A One-step Low-Temperature Closed-loop Eutectic Salt Strategy for Direct Regeneration of Severely Degraded LiFePO4

Abstract

Recycling spent lithium-ion batteries through direct methods provides significant environmental and economic advantages compared to pyrometallurgical and hydrometallurgical approaches. In this research, we introduce a one-step, closed-loop approach for the direct regeneration of severely degraded lithium iron phosphate (LiFePO₄, LFP) black mass, employing a low-temperature molten salt system. The binary molten lithium salts system of lithium iodide and lithium hydroxide enables Li⁺ to fully interact with delithiated LFP particles, thus overcoming the uneven repair issues associated with solid-state sintering methods. The reduction environment caused by the oxidation of I^- to I₂ significantly lowers the Li⁺ migration energy barrier to lithium vacancies and boosts the repair of Li/Fe anti-site defects at reduced temperature of 450°C. In addition, a closed-loop regeneration system is established because the produced iodine can be collected through condensation for reuse in production. The regenerated LFP material exhibits a retention rate of 95.7% in terms of capacity after 300 cycles at 1C. The regenerated LFP-based pouch cell (1Ah) demonstrates a capacity retention rate of 96.84% after 300 charge-discharge cycles at 0.5C rate. Technical and economic evaluations reveal that this innovative regeneration approach holds significant potential for industrial implementation.