Tesla: what to expect from batteries with 4680 cells?

Tesla

The energy efficiency of the batteries used inside electric cars is an aspect of fundamental importance to allow their diffusion on the market, and it is therefore not surprising that a pioneer company in electric mobility such as Tesla is also one of the most committed to the development and in the creation of new types of batteries: for a long time now we have been hearing about batteries with cells in the 4680 format, but only a few months ago Tesla has actually managed to start the production of these cells that are becoming part of the structure of the new Tesla Model Y , thus giving life to a battery pack that becomes a structural element of the car, with net weight savings and a general simplification of production, which therefore becomes more economically sustainable.



In the phase of presentation of the 4680 cells, on the occasion of Tesla Battery Day in 2020, Elon Musk communicated the following data to the world: power increased by 6 times, energy conservation capacity increased by 5 times and + 16% of the mileage range, but in reality the only real news concerns the power, while the other data are a normal increase thanks to the higher volume.| ); }
Ci realizes in an instant that the new 4680 cells have a significantly greater volume than the previous formats, and it is precisely this aspect that has allowed Tesla to make high-sounding statements during the presentation of these cells: the 4680s offer energy 5 times higher than the 2170, 6 times more power, but an increase in mileage that reaches + 16% in the best of scenarios. Why this discrepancy between the stored energy, which seems to be drastically greater, and the autonomy that has increased, but not in a revolutionary way? Blame the marketing, as often happens these days: making the necessary calculations, we verify that the volume of the 4680 cells is 5.5 times higher than that of the 2170, which immediately explains why the new cells can contain so much energy in more.

To make a more correct comparison, we should have talked about energy density, rather than actual energy: in this case the comparison is much less exciting, with the energy density of the 4680 cells reaching 296 Wh / kg, against the current 260 Wh / kg of 2170 cells. This is the data that explains that + 16% of autonomy, the increase in energy density is significant, but it is not a step forward in degree to revolutionize the industry, at least for now.

More than once Elon Musk has pointed out that the 4680 cells are, on balance, still under development and in the coming years it is reasonable to expect important steps forward, with Tesla aiming for a dense one energy of 400 Wh / kg, that would be a step forward!


With the introduction of the new 4680 we are therefore trying to fill the power with pouch cells, a result that Tesla managed to achieve thanks to the new 'tabless' design of the 4680 cells.




Thanks to the tabless design the individual tabs are replaced by a small layer of copper - already present in the battery, not specially added which makes production much faster - which takes care of transmitting the current. Judging from the first tests performed, the resistance recorded in the new tabless batteries is 0.00199 Ohms, a figure perfectly in line with the resistance of the batteries with bag cells. In a 10A battery that normally has an internal power loss of about 2W, using the new tabless design can reduce the power loss to about 0.2W. Here, then, that Tesla can claim to have made batteries with a power 6 times higher than those previously used, but it is still a power level already reached by other competing manufacturers, and in this case Tesla is only getting back on the same plan.

Another aspect of great importance when talking about batteries for electric cars is the cooling of the battery itself: inside the individual cells the heat develops vertically, and therefore it has been realized a lot soon that the best way to cool the cells is to have direct contact between the battery poles and the cooling element. On the new 4680 cells this method works even more efficiently, again thanks to the tabless design: if before the battery poles had a simple tab in contact, now they are in direct contact with an entire layer of copper, a material known for its thermal conductivity, and this translates into a much lower thermal resistance than 2170 cells, and therefore a significantly better cooling capacity than in the past.

Finally, there are a whole host of practical aspects very important related to the use of 4680 cells: as we defined at the beginning, these cells are much larger than those used to date, which means that to create a battery pack you need much fewer cells than in the past, going to make more compact and also lighter battery packs, as less steel was used for the housings of the individual cylindrical cells.

In conclusion, the 4680 cell design brings with it evident benefits both from a production and a performance point of view, even if some of the features presented as revolutionary are nothing more than an adaptation to the standards of today's market - which uses almost entirely batteries with bag cells, rather than cylindrical cells such as says Tesla. The increased power is a very important aspect, as well as the improved performance in terms of cooling, with the latter aspect which can also translate into a longer battery life in the long run.