Tuning single-phase medium-entropy oxides derived from nanoporous NiCuCoMn alloy as a highly stable anode for Li-ion batteries

Incorporating four cations into a single-phase oxide is beneficial for maintaining structural stability during Li⁺ insertion/desertion because of the produced entropy-dominated phase stabilization effects. However, medium-entropy oxides exhibit inherently poor electron and ion conductivity. As such, in this work, a single-phase medium-entropy oxide of Ni_xCu_yCo_zMn_{1–x–y–z}O (named as NCCM@oxides(H₂)) is prepared by modified-NiCuCoMn alloy through the epitaxial-growing-based self-combustion and hydrogen reduction. During hydrogen reduction, some Cu ions are reduced to elemental Cu (defined as Cu⁰), which is distributed among the metal oxides, while generating extensive oxygen vacancies around Cu. The synergetic effect between nanoporous metal-core oxide-shell structure and enriched oxygen/Cu⁰ vacancies greatly enhances the electronic/ionic conductivity. In addition, the lattice of single-phase quaternary metal oxides has the configuration entropy stability, which enables the rock-salt structure to remain stable during repeated conversion reactions. Benefiting from the above-mentioned merits, the anode for Li-ion batteries with entropy-stabled NCCM@oxides(H₂) composite shows a high specific capacity of 699 mAh·g⁻¹ at 0.1 A·g⁻¹ and ultra-stable cycling stability, which maintains 618 and 489 mAh·g⁻¹ at 0.1 and 1.0 A·g⁻¹ after 200 cycles, respectively. This is the first use of this novel and simple strategy for modifying medium-entropy oxides, which paves the way for the development of high-entropy oxides as high-performance electrodes.