A new lithium-sulphur battery with an ultra-high capacity could lead to drastically cheaper electric cars and grid energy storage.
By Donna Lu
Mahdokht Shaibani at Monash University in Melbourne, Australia, and her colleagues have developed a battery with a capacity five times higher than that of lithium-ion batteries. The battery maintains an efficiency of 99 per cent for more than 200 cycles, and a smartphone-sized version would be able to keep a phone charged for five days.
To date, the problem with lithium-sulphur batteries has been that the capacity of the sulphur electrode is so large that it breaks apart over cycles of charging and discharging, and the energy advantage rapidly disappears, says Shaibani. “The electrode will fall apart, and then the battery dies fast.”
That happens because the sulphur electrode expands and contracts as it cycles, with a volume change of about 78 per cent. Volume change also occurs in electrodes in the lithium-ion batteries that power electric cars and smartphones, but is about eight times smaller.
To prevent the electrode disintegrating in their lithium-sulphur battery, the researchers gave the sulphur particles more space to expand and contract. Usually, lithium-sulphur batteries have materials added that bind the particles together inside so the battery doesn’t crack as it expands. Shaibani and her team used a smaller amount of a polymer binding material in their electrode, and created more spaced-out structures between the sulphur particles.
This polymer creates a series of bridges between particles, rather than a dense network, which balances the battery’s resistance to cracking with its ability to discharge a large amount of energy.
Shaibani says this lithium-sulphur battery would drastically reduce the cost of batteries for electric cars and grid energy storage because sulphur is abundant and extremely cheap.
However, lithium-sulphur batteries may face similar ethical problems to lithium-ion batteries. The metal oxides in lithium-ion batteries are typically nickel, cobalt or manganese, which are expensive and diminishing in natural stores. They also have associated ethical problems: a significant proportion of cobalt is sourced by child miners in the Democratic Republic of the Congo, for example.
“In order to have much cheaper energy and more ethical batteries, we need a radically new energy storage system,” says Shaibani. The researchers will further test battery prototypes with a view to manufacturing them commercially in Australia in coming years.