Abstract: A secondary battery in which graphite that is an active material can occlude and release lithium efficiently is provided. Further, a highly reliable secondary battery in which the amount of lithium inserted and extracted into/from graphite that is an active material is prevented from varying is provided. The secondary battery includes a negative electrode including a current collector and graphite provided over the current collector, and a positive electrode. The graphite includes a plurality of graphene layers. Surfaces of the plurality of graphene layers are provided substantially along the direction of an electric field generated between the positive electrode and the negative electrode.

Abstract: Provided is a secondary battery including an electrode including silicon or a silicon compound. The electrode includes, for example, a current collector formed using metal and a silicon film as an active material provided over the current collector. The hydrogen concentration in the silicon film of the electrode may be higher than or equal to 1.0×1018 cm?3 and lower than or equal to 1.0×1021 cm?3. Such a silicon film is formed over a current collector by a plasma CVD method or the like for example, and hydrogen is contained as little as possible in the silicon film, which is preferable. In order to contain hydrogen as little as possible in the silicon film, the silicon film may be formed over the current collector under a high temperature environment.

Abstract: An object is to improve characteristics of a power storage device and achieve a long lifetime. In the case where a lithium nitride is used for a negative electrode active material of a power storage device, a plurality of lithium nitride layers with different lithium concentrations are stacked. For example, in the case where a first lithium nitride layer and a second lithium nitride layer are stacked over a current collector, lithium is contained in the first lithium nitride layer at a lower concentration than lithium contained in the second lithium nitride layer. In this case, a concentration of a transition metal of the first lithium nitride layer is higher than a concentration of the transition metal of the second lithium nitride layer. Note that another alkali metal may be used instead of lithium.

Abstract: To prevent, in the case of irradiating a single crystal semiconductor layer with a laser beam, an impurity element from being taken into the single crystal semiconductor layer at the time of laser irradiation.

Abstract: To provide a lithium-ion secondary battery having higher discharge capacity and higher energy density and a manufacturing method thereof. The lithium-ion secondary battery includes a positive electrode, a negative electrode, and an electrolyte provided between the positive electrode and the negative electrode. The positive electrode includes a positive electrode current collector and a positive electrode active material layer provided over the positive electrode current collector. In the positive electrode active material layer, graphenes and lithium-containing composite oxides are alternately provided. The lithium-containing composite oxide is a flat single crystal particle in which the length in the b-axis direction is shorter than each of the lengths in the a-axis direction and the c-axis direction.

Abstract: A lithium ion secondary battery includes a positive electrode, a negative electrode, and an electrolyte provided between the positive electrode and the negative electrode. The positive electrode includes a positive electrode current collector and a positive electrode active material layer over the positive electrode current collector. The positive electrode active material layer includes a plurality of lithium-containing composite oxides each of which is expressed by LiMPO4 (M is one or more of Fe (II), Mn (II), Co (II), and Ni (II)) that is a general formula. The lithium-containing composite oxide is a flat single crystal particle in which the length in the b-axis direction is shorter than each of the lengths in the a-axis direction and the c-axis direction. The lithium-containing composite oxide is provided over the positive electrode current collector so that the b-axis of the single crystal particle intersects with the surface of the positive electrode current collector.

Abstract: A positive-electrode active material with improved electrical conductivity, and a power storage device using the material are provided. A positive-electrode active material with large capacity, and a power storage device using the material are provided. A core including lithium metal oxide is used as a core of a main material of the positive-electrode active material, and one to ten pieces of graphene is used as a covering layer for the core. A hole is provided for graphene, whereby transmission of a lithium ion is facilitated, resulting in improvement of use efficiency of current.

Abstract: An object is to increase the conductivity of an electrode including active material particles and the like, which is used for a battery. Two-dimensional carbon including 1 to 10 graphenes is used as a conduction auxiliary agent, instead of a conventionally used conduction auxiliary agent extending only one-dimensionally at most, such as graphite particles, acetylene black, or carbon fibers. A conduction auxiliary agent extending two-dimensionally has higher probability of being in contact with active material particles or other conduction auxiliary agents, so that the conductivity can be improved.

