Safety and reliability are important factors for rechargeable batteries with high energy density. All-solid-state batteries using inorganic solid electrolytes without leakage and flammability are one of the solutions for rechargeable energy sources. Sulfide electrolytes exhibit very high lithium ion conductivities around 10^-4-10^-2 S cm^-1 at room temperature, which is comparable to that of organic liquid electrolytes[1]. In spite of such good conductivities, sulfide electrolytes are not stable under ambient atmosphere. On the other hand, oxide-based solid electrolytes are very attractive for application in all-solid-state batteries with safety because of their high chemical stability. In general, it is difficult to use oxide solid electrolytes in all-solid-state batteries because of poor deformability, which results in a huge interfacial resistance between electrolytes and electrodes. Oxide glass electrolytes with low melting properties such as Li₃BO₃ are promising materials for application in all-solid-state batteries. Li₃BO₃ glass showed the conductivity of 3.4×10^-7 S cm^-1 at room temperature. To enhance the conductivity of the Li₃BO₃ glass, we have prepared lithium ion conducting glasses based on Li₃BO₃ by rapid melt-quenching and mechanochemical techniques [2-4]. Especially, by heating 90Li₃BO₃·10Li₂SO₄ (mol%) glass, solid solution between high temperature phase of Li₃BO₃ and Li₂SO₄ were precipitated. This glass-ceramic showed a high lithium ion conductivity of 1.4×10^-5 S cm^-1 and good deformability. The 33Li₃BO₃·33Li₂SO₄·33Li₂CO₃ glass-ceramic electrolyte was prepared. It showed a relatively high conductivity of 2.3×10^-6 S cm^-1 and excellent deformability achieving relative density of 90% by cold-press, which is comparable to the deformability of sulfide electrolytes such as Li₃PS₄ glass [5].

 In this study, all-solid-state Indium / Li(Ni_1/3Mn_1/3Co_1/3)O₂ (NMC) cells using the 90Li₃BO₃·10Li₂SO₄ or 33Li₃BO₃·33Li₂SO₄·33Li₂CO₃ glass-ceramic electrolyte were fabricated. These cells operated as a secondary battery at 25-100^oC. The first discharge capacity at 100^oC of the cell using 90Li₃BO₃·10Li₂SO₄ glass-ceramic electrolyte was 100 mAh g^-1, while the capacity using 33Li₃BO₃·33Li₂SO₄·33Li₂CO₃ glass-ceramic electrolyte was 150 mAh g^-1. This capacity enhancement was caused by the better deformability of 33Li₃BO₃·33Li₂SO₄·33Li₂CO₃ electrolyte than that of 90Li₃BO₃·10Li₂SO₄ electrolyte.

References

[1] Y. Seino et al., Energy Environ. Sci., 7 (2014) 627.

[2] M. Tatsumisago et al., J. Ceram. Soc. Jpn., 95 (1987) 59.

[3] A. Hayashi et al., Phys. Chem. Glasses: Eur. J. Glass Sci. Technol. B, 54 (2013) 109.

[4] M. Tatsumisago et al., J. Power Sources, 270 (2014) 603.

[5] A. Sakuda et al., Sci. Rep., 3 (2012) 2261.