Electrochemo-mechanical effects of Co-free layered cathode on interfacial stability in all-solid-state batteries under high-voltage operation

Abstract

Ni-rich layered oxide cathode active materials (CAMs), such as LiNi_xCo_yMn_zO₂ (NCM), are promising candidates for high-energy all-solid-state batteries (ASSBs) due to their high theoretical capacities. However, Ni-rich NCMs suffer from poor electrochemical performance and mechanical degradation caused by anisotropic volume changes during high-voltage cycling. Cobalt in NCM further promotes irreversible lattice oxygen redox and phase transitions, leading to mechanical and interfacial degradation under high-voltage conditions. In this study, we introduce a Co-free layered oxide (LiNi_0.75Mn_0.25O₂, NMX75) to improve cycling stability under high-voltage operation in sulfide-based ASSBs. A comparative study between NMX75 and NCMs demonstrated that NMX75 effectively mitigates chemo-mechanical degradation by suppressing volume changes and mechanical stress. On the particle level, the NMX75 mitigated internal void formation and enabled structurally stable Li⁺ intercalation/deintercalation. On the interface level, the mitigation of mechanical degradation suppressed solid electrolyte decomposition and enhanced interfacial stability. As a result, the NMX75 delivered 80.6% capacity retention after 100 cycles at 2.5–4.45 V (vs. Li/Li⁺) in sulfide-based ASSBs. The outstanding performance of NMX75 provides fundamental insights into the development of the next-generation ASSBs.