Why Tesla’s Metal Air Range Extender Patent Seems Pointless to Us

4 years ago by Eric Loveday 48

Tesla's Metal Air Patent Drawing

Awhile back, Tesla Motors filed a patent for a range-extending metal air battery (link to patent filing here).

Would One Be Willing to Pay Says $10,000 More for Even More Range?

Would One Be Willing to Pay Says $10,000 More for Even More Range?

Though Tesla filed the patent, we don’t see why the automaker would consider pursuing such a device for use in its vehicles.

Here’s the patent abstract:

Abstract: A power source comprised of a first battery pack (e.g., a non-metal-air battery pack) and a second battery pack (e.g., a metal-air battery pack) is provided, wherein the second battery pack is only used as required by the state-of-charge (SOC) of the first battery pack or as a result of the user selecting an extended range mode of operation. Minimizing use of the second battery pack prevents it from undergoing unnecessary, and potentially lifetime limiting, charge cycles. The second battery pack may be used to charge the first battery pack or used in combination with the first battery pack to supply operational power to the electric vehicle.

The problem is that metal air batteries basically self destruct over time.  Repeated use renders them absolutely useless.

It’s believed that metal air battery technology is at a stage where only approximately 100 charge cycles can be endured before the battery itself is useless.

So, why would Tesla fit an expensive second battery pack to one of its vehicles to increase range?  The answer, at least to us, is that Tesla won’t do this.

The Model S already has more range than anyone could ever desire and we believe that few, if any, buyers would opt for say a $10,000 range extender with an extremely limited lifespan.  And, once depleted, how many Model S owners do you think would whip out another $10,000 for a replacement range extender when they realize they seldom used the original one?

The Model S needs no range extender.  Perhaps other electric vehicles out there with only 80 or so miles of range could use some sort of range-boosting device, but not the Model S with its up to 265 miles of EPA-rated range.

There’s other arguments that could be made against this use of metal air, including that the vehicle’s primary battery pack would have to be made smaller (hence reduced range prior to the kick in of the range-extending battery) to allow room for the metal air.

Upon seeing this patent filing, we thought it immediately absurd.  We know that Tesla will never drop an ICE range extender in one of its vehicles, so the use of a second battery to extend the range would be fitting of Tesla’s promise to remain completely electric, but this metal air tech just ain’t the way to go.

Agree?  Disagree?


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48 responses to "Why Tesla’s Metal Air Range Extender Patent Seems Pointless to Us"

  1. David Murray says:

    I’m going to say it would greatly depend on the cost of this battery and the amount of extended range it could offer. Take my Chevy Volt, for example. With the 40 miles range on battery I only burn gas about once every 6 months. And in most of those cases I could probably avoid it if I wanted to sit at a charging station long enough. So if a Tesla had over 100 miles range on the primary battery, and if the extended range battery offered another 300 or 400 miles… That would be pretty cool. I could see how a person might go 10 or 20 years before cycling the extended range battery 100 times.

    So yes… I could definitely see this as a viable strategy as long as the price and amount of extra range is right.

    1. s says:

      Completely agree with David as a fellow Volt driver. I would absolutely buy a gen 3 Tesla with a 100-mile main battery range and a 200-300-mile extender metal air battery. I assume that would be lighter and cheaper than a 250-mile mini Model S.

      The main advantage as I see it, is that you would get more out of your 30-40 kWh pack if you don’t haul along another 40kWh just to go the extra distance a few times a year. Of course, that’s a moot point if it turns out that the metal air battery is as heavy and as expensive as the lithium-ion battery.

  2. Mark H says:

    I am not going to poo-poo any range extender or any battery chemistry at this early point in the industry.

    Not looking at applications outside of 3 sigma (so don’t bust my chops), but given the mean driving distances, the main battery pack only needs between 40-80 miles to handle 80-90% of US drivers which makes up the bulk of BEVs and EREVs.

    The cost per kWh may make it moot in the end in favor of a big battery, but for now even with the current metal air technology one could have the extended range once per month for ten years. Not implying that metal air is ready for prime time or the best choice, just sayin that if you have enough time and money the final battery/extender could arrive as the EV industry becomes mainstream.

    Lastly, if Tesla felt it was worth filing the patent, it is probably a few notches above absurd.

  3. scott moore says:

    Metal-air batteries (lithium-air) are all potential at this point.

    Come on, that was funny….

