Layered MnO2 nanodots as high-rate and stable cathode materials for aqueous zinc-ion storage

MnO2 has recently received great concern as a cathode material for zinc-based energy storage owing to its many advantages. Unfortunately, the low rate capability and poor cyclability hinder its practical application. Herein, novel layered MnO2 nanodots (δ-MnO2 NDs) are synthesized by a facile redox reaction, and utilized as the cathode for aqueous zinc-ion batteries/hybrid capacitors (ZIBs/ZICs) for the first time. Benefiting from the layered structure and nanoscale size, the δ-MnO2 NDs//Zn ZIBs display a considerable specific capacity of 335 mAh g–1 at 0.1 A g–1, an impressive rate capacity of 125 mAh g–1 at 2.0 A g–1, a large specific energy (466.7 Wh kg–1 at 139 W kg–1), and a superior durability with 86.2% capacity retention after 1000 cycles at 1.0 A g–1. Further, the H+/Zn2+ co-insertion energy storage mechanism of the δ-MnO2 NDs cathode is verified by electrochemical kinetics analyses and ex-situ characterizations. Simultaneously, the novel ZICs based on δ-MnO2 NDs cathode exhibit a high specific energy of 68.7 Wh kg–1 and a satisfactory cycle life with 86.9% capacity retention after 5000 cycles at 1.0 A g–1. The quantization design strategy opens a new gateway for the design and exploitation of advanced cathodes for aqueous ZIBs and ZICs.