Preparation And Performance Of C@GB/PVA-PEI Self-healing Supercapacitor

In recent years,supercapacitors have become an indispensable part of the development of flexible energy storage devices with the advantages of fast charge and discharge speed,long cycle life and high power density.However,the supercapacitors will inevitably suffer from mechanical damage,resulting in the failure of the whole device in the actual using process.Therefore,supercapacitors with self-healing functions have been developed recently.Here,we report a selfhealing supercapacitor using polyvinyl alcohol-polyethylenimine?PVA-PEI?hydrogel as the electrolyte and the carbon-coated glass beads as electrodes,and the supercapacitor is expected to be applied to intelligent electronic products.In this paper,PVA-PEI self-healing hydrogel electrolyte was prepared by hydrogen bonds between the PVA and PEI molecular chains.Hydrogen bonds gave this PVA-PEI hydrogel excellent self-healing ability and remolding ability.Firstly,the effects of the molar ratio of imino group?-NH-?to hydroxyl group?-OH?on the gel fraction,mechanical properties,electrical conductivity and self-healing properties of PVA-PEI hydrogel were investigated.When-NH-:-OH =1.0 : 1.0,the PVA-PEI hydrogel had a fracture stress of 29.02 k Pa,a conductivity of 3.44 m S cm^-1 and a self-healing efficiency of 97.69 %,which meant that the hydrogel had better mechanical properties,electrical conductivity and self-healing property.Therefore,it was found that the optimum ratio of preparing PVA-PEI hydrogel electrolyte was-NH-:-OH =1.0 : 1.0,and this paper further explored the effect of self-healing times and remolding times on the mechanical properties and electrochemical properties of the hydrogel.The results showed that after 4 cutting/healing cycles,the PVA-PEI hydrogel can still achieve 89.56 % mechanical recovery and 91.28 % electroconductibility recovery,and the hydrogel can be remolded at least 5 times without losing any performance.Using glass beads as the substrate of the electrodes,the carbon-coated glass beads?C@GB3-800?with the conductivity of 1.05 S m^-1 were obtained after treatment with Na OH solution for 6 h,polydopamine?PDA?loading 3 times and carbonization at 800 ?.A supercapacitor was assembled by using C@GB3-800 as the electrodes and PVA-PEI hydrogel?-NH-:-OH=1.0 : 1.0?as the gel electrolyte.The capacitor had a mass specific capacitance of 10.52 F g^-1 at the scanning rate of 10 m V s^-1,and had highly symmetrical near rectangular CV curves at the scanning rates of 10 m V s^-1,20 m V s^-1,50 m V s^-1 and 100 m V s^-1,and this device had symmetrical triangle GCD curves at the current density of 0.0005 A g^-1,0.001 A g^-1,0.002 A g^-1 and 0.005 A g^-1,which both indicated that the supercapacitor had excellent electric double-layer capacitance characteristics and better rate capability.In addition,the supercapacitor had excellent self-healing properties.After 4 cutting/healing cycles at room temperature,the device still had a mass specific capacitance of 9.80 F g^-1,and its self-healing efficiency reached 93.15 %.The device can also be recycled after heating at 80 ?,and the mechanical property and electrical conductivity of the C@GB3-800 electrodes and the PVA-PEI electrolyte after recycling were basically unchanged.