Graphite intercalation compounds reduction

Using dilatometry in parallel with cyclic voltammetry (CV) measurements in lmolL 1 LiC104 EC-l,2-dimethoxy-ethane (DME), Besenhard et al. [87] found that over the voltage range of about 0.8-0.3 V (vs. Li/Li+), the HOPG crystal expands by up to 150 percent. Some of this expansion seems to be reversible, as up to 50 percent contraction due to partial deintercalation of solvated lithium cations was observed on the return step of the CV. It was concluded [87] that film formation occurs via chemical reduction of a solvated graphite intercalation compound (GIC) and that the permselective film (SEI) in fact penetrates into the bulk of the HOPG. It is important to repeat the tests conducted by Besenhard et al. [87] in other EC-based electrolytes in order to determine the severity of this phenomenon. 

Further synthetic modifications of 7 and 8 are summarized in Schemes 4 and 5 [14]. CcMiversions of 9 are described in [15]. The reaction with LiSiPh2(NEt2) leads to the elongation of the silicon chain (10, 14). The reduction with the graphite intercalation compound CgK gave the copoly-... 

Cation- and anion-graphite intercalation compounds can be prepared by electrochemical reduction or oxidation of graphite in appropriate electrolytes. Such electrochemical solid-state reactions require mixed conductivity of the solid, i.e., existence of electronic and ionic conductivity. 

Cathodic reduction of graphite in dipolar aprotic solutions of alkali and [NRJ salts (e.g., in ethers, esters, amides) usually yields solvated cation intercalation compounds " however, at high cation density the solvent may be squeezed out . The corresponding phosphonium and sulfonium graphite intercalation compounds are unstable their formation is accompanied by reductive decomposition of these cations . 

II In that same period another type of highly reactive metal was introduced in synthetic organic chemistry graphite intercalation compounds Mg/Cg, prepared by reduction of a metal halide by potassium graphitide, K/Cg [57]. 

The properties of the intercalation compound, potassium graphite, KCg, have been detailed in several review articles.34/35 The bonding in potassium graphite is described in terms of the limiting structure, K+Cg", and it is believed that the anion forms as a result of the transfer of an electron from the alkali metal to the conduction band of graphite. Novikov and Volpin35 have noted a similarity between aromatic radical-anions and alkali metal-graphite intercalation compounds. Their observation was based on inspection of reduction potentials of aromatic hydrocarbons relative to biphenyl, Table 9.2 ... 

First reported by Fredenhagen in 1926 F3, F4), the graphite-alkali-metal compounds possess a relative simplicity with respect to other intercalation compounds. To the physicist, their uncomplicated structure and well defined stoichiometry permit reasonable band-structure calculations to be made S2,12) to the chemist, their identity as solid, "infinite radical-anions frequently allows their useful chemical substitution for such homogeneous, molecular-basis reductants as alkali metal-amines and aromatic radical anions N2, B5). 

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