By Battery Power Online Staff
July 9, 2024 | On July 3, work from the lab of Shirley Meng, University of Chicago, in collaboration with researchers from the University of California San Diego, was published in Nature Energy (doi:10.1038/s41560-024-01569-9).
Battery Power reported the bulk of this work earlier this spring after Meng first shared results at the International Battery Seminar and Exhibit. In this work, Meng and colleagues describe the successful creation of solid-state anode-free sodium-ion batteries that cycle several hundred times.
Editor’s Note: Meng will also be speaking at the upcoming Solid-State Summit in Chicago, August 13-15.
In the press release announcing publication, Meng explained why sodium-ion batteries are desirable: “To keep the United States running for one hour, we must produce one terawatt-hour of energy,” she said. To meet that large demand, she says we need to produce many low-cost batteries quickly. Because sodium is approximately 1,000-fold more plentiful than lithium in the Earth’s crust, it is easier and cheaper to acquire, and could reasonably be expected to help fulfill this demand. Sodium-ion batteries using liquid electrolyte and traditional anode materials unfortunately have much lower energy density compared with lithium-ion cells, but combining a solid-state design with an anode-free architecture actually makes them competitive with lithium-ion technologies. Calculations from the paper show that they can reach theoretical energy densities of 700 Wh/L (350 Wh/kg).
To accomplish success in this format, Meng and colleagues had to make special efforts to enable tight contacts between current collector and electrolyte, ultimately landing on the use of densified, pelletized aluminum as the current collector. First author Grayson Deysher gave further insight into how this densified aluminum enabled successful battery performance. “In any anode-free battery, there needs to be good contact between the electrolyte and the current collector,” he said. “This is typically very easy when using a liquid electrolyte, as the liquid can flow everywhere and wet every surface. A solid electrolyte cannot do this.” That’s where the pellet densification came into play. Focused ion beam scanning electron microscopy experiments from the report showed that when any pores existed in the current collector, such as when the pellets were not sufficiently densified, sodium metal could become trapped and would not be stripped on discharge. The softness of the aluminum pellets ultimately allowed them to be pressed tightly and limit voids, maintaining the tight interfaces necessary to enable repeated cycling.
It remains true in the final publication that the batteries created thus far have a low energy density, largely because of the limited ion conductivity of available sodium catholyte, and efforts to obtain improved conductivity are ongoing. The work remains a significant step toward useful sodium-ion batteries.
