Abstract: A lithium ion battery having excellent discharge characteristics even at a temperature below freezing is provided. The lithium ion battery includes a positive electrode containing a positive electrode active material, an electrolyte solution, and a negative electrode containing a negative electrode active material that is a carbon material; the carbon material has peaks at 2? of greater than or equal to 20° and less than or equal to 24°, 2? of greater than or equal to 42° and less than or equal to 46.5°, and 2? of greater than or equal to 78° and less than or equal to 82° in X-ray diffraction (XRD) analysis; and a value of the discharge capacity obtained by subjecting the lithium ion battery to constant current and constant voltage charging (0.1 C, 4.5 V, and a termination current of 0.01 C) at 25° C. and then discharging at ?40° C. is higher than or equal to 40% of a value of the discharge capacity in discharging at 25° C.

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 novel secondary battery that is highly convenient, useful, or reliable can be provided. The secondary battery includes a positive electrode active material layer, a negative electrode active material layer, and a separator. The separator is interposed between the positive electrode active material layer and the negative electrode active material layer. The negative electrode active material layer includes silicon particles and a binder. The weight ratio of the binder to the silicon particles is greater than or equal to 0.05 and less than or equal to 10. The binder has a carboxy group. The bulk specific gravity of the silicon particles is greater than or equal to 0.02 g/cm3 and less than or equal to 0.5 g/cm3.

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: 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: 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.