Abstract: To provide a battery having excellent charge-discharge characteristics even in a low-temperature environment. The battery includes a positive electrode, a negative electrode, an electrolyte solution, and a separator. The electrolyte solution and the separator are included between the positive electrode and the negative electrode; the negative electrode includes a carbon material; and the electrolyte solution includes a lithium salt, a potassium salt, a fluorinated cyclic carbonate, a fluorinated linear carbonate, and at least one kind of anion. The carbon material includes graphite; the lithium salt includes LiPF6; the potassium salt includes KFSI; the fluorinated cyclic carbonate includes fluoroethylene carbonate; and the fluorinated linear carbonate includes methyl trifluoropropionate.

Abstract: One embodiment of the present invention is to provide a high-capacity lithium ion secondary battery and a production method thereof. To perform surface modification, a spherical resin is subjected to first heat treatment at a temperature higher than or equal to 500° C. in an inert atmosphere. By the heating, the contraction of a particle, the void formation due to a gas release from an inside of the particle, the crack on a particle surface, and the like are caused so as to form a support for sulfur that is to be mixed later. Obtained spherical particles and sulfur powder are mixed and then stored in a container. The mixture in the container is subjected to second heat treatment at a temperature higher than or equal to 120° C. without being exposed to outside air.