All-solid-sate
batteries (ASSBs) with a NASICON-type solid-state
electrolyte (SSE) of Li1.3Al0.3Ti1.7(PO4)3 (LATP) can be accepted as a promising
candidate to significantly improve safety and energy density due to
their high oxidation potential and high ionic conductivity. However,
thermodynamic instability between the cathode and LATP is scarcely
investigated during cosintering preparation for the integrated configuration
of ASSBs. Herein, the structural compatibility between commercially
layered LiNi0.5Co0.2Mn0.3O2 (NCM523) and LATP SSE was systematically investigated by cosintering
at 600 °C. It is noticeable that an extreme side reaction between
Li from NCM523 and phosphate from LATP happens during its cosintering
process, leading to a severe phase transition from a layered to a
spinel structure with high Li/Ni mixing. Consequently, the capacity
of NCM523 is lost during the preparation of the NCM523–LATP
composite cathode. Based on this, we suggested that the interface
modification of the NCM523/LATP interface is valued significantly
to inhibit this extreme side reaction, quickening the application
of LATP-based ASSBs.