Capacity fading of spinel LiMn2O4 during cycling at elevated temperature

A normal spinel LiMn2O4 as cathode material for lithium-ion cells was cycled galvanostatically (0.2 C) at 55℃. To determine the contribution of each voltage plateau to the total capacity fading of the cathode upon repeated cycling, the capacities in each plateau were separated by differentiation of voltage vs. capacity. The results showthat the capacity fading in the upper voltage plateau is more rapidlythan that in the lower during discharging, while in charging process,it fades slower than that in the lower voltage range. The increased capacity shift and aggravated self-discharge/electrolyte oxidation during discharging contribute to a high fading rate in the upper step. Capacity shift also takes place during charging process, which again enhancing the fading rate of the lower voltage plateau. An increase in capacity shift, as a result of an increase in polarization of the cell, plays a major role in determining the fading rate in each voltage plateau, further reflecting the thickening of the passivation layer on the active particles, and the accumulation of electrolyte decomposition. The relative capacity loss for modified spinels is well correlated withthe relative increase in the polarization of the half-cells, confirming the above causes for capacity fade of this kind of cathode material.