(SiC)12Lip nanoclusters. Charge/discharge process
Investigation of the electron density distribution showed its transferring from carbon to silicon atoms that lead to the coordination of the Li atoms near the Carbon. Analysis of the (SiC)12Lip structures (where p = 0,12,20,24,44) and calculated volumes of the matrix VSiC= V(SiС)12Lip - VLip (Fig. 3) demonstrate that lithiation process almost doesn’t influence on geometry (lengths of the Si-C bonds and angles of the four- and six-membered cycles) and volume of the initial (SiC)12 cluster.
In (SiC)12Lip composites, the electron density is transferred from lithium atoms to the silicon-carbon matrix. Moreover, the average charge on lithium atoms is +(0.8 ± 0.1) e, and the negative charge is concentrated on the Si/C matrix. Therefore, the lithiation process leads to the formation of an ionic structure [(SiС)12-∆q…Lim+∆q] where the value of ± ∆q is determined by the degree of lithium p. The discharge process completely restores the initial structure of the nanocluster (SiC)12.
Stabilization of the volume values (it is changing within only 1%) during the charge/discharge process leads to the disappearing of mechanical strain oscillation and improving the quantitative and qualitative electrochemical characteristics of the electrode materials based on (SiC)12 nanocomposites. The electrostatic surface potential, that includes concentrated positive and negative charges on the Si and C atoms, has both nucleophilic (near Si atoms) and electrophilic (near C atoms) regions. Consequently, due to the electrostatic interaction between Si and C atoms of two different clusters (SiC)12, different associative agglomerates of n(SiC)12 could be formed (Fig. 4).
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