V2O5 intercalated with polyaniline for improved kinetics in aqueous ammonium-ion batteries

Abstract

The use of non-metal ammonium ions (NH 4 + ) as effective charge carriers in battery systems is receiving widespread attention because of their light weight and small hydration shells in water as well as abundancy of the elements. The research concerning NH 4 + ion redox chemistry in batteries is still in its infancy, mainly because the large ionic radius of NH 4 + would require a host material to have a wider open structure and thus limits the choice of electrode materials. NH 4 + ion redox chemistry is dominated by non-ionic chemical bonding such as hydrogen bonding with some covalent bonding in nature which plays a significant role in electrochemical performance of the battery. In this work, an in-situ intercalation technique is utilized to synthesize polyaniline-intercalated vanadium oxide with a nanoflower morphology for increased surface area and enhanced NH 4 + ion (de)intercalation kinetics. Through this strategy, an interlayer spacing of 13.99 Å between V-O layers is reached, offering large diffusion channels to accommodate NH 4 + ions which have an ionic radius of 1.48 Å and a hydrated radius of 3.31 Å. The diffusion kinetics of the NH 4 + ions, influenced by the hydrogen bonds formed between NH 4 + ion and O 2− in the host structure, are thus effectively enhanced by the unique π-conjugated structure of PANI, leading to high capacity, improved rate capability and improved cycle life. The as-prepared PANI-intercalated V 2 O 5 (PVO) demonstrates stable, ultrafast NH 4 + ion electrochemical storage based on hydrogen bond chemistry as elucidated by X-ray photoelectron spectroscopy and Raman spectroscopy characterizations. Additionally, the composition of the PVO electrode is optimized with respect to the amount of PANI between the V-O layers. The PVO with an optimal composition exhibits the best overall electrochemical performance, delivering a high capacity of 192.5 mA hg −1 and 39 mA hg −1 at specific currents of 1 and 20 A g −1 respectively, as well as a stable cycle life with a capacity retention of 98% at a specific current of 10 and 20 A g −1 . As such, the present work provides critical insights into the design of promising electrode materials for emerging aqueous non-metal batteries with intrinsic safety and reduced cost.