Direct regeneration of spent LiFePO4 materials via a green and economical one-step hydrothermal process

The rapid development of electronic devices, electric vehicles and mobile energy storage devices, has increasingly emphasized the shortage of lithium resources for us in lithium-ion batteries are developing rapidly. The key to the disposal of spent lithium-ion batteries is to carry out green and efficient regeneration. Herein, we propose a one-step hydrothermal process for the direct regeneration of spent LiFePO4. To reduce the Fe3+ in the spent LiFePO4, the hydroxyl group was oxidized to an aldehyde group via a decarburization reaction, with DL-malic acid utilized as a low-cost and environmentally friendly reducing agent. The effects of various different Li concentrations, hydrothermal times and hydrothermal temperatures on the performance of regenerated LiFePO4 were investigated. The results revealed optimal electrochemical performance under a Li concentration of 1.2 mol L-1, a hydrothermal time of 6 h, and a hydrothermal temperature of 100 °C. The cycling stability of LiFePO4 regenerated under these conditions considerably improved. The initial discharge specific capacity and the discharge specific capacity of the regenerated LFP after 200 cycles were 138.4 mAh g-1 and 136.6 mAh g-1. All coulomb efficiencies of the regenerated LFP were above 97.2 %, and the capacity retention rate was 98.7%. This developed method can therefore be considered a green and feasible means for regeneration of LiFePO4.