Unveiling the Origin of Oxygen Framework Stability in Ultra‐High Nickel Layered Oxide Cathodes

Abstract

Ultra-high nickel layered oxides are recognized as promising cathode candidates for high-energy-density lithium-ion batteries due to their enhanced overall capacity and elevated operating voltage. However, the interlayer sliding of transition metal-oxygen octahedra (TMO6) and the instability of lattice oxygen at high voltages for ultra-high nickel oxide cathodes pose significant challenges to their development. Herein, the origin of oxygen framework stability is investigated by incorporating high-covalent element Mo in both bulk and surface using a one-step integrated method for ultra-high nickel cathode material LiNi_0.92Co_0.08O₂. It is revealed that apart from the isolation and protection effect of the Mo-enriched surface layer, the suppression of Li/Ni antisite defects by Mo⁶⁺ with strong covalency in the bulk plays a critical role in reducing the configurations of the activated anionic redox reaction and stabilizing the lattice oxygen and oxygen framework structure. Benefiting from this, the reversibility of anionic redox reaction and the stability of oxygen framework is significantly enhanced, enabling more oxidized oxygen to exist in the form of oxygen dimer ions <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msubsup><mml:mi>O</mml:mi> <mml:mn>2</mml:mn> <mml:mrow><mml:mi>n</mml:mi> <mml:mo>-</mml:mo></mml:mrow> </mml:msubsup> <mml:annotation>$O_2^{n - }$</mml:annotation></mml:semantics> </mml:math> rather than being lost as gaseous O₂. Consequently, the modified ultra-high nickel material demonstrates improved diffusion kinetics and optimized electrochemical performance at high voltage.