Recovered cobalt-nickel sulfide from spent lithium-ion batteries as an advanced anode material toward sodium-ion batteries

Explosive growth of the electric vehicle market has led to a substantial accumulation of spent lithium-ion batteries (LIBs), causing significant environmental pollution and the wastage of precious metal resources. Thus, we developed a simple hydrothermal method to convert the spent LiNi_0.8Co_0.1Mn_0.1O₂ (NMC-811) cathode into CoNi-MOF. After the subsequent sulfidation process, waxberry-like Co_0.11Ni_0.89S@N-doped carbon composites (Co_0.11Ni_0.89S@NC), as a bimetallic sulfide solid solution, can be successfully synthesized to serve as high-performance anode materials for sodium-ion batteries (SIBs). The waxberry-like structure and strong S-C bonds between the carbon matrix and transition metal sulfides ensure the structural stability of the material during the cycle. Besides, the coexistence of Co and Ni in the bimetallic sulfide solid solution generates abundant lattice defects and modifies the electronic structures that significantly improve the charge transfer ability and Na⁺ diffusivity. The as-prepared Co_0.11Ni_0.89S@NC exhibits a high specific capacity of 622 mAh g⁻¹ at 200 mA g⁻¹, outstanding rate capacity of 370 mAh g⁻¹ at 5000 mA g⁻¹ and good cycling stability (330 mAh g⁻¹ after 1500 cycles at 5000 mA g⁻¹). This study presents a promising approach for the recycling of spent LIBs into high-performance anodes for SIBs, thus achieving the transformation of waste into valuable resources.