Scanning electron microscope images showing a sequence of lithium foils treated by scientists at Rice University. Brushing metal powder into the lithium anodes in rechargeable batteries can prevent the formation of damaging dendrites. The scale bars represent 100µm. Image: Tour Group/Rice University.
Scanning electron microscope images showing a sequence of lithium foils treated by scientists at Rice University. Brushing metal powder into the lithium anodes in rechargeable batteries can prevent the formation of damaging dendrites. The scale bars represent 100µm. Image: Tour Group/Rice University.

A bit of brushing may be the secret to making better rechargeable lithium batteries. The Rice University lab of chemist James Tour has introduced a technique for tuning the surface of anodes for batteries by simply brushing powders into them. The powder adheres to the anode and becomes a thin, lithiated coating that effectively prevents the formation of damaging dendrites.

A powder of phosphorus and sulfur ground into the surface of lithium-metal foil was able to tune the foil’s surface energy without the need for toxic solvents. Anodes so modified and paired with lithium-iron-phosphate-oxide cathodes in test cells retained 70% more capacity after 340 charge-discharge cycles than off-the-shelf batteries. Tour and his team report their findings in a paper in Advanced Materials.

“This would simplify the manufacture of high-capacity batteries while greatly improving them,” Tour said. “Sanding these powdered solids into a lithium-metal anode dramatically reduces dendrite formation that can short-circuit a battery, as well as the accelerated consumption of the materials.”

Lead author and Rice graduate student Weiyin Chen and his lab colleagues applied the necessary elbow grease to test a variety of powder candidates on their electrodes. They first brushed the surface to give it texture, then brushed in powder to create the fine film that reacts with the lithium metal and forms a solid passivation layer.

Next, Chen and co-author Rodrigo Salvatierra, a former postdoctoral researcher and now an academic visitor in the Tour lab, constructed test batteries. Using these, they determined that the treated anodes retained ultralow polarization – another damaging characteristic for lithium-ion batteries – for more than 4000 hours, about eight times longer than bare lithium anodes.

According to Tour, the powders effectively tune the surface energy of the electrodes, making for a more uniform behavior across the material.

“This provides a metal-composite surface that prevents the loss of lithium metal from the anode, a common problem in lithium-metal batteries,” he said. “Lithium-metal batteries far exceed the capacity of traditional lithium-ion batteries, but the lithium metal is often difficult to repeatedly recharge.”

“The powder at the lithium-metal surface produces an artificial passivation layer that improves the stability throughout the charge-discharge cycles,” Chen said. “Using this brush-on method, the metal surface is stabilized so that it can be safely recharged.”

To demonstrate that the technique may have wider applications, the lab also ground powder into a sodium electrode and showed that the process greatly stabilized its voltage overpotential.

This study aligns with the recent discovery by Tour and Rice mechanical engineer Fred Higgs that sanding certain powders into surfaces can make them superhydrophobic, or highly resistant to water (see Sanding surfaces can make them superhydrophobic).

This story is adapted from material from Rice University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.