Synthesis Andapplication Of Lithium Ion Conductive Polymer Electrolytes

Today's environmental problems of the world are increasingly attracting widespread attention. One of the ways to solve this problem is replacing fossil fuel with the efficient, clean and pollution-free electricity. Lithium-ion battery and Lithium-air battery are the most potential electrochemical powers,while the development of electrode and electrolyte materials is the key to Lithium(ion) battery applications. Polymer electrolyte has a good processing performance as well as high ionic conductivity. When used as a separator between the electrodes, it can meet the battery demands of different size and shape with sound safety. As a result, polymer electrolyte meets the development trend of the electrochemical power.In this paper, we synthesized composite polymer electrolytes (CPE) with high electrochemical performance by doping unique nano-sized inorganic materials. The effects of inorganic fillers on the electrochemical performances of CPE and the mechanism were fully studied as below:Firstly,we developed the related technology of phase transfer method, determined PVDF-HFP as polymer electrolyte, DMF as solvent. The best properties of polymer membrane used in Li-ion battery is forming film in 50℃with 30 min; the best properties of polymer membrane used in Li-air battery is forming film in 80℃with 30 min.Secondly, on this basis, we prepared the lithium ion conductive CPE by doping inorganic filler LiFePO₄. When PVDF-HFP: LiFePO₄: DMF equal to 1:8%:8(mass ratio), the membrane owns the best performance. In room temperature, the ionic conductivity is 2.71×10-3mS/cm, the electrochemical stable window is 4.6V, these propertises meet the requirements of Li-ion battery. The type of microporous polymer electrolyte membrane used in Li/LiFePO₄ battery exhibits an initial discharge capacity of 156, 152, 147, 138 mAh/g in 0.1C, 0.2C, 0.5C and 0.8C rate. After 100 cycles in 0.5C, its discharge capacity goes down to 131.9 mAh/g, with the decay rate of 11.44%. When the type of nonporous polymer electrolyte membrane is used in Li-air battery, the initial discharge capacity goes to 3233 mAh/g under 0.1mAh/cm² current density.On the other hand, we prepared the lithium ion conductive CPE by doping inorganic filler LATP. When PVDF-HFP: LATP: DMF equal to 1:20%:8(mass ratio), the membrane owns the best performance. In room temperature, the ionic conductivity is 1.78×10^-2mS/cm, the electrochemical stable window is 4.9V, these propertises meet the requirements of Li-ion battery. The type of microporous polymer electrolyte membrane used in Li/LiFePO₄ battery exhibits an initial discharge capacity of 152.3, 149.7, 147 mAh/g in 0.1C, 0.2C, 0.5C rate. After 50 cycles in 0.5C, its discharge capacity goes down to 125.5 mAh/g, with the decay rate of 17.6%. When the type of nonporous polymer electrolyte membrane used in Li-air battery, the initial discharge capacity goes to 2980 mAh/g under 0.2mAh/cm² current density.