Heterogeneous structure engineering and optimizing the electronic band structure of the VO2(B)/V3O5 cathode: toward a low-cost, long life span and green aqueous ammonium ion battery†

Aqueous ammonium ion batteries are promising because of their high safety and efficient charge transfer rate in energy storage applications, but their wide applicability is hindered by the limited properties of the cathode materials. Heterojunction engineering and ion doping are effective strategies for enhancing the reaction dynamics and structural stability of cathode materials. In this work, we chose an iron-doped heterogeneous structured VO₂(B)/V₃O₅ with a rich heterojunction interface and stability as a research object to test its application in ammonium ion storage. Ex situ XRD and ex situ FTIR tests proved that a phase transition happened during the first charge/discharge process. DFT calculations revealed that iron ion doping can adjust the electronic band structure and promote the phase transition by inducing fast catalytic coupling and NH₄⁺ insertion process. Impressively, Fe-VO₂(B)/V₃O₅ delivered superior electrochemical performance with high capacity and cycling stability when the atomic content of Fe was 0.1. The assembled Fe_0.1VO₂(B)/V₃O₅//PTCDI full cell exhibited a high capacity of 143.8 mA h g⁻¹ at 0.5 A g⁻¹ and energy density of 115.1 W h kg⁻¹ and behaved much better than other full cells with different Fe doping content. This work provides a new strategy to design a high-performance electrode material for ammonium ion storage through heterojunction engineering and ion doping.