Batteries 2013_Nissan_Leaf_cutaway

Published on January 6th, 2016 | by Christopher Arcus

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A Tale of 3 Battery Packs

January 6th, 2016 by  

The Nissan Leaf, Chevy Volt, and Tesla Model S use different batteries, and different battery packs. But how are they constructed, and why are they constructed as they are? First, let’s start with the shape.

The shape of a Leaf pack is not flat, but it hides under the seats and under the floor. The Leaf has a flatter rear floor, as Nissan puts more of the battery under the seat.

2013_Nissan_Leaf_cutaway

The Volt has a T-shaped battery pack. Its rear floor has a hump to accommodate the long narrow pack. The top of the T fits under the back seat.

Chevrolet Volt

2012-chevrolet-volt-battery-pack

Tesla created a flat battery pack that sits underneath the floor. Tesla calls that pack a skateboard.

Tesla_Motors_Model_S_battery pack

So, why are they shaped that way? Well, first we have to discover what’s inside. The battery cells that make up battery packs are of three types: cylindrical, prismatic, or pouch.

A cylindrical cell is as familiar as batteries in a flashlight. Tesla uses small cells called 18650 cells, named after their dimensions in mm — 18 mm x 65 mm.

Tesla Motors battery cell

It’s a fairly small cell.

Then there are prismatic cells. They are larger and heavier, like auto ignition batteries, but a bit lighter because they don’t use lead.

prismatic battery cell

Next, there are pouch cells. Pouch cells are just a sheet of cathode and anode with a separator in between, and a thin covering, not much thicker than a piece of cardboard.

Some pouches are about 8.5 x 11 inches and not very thick, and have to be enclosed by a metal package.

A123 battery pouch cell

All of those cell types start as thin layers of cathode and anode with a separator — like stacks of paper. The difference is that a pouch cell may be only one or a few stacks high. A cylindrical cell rolls the layers into a cylinder. And a prismatic cell folds a stack of these to fit inside a rectangular package. The pouch cell really doesn’t have a case, so one must be provided externally.

prismatic_cell_cross_section_thunderskyAll lithium expands when charged/discharged and heated. Even prismatics must have mechanical pressure to retain their shape. You can find pictures of bulged prismatics (see the image on right).

Cylindrical cells use a metal case. That prevents the contents from expanding. A prismatic case is plastic and does not limit expansion. Because prismatics can swell, some mechanical pressure must be applied to keep their shape.

With pouches, you also have to add the packaging externally to prevent swelling and protect the cell. Since each pouch is rectangular like a piece of paper, that sets their shape.

In the Tesla pack, the cylindrical cells are arranged vertically. You can see the ends of them in the pack picture below. Their length comprises most of the pack thickness. They can be packed in pretty well, but space is allowed for cooling channels. The pack is flat and fits underneath most of the car. It’s thin enough that it’s hard to notice.

Tesla battery pack

The Leaf and Volt both use pouch cells. The Volt pack has arranged rows of pouch cells vertically and like a file cabinet. That makes the pack long and rectangular, but they made it in two sections that form a T shape. All the cells are vertical. The pack sticks up between the seats.

The Leaf has its pouch cells oriented horizontally, stacked like paper in your mailbox. Under the seats, they are stacked higher than under the floor. The pack conforms to the space underneath unobtrusively.

That’s the reason the Volt has a rear floor center hump. The T shape battery concept is one GM created for the EV-1. Nissan put the boxes under the seats and under the car. The pouch boxes are flat enough to put in a skateboard, but they don’t pack as well into the tight corners as the smaller cylindrical cells.
 There really could be a skateboard pack with pouch style cells.

The cells are arranged in series to achieve about 400 volts. This voltage is chosen because it is high enough to allow smaller motors with less copper that have enough horsepower and torque for a car, and so the resistance losses are low. Lithium cells are about 3.6 to 4.0V, so a stack of about 100 of these cells in series is necessary to achieve 400 volts.

There are other advantages that go with Tesla’s cylindrical cell approach. They can have many cells in parallel and any one cell can fail, but the pack will still work.
 Both GM Volt and Nissan Leaf are series cell arrangements. Just as in Christmas lights, if any cell fails, the whole pack fails.
 The downside to so many cells is that it’s harder to guarantee they all work.
 The downside to fewer cells is that they must all work.

2016-chevrolet-volt-inline3-photo-655303-s-original

Now that I just analyzed the Leaf pack, we can compare. The new 2016 Volt pack is 192 cells, and this must also be series parallel, with 96 series. Since the pack is 18.4 kWh, we can tell approximate cell voltage, and capacity. Lithium cells are about 3.8V, so the pack voltage is about 365V. The pack amp-hr rating is twice the cell rating, because the cells are parallel. The pack amp-hr rating is: 18.4 kWh = 50.4 A-hr.

