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Fast charging batteries, technological barriers?

Discussion in 'Electric Vehicles' started by eyedrop, Apr 27, 2018.

  1. eyedrop

    eyedrop Member

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    #1 eyedrop, Apr 27, 2018
    Last edited: Apr 27, 2018
    I've always heard when designing a battery, compromises have to be made. You cant have light weight if you want large capacity, cant have fast charging if you want longevity, etc...

    But Im wondering if automakers and consumers are too focused on range. Its always the first question people ask about my car.

    When I ask about the range on their gas car, they often have no idea and never even considered it during the purchase. In fact, most magazine and YouTube reviews on gas cars dont even mention the word range, because it really doesn't matter.

    Ive never heard of a motorcycle rider with range anxiety, despite the small fuel tanks. My Dad recently calculated that his old HD Sportster that hes had for 20 years only gets about 120 miles of range. Its never bothered him.

    Is it possible to design a battery that compromises capacity and instead focuses on highest charge rate possible? I would gladly take a super light weight, lower cost model S with only 100 miles of range if that meant I could charge in just 3 minutes with 120,000 locations to choose from.

    And when will 350kW charging make it to the low cost EV's? If I were Nissan, I would have kept the 24kWh battery but liquid cool the crap out of it and support 350kW charging rate. This would keep the cost of the car down, weight low and efficiency high. Then I would build out a massive 350kW DCFC network along highway long distance travel routes and watch the cars fly off the shelves.

    This seems like a good recipe. But am I missing the reason why this hasn't happened yet?
     
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  2. Tiger

    Tiger Active Member

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    It's a chicken-and-egg problem. If there are no electic cars to begin with, it is quite costly to bite the bullet and buld a dense enough network of charging stations. In such scenario (current situation), range is king (for example we do not have any superchargers in the whole baltic region). Vice versa, it is a hard sell to sell a car with short range in such a scenario. Also, for example, in crisis situation, you can pack additional gasoline into your car, but you could not pack more charge.
     
  3. R.S

    R.S Active Member

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    Like you mentioned there is always some trade off. But often it's fast charging vs energy capacity. And people still care a lot about the range number. Also, since there still isn't a charging network even comparable to today's gas station network, people will prefer not to have to charge somewhere.

    In general faster charging batteries, with a sufficient fast charging network, would be good. Because nobody really needs more than 200 miles of range, if they could quickly recharge. And then we could have smaller batteries, which cost less to produce, generate less waste (the battery is the biggest part of the carbon footprint, aside from carbon emitted through charging, which could be 0).

    I personally think that we will see, as some point in the future, a reversal, where charging speed, in miles per minute will become more important, especially for people that can't charge at home. But as long as EVs are still mostly for wealthy suburbians, range will be king.
     
  4. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Well-Known Member

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    #4 ItsNotAboutTheMoney, Apr 30, 2018
    Last edited: Apr 30, 2018
    Capacity ~ range ~ power ~ charging rate ~ 1/C rate

    Lower capacity makes life much harder for a battery.

    Also note that while much faster charging would reduce charging time, if you reduce the range, you also have to use public charging _more_, which is a logistical and experiential challenge.

    Higher capacity makes it easier to make a battery with low cost per kWh, and the additional range reduces the number of public charging stops (each of which requires a diversion) , increases fault tolerance and increases tolerance to extreme weather.

    People sometimes write that adding battery capacity has diminishing returns, but the charging challenge means that there are disproportionate benefits to reducing the proportion of total miles and reducing the proportion of trips that require public charging.
     
  5. bxr140

    bxr140 Active Member

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    Small tanks on motorcycles are a bad example. Besides being a source of anxiety in some situations, in context of your thesis they’re absolutely a source of annoyance.

    Stopping every 75-100 miles for any amount of time when you’re traveling somewhere is simply not an adoptable solution.
     
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  6. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Well-Known Member

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    Oh, also:

    350kW / 0.2kWh/mi = 1750mi/h (charging)

    5gal/min x 25mpg/gal x 60min/h = 7500mi/h (refueling)

    Even at 350kW, charging an efficient BEV would be 4 times slower than the refueling of an inefficient gasoline vehicle.

    Now, that doesn't mean that there wouldn't be a market. There would _absolutely_ be a market. But it's technically extremely difficult to get lots of energy very fast into a small battery and have that battery last.

    Note that it will be the expensive, high-end Mission E with a large pack that will have the >150kW DCFC.
     
