NOVELTY - A battery system comprises a metal oxygen battery (304) including a cathode (304a), and anode (304b) having a metal material; and an oxygen containment unit (302) in communication with and external to the metal oxygen battery, and including an oxygen storage material. The metal oxygen battery and oxygen containment unit are in a closed-loop with respect to each other.    USE - In a vehicle (claimed).    ADVANTAGE - The metal oxygen battery is free of water molecules. By using a relatively high concentration of oxygen at the positive electrode, and/or having increased oxygen diffusion rate at the positive electrode, the present metal-oxygen batteries have improved performance. Also the present battery reduces or eliminates requirements for many balance of plant components including positive electrode flow field, blower and air purification system, and susceptibility to contamination from atmospheric air impurities; increases battery system flexibility and reduces packaging costs; has simplified battery cell manufacturing procedures; and has improved battery performance kinetics via a reduction in bulk diffusion and an increase in surface diffusion.    DETAILED DESCRIPTION - A battery system comprises a metal oxygen battery (304) including a cathode (304a), and anode (304b) having a metal material; and an oxygen containment unit (302) in communication with and external to the metal oxygen battery, and including an oxygen storage material. The metal oxygen battery and oxygen containment unit are in a closed-loop with respect to each other. The battery system further comprises a conduit extending between the oxygen containment unit and the metal oxygen battery, the oxygen containment unit is in fluid communication with the metal oxygen battery through the conduit. The system is used under a range of operation conditions including an operational temperature for the metal oxygen battery of 230-310 degrees K and an operational temperature for the oxygen containment unit of 77-500 degrees K; and an operational pressure of 1-100 bar for the metal oxygen battery and an operational pressure of 1-700 bar for the oxygen containment unit, where the oxygen containment unit has an oxygen volumetric capacity of at least 10 grams of oxygen per liter of the oxygen containment unit under the operational pressure range. The metal oxygen battery further includes a gas flow field (304c) in communication with the oxygen containment unit. The gas flow field has a field volume, and the volume ratio of the field volume relative to the total volume of the metal oxygen battery is 40-80 vol.%. The gas flow field has a unit density less than a unit density of the cathode. The battery system further comprises a control module (310) regulating the communication between the oxygen containment unit and the metal oxygen battery. The control module increases, decreases and/or stops oxygen flow from the oxygen containment unit to the metal oxygen battery. An INDEPENDENT CLAIM is included for using the battery system involving: communicating oxygen from a metal oxygen battery into a reversible closed-loop conduit; and communicating oxygen to an oxygen storage material from the reversible closed-loop conduit.    DESCRIPTION OF DRAWING(S) - The figure shows different views of a battery system.    Oxygen containment unit (302)    Metal oxygen battery (304)    Cathode (304a)    Anode (304b)    Gas flow field (304c)    Separator (305)    First conduit (306a)    Control module (310)    First valve (310a)    Second valve (310b)