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Self-Supporting Cobalt Oxide Nanowire Anodes for Li-Ion Batteries Offer High Capacities and Rate Capabilities

22 April 2008

Wu
SEM images of Co3O4 nanowire arrays growing on Ti foil viewed when tilted by 40°. The inset shows the open tips of the nanowires. Click to enlarge.

Researchers at Ohio State University (OSU) led by Professor Yiying Wu have developed a lithium-ion battery anode material from nanowire arrays of a cobalt oxide (Co3O4) that offers increased rate capabilities for high-powered applications, improves the cyclic properties in a rapid charge/discharge process, and increases the energy capacities.

As detailed earlier this year in the journal Nano Letters, at a current of 1C, the self-supported nanowire arrays maintain a stable capacity of 700 mAh/g after 20 discharge/charge cycles. When the current is increased to 50C, 50% of the capacity can be retained. OSU is offering the technology for licensing.

Wu’s team developed a template-free method to enable the large-area growth of the nanowires directly on a current-collecting titanium (Ti) substrate. No carbon or polymer additives are needed, which will save a mixing step.

The Co3O4 nanowire (NW) array reported in the journal shows a capacity close to twice that of the theoretical capacity (372 mAh/g) for graphite.

In previous literature references, there are only a few papers about free-standing NW array anodes prepared by the cumbersome template-synthesis method, including the carbon nanotube membrane (490 mAh/g), the SnO2 NW arrays (~700 mAh/g), and the Fe3O4/Cu composite NW arrays (~800 mAh/g). In addition, there are papers about random nanowire/nanotube anodes, such as multiwall carbon nanotubes (320 mAh/g), TiO2 (305 mAh/g), SnO2 (~400 mAh/g), Co3O4 (~500 mAh/g), CuO (~500 mAh/g), Fe2O3 (510 mAh/g), and MoO3 (150 mAh/g). By comparison, it is easy to tell that our Co3O4 NW arrays show one of the best capacities among the reported NW anode materials.

—Wu (2008)

The team also tested the performance of the arrays at higher currents varied from 2 to 50C. Rate capability is an important parameter for many applications of batteries such as electric vehicles, which require fast discharge and/or charge rate.

The CO3O4 arrays can retain 85% capacity at 8C, 69% at 20C, and 50% at 50C relative to the capacity at 1C. By contrast, the capacity of non-self-supported NWs or powders decays much more sharply with the increase of current. The team also found that their NW arrays show good cyclability at high currents. After 20 cycles, the NW arrays can still maintain a capacity of 450 mAh/g at 20C and 240 mAh/g at 50C.

The researchers attributed the high rate capacity and rate capability of the nanowires arrays to the hierarchical architecture:

  • The NW array configuration can ensure that every NW participates in the electrochemical reaction, because every nanowire is in electric contact with the Ti substrate and also interfaced with the electrolyte solution.

  • The open space between neighboring NWs allows for easy diffusion of the electrolyte. This feature is particularly helpful for high power applications when the battery is charged or discharged at high current.

  • The NWs in this study are mesoporous with an average pore size of 3.3 nm and a BET surface area of 73.5 m2/g. The porosity will enhance the electrolyte/Co3O4 contact area, shorten the Li+ ion diffusion length in the NWs, and accommodate the strain induced by the volume change during the electrochemical reaction.

Resources

  • Yanguang Li, Bing Tan, and Yiying Wu; Mesoporous Co3O4 Nanowire Arrays for Lithium Ion Batteries with High Capacity and Rate Capability; Nano Lett., 8 (1), 265 -270, 2008. DOI: 10.1021/nl0725906

April 22, 2008 in Batteries | Permalink | Comments (9) | TrackBack (0)

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Comments

Why only report performance after 20 cycles? EV cars require 1000's of cycles. Yes, depth of charge affects life.

And at 20 cycles, with a current of 50C the array retains only 50%. They seem to think the time of charge/discharge compensates for this.

