Direct Regeneration of Layered Oxide Cathodes via Seawater

Lithium extraction from seawater can transform lithium resources and help ease upstream supply strain. Besides, the escalating deployment of lithium-ion batteries necessitates sustainable recycling strategies to address resource scarcity and environmental concerns. Herein, we report a green strategy on direct regenerating degraded layered oxide cathodes via a hydrothermal process using simulated seawater containing trace LiCl and high concentration of NaCl, followed by a mild annealing step. The regenerated cathode exhibits a fully restored layered structure, smooth surfaces, and no residual impurities. It delivers a high specific capacity of 146.6 mAh·g-1 at 0.5 C and excellent capacity retention of 91.67% after 100 cycles. We reveal that Li+ and Na+ play a synergistic effect on the regeneration mechanism. Na+ selectively adsorbs at surface defect sites without entering the bulk lattice as a dynamic coating layer to guide morphological repair, while Li⁺ achieves lithium replenishment via ion exchange with Na+ based on its high adsorption energy and excellent diffusion capability. This cost-effective approach bridges sustainable battery recycling with brine resource utilization, establishing a closed-loop "lithium extraction-cathode regeneration" paradigm.