Diagnostic Characterization of High Power Lithium-Ion Batteries for Use in Hybrid Electric Vehicles

A baseline cell chemistry was identified as a carbon anode, LiNi_0.8Co_0.2 O₂ cathode, and diethyl carbonate-ethylene carbonate LiPF₆ 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 LiPF₆ salt in the electrolyte at elevated temperature.