Ionic conductivity and relaxation dynamics in plastic crystals with nearly globular molecules

Role of Bicontinuous Structure in Elastomeric Electrolytes for High-Energy Solid-State Lithium-Metal Batteries

Solid-state lithium (Li)-metal batteries (LMBs) are garnering attention as a next-generation battery technology that can surpass conventional Li-ion batteries in terms of energy density and operational safety under the condition that the issue of uncontrolled Li dendrite is resolved. In this study, various plastic crystal-embedded elastomer electrolytes (PCEEs) are investigated with different phase-separated structures, prepared by systematically adjusting the volume ratio of the phases, to elucidate the structure-property-electrochemical performance relationship of the PCEE in the LMBs. At an optimal volume ratio of elastomer phase to plastic-crystal phase (i.e., 1:1), bicontinuous-structured PCEE, consisting of efficient ion-conducting, plastic-crystal pathways with long-range connectivity within a crosslinked elastomer matrix, exhibits exceptionally high ionic conductivity (≈10^-3 S cm^-1 ) at 20 °C and excellent mechanical resilience (elongation at break ≈ 300%). A full cell featuring this optimized PCEE, a 35 µm thick Li anode, and a high loading LiNi_0.83 Mn_0.06 Co_0.11 O₂ (NMC-83) cathode delivers a high energy density of 437 Wh kg_{anode+cathode+electrolyte} ^-1 . The established structure-property-electrochemical performance relationship of the PCEE for solid-state LMBs is expected to inform the development of the elastomeric electrolytes for various electrochemical energy systems.

Phase-dependent dielectric properties and proton conduction of neopentyl glycol

Phase-dependent dielectric properties and proton conduction of neopentyl glycol (NPG), which is an organic molecular plastic crystal, were studied via variable-temperature broadband dielectric spectroscopy (BDS). Permittivity and conductivity data show the phase transformations of NPG from the crystalline state to the plastic crystalline state at 315 K and then to the molten state at 402 K across the temperature range of 293–413 K. The Vogel temperatures (T_v) fitted from the Vogel–Fulcher–Tammann (VFT) equation agree well with the values extrapolated by the Stickel plot (linearized Vogel plot). Impedance and modulus data display a separation of the −Z′′ (the imaginary part of the complex impedance) and M′′ (the imaginary part of the complex electric modulus) peaks in the crystalline phase. However, they overlap in both the plastic crystalline phase and the molten phase, indicating long-range proton conduction. In both the molten phase and the plastic crystalline phase, the temperature dependence of direct current conductivity (σ_dc) obeys the VFT equation very well. While the vehicle mechanism (translational diffusion) is an intrinsic mechanism for ionic or protonic conduction in the molten phase, it is speculated that the Grotthuss mechanism also works due to the self-dissociation of NPG molecules, which are similar to water molecules. In the plastic crystalline phase, the proton hopping mechanism is most likely the underlying ion-conducting mechanism because of the rotational disorder and intrinsic defects (vacancies) of the NPG molecules. In the ordered crystalline phase, the proton conduction is presumed to follow the proton hopping mechanism as determined from the localized relaxation and the temperature dependence of σ_dc (Arrhenius behavior).

Phase-dependent dielectric properties and proton conduction of neopentyl glycol (NPG) are studied systematically over a wide temperature range via broadband dielectric spectroscopy.