Better texture for better batteries

But one aspect -- the texture of the metals used -- has been historically overlooked.

"Soft metals like lithium and sodium have excellent properties for being batteries' negative electrodes, with lithium considered as an ultimate anode material for future high-energy rechargeable batteries," said UChicago PME Prof. Shirley Meng, the Liew Family Professor in Molecular Engineering. "There is a gap in understanding the grain orientation, also known as the texture, how such factor impacts the rechargeable metal battery performance."

A new paper from Meng's Laboratory for Energy Storage and Conversion and industry partner Thermo Fisher Scientific broke through that barrier, demonstrating that improving the metal's texture greatly improved performance.

The work was published today in the journal Joule.

"In our work, we discovered that adding a thin layer of silicon between lithium metal and the current collector helps create the desired texture," said UChicago PME Research Assoc. Prof. Minghao Zhang, the first author of the new work. "This change improved the battery's rate capability by nearly ten times in all-solid-state batteries using lithium metal."

'Tweaking the texture'

The ideal texture for a battery anode is one where atoms can quickly move along the surface plane. This fast movement helps the battery charge and discharge faster.

"We realized that differences in soft metal's surface energy can really change the way it's textured," Zhang said. "Since batteries with lithium or sodium metal rely on these textures for favored rate capability, the team wondered if tweaking the texture of soft metals could improve power densities."

Researching this required getting past a hurdle in microscopy. To study the material, the group coupled milling within plasma focused ion beam-scanning electron microscope (PFIB-SEM) with electron backscatter diffraction (EBSD) mapping. Together, the two techniques were able to study texture in new ways.

"Collecting texture information on soft metals is challenging, primarily due to difficulties in accessing the area of interest and the lithium and sodium metal's reactivity," said study co-author Zhao Liu, Senior Market Development Manager of Thermo Fisher Scientific, which is a founding member of the UChicago Energy Transition Network. "The PFIB-EBSD combination is well-suited for this study, as PFIB can effectively access the area of interest within the cell stack, producing a high-quality surface with minimal defects, while EBSD provides detailed texture information on the soft metal."

The team has partnered with LG Energy Solution's Frontier Research Laboratory, which will work to commercialize the technology.

"LG Energy Solution actively pursues research collaborations to stay ahead in the rapidly evolving battery market," said LG Energy Solution's Senior Researcher Jeong Beom Lee. "As the demand for electric vehicles and energy storage continues to grow, we recognize the importance of combining our manufacturing expertise with innovative research from universities to develop next-generation battery technologies."

The researchers' next challenge is to lower the pressure used during testing from 5 megapascals (MPa) to 1 MPa, the current industry standard for commercially available batteries. They also plan to study the impact of texture on sodium, which Meng has long studied as an inexpensive, readily available alternative to lithium.

"Because we now understand how the texture forms in soft metals, we predict that sodium metal prefers to have texture for fast atomic diffusion," Zhang said. "This means that using sodium as the battery's anode in all-solid-state batteries could lead to a big breakthrough in future energy storage."