Picture a battery. It’s likely that you’re imagining a standard-format AA or AAA cell, the kind you buy to power various small electrical devices like your television’s remote control or smoke detector.
Now, imagine the battery of an electric vehicle. The image you created looks like a large rectangle instead of a small cylinder.
Although your mind may perceive these two types of batteries as vastly different power-storage devices, the typical store-bought batteries for your various electronic devices and the battery packs in an EV operate on the same general principles. That said, the battery in a hybrid or electric vehicle is a bit more complicated than the lipstick-like cells you’re used to handling.
The battery in an HEV, PHEV, or BEV (which is a hybrid-electric vehicle, plug-in hybrid-electric vehicle, and battery-electric vehicle, respectively) can be made of a variety of materials, each with different performance characteristics. There are specialities. , The individual cells stored in these large battery packs also come in many different shapes and sizes.
How do EV batteries work?
Each cell within an electric vehicle’s battery pack consists of an anode (negative electrode) and a cathode (positive electrode), the two separated by a plastic-like material. When the positive and negative terminals are connected (think switching on a flashlight), ions travel between the two electrodes through the liquid electrolyte inside the cell. Meanwhile, the electrons that these electrodes release pass through the wire outside the cell.
If the battery is providing power (for example, the bulb in the flashlight above) – an action known as discharge – then ions flow from the anode to the cathode through the separator, while electrons flow from the negative (anode) travel on the wire. Positive (cathode) terminal for powering an external load. Over time, the cell’s energy is depleted as it runs off whatever is powering it.
When the cell is charged, however, electrons flow in the other direction (positive to negative) from an external energy source and the process is reversed: electrons flow from the cathode back to the anode, re-energizing the cell. increases.
EV Battery Manufacturing
When you think of the above AA or AAA batteries, you are envisioning a battery cell. But the battery in EVs isn’t a giant version of that single cell. Instead, they are made up of hundreds, if not thousands, of individual cells, usually grouped together in modules. A battery pack can house several dozen modules, which is a complete EV battery.
EV cells can be small cylindrical cells like AA or AAA cells of various standardized dimensions. That’s the approach Tesla, Rivian, Lucid and a few other automakers have taken, which link together thousands of these tiny cells. These companies claim that the advantage is that the smaller cells are much cheaper to produce in volume. Nevertheless, Tesla plans to reduce the number of large cylindrical cells within its cars’ battery packs to reduce the number of connections.
But EV cells come in two other formats: prismatic (rigid and rectangular) or pouch (also rectangular, but in a softer aluminum case that allows some expansion in the cell walls under extreme heat). There are few standardized prismatic- or pouch-cell dimensions, and most carmakers—General Motors and Ford, for example—make their own in partnership with cell manufacturers, such as China’s CATL, Japan’s Panasonic, or Korea’s LG Chem. Let’s imagine
EV Battery Types
The chemistry of an electric vehicle battery – or the material used in its cathode – varies among different cell types. Today, there are essentially two types of battery chemistry under the lithium-ion umbrella, meaning that their cathodes use lithium along with other metals.
Two Types of Lithium-Ion Batteries
The first, most common in North America and Europe, uses nickel, manganese, and cobalt (NMC) or a mixture of nickel, manganese, cobalt, and aluminum (NMCA).
These batteries have a high energy density (energy per weight, or energy per volume), but also a high tendency to oxidize (catch fire) during a drastic short circuit or severe impact. Cell manufacturers and battery engineers spend a great deal of time monitoring cells and modules during manufacture and in use during the life of the car, to limit the potential for oxidation.
The second type, which is far more widely used in China, is known as lithium-iron-phosphate, or LFP. (This is despite the fact that Fe has the symbol for iron on the periodic table, while F is actually fluorine.) Iron-phosphate cells have a much lower energy density, so larger batteries are needed to provide the same amount of energy. (and hence driving range) as NMC-based batteries.
However, this is offset by the fact that LFP cells are less likely to be depleted. LFP cells also do not use rare and expensive metals. Both iron and phosphate are used in a variety of industrial applications today, and neither is considered remotely scarce or resource-limited. For those reasons, LFP cells are less expensive per kilowatt-hour.
Low cost made Tesla (and Ford recently) to use LFP cells in its base-model electric vehicles, saving the expensive and high-energy chemistry for the more expensive models in the lineup.
As for the other cell electrodes, the anodes, today most of them are made of graphite.
ev battery software
Unlike your basic AA or AAA cell, an EV battery requires a lot of software to keep tabs on things. You can expect an AA or AAA cell to last a few years at most. However, automakers warranty the battery components of their EVs, often for about a decade or up to 150,000 miles of use.
All EV batteries lose some charge capacity over time. With the limited data available, it’s difficult to dig into the specifics of these losses. In general, range loss can be in the order of 10 to 20 percent after 100,000 miles. In other words, an EV originally capable of delivering 300 miles of range would still net between 240 and 270 miles of range at this point in its lifecycle.
To ensure this, battery modules and packs contain multiple sensors to monitor the power provided by each component – ideally, the same across all cells and modules – and the heat of the pack. A suite of software known as a battery management system (BMS) monitors this information.
Like humans, batteries are very susceptible to changes in temperature, and they perform best at around 70 degrees Fahrenheit. If an EV’s battery pack shows signs of getting too hot, the BMS of most modern HEV, PHEV, and BEV batteries will circulate coolant through the pack to reduce the heat and bring the temperature closer to 70 degrees. Batteries provide less power in extreme cold. If an EV owner pre-conditions their vehicle, its control software and BMS can use grid energy (if plugged in) or perhaps some battery energy to heat the battery. Preconditioning allows an EV battery to deliver a specific power level as soon as the driver starts up.
New battery technology for electric cars
Battery technology is always evolving. Although today’s EVs overwhelmingly use lithium-ion packs, many battery-powered cars of tomorrow will likely use packs with different chemistry. For example, solid-state batteries using cells with a solid electrolyte are a promising option that many manufacturers are investing in. In fact, Toyota plans to introduce a vehicle with a solid-state battery by the middle of the decade.
Solid-state batteries are due to provide greater energy density, which provides better driving range relative to similar lithium-ion batteries. This breakthrough technology still has some way to go, however, as engineers work to reduce the material cost of producing solid-state cells. Similarly, the lifetime of these cells would need to be dramatically improved to accommodate the thousands of full-discharge cycles of HEV, PHEV, or BEV.
Regardless, the future of battery-powered vehicles is promising. Look for new technologies to improve the efficiency and range of electric cars, and the cost of lithium-ion battery packs to drop significantly in the coming years.
Edited by John Voelker Green Car Report For nine years, publishing more than 12,000 articles on hybrid, electric cars and other low- and zero-emission vehicles and the energy ecosystem around them. He now covers advanced auto technologies and energy policy as a reporter and analyst. His work has been included in print, online and radio outlets. Wired, Popular Science, Tech Review, IEEE Spectrumand NPR’s “All Things Considered.” He splits his time between the Catskill Mountains and New York City, and still hopes to one day become an international man of mystery.