New battery design could give electric vehicles a jolt

Jun 06, 2011 by David L. Chandler
A sample of 'Cambridge crude' — a black, gooey substance that can power a highly efficient new type of battery. A prototype of the semi-solid flow battery is seen behind the flask. Photo: Dominick Reuter

A radically new approach to the design of batteries, developed by researchers at MIT, could provide a lightweight and inexpensive alternative to existing batteries for electric vehicles and the power grid. The technology could even make "refueling" such batteries as quick and easy as pumping gas into a conventional car.

The new battery relies on an innovative architecture called a semi-solid flow cell, in which solid particles are suspended in a carrier liquid and pumped through the system. In this design, the battery’s active components — the positive and negative electrodes, or cathodes and anodes — are composed of particles suspended in a liquid electrolyte. These two different suspensions are pumped through systems separated by a filter, such as a thin porous membrane.

The work was carried out by Mihai Duduta ’10 and graduate student Bryan Ho, under the leadership of professors of materials science W. Craig Carter and Yet-Ming Chiang. It is described in a paper published May 20 in the journal Advanced Energy Materials. The paper was co-authored by visiting research scientist Pimpa Limthongkul ’02, postdoc Vanessa Wood ’10 and graduate student Victor Brunini ’08.

One important characteristic of the new design is that it separates the two functions of the battery — storing energy until it is needed, and discharging that energy when it needs to be used — into separate physical structures. (In conventional batteries, the storage and discharge both take place in the same structure.) Separating these functions means that batteries can be designed more efficiently, Chiang says.

The new design should make it possible to reduce the size and the cost of a complete battery system, including all of its structural support and connectors, to about half the current levels. That dramatic reduction could be the key to making fully competitive with conventional gas- or diesel-powered vehicles, the researchers say.

Another potential advantage is that in vehicle applications, such a system would permit the possibility of simply “refueling” the battery by pumping out the liquid slurry and pumping in a fresh, fully charged replacement, or by swapping out the tanks like tires at a pit stop, while still preserving the option of simply recharging the existing material when time permits.

Flow batteries have existed for some time, but have used liquids with very low energy density (the amount of energy that can be stored in a given volume). Because of this, existing flow batteries take up much more space than fuel cells and require rapid pumping of their fluid, further reducing their efficiency.

The new semi-solid flow batteries pioneered by Chiang and colleagues overcome this limitation, providing a 10-fold improvement in energy density over present liquid flow-batteries, and lower-cost manufacturing than conventional lithium-ion batteries. Because the material has such a high energy density, it does not need to be pumped rapidly to deliver its power. “It kind of oozes,” Chiang says. Because the suspensions look and flow like black goo and could end up used in place of petroleum for transportation, Carter says, “We call it ‘Cambridge crude.’”

The key insight by Chiang’s team was that it would be possible to combine the basic structure of aqueous-flow batteries with the proven chemistry of lithium-ion batteries by reducing the batteries’ solid materials to tiny particles that could be carried in a liquid suspension — similar to the way quicksand can flow like a liquid even though it consists mostly of solid particles. “We’re using two proven technologies, and putting them together,” Carter says.

In addition to potential applications in vehicles, the new battery system could be scaled up to very large sizes at low cost. This would make it particularly well-suited for large-scale electricity storage for utilities, potentially making intermittent, unpredictable sources such as wind and solar energy practical for powering the electric grid.

The team set out to “reinvent the rechargeable battery,” Chiang says. But the device they came up with is potentially a whole family of new battery systems, because it’s a design architecture that “is not linked to any particular chemistry.” Chiang and his colleagues are now exploring different chemical combinations that could be used within the semi-solid flow system. “We’ll figure out what can be practically developed today,” Chiang says, “but as better materials come along, we can adapt them to this architecture.”

Yury Gogotsi, Distinguished University Professor at Drexel University and director of Drexel’s Nanotechnology Institute, says, “The demonstration of a semi-solid lithium-ion battery is a major breakthrough that shows that slurry-type active materials can be used for storing electrical energy.” This advance, he says, “has tremendous importance for the future of energy production and storage.”