    1. Bonaire says:

      Quite ReVolting

      1. James says:

        Maybe a FUSION of the technology?

  4. Loboc says:

    The battery may be a throw-away aluminum-air which could be cheap enough for this application. Once the aluminum is gone just ‘fill-up’ with a new one.

    ‘Outside-the-box’ is Elon’s middle name. I wouldn’t put down anything he tries.

    1. Mark H says:

      ‘Outside-the-box’ is Elon’s middle name. I wouldn’t put down anything he tries.

      That’s really the take away here. Extenders are wide open to possibilities. If you have an EV like the BMW i3 getting 80+ miles you really start to limit the needs and change the requirements for the extender. I can see Tom Moloughney now converting his i3 to run bio-fuel from his restaurant!

      So yes, considering a battery of a different chemistry for the extender is on the table.

    2. Dr. Kenneth Noisewater says:

      Indeed, having 50mi worth of primary battery power and an additional 1000+ worth of burning aluminum for fuel could be cheaper combined than a 300mi battery, it’d certainly be lighter. Presumably there’d be enough water onboard for the Al-Air battery reaction so that you would change it out on an interval that’s compatible with the extended-range battery.

      An efficient onboard SOFC that could get 20-25kWh usable out of a gallon of gas would be a fairly compelling proposition that GM could use to compete against EV-only Tesla. My Volt shows about 18kW while doing 70mph on flat terrain, which is about 78mpg at that speed with 20kWh/gal SOFC.

      However, if we really do get LiS batteries with energy mass-densities within 50% of gasoline, and 250kW burst charging, that’s when the lights start dimming on ICE if you ask me..

  5. GeorgeS says:

    This concept could make sense,

    It can just be looked on as a Hybrid battery pack.

    Envia for example has a high energy density but it has low cycle. so.

    Use a chemistry that has high cycle life but lower energy density for the first 50 miles and recharge this part of the pack on a daily basis.

    Then have a high energy density battery (with low cycle life) in the background that can be used in the case where one exceeds the 50 mile/day rule.

    It doesn’t have to metal air it just needs to be a chemistry with high energy density and low cycle life.

  6. jzj says:

    Everything is a compromise of some sort: the question is what you’re trying to achieve. We want zero safety issues, unlimited range, at no cost, with no weight, and with ideal convenience: in other words, the perfect battery. What we have now are batteries with fairly limited safety issues (certainly when compared to gasoline), some amount of range limitation, at significant cost, that are expensive, and may eventually need to be replaced. And, so, we think to come to a compromise that works around the limitations in our available batteries. For many considering an EV, range is the first stop in the compromise negotiations.

    If you value tremendous range, then a range extender of some sort is a great idea. Will it introduce risk, and cost, and weight (and volume), and inconvenience? Yes. So, just try to limit these downsides. If a metal air battery is a better way to do this than a compact ICE, or a microturbine, or a sterling engine, or a fuel cell, or whatever else you can think of, then go for it.

    For my part, I prefer to assume that battery technology will continue to evolve toward greater perfection. Perhaps by the time you devise the optimal compromise range extender, batteries will be safer and cheaper and more powerful and smaller and lighter and longer-lasting. If this evolution does take place, perhaps the idea of range extenders will fall aside.

    The issue, really, is adoption of EVs with the good but imperfect compromise of today’s batteries.

  7. GeorgeS says:

    Thinking about this some more. This very possibly be what Tesla has up their sleeve for the 35000$ 200 mile model E.

    1. Bonaire says:

      Right – it could be a 100 mile car with “100 mile range extender short-life pack addon optional”.

      1. Rick says:

        Or, the range extender could get 400 miles, one that doesn’t get thrown away after 1000 miles, one that uses a cheap fuel that is readily available, … no wait, that’s petroleum. Never mind.

  8. Anthony says:

    The only problem with this patent is that metal-air batteries wont be ready until 2020-2025, which means this patent will only have about 8 years of useful life (2025-2033).

    By the time metal-air batteries are feasible, I expect Lithium-based batteries to be around 600-700Wh/kg (probably Li-S), with metal air batteries being twice that. It makes sense to patent this approach, but I don’t know if it’ll work out. It really only seems workable if Li-Air batteries are super cheap by comparison to the state-of-the-art battery of the time. A Model S sized vehicle with the same battery cell mass at 600Wh/kg would be 600+ miles. You could drive for 8 hours at 75MPH – do you really need more range than that, given how long it would take to recharge the batteries?

