Tesla’s road to a cheaper electric car has always appeared to lead straight to Reno, where the electric automaker is building a $5 billion gigafactory designed with enough capacity to reduce the per-kilowatt-hour cost of its lithium-ion battery packs by over 30% by the end of 2017.
Many companies are already planning concepts around the promise of cheaper, higher-capacity batteries. But, it turns out that TeslaTSLA 0.40% has more than one path toward its ultimate goal of an electric car that’s 50% cheaper than its luxury Model S.
The newest direction Tesla is headed toward is silicon—not the Valley, but the material that is changing the way batteries are made. Tesla’s new 90 kilowatt-hour battery pack—an upgrade announced Friday that increases pack energy by 5% and adds about 15 miles of range to its vehicles—might look the same. But the inclusion of silicon is an advance for lithium-ion technology.
During a call with reporters last week, CEO Elon Musk said the company had improved the battery by shifting the cell chemistry for the pack to partially use silicon in the anode.
“This is just sort of a baby step in the direction of using silicon in the anode,” Musk said during the call. “We’re still primarily using synthetic graphite, but over time we’ll be increasing silicon in the anode.”
For the unfamiliar, this might sound like minor tinkering. It’s actually an important and challenging step for Tesla (and other battery manufacturers) that could lead to a better, cheaper battery.
“It’s a race among the battery makers to get more and more silicon in,” said Jeff Dahn, a leading lithium-ion battery researcher and professor at Dalhousie University in Nova Scotia who recently signed a 5-year exclusive partnership with Tesla. “The number of researchers around the world working on silicon for lithium-ion cells is mindboggling. A large number of academics and industrial folks are working really hard on this problem.”
A battery contains two electrodes: an anode (negative) on one side and a cathode (positive) on the other. An electrolyte, essentially the courier that moves ions between the electrodes when charging and discharging, sits in the middle.
Graphite is commonly used as the anode in commercial lithium-ion batteries. However, a silicon anode can store about 10 times more (per unit volume) lithium ions. In theory, if you replaced a lot of graphite in the cell with silicon, the thickness of the graphite negative electrode could be reduced. There would be more space to add more active material and you could, in turn, increase the energy density—or the amount of energy that can be stored in a battery per its volume—of the cell.
In other words, you could pack more energy in the same space. Plus, the silicon used in the battery space doesn’t need to be the same quality as what’s used in solar cells and integrated circuits, which means it’s cheaper. The more silicon you put in the battery, the easier it is to drive costs down.
That’s the goal of battery makers everywhere: to improve their product while reducing costs.
Sounds easy enough, right? Hardly, says Dahn, who is currently working on a project funded by 3M and the Natural Sciences and Engineering Research Council of Canada to develop longer lasting, lower cost lithium-ion battery cells. Their exclusive partnership with Tesla will begin in June 2016, once Dahn has completed the 3M research project.
The trick is that when you add lithium to the silicon you end up with almost five times the original number of atoms you started with. And that causes all kinds of problems.