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Using electrochemical methods we have measured the variation of the chemical potential p of intercalated Li in graphite and in boron-substituted graphite as a function of Li concentration x. For small x in Li"(C&,B,)6, p can be predicted from the density of one-electron levels versus energy, and we find good agreement with the data for pure graphite and for a boron-doped sample. In the rigid-band model, dx/dp vs p is directly proportional to the density of states versus energy, and our measurements of dx/dp agree well with empirical tight-binding density-of-states calculations. We show how the values of tight-binding overlap interactions can be directly determined from the electrochemical data.

Using synchrotron radiation we measured the x-ray absorption (XAS) near the C\ s edge for powdered graphite, boron substituted graphite, and a disordered graphitic carbon. The chemical potential of Li intercalated into the same carbons has also been measured as a function of x in Li x C6. When Li is intercalated, the 2s electron is transferred to the C host, filling the same levels as probed by XAS. In XAS, final-state energies contain a contribution from the electron-core-hole interaction which mimics the situation in Li intercalation where Li + interacts with conduction electrons. We show that XAS results correlate well with chemical potential measurements of intercalated Li made on the same materials. PACS numbers: 78.70.Dm, 71.20.-b, 82.45.+Z, 82.60.-s

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