Everything You Need To Know About Tesla’s Lithium-Ion Batteries

2 months ago by EVANNEX 54

Tesla Model 3

Tesla Model 3

UNDERSTANDING TESLA’S LITHIUM ION BATTERIES

Tesla cars are powered solely by the electrical charge stored in batteries and are termed Battery Electric Vehicles or BEVs.  The reason for the existence of Tesla as a company is simply that Lithium ion batteries have the highest charge capacity of any practical battery formulation in history for the money, high enough to make BEVs practical.

Tesla

A look at the new Tesla Model 3 (Image: InsideEVs)

The idea for using Lithium ion rechargeable battery cells was first proposed by a British chemist in the early 1970s.  There is an in-depth review of Lithium ion battery cell development in this Wikipedia article.

The television show NOVA (see below) devoted an episode to lithium ion cells in early 2017 that demonstrates the advantages and dangers associated with Lithium ion cells.  It is illuminating, if a little lightweight, technically.

Above: Nova’s Search for the Super Battery (Source: PBS)

Battery cells are deceptively simple devices consisting of three basic components: two electrodes, the negative anode and the positive cathode separated by a chemical “soup”, called the electrolyte.  When Lithium ion batteries are charged, Lithium ions are forced to migrate to the negative electrode where they are deposited.  During discharge the Lithium ions reverse direction for the Cathode.

*This article comes to us courtesy of EVANNEX (which also makes aftermarket Tesla accessories). Posted by Matt Pressman and authored by George Hawley*.

Tesla

How a rechargeable lithium ion battery works (Image: How Stuff Works)

Tesla has been using 18650 cells manufactured by Panasonic in Asia in the Models S and X cars since 2013.  These are small battery cells, slightly larger than the standard AA cells.  The Tesla cylindrical cells are 18 mm in diameter and 65 mm tall.  The Panasonic design, perhaps with input from Tesla, is by some accounts one of the most robust formulations available today, yielding very long-lived, reliable performance in the harsh automotive environment.

Tesla

Tesla Model X on the Panasonic show stand

The most popular battery pack supplied by Tesla contains 7,104 18650 cells in 16 444 cell modules capable of storing up to 85 kWh of energy.  In 2015 Panasonic altered the anode design, increasing cell capacity by about 6%, enabling the battery packs to store up to 90 kWh of energy.  More recently, Tesla engineers reconfigured the internals of the battery pack to hold 516 cells in each module for a total of 8,256 cells capable of storing a little more than 100 kWh of energy enabling the cars to enjoy a range of over 300 miles.

Tesla

Tesla Energy power module (with new 2170s)

In order to further improve cell efficiency and lower costs Tesla has built a large battery factory in Sparks, NV near Reno called Gigafactory 1 that is now producing a new cell design called the 2170 because it is 21 mm in diameter and 70 mm high to be used initially in Tesla Powerwall home storage products and Powerpack utility storage products as well as the new Model 3 sedan, designed to be smaller and less expensive than the Model S.  The 2170 design is 46% larger in volume than the 18650 and 10-15 % more energy efficient than the 18650 cells, according to J. B. Straubel, CTO  of Tesla.

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Comparing the Model S/X 18650 battery cell with the Model 3 2170 battery cell (Image: DNK Power)

One of the key requirements for electric car batteries, especially on road trips, is that they need to be recharged relatively quickly.

Since batteries are direct current (DC) devices and home electrical service is AC, charging at home typically uses a 240 volt circuit supplying 40 amperes (about 10 kW of power).  The car has built in charging circuitry that rectifies the AC, converting it to DC.  Charging this way typically takes several hours.  Tesla has installed Supercharger DC charging stations worldwide that supply up to about 135 kW of power.  The DC bypasses the car’s charging circuitry and charges the battery pack directly.  This is much faster, requiring 20 to 40 minutes typically.

Tesla

Tesla vehicles charging at a Supercharger station

The Tesla battery packs using Panasonic 18650 batteries can charge no faster than this.  The maximum charging voltage for a Panasonic cell is 4.2 volts.  Panasonic specifies a maximum charging current of 2 amperes per cell.  Tesla allows charging current to be up to 4 amperes.

