New cost-saving method to synthesize vanadium oxide nanowires for Li-ion electrodes; Improved capacity and cycling stability
23 October 2010
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| (a, b) Schematic illustration of formation of the ultralong hierarchical vanadium oxide nanowires during annealing. (c) Side view of two ultralong hierarchical vanadium oxide nanowires near each other. (d) Self-aggregation of short vanadium oxide nanorods. Credit: ACS, Mai et al. Click to enlarge. |
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.
Resources
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
This sounds exciting.
"390 and 201 mAh/g when the lithium ion battery cycled between 1.75 and 4.0 V. "
I'm assuming the discharge curve is typical of other batteries, meaning the voltage and current stay pretty high until it's almost discharged, and then they drop of rapidly. In that case we might conservatively expect an average voltage of 3 V and gravimetric capacity of 300 mAh/g. Multiplying these together gives 900 wh/g (0.9 kWh/kg) energy density for the cathode.
This is 80 or 90% higher than LiCoO2 or LiFePO4 according to the chart on http://en.wikipedia.org/wiki/Lithium-ion
Thew self-aggregation of carbon nanotubes in the Contour/MIT cathodes was also a problem, but they found an electorostatic method to prevent clumping and maintaining porosity. This and the electrospinning/annealing processes seem very promising.
Posted by: Zhukova | 23 October 2010 at 06:35 AM
I remember seeing claims ten years ago that nano-tech would change the world. It looks like that may turn out to be true.
Posted by: DaveD | 23 October 2010 at 09:37 AM
The exciting thing is that this appears to be a manufacturing breakthrough. We've seen many examples of how nanorods, nanotudes, nanoparticles, etc can absorb more lithium in the laboratory. But we haven't seen as much news on manufacturing techniques that can make a battery cheaply (and without expensive heavy metals like cobalt).
Posted by: Zhukova | 23 October 2010 at 10:27 AM
Good point. It's all about the cost to manufacture the materials now and these techniques will allow them to become widely used.
Posted by: DaveD | 23 October 2010 at 10:51 AM
This could have good potential for future higher performance batteries if patent restriction doesn't keep it from being manufactured and marketed.
Wonder how many similar patents were bought out by oil firms.
Posted by: HarveyD | 23 October 2010 at 10:53 AM
A cathode that has 80% more capacity would make more than 80% for the battery. That's because the cathode takes about 40% of the mass of the battery, while the anode is about 20%.
So for a 100g battery, the new cathode would weigh 22 grams instead of 40 g. Using Dr. Qui's silicone nanowire anode means a reduction to about 3 grams from 20. That's more than 50% reduction combined. The separator and packaging could be reduced by 50% too, which is 20 g. So the whole battery now weighs only 45g. This is more than doubling the energy density per kg compared to a LiFeO2.
Posted by: Zhukova | 23 October 2010 at 04:21 PM
Yeah, that is why I'm always excited to see advances in cathodes. They lag far behind anodes and make up a greater percentage of the total weight/volume.
Very encouraging.
Posted by: DaveD | 23 October 2010 at 06:04 PM