Li⁺ Ion Insertion in TiO₂ (Anatase). 1. Chronoamperometry on CVD Films and Nanoporous Films

Abstract

Electrochemical insertion of lithium in nanoporous and CVD samples of TiO2 (anatase) was studied by chronoamperometry. The currents following cathodic and anodic potential steps were monitored as a function of film thickness, temperature, and electrolyte concentration. The time dependence of the currents generally exhibit the behavior of a diffusion-limited process. It is demonstrated that the magnitude of the currents scales directly with the inner area of the electrodes. The potential dependence on the rate of insertion and extraction indicates that the reduction of Ti4+ and oxidation of Ti3+ is kinetically hindered. The double-layer capacitance and the adsorbate concentration at 0 V of the nanoporous structure were determined to be 30−40 μF/cm2 and 1.7−2.4 mol/cm2, respectively. The chemical diffusion coefficient at 25 °C for insertion and extraction in the nanoporous structure was 1 × 10-17 and 4 × 10-17 cm2/s, respectively. The corresponding values for the CVD samples, using the projected area, were 2 × 10-15 cm2/s for insertion and 6 × 10-15 cm2/s for extraction. The activation energy for lithium insertion and extraction was 0.35 and 0.38 eV for the nanoporous films and 0.54 and 0.78 eV for the CVD samples.

On the Supercapacitive Behaviour of Anodic Porous WO3-Based Negative Electrodes

“…It is known that the overall capacitance of a material can be also ascribed to other phenomena such as surface double layer formation or surface faradaic adsorption, and to bulk faradaic intercalation/de-intercalation reactions. The occurrence of these different mechanisms of energy storage can be identified (and differentiated from the others) by analysing the CV data at various sweep rates according to equation (3), and can be illustrated by plotting log (i) vs. log (Ѵ) as a function of potential [67,68]:…”

Synthesis, morphology and electrochemical properties of TiO2 microspheres

“…Although the microspheres of titanium dioxide, as follows from XRD and SEM data, are formed by nanocrystals, the size of the spheres themselves, as well as the diffusion path of the lithium cations from the surface of the sphere to its center are of the micron size. This may influence the properties of the electrode due to limitations caused by the Li + diffusion speed in the anatase structure, which is not so high [18,19]. Another, even more sensible explanation may be based on the insufficient permeability of the pore structure of the microspheres by the electrolyte.…”

The Fundamentals and Advances of Solid‐State Electrochemistry: Intercalation (Insertion) and Deintercalation (Extraction) in Solid‐State Electrodes

“…In most cases, the kinetic studies have been performed assuming a diffusion control concept [45][46][47][48][49][50][51][52], namely, that the diffusion of lithium in the electrode is very sluggish, whereas other reactions (including interfacial charge transfer) are too fast to affect the kinetics of lithium transport. Hence, lithium diffusion in the electrode would become a rate-controlled process of lithium intercalation.…”

“…Using Equations (5.18) and (5.19), a number of PCTs have been analyzed. The slopes of the I(t) versus t À1/2 and ln I(t) versus t curves have been determined in the initial and later stages of lithium intercalation/deintercalation, respectively, to estimate the chemical diffusivity in various lithium intercalation electrodes [45][46][47][48][49][50][51][52]. As discussed in Section 5.3, however, various types of anomalous behavior of lithium transport have been reported in PCTs measured for many transition metal oxides and carbonaceous materials [53][54][55][56][57][58][59][60][61][62][63].…”