Graphene Coating of Silicon Nanoparticles with CO₂‐Enhanced Chemical Vapor Deposition

Abstract

Understanding the growth of graphene over Si species is becoming ever more important as the huge potential for the combination of these two materials becomes more apparent, not only for device fabrication but also in energy applications, particularly in Li-ion batteries. Thus, the drive for the direct fabrication of graphene over Si is crucial because indirect approaches, by their very nature, require processing steps that, in general, contaminate, damage, and are costly. In this work, the direct chemical vapor deposition growth of few-layer graphene over Si nanoparticles is systematically explored through experiment and theory with the use of a reducer, H2 or the use of a mild oxidant, CO2 combined with CH4 . Unlike the case of CH4 , with the use of CO2 as a mild oxidant in the reaction, the graphene layers form neatly over the surface and encapsulate the Si particles. SiC formation is also prevented. These structures show exceptionally good electrochemical performance as high capacity anodes for lithium-ion batteries. Density functional theory studies show the presence of CO2 not only prevents SiC formation but helps enhance the catalytic activity of the particles by maintaining an SiOx surface. In addition, CO2 can enhance graphitization.

Direct Synthesis of Large-Area Graphene on Insulating Substrates at Low Temperature using Microwave Plasma CVD

“…Son et al in 2016 reported that CO 2 helps in graphene growth with lesser defects by etching poor cross-links between growing flakes. 42 The etching property of CO 2 might help in removal of excess sp 3 carbon (eq 4), helping in reduction of vertical growth or diamondlike carbon and, in turn, reducing the defects. With suppressed vertical growth, sp 2 bonded C–C chain might dominate to form lateral graphene, as illustrated in Figure 4b.…”

Synergistic double-shell coating of graphene and Li4SiO4 on silicon for high performance lithium-ion battery application

“…We used a CVD process to get graphene coated Si (Si@graphene) by using CO 2 , a mild oxidant, along with methane (CH 4 ) during CVD process. [19,28] By controlling the CVD temperature, time and ratio of CO 2 /CH 4 , the thickness of graphene coating layer could be steadily controlled. A Two-step procedure was used to coat Li 4 SiO 4 on the surface of graphene encapsulated Si-NPs.…”

“…Si@Li 4 SiO 4 , Si@graphene and Si@graphene@Li 4 SiO 4 display the enhanced cycling stability (Figure 3a and 3b), resulting from the improved conductivity, more stable SEI forming and better toleration for volume change due to the synergistic effect of double shells of graphene and Li 4 SiO 4 . The graphene coating can maintain its continual structure via a layer sliding process with expanded volume change during lithiation, [19,28] thus buffer the expansion of Si-NPs due to its flexible structure and superior mechanical properties. Besides, graphene layers can also supply electron-transfer highway which would be beneficial to the rate performance.…”

Graphene balls for lithium rechargeable batteries with fast charging and high volumetric energy densities

“…For the direct growth of graphene over the surface of SiO 2 , fumed SiO 2 nanoparticles (average diameter: 20–30 nm, Alfa Aesar) were introduced into a fixed-bed vertical tube reactor made of quartz 18 , 19 , 31 , 40 (inner diameter = 27 mm, length = 80 cm). The feed gas was fed through the reactor-containing bed from the top at atmospheric pressure.…”