Particule size and nanostructuration effects

2 Particule size and nanostructuration effects 11.3.2.2.1 Positive impact 

Carbon black is not an active material but a conductor additive. The composite of silicon and carbon prepared by mecanos5mthesis has good electrochemical performance. The technique allows an intimate mixture of materials, 30% of carbon black contributes 

Besides the aspects related to the particle size of silicon, efforts have been focused on the morphology. Indeed, to be reduced to a distortion in two dimensions as in the case of thin films instead of three dimensions for the electrodes usual, it is necessary to synthesize silicon nanoparticles having one or two directions of growth privileged. 

In the case of silicon nanowires spatial location of the volume expansion in one direction provide to corresponding electrode both a very good q clability and a large capacity close to theoretical capacity even when high current densities are used. Chan reported a capacity of 3500 mAh-g after 20 cycles for a C/5. This capacity decreases to 2100 mAh-g when the charge/discharge rate is increased to 1 C. Similar results are obtained by Laika 

The silicon stored in open air is covered with a layer of oxide, Si02, which is formed spontaneously. During the first reduction, the SiO ( is reduced first to form U2O and Si. Then the reaction can be continued by the insertion of Li in silicon. This reaction is assumed irreversible. The reduction of native oxide does not appear at the same time as the decomposition of the electrolyte resulting in the formation of the SEI on the surface of electrode material (active material + electronic conductor). According to a study on the oxide Si02, the curve of differential capacity (dQ/dV vs. V) shows a peak at 0.25 V (vs. Li /Li) during the first reduction that 

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