Honeycomb-Like Interconnected Network of Nickel Phosphide Heteronanoparticles with Superior Electrochemical Performance for Supercapacitors

Transition-metal-based heteronanoparticles are attracting extensive attention in electrode material design for supercapacitors owing to their large surface-to-volume ratios and inherent synergies of individual components; however, they still suffer from limited interior capacity and cycling stability due to simple geometric configurations, low electrochemical activity of the surface, and poor structural integrity. Developing an elaborate architecture that endows a larger surface area, high conductivity, and mechanically robust structure is a pressing need to tackle the existing challenges of electrode materials. This work presents a supercapacitor electrode consisting of honeycomb-like biphasic Ni<sub>5</sub>P<sub>4</sub>–Ni<sub>2</sub>P (Ni<sub><i>x</i></sub>P<sub><i>y</i></sub>) nanosheets, which are interleaved by large quantities of nanoparticles. The optimized Ni<sub><i>x</i></sub>P<sub><i>y</i></sub> delivers an ultrahigh specific capacity of 1272 C g<sup>–1</sup> at a current density of 2 A g<sup>–1</sup>, high rate capability, and stability. An asymmetric supercapacitor employing as-synthesized Ni<sub><i>x</i></sub>P<sub><i>y</i></sub> as the positive electrode and activated carbon as the negative electrode exhibits significantly high power and energy densities (67.2 W h kg<sup>–1</sup> at 0.75 kW kg<sup>–1</sup>; 20.4 W h kg<sup>–1</sup> at 15 kW kg<sup>–1</sup>). These results demonstrate that the novel nanostructured Ni<sub><i>x</i></sub>P<sub><i>y</i></sub> can be potentially applied in high-performance supercapacitors.