The batteries, described in the journal PNAS, could allow
electric vehicles in cold climates to travel farther on a single charge. They
could also reduce the need for cooling systems to keep the vehicles' battery
packs from overheating in hot climates.
The researchers at the University of California (UC) San
Diego in the US developed an electrolyte that is not only versatile and robust
throughout a wide temperature range, but also compatible with a high-energy
anode and cathode.
The anode is the electrode where electricity moves into. The
cathode is the electrode where electricity flows out.
"You need high temperature operation in areas where the
ambient temperature can reach the triple digits and the roads get even hotter.
In electric vehicles, the battery packs are typically under the floor, close to
these hot roads," said Zheng Chen, a professor at the UC San Diego, and
senior author of the study.
"Also, batteries warm up just from having a current run
through during operation. If the batteries cannot tolerate this warmup at high
temperature, their performance will quickly degrade," Chen said.
In tests, the batteries retained 87.5 per cent and 115.9 per
cent of their energy capacity at minus 40 and 50 degrees Celsius, respectively.
They also had high Coulombic efficiencies of 98.2 percent
and 98.7 percent at these temperatures, respectively, which means the batteries
can undergo more charge and discharge cycles before they stop working.
The batteries are both cold and heat tolerant thanks to
their electrolyte, which is made of a liquid solution of dibutyl ether mixed
with a lithium salt.
A special feature of dibutyl ether is that its molecules
bind weakly to lithium ions. In other words, the electrolyte molecules can
easily let go of lithium ions as the battery runs.
This weak molecular interaction, the researchers had
discovered in a previous study, improves battery performance at sub-zero
temperatures.
Dibutyl ether can easily take the heat because it stays
liquid at high temperatures, the researchers said.
What is also special about this electrolyte is that it is
compatible with a lithium-sulfur battery, which is a type of rechargeable
battery that has an anode made of lithium metal and a cathode made of sulfur.
Lithium-sulfur batteries are an essential part of
next-generation battery technologies because they promise higher energy
densities and lower costs, according to researchers.
They can store up to two times more energy per kilogram than
today's lithium-ion batteries -- which could double the range of electric
vehicles without any increase in the weight of the battery pack.
Sulfur is also more abundant and less problematic to source
than the cobalt used in traditional lithium-ion battery cathodes, the
researchers added.