Boosting cationic and anionic redox activity of Li-rich layered oxide cathodes via Li/Ni disordered regulation

Abstract

Lithium-rich layered oxides (LLOs) are increasingly recognized as promising cathode materials for next-generation high-energy-density lithium-ion batteries (LIBs). However, they suffer from voltage decay and low initial Coulombic efficiency (ICE) due to severe structural degradation caused by irreversible O release. Herein, we introduce a three-in-one strategy of increasing Ni and Mn content, along with Li/Ni disordering and TM–O covalency regulation to boost cationic and anionic redox activity simultaneously and thus enhance the electrochemical activity of LLOs. The target material, Li_1.2Ni_0.168Mn_0.558Co_0.074O₂ (L1), exhibits an improved ICE of 87.2% and specific capacity of 293.2 mA h g⁻¹ and minimal voltage decay of less than 0.53 mV cycle⁻¹ over 300 cycles at 1C, compared to Li_1.2Ni_0.13Mn_0.54Co_0.13O₂ (Ls) (274.4 mA h g⁻¹ for initial capacity, 73.8% for ICE and voltage decay of 0.84 mV/cycle over 300 cycles at 1C). Theoretical calculations reveal that the density of states (DOS) area near the Fermi energy level for L1 is larger than that of Ls, indicating higher anionic and cationic redox reactivity than Ls. Moreover, L1 exhibits increased O-vacancy formation energy due to higher Li/Ni disordering of 4.76% (quantified by X-ray diffraction Rietveld refinement) and enhanced TM–O covalency, making lattice O release more difficult and thus improving electrochemical stability. The increased Li/Ni disordering also leads to more Ni²⁺ presence in the Li layer, which acts as a pillar during Li⁺ de-embedding, improving structural stability. This research not only presents a viable approach to designing low-Co LLOs with enhanced capacity and ICE but also contributes significantly to the fundamental understanding of structural regulation in high-performance LIB cathodes.