Study On Micro-porous Gel Li-ion Polymer Electrolytes

Lithium ion batteries are among the category of the most competitive and widely used energy storage and conversion devices.However,safety issue of lithium ion batteries is still a challenge due to the possibility of leakage of liquid electrolyte. Gel polymer electrolytes can prevent the leakage without ruining the performance of the batteries evidently,owing to the depressed fluidness and sufficient ion transfer ability.In this paper,a series of polymer electrolytes with interconnected pores based on poly(vinylidene difluoride-co-hexafluoropropylene)[P(VDF-HFP)]copolymer was prepared by a simple phase separation process using water as both non-solvent and pore inducer.The prepared porous membrane was characterized by SEM,XRD and DSC.With a narrow pore size distribution and low crystallinity,the resulting polymer electrolytes show a high ionic conductivity up to 1.76×10^-3 S cm^-1 at room temperature and exhibit low apparent activation energy of 5.75 kJ mol^-1 for the transportation of ions.The bulk electrolyte impedances of the assembled Li [P(VDF-HFP)[LiFePO₄ polymer batteries are higher than those of batteries with liquid electrolyte,such as Li |PE| LiFePO₄ and C |PE| LiFePO₄,while the interfacial impedance and the overall impedance of selected Li |P(VDF-HFP)| LiFePO₄ batteries are lower than those of liquid ones.What is more,in the charging-discharging circling, the overall impedances of the selected Li |P(VDF-HFP)| LiFePO₄ batteries increase slower than those of the liquid ones,resulting the polymer batteries a better cycling performance.However,the rate discharging capability of the polymer lithium secondary batteries is still a little worse than that of the liquid ones.The safety performance of the assembled polymer batteries was examined on the items of thermal shock simulation during transmission,overcharging and forced discharging under abuse.The results are not worse,sometimes better,than the liquid ones.This method for polymer electrolyte preparation could reduce the use of organic solvent as well as the pollution it causes,is free from solvent removing step and its cost,making it much easier to upgrade to polymer lithium secondary battery with the technology and equipment we have got on liquid lithium ion batteries.