Preparation Of Polycarboxylated Gel Polymer Electrolyte And Its Performance For Aqueous Zinc Ionic Batteries

With the rapid development of electric vehicles and electronics,the demand for energy storage devices is rising rapidly.Lithium-ion batteries（LIBs）have dominated the battery market due to their light mass and high energy density.However,when LIBs are used in large-scale energy storage systems and smart wearable devices,there are still many problems in terms of cost,safety and environmental protection.As a new type of energy storage battery,aqueous zinc-ion batteries（ZIBs）stand out among many metal-ion batteries because of their high ionic conductivity and safety.However,the conventional aqueous electrolyte not only suffers from hydrolysis,evaporation and electrolyte leakage,but also faces problems such as dissolution of cathode materials and growth of cathode dendrites,all of which can lead to degradation of ZIBs performance.As an emerging electrolyte,gel electrolyte is composed of polymer matrix and electrolyte,which can effectively solve the problems existing in traditional aqueous electrolyte.However,the ionic conductivity,electrochemical stability,mechanical properties,and low-temperature performance of gel electrolytes need further improvement if they want to realize industrial applications.In this thesis,from the problems of low ionic conductivity and poor low-temperature performance of gel electrolytes,a gel electrolyte with high ionic conductivity and low-temperature anti-freezing performance was designed and prepared by using biomass sodium alginate as a substrate and investigating its performance in zinc ion batteries through structural modification and introduction of additives.The main research includes:（1）To address the problem of low conductivity of gel electrolytes,a polycarboxylated gel electrolyte（SAI）was designed and prepared by using iminodiacetic acid with a double carboxyl functional group and sodium alginate through an amidation reaction to convert the single carboxyl group in the alginate base structure into a double carboxyl group.The ionic conductivity of the alginate based gel electrolyte was effectively doubled(from 17.59 m S cm^-1 to 35.14 m S cm^-1)by introducing more carboxyl groups on the main chain of sodium alginate to promote the dissociation of the salt and thus increase the ionic concentration.Good electrochemical performance of the assembled aqueous zinc ion battery with a capacity retention of 76.5%after 500 cycles at 1 C;（2）To address the problem of low-temperature freezing of electrolytes,zwitterionic betaine（BA）was introduced into the salt solution and amphoteric permeant was introduced into SAI gel electrolyte by solvent replacement method to prepare zwitterionic low-temperature antifreeze gel electrolyte（SAI-B）.BA binds to water molecules through electrostatically induced hydration,hinders the formation of hydrogen bonding networks between water molecules,and inhibits freezing,thus reducing the freezing point of SAI-B.The SAI-B electrolyte still has an ionic conductivity of up to 20.96 m S cm^-1 and excellent flexibility at-20 ^oC.Using SAI-B to assemble freeze-resistant flexible zinc ion full cells,the cells still have similar electrochemical performance at-20 ^oC as at room temperature,exhibiting high capacity retention（91.6%）and excellent cycling stability.This work broadens the practical applications of flexible aqueous zinc ion batteries at low temperatures.