System of lithium ion battery containing material with high irreversible capacity

Disclosed is a cathode active material comprising a lithium-free metal oxide and a material with high irreversible capacity. A novel lithium ion battery system using the cathode active material is also disclosed. The battery, comprising a cathode using a mixture of a Li-free metal oxide and a material with high irreversible capacity, and an anode comprising carbon instead of Li metal, shows excellent safety compared to a conventional battery using lithium metal as an anode. Additionally, the novel battery system has a higher charge/discharge capacity compared to a battery using a conventional cathode active material such as lithium cobalt oxide, lithium nickel oxide or lithium manganese oxide.