The cell Amp hour rating is half of that, 25.2 A-hr.

It’s a bit less than the Leaf rating of 33.1 A-hr per cell.

The original Volt pack weighed about 400 pounds. The cells are also pouch type, not prismatic. Overall, they have quite a few similarities with the Leaf.

Here is a picture of the Leaf Pack (48 modules, 4 cells per module):

Nissan LEAF battery pack

Each cell:

  • average voltage 3.8V
  • 33.1 A-hr

They must be parallel series, two at a time. 192 cells would give way more than the pack voltage of about 360V.

So, 192/2 x 3.8V = 365V

Two in parallel gives 66.2 A-hr x 365V = 24.16 kWh.

They are side connected. The larger 4-pack is bulkier and packaging is more difficult.

Nissan-Leaf-Battery-Pack-II

This is the best Leaf pack dissection I have found:

It looks as if the cell is a pouch, not a prismatic. (It has soft sides, no hard plastic packaging.)

You can see the advantages of smaller cylindrical cells. Cooling and packaging are both better. Also, pouch cells must be enclosed by an outside mechanical package to limit swelling and to form them properly. Cells expand and contract with heat and charging, if not limited mechanically. Cells are kind of spongy that way.

Oddly, the automotive knock on small-form-factor cylindrical is packing density. But Tesla has it right. You don’t want overheated EV batteries. Space is needed for cooling.

Still, look for innovation in those areas. Tesla would change quickly if it had a better tech. Tesla’s Straubel made a similar point in his interview with the SAE. “The first question we ask when we meet a new cell company is, show us your cost roadmap. Nobody wants to talk about cost – they always leave that to the end of the discussion. That’s silly. For EVs, there are some key safety and performance metrics that are foundational. They have to be there. Beyond that the most important thing is cost efficiency of energy storage. So if anyone has a more cost-efficient cell architecture, we’d be all ears. Right now nobody has proven they have a more cost-effective cell architecture than ours.”

All three battery packs have strengths and weaknesses. The Leaf pack uses all available area under the seats and floor, but does not have cooling. The Volt pack is well protected from intrusion with its T shape, but reduces interior floor space. The Volt pack is cooled. The Tesla pack provides a large amount of cell volume and provides for maximum interior space, but is more vulnerable to intrusion underneath the car. It also provides cooling. The choice between pouch and cylindrical cells is still a matter in progress, with some experts expecting pouch cells to emerge as the cheapest long term.

Addendum: Since this article was written, news reports have surfaced that Volkswagen is moving toward flat batteries. No word yet on whether this means pouch cells, or a flatter battery pack.

Volkswagen’s e-Golf has a battery pack with a center hump, but also uses the space under the seats and floor.

Der neue Volkswagen e-up! Der neue Volkswagen e-up!

The e-Golf differs in that it uses prismatic cells.

VW e-Golf prismatic cells

VW e-Golf battery pack


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About the Author

has studied wind, electric vehicles, and environmental issues. An electrical engineer familiar with power and electronics, he has participated in the Automotive X Prize contest. He is an avid writer, specializing in electric vehicles, batteries, and wind energy.



  • bsw

    How about batteries that only last 4 years, and are swapped out and recycled? But weight much less, and charge quicker.

  • neroden

    The Tesla design is *so* much better. Let me count the ways:
    1 — pack is the right shape: flat
    2 — parallel wiring allows individual cell failure to be harmless
    3 — space between cells for cooling (and heating!)
    4 — space between cells for fire containment

    5 — versatile recycling for failed packs (most cylindrical cells can be extracted and reused whole)

    Basically the Tesla pack is *robust* against lots of failure modes. The other designs are *fragile*.

  • Benjamin Nead

    Easy to understand tech articles with plenty of illustrations are a good thing.
    I’m glad the author took the time and energy to put this one together. As it’s
    been pointed out already, the title claims that it’s the story of 3 packs (Tesla S,
    Nissan Leaf and Chevy Volt,) with a 4th uncredited one (Volkswagen eGolf) added
    on. Here’s details a 5th one (Mitsubishi i-MiEV) . . .

