Mechanistic insights into the lattice reconfiguration of the anode graphite recycled from spent high-power lithium-ion batteries

Abstract The mechanism underlying the anode graphite's regeneration from the spent lithium-ion batteries is investigated by a semi-in situ X-ray diffraction study combined with electron microscopy and Raman spectroscopy. The impacts of thermal treatment temperatures, durations, and atmospheres (including N2, Ar, and He) on the crystal lattice restoration are thoroughly examined to obtain the optimized conditions that impart significant crystal lattice restoration. The N2 atmosphere can activate the carbon through the reaction of oxygen-containing functionalities with the lithium nitride generated by the reaction between N2 and the metallic Li precipitated on the anode surface, resulting in the best graphitization effect under the N2 atmosphere in comparison with the Ar and He. Among all of the investigated calcination temperatures and durations, 3000 °C combined with 6 h is evidenced to be the optimal one for removing the internal stress and achieving the highest degree of graphitization. The regenerated graphite exhibits superior electrochemical properties, with an initial charging capacity of 352.5 mAh·g−1 and capacity retention of 97.3% after 1000 cycles. A pilot-scale test also verifies the effectiveness of the recycling and regeneration method, and the obtained product releases a capacity of 351.9 mAh·g−1 and capacity retention of 87.88% after 1600 cycles.