Bulk-Interface and Dual-Domain Stabilization of Spent LiCoO2 Using Multifunctional Lithium Cysteinate Enables High-Voltage Regeneration of Layered Cathodes

The increasing volume of spent lithium-ion batteries (LIBs) has triggered severe resource and environmental issues, making the environmentally friendly, high-value regeneration of spent LiCoO2 (SLCO) imperative in the new energy field. Upcycling SLCO into high-voltage lithium cobalt oxide (LCO) potentiates its high-value-added utilization; however, single-functional lithium sources in existing regeneration processes only achieve basic lithium compensation and fail to simultaneously address the bottlenecks of bulk structural degradation and uncontrolled interfacial side reactions under 4.6 V high-voltage cycling, which hinders the stable upcycling of SLCO into high-voltage LCO. Herein, a bulk-interface and dual-domain stabilization strategy is proposed via one-step solid-state sintering with lithium cysteinate (Li-Cys). The preferential cleavage of Li-S bonds in Li-Cys first enables targeted lithium compensation for spent LiCoO2, followed by the introduction of NaOH to provide a mild alkaline environment, thereby simultaneously achieving Na/S co-doping in the bulk and the in situ construction of a Li2SO4/LiNxOy coating at the interface. Na+ stabilized the layered structure as an interlayer pillar, S enhanced the lattice oxygen stability, and the coating suppressed interfacial side reactions, jointly improving the structural stability and ion transport kinetics. The regenerated NS-RLCO cathode delivered an initial capacity of 205 mAh/g at 0.1C, 91.9% capacity retention after 100 cycles at 1C, and 158.9 mAh/g reversible capacity at 3C. Economic and life-cycle analyses confirmed its superior cost and environmental benefits over traditional recycling processes, providing a novel route for environmentally friendly, high-value regeneration of spent LCO.