Lithium anomalous behavior

If a complete cell is charged to, e.g., 4.1 V, then the potential Z carbon of the fully lithiated negative electrode will be about 0.1 V vs. Li/Li+. Therefore, the potential Eoxiie of the fully charged positive electrode in this example will be 4.2 V vs. Li/Li+. Needless to say that this trivial relationship must be remembered when data for half cells (vs. metallic lithium) are compared to the data for complete cells. An important consequence of this trivial relationship is the potential excursion of the counterelectrode in the case of an anomalous behavior of the carbon electrode (and vice versa). Imagine that, in the previous example the potential of the carbon would shift to 0.3 V vs. Li/Li+ due to a malfunction of the carbon electrode. If the end-of-charge voltage of the complete cell would be the same, namely 4.1V, then the potential of the positive electrode would be 4.4 V vs. Li/Li+. In such a case, the safety of the entire cell could be compromised. 

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

However, various kinds of anomalous behavior of lithium transport have been reported in many current transients (CTs) and voltammetric curves obtained with a number of transition metal oxides and carbonaceous materials. In spite of the fact that many researchers... 

This Chapter discusses lithium transport through transition metal oxides and carbonaceous material (graphite) during CT experiments. The structure of this review is as follows in Section II, the conventional and modified diffusion control models for explaining the CTs are briefly summarized. Typical experimental CTs from transition metal oxides and carbonaceous material (graphite) are presented and then several anomalous behaviors in these curves are pointed out in Section... 

The issue of later behavioral teratogenesis was studied in 60 lithium children (whose mothers took lithium when pregnant) as compared with 57 normal siblings. Reassuringly, the incidence of anomalous developmental disorders was essentially equal ( 340). 

Lithium has some chemical behavior that resembles the chemistry of Mg. Anomalous properties of Li result mainly from the small size of the atom and the ion the polarization power of Li+ is the greatest of all the alkali metal ions and leads to a singularly great tendency toward solvation and covalent bond formation. There is also evidence to suggest that lithium bonds comparable with hydrogen bonds exist in, e.g., H—F---Li—F and (LiF),.1... 

Although normal Arrhenius behavior was observed for k, anomalous increases of k with decreasing temperature were observed in polar solvents such as THF and dimethoxyethane (glyme) [97-99]. These results have been explained in terms of a temperature-dependent equilibrium between contact and solvent-separated ion pairs as shown in Scheme 7.13. This equilibrium shifts from the less reactive contact ion pairs k ) to the much more reactive solvent-separated ion pairs k ) as temperature is decreased because the contribution from the unfavorable (negative) entropy of dissociation (TAS /g) decreases and the enthalpy of dissociation (AH / ) is negative. The values of k and k are not very dependent upon solvent, but the equilibrium constants are very dependent on the polarity of the solvent (Table 7.2). It is noteworthy that the reactivity of the solvent-separated ion pairs approaches that of the free ions. These results also provide a rationalization for the effect of counterion on kj. Smaller cations such as lithium interact more strongly with solvent and form significant amounts of more reactive, solvent-separated ion pairs. 

Pyun et al. started " their exploration of the anomalous current response with the CTs obtained from Lii.sCoOj which is the cathode material of almost all commercially available rechargeable lithium batteries today. They reported that the CTs obtained from U1.SC0O2 composite and thin fitm " electrodes hardly exhibit a typical trend of diffusion controlled lithium transport, i. e. Cottrell behavior. Furthermore, they have found that the current-potential relation obeys Ohm s law during the CT experiments. They thus suggested that lithium transport at the interface of the electrode and the electrolyte is mainly limited by the internal cell resistance, and not by lithium diffusion in the bulk electrode. This concept is called the cell-impedance controlled lithium transport. 

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