Abstract: A method for forming a positive electrode active material that can be used for a lithium ion battery having excellent discharge characteristics even in a low-temperature environment is provided. The method includes a first step in which lithium cobalt oxide with a median diameter (D50) of less than or equal to 10 ?m is heated at a temperature higher than or equal to 700° C. and lower than or equal to 1000° C. for longer than or equal to 1 hour and shorter than or equal to 5 hours, a second step in which a first mixture is formed by mixing a fluorine source and a magnesium source to the lithium cobalt oxide subjected to the first step, a third step in which the first mixture is heated at a temperature higher than or equal to 800° C. and lower than or equal to 1100° C.

Abstract: A positive electrode active material that is unlikely to generate defects even when charging and discharging at a high voltage and/or at a high temperature is provided. A positive electrode active material in which crystal structures are unlikely to collapse even when charging and discharging are repeated is also provided. The positive electrode active material contains lithium, cobalt, oxygen, and an additive element. The positive electrode active material includes a surface portion, an inner portion. The positive electrode active material contains the additive element in the surface portion. The surface portion is a region extending from a surface of the positive electrode active material to a depth of 10 nm or less toward the inner portion, and the surface portion and the inner portion are topotaxy. A degree of diffusion of the additive element vary between crystal planes of the surface portion, and the additive element is at least one or two or more selected from nickel, aluminum, and magnesium.

Abstract: A method for forming a positive electrode active material that is stable in a high potential state and/or a high temperature state is provided. The method for forming a positive electrode active material includes a step of mixing a composite oxide containing lithium and cobalt with a barium source, a magnesium source, and a fluorine source to fabricate a first mixture containing barium fluoride, magnesium fluoride, and lithium fluoride; a step of heating the first mixture at a temperature higher than or equal to 800° C. and lower than or equal to 1100° C. for longer than or equal to 2 hours; a step of mixing the first mixture with a nickel source and an aluminum source to fabricate a second mixture; and a step of heating the second mixture at a temperature higher than or equal to 800° C. and lower than or equal to 1100° C. for longer than or equal to 2 hours. When a molar ratio of magnesium fluoride to barium fluoride contained in the first mixture is MgF2:BaF2=y:1, y satisfies greater than or equal to 0.

Abstract: A novel positive electrode active material, a novel positive electrode, and a novel lithium-ion secondary battery are to be provided. The lithium-ion secondary battery includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive electrode active material that includes a composite oxide containing lithium and cobalt. The positive electrode active material includes barium, magnesium, and aluminum in a surface portion. When being analyzed, the surface portion preferably includes a region where a first point of the highest barium concentration and a second point of the highest magnesium concentration exist closer to the surface than a third point of the highest aluminum concentration does.

Abstract: An electric automobile incorporating a secondary battery has a disadvantage such as a difficulty in knowing the remaining capacity accurately and in predicting the time when the remaining capacity becomes zero because of deterioration of the secondary battery. The internal resistance is estimated with high accuracy even when the secondary battery deteriorates. Data used for learning or estimation is a data group (also referred to as data with regenerative charging) that is limited to data acquired within a certain time range around the end of regenerative charging. Such data within the limited range is extracted, used for learning, and subjected to the estimation. Thus, a value of the internal resistance can be output with high accuracy, specifically, with a mean error rate of 1% or less.

Abstract: A secondary battery with little deterioration is provided. A highly reliable secondary battery is provided. A positive electrode active material included in the secondary battery includes a crystal of lithium cobalt oxide. The positive electrode active material includes a first region including a surface parallel to the (00l) plane of the crystal and a second region including a surface parallel to a plane intersecting with the (00l) plane. The positive electrode active material contains magnesium. The first region includes a portion with a magnesium concentration that is higher than or equal to 0.5 atomic % and lower than or equal to 10 atomic %. The second region includes a portion with a magnesium concentration that is higher than the magnesium concentration in the first region and is higher than or equal to 4 atomic % and lower than or equal to 30 atomic %.

Abstract: A positive electrode active material in which the number of defects that cause deterioration is small or progress of the defect is suppressed is provided. The positive electrode active material is used for a secondary battery. The positive electrode active material contains lithium cobalt oxide containing an additive element. After a cycle test is performed on a cell that uses the positive electrode active material for a positive electrode and a lithium electrode as a counter electrode, the positive electrode active material includes a defect and contains at least the same element as the additive element in a region in the vicinity of the defect. The additive element is contained also in a surface portion of the positive electrode active material.

Abstract: A secondary battery and a positive electrode active material each having high energy density per weight and per volume are provided. The secondary battery includes a positive electrode, the positive electrode includes lithium cobalt oxide, and the lithium cobalt oxide has a projection containing at least one or two or more selected from Hf, V, Nb, Ce, and Sm. The projection may further contain Mg, F, Ni, or Al as an additive element. The secondary battery is manufactured through a step of forming a mixed solution by mixing the lithium cobalt oxide and a metal alkoxide containing one or two or more selected from Hf, V, Nb, Ce, and Sm. With such a positive electrode active material, a secondary battery with a high charge voltage can be provided.

