The present invention provides a binder composition which suppresses a swelling ratio in an electrolyte solution while having sufficient peel strength. The binder composition according to the present invention contains a copolymer including monomer units derived from vinylidene fluoride, a fluorine-containing alkyl vinyl compound, and a crosslinkable monomer; the content of the monomer unit derived from the fluorine-containing alkyl vinyl compound in the copolymer being not less than 2 mass % and less than 10 mass %; and the content of the monomer unit derived from the crosslinkable monomer being less than 5 mass %.