    The North American spec Mitsubishi i-MiEV is composed of a 16kWh
    under-the-seat pack in a non-metallic clamshell enclosure. Inside is 88
    Lithium Manganese Oxide prismatic cells, 50aH and 3.75V each, configured
    in series for a nominal pack voltage of 330V . . .

    http://media.caranddriver.com/images/10q1/335484/mitsubishi-i-miev-battery-pack-photo-335601-s-1280×782.jpg

    The 88 50Ah prismatic cells (10 subpacks of 8 cells each, 2 subpacks of 4 each) are made by the Japanese/German GS Yuasa/Bosch consortium. The current generation cells carry the LEV50N designation (PDF spec sheet, linked below) . . .

    http://donar.messe.de/exhibitor/hannovermesse/2014/R732819/yuasa-li-ion-battery-datasheet-eng-295494.pdf

    There are some excellent write-ups of the i-MiEV variants from a European perspective on the Push EV blog. This page differentiates between various generations of LEV50 batteries. Note that the newer LEV50N is considered to be
    the equivalent the “Lizard Battery” cells found in later Leafs. . .

    http://pushevs.com/2015/11/04/gs-yuasas-improved-cells-lev50-vs-lev50n/

    One of the things that makes the i-MiEV potentially more attractive than the Leaf
    for people living in extreme climates is the option for heating and cooling the cells more effectively. While both car’s packs are technically passive air cooled systems, i-MiEVs equipped with CHAdeMO L-3 ports (and ones without CHAdeMO, but with the optional cold weather package,) contain an extra fan inside the pack enclosure. With a very basic mechanical alteration to the cabin’s ducting, one can effectively couple the pack with the car’s cabin climate control system to force at least a nominal amount of that air through the pack. It’s described at length on the My i-MiEV Forum . . .

    http://myimiev.com/forum/viewtopic.php?f=23&t=1712

    • eveee

      Nice Benjamin. Thanks.

      • Dag Johansen

        It is only 16KWH. To small to be very useful. I think the vehicle is now dead. It never sold well.

        • eveee

          Mitsubishi has pulled the plug. Sorry for the pun. And yes, the pack is too small.

          Mitsubishi thinks its heading for hybrids. Don’t think that will help. They just didn’t execute right. Although, there seems to be a market for hybrid SUVs.

          http://insideevs.com/mitsubishi-no-next-gen-for-i-miev-will-focus-on-phevs/

          • Benjamin Nead

            “Mitsubishi has pulled the plug.”

            Uh . . . No. Did you actually read that Inside EV article?

            The author speculated that Mitsubishi is distancing itself from
            the I-MiEV (and I don’t doubt the company will continue to promote
            it poorly) But at least this article directly quoted the original
            Masuko interview, where it’s clearly stated that no replacement
            of the I-MiEV is being planned. “No replacement planned” is
            NOT the same as “pulled the plug!”

          • eveee

            Got it. I played with the words. No replacement is planned. Thats a shame. I thought the IMieV filled a market need and could have been improved. Mitsu is going all out for the lucrative PHEV SUV market, which is good, but I wish they would stay in the sedan market. I guess it was just too much competition from Nissan and now Chevy/Tesla.

          • Benjamin Nead

            Actually, I look at the whole thing as lemonade being made out of lemons. That Mitsubishi wants to basically ignore the i-MiEV (ie: not develop a micro car replacement) means they really will continue with it at least for another model year or two here. As mentioned elsewhere, they have Peugeot/Citroen in a contractual deal for 100K units. So, it’s going to be a world presence car for many years to come.

            Mitsubishi probably won’t invest the money in cosmetic changes on i-MiEV variants and only make cursory mechanical/electrical upgrades. That’s actually good new for people like me, who own earlier versions of the car and welcome lots of backward compatibility in a new/used parts inventory. If they really were going to replace the i-MiEV with another new micro car, i-MiEV parts would get scarce and expensive fairly quickly. So, I’m in the “don’t change it too much” camp. The exceptions would be put in a 6.6kW charger, a battery pack with more energy dense cells and to revise the front suspension. Change the bathwater, but don’t throw out the baby.

            Mitsubishi – or, perhaps more accurately, the North American division – is a rather strange company with a conflicting message. They spent almost as much getting the i-MiEV ready for the U.S. market – something on the order of 4.5 billion dollars – as Nissan did with the Leaf. Then, they got a couple of poorly written write ups early on (the Consumer Reports one from a few years back, in particular, really was the slash job that set the tone) and, like a scared kid who got teased at school, went running up to the proverbial bedroom to cry their eyes out. They could have responded to the FUD with a clever ad campaign and sold many more vehicles. But, instead, they refused to promote the i-MiEV in any fashion whatsoever.

            I also don’t buy into the argument that the car is too small for the U.S. market. It’s roughly the same physical size as a Honda Fit and Toyota Yaris. Those vehicle might not move off the lots with the same wild abandon as F150 pickup trucks, but they sell well enough to sustain a market presence year after year. The big difference between an i-MiEV and a Fit/Yaris is the lower operating cost (even with $2 per gallon gas) and no tailpipe pollution. The big downside, of course is the limited range. But how many Fit or Yaris owners drive 65 miles or more every day? People who drive those sort of distances get bigger vehicles as a general rule.

