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Improvement of Rate Performance for All-Solid-State Na15Sn4 / Amorphous TiS3 Cells Using 94Na3PS4・6Na4SiS4 Glass-Ceramic Electrolytes

Tuesday, 10 June 2014
Cernobbio Wing (Villa Erba)
N. Tanibata (Department of Applied Chemistry, Graduate School of Engineering), A. Hayashi, and M. Tatsumisago (Graduate School of Engineering, Osaka Prefecture University)
All-solid-state batteries have been attracting attention because they do not suffer from leakage, volatilization, and flammability of electrolytes. Sodium-ion batteries are considered to be a promising low-cost alternative to common lithium-ion batteries because of the abundance of sodium sources. All-solid-state sodium rechargeable batteries are expected to be highly safe and low-cost. We have found that all-solid-state sodium batteries with a Na3PS4 glass-ceramic electrolyte successfully operated as a rechargeable battery at 25oC [1]. The Na3PS4 glass-ceramic exhibited a high conductivity of 4.6 x 10-4 S cm-1 at room temperature. The all-solid-state Na15Sn4 / amorphous TiS3 (a-TiS3) cell using Na3PS4 glass-ceramic showed a high capacity of about 300 mAh g-1 and good cycle performance [2]. Development of rate performance of the cell is next issue to be solved. We have recently found that 94Na3PS4・6Na4SiS4 (mol%) glass-ceramic showed a higher conductivity of 7.4 x 10-4 s cm-1 at room temperature than the Na3PS4 glass-ceramic [3]. In this study, the addition of acetylene black (AB) as a conductive additive to Na15Sn4 negative electrode and the application of 94Na3PS4・6Na4SiS4 glass-ceramic as a solid electrode were conducted to improve the rate performance of the all-solid-state Na15Sn4 / a-TiS3 cells.

   All-solid-state Na15Sn4 / a-TiS3 cells using Na3PS4 glass-ceramic or 94Na3PS4・6Na4SiS4 glass-ceramic solid electrolyte (SE) were fabricated. Na15Sn4 powder was prepared by ball milling of Na and Sn using a planetary ball milling apparatus. Na15Sn4-AB composite was also prepared by ball milling. Na3PS4 glass-ceramic and 94Na3PS4・6Na4SiS4 glass-ceramic were prepared by ball milling and consecutive heat treatment [1, 3]. a-TiS3 was prepared by ball milling of an mixture of crystalline TiS2 and sulfur [4]. The a-TiS3 positive electrode was prepared by well-mixing a-TiS3, AB and Na3PS4 or 94Na3PS4・6Na4SiS4 glass-ceramics SE with the weight ratio of 20 : 3 : 30.

   AC impedance measurement of the Na15Sn4 / a-TiS3 cells using Na3PS4 glass-ceramic showed that the resistance attributable to the Na15Sn4 negative electrode became bigger with charge-discharge cycles. The resistance was decreased by adding AB as a conductive additive to Na15Sn4 negative electrode. Rate performance of the Na15Sn4-AB / a-TiS3 cell was better than that of the Na15Sn4 / a-TiS3 cell.

   The cell using the 94Na3PS4・6Na4SiS4 glass-ceramic electrolyte showed better rate performance than the cell using the Na3PS4 glass-ceramic electrolyte. The AC impedance measurement showed that the cell resistances attributable to the separator SE and the positive electrode were decreased by using the 94Na3PS4・6Na4SiS4 glass-ceramic.

   The rate performance of all-solid-state Na15Sn4 / a-TiS3 cells was improved by adding AB to the Na15Sn4 electrode and using the 94Na3PS4・6Na4SiS4 glass-ceramic with higher conductivity than Na3PS4 glass-ceramic.

References

[1] A. Hayashi et al., Nat. Commun. 3 (2012) 856.

[2] N. Tanibata et al., Abstracts of the 54th Battery Symposium in Japan, p. 281 (2013).

[3] N. Tanibata et al., submitted.

[4] A. Hayashi et al., Chem. Lett., 9 (2012) 886.

 

Acknowledgement: This research was partially supported by JST, “Advanced Low Carbon Technology Research and Development Program (ALCA)”.