P26
Electrochemical characteristics of Na2FeP2O7 as the cathode material of Na ion batteries
Junichi Ikejiri1*, Hideo Yamauchi1, Fumio Sato1, Tsuyoshi Honma2, and Takayuki Komatsu2
1

Nippon Electric Glass Co. Ltd., 7-1, Seiran 2-Chome, Otsu, Shiga, 520-8639, Japan
jikejiri@neg.co.jp
2Nagaoka University of Technology, 1603-1, Kamitomioka, Nagaoka-shi, Niigata, 940-2188, Japan

Introduction
Na ion batteries (NIBs) have been considered as an attractive alternative to Li ion batteries (LIBs)
from the viewpoints of cost and stable supply. Honma et al. reported that Na2FeP2O7 glass ceramic (NFPg.c.) powder prepared by a glass crystallization method shows good performance as the cathode materialin NIBs [1]. We have investigated the relationship between the BET specific surface area (BET SSA) of
NFP g.c. powder and its charge-discharge characteristics. We also evaluated the diffusion constants ofthe cations in NFP g.c. and LiFePO4 glass ceramic (LFP g.c.) [2].

Reference
1) T. Honma et al., Journal of the Ceramic Society ofJapan, 120 (2012) 344-346.
2) T. Honma et al., Journal of Non-Crystalline Solids,356 (2010) 2032-3036.

Charge(Na extraction)

4+Results and Discussion
Figure 1 shows charge-discharge curves of an NIB
with various BET SSAs of NFP g.c. at a rate of 10C(full charge and discharge in 6min.). The
charge-discharge capacity increased with increasing
BET SSA. The charge-discharge capacity of NFP g.c.
at a rate of 0.1C (full charge and discharge in 10h)
was 90mAh/g. By increasing BET SSA of NFP g.c. to
15m2/g, the ratio of the discharge capacity at a rate of10C to that of 0.1C reached 83%.
Figure 2 shows the diffusion constants of thecations in NFP g.c. and LFP g.c. The charge anddischarge diffusion constants in NFP g.c. are morethan ten times higher than those in LFP g.c. The highdiffusion constants in NFP g.c. indicate its suitability
for use as a rapid chargeable-dischargeable material.
These results show that NFP g.c. is an attractive
cathode material for NIBs.

Voltage [V vs Na/Na ]Experimental
A precursor glass was made by melting raw materials and quenching. Glass ceramic powder wasprepared by heating the precursor glass at 620oC for 3h and grinding with a ball mill. The cathodematerial was processed by coating the surface of the glass ceramic powder with carbon and heating in N2
gas at 620℃ for 3h.
A coin cell was used for electrochemical experiments. The cathode was fabricated by coating an
aluminum foil with slurry. The slurry was a mixture of the cathode material, polyvinylidene fluoride,and acetylene black in a weight ratio of 90:5:5 with N-methylpyrrolidone used as a solvent. The anode
was a sodium metal foil. Each electrode was punched out from the foil and had a diameter of 11mm.
The electrolyte was a 1M NaPF6 solution in a mixture of ethylene carbonate and diethyl carbonate (1:1,v/v).
The diffusion constant of the cations in NFP g.c. was calculated from the slope of the peak current
obtained by cyclic voltammogram measurement at several sweep rates. The diffusion constant of thecations in LFP g.c., which is used as a cathode active material in LIBs, was also evaluated.

215m /g
212m /g
26m /g32Discharge(Na insertion)

1Charge-discharge rate=10C00204060
Capacity [mAh/g]

80100Fig.1 Charge-discharge curves of NIB with various
BET SSAs of NFP g.c.
NFP g.c.

LFP g.c.

Fig.2 Diffusion constants of NFP g.c. and LFP g.c.