Electronic and ionic properties of sintered cathode of LiNi0.6Mn0.2Co0.2O2 (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.