Research Of Supercapacitor Of Aqueous Electrolytes

As a new kind of electric energy,supercapacitors?SCs?have been well known and popular due to their advntages such as fast secondary charge/discharge,long cycle life,high power density,low-cost and no-maintenance in the field of new energy sources.The elecrolytes of supercapacitor devices can be roughly divided into two categories;non-aqueous elecrolytes and aqueous elecrolytes.In commercial devices,non-aqueous elecrolytes were commonly acetonitrile or propylene carbonate based,with many studies currently focusing on development of ionic liquid systems.However,non-aqueous elecrolytes have some disadvantages of high viscosity and toxicity.Advantages of aqueous electrolytes included present several such as high conductivity,low viscosity and environment friendly.Despite their advantages,aqueous electrolytes were restricted in their in device by the decomposition of water?ca.1.23 V?and the low temperature performance was poor.This paper has mainly investigated the effects of different mass ratio of positive electrode and negative electrode and different kinds of high concentration of electrolyte on the energy density of actived carbon?AC?-based capacitors.In addition,different amounts of glucos?Gl?and ethylene glycol?Eg?have been proposed as the anti-freezing additives for high concentration electrolyte in supercapacitors,and we have also discussed the low temperature effect of new hybrid electrolytes.To obtain the following results:?1?In this paper,we have been assembled actived carbon?AC?-based aqueous supercapacitors consisiting of different positive/negative electrode matching ratio of 1.0:1.0,1.2:1.0,1.4:1.0,1.6:1.0,1.8:1.0 and 4 mol/L?NH4?2SO₄ aqueous solution and 5 mol/L NaCl O₄ aqueous solution as electrolytes.According to galvanostatic charge/ discharge,cycle life test and Ragone curves,we concluded that the mass ratio of 1.2:1.0 have the optimal capacity performance.After 100 charge-discharge cycles,AC-based supercapacitor in 4 mol/L?NH4?2SO₄ and 5 mol/LNaClO₄ aqueous solution have the discharge specific capacitance of 76.1 F/g and 81.9 F/g,the discharge capacity retention of 91.1%,102.3% at the voltage up to 1.6 V,1.8 V,respectively.The results also showed that the limitation of the capacitor voltage window in the charging process depends on the positive electrode potential in two kinds of aqueous solutions of three electrodes.?2?In this paper,we have been assembled AC?positive/negative electrode matching ratio of 1.2:1.0?-based aqueous supercapacitors using 7 mol/LNaCl O₄ aqueous solution as aqueous electrolytes,and obtained supercapacitor have a discharge voltage range of 0 2 V.The leakage current of AC-based aqueous supercapacitors was 0.19 mA after constant-voltage charging at 2 V for 3 h.Charge retention performance of SCs showed that specific capacitance retention after constant-current charging at 2 V for resting 5 h was up to 95% for resting 0 h.The results of galvanostatic charge/discharge showed that the discharge capacitance can reach 66.5 F/g,and the energy density can be as high as 9.3 Wh/kg,and the discharge capacitance retention was up 92.4% with the rate of 6 C during 10 000 charge-discharge cycles.Meanwhile,the discharge capacitance retention of aqueous SCs was 88.6% at the operating voltage of 2.2 V with the rate of 6 C during 5 000 charge-discharge cycles.?3?In this work,AC-based aqueous supercapacitors with 7 mol/LNaClO₄ aqueous solution as aqueous electrolytes can well work as low temperature as-30 ?,and the specific capacitance can reach 71.3 F/g,and the specific capacitance retention was up to 85.3% for 25 ?,and the highest withstanding voltage can be as high as 2.55 V.The mixed electrolytes adding glucose/ethylene glycol in 7 mol/LNaClO₄ aqueous solution can lower the freezing point of aqueous solution?<-50 ??,which can charge and discharge at ultra low temperature of-35 ?,and the highest withstanding voltage can be as high as 2.75 V.At 25 ?,the capacitance of aqueous system SCs can be increased by adding glucose in 7 mol/LNaCl O₄ aqueous solution.The specific capacitance of SCs with the mixed electrolytes adding glucose in 7 mol/L NaClO₄ aqueous solution was as high as 89.3 F/g and the energy density can reach 12.3 Wh/kg.At low temperature of-30 ?,the low temperature capacity retention rate of AC-based SCs in the mixed electrolytes of ethylene glycol can reach 82%.