A perspective on the recovery mechanisms of spent lithium iron phosphate cathode materials in different oxidation environments

Oxidative extraction has become an economically viable option for recycling lithium (Li) from spent lithium iron phosphate (LiFePO4) batteries. In this study, the releases behaviour of Li from spent LiFePO4 batteries under different oxidizing conditions was investigated with sodium hypochlorite (NaClO) as the solid oxidant. We revealed that, due to the intervention of graphitic carbon, the generated species of Li in mechanochemical oxidation (NaClO:LiFePO4 at a molar ratio of 2:1, 5 min, and 600 rpm) was lithium carbonate (Li2CO3). The graphite layer provided a channel for the conversion of Li species released by mechanochemical oxidation. While in hydrometallurgical oxidation (NaClO:LiFePO4 at a molar ratio of 2:1 and 12.5 min), the presence of hydrogen species led to the formation of lithium chloride (LiCl). Moreover, life cycle assessment (LCA) demonstrated that for recycling 1.0 kg of spent LiFePO4 batteries, mechanochemical and hydrometallurgical oxidation could reduce carbon footprints by 2.81 kg CO2 eq and 2.88 kg CO2 eq, respectively. Our results indicate that the oxidative environment determines the release pathway of Li from the spent LiFePO4 cathode material, thereby regulating the product forms of Li and environmental impacts. This study can provide key technical guidance for Li recycling from spent LiFePO4 batteries.