Fluorine Migration Regulation for Direct Regeneration of High-Nickel Cathode Scraps

Abstract

Electrode scraps generated in large quantities during lithium-ion batteries (LIBs) manufacturing represent an important secondary resource of cathode materials. Given that these materials have not experienced electrochemical cycling, direct regeneration via thermal treatment to remove polymer binders and aluminum current collectors has been widely regarded as an efficient recycling route. Nevertheless, this study reveals that the thermal decomposition of poly(vinylidene fluoride) (PVDF) inevitably releases fluorine-containing intermediates with high chemical reactivity, which interact with residual Li species on the cathode surface to form LiF passivation layers and induce transition-metal cation disorder. These fluorination side reactions fundamentally constrain the structural reconstruction and electrochemical recovery of regenerated materials. To address this challenge, a Ca-assisted direct regeneration strategy is developed, in which Ca 2+ ions serve as thermodynamically favorable fluorine scavengers owing to the higher bond dissociation energy of Ca-F relative to Li-F. The preferential formation of CaF 2 suppresses cathode fluorination and facilitating the reintegration of residual Li into the host lattice. The regenerated cathode material exhibits a high initial discharge capacity of 175.9 mAh g -1 at 0.1 C, a capacity retention of 97% after 50 cycles, and a high-rate discharge capacity of 117.1 mAh g -1 at 5 C. This study elucidates the previously overlooked yet critical role of PVDF-derived fluorine impurities in constraining the direct regeneration of high-Ni cathode materials and establishes a thermodynamically guided strategy for the controllable and highperformance regeneration of ternary cathode materials.