Failure Mechanism of Graphite/LiNi0.5Mn1.5O4 Cells at High Voltage and Elevated Temperature

The failure mechanism of graphite/LiNi0.5Mn1.5O4 cells cycled at 25 degrees C and 55 degrees C have been analyzed by electrochemical methods and ex-situ surface analysis of the electrodes. Graphite/LiNi0.5Mn1.5O4 cells cycle well at 25 degrees C, but have rapid capacity fade upon cycling at 55 degrees C. Independent electrochemical analysis of anodes and cathodes extracted from cells cycled at 55 degrees C suggest that both electrodes have significant capacity loss, although the cathode capacity can be recovered with longer charging times. Ex-situ surface analysis of the cathode with SEM reveals that the bulk cathode particles and the cathode laminate are retained while XPS confirms the presence of a cathode electrolyte interface composed of the decomposition products of the electrolyte. Ex-situ analysis of the anode reveals a thick anode solid electrolyte interphase (SET), anode delamination, and the presence of Mn. The results suggest that both the anode and the-cathode contribute to performance loss in graphite/LiNi0.5Mn1.5O4 cells. (C) 2013 The Electrochemical Society.