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GM Electrochemists Suggest Ongoing Investment in Both Battery and Fuel Cell Research; Connecting the Science with Vehicle Engineering

Wagner2
Projected incremental mass due to the energy storage and electricity generation system for (a) a 100- and (b) 300-mile range for a battery electric vehicle and a fuel cell electric vehicle. Credit: ACS, Wagner et al. Click to enlarge.

In a Perspective published in ACS’s Journal of Physical Chemistry Letters, researchers from the Electrochemical Energy Research Laboratory (EERL), General Motors Research & Development, suggest that given the strong societal need for full vehicle electrification and the respective technical challenges and commercial risk entailed, both Li-ion batteries and fuel cell systems for powering electric vehicles warrant continued strong development investment.

In their paper, Fred Wagner, a GM Technical Fellow and the Lab Group Manager for Advanced Electrodes of the EERL; Balasubramanian Lakshmanan, the Lab Group Manager for Materials-System Interface of EERL; and Mark Mathias, GM Technical Fellow and the Director of EERL, examine potential routes for improving the specific energy of battery storage, as well as for cost reduction on the fuel cell side. They stress the importance of the scientific developments being connected to vehicle developers who understand implementation realities. EERL is responsible for R&D for both battery and fuel cell systems.

The authors suggest that given the specific energy (Whnet/kg) characteristics of the technologies, full battery electric vehicles could be more suited for shorter range applications, with fuel cells used for longer distance vehicles.

..it is {the] fundamental dependence of the specific energy on the amount of electricity required...which determines the applicability of these systems in vehicles of various size and range. This allows batteries for small low-range pure electric vehicles but excludes them for larger-vehicle long-range applications. Previous studies comparing BEVs and FCEVs have reached similar conclusions that only limited-range BEVs are workable, with somewhat different crossover ranges between BEVs and FCEVs arising from different input assumptions for the two technologies.

...Li ion batteries provide a pathway for efficient use of renewable-sourced electricity in the transportation sector, but it is possible that fundamental physical limitations may prevent pure Li-ion-based BEVs from ever delivering the freedom of providing long trips, with intermittent quick refills, that consumers currently receive from their cars.

In addition to mass considerations, alternative powertrain feasibility is determined by packaging (i.e., volume) considerations. Once physical feasibility is established, commercialization is ultimately determined by cost. Packaging and high volume cost analyses of projected technologies are outside of the scope of this Perspective. Solely on the basis of the mass considerations above, we can conclude that battery-powered options are favored for small vehicles when short-range and long refueling times are acceptable. The fuel cell option is favored for large-vehicle, long-range options.

—Wagner et al.

Wagner3
Estimated mass contributions of automotive Li ion battery technology as compared with USABC goals for advanced batteries for electric vehicles. Credit: ACS, Wagner et al. Click to enlarge.

Li-ion storage. With a focus on mass reduction, the authors estimate the kg/kWh total of various pack elements, concluding that about 50% of the mass is due to the cell materials, and ~70% of the cell material mass comes from the positive and negative electrode materials. Thus, they conclude, the primary mass reduction focus needs to be on improving the specific energy of the positive and negative active materials, in priority order.

New cathode materials with higher storage capacity and/or with substantially higher voltage—the latter also requiring development and implementation of electrolytes/solvents with improved oxidation resistance—are needed, according to the authors. One promising direction is the development of materials that enable the intercalation of more than one lithium ion per transition metal, they note. However, efforts to date have not yet yielded high-capacity durable materials ready for serious implementation efforts.

Replacing graphite anodes with other materials—such as silicon—that offer higher theoretical capacities is also an approach of interest, but the trade-off is swelling upon Li uptake, leading to durability challenges.

Using cell models of new positive and negative electrode material concepts such as those described above, we estimate that the USABC target of 200 Whtotal/kgpack is challenging but achievable. This will also require that the mass of the pack components be reduced by a factor of approximately 2 relative to state-of-the-art, an engineering and materials challenge that we consider achievable but outside of the scope of this paper.

—Wagner et al.

With respect to next-generation approaches, the Li-sulfur system, which relies on the use of low-cost sulfur on the positive electrode, offers promising specific energy because of the potential for storage of 2 moles of lithium for every mole of sulfur, the authors note. However, the sulfur is soluble in the electrolyte when not fully oxidized and is subject to migration and reduction on the negative electrode.

Metal-air systems—such as Zn-air or Li-air—are also of keen current interest.

Li-air cells pose fascinating scientific questions of the thermodynamics and the catalyzed kinetics of interactions of lithium with oxygen. For example, different catalysts may be needed for discharging and charging, and these catalysts must be able to coexist in the positive electrode without poisoning one another. Given the low levels of reversibility and low capacities at high current density demonstrated to date, Li-air cells will likely show impressive percentages of improvement in a number of metrics in the coming years. It is critical that enough attention also be given to fundamental engineering issues and to the absolute, not relative, metrics that reflect product requirements of a full-function BEV.

