Li+ Quasi-Grotthuss Topochemistry Transport Enables Direct Regeneration of Spent Lithium-Ion Battery Cathodes

Abstract

Direct regeneration of spent lithium-ion batteries offers economic benefits and a reduced CO₂ footprint. Surface prelithiation, particularly through the molten salt method, is critical in enhancing spent cathode repair during high-temperature annealing. However, the sluggish Li⁺ transport kinetics, which predominantly relies on thermally driven processes in the traditional molten salt methods, limit the prelithiation efficiency and regeneration of spent cathodes. Here, we introduce a special molecular configuration (benzoate) into molten salts that facilitates rapid Li⁺ transport to the surface of LiNi_0.5Co_0.2Mn_0.3O₂ (NCM) via a quasi-Grotthuss topochemistry mechanism. This approach effectively avoids the phase transitions that could adversely degrade the electrochemical performance due to insufficient lithiation during the repair process. Computational and experimental analyses reveal that the system enables fast Li⁺ migration through the topological hopping of benzoate in organic lithium salt, rather than relying solely on thermally driven diffusion, thereby significantly improving the prelithiation and repair efficiency of spent NCM cathodes. Benefiting from the quasi-Grotthuss Li⁺ topochemistry transport, the degraded structure and Li vacancies in the spent cathode are effectively eliminated, yieding the regenerated cathode with good cycling stability comparable to commercial counterparts. The proposed Li⁺ transport mechanism presents a promising route for the efficient and sustainable regeneration of spent cathodes.