Solid-state battery and solid-state battery group

A solid-state battery comprising:

• a battery element that includes one or more battery constitutional units, each battery constitutional unit including a positive electrode layer and a negative electrode layer facing each other and a solid electrolyte layer arranged between the positive electrode layer and the negative electrode layer;
• a first protective layer covering an upper surface of the battery element, the first protective layer having a first protruding portion that protrudes past the battery element in a sectional view of the solid-state battery;
• a second protective layer covering a lower surface of the battery element, the second protective layer having a second protruding portion that protrudes past the battery element in a sectional view of the solid-state battery;
• and
• a side surface reinforcing portion that reinforces a side surface of the battery element and extends between the first protruding portion of the first protective layer and the second protruding portion of the second protective layer,
• wherein the side surface reinforcing portion is in direct contact with side surfaces of each of the positive electrode layer, the negative electrode layer, and the solid electrolyte layer, and
• wherein the first and second protective layers include an insulating substance other than resin.