Bowl-shaped NiCo2O4 nanosheet clusters as electrode materials for high-performance asymmetric supercapacitors

Abstract

The development of transition metal oxidebased electrode materials with proper controlled structures is highly desirable for high-performance supercapacitors. However, it remains a major challenge. Here, we present the first synthesis of bowl-like NiCo2O4 nanosheet clusters through a simple soft template guided hydrothermal strategy. The resulting bowl-like clusters consist of numerous NiCo2O4 nanosheets with an average thickness of 19 nm and possess a mean diameter of 1 μm along with a specific surface area of 40 m2 g−1. Remarkably, serving as an electrode material in a three-electrode system, the bowl-like NiCo2O4 nanosheet clusters exhibit a high specific capacity of 1068 F g−1 at a current density of 1 A g−1 and excellent cycling stability with 90% capacitance retention after 5000 charge-discharge cycles. Meanwhile, an asymmetric supercapacitor (ASC) assembled with the NiCo2O4 clusters and activated carbon (AC) as the two electrodes exhibits a high specific capacitance of 129 F g−1 at 1 A g−1, along with a high energy density of 33 W h kg−1 at a power density of 0.66 kW kg−1. Such performance is superior to those of many commercial supercapacitors. This study opens a new avenue for the construction of ordered complex particles with controlled architectures for energy storage and conversion applications.