Study On The Preparation And Performances Of PVDF-HFP Based Gel Polymer Electrolytes

Due to the excellent safety and feasible of shape,lithium ion battery gel polymer electrolyte is widely studied by researchers.But it has low ionic conductivity,which leads to the problem of low ratio performance of lithium ion battery.And traditional prepared method of gel polymer electrolyte by phase inversion method is complicated,which seriously restricted application of gel polymer electrolyte in real life.In this paper,we improve ionic conductivity of gel polymer electrolyte for meet practical application.The one step method that we took to prepare porous gel polymer electrolyte simplifies the process of preparation and reduce the material consumption.Then doping the Fe3O4 nanorods into gel polymer electrolyte that oriented by magnetic field,which improve the physical chemical properties and electrochemical properties of the gel polymer electrolyte.Firstly,we prepare the gel polymer electrolyte of abundant pore structure by one step method.Different relative humidity affect the pore structure when preparing the membrane.Among them,the best pore structure of samples is prepared under the relative humidity of 30%,liquid absorption rate reached 160.4%,ionic conductivity reached 2.04x10-3 S/cm.Porous gel polymer electrolyte and commercial LiMn2O4 cathode both assemble the button cell which used to test.It shows good performance and cycle performance,and still possess discharge specific capacity of 71.3 mAh/g under the ratio of 3.0 C.After 40 cycles,the capacity can maintain 92.8%..Doping inorganic magnetic nanorods and oriented by magnetic field further improve the ionic conductivity.The length of α-Fe2O3 nanorods by hydrothermal synthesis is about 600 nm,around 600 nm in diameter,has good crystal type and scattered evenly.After 4h reduction in H2/Ar atmosphere,we can get the Fe3O4 nanorods which consistent with the morphology of precursors,and has a high magnetic induction intensity 75.66 emu/g.Fe3O4 nanorods were doped into gel polymer electrolyte and oriented by magnetic field.From the test results of SEM-EDS,we can see that Fe3O4 nanorods have good response to magnetic fields and orientate successfully.Composite polymer electrolyte can remain abundant and uniform pore structure.The thermal decomposition temperature of composite polymer electrolytes are at about 430 ℃,which have good ability of heat resistant.After doping Fe3O4 nanorods,the crystallinity of polymer electrolyte decreased obviously.Its contact angle reduces to 117.9°,and fluid absorption rate up to 197.8%at the same time.Electrochemical performance test on different orientation of Fe3O4 nanorods,the sample of vertical Fe3O4 nanorods orientation possess the highest ionic conductivity,reaching 3.09x1O-3 S/cm,whose activation energy for ion migration only needs 1.5373 KJ/mol.At a high charge and discharge current 3.0 C,the sample of vertical orientation of Fe3O4 nanorods possess higher discharge specific capacity than other samples,reached 80.2 mAh/g.After 40 times at 0.1 C current,it’s capacity retention is 91.6%.Compared with the inorganic nanometer materials uniform doped,inorganic nanomaterials in vertical oriented is helpful to improve their electrochemical performance,but in horizontal oriented will reduce its electrochemical performance.We uses one step method to prepare porous gel polymer electrolyte,which replace phase inversion method that consume large amounts of pore forming agent.At the same time,we found that directional orientation of inorganic nanomaterials is helpful to improve performance of gel polymer electrolyte.This article puts forward the material preparation and doping orientation method which has applied prospect not only in the field of energy storage,but also in sensors,medicine,polymer materials and other fields.