Reversible specific charge

Figure 7. First- and second- cycle constant-current charge/discharge curves of graphite Timrex KS44 in LiN(S02CF3)2/ethylene carbonate/dimethyl carbonate as the electrolyte (CilT irreversible specific charge Crev =reversible specific charge) [2J.

The latter, so-called "high specific charge" or "high capacity", carbons have received considerable attention in recent research and development. Usually they are synthesized at rather low temperatures, ranging from -500 to -1000 °C, and can exhibit reversible specific charges from -400 to -2000 Ah kg (x= -1.2 to -5 in... 

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. 

Figure 11. Schematic drawing of some mechanisms for reversible lithium storage in "high-specific-charge" lithiated carbons as proposed in Refs, (a) [216], (b) [218, (c) [224], (d) [230], (e) [41], and (f) [238]. The latter figure has been reproduced with kind permission of Kureha Chemical Industry Co., Ltd.

It should also be noted that in those methods in which charged particles are deposited on an electrode under the influence of an electrostatic field, there exists the possibility of reverse contact charging of the particle if the particle is sufficiently conductive. Such contact charging can cause the particle to oscillate between the electrodes, carrying current from one to the other. This phenomenon has often been observed in connection with electrostatic printing and has been specifically reported by Cho (C2). Such a transfer of particles would result in a transfer of charge to the electrodes far in excess... 

It is convenient to adopt the terminology of Miller et al. (1977) and define a center to be an electron trap if e e p and a hole trap if the reverse is true. In addition, a minority-carrier trap is one for which the emission rate of minority carriers emin is greater than that of majority carriers emaj, whereas for majority-carrier traps emaj emin. By these definitions, an electron trap is a majority-carrier trap in an n-type region and a minority-carrier trap in p-type. Note that these definitions are independent of whether the trap is a donor or an acceptor, terms that imply a specific charge state of the center (Pantelides, 1978). Because the emission rates are thermally activated [Eq. (9)], an electron trap usually lies in the upper half of the band gap and a hole trap in the lower. 

Similarities between reversal of charge spectra for colloids with solubility sequences of salts in bulk solution have been indicated (7, 37)— for example, for salts possessing different cations but the same anion, the solubility sequence of the phosphates is K+ > Na+ > Li+, while it is the reverse for the sulfates (7, 30). In view of this similarity, it is natural to introduce this fact as another possible link to explain the reversal of the specific cation effect in tt-A isotherms, though the precise relationship to monolayers is not clear at this time. 

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