Low-Temperature Carbothermic Reduction for Recycling LiCoO2 for the Recovery of Critical Raw Materials: The Role of Cellulose

Abstract

The continuously growing trend for the demand and sales of lithium-ion batteries, LIBs, poses the inevitable consequent challenge of the management of these devices when they reach the end of their primary and secondary lives, becoming a waste. Nowadays, the recycling of spent LIBs is already a well-established and large-scale industrial reality, with hundreds of companies operating in this field. The benchmark industrial technology is represented by the pyrometallurgical approach, involving heating treatments at high temperatures (above 1000 °C). Although these processes are easily implementable and scalable and allow for recovery of some of the most valuable metals (Co, Cu, and Ni) with high yields, they currently do not allow for recovery of Li, which is today considered as critical raw material from various countries and regulations. For this reason, we here present a carbothermic reduction process, belonging to the class of the pyrometallurgical approaches, for the recycling of LiCoO₂, one of the most diffuse cathodes in spent LIBs, in combination with cellulose, the most abundant component of biowastes, here considered for the optimization and rationalization of the thermal process. The carbothermic reduction has been designed with the aims of (i) lowering the operating temperature to reduce the energy consumption and allowing for the recovery of lithium; (ii) tuning the products of the thermal treatments to allow for an ease separation of Co and Li via water leaching; and (iii) rationalizing the effect of cellulose on the carbothermic reduction, as it is one of the main components of the biowaste recently considered for the development of such recycling approach. The final optimized process involves the use of the LiCoO₂-to-cellulose weight ratio of 1:4, treated at 600 °C for 1 h under N₂ flow, and produces a mixture of Co and Li₂CO₃ that can be separated and recovered exploiting the different solubilities in water. The recovery yields reported here are above 70% but can be further enhanced with the scaling up of the procedure; the recovered Li and Co sources have been finally exploited to demonstrate the possibility to use these recycled materials as a source for the synthesis of “recycled” LiCoO₂ for which structural and electrochemical characterization is presented.