Provided is a new 5 V class spinel-type lithium manganese-containing composite oxide which enables the expansion of a high potential capacity region and the suppression of gas generation. The 5 V class spinel-type lithium manganese-containing composite oxide has an operating potential of 4.5 V or more at a metal Li reference potential, and contains Li, Mn, O and two or more other elements. The spinel-type lithium manganese-containing composite oxide is characterized in that, in an electronic diffraction image from a transmission electron microscope (TEM), a diffraction spot observed in the Fd-3m structure as well as a diffraction spot not observed in the Fd-3m structure are confirmed.

A positive electrode active material for a lithium secondary battery according to an embodiment of the present invention includes a lithium transition metal composite oxide and doping metals doped in the lithium-transition metal composite oxide, wherein the doping metals includes at least two kinds and the average oxidation number of the doping metals is greater than 3.5.

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.

A nonlinear optical crystal has a chemical formula Li.sub.2X.sub.4TiOSi.sub.4O.sub.12, wherein X=K or Rb. The nonlinear optical crystal belongs to tetragonal system with space group P4nc and Z=2. The unit cell parameters of Li.sub.2K.sub.4TiOSi.sub.4O.sub.12 are a=b=11.3336(5) Å, c=5.0017(2) Å; and the unit cell parameters of Li.sub.2Rb.sub.4TiOSi.sub.4O.sub.12 are a=b=11.5038(6) Å, c=5.1435(3) Å. The two crystals are thermally stable and show strong second harmonic generation with high laser damage threshold.

A process for producing lithium titanate which includes the steps of synthesizing a lithium titanate hydrate intermediate via aqueous chemical processing, and thermally treating the lithium titanate hydrate intermediate to produce the lithium titanate. The lithium titanate hydrate is preferably (Li.sub.1.81H.sub.0.19)Ti.sub.2O<<2H.sub.2O. The lithium titanate is preferably Li.sub.4Ti.sub.5O.sub.12 (LTO). Synthesizing the lithium titanate hydrate intermediate may include mixing a titanium-containing compound with a lithium-containing compound in a solvent to produce a lithium-titanium precursor mixture. Preferably the titanium-containing compound includes titanium tetrachloride TiCl.sub.4. Also, a lithium titanate obtained according to the process and a lithium battery including the lithium titanate.

A lithium cobalt-based oxide cathode active material powder comprising particles having a median particle size D50 of greater than or equal to 20 μm, preferably 25 μm, and less than or equal to 45 μm, said particles having an averaged circularity of greater than or equal to 0.85 and less than or equal to 1.00, said particles having a general formula Li.sub.1+aCo.sub.1-x-y-zAl.sub.xM′.sub.yMe.sub.zO.sub.2, wherein M′ and Me comprise at least one element of the group consisting of: Ni, Mn, Nb, Ti, W, Zr, and Mg, with −0.01≤a≤0.01, 0.002≤x≤0.050, 0≤y≤0.020 and 0≤z≤0.050, said lithium cobalt-based oxide particles having a R-3m structure and (018) diffraction peak asymmetry factor A.sub.D(018) of greater than or equal to 0.85 and less than or equal to 1.15, said diffraction peak asymmetry factor being obtained by a synchrotron XRD spectrum analysis with an emission wavelength λ value equal to 0.825 Å.

An object of the present invention or a problem to be solved by the present invention is to provide, as a material for use as a positive electrode of a sodium secondary battery, a novel material that allows the resulting battery to have capacity characteristics superior to those of conventional batteries. The composite metal oxide of the present invention has a composition represented by the general formula Na.sub.xMe.sub.yO.sub.2, where Me is at least one selected from the group consisting of Fe, Mn, and Ni, x satisfies 0.8<x≦1.0, and y satisfies 0.95≦y<1.05, and consists of a P2 structure. The sodium secondary battery of the present invention includes: a positive electrode (13) containing the composite metal oxide of the present invention; a negative electrode (16) containing a material capable of absorbing and desorbing Na ions; and an electrolyte containing Na ions and anions.

A positive electrode active material precursor for a lithium secondary battery, in which the following requirements (1) and (2) are satisfied.

Requirement (1): In powder X-ray diffraction measurement using a CuKα ray, α/β that is a ratio of an integrated intensity α of a peak present within a range of a diffraction angle 2θ=19.2±1° to an integrated intensity β of a peak present within a range of a diffraction angle 2θ=33.5±1° is 3.0 or more and 5.8 or less.

Requirement (2): A 10% cumulative volume particle size D.sub.10 obtained from particle size distribution measurement is 2 μm or less.

A positive electrode active material that has high capacity and excellent charge and discharge cycle performance for a secondary battery is provided. A positive electrode active material that inhibits a decrease in capacity in charge and discharge cycles is provided. A high-capacity secondary battery is provided. A secondary battery with excellent charge and discharge characteristics is provided. A highly safe or reliable secondary battery is provided. A positive electrode active material contains lithium, cobalt, oxygen, and aluminum and has a crystal structure belonging to a space group R-3m when Rietveld analysis is performed on a pattern obtained by powder X-ray diffraction. In analysis by X-ray photoelectron spectroscopy, the number of aluminum atoms is less than or equal to 0.2 times the number of cobalt atoms.

The present invention is to provide a cathode active material configured to increase, when used in a lithium battery, the discharge capacity of the lithium battery higher than conventional lithium batteries, and a lithium battery including the cathode active material. Presented is a cathode active material for lithium batteries, wherein the cathode active material is represented by the following composition formula (1) and has a rock salt type crystal structure including formula (1): Li.sub.2Ni.sub.1-x-yCo.sub.xMn.sub.yTiO.sub.4 wherein x and y are real numbers that satisfy x>0, y>0 and x+y<1.