Decoding aromatic diamine polymer for highly stable aqueous ammonium-ion storage with multiple redox-active sites

Abstract

Ammonium-ion batteries (AmIBs), employing non-metallic NH₄⁺ charge carriers in aqueous electrolytes, represent an emerging class of electrochemical energy storage devices. Nevertheless, progress in this field has been constrained by the limited availability of advanced electrode materials with high capacity and cycling stability. This work introduces an aromatic diamine polymer, poly(o-phenylenediamine) (PPDA), as an anode candidate for AmIBs. Various experimental and theoretical data confirm that the high-density CN functional groups and aromatic rings in PPDA serve as effective redox centers, facilitating superior capacity and long-term cyclability at elevated current densities. This intrinsic mechanism facilitates exceptional electrochemical performance, delivering a reversible specific capacity of approximately 130 mAh g⁻¹ at 5 A g⁻¹, without capacity fading after 43 700 cycles. Furthermore, the compound sustains a significant capacity of 114 mAh g⁻¹ even under high-rate discharge at 10 A g⁻¹.