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Small molecule quinone compounds are attractive cathode materials for rechargeable aqueous zinc‐organic batteries (AZOBs) because of their structural diversity and low‐cost merits. Among them, nonpolar quinones are dominant given the relatively low solubilities in aqueous electrolytes. However, their poor electronic conductivity and accumulated Coulombic repulsion lead to underutilized active sites and sluggish redox kinetics. Here, polar 2,6‐dimethoxy‐1,4‐benzoquinone (m‐DMBQ) works as an advanced AZOB cathode with unexpectedly superior performance over the nonpolar isomer of 2,5‐dimethoxy‐1,4‐benzoquinone (p‐DMBQ). The asymmetric charge distribution of active centers in the p−π conjugated backbone of m‐DMBQ induces reduced bandgap with improved electronic conductivity and redox activity, thus achieving a high specific capacity of 312 mAh g−1 approaching the theoretical limit. Additionally, the lowest unoccupied molecular orbital energy level is lowered for an increased average discharge voltage of 0.88 V. Characterizations and computational studies revealed boosted competitiveness of H+ relative to Zn2+ for significantly enhanced charge transfer kinetics and reversibility. As a result, the as‐fabricated AZOB achieves a high energy density of 275 Wh kg−1 based on m‐DMBQ along with high‐rate capability and long‐term cycling stability. This work provides a new molecular engineering strategy through regulating charge distribution symmetry for boosting charge storage in organic cathodes. [ABSTRACT FROM AUTHOR]

The Mn2+ dissolution of MnO2 cathode materials causes rapid capacity decay in aqueous zinc batteries. We herein show that the dissolved Mn2+ can be deposited back to the cathode with the aid of a suitable conductive agent. The active material is thus retained for energy storage, and this MnO2/Mn2+ redox process also provides capacity. In the Mn2+ free ZnSO4 electrolyte, MnO2 delivers 325 mA h g−1 capacity at 0.1 A g−1, and 90.4% capacity retention is achieved after 3000 cycles at 5 A g−1. Our work demonstrates an effective strategy to realize stable cycling of MnO2 cathodes in aqueous zinc batteries without Mn2+ additives. [ABSTRACT FROM AUTHOR]

VOPO4⋅x H2O has been proposed as a cathode for rechargeable aqueous zinc batteries. However, it undergoes significant voltage decay in conventional Zn(OTf)2 electrolyte. Investigations show the decomposition of VOPO4⋅x H2O into VOx in the electrolyte and voltage drops after losing the inductive effect from polyanions.PO43− was thus added to shift the decomposition equilibrium. A high concentration of cheap, highly soluble ZnCl2 salt in the electrolyte further prevents VOPO4⋅x H2O dissolution. The cathode shows stable capacity and voltage retentions in 13 m ZnCl2/0.8 m H3PO4 aqueous electrolyte, in direct contrast to that in Zn(OTf)2 where the decomposition product VOx provides most electrochemical activity over cycling. Sequential H+ and Zn2+ intercalations into the structure are revealed, delivering a high capacity (170 mAh g−1). This work shows the potential issue with polyanion cathodes in zinc batteries and proposes an effective solution using fundamental chemical principles. [ABSTRACT FROM AUTHOR]

[Display omitted] • A zinc-iodine battery with high coulombic efficiency and stability is proposed. • The polyiodide is confined at cathode by doping on polyaniline chains. • The complex in electrolyte is regulated to eliminate free iodide anions. • It delivers 99.2% coulombic efficiency with 2 mAh cm−2 capacity at 6 mA cm−2. • A stable capacity retention of 99.9% is achieved after 1000 cycles. Aqueous zinc-iodine batteries are promising electrochemical energy storage systems due to the high safety and low cost. The application of zinc halide solution as the electrolyte allows the dual-plating mechanism on both electrodes, i.e. the redox reactions of Zn2+/Zn and I 2 /I- at the anode and cathode, respectively. These solid–liquid conversion processes guarantee excellent reaction kinetics. However, soluble polyiodide (I 3 -, I 5 -, etc.) are formed at the cathode either during the oxidation of I- or from the reaction between I- and I 2. The dissolution of polyiodide in electrolytes causes rapid loss of charged products, leading to poor coulombic efficiency and fast self-discharge. Herein, we apply the synergistic regulation of electrode and electrolyte to confine the charged products. The conducting polymer polyaniline (PANI) is used as the polyiodide binder. It contains positively charged nitrogen sites, allowing the doping and effective binding of polyiodide anions through electrostatic attraction. At the same time, the complex in zinc halide electrolytes is regulated to eliminate free iodide anions and prevent the reaction with I 2 to form more polyiodide. The optimized zinc-iodine aqueous battery delivers excellent rate capability thanks to the facile solid–liquid reactions as well as the high electrical conductivity of PANI. More importantly, it achieves a high coulombic efficiency of 99.2% with the capacity of 2 mAh cm−2 at 6 mA cm−2, and an excellent capacity retention of 99.9% after 1000 cycles is realized upon long-term cycling. The work proposes a potential pathway to realize stable energy storage in aqueous zinc-halogen batteries. [ABSTRACT FROM AUTHOR]

