Reversible and Irreversible Specific Charge

The excess charge consumed in the first cycle is generally ascribed to SEI formation and corrosion-like reactions of Li C6[19, 66, 118-120]. Like metallic lithium and Li-rich Li alloys, lithiated graphites, and more generally lithiated carbons are thermodynamically unstable in all known electrolytes, and therefore the surfaces which are exposed to the electrolyte have to be kinetically protected by SEI films (see Chapter III, Sec.6). Neverthe- 

The extent of the irreversible charge losses due to film formation depends to a first approximation on the surface area of the lithiated carbon which is wetted by the electrolyte [36, 66, 120-124]. Electrode manufacturing parameters influencing the pore size distribution within the electrode [36, 121, 124, 125] and the coverage of the individual particles by a binder [124, 126] have an additional influence on the carbon electrode surface exposed to the electro- 

Besides the irreversible charge loss caused by electrolyte decomposition, several authors claim that the following reactions are also responsible for (additional) irreversible charge losses  

In order to improve the electrochemical performance with respect to lower irreversible capacity losses, several attempts have been made to modify the carbon surface. Here the work of Peled s [38, 130-132] and Takamura s groups [133-138] deserves mention. A more detailed discussion can be found Chapter III, Sec. 6. 

and (ii) on the composition of the electrolyte, which is discussed in this section. 

Experimental constant current charge/ discharge curves for Li intercalation/de-intercalation into/out of graphite clearly prove the staging phenomenon (Fig. 7). Nevertheless, there are no sharp discontinuities between the two-phase regions because (i) the packing density of Li Cf, varies slightly (a phase width exists), and 

Since film formation on Li C is associated with the irreversible consumption of material (lithium and electrolyte), the corresponding charge loss is frequently called irreversible specific charge or irreversible capacity . Reversible lithium intercalation, on the other hand, is called reversible specific charge or reversible capacity . The losses have to be minimized because the losses of charge and of lithium are detrimental to the specific energy of the whole cell and, moreover, increase the material expenses because of the necessary excess of costly cathode material which is the lithium source in a lithium-ion cell after cell assembly. 

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