Preparation Of Chitosan-based Gel Electrolyte And Its Application In Supercapacitor

With the rapid development of flexible electronic devices,people have put forward higher requirements for the performances of their energy storage devices.Supercapacitors have the advantages of high rate performance and long cycle life,while the inherent drawbacks of traditional electrolytes make it difficult to meet the requirements of flexible devices.Gel polymer electrolyte carries the liquid electrolyte in the 3D network structure of gel polymer,which overcomes the inherent shortcomings of traditional liquid electrolyte（easy leakage）and solid electrolyte（low ionic conductivity）.However,most matrix materials of gel polymer electrolytes come from non-renewable and difficult to degrade petroleum-based polymer materials,which is not conducive to sustainable development.Therefore,based on renewable and biodegradable natural polymer chitosan,chitosan-based gel polymer electrolytes with wide operating temperature range,high ionic conductivity and strong mechanical properties were prepared in this paper.Its gel mechanism,rheological properties,electrochemical properties,mechanical properties and its application in flexible supercapacitors were studied in depth.The systematic research content is as follows:（1）Based on the homogeneous dissolution of chitosan in[EMIM][OAc]/GVL organic electrolyte solution system,chitosan/nano-Si O₂ nanocomposite organic ion gel electrolytes were prepared via the synergistic effects of chitosan/[EMIM][OAc]/GVL moisture absorption induced gel formation and nano-Si O₂ hydrogen bond in-situ physical crosslinking.[EMIM][OAc]can not only be used as a solvent to dissolve chitosan,but also provide free mobile ions for ionic gel;The introduction of GVL reduces the viscosity and melting point of solvent system.It is proved by rheology that the storage modulus of the prepared gel electrolyte gradually increases to 90 KPa with the increase of nano-Si O₂ content;Mechanical testing further proves that the introduction of nano-Si O₂ can improve energy dissipation and mechanical properties,with compressive stress and strain increased from 0.67 MPa and 55%to 2.25 MPa and74.5%,respectively.Electrochemical tests show that electrolyte has excellent ionic conductivity in a wide temperature range(2.3,24.3 and 60.3 m S cm^-1 at-25,25 and 80^oC,respectively).The flexible supercapacitors assembled by the gel electrolyte and activated carbon electrode assembly possess excellent bending resistance（180^o）and storage capacity(72.8,84.2 and 113.2 F g^-1 mass specific capacitance(C_sp)at-25,25and 80 ^oC at 0.1 A g^-1,respectively),And after 10,000 charging and discharging cycles,the C_sp and Coulombic efficiency possess almost no attenuation,proving its excellent cycling stability.（2）Based on the homogeneous dissolution of chitosan in the biological Betaine hydrochloride saline solution,the chitosan/polyacrylamide/Li Cl double network hydrogel polymer electrolyte was constructed by combining the chemical cross-linking network formed by the free radical polymerization of acrylamide and the physical cross-linking network of chitosan formed by the salting out effect.The chemical cross-linking network ensures the structural integrity of gel electrolyte,and the reversible recombination of physical cross-linking network and hydrogen bond makes it have excellent fatigue resistance.The Solvation effect of Betaine hydrochloride and Li Cl makes gel electrolyte have excellent ionic conductivity,water retention and frost resistance.The ion conductivity of C₅A₃₀HE-8 M at-50 and 25 ^oC is as high as 4.6 and94.8 m S cm^-1;The compressive strength at 80%strain is 4.18 and 6.47 MPa,respectively.The storage modulus of C₅A₃₀HE-8 M remains basically unchanged over a wide temperature range of-50 to 25 ^oC,further demonstrating its excellent frost resistance.The supercapacitors assembled with activated carbon electrodes possess excellent bending resistance（180^o）and electrochemical performance(C_sp at 2 A g^-1,-50,and 25 ^oC are 108.4 and 176.8 F g^-1,respectively).After 50,000 charging and discharging cycles,the C_sp and Coulombic efficiency have almost no attenuation,proving its excellent cycle life...