Regulating the Electronic Configuration of Spinel Zinc Manganate Derived from Metal-Organic Frameworks: Controlled Synthesis and Application in Anode Materials for Lithium-Ion Batteries

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.

Strategy for the Preparation of ZnS/ZnO Composites Derived from Metal-Organic Frameworks toward Lithium Storage

The synergistic effect between multicomponent electrode materials often makes them have better lithium storage performance than single-component electrode materials. Therefore, to enhance surface reaction kinetics and encourage electron transfer, using multicomponent anode materials is a useful tactic for achieving high lithium-ion battery performance. In this article, ZnS/ZnO composites were synthesized by solvothermal sulfidation and calcination, with the utilization of metal-organic frameworks acting as sacrificial templates. From the point of material design, both ZnS and ZnO have high theoretical specific capacities, and the synergistic effect of ZnS and ZnO can promote charge transport. From the perspective of electrode engineering, the loose porous carbon skeleton that results from the calcination of metal-organic frameworks can enhance composite material conductivity as well as full electrolyte penetration and the area of contact between the electrolyte and active material, all of which are beneficial to enhancing lithium storage performance. As expected, ZnS/ZnO anode materials displayed remarkably high specific capacities and outstanding performance at different rates. Combining material design and electrode engineering, this paper provides another idea for preparing anode materials with excellent lithium storage properties.

Engineering Oxygen Vacancies in (FeCrCoMnZn)3O4-δ High Entropy Spinel Oxides Through Altering Fabrication Atmosphere for High-Performance Rechargeable Zinc-Air Batteries

High entropy oxides (HEOs) offer great potential as catalysts for oxygen electrocatalytic reactions in alkaline environments. Herein, a novel synthesis approach to prepare (FeCrCoMnZn)3O4-δ high entropy spinel oxide in a vacuum atmosphere, with the primary objective of introducing oxygen vacancies into the crystal structure, is presented. As compared to the air-synthesized counterpart, the (FeCrCoMnZn)3O4-δ with abundant oxygen vacancies demonstrates a low (better) bifunctional (BI) index of 0.89 V in alkaline media, indicating enhanced electrocatalytic oxygen catalytic activity. Importantly, (FeCrCoMnZn)3O4-δ demonstrates outstanding long-term electrochemical and structural stability. When utilized as electrocatalysts in the air cathode of Zn-air batteries, the vacuum atmosphere synthesized (FeCrCoMnZn)3O4-δ catalysts outperform the samples treated in an air atmosphere, displaying superior peak power density, specific capacity, and cycling stability. These findings provide compelling evidence that manipulating the synthesis atmosphere of multi-component oxides can serve as a novel approach to tailor their electrochemical performance.

Metal-organic-framework derived Zn-V-based oxide with charge storage mechanism as high-performance anode material to enhance lithium and sodium storage

Transition metal oxides have been extensively studied due to their large theoretical capacities, but their practical application has been hampered by low electrical conductivity and dramatic volume fluctuation during cycling. In this work, we synthesized Zn3V2O8 material using Zn-V-MOF (metal-organic framework) as a sacrificial template to improve the electrochemical characteristics of lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). Unique dodecahedral structure, larger specific surface area and higher ability to mitigate volume changes, improve the electrochemical reaction active site while accelerating ion transport. Zn3V2O8 with 2-methylimidazole as a ligand demonstrated a discharge capacity of 1225.9 mAh/g in LIBs and 761.6 mAh/g in SIBs after 300 cycles at 0.2 C. Density functional theory (DFT) calculation illustrates the smaller diffusion barrier energy and higher specific capacity in LIBs that is ascribed to the fact that Li has a smaller size and hence its diffusion is easier. This study may lead to a path for the manufacturing of high-performance LIBs and SIBs.

Nanostructured conversion-type anode materials of metal-organic framework-derived spinel XMn2O4 (X = Zn, Co, Cu, Ni) to boost lithium storage

Bimetallic spinel transition metal oxides play a major part in actualizing eco-friendly electrochemical energy storage systems (ESSs). However, structural precariousness and low electrochemical capacitance restrict their actual implementation in lithium-ion batteries (LIBs). To address these demerits, the sacrificial template approach has been considered as a prospective way to strengthen electrochemical stability and rate performance. Herein, metal-organic frameworks (MOFs) derived XMn₂O₄-BDC (H₂BDC = 1,4-dicarboxybenzene, X = Zn, Co, Cu, Ni) are prepared by a hydrothermal approach in order to discover the effects of various metal cations on the electrochemical performance. Among them, ZnMn₂O₄-BDC displays best electrochemical properties (1321.5 mAh g^-1 at the current density of 0.1 A g^-1 after 300 cycles) and high efficiency with accelerated Li⁺ diffusivity. Density functional theory (DFT) calculations confirm the ZnMn₂O₄ possesses the weakest adsorption energy on Li⁺ with a minimized value of -0.92 eV. In comparison with other XMn₂O₄ through traditional fabrication method, MOF-derived XMn₂O₄-BDC possesses a higher number of Li⁺ transport channels and better electric conductivity. This tactic provides a feasible and effective method for preparing bimetallic transition metal oxides and enhances energy storage applications.