Secondary batteries using lithium cobalt oxide as positive electrode active materials have a problem of a decrease in battery capacity due to repeated charging/discharging, for example. A positive electrode active material particle which hardly deteriorates is provided. In a first step, a container in which a lithium oxide and a fluoride are set is placed in a heating furnace, and in a second step, the inside of the heating furnace is heated in an atmosphere containing oxygen. The heating temperature of the second step is from 750° C. to 950° C., inclusive. By the manufacturing method, fluorine can be contained in the positive electrode active material particle to increase the wettability of the surface of the positive electrode active material so that the surface of the positive electrode active material is homogenized and planarized. The crystal structure of the thus manufactured positive electrode active material is unlikely to be broken in repeated high-voltage charging/discharging. Thus, secondary batteries using the positive electrode active material having such a feature have greatly improved cycle characteristics.

A positive electrode active material having a crystal structure that is unlikely to be broken by repeated charging and discharging is provided. A positive electrode active material with high charge and discharge capacity is provided. A positive electrode active material including lithium, cobalt, nickel, magnesium, and oxygen, in which the a-axis lattice constant of an outermost surface layer of the positive electrode active material is larger than the a-axis lattice constant of an inner portion and in which the c-axis lattice constant of the outermost surface layer is larger than the c-axis lattice constant of the inner portion. A rate of change between the a-axis lattice constant of the outermost surface layer and the a-axis lattice constant of the inner portion is preferably larger than 0 and less than or equal to 0.12, and a rate of change between the c-axis lattice constant of the outermost surface layer and the c-axis lattice constant of the inner portion is preferably larger than 0 and less than or equal to 0.18.

A positive electrode active material having a crystal structure that is unlikely to be broken by repeated charging and discharging is provided. A positive electrode active material with high charge and discharge capacity is provided. One embodiment of the present invention is a positive electrode active material containing lithium, cobalt, nickel, and oxygen; in which a molar ratio of lithium, cobalt, and nickel is lithium: cobalt: nickel=1:1−x: x (0.3<x<0.75); in which the average of a bond distance between cobalt and oxygen and a bond distance between nickel and oxygen is longer than or equal to 1.94×10.sup.−10 m and shorter than or equal to 2.1×10.sup.−10 m in a crystal structure of the positive electrode active material; and in which the average of an angle formed between a line connecting cobalt to an adjacent oxygen and a line connecting cobalt to another adjacent oxygen and an angle formed between a line connecting nickel to an adjacent oxygen and a line connecting nickel to another adjacent oxygen is greater than or equal to 86.5° and less than 90°.

There is provided a method for collecting and reusing an active material from positive electrode scrap. The method of reusing a positive electrode active material of the present disclosure includes (a-1) immersing a positive electrode scrap comprising an active material layer on a current collector into a basic solution to separate the active material layer from the current collector, (a-2) thermally treating the active material layer in air for thermal decomposition of a binder and a conductive material in the active material layer, and collecting an active material in the active material layer, (b) washing the active material collected from the step (a-2) with a lithium compound solution which is basic in an aqueous solution and drying, and (c) annealing the active material washed from the step (b) with a lithium precursor to obtain a reusable active material.

A lithium cobalt-based oxide cathode active material powder having: —a primary phase comprising Li, Co, and O, and —a secondary phase comprising LiNaSO.sub.4, wherein the content of said LiNaSO.sub.4 secondary phase in said powder is of at least 0.4 wt. % and inferior or equal to 1.1 wt. % with respect to a total weight of the cathode active material powder, said cathode active material powder being characterized in that it has a S/Na atomic ratio superior or equal to 0.80 and inferior or equal to 1.20.

There is provided a method for collecting and reusing an active material from positive electrode scrap. The positive electrode active material reuse method of the present disclosure includes (a) thermally treating positive electrode scrap comprising an active material layer on a current collector in air for thermal decomposition of a binder and a conductive material in the active material layer, to separate the current collector from the active material layer, and collecting an active material in the active material layer, (b) washing the collected active material using a lithium precursor aqueous solution which is basic in an aqueous solution and drying, and (c) annealing the washed active material to obtain a reusable active material.

An object of the present invention is to provide a positive electrode active substance for a lithium secondary battery, the positive electrode active substance, when being used as a positive electrode active substance for a lithium secondary battery, being little in deterioration of cycle characteristics and being high in the energy density retention rate, even in repetition of charge and discharge at high voltages, and a lithium secondary battery little in deterioration of cycle characteristics and high in the energy density retention rate, even in repetition of charge and discharge at high voltages. The positive electrode active substance for a lithium secondary battery comprises a lithium cobalt-based composite oxide particle having a Ti-containing compound and an Mg-containing compound adhered on at least part of the particle surface.

This disclosure relates to an SO.sub.2-based electrolyte for a rechargeable battery cell containing at least one conducting salt of the Formula (I) ##STR00001##
wherein M is a metal selected from the group consisting of alkali metals, alkaline earth metals, metals of group 12 of the periodic table of the elements and aluminum; x is an integer from 1 to 3; the substituents R, R.sup.2, R.sup.3 and R.sup.4 are each independently selected from the group consisting of C.sub.1-C.sub.10 alkyl, C.sub.2-C.sub.1 alkenyl, C.sub.2-C.sub.1 alkynyl, C.sub.3-C.sub.10 cycloalkyl, C.sub.6-C.sub.14 aryl, and C.sub.5-C.sub.14 heteroaryl; and Z is aluminum or boron.

A method for reusing a positive electrode active material includes dry-milling a positive electrode scrap comprising an active material layer on a current collector to convert the active material layer into a powdered state and to separate the active material layer from the current collector. The active material layer is a lithium composite transition metal oxide positive material active material layer. The method further includes adding a lithium precursor to a the active material layer. The method further includes thermally treating the active material layer in the powdered state to collect an active material. The method further includes obtaining a reusable active material by washing the collected active material with a basic lithium compound aqueous solution and drying the collected active material.

As for a secondary battery using lithium cobalt oxide as a positive electrode active material, the positive electrode active material with which a decrease in battery capacity due to repeated charge and discharge is inhibited is provided. Alternatively, a positive electrode active material particle which hardly deteriorates is provided. The positive electrode active material includes lithium, cobalt, oxygen, magnesium, aluminum, and fluorine and is a crystal represented by a layered rock-salt structure. The space group of the crystal is represented by R−3m. The concentration of fluorine in a surface portion of the crystal is higher than that inside the crystal. The concentration of magnesium in the surface portion of the crystal is higher than that inside the crystal. The atomic ratio of magnesium to aluminum in the surface portion of the crystal is higher than that inside the crystal.