Understand the Voltage Fade Mechanism of Li-Rich Layered Oxide Cathodes during Extended Cycling

Abstract

Recently, Li-rich layered oxides have attracted much attention for Lithium-ion Batteries (LIBs) because of their high theoretical capacities, low cost, and friendliness. Like other cathodes for a widespread use, Li-rich layered oxides also suffer from natural obstacles, such as low coulombic efficiency at initial charge/discharge process, insufficient rate performance and inferior ability to remain output voltage during the cycles. In this work, Li1.2Mn0.6Ni0.2O2 cathode material was synthesized via a co-precipitation method. Both ex - situ X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) measurements are used to reveal its fundamental voltage fade mechanism. The collected results confirm that the change in valence state of Mn ions and structural evolution lead to its voltage fade. Along with increasing the cycles, a shift of the Mn K-edge gradually shifts to a lower energy region, suggesting that an increasing amount of trivalent manganese ions. In contrast, no change is observed on Ni2+ ions. Ligand oxygen ions are directly involved in the charge compensation mechanism. Figure 1