Ultrathin δ-MnO2 nanoflakes with Na+ intercalation as a high-capacity cathode for aqueous zinc-ion batteries

Abstract

Pristine δ-MnO2 as the typical cathode for rechargeable zinc-ion batteries (ZIBs) suffers from sluggish reaction kinetics, which is the key issue to prepare high-performance manganese-based materials. In this work, Na+ incorporated into layered δ-MnO2 (NMO) was prepared for ZIB cathodes with high capacity, high energy density, and excellent durable stability. By an effective fabricated strategy of hydrothermal synthesis, a three-dimensional interconnected δ-MnO2 nanoflake network with Na+ intercalation showed a uniform array arrangement and high conductivity. Also, the H+ insertion contribution in the NMO cathode to the discharge capacity confirmed the fast electrochemical charge transfer kinetics due to the enhanced ion conductivity from the insertion of Na+ into the interlayers of the host material. Consequently, a neutral aqueous NMO-based ZIB revealed a superior reversible capacity of 335 mA h g-1, and an impressive durability over 1000 cycles, and a peak gravimetric energy output of 459 W h kg-1. As a proof of concept, the as-fabricated quasi-solid-state ZIB exhibited a remarkable capacity of 284 mA h g-1 at a current density of 0.5 A g-1, and good practicability. This research demonstrated a significant enhancement of the electrochemical performance of MnO2-based ZIBs by the intercalation of Na+ to regulate the microstructure and boost the electrochemical kinetics of the δ-MnO2 cathode, thus providing a new insight for high-performance aqueous ZIBs.