Highly lithium ion conductive, Al2O3 decorated electrospun P(VDF-TrFE) membranes for lithium ion battery separators

Abstract

Electrospun battery separators have drawn considerable attention due to their high porosity, surface area, and electrochemical performance. In this paper, a novel Al₂O₃ nanoparticle decorated poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) membrane was fabricated by the electrospinning technique. Both P(VDF-TrFE) and Al₂O₃ are well known for their excellent properties, like mechanical strength, piezoelectric nature, thermal stability etc., and the electrospun membrane was prepared by combining the excellence of these two materials. The physical properties of P(VDF-TrFE) and the influence of nanoparticles on the physical properties were evaluated by morphological, thermal, XRD and FT-IR analysis. SEM and TEM analysis shows that the nanoparticles increase the fiber diameter and are located on the surface as well as in the bulk of the fiber. XRD studies reveal that the nanoparticles were localized at the inter-planar spacing of the polymer chains. The melting temperature of P(VDF-TrFE) is increased by the addition of Al₂O₃ nanoparticles, and all the prepared membranes exhibit superior thermal and dimensional stability compared to the Celgard 2320 separator. The prepared membranes were explored as a lithium-ion battery separator by characterizing their wettability, electrolyte uptake, % porosity, ionic conductivity and charge–discharge performance. The high porosity (>80%) of electrospun P(VDF-TrFE) and the Lewis acid–base character of Al₂O₃ nanoparticles help to improve the ionic conductivity from 4.0 to 5.8 mS cm⁻¹ at room temperature and the electrolyte uptake from 280 to 375%. Finally, 2032 type coin cells (Li/separator/LiFePO₄) were fabricated using P(VDF-TrFE) nanocomposites and the fabricated cell delivered a discharge capacity of 154 mA h g⁻¹, which is superior to the Celgard 2320 separator (120 mA h g⁻¹). This work proves that the Al₂O₃ incorporated electrospun P(VDF-TrFE) membrane is a promising candidate to act as a lithium-ion battery separator.