Olivine-LiNiPO₄ Thin Films: Chemical Compatibility with Liquid Electrolyte and Interface Stability at High Potential

The chemical compatibility between carbon free olivine-LiNiPO₄ thin films used as cathode material and LiPF₆/DMC/FEC/0.2%-TMB liquid electrolyte was studied by soft-photoelectron spectroscopy, Ni L- and O K- XANES combined with electrochemical experiments. The stability of the electrolyte-electrode interface at a high charging potential strongly depends on the temperature of LiNiPO₄ preparation. For the films grown at 740°C, the chemical composition of the interface is not changed even at a charging potential of 5.2 V, whereas the electrolyte-electrode interface of LiNiPO₄ grown at lower temperatures (675°C) decomposes at 5.1 V, involving the cathode material in the chemical reaction.