daveo4porsche

super charge overcapacity is a thing - but it also is becoming less of thing...

currently supercharges from Tesla are 480 volts @ 400 amps - quickly tapering to to 320 amp or less - that matches the feed capacities of the electrical services providing power to the superchargers...

Porsche's system is an accumulator system (by their announcement) which means they can only do 800 volts @ 400 amps if they have stored enough electricity locally to discharge that much at that high of a rate…

we'll have to see what the cycle times are like.

most consumers are only worried about fast charging from the point of view of does the car have it or not - capacity limitations are a temporary thing and pass with time as infrastructure gets more built out...

I doubt anyone considering a mission E will pass on purchasing it because they occasionally might not be able to fill up right away during peak seasons at some fast charging locations...I still dispute this is a real long term concern and is effecting sales in any way…

the bigger effect on sales has been the lack of compelling EV's - and that is changing.

ace37

Question for you guys in the industry:

Are capacitors a decent answer to the question of how to get a high performance EV to run extended track sessions?

In theory it seems to really answer the question well, but it seems too obvious so I wondered if they are simply too large and heavy or otherwise not up to such a task without a big tech breakthrough.

gnochi

The answer is always to add more batteries if you have any space or weight allowance remaining, because more batteries gives you lower resistive losses at the same power draw, and more energy to boot. Capacitors don't have anywhere near the energy density to remain useful, especially with how quickly the voltage drops as you pull current. Batteries also have the advantage that voltage stays somewhat constant as you discharge them, which means you can tune all of your associated hardware around a nominal pack voltage, instead of requiring a DCDC converter for, well, everything in the system.

That said, exactly which battery you want to use may well change. On the track, you are of course concerned with the amount of energy in the pack, but if you use a cell that's differently optimized for power density than energy density - Sony VTC5 at 2600mAh vs VTC6 at 3000mAh for 18650s, for example - you may have a net benefit because you'll be able to pull additional power at the same heat load, which corresponds to more efficient average use of energy. If your power usage profile corresponds to ~14% less energy used per lap between these two cells, the VTC5 will make a better track battery.

That said, there is a big use for capacitors in inverters. Basically, an inverter switches on and off rapidly in different areas to send a step function of current along three phases in the motor. If you put a relatively large capacitor between the battery highside and battery lowside within the inverter, it will mitigate the instantaneous power spikes that the inverter would otherwise demand from the battery, lowering the microscopic stresses and macroscopic heat load considerably - depending on the system, your battery pack might deliver 800A +/- 50A@10kHz (801A RMS (sqrt(I_dc^2 + I_ac^2/2)) instead of 800A +/- 250A@10kHz (820A RMS). That may not seem like much, but the latter case is (820^2/801^2)-1=5% reduction in heat.

So, TL;DR: there are places it's advantageous to put a capacitor, and we already do so, but we don't use capacitors for energy storage as such, just to mitigate current spikes. A breakthrough in supercapacitors may change how we do things but the fact that batteries stay at a relatively constant voltage makes controls a lot easier. In the mean time we use different or more batteries to get the performance we need (and don't get me wrong, we very much design our battery packs around specific use cases; there is no one-size-fits-all pack solution).

ace37

Thanks for the detailed response. The inverter application seems like a great fit - that's a significant RMS and peak current reduction for a small piece of hardware.

I was very interested to hear your comments on battery pack optimization. Perhaps we'll end up with a two stage battery solution in the future - one large battery optimized for base power production (range) and another optimized for surge capacity with high cooling requirements (acceleration/deceleration).

I was hoping for more out of capacitors. Back in 2005 when I got my BS, the school had an electric drag racer powered only by capacitors so I was hoping they had made more progress in the last decade. (used 260 Maxwell Technologies Boostcap ultracapacitors)
https://news.byu.edu/news/byus-elect...ets-new-record
http://www.maxwell.com/images/docume...000615-2EN.pdf
Today they show ~5 W-h / kg and ~10 kW / kg... I was thinking ideally they could carry 10-30 seconds worth of typical acceleration/deceleration and take a big charge/discharge load off of the main pack. 5 W-h = 18 kw-s per kg... so with their numbers a 25 kg cap pack without any battery management support would give ~450 kW-s of power. For a commuter car type scenario that would seem like enough to be a benefit. From your comments, reality doesn't fall out quite so well.

