(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).
.