Structure Design and Performance Study of PVA Based Self-healing Supercapacitor
Author:Wang Zhi Kui
Supervisor:pan qin min
Electrochemical supercapacitor(ESC)has been widely applied to many kinds of electronic and electric devices for its high power density and long cycling life.With the fast development of portable and wearable electronic devices,the ESC possessing outstanding reliability in case of mechanical damage is required.Inspired by the self-repairing ability of living organisms,it is hopeful to solve the problems of safety and durability by designing self-healing ESC.Self-healing will greatly improve the reliability of ESC in case of physical damage.However,the challenge remains in preparing such a smart device capable of repairing its electrodes and the interfaces between electrodes and electrolyte.In this dissertation,the self-healing electrolyte,electrodes and electrode/electrolyte interfaces were obtained by molecular design and microstructure control using polyvinyl alcohol(PVA)as raw material.On this basis,the anti-impact performance of the ESC was improved with the self-healing method.To solve the poor salt tolerance of the PVA self-healing hydrogel electrolyte,PAA was grafted on PVA by free radical reaction.Self-healing PVA-g-PAA hydrogel electrolyte was prepared using borax as cross-linking reagent.The grafted PAA increased the polarity of the PVA chains and improved its salt tolerance performance.The concentration of KCl in PVA-g-PAA hydrogel electrolyte reached 1.0 mol L-1 and the ionic conductivity was as high as 41.6 m S cm-1.The self-healing PVA-g-PAA hydrogel electrolyte enabled the supercapacitor device to be healable.After 15 cutting/healing cycles,the capacitance retention was above 95%.In addition,the self-healing performance made it easy to tailor the capacitor into complicated patterns without significant capacitance decay.(2,3 epoxypropyl)trimethyl-ammonium chloride(TMAC)was grafted onto PVA through a ring-opening reaction to improve the solubility of the resulting copolymer.By cross-linking the PVA-g-TMAC with borax,not only self-healing electrolyte but also self-healing electrodes were prepared.The healing efficiency of PVA-g-TMAC/KCl hydrogel electrolyte reach 97% within 1 min under appropriate cross-linking degree.The healing efficiency of the self-healing electrode was 98.5% within 3 min by elaborately controlling the mass ratios of AB and AC to PVA-g-TMAC.Moreover,the self-healing interfaces between electrodes and electrolyte were achieved and the anti-bending performance of the ESC was improved.The integrated supercapacitor displayed a capacitance retention of 84.4% after bending for 1000 cycles.PVA grafted with monosuccinate groups(PVA-g-SA)was synthesized by reaction of PVA with succinic anhydride.Tough self-healing hydrogel electrolyte was prepared by cross-linking the mixed sol of PVA-g-SA and graphene oxide with borax and calcium chloride as cross-linking reagents.Similarly tough self-healing electrode was prepared by incorporating suitable contents of AB and AC into cross-linked PVA-g-SA network with borax as cross-linking reagent.The anti impact performance of the ESC composed of the self-healing electrolyte and electrodes was improved.The capacitance retention of PVA-g-SA based self-healing ESC was 88.1% after 9 low impacts(1.83 k J m-2).After a destructive impact(5.49 k J m-2),the mass specific capacitance retention of the ESC restored to 89% after self-healing process.In summary,the anti-impact performance of the ESC was achieved not only by increasing mechanical strength but also by self-healing.