Amorphous nickel–cobalt phosphate nanosheets optimized by a micron−sized copper particle array with ultrahigh specific capacitance for asymmetric supercapacitors

Amorphous transition metal phosphides/phosphates show great potential for their application in supercapacitors. However, their electrochemical performances, such as capacitance performance and rate performance, are limited by the poor intrinsic conductivity originating from their amorphous characteristics. Herein, we report an amorphous nickel–cobalt bimetallic phosphate nanosheet electrode optimized by a micron-sized copper particle array, which is prepared via a simple two-step synthesis process. Upon optimization, amorphous nickel–cobalt phosphate grows uniformly on the micron–sized copper particle array without stacking, thereby delivering an improved capacitance performance. Furthermore, the conductivity of amorphous nickel–cobalt phosphate is improved, bringing about a rising rate performance. As the active material, amorphous nickel–cobalt phosphate demonstrates an ultrahigh specific capacitance of 3401.3 F g ⁻¹ at 2 A g ⁻¹ (more than twice that before optimization), and improved rate performance, with a 76% capacitance retention at 30 A g ⁻¹ (capacitance retention before optimization was only 51%). The assembled asymmetric supercapacitor delivers a specific capacitance of 156.1 F g ⁻¹ at 1 A g ⁻¹ , corresponding to an energy density of 43.1 W h kg ⁻¹ at a power density of 400 W kg ⁻¹ . Overall, this work affords a reference for preparing electrodes of ultrahigh specific capacitance for supercapacitors.