| Supercapacitor is a new type of energy storage device.Its principle of energy storage is based on the absorption/desorption of anions and cations in the double layer or the rapid oxidation-reduction reaction on the near surface of the electrode material or insertion into the body phase to achieve energy storage.It has decisive advantages in terms of cycle stability,power density,and rapid charge and discharge.However,the ultra-low energy density of ultracapacitors has led to severe limitations on their large-scale applications.This low energy density completely fails to meet the requirements for high-energy-density energy storage devices in smart grids,rail transit,and consumer electronics in the near future.Therefore,increasing the energy density of supercapacitors and realize the coexistence of high power density and high energy density has become a research focus of supercapacitors.In this dissertation,starting from the preparation and energy storage mechanism of porous carbon,the effects of morphology,pore structure,and specific surface area on the capacitive behavior of porous carbon were studied.And the use of aqueous and non-aqueous electrolyte prepared a high electrochemical performance symmetrical supercapacitors.By further optimizing the positive and negative mass ratios and the positive and negative charge densities,a supercapacitor with high energy density and stable cycling can be designed.The specific research content is as follows:(?)Starch as biomass is used as a precursor to prepare high performance porous carbon materials with different activation temperatures and different activation ratios.From the specific surface area test and analysis,it was concluded that too low or too high activation temperature will cause the specific surface area of the electrode material itself to decrease.SEM and TEM analysis found that too few activators cause insufficient etching of the carbon material.Too high activator will cause a phenomenon with excessive etching.This insufficient etching and excessive etching will affect the electrochemical properties of the electrode material.Therefore,it was finally determined that the activated carbon materials had the highest specific surface area(2259.54 m2 g-1)when the activation ratio was 2 and the activation temperature was 800 ?.From the pore size distribution analysis,the prepared porous carbon material has micropores,mesoporous and macroporous hierarchical porous structures,and SEM and TEM characterization results also prove that there are three-dimensional interconnected hierarchical porous structures.The three-dimensionally interconnected hierarchical porous structure reduces the tortuosity of the internal pores of the electrode material,facilitates the rapid transfer of ions and the charge transfer in the electrolyte,improves the contact area between the electrolyte and the electrode material,and increases the ion-absorbing and desorbing active sites.Thereby improving the electrochemical performance of the electrode material.Subsequently,the electrochemical performance of the material was tested in a three-electrode system.The material had a high specific capacitance of 385.7 F g-1 at a current density of 1 A g-1.Subsequently,2 M KOH and ionic liquid EmimBF4 were used as electrolytes to assemble water-based and non-aqueous supercapacitors,respectively,both exhibiting excellent electrochemical performance.In particular,ionic liquid superconducting symmetric supercapacitors show an ultra-high energy density(133.94 Wh kg-1),and with a high operating potential window of 4V.It also shows an excellent cycle stability(5,000 cycles)at a high current density of 10 A g-1.As well as it possesses a capacitance retention rate of 83.3%.(?)Adopting polyaniline as a carbon source,carbonized and activated by different activators to prepare high specific surface area,rod-like porous carbon materials.The specific surface area test showed that at the activation ratio of 6,the materials exhibited the highest specific surface area(2971.64 m2 g-1).Subsequently,SEM and TEM characterization methods confirmed that the prepared porous material had a rod-like structure.The decomposition voltage of the EmimBF4 electrolyte was then determined by cyclic voltammetry to determine the potential window(-1.8-2.2 V)of the electrode material.Through the galvanostatic charge and discharge test,the capacity of the working electrode under the respective operating potential window was obtained.The cycling stability was significantly improved at a current density of 3 A g-1 at 4 V operating potential window,when the supercapacitor was assembled by mass ratio of the positive and negative electrode was 1.2.The energy density of supercapacitor reached 112.22 Wh kg-1(1 A g-1).In order to further increase the energy density of the supercapacitor,pre-charging at one electrode was used to assemble supercapacitors with equal masses of positive and negative electrodes.The cycling stability was significantly improved at a current density of 3 A g-1 at a 4 V operating potential window,as well as the energy density is further improved(1 A g-1,132.56 Wh kg-1).(?)The resole was successfully prepared by phenol,formaldehyde,and sodium hydroxide.A hydrothermal reaction product of carbonized resole phenolic resin and triblock copolymer F127 was subsequently used to obtain phenolic carbon spheres having a diameter of approximately 140 nm.Then,the effect of different activation on the specific surface area and pore size distribution of porous carbon materials was investigated by BET surface area analyzer,XRD,SEM,and TEM.Finally,it was concluded that the porous carbon material with the highest specific surface area(2869.52 2 m2 g-1)was obtained at an activation ratio of 7.The electrochemical performance of PCS-7 was tested and it has a high specific capacity of 355.7 F g-1 at a current density of 1 A g-1.The cyclic voltammogram at different scan speeds remains approximately rectangular,and the transfer resistance of the electrode material is maintained.With small diffusion resistance,it shows excellent electrochemical performance. |
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