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 LiMn 2 O 4 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 Mn 3 O 4 precipitate. This process yields a high-purity lithium solution (>0.6 mol·L –1 ) that is directly convertible to battery-grade Li 2 CO 3 . Notably, nitrogen from hydrazine is predominantly converted into environmentally benign N 2, 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 LiCoO 2 and LiNi 1/3 Co 1/3 Mn 1/3 O 2, underscoring its potential as a scalable, impurity-free, and environmentally compatible route for closed-loop battery recycling.