Battery

A battery, comprising:

• an electrode layer;
• a counter electrode layer, which is a counter electrode for the electrode layer;
• and
• a solid electrolyte layer between the electrode layer and the counter electrode layer, wherein:
• the solid electrolyte layer has a first region containing a first solid electrolyte material and a second region containing a second solid electrolyte material,
• the first region is positioned within a region where the electrode layer and the counter electrode layer face each other,
• with respect to the first region, the second region is positioned on an outer peripheral side of the region where the electrode layer and the counter electrode layer face each other, and the second region is in contact with the first region,
• a second density is higher than a first density, where the first density is a density of the first solid electrolyte material in the first region and the second density is a density of the second solid electrolyte material in the second region,
• the first region includes a first projecting portion that projects outward from a region where the electrode layer and the counter electrode layer face each other, and
• the second region covers the first projecting portion.