Unlocking Double Redox Reaction of Metal-Organic Framework for Aqueous Zinc-Ion Battery.

Metal-organic frameworks (MOFs) show wide application as the cathode of aqueous zinc-ion batteries (AZIBs) in the future owning to their high porosity, diverse structures, abundant species, and controllable morphology. However, the low energy density and poor cycling stability hinder the feasibility in practical application. Herein, an innovative strategy of organic/inorganic double electroactive sites is proposed and demonstrated to obtain extra capacity and enhance the energy density in a manganese-based metal-organic framework (Mn-MOF-74). Simultaneously, its energy storage mechanism is systematically investigated. Moreover, profiting from the coordination effect, the Mn-MOF-74 features with stable structure in ZnSO4 electrolyte. Therefore, the Zn/Mn-MOF-74 batteries exhibit a high energy density and superior cycling stability. This work aids in the future development of MOFs in AZIBs.

Microfluidic-Assisted 3D Printing Zinc Powder Anode with 2D Conductive MOF/MXene Heterostructures for High-Stable Zinc-Organic Battery.

Zinc powder (Zn-P) anodes have significant advantages in terms of universality and machinability compared with Zn foil anodes. However, their rough surface, which has a high surface area, intensifies the uncontrollable growth of Zn dendrites and parasitic side reactions. In this study, an anti-corrosive Zn-P-based anode with a functional layer formed from a MXene and Cu-THBQ (MXene/Cu-THBQ) heterostructure is successfully fabricated via microfluidic-assisted 3D printing. The unusual anti-corrosive and strong adsorption of Zn ions using the MXene/Cu-THBQ functional layer can effectively homogenize the Zn ion flux and inhibit the hydrogen evolution reaction (HER) during the repeated process of Zn plating/stripping, thus achieving stable Zn cycling. Consequently, a symmetric cell based on Zn-P with the MXene/Cu-THBQ anode exhibits a highly reversible cycling of 1800 h at 2 mA cm-2 /1 mAh cm-2 . Furthermore, a Zn-organic full battery matched with a 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl organic cathode riveted on graphene delivers a high reversible capacity and maintains a long cycle life.

A Multifunctional Zwitterion Electrolyte Additive for Highly Reversible Zinc Metal Anode.

Although zinc metal anode is promising for zinc-ion batteries (ZIBs) owing to high energy density, its reversibility is significantly obstructed by uncontrolled dendrite growth and parasitic reactions. Optimizing electrolytes is a facile yet effective method to simultaneously address these issues. Herein, 2-(N-morpholino)ethanesulfonic acid (MES), a pH buffer as novel additive, is initially introduced into conventional ZnSO4 electrolyte to ensure a dendrite-free zinc anode surface, enabling a stable Zn/electrolyte interface, which is achieved by controlling the solvated sheath through H2O poor electric double layer (EDL) derived from zwitterionic groups. Moreover, this zwitterionic additive can balance localized H+ concentration of the electrolyte system, thus preventing parasitic reactions in damaging electrodes. DFT calculation proves that the MES additive has a strong affinity with Zn2+ and induces uniform deposition along (002) orientation. As a result, the Zn anode in MES-based electrolyte exhibits exceptional plating/stripping lifespan with 1600 h at 0.5 mA cm-2 (0.5 mAh cm-2) and 430 h at 5.0 mA cm-2 (5.0 mAh cm-2) while it maintains high coulombic efficiency of 99.8%. This work proposes an effective and facile approach for designing dendrite-free anode for future aqueous Zn-based storage devices.

Proton-Assisted Aqueous Manganese-Ion Battery Chemistry.

Aqueous manganese-ion batteries (MIBs) are promising energy storage systems because of the distinctive merits of Mn metal, in terms of high abundance, low cost, nontoxicity, high theoretical capacity and low redox potential. Conventional MIBs are based on the Mn2+ ion storage mechanism, whereas the capacity in cathode materials is generally limited due to the high charge density and large solvated ionic radius of Mn2+ ions in aqueous electrolytes. Herein, proton intercalation chemistry is introduced in aqueous MIBs, in which the layered Al0.1 V2 O5 ⋅1.5 H2 O (AlVO) cathode exhibits a consequent Mn2+ and H+ ion intercalation/extraction process. Such an energy storage mechanism contributes to enhanced electrochemical performance, including high capacity, fast reaction kinetics and stable cycling behavior. Benefiting from this proton intercalation chemistry, the aqueous Mn||AlVO cells could deliver high specific energy and power simultaneously. This work provides a route for the design of high-performance aqueous MIBs.

