Super Capacitive Performance Of Self-template Derived Porous Carbon In Ionic Liquids

Supercapacitors,as an emerging energy storage device,which has the advantage of superior rate capability,high power density and long cycling life.While not sacrificing the high-power density of supercapacitors and considering the cost and safety,supercapacitors assembled with ionic liquids can effectively increase the energy density of supercapacitors and become a good alternative to traditional aqueous and organic electrolytes.Therefore,the selection of electrode materials suitable for ionic liquid-based supercapacitors has become a major research topic nowadays.Porous carbon materials are widely preferred as electrode materials due to their chemical inertness,high specific surface area,low cost and diverse structures.Currently,the common methods of preparation include direct carbonization,hydrothermal method,template method and activation method.Among them,the template-assisted chemical activation method combines the advantages of chemical activation and templating methods,in which the chemical activation builds the microporous structure of carbon materials while the intervention of templates also helps to build the pore structure of carbon materials.The template assisted chemical activation method often results in porous carbon materials with both microporous and mesoporous structures.While the use of strong activators can cause certain corrosion problems to equipment and the environment,and the additional template makes the synthesis process complicated and costly.Therefore,it is particularly valuable to find a simple,low-cost and environmentally friendly strategy for the synthesis of carbon materials.In this paper,a self-templating and molten salt-assisted self-templating method was used to prepare porous carbon with high specific surface area and tunable pore size structure and to investigate its electrochemical properties in supercapacitors assembled with 1-ethyl-3-methylimidazolium tetrafluoroborate（EMIMBF₄）ionic liquid.Details of the work are as follows:（1）Three-dimensional honeycomb-shaped porous carbon（HCPC-800）with a specific surface area of 2478.7 m²g^-1was prepared using calcium gluconate as a precursor and potassium oxalate monohydrate as an activator,which could assist the graded activation of potassium oxalate.The supercapacitor assembled with HCPC-800 as the electrode material and EMIMBF₄as the electrolyte can reach an operating voltage of 3.5 V and a specific capacitance of 212.8 F g^-1at a current density of 1 A g^-1.The specific capacitance was212.8 F g^-1at a current density of 1 A g^-1and 131.7 F g^-1at a current density of 50 A g^-1,giving a capacity retention rate of 61.9%.Given the high operating voltage of the EMIMBF₄and the impressive specific capacitance of the HCPC-800,the supercapacitor can achieve an energy density of 90.5 Wh kg^-1at a power density of 0.875 k W kg^-1and64.9 Wh kg^-1when the power density is increased to 26.2 k W kg^-1,giving an energy density retention rate of 71.7%.After 10000 constant current charge/discharge cycles at a current density of 10 A g^-1,the capacity retention rate is 83.7%and the Coulomb efficiency is always close to 100%.（2）Calcium lignosulfonate was used as the precursor and potassium hydrogen tartrate as the activator,which could react to produce calcium hydrogen tartrate,and the addition of a sodium chloride template assists in its synthesis of porous carbon nanosheets with a two-dimensional honeycomb shape（Na Cl-STPC-8）.The supercapacitor assembled with Na Cl-STPC-8 as the electrode materials and 6 M KOH as the electrolyte had a specific capacitance of 312 F g^-1at a current density of 1 A g^-1,and when the current density was increased to 50 A g^-1,the specific capacitance was still 261 F g^-1with a capacity retention rate of 83.7%.Additionally,the supercapacitor assembled with Na Cl-STPC-8 as the electrode materials and EMIMBF₄as the electrolyte can operate at a voltage of 3.5 V,the specific capacitance was 237.7 F g^-1at a current density of 1 A g^-1and 140 F g^-1when the current density was increased to 30 A g^-1,with a capacity retention rate of 58.9%.Given the high operating voltage of EMIMBF₄and the considerable specific capacitance of Na Cl-STPC-8,the maximum discharge energy density of the supercapacitor reached 101.1Wh kg^-1at a power density of 0.875 k W kg^-1and 70.2 Wh kg^-1when the power density was increased to 17.5 k W kg^-1,with an energy density retention rate of 71.7%.The energy density retention rate was 71.7%.After 10000 constant current charge/discharge cycles at a current density of 10 A g^-1,the capacity retention rate is 80%and the coulomb efficiency was always close to 100%.