A non-aqueous electrolyte secondary battery including: a positive electrode having a positive electrode material mixture containing a composite lithium oxide; a negative electrode; a polyolefin separator; a non-aqueous electrolyte; and a heat-resistant insulating layer interposed between the positive and negative electrodes. The positive electrode active material mixture has an estimated heat generation rate at 200° C. of not greater than 50 W/kg. The estimated heat generation rate is determined by obtaining a relation between absolute temperature T and heat generation rate V of the positive electrode material mixture using an accelerating rate calorimeter; plotting a relation between the inverse of absolute temperature T and the logarithm of heat generation rate V according to the Arrhenius law; obtaining a straight line fitted to the plotted points in a heat generation temperature range of T