LITHIUM SECONDARY BATTERY

To provide a lithium ion secondary battery capable of completing charge in a short time of 15 minutes or less. A lithium ion secondary battery comprising a cathode comprising a cathode composite layer on a surface of a cathode collector comprising a cathode active material and a conducting agent; an anode comprising an anode active material; a separator insulating between the positive and anodes; and an electrolyte compsiring lithium ions, wherein the cathode active material is represented by the following formula (I) ; the conducting agent contains particles having an average particle size of 3 µm or more and 12 µm or less in an amount of 1% by weight or more; a thickness of the cathode composite layer formed on the cathode collector is 50 µm or less per one surface; an electrode density of the anode is 1.55 g/cmor more; and an A/C ratio of a lithium capacity A that the anode can insert/desorb to a lithium capacity C that the cathode can insert/desorb is adjusted to 1.8≤A/C≤2.2: LiMPO (I) wherein M is a metal atom and 0