LITHIUM ION BATTERY

There is provided a lithium ion battery having high flame retardancy and good cycle characteristics on a long-term basis. The lithium ion battery according to this exemplary embodiment is a lithium ion battery comprising a nonaqueous electrolytic solution or gel electrolyte containing a Li salt and an oxoacid ester derivative of phosphoric acid; a group of stacked electrode in which positive electrodes comprising a positive electrode layer comprising a positive electrode active material disposed on at least one surface of a positive electrode current collector, and negative electrodes comprising a negative electrode layer comprising a negative electrode active material disposed on at least one surface of a negative electrode current collector are alternately stacked via separators; and a package containing the nonaqueous electrolytic solution or gel electrolyte and the group of stacked electrode, wherein both of two electrodes A disposed on outermost sides of the group of stacked electrode, respectively, satisfy 0 ‰¤ (Wc/Wb) ‰¤ 0.55 when a mass of an electrode active material contained in an electrode active material-coated layer B disposed on a group-of-stacked-electrodes side of an electrode current collector is Wb, and a mass of an electrode active material contained in an electrode active material-coated layer C disposed on a package side of the electrode current collector is Wc.