Towards a low carbon process for lithium recovery from spent lithium-ion batteries by a carbon conversion control strategy of carbothermic reduction

Carbothermic reduction is considered a traditional method to selectively recover lithium from spent lithium-ion batteries (LIBs) using inherent graphite as a reductant. However, the reduction generally occurs at a temperature higher than 650 °C and excess carbon is required to achieve an effective rate of lithium recovery. Hence, there have always been issues of high energy consumption and high carbon emissions associated with processes for lithium extraction. Herein, a systematic investigation was conducted, which revealed that the carbothermic reduction contains multiple-stage reduction reactions. The carbon consumption and conversion processes are highly influenced by competition among these different reactions. Consequently, a control strategy for carbon conversion was proposed, in which waste materials were subjected to a mechanochemical pre-treatment with graphite, aiming to change the carbon conversion pathway and inhibit the needless formation of carbon oxides. Finally, a high leaching efficiency for Li (95.8 wt%) was achieved when cathode materials were roasted at 550 °C for 1 h. Meanwhile, the carbon utilisation ratio increased from 28% to 88%, indicating that the final conversion of carbon is almost completely in the form of CO₃^2-, which in principle improves the atom efficiency of carbon and restrains secondary pollution. Considering global environmental pressures, this study provides a promising and potential direction for the recycling of LIBs following the principles of green chemistry, by significantly minimising greenhouse gas emissions.