Ohta and coworkers fabricated a solid-state battery based on LLZO electrolyte, which showed a limited discharge capacity of 78 mAh/g due to the large interfacial resistance between LiCoO2/ LLZO [24]. Later on, the chemical information at interface between LLZO and LiCoO2 after high temperature sintering was investigated by Park and coworkers, and they identified the cross-diffusion of Co to LLZO and La/Zr to LiCoO2.