The oxygen stacking of O3‐type layered sodium transition metal oxides (O3‐NaTMO₂) changes dynamically upon topotactic Na extraction and reinsertion. While the phase transition from octahedral to prismatic Na coordination that occurs at intermediate desodiation by transition metal slab gliding is well understood, the structural evolution at high desodiation, crucial to achieve high reversible capacity, remains mostly uncharted. In this work, the phase transitions of O3‐type layered NaTMO₂ at high voltage are investigated by combining experimental and computational approaches. An OP2‐type phase that consists of alternating octahedral and prismatic Na layers is directly observed by in situ X‐ray diffraction and high‐resolution scanning transmission electron microscopy. The origin of this peculiar phase is explained by atomic interactions involving Jahn–Teller active Fe⁴⁺ and distortion tolerant Ti⁴⁺ that stabilize the local Na environment. The path‐dependent desodiation and resodiation pathways are also rationalized in this material through the different kinetics of the prismatic and octahedral layers, presenting a comprehensive picture about the structural stability of the layered materials upon Na intercalation.

中文翻译：

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直接观察O3型过渡金属氧化物中交替的八面体和棱晶钠层

O3型层状钠过渡金属氧化物（O3-NaTMO ₂）的氧堆积随全钠的提取和重新插入而动态变化。尽管人们已经很好地理解了过渡金属平板滑动在中间脱灰过程中发生的从八面体到棱柱形Na配位的相变，但对于实现高可逆容量至关重要的高脱灰过程中的结构演变仍是未知的。在这项工作中，O3型分层NaTMO ₂的相变通过结合实验和计算方法来研究高压下的电压。通过原位X射线衍射和高分辨率扫描透射电子显微镜可直接观察到由交替的八面体和棱柱形Na层组成的OP2型相。奇异相的起源是通过涉及Jahn–Teller活性Fe ⁴⁺和耐畸变的Ti ⁴⁺的原子相互作用来解释的，该原子稳定了当地的Na环境。该材料还通过棱柱和八面体层的不同动力学合理化了与路径有关的消泡和复硝化路径，从而提供了有关在插层Na时层状材料的结构稳定性的全面描述。