NON-AQUEOUS ELECTROLYTE SECONDARY BATTERY

This non-aqueous electrolyte secondary battery is characterized by comprising a positive electrode, a negative electrode, a separator that separates the positive electrode and the negative electrode from each other, and a non-aqueous electrolyte, wherein: the positive electrode contains a lithium-containing composite oxide and a sulfonic acid compound present on a particle surface of the lithium-containing composite oxide; the sulfonic acid compound is represented by formula (I); the separator has a base material layer and a heat-resistant layer formed on the surface of the base material layer; the heat-resistant layer faces at least the positive electrode; and the thickness T1 of the base material layer and the thickness T2 of the beat-resistant layer satisfy the relationship T2/T1≥0.2. (In the formula, A is a group 1 element or a group 2 element, R is a hydrocarbon group, and n is 1 or 2.)