Design Of Hydrogel Electrolyte For Flexible Energy Storage Devices

With the rapid emergence of portable and wearable smart electronics,advanced flexible electrochemical energy storage technology has attracted worldwide attention.Compared with flammable and toxic organic electrolyte-based systems,aqueous electrochemical energy storage device has the advantages of low cost,high safety,and environmental friendliness,etc.However,aqueous batteries suffer from numerous drawbacks,such as 1)water has a rather narrow electrochemical stability window and its strong polarity makes most of the materials easily dissolved,which severely restrict the utilization of available electrode materials;2)common aqueous electrolyte easily gets frozen due to the high freezing point of water,suffering from severe performance degradation at subzero temperature;3)conventional liquid electrolytes are prone to leakage and cannot satisfy the requirement of flexible energy storage.On this basis,in this dissertation,the PAM（polyacrylamide）-based lithium（zinc）ion hydrogel electrolyte with low temperature performance was prepared through the electrolyte design.Further,KFe₃（SO₄）₂（OH）₆//K_0.486V₂O₅ and Zn//MnO₂ quasi-solid state flexible energy storage devices were assembled and excellent electrochemical performance was achieved.The research contents are as follows:（1）A novel aqueous anode material,the hexagonal KFe₃（SO₄）₂（OH）₆ nanosheet was synthesized by one-step liquid phase method.Water-in-salt（WIS）electrolyte design strategy was utilized.By regulating the concentration of the Li Cl electrolyte,the strength of H-bonds and ion interactions in solution were balanced and free water content significantly was reduced,which not only solved the material dissolution issue,but also led to excellent low-temperature performance(6.28 m S cm^-1 at-50℃).It was demonstrated that the intercalation pseudocapacitance dominated the charge storage process in KFe₃（SO₄）₂（OH）₆ nanosheets electrode by quantifying the charge storage kinetics.We further designed a PAM-based WIS hydrogel electrolyte with strong mechanical properties,using which,a KFe₃（SO₄）₂（OH）₆//K_0.486V₂O₅ supercapacitor-battery hybrid device was assembled,showing excellent flexibility（stable operation under 180°of bending）,good rate performance and low-temperature performance（a high capacity retention of 74%at-20℃）.（2）Aqueous zinc ion batteries have attracted our attention due to their high energy density.Here,a flexible anti-freezing zinc ion battery was constructed by adopting electrolyte additive strategy.By adjusting the content of DMSO（dimethylsulfoxide）in ZnSO₄ electrolyte to break hydrogen bond between water molecules,we designed a novel PAM-based low-temperature hydrogel electrolyte.The electrolyte exhibited strong mechanical properties,high viscosity and low-temperature performance and could effectively inhibit the growth of zinc dendrites.To enhance the device flexibility,freestanding MnO₂/SWCNT（single-walled carbon nanotube）thin-film electrode was designed;the segregated network structure endowed them with high conductivity,resulting in high specific capacity and excellent rate performance.The quasi-solid flexible zinc ion battery assembled with Zn anode and MnO₂/SWCNT cathode exhibited high capacity and long cycle stability（88%capacity retention after 2000cycles at 4 C）.Moreover,the device can stably operate under extreme conditions including bending,hammering,shearing,burning and low temperature.