Therefore the maximum power that a Tesla battery pack can can use for charging is 4.2 X N X I where N is the number of cells in the pack and I is the maximum current allowed per cell.  For 85/90 kWh packs this is 7,104 X 16.8=119.3 kW.  For the 100 kWh packs it is 8,256 X 16.8=138.7 kW.  There is no way to charge faster without increasing the maximum charging current per cell which might hasten degradation of the cells or worse.

Tesla

Tesla Model S chassis with battery pack

All rechargeable battery cells degrade over time as undesirable side reactions take place in the cells that produce byproducts that block lithium ions from reaching the anode during charging.  Tesla battery packs are warranted against failure but not degradation.  Early indications are that 18650 cell degradation is very slow, losing only a percent or two of capacity per year at worst.  The cells are very resistant to degradation, apparently.

Tesla

Tesla Battery Degradation Analysis

The Tesla Model 3 cars will use the Gigafactory manufactured 2170 cells mentioned above.  The larger cells may be able to use more than 4 amperes of charging current which would hasten charging but, because the 2170 cells have more energy storage capacity than the 18650 cells, proportionately fewer will be needed to create a pack with a given kWh rating.  (N gets smaller, I gets larger). This means that higher power charging is meaningless for these battery packs.  The 4.2 X N X I relationship still applies.  It will be interesting to see how these new battery cells perform.

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*George Hawley has owned a Tesla Model S S85 and a Model X 90D. He also currently has a Model 3 reservation. Hawley worked in telecommunications primarily as a Product Planner for over 40 years.  He started with Bell Telephone Labs in New Jersey for 20 years and finished with several startup companies in California.  His career is described in his book, Tangled Wires, published in 2017.

*Editor’s Note: EVANNEX, which also sells aftermarket gear for Teslas, has kindly allowed us to share some of its content with our readers. Our thanks go out to EVANNEX, Check out the site here.

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54 responses to "Everything You Need To Know About Tesla’s Lithium-Ion Batteries"

  1. Don Zenga says:

    Thanks for the detailed article, but what about the cost of the battery.

    The last time we read was in Jan 2017 which quoted the average price of battery @ $230 / KWh.

    And another article states the large order @ $140 / KWh.

    http://benchmarkminerals.com/lithium-ion-batteries-are-now-selling-for-under-140kwh-new-york-hears-on-benchmark-world-tour-2017/

    1. Alan says:

      Wasn’t one of those the cost of the pack and the other the cost of the cells only ?

      1. Pushmi-Pullyu says:

        Probably, yeah. And for 2017 prices, $230/kWh seems rather inflated for Tesla packs. I’m pretty sure I’ve seen a quote from a Tesla rep which indicated their pack level prices are now below $190/kWh, and that has been at least several months ago, probably well over a year ago.

        Presumably Gigafactory 1 batteries are even lower cost for Tesla, both on the cell level and the pack level. But we don’t know how much lower, and guesses are all over the map on that.

    2. Tom says:

      The article linked is discussing cells. If the cells are $139 then it’s feasible the battery packs fully assembled with everything are still $230. Nobody knows for sure obviously…well hopefully SOMEBODY knows. Note I’m not making any price claims other than the fact that there exist significant differences depending on what you are counting.

      1. Pushmi-Pullyu says:

        Yeah, the various battery makers and EV makers all keep their battery prices and costs as trade secrets. There are various estimates, but they are just that — estimates.

        The only hard figure we have is that LG Chem was charging GM $145 per kWh for cells (not the finished battery pack) for the Bolt EV. According to InsideEVs’ Jay Cole, LG Chem and Samsung are currently involved in a bit of a price war, so prices may have already fallen a bit below that.

        And keep in mind that price is highly dependent on volume of manufacturing. According to one report, VW has already contracted with LG Chem for a price even lower than that $145/kWh, because VW is contracting for a significantly larger amount than GM.

        I don’t think anyone outside Tesla knows just what Tesla’s cost is for 2170 batteries from Gigafactory 1. Some people think the cost is even lower than LG Chem’s price, but I haven’t seen anything definitive on the subject.

        I think there is a general misperception about Gigafactory 1. Tesla has talked a lot about the Gigafactory cells being cheaper and that the 2170 form factor is a better fit for what Tesla needs than the old 18650 form factor. But this ignores and perhaps obscures the reality that the reason Tesla is spending billions of dollars to build its own large battery factory isn’t to lower prices a bit, but rather so Tesla can control its own supply, and therefore can ramp up Model 3 production as fast as it wants. In the past, Tesla has been production constrained by limited battery supply. Gigafactory 1 will eliminate that bottleneck.

