Binder for secondary battery, negative electrode for secondary battery including the same, and lithium secondary battery including the same
Provided are a novel binder for a secondary battery including a copolymer containing specific repeating units, and a binder composition for a secondary battery including the binder for a secondary battery and a compound containing an amine group and a hydroxyl group. When the binder for a secondary battery or the binder composition for a secondary battery is applied to a negative electrode and a secondary battery, expansion of the negative electrode is effectively suppressed, and the charge/discharge cycle characteristics and the performance of the secondary battery are significantly improved. Furthermore, the binder for a secondary battery has improved coatability and adhesion to effectively suppress the exfoliation and desorption of the negative electrode, thereby improving the performance of the secondary battery.
1 . 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:
(i) a binder for a secondary battery comprising a copolymer, 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, a repeating unit (d) of the following Chemical Formula 4, and a repeating unit (e) of the following Chemical Formula 5, wherein the copolymer satisfies the following Equation 2, or
(ii) a binder composition for a secondary battery comprising the copolymer and a compound comprising an amine group and a hydroxyl group, wherein the copolymer comprises the repeating unit (a) of the following Chemical Formula 1, the repeating unit (b) of the following Chemical Formula 2, the repeating unit (c) of the following Chemical Formula 3, the repeating unit (d) of the following Chemical Formula 4, and the repeating unit (e) of the following Chemical Formula 5,
wherein the copolymer satisfies the following Equation 2:
wherein
R 1 and R 3 are independently of each other substituted or unsubstituted hydrocarbyl having 1 to 10 carbon atoms;
R 2 and R 4 are independently of each other hydrogen or substituted or unsubstituted hydrocarbyl having 1 to 10 carbon atoms;
M n+ is a cation having an oxidation number of n other than a hydrogen ion; and
n is an integer of 1 to 3,
0.01< e /( d+e )<0.9 [Equation 2]
wherein
d and e are mole fractions of the repeating units (d) and (e), respectively, in the copolymer;
and a negative electrode active material.
2 . The secondary battery of claim 1 , wherein the negative electrode active material comprises a silicon-based active material.
3 . The secondary battery of claim 2 , wherein the negative electrode active material further comprises a graphite-based active material.
4 . The secondary battery of claim 1 , wherein the binder for a secondary battery or the binder composition for a secondary battery is comprised at 0.5 to 30 wt % with respect to a weight of the negative electrode active material layer.
5 . A method of preparing a binder for a secondary battery, the method comprising:
(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
(B) acidifying the saponified copolymer to prepare an acidified copolymer,
wherein the acidified copolymer is a copolymer comprising: 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, a repeating unit (d) of the following Chemical Formula 4, and a repeating unit (e) of the following Chemical Formula 5,
wherein a degree of acidification in (B) is more than 0.01 and less than 0.9, and the degree of acidification is calculated by e/(d+e), wherein d and e are mole fractions of the repeating units (d) and (e), respectively, in the acidified copolymer:
wherein
R 1 and R 3 are independently of each other substituted or unsubstituted hydrocarbyl having 1 to 10 carbon atoms;
R 2 and R 4 are independently of each other hydrogen or substituted or unsubstituted hydrocarbyl having 1 to 10 carbon atoms;
M n+ is a cation having an oxidation number of n other than a hydrogen ion; and
n is an integer of 1 to 3.
6 . The method of preparing a binder for a secondary battery of claim 5 ,
wherein a degree of saponification is more than 0.45 and less than 1.0, and
the degree of saponification is calculated by (b+d+e)/(a+b+c+d+e), wherein a, b, c, d, and e are mole fractions of the repeating units (a), (b), (c), (d), and (e), respectively, in the acidified copolymer.
7 . The method of preparing a binder for a secondary battery of claim 5 , wherein a degree of acidification in (B) is more than 0.05 and less than 0.5, and
the degree of acidification is calculated by e/(d+e), wherein d and e are mole fractions of the repeating units (d) and (e), respectively, in the acidified copolymer.
8 . The method of preparing a binder for a secondary battery of claim 5 , further comprising: after (B), adding the acidified copolymer and a compound comprising an amine group and a hydroxyl group.