Massive anionic fluorine substitution two-dimensional δ-MnO2 nanosheets for high-performance aqueous zinc-ion battery

Abstract

As one of the most promising materials for rechargeable aqueous zinc ion batteries (AZIBs), manganese oxide (δ-MnO2) need overcome the fatal limitations of structural instability and manganese dissolution for future practical application. Crystal high-orientated two-dimensional δ-MnO2 nanosheets with massive anionic fluorine were synthesized by a lava method with quenching treatment. When employed as a cathode material for zinc ion batteries, it exhibits a long cycling lifespan and high multiplicity performance. The fluorine atoms substitution can not only stabilize the manganese‑oxygen octahedron [MnO6] structure by introducing fluorine‑manganese chemical bonding, but also regulate the Mn3+/Mn4+ ratio by increasing the Mn3+ concentration content. Meanwhile, the obtained high-orientated 2D nanosheets structure can accelerate the ions kinetic behaviors for high rate electrochemical performance by shortening the ion translation and increasing the electronic conductivity. The optimized δ-MnO2 nanosheets exhibit a superior electrochemical performance of 288 mAh g−1 at current densities of 100 mA g−1. An excellent cycling lifespan up to 96 % capacity retention is indicated as well after 200 cycles at a current density of 200 mA g−1. This element doping strategy by molten salt quenching method has the benefits of simple synthesis steps and high yield with high economic efficiency.