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, Li1.3Al0.3Ti1.7(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.