## Boston College team demonstrates nanonet-based heterostructure strategy for high-performance Li-ion cathode materials; high-power and high-capacity vanadium oxide electrode

##### 31 December 2011
 Schematic illustrations of the TiSi2/V2O5 heteronanostructure design. The TiSi2 nanonet is directly grown on a current collector; V2O5 is deposited onto TiSi2 by a hydrolysis process. Upon annealing at 500 °C in O2, V2O5 nanoparticles form. Credit: ACS, Zhou et al. Click to enlarge.

Using a highly conductive two-dimensional TiSi2 nanonet technology they had earlier developed, a team from Boston College has synthesized a vanadium oxide (V2O5)-based cathode material that demonstrates a specific capacity of 350 mAh/g, a power rate of 14.5 kW/kg, and capacity retention of 78% after 9,800 cycles of repeated charge/discharge. In a paper published in the journal ACS Nano, they note that these results demonstrate “a cathode material significantly better than V2O5 of other morphologies.”

The strategy of having multiple components at the nanoscale—heteronanostructures—offers a critical advantage of achieving desired electronic and ionic properties on the same material by tailoring the constituent components, the team suggests in its paper.

Nanoscale materials are expected to contribute significantly to realizing an important goal in the lithium ion battery research of achieving high capacity and power rate and long cycle lifetime simultaneously...How to solve these issues in a concerted fashion, however, remains a challenge because they are intricately correlated at relevant length scales (e.g., charge and ionic behaviors at the nanoscale). Here we present a strategy that has the potential to meet this challenge.

...The key to our design is the capability to control the features of materials on multiple levels concurrently. At the atomic scale, we use Ti-doping to stabilize V2O5 upon lithiation and delithiation, which dramatically improves the cycle lifetime. At the nanoscale, the material is composed of more than one component, each designed for a specific function, the TiSi2 nanonet for charge transport, the Ti-doped V2O5 nanoparticle as the ionic host, and the SiO2 coating as a protection to prevent Li+ from reacting with TiSi2, which otherwise would lead to the destruction of the nanostructures. The strategy of having multiple components at the nanoscale offers a critical advantage of achieving desired electronic and ionic properties on the same material by tailoring the constituent components.

—Zhou et al.

Zhou et al. say that their work, compared to other work using nanostructures, is distinguished by at least three features:

1. The two-dimensional TiSi2 nanonet inorganic framework is highly unique. The combination of mechanical strength and flexibility exhibited by the nanonet may be ideal for energy storage applications, they suggest.

2. The seemingly complex design is realized through simple chemical synthesis, without the involvement of catalysts or templates.

3. The combined power rate, specific capacity, and cycle lifetime render the nanonet-based nanostructure one of the highest performing cathode materials.

They used V2O5 to demonstrate the design principle because the addition of the conductive framework (TiSi2 nanonets) “is particularly useful to solve the key issues of poor conductivity and slow Li+ diffusion that limit the performance of V2O.

 Charge capacity and Coulombic efficiency TiSi2/V2O5 heteronanostructures. (a) After the initial decay during the first 40 cycles, the heteronanostructure exhibits stability for up to 600 cycles, fading only 12% (rate: 300 mA/g). The reversible decrease of capacity between the 180th and 210th cycles (14 mAh/g, or 4.4%) are the result of controlled temperature change from 30.0 to 28.0 °C. One data point for every 10 cycles is shown. (b) The rate-dependent specific capacities. 1C: 350 mA/g. Credit: ACS, Zhou et al. Click to enlarge.

Ti-doping stabilizes V2O5, and the SiO2 layer shields TiSi2 from the electrolyte. More critically, Zhou et al. concluded, the unique two-dimensional nanonet platform bridges different length scales from the nanoscale to the micro/macro scale.

By introducing a dedicated charge transporter, we were able to separate charge and ionic behaviors and thereby obtain unprecedented high power and high capacity on a cathode material that can be cycled extensively. We emphasize our strategy is highly modular, and other high performance cathode compounds (such as LiFePO4) should be readily integrated into the nanonet-based design. Our results demonstrated that advanced functional materials can be obtained by simple chemical synthesis. This approach should be highly complementary to existing efforts of finding highly performing compounds as battery electrode materials.

