Recent progress on sustainable recycling of spent lithium-ion battery: Efficient and closed-loop regeneration strategies for high-capacity layered NCM cathode materials

•Recent progress in recycling spent NCM Lithium-ion batteries through direct and indirect regeneration strategies.•Sol-gel strategy avoids the co-calcination process of precursor and lithium source and has high potential for application.•One of the hottest topics in the direct regeneration of NCM cathode materials in recent years is the molten salt technique.•The appropriate method should be chosen based on the quality of retired NCM batteries. Concerns over non-renewable metal resources and environmental degradation are growing as a result of the exponential increase of market dominance of Lithium (Li)-ion batteries in energy storage devices, for example electric automobile. As one of the leading materials of Li-ion battery—LiNixCoyMnzO2 (NCM), the regenerated technology of NCM has received lots of attention in recent years due to the extreme scarcity of transition metals. The regeneration strategies are innovatively divided into indirect regeneration strategy and direct regeneration strategy according to the damage of cathode material of NCM in the regeneration process. After introducing the pretreatment process and common leaching reagents, the co-precipitation and sol–gel indirect regeneration methods and their respective advantages and disadvantages are summarized. In contrast, based on the degradation mechanism of NCM cathode materials, solid-state and hydrothermal direct regeneration strategies are summed up. Further, some emerging direct regeneration strategies such as Li-based eutectic molten salt, novel coating strategies, and electrochemical methods are discussed. Finally, these methods are systematically summarized and compared, and the prospect of future NCM battery regeneration is proposed to accelerate the recovery and application of cathode materials on an industrial scale.