The Preparation Of PVdF Matrix Polymer Electrolyte Membranes And Its Application In Lithium Ion Batteries

Advancements in technologies directly promote the development of efficient energy storage devices due to increasing demand for energy.Lithium-ion batteries(LIBs)are widely used as power supplies for laptops,smartphones and other common consumer electronic products.However,the safety hazards of flammable and leaking in organic liquid electrolytes hinder development of lithium ion batteries in electric vehicles(EVs)and in renewable energy power storage systems.Therefore,in order to replace the organic liquid electrolyte,the polymer electrolyte composed of polymer matrix and metal salt comes into being.In this paper,two kinds of lithium ion polymer electrolyte membrane:Polyvinylidenedifluoride/cellulose acetate/lithium bis(trifluoromethanesulfonyl)imide/montmorillonite(PVdF/CA/LiTFSI/MMT),Polyvinylidenedifluoride/cellulose acetate(CA)/lithium bis(trifluoromethanesulfonyl)imide/N-methyl-N-butyl pyrrolidinium bis(trifluoromethanesulfonyl)imide(PVdF/C A/LiTFSI/Py14TFSI)based on the method of blending modification of polymer matrix were prepared by solution casting method.The single-factor experiments with the conductivity as the main basis were used to obtain the best polymer electrolyte membrane.The physical properties of the polymer membranes were characterized by scanning electron microscopy,tensile strength testing,thermogravimetric analysis and X-ray diffraction measurement.The electrochemical properties of the polymer membranes were characterized by electrochemical impedance spectroscopy,linear sweep voltammetry,cyclic voltammetry and charge/discharge of Li/electrolyte membrane/LiFePO4 half cell.The results showed that the electrochemical stability window of the membrane with ratio of PVdF:CA:LiTFSI:MMT=50:15:40:2(w:w:w:w)was 4.2 V.The lithium ion conductivity and transference number at room temperature were 3.40×10-4 S/cm and 0.315,respectively.The discharge capacity of LiFePO4/electrolyte membrane/Li half-cell was 111.2 mAh/g for the first time and 112.9 mAh/g after 100 cycles with a coulombic efficiency about 100%.The electrochemical stability window of the membrane with ratio of PVdF:CA:LiTFSI:Py14TFSI=20:4:12:15(w:w:w:w)was 4.95 V.The lithium ion conductivity and transference number at room temperature were 1.45×10-4 S/cm and 0.231,respectively.The discharge capacity of Li/electrolyte membrane/LiFePO4 half-cell was 124.5 mAh/g for the first time and 119.6 mAh/g after 50 cycles,illustrating a good cycling performance.In view of the above-mentioned facts,both PVdF/CA/LiTFSI/MMT and PVdF/CA/LiTFSI/Py14TFSI were good polymer electrolyte materials in lithium ion batteries.