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

A bulk‐type all‐solid‐state battery is produced by co‐sintering the proprietary NMC622 and LLZ. This proprietary NMC622 can avoid the formation of impurity phases under co‐sintering. The reduced Ni2+ fraction in NMC622 and the presence of a self‐formed Li2CO3 surface layer result in this outcome. It is possible to realize a rechargeable all‐solid‐state battery. Abstract Co‐sintering cathode materials with Li7La3Zr2O12 (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 LiNi0.6Mn0.2Co0.2O2 (NMC622), is a pre‐requisite for applying this strategy. To overcome this issue, Li1+xNi0.6Mn0.2Co0.2O2 (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 Li2CO3 layer on the particle surface, ensured by adjusting x, effectively suppresses reactions. Furthermore, good results are observed at sintering temperatures where the proportions of Ni2+ and Co2+, 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 Li1+xNi0.6Mn0.2Co0.2O2 (x = 0.075)/LLZ electrolyte systems. The method reported herein can be potentially adopted for cost‐effective and high‐energy‐capacity ASSB production. A bulk-type all-solid-state battery is produced by co-sintering the proprietary NMC622 and LLZ. This proprietary NMC622 can avoid the formation of impurity phases under co-sintering. The reduced Ni 2+ fraction in NMC622 and the presence of a self-formed Li 2 CO 3 surface layer result in this outcome. It is possible to realize a rechargeable all-solid-state battery. Abstract 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. Advanced Science, Volume 12, Issue 43, November 20, 2025.