A dual-polymer strategy boosts hydrated vanadium oxide for ammonium-ion storage

Recently, aqueous rechargeable batteries employing ammonium-ions (NH4+) as charge carriers have received increasing interest because of their merits of eco-friendly, low cost and sustainability. However, the supercapacitor based on NH4+ charge carriers has rarely been reported probably owing to the lack of a suitable system to achieve acceptable capacitance and cycle performance for NH4+ storage. Herein, we develop a dual-polymer strategy to boost the electrochemical properties of hydrated vanadium oxide (HVO) for outstanding NH4+ storages based on a supercapacitor. One polymer polyaniline (PANI) is intercalated into the interlayer space of HVO (11.0 Å) to synthesize PANI-intercalation-HVO (PVO) with the expanded interlamellar spacing of 13.9 Å, which enhances the kinetics and stabilizes the structure during the NH4+ (de)intercalation. The capacitance at 1 A·g-1 is significantly improved from 156F·g-1 (HVO) to 351F·g-1 (PVO). The other polymer polyvinyl alcohol (PVA) is used to get the quasi-solid-state (QSS) PVA/NH4Cl electrolyte, in which the cycle stability of PVO electrode is effectively improved. The PVO exhibits the capacitance retentions of 82% after 2000 cycles and 56% after 10,000 cycles, whereas this value is only 29% after 3000 cycles in NH4Cl electrolyte. The findings reveal that this strategy can effectively reduce the diffusion resistance of ammonium ions and improve the energy storage efficiency of PVO. The flexible QSS PVO//active carbon hybrid supercapacitor (FQSS PVO//AC HSC) device is assembled and exhibits outstanding capacitance, long cycle stability, good mechanical stability and potential practical applications. This work may open up a new window for the study on the improved electrochemical properties of electrode materials for NH4+ storage.