Research On Design And Performance Of Aqueous Supercapacitors Under Ultra Low Temperature

The electrolyte is an important part of the supercapacitor.The aqueous electrolyte has the advantages of high conductivity,low cost and excellent security,it would freeze and stop working at a low temperature.The freezing point of the aqueous solution could be reduced significantly by adding formamide?FA?.The effect of temperature change on the FA-H₂O-chlorate/sulfate electrolytes conductivity was discussed.The low-temperature performance of the supercapacitor was investigated by using a chlorinated/sulfated electrolytes with the lowest liquid-solid transition temperature?FA-H₂O?as the electrolyte and carbon nanotubes,graphene aerogel as the electrode materials.The FA-H₂O system had the lowest freezing point-37.5? when the volumetric ratio of FA to water was 3:2.The freezing point temperatures of the LiCl,CaCl₂,NaCl,KCl,Li₂SO₄ and Na₂SO₄ in the volume ratio of FA-H₂O mixed solvent decreased,the 3M LiCl had freezing point of-43.3?.The ionic conductivities of the electrolyte solutions were measured from-25±0.5?to 40±0.5?,the ionic conductivity of electrolytes would increase with an increase in temperature.Further studies showed the concentration of solutions has influence on the ionic conductivity.The 1.5 M KCl/FA:H₂O?3:2,vol?had the highest conductivity in chloride electrolyte with same concentration.The working electrodes were prepared with acidified multiwalled carbon nanotubes and graphene aerogel?GA?,respectively.And the electrode was prepared by the chloride and sulfate electrolytes with the lowest liquid-solid transition temperature.The low-temperature performance was investigated.The voltage range of chloride electrolyte,Li₂SO₄,Na₂SO₄ is-0.3⁰.7 V,-0.3¹ V and-0.3⁰.8 V,respectively.The results showed that at-40?,in the chlorinated electrolytes,the specific capacitance of the supercapacitor based on carbon nanotubes and 1.5 M KCl/FA:H₂O?3:2,vol?could reach 63.2 F/g,and energy density was 31.6 Wh/kg.In the sulfated electrolytes,the specific capacitance of the supercapacitor based on graphene aerogel and 1 M Li₂SO₄/FA:H₂O?3:2,vol?,0.1 M Na₂SO₄/FA:H₂O?3:2,vol?could reach 79.8 F/g,45.6F/g and energy density was 67.45 Wh/kg,27.7 Wh/kg,respectively.Figure 25;Table 4;Reference 74...