We are supportive of work on developing reversible Li-air and other advanced electrochemical energy storage systems while keeping the scientific development connected to vehicle developers who understand implementation realities.

—Wagner et al.

Fuel cells. Although fuel cell vehicles could offer the functionality of current automobiles “in an environmentally sustainable form”, the authors note that the issues of hydrogen supply and fuel cell system cost “remain significant.”

Although the platinum content on the anode constitutes a lower limit to the cost of mass-produced fuel cells, the authors state that anode Pt loadings can be low enough to have no real economic impact.

The cathode is another matter entirely. The kinetics of the oxygen reduction reaction (ORR) are notoriously slow (and therefore have received the attention of generations of generally frustrated, though recently more gratified, electrochemists), leading to the current necessity of using~0.4mgPt/cm2 geometric loadings of commercially optimized Pt/carbon black cathode catalysts, costing several thousands of dollars per vehicle.

—Wagner et al.

They outline five potential directions for improved ORR catalysts, with the potential for significant reduction of fuel cell cost:

  • Continuous-Layer Catalysts;
  • Pt Alloy and Dealloyed Catalysts;
  • Monolayer Catalysts;
  • Controlled Crystal Face Orientation Catalysts; and
  • Non-Pt Catalysts.

If the range problems of batteries could be solved, the pathways to acceptably low fuel cell Pt usage could be brought to fruition, and hydrogen and electrical infrastructure issues could be adequately addressed; the choice between these two technologies for electrification of the automobile would come down to matters of the overall system and lifetime operating costs.

Li ion batteries use intrinsically cheap materials but require a very large surface area of very finely controlled thin layers, interfaces, and separators and, by their nature, use monopolar design (current collectors coming out of the side of each cell). Li ion batteries are already mass produced for use in portable electronic devices; therefore, many of the opportunities for cost reduction through scale have already been taken, and therefore, cost reduction must be addressed through the development and implementation of improved materials.

Fuel cells utilize some intrinsically more-expensive materials, though as we have seen, pathways exist for drastic reductions in the amounts used. Due to the much higher current densities obtainable with the more conductive fuel cell electrolyte, the total geometric surface area of the cells is ~30-fold less. The ability to use bipolar construction, with cells stacked in series with the negative current collector of one cell serving also as the positive current collector of the adjacent cell, further simplifies the structures. However, fuel cell systems also require more complex balance of plant, including a hydrogen tank and an air compressor.

In summary, ongoing development work should be coupled to continuous reevaluation of the system-level physical feasibility and relative cost structures of BEV and FCEV systems,with the results informing future strategy setting.

—Wagner et al.

Resources

  • Frederick T. Wagner, Balasubramanian Lakshmanan and Mark F. Mathias (2010) Electrochemistry and the Future of the Automobile. J. Phys. Chem. Lett., doi: 10.1021/jz100553m

Comments

HarveyD

The majority of GM electrified vehicles would be 2 and 2+ tonnes monsters?

It is obvious that GM does not intend to use light weight materials to down size batteries and/or FCs of future PHEV/BEV and FC vehicles.

Somebody else will have to do it.

kelly

As long as an article discusses batteries and investment, what's the status on:

"1,000 times more powerful and 10 times longer-lasting and cheaper than traditional batteries."

http://www.greencarcongress.com/2009/12/prieto-20091217.html

http://thewere42.wordpress.com/2009/12/17/colorado-state-university-spinoff-to-commercialize-%E2%80%9C3d%E2%80%9D-li-ion-battery-technology-for-higher-capacity-longer-life-cells/ (the Preito '3D' battery)?

Considering that in 2009 the article states, "..expects to demonstrate the first prototype of the battery by early next year." - someone's so far apparently 15 days to six months and 15 days late.

Are these huge claims just made for grants, stocks, and publicity?

This has been commented on before, but when a company declares "..batteries up to 1,000 times more powerful and 10 times longer-lasting and cheaper than traditional batteries." a web site that publishes such claims should track and hold responsible those making the claims.

Otherwise, GCC and such are just shuffling EEStor stories for decades and can be ignored.

In fact, without even a prototype, how can:
..
Prieto Batteries can be recharged in minutes
Approaches similar time to filling a tank of gas
Prieto batteries last 2000 + cycles
Charging time and cycle life are key differentiators
Extends e-bike range
Reduces down time
Broadens E-bike market appeal..

claims be made on the Preito web site, especially when no batteries are for sale and there's no way to verify?

SJC

They could use high temperature PEM (HTPEM) and an on board methanol reformer. Since the HTPEM is more tolerant of CO, the reformer is simpler. Since the HTPEM runs above 100C, the balance of system components are simpler and cheaper.

HealthyBreeze

@Kelly,

It does get fatiguing hearing about Silicon nanowires, Lithium-Air, Prieto 3D batteries, not to mention eestor nano-Barium-Titanate supercaps, and the like and thinking, "Shouldn't something be good enough by now?"

