Studies of Si[sub 1−x]C[sub x] Electrode Materials Prepared by High-Energy Mechanical Milling and Combinatorial Sputter Deposition

Abstract

A review of recent literature on Si:C composite and nanocomposite electrode materials is first presented emphasizing that most authors do not compare the experimental specific capacity of the composite with that expected based on the phases present. We provide such a comparison and suggest that much of the apparent confusion in the literature, when taken as a whole, can be understood if nanocomposites prepared by "aggressive" methods like high energy milling and high temperature heat-treatment contain significant amounts of amorphous or nanocrystalline SiC. In order to help resolve the confusion, samples of Si 1−x C x were prepared by high-energy mechanical milling for 0.25 Ͻ x Ͻ 0.5 and by combinatorial co-sputtering for 0 Ͻ x Ͻ 0.8. X-ray diffraction shows the mechanically milled samples to be a mixture of nanocrystalline SiC and Si. Electrochemical studies of the mechanically milled samples show that the attained specific capacity can be described accurately assuming that the Si is active and can reversibly react with 3.75 Li atoms per Si atom ͑Li 15 Si 4 ͒, while the SiC is inactive. The co-sputtered samples are amorphous or extremely nanostructured for all x. For 0 Ͻ x Ͻ 0.5, the specific capacity decreases with increasing x, from about 3580 mAh/g at x = 0, to about 1000 mAh/g at x = 0.5, presumably due to the formation of inactive regions of a-SiC. The capacity of the co-sputtered samples does not reach small values at x = 0.5, unlike the ballmilled samples, because there are presumably some regions of a-Si and a-C among the inactive a-SiC regions due to the high quenching rate of the sputtering process. Commercially relevant compositions are identified.

Polymers with Tailored Electronic Structure for High Capacity Lithium Battery Electrodes

“…Carbon structures provide a conductivity matrix while Si serves as the Li-ion storage material. [9,11,[26][27][28] 3…”

Electrochemistry of CuxSi1−xAlloys in Li Cells

“…Various Si-based alloys have been studied as anode materials for Li-ion batteries, such as C-Si, 9,10 Cr-Si, 11 Fe-Si, 12,13 Ni-Si, 8,14 TiSi, 15,16 etc. The Cu-Si alloy system differs from other M-Si systems because it has no silicon-rich silicide phase.…”

Si/C composite lithium-ion battery anodes synthesized from coarse silicon and citric acid through combined ball milling and thermal pyrolysis

“…Carbon has been frequently used as the active matrix because of its softness, compliance, relatively low mass, good electronic conductivity, reasonable lithium-insertion capability, and small volume expansion. Numerous methods have been employed for preparing Si/C composite anodes [28], including physical mixing of silicon and graphite by ball milling [29], thermal vapor deposition [30], combined ball milling and pyrolysis [31], and the chemical reaction of gels [32]. The in situ formation of carbon by pyrolysis is superior to the physical mixture of silicon with graphite due to the higher homogeneity of silicon dispersion in the carbon matrix obtained and the better contact of carbon with the electrode materials.…”