Fluorination of graphite oxide

Fluorination of graphite oxide 16.4.2.5.3 F6Mg AlCs F6MgRb Al FjMo MoFe... 

Fluorination of graphite oxide leads to a light grey graphite oxyfluoride possibly by replacing the OH groups by fluorine [406]. 

Fig. 11. Discharge characteristics of graphite oxide, those fluorinated at various temperatures in 1 M LiClCVPC solution at 25°C (0.05 Adm 2).

If GO is used as a host lattice for Li+ in aprotic electrolytes, reversibility is improved [577]. The potential level is distinctly more positive than with donor GIC, at about —1 V vs. SHE. An all-solid-state Li/GO battery with PE0/LiC104 as solid electrolyte was reported by Mermoux and Touzain [578], but rechargeability is poor. Recently, the structure of graphite oxide was studied by its fluorination at 50-2()0 °C [579]. C-OH bonds were transformed into C-F bonds. The examples, in conjunction with Section 2, show that the formation or cleavage of covalent C-O (C-F) bonds makes the whole electrochemical process irreversible. Application was attempted in lithium primary batteries, which have a voltage of 2-2.5 V. Really reversible electrodes are only possible, however, with graphite intercalation compounds, which are characterized by weak polar bonds. 

Fluorination of graphite at elevated temperature yields covalent layered C—F compounds with variable fluorine content. The compositions and properties of these preparations depend on particle size and orientation of the pristine carbon material and on the conditions of fluorination. Nevertheless, graphite fluorides are better defined than graphite oxides, and there are at least three different binary graphite fluorides polyfmonocarbon monofluoride), poly(dicarbon monofluoride) and polyftetracarbon monofluoride). 

Covalent fluorination of graphite is a common side reaction to the electrochemical formation of neutral graphite salts of such complex fluoride ions as [PFg] . An indirect RT synthesis of graphite fluoride is by anodic oxidation of graphite in nonaqueous solutions of F plus [BF4] salts C BF, which is formed in the primary step, is converted to graphite fluoride by an exchange process. 

Fluorination of graphite leads to a polycarbon monofluoride of ideal composition CF. Incompletely fluorinated samples with compositions CFq. . .. o.s are nearly black while those of compositions CFo.g 0.95 and CF0.95... 1.13 are grey and white, respectively. Carbon monofluoride was found to be a superior lubricant especially at high temperatures and in oxidizing atmospheres [404]. CF is used... 

Covalent compounds, arising from the attack of strong oxidizing systems, such as fluorine or Mn(VII), on graphite. The aromatic planarity of the graphite sheet is destroyed, and a buckled, sp -hybridized sheet is created. 

With its oxygen functionality, graphite oxide has chemical properties more akin to those of layered disulfides or sheet silicates than to those of graphite (Gi, T1,A2). Many studies have been of an extremely applied nature the possibility of fluorination (LI, N1), redox potentials in the presence of hydrogen peroxide (V2), the apparent density (L2), the adsorption isotherms with nitrogen (L3), and the diffusion of Cs in graphite oxide (R2). 

As with graphite oxide, there are currently two views as to the structure of carbon monofluoride. Although detailed X-ray diffraction work suggested a chair arrangement of the sp -hybridized, carbon sheets (Ml), second-moment calculations of the adsorption mode of the fluorine nuclear magnetic resonance suggested that a boat arrangement is more plausible iE2). The structures are illustrated in Fig. 3. 

Initial discharge potentials of fluorinated graphite oxides, prepared by the modified Staudenmaier method, were in the range of 3.20-3.35 V at a current density... 

In order to increase the reaction rate and capacity, some methods to modify the surface structure and composition were recently attempted [42-49], They are surface oxidation [42-45] and surface fluorination [46-48] of graphite and carbon, and metal coating to carbon surface [49], These show that surface modifications are useful techniques to improve the electrochemical characteristics of graphite and carbon. 

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