Electrochemical inactive matrix

V. The quantification of one electrochemical active component in an electrochemically inactive matrix can also be accomplished with the help of admixture of a standard. In solid solutions (mixed crystals) of copper hexacyanoferrate (htf and copper hexacyanocobaltate (hcc) (i.e., only the htf system is... 

In order to prevent the irreversible capacity loss during the first cycle and to reduce the volumetric expansion of the crystal lattice, the active element can be dispersed, not in situ as above, but ex situ in a electrochemically-inactive matrix. This is a promising technique, because it reduces the phenomenon of clustering of the active species. In order to do this, two methods have been developed embedding of the particles within the support matrix and adhesion to the surface of the particles of the matrix. Various composites have been studied, but generally always we see the presence of particles of silica (Si/C) or tin Sn/C, Sn-Fe/C, Sb/CNT, SnSbo s/CNT. For the latter two compounds, Sb or SnSbo.s is deposited on the surface of carbon nanotubes (CNTs). 

The simplest example of direct silicon nanocluster formation is the electrochemical reaction of SiO with Lb, which proceeds in much the same way as tin convertible oxides (TCOs). Li O formed in situ is known to be an appropriate inactive matrix for accommodating active metal particles, and it is a good ionic conductor for Lb. However, convertible silicon oxides have worse kinetic properties, because silicon is a semiconductor and the bulk conductivity of the resulting nanocomposite is several orders of magnitude less than in case of SnO... 

There are indeed some other methods for producing silicon-based nanocomposites that appeared in the literature. Considerable work has been performed by J. Dahn s group and the decomposition of silane or polysilane pitch within carbonaceous matrices has been widely explored. Other methods based on HEMM of electrochemically inactive phases such as iron, nickel, titanium-nickel, titanium-carbon, silicon-carbon, and so on also have been examined using silicon powder with an initial particle grain size within either micrometric or nanometric ranges. The common problem in all these cases is that it is difficult to predict theoretically the appropriate matrix/silicon particles combination, i.e., there is no simple guidance rule in order to make reasonable predictions. An overview of all the above-described methods is summarized in Table 11.3. 

M is electrochemically inactive transition metal (M = Fe, Ni, Cu, and Co). M also provides a matrix that buffers volume changes occurring with the lithiation-delithiation processes, therefore the mechanical integrity between Sn nanoparticles and with current collector can be maintained. Both preparation of alloy nanopowders and thin films are popular strategies. 

Electrochemical tests performed on simple cobalt oxides demonstrate specific capacities between 700 and 1100 mAh/g and an excellent cycle behavior. The formation of nanoparticles of cobalt dispersed in a Li20 matrix occurs because of the reduction of the cobalt in CoO. Li20 is often inactive in electrochemistry, but its formation in situ in the material means it is able to be electrochemically active. However, the cost of cobalt reduces the commercial prospects of this type of compound. 

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