Structure Design And Properties Of Chitosan-based Gel Polymer Electrolytes

Lithium-ion batteries(LIBs)have become a promising energy storage device due to their excellent cycle stability,high energy density,flexible structure and environmental friendliness.They have been widely used in our daily lives and provide more possibilities for our lives.With the advancement of technology,the electrolytes used in commercial lithium-ion batteries have changed from traditional carbonatebased small molecule liquid electrolytes to safer and more environmentally friendly electrolytes,which can not only effectively provide electrical energy,but also can effectively prevent hazards such as combustion explosion,toxicity and corrosiveness.Therefore,effective safety measures must be taken during manufacture,transportation and use to ensure the safety of personnel and the environment.At present,the solution explored more is to use all-solid electrolyte as an alternative solution.As a new electrolyte material,all-solid electrolyte also has various problems in conductivity,preparation cost,material stability and the like,which limit its practical application in production and life.Gel polymer electrolyte is a kind of material composed of polymer matrix and ion conductor.Its working principle is to capture the ion conductor and promote its ion transport through the gel network structure formed in the polymer matrix,thus realizing the function of electrolyte,and it has higher safety compared with traditional liquid electrolyte due to its gel network structure.Chitosan is a kind of natural product,which is usually composed of shells and chitin of marine organisms such as shells,shrimps and crabs.As a biodegradable material,chitosan can be degraded by microorganisms and enzymes in the environment,and has good sustainability and environmental friendliness,which lays a good foundation for being used as a lithium ion battery electrolyte matrix material.A structural design and graft modification of chitosan enabled the production of a novel gel polymer electrolyte with high ionic conductivity,safety,and environmental sustainability for lithium ion batteries in this paper.The main research contents are as follows:(1)Preparation and study of PEGylated chitosan gel polymer electrolyte.Chitosan has good safety and sustainability,and is expected to be the matrix of gel polymer electrolyte(GPE)for lithium batteries.However,because of the large number of hydrophilic functional groups hydroxyl or amino in macromolecules,they are easy to form hydrogels.Therefore,due to the anhydration requirements of lithium ion batteries,there is a strong need for an amphiphilic gel or organogel based on polysaccharides.In this study,the chemical grafting method was firstly used to design the chitosan with polyethylene glycol(CS-g-PEG),which made it possible to use it as GPE for lithium ion batteries.The ionic conductivity of the coin cell assembled with CS-g-PEG gel polymer electrolyte membrane at room temperature was 1.12×10-3 S cm-1,and the lithium ion transfer number was 0.816.At room temperature,the coin cell,constructed with CS-g-PEG-480,has a discharge capacity of 158 mAh g-1.(2)Preparation and study of chitosan/graphene oxide composite gel electrolyteBecause the chitosan matrix in the gel electrolyte can destroy part of hydrogen bonds in molecules during the grafting modification process,the mechanical properties of the chitosan matrix inevitably lose in the process,and the cycle performance of the gel polymer electrolyte based on the PEGylated chitosan needs to be improved.In this section,a chitosan/graphene oxide composite gel electrolyte was constructed with CSg-PEG as matrix material and graphene oxide as filler.The electrochemical performance of PEGylated chitosan was improved after being compounded with graphene oxide,and the button battery assembled with PEGylated chitosan as electrolyte material also showed good cycle performance.Through IR characterization,it was found that there was interaction between CS-g-PEG and GO filler,which confirmed the successful reaction.Compared with pure CS-g-PEG gel electrolyte,the prepared CP/GO composite gel membrane has better electrochemical performance in some aspects,for example,the ionic conductivity is higher at room temperature,and the interface resistance value after stabilization is relatively lower.In addition,the LiFePO4/Li battery assembled using the CP/GO composite gel polymer electrolyte exhibits relatively better cycle performance.