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

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 Na₂S₂O₈ to generate highly reactive SO₄ ^-· and ·OH radicals. The potent radicals drive surface reconstruction from rock-salt phase into a Ni³⁺-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_1/3Mn_1/3Ni_1/3O₂ 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.