Negative electrode and secondary cell

1. A negative electrode, wherein:

a negative electrode current collector has a conductive foil including a conductive substrate and a multiplicity of conductive lumpy projections provided at a surface of said substrate; and

said multiplicity of lumpy projections are so disposed that a plurality of said lumpy projections are aligned substantially in one direction to form a lumpy projection row and that a plurality of said lumpy projection rows are arrayed side by side at a predetermined interval in a direction substantially orthogonal to said one direction.

2. The negative electrode as set forth in claim 1 , wherein said conductive foil is an electrolytic copper foil wherein a multiplicity of copper particulates serving as said multiplicity of lumpy projections are formed by an electrolytic treatment so as to cover substantially the whole part of a surface of an untreated copper foil serving as said substrate.

3. The negative electrode as set forth in claim 2 , wherein said lumpy projection rows are arrayed side by side at a pitch of 1.3 to 2.8 μm.

4. The negative electrode as set forth in claim 2 , wherein said electrolytic copper foil has a surface roughness in terms of ten-point mean roughness Rz of 1.5 to 5 μm.

5. The negative electrode as set forth in claim 1 , wherein a negative electrode active material layer is formed to have a surface shape reflecting the shape of said lumpy projections of said negative electrode current collector.

6. The negative electrode as set forth in claim 1 , wherein a negative electrode active material layer is formed by a vapor phase process and/or a sintering process.

7. The negative electrode as set forth in claim 1 , wherein a negative electrode active material layer contains elemental silicon or a silicon compound as an ingredient.

8. The negative electrode as set forth in claim 7 , wherein said negative electrode active material layer contains oxygen as an ingredient, and the content of oxygen is 3 to 40 at %.

9. The negative electrode as set forth in claim 8 , wherein said negative electrode active material layer has a high oxygen concentration layer high in oxygen concentration and a low oxygen concentration layer low in oxygen concentration, disposed in the thickness direction of said negative electrode active material layer.

10. A secondary cell comprising:

a positive electrode,

an electrolyte, and

a negative electrode as set forth in any one of claims 1 to 9 ,

wherein said negative electrode extends, in the direction in which said lumpy projection rows are arrayed side by side, during charging to form an extended negative electrode, and

wherein a region capable of accommodating said extended negative electrode is provided at a side of said negative electrode in the direction in which said negative electrode extends.

11. The secondary cell as set forth in claim 10 , wherein said positive electrode and said negative electrode are rolled in an overlapping condition to form a rolled electrode body, and the roll axis direction of said rolled electrode body is a direction intersecting said one direction along which each said lumpy projection row is formed.

12. The secondary cell as set forth in claim 11 , wherein said roll axis direction is said direction in which said lumpy projection rows are arrayed side by side.

13. The secondary cell as set forth in claim 11 , wherein an outer package accommodating said rolled electrode body is of a tubular type, and a space is present between said outer package and a spacer provided on a side of the rolled electrode body in the roll axis direction.

14. The secondary cell as set forth in claim 13 , wherein said outer package is composed mainly of iron or an iron alloy.

15. The secondary cell as set forth in claim 10 , wherein said electrolyte contains a fluorine-containing compound in which a part or the whole part of hydrogen in a cyclic carbonic acid ester or chain carbonic acid ester is replaced by fluorine.

16. The secondary battery as set forth in claim 15 , wherein said fluorine-containing compound is difluoroethylene carbonate.