Preparation And Study Of The PVDF/TPU/PPC Based Gel Polymer Electrolytes For Lithium Ion Battery

The common lithium ion battery has many advantages,such as high energy density,high output voltage and power,small self discharge,wide working temperature range,no memory effect and friendly environment.But it also brings the problems of flatulence and leakage caused by the use of liquid organic electrolyte.The polymer lithium ion battery(PLIB)containing the polymer electrolyte not only owns these many advantages of the common lithium ion battery,but also overcomes the problems of the common lithium ion battery.Polymer lithium ion batteries have been known as the next generation of lithium ion batteries because of the unique advantages of thinning,arbitrary area and arbitrary shape.As the core part of PLIB,polymer electrolytes play a key role in its performance.Getting the polymer electrolytes with good pore structure,excellent mechanical properties and electrochemical properties,is the core technology of PLIB.We use the poly(vinylidene fluoride)(PVDF)with the best comprehensive performance,the thermoplastic polyurethane(TPU)with excellent mechanical properties and the poly(propylene carbonate)(PPC)with high liquid electrolyte absorption as the matrix materials in this paper.The electrospun technology is used to prepare the PVDF/TPU/PPC(PTC)based three-component gel polymer electrolytes with excellent mechanical properties and electrochemical properties.The main contents are as follows:(1)The PTC,PVDF/TPU,PVDF/PPC,pure PVDF and pure TPU based nanofibrous films are prepared by the electrospinning technology.The morphology,mechanical properties,thermal stability and other properties of the nanofibrous films are measured after drying.Then,in the glove box,1 M LiPF6-EC/DMC(1:1,v/v)liquid electrolyte is added to five kinds of electrospun films to activate them to GPEs.Five kinds of GPEs and the Clegard 2400 separator are assembled into the blocking batteries and the button cells respectively.Their ionic conductivities and constant current charge-discharge capacities are tested at room temperature,and the results are compared.It is found that the three-component PTC based GPEs possess the best physical and electrochemical properties.(2)Five kinds of PTC blend solutions with different concentrations are first prepared,and the fiber films are prepared by the electrospinning technology.The physical properties of the films are characterized,such as porosity,thermal stability and mechanical properties.After five PTC based electrospun films with different concentrations are activated to GPEs,we test their electrochemical properties.When the concentration of the spinning solution is 12%,it is found that the morphology and the thermal stability of the electrospun film are the best.It shows the high tensile strength of 9.9 MPa and the maximum elongation of 110.8%.The ionic conductivity of its corresponding GPE is as high as 5.32 mS cm-1,and the electrochemical stability window is up to 5.4 V at room temperature.(3)At the optimum concentration,we change the mass ratio between the three polymers(PVDF,TPU and PPC).And four kinds of GPEs with different mass ratios are prepared by the electrospinning technique.The morphology test,physical property test and electrochemical performance test are also carried out.It is found that the PTC(4:1:1,wt%)electrospun film has the best physical properties.When the GPEs,lithium and LiFePO4 cathode material are assembled into button batteries,the cell containing the GPE(4:1:1)shows a high initial charge capacity of 165.8 mAh g-1 and a high initial discharge capacity of 165.1 mAh g-1,and the battery still delivers a discharge capacity of 159.4 mAh g-1 after 50 cycles,with the capacity retention rate as high as 96.2%.It shows excellent cycle stability and is more suitable for lithium ion rechargeable batteries.