New cost-saving method to synthesize vanadium oxide nanowires for Li-ion electrodes; Improved capacity and cycling stability
A team from Harvard University and the Wuhan University of Technology (China) has synthesized novel ultralong hierarchical vanadium oxide (V2O5 nanowires from attached single-crystalline vanadium oxide nanorods via electrospinning combined with annealing and using low-cost starting materials.
Compared with self-aggregated short nanorods synthesized by hydrothermal methods, the ultralong hierarchical vanadium oxide nanowires exhibit much higher capacity and improved cycling stability, the researchers report in a paper published online 18 October in the ACS journal Nano Letters.
...in the ordinary batteries, owing to the high surface energy, nanomaterials are often self-aggregated, which reduces the effective contact areas of active materials, conductive additives, and electrolyte. How to keep the effective contact areas large and fully realize the advantage of active materials at nanometer scale is still a challenge and of great importance. Hierarchical nanostructured materials such as hollow nanospheres, porous nanostructures, nanotubes, nanowire-on-nanowire structures, and kinked nanowires, etc., can ensure the surface remains uncovered to keep the effective contact areas large even if a small amount of inevitable self-aggregation occurs.
There has been much interest in electrospinning and/or electrochemistry of vanadium oxide nanowires/nanorods because nanostructured vanadium/molybdenum oxides with a typical layed structure have the potential to offer high capacities for lithium ion batteries.
...Compared with previous studies on electrospinning of vanadium oxide nanowires by using expensive organic vanadium oxide isopropoxide as the raw materials, we successfully synthesized vanadium oxide nanowires via electrospinning by using inorganic ammonium metavanadate as precursor, which is cost-saving and more suitable for industrial production of lithium batteries. Moreover, the as-prepared ultralong hierarchical vanadium oxide nanowires were found to offer high charge/discharge capacities and improved cycling stability.—Mai et al.
The initial and 50th discharge capacities of the ultralong hierarchical vanadium oxide nanowire cathodes are up to 390 and 201 mAh/g when the lithium ion battery cycled between 1.75 and 4.0 V. When the battery was cycled between 2.0 and 4.0 V, the initial and 50th discharge capacities of the nanowire cathodes are 275 and 187 mAh/g.
Self-aggregation of the unique nanorod-in-nanowire structures has been greatly reduced, the authors suggest, because of the attachment of nanorods in the ultralong nanowires, which can keep the effective contact areas of active materials, conductive additives, and electrolyte large and fully realize the advantage of nanomaterial-based cathodes.
The high performance of our batteries is attributed to several reasons. We deduce that self-aggregation of the ultralong hierarchical vanadium oxide nanowires can be effectively prevented, which keeps the surface area large to fully realize the advantage of nanostructured materials. Furthermore, after annealing at 480 °C, the vanadium oxide nanorods of high crystallinity in the nanowires make the active materials stable during cycling...Compared with other vanadium oxide nanorods by combining electrospinning with hydrothermal treatment or annealing, our ultralong hierarchical vanadium oxide nanowires have higher specific capacity and better cycling capability.
...The nanorod-in-nanowire described in this paper is a unique structure that will probably have potential applications in chemical power sources, sensors, and other nanodevices.—Mai et al.
Liqiang Mai, Lin Xu, Chunhua Han, Xu Xu, Yanzhu Luo, Shiyong Zhao, and Yunlong Zhao (2010) Electrospun Ultralong Hierarchical Vanadium Oxide Nanowires with High Performance for Lithium Ion Batteries. Nano Lett., Article ASAP doi: 10.1021/nl103343w