Fabrication Of Cobalt-based Nanocomposites And Its Application For Lithium-ion Batteries And Supercapacitors

Since the lithium-ion battery has advantages of high energy density, high voltage, long discharge time, light weight, etc, it occupis a large market in portable electronics, electric vehicles, large power supply. However, the commercialized Lithium-ion battery is still sustaining poor circulation stability, the week ability of large current discharge, low power density, etc.. Supercapacitors, owning both high specific capacity and specific power as a kind of efficient energy storage device, are considered as the next generation of conventional energy storage device, also encountered the problem of low energy density in the actual application. To meet the growing demand for energy storage devices, the innovation of higher-performance lithium-ion battery and Supercapacitor is significant. The key to improve the capability of lithium-ion battery and supercapacitor is to explore electrode material with better performance. Currently, there are two strategies of designing the electrode material : 1) composite materials, integrating different materials to form a suitable composite material, can not only overcome the drawbacks of the individual components but also retain the advantages. Some synergistic effects offered by different materials may also enhance the performance. 2) nano materials with specific structural design, can greatly increase the surface area of the material, enhance the contacting area with the electrolyte, improve electrochemical active sites, shorten the diffusion distance of ions and proton, and thus enhance the performance of the electrode. Under the guidance of these two strategies, some work about cobalt-based materials with a good electrochemical active sites were launched as follow:1. Ni_xCo_1-x（OH）F hollow hexagons woven by multi-walled carbon nanotube（MWCNT） were synthesized by a simple hydrothermal method. The MWCNT in situ thread the hollow Ni_xCo_1-x（OH）F hexagons and form an interconnected three-dimensional network. Owing to the integration of MWCNT and the unique hollow structure of the Ni_xCo_1-x（OH）F hexagon, the composite as materials for lithium-ion battery presents excellent electrochemical properties including high reversible capacity and stable cycle performance.2. Ni_xCo_9-xS₈/MWCNT with two kind different morphologies was prepared by anion exchange using Na₂S as the sulfur source. Owing to good conductivity of MWCNT and sulfide derivatives, the composite displays great electrochemical performance as supercapacitors electrode material.3. One template-free strategy is successfully developed for the synthesis of uniform Co₃O₄ hollow spheres with complex interior structures. The method involves the solution synthesis of uniform metal fructose solid spheres and subsequent thermal annealing in air. The three-electrode electrochemical measurement shows that the capacitance value of this Co₃O₄ can reach 1111 F/g.