All-solid-state sodium ion secondary battery

An all-solid-state sodium ion secondary battery comprising:

• a solid electrolyte layer having a first principal surface and a second principal surface opposite each other and made of a sodium ion-conductive oxide;
• a positive electrode layer provided on the first principal surface of the solid electrolyte layer;
• and
• a negative electrode layer provided on the second principal surface of the solid electrolyte layer, wherein
• the first principal surface has an arithmetic mean roughness Ra of 1.8 μm or more and 3.2 μm or less,
• the thickness of the positive electrode layer is in a range of 10 μm to 150 μm,
• the positive electrode layer contains a positive-electrode active material including sodium transition metal phosphate crystals containing Na, M (where M represents at least one transition metal element selected from Cr, Fe, Mn, Co, V, and Ni), P, and O,
• the solid electrolyte layer contains at least one solid electrolyte selected from the group consisting of β-alumina, β″-alumina, and NASICON crystals, and
• the negative electrode layer contains a negative-electrode active material including crystals containing at least one selected from Nb and Ti, and O, metallic crystals of at least one selected from Sn, Bi, and Sb, and alloy crystals containing at least one selected from Sn, Bi, and Sb.