Hybrid Gel Electrolytes Derived from Keggin-Type Polyoxometalates and Imidazolium-Based Ionic Liquid with Enhanced Electrochemical Stability and Fast Ionic Conductivity

Abstract

New hybrid gel electrolytes, derived from synergetic self-assembling of inorganic polyoxometalates (POMs) and organic ionic liquid (IL) components, have been successfully prepared using Keggin-type heteropolyanions such as {PMo11VO40}4– and {PW11MoO40}3– and ionic liquid N-methyl imidazolium-1-(3-sulfonic group) propyl (MIMPS). Powder X-ray diffraction study reveals that these hybrid gels possess lamellar structure and exhibit characteristic thermo-tropic liquid-crystalline behavior. Ionic conductivity (σ) of ∼0.1 S cm–1 under ambient conduction was observed at 93 °C for [MIMPS]4PMo11VO40 (IL-PMo11V) and [MIMPS]3PW11MoO40 (IL-PW11Mo) hybrid gels. The electrochemical stability window (ESW) of IL-PMo11V and IL-PW11Mo seem to be about 2 and 4 V, respectively, at room temperature. The POM-based IL gel electrolytes show super ionic conductivity and high ESW compared to other known IL-based electrolytes, including 1-dodecyl-3-methylimidazolium-bis(pentafluoro-ethylsolfonyl)imide (σ = 0.003 S cm–1 at 94 °C, ESW = 3.5 V), 1-dodecylimidazolium-bis(pentafluoro-ethylsolfonyl)imide (σ = 0.002 S cm–1 at 94 °C, ESW = 3 V), SiO2/1-methy-3-propylpiperidinium/bis(trifluoro methanesulphonyl)imide (σ = 0.014 S cm–1 at 85 °C, ESW = 1.5 V), and 1-ethyl-3-methylimidazolium tetracyanoborate/poly(vinylidene fluride-co-hexafluoropropylene (σ = 0.027 S cm–1 at 90 °C, ESW = 3.8 V).