Regulating Surface Oxygen Activity by Perovskite-Coating-Stabilized Ultrahigh-Nickel Layered Oxide Cathodes

Abstract

Ultrahigh-Ni layered oxides are proposed as promising cathodes to fulfill the range demand of electric vehicles; yet, they are still haunted by compromised cyclability and thermal robustness. State-of-the-art surface coating has been applied to solve the instability via blocking the physical contact between the electrolyte and the highly active Ni4+ ions on the cathode surface, but it falls short in handling the chemo-physical mobility of the oxidized lattice oxygen ions in the cathode. Herein, a direct regulation strategy is proposed to accommodate the highly active anionic redox within the solid phase. By leveraging the stable oxygen vacancies/interstitials in a lithium and oxygen dual-ion conductor (layered perovskite La4NiLiO8) coating layer, the reactivity of the surface lattice oxygen ion is dramatically restrained. As a result, the oxygen release from the lattice is suppressed, as well as the undesired irreversible phase transition and intergranular mechanical cracking. Meanwhile, the introduced dual-ion conductor can also facilitate lithium-ion diffusion kinetics and electronic conductivity on the particle surface. This work demonstrates that accommodating the anionic redox chemistry by dual-ion conductors is an effective strategy for capacity versus stability juggling of the high-energy cathodes.