Welcome back everyone! I’m Jordan Giesige and this is The Limiting
Factor. This is part sixteen of the Lithium Mine to
Battery Line Series to break down and understand what was unveiled at Tesla Battery Day. This is the second video on the Structural
Battery Pack and will cover the leaks and hints about how the pack could be manufactured
from the cell up. Before we begin, a special thanks to my Patreon
supporters and YouTube members. This is the support that gives me the freedom
to avoid chasing the algorithm and sponsors, and I hope will eventually allow me to do
this full time. As always, the links for support are in the
description. Back to the structural battery pack. First, it’s worth noting that even within
Munro and Associates, there was vigorous disagreement as to exactly how Tesla would design the structural
battery pack. Other websites, like Inside EV’s, had a
different view than Sandy Munro. In other words, at this point, all we have
is conjecture that often conflicts, and that’s from engineers who are in the best position
to make educated guesses. I don’t have an engineering background,
but I do think there’s still a lot missing from the conversation. My approach is different than others because
I’ve tried to incorporate all the leaks and because I’m taking into account cell
design. This approach will inevitably leave me reaching
beyond my expertise and what I’m suggesting may be way off the mark. However, it will provide food for thought
and illustrate challenges I haven’t seen discussed elsewhere. As I’ve said in previous videos, the design
of the battery cell dictates the design of everything that’s built around the battery
cell. In the case of the structural battery pack,
the way the battery cell is wired tells us how it’ll be connected to the battery pack. This is a piece of information we don’t
have, but we can find clues in leaks and official releases by Tesla. Let’s review the evidence on hand. Before Battery Day, we were treated to this
leaked example of the roadrunner cell. Note the copper flanges and skirt at the bottom. We don’t have a clear view of the top, but
we can see that it has a bevelled edge and that it doesn’t appear to be crimped in
any way. At Battery Day, we saw this CGI image. Note that the top is similar to what we might
see in a typical battery cell. It’s crimped and tapered. The diameter of the crimped top is actually
less than diameter of the cell body. There are either no features on the bottom,
or we can’t see them. Finally, in the recruitment video, we again
see something different. This image would be the most reliable because
it’s not CGI and it’s not a leak. Note that at the bottom of the cell, there
again appears to be a skirt. It appears to be a skirt rather than a crimp
because it’s wider than the diameter of the cell body. In other words, what we’re looking at here
appears to be in line with the initial leak that we saw before battery day. There’s a skirt at the bottom and a bevelled
top. If that’s the case, then the image that
Tesla showed us at battery day is a red herring. It was something people could easily recognise
as a battery cell because of its conventional design. It could have been 4D chess and way to throw
competitors off Tesla’s trail, but usually I avoid jumping to those types of conclusions. These seem like minor details, but they matter. For example, Panasonic and LG Chem, who are
also designing 4680 battery cells, would need to know the exact dimensions of the 4680 and
how it’s wired in order supply battery cells that work with Tesla’s structural battery
pack. So what are we to make of this cell design
and what would the benefits be? Honestly, I have no clue because we still
can’t see inside the cell and how the electrical connections are made. I do, of course have some speculation. At the top of the cell there’s a coin sized
disc that appears to be electrically insulated from the rest of the cell. I’ll refer to this as the coin. Inside EV’s suggested that the coin could
be used to position the battery cells. I’m not convinced of this for two reasons. First, there are much better ways to position
battery cells - ways that don’t add extra manufacturing steps and waste metal. We’ll come back to this later in the video. Second, the coin provides a good sized target
for a welder and an electrical connection. Why would there need to be an insulator between
the metal coin and the metal body of the cell? The battery will need a positive and negative
electrical connection. In other words, you can’t connect both the
aluminum current collector at the top and the copper current collector at the bottom
to the same piece of metal. They must be electrically isolated from each
other. In a conventional battery cell, this is achieved
with a highly engineered and complex crimped cap design that contains the insulator. The crimped metal and insulator create a positive
terminal in the battery cap, and the body of the cell becomes the negative. The battery cap also includes safety measures
such as the current interrupt device. I’m not sure how Tesla deals with safety
in their battery, and I’m not seeing any evidence of a safety device in the images
we have, but that doesn’t surprise me. In prior videos I suggested these safety devices
could be redundant with some clever wiring, engineering, and electronics to safely isolate
