New temperature-resistant batteries could mean electric vehicles will be better able to withstand extreme cold and heat, and ultimately travel longer on a single charge.
Researchers at the University of California, San Diego have created lithium-ion batteries that perform well in freezing, scorching temperatures.
They used a special temperature-resistant electrolyte – the substance in a battery that allows electric current to flow.
If introduced into electric vehicle production, batteries could allow electric vehicles in cold climates to travel farther on a single charge.
They could also reduce the need for expensive cooling systems to keep vehicle batteries from overheating in hot climates.
Engineers at the University of California, San Diego have developed lithium-ion batteries that work well in freezing, scorching temperatures. Such batteries could allow electric vehicles in cold climates to travel farther on a single charge. They could also reduce the need for cooling systems to prevent vehicle batteries from overheating in hot climates (stock image)
WHAT ARE LITHIUM-ION BATTERIES?
A lithium-ion battery is a type of rechargeable battery that is charged and discharged by lithium ions moving between the negative (anode) and positive (cathode) electrodes.
Lithium-ion batteries contain lithium which is only present in ionic form in the electrolyte.
In comparison, lithium metal batteries are generally non-rechargeable and contain metallic lithium.
Most lithium metal batteries are not rechargeable, but lithium-ion batteries are.
A lithium metal battery should never be recharged whereas lithium-ion batteries are designed to be recharged hundreds of times.
Because lithium-ion batteries are suitable for high capacity energy storage, they are used in a wide range of applications, including consumer electronics such as smartphones and PCs, industrial robots, production equipment and automobiles.
Source: IATA/Green Batteries/Toshiba
Currently, temperatures that are too hot or too cold can adversely affect the performance of electric vehicle batteries, for example by slowing charging speeds and reducing the distance vehicles can travel before needing to be recharged.
A driver’s fear of running out of charge before being able to get to another charging station is known as “range anxiety” and has been seen as a barrier to mass adoption of electric vehicles eco-friendly.
“You need high-temperature operation in areas where ambient temperatures can reach triple digits and roads get even hotter,” said Professor Zheng Chen of UC San Diego Jacobs School of Engineering.
“In electric vehicles, the battery packs are usually under the floor, near those hot roads.
“Furthermore, the batteries heat up simply because current is flowing through them during operation. If the batteries cannot withstand this high temperature heating, their performance will degrade rapidly.
Batteries have three main components: the anode, the cathode and the electrolyte.
The electrolyte (usually a chemical, in liquid or paste form) separates the anode and cathode and moves the flow of electrical charge between the two.
Lithium-ion batteries move lithium ions from the cathode to the anode during charging.
The batteries developed by Chen and his colleagues are both resistant to cold and heat thanks to their electrolyte, a liquid solution of dibutyl ether mixed with a lithium salt.
The peculiarity of dibutyl ether is that its molecules weakly bind lithium ions, which means that the electrolyte molecules can easily release lithium ions when the battery is working.
This low molecular interaction improves battery performance at sub-zero temperatures.
Lithium-ion batteries contain two electrodes – one lithium (cathode) and one carbon (anode) – immersed in a liquid or paste called the electrolyte. When the battery is charged, the electrons that were attached to the ions pass through a circuit, powering a device
Additionally, dibutyl ether can easily withstand heat because it remains liquid at high temperatures – it has a boiling point of 286°F or 141°C.
In testing, the proof-of-concept batteries retained 87.5% and 115.9% of their energy capacity at -40°C and 50°C (-40°F and 122°F), respectively.
The new batteries also exhibited high “Coulomb efficiencies” of 98.2% and 98.7% at these temperatures, respectively, meaning they can sustain more charge and discharge cycles before failing.
The researchers say their electrolyte is also compatible with a lithium-sulfur battery, a type of rechargeable battery that has a lithium metal anode and a sulfur cathode.
Lithium-sulfur batteries can store up to twice as much energy per kilogram as today’s lithium-ion batteries, which could potentially double the range of electric vehicles without any increase in battery weight.
Most electric cars run on lithium-ion batteries, which are charged and discharged by lithium ions moving between the negative (anode) and positive (cathode) electrodes. Pictured are electric cars charging in Mosjøen, Norway
However, lithium-sulfur batteries have some problems that currently hinder their commercialization, such as responsiveness, especially at high temperatures.
Additionally, lithium metal anodes are susceptible to forming needle-like structures called dendrites that can puncture parts of the battery, causing a short circuit.
As a result, lithium-sulfur batteries only last for dozens of cycles.
The dibutyl ether electrolyte developed by the UC San Diego team avoids these problems, even at high and low temperatures.
The batteries they tested had longer life – the number of charge and discharge cycles they can go through before losing performance – than a typical lithium-sulfur battery.
The team also designed the sulfur cathode to be more stable by grafting it to a polymer, which prevented more sulfur from dissolving into the electrolyte.
In future research, the team plans to increase battery chemistry, run it at even higher temperatures, and further extend cycle life.
They described their temperature-resistant batteries in an article published in Proceedings of the National Academy of Sciences.
ADVANTAGES AND DISADVANTAGES OF LITHIUM-SULFUR BATTERIES
Lithium-sulfur batteries can provide five times the energy intensity of lithium-ion batteries.
Additionally, sulfur is more abundant and less of a problem to find than the cobalt used in traditional lithium-ion battery cathodes.
However, the commercialization of lithium-sulfur has faced many obstacles, including short life, low cycling efficiency, and poor safety.
The main challenges of lithium-sulfur batteries are the low conductivity of sulfur and its massive change in volume during charging.
This change in volume – up to 78% – can lead to a progressive loss of cohesion of the sulfur particles.
This may mean that it reaches lower charge capacities of lithium-ion batteries before the electrode breaks down and the lithium-sulfur battery stops working.
Sulfur is however very cheap and abundant and has a relatively low atomic weight and high energy density.
Lithium-sulfur batteries could potentially replace lithium-ion batteries by providing higher specific energy – or energy per unit mass.
To make lithium-sulfur batteries, scientists replace the lithium electrode – the piece of metal that carries electric current – of a lithium-ion battery with a carbon-sulfur combination.
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