Interesting stuff to think about.

928 GT R

Call me curious, and perhaps a bit optimistic, but I read anything I can find on this subject... So I found this on phys.org while researching ceramic magnets/superconductors and related storage systems. 1000 km range? Pie in the sky?

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Depending on the model, electric carsare equipped with hundreds to thousands of separate battery cells. Each one is surrounded by a housing, connected to the car via terminals and cables, and monitored by sensors. The housing and contacting take up more than 50 percent of the space. Therefore, the cells cannot be densely packed together as preferred. The complex design steals space. A further problem: Electrical resistances, which reduce the power, are generated at the connections of the small-scale cells.

More space for batteries

Under the brand name EMBATT, the Fraunhofer Institute for Ceramic Technologies and Systems IKTS in Dresden and its partners have transferred the bipolar principle known from fuel cells to the lithium battery. In this approach, individual battery cells are not strung separately side-by-side in small sections; instead, they are stacked directly one above the other across a large area. The entire structure for the housing and the contacting is therefore eliminated. As a result, more batteries fit into the car. Through the direct connection of the cells in the stack, the current flows over the entire surface of the battery. The electrical resistance is thereby considerably reduced. The electrodes of the battery are designed to release and absorb energy very quickly. "With our new packaging concept, we hope to increase the range of electric cars in the medium term up to 1000 kilometers," says Dr. Mareike Wolter, Project Manager at Fraunhofer IKTS. The approach is already working in the laboratory. The partners are ThyssenKrupp System Engineering and IAV Automotive Engineering.

Ceramic materials store energy

The most important component of the battery is the bipolar electrode – a metallic tape that is coated on both sides with ceramic storage materials. As a result, one side becomes the anode, the other the cathode. As the heart of the battery, it stores the energy. "We use our expertise in ceramic technologies to design the electrodes in such a way that they need as little space as possible, save a lot of energy, are easy to manufacture and have a long life," says Wolter. Ceramic materials are used as powders. The scientists mix them with polymers and electrically conductive materials to form a suspension. "This formulation has to be specially developed – adapted for the front and back of the tape, respectively," Wolter explains. The Fraunhofer IKTS applies the suspension to the tape in a roll-to-roll process. "One of the core competencies of our institute is to adapt ceramic materials from the laboratory to a pilot scale and to reproduce them reliably," says Wolter, describing the expertise of the Dresden scientists. The next planned step is the development of larger battery cells and their installation in electric cars. The partners are aiming for initial tests in vehicles by 2020.

gnochi

Always glad to talk about this stuff! Conveniently, half the time I get paid for it.

Yeah, there's a lot happening that make this problem a lot more complicated than it may seem initially. That 25kg is 6.2kWh of typically "available" 21700 cells, which would be absolutely wonderful if you could shove it into just about any EV on the road. For the Model S P100D with its 315 miles, that extra 6kWh would be an additional 20 miles of range using the EPA US06 drive cycle, and provides a 5.5% reduction in heat load at the same power (or, correspondingly, a 6% increase in allowable power, provided the connectors, contactors, and inverters can handle it).

I could see a capacitor solution being really good for a PHEV commuter car though, if that's what you meant? For that application you really don't care about range and you really do care about spike power demands; battery capacity doesn't matter at all as long as you get low enough resistance (and you'll typically end up with LiFePO4 or something along those lines, because even though LTO is better in every way it's also several times more expensive).

As an aside, I'm a really big fan of the Prius drivetrain - first, that they got it to work, and second, that someone finally realized "hey, gas engines are pretty awesome if you leave them at a comfortable speed forever... what if I use an electric drivetrain for the rough stuff, let the engine putter along, and somehow make up the slack between the two?" I could see a capacitor solution being a pretty good next step, if there's a huge leap forward in capacitors and there isn't one in battery.

Here are my notes on the Fraunhofer announcement (FYI, they have a tendency to make announcements 15-20 years before their technology enters the market in any appreciable way, if it does at all. The MP3 file format is a notable exception that was adopted almost immediately.) Also note that I'm more than a bit of a skeptic; there are liars, damn liars, and cell suppliers. Please pardon my somewhat frazzled state in the comments; it's been a long month. Interesting announcement though.

