Abstract: To improve the reliability of a power storage device. A granular active material including carbon is used, and a net-like structure is formed on part of a surface of the granular active material. In the net-like structure, a carbon atom included in the granular active material is bonded to a silicon atom or a metal atom through an oxygen atom. Formation of the net-like structure suppresses reductive decomposition of an electrolyte solution, leading to a reduction in irreversible capacity. A power storage device using the above active material has high cycle performance and high reliability.

Abstract: A composite oxide with high diffusion rate of lithium is provided. Alternatively, a lithium-containing complex phosphate with high diffusion rate of lithium is provided. Alternatively, a positive electrode active material with high diffusion rate of lithium is provided. Alternatively, a lithium ion battery with high output is provided. Alternatively, a lithium ion battery that can be manufactured at low cost is provided. A positive electrode active material is formed through a first step of mixing a lithium compound, a phosphorus compound, and water, a second step of adjusting pH by adding a first aqueous solution to a first mixed solution formed in the first step, a third step of mixing an iron compound with a second mixed solution formed in the second step, a fourth step of performing heat treatment under a pressure more than or equal to 0.1 MPa and less than or equal to 2 MPa at a highest temperature more than 100° C. and less than or equal to 119° C.

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: In initial charge and discharge, decomposition products or a gas is generated, degrading a battery. At least one of solvents (e.g., ethylene carbonate) used for an electrolytic solution is brought into contact with a positive electrode and a negative electrode and then charge is performed to some degree, and after that, a different solvent or electrolytic solution (e.g., ethyl methyl carbonate or vinylene carbonate) was added to adjust the electrolytic solution and then charge is performed. Through this process, stable coating films are formed in initial charge and discharge, which stably inhibits a side reaction between the electrolytic solution and an active material.

Abstract: To form graphene to a practically even thickness on an object having an uneven surface or a complex surface, in particular, an object having a surface with a three-dimensional structure due to complex unevenness, or an object having a curved surface. The object and an electrode are immersed in a graphene oxide solution, and voltage is applied between the object and the electrode. At this time, the object serves as an anode. Graphene oxide is attracted to the anode because of being negatively charged, and deposited on the surface of the object to have a practically even thickness. A portion where graphene oxide is deposited is unlikely coated with another graphene oxide. Thus, deposited graphene oxide is reduced to graphene, whereby graphene can be formed to have a practically even thickness on an object having surface with complex unevenness.

Abstract: An object is to provide graphene which has high conductivity and is permeable to ions of lithium or the like. Another object is to provide, with use of the graphene, a power storage device with excellent charging and discharging characteristics. Graphene having a hole inside a ring-like structure formed by carbon and nitrogen has conductivity and is permeable to ions of lithium or the like. The nitrogen concentration in graphene is preferably higher than or equal to 0.4 at. % and lower than or equal to 40 at. %. With use of such graphene, ions of lithium or the like can be preferably made to pass; thus, a power storage device with excellent charging and discharging characteristics can be provided.

Abstract: When a hole in a separator is clogged, the cycle characteristics of a battery might be lowered and the internal resistance of a battery might be increased to reduce the output. Thus, a means for suppression of or recovery from degradation due to a clogged separator in a battery such as a lithium-ion secondary battery is provided. When reverse pulse current is supplied multiple times during charge, a separator is prevented from being clogged and a voltage increase (increase in internal resistance) during charge is suppressed, so that charge can be normally performed repeatedly.

Abstract: A lithium-ion secondary battery including a lithium-containing complex phosphate as a positive electrode active material is provided. Furthermore, a positive electrode active material with high diffusion rate of lithium ions is provided to provide a lithium-ion secondary battery with high output. A positive electrode active material of a lithium-ion secondary battery includes a first plate-like component and a second plate-like component, a third prismatic component between the first component and the second component, and a space between the first component and the second component.

Abstract: A material that can be used in a wide temperature range is provided. A graphene compound includes graphene or graphene oxide and a substituted or unsubstituted chain group, the chain group includes two or more ether bonds, and the chain group is bonded to the above graphene or graphene oxide through a Si atom. Alternatively, a method for forming a graphene compound includes a first step and a second step after the first step. In the first step, graphene oxide and a base are stirred under a nitrogen stream. In the second step, the mixture is cooled to room temperature, a silylating agent that has a group having two or more ether bonds is introduced into the mixture, and the obtained mixture is stirred. The base is butylamine, pentylamine, hexylamine, diethylamine, dipropylamine, dibutylamine, triethylamine, tripropylamine, or pyridine.

Abstract: To improve the reliability of a power storage device. A granular active material including carbon is used, and a net-like structure is formed on part of a surface of the granular active material. In the net-like structure, a carbon atom included in the granular active material is bonded to a silicon atom or a metal atom through an oxygen atom. Formation of the net-like structure suppresses reductive decomposition of an electrolyte solution, leading to a reduction in irreversible capacity. A power storage device using the above active material has high cycle performance and high reliability.

