Preparing Of Separators Made Of PET Non-woven Fabrics For Power Batteries

PET non-woven fabrics can absorb electrolyte effectively due to the three-dimensional pore structure and withstand the pierce of lithium crystal, But PET non-woven fabrics are of big fiber diameters which results in big and inhomogeneous pores. To obtain separators with high electrochemical performance and safety, PET non-woven fabrics were modified, the modifying methods including: coating PAN resin and coating core-shell structured particles. The former separators were of high ionic conductivity while the later separators were of high porosity, tensile strength and shutting down function after coating PVdF-HFP. The main researches of this article are as follows:(1) A porous separator with ionic conductivity of 2.14mS/cm was obtained by coating PAN-MA on PET non-woven fabrics: Phase inversion method was used to prepare(PAN-MA)-PET composite separators, and the thickness was controlled by a slit. PEGDMA was added to the solution to improve the resistance to electrolyte corrosion. PEGDMA was cross-linked by thermal induced polymerization, which was of no residual initiator. The optimum heating time and temperature of PEGDMA were studied by FT-IR, impedance and SEM, besides the effects of PEGDMA on ionic conductivity, porosity, thickness, chemical resistance and tensile strength were also studied: PEGDMA improved the ionic conductivity for the porous structure and the function of C-O chains, comprehensive performances of a PEGDMA-320 modified separator were better than a PEGDMA-550 modified separator. PEGDMA-320 improved the porosity while PEGDMA-550 decreased the porosity for the sack of PEGDMA-550 slowed down the phase inversion of PAN-MA and water. The porosity of PEGDMA-320 modified separators was higher than PEGDMA-550 modified separators, as a result, the ionic conductivity of PEGDMA-320 modified separators were higher than later one. Separators cross-linked by PEGDMA had better chemical resistance.(2) The optimum conditions for preparing core-shell particles were studied. Fumed silica were firstly grafted with γ-methacryloxypropyl trimethoxy silane to prepare SiO2(core)-PMMA(shell) particles. Methanol was used as solvent, and the result showed that reaction accelerated with the improving of temperature, 5 hours were enough under 70°C. Emulsion polymerization was used to prepare PMMA grafted particles, and PVP-K30 was added to form small and uniform particles which was tested by BI-90 plus. KH570 occupied 4.6% of the SiO2 particles after grafted, and the thermal stability of PMMA particles were improved by 10°C. To simplify the preparation process of core-shell particles and reduce the cost, TMPTA, PEGDMA-320 was used as nuclear, suspensions made of TMPTA-PMMA core-shell particles were better.(3) Separators with good comprehensive performances were made by core-shell particles and PVdF-HFP. Core-shell particles were dip-coated firstly, core-shell structured particles provided a rough surface to adhere for PVdF-HFP after strengthened by PEGDMA-320, which was reflected by tensile strength. PVdF-HFP shut down at high temperature. Above all, a separator with high ionic conductivity(0.94mS/cm), high porosity(49.3%), high stability at 160°C and tensile strength of 43.5MPa,thickness of 24μm and low cost was obtained. TMPTA-PMMA core-shell structured particles modified separators had worse performances than SiO2-PMMA core-shell structured particles modified separators, the ionic conductivity was 0.62mS/cm.