J. Cheng (Institute of Chemical Materials, China Academy of Engineering Physics,, Sichuan research center of new materials, Chengdu) and B. Wang (Institute of Chemical Materials, China Academy of Engineering Physics)
Among the existing cathode materials, V
2O
5 is a promising cathode candidate because of its high energy density, abundance, easy synthesis, as well as low cost. However, due to quite low diffusion coefficient of lithium ions (10
-12-10
-13 cm
2 s
-1), irreversible phase transitions during deep discharge, and vanadium dissolution into the electrolyte, the practical use of V
2O
5 as a cathode material shows poor rate capability and cycling stability
1,2. Incorporating the nanostructured V
2O
5 with high conductive materials to build a hybrid material is one of the most promising strategies to improve the electrochemical property of the V
2O
5 based anod
3. Among these conductive materials, graphene nanosheet (GNS), with the exceptional properties of excellent electronic conductivity of 10
3-10
4 S m
-1, high theoretical surface area of 2630 m
2 g
-1, and high mechanical flexibility is much more attractive. Extensive studies of GNS-V
2O
5 nanocomposites have been investigated. However, it is worth noting that most of the reported nanocomposites constitute by the GNS with the zero-dimensional (0-D) nanoparticles or one-dimensional (1-D) V
2O
5 nanofiber/nanorod. To the best of our knowledge, the 3-D nanocomposites combining the GNS layer with 2-D V
2O
5 nanosheets have not been reported so far.
Herein, we demonstrate a simple solvothermal method to directly self-assemble 2-D V2O5 nanosheets on the reduced graphene oxide, forming 3-D nanocomposite (V2O5 nanosheet/RGO hierarchical nanocomposite). Briefly, vanadium oxytriisopropoxide (VO(OiPr)3) and graphene oxide (GO) were dispersed into ethyl alcohol by ultrasonicaiton to produce a V-precursor/GO dispersion. Then, the dispersion was transferred to a Teflon-lined stainless steel autoclave and heat-treated in an electric oven. The obtained composite was further annealed at 300°C in air to make V2O5 crystallized and reduce GO to RGO. The detailed preparation procedures can be found in the experimental section.
When used as a cathode material, the V2O5 nanosheets/RGO nanocomposites exhibits highly reversible capacity and good rate capability over bulk material. The V2O5 nanosheets/RGO nanocomposite anode was able to charge/discharge at high current densities of 15A g-1 (50C), with the discharge capacities of approximately 176 mA h g-1. Meanwhile, a discharge capacity of 102 mA h g-1 can be delivered after 160 cycles at 2C, showing a good cycling stability. The improved performance could be attributed to the enhanced electron transport and Li+ diffusion that result from the hierarchical nanostructure of V2O5 nanosheets/RGO nanocomposite (showing in Figure 1).
Reference:
[1] S. Q. Wang, S. R. Li, Y. Sun, X. Y. Feng, C. H. Chen, Energy & Environmental Science 2011, 4, 2854.
[2] Y. X. Tang, X. H. Rui, Y. Y. Zhang, T. M. Lim, Z. L. Dong, H. H. Hng, X. D. Chen, Q. Y. Yan, Z. Chen, Journal of Materials Chemistry A 2013, 1, 82.
[3] X. H. Rui, J. X. Zhu, D. Sim, C. Xu, Y. Zeng, H. H. Hng, T. M. Lim, Q. Y. Yan, Nanoscale 2011, 3, 4752.
