Magnesium-sulfur (Mg-S) batteries typically exhibit high discharge capacity but suffer from poor cycling performance due to the shuttle effect of polysulfides. In this study, we develop an artificial electrode skin on the SeS₂ cathode in a Mg-SeS₂ battery to effectively suppress the shuttle of polysulfides and polyselenides. A range of electrochemical and spectroscopic characterizations are conducted to investigate the confinement effect of the i-MXene-based electrode skin on dissolved sulfur- and selenium-based species. Theoretical simulations indicate that surface hydroxyl groups and other functional moieties of i-MXene can effectively confine active species to the cathode side. As a result, the Mg–SeS₂ battery with the cathode skin layer demonstrates a high discharge capacity of 750 mAh g⁻¹ at a current density of 0.1 A g⁻¹, with excellent cycling stability. The battery maintains 76% of its capacity after 100 cycles at 0.5 A g⁻¹ and 62% after 300 cycles at 2 A g⁻¹, exceeding or matching the performance of most previously reported Mg–S batteries. This work demonstrates a viable strategy to boost the electrochemical performance of Mg-ion batteries.

Aqueous rechargeable ammonium-ion (NH₄⁺) batteries (AAIBs) with ammonium ions as charge carriers possess many advantages, yet the relatively low discharge capacities (e.g., < 200 mAh·g⁻¹) of the reported NH₄⁺ host materials hinder the development of AAIBs. Herein, we study the NH₄⁺ storage properties of an electrochemically activated NiCo double hydroxide (A-NiCo-DH) in neutral ammonium acetate electrolyte for the first time. The activation process extracts the interlayer anions (NO₃⁻) from the host material, providing additional cation accommodation sites for charge storage. The introduced H vacancies in A-NiCo-DH could activate the O sites, leading to the enhanced cation adsorption capability for the electrode. Therefore, A-NiCo-DH exhibits a high discharge capacity of 280.6 mAh·g⁻¹ at 0.72 A·g⁻¹ with good rate capability. Spectroscopy studies suggest A-NiCo-DH experiences a NH₄⁺/H⁺ coinsertion mechanism. A NH₄⁺-Zn hybrid cell is assembled using A-NiCo-DH as the cathode and Zn foil as the anode, respectively. The device delivers an energy density of 306 Wh·kg⁻¹ at the power density of 745.8 W·kg⁻¹ (based on the active mass of A-NiCo-DH). This work provides a new NH₄⁺ storage material and would push forward the development of aqueous NH₄⁺-based batteries.