Abstract: A power storage device with a high capacity is provided. A power storage device with a high energy density is provided. A highly reliable power storage device is provided. A power storage device with a long lifetime is provided. A method for manufacturing an electrode is characterized by including the steps of: mixing an active material, a binder, and a conductive additive to form a slurry; applying the slurry onto a current collector; drying the applied slurry to form an active material layer; and performing heat treatment in an atmosphere containing oxygen to form a film in contact with the current collector. The film is formed on a surface of the current collector where the active material layer is not provided and includes at least one component of the current collector and oxygen.

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: To provide a manufacturing method of graphene oxide that allows mass production through a relatively simple process, at low costs, and with safety and efficiency. A hydrogen peroxide solution, sulfuric acid, and flake graphite are put in a reaction container, and the mixture is stirred to obtain expansion graphite. The synthesized expansion graphite is washed not with pure water but with a saturated aqueous solution of magnesium sulfate (MgSO4) or an organic solvent, whereby a large amount of sulfuric acid is contained between graphite layers. The expansion graphite is subjected to heat treatment or microwave irradiation to form expanded graphite, and a graphite layer is peeled by ultrasonic treatment and then oxidized to form a graphene compound.

Abstract: To provide a power storage device whose charge and discharge characteristics are unlikely to be degraded by heat treatment. To provide a power storage device that is highly safe against heat treatment. The power storage device includes a positive electrode, a negative electrode, a separator, an electrolytic solution, and an exterior body. The separator is located between the positive electrode and the negative electrode. The separator contains polyphenylene sulfide or solvent-spun regenerated cellulosic fiber. The electrolytic solution contains a solute and two or more kinds of solvents. The solute contains LiBETA. One of the solvents is propylene carbonate.

Abstract: A novel element is provided. A novel film formation method is provided. A novel element manufacturing method is provided. Furthermore, a film including graphene is formed at low cost and high yield. The element includes a first electrode and a second electrode located apart from the first electrode. The first electrode and the second electrode include graphene. The film including graphene is formed through a first step of forming a film including graphene oxide over a substrate, a second step of immersing the film including graphene oxide in an acidic solution, and a third step of reducing graphene oxide included in the film including graphene oxide. Furthermore, before graphene oxide included in the film including graphene oxide is reduced, the film including graphene oxide is selectively removed by a photolithography technique.

Abstract: A lithium-ion secondary battery with a high capacity retention rate is provided. In addition, a fabricating method of a lithium-ion secondary battery with a high capacity retention rate is provided. The lithium-ion secondary battery includes a positive electrode, a negative electrode, and an electrolyte solution. The negative electrode includes a negative electrode active material layer. The electrolyte solution includes at least one of lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) and lithium bis(fluorosulfonyl)amide (LiFSA). The electrolyte solution includes vinylene carbonate (VC). A coating film including lithium oxide is on a surface of the negative electrode active material layer.

Abstract: An object is to provide graphene which has high conductivity and is permeable to ions of lithium or the like. Another object is to provide, with use of the graphene, a power storage device with excellent charging and discharging characteristics. Graphene having a hole inside a ring-like structure formed by carbon and nitrogen has conductivity and is permeable to ions of lithium or the like. The nitrogen concentration in graphene is preferably higher than or equal to 0.4 at. % and lower than or equal to 40 at. %. With use of such graphene, ions of lithium or the like can be preferably made to pass; thus, a power storage device with excellent charging and discharging characteristics can be provided.

Abstract: To provide a power storage device whose charging and discharging characteristics are unlikely to be degraded by heat treatment. To provide a power storage device that is highly safe against heat treatment. The power storage device includes a positive electrode, a negative electrode, a separator, an electrolytic solution, and an exterior body. The separator is located between the positive electrode and the negative electrode. The separator contains polyphenylene sulfide. The electrolytic solution contains a solute and two or more kinds of solvents. The solute contains LiFSA at a concentration of higher than or equal to 0.1 wt % and lower than or equal to 50 wt % in the electrolytic solution. One of the solvents is propylene carbonate.

Abstract: To provide a power storage device having excellent charge/discharge cycle characteristics and a high charge/discharge capacity. The following electrode is used as an electrode of a power storage device: an electrode including a current collector and an active material layer provided over the current collector. The active material layer includes a plurality of whisker-like active material bodies. Each of the plurality of whisker-like active material bodies includes at least a core and an outer shell provided to cover the core. The outer shell is amorphous, and a portion between the current collector and the core of the active material bodies is amorphous. Note that a metal layer may be provided instead of the current collector, the active material bodies do not necessarily have to include the core, and a mixed layer may be provided between the current collector and the active material layer.

Abstract: A power storage device a positive electrode including a positive electrode active material layer and a negative electrode including a negative electrode active material layer. The positive electrode active material layer includes a plurality of particles of x[Li2MnO3]-(1?x)[LiCo1/3Mn1/3Ni1/3O2] (obtained by assigning 0.5 to x, for example) which is a positive electrode active material, and multilayer graphene with which the plurality of particles of the positive electrode active material are at least partly connected to each other. In the multilayer graphene, a plurality of graphenes are stacked in a layered manner. The graphene contains a six-membered ring composed of carbon atoms, a poly-membered ring which is a seven or more-membered ring composed of carbon atoms, and an oxygen atom bonded to one or more of the carbon atoms in the six-membered ring and the poly-membered ring, which is a seven or more-membered ring.