Rational Design of ZnMn2 O4 Quantum Dots in a Carbon Framework for Durable Aqueous Zinc-Ion Batteries.

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, ZnMn2 O4 quantum dots (ZMO QDs) were introduced into a porous carbon framework by in-situ electrochemically inducing Mn-MIL-100-derived Mn3 O4 quantum dots and the carbon composite. In such ZMO QDs and carbon composite, the quantum dot structure endows ZnMn2 O4 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.

A Symmetric All-Organic Proton Battery in Mild Electrolyte.

All-organic proton batteries are attracting extensive attention due to their sustainability merits and excellent rate capability. Generally, strong acids (e.g. H2 SO4 ) have to be employed as the electrolytes to provide H+ for all-organic proton batteries due to the high H+ intercalation energy barrier. Until now, the design of all-organic proton batteries in mild electrolytes is still a challenge. Herein, a poly(2,9-dihydroquinoxalino[2,3-b]phenazine) (PO) molecule was designed and synthesized, where the adjacent C=N groups show two different chemical environments, resulting in two-step redox reactions. Moreover, the two reactions possess considerable voltage difference because of the large LUMO energy gap between PO and its reduction product. More impressively, the C=N groups endow the π-conjugated PO molecule with H+ uptake/removal in the ZnSO4 electrolyte. As a result, a symmetric all-organic proton battery is achieved in a mild electrolyte for the first time, which exhibits enhanced electrochemical performance and also broadens the chemistry of proton-based batteries.

An Ultralow Temperature Aqueous Battery with Proton Chemistry.

Conventional aqueous batteries usually suffer from serious capacity loss under subzero conditions owing to the freeze of electrolytes. To realize the utilization of aqueous batteries in extremely cold climates, low-temperature aqueous battery systems have to be developed. Herein, an aqueous Pb-quinone battery based on p-chloranil/reduced graphene oxide (PCHL-rGO) in H2 SO4 electrolyte is developed. Such aqueous Pb/PCHL-rGO batteries display H+ insertion chemistry, which endows the batteries with fast reaction kinetics and high rate capability. In addition, the hydrogen bonds between water molecules can be significantly damaged in electrolyte by modulating the interaction between SO4 2- and water molecules, lowering the freezing point of electrolyte. As a result, the Pb/PCHL-rGO batteries deliver extraordinary electrochemical performance even at -70 °C. This work will broaden the horizons of aqueous batteries and open up new opportunities to construct low-temperature aqueous batteries.

Electrochemically Induced Metal-Organic-Framework-Derived Amorphous V2 O5 for Superior Rate Aqueous Zinc-Ion Batteries.

The electrochemical performance of vanadium-oxide-based cathodes in aqueous zinc-ion batteries (ZIBs) depends on their degree of crystallinity and composite state with carbon materials. An in situ electrochemical induction strategy was developed to fabricate a metal-organic-framework-derived composite of amorphous V2 O5 and carbon materials (a-V2 O5 @C) for the first time, where V2 O5 is in an amorphous state and uniformly distributed in the carbon framework. The amorphous structure endows V2 O5 with more isotropic Zn2+ diffusion routes and active sites, resulting in fast Zn2+ transport and high specific capacity. The porous carbon framework provides a continuous electron transport pathway and ion diffusion channels. As a result, the a-V2 O5 @C composites display extraordinary electrochemical performance. This work will pave the way toward design of ZIB cathodes with superior rate performance.

Proton Insertion Chemistry of a Zinc-Organic Battery.

Proton storage in rechargeable aqueous zinc-ion batteries (ZIBs) is attracting extensive attention owing to the fast kinetics of H+ insertion/extraction. However, it has not been achieved in organic materials-based ZIBs with a mild electrolyte. Now, aqueous ZIBs based on diquinoxalino [2,3-a:2',3'-c] phenazine (HATN) in a mild electrolyte are developed. Electrochemical and structural analysis confirm for the first time that such Zn-HATN batteries experience a H+ uptake/removal behavior with highly reversible structural evolution of HATN. The H+ uptake/removal endows the Zn-HATN batteries with enhanced electrochemical performance. Proton insertion chemistry will broaden the horizons of aqueous Zn-organic batteries and open up new opportunities to construct high-performance ZIBs.