    1. Bonaire says:

      Li-S will “rule the EV space” about by 2020.

      1. GeorgeS says:

        but doesn’t Li-S do poorly in cold climates?

        1. Bonaire says:

          With bigher energy density and grid connectivity, should do fine in many climates. It is not that one battery must span all climates, though. The point is to apply proper tech appropriately. Some Li Ion batteries will do better in the cold, so run them there, if Li-S works in warmer climates, and this is where most of the population lives, the Li-S sounds like a winner.

      2. Anthony says:

        Speaking of Li-S, Oxis Energy (UK) revamped their website and posted a roadmap with 400Wh/kg and 400Wh/L Li-S cells in 2016.


    2. Dr. Kenneth Noisewater says:

      Incidentally, lithium borohydride is more energy-dense than gasoline, and presumably a hybrid with a rechargeable battery and non-rechargeable (but recycleable) Mg2FeH6-LiBH4 system could have enough onboard for 3000mi, and have routine service to change it out after it’s used, with dealers recycling the used battery materials or sending them off to be ‘recharged’.

  9. miimura says:

    It doesn’t make sense to you because your assumptions are way off base. How about this? Start with a 40kWh Model S that has 140 mile EPA range on the lithium-ion pack only. The Metal-Air option brings the cost up to the same price as the 60kWh model. The Metal-Air battery can add 1,000 miles total over its life. However, it can be “recharged”, actually re-built, with new metal for $250 which gives another 1,000 miles at a net cost of $0.25/mile. If you can do 95% of your driving within the 140 mile lithium-ion range of the car, the Metal-Air battery would last 20,000 miles.

    1. GeorgeS says:

      Yes that is what I posted a little earlier. You just make a hybrid pack. Conventional Li batts with high cycle life and cost for the pack that gets used daily. Then put a high energy density low cycle life low cost pack in the background for the case where you exceed 50 miles/day.

    2. Veselin says:

      +1 All I need is 200km (120m) litium-ion BEV with some sort of range extending battery that I’ll use about 5-10 times per year. Most of the people I know need the same.

  10. Bret says:

    This approach makes all of the sense in the world to me. Like most Americans, I just drive to work and back most of the year, but head out on vacation during the summer. I would definitely purchase a Metal Air battery, instead of hitting a bunch of fast charging stations, every 250 miles. I’m pretty sure many others would as well, provided the battery is affordable.

  11. ItsNotAboutTheMoney says:

    – cheap (purchase cost)
    – short life
    – inefficient
    – low power density
    – high volumetric energy density
    – high gravimetric energy density (lowers as it is used through oxidation.)

    It has potential as a range extender for infrequent use since the vehicle weight and cost are both reduced. Use has to be infrequent because it’s inefficient and has a short life.

    So I’d still want it paired with a relatively large battery. 24kWh not quite, 40kWh yes.

    1. ItsNotAboutTheMoney says:

      But, do note: low power density implies slower charging. So, I still don’t see this as a long trip car.

  12. kdawg says:

    “The Model S already has more range than anyone could ever desire”
    Speak for yourself. More is better. If you had a 2000 mile AER battery, you could charge once a month. Or you could drive across the country on a single charge w/no worries of finding chargers on the way.

    Yes, this is “out there”, but why limit yourself, if batteries keep getting cheaper and denser? Maybe they won’t even be called “batteries” eventually. You’d need something that holds 600kWh of electricity. That seems like a lot, but if you consider a 20 gallon tank of gas holds 670kWh of energy, it’s not that crazy.

    1. Veselin says:

      20 gallon tank of gas holds 670kWh of energy

      Yes, but ICE efficiency is 20-25%

    2. Schmeltz says:

      “The Model S already has more range than anyone could ever desire”…yes KDawg, I saw that too. Since when is 265 miles of range “more range than anyone could ever desire”???

      Eric, I’m sorry man, but what were you smoking when you wrote this article?

    3. Christopher says:

      “The Model S already has more range than anyone could ever desire”

      This is a crazy, limited perspective view! I would argue it’s much more accurate to say that 265 miles of range is less than what most people desire. Yes, of course, most people will normally get by with much less on most days, but when you’re traveling long distances and the superchargers are not on your path of travel or there is not any charging at all at your destination (perhaps not even any electricity, think hiking/backpacking destinations) then you’re going to want much more range on board. Or you’ll have to resort to renting an ICE vehicle once again. Yes, 265 miles range is a great achievement for now (despite the expense), but more will be necessary — and will come in time.

