A salt-free strategy for selective lithium recovery from spent lithium-ion batteries.

In recent years, recycling spent lithium-ion batteries has gained significant attention. Traditional acid-based lithium recovery generates high-salt wastewater during precipitation. This study proposes a novel hydrothermal reduction leaching method for selective lithium extraction from spent ternary lithium battery cathode powder. First, the powder was pretreated with 1 mol L^-1NaOH at 120 °C to remove fluorine, achieving 95.6 % removal efficiency. The fluorine-containing alkaline solution was treated with lime, precipitating fluorine with 95.4 % efficiency. Then, under hydrothermal conditions (175 °C, 60 % hydrazine hydrate, liquid-to-solid ratio of 4 g mL^-1), lithium was selectively leached with 98.2 % efficiency. Leaching efficiencies of nickel, cobalt, and manganese were all below 0.01 %, demonstrating over 99.9 % selectivity. Transition metals were reduced to low-valence states during leaching. XRD analysis of the crystalline products in the leachate confirmed that lithium existed predominantly as LiOH(aq). Lithium carbonate was recovered by reacting the leachate with CO₂(g) at 95 °C and 0.2 (±0.02) MPa, achieving 80.2 % precipitation efficiency. The method offers high lithium recovery, excellent selectivity, and avoids high-salt wastewater generation, thereby promoting environmentally friendly and sustainable recycling of spent lithium-ion batteries.