Toyota, which has been working on solid-state batteries for EVs for a number of years (earlier post), is in the news with a report by the Wall Street Journal that it will be ready to commercialize a solid-state battery by 2022. Solid-state lithium-ion batteries, with higher volumetric energy densities than currently available lithium-ion batteries, offer a number of conceptual advantages including improved packaging efficiency; improved safety; and long cycle life. However, there remain a number of unresolved issues precluding commercialization at this point. A team from Stanford, Carnegie Mellon University, and MIT recently published an open-access paper in the Journal of the Electrochemical Societyreviewing the practical challenges hindering the development of solid-state Li-ion batteries.