2022 was a year to remember - not only was the summer of 2022 England’s joint warmest (2018), the year itself was the warmest on UK record.
But as autumn draws to a close and winter slowly creeps forward, what does the change in seasons mean for EV batteries? And how will colder temperatures affect your EV range?
Let’s get plugged in...
What a (battery) wants
Lithium-ion (or Li-ion) batteries are the powerhouse for most EVs. Without it, the storage of energy in EVs would not be possible.
A lithium-ion battery cell contains two types of electrodes: anode and cathode. Due to their remarkable ability in storing lithium ions (energy), anodes and cathodes are the primary reason why lithium-ion batteries are used in EVs. To learn more about how a lithium-ion battery works, read our blog: How do EVs work?
For this blog, it's important to note that the optimum temperature for lithium-ion battery cells falls between 15 - 45 degrees celsius. If the battery cell temperature falls outside these parameters, the battery cell can be damaged. So, how is battery cell temperature monitored in EVs, and what happens if temperatures fall outside these parameters?
Strategically integrated, the EVs internal thermal management system (ITMS) monitors the battery health to gauge remaining range (mileage) and life. Most importantly, it also regulates the temperature of the battery to ensure that it continues to operate safely and efficiently.
Both external and internal factors can impact battery temperature. For example, when a battery charges, a lot of heat is created (more so with rapid and ultra-rapid charging) which - if unchecked - can ultimately damage the battery. Once the high temperature is flagged by the ITMS, the EV releases coolant to decrease the battery heat. Typically, when an EV first registers a rapid charging session, it will slowly release coolant to ensure that the battery never reaches its temperature limit. If the coolant is not sufficient, the EV will reduce its charging rate - while this means your EV will take longer to charge, the battery will be protected.
So, what happens when temperatures fall below 15 degrees celsius?
What do colder temperatures do to EV batteries?
In the UK, winter temperatures average between 0 - 7 degrees celsius - that’s between 8 to 15 degrees colder than a lithium battery can optimally perform. Due to the internal kinetics of the battery cell, colder temperatures slow the chemical reaction.
What does this mean in real life? 10 - 15% less driving range.
For example, the Tesla Model Y peaks between 260 miles (summer) and 245 miles (winter), while the Mazda MX-30 dips between 105 miles (summer) and 90 miles (winter).
If you’re interested in a more scientific answer, say no more. According to our friends at Recurrent:
“...battery anodes are made of materials, like graphite, that has lattice-like structures. This is important because when a battery charges, lithium ions move from the cathode into the anode and are stored in this grid-like structure. This process is called intercalation. Force (in this case, current) is needed to push the ions into the anode and lodge them in the grid. If this process happens when it is cold out, the ions enter the anode more slowly and the build-up of lithium outside can form a 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.”
Much like the process for temperatures exceeding 45 degrees celsius; when the temperature for an EV battery falls below 15 degrees the ITMS kicks into action and slowly warms the battery. So, why not warm the battery more quickly?
Forcing the chemical reaction to speed up, so that it charges more quickly, can cause the lithium to form dendrites - which in turn, can short-circuit the cell. This is why the ITMS warms the battery gradually.
Unfortunately, colder temperatures do affect the performance of lithium-ion batteries, but there are steps you can take to reduce its impact on your EV range and efficiency.
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