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Are Lithium Ion Batteries the Best Solution For EVs?

 
3,545 views Jul 26, 2009

The Hymotion kit not only fits under the load deck, it also complies with the same rear-crash and emissions standards as any new car.

The Hymotion kit not only fits under the load deck, it also complies with the same rear-crash and emissions standards as any new car.

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Lithium-ion technology has seen use in laptops and cell phones as well as numerous other devices for over a decade.  People have grown accustomed to the expectations of these batteries.  Cell phones lose their charge-holding capacity after a few years, and laptops with strenuous use can see batteries last less than a year.  But car manufacturers claim 10 or more years of dependable service life from their batteries.  What makes an automotive lithium-ion battery more durable and longer lasting than its counterparts in use in other devices?

The real difference does not lie in battery technology.  The difference lies in how the battery is depleted and charged.  In a standard laptop or cell phone system, the battery can be nearly fully depleted before shutting down.  Then it is plugged in for charging and charge to near capacity.  This process is extremely tough on the li-ion technology.  It reduces its useable life, but provides 100 percent of the batteries available power.  In short, batteries can be smaller because they can be charged to full capacity and all of the power can be realized.

In the automotive setup, the lithium-ion battery is treated differently to increase longevity at the expense of output.  Many hybrid and electric vehicles utilize what is known as a 50-80 charge.  In short, this means a li-ion battery would never be discharged below 50 percent and would never be charged over 80 percent of its real capacity.  This area between 50 and 80 percent is where the battery can safely operate for 10 or more years.  It's a gentle discharging and charging process that never allows the battery to drop much below half of its capacity or reach its full capacity.

However, there is a serious drawback to extending the battery life through this method.  In order to provide a decent electric range, EVs are equipped with a battery that is close to twice the size that is actually needed for the application.  This means a vehicle must carry additional weight, weight that is actually useless in increasing the range of the vehicle, but vital for the longevity of the battery.

An example is provided below.  The Chevy Volt carries a 16 kilowatt hour lithium-ion battery pack that weighs in around 400 pounds.  The vehicle is only capable of using 8 kilowatt hours of energy from the battery.  It must carry the additional 200 pounds which in turn decreases its electric only range by a measurable amount.  When the vehicle reaches its end of service life 10 years from now, the battery is expected to still be able to output 12 kilowatt hours of juice.  Still more than is needed to power the vehicle, but not enough to keep the battery in its safe zone for an extended period of time.

Another downside is cost.  Batteries cost roughly $1,000 per kWh.  That puts the battery pack in the Volt at an estimated price of $16,000.  It only needs a battery pack priced at $8,000 outputting 8 kWh.  The additional $8,000 is money spent for energy not needed and weight not desired.

The advancement of battery technology will likely find a way around the dilemma.  But for now, EVs buyers will be reluctantly carrying a lot of dead weight onboard.  Maximizing energy output and maximizing longevity is a battle that battery makers face and the answer is not clear cut right now.  Lithium-ion technology is relatively new and advancements come almost daily, a breakthrough is sure to come and somebody will discover a solution to the problem that currently plagues this technology.

Source:  Car and Driver August 2009





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Comments (12)

  1. By Paul Posted: 7/26/2009 5:37am PDT

    The writer at car and driver can't add. It's 30/80 not 50/80.. If they never go below 50% or above 80% that's an operating window of only 30% of battery capacity. 30/80 give a 50% window!
    Further........ the battery DOES NOT cost $1,000 kwh! These writers who never check facts. The BYD Hybrid has a 16 kWh battery and the entire car sells for $22,000.
     
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  2. By Jay Posted: 7/26/2009 8:15am PDT

    All the more reason that a technology like EEStor would be a complete game changer. In other words, America would, with sufficient investment, come close to eliminating its dependence on foreign oil in about 10 years from the commercialization of EEStor.
     
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  3. By Author Posted: 7/26/2009 9:28am PDT

    To Paul, the numbers of 50-80 are correct under typical usage. A 16kwh battery would provide the needed minimum for the Volt at 50% charge or 8 kwh. At 30 % it would be too low for adequate power. But batteries can fall below 50% under certain conditions. What a vehicle such as the BYD sells for and what the batteries cost do not correlate right now. Many vehicles are sold at as loss to the manufacturer.
     
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  4. By evnow Posted: 7/26/2009 6:46pm PDT

    Paul is correct. To use 8kwh of a 16kwh battery, you need the operating range to be worth 8kwh i.e. 30% to 80%.
     
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  5. By  Chris O Posted: 7/27/2009 3:34am PDT

    The problem with articles like this is that they assume that Li-ion is a fixed chemistry whereas it really is a family of related chemistries with varying properties. So there is not one price/KWH or one power/energy density or one optimal depletion range.
     
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  6. By Bart Posted: 7/27/2009 8:47am PDT

    Tesla does 90% to 10%, but with 200 miles per cycle there will not be as many cycles over the battery lifetime. The user can over-ride the limits to get 100% if needed. Cost: $600/kWh.
    The Volt uses Lithium Iron Phosphate cells, which unlike the Lithium cobalt oxide cells in cell phones, can handle large number of deep cycles, have high power density, but about half the energy density.
     
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  7. By Don J Posted: 7/27/2009 10:55am PDT

    $1000/KWH IS NOT CORRECT. Perhaps $1000/KWH of 'available' KWH which means $1000/KWH for the available 8KWH in a Volt pack. But the actual cost in that case would be $500/KWH for the 16 KWH pack which provides an 'available' 8KWH of power usable to the user.
     
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  8. By Greg Simpson Posted: 7/27/2009 4:21pm PDT

    The Volt does not use lithium iron phosphate cells, it uses lithium manganese spinel. Not quite as stable, but still much better than the lithium cobalt chemistry.
     
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  9. By Author Posted: 7/28/2009 4:03am PDT

    The Tesla uses a laptop format battery unlike the others talked about here. The doubt with the Tesla is the longevity of the battery. many do not think that these batteries will reliably last more than a few years. Automakers want to gaurantee ten years of use.
     
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  10. By  Todd Horst Posted: 7/28/2009 9:40am PDT

    id rather use the bare minimum battery and make it last 5 years. If it goes a little longer than that its great. But aim for 5. Then its less weight, and in 5 years hopefully the pack would be able to make the car go further on a charge. If not at least it would be cheaper 5 years from now. And even if it wasn't, then at least id save on weight in the mean time.
     
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  11. By  Todd Horst Posted: 7/28/2009 9:40am PDT

    I know the smaller the battery the more wear and therefor shorter life span. But im trying to be optimistic on the state of batteries in the coming years.
     
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  12. By omnimoeish Posted: 8/10/2009 8:57pm PDT

    Hey Lyle, great article. I agree with the title of this article. Is Lithium Ion the best solution for EVs?
    It would be interesting to see a comparison to NiMH to achieve 40 miles AER with cost, weight, volume, etc. etc.
     
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