Preparation Of Biopolysaccharide Gel Electrolyte For All-solid-state Supercapacitors And Research On Its Energy Storage Mechanis

In recent years,with the rapid progress of science and technology,people have been highly alarmed by the increasing energy consumption and the consequent environmental pollution.The development of green and clean high-capacity energy storage equipment is an effective strategy to alleviate the energy and environmental problems caused by the excessive exploitation and use of fossil fuels.Supercapacitors（SCs）have become a research hotspot of energy storage devices due to their advantages such as wide electrochemical stability window,fast charge-discharge rate and large capacity.At present,the traditional supercapacitors usually use liquid electrolytes,but the existence of electrolyte leakage and other safety problems greatly limit their further development.At the same time,the increasing demand in the field of high-tech electronic products has put forward more stringent requirements for the design of more secure and portable electronic devices.All-solid-state supercapacitors（SSCs）composed of gel polymer electrolytes（GPE）are promising substitutes for liquid supercapacitors because of their advantages such as high ionic conductivity,simple preparation and safe operation.Currently commonly used polymer substrates such as polyvinyl alcohol,poly acrylamide and poly acrylonitrile are often flammable,poor thermal stability,electrochemical performance is not ideal and other shortcomings.At present,it is urgent to design a new gel polymer system with high specific capacity and high safety.Biological polysaccharides are a kind of natural biomass macromolecules with wide sources,environment-friendly,green and renewable properties.Because of their excellent self-gelation and self-flame-retardant properties,they have great potential in the research of gel polymer electrolytes.At the same time,it is particularly important to reduce the interface impedance and improve the electrochemical performance of the gel polymer electrolyte system by regulating the system structure with additives.In this paper,Agarose and Xanthan are used as gel polymer electrolytes for all-solid supercapacitors by their excellent hydrophilicity and film forming properties.By analyzing the microstructure and surface properties of agarose and xanthan,using the hydroxyl and carboxyl groups on the surface,combined with the principle of hydrogen bonding,biological polysaccharide macromolecular polymer and carbon material were bonded to form a double network structure with high ionic conductivity,and a new method of biological polysaccharide based gel solid electrolyte membrane composite was proposed.The effect of different aggregation structures on lithium oxygen coordination and the effect of macromolecular chain movement on lithium ion diffusion were revealed,and the efficient synthesis of flexible flame retardant biological polysaccharide based gel solid electrolyte materials with high ionic conductivity was realized.（1）Agarose was used as gel polymer matrix,GO as inorganic additive and Li OAc as electrolyte salt,Agarose/GO-GPE（Ag/GO-GPE）with highly ordered layered network structure was prepared through high temperature miscible and cooling film forming processes.Density functional theory（DFT）calculations showed that a long-range ordered hydrogen bond network structure（d’=0.454 nm）was formed between the hydroxyl group on the agarose main chain and the hydroxyl group,carboxyl group and epoxide group distributed on the GO sheet,which promoted the Li⁺migration in the system by modulating the molecular configuration of agarose.The first radial distribution function（RDFs）shows that the Li-O ligand optimization of Ag/GO-GPE system(0.189 nm,g _Li-O（r）=54.8)is better than that of Ag-GPE system(0.189 nm,g _Li-O（r）=45.2),which is beneficial to Li⁺motion.When Ag/GO-GPE films were assembled into SSCs using activated carbon as electrode material,Ag/GO₂-GPE（2 M Li OAc）showed high area specific capacitance(791.67 m F cm^-2)and excellent mechanical strength（0.115 MPa）at current density of 5m A cm^-2,much higher than Ag-GPE(564 m F cm^-2,0.089 MPa).In addition,Ag/GO₂-GPE has excellent flame-retardant properties（heat release rate（HRR）of 11.08 k W m² and total heat release rate（THR）of 0.79 MJ m²）.Finally,under bending conditions,Ag/GO₂-GPE can successfully make LED bulbs glow.Even at 180°bending Angle,the electrochemical performance of Ag/GO₂-GPE does not decrease significantly,indicating that Ag/GO₂-GPE has great application prospects as flexible solid electrolyte.（2）Xan/GO-GPE was prepared with Xanthan as gel polymer matrix,GO as inorganic additive and Li OAc as electrolyte salt by physical blending,Ultraviolet induced crosslinking and scraping coating processes.When Xan/GO-GPE film was assembled into SSCs using activated carbon as electrode material,Xan/GO₂-GPE（2 M Li OAc）showed excellent area-specific capacitance(558.34 m F cm^-2)and ionic conductivity(53.3 m S cm^-1)when the current density was 5 m A cm^-2,much higher than the area-specific capacitance(425 m F cm^-2)and ionic conductivity(24.8 m S cm^-1)of Xan-GPE.Xan/GO₂-GPE has a maximum mass loss rate of 360°C and a mass retention rate of 45%after high temperature of 600°C,showing good flame-retardant performance.Under bending conditions of 180°C,Xan/GO₂-GPE still had electrochemical properties similar to the initial state and successfully powered LED bulbs.