Impact of storage on the LiNi0.4Mn1.6O4 high voltage spinel performances in alkylcarbonate-based electrolytes

The two main degradation mechanisms of the LiNi0.4Mn1.6O4/electrolyte interface are already known to be the electrolyte oxidation and the dissolution of transition metal ions. The impact of these two phenomena on the performances during cycling and after prolonged storage of accumulators is evaluated by modifying the cell configuration. The aim is to understand the mechanisms leading to the decrease in performances of the electrochemical cells. Storage of LiNi0.4Mn1.6O4/Li and LiNi0.4Mn1.6O4/Li4Ti5O12 accumulators confirms that there is no correlation between the ability of alkylcarbonate-based electrolytes to resist to their own oxidation at high potential and the decrease in cell electrochemical performances. This is mainly due to the transition metal ion dissolution from Li1-xNi0.4Mn1.6O4. The use of LiNi0.4Mn1.6O4/Li accumulators for storage tests is not suitable over a long period, owing to the reactivity of reducing lithium, particularly at high temperatures, hindering distinguishing differences between electrolytes. The use of the LiNi0.4Mn1.6O4/Li4Ti5O12 cells reveals that a temperature of 30°C with the EC/EMC electrolyte improves the cell performances after prolonged storage. However, the use of such cells induces Mn2+ and Ni2+ in larger amounts than in the LiNi0.4Mn1.6O4/Li cells, resulting in a minimal reversible capacity loss of 20% related to the total disappearance of the electrochemically active manganese (Mn+IV→Mn+III).