Preparation And Electrochemical Properities Of SnO₂ Micro/nanostructures As Supercapacitor Electrode Materials

With the rapid development of global economy, the problem of environmental pollution, fossil fuel depletion is becoming more and more serious, renewable clean energy and its associated high energy conversion, and the development of storage technology is imminent. As a new type of green pollution-free energy storage devices, supercapacitors with high energy density and power density, and good cycling performance, have attracted the attention of many researchers, becoming the next generation of the most promising energy storage devices, and have broad application prospect in mobile information, electronic technology, electric vehicles, aerospace and defence technology and other fields. Supercapacitors can be roughly divided into two categories based on the mechanism of charge storage, namely the double-layer supercapacitor and constraint capacitance supercapacitor. So far, the research of constraint capacity supercapacitor electrode materials is mainly focused on the development of the commercial prospects of transition metal oxides and transition metal oxide electrode materials with high capacitance, reversibility and good cycle performance. Much attention has been paid to the SnO2 electrode materials due to its rich resources, low cost, good capacitance characteristics and friendly to environment. Although SnO2 materials is one of the candidate material of supercapacitor electrode materials, but the semiconductor characteristics of SnO2 materials produce the problem of poor conductivity. However, synergistic effect between nanocomposite assembly make the materials generate novel properties that the primitive materials do not have. Due to the synergistic effect can remedy the shortcomings of a single component, even produce excellent properties of the original component does not have, so composite materials used for supercapacitor electrode materials has become one of research hot spots. Therefore, this study selects the SnO2 composite materials with large capacitance and carbon fiber with good electrical conductivity as basic assembly units, taking use of synergies between the unit assembly components and used as a good supercapacitor electrode material. As a result, the synthesized SnO2 electrode materials have not only high capacitance, but also good electrical conductivity performance. The main content of the paper summarized as follows:(1) Ultrathin nanosheets assembled SnO2 microflowers were synthesized by solvothermal method using SnCl2·2H2O and C6H5Na3O7·2H2O as precursor, the influence of different reaction time and concentration of precursors on structure and size were discussed. Then the electrochemical properties were tested. In 1 mol L-1 Na2SO4 solution, the specific capacitance is 203.1 F g-1 at the discharge current of 1 A g-1, and the specific capacitance is 85.7 F g-1 at the discharge current of 5 A g-1. After continuous charging and discharging for 2000 cycles, the specific capacitance only reduced about 19%. The above results show that the SnO2 microflowers as supercapacitor electrode material can not only lower ion transport resistance, but also improve the stability of the supercapacitor.(2) SnO2 nanosheet array was synthesized on carbon fiber through a simple hydrothermal method, and directly used as electrode in the three supercapacitor electrode system, avoiding the use of carbon black and binder in the process of preparing electrodes. Electrochemical performance testing results demonstrated that the SnO2 electrode showed excellent electrochemical performance, the specific capacitance reach 391.3 mF cm-2 at the current density of 1 mA cm-2. After charging and discharging for 2000 cycles, the specific capacitance loss only about 9%.(3) Three kinds of SnO2@ MOx(MOx = Co3O4, NiO, MnO2) heterostructures were synthesized through the hydrothermal method and CBD(chemical bath) method by taking SnO2 nanosheet array as a skeleton. The as-prepared products retained the original SnO2 array structure. Experimental results show that the heterostructures have significantly higher capacitance than the SnO2 nanosheet array, and cycle performance of heterostructure is greatly increased. The excellent electrochemical performance of heterostructures is owing to the introducing of MOx, which can reduce the overall battery internal resistance and improve the electrical conductivity of heterogeneous electrodes. At the same time, the synergistic effect between different primitives making greater contributions to capacitance.