The Synthesis Of A New Plasticizer And Properties Of The Gel Polymer Electrolytes

The gel polymer electrolytes (GPE) are a key material for developing polymer lithium ion batteries with high power and energy density and a long life cycle, for the advantage of both high ionic conductivity (the liquid electrolyte) and good handling characteristics (solid polymer electrolyte). Generally, the gel polymer electrolyte for rechargeable lithium ion batteries must satisfy following requirements, such as the high ionic conductivity, high lithium ion mobility number, wide electrochemical windows, excellent thermal stability and electrochemical stability, good mechanical strength and the good compatibility with lithium electrode.The roles of plasticizers in GPE are as follows:(1) decreasing the glass transition temperature of the polymer and increase the segmental motion;(2) enhancing the polarity of polymer by the interaction between the polymer matrix and the dipole, which can promote the dissociation of lithium salt from the polymer matrix;(3) destructing the coordination between the lithium ion and polymer matrix so that systems have more ions in amorphous phase instead of crystalline phase.Propylene carbonate (PC) has many advantages such as high dielectric constant (64.92) and high ability to dissolve a large variety of lithium salt, wide liquid range (Tm-48.8℃and Tb 242℃) and inexpensive. But it also has some disadvantages, the compatibility with the electrode is not very well and PC can easily decompose on graphite and co-insert with Li-ion into graphite electrode, which reduces the reversible capacity of graphite electrode.Plasticizers were added to improve the ionic conductivity, however, the excessive addition of plasticizers such as 30% weight percent will decrease the mechanical strength of polymer electrolytes. Addition of inorganic nanopaticles in GPE is helpful to enhance the ion-conductivity and thermo stability.In our work, we synthesized a new kind of plasticizer TEMP. Then the gel polymer electrolyte containing PEO as the polymer matrix, LiClO4 as the lithium salt and a mixture of TEMP and PC as the plasticizer has been developed. The influences of rate composition between TEMP and PC and the amount of plasticizer on GPE were studied. The thermal properties and electrochemical properties, such as the ionic conductivity, lithium ion mobility number and electrochemical windows were discussed.Finally, the inorganic nanoparticle Al2O3 was added into the gel polymer electrolyte to form nano-composite gel polymer electrolyte. The A.C. impedance was used to investigate the ionic conductivity of the polymer electrolyte system and the thermal property was also discussed.