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Abstract. Polymer electrolyte membranes (PEMs) are potentially applicable in lithium-ion batteries with high safety, low cost and good performance. Here, to take advantages of ionic conductivity and selectivity of borate ester-functionalized small molecules as well as structural properties of polymer nanocomposite, a strategy of immobilizing as-synthesized polyethylene glycol-borate ester/lithium fluoride (B-PEG/LiF) in graphene oxide/poly(vinyl alcohol) (GO/PVA) to prepare a PEM is put forward. Chemical structure of the PEM is firstly characterized by ^sup 1^H-, ^sup 11^B- and ^sup 19^F-nuclear magnetic resonance spectra, and Fourier transform infrared spectroscopy spectra, respectively, and then is further investigated under consideration of the interactions among PVA, B-PEG and LiF components. The immobilization of B-PEG/LiF in PVA-based structure is confirmed. As the interactions within electrolyte components can be further tuned by GO, ionic conductivity (~10^sup -3^ S·m^sup -1^), lithium-ion transfer number (~0.49), and thermal (~273 °C)/electrochemical (>4 V) stabilities of the PEM can be obtained, and the feasibility of PEMs applied in a lithium-ion battery is also confirmed. It is believed that such PEM is a promising candidate as a new battery separator.
Keywords: nanocomposites, polymer electrolyte membrane, borate ester, graphene oxide, lithium-ion batteries
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1. Introduction
Polymer electrolyte membranes (PEMs) are permeable membranes for the electrolyte ions flowing between a battery's anode and cathode [1-4]. They can serve both as ionic conductors of lithium-ions (Li+) and separators with high safety, low cost and good performance when assembled into lithium-ion batteries. In contrast to traditional polyolefin separators which often own 30~50% open porosity [5], PEMs can be non-porous [6], so fabrication of PEMs can be simplified, and be cheaper, without using pore forming technologies that often require expensive processing machines and cumbersome processing route. As the ions which transport through the membranes can have a strong interaction with the polymer matrix, PEMs can have the ion-selective feature, e.g. single-ion transportation of Li+, which is beneficial to improve the performance of lithium-ion batteries [7-9]. Polymer matrix for PEMs is often chosen among PEO, PMMA, PAN, PVC, PVA, PVDF or their derivatives, since the polar groups of these polymer chains can benefit for dissolution of electrolyte salts and endow the membranes with ionic conductivity [10, 11], which can be further enhanced by the incorporation of inorganic nanoparticles (e.g....