Study On Preparation And Properties Of EVOH-SO₃Li/PVDF-HFP/NHA Lithium-ion Battery Separator

The lithium battery separator is a permeable membrane layer disposed between the anode and the cathode of the battery,the main role is to prevent short-circuit contact between positive and negative electrodes,but also can close the channel transport ion charge in the electrochemical cell of the carrier,is an important part of a liquid electrolyte battery.The separator of lithium ion batteries should have certain mechanical properties and thermal stability to cope with the problem of maintaining the integrity of the separator in high-speed winding and laminated batteries and melting of the separator at high temperature when the battery current is too high.In this paper,EVOH-SO₃Li?lithium polyethylene-vinyl alcohol sulfonate?,PVDF-HFP?polyvinylidene fluoride-hexafluoropropylene?and NHA?nano-hydroxyapatite?were blended for high voltage electrospinning.The interaction of hydrogen bonds between EVOH-SO₃Li and PVDF-HFP molecules was used to improve the mechanical properties of composite separator,and high temperature resistant bioceramic particles were also prepared.The addition of nano-hydroxyapatite could further improve the thermal properties of the composite separator and prepare a new type of EVOH-SO₃Li/PVDF-HFP/NHA composite separator material with excellent performance for lithium ion batteries.The composite separator was tested and analyzed by FTIR,SEM,universal tensile tester,TGA analyzer,BMP3electrochemical workstation and battery detection system.The results show that the EVOH-SO₃Li/PVDF-HFP composite separator forms an uniform and dense three-dimensional network structure,and the EVOH-SO₃Li/PVDF-HFP/NHA composite separator presents a three-dimensional network of dendritic shapes after adding PVDF-HFP and NHA,which improves the porosity and liquid absorption rate of the separator.Compared with the pure EVOH-SO₃Li separator,the porosity and liquid absorption rate of the EVOH-SO₃Li/PVDF-HFP/NHA composite separator are increased by 37.5%and 91.6%,respectively.The maximum tensile strength of EVOH-SO₃Li/PVDF-HFP/NHA composite separator increases from 2.01 MPa to 9.68 MPa,and the initial thermal decomposition temperature increases from 274.91?to322.33?.The composite separator can maintain good size and morphology at 200?.The excellent performance of electrochemical is also exhibited.The electrochemical stability window of the assembled lithium ion battery is 5.59 V,and the interfacial impedance is decreased to 182.24?,and the ionic conductivity is increased to2.686×10^-3 S/cm,and the lithium ion transference number is 0.51.Lithium ion battery assembled with EVOH-SO₃Li/PVDF-HFP/NHA composite separator has a capacity retention rate of 96.69%after 100 cycles at 0.5 C discharge current,the properties of EVOH-SO₃Li/PVDF-HFP/NHA composite separator are improved compared with EVOH-SO₃Li.