Carbon-coated lithium iron phosphate of olivine crystal structure and lithium secondary battery using the same

Patent metadata

Field	Value
Publication number	US-9331329-B2
Application number	US-201213623570-A
Country	US
Kind code	B2
Filing date	Sep 20, 2012
Priority date	Apr 21, 2010
Publication date	May 3, 2016
Grant date	May 3, 2016

Abstract

Disclosed is a lithium iron phosphate with an olivine crystal structure wherein the lithium iron phosphate has a composition represented by the following Formula 1 and carbon (C) is coated on the surface of the lithium iron phosphate by chemical bonding via a heterogeneous element other than carbon. Li 1+a Fe 1−x M x (PO 4−b )X b (1) (wherein M, X, a, x, and b are the same as defined in the specification).

First claim

The invention claimed is:

1. Lithium iron phosphate having an olivine crystal structure suitable for lithium secondary battery, wherein the lithium iron phosphate has a composition represented by the following Formula 1 and carbon (C) is coated on the surface of the lithium iron phosphate by chemical bonding via sulfur (S) in form of ‘oxygen-sulfur-carbon’, and
wherein the sulfur (S) is contained in the lithium iron phosphate in an amount of 0.005 to 1% by weight, based on the total weight of the lithium iron phosphate:
Li 1+a Fe 1−x M x (PO 4−b )X b   (1)

wherein
M is at least one selected from Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn and Y,
X is at least one selected from F, S and N,
−0.5 ≦a≦+ 0.5, 0 ≦x≦ 0.5, 0 ≦b≦ 0.1.

2. The lithium iron phosphate according to claim 1 , wherein the lithium iron phosphate is LiFePO 4 .

3. The lithium iron phosphate according to claim 1 , wherein the carbon is coated at an amount of 0.01 to 10% by weight, based on the total weight of the lithium iron phosphate.

4. The lithium iron phosphate according to claim 1 , wherein the carbon is coated on the surface of lithium iron phosphate to a thickness of 2 to 10 nm.

5. The lithium iron phosphate according to claim 1 , wherein the sulfur (S) is derived from a precursor for preparation of lithium iron phosphate.

6. The lithium iron phosphate according to claim 1 , wherein the sulfur (S) is incorporated by coating lithium iron phosphate with a sulfur-containing compound.

7. The lithium iron phosphate according to claim 6 , wherein the sulfur-containing compound is one or more selected from sulfides, sulfites and sulfates.

8. The lithium iron phosphate according to claim 1 , wherein the lithium iron phosphate is prepared by a supercritical hydrothermal method.

9. A method for preparing the lithium iron phosphate according to claim 1 comprising:
(a) primarily mixing precursors as starting materials and an alkalinizing agent;
(b) secondarily mixing the mixture obtained in step (a) with supercritical or subcritical water to synthesize lithium iron phosphate;
(c) mixing the synthesized lithium iron phosphate with a carbon precursor and drying the mixture; and
(d) heating the mixture of lithium iron phosphate and the carbon precursor.

10. A method for preparing the lithium iron phosphate according to claim 1 comprising:
(a′) primarily mixing precursors as starting materials and an alkalinizing agent;
(b′) secondarily mixing the mixture obtained in step (a′) with supercritical or subcritical water to synthesize lithium iron phosphate, followed by drying;
(c′) heating the synthesized lithium iron phosphate; and
(d′) milling the lithium iron phosphate and a carbon powder.

11. The method according to claim 9 , wherein the heating is carried out under an inert gas atmosphere.

12. A method for preparing the lithium iron phosphate according to claim 1 comprising:
(a″) synthesizing lithium iron phosphate using precursors as starting materials by a coprecipitation or solid phase method;
(b″) adding the synthesized lithium iron phosphate to a dispersion bath containing a sulfur-containing compound, followed by stirring;
(c″) drying the mixture obtained in step (b″), followed by baking; and
(d″) mixing the dried/baked lithium iron phosphate with a carbon powder, followed by milling, or mixing the dried/baked lithium iron phosphate and carbon precursor with a solvent, followed by drying and baking.

13. A cathode mix comprising the lithium iron phosphate according to claim 1 as a cathode active material.

14. A lithium secondary battery comprising a cathode in which the cathode mix according to claim 13 is applied to a current collector.

15. The lithium secondary battery according to claim 14 , wherein the lithium secondary battery is used as a unit battery of a battery module that is a power of a medium to large device.

16. The lithium secondary battery according to claim 15 , wherein the medium to large device is a power tool, an electric vehicle, a hybrid electric vehicle, or an electric golf cart.

17. The method according to claim 10 , wherein the heating is carried out under an inert gas atmosphere.

18. The lithium iron phosphate according to claim 1 , wherein the sulfur (S) is contained in the lithium iron phosphate in an amount of 0.01 to 0.7% by weight, based on the total weight of the lithium iron phosphate.

Assignees

• Lg Chemical Ltd

Inventors

• Choy Sang Hoon
• Lee Yong Tae
• Park Hong Kyu
• Chang Sung-Kyun

Classifications

• H01M10/052

  Li-accumulators · CPC title

• Y02T10/7011

  Cross-Sectional Technologies · mapped topic

• C01B25/45

  containing plural metal, or metal and ammonium · CPC title

• C01B25/375

  of iron · CPC title

• B60L11/1879

  Operations & Transport · mapped topic