The Design Of Na₂sS（DMSO） Electrolyte Additives And The Effect Of Supercapacitor Performance

In recent years,supercapacitors have attracted extensive attention in the field of energy storage due to their high power density,fast charging and discharging speed,long cycle life and environmental friendliness.However,carbon based supercapacitors still have some shortcomings in some aspects,such as low energy density and electrolyte freezing at low temperature.Therefore,in order to improve the energy density and electrochemical performance of carbon based supercapacitors at low temperature,we introduce a simple and effective method of electrolyte additives to improve these problems.The results are as follows:1.Supercapacitors with high specific capacitance and high energy density have always been the goal pursued by scientific researchers,and heteroatom doping is an alternative method.In the work of this thesis,we designed an effective strategy.Firstly,the surface of activated carbon is modified with sulfur powder at 700°C to generate sulfur-containing groups on the surface and exhibit good electrochemical performance.Next,the redox additive Na₂S reacts with the sulfur-containing groups on the surface of the carbon material（at the positive electrode）and forms a chemical bond.As a result,when the current density is up to 15 A g^-1,the specific capacitance can still reach 643 F g^-1and the energy density can reach 12.6 Wh kg^-1.This improvement is attributed to the synergistic effect of the sulfur-containing groups on the surface of the carbon material with the S^2-in the redox additives,and the formation of covalent bonds.Therefore,this strategy（the synergistic effect of surface modification and redox additives）provides an effective means to improve the performance of carbon-based supercapacitors.2.The freezing of electrolyte and insufficient conductivity at low temperature are considered to be the main problems of supercapacitor energy storage at low temperature.In the current work,we have proposed a low-temperature aqueous electrolyte additive dimethyl sulfoxide（DMSO）.Take dimethyl sulfoxide with a mole fraction of 0.3 as an additive,among which 6 M–0.3 DMSO–KOH electrolyte(add a 0.3 mole fraction of dimethyl sulfoxide aqueous solution to KOH to prepare 6 mol L^-1DMSO–KOH electrolyte)can still work normally at-40 ^oC.Infrared and Raman spectroscopy research and analysis show that a stable hydrogen bond is formed between DMSO and water molecules,which is why the aqueous electrolyte can work stably under ultra-low temperature conditions.Electrochemical tests show that the capacitance retention rate of the material at room temperature（RT）,-20 ^oC,and-40 ^oC are 94.0%,92.0%,and 90.0%,respectively,after 10,000 charge-discharge cycles.The results show that the material exhibits good cycle stability in the DMSO–KOH electrolyte,especially the maintenance of cycle stability at low temperatures.At the same time,we also extended this design idea to the acidic（H₂SO₄）system and the neutral（NaNO₃）system to achieve satisfactory results.Therefore,the design idea of??this work provides a simple and effective strategy for the development of low-temperature aqueous electrolyte.