Molecular Ionics in Supramolecular Assemblies with Channel Structures Containing Lithium Ions

Decoupling Ion Transport and Matrix Dynamics to Make High Performance Solid Polymer Electrolytes

Transport of ions through solid polymeric electrolytes (SPEs) involves a complicated interplay of ion solvation, ion-ion interactions, ion-polymer interactions, and free volume. Nonetheless, prevailing viewpoints on the subject promote a significantly simplified picture, likening ion transport in a polymer to that in an unstructured fluid at low solute concentrations. Although this idealized liquid transport model has been successful in guiding the design of homogeneous electrolytes, structured electrolytes provide a promising alternate route to achieve high ionic conductivity and selectivity. In this perspective, we begin by describing the physical origins of the idealized liquid transport mechanism and then proceed to examine known cases of decoupling between the matrix dynamics and ionic transport in SPEs. Specifically we discuss conditions for "decoupled" mobility that include a highly polar electrolyte environment, a percolated path of free volume elements (either through structured or unstructured channels), high ion concentrations, and labile ion-electrolyte interactions. Finally, we proceed to reflect on the potential of these mechanisms to promote multivalent ion conductivity and the need for research into the interfacial properties of solid polymer electrolytes as well as their performance at elevated potentials.

Organic Crystalline Solid Electrolytes with High Mg-Ion Conductivity Composed of Nonflammable Ionic Liquid Analogs and Mg(TFSA)2

The development of solid electrolytes with Mg-ion conductivity at room temperature is an important issue to achieve all-solid magnesium batteries. We focus on organic ionic crystals with Mg-ion conduction paths in addition to nonflammable and nonvolatile features as an innovative candidate of solid electrolytes with Mg-ion conductivity. Herein, we show the development of novel organic ionic crystals, [N(CH₃)_4-n(CH₂CH₃)_n][Mg{N(SO₂CF₃)₂}₃] (n = 0 or 2), using analogs of ionic liquids, [N(CH₃)₄][N(SO₂CF₃)₂] (N₁₁₁₁TFSA) and [N(CH₃)₂(CH₂CH₃)₂][N(SO₂CF₃)₂] (N₁₁₂₂TFSA), and magnesium salt, Mg{N(SO₂CF₃)₂}₂ (Mg(TFSA)₂). We also report the crystal structures of the obtained crystals and the high Mg-ion conductivity of 10^-4 S cm^-1 under mild conditions of 80 °C in the solid state. These results indicate that organic ionic crystals with ion conduction paths have significant potential as safe solid electrolytes and provide insights into developing innovative Mg-ion conductors.

High Li-Ion Conductivity in Li{N(SO2F)2}(NCCH2CH2CN)2 Molecular Crystal

There is an urgent need to develop solid electrolytes based on organic molecular crystals for application in energy devices. However, the quest for molecular crystals with high Li-ion conductivity is still in its infancy. In this study, the high Li-ion conductivity of a Li{N(SO₂F)₂}(NCCH₂CH₂CN)₂ molecular crystal is reported. The crystal shows a Li-ion conductivity of 1 × 10^-4 S cm^-1 at 30 °C and 1 × 10^-5 S cm^-1 at -20 °C, with a low activation energy of 28 kJ mol^-1. The conductivity at 30 °C is one of the highest values attainable by molecular crystals, whereas that at -20 °C is approximately 2 orders of magnitude higher than previously reported values. Furthermore, the all-solid-state Li-battery fabricated using this solid electrolyte demonstrates stable cycling, thereby maintaining 90% of the initial capacity after 100 charge-discharge cycles. The finding of high Li-ion conductivity in molecular crystals paves the way for their application in all-solid-state Li-batteries.

Synthesis of an Adduct-Type Organic Ionic Crystal with Solid-State Ionic Conductivity from A Thiocyanate-Based Ionic Liquid and B(C6F5)3

We synthesized the novel adduct-type organic ionic crystal [C3mim][SCN·B(C6F5)3] (1) by the reaction of 1–methyl–3–propylimidazolium thiocyanate ([C3mim][SCN]), which is a room temperature ionic liquid, and B(C6F5)3, a bulky Lewis acid. The formation of a coordinative B–N bond between the SCN anion and the B(C6F5)3 in 1 was revealed by single-crystal X-ray diffractometry. We showed that 1 displays ionic conductivity in the crystalline state and that doping 1 with sodium thiocyanate and B(C6F5)3 results in a dramatic increase in ionic conductivity compared to that of 1.