Chemical Inertness Dominated Intrinsic Safety: Unraveling the “Dissolution–Catalysis–Runaway” Mechanism in Sodium-Ion Battery Cathode Materials

While pursuing high energy density in sodium-ion battery cathodes, ensuring intrinsic safety remains challenging. This study establishes a complete evidence chain linking “intrinsic chemical stability-metal dissolution-electrolyte catalytic decomposition-thermal safety” using NaNi_1/3Fe_1/3Mn_1/3O₂ (NFM), Na₄Fe₃(PO₄)₂(P₂O₇) (NFPP), and NaCrO₂ (NCO) as models. We reveal that multivalent ions (Mn³⁺/Fe²⁺) in both NFM and NFPP trigger severe thermal runaway via a “dissolution-catalysis-runaway” cascade, despite their distinct structures. In contrast, NCO leverages the extreme chemical inertness of Cr³⁺ (unique d³ configuration and high Cr–O bond energy) to effectively sever this catalytic pathway, achieving counterintuitive high safety with minimal capacity sacrifice. This work elucidates that chemical inertness, rather than mere structural robustness, governs thermal safety, providing a new paradigm for designing intrinsically safe cathode materials.