Nonaqueous secondary battery

1. A nonaqueous secondary battery comprising a positive electrode containing a material capable of reversibly intercalating and deintercalating lithium, a negative electrode containing a composite oxide containing tin represented by formula (3):

SnM 3 c M 4 d O t   (3)

wherein M 3 represents at least two elements selected from the group consisting of Al, B, P, and Si; M 4 represents at least one element selected from the group consisting of elements of groups 1 to 3 of the Periodic Table, and halogen elements; c represents a number of from 0.2 to 2; d represents a number of from 0.01 to 1; provided that 0.2<c+d<2; and t represents a number of from 1 to 6, a nonaqueous electrolyte containing a lithium salt, and a separator, wherein at least the positive electrode has at least one protective layer comprising organic fine particles and inorganic fine particles.

2. The nonaqueous secondary battery as in claim 1 , wherein said protective layer is formed on both of the positive electrode and negative electrode.

3. The nonaqueous secondary battery as in claim 1 , wherein said protective layer comprises fine particles of water-insoluble or sparingly water-soluble alkali metal salt or alkaline earth metal salt, and at least two kinds of binders.

4. The nonaqueous secondary battery as in claim 1 , wherein said protective layer has substantially no electrical conductivity.

5. The nonaqueous secondary battery as in claim 1 , wherein said protective layer has electrical conductivity.

6. The nonaqueous secondary battery as in claim 1 , wherein said protective layer contains particles having substantially no electrical conductivity.

7. The nonaqueous secondary battery as in claim 1 , wherein said protective layer contains particles which are electrically conductive.

8. The nonaqueous secondary battery as in claim 1 , wherein said protective layer contains particles which are inorganic chalcogenide particles.

9. The nonaqueous secondary battery as in claim 8 , wherein said inorganic chalcogenide particles contain at least one inorganic oxide selected from the group consisting of oxide of sodium, potassium, magnesium, calcium, strontium, zirconium, aluminum, and silicon.

10. The nonaqueous secondary battery as in claim 9 , wherein said inorganic oxide is selected from the group consisting of alumina, silicon dioxide and zirconia.

11. The nonaqueous secondary battery as in claim 1 , wherein said protective layer contains electrically conductive particles selected from the group consisting of metal powders and carbon particles.

12. The nonaqueous secondary battery as in claim 11 , wherein said electrically conductive particles are carbon particles.

13. The nonaqueous secondary battery as in claim 3 , wherein said water-insoluble or sparingly water-soluble fine particles contained in said protective layer are an alkali metal salt.

14. The nonaqueous secondary battery as in claim 3 , wherein said water-insoluble or sparingly water-soluble fine particles contained in said protective layer are an alkaline earth metal salt.

15. The nonaqueous secondary battery as in claim 13 , wherein said water-insoluble or sparingly water-soluble fine particles are a lithium salt.

16. The nonaqueous secondary battery as in claim 1 , wherein said protective layer has a thickness of from 1 μm to 40 μm.

17. The nonaqueous secondary battery as in claim 1 , wherein said protective layer contains electrically conductive particles in an amount of from 2.5 to 96% by weight.

18. The nonaqueous secondary battery as in claim 1 , wherein said nonaqueous electrolyte contains at least one carbonic ester.

19. The nonaqueous secondary battery as in claim 1 , wherein said protective layer contains polyethylene fine particles and inorganic particles of ZrO 2.