Carbon materials edge planes

The anodic behavior of carbon materials, such as acetylene black, activated carbon, and vapor-grown carbon fiber, in LiC104/PC solution was studied by Yamamoto et al. [102]. Irreversible reactions, including gas evolution and disintegration, were mainly observed on that part of the surface occupied by the edge planes of the... 

The future remains bright for the use of carbon materials in batteries. In the past several years, several new carbon materials have appeared mesophase pitch fibers, expanded graphite and carbon nanotubes. New electrolyte additives for Li-Ion permit the use of low cost PC based electrolytes with natural graphite anodes. Carbon nanotubes are attractive new materials and it appears that they will be available in quantity in the near future. They have a high ratio of the base plane to edge plain found in HOPG. The ultracapacitor application to deposit an electronically conductive polymer on the surface of a carbon nanotube may be the wave of the future. 

In this paper, we presented new information, which should help in optimising disordered carbon materials for anodes of lithium-ion batteries. We clearly proved that the irreversible capacity is essentially due to the presence of active sites at the surface of carbon, which cause the electrolyte decomposition. A perfect linear relationship was shown between the irreversible capacity and the active surface area, i.e. the area corresponding to the sites located at the edge planes. It definitely proves that the BET specific surface area, which represents the surface area of the basal planes, is not a relevant parameter to explain the irreversible capacity, even if some papers showed some correlation with this parameter for rather low BET surface area carbons. The electrolyte may be decomposed by surface functional groups or by dangling bonds. Coating by a thin layer of pyrolytic carbon allows these sites to be efficiently blocked, without reducing the value of reversible capacity. 

Contrarily to the basal plane, the prismatic edges terminating the graphene layers as well as defects in the basal plane are highly reactive and usually saturated, with H, 0, or N atoms being the key players in most of the catalytic applications of carbon materials (see Chapter 19). The abundance of groups illustrated in Fig. 15.5 is well known from organic chemistry. These functionalities define the acidity/basicity and also the hydrophilic character of the nanocarbons. 

The pore structure and surface area of carbon-based materials determine their physical characteristics, while the surface chemical structure affects interactions with polar and nonpolar molecules due to the presence of chemically reactive fimctional groups. Active sites—edges, dislocations, and discontinuities—determine the reactivity of the carbon surface. As shown in Fig. 1, graphitic materials have at least two distinct types of surface sites, namely, the basal-plane and edge-plane sites [11]. It is generally considered... 

Figure 5.4 summarizes in a schematic way the current state of knowledge of carbon surface chemistry, with an emphasis on the details of graphene edges. As discussed in Section 5.2.1, it shows the dominant surface functionalities, all containing oxygen because of the often inevitable contact of realistic carbon materials with 02 from air. The main features of interest here are (i) the existence of free edge sites and (ii) the notion that the basal plane is not as chemically inert as is often... 

The pioneering studies of capacitance exhibited by basal and edge planes of carbons by Yeager and coworkers showed abnormal behavior, which led Randin and Yeager [151] to conclude that the space charge characteristics of graphite must be taken into account in examining the electrochemical properties of this material. ... 

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