Core-shell structural vanadium Oxide/Polypyrrole anode for aqueous Ammonium-Ion batteries

• NH 4 + storage properties of VO x @PPy are studied for the first time. • Synergistic interaction between VO x and PPy enhances the performance of the composite electrode. • The NH 4 + /H + co-insertion mechanism is proposed. • VO x @PPy exhibits a high capacity of 195 mAh g -1 . Aqueous ammonium-ion batteries (AAIBs) are attracting attention, mainly due to the unique interaction between NH 4 + and the host materials. Yet, few studies focus on the development of high-performance anode materials for NH 4 + storage, hindering the applications of AAIBs . Herein, we study the electrochemical NH 4 + storage properties of an electrodeposited vanadium oxide/polypyrrole (VO x @PPy) electrode with a core-shell structure. The strong interaction between PPy and VO x enhances the electrochemical performance of the composite electrode. The electrons in N atoms from PPy are attracted by V cations from VO x , resulting in the enhanced protonation level of PPy and the reduction of V in the composite material. Therefore, VO x @PPy exhibits a high specific capacity of 195.36 mAh g -1 at 0.2 A g -1 in ammonium acetate electrolyte, outperforming other reported anode materials for NH 4 + storage. In addition, the conformal PPy coating can efficiently suppress VO x dissolution, leading to good cycling stability for VO x @PPy. We assembled an aqueous ammonium-ion battery using VO x @PPy as the anode. The device exhibits a good energy density of 74.1 Wh kg -1 at the power density of 75.6 W kg -1 . This work highlights the advantages of the hybrid organic/inorganic materials for NH 4 + storage and could push the development of aqueous ammonium-ion batteries.