—Zhou et al.

Resources

• Sa Zhou, Xiaogang Yang, Yongjing Lin, Jin Xie, and Dunwei Wang (2011) A Nanonet-Enabled Li Ion Battery Cathode Material with High Power Rate, High Capacity, and Long Cycle Lifetime. ACS Nano doi: 10.1021/nn204479n

I won't claim to fully understand 'nanonet-based heterostructure strategy', but specific capacity of 350 mAh/g vs 150 for the Leaf EV battery sounds good.

A 'capacity retention of 78% after 9,800 cycles of repeated charge/discharge' sounds too good.

Now, what's the economics and scaleability?

@kelly.
Those figures are just for the cathode.
There is the anode and electrolyte in the whole pack too, so it should not be compared directly to the Leaf battery.
It does sound good though, but I don't know how common or how expensive vanadium is.

Good points DaveMart....but on the good side, this is a cathode! They always trail behind the anode so it's possible that we could find a compatible anode such as this one at ~1250Ah/kg at ~3.5V and combine the two.
http://www.greencarcongress.com/2011/12/wang-20111217.html

Or perhaps the one from northwestern:
http://www.mccormick.northwestern.edu/news/articles/article_1000.html

Either way, the point is that progress on the cathode is GREAT at this point. Putting it together with one of these anode advances could yield a cell level above 400Wh/kg or even 500Wh/kg.

Of course, we have to all be realistic that it takes 3-5 years to get these advances to market even if they work in the real world and can be produced affordably.

Davemart, what DaveD said - except:

"Of course, we have to all be realistic that it takes 3-5 years to get these advances to market even if they work in the real world and can be produced affordably."

Sony Li-ion batteries went commercial twenty(20) years ago, NiMH 15 years ago. It's already been over four 3-5 year periods for mass producing a really better 3 component battery device.

Every extra second of ICE-based transportation, especially since the 1973 OPEC oil embargo, is like using kerosene refrigerators.

Kelly,

I'm convinced that batteries have been held back though by the economics of the market they serve. It was never in the interest of Eveready, Panasonic or Duracell, etc to do anything but tiny, incremental improvements in batteries.
They made all their money by selling us batteries as fast as we can use them up. Why would they try to improve them? They can't get us to pay anymore for those batteries so why invest money in making them better?
Even the batteries in cell phones and laptops...hell, the device is obsolete after 18 months so what is the point.

Now, suddenly there is a market for long lasting, powerful batteries. They're all scrambling after 100 years of sitting on their keesters and not doing anything to improve the breed.

I think we'll see more improvements in 10 years than we did in the previous 100.

DaveD, agreed.

DaveD is probably correct in his assumptions. With much higher future demand and 100 times mores R & D, the progress in the current decade will be much faster than the last 100 years or more.

Batteries may go from 100 Wh/Kg to over 1000 Wh/Kg by 2020. Useful life expectancy will be equivalent or longer than the vehicles they are used If Iran and large Oil Cos manage to close the Hormuz strait, it would give the process a boost.

I doubt any cunning plan to hold back batteries. Its my understanding that they have had to throw a lot of computing power and other advanced technology at improving and manufacturing batteries, fuel cells of which lithium air are only a special case even more so.
Sometimes it is time to railroad, but the technological nexus has to be all there to do so.

Of course the other major factor is that petrol prices had to go up enough to make competition even feasible.
When it was a dollar or so a gallon you can't buy much battery to compete.

Predictions of 1000Wh/Kg are outside the realm of electrochemical energy storage right now. In fact, that number is touching the theoretical, highest possible energy density, properly calculated, when you figure in world class micro packaging and the need to be rechargeable. The absolute theoretical maximum energy density as I understand it, is 6100 Wh/Kg /2 packaging /3 rechargeable.