[Display omitted] • Doping Zn into Fe lattice enhances the reversibility and stability of Fe electrode. • It is realized by introducing [ZnI]+ to adsorb on negatively charged Fe surface. • Stable Fe plating/stripping for over 2500 h is achieved in symmetric cells. • The Fe plating/stripping coulombic efficiency stabilizes at 98% for 1200 cycles. • The iron-iodine battery delivers 96.7% coulombic efficiency for 1200 cycles. The iron metal electrode based on the Fe2+/Fe redox reaction is a promising anode candidate for aqueous batteries. It possesses high capacity, large abundance, low price, as well as a little higher redox potential than Zn2+/Zn which corresponds to suppressed hydrogen evolution reaction. However, the reversibility and stability of Fe electrodes require improvement. Herein, we regulate the Fe deposition behavior with Zn doping. The positively charged [ZnI]+ complex is introduced into FeCl 2 electrolytes by adding ZnI 2 , which is adsorbed on the negatively charged surface of Fe metal and realizes the doping of Zn into Fe lattice during deposition. In comparison to the large chunks with sole Fe deposition, the Zn doped Fe forms homogeneous small particles with the (110) plane preferred to grow parallel to the substrate. Enhanced coulombic efficiencies of 98% are achieved for over 1200 cycles. Stable Fe plating/stripping is accomplished for over 2500 h at the current density of 1 mA cm−2 and capacity of 1 mAh cm−2, as well as for over 300 h under ultra-high current density and capacity of 10 mA cm−2 and 10 mAh cm−2. Benefiting from the iodine species in electrolyte, an iron-iodine full cell is demonstrated. The battery exhibits excellent capacity retention of 99.8% with average coulombic efficiency of 96.7% for over 1200 cycles. The work provides a potential path for high-performance aqueous Fe-metal batteries. [ABSTRACT FROM AUTHOR]

• Fe 3 O 4 /FeOOH heterostructure is constructed during electrochemical activation. • A built-in electric field is formed near the Fe 3 O 4 /FeOOH interface. • The activated electrode shows an enhanced capacity of 634 mAh g−1. • The assembled Ni-Fe cell shows a high energy density of 161.3 Wh kg−1 at 5.7 kW kg−1. Aqueous Ni-Fe batteries show promise for grid level energy storage due to their high safety and low cost. However, high capacities of Fe-based anodes can only be achieved under slow discharging rates. Moreover, an activation process is often required, the mechanism of which has not been fully understood. Herein, we present a facile and controllable method to uniformly deposit Fe 3 O 4 nanoparticles on a 3D graphite substrate. Post-mortem analysis demonstrates the partial conversion of Fe 3 O 4 to FeOOH during the subsequent in-situ electrochemical activation process, forming a Fe 3 O 4 /FeOOH heterostructure. Density functional theory calculations suggest that a built-in electric field is formed near the Fe 3 O 4 /FeOOH interface, which facilitates the charge transfers and lowers the adsorption energy of OH−. The above modification on the active material significantly improves its electrochemical activity. The activated electrode delivers a high capacity of 509 mAh g−1 at the ultra-high current density of 100 A g−1. A Ni-Fe cell assembled with activated Fe 3 O 4 /FeOOH anode and Ni-Co double hydroxide cathode provides a high energy density of 161.3 Wh kg−1 and a maximum power density of 43 kW kg−1, making it a good candidate for high safety, low cost, and environmental friendliness energy storage systems. [ABSTRACT FROM AUTHOR]