      1. Christopher says:

        You might as well be saying, famously, “64K is all anyone will ever need…”

  13. Francis L says:

    Phinergy has a working solution : a non rechargeable metal-air battery. You can do 1000 miles with 50 aluminum blocks. When a block is done, you just switch it. The question remanning is : how much will it cost?

    But compare to GM and BMW solution (add an ICE extender), this solution has a good advantage : it is really easy to maintain compare to an ICE! And lets remember that the Rex extender isn’t cheap neither!

    So, if you can have a 150 miles battery + Phinergy solution + supercharger, this could make a really good and cheap solution for most of customers.

    1. Dr. Kenneth Noisewater says:

      Silent, no vibration, no emissions, mechanically simple and reliable. All it really comes down to is the cost, and if they can get it to 10 cents/mile or less it’s a contender.

  14. Ocean Railroader says:

    I remember Tesla is using ether 3100 or 2800mAh batteries while I have seen batteries that are rechargeable and the same size that are 3400mAh and even a few 4200mAh and there is even a 5000mAh type out there in a cylinder form. Tesla could up battery capacity by going up from 3100 to 4200 which or if they had a battery break though at 5000 that could add some range to the car with out any real changes in the tech of the car.

    1. René says:

      Most of those mAh written in generic chinese batteries are imaginary. The real capacity is more like 2000 ~ 2400 mAh. Some good cells have a little over 3000mAh, but are very expensive per Wh.

  15. Bill Howland says:

    My tack on this is its another “unpatentable” idea that just got a patent. Like that “Reductive Charger” the tesla Roadster uses that I think would be so obvious an Idea that it couldn’t be patented.. But it was.

  16. Aluminum is so cheap that we throw it away after drinking a few ounces of soda or beer from it – once. (Unless you recycle your own cans, you pay the 5 cents and still toss it. Hopefully you put it in the right bin and someone recycles it downstream).

    Point is, a Phinergy type aluminum air battery could be very, very cheap to reload.

    If, as Miimura pointed out, this was used as a range extender for those rare times it was inconvenient to charge, the cost would be negligible over the life of the vehicle.

    It would likely be a whole lote more efficient than dragging around an ICE.

    What would the value be of having a very safe 100 miles of spare range at all times?

    1. GeorgeS says:

      Oh and PS.
      Hi energy density and low life is what Tesla’s 18650’s are all about.

      Just make the pack huge and cycle life can be as low as 500 cycles.

      You know what I mean Vern?

      Who would’a thunk

    2. Dr. Kenneth Noisewater says:

      IIRC the spot price for Al is currently around $2/kg. Phinergy says they can get 8kWh per kg of Al, so that’s ~$0.25/kWh for the raw materials. In an EV that gets 3mi/kWh call it 8 cents per mile. Presumably there’s markup involved but the Al plates are entirely recyclable so service intervals can probably be done at negligible cost and with core charges swaps could probably be quite a bit cheaper.

  17. JakeY says:

    Tesla is filing this patent while metal-air tech is still being developed.

    And most likely the way Tesla will be using this tech is with a smaller battery size (like 40kWh) and combining with a large capacity metal-air battery. That would keep the costs lower and makes more sense than what you are predicting (combining the largest 85kWh pack for an even larger pack).

  18. Priusmaniac says:

    That sounds to me as quite the contrary, it is very interesting. An extra metal air battery as range extender is interesting because since longer range is less frequent, you can thus accept a shorter cycle number battery to do the job. This is especially true if the battery has a lower $/KWh cost then the main battery.
    In a way there is no sense in using a range extender battery that would have the same cycle performance then the main battery because you would have a mismatch in life expectancy between the main battery and the range extender battery.

  19. Steven says:

    Dumb question… Who says it’s for on-road use?

    1. ItsNotAboutTheMoney says:

      The first image with wheels and drivetrain?

