TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Property: The positive electrode active material layer has area density of 50 mg/cm2 or less. Preferred Composition: The lithium nickel composite oxide includes composite oxide(s) (LixNiyCozM1(1-y-z)Ob, preferably LixNi0.80Co0.15Al0.05O2, where M1 is element(s) chosen from boron, magnesium, aluminum, silicon, phosphorus, sulfur, titanium, chromium, manganese, iron, copper, zinc, gallium, germanium, yttrium, zirconium, molybdenum, silver, barium, tungsten, indium, tin, lead and antimony, x is more than 0.8 to 1.2, y is 0.5-1, z is 0-0.5, y+z is 1 or less and b is 1.8-2.2). The lithium nickel cobalt manganese composite oxide includes composite oxide(s) (LifNigCoiMn(1-g-i-h)M2hO(2-j), preferably LixNi0.80Co0.15Al0.05O2, where M2 is element(s) chosen from magnesium, aluminum, boron, titanium, vanadium, chromium, iron, copper, zinc, zirconium, molybdenum, tin, calcium, strontium and tungsten, f is 0.8-1.2, g is more than 0 to 0.5, h is 0.1-0.5, g+h+i is less than 1, j is -0.1-0.2 and i is more than 0 to 0.5). The lithium manganese composite oxide includes composite oxide(s) (LivNi(2-w)M3wOs, where M3 is element(s) chosen from cobalt, nickel, magnesium, aluminum, boron, titanium, vanadium, chromium, iron, copper, zinc, molybdenum, tin, calcium, strontium and tungsten, v is 0.9-1.1, w is 0.1-0.6 and s is 3.7-4.1). The lithium iron phosphate compound includes phosphate compound(s) (LiuFerM4(1-r)PO4, where M4 is element(s) chosen from cobalt, manganese, nickel, magnesium, aluminum, boron, titanium, vanadium, niobium, copper, zinc, molybdenum, calcium, strontium, tungsten and zirconium, r is more than 0 to 1 and u is 0.9-1.1). The positive electrode active material is mixture of lithium nickel cobalt manganese composite oxide and lithium manganese composite oxide in mass ratio of 5:5-9:1, lithium nickel composite oxide, or mixture of lithium nickel composite oxide and lithium manganese composite oxide in mass ratio of 5:5-10:0.    TECHNOLOGY FOCUS - POLYMERS - Preferred Composition: The porous film is polyolefin resin film. The separator further includes surface layer containing particles and resin. Preferred Property: The separator has thickness of 3-18 mu m.