Suppressing Transition Metal Dissolution in Co and Mn Free Ultrahigh Ni-Rich Cathodes for Lithium-Ion Batteries

Abstract

Ultrahigh nickel-rich layered oxide cathodes have garnered significant attention as next-generation lithium-ion battery (LIB) due to their high specific capacity and potential to eliminate cobalt. However, conventional cathodes such as iNi0.95Mn0.025Co0.025O2 (NMC95) are limited by structural degradation, Li+/Ni2+ cation mixing, oxygen release, and transition-metal dissolution, resulting in poor cycling performance and limited thermal stability, particularly during high-voltage operation. Furthermore, the scarcity, toxicity, and cost volatility of cobalt, along with the instability of Mn3+ due to Jahn–Teller distortion and disproportionation, further constrain their practical viability. Herein, we report Co- and/or Mn-free ultrahigh-Ni-rich cathode materials, LiNi0.95Mn0.025Mg0.025O2 (NMM95) and LiNi0.95Zr0.025Mg0.025O2, as promising alternatives to NMC cathode. Structural characterizations using XRD, Rietveld refinement, and HRTEM reveal enhanced crystallinity, reduced cation disorder, and enlarged interlayer spacing in the NMM95 and NZM95. Substitution with Mg2+ and Zr4+ strengthens the Ni–O bond, suppresses antisite defects, and oxygen-related defects, as confirmed by Synchrotronbased EXAFS, XPS, and wavelet transform analyses. DFT calculations and charge density mappings indicate improved charge delocalization and stronger covalent bonding in NZM95, contributing to structural robustness during cycling. Electrochemical tests demonstrate that NMM95 and NZM95 exhibit an outstanding cycling stability, retaining ~71% and ~78%, respectively, after 200 cycles at 0.1C within a 3.0–4.5 V. In contrast, NMC95 retains only ~60% under identical conditions. Electrochemical impedance spectroscopy confirms reduced CEI layer growth and interfacial resistance in NZM95. Furthermore, differential scanning calorimetry shows superior thermal stability with a higher exothermic peak temperature (~226 °C) and reduced heat evolution. Overall, NZM95 emerges as a highly stable, Co- and Mn-free ultrahigh Ni-rich cathode offering excellent electrochemical and thermal performance. This work provides both theoretical and experimental evidence supporting ultrahigh Nirich cathodes as sustainable and scalable alternatives for next-generation lithium-ion batteries.