Environmental-friendly and effectively regenerate anode material of spent lithium-ion batteries into high-performance P-doped graphite

Recycling graphite from spent lithium-ion batteries has been largely ignored. In the present work, we propose a novel purification process, which modifies the structure of graphite through phosphoric acid leaching-calcination to obtain high-performance phosphorus (P)-doped graphite (LG-temperature) and lithium phosphate products. The content analysis of X-ray photoelectron spectroscopy (XPS), X-ray fluorescence (XRF) and scanning electron microscope focused ion beam (SEM-FIB) indicates that the LG structure is deformed by the doped P atom. The results of In-situ fourier transform infrared spectroscopy (In-situ-FTIR), density functional theory (DFT) calculation and XPS analysis show that the surface of the leached spent graphite contains rich oxygen groups, which react with phosphoric acid at high temperatures and form stable C-O-P and C-P bonds, making it easier to form stable solid electrolyte interface (SEI) layer. The increase of layer spacing is confirmed by X-ray diffraction (XRD), Raman and transmission electron microscope (TEM), which is conducive to the formation of efficient Li+ transport channels. What is more, Li/LG-800 cells possess high reversible specific capacities of 359, 345, 330 and 289 mA h g−1 at 0.2C, 0.5C, 1C and 2C, respectively. After 100 cycles at 0.5C, the specific capacity is as high as 366 mAh g−1, demonstrating the outstanding reversibility and cycle performance. This study proves and highlights a promising recovery route for exhausted lithium-ion batteries anodes, making complete recycling possible.