Cr-Doped Na_3V_2(PO_4)_3/C Nanocomposite with High Power Capability for Advanced Sodium-Ion Batteries

摘要

NASICON-structured Na_3V_2(PO_4)_3 (NVP) is one of the most promising cathode materials for rechargeable sodium-ion batteries. In this study, Na_3V_(2-x)Cr_x(PO_4)_3@C samples with different concentrations of substituted chromium (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.7, and 1.0) were fabricated using a low-cost pyro synthesis technique with the advantage of self-carbon-coating, which is essential for phosphate-based cathodes. The electrochemical properties of the Cr-substituted NVP samples were analyzed to evaluate the structural improvements and enhanced sodium storage among the synthesized samples. The rhombohedral structures of the NVP and Cr-doped NVP samples were confirmed by X-ray diffraction (XRD) analysis. Notably, phase change did not occur upon Cr doping. The introduction of Cr in NVP significantly enhanced the electrochemical performances. The NVP structure with x = 0.4 provided a superior discharge capacity of 49 mA h g~(-1) at a high rate of 70 C. An in-situ XRD investigation demonstrates the high structural stability of the doped sample during the Na~+-ion intercalation/deintercalation. An ex-situ X-ray photoelectron spectroscopy analysis shows changes in the oxidation state of vanadium during charging/discharging.