High-Performance Li-Metal Battery Constructed with Sustainable LiHNT-PVDF Nanohybrid Semi-Solid-State Electrolyte and Sulfonated RGO-Coated LiCu_<i>x</i>/Li||Regenerated NMC622-LiAlO₂ from Spent Batteries

Spent lithium-ion batteries contain valuable critical metals, such as lithium, cobalt, and graphite, making them a key resource for recovery via urban mining. In this study, we developed a closed-loop, eco-friendly, and cost-effective recycling process using organic acids and hydrogen peroxide to recover metal compounds and regenerate graphite. The process, based on microwave-assisted hydrothermal leaching assisted hydro-metallurgical processes, was completed within 45 min at 80–100 °C. Recovered lithium carbonate (Li2CO3) and cobalt oxalate (CoC2O4·2H2O) precursors were used to synthesize LiNi0.6Co0.2Mn0.2O2 (NMC622) cathodes, which exhibited an initial discharge capacity of 173 mAh/g at a 0.5C rate and 80% capacity retention after 200 cycles. For the anode, we developed a direct hot-melt coating of molten lithium metal (LiCux) on copper foil, with a thickness of 53 μm, using an in-situ alloying reaction. To mitigate dendritic growth, we applied a protective layer of di-sulfonated reduced graphene oxide (DSRGO), derived from spent graphite. The sulfonic acid groups in DSRGO served as effective lithium-anchoring sites, guiding a uniform Li-ion flux and reducing dendrite formation. A symmetric cell with LiCux/Li-DSRGO anodes showed excellent cycling stability, with stripping/plating cycles exceeding 1200 h at 0.5 mA/cm2. We also fabricated a semi-solid-state polymer composite electrolyte (SSPCE) by incorporating lithiated halloysite nanotube (LiHNT) clay into a poly(vinylidene difluoride) (PVDF) matrix, which demonstrated an ionic conductivity of 6.7 × 10–4 S/cm and a lithium-ion transference number of 0.9. The full cell, consisting of NMC622-LiAlO2 10% || SSPCE-5 || LiCux/Li-DSRGO, delivered 170 mAh/g at 0.1C and 114 mAh/g at 1C, with 79% capacity retention after 100 cycles. This work presents a sustainable strategy for high-performance lithium-metal batteries (LMBs) derived from spent lithium-ion batteries.