The performance characteristics of lithium-ion battery cathode materials are governed by the surface structure and chemistry. Synthesis is known to affect the structure of these materials; however, a full understanding of the effects of the surface structure is not well understood. Here, we explore the atomic scale structure of lithium-layered oxides prepared with two different thermal treatments. We show that, under certain thermal treatments, the surface perpendicular to the transition-metal layers is enriched in nickel, which results in Ni occupying the lithium layer of the layered oxide structure. Under both thermal treatments, this surface also shows a reduction of Mn, with some of the reduced Mn occupying sites in the lithium layer. The surface parallel to the transition-metal layers under both treatments shows significant Mn reduction, oxygen loss, and reduced Mn in the lithium layer. The Mn reduction and surface reconstruction are the result of unstable surface terminations and are intrinsic to layered oxides. Synthesis can be tuned to eliminate Ni enrichment at the surface; however, it cannot be tailored to eliminate Mn reduction and surface reconstruction.

中文翻译：

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锂离子电池富锂层状氧化物中的表面重建

锂离子电池正极材料的性能特征取决于表面结构和化学性质。已知合成会影响这些材料的结构。然而，对表面结构的影响的充分理解还不是很清楚。在这里，我们探讨了用两种不同的热处理方法制备的锂层氧化物的原子尺度结构。我们表明，在某些热处理条件下，垂直于过渡金属层的表面富含镍，这导致Ni占据了层状氧化物结构的锂层。在两种热处理下，该表面还显示出Mn的还原，其中一些还原的Mn占据锂层中的位点。在两种处理下，与过渡金属层平行的表面均显示出明显的Mn降低，氧损失，并降低锂层中的Mn。Mn的还原和表面重构是不稳定的表面终止的结果，是层状氧化物所固有的。可以调整合成以消除表面的镍富集；但是，不能针对消除锰的减少和表面重构进行定制。