Design, Preparation And Application Of Natural Polymer-based Gel Electrolytes In New Energy Device

Gel polymer electrolyte is a kind of quasi-solid electrolyte,which is composed of liquid electrolyte and polymer matrix and has both the properties of liquid electrolyte and mechanical properties of solid polymer skeleton.Gel polymer electrolyte can not only overcome the shortcomings of liquid electrolytes,such as easy leakage and difficult encapsulation,but also has high ionic conductivity of liquid electrolyte and good mechanical performance of solid electrolytes,therefore showing a broad application prosepect in portable electronic devices,power system and hybrid cars.Based on the comprehensive consideration of safety,wide temperature range and flexibility,the use of gel polymer electrolyte is one of the key research directions in the development of new energy devices.However,at present,most of the gel polymer electrolytes are based on synthetic polymers which are difficult to degrade and expensive.From the economic and environmental perspective,it is extremely urgent to develop the gel polymer electrolyte framework with natural polymer materials.In this thesis,natural polymers such as cellulose,gelatin and corn stalk（lignocellulose）,which are rich in resources,cheap and easy to degrade,were developed as gel polymer electrolyte skeleton.Taking supercapacitor as application model,the construction strategy of gel electrolyte was studied,the relationship between physical,chemical structure and electrochemical performance of materials was clarified,and a new controllable preparation technology of natural polymer gel electrolyte was established.The detailed research contents are as follows:（1）Based on the newly developed CO₂/DMSO/Superbase system for cellulose dissolution,we prepared a kind of cellulose-based protic ionogel electrolyte using succinic anhydride as derivatization reagent and epichlorohydrin as crosslinking agent.Here,organic base not only forms a part of cellulose dissolution system and plays the role of activating and dissolving cellulose,but also acts as a super nucleophilic acylation catalyst when anhydride reacts with hydroxyl groups on cellulose,which greatly improves the reaction efficiency;thus,the cation of organic superbase is grafted onto the chain end of cellulose ester,and protic ionic liquid groups are introduced into the original structure of cellulose finally.DMSO can be used not only as a solvent for cellulose,but also as an ion transport carrier in gel electrolyte.The ionic conductivity of the prepared ionic gel electrolyte can reach 4.1 m S/cm at room temperature.Supercapacitors assembled with the prepared ionogel as electrolytes prevents a high power density of 17.38 Wh/Kg and excellent cycling performance.The preparation of gel electrolytes by grafting ion groups onto the biomolecular polymer matrix does not affect the charge transfer efficiency,and it also proves that the strategy of grafting ion groups onto the biomolecular polymer has great potential in flexible electronics.（2）Gelatin matrix,a natural polymer containing a large number of amino,carboxyl,hydroxyl and other active functional groups,was used to dissolve gelatin in a hypoeutectic dissolution system（DES）prepared by choline chloride and polyols.The polyols in the system were in situ oxidized into aldehydes.A new type of chemically crosslinked DES gel electrolyte with good self-healing performance were fabricated.The prepared DES gel electrolytes show excellent ionic conductivity up to 10¹-10²m S/cm in a wide temperature range of-40-80°C.Supercapacitors and flexible sensors were designed and assembled based on the prepared ionic gel polymer electrolytes.Show good performance.This kind of ionic gel based on natural polymer has good mechanical properties,high ionic conductivity and wide operating temperature range,showing great application value in the next generation of high-performance electrochemical devices.（3）Corn straw is the largest natural polymer resource in the world.The government has launched a number of policies to improve the utilization rate of corn straw resources,so as to control the environmental pollution caused by agricultural waste.This work follows the research strategy of the work part 1.We prepared a new composite ionogel polymer electrolyte,based on our newly developed CO₂/DMSO/superbase system for cellulose dissolution,with corn stalk waste as raw materials and polymer framework.The prepared ionogel electrolyte exibits both high ionic conductivity up to 2.78 m S/cm at room temperature,and good temperature adaptability.The energy density of the supercapacitor assembled with the prepared electrolyte is 16.05 Wh/Kg.It is of great significance to promote the resourcefulness and high-value utilization of straw as well as green development.