The magnetism of electrospun porous high-entropy spinel oxides can be tuned by changing a single cation.

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In the last few years, high-entropy oxides (HEOs), a new class of single-phase solid solution materials, have attracted growing interest in both academic research and industry for their great potential in a broad range of applications. This work investigates the possibility of producing pure single-phase HEOs with spinel structure (HESOs) under milder conditions (shorter heat treatments at lower temperatures) than standard solid-state techniques, thus reducing the environmental impact. For this purpose, a large set of HESOs was prepared via sol-gel and electrospinning (by using two different polymers). Ten different equimolar combinations of five metals were considered, and the influence of the synthesis method and conditions on the microstructure, morphology and crystalline phase purity of the produced HESOs was investigated by a combination of characterization techniques. On the other hand, the presence of specific metals, such as copper, lead to the formation of minority secondary phase(s). Finally, two representative pure single-phase HESOs were preliminarily evaluated as active anode materials in lithium-ion batteries and possible strategies to enhance their rate capability and cyclability were proposed and successfully implemented. The approaches introduced here can be extensively applied for the optimization of HEO properties targeting different applications.

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Entropy-stabilized oxides (ESOs), such as (Mg 0.2 Co 0.2 Ni 0.2 Cu 0.2 Zn 0.2 )O, have recently gained significant interest as novel anodes for lithium-ion batteries (LIBs) due to their stable crystal structure and robust lithium-storage properties. In this work, (Mg 0.2 Co 0.2 Ni 0.2 Cu 0.2 Zn 0.2 )O oxides with different morphologies are prepared by electrospinning and solvothermal method and are applied as anode active materials for LIBs. It is found that different morphologies possess different characteristics, namely particle size, particle size range, and defect density, which have a significant effect on the electrochemical behavior. The most active (Mg, Co, Ni, Cu, Zn) ESO shows outstanding electrochemical properties in terms of high reversible capacity (480 mAh g -1 at 20 mA g -1), superior rate capability (206 mAh g -1 at 2 A g -1 ), and excellent cycling stability (390 mAh g -1 at 500 mA g -1 after 300 cycles). The strategy demonstrates the importance of engineering microstructures in tailoring the electrochemical performance.

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