Preparation And Study Of High-performance Gel Polymer Electrolytes For Lithium Ion Battery

Along with the advance in technology social development, more and more non-renewable resources are consumed, new energy resources superiority causes it to become the theme of our age. Lithium ion battery has been applied widely in the energy sources rapid growth time, due to its high specific energy, high efficiency, nonmemory effect and long cycle life. Polymer electrolyte is an important part of lithium ion battery, and the research on it is much slower than that of the electrode, which greatly restricts the electrochemical performance of the battery. This paper aims to prepare a new kind gel polymer electrolyte by electrospinning technique which has good mechanical properties and high conductivity. Through a series of experiments, the physical and chemical properties of gel polymer electrolytes were studied, and the cycle performances and the rate capabilities of gel polymer electrolyte in lithium ion polymer battery were discussed. The research work is mainly carried out as follows:Firstly, blending PVDF/PAN,TPU/PAN and PVDF/TPU/PAN films have been prepared by electrospinning technique. These films are activated with a 1 M LiPF6–EC/DMC solution. The PVDF/TPU/PAN electrospun membranes show a high ionic conductivity about 4.98×10-3 S cm-1 at room temperature. First discharge capacity of Li/GPE/LiFePO4 cells is 163.4 mAh g-1 and the battery shows good cycle performance. PVDF/TPU/PAN based gel polymer electrolyte is more suitable than the other two kinds of composite films for lithium rechargeable batteries.Secondly, based on the previous studies, series of PVDF/TPU/PAN membranes were prepared by electrospinning with different concentrations of polymer in order to determine a gel polymer electrolyte which can exhibit the best properties. Then PVDF/TPU/PAN electrospun membranes are activated with a 1 M LiPF6–EC/DMC solution to get gel polymer electrolyte. The gel polymer electrolyte which is prepared by electrospinning 9% polymer solution shows the best performance. It shows a first discharge capacity of 165.4 mAh g-1 when the GPE is evaluated in a Li/PE/LiFePO4 cell at 0.1 C rate at 25 °C. After 50 cycles of charge-diacharge tests, the discharge capacity reached 158.3 mAh g-1, with little attenuation.Finally, different mass ratios of PVDF/TPU/PAN nonwoven films were prepared by electrospinning 9% polymer solution at room temperature. Then PVDF/TPU/PAN electrospun membranes are activated with a 1 M LiPF6–EC/DMC solution to get gel polymer electrolyte. The performances of PVDF/TPU/PAN films with mass ratio of 2:2:1 is the most excellent. It exhibits a high ionic conductivity of 6.91×10-3 S cm-1, the electrochemical stability window of 5.7 V. It shows a first discharge capacity of 167.8 mAh g-1 when the GPE is evaluated in a Li/PE/LiFePO4 cell at 0.1 C rate at 25 °C. After 50 cycles of charge-diacharge tests, the discharge capacity reached 163.4mAh g-1, with little attenuation. The PVDF/TPU/PAN(2/2/1) films exhibit a high tensile strength(10.31 MPa) and elongation(102.51%). It is observed that PVDF/TPU/PAN(2/2/1) based GPE is more suitable than the other two kinds of composite films for high-performance lithium rechargeable batteries.