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  7. scaesare

    scaesare Well-Known Member

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    Sure. There are battery chemistries that allow for charge/discharge rates 10-20C or more. (The "C rate" is typically defined as a battery charging/discharging it's full energy capacity in an hour). That would imply getting a charge in the neighborhood of 5 minutes or less.

    There are some batteries used in RC cars and other applications today that do this.

    Probably. The issue usually lies on some other aspect of performance that ends up compromised. Cells with high C-rate capability usually don't have good energy density. Or are expensive. Or don't have good cycle life ( a real killer for EV's). Or it may suffer from several such simultaneously.

    That's not to say there aren't some cars that have biased their design around faster charging... the Ioniq is one of them. How well they fare remains to be seen.

    Here's a decent comparison of the axes of performance for various li-ion chemistries: Battery University.
    As for the 350kW stations... there's something like 1, maybe 2, out in the wild. But nothing that can really take advantage of them yet... for much of the same reason discussed above: Any vehicle currently capable of accepting that kind of charge either would have to have a battery 2-3X larger than the largest EV's today, or employ a chemistry that may not really be well suited for EV's.

    There are some other holdups with 350kW charging... amongst them is a jump in pack voltage that we really haven't seen adopted.
     
  8. renim

    renim Active Member

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    Japanese Mitsubishi spec iMIEV for a while had option of special batteries from Toshiba (SCiB) that could charge at about 6C rate.
    problem is, range was almost halved. (capacity)
    Rapid discharge is not a safety concern, but is longevity concern.
    Rapid recharge is both longevity and safety concern, pushing the recharge too aggressively results in plating inside the anode, -> short circuits -> fires etc.

    some EVs (particularly) GM bolt actually limit recharge rate until the battery has warmed up sufficiently for safety reasons.

    anodes that can safely handle 15min recharge rates are not that expensive, but they do take up more space.
    anodes that can safely handle 6min recharge rates are both more expensive and take up even more space again.

    I don't see mass market passenger EVs usefully using above 150 kW for a long time. Which make is desirable from a premium luxury perspective. i forsee premium brands going 350kW as a way to differentiate themselves from their lesser stablemates. But it will be either at a severe opportunity cost in range. (or much more likely, 350kW will sound great but be so severely tapered as to only provide a token upgrade in recharge speed)

    the choice really is easy to explain this way.
    for the same volume, for 0-80% SOC

    100kWh (tesla supercharger tapered)
    or
    75-85kWh (Tesla supercharger full speed, 350kW tapered)
    or
    60kWh (350kW not tapered)

    but remember, discharge is not improved, so discharge of the 100kWh is ludicrous capable, but the discharge of the 60kWh is not.

    Its not an easy sell proposition, fast charging has a range cost.

    would you buy a 300mile range 6min fast charge EV if the same manufacturer also sold a 500mile range car with 30min fast charge?
     
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  9. eyedrop

    eyedrop Member

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    #9 eyedrop, May 1, 2018
    Last edited: May 1, 2018
    Maybe the solution isn’t to focus on faster charging just yet, due to limitations of battery chemistry.

    The upcoming Roadster has an amazing range that is longer than most gas cars. Maybe we will get to the point of having 1000+ mile range, which will solve recharging time issues since no lunatic will drive more than that in a day. An overnight 8hr charge on a “lowly” 50kW DCFC system should recover most of that range...

    Although there would still be the issue of planning ahead. Currently, you can leave for a road trip on an empty gas tank and it won’t impact your trip time. People have been taking that for granted for decades. You can’t do that with a long range EV...
     
  10. renim

    renim Active Member

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    perhaps not 1000mile but 1000kms,
    625mile range should be doable for an EV thats roughly 160kWh
    upload_2018-5-2_12-4-30.png
    160kWh is 8 hours x 22kW
    its not hard to get a 20kW AC connection

    i don't see mass market racing to get to 160kWh EVs,
    but I do see premium market EVs are in a race to 160kWh, and in doing so make DC infrastructure mostly uneconomic.
     
  11. WannabeOwner

    WannabeOwner Active Member

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    My wife thinks that Supercharging (a once-a-month occurrence) is a huge waste of time ... it is pretty much exactly the same amount of time (in total) as she, collectively, used to spend fuelling her ICE once a week ... but she is irked by the one-time-wait at Supercharger (during which she can actually do something useful; whereas fuelling an ICE, here in UK, does not have auto-stop pump, and rarely credit-card-at-pump, so you have to stand-and-pump and then queue-in-line to pay ...)

    Nope, I don't know why she rationalises it that way ... but I suspect she is not alone.
     

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