Preparation and properties of polyethylene-SO₃Li/poly(vinylidene fluoride-hexafluoropropylene) lithium-ion battery separator

High-porosity and uniform-thickness composite separator was prepared by high-pressure electrospinning using polyethylene-vinyl alcohol sulfonate (EVOH-SO₃Li) and poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) as raw materials. The performance of the EVOH-SO₃Li/PVDF-HFP separator was characterized by FTIR, SEM, universal tensile tester, TGA, BMP3 electrochemical workstation and battery testing system. The test results show that the EVOH-SO₃Li/PVDF-HFP separator forms a dense three-dimensional network structure with uniform fiber thickness and uniform pore size. The porosity and liquid absorption rate of EVOH-SO₃Li/PVDF-HFP separator are 85% and 437%, respectively. Compared with pure EVOH-SO₃Li separator, the maximum tensile strength of EVOH-SO₃Li/PVDF-HFP composite separator is increased from 2.17 MPa to 8.33 MPa. The initial thermal decomposition temperature also raises to 310℃. The excellent performance of electrochemical and battery is exhibited. The electrochemical stability window is increased from 5.6 V to 5.8 V, the interfacial impedance is reduced from 425.51 Ω to 115.24 Ω, and the ionic conductivity is increased from 1.592×10^-3 S/cm to 3.102×10^-3 S/cm. Lithium-ion batteries assembled with EVOH-SO₃Li/PVDF-HFP separators have a capacity retention rate of 96.65% after 100 cycles at 0.5 C discharge current.