▎ 摘　　要

It is still a great challenge to improve the rate capability and cyclability of a new conversion-type anode material, VPO4, for lithium-ion batteries. In this work, three-dimensional graphene, carbon and in situ formed V2O3 with high theoretical capacity are introduced into VPO4 to improve the capacity, rate performance and cycle performance. The three-dimensional graphene (3DG) modified VPO4/C (VPO/C@3DG) are prepared by a combination of hydrothermal reaction, freeze-drying and calcination processes, and the VPO/C@3DG composite is investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectrum and electrochemical tests. The results indicate that VPO/C@3DG composite contains VPO4, V2O3, carbon and three-dimensional graphene, and dispersive VPO4 and V2O3 nanoparticles and carbon form carbon coated sphere-like VPO/C particles, and VPO/C particles are covered by three-dimensional graphene. The VPO/C@3DG composite exhibits much higher capacity, better rate capability and cyclability than the control VPO4/C and three-dimensional graphene (3DG). In the voltage range of 0.01-3.0 V (vs Li+/Li), the second cycle discharge capacities of VPO/C@3DG are 654.6, 551.6, 486.8, 420.6 and 343.1 mAh.g(-1) at 0.2, 0.5, 1, 2 and 5C (2750 mA g(-1)), respectively, significantly higher than 507.8 (0.2C), 384.9 (0.5C), 294.2 (1C), 219.3 ( 2C) and 124.1 mAh.g (1)(5C) of VPO4/C and 393.1(0.2C), 298.2 (0.5C), 252.1(1C), 217.8 (2C), 169.7 mAh.g(-1) ( 5C) of 3DG. After cycled 30 cycles at 0.2C, the discharge capacity of VPO/C@3DG still remains 631.9 mAh.g(-1), while the discharge capacities of VPO4/C and 3DG are 352.4 and 308.5 mAh.g(-1), respectively, under the same conditions. Even at high current rate of 5C, the discharge capacity of VPO/C@3DG is 338.8 mAh.g(-1) after 100 cycles, significantly higher than that of VPO4/C (101 mAh.g(-1)) and 3DG ( 142.1mAh.g(-1)). The results indicate that the special composition and microstructure are responsible for the superior electrochemical performance of VPO/C@3DG. The results suggest that introduction of three-dimensional graphene and construction of special microstructure is substantially beneficial for improvement of electrochemical performance of conversion-type electrode materials. (C) 2018 Elsevier Ltd. All rights reserved.