I'd guess we will see significant improvement in upcoming years. But we won't see batteries match the ICE, not even close. When I can drive a modern diesel jetta 600 high speed, highway miles before refueling And where the refueling task takes mere minutes and I'm on my way again. And I can compare that to how batteries behave and how much energy they can store. They won't ever match the overall performance of petro fuels.

But 1000 Wh/kg would be more than 10 times better than current 75 Wh/kW of Chevy Volt's battery pack - 150 kg battery pack and 10 kWh useful with 5000 cycles and price more than $1000/kWh. @ cujet: Keep in mind that it's not necessary to achieve energy density in a battery equivalent to that of fossil fuels. Efficiency of electric drive trains is four times better than ICEs. Conversely, a battery with 1/4 energy density of fossils is just fine and definitly within the reach of technical possibilities. ^+1 Not to mention in a world of increasing oil prices and volatility people won't care about being able to travel 600 miles on a tank, they want to get to work and the store reliably at reasonable cost. In truth current density is good enough, it just costs too much. If we hit around 200wh/kg pack level density and around$200/kWh pack costs we don't need much further improvement. With some good aero design and lightweight building materials you could do a $25K car with 150 mile range and make a profit. cujet: That's why we are always going to need fuel cells to supplement batteries in applications where energy density and weight are important. Hydrogen comes in at around 40kwh/kg. Right now we are able to store it at about 5% by weight, so that is around 2kwh/kg. Even after allowing for conversion losses in the fuel cell, the weight of the equipment and so on we are talking ~1kw/kg. Those figures will only get better, so where batteries don't cover the application hydrogen fits the bill. The significant claim this work is the use of a nanonet structure to decouple optimization of capacity, power and cycle life, i.e., the "capability to control the features of materials on multiple levels concurrently". Typically, a battery design is a trade-off of energy, power and life for a given chemistry. For example, the NiMH batteries in the Prius have limited energy storage capability but relatively high power and cycle life. The ability to achieve this with simple processes and relatively abundant materials is equally significant. I am beginning to believe more in EVs. There may only be 1 million out of 200 million on the road in the U.S. in 10 years, but that is a start. cujet - I suspect almost no one desires a 600 mile range with 'mere minutes' refueling if it's going to cost them significantly more per mile and save them very little time to do that driving. Get EV range up to something around 175 highway miles with <20 minute recharges and you can do a 500 mile day with two short stops. (The Toshiba SCiB lithium-ion which will be used in the Honda Fit EV can be 95% recharged in 18 minutes.) How many people are going to drive 500 miles without a meal stop? Even if you could get away with driving 70MPH you're still dealing with a 7 hour drive day. Then there's operating cost.$0.03/mile in an EV vs. $0.12/mile in a 34MPG Jetta burning$4/gallon diesel.

The Jetta driver is spending an extra thou a year for a 12k driving year. Plus oil/filter changes and more on repairs.

