Ultra-low diffusion barrier tetramethyl ammonium cation-intercalated layered MnO2 for high-performance aqueous zinc-ion batteries†
Abstract
The distinctive layered configuration of δ-MnO2 renders it an exceptionally promising candidate as a cathode material for aqueous zinc-ion batteries (ZIBs). However, its practical utilization is constrained by the sluggish diffusion kinetics of Zn2+ and the capacity degradation resulting from lattice distortions occurring during charge and discharge cycles. To address these challenges, we have developed TMA–MnO2 by pre-intercalation of both tetramethylammonium ions (TMA+) and H2O molecules. The incorporation of TMA+ within the interlayer of δ-MnO2 results in the expansion of the interlayer spacing to 0.96 nm, thereby establishing a rapid diffusion pathway for Zn2+. At a rate of 0.2 A g−1, the ZIB employing TMA–MnO2 exhibits a specific capacity of 310.3 mA h g−1. Furthermore, after 1000 cycles at 2 A g−1, it maintains 91% of its initial capacity. Ex situ characterization techniques provide evidence of the co-intercalation mechanism of Zn2+/H+, concurrently indicating the stable presence of TMA+ as a structural support between layers during charge–discharge cycling. Density functional theory calculations provide evidence of the transformative impact of TMA+ introduction on the electron cloud density distribution within MnO2. This alteration leads to an enhancement in material conductivity and a substantial reduction in the diffusion barrier for Zn2+, consequently facilitating rapid diffusion kinetics.
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