Graphite, intercalation compounds covalent

GO does not seem to be suitable as a reversible battery electrode. The reason is the irreversible formation of covalent C-O(H) bonds in the course of anodic formation. According to Boehm and to Ubbelohde, graphite intercalation compounds do play the role of a precursor ... 

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. 

Compounds of graphite are formed when foreign species such as atoms, ions, or molecules are inserted between the layers of the graphite lattice. These compounds can be divided into two general classes with clearly different characteristics a) the covalent compounds, and (b) the intercalation compounds.t ... 

Like the covalent graphite compounds, the intercalation compounds are formed by the insertion of a foreign material into the host lattice. The structure however is different as the bond, instead of being covalent, is a charge-transfer interaction. This electronic interaction results in a considerable increase in electrical conductivity in the ab directions. 

Although the covalent compounds of graphite are thus important in their own right, they represent the extreme form of oxidative intercalation. The use of fluoride compounds to achieve highly conductive materials may ultimately lead to new forms of graphite fluoride SI). 

Fig. 17. Pictorial representation of intercalated superconducting compound of 2-dimensional graphite (carbon atoms interconnected with solid lines each line represents a pair of covalent bond) interleaved with potassium (circles) which ionizes easily to K. and provide free electrons . According to the model, COVALON conduction takes place within the graphite plane and affects the COVALON on the adjacent graphite plane through plasmon waves provided by the free electrons from the potassium metal.

Covalent C—F bonds are also detectable in lamellar n charge-transfer graphite compounds such as CjSbFj C KrFj and halogen fluorides (see 16.4.2.1.1 and reviews ). These mixed covalent-rr charge-transfer compounds arise from internal fluorination by the intercalant. 

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