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For rechargeable aqueous Zn-ion batteries (ZIBs), MnO2 is a desirable cathode material because of its structural diversity and high theoretical capacity of ~308 mA h g−1. MnO2 materials' poor cycle life and inferior conductivity, however, continue to be key obstacles to their application in ZIBs. These problems are anticipated to be resolved by developing a nanocomposite system consisting of MnO2 and a carbon-based matrix. Herein, a series of graphite carbon-coated δ-MnO2 nanoparticles (denoted as GC-δ-MnO2-X; X = 1, 2, and 3) for ZIB cathode materials is prepared via a feasible redox route and varying the amount of KMnO4 (7, 8, and 9 mmol). Benefiting from the abundant active sites and boosted Zn2+ ion diffusion rate, the GC-δ-MnO2-2 nanoparticles (8 mmol KMnO4) display excellent capacity of 299.6 mA h g−1 at 0.3 A g−1 with good cycle stability (62% capacity retention after 1500 cycles at 2 A g−1), surpassing that of the GC-δ-MnO2-1 (7 mmol KMnO4) and GC-δ-MnO2-3 (9 mmol KMnO4) samples. Moreover, the constructed quasi-solid-state ZIBs based on the GC-δ-MnO2-2 cathode show respectable capacity of 194.3 mA h g−1 at 0.3 A g−1, as well as outstanding safe properties. [ABSTRACT FROM AUTHOR]

Manganese phosphate‐based materials show great potential in the electrochemical energy field due to the structurally flexible phosphate framework stabilizing active sites. However, the insufficient number of active sites causes unsatisfactory activity. Herein, we prepare Mn3(PO4)2 ⋅ 3H2O nanosheets via simple liquid‐phase precipitation with hydrogen peroxide as an oxidant, which conduces to expose more Mn3+ active sites, thereby accelerating the four‐electron transfer pathway during oxygen reduction reaction. Accordingly, the optimal catalyst (MnPi‐1.0) possesses excellent catalytic performance with a half‐wave potential of 0.81 V and a diffusion‐limited current density of 5.38 mA cm−2 in contrast to the 0.73 V and 5.07 mA cm−2 of the pristine one, respectively. Furthermore, the zinc‐air battery based on MnPi‐1.0 delivers a high peak power density (132 mW cm−2) and outstanding spcific capacity(797 mAh gZn−1). This work provides a facile and feasible solution to tune the density of active sites of manganese phosphate‐based materials for favorable electrochemical performance. [ABSTRACT FROM AUTHOR]