Free standing film for dry electrode, manufacturing method thereof, dry electrode comprising the same, and secondary battery
A free-standing film for a dry electrode, the free-standing film comprising an active material, a binder including a fibrous polymer, and a support. The support is a surface-oxidized vapor grown carbon fiber (Ox-VGCF). A manufacturing method of the free-standing film, a dry electrode including the same, and a secondary battery are also provided.
1 . A free-standing film for a dry electrode,
the free-standing film comprising an active material, a binder including a fibrous polymer, and a support,
wherein the support comprises a surface-oxidized vapor grown carbon fiber (Ox-VGCF) comprising a surface oxygen functional group in an amount of 5 to 15 wt % based on a total weight of the surface-oxidized vapor grown carbon fiber (Ox-VGCF).
2 . The free-standing film according to claim 1 , wherein:
the fibrous polymer is fiberized to bind the active material and the support.
3 . The free-standing film according to claim 1 , wherein:
the support comprises the surface-oxidized vapor grown carbon fiber (Ox-VGCF) having an average diameter of 50 nm to 500 nm, and an average length of 1 μm to 30 μm.
4 . The free-standing film according to claim 1 , wherein:
the support comprises the surface-oxidized vapor grown carbon fiber (Ox-VGCF) having a specific surface area of 10 m 2 /g to 150 m 2 /g.
5 . The free-standing film according to claim 1 , wherein:
the support comprises the surface-oxidized vapor grown carbon fiber (Ox-VGCF) having a graphitization degree of 0.1 to 2.0.
6 . The free-standing film according to claim 1 , wherein:
an amount of the support is in a range of 0.1 wt % to 10 wt % based on a total weight of the free-standing film.
7 . The free-standing film according to claim 1 , wherein:
the fibrous polymer is polytetrafluoroethylene (PTFE).
8 . A method for manufacturing the free-standing film as set forth in claim 1 , the method comprising:
(a) mixing the binder including the fibrous polymer and the support to obtain a first mixture;
(b) mixing the mixture and the active material together to obtain a second mixture and high-shear mixing the second mixture to obtain a fiberization composition; and
(c) forming the fiberization composition into a film form,
wherein the support is the surface-oxidized vapor grown carbon fiber.
9 . The method for manufacturing the free-standing film according to claim 8 , wherein:
the fibrous polymer is polytetrafluoroethylene (PTFE).
10 . The method for manufacturing the free-standing film according to claim 8 , wherein:
the mixing (a) comprises mixing the binder including the fibrous polymer and the support at 19° C. or less, or charging the binder including the fibrous polymer and the support mixture together into a grinder after the mixing.
11 . The method for manufacturing the free-standing film according to claim 10 , wherein:
the grinder is an air jet mill.
12 . The method for manufacturing the free-standing film according to claim 8 , wherein:
the mixture has a structure in which primary particles of the fibrous polymer are uniformly dispersed and supported on a surface of the support.
13 . The method for manufacturing the free-standing film according to claim 8 , wherein:
the high-shear mixing (b) is performed in a range of 10 rpm to 500 rpm for 1 minute to 30 minutes.
14 . The method for manufacturing the free-standing film according to claim 8 , wherein:
the forming (c) is performed by a hot rolling method by a calender.
15 . A dry electrode comprising:
a current collector, and the free-standing film of claim 1 , which is formed on the current collector,
wherein the current collector has a structure in which a primer layer is coated on a metal foil.
16 . A secondary battery comprising the dry electrode of claim 15 ,
wherein an electrode assembly including the dry electrode, a counter electrode, and a separator is incorporated into a battery case together with a lithium-containing non-aqueous electrolyte.