Preparation Of Hydrogel Electrolyte And Its Application In Flexible Supercapacitors

Flexible supercapacitors are considered as promising flexible power sources in wearable electronic devices due to their high power density and long cycle life.In daily applications,wearable devices will inevitably cause the problems of bend,stretch,compress,change in ambient temperature and even short circuit.Hence,it is required to develop flexible energy storage devices to meet the requirements of various wearable electronic devices.In this thesis,the hydrogel electrolyte is employed as research objects,the hydrogel electrolyte is prepared by using low-cost raw materials and simple preparation method,then make it applied for flexible supercapacitors.The PVA-PA_Xhydrogel is synthesized with high transparency and high toughness by a one-step freeze-thaw method.The effects of different raw material ratios and different agents on the ionic conductivity and mechanical properties of the hydrogel electrolyte are investigated.The results show that the PVA-PA_21%hydrogel has large fracture stress（805 k Pa）.The PVA-PA_21%-2 M H₂SO₄ hydrogel has an ultra-high ionic conductivity of 62.75 m S cm^-1.Flexible supercapacitors fabricated with PVA-PA_21%-2 M H₂SO₄ hydrogel still have high specific capacitance at 1 A g-1 after bending 90°and bending 30 times(64.8 F g^-1 and 67.3 F g^-1,respectively).Moreover,the energy densities are 13.5 Wh kg^-1 and 14.0 Wh kg^-1 at power density of 300 W kg^-1.After 10,000 constant current charge and discharge cycles at a current density of 4 A g^-1,the capacity retention is 72.52%.PVA_X-CNF_Z organic-hydrogels are prepared with low temperature resistance by one-step solvent-gel method.DMSO/H₂O binary solvent is used to reduce the freezing point of the gels.The effect of different contents of PVA content,CNF content and different agents on ionic conductivity and mechanical properties are investigated.The results show that the PVA_15%-CNF_2%organic-hydrogel has a fracture stress of 191.1 k Pa and a compressive stress of 2951.1k Pa under 80%compressive strain.After introducing the agent of 4 mol L^-1H₂SO₄,it has a high ionic conductivity of 46.5 m S cm^-1.Flexible supercapacitors based on the assembly of PVA_15%-CNF_2%-4 M H₂SO₄ organic-hydrogel have a specific capacity of 54.3 F g^-1 at a current density of 1 A g^-1.When keeping at low temperature（-20°C）and returning to room temperature,the specific capacities still maintain 47.9 F g^-1 and 53.9 F g^-1.After 10,000 cycles at current density of 4 A g^-1,the capacity retention is 68.27%,which provides an idea for the preparation of low-temperature flexible energy storage devices.Self-healing PAA-g-GL_X-Y/KOH hydrogels are prepared by one-pot method.The effects of different raw material ratios and different KOH absorption on the ionic conductivity,mechanical properties and the self-healing mechanism are explored.The results show that the PAA-g-GL_45%-0.2/KOH hydrogel has an ionic conductivity of 46.2 m S cm^-1 and a fracture stress of 264.6 k Pa.The self-healing function mainly relies on the synergy of hydrogen bonds and dynamic ester bonds.Self-healing supercapacitor assembled with PAA-g-GL_45%-0.2/KOH hydrogel still retain 57.6 F g^-1 and 54.6 F g^-1 after destruction-self-healing 20 times.Moreover,when the power density is 350 W kg^-1,the energy density can still reach 15.9 Wh kg^-1.After10,000 cycles at a current density of 4 A g^-1,the capacity retention is 70.71%,presenting guiding significance for self-healing energy storage devices.