Improved ionic conductivity and cycling stability via composite separator constructed by coating organic-modified sepiolite/PVDF layer on PP via electrospinning technology

Commercial polyolefin separators are usually encountered by the inherent shortcomings of poor wettability and thermal stability. To remedy these deficiencies, a multifunctional composite separator was prepared by coating PVDF/sepiolite layer on one side of polypropylene (PP) separator via electrospinning technology, where sepiolite was modified by vinyltriethoxysilane (VTES) to improve its dispersibility and miscibility with PVDF matrix. The effects of VTES contents on the physical and electrochemical properties of composite separator was systematically investigated. It is found that the porous structure obtained by electrospinning technology together with the introduction of VTES-modified sepiolite are confirmed to boost wettability, porosity, electrolyte uptake, ionic conductivity, Li+ ions transfer number and thermal stability of composite separator, with 10VS-PVDF/PP separator showing the optimal properties. As expected, Li|LiFePO4 battery based on 10VS-PVDF/PP separator exhibits excellent performance at high rate (115.3 mAh g−1 at 10 C) and enhanced cycle stability (97.06% after 200 cycles at 1 C). Experiment and DFT calculations confirm the adsorption of sepiolite in the electrospun layer to HF species generated during cycling, which can alleviate Fe2+ dissolution from LiFePO4 and improve the cycling performance of Li|LiFePO4 battery. The addition of VTES-modified sepiolite offers a multifunctional approach to improve the performance of separators in LIBs. [Display omitted] •Multifunctional composite separator was constructed by coating sepiolite/PVDF layer on PP via electrospinning method.•Sepiolite was modified by VTES to enhance dispersibility and miscibility with PVDF matrix.•VTES contents have an effect on the physical and electrochemical properties of composite separator.•Sepiolite can immobilize PF6- anion and absorb HF, thus enhancing electrochemical performance of LiFePO4 battery.