Intercalation/deintercalation cycle

Figure 16. Voltage profiles for the first two lithium intercalation/deintercalation cycles realized on graphite anode in t-BC/EMC and c-BC/EMC solutions of 1.0 M LiPEe. (Reproduced with permission from ref 255 (Eigure 7). Copyright 2000 The Electrochemical Society.)...

As discussed in the next section, lithiated carbon electrodes are covered with surface films that influence and, in some cases, determine their electrochemical behavior (in terms of stability and reversibility). They are formed during the first intercalation process of the pristine materials, and their formation involves an irreversible consumption of charge that depends on the surface area of the carbons. This irreversible loss of capacity during the first intercalation/deintercalation cycle is common to all carbonaceous materials. However, several hard, disordered carbons exhibit additional irreversibility during the first cycle, in addition to that related to surface reactions with solution species and film formation. This additional irreversibility relates to consumption of lithium at sites of the disordered carbon, from which it cannot be electrochemically removed [346-351],... 

Residue compounds of graphite are prepared from the corresponding lamellar compounds by partial deintercalation. This process ultimately yields residue compounds via more dilute lamellar compounds. Figure 1 shows a typical composition isotherm for an intercalation-deintercalation cycle. Lamellar compounds that form spontaneously by action of the intercalant on graphite can be deintercalated simply by thermal or in vacuo treatment deintercalation of graphite salts requires a reductant. 

The one main disadvantage of electrochemical as compared to chemical preparations is the difficulty in scaling up since, due to transport limitations, the size of the electrode cannot be increased as desired. This is especially troublesome with poorly oriented graphite, since the mobility of ions in graphite compounds, and consequently the rate of electrochemical intercalation and deintercalation reactions, decreases with decreasing order of the host lattice. The reactivity of poorly oriented material, however, can be increased considerably by prior electrochemical intercalation-deintercalation cycles. ... 

Finally, a third possible effect in causing the capacity decline is the isolation of some of the IC electrode particles within the composite positive membrane, due to losses of electrical contact resulting from the repeated volume contractions and expansions associated with the intercalation-deintercalation cycles. 

Figure 26 FTIR spectra measured from graphite electrodes after being treated in BL-LiAsF6 solution under argon and under COj, as indicated. One complete intercalation-deintercalation cycle. Graphite powder from electrodes (after washing and drying) was pelletized with KBr (transmittance mode). Reprinted with copyright from Elsevier Science. (See [78].)...

Different investigations of the mechanisms of capacity degradation during cycling show that one of the main reasons of this degradation is significant change (by a factor of 3-4) in AM volume on the intercalation-deintercalation of lithium, followed by AM destruction [2-3],... 

Furthermore, for pseudocapacitive materials, the cycle stability is a major concern. Besides the repeated ion intercalation/deintercalation-related failure mechanism, it was also found that the decrease of the capacitive performance after long-term charging/discharging cycling might also be related to the dissolution of electrode materials in alkaline electrolytes [142]. Joseph et al. [142] found the cycling stability of Ni3(N03)2(0H)4 in LiOH was higher than that in KOH and NaOH electrolytes. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis showed the evidence of the Ni dissolution into the electrolyte and found the dissolution of... 

---