Abstract: A power storage system with excellent characteristics is provided. A power storage system with a high degree of safety is provided. A power storage system with less deterioration is provided. A storage battery with excellent characteristics is provided. The power storage system includes a neural network and a storage battery. The neural network includes an input layer, an output layer, and one or more hidden layers between the input layer and the output layer. The predetermined hidden layer is connected to the previous hidden layer or the previous input layer by a predetermined weight coefficient, and connected to the next hidden layer or the next output layer by a predetermined weight coefficient. In the storage battery, voltage and time at which the voltage is obtained are measured as one of sets of data. The sets of data measured at different times are input to the input layer and the operational condition of the storage battery is changed in accordance with a signal output from the output layer.

Abstract: A semiconductor device in which a circuit and a battery are efficiently stored is provided. In the semiconductor device, a first transistor, a second transistor, and a secondary battery are provided over one substrate. A channel region of the second transistor includes an oxide semiconductor. The secondary battery includes a solid electrolyte, and can be fabricated by a semiconductor manufacturing process. The substrate may be a semiconductor substrate or a flexible substrate. The secondary battery has a function of being wirelessly charged.

Abstract: A secondary battery has a high capacity and little deterioration can be provided. Alternatively, a novel power storage device is provided. The secondary battery includes a positive electrode and a negative electrode. The negative electrode includes a first active material, a second active material, and a graphene compound. At least part of a surface of the first active material includes a region covered with the second active material. A surface of the second active material and at least part of the surface of the first active material each include a region covered with the graphene compound. The first active material includes graphite. The second active material includes silicon. The capacity of the positive electrode is greater than or equal to 50% and less than 100% of the capacity of the negative electrode.

Abstract: A positive electrode active material that inhibits a decrease in discharge capacity in charge and discharge cycles and a battery using the positive electrode active material are provided. A high-safety battery is provided. The battery includes a positive electrode including a positive electrode current collector and a positive electrode active material layer. The positive electrode current collector is a carbon sheet. The positive electrode active material contains lithium cobalt oxide containing nickel and magnesium. The detected amount of nickel in a surface portion of the positive electrode active material is larger than that in an inner portion of the positive electrode active material. The detected amount of magnesium in the surface portion of the positive electrode active material is larger than the detected amount of magnesium in the inner portion of the positive electrode active material.

Abstract: Novel graphene is provided. A novel graphene compound is provided. An electrode having a high output is provided. A novel electrode is provided. A secondary battery with little deterioration is provided. A secondary battery with a high degree of safety is provided. Graphene has a vacancy formed with a many-membered ring that is a nine- or more-membered ring composed of carbon atoms. One or more of the carbon atoms included in the many-membered ring are terminated with fluorine.

Abstract: A negative electrode active material, a negative electrode active material layer, and a secondary battery including them, or a formation method thereof are provided. In one embodiment of the present invention, carbon particles and a silicon-based material are mixed and used as a negative electrode active material. A polymer including a polar substituent such as a carboxy group is used as a binder. Specifically, as the binder for the carbon particles and the silicon-based material, a polymer containing glutamic acid is used. As the silicon-based material, nanosilicon particles each having a particle diameter less than 1 ?m is used.

Abstract: A semiconductor device in which a circuit and a battery are efficiently stored is provided. In the semiconductor device, a first transistor, a second transistor, and a secondary battery are provided over one substrate. A channel region of the second transistor includes an oxide semiconductor. The secondary battery includes a solid electrolyte, and can be fabricated by a semiconductor manufacturing process. The substrate may be a semiconductor substrate or a flexible substrate. The secondary battery has a function of being wirelessly charged.

Abstract: A lithium-ion secondary battery having high capacity and excellent charge and discharge cycle performance is provided. A secondary battery having high capacity is provided. A secondary battery with excellent charge and discharge characteristics is provided. A secondary battery in which a reduction in capacity is suppressed even when a state being charged with a high voltage is held for a long time is provided. In the secondary battery, after constant current charging is performed in an environment at 60° C. with a current value of 0.5 C until a voltage reaches 4.5 V, a charging process of performing constant voltage charging until a current value reaches 0.2 C and a discharging process of performing constant current discharging with a current value of 0.

Abstract: A semiconductor device in which a circuit and a power storage element are efficiently placed is provided. The semiconductor device includes a first transistor, a second transistor, and an electric double-layer capacitor. The first transistor, the second transistor, and the electric double-layer capacitor are provided over one substrate. A band gap of a semiconductor constituting a channel region of the second transistor is wider than a band gap of a semiconductor constituting a channel region of the first transistor. The electric double-layer capacitor includes a solid electrolyte.

