Enhancing ammonium-ion storage in Mo-doped VO₂ (B) nanobelt-bundles anode for aqueous ammonium-ion batteries

The recent surge in interest in aqueous ammonium ion rechargeable batteries (AAIBs) has been fueled by their eco-friendliness, efficiency, safety, and sustainability. However, finding the optimal anode material for effective ammonium ion (NH₄⁺) storage remains a nascent and significant challenge. The research presented here focuses on the enhancement of aqueous ammonium rechargeable batteries by incorporating Mo atoms into VO₂ (B) (denote as MVO), a material that has shown promise as an anode for NH₄⁺ storage. The introduction of Mo ions was found to optimize the electronic structure and morphology of pristine VO₂ (B) (label as PVO), resulting in the transformation of its nanobelts into thin nanobelt-bundles. This alteration exposes more active sites and increases oxygen vacancies, which in turn improve the conductivity and diffusion rate of NH₄⁺ ions, thereby enhancing the overall electrochemical performance of the material. The MVO material demonstrates a high initial capacity of 283.5 mA h g^-1 at 0.3 A g^-1, and maintained 86.7% of its capacity after 4500 cycles, indicating excellent long-term stability. To further validate the practical application, a full cell was garnered utilizing MVO as the anode and Cu₃[Fe(CN)₆]₂ (CuHCF) as the cathode. The resulting AAIB displays remarkable cycling stability, with 81.5% capacity preservation after 1000 cycles and large energy density of 57.9 W h kg^-1. The study reveals that the doping of Mo ions can significantly improve both the stability and NH₄⁺ storage capacity of PVO, offering a promising new direction for the exploitation of efficacious and sustainable NH₄⁺ host materials for rechargeable batteries.