Tesla Structural Battery Pack, the good and the bad
May 26, 2021
By Henry Farkas
Back in September of last year, Tesla had its Battery Day presentation (full video below). In January of this year, Electrek wrote an article about the Tesla structural battery. So why am I writing about this now? The structural battery pack was just a gleam in Elon Musk's eye at that time, but soon, there will be cars that incorporate the new design. Here's what you should think about if you're considering buying a Model S Plaid or a Cybertruck with the structural battery pack.
As Elon said during the presentation, the structural battery pack was inspired by the airline industry. They used to put gas tanks in the wings of airliners. The tanks added weight. More weight meant more fuel needed to fly. Eventually, the aircraft manufacturers figured out that they could save weight if the wings were the gas tanks. They saved weight that way. It's the same with battery packs. Right now, there are battery cells that are put together in modules. The modules add weight. Then the modules are put together into a large battery pack. That adds more weight. Then all that stuff is put into the structure. More weight means less range.
Tesla engineers figured out that they could save lots of weight if they eliminated modules and if the battery pack was the structure. They do that by making a honeycomb structure with all the wiring and cooling coils inside it. Then they drop in the 4680 cells and epoxy them to the honeycomb structure. For those of you who are not aware, the designation, 4680 refers to the 46mm diameter of the battery cells and the 80mm height of the Tesla cells. Those battery cells are larger than the ones currently in use by all previously made Teslas so they store more power in each cell. For comparison, visualize the current Tesla battery cells being like AA batteries and the 4680 cells being like D batteries. Remember D batteries?
The following picture is from the article in Electrek cited above. You can appreciate the honeycomb pattern of the pack, a structure known for strength and light weight. The coolant loops are built into the sides of the pack.
So saving weight, stronger cells, less of them. More battery, less other stuff. It's all good, right? Maybe.
Here's the bad part.
If the car gets in an accident and the battery pack is breached, you can't just take out the old pack and drop in another pack. That might not matter because chances are pretty good that an accident bad enough to damage the battery pack will total the car. From an individual's perspective, that's why you get insurance. But there are other considerations if you care about the environment you're leaving to my grandchildren.
Batteries should be recycled. So far, they're not designed for recycling. With technology at its current state, it's cheaper to mine new materials than it is to recycle the materials from used batteries. The ability to recycle gets worse when the batteries are epoxied into a big honeycomb structure. I'm not a chemical engineer so I can't offer any suggestions about how battery cells could be designed to make recycling cheaper than mining new materials, but they should be designed that way.
The other bad thing about the structural battery pack is that cells don't all deteriorate at the same rate. With the current battery packs, bad cells can be detected and switched out for good cells to rejuvenate the range of an old Tesla. That won't be feasible with the structural battery pack. That may or may not be important. It depends on whether the cells last as long as the rest of the car or not. Time will tell, but it's something to think about if you plan to keep your car for the million miles that Tesla claims their cars are designed to last.
Here is Tesla's 'Battery Day' presentation. If you care exclusively about the structural battery, you can jump to the 1 hour, 19 minute mark.
Henry Farkas is a retired country doctor. He bought his Tesla Model 3 in the middle of the pandemic. If you plan to buy a Tesla, you'll want a referral code. That will get you and the person whose code you use 1,000 miles of free supercharging. If you need one, use this one: https://ts.la/henry80997.