Research on Sodium Storage Mechanism of Sodium Ion Batteries with High Entropy Oxide (FeCoNiCuMn)3O4/CNT as Anode

Abstract

Purposes Exploration of anode materials with excellent electrochemical properties is essential to improve the performance of sodium ion batteries (SIBs). High-entropy oxides (HEO), with their unique structural characteristics, tailorable chemical composition, and tunable functional properties, have drawn increasing interest in the fields of environmental science and renewable energy technology. However, when HEO are directly used as anode materials for SIBs, a problem of agglomeration limits the electrochemical performance. In general, carbon nanotubes (CNT) are used to optimize battery performance because of their high electrical conductivity and good mechanical stability. Methods Spinel-type high-entropy oxide (FeCoNiCuMn)3O4/CNT composites (HEO/CNT) with space group Fd-3m have been synthesized through hydrothermal treatment followed by annealing method. Findings As the anode material in SIBs, at a current density of 0.5 A/g, HEO/CNT has a reversible capacity of 231 mAh/g after 200 cycles. Additionally, the HEO/CNT exhibits high reversible capacities of 363.3, 350, 341.1, 310.2, and 290.2 mAh/g at the current densities 0.1, 0.2, 0.5, 1, and 2 A/g, respectively. In situ X-ray diffraction analysis has been employed to reveal that the sodium ion storage process is a result of a combined Na＋ intercalation and conversion reaction between Na＋ and HEO/CNT. Conclusions Thanks to the “high entropy effect” of the high entropy oxide/carbon material, the volume change of the active material is mitigated during the charge/discharge process. Therefore, HEO/CNT is expected to be an electrode material with good sodium storage performance. This work provides a new template strategy for the application of high entropy materials.

Keywords

• high entropy oxide
• sodium ion batteries
• carbon nanotube
• in situ xrd
• energy storage