Bimetal-organic framework-templated Zn-Fe-based transition metal oxide composites through heterostructure optimization to boost lithium storage

Transition metal oxides (TMOs), especially zinc- and iron-based materials, are known to be one of the most innovative anode materials based on their high theoretical capacity, low price and abundant natural reserves. However, the application of these materials is limited by poor electronic conductivity, slow ion mobility and large structural transformations during charging/discharging processes. To overcome these drawbacks, sacrificial template technology has been proposed as a promising strategy to optimize the electrochemical performance and structure stability of TMOs, showing its potential especially in the storage design of lithium-ion batteries (LIBs). In this paper, we successfully synthesized a series of ZnFe₂O₄/Fe₂O₃ compounds (named as ZFFO) with Zn/Fe-MOFs (metal-organic frameworks) as sacrificial templates, and then obtained single-component ZnFe₂O₄ contrast samples (named as ZFO) by etching ZFFO with NaOH. Density Functional Theory (DFT) calculations display that the bi-component ZFFO materials formed by the introduction of Fe₂O₃ exhibit a lower Li⁺ migration energy barrier compared to the single-component ZFO materials, indicating better ion diffusion kinetics of ZFFO. The bi-components of ZnFe₂O₄ and Fe₂O₃ in ZFFO electrodes can exert a synergistic effect to achieve mutual constraints on volume expansion and alleviate volume strain during charging/discharging processes, thus improving structural stability and electrochemical performance. Besides, the ZnFe₂O₄/Fe₂O₃ constructed with 2-methylimidazole as a ligand not only has the synergistic effect of bi-components, but also exhibits a uniformly distributed small-size particle morphology, so that the discharge capacity is 864.2 mAh g^-1 after 200 cycles at 0.1 A g^-1 when used as an anode for LIBs. This approach presents a feasible and efficient way to synthesize bi-component transition metal oxides with improved practical applications for LIBs.