Study On The Application Of Zwitterionic Polymer In Lithium Metal Batteries

With the increasing demand for high energy density devices,traditional lithium ion batteries are difficult to meet people's demonds.Lithium metal,with very high specific capacity(3860 m A h g^-1),the lowest reduction potential(-3.040V,vs.Standard hydrogen electrode)and excellent mechanical flexibility,has been considered as the most promising anode electrode materials for the next generation high energy density batteries.However,the irreversible dendrite growth during cycling of lithium metal battery is one of the biggest challenges for its further application.In order to solve the dendrite growth problem,researchers have done a lot of work.Polymer gel electrolyte wraps organic liquid electrolyte inside is flexible and can provide great interface contact with electrode.In addition,with the organic liquid electrolyte inside the gel,the safety issue is greatly improved.Among all polymer gel electrolyte,zwitterionic polymer can provide higher electrochemical performance due to its superiority on stabilizing interface contact with electrolde and improving lithium ion transport for higher ion conductivity and transference number.Herein,based on zwitterionic polymer,the following two aspects were studied:(1)Study on the application of polymer gel electrolyte containing polyzwitterion with high mechanical properties to anti-swelling in lithium metal batteries;(2)Study on the application of gel electrolyte containing zwitterionic poly(ionic liquid)in lithium metal batteries.The feasibility of its application in inhibiting dendrite growth of lithium metal batteries and the corresponding characterization of battery performance were studied.The thesis is divided into four parts:1.The first chapter is the introduction.Firstly,the development history,the composition and the working principle of lithium ion battery,the principle of dendrite growth and the common anode and cathode materials are all introduced.Secondly,the chapter introduce the research of solid electrolyte,mainly including the research of all solid electrolyte and polymer solid electrolyte.Thirdly,the chapter focus on the application of gel electrolyte in lithium metal batteries.Finally,the concepts of zwitterion and ionic liquids are briefly explained,and the functions of polyzwitterion and poly(ionic liquids)in gel electrolytes are introduced accordingly.2.The second chapter is mainly about the research of gel electrolyte containing zwitterion in lithium metal batteries.The as-designed zwitterionic polymer gel electrolyte has the following advantages:first,due to the dipole-dipole interaction between VIPS,the mechanical strength of the polymer gel electrolyte is greatly improved.Second,the ion-dipole interaction between3-(1-Vinyl-3-imidazolio)propanesulfonate(VIPS)and lithium salt promotes the dissociation of lithium salts,thus greatly increasing the ion transference number.Third,the ion-dipole interaction between lithium salts and VIPS improves the solubility of hydrophilic VIIPS in ester electrolyte,and optimized the polymerization progress.Furthermore,by copolymerizing the hydrophilic VIPS and the esters 2-methoxyethyl acrylate(MEA),the polymer gel electrolyte exhibits anti-swelling properties in liquid electrolyte,which ensuring the mechanical strength of the electrolyte in liquid electrolyte during cycling.As a result,the polymer gel electrolyte containing zwitterionic performs excellent cycling stability in lithium symmetric batteries.Even under high current density of 5C,the Li Fe PO₄(LFP)cell with zwitterion polymer electrolyte can still perform well.3.The third chapter mainly introduces the application research of polyionic liquid gel electrolyte([VIPS][Li TFSI])in lithium metal batteries.The mechanical and electrochemical properties were mainly characterized.The effects of ionic liquid on the mechanical strength and ionic conductivity of the system are discussed.The interaction between ionic liquid and anions in lithium salt limits the migration of anions under the effect of electric field,promots the migration of lithium ions,inhibits the formation of space charge,and significantly improves the ionic conductivity.As a result,the poly(ionic liquid)gel electrolyte is also applied in LFP cell,which can achieve stable cycle and ultra-high specific discharge capacity under the high current density of 10C.4.The fourth chapter summarizes all contents of the thesis,including the physicochemical properties and electrochemical performance of the as-engineered polymer gel electrolyte containing zwitterionic polymer and gel electrolyte containing ionic liquid,and prospects the application of two kinds of polymer gel electrolyte in lithium ion batteries.