Study On Improving The Performance Of Supercapacitor Based On The Carbon Structure Regulation And Electrolyte Additives

In recent years, the rapid growth of the market demand in the area of intelligent electrical equipment has given rise to extensive requirements for high energy storage devices. Supercapacitor (also called electrochemical capacitor),as a new generation energy storage device, have a wide range of application including consumer electronics by virtue of the long cycle life, high energy density and power density. In view of the supercapacitor, it is fundamental that the nanoporous carbon materials with opportune microstructure and electrolytes. It is well known that the specialization of template carbonization process through the nano-space to regulate the micro-structure of carbon material at the nano-level, and thus there has been extensive interest in developing commercial attractive template carbon material for the supercapacitor electrode material.In present work,a simple but effective method has been developed to produce nanoporous carbon materials with hierarchical porosities, besides, some interesting strategies,incorporating redox-active mediators into electrolytes (acidic and alkaline electrolyte) or electrode materials, have been revealed to effectively improve the capacitances of supercapacitors, and the discussions of the synergistic effects between redox electrolytes and electrode materials for improving the supercapacitor performance.Besides, some influencing factors of the application have been discussed. The main contents of the dissertation are listed below:1. Nanoporous carbon materials with hierarchical porosities have been produced via a template carbonization method, in which potassium citrate (or gelatin) serves as carbon precursor and Mg(OH)2 powder as template. The P-3:1 sample derived from potassium citrate and Mg(OH)2 (with mass ratio of 3:1 at 800 ?) possesses high BET surface area of 1894.7 m2 g-1 and large total pore volume of 2.27 cm3 g-1. To further improve the electrochemical performance, the p-phenylenediamine (PPD, as redox-additive) of 5, 10, and 15 mmol L-1 are introduced into the 6 mol L-1 KOH as mixed electrolyte, forming the P-3:1-5/10/15 samples. Interestingly, the specific capacitances toward the P-3:1-5/10/15 samples have been greatly enhanced up to 579.2,712.8 and 852.3 F g-1 at 2 A g-1, respectively, which are greatly higher than that of 325 F g-1 for the case of pristine P-3:1 sample when measured at 6 mol L-1 KOH electrolyte. Furthermore, the P-3:1-15 sample delivers high capacitance retention of 70.5% even after 5000 charge/discharge cycles. What's more, the synthesis method has been readily extended for the case of gelatin and Mg(OH)2, and similar electrochemical trend to the cases of the P-3:1-5/10/15 samples also occurs.2. In present work, we demonstrate a simple but effective strategy for high-performance supercapacitor by adding the p-nitroaniline (PNA) into alkaline electrolyte of KOH. Furthermore, another effective additive of the dimethylglyoxime(DMG) has been incorporated into carbon materials for further improving the performances of supercapacitors with PNA+KOH electrolyte. As for the DMG+PNA+KOH system, a galvanostatic capacitance up to 386.1 F g-1 of the DMG-0.15-PNA-0.15 sample at 3 A g-1, which is nearly two times higher than that of the PNA-0.15 sample (183.6 F g-1) in the PNA+KOH system and nearly three-fold capacitance of the Carbon-blank (132.3 F g-1) in the KOH system at same current density. Furthermore, the specific capacitance still can reach up to 260.0 F g-1 even at 40 A g-1 with 67.4% capacitance retention ratio. Besides, the DMG-0.15-PNA-0.15 sample exhibits exceptional capacitance retention of 113% after 5000 charge/discharge cycles by virtue of the potential activated process, which clearly reveals the excellent cycling stability. These remarkable enhancements are ascribed to synergistic effects of the PNA and DMG.3. we have developed a simple but effective template carbonization method for producing hollow carbon materials with high content of nitrogen and oxygen from thiocarbanilide. Among all samples, the NPC-1 exhibits high specific surface area(736 m2 g-1) and large pore volume (5.93 cm3 g-1) with high content of heteroatoms(?11.25 at% nitrogen and -5.74 at% oxygen), which is conducive to the improvement of electrochemical performance. Specifically, the high specific capacitance and excellent cycling stability over 5000 cycles of the NPC-1-based electrode are achieved in 1 mol L-1 H2SO4 electrolyte. Additionally, pyrocatechol and rutin as novel redox additives that can easily cause redox-reactions have been incorporated into H2SO4 electrolyte to improve the capacitances. As a result, the NPC-1-R-0.15 and NPC-1-P-0.15 samples deliver high specific capacitances of 120.5 and 368.7 F g-1 at 2 A g-1, respectively,which are much higher than that of the NPC-1 sample (66.2 F g-1) without redox-additives at same current density. Furthermore,the large energy density of 18.9 and 11.9 Wh kg'1 of the NPC-1-based symmetric supercapacitors have been obtained in H2SO4+pyrocatechol and H2SO4+rutin electrolyte, respectively, and both samples also demonstrate excellent cyclic performance for 5000 cycles.