One-step synthesis of copper-cobalt carbonate hydroxide microsphere for electrochemical capacitors with superior stability

Copper cobalt carbonate hydroxide (Cu-Co CH) microspheres were synthesized as a pseudocapacitive electrode material via a simple one-step hydrothermal method. Morphological characterization of the Cu-Co CH microspheres was carried out by scanning electron microscopy and transmission electron microscopy, showing their dandelion-like structure with the size approximately 4-7 μm. The crystalline structure, morphology and electrochemical performances of Cu-Co CH materials could be readily dominated by the molar ratio of Cu to Co. Among various stoichiometries of Cu-Co CHs, sample Cu0.48Co1.52 CH delivered the highest specific capacitance of 397.3 F g− 1 at 1 A g− 1 with a good rate capability. Cu0.48Co1.52 CH electrode material also exhibited a remarkably excellent cycling stability, ~ 99% of initial capacitance retention even after 10,000 charge/discharge cycles at 2 A g− 1. An asymmetric energy storage device was assembled by using Cu0.48Co1.52 CH as positive electrode and activated carbon as negative electrode in 2 M KOH electrolyte. The hybrid capacitor device could deliver an energy density of 26.3 Wh kg− 1 at a power density of 400.2 W kg− 1, and remain 16.7 Wh kg− 1 at 8374.2 W kg− 1. Meanwhile, it also showed amazing stability with ~ 99% capacity retention after 10,000 cycles. Based on the above results, Cu-Co CH microspheres possessed practical application as electrode materials for electrochemical capacitors due to their good structural stability in KOH electrolyte.