Why don’t lithium-ion batteries work well in the cold? A battery researcher explains.

Wesley Chang is an assistant professor of mechanical engineering and mechanics at Drexel University.

Rechargeable batteries are ideal for storing energy and powering electronics, from smartphones to electric vehicles. However, in cold environments they can be more difficult to charge and can even catch fire.

I am a professor of mechanical engineering and have been interested in batteries since college. I now lead a battery research group at Drexel University.

In the past decade alone, I have seen the price of lithium-ion batteries drop as the manufacturing market has become much larger. Future forecasts predict that the market could reach thousands of GWh per year by 2030, a significant increase.

But lithium-ion batteries aren’t perfect; this rise comes with risks, such as a tendency to slow down in cold weather and even catch fire.

Evidence collected by the New York City Fire Department of fires caused by lithium-ion batteries. December 2023.

CBS News

Behind the Li-ion battery

The electrochemical energy storage in batteries works by storing electricity in the form of ions. Ions are atoms that have a non-zero charge because they have too many or too few electrons.

When you plug in your electric car or phone, the electricity supplied by the wall socket drives these ions from the positive electrode of the battery to the negative electrode. The electrodes are solid materials in a battery that can store ions, and all batteries have both a positive and a negative electrode.

Electrons pass through the battery as electricity. For every electron that goes to one electrode, a lithium ion also goes to the same electrode. This ensures the balance of the charges in the battery. As you drive, the stored ions in the negative electrode move back to the positive electrode, and the resulting flow of electricity powers the engine.

Although AA or AAA batteries can power small electronics, they can only be used once and cannot be recharged. Rechargeable Li-ion batteries can be fully charged and discharged for thousands of cycles. They can also store a much larger amount of charge for each cycle than an AA or AAA battery.

Because lithium is the lightest metal, it has a high specific capacity, meaning it can store a huge amount of charge per weight. This is why lithium-ion batteries are useful not only for portable electronics, but also for powering transportation vehicles with limited weight or volume, such as electric cars.

Battery is on

However, lithium-ion batteries have risks that AA or AAA batteries do not. First, they are more likely to catch fire. For example, the number of electric bicycles battery fires reported in New York City has increased from 30 to almost 300 in the past five years.

There are many different problems that can cause a battery fire. Poorly manufactured cells may contain defects such as traces of impurities or particles left behind during the manufacturing process, increasing the risk of an internal defect.

Test demonstrates the explosive power of a thermal runaway from a lithium-ion battery

The climate can also affect battery performance. Electric vehicle sales have been rising in the U.S., especially in cold regions like the Northeast and Midwest, where frigid temperatures can hamper battery performance.

Batteries contain fluids called electrolytes, and cold temperatures make fluids flow more slowly. So the electrolytes in batteries slow down and thicken in the cold, causing the lithium ions inside to move more slowly. This delay can prevent the lithium ions from being properly introduced into the electrodes. Instead, they can deposit on the electrode surface and form lithium metal.

If too much lithium ends up on the surface of the electrode during charging, it can cause an internal short circuit. This process can cause a battery fire.

Making safer batteries

My research group, together with many others, is investigating how batteries can be made that work more efficiently in the cold.

For example, researchers are investigating how the usual battery electrolyte can be replaced with an alternative electrolyte that does not thicken at low temperatures. Another possible option is to warm up the battery before charging, so that the charging process takes place at a higher temperature.

My group is also investigating new types of batteries besides lithium-ion. These may include battery types that are more stable over wider temperature ranges, types that do not use liquid electrolytes at all, or batteries that use sodium instead of lithium. Sodium ion batteries could work well and cost less since sodium is a very abundant resource.

Solid state batteries use solid electrolytes that are non-flammable, reducing the risk of fire. But these batteries don’t work as well as Li-ion batteries, so more research will be needed to determine if this is a good option.

Lithium-ion batteries power technologies that people across the country use every day, and research in these areas aims to find solutions that make this technology even safer for consumers.

This article is republished from The conversation under a Creative Commons license.

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