In principle, reactions limited by surface area should be helped substantially by clever nano materials. However, integrating those nano materials into robust and affordable macro systems is non-trivial. Still, all we need is one of these purported big leaps forward to make it to market and work.

Mannstein

"Li ion batteries are already mass produced for use in portable electronic devices; therefore, many of the opportunities for cost reduction through scale have already been taken, and therefore, cost reduction must be addressed through the development and implementation of improved materials."

At a cost of $300/Kwhr for a lap top battery which does not require cooling it is highly unlikely that the cost of a vehicle battery will ever be less than $500 even with mass production.

Thus a 40 kwhr battery needed for a 100 to 120 mile range vehicle would cost $20,000 which would put the vehicle cost into the low $30,000.

Who in his right mind would make such a purchase?

clett

@ Mannstein, are you really suggesting that as much as $200 per kWh needs to be added to battery pack cost for a cooling system?

That would mean the cooling system in the Volt would cost $3,200, far too much for what's simply a bunch of channels and a radiator.

Also, the Nissan Leaf battery pack makes do without any liquid cooling circuit at all.

kelly

No doubt, batteries are tough, but when "..expects to demonstrate the first prototype of the battery by early next year." - the public was given an expectation.

If this is broken, a reason should be given. Otherwise, future battery claims are dismissed.

Zhukova

I can't believe current Li-Ion batteries cost GM and Toyota $500/kwr. You can buy them retail from Rebirth for $460/kwh - http://rebirthauto.com/lithiumlifepo4cells.aspx That's got to have a significant markup. I'll bet a 40 kwh battery cost GM only $10,000. If you drive 40 miles a day with such a battery, you could save about $6,900 in five years in energy cost (4 miles/kwh, $.09 /kwh) over an ICE car ($2.90/gal, 25 mpg). That energy cost savings puts buyer of a Li-Ion powered car in his right mind. BEVs have other advantages like only one moving part in the motor = reliability, great low-end torque, little noise, no exhaust system, etc. Plus the big rebate.

SJC

We will see what all the battery and car makers do to the price of batteries. At some point the rebate has to be phased out and the makers and customers have to go without "training wheels".

wintermane2000

Its simple zhukova..

The CELL might coist say 300 bucks but then you have to put it in a pack and test the pack for quite awhile in a very intense testing device and fix any problems...

And just the controller for the pack costs quite a bit of money and so does the colling system...

And then you have to remember just as with all batteries alot of them will fail ahead of curve. Far too many for normal warranty rates.. so they have to pay for the extra failures under wanranty... Oh and just installing the dang things is very tricky far more so then installing an engine.

It all adds up to alot of money to get the pack into the car.

Zhukova

Of course assembly and testing drives the cost higher, but that doesn't affect my argument. Similar assembly and testing costs are associated with any other battery type. Li-Ion cells are the most expensive now and are by far the largest portion of total battery pack cost. In any case the energy savings over an ICE are still there.

Another thing is the retail cost of cells is higher than a wholsale cost that GM would pay their subsidiary. But they still have their own markup embedded in the retail cost of the completed vehicle. I believe the markup is not as much as when buying small quantities of cells from a independent distributor.

Assembling and testing the EV drive train and power system can't be anywhere near that of an ICE. The ICE has all those 250 moving parts: cams, sprockets, timing chains, valves, springs, pistons, pumps, levers, pins, etc., etc. Plus hundreds of non-moving parts not in the EV. The motor controller isn't that complex except that it has to handle very large current. Except for the Li-Ion cells, EV drive train systems should be a lot cheaper to build than ICE drive trains, including their exhaust systems, fuel injection, automatic transmission, and cooling systems, that EVs don't have.

Zhukova

Maybe not hundreds of non-moving parts, but dozens of screws, bolts, brackets, wires, etc. Not to forget the very complex machined parts, the block, cylinder heads, and intake manifold. The EV's electric motor is so much simpler, only one moving part, and only a handful of non-moving parts, all very easy to manufacture.

SJC

They have been making the I.C.E. for 100 years by the millions every year. It has come down the cost curve so that now you have an engine with all those high temperature parts at less than 1/10th the cost of a fuel cell.

wintermane2000


To test an ice engine you just drive it off the line and park it in the lot.

The battery pack test supposedly takes all day.

JRP3

Regardless of any possible advances in FCVS the non existent infrastructure alone makes them a waste of time. Sad thing is the basic large scale prismatic LiFePO4 cells from Thundersky and CALB are cheap enough, (under $400/kwh in quantity), and good enough to make affordable 200+ mile EV's possible, IF they are put into lightweight aerodynamic vehicles. Solectria Sunrise did over 300 miles with NiMH 15 years ago, it would do even better with Lithium today.

SJC

Solectria made some great stuff and still does as Azure Dynamics. It is these innovators that should be encouraged. Large companies can make it on their own, but often take no chances in exchange for quarterly profits, while the small companies struggle every day to survive.

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