  2. notting says:

    I read all of that in severaly places on the internet. More interesting would be the situation concerning Renault. Couldn’t find e.g. a battery degradation diagram basing on many cars concerning Renault.

    notting

  3. Dr says:

    What about all the other manufacturer batteries. Enough with so much Tesla!!! Maybe rebrand the site as insidetesla and then leave insideev foo ALL Ev’s.

    1. CDAVIS says:

      There is a good reason Apple gets the lion’s-share of the smartphone media coverage… same for Tesla.

    2. Pushmi-Pullyu says:

      Nobody is stopping you from creating your own EV news website. You could certainly ignore Tesla related articles if you wanted to.

      More to the point, nobody is putting a gun to your head and forcing you to click on headlines with the word “Tesla” in them. It’s your choice.

      The reality is that the word “Tesla” in a headline attracts a lot of readers on the internet, and news sites like InsideEVs want to attract as many readers as possible.

      That’s why we sometimes see the word “Tesla” in headlines even when the article doesn’t have much to do with Tesla. But that’s obviously not the case here; only Tesla’s Gigafactory 1 is making the new 2170 cells.

  4. CDAVIS says:

    Of interest is that Tesla will be adding the ability for a used Tesla Battery Pack to go into one end of the Tesla Gigafactory and come out the other end new (recycled). Nearly all the materials that go into Lithium-Ion Batteries can be recycled at low cost (below cost of the materials) if the packs and factory are in advanced engineered for efficient battery recycling… otherwise it’s not cost effective. This means that downstream battery companies that are today designing-in recycling will tomorrow have a lower effective material cost.

    1. Pushmi-Pullyu says:

      It will be good if they can recover and recycle the cobalt from the batteries. The lithium isn’t as important, as that’s relatively cheap and widely available, contrary to all those articles trying to sell you speculative stocks in mineral exploration companies, articles which falsely claim there is a looming lithium shortage.

    2. Doggydogworld says:

      That’s a myth, CDavis. Lithium-ion battery recycling is currently very expensive. Tesla has no recycling capability. They talk about it because that’s what people want to hear, but they’ve not committed to any schedule. Tesla’s recycling claims have less substance than VW’s “great new EVs coming soon” claims.

      1. CDAVIS says:

        @Doggydogwod said: “Tesla’s recycling claims have less substance than VW’s “great new EVs coming soon” claims.”
        —–

        Wrong… the opposite is true.

        Tesla has since as early as 2011 made real substantive (unlike VW’s “coming soon”) progress towards recycling its battery packs and continues to do so with the aim of integrating battery recycling as a direct materials feed source for their Gigafactories.

        “Tesla’s Closed Loop Battery Recycling Program” -2011″:
        https://www.tesla.com/blog/teslas-closed-loop-battery-recycling-program

        “The [Giga]factory will be decked out with a state-of-the-art recycling system and will provide recycling capability for old battery packs.” -2016:
        https://www.google.com/amp/s/amp.businessinsider.com/tesla-gigafactory-facts-2016-9

  5. Warren says:

    The author should mention that these limits apply to discharge rate as well as charge rate, and for any manufacturer’s battery pack. Smaller packs cannot be charged, or discharged as fast as bigger packs, and maintain the same C rate/battery life. So a “50 kWh” base Model 3 cannot discharge, or charge, as fast as the “75 kWh” version. And the “75 kWh” version can’t match a 100 kWh Model S. However, being half a ton lighter, it might not need to, to match its range and performance.

    1. Warren says:

      I should clarify. I am assuming the same chemistry, and construction across the different pack sizes. Obviously, changing the chemistry, or going to thinner foils internally can increase the C rate of a cell. Unfortunately, this is usually at the expense of lower energy density

  6. Bul_gar says:

    What was the energy density of 18650 cells 256wh/kg so for 2170 will be 256*1.15=294wh/kg.
    That means Model s 100d with 2170 will be 1 person lighter.

    1. Terawatt says:

      Your skull density is much too high. He said 10-15% more efficient, not energy dense.

      As I’ve pointed out in another comment, this means the cells are now 95.5-95.75% efficient, versus 95% before. Not quite as impressive consequences as you imagined.