Abstract: A lithium ion battery having excellent charge characteristics and discharge characteristics even in a low-temperature environment is provided. The lithium ion battery includes a positive electrode active material and an electrolyte. The positive electrode active material contains cobalt, oxygen, magnesium, aluminum, and nickel. The electrolyte contains lithium hexafluorophosphate, ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate. Second discharge capacity of the lithium ion battery is higher than or equal to 70% of first discharge capacity. The first discharge capacity is obtained by performing first charge and first discharge at 20° C., and the second discharge capacity is obtained by performing second charge and second discharge at ?40° C. The first discharge and the second discharge are constant current discharge with 20 mA/g per positive electrode active material weight.

Abstract: 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 projection is provided on the surface of the positive electrode active material. The projection preferably contains zirconium and yttrium and is a rectangular solid. The projection preferably has a crystal structure that is tetragonal, cubic, or a mixture of two phases, tetragonal and cubic. In the positive electrode active material, the transition metal is one or two or more selected from cobalt, nickel, and manganese, and the additive elements are at least two or more selected from magnesium, fluorine, aluminum, zirconium, and yttrium.

Abstract: According to one embodiment of the present invention, a positive electrode active material with high charge and discharge capacity is provided. Alternatively, a positive electrode active material with high charge and discharge voltage is provided. Alternatively, a positive electrode active material with little deterioration is provided. To improve the reliability of the positive electrode active material, the surface of the positive electrode active material is prevented from reacting with an electrolyte solution and being reduced. The provision of a projection on part of the positive electrode active material surface decreases the reduction of the positive electrode active material surface from reacting with the electrolyte solution, thereby improving the cycle performance.

Abstract: 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.

Abstract: 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?10 m and shorter than or equal to 2.

Abstract: To provide a method of forming a positive electrode active material with high productivity. To provide a manufacturing apparatus capable of forming a positive electrode active material with high productivity. Provided is a method of forming a positive electrode active material including lithium, a transition metal, oxygen, and fluorine. An adhesion preventing step is performed during heating of an object. Examples of the adhesion preventing step include stirring by rotating a furnace during the heating, stirring by vibrating a container containing an object during the heating, and crushing performed between the plurality of heating steps. By these manufacturing methods, a positive electrode active material having favorable distribution of an additive at the surface portion can be formed.

Abstract: A positive electrode active material that has high capacity and excellent charge and discharge cycle performance for a secondary battery is provided. The positive electrode active material includes a group of particles including a first group of particles and a second group of particles. The group of particles includes lithium, cobalt, nickel, aluminum, magnesium, oxygen, and fluorine. When the number of cobalt atoms included in the group of particles is taken as 100, the number of nickel atoms is greater than or equal to 0.05 and less than or equal to 2, the number of aluminum atoms is greater than or equal to 0.05 and less than or equal to 2, and the number of magnesium atoms is greater than or equal to 0.1 and less than or equal to 6.

Abstract: A positive electrode active material in which a discharge capacity decrease due to charge and discharge cycles is suppressed and a secondary battery including the positive electrode active material are provided. A positive electrode active material in which a change in a crystal structure, e.g., a shift in CoO2 layers is small between a discharged state and a high-voltage charged state is provided. For example, a positive electrode active material that has a layered rock-salt crystal structure belonging to the space group R-3m in a discharged state and a crystal structure belonging to the space group P2/m in a charged state where x in LixCoO2 is greater than 0.1 and less than or equal to 0.24 is provided. When the positive electrode active material is analyzed by powder X-ray diffraction, a diffraction pattern has at least diffraction peaks at 2? of 19.47±0.10° and 2? of 45.62±0.05°.

Abstract: An electric automobile incorporating a secondary battery has a disadvantage such as a difficulty in knowing the remaining capacity accurately and in predicting the time when the remaining capacity becomes zero because of deterioration of the secondary battery. The internal resistance is estimated with high accuracy even when the secondary battery deteriorates. Data used for learning or estimation is a data group (also referred to as data with regenerative charging) that is limited to data acquired within a certain time range around the end of regenerative charging. Such data within the limited range is extracted, used for learning, and subjected to the estimation. Thus, a value of the internal resistance can be output with high accuracy, specifically, with a mean error rate of 1% or less.

Abstract: A positive electrode active material for a lithium-ion secondary battery and with high capacity and excellent charging and discharging cycle performance is provided. The positive electrode active material contains lithium, cobalt, nickel, aluminum, and oxygen, and the spin density attributed to one or more of a divalent nickel ion, a trivalent nickel ion, a divalent cobalt ion, and a tetravalent cobalt ion is within a predetermined range. It is preferable that the positive electrode active material further contain magnesium. An appropriate magnesium concentration is represented by a concentration with respect to cobalt. It is preferable that the positive electrode active material further contain fluorine.

Abstract: 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.

Abstract: Provided is a positive electrode active material that achieves improvement in load resistance such as rate performance and output resistance when used as a positive electrode active material in a lithium-ion secondary battery, achieves improvement in powder properties, has a short manufacturing cycle time, and is low in cost. The positive electrode active material is manufactured by a first step of forming a first mixture by separately pulverizing a compound containing one or more elements selected from magnesium, calcium, zirconium, lanthanum, and barium; a compound containing halogen and an alkali metal; and a fluoride containing one or more metals selected from nickel, aluminum, manganese, titanium, vanadium, iron, and chromium, and then mixing them with metal oxide powder; and a second step of performing heating at a temperature higher than or equal to 700° C. and lower than or equal to 950° C.