Researchers at Northeastern University in Boston and the Department of Energy’s (DOE) Argonne National Laboratory have developed a new way to build better all-solid-state lithium batteries (SSBs), a significant step toward electrifying future transportation.
The scientists tested how the composition of thick cathodes affected electrochemical reactions in SSBs. The team used the resources of the Advanced Photon Source (APS), a DOE Office of Science user facility at Argonne.
Electrifying transportation is an essential step toward mitigating climate change. To improve the power, efficiency and safety of electric vehicles, researchers must continue to develop better batteries. All-solid-state lithium batteries (SSBs), which have a solid electrolyte instead of a liquid, are safer than traditional lithium-ion batteries because they are less flammable and more stable at higher temperatures. They could also have higher energy densities than lithium-ion batteries, allowing for longer lasting batteries in smaller sizes for portable electronics and other applications.
While SSBs don’t require traditional separators because the electrolyte separates the anode and cathode, they do require thick cathodes. The team evaluated batteries with thick cathodes that were comprised of two materials: a sulfide solid electrolyte called LPSC and a nickel, manganese and cobalt (NMC) cathode active material (CAM).
Researchers altered the composition of these two materials so that some batteries were 80% CAM, 20% LPSC, while others were 70% CAM, 30% LPSC and 40% CAM, 60% LPSC. They used X-ray imaging and scattering at APS beamline 6-BM-A to measure six slices within the cathode and solid-state electrolyte.
“If you divide the cathode into slices, you want all the slices to act the same,” said Joshua Gallaway, a professor at Northeastern University. Changing the composition or thickness of the cathode can change where the electrochemical reactions occur.
The results were that cathode composition had a huge impact on how electrochemical reactions take place. An SSB with an 80% CAM cathode, the cathode slice nearest the anode reacted first and the farthest slice reacted last. But an SSB with a 70% CAM cathode, the farthest slice reacted first and the nearest slice reacted last.
“The reaction is highly non-uniform — and we don’t really see a situation where it is uniform,” Gallaway said.