cells. I haven’t investigated further but I also
haven’t come across any evidence that my suggestion is technically implausible. Let’s get back to the coin connection. If the coin is the positive electrical connection,
it appears to be a much simpler design than a crimped cap and therefor cheaper and easier
to manufacture. However, this leaves us with an engineering
challenge. The diameter of the coin is smaller than the
diameter of the top. In a conventional cell, the entire top is
electrically insulated from the body and there’s a single tab from the electrode to the positive
terminal. With a tabless electrode on top, it would
create a large amount of exposed aluminum and there would be a risk that the aluminum
current collector would touch both the body and the coin. In other words, how would the aluminum current
collector be attached through the top of the battery cell to the coin while maintaining
electrical isolation between the tabless electrode and the body? I haven’t solved this challenge, but I’m
guessing it has something to due to the disc at the top of the battery cell. Many people have said this disc is made of
metal. I can’t tell what it’s made of due to
the angle of the camera and I think it could be metal or plastic. If the disc is metallic, it would potentially
create an electrical connection between the aluminum current collector, the coin, and
the body. This would mean both the copper and aluminum
are touching the cell can, meaning no distinct positive and negative terminal, meaning it
wouldn’t work. The only way I can see around this would be
an insulative gasket above the disc. If the disc is an electrically insulative
material, such as plastic, it might keep the aluminum current collector from touching the
body. This would allow a separate electrical connection
to be made from the coin, through a hole in the top of the cell and a hole or holes in
the plastic disc, to the aluminum current collector. If you have any ideas for a better way to
do this, let me know in the comments below. Regardless, without better insights or information
from any source I’ve seen, we’ll continue on the assumption that the body is the negative
electrical contact, and the coin is the positive electrical contact. This is because the cathode of a lithium ion
battery is painted on aluminum foil and the anode is painted on copper foil. This makes the aluminum positive and the copper
negative. It would make sense for the aluminum to connect
to the adjacent coin at the top of the cell. Meanwhile, the copper flange at the bottom
of the cell would clearly touch the skirt, making the body negative. The assumption here is that the entire shell
of the cell is conductive and electrically unified from skirt to body. If there’s an electrically insulative gasket
between the skirt and body, I can’t see one. I’m looking forward to Sandy Munro tearing
into one of these structural battery packs to find out how the cell itself is wired. The result could be mundane, but the internal
wiring of the cell could also be one of dozens of improvements that were hidden in the Battery
Presentation. As Elon said at Battery Day, “There’s
a whole bunch of things that we’re keeping a little secret sauce here that we’re not
telling…”. I think a lot of that secret sauce is in how
the battery cell design, structural pack, electronics, and cooling system nest elegantly
with each other in the physical space of the battery pack. Let’s bring another leak into the picture
see if we can work out anything about the pack design and how that might dovetail with
the cell design. This leak is from Electrek and shows what
appears to be a hard plastic or epoxy honeycomb structure. I’ll refer to it as epoxy because Elon said
at Battery Day that there would be a flame retardant epoxy filler. This image could be a hoax, but Electrek has
been good about vetting sources in the past and the image looks legit. Given how clean this honeycomb structure is,
I’m assuming that the cells haven’t been inserted yet. If the cells had been epoxied in and removed,
the honeycomb structure would have been destroyed. If that’s correct and the honeycomb structure’s
partially prefabricated, what could the pack assembly process look like? First, we start with the 4680 cell from the
b-roll instead of the CGI image from battery day. Rather than using the coin to position the
cells, the cell would be flipped over and inserted head first into the flame retardant
epoxy honeycomb. The skirt would catch on the honeycomb. The entire assembly would then be flipped
over. Note that some of the coin side and some of
the skirt side would be exposed. The exposed skirts would be placed on the
bucketed tray shown at battery day. The bucketed tray would include a caste in
place or stamped cooling plate at the base. At the top, a rigid printed circuit board
or rigid gaskets would be welded to the cell tops. The lid would be sealed tightly over the circuit
board or gaskets, holding it them place. The entire assembly would be bolted together
and injected with epoxy. The epoxy would fill the slight gap between
the cells, honeycomb, and face sheets to bond the entire pack together in seamless and rock
solid assembly. In fact, mechanical engineer and friend of
the channel Nick Butler has done CAD analysis of a conventional battery pack vs a structural