I've noticed that 20 cycles is used a lot to test out experimental chemistries.

Also, anyone care to chime in on what discharge rate is reasonable for an EV? I'm not an EE, but I suspect that 50C is a VERY large amount of current. Is 8C reasonable or too low?

I have noticed that most charge cycle data given by Altair, A123, EnerDel, etc. is under 1-10C conditions which indicates to me those are the conditions seen in EVs.

Did they mentionned the voltage and the energy density in Wh/Kg?

Twice the normal li-On capacity is claimed. What would the operational energy density, (2 x 160 Wh/Kg) = 320 Wh/kg? If so it would be very close to the existing Electrovaya 330 Wh/Kg unit.

Could it be as good as twice the Electrovaya unit energy density = (2 x 330 Kw/Kg) = 660 Kw/Kg? If so, it good be a very good unit for PHEVs and BEVs.

With time, the final energy density may not reach expectation.

With my understanding, the capacity of a anode should match the capacity of a cathode in a battery. Since the cathode capacity is still quite low, advancements of the anode has a smaller impact to energy density at this moment. Once we come up with better cathode materials then these advanced anodes will be more effective.

Anyway, I am a little shocked by all these new chemistries coming out from the labs at a rate of almost one per week!

There are a variety of nano-wire products in testing, and each shows an improvement over the previous generation of Li batteries. Some have claimed an improvement of 10x.

Although we are still waiting to see these in production and at a low price, the speed of improvements, and the many in testing show that we can expect to see viable battery electric cars available soon.

Keep it coming. The more, the merrier. I'd love to be driving an EV to work five years from now.

Well - as to the 'C' Rating of the cells - since most of us interested in Electric Vehicles (Cars or Trucks) aren't actually planning on burning up the 1/4 mile in under 7 seconds - extremely High 'C' Rates are not as important as long life, safety, durability under abuse (Shock from the potholed roads, etc., punching it for 5 seconds to get in front of that Semi-Trailer) - let me say this: looking at my car - using about 200 - 210 watt hours per kilometer (Wh/kM) suggests that to get a range of 5 km (3 miles) I would need a 1 kWh energy storage, so 30 mi/50 km would need about 10 kWh.

Now - a pack made with 1600 existing A123ANR26650M1 Cells - at 115 Ah x 105.6V Nominal - could deliver - at a continuous 30 C - some 3450 Amps and at a surge of 50C - would be 5750 Amps! That is way more than the 150 to 180 amps I use while driving on the Highway at this time - with basic 100 Ah, 12V Lead Acid Batteries - which drop about 25% of the at rest pack voltage while sucking that 180 amps, so a 'Stiffer' chemistry - that can deliver even 5 - 10 C without any thing more than a 1-2% voltage drop - would use even lower Amperage as the Voltage would remain higher, and so - the most I need - would be 200 Amps continuous and Maybe - 300 amps for 10 - 20 seconds.

Note -- I only run a 96V system - consider that at a higher voltage pack like 160 - 320V - amps needs would go way down - unless your are talking about a Big Rig - hauling its 80,000 pound load!

Even then - compared to a lower voltage pack based drive - higher voltages use less amps - that is why our industrial motors are running at 575 volts and use just 10 20 amps for a 35 Hp motor on an industrial machine in a factory!

Basic need = good 'C' ratings of 5-10C, along with lighter weight and lower manufacturing costs! if we can get the acquisition cost down to about 3-4 X what lead acid batteries cost for EV's, and still save 1/2 to 3/4 of the weight - then we will have a winner, as long as the cycle life comes up to a minimum of 2000 cycles - with a goal of 5000 cycles!, since Lead Acid only makes 300 - 500 cycles in typical use!

(The 155 Ah A123 Pack for my car would - cost me about $32,000 for cells alone - but... would save about 50% in Battery Weight compared to the 400 pounds in there now - and it could be fitted in the gas tank well and along under the floor pan for better centered weight!)

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