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.degree. 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<200.degree. C.; and extrapolating the straight line to the
temperature of 200.degree. C.