Abstract: To provide a cathode active material with which a lithium ion secondary battery having favorable cycle characteristics and having a high energy density even when discharged at a high voltage can be obtained; a cathode comprising the cathode active material; and a lithium ion secondary battery having the cathode. A cathode active material comprising a composite oxide (A) containing Li and at least one transition metal element selected from the group consisting of Ni, Co and Mn, and the following particles (B) and the following fluorinated carbon material (C) present on the surface of the composite oxide (A): particles (B): particles containing an oxide of at least one metal element selected from the group consisting of Ti, Sn, Si, Al, Ce, Y, Zr, Co, W, V, Nb, Ta, La and Mg; and fluorinated carbon material (C): a fluorinated carbon material in the form of particles or fibers.

Abstract: To provide a cathode active material with which a lithium ion secondary battery having favorable cycle characteristics and having a high energy density even when discharged at a high voltage can be obtained; a cathode comprising the cathode active material; and a lithium ion secondary battery having the cathode. A cathode active material comprising a composite oxide (A) containing Li and at least one transition metal element selected from the group consisting of Ni, Co and Mn, and the following particles (B) and the following fluorinated carbon material (C) present on the surface of the composite oxide (A): particles (B): particles containing an oxide of at least one metal element selected from the group consisting of Ti, Sn, Si, Al, Ce, Y, Zr, Co, W, V, Nb, Ta, La and Mg; and fluorinated carbon material (C): a fluorinated carbon material in the form of particles or fibers.

Abstract: A membrane/electrode assembly 10 for a polymer electrolyte fuel cell, which comprises an anode 15 having an anode catalyst layer 11 containing an anode catalyst and an ion-exchange resin, a cathode 16 having a cathode catalyst layer 13 containing a cathode catalyst and an ion-exchange resin, and a polymer electrolyte membrane 17 disposed between the anode 15 and the cathode 16, wherein the anode catalyst is one having platinum or a platinum alloy supported on a carbon, and the amount of platinum or a platinum alloy supported in the anode catalyst is from 1 to 25 mass %; and the anode catalyst layer 11 contains fine particles made of at least one member selected from iridium oxide, iridium, ruthenium oxide and ruthenium, and the fine particles have a specific surface area of from 2 to 50 m2/g.

Abstract: To provide a membrane/electrode assembly for a polymer electrolyte fuel cell which has a high power generation performance in an environment ranging from a low humidity to a high humidity and is scarcely susceptible to deterioration in the performance of the electrode even when fuel becomes deficient.