Cathode active material for sodium secondary battery and method for manufacturing the cathode active material for sodium secondary battery

Patent metadata

Field	Value
Publication number	US-10135068-B2
Application number	US-201314383646-A
Country	US
Kind code	B2
Filing date	Mar 7, 2013
Priority date	Mar 9, 2012
Publication date	Nov 20, 2018
Grant date	Nov 20, 2018

Abstract

Provided are a cathode active material for a sodium ion secondary battery that is excellent in alkali ion diffusivity, structural stability, and cycle performance, and a synthesis method therefor. The cathode active material for a sodium ion secondary battery includes a melt-solidified body or oxide glass represented by the general formula Na x M y P 2 O 7 (where M represents at least one or more kinds of transition metal elements selected from Cr, Fe, Mn, Co, and Ni, x satisfies a relationship of 1.20≤x≤2.10, and y satisfies a relationship of 0.95≤y≤1.60).

First claim

The invention claimed is:

1. A cathode active material for a sodium ion secondary battery, comprising a crystalline substance represented by the formula Na x M y P 2 O 7 , where M is at least one transition metal element selected from the group consisting of Cr, Fe, Mn, and Ni, x satisfies a relationship of 1.20≤x≤2.10, and y satisfies a relationship of 0.95≤y≤1.60, and wherein the crystalline substance forms a crystal structure belonging to any one of triclinic space groups P 1 and P 1 − and has an average grain size of from 0.7 μm to 50 μm.

2. The cathode active material for a sodium ion secondary battery according to claim 1 , wherein the transition metal element M is Fe.

3. The cathode active material for a sodium ion secondary battery according to claim 1 , further comprising conductive carbon for coating a surface thereof, the carbon for coating having a thickness of from 1 nm to 100 nm.

4. The cathode active material for a sodium ion secondary battery according to claim 1 , wherein the cathode active material is formed of powder having an average grain size of from 1 μm to 50 μm.

5. A method of manufacturing a cathode active material for a sodium ion secondary battery comprising a crystalline substance represented by the formula Na x M y P 2 O 7 , where M is at least one transition metal element selected from the group consisting of Cr, Fe, Mn, and Ni, x satisfies a relationship of 1.20≤x≤2.10, and y satisfies a relationship of 0.95≤y≤1.60, and wherein the crystalline substance forms a crystal structure belonging to any one of triclinic space groups P 1 and P 1 − and has an average grain size of from 0.7 μm to 50 μm,
the method comprising the steps of:
blending raw material powders comprising (1) sodium raw material and phosphate raw material, or a composite oxide of the sodium raw material and the phosphate raw material, and (2) a raw material comprising a transition metal compound comprising the transition metal element M,
melting the raw material powders at a temperature equal to or higher than a temperature at which the transition metal compound forms a liquid phase; and
cooling the melt to obtain a melt-solidified body.

6. The method of manufacturing a cathode active material for a sodium ion secondary battery according to claim 5 , wherein the transition metal element M is Fe.

7. The method of manufacturing a cathode active material for a sodium ion secondary battery according to claim 5 , wherein melting the raw material powders is in a reducing atmosphere or an inert atmosphere.

8. The method of manufacturing a cathode active material for a sodium ion secondary battery according to claim 5 , wherein the melt-solidified body is an oxide glass.

9. The method of manufacturing a cathode active material for a sodium ion secondary battery according to claim 5 , further comprising pulverizing the melt-solidified body to obtain a powder.

10. The method of manufacturing a cathode active material for a sodium ion secondary battery according to claim 9 , further comprising crystallizing the powder through a heat treatment in an inert atmosphere or a reducing atmosphere.

11. The method of manufacturing a cathode active material for a sodium ion secondary battery according to claim 10 , wherein crystallizing the powder forms a crystal structure belonging to any one of triclinic space groups P 1 and P 1 −.

12. The method of manufacturing a cathode active material for a sodium ion secondary battery according to claim 9 , the method further comprising:
adding a carbon source to the powder; and
crystallizing the powder to which the carbon source is added through a heat treatment in an inert atmosphere or a reducing atmosphere.

13. The method of manufacturing a cathode active material for a sodium ion secondary battery according to claim 12 , wherein the carbon source is added in an amount of from 1 to 20 parts by mass.

14. The method of manufacturing a cathode active material for a sodium ion secondary battery according to claim 12 , wherein crystallizing the powder forms a crystal structure belonging to any one of triclinic space groups P 1 and P 1 −.

Assignees

• Nippon Electric Glass Co

Inventors

• Honma Tsuyoshi
• Komatsu Takayuki
• IKEJIRI Junichi
• Yamauchi Hideo

Classifications

• H01M4/625

  Carbon or graphite · CPC title

• H01M4/366

  as layered products · CPC title

• H01M10/054

  Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium · CPC title

• C01P2006/40

  Electric properties · CPC title

• C01B25/45

  containing plural metal, or metal and ammonium · CPC title