Research Of Water-in-Salt And Hybrid Electrolyte For Supercapacitors

Supercapacitor?SC?is a novel energy storage device based on electric double layer adsorption or surface redox reaction or bulk phase intercalation reaction,and its performance is between physical capacitor and secondary battery.SCs are widely used in some related fields,due to its high power density,fast discharge performance and long cycle life.The disadvantages of low energy density of SCs are gradually exposed with the high energy density requirements of energy storage devices in modern.Therefore,the way is the focus on the current and future research at that how to improve the energy density of SCs."Water-in-Salt"?WIS?electrolyte is a new type of electrolyte widely used in aqueous high-voltage lithium-ion batteries with non-flammability and wide electrochemical stable voltage window?ESW?.Energy storage devices using such electrolytes provide better safety and higher operating voltage.The wide ESW of electrolyte not only brings high operating voltage,but also enables more high-capacitance electrode materials for complete electrochemical energy storage,which can increase the high energy density of energy storage devices using such electrolytes.The specific research contents and main conclusions are as follows:?1?A polyaniline carbon nanorod having a high specific surface area and a reasonable pore size distribution is obtained by a simple preparation process using polyaniline as a raw material It was assembled as an electrode material with WIS electrolyte to assemble a aqueous symmetric SC.The SC exhibited an operating voltage of 2.2 V,a specific capacity of 44 F g^-1,excellent rate performance and long cycle life.In addition,the SC showed an energy density of 29.6 Wh kg^-11 and a power density of 1.1 kW kg^-1,which is at a higher level than other reported aqueous symmetric SCs.This study provides a strategy for studying high energy density aqueous SCs.?2?Based on the organic solvent/WIS hybrid electrolyte,the effects of the type of organic solvent and the ternary ratio of the hybrid electrolyte on the physicochemical properties of the hybrid electrolyte were investigated.Four different organic solvents with different structures and properties were added as additives to the 21 m WIS electrolyte.This process caused a certain degree of change in the physicochemical properties of the electrolyte.According to the above research results,the addition of acetonitrile is the most effective way to improve the high viscosity and low ionic conductivity of the 21 m WIS electrolyte.On this basis,the physicochemical properties of LiTFSI/H₂O/acetonitrile ternary hybrid electrolytes with different ratios were further studied,and the ternary phase diagram was drawn.Using the ternary phase diagram and the ESWs of the partially hybrid electrolytes,the ternary mixed electrolyte which is most suitable for the SC was optimized.A symmetric SC with high voltage,excellent rate performance and long cycle life was successfully constructed with the optimal hybrid electrolyte and commercial activated carbon.The SC achieved high energy density by the improvement of the electrolyte.Therefore,this research is not only helpful for the study of hybrid electrolytes,but also for the development of safe symmetrical SCs with high energy density.