A surface sensitive hard X-ray spectroscopic method applied to observe the surface layer reduction reaction of Co oxide to Co metal

Co-sintering process of LiCoO2 cathodes and NASICON-type LATP solid electrolytes studied by X-ray diffraction and X-ray absorption near edge structure

The composites of a high-capacity cathode material in lithium-ion batteries, LiCoO₂ (LCO) and an oxide-based solid electrolyte, Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP), were sintered at various temperatures and their reaction products were subsequently identified by X-ray diffraction (XRD) and X-ray absorption near edge structure (XANES). Rietveld analysis of XRD and the linear combination fitting of XANES showed that the reaction of LCO and LATP proceeds via three major steps; from 300 °C to 500 °C, LCO and LATP react with each other to form Co₃O₄, amorphous TiO₂ and Li₃PO₄; from 500 °C at which crystalline LCO is completely decomposed, LATP reacts not only with remaining amorphous/low crystalline LCO but also with Co₃O₄ to form LiCoPO₄ and TiO₂; from 700 °C to 750 °C, Co₃O₄ and TiO₂ react with each other to form CoTiO₃. The final products at 900 °C are LiCoPO₄, CoTiO₃, TiO₂, and Li₃PO₄.