Title: Tailoring the redox-active transition metal content to enhance cycling stability in cation-disordered rock-salt oxides

Authors: Ke Zhou, Yining Li, Shiyao Zheng, Maojie Zhang, Chunyang Zhang, Corsin Battaglia, Haodong Liu, Kuan Wang, Pengfei Yan, Jianjun Liu, Yong Yang*

Abstract: Lithium-excess cation-disordered rock-salt oxides (DRXs) are investigated intensively as cathode materials for future lithium-ion batteries combining cationic and anionic redox reactions. However, the lattice oxygen redox can cause severe oxygen release resulting in rapid capacity fading. Here, we investigate a series of xLi₂TiO₃-(1 - x)LiMnO₂ (0 ≤ x ≤1) materials and find that only Li_1.2Mn_0.4Ti_0.4O₂ (x = 0.4) and Li_1.1Mn_0.7Ti_0.2O₂ (x= 0.2) can form phase-pure DRXs, which both deliver high capacity (> 250 mAh g⁻¹). The newly discovered Li_1.1Mn_0.7Ti_0.2O₂ DRX exhibits remarkably high capacity retention of 84.4% after 20 cycles compared to only 60.8% for Li_1.2Mn_0.4Ti_0.4O₂. Our result indicates that the irreversible oxygen loss is reduced by raising the Mn content. Theoretical calculations further reveal that increasing the redox-active Mn content from Li_1.2Mn_0.4Ti_0.4O₂ to Li_1.1Mn_0.7Ti_0.2O₂ causes the orbitals near the Fermi level to change from O 2p non-bonding (LiOLi unhybridized orbitals) to (MnO)* antibonding bands, exhibiting a high OO aggregation barrier, preventing O₂ release and resulting in sustained capacity retention. Hence, these new findings demonstrate that regulating oxygen redox by tailoring the redox-active transition metal content is an effective strategy to enhance the cycling stability of DRXs.

Full-Link: https://www.sciencedirect.com/science/article/pii/S2405829721004153