  7. georgeS says:

    “The Tesla Model 3 cars will use the Gigafactory manufactured 2170 cells mentioned above. The larger cells may be able to use more than 4 amperes of charging current which would hasten charging but, because the 2170 cells have more energy storage capacity than the 18650 cells, proportionately fewer will be needed to create a pack with a given kWh rating. (N gets smaller, I gets larger). This means that higher power charging is meaningless for these battery packs. The 4.2 X N X I relationship still applies. It will be interesting to see how these new battery cells perform.”

    and if you compare Model S charging rate to Model 3, according to Tesla they charge at exactly the same rate. 170 miles in 30 minutes.

    You can verify by yourself. Tesla has a calculator on it’s site for Model S. Type in 170 miles and you get 30 minutes.

    That’s the same rate that Tesla quoted for Model 3 specs.

    1. Bul_gar says:

      Model 3 uses 25% less energy per mile than Model S and will need less charge for 100 miles. Even if the charging rate is bit lower will take less time for 100 miles charge.

      1. georgeS says:

        Bul,

        I don’t think you get it. The article says that the 2 cell formats should charge at the same KW.

        That makes sense.

        …but the m3 is a smaller lighter car so it should pull down more miles per hour charging rate for the same Kw into the battery..

        But the miles per hour on tesla’s site says MPH charging rate is the same for the M3 and the MS..

        So the numbers on Tesla’s site don’t make sense.

        1. Terawatt says:

          You seem to be the one who doesn’t get it.

          If you have more cells in parallel you can supply more power (kW) to the pack and still supply the same power to each cell.

          This isn’t hard to grasp. If you charge two batteries at the same time, in parallel, you can store more energy in a given time than if you charged only one.

          A 100 kWh pack made from the same cells as a 50 kWh pack, with the same pack voltage, is in this regard basically two of the later in parallel.

          The power electronics can cope with a fairly wide voltage window, so you don’t necessarily need to design all the packs for exactly the same voltage.

          Model 3 cells, if the chemistry was identical to the 18650s Tesla’s using, ought to take the same C rate and thus about 50% more power. But this would be countered (exactly) by fewer cells in parallel for every kWh of capacity.

          Hence you should still expect pack size to determine maximum charging power. Smaller battery pack but more efficient car may well work out to about the same miles per hour figure.

          Something is however very odd of the long range Model 3 doesn’t charge significantly faster than the standard one. My guess would be Tesla doesn’t want Model 3 to be too obviously better than Model S, in any regard. Even though I suspect Model 3 is the superior car in nearly every way. (Suspect – it is too soon to call. But I sure am looking forward to the reviews as the year draws to a close!)

          1. georgeS says:

            Terrawatt,
            Finally pieced it together. Looks like 170 miles in 30 minutes is the charge speed for the 100D. So Tesla is claiming the M3 310 mile range will charge at the same rate (170 miles in 30 minutes)

            https://www.tesla.com/models/design

            That’s definitely a plus for M3

      2. georgeS says:

        @Bul- gar

        My apology, I mis-read your post. You do get it. That’s basically what I was trying to say.

  8. Morrisg says:

    In the calculation of max charging energy, the author uses 4.2v as the max voltage of charging a cell. This is incorrect as that is the voltage the cell only reaches when it is 100% fully charged. Since fastest charging (constant current portion of the charge cycle) is only achieved during the 0% to 80% region of cell capacity, a better number would be 3.6v for a cell. See a typical Panasonic datasheet and look at the charging graph, green trace is current, flat portion is constant current: https://na.industrial.panasonic.com/sites/default/pidsa/files/ur18650zy.pdf
    Sorry if this is too nerdy.

  9. FISHEV says:

    “The 2170 design is 46% larger in volume than the 18650 and 10-15 % more energy efficient than the 18650 cells, according to J. B. Straubel, CTO of Tesla.”

    That seems to be going backwards as one is increasing volume a three times the rate one is increasing energy efficiency. Seem like 50% SMALLER and 10% more energy efficient would be the way to go.

    More important than volume would be weight. Does the near 50% larger battery weight proportionally more also? Recharge time is very much secondary to weight and energy efficiency as effective EV usage requires ability to charge slowly and cheaply over 10 hours at night.

    One of the fact of Lion battery tech not mentioned is that usage can greatly effect degradation with frequent deep discharges and fast recharges greatly increasing battery degradation, another reason that fast recharge rate is secondary to weight and energy efficiency.