            But, yes, Mitsubishi is making noises about getting into the evolving and potentially lucrative PHEV SUV market.
            Yet it seems they are approaching it in much the same lackadaisical way they did with the i-MiEV. They’re behind schedule with the product rollout and the shrinking U.S. presence of the company in general is going to make it very tough. They could have had that new market all to themselves but will now getting challenged by the Chrysler Pacifica PHEV minivan and, on the upper end, by the Tesla X. It’s going to be a lot harder for them now.

          • eveee

            Yes. Its so nice to hear from a someone with real EV technical knowledge and experience. You get it. The Leaf and the iMieV are both under rated and a steal for someone who knows how to use their strengths. I know of one guy that picked one up for his commute and got a real nice deal. Used Leafs are another.
            You are right about Mitsubishi. They didn’t push their EV enough. They are a small car company, so doing one product is a lot for them. Still, I have to say I am very happy with their entry into the larger SUV PHEV business. They show a willingness to try that is admirable and rare for a small company and it needs to respected and lauded.
            I hope they succeed. If nothing else, IMO, they will pull other car cos into the field. I hope they make some money on it.

        • Benjamin Nead

          The marketing of the I-MiEV in North America has been horrendous. But the car deserves better than the tepid reviews it received. Also . . . 16kWh isn’t “To (sic) small to be useful” if you’ve only got a 2500 vehicle to move around. I’d be interested to see how far a Leaf could go with a 16kWh pack, much less a Model S. Big heavy EVs need big heavy batteries.

          The reports of the I-miEV being axed are untrue. There was an interview with Mitsubishi’s CEO, Osamu Masuko, on the Automotive News web site, on Nov. 30, 2015, where he clearly stated that “there would be no new dedicated electric vehicle to replace the subcompact I-MiEV.”

          http://www.autonews.com/article/20151130/OEM02/311309981/mitsubishi–ceo-promises–an-electrified-u.s.-rebound

          But, in what had to be some of the poorest speculation among a rather large number of automotive sites in recent memory, legions of “professional reporters” were suddenly declaring that the I-MiEV was going to be pulled from production. None of these web articles linked back to original sources or cited the name of a Mitsubishi official contradicting their CEO. They only speculated and fed off each other. So, I emailed Mitsubishi North American headquarters just before Christmas and they confirmed that, in fact, production of the i-MiEV is continuing.

          Additionally, Peagout-Citroen is under contractual commitment to buy 100,000 I-MiEVs from Mitsubishi. All the variants are made on the same Tokyo production line and, as of March 2015, 50,000 of all variants of the car have been produced since production began in 2009 . . .

          http://www.autonews.com/article/20151130/OEM02/311309981/mitsubishi–ceo-promises–an-electrified-u.s.-rebound

          So, as much as you will sad to hear this, expect to see a 2018 announced within the year. My guess is that Mitsubishi will do little to update the car and will do even less to promote it. But that seems to be their curious style when it comes to this particular vehicle.

  • Steven F

    In my opinion this article missed the most important reasons for the battery arrangement.

    First the volt is a plug in hybrid with a large heavy engine, electric motors and transmission in the front. Second the body of the car was originally designed for a standard gas only car. The end result of this is that without the battery the volt is already front heavy. The T shape puts more of the battery weight on the rear wheels. Furthermore the charge controller is located under the floor in the back of the car moving even more weight to the back wheels. End result is that all wheels are evenly loaded for better traction . Since GM decided to use an existing body (for cost savings the battery had to fit the body with minimal modifications to the body. The T shape des that very well.

    Tje leaf doesn’t have a heavy gas engine so Nissan had an easier time getting even wheel loading. Nissan also used an existing ICE body so a the T shape chevey used was not needed but it still had to fit in the body.

    Tesla is the only of the 3 cars to be only EV and have the body designed specifically for it. So Tesla didn’t have to design the battery to fit the body. Furthermore the battery body design allows for automatic battery swapping in the future (the only one of the three with that capability).

    Also the square shape of the battery cells on the volt and leaf should not swell under normal use. Swelling and bulging is an indication of overheating which you never want to see. Over heating batteries can catch fire which must not happen. Also Square batteries are easier to cool with liquid cooling systems. Metal plates with cooling tubes can be designed to fit easily between cells. The square shape of the cells results in battery with a larger surface area compared to volume which also helps in heat removal.

    The round cells Tesla uses have a higher volume to surface area and designing a liquid cooling system that effectively removes heat is a bit more difficult. However the older battery shape is more economical to produce resulting in lower cells cost compared to the newer square shape.

    • eveee

      But does it explain the hump? The second gen was a clean sheet. Still has it. But the Bolt doesn’t. Could be just me, but I think GM is learning.

      • Julien

        Maybe the hump in gen 2 Volt can be explained because of the platform it uses : the Cruze platform as opposed to the real clean sheet that is the Bolt

        • eveee

          But does the Cruze have a hump that large? I don’t think so. Its GMs battery pack design shape. It changed on the Bolt. GM got much of the electrical design of the Bolt from LG Chem. I can only speculate on how much input each company had in the pack design.

