Synthesis of LiNi_0.9Co_0.05Mn_0.05O₂ and modification with co-doping of Zr⁴⁺ and W⁶⁺ using acid leaching solution from spent lithium-ion batteries

Considering the increase in raw material prices and environmental pollution, the spent lithium-ion battery cathode material was leached with oxalic acid and sulfuric acid, and LiNi_0.9Co_0.05Mn_0.05O₂ (NCM955) was prepared from the leaching solution. Then, the Ni-rich cathode material NCM955 was doped with ZrO₂ and WO₃. The co-doping of Zr⁴⁺ and W⁶⁺ in Ni-rich NCM955 cathode exhibits exceptional cycle stability performance. Specifically, the Zr⁴⁺ and W⁶⁺ co-doped sample demonstrates a remarkable capacity retention improvement of 89.21% at 0.5 C after 100 cycles compared to the pristine sample (69.15%). Meanwhile, at a high rate of 5 C, the co-doped sample shows a significantly higher specific capacity of 125.37 mAh·g⁻¹ compared to the pristine sample’s value of only 63.98 mAh·g⁻¹. The results of XRD, XPS, and SEM indicate that the co-doping of Zr⁴⁺ and W⁶⁺ can enhance the stability of the material. Electrochemical impedance spectroscopy (EIS) results show that the co-doping of Zr⁴⁺ and W⁶⁺ effectively reduces the electrochemical impedance, and galvanostatic intermittent titration technique (GITT) shows that the co-doping of Zr⁴⁺ and W⁶⁺ increases the diffusion rate of Li⁺. Therefore, dual doping modification with Zr⁴⁺ and W⁶⁺ is beneficial for enhancing both structural stability and electrochemical performance of Ni-rich layered oxide cathode materials.