Abstract: A positive electrode for a secondary battery having excellent cycle performance is provided. The positive electrode for a secondary battery includes a positive electrode current collector layer, a base film, a positive electrode active material layer, and a cap layer; the base film contains titanium nitride; the positive electrode active material layer contains lithium cobalt oxide; and the cap layer contains titanium oxide. The use of titanium nitride for the base film can inhibit oxidation of the positive electrode current collector and diffusion of metal atoms while ensuring an adequate conductivity. The use of titanium oxide for the cap layer can inhibit a side reaction between the positive electrode active material layer and an electrolyte and collapse of a crystal structure of the electrode active material, improving the cycle performance.

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 negative electrode active material particle with little deterioration is provided. Alternatively, a novel negative electrode active material particle is provided. Alternatively, a power storage device with little deterioration is provided. Alternatively, a highly safe power storage device is provided. Alternatively, a novel power storage device is provided. The electrode includes an active material and a conductive additive; the active material contains a metal or a compound including one or more elements selected from silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, and indium; the conductive additive contains a graphene compound; and the graphene compound contains fluorine.

Abstract: Positive electrode active material particles that inhibit a decrease in capacity due to charge and discharge cycles are provided. A high-capacity secondary battery, a secondary battery with excellent charge and discharge characteristics, or a highly-safe or highly-reliable secondary battery is provided. A novel material, active material particles, and a storage device are provided. The positive electrode active material particle includes a first region and a second region in contact with the outside of the first region. The first region contains lithium, oxygen, and an element M that is one or more elements selected from cobalt, manganese, and nickel. The second region contains the element M, oxygen, magnesium, and fluorine. The atomic ratio of lithium to the element M (Li/M) measured by X-ray photoelectron spectroscopy is 0.5 or more and 0.85 or less. The atomic ratio of magnesium to the element M (Mg/M) is 0.2 or more and 0.5 or less.

Abstract: To provide a positive electrode active material film that does not have a (003) orientation and has a layered rock-salt crystal structure even though an inexpensive substrate such as a glass substrate is used, and a positive electrode including the positive electrode active material film. The positive electrode includes a substrate, a positive electrode current collector film, and the positive electrode active material film. The positive electrode current collector film has a stacked structure of a titanium film and a titanium nitride film. The titanium film has a crystal structure belonging to a space group P63/mmc and a (101) orientation, the titanium nitride film has a crystal structure belonging to a space group Fm-3m and a (311) orientation, and the positive electrode active material film has a layered rock-salt crystal structure and a (116) orientation.

Abstract: 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.

Abstract: A positive electrode active material which can improve cycle characteristics of a secondary battery is provided. Two kinds of regions are provided in a superficial portion of a positive electrode active material such as lithium cobaltate which has a layered rock-salt crystal structure. The inner region is a non-stoichiometric compound containing a transition metal such as titanium, and the outer region is a compound of representative elements such as magnesium oxide. The two kinds of regions each have a rock-salt crystal structure. The inner layered rock-salt crystal structure and the two kinds of regions in the superficial portion are topotaxy; thus, a change of the crystal structure of the positive electrode active material generated by charging and discharging can be effectively suppressed.

Abstract: A positive electrode active material having high capacity and excellent cycle performance is provided. The 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 charge and discharge as compared with those of a known positive electrode active material.

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: 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 secondary battery with favorable cycle performance is provided. Alternatively, a secondary battery with higher capacity is provided. A positive electrode active material layer including a first graphene layer, a second graphene layer, and a positive electrode active material. The first graphene layer includes a first region covering the positive electrode active material. The second graphene layer includes a second region covering the positive electrode active material and a third region overlapping with the first region. The first region includes a plane positioned between the positive electrode active material and the third region and formed of arranged six-membered carbon rings. The positive electrode active material includes a fourth region with a layered rock-salt structure. A lithium layer with a layered rock-salt structure included in the fourth region is substantially perpendicular to the plane formed of six-membered carbon rings and included in the second region.

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 secondary battery that can withstand at least high temperature is achieved by designing the structure of the secondary battery. The secondary battery uses: a positive electrode active material obtained by a formation method including a first step of forming a first mixture by pulverizing magnesium fluoride, lithium fluoride, a nickel source, and an aluminum source and then mixing the pulverized materials with powder of lithium cobalt oxide, and a second step of forming a second mixture by heating the first mixture at a temperature lower than an upper temperature limit of the lithium cobalt oxide; and an electrolyte solution to which LiBOB is added.

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: A positive electrode active material having high capacity and excellent cycle performance is provided. The 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 charge and discharge as compared with those of a known positive electrode active material.

Abstract: Provided is a positive electrode active material which suppresses a reduction in capacity due to charge and discharge cycles when used in a lithium ion secondary battery. A covering layer is formed by segregation on a superficial portion of the positive electrode active material. The positive electrode active material includes a first region and a second region. The first region exists in an inner portion of the positive electrode active material. The second region exists in a superficial portion of the positive electrode active material and part of the inner portion thereof. The first region includes lithium, a transition metal, and oxygen. The second region includes magnesium, fluorine, and oxygen.

Abstract: A positive electrode active material, which has higher capacity and excellent charge and discharge cycle performance, for a lithium-ion secondary battery is provided. The positive electrode active material includes lithium, cobalt, magnesium, oxygen, and fluorine; when a pattern obtained by powder X ray diffraction using a CuK?1 ray is subjected to Rietveld analysis, the positive electrode active material has a crystal structure having a space group R-3m, a lattice constant of an a-axis is greater than 2.814×10(?10th power) m and less than 2.817×10(?10th power) m, and a lattice constant of a c-axis is greater than 14.05×10(?10th power) m and less than 14.07×10(?10th power) m; and in analysis by X-ray photoelectron spectroscopy, a relative value of a magnesium concentration is higher than or equal to 1.6 and lower than or equal to 6.0 with the cobalt concentration regarded as 1.

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 having high capacity and excellent cycle performance is provided. The 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 charge and discharge as compared with those of a known positive electrode active material.