The design, says the team, overcomes a key technical problem with lithium-sulphur batteries – battery degradation caused by the loss of material within it.
Researchers are interested in lithium-sulphur batteries because they should have a much higher energy density. However, when the battery discharges, sulphur molecules transform into chain-like structures called polysulphides. Following several charge-discharge cycles, bits of the polysulphide can enter the electrolyte, meaning the battery gradually loses active material.
To prevent this, the researchers have created a functional layer of zinc oxide nanowires which lies on top of the cathode and fixes the active material to a conductive framework so it can be reused. Essentially, the framework traps fragments of the active material when they break off, keeping them electrochemically accessible and allowing the material to be reused.
“It’s a tiny thing, this layer, but it’s important,” said Dr Paul Coxon from Cambridge’s Department of Materials Science and Metallurgy. “This gets us a long way through the bottleneck which is preventing the development of better batteries.”
The researchers point out the device is a proof of principle, adding that commercially-available lithium-sulphur batteries may be some years away. Additionally, while the number of times the battery can be charged and discharged has been improved, it is still not able to go through as many charge cycles as a lithium-ion battery. However, since a lithium-sulphur battery does not need to be charged as often as a lithium-ion battery, it may be the case that the increase in energy density cancels out the lower total number of charge-discharge cycles.
“This is a way of getting around one of those awkward little problems that affects all of us,” said Dr Coxon. “We’re all tied into our electronic devices – ultimately, we’re just trying to make those devices work better.”
