Carbon-coated V0.6Mo0.4Zr0.4Nb8.6O25 with an enlarged crystal structure for high-performance lithium-ion batteries

VNb9O25 has emerged as a highly promising Li+-storage anode material due to its excellent safety and high theoretical capacity. However, it suffers from poor electrochemical kinetics. Here, the electrochemical performance of VNb9O25 is improved through dual modifications. The large-ion (Mo6+ and Zr4+) substitution enlarges the crystal structure of VNb9O25, not only enhancing the Li+ diffusivity but also reducing the unit-cell volume expansion during Li+ insertion. Additional carbon coating further enhances the electrochemical kinetics. Consequently, the resulting ~1 wt% carbon-coated V0.6Mo0.4Zr0.4Nb8.6O25 (C-V0.6Mo0.4Zr0.4Nb8.6O25) exhibits a larger reversible capacity (254 mAh g−1 vs. 173 mAh g−1 at 0.05 A g−1), higher rate capability (108 mAh g−1 vs. 80 mAh g−1 at 2 A g−1), and better cycling stability (95.4 % vs. 84.8 % capacity retention at 2 A g−1 after 2000 cycles) than those of VNb9O25. Moreover, at 45 °C, C-V0.6Mo0.4Zr0.4Nb8.6O25 delivers even higher rate capability (133 mAh g−1 at 2 A g−1) and good cycling stability (80.2 % capacity retention at 2 A g−1 after 1000 cycles), because the enlarged crystal structure enables high capability of accommodating unit-cell-volume expansion after excessive Li+ insertion at the high temperature. Therefore, C-V0.6Mo0.4Zr0.4Nb8.6O25 can be a high-performance anode material practically working in a wide temperature range.