Triple Stabilization of Phase, Electron, and Cation to Enhance the Lithium Storage Performance of High-Voltage Medium-Ni, Low-Co Layered Oxide Cathodes

High-voltage medium-Ni, low-Co lithium-layered oxide cathodes have the advantage of high capacity, low cost, and high safety. Unfortunately, high voltage represents deep redox reactions and Li⁺ deintercalation, and low cobalt content means poor conductivity and more cation mixing, seriously endangering the cycle life and charging speed of the batteries. Here, a unique Y element located between transition metals and rare earth elements is doped to modify the LiNi_0.7Co_0.05Mn_0.25O₂ (NCM and NCMY) medium-Ni, low-Co cathode. Y³⁺ acts as a pillar in the lithium layer to suppress drastic volume changes. Strong Y–O bonds effectively suppress oxygen evolution. The low magnetic Y³⁺ with no unpaired electrons suppresses hazardous Li⁺/Ni²⁺ mixing. The triple stability of phase, electron, and cation greatly improves the bulk layered structure and electrolyte–electrode interface stability. At a high voltage of 4.5 V, NCMY displays exceptional cyclical stability (retained capacity at 100 cycles: 90.7% vs 83.0%) and rate capability (capacity at 5C rate: 127 mAh g^–1 vs 87 mAh g^–1) compared to NCM. The NCMY//graphite full battery achieves 83.7% capacity retention after 500 cycles with a high energy density of 268 Wh kg^–1. The unique and comprehensive Y doping modification will enable the high-voltage medium-Ni, low-Co cathodes to be applied in practice earlier.