Performance Improvement And Research Of Wide Voltage Aqueous Supercapacitors

Supercapacitors,as a new energy storage equipment,have been attracting attention.Although organic supercapacitors widely used at present have operating windows as high as2 V or more,they have many limitations in practical applications due to the shortcomings of organic electrolytes such as flammability and volatility.The aqueous supercapacitors are safe and cheap,and aqueous electrolytes have high ionic conductivity,so they have a wide range of applications.However,the thermodynamic decomposition potential of water is only1.23 V,which leads to a low operating voltage of aqueous supercapacitors,around 1.0 V.Therefore,how to increase the operating voltage of the aqueous supercapacitors and improve the capacitance performance is still a challenge.This thesis focuses on improving the operating voltage and capacitance performance of aqueous supercapacitors.Using Mg SO₄or Mn SO₄saturated solution as the electrolytes,the operating voltage has been successfully improved.The operating voltage of Mg SO₄and Mn SO₄electrolyte is 1.8 V and 1.9 V,respectively.The cyclic voltammetry curves and galvanostatic charge-discharge curves of the Mg SO₄and Mn SO₄electrolytes in the three-electrode systems were systematically tested and studied.The experiments confirmed that the Mg SO₄and Mn SO₄electrolytes can operate safely at 1.8 V and 1.9 V,respectively.The capacitance performance of Mg SO₄electrolyte is better,but the specific capacitance of both is smaller than H₂SO₄electrolytel.On the basis of high operating voltage,adding Fe²⁺and Cr³⁺to the Mg SO₄and Mn SO₄electrolytes has successfully improved the capacitance performance.The experiment completely tested the cyclic voltammetry curve and galvanostatic charge-discharge curve of the three-electrode systems and the symmetric supercapacitor devices,and systematically studied the influence of Cr³⁺and Fe²⁺on the capacitancer performance.The experiments confirmed that the combined effect of Cr³⁺and Fe²⁺can increase the specific capacitance,but the addition of Cr³⁺will lead to a decrease in the rate performance.Adding Fe²⁺with appropriate concentration can not only provide pseudocapacitance to increase the specific capacitance,but also does not affect the rate performance.In addition,it was confirmed that the optimal concentration of Fe²⁺is 0.05 M.The symmetrical supercapacitors prepared with Mg SO₄electrolyte added with 0.05 M Fe²⁺have a specific capacitance of 157 F/g（current density of 0.5 A/g）and an energy density of 17.7 Wh/kg in the voltage range of 0-1.8 V.After 50 cycles,the specific capacitance decreased only slightly in the first 10 cycles,and then remained almost unchanged..