AI 中文总结
以低能ε-LiMnO₂为模型，结合第一性原理计算等方法，揭示0-TM基元连通性差异调控LiMnO₂多形相的Li迁移能垒与脱锂电压，为亚稳态正极设计提供依据。
AI 中文摘要
在岩盐衍生的氧化物正极材料中，围绕O4四面体中间体的局部锂迁移环境通常由共面过渡金属（TM）相邻原子的数量分类。在LiMnO₂中，过渡金属物种为Mn，0-TM表示不存在共面Mn相邻原子。然而，锂迁移和脱锂过程也可能取决于更高壳层的配位和四面体连通性。本研究以最近报道的低能ε-LiMnO₂多形相为模型，通过键价位点能、键价路径分析结合第一性原理计算，探究上述因素的影响。所得迁移图和四面体统计数据揭示了四种LiMnO₂多形相具有不同的拓扑结构和维度。尽管ε相与锂化尖晶石Li₂Mn₂O₄（以下简称尖晶石）的四面体类型占比相同，但它们的0-TM基元分别形成准一维链和三维网络。攀爬图像 nudged elastic band 计算进一步区分了两种结构：ε相的迁移能垒为0.35-0.36 eV，而尖晶石的能垒为0.41-0.53 eV，该差异可能与不同的次近邻共角壳层有关。从头算分子动力学得到表观活化能为0.32 eV，而方向分辨的均方位移显示锂优先沿c轴迁移，支持低能垒的准一维扩散。脱锂计算表明，ε相与尖晶石之间0-TM连通性和Li-Li间距的差异与锂位点演化和计算的电压阶跃相关，提示基元连通性可能影响电压响应。这些结果将0-TM基元的局部环境和空间连通性与锂迁移和脱锂过程关联起来，为亚稳态正极结构的设计提供了见解。
英文摘要
In rocksalt-derived oxide cathodes, the local Li-migration environment around an O$_4$ tetrahedral intermediate is commonly classified by the number of face-sharing transition-metal (TM) neighbors. In LiMnO$_2$, the TM species is Mn, and 0-TM denotes the absence of face-sharing Mn neighbors. However, migration and delithiation may also depend on higher-shell coordination and tetrahedral connectivity. Using the recently reported low-energy $\varepsilon$-LiMnO$_2$ polymorph as a model, we examine these factors through bond-valence site-energy and bond-valence pathway analyses combined with first-principles calculations. The resulting migration maps and tetrahedral statistics reveal distinct topologies across four LiMnO$_2$ polymorphs. Although the $\varepsilon$ phase and the lithiated-spinel phase Li$_2$Mn$_2$O$_4$ (hereafter spinel) have identical tetrahedral-type fractions, their 0-TM motifs form quasi-one-dimensional chains and a three-dimensional network, respectively. Climbing-image nudged elastic band calculations yield $\varepsilon$-phase barriers of 0.35--0.36~eV, compared with 0.41--0.53~eV in spinel, a difference that may be associated with distinct next-nearest corner-sharing shells. Ab initio molecular dynamics yields an apparent activation energy of 0.32~eV, while direction-resolved mean-squared displacements show preferential Li migration along $c$, supporting low-barrier quasi-one-dimensional diffusion. Delithiation calculations further show that differences in 0-TM connectivity and Li--Li separation between the $\varepsilon$ phase and spinel are associated with Li-site evolution and calculated voltage steps. These results link local environments and the spatial connectivity of 0-TM motifs to Li migration and delithiation, providing a structural perspective for metastable cathode design.
Comments9 pages, 7 figures
