A baseline cell chemistry was identified as a carbon anode, LiNi 0.8 Co 0.2 O 2 cathode, and diethyl carbonate-ethylene carbonate LiPF 6 electrolyte, and designed for high power applications. Nine 18650-size advanced technology development cells were tested under a variety of conditions. Selected diagnostic techniques such as synchrotron infrared microscopy, Raman spectroscopy, scanning electronic microscopy, atomic force microscopy, gas chromatography, etc., were used to characterize the anode, cathode, current collectors and electrolyte taken from these cells. The diagnostic results suggest that the four factors that contribute to the cell power loss are solid electrolyte interphase deterioration and nonuniformity on the anode; morphology changes, increase of impedance, and phase separation on the cathode; pitting corrosion on the cathode current collector; and decomposition of the LiPF 6 salt in the electrolyte at elevated temperature.

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The electrochemical quartz crystal microbalance ͑EQCM͒ and cyclic voltammetry have been applied simultaneously to characterize electron-beam deposited carbon film electrodes in LiClO 4 -containing mixed electrolytes of ethylene carbonate ͑EC͒ and dimethyl carbonate ͑DMC͒. The structure of the carbon electrode was found to be amorphous/disordered using Raman spectroscopy. Cyclic voltammetry in LiClO 4 /EC ϩ DMC demonstrated features typical of Li intercalation/deintercalation into/from the disordered carbon electrode, and EQCM showed a corresponding mass increase/decrease. Combined EQCM and spectroscopic ellipsometry data were compared, and the solid electrolyte interphase density after the first cycle in LiClO 4 /EC ϩ DMC was estimated to be 1. Carbon electrodes, in both graphitic and amorphous forms, are used as negative electrodes in secondary Li-ion batteries. The limiting capacity of LiC 6 is 372 mAh/g for graphite, but higher capacities have been observed with certain disordered carbons. When a carbon electrode in a nonaqueous electrolyte is charged for the first time from its open-circuit voltage ͑OCV͒ down to 0 V vs. Li/Li ϩ , Li ions are intercalated into the carbon structure. The potential region over which Li ions are intercalated depends on the structure of the carbon and the type of electrolyte. Along with Li intercalation, other electrochemical/chemical reactions that occur during the first few cycles are electrolyte decomposition on the carbon surface and the formation of an electrode surface layer, often referred to as the solid electrolyte interphase ͑SEI͒. The reactions involved in SEI formation are associated with so-called irreversible capacity loss. The SEI properties and chemical composition have been subjects of intense scientific interest because the SEI plays a critical role in the safety and cycle life of secondary Li-ion batteries.1-5 The current understanding of the role of the SEI is that solvated Li ions in the liquid electrolyte lose their solvation shells while penetrating the SEI and are incorporated into the carbon structure in a solvent-free form. In addition, the SEI not only dramatically slows the kinetics of electrolyte decomposition but also reduces active lithium consumption by forming a physical barrier between the lithiated carbon electrode and the electrolyte.Spectroscopic ellipsometry ͑SE͒ is a surface-sensitive tool that is capable of detecting changes in the surface composition/structure at the molecular level. Even a small change in species adsorption on a surface or the formation of nanometer-scale surface film can lead to measurable changes in the ellipsometry parameters ⌬ and ⌿. However, to obtain a direct and unambiguous correlation between the detailed processes occurring on the electrode surface with the changes in the ellipsometric parameters requires precise information on the optical properties of the surface and all candidate film components.The electrochemical quartz crystal microbalance ͑EQCM͒ technique is based on the piezoelectric effect of a quartz cry...

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