Superior High-Rate and Ultralong-Lifespan Na3V2(PO4)3@C Cathode by Enhancing the Conductivity Both in Bulk and on Surface

Na₃V₂(PO₄)₃ has shown great promise in next-generation cathode materials for sodium-ion batteries owning to its fast Na⁺ diffusion in the three-dimensional open NASICON framework and high theoretical energy density. However, Na₃V₂(PO₄)₃ suffers from undesirable rate performance and unstable cyclability arising from low electronic conductivity. Herein, we propose a facile approach for significantly enhancing the electrochemical properties of Na₃V₂(PO₄)₃ by Ti doping at V site and constructing nanoparticle@carbon core-shell nanostructure. This material design provides fast electron conduction network within the whole active particles because of the mixed valence Ti^4+/3+ in bulk and highly conductive carbon shell on the surface. Lattice doping and carbon coating reduce the electrode polarization and facilitate the electrode reaction kinetics, while the nanostructure enhances the ionic conduction by shortening the diffusion distance and offers sufficient contact of active particles with organic electrolyte. The multiple synergetic effects enable a superior electrochemical performance. The optimized Na₃V_1.9Ti_0.1(PO₄)₃@C cathode shows a high specific capacity (116.6 mAh g^-1 at 1C), an unprecedented rate performance (93.4 mAh g^-1 at 400C), and an exceptional long-term high-rate cycling stability (capacity retention of 69.5% after 14 000 cycles at 100C, corresponding to 0.0002% decay per cycle).