Research On Multifunctional Flexible Supercapacitors Based On PDA And Application Of Stress Sensors

With the development of flexible electronic devices,the demand for flexible supercapacitors（Flexible Supercapacitors,FSCs）is increasingly urgent.The stacked structure of traditional supercapacitors is easily disintegrated due to repeated deformation,resulting in unsatisfactory energy storage performance.To solve this problem,all-in-one supercapacitors have attracted attention in recent years.Electrode materials with high conductivity and good mechanical properties and gel polymer electrolytes are important components of integrated FSCs,so that the development of FSCs is no longer limited to the direction of energy storage,but also expands its application in the direction of flexible sensing.In this study,polypyrrole（Polypyrrole,PPy）was firstly doped with carbon nanoparticle-containing pen ink（ink）,which has strong adhesion and low cost,and made use of the adhesive properties of polydopamine（Polydopamine,PDA）Wettability,to obtain PPy-ink_X/PDA ternary composite electrode material.The effect of ink content on the energy storage performance of the composite electrode was studied by cyclic voltammetry,galvanostatic charge-discharge and AC impedance.The results showed that proper amount of ink could improve the energy storage performance of PPy-ink_X/PDA electrode material due to contained nano carbon particles.The specific capacitance of PPy-ink/PDA electrode material reached 530 F g^-1 at the current density of 1 A g^-1.By introducing PDA into polyvinyl alcohol（Polyvinyl Alcoho,PVA）and polyethylene glycol（Polyethylene Glycol,PEG）to form a chemically cross-linked network hydrogel PDA_X-PVA/PEG,the integrated FSCs formed with it have high Resilience and sensitivity.The effect of PDA content on the mechanical properties of PDA_X-PVA/PEG electrolyte was studied by using the stress-strain curve.The results show that PDA can regulate the mechanical strength of PVA/PEG hydrogel,and the PDA-PVA/PEG gel electrolyte has high elongation strain（about 160%）and tensile strength（about 55 k Pa）capabilities,and a compressive strength of 19.9 k Pa,and its modulus was the lowest.In order to reveal the effect of PDA on the all-in-one FSCs,PPy-ink/PDA electrode material and PDA_X-PVA/PEG gels were synthesized into all-in-one FSCs by in-situ polymerization.The results showed that the device based on PDA-PVA/PEG hydrogel electrolyte had the highest energy storage performance and excellent cycle stability（the specific capacitance still retained 81.2%of the initial value after 3000charge-discharge cycles）,compared with the device based on PVA/PEG hydrogel electrolyte,its specific capacitance capacity was increased by 48.7%.After multiple stretching and bending cycles,the energy storage performance of the capacitor was almost unaffected.In addition,using the capacitor as a stress sensor could sensitively monitor human movements,including wrist pulse,grip,wrist bending,swallowing,etc.