A Strategy for Mitigating Lattice Stress and Enhancing Cycle Stability Through Modulating Transition Metal Redox Sequence

Abstract

Modifying the redox properties of transition metals within layered cathode materials represents a pivotal approach in the pursuit of high-performance cathode materials. The recent research has revealed a novel finding: the introduction of Mg²⁺ into LiNi_1/3Co_1/3Mn_1/3O₂ leads to a shift in the oxidation sequence of transition metals during lithium extraction, with Co³⁺ supplanting Ni²⁺ as the primary oxidized species during the initial stages of lithium extraction. This alteration in the lattice constants and volume, among other structural parameters, serves to mitigate lattice stress during the charging and discharging cycles. The abundance of Co⁴⁺ during the early stages of lithium extraction effectively curtails structural alterations and the dissolution of transition metal ions, thereby bolstering the material's cyclability. This effect is attributed to the enhanced Ni─O bond strength imparted by Mg²⁺ doping, which, in concert with Co³⁺, stabilizes the Li─O structure at the outset of lithium extraction, conferring a thermodynamic advantage to Co³⁺ for preferential oxidation. The exploration of the underlying mechanism of this induced effect and its influence on electrochemical performance holds the potential to offer fresh perspectives for the design of materials with exceptional cycle stability.