Recovery of LiNi0.5Mn0.3Co0.2O2 cathode material from spent lithium-ion batteries with oxygen evolution reduction in ammonium sulfate low-temperature molten salt

Abstract

The advancement and extensive application of lithium-ion batteries (LIBs) as an energy storage device has led to an increase in the number of spent LIBs, and recycling spent LIBs is an urgent need to address their resource and environmental sustainability issues. Herein, an efficient and comprehensive recycling method for spent LiNi0.5Mn0.3Co0.2O2 cathode material (NMC 532), one of the most important materials for electric vehicles and grid storage applications, is developed based on ammonium sulfate low-temperature molten salt (LTMS) reduction with oxygen evolution, and the feasibility of the strategy is systematically investigated. The results demonstrate that (NH4)2SO4 LTMS can effectively realize the sulfate conversion of spent NMC 532, in which the sulfate conversion rates of Li, Ni, Mn, and Co all reach more than 90%. Through mechanism analysis, it is found that the induced superoxide ion (O2·-) and H+ are the keys to the reduction of transition metal oxides in LTMS. Meanwhile, O2·-, as a single electron reducing agent in the intermediate state, can be used to explain the reduction behavior of transition metal oxides in other ammonium salts, mineral acids, and H-containing salts in molten. Based on (NH4)2SO4 LTMS reduction, water leaching, thermodynamic analysis of coprecipitation, and a series of precipitation and separation experiments, this study provides an effective strategy for recycling spent cathode materials, which can realize the combination of spent material recycling and electrode material regeneration.