Abstract: A novel ionic liquid is provided. A highly safe secondary battery with high charge and discharge capacity is provided. The ionic liquid includes a cation represented by General Formula (G1) and an anion represented by Structural Formula (200). In the formula, X1 to X3 each independently represent any one of fluorine, chlorine, bromine, and iodine. One of X1 to X3 may be hydrogen. In addition, n and m each independently represent 0 to 5. Furthermore, a secondary battery including the above-described ionic liquid is provided.

Abstract: A secondary battery with little deterioration is provided. A secondary battery with high safety is provided. A separator having excellent characteristics is provided. A separator achieving the secondary battery with high safety is provided. A novel separator is provided. In the separator, a polymer porous film and a layer including a ceramic-based material containing a metal oxide microparticle are stacked, the thickness of the layer including a ceramic-based material is greater than or equal to 1 ?m and less than or equal to 100 ?m, and the film thickness of the polymer porous film is greater than or equal to 4 ?m and less than or equal to 50 ?m.

Abstract: A lithium-ion secondary battery with high capacity and excellent charge and discharge cycle performance is provided. A secondary battery with 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 inhibited even when a state being charged with a high voltage is held for a long time is provided. A secondary battery includes a positive electrode, a negative electrode, and an electrolyte, and the amount of moisture in the electrolyte is less than 1000 ppm.

Abstract: A secondary battery stable in a high-potential state and/or a high-temperature state is provided. The secondary battery includes a positive electrode and a negative electrode, and one or both of the positive electrode and the negative electrode contain an active material and a composite compound with a crystal structure. The composite compound has a function of a binder. The composite compound can also be used as an electrolyte. The composite compound with a crystal structure has typically a molecular crystal. The composite compound with a crystal structure can be obtained by mixing a first compound and a second compound while heating is performed at higher than or equal to a temperature at which a mixture of the first compound and the second compound is melted.

Abstract: To provide a high-safety battery. The battery includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and an electrolyte solution. The positive electrode active material includes a first region and a second region. The first region contains cobalt, magnesium, fluorine, and oxygen. The second region contains cobalt and oxygen. The first region is closer to a surface of the positive electrode active material than the second region is. The negative electrode active material contains graphite. The electrolyte solution contains a mixed organic solvent. When the battery in a fully charged state undergoes a nail penetration test in which the nail diameter is 3 mm and the nail penetration speed is 5 mm/sec, the voltage of the battery decreases from a first voltage Vb to a second voltage Vc and then exceeds the second voltage Vc.

Abstract: One embodiment of the present invention further improves thermal safety of a lithium-ion secondary battery for stable power supply from the lithium-ion secondary battery. To improve thermal safety, fluorine is contained in a positive electrode active material or adsorbed on a surface portion of the positive electrode active material so that overheating or ignition of the lithium-ion secondary battery is inhibited. When fluorine is adsorbed on the surface of the positive electrode active material, the adsorbed fluorine can react with its vicinity electrolyte solution or the like, leading to inhibition of thermal decomposition or the like of the electrolyte solution.

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: A storage battery that is less likely to be affected by the ambient temperature is provided. A storage battery that can be charged and discharged at low temperatures is provided. In the storage battery, a secondary battery that can be charged and discharged at low temperatures is provided adjacent to a general secondary battery. The storage battery having such a structure can use, as an internal heat source in a low temperature environment, heat generated by charging and discharging of the secondary battery that can be charged and discharged at low temperatures. Specifically, the storage battery includes a first lithium-ion secondary battery and a second lithium-ion secondary battery adjacent to each other. The first lithium-ion secondary battery contains at least one of an ionic liquid, a molecular crystalline electrolyte, a semi-solid-state electrolyte, an all-solid-state electrolyte, and lithium titanate. The second lithium-ion secondary battery contains an organic electrolyte solution.