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 material 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 absorption 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 investigation 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.