Toyota researchers develop Li–O2/CO2 battery with very high discharge capacity
14 February 2011
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| Discharge curves of the Li–O2/CO2 batteries with various ratio of CO2 in O2/CO2 mixed gas at 25 °C (current density: 0.2 mA cm-2). Inset shows CO2 ratio dependence on relative capacities as compared with the Li–O2 battery (CO2 0%). Credit: RSC, Takechi et al. Click to enlarge. |
Researchers at the Advanced Battery Lab, Toyota Central R&D Laboratories, Inc., have developed a new advanced gas-utilizing battery using a mixture of O2 and CO2 and featuring a very high discharge capacity of up to almost three times that of a non-aqueous Li–air (O2) battery. A paper on their work was published in the Royal Society of Chemistry journal Chemical Communications.
Although the new battery has to be a primary battery (i.e., non-rechargeable) due to the difficulty of electrochemical decomposition of Li2CO3 in the cathode, its very high discharge capacity offers the potential for an alternative energy source with the use of CO2-rich gas such as exhaust gas from vehicles or factories, the researchers conclude. Additionally, the basic mechanism of this battery can in principle be extended to non-lithium systems.
Because of its potential very high energy density, Li–air (O2) chemistry is one of the promising candidates looked to for providing the significant improvement in batteries required to meet the demands of future vehicles, electronics and other applications. (Earlier post.) The oxygen reduction at the cathode (air electrode) is the most important process in the battery. However, the team of Kensuke Takechi, Tohru Shiga and Takahiko Asaoka explain, the reduced oxygen forms superoxide anion radical species (O2•-) in non-aqueous electrolyte. A subsequent reaction between O2 and Li+ leads to final discharge products: Li2O2, Li2O, and/or the decomposed compounds of solvent in the electrolyte.
Because these discharge products are expected to be stored in the cathode, many researchers have selected porous carbon material due to its large void volume. However, Takechi et al. note, since the usual Li–air battery only consumes oxygen, an intermittent radical species, highly reactive LiO2•, is generated during the discharge reaction.
This reactive species limits the discharge capacity of the battery due to the rapid precipitation of the discharge products and their poor electron conducting property, which causes the incomplete filling of the void volume in the cathode.
In this study, we developed a new strategy in enhancing the discharge capacity of Li–air battery by introducing a mixed gas of O2 and CO2 (Li–O2/CO2 battery). It is well known that O2•- can be captured by CO2, and the reaction has been applied for CO2 sensors or molten-carbonate fuel cells (MCFC). We noticed that the series of the reactions between O2•- and CO2 was expected to slow down the precipitation speed of the discharged products in the cathode and have demonstrated the performance of the Li–O2/CO2 battery.
—Takechi et al.
In their experiments, the basic structure of the cell and electrodes were identical to those of the Li–O2 battery. The team introduced a mixed gas of O2 and CO2 in different concentrations into the cell directly with a pressure of 2 kgf cm-2 (28 psi) at 25 °C.
Among their findings were that the discharge capacity of the Li–O2/CO2 battery (CO2 ratio: 50%) was 5860 mAh g-1, or 289% as compared with that of the Li–O2 battery (CO2 ratio: 0%). Only 10% of CO2 in the mixed gas boosted the discharge capacity of the battery twice as much as the standard Li–O2 cell, and 30% CO2 enhanced the performance almost three times as much. The appropriate CO2 ratio to obtain the maximum capacity was from 30 to 70%. When the CO2 ratio was higher than 80%, the capacity was dramatically reduced because of the low O2 concentration.
The unique point of the battery, the researchers say, is the rapid consumption of the superoxide anion radical by CO2 as well as the slow filling property of the Li2CO3 in the cathode.
Resources
Kensuke Takechi, Tohru Shiga and Takahiko Asaoka (2011) A Li–O2/CO2 battery. Chem. Commun., doi: 10.1039/C0CC05176D
A primary battery, which is cheap, easy to replace, safe for the environment, would be great even for cars with this kind of capacity. Co2 is abundant and easily stored and transported. If they could get 30% of the laboratory-observed capacity, it would be more ten times the capacity of current Li-Ions. Maybe 3,000 Wh/kg. Considering the efficiency difference between ICE and electric motors, this capacity is 10-20% more than what gasoline can provide.
