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 positive electrode active material comprising a lithium metal composite oxide having a layered crystal structure provides a novel lithium metal composite oxide powder which can suppress the reaction with an electrolytic solution and raise the charge-discharge cycle ability of a battery, and can improve the output characteristics of a battery. A lithium metal composite oxide powder comprises a particle having a surface portion where one or a combination of two or more (“surface element A”) of the group consisting of Al, Ti and Zr is present, on the surface of a particle comprising a lithium metal composite oxide having a layered crystal structure, wherein the amount of surface LiOH is smaller than 0.10% by weight, and the amount of surface Li.sub.2CO.sub.3 is smaller than 0.25% by weight; in an X-ray diffraction pattern, the ratio of an integral intensity of the (003) plane of the lithium metal composite oxide to that of the (104) plane thereof is higher than 1.15; and the amount of S obtained by a measurement using ICP is smaller than 0.10% by weight of the lithium metal composite oxide powder (100% by weight).

A cathode active material for a lithium secondary battery according to embodiments of the present invention has a high-nickel composition and includes a lithium-nickel composite metal oxide particle in which lithium, nickel and a metal having an oxidation number of +2 are combined in a predetermined range. A cation disorder caused when a nickel ion is present at a lithium-ion site is reduced to improve structural stability of the cathode active material. An initial capacity and a battery efficiency of a lithium secondary battery can be improved using the cathode active material.

The invention relates to novel materials of the formula: A.sub.1-δM.sup.1.sub.VM.sup.2.sub.WM.sup.3.sub.XM.sup.4.sub.YM.sup.5.sub.ZO.sub.2 wherein A is one or more alkali metals comprising sodium and/or potassium either alone or in a mixture with lithium as a minor constituent; M.sup.1 is nickel in oxidation state +2; M.sup.2 comprises a metal in oxidation state +4 selected from one or more of manganese, titanium and zirconium; M.sup.3 comprises a metal in oxidation state +2, selected from one or more of magnesium, calcium, copper, zinc and cobalt; M.sup.4 comprises a metal in oxidation state +4, selected from one or more of titanium, manganese and zirconium; M.sup.5 comprises a metal in oxidation state +3, selected from one or more of aluminum, iron, cobalt, molybdenum, chromium, vanadium, scandium and yttrium; wherein 0≦δ≦0.1 V is in the range 0<V<0.5; W is in the range 0<W≦0.5; X is in the range 0≦X<0.5; Y is in the range 0≦Y<0.5; Z is ≧0; and further wherein V+W+X+Y+Z=1. Such materials are useful, for example, as electrode materials in sodium ion battery applications.

Provided is a nickel-containing composite hydroxide that is a precursor of a positive-electrode active material with which a nonaqueous-electrolyte secondary battery having a low irreversible capacity and a high energy density can be configured. An aqueous alkaline aqueous solution and a complexing agent are added to an mixed aqueous solution including at least nickel and cobalt to regulate the pH (measured at a reference liquid temperature of 25° C.) of this mixed aqueous solution to 11.0 to 13.0, the ammonium concentration to 4 to 15 g/L, and the reaction temperature to 20° C. to 45° C. Using stirring blades having an inclination angle of 20° to 60° with respect to a horizontal plane, the mixture is stirred to conduct a crystallization reaction under such conditions that when the nickel-containing composite hydroxide to be obtained is roasted in air at 800° C. for 2 hours, the roasted composite hydroxide has a BET value of 12 to 50 m.sup.2/g. Thus a nickel-containing composite hydroxide expressed by Ni.sub.1−x−yCo.sub.xAl.sub.yM.sub.t(OH).sub.2+α (where, 0<x≦0.20, 0<y≦0.15, 0≦t≦0.10, 0≦α 0.50, and M is one or more kind of element selected from among Mg, Ca, Ba, Nb, Mo, V, Ti, Zr and Y), or the general formula: Ni.sub.1−x−zCo.sub.xMn.sub.zM.sub.t(OH).sub.2+α (where 0<x≦0.50, 0<z≦0.50, x+z≦0.70, 0≦t≦0.10, 0≦α≦0.50, and M is one or more kind of element selected from among Mg, Ca, Ba, Nb, Mo, V, Ti, Zr and Y) is obtained.

