A high-capacity double-layered (NH4)0.5V2O5 in micro-rods structure for sodium storage

Abstract

An ammonium vanadium bronze (NH₄)_0.5V₂O₅ (NVO) was synthesized via a hydrothermal route and investigated the Na-insertion/extraction process as a cathode for Na-ion batteries. The structural analysis confirms that the double-layered NVO in the micro-rods structure is formed by the double-sheet [VO₆] with a large distance interlayer of 9.717 Å to be suitable for reversible Na-storage. The charge–discharge cycling performance delivers ∼160 mAh/g for long-term 200 cycles with structural stability. The ex-situ EXD at various Na-content states demonstrates the shrinkage/expansion of the interlayers during Na-migration, and the NH₄⁺-ions play an essential role as the “pillar” of double-layered V₂O₅ to assure cycling stability. This work contributes to a high-capacity member of the V₂O₅ polymorph family in the context of Na-ion batteries.