• 1000km is not inherently pie-in-the-sky in terms of feasibility, but is a bit out there in terms of practicality.
• The main reason we don't go for 1000km = 621mi range cars is that the battery would literally weigh a ton and a half (P85D pack at 1200lb and 253mi leads to 2900lb ignoring weight effects on range from the additional weight; likely it'll be closer to 3600lb and 250kWh). The main thing stopping energy density increases in cells is that the electrolyte decomposes (read: likely fire) above 4.5V (chemistry independent) and life is drastically shortened above ~4.2V (depending on chemistry), and we don't have anything better (solid or otherwise) available outside of a lab setting. Being able to fit more lithium ions in a given crystal lattice is of course beneficial, but if we can do the same number of ions at higher voltage that's more energy.
• Everything is already working in a laboratory, most of it can't scale beyond that in a method that's remotely economically viable.
• The other reason we don't go for 1000km is that very few people will actually drive that far without taking a break for an hour or so. Stints tend to top out at around 400mi. If you can charge the battery inside of an hour for 400mi range, you'll hit the vast majority of customers. Of course there are exceptions, but we can't really design for a .01% of users edge case without another reason to do so. (I am personally one of these edge cases; I tend to do an ironbutt 2-3x per year.)
• Please also note that with the largest man-portable cable being 400A continuous (with a pretty short thermal time constant), and most EVs topping out between 400V and 450V, we're looking at about 160kW of maximum charging power (once we account for system losses). We're working on ways to be able to charge at this rate at higher states of charge - typically, a supercharger stops supercharging at around 80% SOC - but either way with a 250kWh pack you're looking at a bare minimum of 1.6h charge time at a supercharger, and you don't get any more range in the first half hour than you would with a smaller pack - in fact, the vehicle with the smaller pack would likely travel further on a short charge anywhere but a freeway on the Great Plains, because the pack weighs so much less. With a 22kW at-home charger or a 1.5kW wall outlet charge times are on the order of 11h and 167h respectively.
• Yes, a non-man-portable-cable-based charging solution could improve the time efficiency significantly as we get to larger packs (for cycle life reasons, you're typically limited to around 1.3C RMS charge rate = 46m for 0-100SOC). We're working on it but honestly I wouldn't say there are any front runners.
• The housing doesn't take up 50%+ of the available space with any design I've participated in; if that's happening, step one is to look at the requirements list being handed to the pack engineers. 30% is a more reasonable number, when you include all of the distribution components (that you need anyway), the crash structure (that you also need anyway), and the cell can (that you need for cylindrical cells).
• I've seen some significant breakthroughs in cell connection methodology (read: shorter wire bonds with larger diameter) over the last few months and it's common to see connection resistances on the order of 15% of cell resistance (down from ~25%). The vast majority (98% of what's left) of resistance is due to the lithium ion moving about - turns out it's not trivial to shove atoms through a crystal lattice - and the remaining ~2% is from the connection between the foil in the jelly roll and the tabs to the button and bottom of a cylindrical cell. Any reduction in this is good, but you do need some I2R heating in a connection in order to have the (highly recommended) cell-level fuses, since CIDs within the cells are unreliable. Note that pouch cells don't have CIDs, and are therefore vulnerable to overcharge- and short-circuit-induced thermal runaway, regardless of what insert-cell-supplier-here is telling you. I have the (proprietary and not available to be shared) videos to prove it.
• Non-cylindrical cells are not inherently structural, and this architecture would need significant mechanical support. There's an upper limit to automotive pouch cell size resulting from floppiness, depending on the shocks your particular system sees. Remember that a beam 2x as long is 1/8 as stiff, and remember that the more these cells flex the more likely something bad (read: fire) will occur.
• "Double-sided electrode" worries me; I've yet to see any indication that any truly viable-in-scale solid electrolytes are coming soon, and laminating to a liquid is an exercise in futility. Laminating the anode and cathode on opposite sides of the separator would have many of the same manufacturing benefits and also use proven technology (and was most recently granted a patent in 2015 based on 30s of google).
• If they can scale the technology to lab-manufactured 5+ Ah cells by this time next year, prototypes running in-vehicle by 2020 is realistic. One vehicle, maybe 2. That's a big if.
• If this technology is scalable to mass production, doesn't come with severe cycle-life- or safety-related drawbacks, and especially if it reduces the dependency on cobalt, I can see this leading to further price decreases in LiB production, and a corresponding decrease in EV costs, especially at the low end. I don't expect the pack size for a non-specialty vehicle to get much larger than maybe - maybe -150kWh, with occasional exceptions like the Tesla Roadster (which I don't expect they'll sell too many of).

