Approaching Sustainable Lithium‐Ion Batteries through Voltage‐Responsive Smart Prelithiation Separator with Surface‐Engineered Sacrificial Lithium Agents.

The surge in lithium‐ion batteries has heightened concerns regarding metal resource depletion and the environmental impact of spent batteries. Battery recycling has become paramount globally, but conventional techniques, while effective at extracting transition metals like cobalt and nickel from cathodes, often overlook widely used spent LiFePO4 due to its abundant and low‐cost iron content. Direct regeneration, a promising approach for restoring deteriorated cathodes, is hindered by practicality and cost issues despite successful methods like solid‐state sintering. Hence, a smart prelithiation separator based on surface‐engineered sacrificial lithium agents is proposed. Benefiting from the synergistic anionic and cationic redox, the prelithiation separator can intelligently release or intake active lithium via voltage regulation. The staged lithium replenishment strategy was implemented, successfully restoring spent LiFePO4's capacity to 163.7 mAh g−1 and a doubled life. Simultaneously, the separator can absorb excess active lithium up to approximately 600 mAh g−1 below 2.5 V to prevent over‐lithiation of the cathode This innovative, straightforward, and cost‐effective strategy paves the way for the direct regeneration of spent batteries, expanding the possibilities in the realm of lithium‐ion battery recycling. [ABSTRACT FROM AUTHOR]