Temperature, range, and charging are closely connected in the minds of most electric car owners. Why? Basically, chemical reactions happen faster at higher temperatures. Think of the electrons inside your battery as minions. During charging, they move from the cathode to the anode. While driving, the process is reversed.
When your battery is nice and warm, those helpful minions are full of energy and running around like crazy doing minion-like things. When its below freezing, those minions are like, “Dude. Do we really have to do this?” They move, but more slowly.
Recurrent is devoted to overcoming the fear, uncertainty, and doubt that is holding the EV revolution back. Recently it published a detailed explanation of how temperature, charging, and range are related, using a graph sourced from Autoblog.
Notice anything interesting? Every electric car in that chart has less range when the temperature drops, which means EV drivers have to be aware of the weather, especially on trips. [Most combustion engine cars suffer some loss of range in cold weather as well.]
Recurrent explains that cold weather slows the chemical and physical reactions that make electric car batteries work, specifically conductivity and diffusivity, leading to:
- Longer charging time (increased impedance)
- Temporary reduction in range (lower capacity), primarily due to heating systems. Since the energy for heating and cooling your car comes from the same battery that propels the car, use of climate control can pull charge away from the primary battery
Even though cold-related range effects are temporary, your battery should be above freezing before charging, it advises. Most vehicles do have some sort of temperature regulation in their battery management system (BMS) that will prevent high voltage or fast charging if the battery is too cold.
In general, if your vehicle is turned on or plugged in, energy will be drawn to keep the temperature in a healthy range. The two outliers for this are Nissan Leaf, which only has thermal regulation kick on when the temperature is below -20C (-4F), and Tesla, which will activate thermal management even if the vehicle is off or not plugged in. Tesla’s temperature regulation protects your battery health, but can also cost you some range if the car is heating the battery while not plugged in.
Here is a chart Recurrent created that shows how cold temperatures affect the range of several popular electric cars.
How To Charge Your Electric Car When It’s Cold
Range is one thing. Charging is something else entirely. Cold weather makes ions flow through battery cells more slowly, causing lithium to build up outside the node and turn into an inert metal. This lithium plating disrupts the future flow of energy and uses up some of the lithium that is supposed to power the battery, which can lead to a decrease in power and range.
If you’re interested in more detail, Recurrent says battery anodes are made of materials like graphite that have lattice-like structures. When a battery charges, lithium ions move from the cathode into the anode and are stored in those lattice spaces. If charging takes place when it is cold out, the ions enter the anode more slowly and the build up of lithium outside can result in metallic plating. Some of these ions will gradually enter the anode over time, but some will remain plated outside, permanently reducing capacity and increasing internal battery resistance.
The computer in most electric cars will preheat the battery and slow the rate of charging until it is safe to charge normally. That’s a good thing, but it also decreases range unless the car is plugged in while preheating is taking place. On the other hand, even when it’s very cold, you can use an already charged lithium-ion battery worry free, Recurrent says. “You’ll notice short term reduced range since the cold weather inhibits ion flow, but there is likely no long term damage.”
Hot Weather Affects Batteries Too
Did you know more batteries fail in summer than in winter? AAA does. It replaces many more batteries in hot weather than in cold weather. Hot weather also affects EV batteries. Recurrent says higher temperatures mean there is more total energy in a system, which leads to faster reactions across the board. This means that all reactions happen faster in high heat — both the ones that produce energy and the “unwanted” chemical reactions that make batteries degrade.
If you want to get into the nerdy specifics, high temperatures increase the rate of reactions in the Solid Electrolyte Interphase (SEI) — a layer of inactive lithium that forms on the anode surface. The SEI is made up of lithium salts that react with the electrolyte solvent and become inert. It is permeable to the lithium ions that make the battery work, but impermeable to the electrolyte, so it serves as a protective barrier between the anode and electrolyte. To clarify, this layer is not the same as lithium plating. While it does use up some of the lithium available to power the battery, it also makes the electrolyte stable and helps protect the anode from corrosion.
The problem is that high heat can affect the composition and organization of the SEI layer inside battery cells. That may trigger reactions that use up too much active lithium or create inert compounds that prevent ions from flowing freely. It’s all a matter of degree, no pun intended. Some SEI is necessary to protect the battery and ensure long term stable use. Too many reactions in the SEI pull too much lithium away from producing energy and can prevent ions from moving around in the battery.
The exact way that the heat degradation mechanism works is different for batteries at rest, batteries charging, and batteries being cycled. The heat effects also differ between specific battery chemistries. In most cases, though, higher temps will lead to faster degradation.
A process known as “calendar aging” refers to battery degradation that happens regardless of use. It is largely due to growth in the protective layer around the anode (SEI). At high temperatures, normal chemical reactions in the battery happen faster and the protective structure can degrade, causing more lithium to be pulled into the protective layer.
High temperatures can damage batteries during charging because they increase the effective force of the electric current that drives lithium ions from one node of the battery to the other. That causes physical stress and damage on the receiving end. The higher the temperature — or the higher the current — the more stress fractures and damage the battery node experiences. All these little fissures and cracks become surfaces for secondary reactions, using up available lithium and creating compounds that hinder the free flow of energy.
For more on the effect hot weather has on an electric car, check out this video from Recurrent.
The Electric Car Takeaway
Electric cars are different from conventional cars. People who don’t understand the differences make up all sorts of things about EVs that just aren’t true. I had a neighbor last week tell me I couldn’t drive my Tesla in the rain or through a puddle. The cure for such misunderstandings is to supply accurate information. That’s what the people at Recurrent try to do. We think they have succeeded in spectacular fashion.
Appreciate CleanTechnica’s originality and cleantech news coverage? Consider becoming a CleanTechnica Member, Supporter, Technician, or Ambassador — or a patron on Patreon.
Have a tip for CleanTechnica, want to advertise, or want to suggest a guest for our CleanTech Talk podcast? Contact us here.
Source: Clean Technica