Layered Intercalation Electrodes

For x = 0.1, the three higher values resulting from Eq. (28.1) were obtained for n = 0 (53.14%), n= I (35.43%), and n = 2 (9.84%). None of these values agrees with the relative Intensities of the two doublets (86 and 14%) found experimentally for LiFeo.1Nio.9O2. This discrepancy could imply a certain level of clustering of iron atoms, as it has been recently 

Simultaneously, Delmas et al. suggested that the Mossbauer spectra were fitted by considering a distribution of quadrupole splitting values. They also found that a statistical distribution did not fit to the experimental values, and a bimodal distribution emerged [7]. A combined Ni and Fe Mossbauer spectroscopy study by Giitlich and coworkers [8] unfolded the cationic site assignment in Li, Ni +x02 and explained the ferromagnetic properties of this material 

Besides the characterization of the pristine electrode materials, MS can give invaluable information about the electroactive atoms in used electrodes. In this way, it has been demonstrated that iron is also active in the doped LiNi02 electrodes, and participates in a Fe Fe oxidation process during the charge process of lithium test cells [7]. 

---

Molybdenum disulphide is another layered intercalation host, similar to titanium disulphide. This material occurs naturally and formed the basis of the positive electrode for the first high production cylindrical AA-sized cell, manufactured by Moli Energy Ltd in Canada in the 1980s. Cycle life of 100-300 was achieved in practical cells with average discharge voltages of 1.8 V for low rates, giving a theoretical density of approximately 300 Wh/kg. 

Some of the very interesting applications of these layered intercalates are in material design [3], ion exchange [4], catalysis [5], in the study of quantum-sized semiconductor particles [6], assembly of molecular multilayers at solid-liquid interfaces [7], designer electrode surfaces [8], preparation of low-dimensional conducting polymers [9], and so forth. 

Quine, T.E., Duncan, M.J., Armstrong, A.R., Robertson, A.D., and Bruce, P.G., Layered Li ni yNiy02 intercalation electrodes, J. Mater. Chem., 10, 2838, 2000. Ohzuku, T., and Makimura, Y, Layered lithium insertion material of LiNii Mni,202 a possible alternative to LiCo02 for advanced lithium-ion batteries, Chem. Lett., 8, 744, 2001. 

Fig. 25. Scheme of an evaporation-intercalation solar cell. 1 layer-type electrode into which guest molecules or atoms are intercalated and from which they are evaporated. 2 solid or liquid electrolyte. 3 porous counter electrode at which the carrier species is converted into an ion... 

In evaporation-intercalation devices solar energy conversion would, at least in the more efficient case of a thermal system, not be converted by exciting electrons and rapidly separating them from holes, but by transferring atoms or molecules across a phase boundary by evaporation which is usually a very efficient process. It is, consequently, neither necessary to use materials which are well crystallized like those developed for photovoltaic cells nor is it necessary to prepare sophisticated junctions. A compacted polycrystalline sheet of a two-dimensional material which is on one side placed in contact with an electrolyte, sandwiched between the layer-type electrode and a porous counter electrode, as it is used in fuel cells, would constitute the central energy conversion unit. Some care would have to be taken to choose an electrolyte which is suitable for intercalation reactions and which is not easily evaporated through leaks in the electrodes. Thin layers of polymeric or solid electrolytes would seem to be promising. 

The contribution of electric field to lithium transport has been considered by a few authors. Pyun et argued on the basis of the Armand s model for the intercalation electrode that lithium deintercalation from the LiCo02 composite electrode was retarded by the electric field due to the formation of an electron-depleted space charge layer beneath the electrode/electrolyte interface. Nichina et al. estimated the chemical diffusivity of lithium in the LiCo02 film electrode from the current-time relation derived from the Nernst-Planck equation for combined lithium migration and diffusion within the electrode. 

The other common intercalation electrode, the LiV30s vanadium bronze, has a basic structure formed by octahedra and trigonal bipyramids arranged to form puckered layers between which the Li" ions are situated [22]. The unit cell comprises six empty tetrahedral sites which may easily accommodate up to three Li per mole ... 

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. 

Positive and negative intercalation electrodes (lithium-ion) with a porous polymer separator layer filled with a liquid electrolyte (PVDF-based). 

Positive intercalation electrode-lithium anode (lithium-metal) with a dry polymer electrolyte layer. 

MOF Applications as Energy Storage Electrode Materials. The nature, size and accessibility of the pores within MOFs have led to these frameworks being suggested as possible rechargeable intercalation electrode materials, especially for the case of Li-ion batteries, but also for electrochemical double layer capacitors. An excellent recent review has appeared covering MOF applications, in particular in fuel cell and Li-battery technologies. ... 

A.D. Robertson, A.R. Armstrong and P.G. Bruce, Layered Li ,Mnj yCOy02 intercalation electrodes—Influence of ion exchange on capacity and structure upon cycling, Chem. Mater. 13, 2001, 2380-2386. 

Graphite reacts with alkali metals, for example potassium, to form compounds which are non-stoichiometric but which all have limiting compositions (for example K C) in these, the alkaU metal atoms are intercalated between the layers of carbon atoms. In the preparation of fluorine by electrolysis of a molten fluoride with graphite electrodes the solid compound (CF) polycarbon fluoride is formed, with fluorine on each carbon atom, causing puckering of the rings. 

Carbon materials which have the closest-packed hexagonal structures are used as the negative electrode for lithium-ion batteries carbon atoms on the (0 0 2) plane are linked by conjugated bonds, and these planes (graphite planes) are layered. The layer interdistance is more than 3.35 A and lithium ions can be intercalated and dein-tercalated. As the potential of carbon materials with intercalated lithium ions is low,... 

In redox flow batteries such as Zn/Cl2 and Zn/Br2, carbon plays a major role in the positive electrode where reactions involving Cl2 and Br2 occur. In these types of batteries, graphite is used as the bipolar separator, and a thin layer of high-surface-area carbon serves as an electrocatalyst. Two potential problems with carbon in redox flow batteries are (i) slow oxidation of carbon and (ii) intercalation of halogen molecules, particularly Br2 in graphite electrodes. The reversible redox potentials for the Cl2 and Br2 reactions [Eq. (8) and... 

---