Preparation of Li3V2(PO4)3 as cathode material for aqueous zinc ion batteries by a hydrothermal assisted sol–gel method and its properties

Abstract

To alleviate the depletion of lithium resources and improve battery capacity and rate capacity, the development of aqueous zinc-ion batteries (AZIBs) is crucial. The open channels monoclinic structure Li₃V₂(PO₄)₃ is conducive to the transfer and diffusion of guest ions, making it a promising cathode material for AZIBs. Therefore, in this study, nanoneedles and particles Li₃V₂(PO₄)₃ cathode materials for AZIBs were prepared by a hydrothermal assisted sol–gel method, and the effect of synthesized pH values was studied. XRD results show that all samples had the monoclinic structure, and the Li₃V₂(PO₄)₃ sample prepared at pH = 7 exhibits (LVP-pH7) the highest peak tips and narrowest peak widths. SEM images demonstrate that all samples have the morphology character of randomly oriented needles and irregular particles, with the LVP-pH7 sample having more needle-like particles that contribute to ion diffusion. EDS results show uniform distribution of P, V, and O elements in the LVP-pH7 sample, and no obvious aggregation phenomenon is observed. Electrochemical tests have shown that the LVP-pH7 sample exhibits excellent cycling performance (97.37% after 50 cycles at 200 mA g⁻¹) and rate ability compared to other samples. The CV test results showed that compared with other samples, the LVP-pH7 sample had the most excellent ionic diffusion coefficient (2.44 × 10⁻¹² cm² s⁻¹). Additionally, the R_ct of LVP-pH7 is the lowest (319.83 Ω) according to the findings of EIS and Nyquist plot fitting, showing a decreased charge transfer resistance and raising the kinetics of the reaction.