    1. Pushmi-Pullyu says:

      FISHEV said:

      “[quote] The 2170 design is 46% larger in volume than the 18650 and 10-15 % more energy efficient than the 18650 cells, according to J. B. Straubel, CTO of Tesla. [unquote]

      “That seems to be going backwards as one is increasing volume a three times the rate one is increasing energy efficiency. Seem like 50% SMALLER and 10% more energy efficient would be the way to go.”

      No, not really. If you need X amount of kWh, then it’s more cost-efficient — in terms of the manufacturing cost of the cells, as well as the labor needed to assemble the battery pack — to use larger cells. In fact, other auto makers use significantly larger (by volume) cells, but they have to use lower energy density as those larger cells have more problems with overheating during fast charging and fast discharging.

      Sure, increasing energy efficiency is the more important goal, but that can’t be improved by changing the size and shape of the cell. That comes only with improvements in the chemistry and internal design of the cells.

      “More important than volume would be weight.”

      Actually, it’s the reverse. Volume is much more important than weight. Larger cells mandate a larger car to hold them, which drives up the price of the car significantly. Contrariwise, if the car is heavier, you only need to beef up the suspension a bit.

      Sure, a heavier car is less efficient in terms of miles/kWh, but the difference isn’t nearly as great as having to make the car larger. Increased size means a larger frontal area, which increases the car’s drag, and that has a much bigger effect on the miles/kWh rating than making the car a bit heavier.

      Nobody, but nobody, says “Well, I would have bought that car, but the curb weight is too high!”

      1. Four Electrics says:

        Were volume the constraining factor, Tesla EVs would not have a frunk, deep trunk, a flat floor, or space under the rear bench, yet they have all four.

        1. Pushmi-Pullyu says:

          Considering how often you post here, it’s hard to believe you have so little understanding of the subject.

          The Tesla Models S and X are very wide cars for their size. The reason they’re so wide is that gives them more room for a large battery pack.

      2. FISHEV says:

        “Volume is much more important than weight.”

        Not in this universe, at least not for cars and range from energy source.

        In the numbers quoted by the article, the new battery’s negative factors, volume increased by more than its positive factors, efficiency. That would seem to add up to a net negative.

        1. Ambulator says:

          I think Straubel was talking about specific energy where this article mentions efficiency. You’re arguing about a red herring.

          The most important parameter is now $/Wh. Back in the lead acid days it was Wh/kg. I agree with Pushmi-Pullyu that energy density (Wh/l) is next more important nowadays, but it’s close. Both are important. Luckily, with all lithium ion batteries the specific gravity of the cells stays in a narrow region, so if you change one the other will follow.

          1. FISHEV says:

            “I think Straubel was talking about specific energy where this article mentions efficiency.”

            Well we’ll have to go by what was actually quoted at this point which raises the questions.

        2. Pushmi-Pullyu says:

          Well, my mistake for trying to engage a serial EV basher like you in a meaningful discussion. Trying to correct your misunderstanding is casting pearls before swine.

          1. FISHEV says:

            Your constantly resorting to name calling indicates a losing argument. You might want to try a different tactic.

            1. Pushmi-Pullyu says:

              No, your failure to grasp the facts and logic here isn’t an indication that I have lost the argument. It’s an indication that you’re either incapable of informed debate on the subject, or unwilling to admit you’re wrong.

              1. FISHEV says:

                It’s your name calling that indicates you lost the argument. A losing tactic.

      3. Tom says:

        Ah. More on the volume and weight. ‘nobody, but nobody’ might be a little extreme. Surely that happens. However the reverse does happen and has happened to me. In other words the vehicle is too light. I live in the great white north and out sort of on the treeless prairie. This causes winter weather to be vicious and not unusual for March winds to hit 50 mph sustained when the weather warms. Ice, snow, and high wind do NOT go together very well. A main reason of hesitance on full BEV is not the range just there’s no way the heater could keep up with something like some of our weather. But I digress. I have seen cars blown off the road. Not trucks (that’s common)…cars. Happened to my sister in law. I’ve gotten rid of vehicles that were too light. I had a Hyundai Accent for instance. It was a great little car but downright frightening in bad weather. My 2003 Jetta though? Dang that thing was the ticket. Narrow and small car as heavy as a brick. Narrow tires. Narrow tires are WAY better in snow. Later I had a 2009 Audi and it had wide tires and the thing was straight up not able to drive in snow. The car ‘floats’ too much and doesn’t get down to direct contact with the ground as easily.

