Dual-halide engineered interphases for combustion-resistant and high-performance sodium-based batteries

Unstable electrode-electrolyte interfaces in high-voltage sodium-ion batteries (SIBs) significantly hinder Na⁺ transport and pose severe safety risks. Herein, we propose a cost-effective strategy by introducing trichloromethane (TCM) as an additive into conventional carbonate-based electrolytes. This approach enables the in situ formation of a robust chlorine/fluorine-rich interphase that enhances Na⁺ transport kinetics and provides intrinsic flame retardancy. The interphase suppresses flammability through the release of chlorine radicals, effectively mitigating combustion in 1 Ah pouch cells. As a result, the modified electrolyte enables Na₃V₂(PO₄)₃/Na cells to retain 80.6% of their capacity over 800 cycles at 1 C and 4.3 V at room temperature, and 92.1% after 150 cycles at 4.5 V. Furthermore, under wide voltage windows and harsh thermal conditions, the cells maintain 87.8% and 98.0% capacity retention after 440 and 200 cycles at 55 °C and -24 °C, respectively, Fast-charging capability is also retained. This work demonstrates a feasible and scalable electrolyte design that simultaneously improves interfacial stability, thermal safety, and high-voltage operation. It also offers mechanistic insights into designing safer, high-performance sodium-based batteries.