Low-Content Mg ²⁺ Preintercalation-Mediated Structural Stabilization in the NH ₄ V ₄ O ₁₀ Cathode Enables Ultrastable Zinc-Ion Storage

The application of NH4V4O10 with high theoretical specific capacity is restricted due to irreversible deamination and structural instability during repeated Zn2+ (de)intercalation processes. Previous studies have predominantly utilized the preintercalation of excessive inactive metal ions to partially substitute NH4+ ions, achieving improved cycling stability but at the cost of reduced reversible specific capacity. Herein, a low-content Mg2+ preintercalated NH4V4O10 (MNVO, Mg:V = 0.036:4), without replacing interlayer NH4+ ions, is synthesized to achieve structural stabilization for highly stable zinc-ion storage. Characterization results reveal that the preintercalation of low-content Mg2+ induces favorable morphological and structural effects. MNVO features a 3D hierarchical spherical architecture constructed from curled nanosheets, which can facilitate uniform stress distribution and effectively mitigate structural degradation during prolonged Zn2+ (de)intercalation cycles. More importantly, Ex-situ XRD and XPS results reveal that low-content Mg2+ preintercalation fundamentally suppresses the dual degradation pathways of irreversible deamination and byproduct formation in MNVO, thereby preserving structural integrity. Benefiting from these advantages, MNVO achieves an outstanding capacity retention under both low current density (94% after 500 cycles under 0.5 A g–1) and high current density (94% after 5000 cycles under 5 A g–1). This low-content cation preintercalation strategy offers new insight for developing highly stable layered vanadium-based cathode materials for aqueous zinc-ion batteries.