Modulating residual ammonium in MnO2 for high-rate aqueous zinc-ion batteries

Abstract

Manganese dioxide (MnO₂), as a promising cathode candidate, has attracted great attention in aqueous zinc ion batteries (ZIBs). However, the undesirable dissolution of Mn²⁺ and the sluggish kinetic reaction are still two challenges to overcome before achieving good cycling stability and high-rate performance of ZIBs. Herein, β-MnO₂ with chemically residual NH₄⁺ (NMO) was successfully fabricated by controlling the washing condition and utilized as a cathode in a ZIB. Interestingly, NH₄⁺, as a layer pillar in the tunnel structure of NMO, could enhance its conductivity by changing the chemical structure, contributing to accelerating the kinetics of the charge carrier. Moreover, the residual NH₄⁺ in NMO could stabilize the chemical microstructure through the cationic electrostatic shielding effect and the formation of Mn–O⋯H bonds in NMO, promoting the reversible and successive insertion/extraction of H⁺/Zn²⁺ in the ZIB. As a result, the Zn/NMO battery exhibits excellent rate performance (up to 8.0 A g⁻¹) and cycling stability (10 000 cycles). This work will pave the way for the design of cathode materials with nonmetallic doping for high-performance ZIB systems.