  20. Anderlan says:

    Many of these Tesla guys are computer hardware guys. ANY computer or storage module (like an SSD) has memory arranged in strangely complicated ways that seem trivial to a layman but have to do with optimizing cost, speed, size, number of use cycles in typical lifespan, refresh rate-if any, and potentially hundreds of other variables. Now they surveying all current battery technologies and research paths and are replacing data storage with energy storage in this type of thinking. This patent surprises me not at all. http://www.youtube.com/watch?v=wxlhyX-4qKI (over the top but obligatory and funny 🙂

  21. Schmeltz says:

    I’m coming in here late on this thread but wanted to weigh in anyway. I am just suprised at the stance taken against the patent’s concept. Personally, I think it is brilliant. I’m not an insider, but then again I doubt anyone else is here either. So, why are we positive at this early stage of developement that all metal air batteries are good for 100 cycles or less? Even if that is indeed true, why wouldn’t the above concept be a good set-up? Say for example, the best metal air battery is good for a max. 100 charges. So if a customer uses the range extender metal air battery maybe 100 times in 5 years until it’s spent, and then swaps for a new one in and out, he’s good to go for another 5 years or so. What is so crazy and “absurd” (InsideEv’s words, not mine) about that? I’m not trying to be a defender of Tesla or metal air batteries, but it puzzles me a pro-EV site like this calls a new idea “absurd” when very, very little is known about it.

  22. jumpjack says:

    If metal air will allow 500 miles per cycles as promised, this will mean 50.000 km lifespan, but it will be used only in (rare) cases of long trips: supposing 10 long trips per year and 100 cycles lifespan, battery will last 10 years.
    Having low-lifespan and high-lifespan batteries separatedly replaceable is a very good idea.

  23. Andrei says:


    I consider this to be a very good idea, I would love to buy a gen 4 vehicle, a very chip Tesla Model E (from example), at a price up to 15k Euro ( 20k $ ) with a range of up to 160 km (100miles) and an electric range extender, because my every day needs will be fulfilled by that range. I will use electric charging station from highways for the trips between cities and only use the range extender in vacation or in very long trips. A 100 times “long range mode” will be more then sufficient for the life of the vehicle (even with a life of 7 to 10 years), because I do not do more then 3 or 4 long trips in a year (4 x 2 =8 charges) and maybe 1 or 2 trips in very remote areas without any access to electricity.

    For me this will be the ideal one car (without the need for a second car used in vacation) Even now I have to carry my fuel when I go to the mountains, to the sea or to the delta (remote areas).

    Best regards,

  24. Brad B says:

    I did a bit of study 6 months ago when I first saw the Tesla patent Mr. Loveday mentions in this article and what I came up with seems to make such a method quite logical and quite workable. The Metal air battery I believe Tesla has in mind is either the Phynergy Aluminum Air battery or something like it, that consumes the aluminum and has approximately the same energy density by weight as gasoline and takes up about half the space as gas because of its density. Most cars have a gas tank under the back seat and the Tesla has a flat battery, and to the best of my knowledge, this leaves an empty space under the seat above the battery. I think Tesla is planning to use that space as yet another range anxiety relief system, by placing an aluminum air battery and its small but required water tank in that space in the Gen three car. This will provide the new car with 1000 miles of additional back up range, and take 5 fill ups of water to consume the aluminum plates. This will be a very inexpensive battery to produce and will require plate replacement every thousand miles of use, which would be done by Tesla and would require the removal of the primary battery to access the range extender battery. That would be quick swapped with a reloaded pack. The whole thing could be done in 5 minutes if automated and add about 70 lbs to the car. My guess is that the Gen three car will have a main battery range of at least 300 EPA miles on a charge. This is based on the current improvement of lithium Ion commodity battery technology and its likely progression by the 2017 introduction of the Gen III with 18650’s having 5000 mAh capacity as noted by Ocean Railroader. And for those times when you go off the beaten path you could do so with out worry, away from superchargers, as many of us like to do. You would have this backup battery you could call on at any time and charge the main pack faster than you could use it. This would give you an unrecharged range when needed of 500 miles, and with the addition of a couple gallons of water, more emergency backup up range, up to 1000 miles. This is all very possible and I believe that it is likely Tesla will do it if there are no near term battery breakthroughs. They probably would not do it if Envia’s battery technology becomes successful or others. The Envia would give the Gen III car with a full size bottom of the car, Model s style battery, a 750 mile range on a charge, negating the need for a backup battery. The same is true if Lithium sulfur, lithium silicon nano particle, lithium silicon nano wire, lithium air or a number other technology as they become perfected. But if not, this is their ace in the hole, to make their cars better than any ICE car in practicality and convenience with Super chargers, battery swap and long distance backup battery, The ability to fill at home and 300 mile main pack range with 1000 mile backup range any where you go. This will make Ice cars obsolete, making a mass market for the Gen three product.