The structure and properties of a new type of nanostructured composite Si/C electrodes for lithium ion accumulators

Comparative Quantum Chemical Examination of Lithiation/Delithiation Processes in Sin Nanoclusters and CmSin Nanocomposites

“…The structures of C m>13 Si 13 nanocomposites most probably resemble a solution of silicon atoms in a carbon matrix, what agrees with data [11]. The results of calculations of atomic coordinates of carbon atoms in C m subclusters testify that at m/n 1 interatomic distances are more than 2.6 Å (there are no chemical bonds ).…”

“…The results obtained can mean that for Si/C electrode materials these is a clear limit of carbon percentage (~25-30 %) when the process of lithiating material does not effect practically on its geometric parameters (dimensions of C m Si n nanocomposites). This fact coincides with the experimental data [11] for Si/ electrodes (sample 1) with the best field-performance and electrochemical data. According to our calculations, the Si/ systems with carbon content l e s s t h a n 1 7 % ( C 6 Si 13 nanocomposites, samples 2, 4 [11]) or more than 35 % (C 18 Si 13 nanocomposites, samples 5, 6 [11]) cannot meet the requirements of necessary mechanica stability as due to lithiation at k/13 0÷4 great volume expansion (>50 %) of silicon-carbon matrix takes place in such systems.…”

“…This fact coincides with the experimental data [11] for Si/ electrodes (sample 1) with the best field-performance and electrochemical data. According to our calculations, the Si/ systems with carbon content l e s s t h a n 1 7 % ( C 6 Si 13 nanocomposites, samples 2, 4 [11]) or more than 35 % (C 18 Si 13 nanocomposites, samples 5, 6 [11]) cannot meet the requirements of necessary mechanica stability as due to lithiation at k/13 0÷4 great volume expansion (>50 %) of silicon-carbon matrix takes place in such systems. Nevertheless, it is necessary to note that in the Si/ systems the limiting value of carbon content may also depend on the size, structure, atomic coordination type in Si n and C m clusters as well as on the lithium diffusion coefficients for silicon and carbon matrices [11].…”

“…Such an increase in V /13=3,23 (Si 13 ) (see Fig. 4) due to lithiating Si 13 silicon cluster is caused by formation of more small Li k'<k Si n'<13 clusters and, according to [11], can be determined by a change in the structural states of silicon component of the nanoalloy.…”

“…Covering silicon micro-or nanoparticles with carbon is shown in [6][7][8][9][10][11][12][13][14] to result in an increase in the reversible capacity and the number of chargedischarge cycles of silicon-carbon (Si/C) electrodes as well as of the Coulomb component of the first cycle. Si/ composites are produced by various methods: powdering silicon mixed with graphite in a ball mill, deposition of carbon atoms from gas phase (or plasma), pyrolysis of a silicon mixture with carbon-containing precursors [15][16][17][18][19][20].…”