From Waste to Wealth: A Review of Eutectic Molten Salt Method for Direct Regeneration of Spent Lithium-Ion Battery.

The rapid growth of electric vehicles (EVs) has significantly increased the demand for lithium (Li)-ion batteries (LIBs), bringing environmental, economic, and technical challenges. Developing recycling methods that ensure economic viability and reduce environmental impact is now critical. Traditional hydrometallurgical and pyrometallurgical routes, while established and widely applied for LIB recycling, generate substantial volumes of waste (wastewater, slag, toxic gas) and low-value chemical components, e.g., LiCO, Nickel (Ni)/Cobalt (Co)/Manganese (Mn) salts, limiting their sustainability. Nowadays, the eutectic molten salt method, a typical direct regeneration technology, is gaining attention, standing out for its non-destructive repair, cost-effectiveness, and environmental benefits. It allows flexible salt combinations, adjustable lithiation, and annealing temperatures, and the use of additives to meet specific recycling needs, improving the electrochemical performance of spent cathode materials. This review begins with an overview of LIB composition and degradation mechanisms, then delves into recent advances in the eutectic molten salt method, covering pre-treatment, salt selection, thermal optimization, and cost-benefit analysis. In addition, these eutectic molten salt methods are compared with traditional hydrometallurgical and pyrometallurgical methods in terms of both economic and environmental impacts. Finally, the considerable industrial potential of eutectic molten salt methods for LIB recycling is highlighted, especially today when the EV sector is booming.