Lithium-ion battery (LIB) recycling is an urgent need to address the massive generation of spent LIBs from portable devices and electrical vehicles. However, the large-scale recycling is hampered by economic and safety issues associated with today's recycling processes. Here, we demonstrate a safe and energy efficient direct regeneration process based on low-temperature hydrothermal relithiation (LTHR) at low pressure for spent LiNi_xCo_yMn_zO₂ (0 < x,y,z <1, x + y + z = 1, or NCM) cathode materials. A low concentration of low-cost redox mediator is employed to improve the relithiation kinetics of spent NCM materials, enabling full relithiation temperature to be reduced from 220 °C to 100 °C or below. Correspondingly, the pressure incurred in the relithiation process can be reduced from ∼25 bar to 1 bar, offering significantly improved operation safety. Specifically, three NCM materials, including chemically delithiated NCM111, cycled (degraded) NCM111, and cycled NCM622, were successfully regenerated with complete recovery of composition, crystal structure, and electrochemical performance, achieving the same effectiveness as that achieved at high temperature process. Meanwhile, the total energy consumption of spent cell recycling and the greenhouse gas emission is also reduced. This work provides a facile and scalable way to more sustainable LIB recycling with high economic return, high operation safety and low cost.

锂离子电池 (LIB) 回收是解决便携式设备和电动汽车大量产生废锂电池的迫切需要。然而，大规模回收受到与当今回收过程相关的经济和安全问题的阻碍。在这里，我们展示了一种基于低压低温水热再锂化 (LTHR) 的安全且节能的直接再生工艺，用于废 LiNi _x Co _y Mn _z O ₂ (0 < x,y,z <1, x  +  y  +  z = 1，或 NCM) 正极材料。使用低浓度的低成本氧化还原介质来改善废NCM材料的再锂化动力学，使完全再锂化温度从220°C降低到100°C或更低。相应地，再锂化过程中产生的压力可以从~25 bar降低到1 bar，从而显着提高操作安全性。具体而言，化学脱锂的NCM111、循环（降解）的NCM111和循环的NCM622三种NCM材料成功再生，成分、晶体结构和电化学性能完全恢复，达到与高温工艺相同的效果。同时，废电池回收的总能耗和温室气体排放也减少了。