Recovery of valuable metals and modification of cathode materials from spent lithium-ion batteries

Highlights: • Scrapped Li(Ni-Co-Mn)O₂ was recycled from spent lithium-ion batteries. • Valuable metals were efficiently leached out by hydrothermal reaction. • The closed-loop recycling process can improve the utilization of valuable metals. • Na-F co-doping can enhance the properties of regenerated materials. -- Abstract: Improper disposal of used lithium-ion batteries will cause serious environmental pollution and waste of resources. A closed-loop recycling process based on hydrothermal leaching and co-doping is developed to recycle valuable metals by regenerating cathode material from spent lithium-ion batteries. Valuable metals in scrapped cathode material are efficiently leached out by hydrothermal leaching with a lower concentration of H₂SO₄ solution. In this work, 93.11% of Ni, 92.84% of Co and 90.18% of Mn can be leached out under the optimal hydrothermal leaching condition (0.5 M H₂SO₄, 0.1 M Na₂SO₃, 20 g/L, 120 ℃ and 8 h). The Na-F co-doped materials Li_1−xNa_xNi_0.6Co_0.2Mn_0.2O_2−xF_x (x = 0, 0.02, 0.04, 0.06) regenerated by co–precipitation are studied in this paper. The micro substitution of Na for Li can compensate for the effect of fluorine doping on capacity reduction. Na-F co-doping can stabilize the crystal structure, reduce the cation mixing degree and enhance the electrochemical performance. The material with a doping amount of 0.02 exhibits the best crystal structure, the lowest degree of cation mixing, the lowest electrochemical polarization and the minimal resistance, playing the highest discharge capacity (176.37 mAh g⁻¹) with the highest capacity retention (93.07%) at 0.2 C after 100 cycles.