The Preparation Of Porous Carbon And Their Capacitance Properties In Different Electrolyte Systems

As new energy storage devices, supercapacitors show a higher power density and a higher energy density and can fill the gap between batteries and conventional capacitors, combining with long cycle life, safety, environmental protection and other advantages, supercapacitors are widely used in electric power system, the smart grid, military and aerospace in recent years. Typically, a supercapacitor consists of electrodes, electrolyte, and separator that electrically isolates the two electrodes. The electrodes and electrolyte, significantly affect the performances of a supercapacitor. Thus, tremendous research effort has been performed in the field of electrode materials and electrolyte, including the design of high performance electrode materials, the matching of electrode materials pore size with electrolyte ions, and the development of the electrolyte. Considering the important role of the pore size of the electrode material and electrolyte, herein, my research works have focused on designing and synthesizing a series of porous carbon using chitosan as precursor and investigating the correlation between the electrochemical properties and the pore size in gel and ionic liquid electrolytes. Details include the following two aspects:(1) Two different series of carbon materials with approximate specific surface area but different pore structure were used as electrode materials to investigate the influence of pore structure on the electrochemical performances in the gel and ionic liquid electrolyte. The results show that the capacitance value of micro-mesoporous carbon is higher than microporous carbon under the same current density in gel electrolyte and ionic liquid electrolyte, indicating that the mesopore is favorable to obtain high capacitance. The sample with pore size of 4 nm, has the highest specific capacitance value under the current density of 0.5 A g-1 in the ionic liquid electrolyte, which shows that the pore size of 4 nm is favorable for the formation of electric double layer in ionic liquid system, and the pore size which is bigger than 4 nm can improve the dynamical process of capacitor and show the most excellent rate performance.(2) When chitosan used as carbon and nitrogen source, and F127 as a soft template micelles, the chitosan was in attachment in the surface of F127 through hydrogen bonding interaction. CS is of positive charge due to its amino groups and graphite oxide is of negative charge, therefore rGO was combined with chitosan in the process of hydrothermal reaction, and nitrogen doped mesoporous carbon materials were obtained after the removal of the template. The samples with pore size of 4 nm are large enough for the ions to access a large percentage of the pores and small enough to allow for double-layer formation on the walls of the pore. At the same time, rGO as structure-directing agents benefits the connectivity of pore structure which can effectively shorten the transmission path of electrolyte ions and improve the conductivity of the material. The specific capacitance value of porous carbon is 200 F g-1 under the current density of 0.5 A g-1 in ionic liquid electrolyte systems, and the energy density is 110 Wh kg-1; in the gel electrolyte system, the specific capacitance value of porous carbon is 131 F g-1 under the current density of 0.2 Ag-1.