The critical role of H2 reduction roasting for enhancing the recycling of spent Li-ion battery cathodes in the subsequent neutral water electrolysis

Effective and sustainable recycling of lithium-ion batteries is critically important for comprehensive resource utilization and environmental protection. Herein, we propose a novel recycling process that combines H2 reduction roasting and neutral water electrolysis to recover valuable metal elements from the waste cathodes of spent lithium-ion batteries. Firstly, the waste cathode materials were calcined in H2 to form oxides with lower valence transition metal ions. Then, the low-valence transition metal ions were leached from the reduced materials in the low-pH chamber and precipitated as hydroxides in the high-pH chamber of the neutral water electrolyzer. Three common LIB cathodes (i.e., LiCoO2, LiMn2O4, LiNi0.5Co0.2Mn0.3O2) were processed with this new combined method, and the leaching efficiencies of the Li ion and the transition metal ions significantly improved versus not using the reductive H2 roasting. The leaching kinetics of LiCoO2, LiMn2O4, LiNi0.5Co0.2Mn0.3O2, CoO, MnO, and NiO were carefully analyzed and compared to further understand the advantages of the combined method. The kinetics study supports the experimental finding that the transition metal elements are more easily leached from the roasted products than from the pristine cathode materials. Moreover, the H2 produced at the cathode chamber of the neutral water electrolyzer can be recycled to the first step of reduction roasting, realizing the closed-loop utilization of H2. This work highlights the critical role of H2 reduction roasting in improving the recycling of the waste cathodes in the subsequent neutral water electrolysis.