Understanding the Effects of Al and Mn Doping on the H2-H3 Phase Transition in High-Nickel Layered Oxide Cathodes

High-nickel layered oxide cathodes make up a promising family of materials for next-generation lithium-ion batteries (LIBs). Deleterious phase transitions and surface instabilities, however, have hindered their mass adoption. Al doping and Mn doping have both been shown to improve cyclability at the expense of the initial capacity. However, the effects of these dopants on the performance of the high-voltage H2-H3 phase transition remain unexplored. Herein, we examine the effects of Al and Mn doping on the H2-H3 phase transition in Li[Ni0.95Al0.05]O-2 and Li[Ni0.95Mn0.05]O-2 in comparison to that in undoped LiNiO2 (LNO). We find that 5% Al doping and 5% Mn doping both suppress and delay the phase transition to a higher voltage but appear to affect its reversibility only minimally. We further find that the dopants reduce the increase in impedance with voltage when passing through the phase transition but do so at the expense of capacity. Cyclic step chronoamperometry shows that Al and Mn both improve the rate performance through the H2-H3 phase transition compared to that of undoped LNO. This is attributed to widened lithium diffusion channels at high states of charge enabled by the dopants, which is verified with X-ray diffraction. This work provides insights into the H2-H3 phase transition, necessary for optimized cycling protocols for next-generation LIBs, and improves our general understanding of these crucial energy materials.