Understanding the Lithium Storage Mechanism of Mesoporous Structured High-Entropy Metal Oxide Anode with In Situ Transmission Electron Microscope.

High-entropy oxides represent a burgeoning class of anode materials for lithium-ion batteries. They reduce the mutual repulsion among constituent elements, enhance structural stability, and effectively mitigate volume changes-induced structural collapse and capacity decay during charge-discharge cycles. However, the complex elemental composition of high-entropy oxides complicate their lithium storage mechanism, particularly the evolution of structural stability during cycling, which requires further elucidation. In this work, the spinel-type (ZnMnFeCoNi)O high-entropy oxide was synthesized via the solvothermal method. Transmission electron microscopy reveals that it exhibits an uniform mesoporous microsphere morphology. As an anode material for lithium-ion batteries, it exhibits excellent electrochemical properties, maintaining a reversible capacity of 757.8 mAh g after 1000 cycles at 1000 mA g. In situ transmission electron microscopy clearly indicates that it undergoes only minor volume changes during lithiation and delithiation, with no evidence of structural collapse or cracking. Furthermore, detailed analysis through multiple consecutive charge-discharge cycles elucidate the conversion reaction mechanism of (ZnMnFeCoNi)O high-entropy oxide, involving transformations from high-entropy oxide to metal monomers and back to high-entropy oxide phases. Therefore, optimizing the spinel-type structure of the high-entropy oxide anode material is of great significance for the development of lithium-ion batteries.