Understanding fast-ion conduction in solid electrolytes

The ability of some solid materials to exhibit exceptionally high ionic conductivities has been known since the observations of Michael Faraday in the nineteenth century (Faraday M. 1838 Phil. Trans. R. Soc. 90 ), yet a detailed understanding of the atomic-scale physics that gives rise to this behaviour remains an open scientific question. This theme issue collects articles from researchers working on this question of understanding fast-ion conduction in solid electrolytes. The issue opens with two perspectives, both of which discuss concepts that have been proposed as schema for understanding fast-ion conduction. The first perspective presents an overview of a series of experimental NMR studies, and uses this to frame discussion of the roles of ion–ion interactions, crystallographic disorder, low-dimensionality of crystal structures, and fast interfacial diffusion in nanocomposite materials. The second perspective reviews computational studies of halides, oxides, sulfides and hydroborates, focussing on the concept of frustration and how this can manifest in different forms in various fast-ion conductors. The issue also includes five primary research articles, each of which presents a detailed analysis of the factors that affect microscopic ion-diffusion in specific fast-ion conducting solid electrolytes, including oxide-ion conductors Gd 2 Zr 2 O 7 and Bi 4 V 2 O 11 , lithium-ion conductors Li 6 PS 5 Br and Li 3 OCl , and the prototypical fluoride-ion conductor β - PbF 2 . This article is part of the Theo Murphy meeting issue ‘Understanding fast-ion conduction in solid electrolytes’.

The Origins of Ion Conductivity in MOF-Ionic Liquids Hybrid Solid Electrolytes

Fast Li+ solid ion conductors are a key component of all-solid-state batteries, a technology currently under development. The possible use of metallic lithium as active material in solid-state batteries warrants a quantum step improvement of battery specific energy, enabling further electric vehicles application. Hereby, we report the synthesis and ion conduction properties of a new solid hybrid electrolyte based on the MIL-121 metal organic framework (MOF) structure. After an ion exchange procedure that introduces Li+ in the structure, a known quantity of a soaking electrolyte is incorporated. The soaking electrolyte is based on the EMIM-TFSI ionic liquid, thus we can classify our formulation as a MOF–ionic liquid hybrid solid electrolyte. Electrical conductivity is investigated by impedance spectroscopy and preliminary studies of ion dynamics are conducted by 7Li NMR. The field of MOF-based ion conductors remains in incipient stages of research. Our report paves the way towards the rational design of new solid-state ion conductors.