'Anti-short layer' helps to prevent Li-ion battery fires

Materials scientists from Nanyang Technological University, Singapore (NTU Singapore) have found a way to prevent internal short circuits, the main cause of fires in lithium-ion (Li-ion) batteries.

Billions of Li-ion batteries are produced annually for use in mobile phones, laptops, personal mobile devices, electric vehicles and aircraft. But even with an estimated failure rate of less than one in a million, in 2020 there were 26 power-assisted bicycle fires and 42 cases of personal mobility device fires in Singapore.

In most Li-ion battery fires, the cause is due to a build-up of lithium deposits known as dendrites (tiny wire-like tendrils) that cross the separator between the positive (cathode) and negative (anode) electrodes of the battery when it is being charged, causing a short circuit and leading to an uncontrolled chemical fire. To prevent this short circuit from happening, Professor Xu Zhichuan and his team invented an additional ‘anti-short layer’ on the separator, preventing any dendrite from reaching the cathode.

“We know that for a Li-ion battery to work, Li-ions must be able to travel between the positive and negative sides during charge and discharge cycles,” Prof Xu said. “However, the transfer of the Li-ions also means the formation of dendrites is inevitable for current commercial Li-ion batteries.

“Instead of preventing the formation of dendrites, we decided to make use of their intrinsic properties by coating an additional layer of conductive material on the separator for these dendrites to connect with. Once the dendrites make the connection it will not be able to continue their growth further, thus preventing them from ever reaching the other side.”

A Li-ion battery could be likened to two bookshelves in a library facing each other (cathode and anode), separated by an aisle (separator). When the battery is charging, Li-ions are transferred from the cathode to the anode, and when discharging, the Li-ions move vice-versa.

NTU’s anti-short layer is akin to putting a librarian desk in between both bookshelves in the middle of the aisle — so that when the build-up of used books reaches the librarian’s desk (dendrites), they stop there, while the librarian continues to interact with the other side. Prof Xu’s team have tested their technology in the laboratory on over 50 cells with different Li-ion battery compositions and no short circuits have been detected during the charging phase, even when the battery cells are used beyond their life cycle.

The anti-short layer is a common material used in battery manufacturing and can be easily integrated into the current separator manufacturing process, making it easy for companies to adopt and scale up. The team estimates that the cost increase after adopting this technology would be around 5% more than the existing production cost of a Li-ion battery.

The technology is now patent-pending and is being commercialised by NTUitive, NTU’s innovation and enterprise company, having already gained the interest of several battery technology firms. The NTU team will be further developing the technology and will soon test it on commercial standardised Li-ion battery cells, in partnership with interested companies.

Image caption: The NTU anti-short layer (held by tweezers) stops short circuits from happening in Li-ion batteries. Image credit: NTU Singapore.

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