constant charge and discharge current
(C/20) at room temperature (top) and 50°C (bottom). Inset top figure: capacity variation vs.
cycle number.