Electrochemical Relithiation for Direct Regeneration of LiCoO₂Materials from Spent Lithium-Ion Battery Electrodes

Increased generation of spent lithium-ion batteries (LIBs) has driven the exploration of new methods for reusing and/or recycling LiCoO2 cathode materials. Herein, an electrochemical relithiation method was proposed to directly regenerate LiCoO2 cathode materials using the waste LixCoO2 electrode as a base. It was shown that Li+ was successfully inserted into the waste LixCoO2 electrode, and this relithiation process became faster with either a higher Li2SO4 concentration or a higher cathodic current density. The XRD analysis confirmed that the peak positions of the relithiation products were consistently close to those of a standard LiCoO2 material. The crystal structure of the relithiation products was restored with a post-annealing process. The activation energy for electrochemical relithiation (Ea) was estimated at 22 kJ mol-1, and the constant of equilibrium constant k0 was determined as 1.35 × 10-6 cm s-1. The relithiation process was controlled by the charge transfer process when the Li2SO4 concentration was high (e.g., 1, 0.8, and 0.5M), and a lower concentration at 0.01-0.3 M led to a diffusion control pattern. The electrode made of the regenerated LiCoO2 materials had a charge capacity of 136 mAh g-1, close to that of the commercial LiCoO2 electrode (140 mAh g-1). A potential mechanism of electrochemical relithiation was proposed involving lithium defects, relithiation, and crystal regeneration.