Oxides 246 alkali metal intercalates

Since the discovery of high temperature superconductivity in cuprates, there has been intense interest in transition metal oxides with strongly layered, (quasi) two-dimensional (2D) crystal structures and electronic properties. For several years now alkali-metal intercalated layered cobaltates, particularly Na CoCL (NxCO)withx 0.50 — 0.75, have been pursued for their thermoelectric properties [1] IAX C0O2 is of course of great interest and importance due to its battery applications. The recent discovery[2] and confirmation[3-5] of superconductivity in this system, for x 0.3 when intercalated with H20, has heightened interest in the NxCO system. 

Alkali metal intercalation in dichalcogenides is also achieved by direct reaction of the elements at around 1070 K e.g. AxMCh2 whereM=V, Nb or Ta) in sealed tubes. Alkali metal intercalation compounds with dichalcogenides form hydrated phases, A HjOJy MCh2, just like some of the layered oxides e.g. 

Alkali metal intercalation reactions have been intensively studied for systems involving lithium. Host oxides are those of elements in high oxidation states that possess lower valence states that are also stable in oxides. Lithium intercalation may be carried out by Lil solutions for easily reducible systems, for example. 

In this section we limit our discussion to a general presentation of the alkali-metal intercalation compounds the synthesis of ICs and the geometrical factors affecting the intercalation in lamellar compounds, i.e., transition-metal dichalcogenides and transition-metal oxides are discussed. The electronic side is described in the following Chapter. 

Layered structures are also found for many oxides and sulfides of transition metals. They can be intercalated with alkali metals (Li, Na, K) to give superconducting solids and conducting solids that are useful for solid state battery materials. 

Are the mechanisms described here applicable to cells operating in nonaque-ous environments It is conceivable that the sequence described by Eqs. (12)-( 14) occurs under certain conditions. The more complex sequence involving coupled electron and cation transfer probably does not. Although Li+ (the electrolyte cation most often used in Gratzel-type cells) is known to intercalate into high-area metal oxide semiconductors [49,90,108-111], the rate is probably too slow to be coupled to injection and back ET in the same way that aqueous proton uptake and release are coupled to these processes. The ability to use water itself as a proton source means that solution-phase diffusional limitations on proton uptake are absent. Alkali metal ion uptake from nonaqueous solutions, on the other hand, clearly is subject to diffusional limitations. 

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... 

Lost of the reactants that bring about intercalation of graphite are either strong oxidants or reductants such as nitric acid or alkali metal (1-3). The oxidation or reduction of the graphite that accompanies the intercalation was clearly shown by Ubbelohde and co-workers (4-6) to be... 

The presence of alkali metal ions is crucial for the stabilization of excess charge trapped within the nanopartides. Intercalation of metal ions within the nanoparticle thus becomes a limiting factor as the rate of transport of these ions becomes slower in thicker metal oxide films. This in turn controls the rate of coloration and recovery of the electrochromic effects. Limited efforts have also been made to employ mixed Ti02/W03 [145], WO3/V2O5 [146], and WO3/M0O3 [147] systems to enhance the efficiency of electrochromic effects. The beneficial aspect of these nanostructured semiconductor films in electrochromic devices is yet to be explored in a systematic way. 

There are two theories developed to explain the processes for charge storage in MnC>2.197 One theory suggests that proton (H+) and alkali metal cations (C+), present in the electrolyte, can be reversibly intercalated into the bulk of Mn02 through a reduction reaction and deintercalated via an oxidation reaction 198... 

The use of organometallic compounds is efficient in the case of Li. Solvent is not cointercalated which is an advantage compared to the liq NHj case, but a disadvantage concerning the diffusion of the alkali-metal ions, and a complete intercalation may not be achieved (the NH3 molecule separates the sheets and favors A ion diffusion). Solid-state high-T techniques are well adapted to preparing the stoichiometric samples, each time mixtures of sulfides or oxides are used. Well-crystallized products are obtained. 

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