Most electric car batteries are made of varying quantities of lithium-ion, cobalt, nickel, manganese, silicon and electrolytes. Within that are battery cells, which consist of the anode and cathode, the separator, the electrolyte, and the positive and negative current collectors (think flat side and side with the bump in an AA battery). But what does that mean exactly? Why lithium? Which ions? Fear not — Edmunds explains what electric car batteries are made of.
To start, let's establish that even though a Tesla battery and a Chevrolet Bolt battery are both lithium-ion batteries, that doesn't mean that they're made the same. Battery chemistry has a huge impact on the way a battery pack charges and discharges, how it manages heat, how much energy each cell in the battery pack can store, and what each cell costs. That's why battery manufacturers like Panasonic, CATL, Samsung SDI and LG are always trying to tweak their chemistry to get the best performance and lowest costs.
The exact recipes for most manufacturers' battery cells aren't public information, as each company has its proprietary formula. Still, the basic ingredients are more or less the same, so let's break down what they are and what they do, starting with lithium.
Lithium
The lithium in a lithium-ion ("Li-ion" for short) battery makes up the cathode and anode, a.k.a. the positive and negative sides of a battery cell. The lithium ions move around inside the positive side of the cell (cathode) and generate electrons that, being negatively charged, want to get to the negative side (anode) of the battery but can't because of the separator between the cathode and anode. This means that the electrons will flow out of the positive side of the battery, through your device, powering it, and then back to the anode.
The lithium in the cell isn't pure elemental lithium because it's far too reactive with other elements to be safe. Instead, the lithium used is in the form of a lithium metal oxide, which stabilizes the mix. In most cases, manufacturers use lithium cobalt oxide on the cathode side of the battery and lithium-carbon compounds on the anode.
Cobalt
Cobalt is used in batteries for two main reasons. First, it offers excellent energy density, meaning that the more cobalt a battery cell uses (to a point), the more electricity it can store. The other advantage is that cobalt increases the thermal stability of a battery cell. Why is thermal stability important? In our related article about electric car fires, we noted that the less a battery is reactive to temperature changes, the less prone it is to thermal runaway, and therefore less prone to bursting into a difficult-to-extinguish lithium fire.
The overreliance on cobalt does have its downsides. Cobalt is considered a rare-earth element, and as the name implies, it isn't very common. That makes it expensive to source. It also tends to be found in regions that suffer from a great deal of political and societal instability, which can lead to wild price fluctuations as well as significant human rights abuses by mining companies and the countries in which they operate.
These issues have led battery manufacturers to try to reduce the amount of cobalt in their chemistries. They offset the cobalt with nickel, which is considerably cheaper and less rare, but it too has its downsides.
Nickel
Nickel is used in batteries to increase a cell's energy density, similar to cobalt. Unlike cobalt, however, nickel-rich battery cells can have issues with microcracking on the surface of the cathode. This can cause performance degradation in a shorter time than a battery with less nickel and more cobalt.
There are still plenty of upsides to using nickel. First, it sells for about $18,000 to $21,000 per ton, compared to cobalt, which regularly goes for over $30,000 per ton and has greater price fluctuations. Next, those microcracks that cause performance loss can be mitigated by using a "gradient" in the cathode construction. This means that the centre of the cathode is mostly nickel, and then other metals with different performance characteristics are layered over it.
Manganese
The third main ingredient in many battery chemistries is manganese. While nickel and cobalt work with lithium to increase energy storage, manganese keeps everything together and stable. It's a structural additive, and as such, is used in smaller percentages than nickel or cobalt.
Silicon
Silicon is used in the anode alongside lithium and carbon to increase energy density. When you increase the energy density on the positive side of the cell with nickel and cobalt, those electrons will need a place to go after their trip through your EV's motors. Silicon is great because it's stable, inexpensive, and can hold around 10 times as many electrons as graphite.
Electrolyte
Without an electrolyte in a battery cell, there would be no way for electrons to move from the anode to the cathode during charging. It's the secret sauce that makes the whole battery work. There are several kinds of electrolytes and the chemistry can get complex, but they break down into a few different families.
Aqueous solutions are liquid, while non-aqueous solutions aren't. Then there are ionic liquids, which are more temperature-stable and have better transfer characteristics than organic aqueous and non-aqueous solutions. Next, there are polymer electrolytes, which use plastics as their binding agents. Lastly, there are hybrid electrolytes, which are hybrids of the other types.
Separator
The separator's main job inside a cell is to prevent short circuits from occurring by separating the cathode and anode. The separator is typically made from microporous plastic and allows some electron flow from the cathode directly to the anode, which is known as self-discharge. This is normal, but when a cell gets too hot, the separator acts as a kind of fuse for the cell. The plastic in the separator melts and those micropores close up, fully sequestering one side of the cell from the other and hopefully preventing a nasty fire.
Edmunds says
There's plenty of advanced chemistry happening inside an electric car's battery. Since many EV batteries rely on rare-earth metals, they make up the most expensive part of the vehicle and are part of the reason why MSRPs remain high.
This story was produced by Edmunds and reviewed and distributed by Stacker Media.
