Antisolvent crystallization from deep eutectic solvent leachates of LiNi1/3Mn1/3Co1/3O2 for recycling and direct synthesis of battery cathodes

Abstract

Deep eutectic solvents (DES) are a new class of environmentally friendly, safe, and inexpensive solvents with a remarkable ability to dissolve metal oxides, proposed as green alternatives to traditional acid leaching in the recycling of lithium-ion battery (LIB) cathode materials. In this work, a closed-loop process is targeted, where LiNi1/3Mn1/3Co1/3O2 (NMC) is leached by a DES (choline chloride and l-(+)-tartaric acid), and the metals are recovered by antisolvent crystallization. Five organic antisolvents have been evaluated, amongst which ethanol provides the highest metal recovery efficiency. The suitability of the solid precipitates as precursors for the sol-gel synthesis of new NMC, and the resulting cycling performance as battery cathodes, have been tested. The effect on the process of impurities Al and Cu from current collectors has been investigated. The impurities partially precipitate with the targeted metals, but the product impurity content can be significantly reduced through the selection of antisolvent, antisolvent-to-leachate ratio, crystallization residence time, and the rate of supersaturation generation in semi-batch mode. The resulting solids can be suitable for direct cathode resynthesis without the addition of a chelating agent, but impurities from current collectors decrease cycling performance. The results highlight the potential of combining DES leaching and antisolvent crystallization as a sustainable and efficient LIB cathode recycling method.