Direct Generation of High-Purity Lithium Solution from Spent Lithium-Ion Batteries via an Impurity-Free Hydrazine-Assisted Hydrothermal Route

The targeted recovery of lithium from end-of-life lithium-ion batteries (LIBs) is essential for sustainable resource cycling. However, existing methods often produce low-concentration lithium leachates contaminated with extraneous metal ions, complicating subsequent purification and lithium reclamation. Here, we report a hydrazine-assisted hydrothermal reduction process that enables a highly efficient and selective lithium extraction. Thermodynamic and experimental analyses confirm a lithium recovery rate of 99.06% from LiMn2O4 with selectivity over 99%. Mechanistic studies reveal that hydrazine disrupts the spinel structure via the attack on lattice oxygen, generating oxygen vacancies and facilitating preferential Li release over stronger-bonded Mn ions, ultimately forming a Mn3O4 precipitate. This process yields a high-purity lithium solution (>0.6 mol·L–1) that is directly convertible to battery-grade Li2CO3. Notably, nitrogen from hydrazine is predominantly converted into environmentally benign N2, with residual ammonia nitrogen as low as 26.5 mg·L–1 in the effluent. Comparative analysis shows our method achieves a superior lithium concentration of 4.58 g·L–1, leading to a 37.8% reduction in carbon footprint and 35.6% improvement in economic efficiency relative to conventional routes. The strategy also proves to be effective for LiCoO2 and LiNi1/3Co1/3Mn1/3O2, underscoring its potential as a scalable, impurity-free, and environmentally compatible route for closed-loop battery recycling.