Characterization of Spontaneous Reactions of LiCoO[sub 2] with Electrolyte Solvent for Lithium-Ion Batteries

Positive electrode materials commercial and nanosized, bare and -coated, are soaked in a mixture of battery-grade ethylene carbonate and dimethyl carbonate, with and without Strong spontaneous reactions have been observed between and the solvent. These reactions become less obvious in practical electrolyte. The composition of the soakage-induced gas, liquid, and solid products are characterized with gas chromatography and mass spectroscopy, Raman and Fourier transformed infrared spectroscopy, respectively. The atomic ratios of Co/Li in the liquid and in the solid are analyzed by inductively coupled plasma technique. The surface morphologies of the solvent- and electrolyte-soaked commercial particles are observed with scanning electron microscopy. Significant impacts of the spontaneous reactions on the structure and electrochemical performance of the electrode material are evaluated with X-ray diffraction (XRD) and electrochemical cycling, respectively. Based on these results, other important aspects of the performance improvement mechanism by surface modification to and the limitation of surface modification are proposed. © 2004 The Electrochemical Society. All rights reserved.