928 GT R

gnochi,

Thanks again for your explanations.

Another company I've been reading about is Ionic Materials. They claim a solid state polymer battery that can be shot through or cut up without thermal runaway.

Alas, probably another case of vaporware...

Regards

928 GT R

Just read on page 24 of my November 2017 issue of Panorama that Porsche has acknowledged that it is researching solid state batteries.

This was apparently disclosed by Porsche at the Frankfurt Auto Show last month.

Thoughts or insights?

gnochi

Ionic Materials is one of the companies that's been talking a whole bunch but I've yet to actually see anything from them. The whole cut up or shot without thermal runaway is feasible depending on chemistry - LTO in particular is very stable - but I've yet to see any high-energy reasonable-power cells that are also non-reactive. I'm not confident that just switching to solid electrolyte would be sufficient, but I may well be surprised in the near future.

Pretty much everyone is interested in solid state cells for the theoretical benefit - reduced charge time, increased cell voltage, increased energy density, maybe increased power density, and keeping up with research means a company will be able to readily take advantage of any breakthroughs; firstly, some of the learnings may be applicable to current vehicles, like how Tesla pushes OTA updates to prevent actions that may cause increased degradation, and secondly, if you know what a cell is going to look like a couple years in advance, you can design the next platform to accept either those cells or whatever you're using now, to protect for the possibility of change without causing a major tearup right before a product release, while not locking yourself into a purely theoretical set of benefits.

As a brief example of the latter, and without giving away anything proprietary, there's been a big hullabaloo over the last few years about switching from 18650s to 21700s, at least somewhat driven by the power tool industry wanting larger capacity packs without increasing the number of electrical connections they need to make. EV companies have known about this upcoming shift for a while now, and every design I've seen using cylindrical cells is almost trivial to swap between 18650s and 21700s with minor change in pack energy or power densities. Once you get above about 10 cells in the flat directions of a parallel-axis cylindrical cell module, and if you keep a 5mm buffer in the cell-axial direction (itself useful for venting of thermal runaway gasses, crush structure for crash, etc.), it's a minor matter of adjusting the details of the busbars, end caps, coolant tubes, and what have you, and then running a quick suite of tests to make sure you didn't miss any details, without needing to fully develop a new architecture.

JustinL

Perhaps we've covered this already, but could someone explain why we can't get more energy back from braking? In a friction-less world with 100% efficiency slowing a car down from 60mph should generate enough energy to get it back to that speed. Every Joule of energy converted to heat in the brake discs is completely wasted. Is the problem that we can't pull the energy out of the system fast enough with electrical regeneration, or is it some other factor like laws requiring an independent hydraulic system?

W8MM

You’ve answered your own question ;~}

The one-word answer is “entropy”

We don’t live in a frictionless world. Mechanical friction, electrical friction (resistance), aerodynamic friction (drag) all contribute to less than 100% system efficiency. Numbers I’ve heard indicate that recovered energy from battery-charging-deceleration is likely to be less than 85% of the mass times velocity-squared available.

Friction brakes are only used if the deceleration rate desired eclipses the regen-braking capabilities of the vehicle. My wife’s Tesla Model S and Tesla Roadster 1.5 both respond well to 1-pedal driving, unless there is a traffic surprise. Battery pack internal resistance and motor controller performance are limiting factors in regen energy recovery.

unclewill

What if there was no such thing as a gasoline powered car and Elon Musk tried to introduce one to the public today:

"This vehicle is powered by 20 gallons of toxic and flammable gasoline which will be carried in an onboard tank. The fuel will then be highly pressurized and injected into cylinders where it will be burned a few feet from the passengers with the resultant smoke released into the surrounding air. The burning will take place within an engine consisting of hundreds of moving parts which transfer power through a complex automatic clutch to a multi-speed transmission, then through a final drive with multiple clutches to the wheels. The vehicle will minimally be taken out of service every 7500 miles for repairs and fluid changes of varying cost and complexity with a total service life of approximately 150,000 miles between major overhauls."

