Binder for Secondary Battery, Negative Electrode for Secondary Battery Including the Same, and Lithium Secondary Battery Including the Same
Provided are a binder for a secondary battery, a negative electrode including the same, and a secondary battery including the same. More particularly, the binder for a secondary battery including a crosslinked product of a copolymer with a silane-based crosslinking agent according to the present invention may have excellent thermal resistance and mechanical properties and effectively improve a binding force, and the negative electrode for a secondary battery and the secondary battery including the same may effectively suppress expansion of a negative electrode to improve charge/discharge cycle characteristics and performance of the secondary battery.
1 . A binder for a secondary battery, the binder comprising a copolymer which is crosslinked with a silane-based crosslinking agent,
wherein the copolymer comprises a repeating unit (a) of the following Chemical Formula 1, a repeating unit (b) of the following Chemical Formula 2, a repeating unit (c) of the following Chemical Formula 3, and a repeating unit (d) of the following Chemical Formula 4:
wherein
R 1 and R 3 are independently substituted or unsubstituted hydrocarbyl having 1 to 10 carbon atoms;
R 2 and R 4 are independently hydrogen or substituted or unsubstituted hydrocarbyl having 1 to 10 carbon atoms;
M n+ is a cation having an oxidation number of n except for a hydrogen ion; and
n is an integer of 1 to 3.
2 . The binder for a secondary battery of claim 1 , wherein (a+b):(c+d) of the copolymer is 0.05 to 0.95:0.95 to 0.05, in which a, b, c, and d are mole fractions of the repeating units (a), (b), (c), and (d), respectively in the copolymer.
3 . The binder for a secondary battery of claim 1 , wherein the copolymer satisfies the following Equation 1:
0.45 21 ( b+d )/( a+b+c+d )<1.0 [Equation 1]
wherein
a, b, c, and d are mole fractions of the repeating units (a), (b), (c), and (d), respectively in the copolymer.
4 . The binder for a secondary battery of claim 1 , wherein the silane-based crosslinking agent is represented by the following Chemical Formula 5:
(R 5 O) x Si(R 6 ) y [Chemical Formula 5]
wherein
x+y=4, and x is 2 or 3;
R 5 is substituted or unsubstituted hydrocarbyl having 1 to 7 carbon atoms;
R 6 is substituted or unsubstituted hydrocarbyl having 1 to 7 carbon atoms or heterohydrocarbyl having 1 to 7 carbon atoms;
the hydrocarbyl and the heterohydrocarbyl may be optionally substituted by one or more selected from glycidyl, amino, and cyano; and
when y is 2, each R 6 may be the same as or different from each other.
5 . The binder for a secondary battery of claim 1 , wherein the silane-based crosslinking agent is one or a combination of two or more selected from the group consisting of dimethyldimethoxysilane, diethoxydimethylsilane, methyltriethoxysilane, (3-glycidoxypropyl)methyldimethoxysilane, (3-glycidoxypropyl)methyldiethoxysilane, (3-glycidoxypropyl)trimethoxysilane, (3-glycidoxypropyl)triethoxysilane, (3-aminopropyl)methyldimethoxysilane, (3-aminopropyl)methyldiethoxysilane, (3-aminopropyl)trimethoxysilane, (3-aminopropyl)triethoxysilane, [3-(2-aminoethylamino)propyl]methyldimethoxysilane, [3-(2-aminoethylamino)propyl]methyldiethoxysilane, [3-(2-aminoethylamino)propyl]triethoxysilane, [3-(2-aminoethylamino)propyl]trimethoxysilane, 3-(trimethoxysilyl)propionitrile, and 3-(triethoxysilyl)propionitrile.
6 . The binder for a secondary battery of claim 1 , wherein the silane-based crosslinking agent is one or a combination of two selected from the group consisting of (3-aminopropyl)triethoxysilane and [3-(2-aminoethylamino)propyl]trimethoxysilane.
7 . The binder for a secondary battery of claim 1 , wherein the silane-based crosslinking agent is comprised at 0.1 to 20 wt % with respect to the binder for a secondary battery.
8 . The binder for a secondary battery of claim 1 , wherein the binder for a secondary battery is a binder for a lithium secondary battery negative electrode.