        My brother bought a Volt though…first one in the state back in 2011 or whatever and despite many people here saying all the bad vibe about a Volt (especially gen 1) it handles winter like a champ. First it has a vital feature (often mocked here) in that if it is very cold out, it insists on running the engine. It needs it for the waste heat to use a standard heater…the only real functional way around here. Second is that the extra battery weight creates awesome traction in snow. He claims it can go through as much snow as his Subaru did. Front wheel drive is ideal for this and the only real advantage AWD will offer is if there’s extra clearance that goes with it ala an SUV. AWD car kind of useless. It handles better in snow but won’t actually go through deeper snow. RWD is a crutch in snow because the front wheels are pushing not pulling.

        Anyway my intention was to buy a PHEV or BEV but my commute was 100 miles and I couldn’t wait until the Bolt came out. At 90 miles round trip there’s no way a Leaf would work in winter. So I was thinking the new Volt 2 but my old car died before the Volt 2 made it here and I bought a used Ford Fusion as interim vehicle in summer 2016 until probably spring 2018 when I figure I can afford a new PHEV.

        I’m still digressing. That Ford SUCKS in wind, on ice, and in snow. Wide useless tires aside, in windy snow/ice situations driving that thing is frightening. It has literally blown to the side of the road before. Why? Because it’s a VERY large car but is light. I’m not sure who is counting ‘mid size’ these days but that thing is as long and wide as my Dodge minivan. Comfortable car…lies about MPG. Anyway Ford made a concerted effort to use high strength steel and all that to reduce weight. As such this vehicle weights about the same as my 2003 Jetta used to. The Jetta was probably 1/3 the size. It’s cross section in the wind was minuscule compared to that Ford.

        In my situation that vehicle cross section you mention is exaggerated and is causing me consternation. I bought it thinking I couldn’t get by with a little Hyundai Accent type vehicle (which is also true) and needed the heft of a ‘real’ vehicle when I meet a semi at 70 mph on a 2 lane road in January with a 30 mph cross wind on ice! Yeah well I think the Hyundai would be better. I even considered looking up an older VW and retrograding back.

        But then Kia has answered my prayers. The Niro PHEV is going to be dead perfect fro me. I will wait. The Hybrid probably in my case would use maybe about the same gas as the PHEV, but I’m counting on the couple hundred extra pounds the PHEV will bring for ‘ballast’. People still put bags of sand in the bed of their trucks around here. Anyway the Niro with its super high MPG and PHEV with a little extra weight and the little extra ground clearance will be just the ticket. One more inch of clearance and AWD would be even better but the lower profile will help the wind thing and result in better mileage. Now why is clearance an issue? Most people even in the north don’t need AWD because realistically they never go out on the road when there is 6 inches of snow on the level…that’s what snow plows are for. But I live on a gravel road 1.5 miles from the nearest road where a plow will go. It takes a week sometimes for the snow plot to get to us after a snow.

        Anyway…cross section matters….a lot.

        Oh and I will be getting the 16 inch wheels not the 18 inch. Learned my lesson on wide, low profile tires which always accompanies the larger diameter.

        Oh and the BMW i3 tires everyone hates? Some articles I’ve read point out their high grip in snow. They have a large longitudinal contact patch.

    2. Bul_gar says:

      I think J.B.Str. means that one 2170 cell 3.6V will have 7Ah. For example one 18650 is 3.6V 3.4Ah

      1. Muchski says:

        That’s how I understood it too. More volume means you can fit more anode and cathode in too. Cylindrical batteries are essentially sheets of anode, separator, and cathode rolled together, electrolyte, added and then sealed.

        The chemistry inside of the 21700 represent a jump in energy density of 10-15% over that used in 18650.

        I realize there is a difference between volumetric density or by weight with most people quoting the latter for specs.

        Let’s assume roughly 46% more energy density by kg as well for the purposes of comparing the cells. Not only would that give you 46% more room too stuff in anode and cathode but they’ve also achieved a boost in energy density by 10-15%. Basically even more ene ft density and lower cost.

        It would be silly to occupy almost 50% more space and only increase energy density by 10-15%. Clearly they would have stuck with 18650 if that was the tradeoff. JB and Elon have stated the 21700 is an optimal size for capacity and cost:

        “Straubel said that Tesla has spent a long time thinking about battery formats, and had questioned why the 18-650 lithium-ion battery had become the standard. Its standardization was “an accident of history,” said Straubel.

