The performance of a class of next-generation solid-state batteries may depend on a coating just a nanometer thick, roughly 100,000 times thinner than a human hair. Scientists at the US Department of Energy’s Argonne National Laboratory combined computation and experiment to identify protective coatings for sulfide-based solid electrolytes, and pointed to magnesium oxide in particular.
Solid-state batteries could store more energy and improve safety compared with today’s lithium-ion cells, but some solid electrolytes are chemically fragile. Sulfide-based electrolytes can react at key battery interfaces, especially where the electrolyte meets lithium metal, and those reactions can degrade performance and shorten battery life.
The team focused on a sulfide electrolyte called lithium phosphorus sulfur chloride (LPSCl). Using density functional theory, they screened a range of oxide coatings made by atomic layer deposition (ALD), a method that deposits ultrathin, uniform layers with near-atomic precision. The screening predicted how each coating would behave at three interfaces: where the coating meets the electrolyte, the lithium metal and the cathode.
The best coatings were not always the least reactive. The team found that the more important factor was what compounds formed when a coating reacted at an interface, and that the best performers formed reaction products that still let lithium ions move while limiting electron flow. A layer that passes ions but blocks electrons helps prevent the electrolyte from being continuously reduced at the lithium interface, limiting how far the reaction spreads.
The researchers applied several candidate coatings to LPSCl powder using ALD. Magnesium oxide stood out: it made the electrolyte more stable in contact with lithium metal, reduced resistance at the interface, and improved performance, blocking electron flow while still allowing lithium ions to move efficiently.
Scanning transmission electron microscopy and energy dispersive X-ray spectroscopy at Argonne’s Center for Nanoscale Materials confirmed that the coatings were uniformly distributed across the powder surfaces. Beyond identifying the coatings themselves, the work gives researchers a faster way to search a much larger materials design space for sulfide electrolytes.
Source: Argonne National Laboratory