The invention relates to novel materials of the formula: A.sub.uM.sup.1.sub.vM.sup.2.sub.wM.sup.3.sub.XM.sup.4.sub.yM.sup.5.sub.ZO.sub.2 wherein A comprises one or more alkali metals selected from lithium, sodium and potassium; M.sup.1 is nickel in oxidation state +2 M.sup.2 comprises a metal in oxidation state +4 selected from one or more of manganese, titanium and zirconium; M.sup.3 comprises a metal in oxidation state +2, selected from one or more of magnesium, calcium, copper, zinc and cobalt; M.sup.4 comprises a metal in oxidation state +4, selected from one or more of titanium, manganese and zirconium; M.sup.5 comprises a metal in oxidation state +3, selected from one or more of aluminum, iron, cobalt, molybdenum, chromium, vanadium, scandium and yttrium; further wherein U is in the range 1<U<2; V is in the range 0.25<V<1; W is in the range 0<W<0.75; X is in the range 0≦X<0.5; Y is in the range 0≦Y<0.5; Z is in the range 0≦Z<0.5; and further wherein (U+V+W+X+Y+Z)≦3. Such materials are useful, for example, as electrode materials in sodium and/or lithium ion battery applications.

A lithium metal oxide powder for a cathode material in a rechargeable battery comprises a core and a surface layer. The surface layer is delimited by an outer and an inner interface. The inner interface is in contact with the core. The cathode material has a layered crystal structure comprising the elements Li, M, and oxygen. M has the formula M=(Ni.sub.z(Ni.sub.1/2 Mn.sub.1/2).sub.y Co.sub.x).sub.1-k A.sub.k, with 0.15≤x≤0.30, 0.20≤z≤0.55, x+y+z=1 and 0<k≤0.1. The Li content is stoichiometrically controlled with a molar ratio 0.95≤Li:M≤1.10. A is at least one dopant and comprises Al. The core at the inner interface has an Al content of 0.3-3 mol %. The surface layer comprises an intimate mixture of Ni, Co, Mn, LiF and Al.sub.2O.sub.3 determined by XPS. The surface layer has a Mn content that decreases from the Mn content at the inner interface to less than 50% of the Mn content at the outer interface.

A method for forming a positive electrode active material of a lithium ion secondary battery is provided. In the method for forming a positive electrode active material, a first container that includes a mixture of lithium oxide, fluoride, and a magnesium compound and fluoride that is outside the first container are provided in a heating furnace, and the heating furnace is heated at a temperature higher than or equal to a temperature at which the fluoride is volatilized or sublimated. It is further preferable that the fluoride be lithium fluoride and the magnesium compound be magnesium fluoride.

An electrochemical half-cell includes an electrical terminal lead in contact with a solid electrolyte, wherein the solid electrolyte includes a doped high-entropy oxide. The electrochemical half-cell can be used as either a reference half-cell or a measuring half-cell. Methods of manufacturing the solid electrolyte and the electrochemical half-cell are further disclosed.

A positive electrode active material includes a lithium transition metal oxide, which is doped with doping element M.sup.2, wherein M.sup.2 includes at least one of Al, Ti, Mg, Zr, W, Y, Sr, Co, F, Si, Na, Cu, Fe, Ca, S, or B, and contains nickel in an amount of 60 mol % or more based on a total number of moles of transition metals excluding lithium, wherein the lithium transition metal oxide has a single particle form, and includes a center portion having a layered structure and a surface portion having a rock-salt structure, and the doping element M.sup.2 is included in an amount of 3,580 ppm to 7,620 ppm based on a total weight of the positive electrode active material.