Gogotsi cautions that making a practical, commercial version of such a battery will require research to find better cathode and anode materials and electrolytes, but adds, “I don’t see fundamental problems that cannot be addressed — those are primarily engineering issues. Of course, developing working systems that can compete with currently available batteries in terms of cost and performance may take years.”

Chiang, whose earlier insights on lithium-ion chemistries led to the 2001 founding of MIT spinoff A123 Systems, says the two technologies are complementary, and address different potential applications. For example, the new semi-solid flow batteries will probably never be suitable for smaller applications such as tools, or where short bursts of very high power are required — areas where A123’s batteries excel.

The new technology is being licensed to a company called 24M Technologies, founded last summer by Chiang and Carter along with entrepreneur Throop Wilder, who is the company’s president. The company has already raised more than $16 million in venture capital and federal research financing.

The development of the technology was partly funded by grants from the U.S. Department of Defense’s Defense Advanced Research Projects Agency and Advanced Research Projects Agency – Energy (ARPA-E). Continuing research on the technology is taking place partly at 24M, where some recent MIT graduates who worked on the project are part of the team; at MIT, where professors Angela Belcher and Paula Hammond are co-investigators; and at Rutgers, with Professor Glenn Amatucci.

The target of the team’s ongoing work, under a three-year ARPA-E grant awarded in September 2010, is to have, by the end of the grant period, “a fully-functioning, reduced-scale prototype system,” Chiang says, ready to be engineered for production as a replacement for existing electric-car batteries.


This story is republished courtesy of MIT News (web.mit.edu/newsoffice/), a popular site that covers news about MIT research, innovation and teaching.

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More information: Semi-Solid Lithium Rechargeable Flow Battery, DOI: 10.1002/aenm.201100152

Abstract
A new kind of flow battery is fueled by semi-solid suspensions of high-energy-density lithium storage compounds that are electrically ‘wired’ by dilute percolating networks of nanoscale conductor particles. Energy densities are an order of magnitude greater than previous flow batteries; new applications in transportation and grid-scale storage may result.

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ereneon
5 / 5 (3) Jun 06, 2011
Great idea. I think practical re-fillable batteries could be a game-changer for electric cars.
mosahlah
not rated yet Jun 06, 2011
This could finally be the break we've been all been waiting for to cut loose our dependence on oil and the stranglehold it has taken on our economy. How do I invest?
Shakescene21
not rated yet Jun 06, 2011
This looks great, but we'll probably have to wait until September 2013 to see a fully-functioning prototype.

I considered buying a Tesla sportscar, but discovered that the batteries weighed 1000 lb, and accounted for 40% of the car's 2500-lb weight. This new design might be the breakthrough I've been waiting for.
krundoloss
2.3 / 5 (3) Jun 06, 2011
And we will see this technology, in about, say, NEVER! Let me start the countdown until the Oil Companies snuff this one out. T Minus 633 days, 4 hours, 12 mins.
Haven't we seen over and over again that we are not really allowed to have efficient motor vehicles. How many inventions have been created only to be buried by people benefitting from the current system. It will continue to happen, and this breakthrough is no exception.
Eikka
5 / 5 (2) Jun 06, 2011
And we will see this technology, in about, say, NEVER! Let me start the countdown until the Oil Companies snuff this one out. T Minus 633 days, 4 hours, 12 mins.
Haven't we seen over and over again that we are not really allowed to have efficient motor vehicles. How many inventions have been created only to be buried by people benefitting from the current system. It will continue to happen, and this breakthrough is no exception.


Never ascribe to malice that which is more easily explained by incompetence.

In this case, the fact that out a thousand good ideas, only about 1 ever actually works the way it was envisioned.

