image: Analysis of the nanostructure and in-situ structural evolution of Zr-doped NVPF completely coated with nitrogen-doped carbon.
Na3V2(PO4)2F3(NVPF), a cathode material used in sodium-ion batteries (SIB), features ultrafast Na+ migration and high structural stability because of its three-dimensional open framework. However, the poor intrinsic electronic conductivity of NVPF often leads to high polarization, low Coulombic efficiency, and unsatisfactory rate performance, which hinder its commercial application.
Recently, a group led by Prof. Shuangqiang Chen and Prof. Yong Wang from Shanghai University synthesized zirconium-doped NVPF nanoparticles coated with a nitrogen-doped carbon layer and demonstrated a synergistic effect on the overall electrochemical performance. Specifically, the optimized NVPF-Zr-0.02/NC electrode led to high reversible capacity (119.2 mA h g-1 at 0.5 C), superior rate capacity (98.1 mA h g-1 at 20 C), and excellent cycling performance (capacity retention of 90.2% in 1000 cycles at 20 C). In situ XRD characterization of the NVPF-Zr-0.02/NC electrode was performed to monitor the real-time structural evolution in different charge/discharge states. The results confirmed the presence of several intermediates with new phases, following a step-wise Na-extraction/intercalation mechanism with reversible multiphase changes. In addition, NVPF-Zr-0.02/NC//hard carbon full cells demonstrated a high reversible capacity of 99.8 mA h g-1 at 0.5C, with an average output voltage of 3.5 V, high energy density of ~194 Wh kg-1, and good cycling stability, thus indicating excellent potential for practical application.
"Such attempts provide meaningful guidance and reference for practical SIBs with high capacity, long cycle life, and good structural stability," said Prof. Chen.