Low-acid leaching of lithium-ion battery active materials in Fe-catalyzed Cu-H2SO4 system

Abstract

Leaching of active cathode materials of Li-ion batteries (LIB) is a hotly contested topic. In the published literature, the best processes utilize concentrated acid (e.g. 2–3 M H2SO4) and elevated temperatures for waste LIB leaching, along with unstable reduction reagents such as H2O2. In this study, we demonstrate the dissolution of LiCoO2 (LCO) in a low-acid leaching system that utilizes typical battery elements which can be found in impure, recycled black masses; Fe2+ as a reducing agent towards LCO, and Cu as a reducing agent towards Fe3+. We show for the first time that the Cu-Fe2+-H2SO4 system can provide an excellent performance in dissolving LCO materials at low acid environment and near-room temperature (T = 30 °C), even to the point where the acidity of the solution decreases to pH = 1.89 while reaching Co extraction of 92%. To the best of our knowledge, such high leaching efficiency has not been previously reported under such mild conditions. Nowadays, recyclability of the process waters may also be important, and herein we highlighted the influence of Na2SO4 on leaching of LCO active materials as well in this system. Minimization of the lixiviant concentration and temperature is beneficial in allowing decrease in chemical and energy consumption. High pH operation also can support further downstream processing, helping to avoid the problem of sodium accumulation towards the end-stage where lithium is recovered.