K3V3(PO4)4/C: A new carbon-coated layered structure cathode material for potassium-ion batteries

The emergence of layered structure materials has positioned itself as a focal point in the progress of potassium-ion battery (KIBs) cathode materials, as it faces challenges concerning cycling-induced structural stability. In this particular investigation, the successful synthesis of a carbon-coated polyanionic layered composite denoted as K3V3(PO4)4/C has been achieved. K3V3(PO4)4/C was subsequently employed as a novel positive electrode ma-terial for KIBs. Upon subjecting it to 100 cycles at a current density of 200 mA g- 1, the discharge specific capacity exhibited a remarkable value of 37 mAh g- 1, thus showcasing a capacity retention of 88%. Impressively, even after undergoing 300 cycles at a high current density of 400 mA g- 1, the capacity retention remained constant at 85%. The superior long-term cycling performance and high capacity retention observed in K3V3(PO4)4/C can be attributed to the inherent stability of the polyanionic layered structure and the dual contributions derived from the carbon coating. Furthermore, the application of characterization techniques such as synchrotron X-ray ab-sorption near-edge structure spectroscopy (XANES) revealed a V valence state of + 3 within the synthesized sample. By establishing a structural model for K3V3(PO4)4/C and conducting first-principles calculations on its band structure and density of states, it was confirmed that the material facilitates electron transfer. An inves-tigation into potassium ion migration and diffusion elucidated the involvement of tetrahedral site hopping (TSH). The successful synthesis of K3V3(PO4)4/C material not only provides valuable insights but also serves as a reference for the development of KIBs cathode materials.