Direct regeneration and performance of spent LiFePO4 via a green efficient hydrothermal technique.

With the quick development of electric vehicles and grid energy storage, the demand and production of lithium ion batteries (LIBs) are rapidly increasing, and the problem of lithium resource shortage becomes more and more serious. Both in terms of economic value and environmental protection, the recycling and regeneration of the spent lithium batteries is extremely urgent. Herein, a green and efficient hydrothermal technique for direct regeneration of spent lithium iron phosphate (LiFePO 4 or LFP) was proposed. LFP loses the partial lithium during the long cycle and converts to FePO 4 (FP), therefore, the replacement of the lost lithium is crucial for the regeneration of spent LFP. Herein, the effects of hydrothermal conditions such as reaction temperature, Li+ concentration and reducing agent concentration on the performance of product are systemically studied. Besides, it has been found that the control of hydrothermal condition is conductive to the supplement of Li and the enhancement of electrochemical performance of the product. Under hydrothermal conditions of 200 °C for 3 h, the regenerated LFP shows the optimal electrochemical performance of 165.9, 151.93, 145.92, 133.11 and 114.96 mAh g−1 at 0.1, 0.5, 1, 2, and 5 C, respectively. In addition, the capacity retention is as high as 99.1% after 200 cycles at 1 C. Therefore, this work provides a new idea for the direct regeneration of spent LFP cathode materials. [Display omitted] • Spent LiFePO 4 was repaired by a green and efficient hydrothermal process. • Fe3+ in S-LFP was reduced to Fe2+ by tartaric acid. • Soluble Li+ salt can adequately contact with the spent LFP in hydrothermal process. • The lithium defect in the spent LFP is well repaired. • The repaired materials of R-LFP-700 exhibit excellent electrochemical properties. [ABSTRACT FROM AUTHOR]