Tesla LFP Model 3 — Battery Design
Author: ZHU Yulong
I will use the photographs I have recently received to discuss this compatible remodeling. Actually it is entirely identical to my earlier thinking.
I think that the LFP battery is most probably what Elon Musk will use to build $ 25K car that he mentioned at Tesla’s Battery Day. From the perspective of low cost, it is based on LFP’s long life-cycle and on the battery design that is sensitive to weight.
Overview of LFP design
1) Module dimensions
Due to Tesla battery pack design, the height is only ca 120 mm, so the height of corresponding module is ca 81 mm. This is why LFP design adopted compatible design.
Two different arrangements were adopted, 25 cells and 28 cells, total of 106 cells, which were turned into two modules that were made compatible with the original ternary module design.
Actually, the above photo has several special features. As the original dimensions were kept, connecting outlet of the water cooling plate has quite a spacing (in reality, 4 cells can be added). Here the design kept a certain spacing between the cells. Further, end plate was made sturdy as to enable so many cells to sustain force.
Note: From what I can see, there is enough space if one decided to replace LFP cells with NMC811 and add thermal insulation. In fact, beside LFP version, prismatic cells in a long spacing version can also be designed, but I guess that is the matter for 2021.
In the side view of the end plate, we can see a complete standard design. Water cooling plate is integrated onto bottom, while external part has a complete structure which matches with the cooling plate. On one side, the module has a sufficient mechanical strength, on the other side it also has a sufficient thermal insulation gap. Water cooling plate on LFP is primarily about low temperature heating, so heat dissipation will have to be solved in the subsequent NMC version. In design of 82 mm thick cell, 250 kW supercharging can be challenging. Due to the height of prismatic cells and corresponding module’s sampling board and insulation plate in this design, Tesla changed the layout of CMU sampling board, so it did not adopt extended mode of the flexible circuit board. Here we only have the cut off part.
Y-axis dimensions have also kept sufficient spacing. As below photo shows, it uses a complete fixed structure to cover each of fixing points of ternary cylindrical module and installation points of the module.
Below photo is clearer. Prismatic design used a lot less thermally conductive filing glue, black part of the side plate and water cooling plate are affixed together through a structure.
Strictly speaking, this is the water cooling plate that has been increasingly built in pouch and prismatic modules of the cars mass produced in 2020. Its biggest advantage is that it can reduce requirements for dimension tolerance chain as well as usage of thermally conductive glue in the link between cell and water cooling plate. At the same time it also tackles design requirements that gradually increase with the next generation.
Conclusion: I think this design is worth considering. Before the next generation of module design brought by CTC occurs, this design philosophy can really balance between the costs, maintainability and energy density requirements.