Intercalation lithiated carbons

The electrochemical performance of lithiated carbons depends basically on the electrolyte, the parent carbonaceous material, and the interaction between the two (see also Chapter III, Sec.6). As far as the lithium intercalation process is concerned, interactions with the electrolyte, which limit the suitability of an electrolyte system, will be discussed in Secs. 5.2.2.3,... 

On the basis of the above observation, Dahn and co-workers proposed a thermal reaction scheme for the coupling of carbonaceous anodes and electrolytes. The initial peak, which was almost identical for all of the anode samples and independent of lithiation degrees, should arise from the decomposition of the SEI because the amount of SEI chemicals was only proportional to the surface area. This could have been due to the transformation of the metastable lithium alkyl carbonate into the stable Li2C03. After the depletion of the SEI, a second process between 150 and 190 °C was caused by the reduction of electrolyte components by the lithiated carbon to form a new SEI, and the autocatalyzed reaction proceeded until all of the intercalated lithium was consumed or the thickness of this new SEI was sufficient to suppress further reductions. The corresponding decrease in SHR created the dip in the least lithiated sample in Eigure 35. Above 200 °C (beyond the ARC test range as shown in Eigure 35), electrolyte decomposition occurred, which was also an exothermic process. 

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],... 

There is another type of rechargeable lithium battery, however, which uses a lithiated carbon or other intercalation material for the negative electrode in place of lithium. The absence of metallic lithium in these lithium-ion batteries minimizes these safety concerns. This type of battery is covered in Chap. 35. 

It should be noted that the study of noble metal electrodes in nonaqueous Li salt solutions is even more relevant to the understanding of the behavior of lithiated carbon anodes because, in the latter case, the carbon electrodes that are initially nearly surface film-free, are also polarized from OCV ( 3 V ra. IA/lU, see also Figure 2) to low potentials in the course of Li intercalation, and surface films are gradually formed on the carbon electrode as it reaches lower potentials. Hence, the order of surface reactions may be similar to that described in Figure 2, except for the Li under potential deposition and stripping processes, which are irrelevant to carbon electrodes (into which lithium is inserted at potentials higher than that of Li deposition). 

Lithium ion can be intercalated, more or less, into most kinds of carbon, and the resulting lithiated carbons show extremely negative electrochemical potentials close to that of the metallic lithium electrode. The reversible intercalation/deintercalation reactions overcome the problem of dendrite formation of lithium and provide dramatic improvements in safety and cycleability. The carbon anodes are combined with non-aqueous electrolyte solutions and lithium-transition metal oxides such as LiCoOg as cathodes to fabricate 4 V-class LIBs. Only lithium ion moves back and forth between the cathode and the anode upon charging and discharging, which give rise to a potential difference of about 4 V between the two electrodes. The name, "lithium-ion" batteries came from this simple mechanism. 

The first lithiated graphitic carbons (lithium-graphite intercalation compounds, abbreviated as Li-GIC s),... 

Whereas the electrochemical decomposition of propylene carbonate (PC) on graphite electrodes at potentials between 1 and 0.8 V vs. Li/Li was already reported in 1970 [140], it took about four years to find out that this reaction is accompanied by a partially reversible electrochemical intercalation of solvated lithium ions, Li (solv)y, into the graphite host [64], In general, the intercalation of Li (and other alkali-metal) ions from electrolytes with organic donor solvents into fairly crystalline graphitic carbons quite often yields solvated (ternary) lithiated graphites, Li r(solv)yC 1 (Fig. 8) [7,24,26,65,66,141-146],... 

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