As commercial cathodes with the highest practical capacity, the structural nature of Li-rich Mn-based (LMR) cathodes, composite or solid solution, is still under debate. Due to the extreme structural similarity of two layered-phase components, namely, the monoclinic phase (C2/m) and rhombohedral phase (Rm), no single tool can resolve this concern alone. Herein, we combined multiple advanced techniques to comprehensively study the structural changes during synthesis of LMR cathodes from different aspects such as the elemental distribution, local structure, long-range structure, and short-range structure, revealing a clear process from the formation of two phases to the gradual phase fusion and eventually to a nearly solid solution. Particularly, X-ray pair distribution function (PDF) analysis combined with theoretical simulations reveals for the first time that the transition metal (TM)–TM distance increases with the progress of the phase fusion, which makes the short-range structural change in TM–TM atomic pairs an effective parameter for judging the extent of phase fusion. Eventually, excellent electrochemical performance was achieved by balancing capacity and cycling stability through adjusting the phase fusion to a medium extent in lithium and sodium two layered-phase components. This study establishes an approach to investigate the structural evolution in the complicated multiple-phase system and provides valuable insights into the design and optimization of cathodes by tuning the phase fusion extent.

中文翻译：

---

富锂锰基正极相演化的多角度跟踪合成动力学

作为具有最高实际容量的商业正极，富锂锰基（LMR）正极、复合材料或固溶体的结构性质仍然存在争议。由于两种层状相组分（即单斜相（C 2/ m）和菱形相（R m））的结构极其相似，没有任何一种工具可以单独解决这个问题。在此，我们结合多种先进技术，从元素分布、局域结构、长程结构、短程结构等不同方面全面研究了LMR阴极合成过程中的结构变化，揭示了从两种材料形成的清晰过程。相到逐渐相融合并最终接近固溶体。特别是，X射线对分布函数（PDF）分析与理论模拟相结合，首次揭示了过渡金属（TM）-TM距离随着相融合的进展而增加，这使得TM的短程结构变化–TM原子对是判断相融合程度的有效参数。最终，通过将锂和钠两层相组分中的相融合调整到中等程度来平衡容量和循环稳定性，从而实现了优异的电化学性能。这项研究建立了一种研究复杂多相系统中结构演化的方法，并通过调整相融合程度为阴极的设计和优化提供了宝贵的见解。