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Maxwell Technologies and Argonne National Lab to Collaborate on Testing Ultracapacitor/Lithium-Ion Battery Combination for Hybrid Vehicles

Maxwell Technologies, Inc. will supply ultracapacitor cells and integration kits to the US Department of Energy’s Argonne National Laboratory for a collaborative research project to assemble and evaluate an integrated ultracapacitor/lithium-ion battery energy storage system for hybrid-electric and plug-in hybrid vehicles.

Argonne will provide batteries and power electronics, and design and fabricate the integrated energy system for installation in the Hardware-in-the-Loop (HIL) of the Advanced Powertrain Research Facility (APRF) in Argonne’s Center for Transportation Research. APRF’s primary focus is technology validation and benchmark testing for advanced vehicles and their supporting subsystems.

Argonne and Maxwell have agreed on an active parallel system configuration that will combine a standard lithium-ion plug-in hybrid battery with a string of 112 of Maxwell’s BOOSTCAP BCAP0650 P270 650-farad ultracapacitor cells, along with appropriate power electronics and cooling and safety-related features. The system will undergo HIL validation during the summer of 2007.

We are intrigued with ultracapacitors’ rapid charge/discharge capabilities and their ability to handle the heavy cycling involved in regenerative braking, torque assist and other demands on energy storage systems for hybrid-electric and plug-in hybrid vehicles.

—Dr. Don Hillebrand, director of Argonne’s Center for Transportation Research



This is a good example of public/private partnerships that benefit everyone. A national lab and a private company doing development that will be published without bias. Now people in the business can get some straight data without all the marketing spin.


Using nanotech lithium-ion (such as A123 or Altair), there should be no need for very expensive and heavy ultracaps to perform power-levelling or longevity purposes.


Yes but A123 and Altair lack the energy density of more conventional polymer lithium ion batteries. So its a trade off between energy density, max discharge rate and longevity

Rafael Seidl

Clett -

in HEV/PHEV/BEV applications, the batteries must simultaneously achieve excellent values in all of the following categories: bulk, weight safety, power, capacity, longevity and cost. This is proving extremely hard to deliver.

It therefore seems sensible to invest R&D funding in multiple alternate strategies in parallel, e.g. new Li-ion chemistries, new Li-ion cell manufacturing technologies, new Li-ion packaging strategies as well as Li-ion/Ultracap combos.

The latter does add yet another layer of complexity to an already complex hybrid ICE-electric drivetrain. However, UCs excel at handling brief power spikes in charge/discharge and, they permit further downsizing of the ICE (if present). Indeed, UCs may yet turn out to be a key component of future pure EV designs for the mass market.

UC cell cost is currently high mostly because manufacturing volumes are still low. Maxwell's technology also differs markedly from that of e.g. Power Systems', which are based on Prof. Okamura's work in Japan.


For PHEVS, the bigger the battery, the less the requirement for capacitors. Once you get to 4 kWh and above, the power density really isn't an issue, and 100 Wh/kg of A123/Altair is fine for PHEV.

If the notion is to improve things for hybrid only use, where power and cycle life is required and only very small kWh (eg 1.3) are required, it still makes sense to use battery only. Toyota are managing fine with primitive 46 Wh/kg ; 1300 W/kg NiMH and those packs are lasting 200k miles. Where is the benefit of adding ultracapacitors for hybrids, EVs or PHEVs?

At the current 5 Wh/kg for Maxwell caps I don't see any benefit (although if EESTOR or ECASS etc came up with something above 100 WH/kg it could prove useful).


Let’s not forget about other companies that have research projects that may pay off as well. EESTOR or EPODI?

EPOD/UBC Get Approval for $300,000 Government of Canada Grant for Revolutionary Hybrid Battery Super Capacitor


Noting on what Rafael and Clett posted...

What Clett said would seem to be correct for pure EVs, such as RAV4 EV or Tesla. Once you put a large, full range, battery pack in the car, even with today's common technology it can push out enough power for good, or in Tesla's case spectacular, performance.

However, for PHEV I can see possible advantages for adding caps. Currently, a limitation of the Prius is that above a certain speed (I think roughly 35mph) the electric system can't handle the power alone and the ICE has to come on. It may even happen with hard acceleration below that speed. This is why studies of PHEV converted Prii show that the total tailpipe emissions (other than CO2) likely go up after the conversion because the engine performs multiple cold starts. Adding caps to the mix to handle instantaneous demands for added power might prevent the need for some of those cold starts.



The Prius only uses about 500 Wh of its battery pack to prolong life. A 500 Wh ultracap could outperform the Prius NiMH battery by improving electric-only acceleration and regen capture and efficiency. A 500 Wh Maxwell ultracap would weigh 100 kg -- twice as much as the Prius battery. It would also cost about twice as much. But if they can double their energy density and halve their cost they'll be competitive for HEV markets. That's not so farfetched considering the progress they've made so far.

I agree advanced lithium batteries from A123 and others will probably beat Li-ion + ultracap PHEV designs. But note the Volt's battery weighs 350 lbs. A Li-ion + ultracap pack could possibly beat that by 100+ lbs, so it's still too early to declare a winner.


Doggydogworld, agreed the Prius only uses about 500 Wh of capacity, but remember the output voltage of an ultracapacitor drops as it discharges, so you would actually need about 800 Wh of capacitor to avoid the huge current conversions required at the low end to keep power at low voltage. Moreover, the cost of the electronics to convert the plummeting capacitor voltage to steady motor voltage would add a lot of weight/cost/losses, while of course the battery would provide a decent voltage at all SOCs.

As for the battery in the Volt, it is only that heavy because of the requirement for ENERGY storage (40 mile range), not power. It is NOT that big because they couldn't achieve enough burst power otherwise. Even limiting the battery to 1 kW per kg (A123 manages 3 kW per kg) means a 100 kW vehicle could make do with a 100 kg battery. Adding capacitors to the Volt would add no benefit, but lower overall energy density and increase cost/complexity.


Clett, I thought ultracap energy density was rated down to Vmax/2, but if not you're right about oversizing. The Prius dc-dc converter handles a 2.5x voltage range, a converter that handled a 3x range could deliver 89% of an ultracap's energy. So you'd need 560 Wh of caps to get 500 Wh usable.

You are right that an ultracap would be useless in a Volt-type PHEV with A123 batteries. But A123 and other high-power cells only store about 100 Wh/kg. Other Li-ion chemistries cannot match A123's power, but store 200 Wh/kg or more. At 200 Wh/kg a 16 kWh pack only weighs 80 kg. Add 30 kg for an ultracap and you're at 110 kg total -- 50 kg less than a 16 kWh A123 pack.

Personally I think 16 kWh is too much. 10-12 kWh should be enough for a mid-sized PHEV, and at that size the weight advantage narrows. But SUVs and pickups need larger packs; the Li-ion + ultracap architecture may find a home there.


I have to disagree, clett, because:

1) you diminish the instaneous storage ability of ultra capacitors, i.e., there are advantages to explore with quicker, greater "regen" and "brake by wire"

2) Assumptions about weight/cost/losses seems predicated on older models. What of the newer silicon carbide power electronics? Maximum power point tracking? Carbon Nano Tubes?

"It's not a box, it's a textarea."


I'm phd student.
I work on the field of hybrid vehicle.

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