A secondary battery comprising: an electrode assembly comprising a plurality of radical units in which a first electrode and a second electrode are alternately laminated with a separator therebetween and a separation film surrounding the plurality of radical units to be repeatedly laminated, characterized in that the electrode assembly comprises a protection unit laminated on an outermost separation film disposed on the uppermost end or lowermost end of the separation film , the protection unit has a structure, wherein a second protection electrode , a separator , a first protection electrode are successively laminated from the outermost separation film disposed on the uppermost end or lowermost end of the electrode assembly , the second protection electrode has a cross-sectional coating structure comprising a second collector and a second electrode active material portion coated with a second electrode active material on an inner surface of the second collector, wherein the inner surface is a surface facing a center of the electrode assembly and the second electrode active material is applied to only one surface of the second protection electrode , and the first protection electrode has a cross-sectional coating structure comprising a first collector and a first electrode active material portion coated with a first electrode active material on an inner surface of the first collector, wherein the inner surface of the first collector is a surface facing the center of the electrode assembly and the first electrode active material is applied to only one surface of the first protection electrode ,the second collector has non-coating portion which is not coated with the second electrode active material, is formed on an outer surface of the second collector , and the second collector provided in the second protection electrode has a thickness greater than that of the second collector provided in the second electrode of the radical unit. an electrode assembly comprising a plurality of radical units in which a first electrode and a second electrode are alternately laminated with a separator therebetween and a separation film surrounding the plurality of radical units to be repeatedly laminated, characterized in that the electrode assembly comprises a protection unit laminated on an outermost separation film disposed on the uppermost end or lowermost end of the separation film , the protection unit has a structure, wherein a second protection electrode , a separator , a first protection electrode are successively laminated from the outermost separation film disposed on the uppermost end or lowermost end of the electrode assembly , the second protection electrode has a cross-sectional coating structure comprising a second collector and a second electrode active material portion coated with a second electrode active material on an inner surface of the second collector, wherein the inner surface is a surface facing a center of the electrode assembly and the second electrode active material is applied to only one surface of the second protection electrode , and the first protection electrode has a cross-sectional coating structure comprising a first collector and a first electrode active material portion coated with a first electrode active material on an inner surface of the first collector, wherein the inner surface of the first collector is a surface facing the center of the electrode assembly and the first electrode active material is applied to only one surface of the first protection electrode ,the second collector has non-coating portion which is not coated with the second electrode active material, is formed on an outer surface of the second collector , and the second collector provided in the second protection electrode has a thickness greater than that of the second collector provided in the second electrode of the radical unit. <EOS>