      • Steven F

        The second generation volt was not a clean sheet design. There were engine and center console design changes and a small change in the battery The car body was largely unchanged. The center hum in the body was originally designed to accommodate the hot exhaust pipe in the chevy cruze. The fuel tank andfuel systems were also in the same area.

        IN the volt the mufler got moved to the space once occupied by the spare tire (the volt doesn’t have a spare tire, just a leak repair kit) and the exhaust pipe was move to the side

        the bolt and leaf don’t have mufflers and exhaust pipes gas tanks and fuel systems which allow for a flatter floor.

  • John Locke

    I would just like to point out that there have been roughly 2 problems per million cells produced for the first gen volt. So even though it is wired in series, the likelihood of your battery failing because one of the cells fails is pretty slim.

    • Dragon

      I think the bigger concern is what happens as a battery ages. If one cell fails or even drops too much voltage, it drags everything connected in series down with it.

      Not only can Tesla cells be individually cut out of the pack if they fail too badly, but the whole pack can be removed in 6 minutes for repair if necessary. I don’t think any other manufacturer makes the entire pack easy to remove for repairs (or battery swapping), which is something this article failed to investigate. Maybe next article!

      • Steven F

        The Tesla battery pack shown in this article has it’s solid metal cover removed. Each series array of cells is in its own metal frame with a charge monitor and tubing for cooling. Also finding the failed cell in such a large battery is not a trivial task. In all likelihood if a battery fails Tesla will remove and recycle it, and install the new and improved battery. I don’t believe Nissan, Chevy, or Tesla are planning on repairing and reinstalling these batteries.

        • eveee

          Tesla does have a battery warranty that covers factory reconditioning, not just replacement.

          https://www.teslamotors.com/blog/creating-world’s-best-service-and-warranty-program-0

          The Leaf is a repair or replace warranty.

          http://www.engadget.com/2012/12/28/nissan-will-now-restore-leafs-battery-charge/

          For the Leaf, Volt, and Golf, serial devices, (modules) could be identified and replaced. This is not too difficult, because the BMS monitors cell voltages accurately to match them.

          The same could be done for the Tesla, even though only a few cells in one module might be the cause. No need to identify individual cells.

        • Dragon

          Tesla has a fuse on each cell (or small group of cells?) that can be blown to remove those cells from the circuit if they fail.

          Tesla has also been known to remove the whole battery pack and put in a replacement, then ship the bad pack to the factory for repair.

          There are screenshots of a display on the Model S main screen (protected by a password) showing the health of each set of cells. Finding a bad set of cells can clearly be done using that data and I don’t think finding an individual bad cell amongst the subset would be difficult at all using a volt meter or other special equipment, nor would replacing it. There’s no way they’re going to recycle a $10k battery pack instead of repairing one or two cells and using the pack as a warranty replacement, temporary loaner, or battery swap candidate.

      • eveee

        Actually, one cell will not drag down the other cells if it shorts. The Tesla modules are arranged with fuses in series with each cell. It still won’t stop a leaky bad cell from having an effect.

    • eveee

      True. But if you are the lucky winner, it’s a scramble for the warranty info.

    • Steven F

      The author early states the leaf and volt used a series cell arrangement.. However when he gets into detail on the leaf and volt he states the battery cells are in a series parallel arrangement. Same as the Tesla. I did a google search that did confirm all three cars use series parallel arrangement. So none of the batery packs are going to fail if one cell fails.

  • Foersom

    “Cylindrical cells use a metal case. That prevents the contents from expanding.”

    The downside is that with the casing of the cylindrical cell it is heavier per stored joule than with pouch cells (Lipo) including their packaging. So Lipo gives a lighter battery.

    Drones / UAS (Unmanned Aircraft Systems) uses Lipo rather than round cells because when flying energy per mass is even more important than in an electric car. Mobile phones and tablets uses Lipo because it allows to shape the device flat and thin.

    • eveee

      LiPo?

      • Foersom
        • eveee

          The designation has some unfortunate confusion. Thats why the term pouch cell is used. Its more clear than LiPo. Unless you meant lithium polymer.

          • Foersom

            Yes, when you look on the market, Li-ion pouch cells are named LiPo referring to the soft moldable enclosure, see Wikipedia article.

            Could we discuss the points in my original comment?

          • eveee

            Yes. You are right about the cylindrical casing. Its heavier. Pouch has the potential for lowering weight because less casing is used. The upside to cylindrical is that the case is a good heat conductor, too. A potential downside to pouch is packing. The shapes dictate the pack shape. Cost, performance, and reliability are key questions. It could be more expensive to make the many connections to the approximately 7000 cells in the Model S. The upside to that is packs are relatively reliable. Seems like this could also be done with pouches to some degree.

