Lithium intercalation-deintercalation processes

The feasibility of the gel electrolytes for lithium-ion batteries development has been tested by first examining their compatibility with appropriate electrode materials, i.e., the carbonaceous anode and the lithium metal oxide cathode. This has been carried out by examining the characteristics of the lithium intercalation-deintercalation processes in the electrode materials using cells based on the given polymer as the electrolyte and lithium metal as the counter electrode. 

As in the case of the graphite anode, the electrochemical response of the cathodes can also be evaluated by following the lithium intercalation-deintercalation processes, again... 

In this case a potassium-graphite (KCg) electrode has been used as the carbonaceous anode material. Upon anodic polarisation this electrode irreversibly deintercalates potassimn resulting in a graphite-like compound, which on subsequent cycles performs with fast kinetics of its lithium intercalation-deintercalation process [89, 90]. Accordingly, the first charging process of the battery may be written as shown in Equation 7.7 at the anode. 

Peramunage and Abraham have recently reported an advanced lithium-ion polymer cell [106, 107]. In this case, a material of the Li [Lij/3Tij/3]04 family [108, 109], e.g., the Li4Ti50i2, intercalation compound, has been used as an anode. The lithium intercalation-deintercalation process in this compound is shown in Equation 7.14. 

This may be achieved by determining the charactereristics of the lithium intercalation-deintercalation processes of these materials in ceUs based on the given membrane as the electrol and lithium metal as the counter electrode. 

As in the case of the cathodes, also the electrochemical response of the anodes, can be evaluated by following their lithium intercalation-deintercalation processes, again in cells using the gel membrane as the electrolyte and Li metal as the counter electrode. Figure 9 shows the voltage response of a graphite electrode cycled in a LiCl04/EC/DMCyPAN electrolyte cell. Also in this case, the response, which is associated with the process ... 

This battery concept is interesting because it is based on an unusual electrode operation. The graphite electrode operates on the well known lithium intercalation-deintercalation process ... 

The potentiostatic current transient (PCT) technique has been known as the most popular method to understand lithium transport through an intercalation electrode, based on the assumption that lithium diffusion in the electrode is the rate-determining process of lithium intercalation/deintercalation [45]. By solving Eick s second equation for planar geometry with I.C. in Equation (5.28), impermeable B.C. in Equation (5.29), and potentiostatic B.C. 

The most frequent method for the analysis of CTs from intercalation electrodes is based on the grounds that lithium diffusion in the electrode is the rate-determining process in lithium intercalation/deintercalation. " This involves the following the system is so kinetically fast that the equilibrium concentration of lithium is quickly reached at the interface... 

Figure 7.12 Typical voltage response of the Li intercalation-deintercalation process of a graphite electrode in a LiC104-EC-DMC-PAN electrolyte cell. Temperature 25 °C. Lithium counter electrode. Cycling rate C/4.

To ensure good cycling performance, intercalation/deintercalation of lithium ions should be reversible during the whole intercalation/ deintercalation process, and there should be little or no change in the main host structure. 

At the end of the 1990s in Japan, large-scale production of rechargeable lithium ion batteries was initiated. These contained lithium compounds intercalated into oxide materials (positive electrodes) as well as into graphitic materials (negative electrode). The development of these batteries initiated a further increase in investigations of the properties of different intercalation compounds and of the mechanism of intercalation and deintercalation processes. 

Experiments were performed with various LiAl-X LDHs, with X = Br, NO3 and ISO4. As with the intercalation process, the nature of the anion exerts a powerful influence on the reaction. In the case of sulfate, the deintercalation reaction does not go to completion - only 40% of the available lithium sulfate was released. The deintercalation reaction initially proceeds very quickly, but the process is then halted. The rate of deintercalation is NOs" > Cl > Br . This series does not correspond with data on the anion selectivity for intercalation into Al(OH)3, which is S04 > Cl" > Br" > NO3". Neither is there a correlation of the release data with the heats of hydration of the anions. The series observed arises because the intercalation and deintercalation processes are a balance of a number of factors, including interactions between the guest ions and the host matrix. 

Figure 1. Schematic description of a (lithium ion) rocking-chair cell that employs graphitic carbon as anode and transition metal oxide as cathode. The undergoing electrochemical process is lithium ion deintercalation from the graphene structure of the anode and simultaneous intercalation into the layered structure of the metal oxide cathode. For the cell, this process is discharge, since the reaction is spontaneous.

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],... 

As mentioned earlier, intercalation of alkali metals in host solids in readily accomplished electrochemi-cally. It is easy to see how both intercalation (reduction of the host) and deintercalation (oxidation of the host) are processes suited for this method. Thus, lithium intercalation is carried out using a lithium anode and a lithium salt in a non-aqueous solvent... 

Figure 10.6 shows the CV of a LiMn2O4 electrode on a cell with Li foil for both the reference and auxiliary electrodes in ethylene carbonate plus dimethyl carbonate solution of LiAsFg (1 M) (Sinha and Munichandraiah, 2008). The pair of peaks at larger potential corresponds to the deintercalation/intercalation of Li in the range 0 < X < 0.5 for Li Mn2O4, whereas the pair of peaks at lower potentials is attributable to this process for 0.5 < x < 1, both accompanied by reversible Mn(lV)/Mn(lll) redox reactions. Following Xia and Yoshio (1996), the later electrochemical process corresponds to the removal/addition of Li+ ions from/into half of the tetrahedral sites in which the lithium intercalation occurs. The former couple is then attributed to this process at the other tetrahedral sites where lithium intercalations do not occur. 

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