Graphite Compounds with Polar Bonding

Potassium- RusmiuM- and Cesium-Graphite 1. Composition and Properties 

The composition of the blue product was not established with certainty in Fredenhagen s work and Schleede and Wellmann (79) first derived the formula CigMe from crystal-structure measurements. However, further analytical and X-ray investigations by Riidorff and Schulze (66, 67) showed conclusively that the blue compounds contained less alkali metal and had the formula C24Me. This conclusion is supported by Harold s work (32) which show ed that in the isobaric breakdown curve of CgK the first clear break occurs at C24K. This product gave the same X-ray powder pattern as the blue compound studied by Schleede (31). 

Fredenhagen found calorimetrically a value of 12 kcal/mole for the heat of formation of CgK formed by introducing graphite into an excess 

The alkali metal-graphite compounds are extremely reactive. They ignite in air and may react explosively with water. In the controlled reaction with water or alcohol only alkali hydroxide and hydrogen result there is no acetylene or any other hydrocarbon. Fredenhagen concluded from this that the compounds could not be carbides. Mercury dissolves the alkali metal out of the lattice. When treated with liquid ammonia, CgMe gives up only a third of the alkali metal and takes in its place two molecules of ammonia (see Section IIIA4). 

The crystal structure of these compounds was first determined by Schleede and Wellmann 79). In the compound CgMe a layer of alkali metal atoms is present between each pair of carbon planes, whereas in the blue alkali-poor compound this occurs between every other pair. Introduction of the alkali metal increases the interplanar distance to 5.41 A for potassium, 5.61 A for rubidium, and 5.95 A for cesium. According to the definition given in the introduction these two compounds are referred to as the first and second stage. 

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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. 

These are formulae in which bonded atoms are coimected up with a single stroke, with no indication of bond mrniber or polarity. They are usually used for compounds in which the bonds have an intermediate bond number or polarity (Chaps. 7 and 8). An example is the following representation of one layer of graphite ... 

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