Structure-designed synthesis of Cu-doped Co₃O₄@N-doped carbon with interior void space for optimizing alkali-ion storage

Co₃O₄ is a promising anode candidate for Li-ion and Na-ion batteries (LIBs and SIBs) owing to its intrinsic merits. Nevertheless, drastic volume expansion upon charge/discharge causes fast capacity decay, which hugely hinders its commercial application. Introducing carbon materials as a coating layer is considered to be an effective strategy to improve the structural stability. However, the coating layer may be fractured upon repeated insertion/extraction due to the lack of void space. Therefore, constructing void space is crucial for achieving prolonged cycling stability. Herein, we design a successive coating-eching strategy to fabricate Cu-doped Co₃O₄@N-doped Carbon with interior void space (Cu-Co₃O₄@Void@NC). The void space allows the inner active material to expand freely without breaking the outer protective layer. Simultaneously, the unbroken NC layer is conductive to the formation of a stable SEI film. In addition, Cu-doping can enhance the inherent electrical conductivity of Co₃O₄, which is proved by the density functional theory (DFT) calculations. When evaluated as LIBs and SIBs anode, Cu-Co₃O₄@Void@NC delivers superior electrochemical performance (562 mAh g⁻¹ after 1000 cycles at 5 A g⁻¹ in LIBs and 312 mAh g⁻¹ after 300 cycles at 2 A g⁻¹ in SIBs).