battery pack and found that it may be up to 5 times stiffer. Thanks for the analysis Nick! Although the assembly process described in
this video is a Frankenstein of all the leaks and engineering assessment out there, I’m
relatively happy with what I’ve proposed. Using a preformed mould could accelerate manufacturing
by holding the cells in place while they’re bonded to the upper and lower face sheets. After topping up with epoxy to fill the voids,
it would then harden into a fully unified honeycomb structure, with zero joints or weak
points. This leaves us with the overall design of
the battery pack. A structural floor pan with cooling channels,
the honeycomb matrix with cells, a wiring matrix that’s flat and robust to being part
of the structure, and then the top plate. This is a good place to stop and point out
a similarity between Tesla’s illustration and the honeycomb structure that was leaked. Notice on the right side of the honeycomb
structure that there are triangle-shaped metallic retainers and that the point of the triangle
is up. As I said earlier, imagine that we’ve inserted
cells skirt up and flipped the whole thing over. Now the point of the triangle is facing down,
with the broad side up. Compare this to what we see in Tesla’s image. The broad side of the triangle is up and if
you look very closely, you can see the positive coin contact on the top of the cells. One of the counterarguments to what I’ve
suggested here is that the triangles could just be coincidence and Tesla’s image is
a rough illustration. For example, there are some discrepancies
in Tesla’s illustration, such as the unequal spacing on the left and the right. It definitely may be the case that I’ve
read too much into a connection between the leak and Tesla’s illustration, but it’s
also a strange coincidence and structurally, it makes sense to use an inverted triangle
here. As a side note, the Electrek article stated
that the black tubing that we see in this image would be coolant loops. I don’t buy that analysis for two reasons
and I think it’s actually wiring rather than coolant loops. First, as I said before, my view is that the
cells would be inserted skirt up and the entire assembly would be flipped over, putting the
wiring at the top. This would place the wiring in closer proximity
to the rest of the wiring in the vehicle. Second, given that the coolant channels appear
to run lengthwise down the vehicle, I would think it would make more sense to put the
connections for the coolant channels at the front and rear of the pack rather than down
the sides. Wires, on the other hand would need to be
wired in series and parallel, which would require wiring connection points along the
sides. After I’d fully scripted and recorded this
video, Sandy Munro released an image of what he believes is the structural battery pack. It looks authentic, but it doesn’t align
with what I’ve described today based on the other leaks. I can only assume that this image is before
the epoxy is added because we can still see the cells. I showed the epoxy as clear in my images as
an artistic choice, but I’d be very surprised if it’s actually clear. Next, the gap between the side of tray and
the pack is quite wide here, and it seems like a waste of space and a structural weakness. The way I dealt with this in my model is for
the entire tray, not just the spaces between the cells, to be injected with epoxy. Because of that, I modelled a tight fight
between the edge of the pack and the side of the tray to minimise the amount epoxy used
to fill, seal, and bind the pack together. Next, the points of the triangles face up
here, which doesn’t match what’s in Tesla’s presentation. I don’t think this pack is upside down because
there appears to be two wiring chimneys at the lower left which would connect to the
rest of the vehicle wiring. Finally, the cells are coated in what appears
to be the same green shrink wrap that we saw with the cells in this image. I don’t see the purpose of shrink wrap if
the cells are going to be surrounded by epoxy. In other words, I’m not sure what to make
of this leak and I find it difficult to square with the other leaks. But, I only had my first look at this leak
a few days ago whereas the other leaks have been stewing in my brain for several months. It could be that the earlier leaks were of
earlier prototypes. Then again, it could be the reverse, and maybe
the pack see here is a prototype that was scrapped. Either way, I’ve hopefully provided enough
open ended thinking in this video to trigger some brainstorming in the community. All this conflicting information only makes
me more excited to see the final product. The last video contained a thorough summary
of the benefits of the structural battery pack so we’ll close it out here for the
day. I’m looking forward to the discussion and
feedback in the comments. In the next video, we’ll be discussing the
gigacastings. There’s been a lot of discussion on gigacastings,
but I’ll attempt to wrap up all the key points in one video along with a few bits
and pieces that you might not know. If you enjoyed this video, please consider
supporting me on Patreon with the link at the end of the video. I am also active on Twitter and Reddit. You can find the details of those in the description
and I look forward to hearing from you. A special thanks to Andy D and Vegar Wang
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for tuning in.
