Study On Manganese Dioxide/activated Mesocarbon Microbead For Supercapacitor Electrode Materials

Forced by the pressure of the oil crisis and environmental protection, governments all over the world are seeking to develop new energy automotive industry. The high-energy, high power energy storage device has become one of the most critical technologies in this industry. Supercapacitor (electrochemical capacitor) is a promising energy storage device, with features of excellent charge and discharge performance, good pulsed power performance, long life, affordable and environmentally friendly, which is expected to play the major role in the new energy automotive industry and other industry as energy devices.Based on the advantages of current two categories of supercapacitor electrode material-- carbon and metal oxides, in this article, manganese dioxide (MnO2), one of the affordable, abundant resources, environmentally friendly and high theoretical specific capacity metal oxide, and activated mesocarbon microbead (AMCMB) with good conductivity and large specific surface area and good sphericity, were designed into a new type of nano-metal oxide/ spherical activated carbon (MnO2/AMCMB) composite materials. The preparation method, microstructure and electrochemical properties of composite materials were demonstrated, in order to obtain high performance supercapacitor electrode materials, and promote the development of high-energy, high-power energy storage technology.Firstly, for the first time, a high surface area activated mesocarbon microbead AMCMB with wide size distribution and good sphericity were successfully prepared, by selecting MCMB with different particle sizes as the mixed precursor, using KOH chemical activation. In addition, a comparative performance study was conducted in symmetrical supercapacitor for the AMCMB electrodes in 30% KOH water electrolyte and 1 mol/L LiPF6/(DMC+EC) organic electrolyte. The as-prepared AMCMB has good spherical degree and diameter between 5-40μm, the particle size distribution is relatively uniform, the specific surface is 3290.4 m2g-1, with a 5-20nm of the pore structure as well as a high mesopore content of 64.5%. The energy density of as-prepared AMCMB electrode in 1 mol/L LiPF6/(DMC+EC) organic electrolyte is up to 68.13 Wh/kg, which is 8 times as much as that in 30% KOH electrolyte. This is expected to lay the foundation for excellent performance of MnO2/AMCMB high-energy electrode materials.Secondly, three preparation methods with industrial prospects--room-temperature liquid phase redox method, liquid chemical precipitation method and low-temperature solid phase synthesis method, were applied to prepare three novel spherical MnO2/AMCMB composites in different morphologies: granular MnO2/AMCMB(GMAM) composite, flake-like MnO2/AMCMB(FMAM) and needle-like MnO2/AMCMB(NMAM) composite. The effects on capacitive performance of MnO2 morphologies were studied in 1 mol/L LiPF6/(DMC+EC) organic electrolyte in symmetrical supercapacitor. The as-prepared GMAM composite has MnO2 particle size of 100-200nm, FMAM composite has MnO2 particle size of 200×80×20nm, NMAM composite has MnO2 particle size of (2-3)μm×(20-30) nm, in which NMAM one-dimensional MnO2 has the smallest nano-scale and the highest nano-level degree. For the as-prepared MnO2/AMCMB composite electrode, the energy density of GMAM, FMAM, and NMAM are 98.2 Wh kg-1, 106.3 Wh kg-1 and 127.4 Wh kg-1, in which the NMAM composite electrode has more excellent power characteristics and higher coulomb efficiency. Supercapacitors prepared with these composite electrodes are of highly potential alternative to traditional secondary battery. Moreover, the three preparation methods used are simple and easy, so GMAM, FMAM, and NMAM composite electrode materials have great potential for industrialization.Thirdly, we successfully prepared a novel AMCMB-CNT compound without adding any CNT product by changing the activation conditions of AMCMB, and further prepared a novel MnO2/(AMCMB-CNT) composite. At the same time, the capacitive performance of the MnO2/(AMCMB-CNT) composite electrode was studied in symmetrical supercapacitor assembled studied in 1 mol/L LiPF6/(DMC + EC) organic electrolyte. The as-prepared MnO2/(AMCMB-CNT) composite is a dual-composite, that is the MnO2/AMCMB and MnO2/CNT double composites. The MnO2 on AMCMB has a wide particle size distribution between 40-160 nm with peak at 110nm. The MnO2 on CNT has a narrow particle size distribution, mostly lied in 40-50 nm that is smaller than the former one. The as-prepared MnO2/(AMCMB-CNT) dual-composite has energy density of 113.7 Wh kg-1, which demonstrated more excellent electrochemical performance compared to MnO2/AMCMB(GMAM).Fourthly, an interesting MnO2 nanowire-sphere with wide size distribution and good spherical morphology has been prepared by a hydrothermal method. A novel non-aqueous hybrid supercapacitor was fabricated from two spherical materials of spherical activated mesocarbon microbead (AMCMB) and MnO2 nanowire-sphere as the negative and positive electrodes, respectively, using 1 M Et4NBF4 in acetonitrile (AN) as electrolytes. The as-prepared MnO2 nanowire-sphere showed good spherical distribution of diameter 5~20μm and the size distribution is relatively uniform. The MnO2 nanowire-sphere is the filamentous sphere rather than solid sphere, made up of nanowires with diameter of about 80nm and the length between 3~5μm, the specific surface area of the MnO2 nanowire-sphere is up to 352 m2 g-1. The as-prepared AMCMB||MnO2 hybrid supercapacitor has an energy density up to 128 Wh kg-1, which is quite close to the energy density of lithium-ion battery. After 1200 cycles of charge-decharge, the capacity of the hybrid supercapacitor maintain a rate of >86%, and very excellent power performance.Overall results showed that, the combination of the good-nanostructured MnO2 and AMCMB with high spherical degree, the full use of advantages for spherical activated carbon and nano-metal oxides, and the advantage of the high voltage of organic electrolyte supercapacitor, contributed the objective of improving the voltage and energy density of superapacitors, while maintaining a good power characteristic. In short, this study has achieved the predetermined target and laid the theoretical and experimental foundation for the industrial application of MnO2/AMCMB electrode material.