Posted by: Zhukova | 14 February 2011 at 10:24 AM
Correction - 30% is kind of low to expect for a practical battery. At 40% or about 4,000 wh/kg you get more than double what gasoline can provide (1,700 wh/kg @ 12.6% efficiency).
Posted by: Zhukova | 14 February 2011 at 10:34 AM
Were they not working on a rechargeable version?
Alternatively, could the used elements be replaced and recycled at a low cost.
Posted by: HarveyD | 14 February 2011 at 12:02 PM
That's what I mean - the CO2 obviously could be pumped in, or dry ices could be used instead. The lithium could be made in canisters or something easily replaceable. People put up quite well refueling a few times a week at service stations. If I needed to spend 15 minutes a week at the service station and could just replace a canister like changing an air filter, and pump in some CO2, it would be fine. It depends on how easy it is and how much time and cost.
Obviously materials need to be recycled. Rechargable batteries will have to be recycled too, on a somewhat different scale. Airplanes and helicopters would really benefit from such high energy density. Facilities at airports might deal with battery replacement easier than auto service stations.
Posted by: Zhukova | 14 February 2011 at 02:27 PM
"Additionally, the basic mechanism of this battery can in principle be extended to non-lithium systems." = electric power plant chimneys.
A 5 second 1/4 mi. electric White Zombie dragster?
A 'nitrous' power boost for the Prius?
A 'cross-country' swap-in battery option for Better Place?
Oh to be a young electrical engineer..
Posted by: kelly | 15 February 2011 at 06:07 AM
"Obviously materials need to be recycled. Rechargable batteries will have to be recycled too, on a somewhat different scale. Airplanes and helicopters would really benefit from such high energy density. Facilities at airports might deal with battery replacement easier than auto service stations." - Zhukova
A few dozen key airports recycling such high energy/power density batteries could replace $5-10/gal fuel aircraft with a lot of electric planes in short time.
Posted by: kelly | 15 February 2011 at 07:34 AM
Interesting potential use Kelly. For airplanes, standardized detachable under the wings or belly battery pod(s) could be exchanged in a few minutes. The same could apply for trucks, buses, locomotive and cars.
The question would be the recycle cost vs a secondary battery recharge cost.
Posted by: HarveyD | 15 February 2011 at 09:15 AM
There are several battery-powered light planes on the market - Yuneec and ElectraFlyer are two. But their Li-Ion batteries provide only short range and low payload capacity. Electric commercial aircraft would be practical with the Li-CO2 battery, if they could provide enough current.
Does the CO2 also produce a higher current than normal Li-Air batteries? If not they may not be practical for cars either. Li-Air batteries have such low current, you would have to have a very large one in the car and it would take a week to charge it, if it is rechargable. Wish the article metioned the current output.
Posted by: Zhukova | 15 February 2011 at 10:05 AM
From info given, corrosion of the electrolyte and electrode surface forces recycle. Perhaps draining the battery, flushing corrosion, and cleaning/refilling/CO2ing(?) electrolyte would rejuvenate many times - until electrodes were gone.
Automating this process might make it relatively cheap at an airport per city vs. 115,000 US gas stations.
In any case, losing CO2 for ~gasoline battery energy density seems to have high potential juice.
Posted by: kelly | 15 February 2011 at 10:10 AM
Actually this battery, if you multiply the voltage and capactity, is 2.5 x 5800 = 14,500 wh/kg. Gasoline is 13,000 wh/kg. The practical battery would be .4 x 14,500 = 5800 wh/kg. With battery to wheel efficiency of 90% (Earlier Post link in article), we get 5220 wh/kg. The ICE at 12.6 % efficiency is only 1700 wh/kg. So the Li-O/CO2 battery would probably be more than triple the effective energy density as gasoline. Hard to argue against a primary battery like this. It might make recycling worth it.
