Avoiding CO_2 Improves Thermal Stability at the Interface of Li_7La_3Zr2O_(12) Electrolyte with Layered Oxide Cathodes

摘要

Solid-state batteries promise higher energy densities and better safety than Li-ion batteries with liquid electrolytes. However, the interface between solid electrolyte and cathode is unstable at the elevated temperatures that are needed while sintering to achieve good bonding between ceramic components. Here, the hypothesis is that, the gas environment, especially the presence of CO2, is critical in determining the stability of the solid electrolyte-cathode interface. The effect of gas species on the interface is systematically probed, by a using Li7La3Zr2O12 (LLZO) solid electrolyte with a thin film LiNi0.6Mn0.2Co0.2O2 cathode as a model system to enable interface sensitivity. Detrimental phases formed at the interface and their onset conditions are identified by X-ray absorption spectroscopy, X-ray diffraction, and Gibbs free energy analysis. As a result, removing CO2 and minimizing H2O(g) during sintering is necessary to obtain good contact at the LLZO|cathode interface without forming secondary phases. Sintering in O-2 is ideal, yielding excellent chemical stability and low interfacial resistance. Secondary phases also do not form in N-2,N- but oxygen loss occurs at elevated temperatures. The interfacial resistance obtained upon sintering in pure O-2 is comparable to the lowest values at LLZO interfaces with protective coatings, but here without the need for interface coatings.