Synergistic modulation of d-Band Center in δ-MnO₂ via Tungsten Doping and Oxygen Defects for Boosted Aqueous Magnesium-Ion Storage Performance

Abstract

Poor inherent conductivity, sluggish reaction kinetics, and structural instability have widely limited the use of layered δ-MnO₂ in aqueous magnesium-ion storage. Inspired by the d-band center (ε_d) theory, this study synthesizes oxygen defective W-doped δ-MnO₂ (O_d-WMO) with a tailored d-band center through a two-step hydrothermal-calcination method to address the above bottlenecks. The results of theoretical calculation demonstrate that synergistic modulation mechanism of tungsten doping and oxygen defects not only promotes the upward shift of the ε_d of Mn, significantly enhancing the adsorption capacity for Mg²⁺, but also simultaneously strengthens Mn-O bonds, thereby markedly improving structural stability. Moreover, the synergistic modulation effect of the two also dramatically narrows the band gap, lowers the migration energy barrier, as well as speeds up the dynamics of charge transport/ion diffusion. As expected, O_d-WMO demonstrates outstanding structural durability and remarkable storage capacity (185.2 mAh g^-1 at 0.1 A g^-1). Moreover, 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) as anode to assembled O_d-WMO//PTCDI full cell also exhibit a stable working state. This study uncovers the synergistic modulation mechanism of doping and defect engineering on MnO₂'s ε_d, makes up for the limitation in current research that focuses solely on individual regulatory effects of doping or defects. It provides valuable insights for the rational design of high-performance electrode materials for AMIBs and other electrochemical energy storage systems via d-band center engineering.

Keywords

aqueous magnesium-ion batteries / D-band center / doping and defect / electronic structure / δ-MnO₂

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