To secure an electric potential of a negative electrode 0.4 V or less in the end of electric discharging of a lithium ion cell and prevent electrochemical oxidation of a negative electrode copper collector in an over charged condition.

This lithium ion cell positive electrode is formed on aluminum foil by adding 30 to 50 mass % of LiCO1-XMXO2 (Here, M is one kind of Ni, Fe and Al.) to spinel lithium manganese double oxide and adding a conductive agent and a binding agent. This rocking chair type lithium ion cell has the lithium ion cell positive electrode and a negative electrode of a graphite intercalation compound.