For example, in this case, a possible caveat: what happens to the slurry when the temperature drops below 0 C? Can you still pump it, or do you have to heat the entire tank before you can drive?
EWH
1 / 5 (2) Jun 06, 2011
Here are the payoff paragraphs from the article with a little trimming for length and clarity:

"...LiCoO2graphite (3.8 V average discharge voltage) has 615 Wh /L (309 Wh/kg). With reasonable allowances for [the other stuff in a battery]... could have energy densities of 300-500 Wh/L (specific energy 130-250 Wh/kg), which would [allow] widespread adoption of all-electric vehicles. Further improvements would be possible by dropping in higher-energy-density or lower-cost storage compounds in the SSFC platform as they are developed."

"... At near-term costs of $10-15/kg for active materials and $14/kg for nonaqueous electrolyte, the semi-solid suspensions alone have an energy-specific cost of $40-80 /kWh depending on the specific chemistry, which leaves substantial room to achieve system-level cost targets of $250/kWh and $100/kWh for transportation and grid level storage, respectively."

Assuming 85% efficiency electric vs. 35% efficient gas, 16kWh=1 gal gas=$640-$1280 electro-goop
EWH
1 / 5 (2) Jun 06, 2011
The target price of $250/kWh for transportation means the equivalent of a 50-liter (13.2 gal.) fuel tank would cost $52,800, of which $8,450 - $16,900 would be electro-goop and $35,900-$44,350 would be the rest of the battery. Even after counting recycling credits, the goop would effectively wear out after perhaps 1000 charge cycles, giving a consumable cost of energy storage of $0.64 - $1.28 per gallon equivalent. If the rest of the battery lasts 100,000 miles, that's $1.00 - $1.72 per gallon equivalent. At $0.10 - $0.25 per kWh to buy the actual electricity, that's $2.60 - $5.72 per gallon equivalent, not counting the substantial financing costs for the battery itself, which could run $150-$200 per month at 5-5.5%.

This looks like it could be a breakthrough technology, but the cost of the battery structure itself needs to be comparable to the cost of the active chemicals, bringing the target down to $125/kWh for it to be fully competitive with gas.
EWH
1 / 5 (2) Jun 07, 2011
One other thing - the battery equivalent of a 50-liter /13.2 gallon tank will take up 111-185 gallons of space and weigh 1860-3575 pounds. (420-700 liters, 845-1625 kg). Cars carrying that kind of weight will have trouble being efficient, even with regenerative braking.

The increased efficiency of electric power is already built into the above calculations, so at 16kWh <--> 1 gallon conversion these cars will get 20-40 mpg (5.9-11.8 liters/100km) thus 265-530 mile range (420-840 km). Perhaps a shorter range is workable, but not so much shorter as to make these calculations qualitatively incorrect.
Eikka
not rated yet Jun 07, 2011
You shouldn't take a direct comparison with what ordinary cars are, but what is required of them.

A typical small sedan for example goes 600 km on a tank, and takes 20 kWh/100km to drive as an electric vehicle city and highway (60mph). It will do with less, about 16 kWh/100km if you drive it carefully and with everything else off.

So, 6 x 20 kWh equals 120 kWh and would thus weigh 480...923 kg and cost $12-30,000

If the electrolytes last a thousand recharce cycles, you don't really need to change them once. 600,000 kilometers is more than enough for the rest of the car, unless you plan to keep it running for 40 years.
EWH
1 / 5 (2) Jun 07, 2011
Eikka - on looking around for EV mileage statistics, your numbers seem supported, and your point about cycle life is good (though I think >500 cycles is likely), but I don't see how electric vehicles can really be that much more efficient. 20-40 mpg is 0.23-0.46 km/MJ (gross energy of the gasoline). Your numbers are equivalent to 1.39-1.74 km/MJ. I've seen claims that the Tesla gets 2.18km/MJ, so we're talking roughly 3-9.5 times as efficient. Well-to-wheels analysis would cut that by roughly half, but comparing wall-plug to gas-pump, pretty much all the sources of inefficiency such as drag and friction are the same between comparable EV and gas cars except for the motor and energy storage and the EV is about 0.85 efficient vs. the ICE at 0.25-0.35, which is a factor of 2.4-3.4. I don't think regenerative braking is enough to make up for the difference, given the inefficiency and the extra several hundred kilos that an EV has to accelerate.

EV mileage is likely a bit overstated.

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