Mechanochemistry-driven acid-free strategy for synergistic recycling of mixed spent lithium-ion batteries

The recovery of valuable metals from spent lithium-ion batteries (LIBs) has attracted increasing attention in recent years. However, conventional recycling processes typically rely heavily on chemical reagents, leading to significant secondary pollution. To address this issue, this study proposes a mechanochemical reaction (MR) induced synergistic strategy for the recycling of spent LiNi_xCo_yMn_zO₂ and LiFePO₄. In this process, the MR process was coupled with the intrinsic redox properties of the cathode materials, utilizing Fe₂(SO₄)₃ as an inducer. As a result, valuable metals can be efficiently and selectively leached under acid-free conditions without the need for additional oxidants or reductants. The results indicate that the MR process induced structural activation and solid-state redox reactions in the mixed powder, thereby markedly enhancing the reactivity of the system. Under optimized conditions, the leaching efficiencies of Li, Ni, Co and Mn all exceeded 99.0%, while the dissolution of Fe and P was limited to 2.5% and 0.5%, respectively. Compared to systems without MR process, the MR process reduced the Fe₂(SO₄)₃ dosage by 66.7% while improving the leaching efficiency and selectivity of valuable metals. Kinetics analysis further revealed that the rate-limiting step shifted from surface chemical control to solid product layer diffusion control, significantly decreasing the apparent activation energy. This strategy minimizes chemical reagents consumption, simplifies subsequent separation and purification steps, and provides a novel route for the efficient and sustainable recycling of spent LIBs.