Tesla's Battery Options & Nickel Buried within Tesla Motors’ hour-and-fifteen-minuteearnings call earlier this month was the nugget that the electric automaker plans to use two different variations of lithium-ion batteries for its two different grid battery products.
The news could easily be dismissed as just a bit of battery geekery, but there’s more to it than that. It suggests that Tesla is not just increasing how many types of batteries it uses in its products, but that it has the ability to produce both models at its planned battery “gigafactory.” The batteries could influence how the facility is designed.
But before we understand how much this could affect Tesla’s factory, let’s take a step back to explain the nuts and bolts of battery making and why Tesla wants to do this.
Lithium-ion battery basics
Most traditional lithium-ion batteries that are found in devices like cell phones are made using a cathode that’s a mixture of lithium cobalt oxide. The structure of a battery is made up of two electrodes—a cathode (positive) and an anode (negative)—and a medium, called the electrolyte, through which the electric charge flows. Lithium ions move back and forth between the cathode and the anode when a lithium-ion battery charges and discharges.
The cathode part of the battery is the place where traditionally the lithium-ion battery industry can tweak the energy and power density—or how much energy and power can be stored per volume. (Power is basically how quickly the energy can be taken out and put to work.) Different material combinations can make the battery able to store more energy or produce more power, and likewise make the battery more or less stable. (The energy created in a battery is, by its nature, volatile.)
The batteries that Tesla has been using, sourced from Panasonic, for its Model S electric car are mostly likely a lithium-ion battery with a cathode that is a combination of a lithium, nickel, cobalt, aluminum oxide. The battery industry calls this an “NCA battery” and they’ve been around—and made by Panasonic—for many years.
Typically, lithium-ion NCA batteries use a combination of 80% nickel, 15% cobalt and 5% aluminum. It’s unclear what mix Tesla and Panasonic’s battery combination is. (The anodes in these traditional lithium-ion batteries is usually a graphite combination, which acts as a host for the lithium ions.) The addition of the aluminum to the NCA battery makes it more stable.
Tesla CEO Elon Musk said on the company’s earnings call that Tesla will be using a high energy lithium-ion NCA battery for its new grid battery. Similar to the one it uses in its cars, the grid battery is intended for use by utility companies for back-up power. These are the batteries that, when used in a big battery “farm,” could replace so-called peaker power plants, the “dirty” and expensive power plants that utilities use only when grid demand peaks, such as during a sweltering summer afternoon. (The Tesla website describes this as the back-up battery with a capacity of 10 kilowatt-hours and a price of $3,500.)
In contrast, Musk said that Tesla will use a lithium-ion battery with a nickel, manganese, cobalt oxide cathode for its grid battery. Called an NMC battery, it’s meant to be used for daily cycling for a home, business, or certain types of clean power. “There’s quite a lot of manganese in there,” Musk said.
The other option uses one-third equal parts nickel, manganese, and cobalt. Again, it’s unclear what the combination of Panasonic and Tesla’s version is.
Different applications
The choice of these two batteries makes sense for what Tesla wants its customers to do with the batteries. The back-up battery is intended to offer a lot of energy, quickly, to smooth out that “heat wave” grid peak without using a peaker plant. It’s like when someone driving a Tesla Model S punches the accelerator.
On an electrical grid, these type of events rarely happen—but they do. A back-up battery doesn’t need to be charged and discharged on a regular daily basis, just when it’s really needed. Tesla says its battery has 60 or 70 cycles—charge and discharge
Musk optimistically says that the lifetime of that battery is 1,000 to 1,500 cycles, or “maybe 15 years calendar life.” Those numbers should be taken with a grain of salt—they are likely based on a situation in which the battery isn’t always using its full capacity.
Tesla’s daily charging grid battery, on the other hand, is meant to offer more reliable sustained charging every day. If you paired this battery with a utility’s solar energy farm, the batteries would be expected to store the energy from the solar panels during the day to potentially be used at night.
The daily battery can have a lower energy density, but it needs a longer cycle life—that is, it needs to be able to be charged and discharged many more times than the backup battery. The daily battery has a 5,000 cycle life, Musk said on the call, and a similar lifespan as the back-up battery—but again, take those numbers with a grain of salt.
An NCA battery typically has a shorter cycle life and a higher energy density (and less stability). An NMC battery generally has a longer cycle life, more stability, and less energy density.