Solid electrolytic capacitor with improved moisture resistance properties and method of manufacturing the same

1. A solid electrolytic capacitor comprising:

an anode conductor including a porous valve-acting metal and having pores with openings in a surface thereof;

a solid electrolyte layer formed on the surface of the anode conductor so as to be filled in at least a portion of each of the pores and to close the openings; and

a cathode conductor formed on the solid electrolyte layer;

wherein the solid electrolyte layer comprises:

an inner polymer layer spread along the surface of the anode conductor;

a first polymer layer formed on the inner polymer layer; and

a second polymer layer formed on the first polymer layer and having a particle size that is greater than a particle size of the first polymer layer;

wherein the inner polymer layer and the first polymer layer cooperatively close the openings; and

wherein the first polymer layer is formed by drying a first polymer solution which contains a conductive polymer having a particle size that is smaller than a diameter of each of the openings, and which is adhered to the inner polymer layer.

2. The solid electrolytic capacitor according to claim 1 , wherein the anode conductor has a dielectric layer at the surface thereof and the solid electrolyte layer is formed on a surface of the dielectric layer.

3. A method of manufacturing a solid electrolytic capacitor, comprising:

preparing an anode conductor including a porous valve-acting metal and having pores with openings in a surface thereof; and

forming a solid electrolyte layer on the surface of the anode conductor so as to be filled in at least a portion of each of the pores and to close the openings;

wherein forming the solid electrolyte layer comprises:

forming an inner polymer layer spread along the surface of the anode conductor;

forming a first polymer layer on the inner polymer layer; and

forming a second polymer layer on the first polymer layer, the second polymer layer having a particle size that is greater than a particle size of the first polymer layer;

wherein the inner polymer layer and the first polymer layer cooperatively close the openings; and

wherein forming the first polymer layer comprises:

preparing a first polymer solution containing a conductive polymer having a particle size that is smaller than a diameter of each of the openings; and

forming the first polymer layer by adhering the first polymer solution to the inner polymer layer and drying the adhered first polymer solution.

4. The method according to claim 3 , wherein the particle size of the first polymer solution is 20% or less of the diameter of each of the openings.

5. The method according to claim 3 , wherein D 90 is 100 nm or less in a particle size distribution of the first polymer solution.

6. The method according to claim 3 , wherein the first polymer solution has a same type of polymer backbone as the inner polymer layer.

7. The method according to claim 3 , wherein forming the second polymer layer comprises:

preparing a second polymer solution containing a conductive polymer having a particle size that is greater than the particle size of the first polymer solution; and

forming the second polymer layer by adhering the second polymer solution to the first polymer layer and drying the adhered second polymer solution.

8. The method according to claim 7 , wherein the particle size of the first polymer solution is 20% or less of the diameter of each of the openings.

9. The method according to claim 7 , wherein D 90 is 100 nm or less in a particle size distribution of the first polymer solution.

10. The method according to claim 7 , wherein the first polymer solution has a same type of polymer backbone as the inner polymer layer.

11. The method according to claim 7 , wherein D 10 is 1 μm or more in a particle size distribution of the second polymer solution.

12. The method according to claim 7 , wherein the second polymer solution has a same type of polymer backbone as the first polymer solution.

13. The method according to claim 7 , wherein the conductive polymer of each of the first and second polymer solutions contains at least one monomer selected from pyrrole, thiophene, 3,4-ethylene dioxythiophene, and derivatives thereof.

14. The method according to claim 3 , wherein the valve-acting metal is at least one of aluminum, tantalum, and niobium.

15. The method according to claim 3 , further comprising forming a cathode conductor on the solid electrolyte layer.