All-solid-state lithium batteries in cold environments of -20 ℃ enabled by amorphous halide-based electrolytes LiNbCl5X and LiTaCl5X

Abstract All-solid-state lithium batteries (ASSLBs) using inorganic solid state electrolytes (SSEs) have earn good reputation owing to their good performances at room temperature, including high safety, long cycling life and high energy density. However, at extremely low-temperature environments, ASSLBs can hardly operate well due to seriously enlarged inner resistance arising from impedances from SSEs themselves and interfaces between electrodes and SSEs. In this work, to solve the problem, we introduce amorphous halide electrolytes LiNbCl5Xn- 1/n and LiTaCl5Xn- 1/n (Xn- = Cl-, O2-, F-) with ultrahigh room-temperature ionic conductivity higher than 10 mS/cm and even retaining 4 mS/cm at -20 ℃. Their grain boundary free characteristic and high Li+ migration speed even at extremely low temperatures realize efficient and effective ion transport throughout the ASSLBs inside. To determine an appropriate running voltage for LiNbCl5Xn- 1/n and LiTaCl5Xn- 1/n, their high cathode interface stability at potential 4.3 V is examined by TOF-SIMS. It is attractive that they enable ASSLBs using high nickel cathode (LiNi0.91Co0.06Mn0.03O2) to retain 94 % capacity after 3,000 cycles and 85 % capacity after 4,000 cycles (4.4 V, ~25 mg/cm2 loading, >5 mAh/cm2, 1.3 C rate) under -20 ℃. This work will contribute to realizing high performance ASSLBs at extremely low-temperature environments using amorphous SSEs.