Synthesis And Properties Of A Novel Comb-like Solid Polymer Electrolyte

As a kind of power source, lithium ion battery （LIB） has many advantages such as highspecific capacity, long charge-discharge life, none memory effect, light pollution, fastcharging and low self-discharge. However, traditional lithium ion batteries have noneflexibility in shapes because they have to be packed with metal. Besides, there are dangers ofleakage and combustion due to using liquid electrolytes in LIBs.Polymer lithium-ion battery （PIB） sovles these problems. So it has been a trend thatpolymer electrolytes take place of liquid electrolytes in LIB. But polymer electrolytes,especially solid polymer electrolytes have not been widely used currently because of lowionic conductivity at room temperature.In this paper, a novel comb-like poly（ethylene oxide）（PEO） containing borate wassynthesized. Comb-like design was aimed to destroy crystalline in PEO and introduce ofborate was expected to increase conductivity and transference number. The results of FTIRand NMR showed that the polymer had been prepared successfully. There was almost nonecrystalline in the novel comb-like PEO from the differential scanning calorimeter （DSC）investigation. Also, the polymer had good thermal stability through thermogravimetricanalysis （TGA）.Solid polymer electrolyte （SPE） films were prepared with casting method based onprevious synthesis. Electrochemical properties and thermal properties have been investigated.Through these investigations, we found that ionic conductivity depended on lithium saltcontent, temperature, crystalline and glass transition temperature （Tg）. The maximumconductivity could be obtained when the [EO]:[Li⁺] was10and30. The highest conductivityof the polymer electrolyte reached3.15×10^-5S/cm at30℃. Ionic conductivity increased whentemperature increased. Additionally, conductivity of SPEs followed the VTF equation andArrhenius equation at different temperature. Ea of conductivity for SPE-5was obviouslygreater than others. The results of DSC showed that a new crystalline emerged with meltingpoint between170℃and180℃. Conductivity was related to crystalline and Tg of main chain.Results of TGA showed T₉₅got low when LiClO₄added. Temperature of thermal degragationraise fisrt, then droped when LiClO₄content increased. T₉₅was174.3℃for SPE-15, which was the highest. Thermal stability got worse when lithium salt content increased.Decomposition voltage of SPE-5is3.7-4.4V and lithium-ion transference numbers of SPEswere between0.1and0.3.Composite polymer electrolytes were prepared by adding nano-TiO₂in SPE-10.Nanoparticles reunited more and more serious when content of nano-TiO₂increased. Whencontent exceeded5phr, the mechanical strength of the electrolyte film was very poor. Resultsof TGA showed thermal stability increased when nano-TiO₂was added.T₉₅got higher whenamount of nano-TiO₂increased.