Considering the impact of Tesla's new "tabless" cells.
Most of the discussion of the new "tabless" cells has focused on the cost benefits of eliminating the tabs themselves. However, there's much more at play.
Here is a typical mass-market 18650 cylindrical cell.
Most of the discussion of the new "tabless" cells has focused on the cost benefits of eliminating the tabs themselves. However, there's much more at play.
Here is a typical mass-market 18650 cylindrical cell.
Ratios will vary between cells, but the main takehome is that anode / copper / graphite-adjacent tap forms the exterior of the cell, and the cathode / alumium / positive tap forms the interior of the cells. The difference in choice of metals is electrochemical compatibility.
There's a few implications of this which stem from the fact that to close a circuit, current must flow through the entire length of the foil. One, Joule heating (I^2*R) is linearly proportional to resistance, which is linearly proportional to both length and cross sectional area.
In the new tabless design, current travels straight to the caps, e.g. along the height of the cells, not spiraling out to the edges. This vastly shorter distance means vastly less resistance, and thus vastly less joule heating for a given current and foil thickness.
A less obvious implication is that current increases the closer you get to the tap - and remember that heating is proportional to current *squared*. For the cathode / alumium / positive tap, this is on the exterior, where the cell is easiest to cool. For the anode / copper / ...
... negative tap, however, this is at the centre, where the cell is hardest to cool. There can often be a visible temperature difference between the anode and cathode taps on IR. Uneven heating limits your ability to maintain target temperatures at high currents.
While on its own, a significant lowering of internal resistance would be good, one could instead use thinner foils (potentially significantly thinner, except you could run into the tensile limits of the foils during winding). This allows for a greater ratio of active materials.
For the above 18650, for a scenario of 6mg/cm2 anode loading and 8mg/cm2 cathode loading, copper makes up 29% of the internal mass and alumium 13% of the mass, for a total of 52%. At double the loading, these drop to 20%, 9%, and 29%, respectively.
While internal mass is only part of the cell mass, it's clear that any ability to reduce foil thickness can have a significant impact on energy density for a given internal resistance. Furthermore, most for that is copper, which is a relatively expensive metal.
Summary: I can see why @elonmusk is excited about this; it looks like it could potentially offer quite a significant improvement, to even cell heating and some combination between reduced internal resistance (heating, power) and energy density while reducing cost per kWh.
