The present invention relates to a catalyst for converting CO.sub.2 to synthetic fuel such as CO using metal oxides and a conversion method using the same. The CO.sub.2 conversion catalyst according to the present invention can treat a large amount of CO.sub.2 per unit mole and is oxidized. In the reduction cycle, the catalyst has relatively high structural stability and excellent long-term stability as a catalyst, and it has excellent activity as a CO.sub.2 decomposition catalyst that can be used in a continuous flow reactor, such as for CO.sub.2 decomposition at a relatively low temperature.

A Co.sub.2Z hexaferrite composition is provided containing molybdenum and one or both of barium and strontium, having the formula (Ba.sub.2Sr.sub.(3-Z)Co.sub.(2+X))Mo.sub.xFe.sub.(y-2x)O.sub.41 where x=0.01 to 0.20; y=20 to 24; and z=0 to 3. The composition can exhibit high permeabilities and equal or substantially equal values of permeability and permittivity while retaining low magnetic and dielectric loss tangents and loss factors. The composition is suitable for high frequency applications such as ultrahigh frequency and microwave antennas and other devices.

Mixed-metal oxides and lithiated mixed-metal oxides are disclosed that involve compounds according to, respectively, Ni.sub.xMn.sub.yCo.sub.zMe.sub.O.sub. and Li.sub.1+Ni.sub.xMn.sub.yCo.sub.zMe.sub.O.sub.. In these compounds, Me is selected from B, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ru, Ag, In, and combinations thereof; 0x1; 0y1; 0z<1; x+y+z>0; 00.5; and x+y+>0. For the mixed-metal oxides, 15. For the lithiated mixed-metal oxides, 0.11.0 and 1.93. The mixed-metal oxides and the lithiated mixed-metal oxides include particles having an average density greater than or equal to 90% of an ideal crystalline density.

A lithium cobalt-based positive electrode active material is provided. The lithium cobalt-based positive electrode active material includes a core portion including a lithium cobalt-based oxide represented by Formula 1 and a shell portion including a lithium cobalt-based oxide represented by Formula 2, wherein the lithium cobalt-based positive electrode active material includes 2500 ppm or more, preferably 3000 ppm or more of a doping element M based on the total weight of the positive electrode active material. An inflection point does not appear in a voltage profile measured during charging/discharging a secondary battery including the lithium cobalt-based positive electrode active material.

Provided is a novel compound which can be used for positive-electrode catalysts of metal-air batteries. The melilite-type complex oxide according to the present invention is represented by a general formula (BazSr1z)2CoxFe22x(SiyGe1y)1+xO7 (in the formula, 0x1, 0y1, and 0z1, excluding the case where x=1, y=1, and z=0, the case where x=1, y=1, and z=1, the case where x=1, y=0, and z=0, the case where x=1, =0, and z=1, the case where x=0, y=0, and z=0, and the case where x=0, y=0, and z=1).

An electrode includes a material represented by L.sub.1-xM.sub.xCoO.sub.2-d where 0<x0.2 and 0d0.2. The variable M includes a metal selected from the group consisting of transition metals, Group I elements, and Group II elements.

The present disclosure relates to a positive electrode material which includes a first positive electrode active material, and a second positive electrode active material in the form of a single particle, wherein an amount of lithium impurities on a surface of the second positive electrode active material is 0.14 wt % or less based on a total weight of the second positive electrode active material, and at least one of nickel, cobalt, and manganese included in the second positive electrode active material has a concentration gradient gradually changing from the center of the particle to a surface thereof, a method of preparing the positive electrode material, and a positive electrode for a lithium secondary battery and a lithium secondary battery which include the positive electrode material.

A high-rate lithium cobaltate cathode material, which contains a multi-channel network formed by fast ionic conductor Li.sub.M.sub.O.sub., mainly consists of lithium cobaltate. The lithium cobaltate is melted together with the fast ionic conductor Li.sub.M.sub.O.sub. in the form of primary particles to form secondary particles. Besides, the lithium cobaltate is embedded in the multi-channel network formed by fast ionic conductor Li.sub.M.sub.O.sub.. The element M in Li.sub.M.sub.O.sub. is one or more of Ti, Zr, Y, V, Nb, Mo, Sn, In, La, W and 14, 15, 212. The lithium cobaltate cathode material is mainly obtained by uniformly mixing cobaltous oxide impregnated with a hydroxide of M and lithium source, then by the sintering reaction in an air atmosphere furnace at a high temperature. The product of the present invention can greatly promote the lithium ion conductivity of the lithium cobaltate cathode material during the charging and discharging process of the lithium-ion battery, and improve the rate performance of the material.

A positive electrode active material has a small difference in a crystal structure between the charged state and the discharged state. For example, the crystal structure and volume of the positive electrode active material, which has a layered rock-salt crystal structure in the discharged state and a pseudo-spinel crystal structure in the charged state at a high voltage of approximately 4.6 V, are less likely to be changed by charging and discharging as compared with those of a known positive electrode active material. In order to form the positive electrode active material having the pseudo-spinel crystal structure in the charged state, it is preferable that a halogen source such as a fluorine and a magnesium source be mixed with particles of a composite oxide containing lithium, a transition metal, and oxygen, which is synthesized in advance, and then the mixture be heated at an appropriate temperature for an appropriate time.

An electrode formed from a material represented by Li.sub.1-xM.sub.xCo.sub.1-yM.sub.yO.sub.2-d where 0<x0.2, 0y<1, and 0<d0.2. M and M each independently comprises a metal selected from the group consisting of transition metals, Group I elements, and Group II elements.