Second battery and separator used therein

1. A secondary battery, comprising:

a positive electrode;

a negative electrode comprising alkali metal;

a separator comprising a layer of tetrafluoroethylene (TFE) polymer or copolymer that reacts with a dendrite of the alkali metal, the separator is configured to be hydrophilized at a rate of not less than 10% and not more than 80%; and

a layer that does not react with a dendrite of the alkali metal located between the separator and the negative electrode.

2. The secondary battery according to claim 1 , wherein the layer that does not react with a dendrite of the alkali metal is a part of the separator, and, in the layer that does not react with a dendrite of the alkali metal, the inner surface of its pores is at least partially covered with a material that does not react with a dendrite of the alkali metal.

3. The secondary battery according to claim 1 , wherein the layer that does not react with a dendrite of the alkali metal is independent of the separator.

4. The secondary battery according to claim 3 , wherein the layer that does not react with a dendrite of the alkali metal comprises any one of glass comprising SiO x (0<x≦2), polyvinylidene fluoride (PVDF), polyimide (PI), polyethylene (PE), or polypropylene (PP) or a mixture thereof.

5. The secondary battery according to claim 3 , wherein the layer that does not react with a dendrite of the alkali metal comprises any one of inorganic oxides selected from the group consisting of alumina, titanium oxide, sodium oxide, calcium oxide, boron oxide, potassium oxide, and lead oxide or a mixture thereof and a binder.

6. The secondary battery according to claim 1 , wherein in the layer that does not react with a dendrite of the alkali metal, the inner surface of its pores is covered with a material other than tetrafluoroethylene (TFE) polymer or copolymer.

7. The secondary battery according to claim 6 , wherein the material other than tetrafluoroethylene (TFE) polymer or copolymer is any one of glass comprising SiO x (0<x≦2), polyvinylidene fluoride (PVDF), polyimide (PI), polyethylene (PE), or polypropylene (PP) or a mixture thereof.

8. The secondary battery according to claim 1 , wherein the layer that does not react with a dendrite of the alkali metal is hydrophilized.

9. The secondary battery according to claim 1 , wherein the tetrafluoroethylene (TFE) polymer or copolymer is expanded or expanded porous.

10. The secondary battery according to claim 1 , wherein the tetrafluoroethylene (TFE) polymer or copolymer is expanded polytetrafluoroethylene, perfluoro alkoxy alkane (PFA), tetrafluoroethylene/hexafluoropropene copolymer (FEP), ethylene/tetrafluoroethylene copolymer (ETFE), or ethylene/chlorotrifluoroethylene copolymer (ECTFE) or a mixture thereof.

11. The secondary battery according to claim 1 , wherein the thickness of the layer that does not react with a dendrite of the alkali metal is 0.1 μm or more.

12. The secondary battery according to claim 1 , wherein the separator at least comprises fluorine that can react with the total mass of the alkali metal constituting the negative electrode.

13. The secondary battery according to claim 1 , wherein the alkali metal is lithium or sodium.

14. The secondary battery according to claim 1 , wherein the secondary battery further comprises a shut-down layer.

15. The secondary battery according to claim 14 , wherein the shut-down layer is located between the separator and the positive electrode.

16. The separator used in the secondary battery according to claim 1 .