Binder for secondary battery providing excellent cycle property

A binder for secondary battery electrodes, comprising:

• a gel comprising a polymer particle obtained by copolymerizing three or more types of monomers, the binder having a gel content ranging from 97 to 99% by weight and a swelling index in the presence of an electrolyte ranging from 1. 3 to 1.9, wherein the electrolyte comprises ethylene carbonate, propylene carbonate and diethyl carbonate, wherein a mass ratio of diethyl carbonate to ethylene carbonate and propylene carbonate is 1:1 and
• wherein the three or more types of monomers are an ethylenically unsaturated carbonic acid ester monomer, at least one monomer selected from the group consisting of a vinyl monomer and a nitrile monomer, and an ethylenically unsaturated carbonic acid monomer,
• wherein the ethylenically unsaturated carbonic acid ester monomer and the at least one monomer selected from the group consisting of a vinyl monomer and a nitrile monomer are present in an amount of 80 to 99% by weight, based on the total weight of the binder, and the ethylenically unsaturated carbonic acid monomer is present in an amount of greater than 5% to 20% by weight, based on the total weight of the binder,
• wherein the cross-linking agent is present in an amount of 0.1 to less than 1% by weight, based on the total weight of the copolymer, and
• wherein the cross-linking agent is at least one monomer selected from the group consisting of difunctional monomers, trifunctional monomers, tetrafunctional monomers, pentafunctional monomers, and hexafunctional monomers.