Balancing the Stability-Energy Trade-Off in Ultrahigh-Nickel Layered Oxide Cathodes through Mg/Zr-Induced Compositional Engineering

Abstract

Ultrahigh-nickel layered oxide cathodes LiNixMnyCozO2 (NMC, x + y + z =1, x ≥ 0.9) are attractive for energy-dense lithium batteries but suffer from rapid capacity decay and oxygen release during high-voltage operation, compromising cycle life. Although surface coating or elemental doping can improve performance, a complete compositional overhaul remains elusive. Here, we show that compositional engineering of Ni-rich LiNi0.95Mn0.025Co0.025O2 (NMC95) by low-valence (Mg2+) and high-valence (Zr4+) cations strategically replacing Co3+ and Mn4+ yields structurally robust Co-free cathodes—LiNi0.95Mn0.025Mg0.025O2 (NMM95) and LiNi0.95Zr0.025Mg0.025O2 (NZM95) with superior stability and cycle life. Rietveld refinement of powder X-ray diffraction data confirms the formation of ordered layered structures with expanded unit cell volume upon Mg2+/Zr4+ co-substitution, enlarging Li–O interslab spacing from ∼2.64 (NMC95) to ∼2.70 Å (NZM95) and facilitating faster Li+ diffusion, while density functional theory calculations illustrate Mg2+ acts as an ionic stabilizer, and Zr4+ induces charge delocalization, collectively suppressing Li+/Ni2+ antisite defects (NMC95: ∼11.1% to NZM95: ∼9.1%) and stabilizing the oxygen framework. As a result, the NZM95 cathode delivers an initial discharge capacity of ∼207 mAh g–1 with ∼78% retention after 200 cycles at 0.1C, excellent rate capability (∼118 mAh g–1 at 1C), and much-improved thermal stability (∼226°C). Overall, this work underscores the importance of compositional tuning in layered oxides, with Mg/Zr co-substitution affording cobalt-free Ni-rich cathodes with a competitive edge.