富锂层状氧化物(LLOs)是下一代高容量锂离子电池正极材料的有利竞争者. 然而, LLOs材料常掺杂的Co元素不仅价格昂高, 且环境有害. 因此, 本工作使用价格便宜、环境友好的Fe元素代替Co, 构建了具有聚集和分散LiMn₆的Li_1.17Ni_0.17Fe_0.17Mn_0.49O₂体系. 使用密度泛函理论(DFT)计算方法对体系结构、氧化过程、氧释放焓、过渡金属离子迁移及Fe掺杂作用等进行了研究. 研究发现, 掺杂的Fe激活了更多的氧参与电荷补偿, 分散的LiMn₆抑制了由Fe引起的Jahn-Teller效应畸变、氧的释放和Mn⁴⁺的迁移, 进而稳定了结构. 特别需要指出的是不同环境O的活性不同, 线性Li-O-Li中O是主要氧化还原中心, 主导氧化还原反应; 其次Fe-O-Li中O也参与氧化, LiTMO₂相O前期参与氧化, LiTMO₂与Li₂MnO₃相的边界O后期参与氧化. 本工作为设计无Co且结构稳定容量高的锂离子电池富锂层状正极材料提供了新的见解.

Lithium-rich layered oxides (LLOs) are a favorable competitor for the next generation of high-capacity lithium-ion battery cathode materials. However, the doped Co in LLOs materials is not only expensive, but also harmful to the environment. Furthermore, in LLOs cathodes, the aggregation of Li₂MnO₃ domains and lattice oxygen release lead to severe capacity/voltage degradation, ultimately impeding their commercial viability. Therefore, in this work, we substituted environmentally friendly and cost-effective Fe for Co, and designed two structural models—local distribution (LD) and delocalized distribution (DD) in the Li_1.17Ni_0.17Fe_0.17Mn_0.49O₂ system. A spin-polarized generalized gradient approximation (GGA) method with the PBE (Perdew-Burke-Ernzerhof) exchange-correlation functional was explored. A 2×2×1 supercell with a total of 96 atoms, namely Li₂₈Fe₄Ni₄Mn₁₂O₄₈ is selected. We systematically investigated geometrical and electronic structures of DD and LD systems, oxidation processes, oxygen release enthalpy, transition metal ion migration and the role of Fe using density functional theory (DFT) calculations. It was found that the doped Fe activates more interfacial oxygen ions to participate to the charge compensation and disperses oxygen oxidation, thereby sharing the oxidation pressure of oxygen in the Li-O-Li configuration, which would be beneficial for suppressing the release of lattice oxygen. The dispersed LiMn₆ in the Li_1.17Ni_0.17Fe_0.17Mn_0.49O₂ system inhibits the Jahn-Teller distortion caused by Fe and the migration of Mn⁴⁺ ions, thus stabilizing the structures. Oxygen in the linear Li-O-Li structure serves as the primary redox center, driving the redox reactions. Additionally, oxygen in Fe-O-Li-based systems also participates in the oxidation process. Specifically, the oxygen in the LiTMO₂ phase contributes to the early-stage oxidation, while oxygen at the interface between the LiTMO₂ and Li₂MnO₃ phases plays a role in the later stages of oxidation. This work provides new insights into the design of lithium-rich layered cathode materials without Co and with the high structural stability and the high capacity for lithium-ion batteries.