Intercalation/deintercalation time

Next let us examine the current-potential relation with increasing lithium intercalation/deintercalation time. For this purpose, the values of current at the times when various amounts of cathodic or anodic charge have passed (open symbols in Figures 9a-e) were obtained as a function of potential step. For example, in order to determine the open circle A in Figure 9(a), the cumulative charge vs. time plot is first... 

Lithium ferrous(II) phosphate (LiFeP04) is a positive electrode material for lithium-ion batteries, which, so far, has been mainly used in power lithium-ion batteries [1]. It is commonly called lithium iron(II) phosphate and is also used in fertilizers. In 1996, the Japanese NTT Corporation disclosed for the first time an olivine structured compound, A MP04 (A is an alkali metal and M a combination of Co and Fe) as a positive electrode material for lithium-ion batteries. In 1997, Prof. John B. Goodenough and his group at the University of Texas at Austin, United States, reported the characteristics of reversible lithium intercalation/deintercalation into/from LiFeP04. However, at the initial stage, this positive electrode material did not raise much attention since its electronic and ionic conductivities are very low and... 

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. 

While several hours (e.g., 7h) are required for conventional LIBs with a graphite anode and a LiFeP04 cathode for the completion of the necessary intercalation processes in one of the electrodes and deintercalation in the other electrode, the time of ion migration in lithium-cation-exchange capacitors is several minutes. Further studies are required for a more clear determination of the main mechanisms of energy storage in such PsCs. 

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. 

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