Introduction
In recent years, tremendous interest has been focused on the usage of
silicon (Si) as anode material for lithium-ion batteries (LIB). Silicon
has received increasing attention because it is abundantly available,
cost-effective, eco-friendly, has the highest theoretical specific
capacity (4200 mA*H*g-1) and satisfactory working
potential (~0.4 V vs Li+/Li).1-3 Simultaneously, electrode materials based on Si-Li
alloys suffer from the main drawback – appearance of the strong
anisotropic mechanical strain at lithium/delithium process, that leads
to degradation of the electrochemical system and its huge volume change
resulting the shunt contact loss, irreversible capacity fast loss, low
initial coulombic efficiency, i.e. decreasing in quantitative and
qualitative cycling characteristics. 4-7
Covering Si particles with carbon is one of the most effective solutions
to overcome the above disadvantages. Silicon-carbon (Si/C) electrodes
have a higher reversible capacity and number of charge/discharge cycles
compared to the uncovered Si. 8, 9It was found that
the best performance characteristics have electrode materials with
carbon content approximately 30% per mass. Such experimental data were
confirmed by our previous quantum-chemical study concerning
lithium/delithium process modeling using
СmSi13 (m = 0, 6, 10, 13, 18, 26, 39,
45) model clusters. 10
Today various methods exist for the Si/C composites synthesis and any of
them provide deposition or adsorption carbon atoms or their associates
on the surface of Si producing more complex fragments of carbon
nanostructure. 11-13 A wide variety of carbon
nanostructures (graphene, CNT, fullerenes, etc.) have been used for the
synthesis of Si/C composites. 2, 14, 15 Fullerene is a
good alternative for Si coating because of its high electron affinity,
high chemical, and mechanical stability, which is useful for
electrochemical devices. 16 Moreover, fullerene could
form a thin polymeric film on Si that acts as a buffer layer to reduce
the volume expansion and to improve the LIB kinetic properties.17-19 In addition, fullerene could be easily modified
via attaching different functional groups (carboxyl, ester, piperazine)
for decreasing the Si/C composite solubility or via doping of the other
elements. 20-22 Simultaneously, it is well known, that
after the metal intercalation to the fullerene cage the obtained
material becomes soluble in the polar organic electrolyte solution that
limited the use of pure C60 anodes. Synthesis of the
fullerene-type composite material with Si-C covalent bonds could be a
great alternative to solve this problem.
The quantum-chemical calculation is a powerful tool for the study of
various characteristics of Si/C anode materials. A lot of different
clusters via various theoretical methods have been investigated earlier.23-26 Continuing on our previous studies10, 27, 28 and to expand our knowledge on the role of
the electronic structure of Si/C nanocomposites to the lithium/delithium
process, here we explore a series of
SinCm clusters with various atomic
ratios. In total, we report diffusion of Li in the Si/C systems and
volume change under lithiation via first-principle calculations.