Secondary battery, battery pack, and vehicle

A secondary battery, comprising:

• a positive electrode;
• a negative electrode;
• a separator layer comprising a first porous layer containing at least one solid electrolyte selected from the group consisting of a lithium phosphate solid electrolyte having a NASICON type structure, amorphous LIPON, and LLZ having a garnet-type structure, and a second porous layer in contact with a first surface of the first porous layer and containing fibers, the separator layer being positioned between the positive electrode and the negative electrode, a second surface of the first porous layer parallel to the first surface being in contact with the positive electrode;
• and
• a nonaqueous electrolytic solution comprising a first solvent including at least one of methyl propionate and ethyl propionate, and a second solvent different from the first solvent,
• the first porous layer having a void fraction of 10% by volume or greater and 50% by volume or less, and the second porous layer having a void fraction greater than the void fraction of the first porous layer.