by Charles Morris
It sounded like a crazy idea back in the early 2000s, using “laptop batteries” to power the Tesla Roadster. In fact however, it was quite sane. Panasonic’s 18650 battery cell was an industry standard with a proven record of performance that was being produced in large numbers. While other EV pioneers such as Fisker ran into problems with proprietary battery technology, Tesla could count on a secure supply of tried-and-true cells. Since then, Tesla has steadily improved the cells, but it stuck with the 18650 format (named for its size: 18 mm in diameter and 65 mm high) for Models S and X. While other EV-makers opted for larger pouch-style cells, Tesla continued to see the 18650 cells as the most compelling option.
Above: A look at Tesla’s new 2170 battery cell (Instagram: bypantheon)
“We’ve totally custom-engineered that cell, working jointly with Panasonic to create…an automotive cell, tested to automotive standards,” Chief Technical Officer JB Straubel told the Society of Automotive Engineers (SAE) in 2013. “It doesn’t go into laptops anywhere. What keeps us in that general shape and size is the production and cost efficiency. We’re seeing price points that none of the larger-format cells are able to meet.”
Above: Tesla’s older 18650 battery (Image: Charged)
However, all good things must come to an end. Tesla and Panasonic have now developed a new and improved type of cell, which will be used in the upcoming Model 3. The new 2170 cell, which is now being produced at the Gigafactory, is slightly larger – 21 mm by 70 mm. More importantly, it can store a lot more energy. According to Elon Musk, it’s “the highest energy density cell in the world, and also the cheapest.” The 2170 cell is around 50% larger by volume than the 18650, but it can deliver almost double the current (the 18650 delivers 3,000 mA, and the 2170 has been tested at 5,750-6,000 mA).
Above: Inside the 2170 battery cell (Youtube: Portable Electric Vehicle)
Tesla hopes to produce these new, larger cells at the same cost as the old cells, which means a reduction in total battery cost. It’s also assumed (though Tesla won’t confirm any numbers at this point) that the battery chemistry has been improved, yielding a higher energy density. Producing the cells in mass quantities at the massive Gigafactory will allow Tesla to achieve economies of scale.
Above: Comparing the 2170 and 18650 battery cells (Youtube: Portable Electric Vehicle)
Adding all these factors together, plus advances in the way the cells are assembled into modules and complete battery packs, should yield a significant reduction in battery costs. But how much? This question is being discussed at great length, and not only by techies. It’s of great importance to stock market analysts, because it’s bound up with the question of how much profit Tesla is going to be able to make on the “moderately priced” Model 3.
Above: Randy Carlson estimates that a battery module with a single layer of horizontally arranged cells, sized to fit Model 3’s wheelbase and tire size, would hold 220 of the “2170” GigaFactory cells in a 22 Parallel x 10 Series arrangement (Source: Seeking Alpha)
Stock pundit Randy Carlson of Seeking Alpha (usually a forum for diehard Tesla bears) has gone into excruciating detail about the thickness of Model 3’s floor, reasoning that whether the battery cells are mounted vertically (as in the Model S/X battery pack) or horizontally will yield some priceless insight into how great an improvement in energy density Tesla and Panasonic have been able to achieve.
Above: Tesla showed an arrangement of eight battery modules when the Model 3 was unveiled; the length of the modules is constrained by the available distance between front and rear wheelwells (Source: Seeking Alpha)
At the Model 3 unveiling, Tesla showed a drawing with eight large, flat battery modules, but offered no details about how the cells would be arranged within the modules. “If we know [the thickness of] the floor of Model 3, and we know its range, we will have a pretty good idea [of the efficiency of] the GigaFactory cell chemistry,” writes Carlson.