Controllable synthesis of NiCo2O4, NiCo2O4/graphene composite and their electrochemical application in supercapacitors

As traditional energy storage devices, supercapacitors exhibit the advantage of low cost, fast charge/discharge, long-term cycling stability and high powder density. The development of electrode materials is a major task for constructing high-performance supercapacitors. Among existing transition metal oxides, NiCo 2 O 4 has a high theoretical capacitance, which has been received much more attention. In view of the excellent electrochemical performance of NiCo 2 O 4 , herein, we highlight the research advance of NiCo 2 O 4 and NiCo 2 O 4 /graphene composites in supercapacitors. The controllable synthesis of NiCo 2 O 4 and the electrochemical performance are introduced firstly, including commonly used methods, such as, hydrothermal/ solvothermal method, coprecipitation, chemical bath deposition, electrochemical deposition, and template method. According to the dimension feature of graphene matrix, we classify NiCo 2 O 4 /graphene composite into two-dimensional (2D) and three-dimensional (3D) composite, and summarize the design principle, microstructure and their application performance in supercapacitors. Finally, we summarize the existing problems about NiCo 2 O 4 and NiCo 2 O 4 /graphene composite, and propose the solving strategies and future perspectives. The major purpose is to provide theoretical guidance for related researchers in supercapacitors. • Synthetic methods of NiCo 2 O 4 are classified into six types. • The design of 3D graphene frameworks is introduced in detail. • Research progress of 2D and 3D NiCo 2 O 4 /graphene composite is summarized. • The relationship between the microstructure and performance of NiCo 2 O 4 is compared.