Cathode active material comprising polyimide, manufacturing method thereof, and lithium-sulfur battery comprising same
The present invention relates to a positive electrode active material for a lithium-sulfur battery containing polyimide, more specifically, a positive electrode active material formed by complexing the composite of polyimide and carbon-based secondary particles with sulfur particles, a preparation method thereof and a lithium-sulfur battery comprising the same. If the positive electrode active material formed by including and complexing the polyimide according to the present invention is applied to the lithium-sulfur battery, the elution of the polysulfide is suppressed, and thus lifetime characteristics and energy efficiency are improved.
1. A polyimide-carbon-sulfur composite comprising porous carbon-based secondary particles formed by assembling and aggregating a plurality of carbon-based primary particles; a coating layer of polyimide coated on the inside and outside of the pores of the carbon-based secondary particles; and sulfur (S) supported in the pores of the carbon-based secondary particles.
2. The polyimide-carbon-sulfur composite according to claim 1 , wherein the polyimide coating layer continuously or discontinuously forms a coating layer on the surface of the porous carbon-based secondary particles, or the polyimide coating layer allows the pores to be maintained and forms a porous coating layer.
3. The polyimide-carbon-sulfur composite according to claim 1 , wherein the weight ratio of the polyimide to the carbon-based secondary particles is 5:95 to 20:80.
4. The polyimide-carbon-sulfur composite according to claim 1 , wherein the carbon-based secondary particles are at least one selected from the group consisting of graphite series including natural graphite, artificial graphite, expanded graphite, graphene, graphene oxide, Super-P and Super-C; active carbon series; carbon black series including Denka black, Ketjen black, channel black, furnace black, thermal black, contact black, lamp black, acetylene black; carbon nanostructure including carbon fiber series, carbon nanotube (CNT), and fullerene; and combinations thereof.
5. The polyimide-carbon-sulfur composite according to claim 1 , wherein the carbon-based secondary particles have an average particle size of 1 to 50 μm.
6. The polyimide-carbon-sulfur composite according to claim 1 , wherein the carbon-based secondary particles have a pore volume of 0.2 to 4.0 cm 3 /g.
7. The polyimide-carbon-sulfur composite according to claim 1 , wherein the carbon-based secondary particles have a specific surface area of 100 to 2000 m 2 /g.
8. The polyimide-carbon-sulfur composite according to claim 1 , wherein sulfur is at least one selected from the group consisting of elemental sulfur (S 8 ), solid Li 2 S n (n≥1), catholytes in which solid Li 2 S n (n≥1) is dissolved, organosulfur compounds, and carbon-sulfur polymers [(C 2 S x ) n , where x=2.5 to 50, and n≥2].
9. The polyimide-carbon-sulfur composite according to claim 1 , wherein the content of sulfur is 30 to 90% by weight based on the total weight of the composite.
10. A preparation method of a polyimide-carbon-sulfur composite, comprising:
(i) assembling and aggregating a plurality of carbon-based primary particles under conditions effective to provide carbon-based secondary particles;
(ii) mixing the carbon-based secondary particles with a solution of a polyimide precursor to provide a first solution;
(iii) converting the first solution under effective reaction conditions to provide a polyimide-carbon composite; and
(iv) complexing sulfur with the polyimide-carbon composite to provide a polyimide-carbon-sulfur composite,
wherein a coating layer of polyimide is present on the inside and outside of the pores of the carbon-based secondary particles, and
wherein the sulfur is supported in the pores of the carbon-based secondary particles.
11. The preparation method of the polyimide-carbon-sulfur composite according to claim 10 , wherein the carbon-based secondary particles in (i) are prepared by spray-drying a solution containing the carbon-based primary particles.
12. The preparation method of the polyimide-carbon-sulfur composite according to claim 10 , wherein the polyimide precursor in (ii) is a polyamic acid (PAA).
13. The preparation method of the polyimide-carbon-sulfur composite according to claim 10 , wherein the first solution is converted to a polyimide-carbon composite in (iii) by a heat treatment comprising raising the temperature stepwise within a range of 60 to 400° C.
14. A lithium-sulfur battery comprising a positive electrode; a negative electrode; a separator interposed therebetween and an electrolyte, wherein the positive electrode comprises the polyimide-carbon-sulfur composite according to claim 1 .