High‐Voltage Performance of Ni‐Rich NCA Cathodes: Linking Operating Voltage with Cathode Degradation

Abstract

AbstractHigh‐voltage Ni‐rich cathodes have been studied as a possible way to achieve high energy density in Li‐ion batteries. However, capacity fade due to structural changes at high voltages has limited their applications. This study identifies 4.5 V (vs. graphite) as the optimum upper cutoff voltage (UCV) for a Ni‐rich NCA cathode [LiNi0.8Co0.15Al0.05O2]. At this UCV, NCA delivers a 12 % increase in reversible capacity (when discharged to 2.5 V) and retains 92 % of its initial capacity after 100 cycles at 1C/‐1C cycling when compared to 4.2 V as UCV. By increasing UCV to 4.7 V, the discharge capacity can be raised to >200 mAh/g. However, the rate of capacity fade is greater when compared to 4.5 V as UCV. This increased rate of capacity fade, at higher UCV, is related to irreversible lattice contractions that leads to structural rearrangement at charged states during high‐voltage cycling. Our results show a change in transition metal oxidation states and an onset of structural ordering occurs when the UCV is 4.7 V.