The P100D Has Arrived, As Well As New Battery Pack Architecture
The latest Tesla splash is their new 100 kwh battery pack unveiled August 23, 2016 in a conference call with journalists.
“The cell is the same - but the module and pack architecture has changed significantly in order to achieve adequate cooling of the cells in a more energy dense pack, and to make sure that we don’t have cell to cell combustion propagation” - Tesla CEO Elon Musk from the conference call on the new 100 kWh options
So Tesla is using the same battery cells as in the P90, but they have somehow figured out how squeeze in more cells and remove heat more efficiently.
How can this feat be accomplished?
Before we conceptualize let’s look at how the current pack is cooled.
The current pack is cooled by a Tesla patented cooling ribbon that snakes thru the cells as shown below.
The current Tesla battery cooling configuration uses a cooling ribbon that snakes thru the cells. Glycol coolant is circulated in the cooling ribbon.
The actual configuration is a tad more complicated than shown in figure 1. Teardown photos of the 85 kwh pack have been well documented but the photos are copyrighted. If you are interested in more detail then you can visit this Tesla TMC forum post or this Ricardo Engineering presentation.
The cooling ribbon in Tesla’s 85 kwh pack takes up room. If we wanted to pack the cells tighter, what could we do?
In our conceptual cooling configuration the coolant is moved from in between the cells to a bottom plate located beneath the cells.
The cooling plate concept is not new. BMW uses it in the i3 and GM uses it in the new Chevy Bolt EV. BMW uses refrigerant directly in the pack cooling plate while GM’s Chevy Bolt EV uses glycol liquid in the cooling plate.
The cooling plate by itself may not provide sufficient heat transfer so, in the concept, thin aluminum fins are thermally connected to the cooling plate to increase heat transfer. These thin aluminum cooling fins transfer heat from the cell to the bottom cooling plate in our concept as shown below:
Conceptual P100D Battery cooling configuration
Figure 2 shows the basic concept. However there are many permutations one could hypothesize using the bottom cooling plate design. Here’s just a few:
-Use refrigerant in the cooling plate instead of liquid glycol. This would result in a thinner bottom plate than with glycol coolant
- wrap each cell in a thin aluminum shell to increase contact area with the cell
Cells wrapped in thin aluminum cylinder and placed on dimpled bottom plate
-eliminate the aluminum fins completely and just use the battery case as the conductor. Once Tesla is making their own cells, we would think that as a definite possibility.
Readers please feel free to comment on the proposed configuration and conceptualize your own version in the comments section.
About the authors: George Bower is a retired mechanical engineer with over 20 years experience in gas turbine power systems.
Co-Author of the piece, Keith Ritter is a mechanical engineer, and licensed professional engineer with over 35 years of experience in heating ventilation and air conditioning systems.