Electronic and ionic properties of sintered cathode of LiNi _0.6 Mn _0.2 Co _0.2 O ₂ (NCM622)

Li‐ion solid‐state batteries have the potential for high energy densities and improved safety. Oxidic all solid‐state batteries require co‐sintering of the Li‐ion conductive solid electrolyte, the active electrode material, and an electronic conductive additive to give a composite electrode. A first step for the realization of this complex system is the study of the sintering behavior of the active material itself as a single‐phase component and to investigate the electrochemical activity as well as the electronic properties after heat treatment. In this study monolithic NCM622 cathodes with a thickness of about 90 μm were sintered at temperatures up to 900°C by using a low‐melting glass as sintering additive. For these ceramic cathodes sintered at T = 800°C, an electronic conductivity of 3.0 × 10 –3 S cm –1 and six orders of magnitude lower Li‐ion conductivity of about 10 –9 S cm –1 were determined by DC conductivity measurement. To investigate the electrochemical performance of the sintered cathode material, the porous microstructure was infiltrated with liquid electrolyte and a charging capacity of 140 mAh g –1 (92% of the theoretical capacity) was measured with C/50 cycling rate. In comparison, the electrochemical performance without infiltration of a Li‐ion conductive liquid was tested with polyethylene oxide as polymeric separator. With these measurements the ability of the sintered cathode to charge/discharge as well as to provide sufficient high electronic conductivity has been demonstrated.