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Rechargeable aqueous Zn//MnO 2 batteries are the promising alternatives to lithium-ion batteries owing to their high safety, high energy density, low cost, and environmental friendliness. However, the unstable MnO 2 cathode causes poor practical energy density and serious capacity fading. To overcome this issue, herein, a unique 2D nanosheets self-supported 3D δ -MnO 2 microflower hierarchical architecture is rationally designed and synthesized by taking advantage of its microwave-absorbing characteristics. The 2D nanosheets with high surface area could expose numerous active sites for ions/electrons transfer. Also, the 3D assembled structure acting as building blocks would ensure structural stability for long-life cycles. Benefiting from these synergistic merits, the δ -MnO 2 microflowers deliver a high capacity of 287.6 mA h g−1 at 0.5 C, an excellent rate capability of 202.7 mA h g−1 at 5 C, and a superior cycling retention of 76.5% over 1000 cycles at 10 C. Furthermore, a storage mechanism of H+/Zn2+ co-insertion accompanied by the deposition of zinc sulfate hydroxide hydrate is clarified by the aid of ex-situ XRD and SEM technologies. This work provides a new pathway for developing high capacity and long lifespan ZIBs. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • An anti-perovskite Ni 3 FeN/VN heterostructure is designed for Zn-air batteries. • The anti-perovskite Ni 3 FeN with the metallic behavior contributes to electron transfer. • Abundant catalytic active sites are formed at the heterogeneous interface. • The Ni 3 FeN/VN–NG displays excellent bifunctional activity with a ΔE value of 0.69 V. High-performance rechargeable zinc–air battery is highly relying on the efficient and stable bifunctional electrocatalysts. Herein, an anti-perovskite Ni 3 FeN/VN heterostructure encapsulated N–doped graphene (Ni 3 FeN/VN–NG) was synthesized by a two-step transformation of trimetallic NiFeV–layered double hydroxide. The Ni 3 FeN/VN–NG showed excellent bifunctional catalytic activity (ΔE = 0.69 V) and stability. The excellent bifunctional electrocatalytic performance is benefited from the extraordinary catalytic behavior of Ni 3 FeN/VN heterostructure. The intrinsic metallic properties and remarkable superconductivity of anti-perovskite Ni 3 FeN can enhance the electrocatalytic performance. Density functional theory calculations confirm that the electronic coupling between Ni 3 FeN and VN facilitates the charge transfer between the two components, simultaneously generates abundant catalytic active sites at the heterogeneous interface. When the Ni 3 FeN/VN–NG was used as the air cathode, in zinc–air battery, the zinc–air battery exhibits a high-power density of 168 mW cm−2 and a long cycle life of over 200 h. [ABSTRACT FROM AUTHOR]

A series of N-doped graphitic carbons with different carbonization temperatures (denoted as ENGC-T) are controllably synthesized. The correlation between different N-doping species and interlayer spacing is explored, and thus demonstrating that pyrrolic-N (N-5) content has a substantial effect of the expanded interplanar spacing. The resulting ENGC-850 with the optimal N-5 configuration achieves excellent electrochemical performance in terms of capacity, rate capability, and cycling stability. [Display omitted] • A series of N-doped graphitic carbons are controllably synthesized. • High edge-N doping ratio is conducive to promote capacitive-controlled K-storage. • Pyrrolic-N configuration has a substantial effect on the interlayer spacing. • The resultant product delivers excellent rate capability and exceptional cyclability. Nitrogen (N) doped graphitic-carbon materials as anode have been intensively studied for potassium-ion batteries (PIBs). However, insufficient N-doping content, especially the low edge-N ratio composed of pyridinic-N (N-6) and pyrrolic-N (N-5) cannot provide excellent rate capability and ultra-long cycle lifespan. Meanwhile, the intercorrelation between N-doping species and enlarged interlayer spacing remains unclear and needs to be further explored. Based on this, a series of N-doped graphitic carbons with different carbonization temperatures (denoted as ENGC-T) are controllably synthesized. It is found that a high edge-N doping ratio is conducive to increase active sites to promote capacitive-controlled K-storage. And the correlation between N-doping species and interlayer spacing reveals that N-5 configuration has a substantial effect on the interlayer spacing, due to its stronger electrostatic repulsion. Accordingly, the resultant ENGC-850 with both an ultra-high edge-N ratio (76.6%) and N-5 content (42%) achieves the most abundant defects and the largest interspacing, ensuring high capacity and cycling stability. Besides, good crystallization characteristics guarantees fast electron transfer, favoring conductivity. As expected, ENGC-850 electrode delivers high capacity, excellent rate (228.9 mAh g−1 at 2 A g−1), and prolonged cycle lifespan (188.9 mAh g−1 over 2200 cycles). [ABSTRACT FROM AUTHOR]