High-entropy oxides (HEOs) have received growing recognition as an anode candidate for lithium-ion batteries, primarily attributed to their decent lithium storage capabilities and high cycling durability. However, the underlying lithium storage mechanism of HEOs remains ambiguous, particularly the origins for their high structural stability, necessitating more comprehensive investigations. In this research, the working mechanisms of one representative HEO anode, the rock salt-structured MgCoNiCuZnO, are explored via state-of-the-art in-situ characterizations. Findings point to an interesting mesocrystal-stabilized lithium-ion storage mechanism responsible for maintaining the structural stability of HEOs during cycling, where, upon lithiation, Mg remains electrochemically inactive within the oxygen lattice to stabilize the overall oxide framework. Co and Zn can be reversibly reduced/oxidized upon (de)lithiation, contributing to the electrochemical capacity; while for Cu and Ni, once reduced to metallic state under a relatively high current density, could not be re-oxidized but interconnect to form an electron-conductive network through the HEO body, contributing for the decent lithium-storage performance. Such feature depends on the applied current density, i.e. when decreasing the current, Ni regains its redox capability upon cycling with only Cu sustaining the conductive metallic network. This work is expected to serve as a benchmark for structurally and compositionally designing the next-generation high-entropy electrode materials for lithium storage.

中文翻译：

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高熵氧化物中介晶稳定的锂存储

高熵氧化物（HEO）作为锂离子电池的阳极候选材料越来越受到认可，这主要归功于其良好的锂存储能力和高循环耐久性。然而，HEO 的潜在储锂机制仍然不明确，特别是其高结构稳定性的起源，需要更全面的研究。在这项研究中，通过最先进的原位表征探索了一种代表性 HEO 阳极（岩盐结构 MgCoNiCuZnO）的工作机制。研究结果指出了一种有趣的介晶稳定的锂离子存储机制，负责在循环过程中维持 HEO 的结构稳定性，其中，在锂化时，镁在氧晶格内保持电化学惰性，以稳定整个氧化物框架。Co和Zn在脱锂时可以可逆地还原/氧化，从而有助于电化学容量；而Cu和Ni一旦在相对高的电流密度下还原为金属态，就不会再被氧化，而是通过HEO体互连形成电子传导网络，从而有助于良好的储锂性能。这种特性取决于所施加的电流密度，即当降低电流时，Ni在循环时恢复其氧化还原能力，而只有Cu维持导电金属网络。这项工作有望成为下一代锂存储高熵电极材料结构和成分设计的基准。