Abstract
Ionic liquid (IL) properties, such as high ionic conductivity under ambient conditions combined with nontoxicity and nonflammability, make them important materials for future technologies. Despite high ion conductivity desired for battery applications, cation transport numbers in ILs are not sufficient enough to attain high power density batteries. Thus, developing novel approaches directed toward improvement of cation transport properties is required for the application of ILs in energy-storing devices. In this effort, we used various experimental techniques to demonstrate that the strategy of mixing ILs with ultrasmall (1.8 nm) nanoparticles (NPs) resulted in melt-processable composites with improved transport numbers for cations at room temperature. This significant enhancement in the transport number was attributed to the specific chemistry of NPs exhibiting a weaker cation and stronger anion coordination at ambient temperature. At high temperature, significantly weakened NP–anion associations promoted a liquid-like behavior of composites, highlighting the melt-processability of these composites. These results show that designing a reversible dynamic noncovalent NP–anion association controlled by the temperature may constitute an effective strategy to control ion diffusion. Our studies provide fundamental insights into mechanisms driving the charge transport and offer practical guidance for the design of melt-processable composites with an improved cation transport number under ambient conditions.
Highlights
Ionic liquids (ILs) are materials of great importance for various energy applications because of their high ionic conductivity.[1]
Www.acsami.org the increasing distribution of segmental relaxation times of the IL in the composite that arises because of heterogeneity that scales with an increase in particle concentration
The dielectric data of pure IL and IL−octaaminophenyl silsesquioxane (OAPS) composites were gathered over a wide temperature range
Summary
Ionic liquids (ILs) are materials of great importance for various energy applications because of their high ionic conductivity.[1]. A small contribution of the cation to conductivity creates a significant gradient in ion concentration that leads to increased cell polarization, thereby reducing the power capability of a battery.[3,4] To advance the application of ILs in energy-harvesting and storage devices, the development of novel approaches leading to high cation transport numbers is desired. The strategies toward increasing t+ are related to anion immobilization through covalent or noncovalent interactions with polymers[4] and/or various ceramics.[5−12] Covalently attaching anions to polymers results in the transport number of cations close to unity,[4] yielding single-ion-conductive materials. Only a few examples of such materials[13,14] are available in the literature
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