Nonaqueous electrolyte secondary battery including separator with filler layers on opposite sides of substrate

A nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode and a separator, wherein

• the separator comprises a substrate, a first filler layer disposed on one side of the substrate and containing phosphate salt particles, and a second filler layer disposed on the other side of the substrate and containing inorganic particles with a higher melting point than the phosphate salt particles, the separator being disposed between the positive electrode and the negative electrode in such a manner that the first filler layer is directed to the positive electrode side, and
• the BET specific surface area of the phosphate salt particles is not less than 5 m2/g and not more than 100 m2/g,
• wherein the average particle size of the phosphate salt particles is 0.05 μm to 1 μm and is smaller than the average pore size of the substrate,
• wherein the separator further comprises a resin layer containing a polyolefin, said resin layer being disposed on the surface of the first filler layer and in contact with the positive electrode,
• wherein the first filler layer comprises a continuous layer configured to cover an entirety of a surface of the substrate on which the first filler layer is disposed,
• wherein the phosphate salt particles contained in the first filler layer are configured to undergo melting and polycondensation by heat and a potential of the positive electrode, so as to fill pores in the substrate upon generation of a heat, and
• wherein a porosity of the first filler layer is 30% or more and 70% or less.