        Instead, Musk said that Tesla thought about what would be the optimal battery size to produce the product Tesla wants, if no battery standard existed. They say after much consideration they realized that would be the 21-70.

        “It really comes from the first principles of physics and economics. That’s the way we try to analyze everything,” said Musk.”

  10. orinoco says:

    Comment on “Search for the Super Battery”:
    When it comes to the battery scalability necessary to buffer the green power grid, I’m convinced you can forget about all the battery types presented in this documentary.
    They do not scale as you have to produce or manufacture the matter that stores the energy. Nothing more than the tiny drop in the bucket compared to grid power.
    Actually there is another one that is not just truely scalable, it’s really “think big”.
    It’s the gravity or hydraulic rock storage as design by Heindl. It actually lifts and lowers a piece of rock with the size of a mountain with standard pumped hydro storage technology. And the bigger it gets the more the costs per kWh-capacity drop as the capacity raises by the power of 4(!), but total costs only by the square of the radius of the rock. This way cost can drop to about 10$/kwh(cap). Just google it.

    1. Pushmi-Pullyu says:

      I’ve read about the concept, but so far as I know, nobody has built even a small-scale prototype.

      There was a company called Isentropic Ltd., a startup touting energy storage using heat differential in gravel-filled silos. It was an interesting concept, one which could have been built almost anywhere. I had hopes that they could succeed in commercializing the tech, but I see they have gone bankrupt. 🙁

      Anyway, I think we have yet to see the “killer app” for grid-scale energy storage. I can’t understand why flow batteries aren’t being used; it seems to me those are a much better fit to large-scale grid energy storage than li-ion batteries. I’m guessing li-ion batteries are currently being used for that only because they are made in such quantities that it’s actually cheaper to use those, even though they aren’t really a good fit to the needs of large-scale grid energy storage.

    2. Doggydogworld says:

      Or just haul rocks up and down a mountainside 🙂
      http://www.aresnorthamerica.com/grid-scale-energy-storage

      1. Pushmi-Pullyu says:

        Very interesting, thanks! I’ve never seen such a proposal before, and it looks far more practical than the idea of raising and lowering a mountain-sized granite plug, which I’ve seen proposed elsewhere.

        I’d love to see a cost/benefit analysis of this proposal.

  11. Paul K says:

    I wonder if grid storage would be a good application for hydrogen cells. Wind and solar could be used to “break” water into hydrogen and oxygen when their power isn’t needed by the grid. When demand is high the hydrogen could then be consumed in the fuel cells. I’m not knowledgeable enough about the chemistry to know if this would be cost effective.

    1. Ambulator says:

      At the moment it is both too expensive and too inefficient, but if the fuel cell advocates are right it could be viable in the future. Much more likely than running cars on hydrogen.

    2. Pushmi-Pullyu says:

      Basic physics prevent hydrogen from being a useful energy storage mechanism. The best you can get, round-trip, from using hydrogen to store energy is about 50-60%. In other words, that’s throwing away about half the energy you want to store.

      In fact, hydrogen is just about the worst, most inefficient way to store energy from excess electricity. This is well understood by everyone who has a good grasp of the fundamentals of science. This won’t change in the future, because the limitations are imposed by basic thermodynamics and the physical/chemical properties of the hydrogen molecule. This isn’t mere opinion; it’s well established fact.

      The only reason you see the idea promoted so much is that Big Oil uses it as a propaganda tool to distract from investments in battery-powered cars and renewable energy.

      https://phys.org/news/2006-12-hydrogen-economy-doesnt.html

      https://web.archive.org/web/20150419031629/http://www.energyandcapital.com/articles/hydrogen-economy-fuel+cell/480

      1. FISHEV says:

        Actually hydrogen gets promoted for a lot of good reasons.
        1. Essentially free resource.
        2. Can easily be produced via free solar energy.
        3. Has equivalent energy content as gasoline. 1 kg of gasoline having 117 MJ a gallon, 1 kg of liquid hydrogen having 120MJ a gallon.
        4. Liquid hydrogen can burned in ICE engines with slight modification.
        5. Liquid hydrogen volume is 3.6 times that of gasoline, a 15 gallon tank becomes a 54 gallon tank(s).
        6. It is non polluting.
        7. It allows fast refueling.
        8. It is easily transportable.

