Research On Self-healing Hydrogel Electrolyte And Its Application In Supercapacitors

Advances in science and technology have accelerated the rapid development of portable/wearable electronic equipment,and at the same time put forward more stringent requirements for its energy storage devices.In practical applications,various inevitable accidents will cause great damage to electronic equipment and its energy storage devices.Self-healing supercapacitors,the combination of self-healing hydrogel electrolytes and supercapacitors,with the ability to automatically heal damage,will become one of the important development directions of energy storage devices for portable/wearable electronic devices in the future.So,this paper is devoted to develop a simple and novel method to prepare self repairing hydrogel electrolyte and apply it to supercapacitors,so as to prepare self repairing supercapacitors.We modified the traditional supercapacitor solid electrolyte PVA and used agarose and borax to enhance the material properties to prepare a tough self-healing hydrogel electrolyte PVA_10wt%/AG/Borax-NaCl _{0.1 M}.Through characterization analysis,the self repairing function of the hydrogel electrolyte is provided by the PVA chemical crosslinking network with borate ester bond as the cross-linking core.The electrolyte shows a fracture stress of 38.2 kPa,an ionic conductivity of 36.7 mS cm^-1 and a self-healing efficiency of 81.6%based on fracture stress.The supercapacitor assembled with the PVA modified self-healing hydrogel electrolyte,has a specific capacitance of 46.9 F g^-1 at the current density of 1 A g^-1,and can reach a maximum of23.4 Wh kg^-1.And the specific capacitance can be maintained at 71.6%after 10,000 cycles at a current density of 1 A g^-1.What’s more,the supercapacitor shows a specific capacitance of 46.8F g^-1 at a bend of 90°;and the specific capacitance maintained of 96.6%after broken/healing process.Inspired by the high viscosity and high water absorption of polyacrylic resin,we copolymerized acrylic acid and ethylene glycol to prepare a PAA-g-EG hydrogel with self-healing function.Its self-healing function Mainly rely on the hydrogen bond,molecular chain flow and ester bond break-form.The swelling ratio of this hydrogel is up to 119.7%.PAA-g-EG_50%/KOH hydrogel electrolyte is prepared by using KOH solution as a conductive agent,shows a fracture stress of 253.2 kPa,an ionic conductivity of 16.7 mS cm^-1 and a self-healing efficiency of 89.1%based on fracture stress.After assembling to supercapacitor,the supercapacitor exhibits a high specific capacitance 67.1 F g^-1 at a current density of 1 A g^-1;after 40 times of damage-heal,the specific capacitance energy maintains 68.2%;its energy density can reach up to 21.3 Wh kg^-1;and it can still reach 12.4 Wh kg^-1 after 40 damage-heal cycles.Performing 10,000 cycles at a current density of 4 A g^-1,the supercapacitor can maintain an initial specific capacitance value of 65.7%.By improving the PAA-g-EG_50%/KOH hydrogel electrolyte,we copolymerized acrylic acid with humic acid to prepare PAA-g-HA_0.25%/KOH hydrogel electrolyte.The electrolyte exhibits a fracture stress of 3.2 MPa,an ionic conductivity of 71.7 mS cm^-1 and a self-healing efficiency of 96.9%based on fracture stress.By analyzing its composition,we speculate that the self-healing function of the hydrogel mainly depends on the combined actions of hydrogen bonding,molecular chain flow,and ester bond breaking-forming.The electrolyte and reduced graphene oxide are assembled into a supercapacitor.The supercapacitor exhibits a specific capacitance of 62.2 F g^-1 at a current density of 0.5 A g^-1;after bending 50 times,the specific capacitance is 60.5 F g^-1,after the damage-heal,the specific capacitance of 90.8%can be maintained;in addition,the supercapacitor exhibits an energy density of 16.9 Wh kg^-1.