Preparation And Study Of Novel High-performance Electrospun TPU/PVDF Gel Polymer Electrolytes

Polymer electrolyte is the important part of lithium-ion batteries and it plays avital role in the performance for lithium-ion battery. In recent years, gel polymerelectrolyte aroused general interest. This paper aims to prepare a novel kind gelpolymer electrolyte by electrospinning technique which has high ionic conductivityand excellent mechanical properties. Study the physical and chemical properties of gelpolymer electrolytes, and investigate the cycle performances and the rate capabilitiesof gel polymer electrolyte in lithium ion polymer battery. The main contents of thisdissertation are as follows:Firstly, we chose thermoplastic polyurethane （TPU） and poly （vinylidene fluoride）（PVDF） as matrixs for gel polymer electrolytes （GPEs）. Then a novel blend-based gelpolymer electrolyte （GPE） films have been prepared with electrospinning. TheTPU/PVDF electrospun membranes are activated with a1M solution of LiClO₄inEC/PC and show a high ionic conductivity about1.6×10^-3S·cm^-1at room temperature.The electrochemical stability is at5.0V versus Li+/Li. Cycling performances ofLi/GPE/LiFePO₄cells are also performed well to test the suitability of the electrospunmembranes.Secondly, nonwoven films of composites of TPU with different proportion ofPVDF are prepared by electrospinning9wt%polymer solution at room temperature.Then GPEs are prepared by soaking the electrospun TPU/PVDF blending membranesin1M LiClO₄/ethylene carbonate （EC）/propylene carbonate （PC） for1h. The gelpolymer electrolyte （GPE） shows a maximum ionic conductivity of3.2×10^-3S·cm^-1atroom temperature and electrochemical stability up to5.0V versus Li+/Li for the1:1blend ratio of TPU:PVDF system. At the first cycle, it shows a first charge–dischargecapacity of168.9mAh·g^-1when the gel polymer electrolyte （GPE） is evaluated in aLi/PE/lithium iron phosphate （LiFePO₄） cell at0.1C-rate at25oC. TPU/PVDF （1:1,w/w） based gel polymer electrolyte is observed much more suitable than thecomposite films with other ratios for high-performance lithium rechargeable batteries.Thirdly, a series of fibrous membranes based on TPU/PVDF were prepared byelectrospinning with different concentrations of polymer solution. Then TPU/PVDFelectrospun membranes are activated with a1M solution of LiClO₄in EC/PC to formGPEs. The GPE which is prepared by electrospinning9wt%polymer solution shows ahighest ionic conductivity. Finally, gel polymer electrolyte films based on TPU/PVDF with and without insitu ceramic fillers are prepared by electrospinning9wt%polymer solution at roomtemperature. The electrospun TPU/PVDF blending membrane with in situ TiO2shows a highest ionic conductivity of4.8×10^-3S·cm^-1with electrochemical stabilityup to5.4V versus Li+/Li at room temperature and has a high tensile strength （8.7±0.3MPa） and%elongation at break （110.3±0.2）. With the superior electrochemicaland mechanical performance, it is very suitable for application in polymer lithium ionbatteries.