How many people are going to pay an extra $100/month to avoid a second short recharge stop on the few long drive days that most people make? Especially if they can check their messages and play Angry Birds. SJC...Mitsubishi claims that they will produce 1+M EVs/yr by 2020. With all the R & D going on, there are no logical reasons why the WORLD cannot develop quick charge, long lasting, affordable, improved batteries and/or super-ultra caps by 2020 or shortly thereafter. FCs and hydrogen lower cost production and storage will also improve. It could become a viable alternative, specially for heavy long range vehicles. Interesting decade ahead, specially if Iran closes the Hormuz Strait soon and long enough. @Bob, For 175 miles in most weathers at highway speed you would need 75-100kwh.$200kwh is still pushing it before 2020, so you are talking about a $15-20k battery. Even if the battery can take a heck of a fast charge, you need a hell of a charger to pump that full of juice in minutes, and would give quite a hit to the grid. I don't really believe in ultra large batteries, which is why I favour fuel cell/battery plug in hybrids, with the battery large enough for highly efficient everyday running around at 12-13kwh but the fuel cell doing what it is good at, and providing the power for high speed long distance travel and refills in minutes. Oil prices should rise substantially by around 2016. They might only have 1 million EV's on the road in the US, but I would expect perhaps 3 million in France alone. They will not need to build more nuclear power stations until they have 7-8 million on the road, their oil is 100% imported and the CO2 emissions using the French grid for an EV run at 2grams/kilometre. That's right, 2 grams. Bob Wallace, I agree with your points, and I love this stuff. Don't take it the wrong way. However, I do quite a bit of highway driving. Plenty of people are traveling and using the "interstate system". It's really amazing how many, in fact. And, if you go 70MPH, you are among the slowest! The real world speeds are often much higher. We must also remember that the DOD (depth of discharge) in a battery's application severely limits Wh/Kg. So, our theoretical 1KWh/Kg battery will automatically be reduced to 500W/Hr. We must also remember that while today's gasoline engines are marginally efficient, it's technically possible to achieve 50% ICE efficiency. The big diesels do it regularly. In fact, even the E-85 fueled and natural gas engines can achieve those levels of thermal efficiency. The comparison still stands. A workable 500W/Hr battery is, as I understand it, the "holy grail" of batteries. Natural gas engines can compare, efficiency problems included, at 7000Wh/Kg. Diesels and gasoline only slightly worse. Hybrids and Chevy Volt "like" technologies are going to be the next level of production. Due to the remaining technical limitations of batteries. Regardless, I'm fascinated by it. @cujet: The only battery system which uses anything like the 50% DOD you refer to is that on the Volt. The Leaf for instance uses up to 22kwh out of 24kwh, but you would not want to do that all the time. 80% DOD is little problem though. The Volt is more cautious mainly because being a plug in hybrid the battery will drain more more often than the larger packs on a BEV. Your more general argument is correct however, as we are nowhere near even 500Wh/kg, let alone 1,000Wh/kg. Check out my earlier comments on fuel cell/battery hybrids though. Improvement of existing Chevy Volt pack by factor 2 would solve extended range EV competitevness vs pure ICE vehicles in near future. That would give us battery pack 75 kg, 22 kWh useful,$220/kWh and 10 000 cycles with short power output 100 kW. Are any promises of that?

yoatmon

"Conversely, a battery with 1/4 energy density of fossils is just fine and definitly within the reach of technical possibilities."

energy density of gasoline is about 10 kWh/kg, so what you're saying is that an energy density of 2.5 kWh/kg is within the reach of technical possibilities, which it is not.
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People lay too much emphasis on these super high energy density. While energy density was below 70 Wh/kg, the usability of the EV was very limited. As soon as you pass that limit, the usability quickly increases until you reach about 200 Wh/kg. Progress beyond that point is nice to have, but not essential for widespread use of the EV.

At 200 Wh/kg a 50 kWh battery (good for a ~200 mile range) would weigh 250 kg, which is perfectly acceptable in a modern car, given the fact that the other components are much lighter. It would yield an EV with an overall weight comparable to an ICE car.

Improving the battery to more than 200 Wh/kg would increase the range beyond 200 miles, which most people would find they rarely need. Especially if ubiquitous wireless charging takes hold. How often do you drive more than 200 miles without stopping?

@Anne:
You are talking there about doubling the capacity of the Leaf battery.
Under ideal conditions that could travel well over 200 miles, but not in all conditions and speeds.
The EPA figure for the Leaf is 73 miles, which would put the range at 146 miles.
If you are travelling a long distance it is likely on the highway though, and at speed that would drop a lot, perhaps to around 100 miles.
That is before you consider the effects of bad weather, which could further limit this.

I would suggest that you would need around 100kwh, not 50 kwh, to have real near comparability with a petrol car.

Such a large battery would also not recharge nearly as quickly, so using the level 3 fast charge standard to 80% capacity would take of the order of 2 hours rather than 30 minutes.

With anything we are anywhere close to being able to engineer short of the expense of the Tesla, and that the top spec one, RE's are a far bettter bet for distance travel than pure batteries.

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