Radical‐Driven Surface Pre‐Oxidation Enabling Efficient Regeneration of Spent Sodium‐Ion Battery Cathodes

ABSTRACT The escalating accumulation of retired sodium‐ion batteries (SIBs) has rendered efficient recycling a pressing imperative. Direct regeneration presents a compelling solution due to economic viability and high value‐added output. However, severe surface degradation of spent cathode materials impedes Na ⁺ replenishment, compromising regeneration efficacy. Herein, a novel pre‐oxidation strategy is proposed that capitalizes on water‐triggered Na ⁺ /H ⁺ exchange in spent cathodes to establish an alkaline environment, which catalyzes the decomposition of Na ₂ S ₂ O ₈ to generate highly reactive SO ₄ ^– · and ·OH radicals. The potent radicals drive surface reconstruction from rock‐salt phase into a Ni ³⁺ ‐layered configuration, optimizing Na ⁺ transport channels. Furthermore, the treatment refines particle morphology and eliminates residual aluminum and fluoride impurities, enhancing interfacial reaction homogeneity, thereby enabling efficient solid‐state regeneration. As a result, the pre‐oxidation regenerated NaFe _1/3 Mn _1/3 Ni _1/3 O ₂ cathode exhibits an initial capacity of 134.33 mAh g ⁻¹ and superior cycling stability with 84.4% retention after 150 cycles at 0.5 C, restoring performance comparable to commercial counterparts. This study provides an innovative and integrated strategy for efficient regeneration of highly degraded cathode materials.