Electric passenger planes might be unpopular because prop planes aren't as fast as jets. That's generally because the propeller efficiency drops at high speed. but turboprops are making a comeback and give 400 mph speeds.
Posted by: Zhukova | 15 February 2011 at 11:07 AM
If carbon granules can be replaced, this system could work like the zinc-air fuel cell. The lithium would be regenerated externally, and the CO2 probably recaptured.
The net energy density depends on the ratio of carbon and electrolyte to lithium and CO2, but still... this is remarkable.
Posted by: Engineer-Poet | 15 February 2011 at 09:25 PM
Zhukova,
This 12.6% figure you´re using for ICE thermal efficiency is too low. If you´re comparing technologies it would be more adequate to represent what you can reasonably expect with incremental upgrades to ICE than to use artificially bad numbers for this context. (This way it seams as fair as an Electric-scooter x Dodge Viper!)
Small [turbo-]diesels achieve 40% brake efficiency now. With Direct Injection (DI) being popularized, using "stratified" injection, and turbo+downsizing gasoline engines achieve far better results today than those 12.6%.
In a context of competing technologies, it´s reasonable to assume even more advances to current ICE technologies including something from the researches in HCCI, LTC, PPC.
The paper from Lund university on PPC (Partially Premixed Combustion, http://www.greencarcongress.com/2010/09/ppc-20100928.html , http://feerc.ornl.gov/pdfs/Bengt_Johansson.pdf) shows gas engines running on lab with more than 50% of brake efficiency.
(Next stage for GM´s Ecotect-DI, Ford-Ecoboost, VW-TSI?)
Well designed hybridized applications allows engines to run near it´s best BSFC (Break Specific Fuel Consumption) most of the time, harnessing this sweet spot into the effective energy conversion ratio. This point in the design space can be realized today with current technology an in fact is coming to the markets.
Those foreseen advances only raise the bar (a bit) for the ROI analysis, as they don´t change the source of the energy, and oil is still scarce and finite.
The comparison of efficiency among the diverse pathways from sources of primary energy into automotive motion changes a bit.
Posted by: CelsoS | 16 February 2011 at 02:26 PM
In practical terms, the 12% tank to wheels efficiency may be slightly low but is close to the current fleet average.
Posted by: HarveyD | 16 February 2011 at 03:32 PM
40% or 50% never been demostrated and will never be for auto aplications. Those figures are applicable to large scale power generation.
Posted by: Darius | 16 February 2011 at 10:57 PM
This new battery will make a lot of things more practical. For example Darpa's new hummingbird drone can fly only 8 minutes, which is fantastic already. But the Li-O2/Co2 battery may give it 20-30 minutes. So the reconaisance crew could be a couple miles away from some terrorist activity, send the tiny, quiet bird into the camp, and get video more safely. I guess Ford could use it to spy on GMs testing grounds too. In the future the high-capacity batteries could enable fly-sized drones.
Posted by: Zhukova | 18 February 2011 at 10:34 AM
Darius,
I don´t get how and why do you state this:
40% or 50% never been demostrated and will never be for auto aplications.
I took my time and read the thesis from Lund, and some presentations from Mr. Bengt Johansson including the one for DOE/DEER. Those and many others state just this for current levels (Gas 35-40%, Diesel 50-55%) and future prospects (Gas 40-50%, Diesel 50-60%). Are they all liars ?
I found some links on the topic that might explain some of discrepancies and misunderstandings:
http://www.fueleconomy.gov/feg/atv.shtml
http://en.wikipedia.org/wiki/Fuel_economy_in_automobiles
http://en.wikipedia.org/wiki/File:Energy_flows_in_car.svg
The first link offers exactly this 12.6% number as the usable mechanical energy. If read carefully, one will see it´s a balance for the whole system including it´s (probable) use, not the engine alone.
There is a stated a 17.2% idling loss! It´s not intrinsic inefficiency of the ICE in chemical to mechanical energy conversion, but the way it is used to build and operate a (cheap) system. A hybrid or a start stop eliminates this, from the system.
