Microscopic theory of ionic motion in crystals

The drive towards an electricity based economy and emerging green technologies has resulted in a tremendous push to create safer and more efficient energy storage devices.1–3 The development of solid-state batteries is a major effort in this direction4,5. Unlike the case of a traditional electrochemical apparatus, in solid-state batteries ions move through a solid crystalline electrolyte. Ionic motion is thus intimately linked to the condensed matter description of the system – that is, the periodic electronic and ionic properties of the crystal - and is not adequately described by the existing electrochemical tenet. In the present article, we propose a microscopic, first-principles, description of the ionic conduction in crystals. This allows us to understand the ideal characteristics of materials for ionic conduction in general, and for solid-electrolyte applications in particular. Using ab initio calculations, we show that our formalism results in ionic mobilities consistent with experiments for several materials. Our work opens the possibility for the development of solid electrolytes based on fundamental physical principles rather than empirical descriptions of the underlying processes.

Photoinduced ion-redistribution in CH3NH3PbI3 perovskite solar cells

We use photoinduced absorption spectroscopy (PAS) to study the ionic motion in CH3NH3PbI3 perovskite solar cells, consisting of indium tin oxide (ITO)/NiOx/perovskite/phenyl-C61-butyric-acid–methyl ester (PCBM)/aluminum-doped zinc oxide (AZO)/ITO.

Apprehending the effects of mechanical deformations in cardiac electrophysiology: A homogenization approach

We follow a formal homogenization approach to investigate the effects of mechanical deformations in electrophysiology models relying on a bidomain description of ionic motion at the microscopic level. To that purpose, we extend these microscopic equations to take into account the mechanical deformations, and proceed by recasting the problem in the framework of classical two-scale homogenization in periodic media, and identifying the equations satisfied by the first coefficients in the formal expansions. The homogenized equations reveal some interesting effects related to the microstructure — and associated with a specific cell problem to be solved to obtain the macroscopic conductivity tensors — in which mechanical deformations play a nontrivial role, i.e. they do not simply lead to a standard bidomain problem posed in the deformed configuration. We then present detailed numerical illustrations of the homogenized model with coupled cardiac electrical–mechanical simulations — all the way to ECG simulations — albeit without taking into account the abundantly-investigated effect of mechanical deformations in ionic models, in order to focus here on other effects. And in fact our numerical results indicate that these other effects are numerically of a comparable order, and therefore cannot be disregarded.

From the Potential of the Mean Force to a Quasiparticle’s Effective Potential in Narrow Ion Channels

We consider the selective permeation of ions through narrow water-filled channels in the presence of strong interaction between the ions. These interactions lead to highly correlated ionic motion, which can conveniently be described via the concept of a quasiparticle. Here, we connect the quasiparticle’s effective potential and the multi-ion potential of the mean force, found through molecular dynamics simulations, and we validate the method on an analytical toy model of the KcsA channel. Possible future applications of the method to the connection between molecular dynamical calculations and the experimentally measured current-voltage and current-concentration characteristics of the channel are discussed.

Spectroscopic elucidation of ionic motion processes in tunnel oxide-based memristive devices

Operando photoelectron spectroscopy of memristive devices indicates a reversible shift of oxygen during biasing which proceeds even after device breakdown.