Batteries, the Achilles Heel

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Batteries, the Achilles Heel

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Published on Friday, 29 March 2013 12:51

Written by Donn Dears

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The sale of EVs and PHEVs has been sluggish, probably because of the high cost of the battery. The 16 kWh battery for the Volt, for example, Cost of the battery for the all electric Leaf is around $15,000, and it would require roughly 11 years to recover its added cost costs around $10,000, while the 24 kWh battery for the Leaf costs around $15,000.

From the buyer’s perspective, the savings from not using gasoline is an important economic factor in the buying decision.

For the Volt, assuming the vehicle is only used for commuting less than 25 miles, it might be possible to travel the usual 12,000 miles per year without using gasoline. At $4 per gallon, and, assuming 35 mpg for comparable ICE vehicles, the buyer would save approximately $1,400 per year.

The buyer could, in this instance, recover the extra cost for the Volt battery in slightly over 7 years.

If, the Volt is used for longer drives, where it uses gasoline for half the miles driven, or 6,000 miles, it would take over 14 years to recover the added cost of the battery.

The cost of the battery for the all electric Leaf is around $15,000, and it would require roughly 11 years to recover its added cost.

In both instances, estimated battery life is around 8 to 10 years, so that, in most instances, the buyer will never recover the added cost of the battery.

What would it take to cut recovery periods to four years, the length of time many buyers plan on keeping a new vehicle?

With savings of $1,400 per year, it would require that the battery for the Volt and the Leaf cost around $5,500; or roughly half the cost of the current Volt battery and one-third the cost of the current Leaf battery. – Remember also, that the Leaf can only travel 100 miles on this size battery.

But, is cutting the cost of the battery to $5,500 realistic?

There is considerable hype in the media on this question, so here is some information that may help you decide.

Li-ion Cost and Energy Density Curve

It’s evident from this graph that energy density, Wh/kg, in green, is plateauing, while the cost curve, blue, is asymptotic, or leveling off, indicating that cost improvements are likely to be minuscule. To arrive at total battery cost, it’s necessary to add the cost of packaging, which is currently around $300 kWh, to the cost of Li-ion cells.

To cut the cost of the Volt battery in half, requires either cutting the cell cost, $/Wh, or doubling the energy density, while achieving comparable reductions in packaging costs.

Focusing on cells, it means increasing energy density from 202 Wh/kg, to over 400 Wh/kg for the Volt. For the Leaf, it means tripling the energy density to over 600 Wh/kg.

Even if the Leaf can achieve this objective, it wouldn’t increase its range beyond 100 miles.

The Argonne National Laboratory has proposed theoretical solutions to the problem, including entirely different battery chemistries. Even DOE, in its 2011 presentation¹, categorizes these solutions as high risk. The Argonne Lab’s high risk proposals don’t double energy density until, possibly, 2030, while not even proposing to triple energy density in this time frame.

A glance at the accompanying chart demonstrates that it’s not possible to achieve the required lower battery costs without revolutionary breakthroughs.

The DOE report, Applied Battery Research (ABR) for Transportation Program, said:

“There are no commercially available high energy materials that can produce a battery capable of meeting the 40-mile all-electric-range (AER) within the weight and volume constraints established for PHEVs by DOE and the USABC.²”

It’s worth keeping in mind that there has been tremendous interest in batteries for at least the past 20 years – actually for at least 30 years when GE had a battery business in Gainesville, Florida, and GE’s scientists decided the obstacles were too great to consider growing the business in anticipation of the automotive market.

The current Li-ion batteries, with six times the energy density of lead-acid batteries, are the only big automotive battery breakthrough in the past 25 years.

It’s also worth recognizing that the consumer products industry has built millions of Li-ion batteries while attempting to cut costs.

With this prior concentration of effort, one could assume that major breakthroughs are going to be very difficult to achieve.

Prospects for cutting battery costs are not good.

Whatever conclusions individuals reach, it will affect their buying decisions, and also how they feel about using tax-payer money for subsidies and investments.

Notes:

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1. DOE Battery R&D progress update, November 3, 2011 PDF REPORT
2. The DOE, Applied Battery Research (ABR) for Transportation Program, report describes, in technical terms, a multitude of experimental efforts being undertaken to support PHEVs PDF REPORT