In situ spectroscopic applications to the study of rechargeable lithium batteries. Final report

摘要

A new experimental approach has been developed and implemented for the study of various aspects of lithium electrochemistry under utmost conditions of cleanliness. This novel strategy takes advantage of the low vapor pressure of ultrapure lithium salt/polyethylene oxide electrolytes for conducting conventional electrochemical experiments in ultrahigh vacuum environments with a wide variety of electrodes prepared and characterized by surface analytical techniques. Two processes were investigated using a LiClO(sub 4)/PEO electrolyte at temperatures in the range of 55-70 (degrees)C: (1) electrochemical insertion of lithium into the basal plane of highly ordered pyrolytic graphite, HOPG(bp), (2) underpotential deposition (UPD) of Li onto polycrystalline Au. The results provided conclusive evidence (except for impurity effects) that the electrochemical behavior observed in UHV is indeed characteristic of the systems selected for these studies, and therefore, is not affected in any discernible way by the ultralow pressures. In the case of Li UPD on polycrystalline Au, the voltammetric curves were similar to those observed in liquid non- aqueous solvent electrolytes, displaying deposition and stripping peaks with a charge equivalent to the adsorption and desorption of a single Li(sup +) per surface site.