          • Foersom

            As far as I know only Tesla use the 18650 round cells. Every other manufacturer use LiPo pouch.

          • eveee

            VW e-Golf uses prismatic. Prismatic LiFeP is about the safest.
            You must remember that the outside casing may be an electrode, too.The extra weight is only that part that is used for pressure. The rest may be used for the cell. Or not. Depends on how they do it. That said, IMO, the pouch might be optimized better. The possible downside to the pouch is cooling. A metal case is a better heatsink. The large pouch surface is good, but getting coolant to all that surface is not easy. Pouch might benefit from parallel/series if its done right. Doesn’t look like this is fully used, yet.

  • Bob Fearn

    Thanks for great article. Something that I didn’t see mentioned. The Tesla design leads to a more aerodynamically possible car design.

  • serge delinois

    That was a great article. Thanks for all the knowledge I just gained.

    • hybridbear

      I agree. I think this is the best article I’ve ever read on Clean Technica!! Many thanks!

  • Dan Johnson

    As a lithium battery pioneer, this article is fascinating and heart warming. I’m interested in the characteristics of the Porche Mission E that boast 15 minutes charge to 80% capacity. Must be cooling issues there, I’d have thought?

  • Jenny Sommer

    The flat bottom seems to be the favourite way to go. FFs platform and Volkswagen MEB look like that.

    • serge delinois

      Not only is it out of the way, it reduces road noise, lowers the cars center of gravity and protects the cabin in the case of a crash.

      • GregS

        Also greatly helps aero by not having all that turbulence under the car

        • neroden

          Yep, the aerodynamics on the bottom of the car are a fascinating and important result. It’s why the rear of every Model S is always dirty, though. 🙂

          • Bob_Wallace

            Really? Never heard that before?

            Airflow sucks dirt up and in?

          • eveee

            You can see how it works in this video. The rear of the car is shaped for air to flow gradually upward.

            https://www.youtube.com/watch?v=cPQS2GRBqjI

          • eveee

            You mean it needs a wash? Not aerodynamically dirty.

          • neroden

            Yes, I mean it needs a wash. Even if you left the car wash 5 minutes ago.

            What happens is this: dirt is kicked up by the tires, or blown along the road by wind (as on all cars). On *most* cars, this dirt attaches to the underside of the car, which then looks filthy if you look underneath.

            But on the Model S, the aerodynamic flat shape of the underside causes all the dirt to whoosh right along the bottom of the car — and then it jumps up at the back and deposits on the rear end of the car, on the rear license plate and so forth.

            The bottom of the car is typically shiny clean when I take it into my local tire shop and have it picked up on the lift. The back end is covered with dirt *all the time*. It’s most obviously visible on a white Model S. Leaning against the rear bumper will leave big splotches on your pants.

            Harmless. But kind of funny.

          • eveee

            Got it. I think an aerodynamicist would say the flow doesn’t separate, but remains attached until well in the back of the vehicle. An normal vehicle disturbs the flow under the car, but with the Tesla, the floorpan is smooth.

      • Bob_Wallace

        Side impact protection is an oft overlooked advantage of the skateboard design. Large mass that is hard to compress….

  • Matt

    I wonder how much of the decision by GM to use the T shape, is the fact that ICE engineers did it. Hey there is space here when we take out the transmission and drive train to the rear wheels. It is amazing how much design if “fixed” at the start by your experience. Don’t believe me? Research why the track on US rails are the width they are. Just wondering on the impact.

    • neroden

      The gauge (width) of railroad tracks is driven primarily by the overriding need for standardization: it didn’t matter so much what the gauge *was* as that it was the *same* everywhere. After getting multiple gauges built, Britain ended up passing a law standardizing on “Stephenson’s” gauge, rather than “Brunel’s” gauge or one of the others. The US had a similar history; the South used to have a different gauge and was regauged to match the North at one point.

  • Iain Palmar

    I think they are all missing the point – that is weight! Weight is the biggest hinderance to a cars performance. The extra weight has an negative effect on all aspects of car performance – acceleration, breaking, steering, handling and the overall efficiency of the car. Weight is the biggest killer of performance and it is my opinion that the weight of the batteries have to be seriously reduced in order to make electric and hybrid cars even more attractive.

    • eveee

      Does the P90D in ludicrous mode not have enough performance for you?
      Yes, lowering weight is good, but it seems not to have hindered Tesla performance.
      Frankly, its not weight that matters anymore. Its cost per range.

      • Iain Palmar

        Yes the P90D does have plenty of performance however, if they reduced the weight of the batteries by 50% on all electric and hybrid cars the vehicle dynamics and efficiency would be even better and most importantly the range would be improved.

