Gaze upon Tesla's new battery cell, but don't despair.
Enlarge / Gaze upon Tesla’s new battery cell, however do not despair.

Aurich Lawson / Tesla / Getty Pictures

Tesla’s “battery day” Tuesday revealed a shocking quantity of details about initiatives the corporate has stored below wraps. The presentation described adjustments and enhancements to only about each side of its battery packs, with big-picture implications for the declare {that a} $25,000 Tesla automobile can be attainable in about three years. (See the previous coverage from Ars’ Timothy Lee for extra on that.) But it surely wouldn’t be a Tesla announcement with out obscure timelines, and it was just a little unclear which enhancements are able to go now—and which of them they’re simply anticipating to achieve the following couple of years.

With out particular numbers or concrete particulars, assessing the bulletins takes just a little guesswork. However we will examine all this to different trade traits and to revealed analysis to get some concept.

Battery in a can

Let’s begin with two issues Tesla claimed exist already at its pilot manufacturing plant: its new cell design and a few enhancements in manufacturing. Tesla acquired off the bottom utilizing present and generally out there cylindrical 18650 lithium-ion cells, whereas most EVs have been constructed with flat pouch or prismatic cells (extra like the skinny batteries in telephones and laptops). In a cylindrical cell, lengthy sheet-like anodes, separators, and cathodes are sandwiched, rolled up, and packed right into a cylinder-shaped can. The cathode and anode sheets every have one skinny “tab” that connects to the constructive and damaging terminals of the battery can.

The most effective methods to make a battery extra vitality dense is to do away with as a lot packaging as attainable. Make the separator tremendous skinny and decrease the space-eating outer container and battery pack parts, and also you’ve acquired extra electrical energy saved per kilogram. Clearly there are limits to how a lot you’ll be able to shave off, so one other approach of doing that is growing the ratio of battery quantity to packaging space. That’s, make an even bigger can.

Tesla did this when it launched the 2170 cell with the Mannequin 3 and Powerwall. This cylinder was 21 millimeters by 70 millimeters slightly than the 18 by 65 dimensions of the 18650 cell. However going larger offered Tesla with challenges as a result of an even bigger can holds longer rolls, and longer rolls imply the anode and cathode stretch out farther from the tab connecting them to the battery terminals. The longer path for electrons causes issues for secure speedy charging and creates extra warmth that has a tougher time escaping.

Tesla’s resolution to this, resulting in a a lot bigger 4680 cell, is a brand new “tabless” design with contacts operating the size of the anode and cathode sheets—forming a rose-like gathering on the ends when all the things is rolled up—maintaining {the electrical} path size to the terminal quick all through the sheet. “Generally, what’s elegant and easy continues to be arduous,” Tesla’s Drew Baglino stated. “And it took us a variety of trials, however we’re comfortable the place we ended up.”

“It might kind of sound a bit foolish to some folks,” Musk added, “[but] for those who actually know cells, it is a huge breakthrough.”

Elon Musk and Drew Baglino present in front of a slide showing Tesla's new "tabless" cell design.
Enlarge / Elon Musk and Drew Baglino current in entrance of a slide exhibiting Tesla’s new “tabless” cell design.


It’s genuinely arduous to know exactly how this stacks up with cells utilized in different EVs, given how secretive producers are, but it surely could possibly be that this tabless design validates Tesla’s selection to stay with the cylindrical cell form.

The opposite half of constructing a brand new form of cell is designing the machines that do the making. As detailed in our companion story, Tesla has discovered methods to considerably enhance the throughput of parts of the battery line. The tabless design truly helps with this, because the electrode sheet can simply maintain flying by the rollers. And along with different adjustments we’ll get into in a second, they’re speaking about growing manufacturing whereas utilizing much less manufacturing unit floorspace and fewer vitality. That may assist them attain price discount targets and ramping output targets.

Pack it up, pack it in

An EV doesn’t run on a battery cell, in fact, however slightly a battery pack filled with cells. There’s so much occurring in these battery packs, together with cost administration, cooling, and security measures in case of fireside. That makes the engineering of the pack very a lot related to the total vitality density of the automobile’s storage, and subsequently its vary.

Tesla described a brand new pack design that reduces a number of the structural helps, which suggests extra cells in much less quantity. And as this includes a redesigned pack that doubles as construction for the automobile, it most likely carries some price advantages on the automobile stage, as nicely.

This pack design presumably exists, however there was no phrase on which autos it’ll go into. May manufacturing swap over on an present automobile, or is that this design merely a part of the Cybertruck, Tesla Semi, or unnamed $25,000 automobile? Musk didn’t say.

However he did have so much to say in regards to the chemistry inside the brand new battery cells. And that is the place the timelines get hazier. New chemistries for each the anode and cathode had been mentioned—each would break new floor.

The anode in fashionable lithium-ion batteries is graphite. The construction of graphite permits it to host the lithium atoms that transfer towards the anode throughout charging, however that’s all it does. Which means that a considerable portion of the cell’s quantity and weight doesn’t immediately contribute to vitality storage past merely maintaining the factor working. In the event you might ditch some quantity and weight there, the vitality density of the cell would enhance.

Tesla and another producers at present add a little bit of silicon inside that graphite, as this allows the identical quantity of anode to carry extra lithium. A considerably higher (and cheaper) choice can be using pure silicon. However whereas graphite permits lithium out and in with out altering form, silicon has a nasty behavior of increasing because it hundreds up with lithium. That creates structural failures inside the silicon, degrading efficiency over time, and probably harmful failures of the cell container.

There’s a variety of analysis on different anodes for lithium-ion batteries, however none has fairly reached the market. Tesla claims to have designed an anode with tiny silicon particles in a conducting, elastic polymer. That enables for a long-lived and secure silicon anode cell, it says—which might be an enormous deal.

This cell comes with a claimed price lower from about $10 per kilowatt-hour for silicon-in-graphite to extra like $1 per kilowatt-hour for pure silicon. As for automobile vary, the corporate claims a 20-percent enchancment. However no different properties (like longevity in comparison with its present anode) had been described, so it’s unclear whether or not Tesla is able to put this in a battery and promote it in the present day. (Although for what it’s value, it doesn’t sound too different from an anode materials Sila Nano—an organization with some Tesla alumni—says it’ll begin offering for digital gadget batteries this yr.)

Tesla can be transferring to (barely) totally different chemistries on the cathode aspect. And sure, that’s plural chemistries, which is at the very least as noteworthy because the nitty-gritty chemical particulars. Tesla now desires to offer three several types of lithium-ion batteries, starting from extra economical to I’m-giving-her-all-she’s-got-captain.

Here's how Tesla presented its plan to use three different cathode chemistries for different applications.
Enlarge / Here is how Tesla offered its plan to make use of three totally different cathode chemistries for various functions.


Tesla at present makes use of an NCA chemistry (that’s lithium-nickel-cobalt-aluminum), whereas lithium-nickel-manganese-cobalt (NMC) chemistries are widespread throughout the remainder of the EV trade. Cobalt is the most costly of those parts, and most of it’s sourced from mines within the Democratic Republic of the Congo, the place unsafe working situations and youngster labor are severe issues. Consequently, the trade has been making an attempt to scale back cobalt utilization.


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