Defect-Directed Regeneration of LiCoO 2 Cathodes via Gradient Cobalt Reprogramming

Abstract

Direct regeneration establishes a low-carbon and resource-efficient route for recycling lithium-ion batteries, yet its practical impact is constrained by inadequate defect homogenization and an exclusive focus on restoring pristine structures rather than functional stability. Herein, we report an integrated regeneration strategy that transforms degradation in spent lithium cobalt oxide (LCO) into a functional and gradient-stabilized architecture. An ethylene glycol–lithium acetate solvent simultaneously removes interfacial impurities and redistributes residual lithium and cobalt through cooperative hydroxyl cleaning and acetate coordination, thereby homogenizing defects and activating rapid cation transport pathways. Upon thermal activation, interfacially accumulated cobalt migrates into vacancy-rich regions, featuring an interlayer cobalt gradient occupation comprised of a cobalt-rich rock-salt surface layer and a subsurface short‑range disordered zone. This hierarchical architecture synergistically stabilizes lattice oxygen, suppresses cobalt migration, and buffers stress accumulation during deep delithiation. Consequently, the regenerated LCO delivers a capacity of 192.22 mAh g−1 at 0.2 C, while structural upgrading enables stable high-voltage operation, achieving 214.24 mAh g−1 and over 80% capacity retention after 900 cycles at 0.5 C. By shifting direct regeneration from defect elimination to defect-enabled functional architecture design, this work establishes a general pathway for regenerating spent layered cathodes beyond their original performance limits.