Failure Mechanism of Graphite/LiNi_0.5Mn_1.5O₄Cells at High Voltage and Elevated Temperature

The failure mechanism of graphite/LiNi 0.5 Mn 1.5 O 4 cells cycled at 25°C and 55°C have been analyzed by electrochemical methods and ex-situ surface analysis of the electrodes. Graphite /LiNi 0.5 Mn 1.5 O 4 cells cycle well at 25°C, but have rapid capacity fade upon cycling at 55°C. Independent electrochemical analysis of anodes and cathodes extracted from cells cycled at 55°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 (SEI), anode delamination, and the presence of Mn. The results suggest that both the anode and the cathode contribute to performance loss in graphite/LiNi 0.5 Mn 1.5 O 4 cells.