Provided is a lithium ion battery which has high flame retardancy over a long period and excellent cycle characteristics. The lithium ion battery comprises: a non-aqueous electrolyte or gel electrolyte that contains an Li salt and an oxo-acid ester derivative of phosphoric acid; a stacked electrode group; and a casing that contains the non-aqueous electrolyte or gel electrolyte and the stacked electrode group. The stacked electrode group is constituted by alternately stacking, with the interposition of a separator therebetween, positive electrodes having arranged therein a positive electrode layer containing a positive electrode active substance on at least one face of a positive electrode current collecting body, and negative electrodes having arranged therein a negative electrode layer containing a negative electrode active substance on at least one face of a negative electrode current collecting body. For both of the two electrodes (A) that are respectively arranged on the outermost sides of the stacked electrode group, if the amount of electrode active substance contained in an electrode active substance coating layer (B) that faces the electrode current collecting body and is arranged on the stacked electrode group side is Wb, and the amount of electrode active substance contained in an electrode active substance coating layer (C) that faces the electrode current collecting body and is arranged on the casing side is Wc, 0<=(Wc/Wb)<=0.55 is satisfied.