<p>The development of aqueous ammonium-ion batteries (AAIBs) is constrained by the scarcity of robust anode materials. MoO₃, featuring large ionic migration channels and high theoretical capacity, has been extensively studied as a potential host anode material for the reversible intercalation and deintercalation of NH₄⁺. However, the sluggish ionic migration kinetics, structural degradation caused by the stress of large-sized NH₄⁺ ions, and chemical corrosion in the electrolytes lead to dramatic capacity fading and short lifespan of MoO₃. Herein, we propose an interphase engineering approach to simultaneously achieve high capacity and excellent cycling stability for AAIBs by employing a concentrated 24&#xa0;m NH₄CF₃SO₃ electrolyte to construct a stable solid electrolyte interface that inhibits parasitic reactions and dissolution. The strategy endows the MoO₃ anode with remarkable cyclability, retaining 73.6% of its initial capacity after 500 cycles at 25&#xa0;A&#xa0;g⁻¹. When evaluated in full-cell configurations, our approach achieves high energy density of 80.8&#xa0;Wh&#xa0;kg⁻¹ and outstanding durability, with 64.1% capacity retention over 4000 cycles at 20&#xa0;A&#xa0;g⁻¹. This work offers valuable insights into the design of interface chemistry for high-performance AAIBs.</p>