Preparation And Study The Performance Of Supercapacitor Materials

Bridging the properties of batteries and conventional capacitors, supercapacitors (SCs) are an emerging technology that fills a crucial gap in today’s rapidly evolving energy storage needs. With desirable properties of high power density, fast charge-discharge rate, and long life cycle, SCs can be used in a wide range of applications such as memory back-up systems, hybrid vehicles, portable electronics, etc. However, most of the commercial supercapacitors using porous carbon-based electrodes are not capable of delivering high energy densities (being less than10Wh kg-1), which significantly restricts their widespread application. Therefore, the energy density of the SCs should be substantially increased without sacrificing the merits of power density and cycle life for future applications. According to the equation E=(CV)2/2, the energy density of a SC can be improved by increasing the specific capacitance (C) of the electrode materials and/or the cell voltage (V). The present work focuses on increase the energy density by improving the capacitance of electrode materials and the cell voltage.The main results and conclusion can be summarized as following:(1) Due to the Young’s modulus and tensile strength of bacterial cellulose (BC) are estimated to138GPa and2GPa, We fabricated the flexible paper electrodes by using BC, multiwalled carbon nanotubes and polyaniline, the paper electrodes exhibits appreciable specific capacitance (656F g-1at a discharge current density of1A g-1) and remarkable cycling stability with capacitance degradation less than0.5%after1000charge-discharge cycles.(2) Due to BC is consisted of continuous nanofiber which is about10nm thickness and50nm width, we in situ polymerize the polypyrrole on the surface of BC nanofiber to get the BC-PPy nanofiber, and then fabricated the freestanding BC-PPy nanofibers/MWCNTs hybrid electrodes. The electrodes are with high mass loading in the range of7-12mg cm-2. The highest capacitance of2.43Fcm-2was obtained at the mass loading of11.23mg cm-2. The devices are able to offer large capacitance (590mF cm-2) and excellent cycling stability (94.5%retention after5000cycles).(3) Nitrogen-doped hollow carbon nanospheres were prepared by using silica nanospheres as hard temple, resorcinol/formaldehyde as carbon source and ethylenediamine as both a base catalyst and nitrogen presence, followed by carbonization in nitrogen, template elimination, and activation with KOH. The activated nitrogen-doped hollow carbon nanosphere can achieve a maximum specific capacitance of285F g-1. The maximum energy density based on the symmetric devices is up to7.7Wh/kg, and the internal tandem device with the same material can be achieved to12.1Wh kg-1.(4) An asymmetric supercapacitor (ASC) with high energy and power densities has been assembled using honeycomb porous MnO2/N doped carbon nanotubes (MnO2-PT) as positive electrode and chemically activated of N doped carbon nanotubes (a-CPT) as negative electrode in a neutral aqueous electrolyte. The ASC exhibits a high energy density of37.2Wh kg-1, and wonderful cycling stability with95.2%specific capacitance retention after3000cycles.