Rational Design of ZnMn₂O₄ Quantum Dots in a Carbon Framework for Durable Aqueous Zinc‐Ion Batteries

Abstract

Manganese oxides are promising cathode materials for aqueous zinc‐ion batteries (ZIBs) due to their high energy density and low cost. However, in their discharging processes, the Jahn–Teller effect and Mn3+ disproportionation often lead to irreversible structural transformation and Mn2+ dissolution, deteriorating the cycling stability of ZIBs. Herein, ZnMn2O4 quantum dots (ZMO QDs) were introduced into a porous carbon framework by in‐situ electrochemically inducing Mn‐MIL‐100‐derived Mn3O4 quantum dots and the carbon composite. In such ZMO QDs and carbon composite, the quantum dot structure endows ZnMn2O4 with a shorter ion diffusion route and more active sites for Zn2+. The conductive carbon framework is beneficial to the fast transport of electrons. Furthermore, at the interface between the ZMO QDs and the carbon matrix, the Mn−O−C bonds are formed. They can effectively suppress the Jahn–Teller effect and manganese dissolution of discharge products. Therefore, Zn/ZMO QD@C batteries display remarkably enhanced electrochemical performance.

Structural Regulation of Oxygen Vacancy‐Rich K0.5Mn2O4Cathode by Carbon Hybridization for Enhanced Zinc‐Ion Energy Storage

“…The specific capacity originates from the surface‐controlled capacitive effect and the diffusion‐induced effect, which is reflected in the relationship between peak current ( i ) and scan rate ( v ) [Eq. ]: [45] …”

Material Design and Energy Storage Mechanism of Mn‐Based Cathodes for Aqueous Zinc‐Ion Batteries

“…Constructing unique nanostructures to enhance the electrochemical reactivity and structural stability is widely considered as an effective strategy [117,118] . Recently, Niu′s group introduced ZnMn 2 O 4 quantum dots into a porous carbon framework (ZMO QDs@C) by in situ electrochemical induction of Mn‐MIL‐100‐derived Mn 3 O 4 quantum dots and carbon composites [27] . Benefiting from the ZMO QDs with an average crystallite size of 5.6 nm and carbon skeleton (Figure 9a–b), the ZMO QDs@C shows a shorter ion diffusion pathway and more active sites for Zn 2+ storage.…”

“…Based on the existing storage mechanisms, accompanied by generating complex products and undergoing severe phase transitions as well as slow reaction kinetics in the process of ions storage, it is difficult to realize the potential of Mn‐based materials [20,25] . Furthermore, the large ion‐diffusion resistance [21] and irreversible phase conversions of Mn‐based materials, the distasteful Mn 3+ disproportional reactions and the Jahn‐Teller effect make them show limited rate capability and cycling performance [26,27] …”

“…[20,25] Furthermore, the large ion-diffusion resistance [21] and irreversible phase conversions of Mn-based materials, the distasteful Mn 3 + disproportional reactions and the Jahn-Teller effect make them show limited rate capability and cycling performance. [26,27] So far, many effective strategies such as constructing composites with improved electrical conductivity, [28] defects engineering, [29] elemental doping, [30,31] and optimizing electrolytes [25] have been proposed to improve the electrical properties, ionic kinetics, and structural stability of Mn-based cathodes. More interestingly, more understanding of the existing storage mechanisms gives rise to the resurrection of Mn-based cathodes for ZIBs, such as enlarged specific capacity, higher operating voltages close to 2 V, and rescuing dead-MnO 2 electrodes to extend the lifetime, enabling the Mnbased materials as promising cathodes for ZnÀ Mn batteries with a higher energy density.…”

Ultrathin Polyaniline-Coated Single-Crystalline Mn2O3 Nanoporous Ellipsoids with High Energy Density and Cyclability for Low-Cost Zinc-Ion Batteries

“…However, the cycling performance still cannot meet the applicable standards. Mn oxides, as the most promising candidate, can provide a decent working voltage of over 1.2 V and reversible capacity of over 200 mA h g –1 . , However, the low inherent electrical conductivity of these Mn oxides and obvious structure instability during long-term cycling still limit the development of ZIBs. , To tackle these issues, nanostructured Mn oxides such as MnO x nanorods, α-MnO 2 nanofibers, and ZnMn 2 O 4 nanoparticles have been prepared, − which can shorten the transport distance of ion/electron and reduce the size effect of volume change. Among the Mn oxides, Mn 2 O 3 is an important member of the Mn-based oxides family and has been reported by several research groups in recent years as it possesses the virtues of high energy density and liability to synthesis. − However, the electrochemical behavior of Mn 2 O 3 and the mechanisms of insertion/extraction during the charge/discharge process are still under debate.…”