Interrupting Surface‐to‐Bulk Domino Propagation: A Thermal Failure Mitigation Strategy for Layered Oxide Cathodes

ABSTRACT Layered transition‐metal oxide cathodes are pivotal for lithium‐ion batteries (LIBs)‐powered energy‐storage systems. However, the relentless pursuit of high performance is severely bottlenecked by intrinsic thermal safety concerns, where structural degradation and interfacial instability can trigger catastrophic thermal runaway. Herein, a thermally triggered domino effect, manifesting as a destructive chain reaction that initiates with severe interfacial side reactions at the cathode surface and sequentially propagates toward profound bulk structural collapse, is identified as the headstream of thermal failure. To mitigate these vulnerabilities, a scalable crystalline‐state composite strategy is proposed by integrating micrometer‐scale layered oxides with nanosized olivine‐structured oxides (LMFP). This rationally designed architecture also synergistically realizes volumetric compacted density up to 3.75 g cm −3 and 86% capacity retention over 1000 cycles. Specifically, LMFP affords a dual‐spatial stabilization: it directs the formation of a robust inorganic‐rich cathode–electrolyte interphase while simultaneously functioning as an internal thermal barrier to effectively interrupt this detrimental chain reaction, resulting in 61.3°C and 21.4°C thermal failure delay for both cathodes and ampere‐hour‐level cells, respectively, which creates more than 16 min for evacuation during thermal runaway. This work elucidates a previously overlooked surface‐to‐bulk failure mechanism and delineates a highly viable trajectory for designing intrinsically safe, highly stable cathode architectures.