Fabrication of heteroatom-doped cobalt oxide yolk–shell microsphere using recycled solution from waste materials and their excellent electrochemical properties as an anode material for lithium-ion batteries

Heteroatom-doped transition metal oxides have attracted great attention as advanced anode materials for lithium-ion batteries due to their high theoretical capacity and superior properties. However, the limited resource availability has led to a substantial rise in prices for valuable metals such as Ni and Co, posing a significant challenge for their application. To address this issue, recycling of these metals from waste materials have gained prominence, and particularly the recovery of Co has been mostly focused on its economic benefits. Herein, we introduced a novel recycling strategy for fabrication of heteroatom-doped CoO_x (comprising mainly Co₃O₄ with a minor CoO phase) anode with a yolk–shell structure for lithium-ion batteries, by separating Co from cemented tungsten carbide waste. By employing a simple leaching process and subsequent spray pyrolysis, the yolk–shell structured microsphere comprising CoO_x was successfully synthesized. Moreover, the presence of other waste metals in the leachate facilitated multi-heteroatom doping during synthesis. Interestingly, the introduction of various dopants into CoO_x induced oxygen vacancy formation, thereby enhancing the electrochemical properties of the CoO_x anode. As a result, compared with the phase-pure (un-doped) CoO_x yolk–shell, the heteroatom-doped CoO_x yolk–shell exhibited robust cycling stability (602 mAh·g⁻¹ for 200 cycles at 1 A·g⁻¹) and excellent rate capability (210 mAh·g⁻¹ at 10 A·g⁻¹). Graphical abstract: (Figure presented.)