Twin boundaries—which are small, symmetrical defects in materials—may present an opportunity to improve lithium-ion batteries, according to researchers at the Michigan Technological University in the U.S. The twin boundary defects act as energy highways and could help get better performance from the batteries.

The yellow streaks, highlighted by green arrows, show where lithium ions travel along twin bounderies. Source: Michigan Tech NewsThe researchers say that symmetry causes problems because it creates weak spots. At the same time, that symmetry is what provides a route for ions to travel along. This finding was published in Nano Letters.

Anmin Nie, a senior postdoctoral researcher who conducted the study says that movement of ions is key to making better, stronger batteries. Nie says that material defects, including twin boundaries, are naturally occurring and most research previously has focused on removing them from materials.

Co-author Reza Shahbazian-Yassar says the focus over the past few years has been on rechargeable batteries—most specifically the lithium-ion battery. That is because lithium-ion batteries are lightweight, offer energy density and continue to experience efficiency improvements. Like all basic batteries, the ones that run on lithium ions rely on shuttling ions from the anode to the cathode with an electric current that coaxes the ions to move between them. A low battery means there is less exchange happening between the anode and the cathode. Twin boundaries could help hustle that exchange along or perhaps extend it, possibly without losing battery life.

Twin boundaries basically are places in a material where one side of an atomic arrangement reflects another. They often result while making a material, which shifts the atoms out of place.

The research team examined twin boundaries in tin oxides, but Shahbazian-Yassar says their technique is applicable to many battery materials. The next step is to learn out how to optimize these defects to balance mechanical integrity with the amount of twin structures.