Solid-state diffusion of ions

At the same time, mechanisms of the solid-state diffusion of ions in the intercalation electrodes are numerous and more complicated than the mechanisms of surface diffusion. Crystallographic fea-... 

In contrast to the above, precipitates that adhere to the metal surface as continuous, nonporous films greatly reduce corrosion rates because the controlling mechanism becomes the slow solid-state diffusion of ions through the films. Further, if the film is a poor conductor of electrons, then the oxidation (corrosion) reaction is retarded because electrons have difficulty reaching the solution interface to enter into the cathodic reaction. 

For solid state diffusion of ions there must be good contact among the grains of the solid. If there is reaction with volatile intermediates such contact among the particles of the reactant powders is not necessary. Thus zinc ferrite is formed from zinc oxide and ferric oxide ... 

An alternative, well-studied approach to develop Na metal anode rechargeable cells is to isolate the Na electrode from the cathode via a ceramic Na ion conductor, i.e., a solid electrolyte. Such batteries are operated above the melting point of Na, thereby enhancing electrode kinetics and solid state diffusion of Na ions through the special alumina ceramic. The most commonly employed material is beta double prime alumina, which has channels permitting the facile diffusion of Na ions. 

Since the slow solid-state diffusion of Lb in the bulk of carbon may control the rate-determining step of the intercalation process and consequently affect the power density of Li -ion batteries, the chemical diffusion coefficient of Lb (Dy ) becomes a very key kinetic parameter. Several electrochemical relaxation techniques such as... 

Nanoparticulate electrode materials are considered by many as a viable solution to the limitations in the rate capability of Li-ion batteries [17-19]. The charge and discharge current rate limitations are mainly caused by slow solid-state diffusion of Li ions in the electrode materials [19,20]. Amongst the potential advantages of nanoparhcles are ... 

Calcium sulfate product layer is essentially nonporous and the difhision process through this layer is generally considered as a solid state migration of ions. The effective diffusivity values reported in the literature for the diffusion coefficient of SOi in the calcium sulfate layer ranged between lO m /s - 10 mVs and it is defined in Arrhenius form as follows ... 

Features of the impedance spectra of Fig. 3.15a may be modeled by a simple modified Randles-Ershler equivalent circuit shown in Fig. 3.15c. In this model, is the solution resistance, and is the charge-transfer resistance at the electrode/eIectrol e interface. A constant phase element (CPE) was used instead of a doublelayer capacitance to take into account the surface roughness of the particle. Qn is the insertion capacitance, and Zw is the Warbui impedance that corresponds to the solid-state diffusion of the Li-ion into the bulk anode. The Warburg element was used only for impedance data obtained at the tenth charge. The electrical components of the surface film which is likely formed on the electrode were disregarded, because no time constant related to this process could be seen in the electrochemical impedance spectroscopy (EIS) spectra. It was also checked that their inclusion in the model of Fig. 3.15c does not improve the fit. 

Hence, we suggest a simple, serial equivalent circuit analog that describes the impedance behavior of carbon electrodes as seen in Figure 12. It contains a Voight-type analog in series with R-C, which reflects the charge transfer, a potential-dependent Warburg -type element (solid state diffusion of Li-ions), and, finally, a capacitive potential-dependent element that reflects the accumulation of lithium. This relatively simple model has already been discussed in depth [105-107]. 

Li insertion processes into the most important cathode materials for Li-ion batteries, namely LiCoOj, LiNi02, and LiMn204. have several important denominators. Li intercalation into these host materials occur via phase transitions [195], and include the obvious necessary stage of solid state diffusion of Li-ions inside the active mass. Figure 19 demonstrates some aspects of the similar electroanalytical response of LiCo02, LiNi02, and... 

In most cases the study of equilibria between solid solutions and aqueous solutions containing their ions is extremely difficult, since solid state diffusion is virtually absent at ordinary temperatures. Most ionic solid solutions can be made homogeneous only at temperatures above 500°C, where solid state diffusion is relatively fast. 

The immobilization of dissolved chemical species by adsorption and ion exchange onto mineral surfaces is an important process affecting both natural and environmentally perturbed geochemical systems. However, sorption of even chemically simple alkali elements such as Cs and Sr onto common rocks often does not achieve equilibrium nor is experimentally reversible (l). Penetration or diffusion of sorbed species into the underlying matrix has been proposed as a concurrent non-equilibration process (2). However, matrix or solid state diffusion is most often considered extremely slow at ambient temperature based on extrapolated data from high tem-... 

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