Cu2Se@C thin film with three-dimensional braided structure as a cathode material for enhanced Cu2+ storage

In the face of multiple challenges brought by the changes of global climate and environment, developing clean energy and updating green energy storage equipment are important ways to achieve carbon peak and carbon neutrality. Aqueous batteries have become a research hotspot due to their advantages of using the multivalent charge carrier, high ionic conductivity, environmental friendliness and cost effectiveness. In this work, the Cu2Se@C (Cu2Se coated on carbon clothes) thin film with a three-dimensional braided structure is fabricated by a simple electrochemical deposition method for Cu2+ storage for the first time. Compared with the commercial Cu2Se powder, the well-designed Cu2Se@C film shows enhanced specific capacity (640 mAh/g at 0.5 A/g) and rate performance (542 mAh/g at 5 A/g) as well as superior cycling stability (82.7% capacity retention after 1000 cycles at 1 A/g). The Cu2+ storage mechanism of the Cu2Se@C electrode is based on a reversible phase transition process of Cu2Se ↔ Cu2-xSe ↔ CuSe ↔ CuSe2. In kinetic characteristic analysis, the Cu2Se@C electrode demonstrates faster Cu2+ diffusion in discharge process than charge process resulting from the phase transition and the variation of interplanar spacing. This work highlights a facile one-piece design strategy and opens a new gateway for the exploration of advanced aqueous energy storage systems.