Structural Instability of NCM-LATP Composite Cathode During Co-Sintering

Ni-rich layered cathode LiNi_xCo_yMn_1-x-yO₂ (NCM) and NASICON-type electrolyte Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) are promising candidates for oxide-based all-solid-sate batteries (ASSBs). Co-sintered at elevated temperatures is necessary to attain high ionic conductivity and minimize interfacial resistance between active cathode materials and electrolytes. However, the co-sintering leads to undesirable chemical reactions and degrades the electrochemical performance of the composite cathode. In this study, the co-sintering of single-crystalline NCM cathodes and LATP electrolytes is systematically investigated. It is found that the major reason for the degradation of NCM-LATP composite cathode during co-sintering is the severe O₂ evolution and phase transitions in NCM as sintering temperature rises, which mainly originates from the Li loss in NCM due to the Li⁺-concentration disparity between NCM and LATP. The capacity of NCM after co-sintering decreases sharply with the increasing Ni content, which can be attributed to the lower migration energy barrier of Ni ion and formation energy of oxygen vacancy around Ni ion. Therefore, modifying the NCM|LATP interface and employing novel sintering technologies are essential to inhibit the side reactions and optimize the performance of composite cathodes, thereby advancing the application of oxide-based ASSBs.