High-Performance Sodium Storage Enabled by Structural Optimization of Oxidized (NH4)0.5V2O5

This study reports the design of an oxidation-engineered (NH4)0.5V2O5 (oxidation-NVO) cathode via selective ammonium ion extraction using Na2S2O8 to modulate the interlayer framework for enhanced sodium-ion storage. The oxidation process partially removes NH4⁺ ions while preserving the layered monoclinic structure, leading to expanded interlayer spacing and improved ion accessibility. Structural characterizations confirm the retention of a stable [VO6]n framework supported by residual NH4⁺ species acting as structural pillars. Morphological analysis reveals highly crystalline rod-like microstructures, and chemical state analysis confirms the coexistence of V4⁺/V5⁺ state, favorable for redox activity. Electrochemical testing shows that the oxidation-NVO electrode delivers a high reversible capacity of 192 mAh g⁻1, approximately 20% higher than the pristine NVO counterpart, with excellent cycling stability, low polarization, and full capacity recovery after rate variation. Further transport and structural analyses under dynamic conditions demonstrate improved Na⁺ transport and a reversible breathing-type interlayer response. These findings highlight the effectiveness of interlayer chemistry modulation through oxidation as a simple and scalable strategy for advancing vanadium-based cathode materials in sodium-ion batteries.