Phosphate-Modified NiCo2O4@NiCoS Heterointerface Boosting Electrochemical Performance for Supercapacitors

Abstract

Supercapacitors have attracted great interest in the field of energy storage devices owing to their high power density for quick charging and discharging. Nickel–cobalt-based materials are credited as promising cathode materials due to their rich valence and high redox reversibility. However, the poor conductivity and slow reaction kinetics of the nickel–cobalt-based electrode materials caused unsatisfactory rate capability of the devices. In this work, a phosphate-modified nickel–cobalt-based material with a core-branched structure was designed and fabricated by combining electrochemical and hydrothermal methods, in which nickel cobalt oxide (NCO) acted as the core and nickel cobalt sulfide (NCS) acted as the branches. The active materials were fully employed due to the 3D skeleton of the core-branched structure, facilitating ion transfer. Meanwhile, the phosphate-modified interface between NCO and NCS enhanced the electron transfer inside the material and changed the ratios of Co²⁺/Co³⁺ and Ni²⁺/Ni³⁺, leading to excellent capacity and rate performance. The elaborate design of the structure makes the phosphate-modified NCO@NCS (P-NCO@NCS) electrode exhibit a high specific capacity of 1050 C g^–1 at 2 A g^–1 and an excellent capacity retention of 86.4% when the current density is increased to 30 A g^–1. Our findings proposed an essential role of phosphate modification of the heterointerface, providing a strategy to design a structure for highly conductive electrodes.