Pouch film for secondary battery and manufacturing method thereof
A pouch film for a secondary battery and a method for manufacturing the same. In some embodiments, the pouch film includes a stretchable auxiliary layer that is a multi-layered structure comprising a plurality of layers, wherein layers in the plurality of layers have different elongation rates. The stress at the interface of each layer is relieved and the moldability of a pouch is improved. The risk of breakage of a pouch is significantly reduced and defect rates are reduced in a pouch manufacturing process, thereby reducing manufacturing costs.
1 . A pouch film for a secondary battery for manufacturing a pouch-type battery case, the pouch film comprising:
a sealant layer formed as the innermost layer;
a surface protection layer formed as the outermost layer;
a gas barrier layer laminated between the sealant layer and the surface protection layer; and
a stretchable auxiliary layer laminated between the gas barrier layer and the surface protection layer,
wherein the stretchable auxiliary layer is a multi-layered structure comprising a plurality of layers, and
wherein the plurality of layers includes:
a first modification PET layer having an elongation rate of 45% to 55%,
a second modification PET layer bonded to the first modification PET layer, the second modification PET layer having an elongation rate of 65-75%, and
a third modification PET layer bonded to the second modification PET layer, the third modification PET layer having an elongation rate of 85% to 95%.
2 . The pouch film of claim 1 , wherein the stretchable auxiliary layer has a greater elongation rate toward the surface protection layer.
3 . The pouch film of claim 1 , wherein, in the stretchable auxiliary layer, each layer in the plurality of layers has an elongation rate of 20% to 130%.
4 . A method for manufacturing a pouch film for a secondary battery, the method comprising:
laminating a gas barrier layer on a sealant layer;
laminating a stretchable auxiliary layer on the gas barrier layer, wherein the stretchable auxiliary layer is a multi-layered structure comprising a plurality of layers; and
laminating a protection layer on the stretchable auxiliary layer, such that the sealant layer, gas barrier layer, stretchable auxiliary layer, and protection layer are sequentially arranged,
wherein the plurality of layers includes:
a first modification PET layer having an elongation rate of 45% to 55%,
a second modification PET layer bonded to the first modification PET layer, the second modification PET layer having an elongation rate of 65-75%, and
a third modification PET layer bonded to the second modification PET layer, the third modification PET layer having an elongation rate of 85% to 95%.
5 . The method of claim 4 , wherein the stretchable auxiliary layer has a greater elongation rate toward the surface protection layer.
6 . The method of claim 4 , wherein, in the stretchable auxiliary layer, each layer in the plurality of layers has an elongation rate of 20% to 130%.