Toyota recently published a patent for an all-solid-state battery:
"An all-solid-state battery includes a positive electrode layer, a solid electrolyte layer, and a negative electrode layer. The solid electrolyte layer separates the positive electrode layer from the negative electrode layer. The positive electrode layer includes a positive electrode active material, a conductive material, an oxide-based lithium ion conductor, and a sulfide-based solid electrolyte. A cross section of the positive electrode layer satisfies a relational expression (1): 3%≤SB/SA≤30%. In the relational expression (1), “SA” represents a partial area of the oxide-based lithium ion conductor that is in contact with the positive electrode active material, and “SB” represents a partial area of the oxide-based lithium ion conductor that is surrounded by the sulfide-based solid electrolyte."
In the same patent, they mention a way to solve or mitigate the possible internal resistance increase associated with solid state batteries:
"For reducing interface resistance, use of a covering layer has been proposed. More specifically, a positive electrode active material (particles) is covered with an oxide-based Li ion conductor. Thus, a covering layer consisting of the oxide-based Li ion conductor is formed. The covering layer may reduce the number of contacts between the sulfide-based solid electrolyte and the positive electrode active material. As a result, the interface resistance may be reduced. The covering layer is also called a buffer layer or a reaction-reducing layer, for example."