JustinL

I'm sure something equally scary could be written about sitting on a 400 volt battery if you frame it in a similarly alarmist tone. On the other side if you were writing it with a positive perspective, it could sound very different too.

928 GT R

News from Samsung & MIT regarding Graphene as a battery and or lightweight ultra low resistance conductor.

Graphene: Super lightweight, highly conductive of heat and electricity and, pound for pound, stronger than steel, it was all the rage a decade ago. In 2010, the scientists who first extracted it won the Nobel Prize in Physics. “The perfect atomic lattice,” the announcement gushed.

Then things stalled as manufacturing it in useful quantities proved difficult.

In November, the Samsung Advanced Institute of Technology announced that its researchers had developed a “graphene ball,” a material that would allow lithium-ion batteries to charge five times faster and have 45 percent more capacity. That alone could have big impact on both consumer electronics and the automotive industries.

Recently, a team of researchers at the Samsung Advanced Institute of Technology (SAIT) developed a “graphene* ball,” a unique battery material that enables a 45% increase in capacity, and five times faster charging speeds than standard lithium-ion batteries. The breakthrough provides promise for the next generation secondary battery market, particularly related to mobile devices and electric vehicles. In its research, SAIT collaborated closely with Samsung SDI as well as a team from Seoul National University’s School of Chemical and Biological Engineering.In its research, SAIT sought for an approach to apply graphene, a material with high strength and conductivity to batteries, and discovered a mechanism to mass synthesize graphene into a 3D form like popcorn using affordable silica (SiO2). This “graphene ball” was utilized for both the anode protective layer and cathode materials in lithium-ion batteries. This ensured an increase of charging capacity, decrease of charging time as well as stable temperatures.

Dr. Son In-hyuk, who led the project on behalf of SAIT, said, “Our research enables mass synthesis of multifunctional composite material graphene at an affordable price. At the same time, we were able to considerably enhance the capabilities of lithium-ion batteries in an environment where the markets for mobile devices and electric vehicles is growing rapidly. Our commitment is to continuously explore and develop secondary battery technology in light of these trends.”

SAIT’s research results are covered in-depth in this month’s edition of the science journal Nature Communications in an article entitled, “Graphene ***** for lithium rechargeable batteries with fast charging and high volumetric energy densities.”SAIT has also filed two applications for the “graphene ball” technology patent in the US and Korea.

Three days ago MIT announced a process for a scalable manufacturing method that spools out strips of graphene for use in ultra thin membrane technology. I do not see how the application would not work for creating ultra-lightweight battery connective material.

http://news.mit.edu/2018/manufacturi...membranes-0418

gnochi, what are your thoughts on the subject of graphene.. Thanks!

cometguy

gnochi, what is your advice on the following? I'm awaiting arrival soon of a Panamera E-Hybrid. Questions:

(1) is there any way to best optimize the new E-battery pack? In another thread, somebody said they were doing three full charges and three full depletions of the E-power battery pack to optimize the battery for best performance. Any validity to this?

(2) I've seen it written above that it's not good to constantly fully charge such car batteries; is this true, and is there a difference to this answer in BEV vs. PHEV?

(3) What would your recommendation be to prolong the life and range of PHEV batteries like in the Panamera E-Hybrid, from a driver/owner perspective? I'm mainly interested in having and maintaining driving-range (mileage) capacity to the highest possible level. I plan to use electric extensively for commuting in city driving, and hybrid/ICE power for outside cities.

(4) Do you know if Panamera E-Hybrids have heated batteries at all for cold weather? And do you have any idea if Porsche E-Hybrids use both E-batteries and ICE for heating and air-conditioning the cabin, depending on whether the ICE is running or not? I wonder if there's a way to optimize the E-battery capacity better in cold or hot weather where the heater/AC is needed heavily.

Thanks!