Lithium ion storage device

There is provided a lithium ion storage device. A lithium ion storage device includes a positive electrode (18) having a positive electrode active material (22) that is a lithium-containing compound and is capable of absorbing and desorbing lithium ions, and a negative electrode (12) having a negative electrode active material (16) capable of absorbing and desorbing lithium ions. The irreversible capacity of the positive electrode active material (22) that is a capacity at which lithium ions cannot be reabsorbed after being desorbed from the positive electrode active material (22) is 6 % to 40 % of a usage capacity of the negative electrode (12) that is a capacity at which lithium ions are reversibly absorbed and desorbed by the negative electrode active material (16).