        • eveee

          Yes. I agree. What I am saying is that there is a tradeoff between weight, cost, and performance. Thats where weight really comes in. I am assuming performance means acceleration for purposes of discussion. Both range and acceleration benefit from weight reduction. At this stage of EV development, the penalty for aerodynamic drag is worse.
          All the EVs out there, save Tesla, have poor highway range, but good city range. Regen does that. It tends to blunt the weight penalty. Not so aero drag. You are lucky if most EVs will get two thirds of their city range as highway range at 65mph. A 100 mile city range EV might be only 66miles highway. Readers? Any EV owners out there with highway vs city range estimates?

    • kart

      They covered that when they spoke about energy density. Thats what it stands for.When we have improved energy density the overall mass automatically decreases. because you don’t need many cells as before to achieve the same energy capacity.

    • Ron Beilman

      It would seem logical that any given automobile platform (compact to SUV) would have an optimum overall weight and center of gravity and not just be dependent on lowering weight to make better performance. A vehicle that is too light or with a high center of gravity will handle very poorly at high speeds, with cross winds and/or wet and snowy road conditions. Check reviews on the BMW i3? I’m sure the designers and engineers pursue these parameters more holistically as they relate to all systems performance and the all important ‘retail cost’…not just weight.

    • Hazel

      The issues for performance are power/weight and torque/weight. At low speed, torque/weight is more important (battery current/weight); at high speed it’s power/weight.

      Those ratios are clearly high enough in lithium batteries for good performance. Though the Prius plug-in is wimpy and not worth it, even the Ford plug-ins with small 7.5 kWh batteries have strong enough low-end torque to routinely engage traction control, and decent power. The Volt is double that and has good all-electric 0-60, the Leaf 50% more than the Volt, and the Model S 2.5-3.8 times the Leaf.

      Bottom line: with an electric powertrain and enough batteries for ≥100 mile range, performance/weight is a non-issue.

      • Iain Palmar

        You are correct re power/weight and torque weight. However, when it comes to handling – the performance in corners etc weight has a major affect on a car, as you can feel the affect of the weight when its changing direction quickly. The cars that have mastered hybrid tech are the Ferrari La Ferrari, McLaren P1 and the Porsche 918. In these cars they have used the instant torque of the electric motor to ‘fill in’ the gaps (or what they call Torque Fill) to aid the performance of the petrol engine. it is for this reason (as i’m in to performance driving) that I see the benefit of an electric motor. I think that as advances are made in battery technology in terms of reducing weight, increasing the power, and the range the batteries provide, would benefit all. However, its is the F1 teams that are really pushing the boundaries and innovating with battery and hybrid technology.

        • Kraylin

          I am also a performance enthusiast. Out of curiosity, do you have any interest in Formula E?

          • Benjamin Nead

            Formula E is very interesting. First season cars (2014-15) were all identical. Current season rules allow for individual teams to experiment with different gearboxes and multiple motors in their cars. At least one team decided that the 1st season format was the best, while other teams diverged. It will be interesting to see whose car ends up preforming best.

          • Iain Palmar

            I’ve been to one race – the final round in London Battersea Park which was good however, something was missing and that was the sound of a petrol engine! Nevertheless, the racing was good and competitive.

    • Bob_Wallace

      The Tesla two-motor P85D weighs 4936 pounds, or 291 pounds more than a rear-drive P85.

      The BMW 7 series weighs 4225 pounds. Around 4350 with a full gas tank. There’s not a huge difference.

      Battery weight will continue to drop (if range is kept constant). However, right now we’re not hearing complaints about acceleration, steering, handling and the overall efficiency. Kind of hard to complain about the acceleration of the Tesla….

    • eveee

      It depends on whether you are talking city or highway. At highway speeds on level ground, aerodynamics dominate. Weight has little impact on resistance.
      In stop and go low speed, weight dominates.

  • Stan Hlegeris

    “The Tesla pack … is more vulnerable to intrusion underneath the car.”

    Is there any evidence that this has actually been a problem for Tesla? In the event of a serious puncture from below, would the other batteries be much better protected than Tesla’s? It seems unlikely.

    • eveee

      Just that the floor area is greater for the Tesla. Tesla has a pretty thick metal shield underneath the skateboard pack. There have been two reported incidents where the skateboard was penetrated underneath the vehicle. It was pretty extreme. The vehicle ran over a large metal object that penetrated from below.

      An ICE vehicle could have encountered a similar fate if its gas tank or fuel line was ruptured by a similar object.

      http://articles.latimes.com/2014/mar/28/autos/la-fi-hy-tesla-recall-nhtsa-fire-20140328

      • Knetter

        In an ICE vehicle, it could come thru the floor pan into the passenger compartment as it’s just sheet metal.

        • eveee

          As long as it misses fuel or brake lines and gas tank.

