Safer Li-ion batteries

C&I Issue 7, 2018

Lithium ion battery fires have resulted in burns and house fires, and even a plane crash. But now researchers claim to have hit on a practical and inexpensive way to make electronic gadgets safer, they reported at the ACS meeting in Boston in August 2018.

Battery fires occur after laptops and other electronic items are damaged or improperly packaged, when the two battery electrodes come into contact. One way to make the batteries safer is to replace the liquid electrolyte with a solid one, but that requires significant modifications to the existing manufacturing process. Instead, researchers at Oak Ridge National Laboratory (ORNL) and the University of Rochester have created an alternative impact-resistant electrolyte simply by mixing an additive into the conventional electrolyte.

The idea exploits the process of ‘shear thickening’, exemplified by the familiar childhood experiment of mixing cornstarch and water, said ORNL researcher Gabriel Veith. The mixture flows like a liquid until it is prodded, whereupon it becomes solid and then liquifies again once the pressure is removed – which happens because the cornstarch particles are present as a colloidal suspension in water.

In the case of the battery, the researchers used perfectly spherical 200nm silica particles – essentially a superfine sand - suspended in common liquid electrolytes for lithium-ion batteries, Veith explained. On impact, the silica particles clump together and block the flow of liquids and ions, so avoiding electrolyte-electrolyte contact.

Longer term applications may include batteries for EVs, where as well as improving safety they could also reduce the battery size by around a quarter, by requiring less safety steel, and free up more space inside cars. The group now has plans to make a bigger bullet-proof battery that could double up as body armour for soldiers. Currently, soldiers often carry 20 pounds of body armour plus 20 pounds of batteries, so this would potentially lighten their load by half. In addition, the researchers are exploring ways to enhance the system so only the part of the battery that’s damaged would remain solid while the remainder would carry on working.

Other labs investigating shear thickening batteries have also looked at fumed silica and rod-shaped silica particles. However, Veith believes his spherical particles might be easier to make than rod-shaped silica, and have a faster response and more stopping power on impact than fumed silica.

‘If you have that very uniform [200nm] particle size, the particles disperse homogeneously in the electrolyte, and it works wonderfully,’ he said.

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