PNNL

Abstract

Thio-Lithium Superionic Conductor (Thio-LISICON) Li10GeP2S12 equivalent Li10SnP2S12 (LSPS) is comparable in ionic conductivity yet with a lower cost as an electrolyte for all solid-state batteries (ASSBs). ASSBs with LSPS solid electrolyte (SE), lithium-indium alloy anode, and LiCoO2 (LCO) cathode were successfully fabricated and their electrochemical performance at 60 °C was examined. Atomic layer deposition of Li3NbO4 on LCO was conducted to improve the interfacial stability. The Li3NbO4 coating significantly improves the cycle stability of the ASSB, which retains about 85% of the initial capacity after 70 cycles at a current density of 0.13 mA/cm2, while the ASSB with uncoated LCO retains ~ 60% of the initial capacity after 70 cycles. Electrochemical impedance spectroscopy tests indicate a rapid growth of charge transfer resistance upon cycling for the cell with the uncoated LCO, primarily due to the surface instability and build-up of a space charge layer between LSPS and LCO. However, the ASSBs with Li3NbO4 coated LCO show a more stable interface with a negligible impedance increase upon cycling, attributable to the buffering and passivating roles of the Li3NbO4 coating. The interfacial microstructure was analyzed to elucidate at the underlying reasons for the impedance increase and the pivotal role of the Li3NbO4 coating. Our study indicates that the surface coating significantly improves the cycle stability of the ASSBs with LSPS as the electrolyte, mostly due to an improvement of the charge transfer mechanism. The coating reduced the interphase thickness and the interfacial resistance to about a third of the uncoated one after 10 cycles.