ACRYLIC BINDER FOR LITHIUM-SULFUR SECONDARY BATTERY CATHODE

Abstract

The present invention relates to a binder for a lithium-sulfur secondary battery cathode, and a composition containing the same. The binder of the present application enables a cathode active material electrolyte to have excellent resistance.

Claims

1. An acrylic binder for a lithium-sulfur secondary battery cathode, comprising polymerized units of a polymerizable monomer having a polar functional group interacting with a cathode active material.

2. The acrylic binder for a lithium-sulfur secondary battery cathode according to claim 1, wherein the polymerizable monomer having a polar functional group is contained in a polymerized unit ratio of 30 to 100 parts by weight.

3. The acrylic binder for a lithium-sulfur secondary battery cathode according to claim 1, wherein the polar functional group is at least one selected from a nitrogen-containing functional group, an alkylene oxide group, a hydroxy group and an alkoxysilyl group.

4. The acrylic binder for a lithium-sulfur secondary battery cathode according to claim 1, wherein the cathode active material has a compound comprising a sulfur element.

5. The acrylic binder for a lithium-sulfur secondary battery cathode according to claim 4, wherein the cathode active material is a sulfur-carbon composite.

6. The acrylic binder for a lithium-sulfur secondary battery cathode according to claim 1, wherein the interaction is an interaction between the polar functional group and the sulfur element.

7. The acrylic binder for a lithium-sulfur secondary battery cathode according to claim 1, further comprising polymerized units of alkyl (meth)acrylate.

8. The acrylic binder for a lithium-sulfur secondary battery cathode according to claim 7, wherein the alkyl (meth)acrylate is contained in a polymerized unit ratio of 5 to 30 parts by weight.

9. The acrylic binder for a lithium-sulfur secondary battery cathode according to claim 1, having a particle diameter of 10 nm or less.

10. The acrylic binder for a lithium-sulfur secondary battery cathode according to claim 1, having a glass transition temperature in a range of 80 C. to 50 C.

11. The acrylic binder for a lithium-sulfur secondary battery cathode according to claim 1, having a weight average molecular weight in a range of 5,000 to 3,000,000.

12. A composition for forming a cathode active layer of a lithium-sulfur secondary battery comprising the acrylic binder according to claim 1, a cathode active material and a conductive material.

13. The composition for forming a cathode active layer of a lithium-sulfur secondary battery according to claim 12, wherein the acrylic binder is contained in a ratio of 0.01 to 10 parts by weight, relative to 100 parts by weight of the solid content of the composition.

14. The composition for forming a cathode active layer of a lithium-sulfur secondary battery according to claim 12, wherein the cathode active material is a sulfur-carbon composite.

15. The composition for forming a cathode active layer of a lithium-sulfur secondary battery according to claim 12, wherein the cathode active material is contained in a ratio of 30 to 95 parts by weight, relative to 100 parts by weight of the solid content of the composition.

16. The composition for forming a cathode active layer of a lithium-sulfur secondary battery according to claim 12, further comprising a non-acrylic binder.

17. The composition for forming a cathode active layer of a lithium-sulfur secondary battery according to claim 12, wherein the conductive material is contained in a ratio of 2 to 70 parts by weight, relative to 100 parts by weight of the solid content of the composition.

18. A cathode for a lithium-sulfur secondary battery having: a current collector; and an active layer formed on the current collector and comprising the acrylic binder according to claim 1.

19. The cathode for a lithium-sulfur secondary battery according to claim 18, wherein the active layer has a thickness in a range of 1 to 200 m.

20. A lithium-sulfur secondary battery comprising the cathode of claim 18.

Description

RESIN PRODUCTION EXAMPLE 1

Production of Acrylic Binder (Al)

[0131] In a 250 mL round bottom flask, 7.5 g of polyethyleneoxide methylether methacrylate, 6.0 g of N-vinyl-2-pyrrolidone, 1.5 g of acrylonitrile and 60 g of water were charged and the inlet was sealed. Oxygen was removed through nitrogen bubbling for 30 minutes, the reaction flask was immersed in an oil bath heated to 60 C., and then 0.03 g of V-50 (Wako Chemical) was added to initiate the reaction. In 24 hours when the monomer conversion was 87%, the reaction was terminated to obtain an acrylic binder having a weight average molecular weight of about 300,000.

RESIN PRODUCTION EXAMPLES 2 TO 4

Production of Acrylic Binders (A2, A3, A4)

[0132] An acrylic binder was prepared in the same manner as in Production Example 1, except that the kinds and contents of the monomers used upon the polymerization were adjusted as in Table 1 below.

TABLE-US-00001 TABLE 1 A1 A2 A3 A4 PEOMA (part by 50 50 50 50 weight) VP (part by 40 25 40 weight) DMAA (part by 40 25 weight) AN (part by 10 10 weight) MMA (part by 10 weight) Mw 300,000 350,000 500,000 400,000 PEOMA: Poly(ethylene oxide) methyl ether methacrylate VP: N-vinyl-2-pyrrolidone DMAA: N,N-dimethylacrylamide AN: acrylonitrile MMA: Methyl methacrylate

EXAMPLE 1

Manufacture of Lithium-Sulfur Secondary Battery

[0133] A lithium-sulfur secondary battery was manufactured using a cathode having an active layer comprising an acrylic binder (A1) prepared according to Production Example 1 above. The charge/discharge was evaluated with 0.1 C/0.1 C by 50 cycles between 1.5 V and 2.8 V, and then the remaining capacity in the second cycle and the remaining capacity in the 50th cycle were calculated relative to the initial capacity to measure the capacity retention rate and the result was shown in Table 2.

EXAMPLES 2 TO 4

Manufacture of Lithium-Sulfur Secondary Battery

[0134] A battery was manufactured in the same manner as in Example 1, except that a lithium-sulfur secondary battery was produced using a cathode having an active layer comprising each acrylic binder (A2, A3, A4) prepared according to Production Examples 2 to 4, and the capacity retention rate was evaluated and shown in Table 2.

COMPARATIVE EXAMPLES 1 AND 2

Manufacture of Lithium-Sulfur Secondary Battery

[0135] A battery was manufactured in the same manner as in Example 1, except that a polyvinylidene fluoride (PVDF) binder or a mixture of styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) in a ratio of 1:1 was used as a cathode binder instead of acrylic binders (A1, A2, A3, A4), and the capacity retention rate was evaluated and shown in Table 2.

TABLE-US-00002 TABLE 2 Example Comparative Example 1 2 3 4 1 2 Binder A1 A2 A3 A3 PVDF SBR + CMC Capacity retention rate (%) 86 85 88 88 75 80

[0136] As shown in Table 2, in the case of the lithium-sulfur secondary battery according to Examples, the phenomenon that the sulfur was dissoluted into the electrolyte could be inhibited by comprising the acrylic binder containing the polymerized units of the polymerizable monomer having the polar functional group interacting with sulfur, which is the cathode active material, in the active layer, and thus it was shown that the capacity retention ratio according to the cycle progress was high.

INDUSTRIAL APPLICABILITY

[0137] The present application can provide an acrylic binder contained in a cathode active layer of a lithium-sulfur secondary battery, which can effectively prevent dissolution of a cathode active material and ultimately ensure excellent cycle characteristics, and a composition comprising the same.

[0138] Also, the present application can provide a composition for forming a cathode active layer of a lithium-sulfur secondary battery, which can comprise an appropriate amount of a conductive material by having excellent dispersion characteristics, and a cathode comprising the active layer formed therefrom.