Implications of Oxygen Release and Crossover for Thermal Stability in Solid-State Batteries

Abstract The pursuit of high-energy solid-state batteries (SSBs) has propelled the adoption of Ni-rich-layered LiNixMnyCozO2 cathodes. However, how Ni content governs interfacial stability and thermal response in SSB architectures remains unclear. In this work, we systematically examine LiNixMnyCozO2-based solid-state cells with controlled Ni stoichiometry to reveal composition-dependent oxygen release behavior and associated thermo-electrochemical instability pathways. Ni-rich compositions deliver higher initial capacities but accelerate structural evolution, lattice oxygen release, and interfacial reactivity with the sulfide solid electrolyte, lowering the onset of self-heating and promoting earlier thermal runaway. In contrast, Ni-lean compositions exhibit greater structural robustness, suppressed interfacial decomposition, and delayed exothermic response, albeit at reduced energy density. By correlating electrochemical behavior, phase evolution, interfacial chemistry, and calorimetric signatures, we identify Ni-induced oxygen release and its crossover behavior as the mechanistic link between energy density and thermal instability, establishing a cathode composition−safety framework for sulfide SSBs.