Surface‐Coating‐Mediated Electrochemical Performance in CuO Nanowires during the Sodiation–Desodiation Cycling

The rate performance and cycling numbers of CuO‐based sodium‐ion batteries (SIBs) suffer from large volume change and the poor conductivity during the ion transportation process. Herein, it is found that the surface coating with C and Au could effectively constrain the nanowire (NW) elongation rate along the 〈110〉 growth direction as well as increase the electrochemical reaction speed, which result in the improved cycling performance. Additionally, the in situ transmission electron microscopy observation of sodiation–desodiation cycling in coated CuO NWs indicates the detailed electrochemical reaction pathways, whereas the CuO shows the irreversible reaction scheme: transform to Cu during the sodiation while CuO and Cu 2 O coexist after desodiation. The irreversibility contributes to the capacity loss in CuO‐based SIBs. In contrast, the fully reversible Na + insertion and extraction in Au suggest that Au could be an effective material for Na + storage. Based on the real‐time experimental observations, these results reveal the vital role of surface coating in affecting the electrochemical performance of CuO, which may also provide insight into the behavior of other transition oxide electrode materials.