Influence of the Sintering Temperature on LLZO-NCM Cathode Composites for Solid-State Batteries Studied by Transmission Electron Microscopy

The high impedance of the solid electrolyte (SE)|cathode active material (CAM) interface often limits the charge transfer in oxide-based solid-state battery (SSB) cells. Lowering the interfacial impedance by maximizing the contact between SE and CAM is usually attempted by co-sintering the materials at elevated temperatures. In this work Li6.25Al0.25La3Zr2O12 (LLZO) and LiNi0.6Co0.2Mn0.2O2 (NCM) composite cathodes co-sintered at different temperatures were investigated by employing various transmission electron microscopy (TEM) techniques to study the influence of the sintering temperature on the material’s integrity. High-resolution TEM images of the layered NCM phase (R3¯m) degraded to a NiO (rock salt)-like structure (Fm3¯m), as well as the formation of a LaNiO3-like transition phase between LLZO and NCM grains in direct contact, are presented for samples co-sintered at a temperature as low as 500°C. This is significantly lower than previously reported and questions the viability of an LLZO-NCM composite cathode.