Synthesis And Properties Of Polyurethane Lithium Sulfonate Single-ion Conductors

Today portable devices such as laptops and cell phones rely heavily on lithiumion batteries.These power sources offer significant advantages in terms of high specific energy and energy density.However,the flammability of the employed liquid electrolytes used in lithium-ion batteries presents a significant drawback which causes safety issues and limits not only the operating temperature range,but also the battery lifetime.Solid polymer electrolytes are widely used because of their good safety performance and flexible shape.Polyurethane single-ion conductors with two-phase structure can simultaneously have excellent electrical conductivity and good mechanical strength.Therefore,in this dissertation,two series of single-ion conductors,polyurea polyurethane(PUA)and polyester polyurethane(PUE),have been designed,prepared and characterized.In this dissertation,4,4?-methylenebis(phenyl isocyanate),lithium diaminobenzenesulfonate and polyethylene glycol(molecular weight of 1000 g·mol-1)were used as the reaction materials.A series of polyurea polyurethane-type single-ion conductors PUA were synthesized by changing the amount of diaminobenzenesulfonicacid and polyethylene glycol diamine with the one-step method.In order to improve the conductivity of the system,a series of polyester polyurethane single ion conductor PUE with different Li+/EO molar ratio was successfully synthesized by two-step method.And the raw materials are lithium dicarboxybenzenesulfonate,polyethylene glycol with different molecular weight(including: 300 g·mol-1,600 g·mol-1 and 1000 g·mol-1),4,4'-methylenebis(phenylisocyanate).Then the synthetic samples were formed to films by solvent casting method.Structural characterization and performance testing of these two series of electrolytes were conducted to explore the effect of lithium ion concentration on its performance.Using nuclear magnetic resonance spectroscopy(1H NMR)and infrared spectroscopy(FT-IR)to characterize the material structure,it was shown that both PUA and PUE single-ion conductors have a two-phase structure.And physical crosslinking caused by hydrogen bond can be found between segments.Passing differential scanning calorimetry(DSC)test,as the concentration of lithium salt increases,the glass transition temperature(Tg)of the single-ion conductor changes a lot.It is obtained from the thermal weight loss test(TG)that both types of single ion conductors have good thermal stability.The mechanical propertie s of the materials were tested by tensile test.Both types of polymer films had certain mechanical strength and could meet the requirements of lithium batteries.However,the tensile strength of PUE films was lower than that of PUA.Through the AC impedance method,the room temperature conductivity of the single ion conductors was characterized,and the highest electrical conductivity was up to 10-7S·cm-1.The maximum ionic conductivity at room temperature of PUE is 3.56×10-7S·cm-1 which is more excellent than PUA.Finally,the PUA-40 single-ion conductor was modified with different organic plasticizers,and their highest electrical conductivity was 1.17×10-5S·cm-1.The button cell with the modified PUA single-ion conductor as the electrolyte was assembled,and the battery performance has been tested.The polymer lithium battery has high capacity and excellent cycle performance.