A slurry including at least a carbon black and a dispersion medium, wherein a concentration of the carbon black in the slurry is 5% by mass or more and 25% by mass or less, and wherein in a volume-based frequency distribution of particle size of the carbon black measured by a laser diffraction/scattering method, provided that a volume concentration of carbon black with a particle size of 0.6 μm or more is x (%), a volume concentration of carbon black with a particle size of 0.3 μm or more and less than 0.6 μm is y (%), and a volume concentration of carbon black having a particle size of less than 0.3 μm is 100−(x+y) (%), the slurry satisfies 10≤x≤70, 30≤y≤90, and 0≤100−(x+y)≤30.