Modulating the Voltage Decay and Cationic Redox Kinetics of Li-Rich Cathodes via Controlling the Local Electronic Structure

Li-rich layered oxide cathodes with conventional transition metal cation and unique oxygen anion redox reactions deliver high capacities in Li-ion batteries. However, the oxygen redox process causes the oxygen release, voltage fading/hysteresis, and sluggish electrochemical kinetics, which undermine the performance of these materials. By combining operando quick-scanning X-ray absorption spectroscopy with online gas chromatography, the effect of the local electronic structure is elucidated on the reaction mechanism and electrochemical kinetics of Li-rich cathodes. The local electronic structure of Li-rich cathodes varies with the excess Li (i.e., Li2MnO3 phase) and Ni contents. Compared to the Li-rich cathodes with higher amounts of Li2MnO3 phase (high excess lithium content (HLC) cathode), those with lower Li2MnO3 contents (low excess lithium content (LLC) cathode) exhibit reversible anion redox reactions and suppressed voltage hysteresis. The cation oxidation process of LLC cathode is kinetically slower than that of HLC cathode and the cation oxidation potential is shifted, likely due to the local coordination associated with different Li/O ratios. The obtained insights into the effect of local electronic structure on the reaction mechanism and kinetics provide a better understanding and control of Li-rich cathodes.