One purpose of the present invention is to suppress variation of the open-circuit voltage among batteries that use a positive electrode active material having a high nickel content. The present invention relates to a nonaqueous electrolyte secondary battery which is provided with a positive electrode containing a positive electrode mixture, a negative electrode, and a nonaqueous electrolyte containing a nonaqueous solvent and a lithium salt that is dissolved in the nonaqueous solvent, and wherein: the positive electrode mixture contains a positive electrode active material and a phosphate salt; the positive electrode active material contains a lithium-nickel composite oxide represented by formula (1) LixNi1-yM1yO2 (wherein 0.9 <= x <= 1.1, 0 <= y <= 0.7 and M1 represents at least one element selected from the group consisting of Co, Mn, Fe, Ti, Al, Mg, Ca, Sr, Zn, Y, Yb, Nb, Cr, V, Zr, Mo, W, Cu, In, Sn and As); and the nonaqueous solvent contains a trifluoropropionic acid ester represented by formula (2) F3C-CH2-CO-O-R1 (wherein R1 represents a C1-3 alkyl group).