High-Entropy Inorganic Solid Electrolyte Interphase Enables Thermally Safe Sodium-Ion Battery with Deep Sodium Storage

Thermal safety remains a critical factor for the widespread adoption of sodium-ion batteries as next-generation energy storage technology. Conventional organic interfaces with poor thermal stability fail to protect the sodiated hard carbon formed through multimodal sodium storage under various abuses, particularly the highly reactive sodium clusters formed by pore filling, thus introducing substantial potential safety risks. Herein, a dual-functional high-entropy solid electrolyte interphase featuring a disordered hybrid of inorganic components is constructed on hard carbon. The high-entropy inorganic interface contains multidimensional ion transport channels with low diffusion energy barriers to drive sodium-ion deep storage with more pore-filling pathways in hard carbon, largely increasing the sodium storage capacity. NaNi_1/3Fe_1/3Mn_1/3O₂/hard carbon coin cell demonstrates 80% capacity retention after 800 cycles at a cathode loading of 17 mg cm^-2. The energy density of 146.2 Wh kg^-1 is achieved for the 3.7 Ah 26700 cylindrical cell. Concurrently, the thermally stable inorganic-rich interface strongly hinders the heat production from electrode-electrolyte reactions, significantly enhancing thermal safety of sodium-ion batteries. The thermal runaway onset temperature of the fully charged pouch cell is increased from 52.4 to 161.9 °C, and the maximum temperature rise rate is decreased from 1628.5 °C min^-1 to 17.4 °C min^-1. This work provides new insights into modulating the sodium storage mechanism and enhancing the safety of sodium-ion batteries.