The secret ingredient to stable lithium-sulfur batteries

In an effort to lengthen the battery life of common electronic devices, researchers at The University of Texas at Dallas have developed a high-powered, environmentally safe lithium-sulfur substitute.

Many smartphone users are familiar with the shelf life of lithium-ion batteries, with a typical charge lasting for roughly one day. According to Dr Kyeongjae ‘KJ’ Cho from UT Dallas, most would agree it would be more convenient if that charge lasted a week or more.

“Common lithium-ion batteries only have a certain capacity,” said Dr Cho. “And most people want to use their phones for a longer time.”

Dr Cho and his colleagues have been working together to improve lithium-sulfur batteries, long considered by many to be an evolution from lithium-ion batteries. Lithium-sulfur batteries have several advantages over lithium-ion batteries, according to Dr Cho: they are less expensive to make, they weigh less, they store almost twice the energy of lithium-ion batteries and they are better for the environment.

“A lithium-sulfur battery is what most of the research community thinks is the next generation of battery,” Dr Cho said. “It has a capacity of about three to five times higher than lithium-ion batteries, meaning if you are used to a phone lasting for three hours, you can use it for nine to 15 hours with a lithium-sulfur battery.”

The downside is, sulfur is a poor electrical conductor and can become unstable over just several charge-and-recharge cycles. Electrodes breaking down is another reason lithium-sulfur batteries aren’t mainstream.

Scientists have previously tried to improve lithium-sulfur batteries by putting lithium metal on one electrode and sulfur on the other; however, lithium metal often is too unstable, and sulfur too insulating. Now, Dr Cho and his team have discovered a technology that produced a sulfur-carbon nanotube substance that created more conductivity on one electrode, and a nanomaterial coating to create stability for the other.

The researchers found that molybdenum, a metallic element often used to strengthen and harden steel, creates a material that adjusts the thickness of the coating when combined with two atoms of sulfur — a coating thinner than the silk of a spiderweb. They found it improved stability and compensated for poor conductivity of sulfur, thus allowing for greater power density and making lithium-sulfur batteries more commercially viable.

“This was what everyone was looking for, for a long time,” Dr Cho said. “That’s the breakthrough.”

Publishing their results in the journal Nature Nanotechnology, the scientists say this finding could change the way we look at batteries and experience battery life. Dr Cho is particularly optimistic, stating, “We are taking this to the next step and will fully stabilise the material, and bring it to actual, practical commercial technology.”

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