A gel polymer electrolyte with Al2O3 nanofibers skeleton for lithium—sulfur batteries

Abstract

As a promising secondary battery system, lithium—sulfur (Li—S) batteries have attracted extensive attention due to their high energy density. However, the development of Li—S batteries is hindered by the detrimental shuttling of soluble lithium polysulfides (LiPs) in traditional liquid electrolytes. In this work, we fabricate a functional gel polymer electrolyte for Li—S batteries. This electrolyte consists of poly(vinylidene fluoride-co-hexaflfluoropropylene) (PVDF-HFP) polymer matrix and a continuous γ-Al2O3 three-dimensional skeleton with structural and thermal stability. PVDF-HFP offers lithium-ion transport pathways and equips the electrolyte with flexibility, whereas the inorganic γ-Al2O3 skeleton as Lewis acid can suppress the shuttling of LiPs through strong Lewis acid-base interactions between γ-Al2O3 and LiPs. In addition, γ-Al2O3 has an effect on the Lewis base of bis(trifluoromethanesulphony)imide anion, facilitating the dissociation of lithium salts and leading to a high lithium-ion transference number. Moreover, γ-Al2O3 can improve the ionic conductivity by reacting with LiF to partly form the lithium-ion conductors of LiAlO2 and Li3AlF6. Benefiting from the synergistic effect of PVDF-HFP and γ-Al2O3, Li—S cells with this gel polymer electrolyte present improved cycling stability in terms of cathode capacity retention and anode morphology. This work provides a promising strategy for fabricating multifunctional gel electrolytes for high-energy Li—S batteries.