Fabrication of All-Solid-State Batteries Using Li3BO3-Based Glass-Ceramic Electrolytes

Abstract

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(Ni1/3Mn1/3Co1/3)O2 (NMC) cells using the 90Li3BO3·10Li2SO4 or 33Li3BO3·33Li2SO4·33Li2CO3 glass-ceramic electrolyte were fabricated. These cells operated as a secondary battery at 25-100oC. The first discharge capacity at 100oC 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.