Post
by jonescg » Sat, 21 Apr 2018, 14:19
Some interesting observations:
It appears that the cells are all standing up in the same orientation. The negative busbar (you can see the black pen) has the fusible links connected to the side of the cell can (negative terminal) while the positive terminals are fused to the next busbar along in a similar fashion. I assume this was an effort to make manufacturing easier, as modules that big start to get quite unwieldy when flipping and rotating to terminate the opposite side.
The silicone gel stuff serves to both provide some damping to the cells against vibration, as well as acting as a thermally conductive encapsulant. Robo-pumping the goop into a battery module must be a slow process.
The silicone gloop is then used to form a thermally conductive path between the cells and the cooling loop - which is a large flat cooling plate on the top (and presumably the bottom too). It The cooling inlet tubes are still attached in the last 2 images above.
Elsewhere, there have been discussions about the holdups in the Model 3 production line, and they mentioned 'bandoleers' of cells, glued together and slapped together in the plastic tub. I can see how a CNC trying to ultrasonically weld fuse wire to the sides of the cells would struggle!
The shift to the 21700 cell format doesn't add a huge amount of energy density - the bigger volume of active material relative to the non-active material is hardly worth writing home about. But the larger axial surface area as a result of the new aspect ratio makes axial surface cooling more practical. Moreover, the process of wire-bonding to the outer rim of the cell can for the negative terminal is made easier with the larger cell - seems to have a good 2 mm of edge offset there.
Whole modules of a few thousand cells are risky - one fault and the whole thing is in trouble. They must be confident in their cell QC and wire bonding technique...
AEVA National Secretary, WA branch vice-chair