Abstract: An electrode with excellent characteristics is provided. An active material with excellent characteristics is provided. A novel silicon material is provided. An electrode includes a plurality of particles and a graphene compound. At least part of the surface of each of the plurality of particles is terminated by a functional group containing oxygen, the graphene compound contains the plurality of particles so as to cover the surrounding of the plurality of particles, and the graphene compound is graphene containing at least one of a carbon atom terminated by a hydrogen atom and a carbon atom terminated by a fluorine atom in a two-dimensional structure formed with a six-membered ring of carbon.

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 highly purified positive electrode active material is provided. Alternatively, a method for manufacturing a positive electrode active material whose crystal structure is not easily broken even when charge and discharge are repeated is provided. The method for manufacturing a positive electrode active material containing lithium and a transition metal includes a first step of preparing a lithium compound, a phosphorus compound, and water; a second step of forming a first mixture by mixing the lithium compound, the phosphorus compound, and the water; a third step of forming a second mixture by adding a first aqueous solution to the first mixture to adjust a pH; a fourth step of forming a third mixture by mixing an iron(II) compound with the second mixture; a fifth step of forming a fourth mixture by heating the third mixture; and a sixth step of obtaining a positive electrode active material by filtering, washing, and drying the fourth mixture.

Abstract: An electrode with little deterioration or a secondary battery with little deterioration is provided. An electrode includes a first region and a second region. The first region includes a particle containing silicon. The second region includes a particle containing silicon and a graphene compound. The second region is in contact with the first region to cover at least part thereof. Alternatively, an electrode includes a plurality of particles containing silicon and a graphene compound. Each of the plurality of particles containing silicon includes a functional group containing oxygen and carbon, a functional group containing oxygen, or a fluorine atom in at least part of the surface. The graphene compound includes at least one of carbon terminated with hydrogen and carbon terminated with fluorine in a plane of the graphene compound. The graphene compound is in contact with the plurality of particles containing silicon to closely cling thereto.

Abstract: A negative electrode with little deterioration is provided. A novel negative electrode is provided. A power storage device with little deterioration is provided. A novel power storage device is provided. The electrode contains silicon, graphite, and a graphene compound. A silicon particle with a particle diameter of less than or equal to 1 µm is attached to a graphite particle with a particle diameter 10 times or more that of the silicon particle. The graphene compound is in contact with the graphite particle so as to cover the silicon particle.

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 power storage device with high capacity or high energy density is provided. A highly reliable power storage device is provided. A long-life power storage device is provided. An electrode includes an active material, a first binder, and a second binder. The specific surface area of the active material is S [m2/g]. The weight of the active material, the weight of the first binder, and the weight of the second binder are a, b, and c, respectively. The solution of {(b+c)/(a+b+c)}×100÷S is 0.3 or more. The electrode includes a first film in contact with the active material. The first film preferably includes a region in contact with the active material. The first film preferably includes a region with a thickness of 2 nm or more and 20 nm or less. The first film contains a water-soluble polymer.

Abstract: According to one embodiment of the present invention, a secondary battery that can be used at a wide range of temperatures and is less likely to be influenced by an environmental temperature is provided. Furthermore, a secondary battery with high safety is provided. An electrolyte obtained by mixing an acyclic ester having high temperature characteristics with a fluorinated carbonic ester at 5 vol. % or higher, preferably 20 vol. % or higher, is used for the purpose of reducing interface resistance between an electrode and an electrolyte, whereby a secondary battery capable of operating at a wide range of temperatures, specifically, at temperatures higher than or equal to ?40° C. and lower than or equal to 150° C., preferably higher than or equal to ?40° C. and lower than or equal to 85° C. can be achieved.

Abstract: An object is to provide a nonaqueous solvent, a secondary battery, or a vehicle having a wide usable temperature range and high heat resistance. The nonaqueous solvent of the present invention contains an ionic liquid at greater than or equal to 50 vol % and less than or equal to 95 vol % and a fluorinated cyclic carbonate, and the ionic liquid contains an imidazolium cation. The nonaqueous solvent of the present invention has low viscosity at low temperatures and high heat resistance, thereby having a wide usable temperature range.

Abstract: An object is to suppress electrochemical decomposition of an electrolyte solution and the like at a negative electrode in a lithium ion battery or a lithium ion capacitor; thus, irreversible capacity is reduced, cycle performance is improved, or operating temperature range is extended. A negative electrode for a power storage device including a negative electrode current collector, a negative electrode active material layer which is over the negative electrode current collector and includes a plurality of particles of a negative electrode active material, and a film covering part of the negative electrode active material. The film has an insulating property and lithium ion conductivity.

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.