Abstract: A power storage device is reduced in weight. A metal sheet serving as a negative electrode current collector is separated and another negative electrode current collector is formed. For example, through the step of forming silicon serving as a negative electrode active material layer over a titanium sheet and then performing heating, the titanium sheet can be separated. Then, another negative electrode current collector with a thickness of more than or equal to 10 nm and less than or equal to 1 ?m is formed. Thus, light weight of the power storage device can be achieved.

Abstract: A power storage device with high capacity, a power storage device with high energy density, a highly reliable power storage device, and a long-life power storage device are provided. The power storage device includes a positive electrode, a separator, a negative electrode, and an electrolytic solution. The electrolytic solution contains an alkali metal salt and an ionic liquid. The separator is located between the positive electrode and the negative electrode. At least part of the positive electrode overlaps with the negative electrode. At least part of an end portion of the negative electrode is located inside a region between end portions of the positive electrode.

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 carbon-based negative electrode material which can be used with an electrolyte containing PC as a main ingredient, a carbon-based negative electrode material having a graphene layer structure is crystalline and has pores. That is, the crystal structure of the carbon-based negative electrode material is distorted more significantly than that of graphite. Accordingly, the carbon-based negative electrode material has a larger interlayer distance between graphenes than graphite. It has been shown that such a negative electrode material can be used for a secondary battery which contains an electrolyte containing PC as a main ingredient.

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 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.

Abstract: To improve the adhesion between a current collector and an electrode active material so as to improve long-term reliability. An electrode is formed in the following manner: an electrode active material (a negative electrode active material or a positive electrode active material) is formed over a base, a conductive film is formed over the electrode active material by a sputtering method, the base and the electrode active material are separated at the interface therebetween, and the electrode active material is made in contact with a current collector. The conductive film has a surface with projections and depressions because the conductive film is formed on the electrode active material containing particles. Accordingly, moderate adhesion can be provided between the conductive film and the current collector, with which stress at the interface between the conductive film and the current collector can be reduced while conductivity is maintained.

Abstract: To achieve a power storage unit that can be repeatedly bent without a large decrease in charge and discharge capacity. In the flexible power storage unit, the content of a binder in an active material layer containing an active material is greater than or equal to 1 wt % and less than or equal to 10 wt %, preferably greater than or equal to 2 wt % and less than or equal to 8 wt %, and more preferably greater than or equal to 3 wt % and less than or equal to 5 wt %.

Abstract: To provide a carbon-based negative electrode material which can be used with an electrolyte containing PC as a main ingredient, a carbon-based negative electrode material having a graphene layer structure is crystalline and has pores. That is, the crystal structure of the carbon-based negative electrode material is distorted more significantly than that of graphite. Accordingly, the carbon-based negative electrode material has a larger interlayer distance between graphenes than graphite. It has been shown that such a negative electrode material can be used for a secondary battery which contains an electrolyte containing PC as a main ingredient.

Abstract: A power storage device with reduced initial irreversible capacity is provided. The power storage device includes a positive electrode, a negative electrode, and an electrolyte solution. The negative electrode includes a negative electrode active material and a water-soluble polymer. The electrolyte solution includes an ionic liquid. The ionic liquid includes a cation and a monovalent amide anion.

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.

Abstract: A power storage device which has high charge/discharge capacity and less deterioration in battery characteristics due to charge/discharge and can perform charge/discharge at high speed is provided. A power storage device includes a negative electrode. The negative electrode includes a current collector and an active material layer provided over the current collector. The active material layer includes a plurality of protrusions protruding from the current collector and a graphene provided over the plurality of protrusions. Axes of the plurality of protrusions are oriented in the same direction. A common portion may be provided between the current collector and the plurality of protrusions.

Abstract: An object is to provide an electrochemical device in which lithium deposition and reduction in battery capacity can be inhibited even when the concentration of a lithium salt in an electrolytic solution is lower than 1.0 M. Lithium deposition can be inhibited and lithium whiskers can be dissolved by applying an inversion pulse current for a short time more than once in a charging period of a secondary battery which deteriorates. By applying the inversion pulse current more than once, deterioration of a lithium-ion secondary battery due to repeated charging can be suppressed even when it is a secondary battery in which the concentration of a lithium salt in an electrolytic solution is lower than 1.0 M and therefore lithium is easily deposited.

Abstract: A power storage device which has high charge/discharge capacity and less deterioration in battery characteristics due to charge/discharge and can perform charge/discharge at high speed is provided. A power storage device includes a negative electrode. The negative electrode includes a current collector and an active material layer provided over the current collector. The active material layer includes a plurality of protrusions protruding from the current collector and a graphene provided over the plurality of protrusions. Axes of the plurality of protrusions are oriented in the same direction. A common portion may be provided between the current collector and the plurality of protrusions.

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: An electrode for a power storage device with good cycle characteristics and high charge/discharge capacity is provided. In addition, a power storage device including the electrode is provided. The electrode for the power storage device includes a conductive layer and an active material layer provided over the conductive layer, the active material layer includes graphene and an active material including a plurality of whiskers, and the graphene is provided to be attached to a surface portion of the active material including a plurality of whiskers and to have holes in part of the active material layer. Further, in the electrode for the power storage device, the graphene is provided to be attached to a surface portion of the active material including a plurality of whiskers and to cover the active material including a plurality of whiskers. Further, the power storage device including the electrode is manufactured.

Abstract: A power storage device including a negative electrode having high cycle performance in which little deterioration due to charge and discharge occurs is manufactured. A power storage device including a positive electrode, a negative electrode, and an electrolyte provided between the positive electrode and the negative electrode is manufactured, in which the negative electrode includes a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer includes an uneven silicon layer formed over the negative electrode current collector, a silicon oxide layer or a mixed layer which includes silicon oxide and a silicate compound and is in contact with the silicon layer, and graphene in contact with the silicon oxide layer or the mixed layer including the silicon oxide and the silicate compound.

Abstract: To provide a lithium-ion secondary battery which has high charge and discharge capacity, is capable of being charged and discharged at high rate and has good cycle characteristics. A negative electrode includes a current collector and a negative electrode active material layer. The current collector includes a plurality of protrusion portions extending in the direction substantially perpendicular to the current collector and a base portion connected to the plurality of protrusion portions. The protrusion portions and the base portion are formed using the same material containing titanium. At least side surfaces of the protrusion portions are covered with the negative electrode active material layer. In the negative electrode active material layer, silicon layers and silicon oxide layers are alternately stacked between a plane where the protrusion portions are in contact with the negative electrode active material layer and a surface of the negative electrode active material layer.

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: An electrode for a power storage device with good cycle characteristics and high charge/discharge capacity is provided. In addition, a power storage device including the electrode is provided. The electrode for the power storage device includes a conductive layer and an active material layer provided over the conductive layer, the active material layer includes graphene and an active material including a plurality of whiskers, and the graphene is provided to be attached to a surface portion of the active material including a plurality of whiskers and to have holes in part of the active material layer. Further, in the electrode for the power storage device, the graphene is provided to be attached to a surface portion of the active material including a plurality of whiskers and to cover the active material including a plurality of whiskers. Further, the power storage device including the electrode is manufactured.