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

In recent years, transition metal oxides have been considered as the most promising anode materials due to their high theoretical capacity, low price, and abundant natural reserves. Among them, zinc manganate is used as an electrode material for anodes, whose application is mostly hindered due to its poor ionic/electronic conductivity. In this work, a series of ZnMn₂O₄ (ZMO) are synthesized by a hydrothermal technique coordinated with a metal-organic framework-based high-temperature calcination process for their application as an anode in lithium-ion batteries (LIBs). Meanwhile, this study systematically explores the influence of carbon doping and the types of organic ligands and oxygen vacancies on the electrochemical properties of the synthesized ZMO. Density functional theory (DFT) calculations and experimental investigations reveal that the introduction of carbon and oxygen vacancies can enhance electronic conductivity, more active sites and faster Li⁺ adsorption, resulting in better electrochemical performances. As expected, all ZMOs with carbon doping (PMA-ZMO, MI-ZMO, and BDC-ZMO) derived from 1,2,4,5-benzenetetracarboxylic acid, 2-methylimidazole, and 1,4-dicarboxybenzene achieve outstanding electrochemical performance. Meanwhile, the introduction of oxygen vacancies can enhance the electronic conductivity and can significantly reduce the activation energy of Li⁺ transport, thereby accelerating the Li⁺ diffusion kinetics in the lithiation/delithiation process. Furthermore, an optimal ZMO anode material synthesized by 2-methylimidazole delivers a high reversible capacity of 1174.7 mA h g^-1 after 300 cycles at 0.1 A g^-1 and 600 mA h g^-1 at 0.5 A g^-1 after 300 cycles. After high-rate charge and discharge cycles, the specific capacity rapidly recovers to a value greater than the initial value, which proves the unusual activation and thereby an excellent rate property of the electrode. Hence, we conclude that ZMO provides potential application prospects as an anode electrode material for LIBs.