Electrochemical Investigation of the Effect of Inorganic Fillers in Gel Polymer Electrolytes for Li-O2 Batteries
Authors: Chamaani Amir , Safa Meer , Chawla Neha , El-Zahab Bilal 
Published: February 2020

As the world moves towards electrification of transportation and renewable recourses for grid power applications, there is an increased demand for more efficient energy storage systems. This has fueled fundamental research into newer battery chemistries beyond Li-ion batteries (BLI) [1]. Li-O2 chemistry is a typical example of BLIs, which has garnered much attention owing to its high theoretical energy density [1]. The current design of Li-O2 batteries consists of lithium anode, porous cathode open to the air, and an ionically conductive electrolyte separating these electrodes. The usage of liquid electrolyte in Li-O2 batteries poses many technical difficulties ranging from liquid electrolyte evaporation during cycling to limited choices in cell design [2]. Substituting the liquid electrolyte with a solid-state electrolyte would be a promising option to overcome the aforementioned shortcomings. Among solid-state electrolytes, gel polymer electrolytes composed of liquid electrolytes and polymer matrices have been studied due to their impressive ionic conductivity and mechanical flexibility [2-5]. As of today, limited success has been reported in gel polymer electrolyte for Li-O2 batteries [6]. The introduction of inorganic fillers to gel polymer electrolytes has been proposed as a possible method to improve the ionic conductivity, processability, and mechanical durability [2, 3]. However, little improvements have been reported for these fillers on recyclability and discharge capacity of Li-O2 batteries. This study aims to fully explore the effect of one-dimensional silicon dioxide fillers in gel polymer electrolytes. These electrochemical characterizations include cyclic voltammetry, charge/discharge cyclability, electrochemical impedance spectroscopy (EIS); in addition to scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman Spectroscopy.
The gel polymer electrolyte was prepared by mixing different ratios of electrolyte solution, 1 M bis (trifluoromethane) sulfonamide (LiTFSI) lithium salt in tetraethylene glycol dimethyl ether (TEGDME) with the UV-curable polymer ethoxylated trimethylolpropane triacrylate (ETPTA), and silicon dioxide fibers. Mixture solutions were layered on substrates and irradiated with UV light for 10 min. The curing process yielded freestanding flexible films with 150-250 microns thickness. The cathodes were prepared by coating MWCNT/ polyvinylidene fluoride (PVDF) on 0.5 inch conductive porous carbon cloth. The typical MWCNT loading was 0.5 mg per cathode. Figure 1 illustrates discharge cycle performance of gel polymer electrolyte with and without the fillers at current density of 250 mA/g-MWCNT with a fixed capacity of 500 mAh/g-MWCNT. All of the cycling tests were performed under ultra-dry O2. Introducing the filler materials increased the recyclability by approximately 2-fold. Further electrochemical analyses and investigation of source of the improvement are detailed in this study.

References:
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2- Wen-bin Lue et al., “A hybrid gel–solid-state polymer electrolyte for long-life lithium oxygen batteries”, Chem. Commun., 2015, 51, 8269-8272
3- Jin Yi et al., “Novel Stable Gel Polymer Electrolyte: Toward a High Safety and Long Life Li–Air Battery, ACS Appl. Mater. Interfaces 2015, 7, 23798−23804
4- J. Zhang et al., “Enhancement of stability for lithium oxygen batteries by employing electrolytes gelled by poly (vinylidene fluoride-co-hexafluoropropylene) and tetraethylene glycol dimethyl ether”, Electrochimica Acta, 2015, 183, 56–62
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6- Funjun Li et al., Energy Environ. Sci., “The pursuit of rechargeable solid-state Li-air batteries”, 2013, 6, 2302

Figure 1