Electrochemical Relithiation for Direct Regeneration of LiCoO2 Materials from Spent Lithium-Ion Battery Electrodes

Abstract

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.