Synthesizing Cu-doped CoSe2 nanoframe cubics for Na-ion batteries electrodes

Transition metal selenides have attracted much attention as electrode materials for Na-ion batteries (NIBs) because of their great potential as electric energy storage. Here, we report a facile strategy for synthesis of Cudoped CoSe2 nanoframe cubics (Cu-CoSe2 NFCs) structures through standing aging, chemical etching and ion exchange. In the experiment, the Co-Co PBA cube was etched from eight corners into a hollow frame structure. This hollow frame structure provides a good solution for the ion diffusion effect of the sodium battery. After ion exchange, the presence of Se and Cu after ion exchange greatly increases the capacity of the electrode. The synthesized Cu-CoSe2 NFCs electrode exhibits excellent reversible charge and discharge capacity (470 mAh g-1 at 0.1 A g-1). Even at a high current density of 2 A g-1, Cu-CoSe2 NFCs can still provide an excellent specific capacitance of 387 mAh g- 1.