        The storage tech exists, it would require the redesign of the car around the extra 38 gallons of storage, no different than redesign to accommodate batteries.

        The only real downside to hydrogen is building the solar distilleries and pipelines and the retail gas station system.

        Electric and oil have these infrastructures in place.

        Where hydrogen will likely start to be used to get to the non-fossil fuel points of 2025 is the resource issues with Lion batteries. We have enough for the limited current qty but if every car and light truck were to have lion batteries, it is not clear the resources exist to do that on year to year basis.

        BMW H7 being the model.

        But a different discussion.

      2. Doggydogworld says:

        Pushmi – I also obsess over efficiency, but it’s not really important for renewable storage. Large scale wind and solar are now 2-3 cents/kWh. Storage is 10+ cents/kWh. A 3 cent/kWh storage method would be a big win even at 50-60% efficiency. Not saying H2 can do 3 cents, but if it (or some other method) does it will beat batteries hands-down for grid-scale storage.

        It’s actually even better than depicted above, since cheap storage lets you oversize solar such that output becomes high enough to meet demand earlier in the AM and later in the PM.

        1. Pushmi-Pullyu says:

          You argue your case well, Doggydogworld, but there is a rather large hole in your logic:

          Even if the electricity itself is cheap, the infrastructure needed to store that energy is very far from cheap! That’s true whether it’s banks of battery packs or banks of electrolyzing hydrogen generators plus H2 storage tanks linked to fuel cells.

          And the less efficient the round-trip operation is, the more you’d have to spend on buying infrastructure. If the round-trip efficiency is only 50%, then (assuming equal per-kWh storage costs) you’d need to spend 60% more than you’d need to spend if it’s 80% efficient, to store the same number of kWh.

          That is a difference that no competent businessman is going to ignore.

          1. FISHEV says:

            But building the infrastructure was not a problem for oil or electricity and it won’t be for hydrogen.

            There is already substantial infrastructure in place. You see liquid gas tankers on the the highway right next to gasoline tankers. Storage tanks, pipelines, refineries, distribution systems already exist and would be expanded.

  12. Ambulator says:

    This article tells me nothing about Tesla batteries that I want to know. Is NCA still being used? What are the specific energy and energy density of the cells? Of the packs? What do they cost, both for cells and packs?

    Of course, Tesla seems to be keeping much of this secret, but that’s the information the title seemed to promise me.

    1. Pushmi-Pullyu says:

      Yeah, it’s much more of a “…for Dummies” article than an actual “Everything you wanted to know” article.

    2. Alex says:

      Is it because major funder of the movie is David H. Koch Fund for Science?

  13. Pushmi-Pullyu says:

    Tom said:

    ” ‘nobody, but nobody’ might be a little extreme. Surely that happens.”

    Well, I admit I hesitated before writing that glittering generality, claiming that literally nobody makes a buying decision based on a car’s curb weight being too high. One might, for example, cite a case of someone who lives past an old wooden bridge, and thus may have a very real limit to how heavy a car they would consider buying. But hey, at worst I’ve opened up the possibility of some interesting discussion of the exceptions. 🙂

    “All generalizations are false, including this one.” — Mark Twain

    But this is rather out of context to the subject under discussion, which is whether or not weight is an important consideration in modern EV design, or more precisely, if it’s really an important influence on the car’s energy efficiency in the way that the aerodynamics (drag) of the car is.

  14. Priusmaniac says:

    In the film, the interesting thing with Amber Kinetics http://amberkinetics.com/products-2/ is that it comes down to finding the material with the lowest dollar cost per tensile stress unit (tau/$).

    They choose steel, but it is not certain that it indeed correspond to the lowest possible value. But even so, with steel at roughly 0.5 $/Kg and 32 KWh stored with 2500 Kg, it gives a cost of 39 $/KWh.

    Of course that goes up a bit for the system and mainly because of the need for a pressure resistant enclosure.

    But ironically once again, like for rockets remaining the only non electric vehicles, in space, since vacuum is free that cost is disappearing. So on Mars or on the Moon it would be cheaper to store energy in a flywheel than in a battery.

    Moreover finding iron on Mars is going to be way easier then Lithium, Nickel and Cobalt.

    The lower gravity would also be beneficial since magnetic weight compensation would be reduced.

    No special required operating temperature is also a bonus.

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