Conductivity and Morphology Correlations of Ionic-Liquid/Lithium-Salt/Block Copolymer Nanostructured Hybrid Electrolytes

Abstract

The most daunting challenge in solid-state polymer electrolyte membranes (PEMs) is to achieve high ionic conductivity close to that of the liquid electrolytes, while maintaining enhanced thermal and mechanical performances. The ionic conductivity in relation to the morphology of PEMs composed of diblock copolymer (polystyrene-block-poly­(ethylene oxide); PS-b-PEO), lithium salt (lithium trifluoromethanesulfonate; LiTf), and ionic liquid (1-ethyl-3-methylimidazolium trifluoromethanesulfonate; EMIMTf) is investigated. The optimized functional nanostructured PEMs are achieved with room-temperature ionic conductivities higher than a 1 mS cm–1 benchmark. The morphology of these microphase-separated electrolytes is composed of a major soft high ionic-conductive PEO/LiTf/IL matrix with minor glassy high-modulus PS nanodomains. The ionic-liquid upload in hybrid electrolytes inhibits the PEO crystallization, reduces the PEO glass transition temperature, promotes an extended PEO chain conformation, and enhances the solubilization of the non-dissociated lithium salt at the PS–PEO domain interfaces. These intrinsic properties caused by the ionic-liquid loading serve to achieve stable and robust nanostructured electrolyte membranes and can explain the achieved benchmark conductivity.

Stable Room Temperature Thermoelectric Properties in a Supramolecular Assembly of an n‐Type Naphthalene‐diimide‐based Amphiphile

“…Same films were used for the measurements of both σ and S. The nature of the curve is linear as shown in the figures. After calculating sheet resistance we obtained the σ value for the film in THF as ∼10 −7 S/cm and that in water as ∼1.6×10 −6 S/cm which are comparable to the earlier reports of n‐type NDI based molecule 2S‐trans‐PNDIT2 and PNDIT2 in pristine undoped state [41] . Room temperature power factor of cNDI‐1 is calculated to be ∼0.05×10 −5 μW/mK 2 in THF and ∼0.6×10 −5 μW/mK 2 in water.…”

Simultaneous Improvement of Ionic Conductivity and Mechanical Strength in Block Copolymer Electrolytes with Double Conductive Nanophases

“…Being different from the BCP electrolytes with single conductive phase that the microphase‐separated morphology has a remarkable influence on conductivity, [ 9,14,30–32 ] our system with double conductive phases shows a weak correlation between the conductivity and microphase‐separated structure. Because of the different regularity of the microphase‐separated structures in PPMTC 59 ‐ b ‐PEO 44 ‐1/12 and PPMTC 59 ‐ b ‐PEO 44 ‐1/3, their ionic conductivity is possibly related to the interphase structure.…”

Block Copolymer Electrolytes with Excellent Properties in a Wide Temperature Range

“…To enhance the ionic conductivity of polymer electrolytes at ambient temperature, a common route is adding plasticizers, such as organic solvents and ionic liquids (ILs). − ILs have attracted much interest because of their advantages including extremely low vapor pressures, nonflammability, excellent ionic conductivity, wide electrochemical window, and remarkable stability. , In addition, ILs have excellent affinity to PEO, which contributes to the microphase separation of PEO-based BCPs and thus the transport of the lithium ions. The morphology, electrical, and mechanical properties of several series of BCP/IL complexes have been studied for battery applications. − However, the decrease in mechanical strength at high temperatures remains to be a security risk for gel polymer electrolytes, especially because of the existence of liquid plasticizers. Thermal stability should be seriously considered in the structure design of the polymer matrix for further applications.…”