Aqueous electrochemical delithiation of cathode materials as a strategy to selectively recover lithium from waste lithium-ion batteries

Abstract

Lithium recovery from end-of-life Li-ion batteries (LIBs) through pyro- and hydrometallurgical recycling processes involves several refining stages, with high consumption of reagents and energy. A competitive technological alternative is the electrochemical oxidation of the cathode materials, whereby lithium can be deintercalated and transferred to an electrolyte solution without the aid of chemical extracting compounds. This article investigates the potential to selectively recover Li from LIB cathode materials by direct electrochemical extraction in aqueous solutions. The process allowed to recovering up to 98% of Li from high-purity commercial cathode materials (LiMn₂O₄, LiCoO₂, and LiNi_1/3Mn_1/3Co_1/3O₂) with a faradaic efficiency of 98% and negligible co-extraction of Co, Ni, and Mn. The process was then applied to recover Li from the real waste LIBs black mass obtained by the physical treatment of electric vehicle battery packs. This black mass contained graphite, conductive carbon, and metal impurities from current collectors and steel cases, which significantly influenced the evolution and performances of Li electrochemical extraction. Particularly, due to concomitant oxidation of impurities, lithium extraction yields and faradaic efficiencies were lower than those obtained with high-purity cathode materials. Copper oxidation was found to occur within the voltage range investigated, but it could not quantitatively explain the reduced Li extraction performances. In fact, a detailed investigation revealed that above 1.3 V vs. Ag/AgCl, conductive carbon can be oxidized, contributing to the decreased Li extraction. Based on the reported experimental results, guidelines were provided that quantitatively enable the extraction of Li from the black mass, while preventing the simultaneous oxidation of impurities and, consequently, reducing the energy consumption of the proposed Li recovery method.