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Solution found for major flaw in lithium-sulphur batteries

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Scientists believe they have taken a big step to commercialising lithium-sulphur batteries, which are touted as being possible next-gen replacements for the lithium-ion technology relied on today.

Lithium-sulphur batteries can be produced at a reduced cost compared to lithium-ion due to the abundance of sulphur and they have a much higher energy density, meaning they can last longer on a single charge.

But their Achilles heel is that they cannot be recharged many times before suffering a drastic loss in capacity.

Lithium is a reactive element that tends to break down other elements around it.

Every cycle of a lithium-sulphur battery – the process of charging and discharging it – can cause mossy, needle-like deposits to form on the lithium-metal anode, the negative electrode of the battery. This starts a reaction that can lead to the battery’s overall degradation.

The deposits break down the electrolyte that shuttles lithium-ions back and forth. This can trap some of the lithium, keeping the electrode from delivering the full power necessary for the ultra-long use the technology promises. The reaction can also cause the battery to short-circuit and potentially catch fire.

A group of researchers in the Cockrell School of Engineering at The University of Texas at Austin has found a way to stabilise the batteries which could bring them closer to commercial viability.

They found that creating an artificial layer containing tellurium, inside the battery in-situ, on top of lithium metal, can make it last four times longer.

“Sulphur is abundant and environmentally benign with no supply chain issues in the US,” said Arumugam Manthiram, a professor of mechanical engineering and director of the Texas Materials Institute.

“But there are engineering challenges. We’ve reduced a problem to extend the cycle life of these batteries.”

The artificial layer formed on the lithium electrode protects the electrolyte from being degraded and reduces the mossy structures that trap lithium from forming during charges.

“The layer formed on lithium surface allows it to operate without breaking down the electrolyte, and that makes the battery last much longer,” said Amruth Bhargav, who co-authored the paper.

Manthiram added that this method can be applied to other lithium- and sodium-based batteries.

“The stabilising layer is formed by a simple in-situ process and requires no expensive or complicated pre-treatment or coating procedures on the lithium-metal anode,” said co-author Sanjay Nanda.

Solving the instability of this part of the battery is key to extending its cycle life and bringing about wider adoption.

Lithium-sulphur batteries are currently best suited for devices that need lightweight batteries and can run for a long time on a single charge and don’t require a large number of charge cycles, such as drones. But they have the potential to play an important role in extending the range of electric vehicles and increased renewable energy adoption.

Both the positive and negative electrodes in lithium-sulphur batteries hold 10 times as much charge capacity as the materials used in today’s lithium-ion batteries, Manthiram said, which means they can deliver much more use out of a single charge.

Sulphur is widely available as a by-product from the oil and gas industry, making the batteries inexpensive to produce. Sulphur is also more environmentally friendly than the metal oxide materials used in lithium-ion batteries.

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