Kinetics of Intercalation and Deintercalation

16(c) sites, so as to avoid the repulsive interaction between lithium ions that increases the ensemble energy of the lattice. 

As noted in Section 5.2.1, most thermodynamic approaches to lithium intercalation have been focused on the analysis of the chemical potential of lithium ions, under the assumption that the chemical potential of electrons is constant in the metallic intercalation compounds. When the electrons generated by the intercalation reaction are localized, however, the compound remains semi-conducting as intercalation proceeds. In this case, it is necessary also to take into account the coulombic interaction between electrons and ions. 

In order to consider the contribution of electrons to the chemical potential of intercalation compounds, several groups have applied an ah initio or first principles calculation method to analyze the thermodynamics of lithium intercalation [37—44]. 

A typical ab initio (first principles) calculation for lithium intercalation consists of two steps (i) energy calculation at 0 K to determine the ground states and relative energy difference between crystal structures and (ii) the construction and calculation of a free energy model to determine the phase stability at non-zero temperature. Dahn ef al. [37], Ceder ef al. [38] and Benco ef al. [41] all reported that the electrode potentials of transition metal oxides could be very well predicted by this method. In addition, Ceder ef al. constructed (on a theoretical basis) the phase diagram of IiCoO2 [40, 42, 

However, various types of anomalous behavior of lithium transport have been 

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The kinetics of intercalation and deintercalation of alkali metal ions were investigated in pressure-jump experiments while monitoring the electrical conductivity of the samples (32). These studies indicate biphasic kinetics whose magnitudes are in milliseconds the rates of the fast and slow components increased with increased concentrations of the metal ions. The forward and reverse rates depend on the interlayer distances, and the fast and slow components have been attributed to the ingress of ions into the galleries and interlayer diffusion, respectively. Similar biphasic kinetics on millisecond-second time scales were also observed in pressure-jump experiments for the deprotonation-reprotonation of a-ZrP (33). In the latter case, the slow and fast components have been attributed to deprotonation from the surface and from the interlayer regions of the solid, respectively. 

Apart from the work toward practical lithium batteries, two new areas of theoretical electrochemistry research were initiated in this context. The first is the mechanism of passivation of highly active metals (such as lithium) in solutions involving organic solvents and strong inorganic oxidizers (such as thionyl chloride). The creation of lithium power sources has only been possible because of the specific character of lithium passivation. The second area is the thermodynamics, mechanism, and kinetics of electrochemical incorporation (intercalation and deintercalation) of various ions into matrix structures of various solid compounds. In most lithium power sources, such processes occur at the positive electrode, but in some of them they occur at the negative electrode as well. 

Chemical relaxation methods can be used to determine mechanisms of reactions of ions at the mineral/water interface. In this paper, a review of chemical relaxation studies of adsorption/desorption kinetics of inorganic ions at the metal oxide/aqueous interface is presented. Plausible mechanisms based on the triple layer surface complexation model are discussed. Relaxation kinetic studies of the intercalation/ deintercalation of organic and inorganic ions in layered, cage-structured, and channel-structured minerals are also reviewed. In the intercalation studies, plausible mechanisms based on ion-exchange and adsorption/desorption reactions are presented steric and chemical properties of the solute and interlayered compounds are shown to influence the reaction rates. We also discuss the elementary reaction steps which are important in the stereoselective and reactive properties of interlayered compounds. 

The fast reactions of ions between aqueous and mineral phases have been studied extensively in a variety of fields including colloidal chemistry, geochemistry, environmental engineering, soil science, and catalysis (1-6). Various experimental approaches and techniques have been utilized to address the questions of interest in any given field as this volume exemplifies. Recently, chemical relaxation techniques have been applied to study the kinetics of interaction of ions with minerals in aqueous suspension (2). These methods allow mechanistic information to be obtained for elementary processes which occur rapidly, e.g., for processes which occur within seconds to as fast as nanoseconds (j0. Many important phenomena can be studied including adsorption/desorption reactions of ions at electri fied interfaces and intercalation/deintercalation of ions with minerals having unique interlayer structure. 

In this respect, this chapter details the fundamentals and most important advances in the research activities on lithium intercalation into and deintercalation from transition metals oxides and carbonaceous materials, especially from thermodynamic and kinetic points of view, including methodological overviews. The thermodynamics of lithium intercalation/deintercalation is first introduced with respect to a lattice gas model with various approximations, after which the kinetics of lithium intercalation/deintercalation are described in terms of a cell-impedance-controlled model. Finally, some experimental methods which have been widely used to explore the thermodynamics and kinetics of lithium intercalation/deintercalation are briefly overviewed. 

In this chapter we have summarized the fundamentals and recent advances in thermodynamic and kinetic approaches to lithium intercalation into, and deintercalation from, transition metals oxides and carbonaceous materials, and have also provided an overview of the major experimental techniques. First, the thermodynamics oflithium intercalation/deintercalation based on the lattice gas model with various approximations was analyzed. Lithium intercalation/deintercalation involving phase transformations, such as order-disorder transition or two-phase coexistence caused by strong interaction oflithium ions in the solid electrode, was clearly explained based on the lattice gas model, with the aid of computational methods. 

Finally, a brief overview was presented of important experimental approaches, including GITT, EMF-temperature measurement, EIS and PCT, for investigating lithium intercalation/deintercalation. In this way, it is possible to determine - on an experimental basis - thermodynamic properties such as electrode potential, chemical potential, enthalpy and entropy, as well as kinetic parameters such as the diffusion coefficients of lithium ion in the solid electrode. The PCT technique, when aided by computational methods, represents the most powerful tool for determining the kinetics of lithium intercalation/deintercalation when lithium transport cannot be simply explained based on a conventional, diffusion-controlled model. 

In this chapter, the authors focused on three fundamental aspects of electrochemical hthium intercalation, ie. intercalation/deintercalation mechanisms, kinetics, and surface film formation. Since the commercialization if 1991, much effort has been devoted to improve the performance of LEBs, and actually the capacity of 18650-fype cells has incrcased to about 1800 mAh, which is about twice that of the cells in 1991, for the past decade. However, rapid... 

The kinetics of lithium intercalation/deintercalation has been underestimated despite of its importance for practical use. To increase the power density of EIBs, e.g. for use in hybrid electric vehicles, the diffusivity of lithium ion in various carbonaceous materials should be accurately evaluated, and for this purpose we need to develop a method that can precisely give the diffusivity of lithium ion not only in carbon anodes, but also in cathode materials in LIBs. As described in the text, not only the diffusivity, but also the rate of the interfacial charge-transfer reaction may he the rate-determiiting step, and further investigation is necessaiy on this issue. 

Figure 8 shows the cyclic voltammmetry of the Li4TisOi2 single electrode. The current-voltage trend reflects the previously outlined fast kinetics associated with the 1.5V electrochemical process, which involves the highly reversible Li intercalation-deintercalation process into and out the stable host structure. 

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