Abstract

Aqueous ammonium-ion (NH₄⁺) storage has emerged as a promising alternative to metal-ion systems because NH₄⁺ combines a low molar mass with favorable transport kinetics. However, cooperative Jahn–Teller distortion, sluggish ion transport, and Mn dissolution limit the reversibility of layered MnO₂ cathodes. Here, we report La/NH₄⁺-co-intercalated δ-MnO₂ (LAMO), prepared by ultrafast CO₂-laser-assisted synthesis and subsequent ion exchange, to regulate both the electronic structure and interlayer chemistry of δ-MnO₂. La³⁺ pillaring increases the Mn⁴⁺ population, suppresses cooperative Jahn–Teller distortion, and stabilizes the MnO₆ octahedra, whereas NH₄⁺ establishes dynamic N–H···O hydrogen-bond networks that enable low-barrier twist-and-rotate transport. LAMO exhibits a specific capacity of 252 C g⁻¹ at 0.5 A g⁻¹. In situ Raman spectroscopy and ex situ XRD, XPS, and TOF-SIMS support a reversible, solid-solution-like NH₄⁺ storage mechanism accompanied by symmetric lattice breathing. Density functional theory calculations further indicate La-induced electronic delocalization, strengthened Mn–O interactions, and a reduced NH₄⁺ migration barrier of 0.31 eV. These findings identify coupled electronic and interlayer engineering as an effective strategy for stabilizing layered oxides for fast and durable ammonium-ion storage.