From Spent Lithium‐Ion Batteries to High‐Performance Supercapacitors: Enabling Universal Gradient Recycling via Spin Capacitance

Abstract Driven by environmental imperatives and the growing economic challenges posed by the accumulation of spent batteries, developing effective recycling strategies has become paramount. Current direct battery recycling methodologies primarily focus on structural restoration, but the universality of this approach is hampered by the variability in electrode degradation mechanisms and the extent of irreversible damage sustained after cycling. To overcome these inherent limitations, this research introduces a universally applicable in situ recycling strategy that rejuvenates the metal components within batteries. Through an in situ facile electrochemical treatment, the cathode material is engineered to create a nanostructured interface composed of transition metal/lithium compounds, enhancing intrinsic electron/ion conduction and enabling substantial charge storage with accelerated transfer capabilities. Furthermore, operando magnetometry reveals that the energy storage mechanism aligns with a space charge mechanism, manifesting as spin‐polarized capacitance. As proof of concept, the recycled LiFePO 4 ‐based batteries are in situ converted into high‐performance supercapacitors, boasting an energy density of 106 Wh kg −1 and a power density of 10,714 W kg −1 , alongside impressive cycling stability with 91.3% capacitance retention after 2000 cycles. This approach demonstrates feasibility with LiFePO 4 and extends to other commercial cathodes such as LiCoO 2 , LiNi 1/3 Co 1/3 Mn 1/3 O 2 , and even their blends, offering a groundbreaking solution for lithium‐ion battery recycling.