Reaction Suppression Between a High‐Ni Cathode Material (NMC622) and Li₇La₃Zr₂O₁₂ on Co‐Sintering for Manufacturing Bulk‐Type All‐Solid‐State Batteries: A New Method and Its Mechanism

Co‐sintering cathode materials with Li 7 La 3 Zr 2 O 12 (LLZ) is a promising strategy for fabricating bulk‐type all‐solid‐state batteries (ASSBs). However, preventing reactions between different materials, which is difficult with high‐capacity cathode materials such as LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622), is a pre‐requisite for applying this strategy. To overcome this issue, Li 1+ x Ni 0.6 Mn 0.2 Co 0.2 O 2 ( x = 0.01–0.2), which intentionally deviates from the stoichiometric NMC622 composition, is synthesized here. The formation of impurity phases in the co‐sintering process can be controlled by adjusting the co‐sintering temperature and x . Impurity phases are not formed on co‐sintering with x = 0.075 at 800 °C because reduced cation mixing in NMC622 and the presence of a self‐formed Li 2 CO 3 layer on the particle surface, ensured by adjusting x , effectively suppresses reactions. Furthermore, good results are observed at sintering temperatures where the proportions of Ni 2+ and Co 2+ , which promote cation mixing, are low. This study clarifies relevant reaction mechanisms using various analytical methods (such as temperature‐rise X‐ray absorption fine structure analysis and scanning transmission electron microscopy‐electron energy loss spectroscopy), and confirms the repetitive operation of bulk‐type ASSBs assembled using co‐sintered Li 1+ x Ni 0.6 Mn 0.2 Co 0.2 O 2 ( x = 0.075)/LLZ electrolyte systems. The method reported herein can be potentially adopted for cost‐effective and high‐energy‐capacity ASSB production.