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.

A perturbation solution to the full Poisson–Nernst–Planck equations yields an asymmetric rectified electric field

We derive a perturbation solution to the one-dimensional Poisson–Nernst–Planck (PNP) equations between parallel electrodes under oscillatory polarization for arbitrary ionic mobilities and valences.

EFFECT OF VOLTAGE ON TIO2 NANOTUBES FORMATION IN ETHYLENE GLYCOL SOLUTION

The crystalline phase of the TiO2 nanotubes without further heat treatment were studied. The TiO2 nanotube arrays were produced by anodization of Ti foil at three different voltage; 10, 40, and 60 V in a bath with electrolytes composed of ethylene glycol (EG), ammonium fluoride (NH4F), and hydrogen peroxide (H2O2). The H2O2 is a strong oxidizing agent which was used as oxygen provider to increase the oxidation rate for synthesizing highly ordered and smooth TiO2 nanotubes. Anodization at voltage greater than 10 V leads to the formation of tubular structure where higher anodization voltage (~ 60 V) yield to larger tube diameter (~ 180 nm). Crystallinity of the nanotubes is improved as the voltage was increased. The transformation of amorphous to anatase can be obtained for as anodized TiO2 without any heat treatment. The Raman spectra results show the anodization at 40 V and 60 V gives anatase peak in which confirms the crystalline phase. The stabilization of the crystalline phase is due to the oxygen vacancies and ionic mobilities during the anodization at high voltage.