Lithium chemical diffusion

It is thus much better to measure the chemical diffusion coefficient directly. Descriptions of electrochemical methods for doing this, as well as the relevant theoretical background, can be found in the literature [33, 34]. Available data on the chemical diffusion coefficient in a number of lithium alloys are included in Table 3. 

Table 3. Data on chemical diffusion in lithium alloy phases.

Table 5. Chemical diffusion data for lithium-tin phases at 25 °C.

This concept has also been demonstrated at ambient temperature in the case of the Li-Sn-Cd system [47,48]. The composition-de-pendences of the potentials in the two binary systems at ambient temperatures are shown in Fig. 15, and the calculated phase stability diagram for this ternary system is shown in Fig. 16. It was shown that the phase Li4 4Sn, which has fast chemical diffusion for lithium, is stable at the potentials of two of the Li-Cd reconstitution reaction plateaus, and therefore can be used as a matrix phase. 

Wen CJ, Huggins RA. Chemical diffusion in intermediate phase in the lithium-silicon system. J Solid State Chem 1981 37 271-278. 

Diffusion-controlled lithium transport involves the following the system is so kinetically facile that the equilibrium concentration of lithium is quickly reached at the interface between the electrode and electrolyte at a moment of potential stepping for CT experiments. The instantaneous depletion and accumulation in the lithium concentration at the interface caused by the chemical diffusion away from and to the interface (and to and away from the bulk electrode) is completely compensated by the supply and release away from and into the electrolyte, respectively. This condition is referred to as real potentiostatic constraint at the interface between the electrode and the electrolyte. 

The chemical diffusivity of lithium ions 0 + in the transition metal oxides and graphite is taken as 10 10 cm s [13, 97-100] on the basis of scanning electron microscopy (SEM) inspections, the average radius R is estimated to be 1-10 pm. The electrochemically active area A a is calculated from the radius R, and the theoretical density of the particles considered assuming that A a is identical to the total surface area of the electrode comprised of the spherical particles. 

Ana is the electrochemical active area of the electrode Du is the chemical diffusivity of lithium L is the thickness of the electrode, and c and represent the final and initial equilibrium concentration of lithium in the electrode, respectively. 

Using Eqs. (1) and (2), a number of CTs have been analyzed. The slopes of l t)vs. (or the values of l(t) t ) and In I t) vs. t curves have been determined in the initial and later stages of lithium injection/extraction, respectively, to estimate the chemical diffusivity of lithium in the electrode. However, it has been pointed out that there is a great discrepancy between the values of the chemical diffusivity determined by the CT technique using the dijfusion control concept and those values obtained hy other electrochemical techniqnes... 

The chemical diffusivity of lithium has been estimated by curve fitting ofthe observed CTs to those CTs calculated according to Eq. (3). 

The contribution of electric field to lithium transport has been considered by a few authors. Pyun et argued on the basis of the Armand s model for the intercalation electrode that lithium deintercalation from the LiCo02 composite electrode was retarded by the electric field due to the formation of an electron-depleted space charge layer beneath the electrode/electrolyte interface. Nichina et al. estimated the chemical diffusivity of lithium in the LiCo02 film electrode from the current-time relation derived from the Nernst-Planck equation for combined lithium migration and diffusion within the electrode. 

In spite of the many efforts briefly described above and some other attempts which are not mentioned here, the atypical trajectories of CTs from various transition metal oxides and carbonaceous materials for rechargeable lithium battery, and the great difference between the chemical diffusivities determined by the CT technique and other electrochemical techniques were not clearly understood. 

The chemical diffusivity of lithium, Du, in the transition metal oxides and graphite is estimated by GITT and/or FIS. The average radius of particle R of transition metal oxides and graphite can be determined by e.g., microscopic investigation. In this review, the... 

R P. Prosini, M. Lisi, D. Zanec, and M. PasqnaU [2002] Determination of the Chemical Diffusion Coefficient of Lithium in LiFeP04, Solid State Ionics 148, 45-51. 

The chemical diffusion coefficient of the lithium ions, in a solid host lattice, is about 10 cm. s (mean value on different cathodic materials). 

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