Carbon-based transition metal compounds for high-performance electrochemical energy storage devices

Abstract

With increasing attention to the storage of renewable energy sources, portable electric devices and environmentally friendly hybrid electric vehicles, representative Zn ion batteries and supercapacitors have been widely explored in recent years because of their high energy density, fast recharge capability and long cycle life. Transition metal compounds, especially Ni, Cobased oxides and hydroxides, with high theoretical specific capacity and environmental friendliness, have been extensively investigated. However, the issues of much lower energy storage capacity than theoretical value and poor electrical conductivity remain to be solved. This thesis is mainly focused on three types of novel transition metal compounds, their electrochemical performance and their applications for the development of aqueous alkaline Zn-Ni batteries and supercapacitors. In addressing the poor electrical conductivity of NiO, an interconnected conductive network of C/Ni was synthesized via a template-assisted hydrothermal method and heat treatment. The network includes intertwined carbon nanotubes wrapped in hollow carbon and evenly distributed Ni particles. Afterward, a facile electrochemical deposition was applied to achieve heterogeneous Ni/NiO nanostructure on the surface. Compared with conventional methods to integrate electrochemically active material with conductive parts via subsequent high temperature treatments, the bottom-up method developed in this thesis effectively prevents the morphology of the bottom conductive network from destruction. By exploring an appropriate deposition time, the optimized as-synthesized HC@Ni/NiO exhibits an excellent rate performance of 73% capacity retention as the current density increases from 0.5 to 20 A g-1.

Afterward, its assembled aqueous alkaline Zn-Ni battery with Zn foil anode provides useful guidance in developing practical Zn-Ni batteries in a wide range of current densities and rapid charge-discharge scenarios.