| Polymer lithium ion battery (PLB) is a novel rechargeable system based on liquid lithium-ion battery. It has outstanding properties such as high energy density, long cycle life, low leakage, light weight and flexible shape. The PLB is attractive as power sources of mobile gear including cellular phones,PDAs,notebook computers and portable audiovisual equipment. Therefore, the demand of polymer electrolyte membrane is increasing. The main technical problems of polymer electrolyte include: firstly, the ion conductivity of gel polymer electrolyte (GPE) can reach the magnitude of 10-3S/cm, which can satisfy the practical request. However, it is still lower than that of liquid electrolyte (10-2S/cm), which causes the fall of high rate discharge and low temperature performance of lithium battery. Secondly, the mechanical property of polymer electrolyte is poor. As usual, the method to enhance the ion conductivity of polymer electrolyte would reduce its mechanical property. Fluoropolymers have attracted more and more attentions due to their good chemical, electrochemical stability and good mechanical processability. Focusing on the main problems of gel polymer electrolyte, in this paper, we studied fluotopolymers and prepared three kinds of gel polymer electrolyte. The chemical characteristics, surface morphology, thermal behavior, ionic conductivity, interfacial stability of polymer electrolyte have been investigated by using of FT-IR, Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM), Optical microscopic images, Alternating Current Impedance (AC Impedance) and Linear Sweep Voltammetry (LSV), respectively. The main results are summarized as follows:1. Methyl methacrylate (MMA) was grafted on the surface of multi-porous poly(vinylidine fluoride) (PVDF) films via electron beam pre-irradiation grafting method to prepare multi-porous PVDF-g-PMMA polymer electrolyte. The degree of graft (DOG) increased with increasing irradiation dose. The DOG increased quickly with the increasing monomer concentration, and came to climax when monomer concentration was 40%. The DOG began to increase slowly at forty centigrade and increased quickly at sixty centigrade and then kept constant. When the DOG was 37.2%, the maximum uptake of liquid electrolyte was 280%, and ionic conductivity at room temperature was 6.1×10-3S/cm and the electrochemical stability window was up to 5.5V.2. MMA was grafted on the surface of PVDF non-woven fabrics by electron beam pre-irradiation grafting technique to prepare PVDF-g-PMMA non-woven fabrics polymer electrolyte. Effect of pre-irradiation dose, monomer concentration and reaction temperature was similar with the grafting reaction on the surface of PVDF multi-porous films. The liquid electrolyte uptake process was very fast and the maximum amount of electrolyte penetrated into the membrane within a few seconds. The pristine PVDF non-woven fabrics needed only 10 seconds to reach saturated state, and the maximum uptake of liquid electrolyte was 210%. The PVDF-g-PMMA non-woven fabrics needed 50 seconds to reach saturated state when the DOG was 111.8%, and the maximum uptake of liquid electrolyte was 260%, and ionic conductivity at room temperature was 7.9×10-3S/cm. if the discharge capacity percentage was supposed to be 100% at 0.1C discharge rate, and the discharge capacity percentage was 85% at 5C discharge rate.3. The pore former was dispersed into fluorosilicone rubber by mechanical mixing and solution mixing respectively. The fluorosilicone film was prepared by sulfuration reaction. The pore former was extracted by organic solvent and then multi-porous fluorosilicone film was prepared. In the multi-porous fluorosilicone film prepared by solution mixing method, the amount of pores was very high and the size of the pores was very small and the distribution was uniform. The solution mixing method was better than the mechanical mixing method.4. The multi-porous fluorosilicone film was prepared by solution mixing method using polystyrene as pore former. If the weight ratio of fluorosilicone to polystyrene was 1:1, the degree of porosity was up to 43% and the maximum size of pores was less than 1μm. The liquid electrolyte was 1mol/L LiClO4/EC-DMC (1:1, V/V). The maximum uptake of liquid electrolyte was 220%, and ionic conductivity at room temperature was 1.3×10-3S/cm and the electrochemical stability window was up to 5.5V. If the discharge capacity percentage was supposed to be 100% at 0.1C discharge rate and the discharge capacity percentage was 90.4% at 1C discharge rate. The discharge capacity percentage was more than 85% after 20 cycles at 1C discharge rate.
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