A power storage device with favorable battery characteristics and a manufacturing method thereof are provided. The power storage device includes at least a positive electrode and a negative electrode provided so as to face the positive electrode with an electrolyte provided therebetween. The positive electrode includes a collector and a film containing an active material over the collector. The film containing the active material contains LieFefPgOh satisfying relations 3.5≦h/g≦4.5, 0.6≦g/f≦1.1, and 0≦e/f≦1.3 and LiaFebPcOd satisfying relations 3.5≦d/c≦4.5, 0.6≦c/b≦1.8, and 0.7≦a/b≦2.8. The film containing the active material contains the LiaFebPcOd satisfying the relations 3.5≦d/c≦4.5, 0.6≦c/b≦1.8, and 0.7≦a/b≦2.8 in a region which is in contact with the electrolyte.