      • crevasse

        Happened to me in an ICE some years ago. We were driving over one of the bridges out of Manhattan and ran over some metal object. It punctured the gas tank and we we went from full to empty in seconds. No fire luckily. We called the rental car company and they said to just leave it and they would take care of it. Needless to say, the weekend didn’t happen!

        • eveee

          Thank you. Case in point. Luckily no fire. If the gasoline had landed on the exhaust, .. could have been worse.

        • neroden

          I’ve had a gas tank punctured from below. No fire. Also no fun.

      • Kevin Saxon

        Yup A friend ran over a small pc of girder and punctured the Gas Tank Drained in seconds.

    • GCO

      To complement what @disqus_MOZiUpcqXO:disqus wrote: locating the battery further aft, like other manufacturers did, also reduces the chances it’ll be the first thing to hit road debris or obstacles — apparently successfully so far.

    • serge delinois

      Tesla added the titanium shield after a couple people ran over some huge things and broke into the battery. Since then no more issues.

      • MorinMoss

        Yup, for all the fuss the naysayers made, Tesla’s solution didn’t take long and we’ve not heard of a single case since.

    • Bob_Wallace

      Was a problem. Twice. Titanium shield installed. No reported problems since.

    • Dragon

      A ran over a granite rock a couple days ago in Model S. Heavy rain had caused a dozen rock slides along highway 18 and we kept having to skirt around big rocks on the road or roll them out of the way. At one point a small rock looked like it would fit under the car, but apparently not because it banged along under the car at least 6 times going around 20 mph. I wasn’t too happy but I can’t see any damage.

  • Freddy D

    Any word on the Bolt battery architecture?

    • Keanwood

      I heard its flat but besides that idk.

    • As Keanwood said, we just heard it’s flat, but Chris has some hunches and is going to do a piece on that as well.

  • JeffJL

    Miss-leading title. You covered four battery packs. Not sure of how much more of this miss-information I can take.

    Seriously though. Good article.

  • That’s 18mm x 65mm, for an 18650.

    • patb2009

      yeah 650 mm would be almost 2′ long….

    • natch. updating.

      • eveee

        Duh.

      • dogphlap dogphlap

        The zero at the end of 18650 says cylindrical or so I’ve read.

  • Andy

    Great article! This is the type of detailed breakdown that got me hooked on Cleantechnica. I’d love to see similar articles that break down how the various solar technologies work, or a walk-through of a wind turbine’s parts.

    • hmm. okay, we can do that kind of thing. hadn’t really considered it, but if you are so enthusiastic about it and already got a handful of upvotes, i’m thinking these would be appreciated.

      • neroden

        Actually it would be a blast to go through solar tech in detail. Might take quite a lot of articles (one for the various types of silicon panels, one for the various ways to wire them up for DC, one for the thin-films, one for inverters, ….)

      • ROBwithaB

        What you might consider is having a sort of 101 section on the site, with a series of standard introductory articles, accessible via an index.
        Something like a simple online textbook or encyclopedia, that starts at the very beginning, that allows people to bring themselves up to speed on the various issues.
        Headings for wind, solar, hydro, nuclear, coal, etc. Simple expalanations of how each technology works, with sub-headings going into increasingly more detail.
        Someone unfamiliar with a particular topic educate themselves in a very systematic way, one module at a time.

        You already have a lot of the material on hand, buried within your existing stories. Some of it might need to be updated, to reflect the constant changes within the greentech field. But some of it, like the basic physics, can just be cut and pasted from elsewhere (with the necessary attribution and/or permission, of course.)
        It is essentially a job of collating information, bringing it all under one roof in an easily accessible way. The advantage of this one-stop “encyclopaedia” approach is that the modern search algorithms LOVE the kind of activity it generates. And it tends to be a self-reinforcing loop. (Which explains why wikipedia is in the first page for almost ANY search term.) Lots of clicks. Lots of back links. Lots of citations. Lots of credibility. In case you haven’t gotten where I’m going with this yet, here’s a hint. Advertisers like that sort of thing.
        You can flesh it out slowly. Can go live incrementally, over time.

        If you build it, they will come.

    • Coley

      Ditto, though the maths always confuses me,

  • Martin

    Very informative and to the point, also explains why EV’s have such a low center of gravity, not that it makes much of a difference in normal driving?

    • Keanwood

      The low center of gravity is nice. It gives better handling. And decreases the chance of flipping the car.

    • A low center of gravity is very noticeable on every drive as reduced pitch and roll and increased stability without having to resort to overly stiff suspension

  • t1oracle

    The Tesla design is so much cleaner than the others.

    • eveee

      Its all about vehicle packaging. Its a big deal for EV design and the reason why purpose built EVs are so much better than ICE platform retrofits. Tesla managed to do a superb packaging job. Compare the packaging to the e-Golf.
      It all works so much better when energy density is high enough.

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