A single zinc dendrite growth on the surface of an electrode. A "forest" of these growths can lead to short circuits or an explosion in batteries. In a new paper Professor Jiandi Wan's team proved that dendrite growth could be reduced by flowing ions into a battery's cathode. (Photo courtesy of Jiandi Wan)

Scientists at University of California, Davis, have proposed a solution to dendrite growth in rechargeable lithium metal batteries using microfluidics. The group proved that flowing ions near the cathode can potentially expand the safety and lifespans of these next-generation rechargeable batteries.

Lithium (Li) metal batteries are a type of battery that uses Li metal as the anode. These batteries have a high charge density and potentially double the energy of conventional Li-ion batteries, but safety is a big concern. When they charge, some ions are reduced to Li metal at the cathode surface and form irregular, tree-like microstructures known as dendrites, which can eventually cause a short circuit or even an explosion.

The theory is that dendrite growth is caused by the competition of mass transfer and reduction rate of Li ions near the cathode surface. When the reduction rate of ions is much faster than the mass transfer, it creates an electroneutral gap, called the space-charge layer, which contains no ions, near the cathode. The instability of this layer is thought to cause dendrite growth, so reducing or eliminating it might reduce dendrite growth and therefore extend the life of the battery.

The idea was to do this by flowing ions through the cathode in a microfluidic channel to restore a charge and offset this gap. In their paper, the team outlined their proof-of-concept tests that bringing more ions into the cathode is an effective strategy for reducing dendrites, finding that this flow of ions could reduce dendrite growth by up to 99%.

Though it is likely not possible to directly incorporate microfluidics in real batteries, the group is looking at alternative ways to apply the fundamental principles from this study and introduce local flows near the cathode surface to compensate cations and eliminate the space charge layer.