Abstract: A secondary battery to be provided includes an electrode including silicon or a silicon compound, and the electrode includes, for example, a current collector formed using metal and a silicon film as an active material provided over the current collector. The hydrogen concentration in the silicon film of the electrode may be higher than or equal to 1.0×1018 cm?3 and lower than or equal to 1.0×1021 cm?3. Such a silicon film is formed over a current collector by a plasma CVD method or the like for example, and hydrogen is contained as little as possible in the silicon film, which is preferable. In order to contain hydrogen as little as possible in the silicon film, the silicon film may be formed over the current collector under a high temperature environment.

Abstract: A power storage device with favorable battery characteristics and a manufacturing method thereof are provided. The power storage device includes at least a positive electrode and a negative electrode provided so as to face the positive electrode with an electrolyte provided therebetween. The positive electrode includes a collector and a film containing an active material over the collector. The film containing the active material contains LieFejPgOh satisfying relations 3.5?h/g?4.5, 0.6?g/f?1.1, and 0?e/f?1.3 and LiaFebPcOd satisfying relations 3.5?d/c?4.5, 0.6?c/b?1.8, and 0.7?a/b?2.8. The film containing the active material contains the LiaFebPcOd satisfying the relations 3.5?d/c?4.5, 0.6?c/b?1.8, and 0.7?a/b?2.8 in a region which is in contact with the electrolyte.

Abstract: An object is to provide a secondary battery having excellent charge-discharge cycle characteristics. A secondary battery including an electrode containing silicon or a silicon compound is provided, in which the electrode is provided with a layer containing silicon or a silicon compound over a layer of a metal material; a mixed layer of the metal material and the silicon is provided between the metal material layer and the layer containing silicon or a silicon compound; the metal material has higher oxygen affinity than that of ions which give and receive electric charges in the secondary battery; and an oxide of the metal material does not have an insulating property. The ions which give and receive electric charges are alkali metal ions or alkaline earth metal ions.

Abstract: The present invention relates to a power storage system including a negative electrode which has a crystalline silicon film provided as a negative electrode active material on the surface of a current collector and contains a conductive oxide in a surface layer section of the crystalline silicon film. Alternatively, the present invention relates to a method for manufacturing a power storage system, which includes the step of forming an amorphous silicon film on a current collector, adding a catalytic element for promoting crystallization of the amorphous silicon, onto a surface of the amorphous silicon film, heating the amorphous silicon film with the catalytic element added to crystallize the amorphous silicon film and thereby form a crystalline silicon film, and using the crystalline silicon film as a negative electrode active material layer.

Abstract: An object is to improve characteristics of a power storage device. The present invention relates to an electricity storage device comprising a current collector and a negative electrode-active material layer formed over the current collector. The negative electrode-active material layer includes a negative electrode comprising a first negative electrode layer in contact with the current collector; a second negative electrode layer in contact with the first negative electrode layer, having a smaller capacitance than the first negative electrode layer and containing one material selected from a nitride of lithium and a transition metal represented by LiaMbNz (M is a transition metal, 0.1?a?2.8, 0.2?b?1 and 0.6?z?1.4), a silicon material, and lithium titanate; a positive electrode that is paired with the negative electrode; and a solid electrolyte interposed between the positive electrode and the negative electrode.

Abstract: An object is to improve characteristics of a power storage device and achieve a long lifetime. In the case where a lithium nitride is used for a negative electrode active material of a power storage device, a plurality of lithium nitride layers with different lithium concentrations are stacked. For example, in the case where a first lithium nitride layer and a second lithium nitride layer are stacked over a current collector, lithium is contained in the first lithium nitride layer at a lower concentration than lithium contained in the second lithium nitride layer. In this case, a concentration of a transition metal of the first lithium nitride layer is higher than a concentration of the transition metal of the second lithium nitride layer. Note that another alkali metal may be used instead of lithium.

Abstract: To prevent, in the case of irradiating a single crystal semiconductor layer with a laser beam, an impurity element from being taken into the single crystal semiconductor layer at the time of laser irradiation.