Provided is a binder for secondary battery electrodes wherein the content of a gel comprising a polymer particle obtained by copolymerizing three or more types of monomers is 50 to 100% by weight and a swelling index of the binder to an electrolyte is 1.1 to 5.0. The binder fundamentally improves electrode stability due to the gel content defined above and increases ionic conductivity due to the swelling index, thus providing secondary batteries with superior cycle properties.