New temperature-resistant batteries could make electric vehicles better able to withstand extreme cold and heat—and ultimately drive longer on a single charge.
Researchers at the University of California San Diego have developed lithium-ion batteries that work well in freezing cold and scorching heat.
They used a special temperature-resistant electrolyte – the substance in a battery that allows an electric current to flow.
When introduced into EV production, the batteries could allow EVs in cold climates to go further on a single charge.
They could also reduce the need for expensive cooling systems to keep vehicles’ battery packs from overheating in hot climates.
Engineers at the University of California San Diego have developed lithium-ion batteries that perform well in freezing cold and scorching heat. Such batteries could allow electric vehicles in cold climates to go further on a single charge. They could also reduce the need for cooling systems to prevent vehicles’ battery packs from overheating in hot climates (stock image)
Currently, temperatures that are too hot or too cold can affect the performance of batteries in electric vehicles, for example by slowing down the charging speed and reducing the vehicles’ range before they need to be recharged.
A driver’s fear of running out of charge before reaching another charging station is referred to as “range anxiety” and is seen as a barrier to mass adoption of green electric vehicles.
“You need high-temperature operation in areas where the ambient temperature can be in the hundreds and the streets get even hotter,” said Professor Zheng Chen of the UC San Diego Jacobs School of Engineering.
“In electric vehicles, the battery packs are typically under the floor, near those hot roads.
“Furthermore, batteries heat up simply because current flows during operation. If the batteries cannot withstand this warming up at high temperatures, their performance will deteriorate quickly.”
Batteries consist of three main components – anode, cathode and electrolyte.
The electrolyte (usually a chemical in the form of a liquid or paste) separates the anode and cathode and moves the flow of electrical charge between the two.
When charging, lithium-ion batteries move lithium ions from the cathode to the anode.
The batteries developed by Chen and colleagues are resistant to both cold and heat thanks to their electrolyte, a liquid solution of dibutyl ether mixed with a lithium salt.
What is special about dibutyl ether is that its molecules bind weakly with lithium ions, allowing the electrolyte molecules to easily release lithium ions during operation.
This weak molecular interaction improves battery performance in sub-zero temperatures.
Lithium-ion batteries contain two electrodes — one made of lithium (cathode) and one made of carbon (anode) — that are immersed in a liquid or paste called the electrolyte. When the battery charges, electrons that were bound to the ions flow through a circuit, powering a device
Also, dibutyl ether can easily withstand heat because it remains a liquid at high temperatures — it has a boiling point of 286°F or 141°C.
In tests, the proof-of-concept batteries retained 87.5 percent and 115.9 percent of their energy capacity at -40 °C and 50 °C (-40 °F and 122 °F), respectively.
The new batteries also had high “Coulombic efficiency” at these temperatures of 98.2 percent and 98.7 percent, respectively, meaning they can go through more charge and discharge cycles before they stop working.
Researchers say their electrolyte is also compatible with a lithium-sulfur battery, a type of rechargeable battery that has a lithium metal anode and sulfur cathode.
Lithium-sulfur batteries can store up to twice more energy per kilogram than today’s lithium-ion batteries, which could potentially double the range of electric vehicles without increasing the weight of the battery pack.
Most electric cars are powered by lithium ion batteries that are charged and discharged by lithium ions moving between the negative (anode) and positive (cathode) electrodes. Pictured is charging electric cars in Mosjøen, Norway
However, lithium-sulfur batteries have some problems that currently stand in the way of their commercialization, such as: B. the reactivity, especially at high temperatures.
In addition, lithium metal anodes tend to form needle-like structures called dendrites, which can puncture parts of the battery and cause a short circuit.
As a result, lithium-sulfur batteries only last up to ten cycles.
The dibutyl ether electrolyte developed by the UC San Diego team prevents these problems, even at high and low temperatures.
The batteries they tested had longer lifespans — the number of charge and discharge cycles they can go through before losing performance — than a typical lithium-sulfur battery.
The team also engineered the sulfur cathode to be more stable by grafting it onto a polymer that prevented more sulfur from dissolving in the electrolyte.
In future research, the team plans to scale up the battery chemistry, make it operate at even higher temperatures, and further extend cycle life.
They described their temperature-resistant batteries in an article published in the Proceedings of the National Academy of Sciences.