9 . A secondary battery comprising: a positive electrode and a negative electrode for a secondary battery,
wherein the negative electrode for a secondary battery comprises a current collector; and a negative electrode active material layer disposed on the current collector, and the negative electrode active material layer comprises the binder for a secondary battery of claim 1 and a negative electrode active material.
10 . The secondary battery of claim 9 , wherein the negative electrode active material comprises a silicon-based active material.
11 . The secondary battery of claim 10 , wherein the negative electrode active material further comprises a graphite-based active material.
12 . The secondary battery of claim 11 , wherein a mass ratio between the silicon-based active material and the graphite-based active material is 97:3 to 3:97.
13 . The secondary battery of claim 9 , wherein the binder for a secondary battery is comprised at 0.1 to 30 wt % with respect to the negative electrode active material layer.
14 . A method of preparing a binder for a secondary battery, the method comprising the steps of:
step (A) saponifying a copolymer comprising a repeating unit (a) of the following Chemical Formula 1 and a repeating unit (c) of the following Chemical Formula 3 to prepare a saponified copolymer; and
step (B) reacting the saponified copolymer and a silane-based crosslinking agent to perform crosslinking,
wherein the saponified copolymer comprises the repeating unit (a) of the following Chemical Formula 1, a repeating unit (b) of the following Chemical Formula 2, the repeating unit (c) of the following Chemical Formula 3, and a repeating unit (d) of the following Chemical Formula 4:
wherein
R 1 and R 3 are independently substituted or unsubstituted hydrocarbyl having 1 to 10 carbon atoms;
R 2 and R 4 are independently hydrogen or substituted or unsubstituted hydrocarbyl having 1 to 10 carbon atoms;
M n+ is a cation having an oxidation number of n except for a hydrogen ion; and
n is an integer of 1 to 3.
15 . The method of preparing a binder for a secondary battery of claim 14 ,
wherein a degree of saponification in step (A) is more than 0.45 and less than 1.0, and
the degree of saponification is calculated by (b+d)/(a+b+c+d), in which a, b, c, and d are mole fractions of the repeating units (a), (b), (c), and (d) in the saponified copolymer.
16 . The method of preparing a binder for a secondary battery of claim 14 , wherein the silane-based crosslinking agent is represented by the following Chemical Formula 5:
(R 5 O) x Si(R 6 ) y [Chemical Formula 5]
wherein
x+y=4, and x is 2 or 3;
R 5 is substituted or unsubstituted hydrocarbyl having 1 to 7 carbon atoms;
R 6 is substituted or unsubstituted hydrocarbyl having 1 to 7 carbon atoms or heterohydrocarbyl having 1 to 7 carbon atoms;
the hydrocarbyl and the heterohydrocarbyl may be optionally substituted by one or more selected from glycidyl, amino, and cyano; and
when y is 2, each R 6 may be the same as or different from each other.
17 . The method of preparing a binder for a secondary battery of claim 14 , wherein the silane-based crosslinking agent is one or a combination of two or more selected from the group consisting of dimethyldimethoxysilane, diethoxydimethylsilane, methyltriethoxysilane, (3-glycidoxypropyl)methyldimethoxysilane, (3-glycidoxypropyl)methyldiethoxysilane, (3-glycidoxypropyl)trimethoxysilane, (3-glycidoxypropyl)triethoxysilane, (3-aminopropyl)methyldimethoxysilane, (3-aminopropyl)methyldiethoxysilane, (3-aminopropyl)trimethoxysilane, (3-aminopropyl)triethoxysilane, [3-(2-aminoethylamino)propyl]methyldimethoxysilane, [3-(2-aminoethylamino)propyl]methyldiethoxysilane, [3-(2-aminoethylamino)propyl]triethoxysilane, [3-(2-aminoethylamino)propyl]trimethoxysilane, 3-(trimethoxysilyl)propionitrile, and 3-(triethoxysilyl)propionitrile.
18 . The method of preparing a binder for a secondary battery of claim 14 , wherein the silane-based crosslinking agent is one or a combination of two selected from the group consisting of (3-aminopropyl)triethoxysilane and [3-(2-aminoethylamino)propyl]trimethoxysilane.
19 . The method of preparing a binder for a secondary battery of claim 14 , wherein the silane-based crosslinking agent is comprised at 0.1 to 20 wt % with respect to the binder for a secondary battery.