Li/graphite and Li/petroleum coke cells using a 1M LiAsF6 in a 50:50 mixture of propylene carbonate (PC) and ethylene carbonate (EC) electrolyte exhibit irreversible reactions only on the first discharge. These irreversible reactions are associated with electrolyte decomposition and cause the formation of a passivating film or solid electrolyte interphase on the surface of the carbon. The amount of electrolyte decomposition is proportional to the specific surface area of the carbon electrode. When all the available surface area is coated with the film of decomposition products, further decomposition reactions stop. In subsequent cycles, these cells exhibit excellent reversibility and can be cycled without capacity loss.

We report electrochemical and x-ray-diffraction studies of the intercalation of lithium in graphite and in disordered carbons. The phase diagram of electrochemically intercalated graphite agrees well with previous work on samples prepared by chemical methods. The we11-known staged phases present in intercalated graphite are absent in intercalated petroleum coke. Furthermore, the voltage V(x) of Li/Li"C6 cells differs greatly when graphite or coke is used as the host. By heating coke to successively higher temperatures, we are able to increase the graphitization or crystalline order of the host in a continuous fashion and study the effect of this variation on the phase diagram of Li"C, and on V(x). We find that staged phases are suppressed at room temperature for hosts less ordered than a "critical disorder. " A lattice-gas model with random site energies is used to model the effects of host disorder and qualitatively explains the suppression of staged phases and the changes in V(x) with increasing disorder in the host. For a rectangular "density of sites, " staged phases are suppressed when the width of the site energy distribution is greater than the magnitude of the mean-field attractive Li-Li interaction, which causes island growth and staging in intercalated graphite.

The charge and discharge mechanisms of normalLi/FeS2 and normalLi/Li2FeS2 cells near room temperature are studied by in situx‐ray diffraction and in situ 57Fe Mössbauer spectroscopy. The electrochemical behavior of these cells are compared, and their cell reactions are described. For 00.8 , structural decomposition of Li2−xFeS2 occurs, and disproportionation to nonstoichiometric normalFeS false(FeSyfalse) and S is observed. Similarly, when normalLi/FeS2 cells are recharged to 2.8V, the cathode is a mixture of FeSy and S. Examination of the mixture by differential scanning calorimetry shows that FeSy and S react to form FeS2 above 200°C. This explains why high temperature normalLi/FeS2 cells cycle reversibly while ambient temperature normalLi/FeS2 cells show poor reversibility.

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