SECONDARY BATTERY

A secondary battery includes a positive electrode, a negative electrode, and an electrolytic solution. The negative electrode includes a film covering a negative electrode active material layer. The electrolytic solution includes a chain carboxylic acid ester. According to an analysis of the film by inductively coupled plasma optical emission spectroscopy, a content of boron in the film is greater than or equal to 10 μmol/mand less than or equal to 30 μmol/m, a content of sulfur in the film is greater than or equal to 20 μmol/mand less than or equal to 70 μmol/m, and a ratio of the content of sulfur to the content of boron is greater than or equal to 1.0 and less than or equal to 3.0.