Lithium transition intercalations

Upon discharge lithium is intercalated. This results in shifts of the (101), (002) and (100) Bragg peaks. Detailed studies of the various shifts as functions of the state of charge/discharge reveal further information on the mechanism of the different phase transitions [12]. Reactions of lithium with Sg in a secondary Li/S cell have been tracked with in situ X-ray diffraction [15]. The electrochemical reaction... 

The electrochemical reversibility of the employed redox material in a pseudocapacitor normally means that the redox process follows Nerstian behavior [2]. These redox materials include (1) electrochemically active materials that can be adsorbed strongly on an electrically conductive substrate surface such as a carbon particle and (2) solid-state redox materials that can combine with or intercalate into an electrode substrate to form a hybrid electrode layer. For example, adsorption on an electrode substrate surface is commonly observed as underpotential deposition of protons on the surface of a crystalline metal electrode (Ft, Rh, Pd, Ir, or Ru). In the case of Ru, the protons can pass through the surface into the metal lattice by an absorption process, similar to the transitional behavior seen in lithium battery intercalation electrodes. 

To improve the safety of secondary lithium batteries, the metallic lithium is replaced by another intercalation compound such as graphite. In addition, the cathode would contain ionic lithium in its structure, which is intercalated in the anode or the cathode depending on the direction of the current. Lithium-ion cells are the most advanced batteries now in the market. These cells supply up to 4 volts, have an energy density close to 120 Wh/kg, and have a long life at room temperature. The technology is based on the use of appropriate lithium intercalation compounds as electrodes. Normally a lithium transition metal oxide is used as the cathode and carbonaceous materials serve as the anode. 

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. 

M.K. Aydinol, A.F. Kohan and G. Ceder, Ab initio calculation of the intercalation voltage of lithium-transition-metal oxide electrodes for rechargeable batteries, /. 

In contrast, LiMn204 has a spinel structure. This material has the space group Fd3m in which the transition-metal and lithium ions are located at octahedral 8(a) and tetrahedral 16(d) sites, respectively, and the oxygen ions are at 32(e) sites. There are octahedral 16(c) sites around the 8(a) sites and lithium ions can diffuse through the 16(c) and 8(a) sites. As this structure contains a diffusion path for the lithium ions, these ions can be deinter-calated and intercalated in these compositions. 

Numerous intercalation reactions are known in which one reactant enters the lattice of the other. Such behaviour is conveniently illustrated by reference to two recent studies. Lithium undergoes a low temperature (298 K) topochemical reversible reaction with transition metal compounds (e.g. TiS2, NbSe3) [1211] in which the host lattice structure may be partially retained (e.g. in Li TiS2, LijNbSe3). The reaction [1212]... 

A number of transition metal oxides can also be intercalated by lithium. One of the best known examples is VsOi3. The VgOu structure, shown in Fig. 11.19, consists of alternate double and single layers of V2OS ribbons. The layers are connected by vertex sharing of octahedral sites, and this leads to a relatively open framework structure (Wilhelmi, Waltersson and Kihlburg, 1971). Insertion of lithium into the oxide 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.

Magnetic susceptibility and Li and magnetic resonance results of FePSj and their lithium intercalates reveal that iron remains in the high-spin divalent state. In Li NiPSj, electrons added by intercalation of lithium seem to go to the transition-metal 4s or higher empty sulphur orbitals. The disappearance of magnetism in Li NiPSj for x > 0.5 is not understood. 

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