Hybrid gel electrolytes derived from keggin-type polyoxometalates and imidazolium-based ionic liquid with enhanced electrochemical stability and fast ionic conductivity

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).