Lithium-rich layered oxides (LLOs) are considered promising cathode materials for lithium-ion batteries because of their high reversible capacity, which is attributed to the exploitation of the novel anionic redox in addition to the conventional cationic redox process. Transition metal (TM) migration, which is known to be the main cause of the voltage decay in LLOs, is now understood to also be the critical factor triggering anionic redox, although this origin is still under debate. A better understanding of the specific TM migration behavior and its effect during charge/discharge would thus enable further development of this class of materials. Herein, we demonstrate that the unique TM migration during charge/discharge significantly alters the lithium diffusion mechanism/kinetics of LLO cathodes. We present clear evidence of the much more sluggish lithium diffusion occurring during discharge (lithiation) than during charge (de-lithiation), which contrasts with the traditional lithium diffusion model based on simple topotactic lithium intercalation/deintercalation in the layered framework. The reversible but asymmetric TM migration in the structure, which originates from the non-equivalent local environments around the TM during the charge and discharge processes, is shown to affect the lithium mobility. This correlation between TM migration and lithium mobility led us to propose a new lithium diffusion model for layered structures and suggests the importance of considering TM migration in designing new LLO cathode materials.

中文翻译：

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基于不对称但可逆过渡金属迁移的层状氧化物锂扩散新模型

富锂层状氧化物（LLO）被认为是锂离子电池的有前途的正极材料，因为它们具有高的可逆容量，这归因于除传统的阳离子氧化还原工艺之外还采用了新型的阴离子氧化还原。过渡金属（TM）迁移是众所周知的LLO电压衰减的主要原因，现在人们认为过渡金属（TM）迁移也是引发阴离子氧化还原的关键因素，尽管这种起源仍在争论中。因此，对特定的TM迁移行为及其在充电/放电过程中的影响的更好理解将有助于进一步开发此类材料。在本文中，我们证明了在充电/放电过程中独特的TM迁移显着改变了LLO阴极的锂扩散机制/动力学。我们提供了明显的证据，表明放电（锂化）过程中发生的锂扩散比充电（去锂化）过程中的锂扩散慢得多，这与基于分层框架中简单的全能锂嵌入/脱嵌的传统锂扩散模型形成了鲜明的对比。结果表明，结构中可逆但不对称的TM迁移会影响锂的迁移率，这种迁移源自于在充电和放电过程中TM周围的非等效局部环境。TM迁移与锂迁移率之间的这种相关关系使我们提出了一种用于层状结构的新锂扩散模型，并提出了在设计新的LLO阴极材料时考虑TM迁移的重要性。与传统的锂扩散模型相反，传统的锂扩散模型基于在分层框架中简单的定向锂嵌入/脱嵌。结果表明，结构中可逆但不对称的TM迁移会影响锂的迁移率，这种迁移源自于在充电和放电过程中TM周围的非等效局部环境。TM迁移和锂迁移率之间的这种相关关系使我们提出了一种用于层状结构的新锂扩散模型，并提出了在设计新的LLO阴极材料时考虑TM迁移的重要性。与传统的锂扩散模型相反，传统的锂扩散模型基于在分层框架中简单的定向锂嵌入/脱嵌。结果表明，结构中可逆但不对称的TM迁移会影响锂的迁移率，这种迁移是由于在充电和放电过程中TM周围的非等效局部环境引起的。TM迁移和锂迁移率之间的这种相关关系使我们提出了一种用于层状结构的新锂扩散模型，并提出了在设计新的LLO阴极材料时考虑TM迁移的重要性。它在充电和放电过程中源自TM周围的非等效局部环境，它会影响锂的迁移率。TM迁移和锂迁移率之间的这种相关关系使我们提出了一种用于层状结构的新锂扩散模型，并提出了在设计新的LLO阴极材料时考虑TM迁移的重要性。它在充电和放电过程中源自TM周围的非等效局部环境，它会影响锂的迁移率。TM迁移和锂迁移率之间的这种相关关系使我们提出了一种用于层状结构的新锂扩散模型，并提出了在设计新的LLO阴极材料时考虑TM迁移的重要性。