Synthesis And Electrical Conductivity Of Polyurea And Polyurethane-urea Single-ion Polymer Electrolyte

The current electrolyte used in lithium-ion batteries are mostly organic liquid state,which may cause dangerous such as the leakage of battery,fire breaking out and explode,etc.Compared with the traditional liquid-state electrolyte lithium-ion batteries,the substitution of solid-state polymer electrolyte for liquid-state electrolyte could not only solve the dangerous problems,but also make the shape of batteries more diversified.Better mechanical performance and excellent electroconductivity could not be both achieved in practical researches on polymer electrolyte,while micro-phase separation of hard and soft segment could improve these two properties at the same time.In this research,three new kinds of polyurethane-urea and polyurea single-ion electrolytes with micro-separation structure have been prepared and characterized.In the first part,1,4-phenylene diisocyanate,diaminobenzenesulfonicacid and polyethylene glycol diamine(formula weight,1000)were chosen as synthetic materials,and polyurea single-ion electrolytes series I(PUI)with different concentrations of lithium salts were successfully prepared by changing the amount of diaminobenzenesulfonicacid and polyethylene glycol diamine.The synthetic samples were formed to films by solvent casting method,and nuclear magnetic resonance(NMR)and Fourier transform infrared spectrometer(FT-IR)was used to investigate the structure of the films.Moreover,differential thermal analysis(DTA),thermal gravity analysis(TGA),tensile test and electrochemical impedance spectroscopy(EIS)were carried out to study the thermal properties,mechanical properties and electroconductivity of the films respectively.In order to further reduce the glass transition temperature of the system and enhance the conductivity of the electrolyte,polyurea single-ion electrolytes series II(PUII)and polyurethane urea electrolyte(PUU)were prepared by the substitution of polyethylene glycol diamine(formula weight,2000)and polyethyleneglycol for polyethylene glycol diamine(formula weight,1000)in PUI.The structures and performances of the three series of electrolytes were compared and analyzed.The results show that two phase structure are all exist in the synthetic three series of electrolytes,and physical crosslinking caused by hydrogen bond can be found between segments.Glass-transition temperature(Tg)of soft segments will rise with the increased concentration of lithium salt,while Tg of soft segments in PUII and PUU are lower than that of the PUI.The results of ionic conductivity test at room temperature show that,with the increased concentration of lithium salt,the ionic conductivity will increase at first and then experience a de clining trend after a maximum value.The maximum ionic conductivity at room temperature of PUI is 2.84×10-7S·cm-1.The maximum room temperature conductivity of the PUII and PUU series of electrolytes have been improved compared to PUI,which is 5.81×10-7S·cm-1 and 1.81×10-6S·m-1.When the temperature is below 254 oC,all the synthetic polymer electrolytes show good thermal stability and excellent mechanical properties,and in terms of mechanical properties,PUI is the strongest while PUU is the weakest.