Abstract: A positive electrode active material, which has high capacity and excellent charge and discharge cycle performance, for a lithium-ion secondary battery is provided. The positive electrode active material contains lithium, cobalt, an element X, and fluorine, and includes a region represented by a layered rock-salt structure. The space group of the region is represented by R-3m. The element X is one or more selected from elements that have a property in which ?E3 obtained by subtracting, from the stabilization energy in the case of substitution of the element at a lithium position in lithium cobalt oxide, the stabilization energy before the substitution is smaller than ?E4 obtained by subtracting, from the stabilization energy in the case of substitution of the element at a cobalt position in lithium cobalt oxide, the stabilization energy before the substitution. ?E3 and ?E4 are calculated by the first-principles calculation.

Abstract: The safety is ensured in such a manner that with an abnormality detection system of a secondary battery, abnormality of a secondary battery is detected, for example, a phenomenon that lowers the safety of the secondary battery is detected early, and a user is warned or the use of the secondary battery is stopped. The abnormality detection system of the secondary battery determines whether the temperature of the secondary battery is within a temperature range in which normal operation can be performed on the basis of temperature data obtained with a temperature sensor. In the case where the temperature of the secondary battery is high, a cooling device is driven by a control signal from the abnormality detection system of the secondary battery. The abnormality detection system of the secondary battery includes at least a memory means. The memory means has a function of holding an analog signal and includes a transistor using an oxide semiconductor for a semiconductor layer.

Abstract: A battery control circuit with a novel structure, a battery protection circuit with a novel structure, and a power storage device including either of the battery circuits are provided. The power storage device includes a first circuit portion, a second circuit portion, a third circuit portion, and a secondary battery; the first circuit portion has a function of controlling charging of the secondary battery; the first circuit portion has a function of supplying the start time and the end time of the charging of the secondary battery to the third circuit portion; the second circuit portion has functions of generating a first voltage and a first current and supplying them to the third circuit portion; the third circuit portion has a function of generating a second voltage by charging the first current in a capacitor; and the third circuit portion has a function of comparing the first voltage and the second voltage.

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, 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: 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 a high capacity and excellent charge and discharge cycle performance, for a lithium-ion secondary battery is provided. Alternatively, a positive electrode active material that inhibits a decrease in capacity in charge and discharge cycles when used in a lithium-ion secondary battery is provided. Alternatively, a high-capacity secondary battery is provided. Alternatively, a highly safe or reliable secondary battery is provided. The positive electrode active material contains a first substance including a first crack and a second substance positioned inside the first crack. The first substance contains one or more of cobalt, manganese, and nickel, lithium, oxygen, magnesium, and fluorine. The second substance contains phosphorus and oxygen.

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 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 conduction path in an all-solid-state secondary battery is difficult to keep with a volume change in an active material due to charging and discharging in some cases. A positive electrode active material with a small volume change between the charged state and the discharged state is used for an all-solid-state secondary battery. For example, a positive electrode active material that has a layered rock-salt crystal structure in the discharged state and a crystal structure similar to the cadmium chloride type crystal structure in the charged state with a depth of charge of approximately 0.8 changes less in its volume and crystal structure between charging and discharging than known positive electrode active materials.

Abstract: A method for manufacturing a lithium-ion secondary battery more safely at a lower cost is provided. A method for manufacturing a positive electrode for a secondary battery includes a step of forming slurry by mixing graphene oxide, a binder, and a positive electrode active material in a solvent containing water; a step of applying the slurry on a positive electrode current collector; and a step of reducing graphene oxide by at least one of chemical reduction and thermal reduction. As a reducing agent for the chemical reduction, ascorbic acid can be used.

Abstract: A mixture of amorphous PAHs and at least one of a carrier ion storage metal, a Sn compound, a carrier ion storage alloy, a metal compound, Si, Sb, and SiO2 is used as the negative electrode active material. The theoretical capacity of amorphous PAHs greatly exceeds that of a graphite based carbon material. Thus, the use of amorphous PAHs enables the negative electrode active material to have a higher capacity than in the case of using the graphite-based carbon material. Further, addition of at least one of the carrier ion storage metal, the Sn compound, the carrier ion storage alloy, the metal compound, Si, Sb, and SiO2 to the amorphous PAHs enables the negative electrode active material to have a higher capacity than the case of only using the amorphous PAHs.

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 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 negative electrode active material with high capacity and excellent cycle performance and rate performance is provided. In addition, a secondary battery including the negative electrode active material, and an electronic device including the secondary battery are provided. Nanosilicon is mixed with a solid electrolyte containing lithium, titanium, phosphorus, and oxygen, and graphene oxide is further added thereto. Then, graphene oxide contained in the mixture is reduced with ethanol in which ascorbic acid and lithium hydroxide hydrate are dissolved, so that the negative electrode active material is manufactured.

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 sensor element with excellent characteristics is provided. An electronic device including a power storage system with excellent characteristics is provided. A vehicle including a power storage system with excellent characteristics is provided. A novel semiconductor device is provided. The power storage system includes a storage battery, a neural network, and a sensor element; the neural network includes an input layer, an output layer, and one or a plurality of middle layers provided between the input layer and the output layer; a value corresponding to a first signal output from the sensor element is supplied to the input layer; the first signal is an analog signal; the sensor element includes a region in contact with a surface of the storage battery; and the sensor element has a function of measuring one or both of strain and temperature.

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 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.