The ICE setup evaluated is reminiscent to an old V8 from the 60´s with no advancements currently in the mass market or being popularized (VVT, VVL, DI, Turbo, CVTs/DSGs/ 6 to 9 speed transmissions, EPS, tight control of engine temp, piston oil jet coolers, variable displacement and load for water, oil, and HVAC pumps, start/stop,...). Sure this is not what is expected from current and future ICE, hybrid, or EREV cars.
Then there is the dynamic aspect of the real load imposed on the ICE in regular cars against a steady state load in serial hybrids and EREVs (Volt). When engines can be run at steady state near their best spots of BSFC (http://en.wikipedia.org/wiki/Brake_specific_fuel_consumption) there can be big possible efficiency gains within some a 30 to 100%.
(Just look at a BSFC chart for steady state use of engines against speed and load as in http://en.wikipedia.org/wiki/File:Brake_specific_fuel_consumption.svg).
Even a mild hybrid as the Buick Lacrosse/Regal with eAssist, which is just a small evolution will show far better numbers, and gain of 25% over the non eAssist.
In my view, to be fair, when comparing technologies, first we should compare battery to ICE+generator or system to system, and not battery to system.
Second, when using an ICE as a means to extract chemical energy into electricity for an EV extender or hybrid, an efficiency number higher than 30% should be used. With HCCI, PPC, Atkinson/Miller (Prius) cycles, it may be even better.
If you have hard facts that contradict it please let us know.
Posted by: CelsoS | 18 February 2011 at 02:13 PM
We used to talk about this twenty years ago, that you could run a gas ICE at constant "sweet spot" rpm and max efficiency in a hybrid. That would drive only a generator used to keep the battery charged. We talked about 40% efficiency then. But, this is easier said than done. It doesn't seem to make much sense when you consider an ICE, exhaust system, fuel tank, generator, etc., which adds up to a lot of weight, in addition to the electric motor and its batteries and converter. Complexity and cost (like the Volt).
The typical ICE without the transmission and other drive components probably runs closer to 20%. But an EV hardly needs a transmission, certainly only a simple one with less frictional loss. If somebody could get an ICE to run at 50% theoretical conditions in a normal driving cycle, they would have done it by now.
Posted by: Zhukova | 18 February 2011 at 03:17 PM
@CeliosC
Thanks for looking up those links. Over the years I read about ICE efficiencies, theoretical or practical, and the practical was always 25% or less. But, most of what I read was before the internet made it easy to verify this. Even I was surprised to see the 12.6%. But knowing that ICEs have different power and torque curves, intake and exhaust manifold performance dependence on temperature and pressure, timing dependence on rpm, compression ratios, and other variables, testing an engine at its sweet spot says nothing about how it will operate in normal driving. Most driving is done at low speed and a lot just idling for 20-30 traffic lights and accelerating away from them each day.
Posted by: Zhukova | 19 February 2011 at 06:35 AM
One should not make a confusion among the roles of an ICE as in a legacy setup we are used to and as a range extender or generator.
ICE used as generators at their best BSFC regions in electrified transportation will deliver far higher effective conversion from chemical energy to movement.
I'm cross linking below with new info from Toyota on the thermal efficiency of Prius engines (~37%) and future developments (~45%).
Toyota targeting thermal efficiency of more than 45% for next-generation gasoline engines for hybrids
http://www.greencarcongress.com/2011/04/nakata-20110411.html
The engine used in the first- and second-generation Prius (the 1.5L 1NZ-FXE) had a thermal efficiency of about 37%; the thermal efficiency of the new 1.8L unit in the third-generation Prius (2ZR-FXE) has a thermal efficiency of about 38%. Toyota is targeting a thermal efficiency of more than 40% with what Nakata called its Future Concept 1, followed by thermal efficiency of more than 45% in Future Concept 2 (which is based on concept 1).
Posted by: CelsoS | 11 April 2011 at 03:53 PM