Achieving Low-Temperature Aqueous Relithiation for Direct Regeneration of Spent Lithium Iron Phosphate via Hydroxylamine Mediation

Lithium iron phosphate batteries are widely adopted because of their cost-effectiveness. However, the large-scale recycling of these batteries is constrained by the economic and safety challenges posed by existing recycling technologies. Here, a sustainable and universal strategy based on low-temperature aqueous relithiation is proposed for LFP regeneration utilizing hydroxylamine sulfate as a mediator. The enhanced reductive environment created by hydroxylamine sulfate significantly lowers the Li+ migration energy barrier to lithium vacancies and enhances the repair of FeLi antisite defects at a reduced temperature of 40 °C, simplifying the operational process substantially. By combination with a short annealing step, the Li loss and structural degradation in LFP are effectively mitigated, enabling further restoration of electrochemical performance. Notably, the results of in situ X-ray diffraction (XRD) during the lithiation process reveal that the final step of complete lattice repair is a critical factor in controlling the lithium replenishment process. Furthermore, this process exhibits integration, sustainability, and universality, thereby overcoming the barriers to transitioning direct recycling from lab-scale to industrial applications.