Influence of the sintering temperature on LLZO-NCM cathode composites for solid-state batteries studied by transmission electron microscopy

Abstract

•Co-sintered LLZO|NCM composites were investigated using various TEM techniques •The formation of a LaNiO3-like phase starts at a temperature as low as 500°C •HRTEM images of the LLZO|NCM interface evidence the phase transition 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 ( R 3 ¯ m ) degraded to a NiO (rock salt)-like structure ( F m 3 ¯ 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. 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 ( R 3 ¯ m ) degraded to a NiO (rock salt)-like structure ( F m 3 ¯ 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.