NOVELTY - A high temperature rechargeable battery system is obtained by introducing oxygen-deficient ferrites (I) and/or lanthanum nickelate-based materials into lithium/titanium/magnesium-carbon dioxide rechargeable batteries. During discharge of the battery, the oxygen-containing gases such as greenhouse gas can be decomposed into syn-gas or solid carbon and renewable energy such as solar or wind energy can be used to charge the battery and produce pure oxygen.    USE - High temperature rechargeable battery system used in integrated gasification combined cycle power plant for decomposing oxygen-containing gas such as nitrogen oxide (NOx), sulfur dioxide, water, carbon dioxide and greenhouse gas, and for solar or wind power energy storage.    ADVANTAGE - Since the high temperature rechargeable battery system uses oxygen ion conducting electrolyte, the safety of the battery system is improved, cathode clogging is prevented and high ionic oxygen conductivity at elevated operating temperatures and battery efficiency are improved. The elevated operating temperature overcomes the obstacles of high resistivity of titanium/titanium dioxide and magnesium/magnesium oxide electrodes at room temperature and intermediate temperature. The carbon dioxide gas is a directly usable gas for the battery system and the energy consumption for carbon dioxide decomposition is self-sustainable with the utilization of the renewable energy source. The battery system produces high quality oxygen on the cathode during the charging mode and generates electricity and decomposes byproduct during the discharge mode, and reduces the cost of greenhouse gas decomposition/sequestration. The system is capable of in-situ methanation which can be used to remove deposited carbon which can further be removed by chemical or mechanical process. Since anode material other than lithium is used, the battery system is manufactured economically.    DETAILED DESCRIPTION - A high temperature rechargeable battery system is obtained by introducing oxygen-deficient ferrites and/or lanthanum nickelate-based materials into lithium/titanium/magnesium-carbon dioxide rechargeable batteries. During discharge of the battery, the oxygen-containing gases such as greenhouse gas can be decomposed into syn-gas or solid carbon and renewable energy such as solar or wind energy can be used to charge the battery and produce pure oxygen. The oxygen-deficient ferrite is of formula: MxFe3-xO4-d (I), where M is Fe(II), Cu(II), Co(II), Mn(II) or Ni(II).    DESCRIPTION OF DRAWING(S) - The drawing shows the principle view of the battery in discharging and charging mode.    Anode (1)    Cathode (2)    Oxygen ion conducting electrolyte (3)    Introduced gas (4)    Under potential (5)