NON-AQUEOUS ELECTROLYTE SECONDARY BATTERY

In a non-aqueous electrolyte secondary battery according to an embodiment, a positive electrode includes a lithium-containing transition metal composite oxide and a sulfonic acid compound present on the surface of particles of the composite oxide. The sulfonic acid compound is represented by formula (I). In the formula, A is a Group 1 or Group 2 element, R is a hydrocarbon group, and n is 1 or 2. A negative electrode includes a silicon-containing material (). The silicon-containing material () contains an ion-conducting phase () and a Si phase () dispersed in the ion-conducting phase (), and the size of the Si phase () is 110 nm or less.