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

Patent metadata

Field	Value
Publication number	US-9812707-B2
Application number	US-201414251333-A
Country	US
Kind code	B2
Filing date	Apr 11, 2014
Priority date	Apr 21, 2010
Publication date	Nov 7, 2017
Grant date	Nov 7, 2017

Abstract

Disclosed is lithium iron phosphate having 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 particle surface of the lithium iron phosphate containing a predetermined amount of sulfur (S).

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, wherein the lithium iron phosphate has a composition represented by the following Formula 1 and carbon (C) is coated on the particle surface of the lithium iron phosphate containing a predetermined amount of sulfur (S):
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, and
−0.5≦a≦+0.5, 0≦x≦0.5, 0≦b≦0.1
wherein the sulfur (S) is contained at an amount of 0.1 to 2% by weight, based on the total weight of the lithium iron phosphate, wherein the sulfur (S) is derived from a precursor for preparation of the lithium iron phosphate, and
wherein the sulfur and the carbon are present in the form of a structure in which carbon is coated on the surface of lithium iron phosphate particles and the sulfur is contained inside of lithium iron phosphate particles.

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 (C) 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 particle surface of the lithium iron phosphate to a thickness of 2 to 50 nm.

5. Lithium iron phosphate having an olivine crystal structure wherein the lithium iron phosphate has a composition represented by the following Formula 2 and carbon (C) is coated on the particle surface of the lithium iron phosphate containing a predetermined amount of sulfur (S):
Li (1−a−b) Fe a/2 M′ b/2 Fe 1−c M″ c P 1−d X d O 4−e S e   (2)

wherein M′ is at least one selected from the group consisting of Mg, Ni, Co, Mn, Ti, Cr, Cu, V, Ce, Sn, Ba, Ca, Sr and Zn;
M″ is at least one selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Cr, Cu, V, Ce, Sn, Ba, Ca, Sr and Zn;
X is at least one selected from the group consisting of As, Sb, Bi, Mo, V, Nb and Te; and
0≦a≦0.6, 0≦b≦0.6, 0≦c≦1, 0≦d≦0.05, 0≦e≦3.5,
wherein the sulfur (S) is contained in an amount of 0.1 to 2% by weight, based on the total weight of the lithium iron phosphate, and is derived from a precursor for preparation of the lithium iron phosphate, and
wherein the sulfur and the carbon are present in the form of a structure in which carbon is coated on the surface of lithium iron phosphate particles and the sulfur is contained inside of lithium iron phosphate particles.

6. A cathode mix comprising the lithium iron phosphate according to claim 5 as a cathode active material.

7. A method for preparing the lithium iron phosphate according to claim 1 comprising:
(a) primarily mixing a lithium precursor, an iron (Fe) precursor and a phosphorus precursor as starting materials, wherein the lithium precursor is Li 2 CO 3 , Li(OH), Li(OH)H 2 O or LiNO 3 , wherein the iron precursor is FeSO 4 , FeC 2 O 4 .2H 2 O or FeCl 2 , wherein the phosphorus precursor is H 3 PO 4 , NH 4 H 2 PO 4 , (NH 4 ) 2 HPO 4 , P 2 O 5 ;
(b) secondarily mixing a mixture obtained in step (a) with supercritical or subcritical water to synthesize lithium iron phosphate;
(c) mixing a synthesized lithium iron phosphate with a carbon precursor and drying a resulting mixture, wherein the carbon precursor is a polyol-type carbon-containing precursor; and
(d) heating the mixture of the lithium iron phosphate and the carbon precursor.

8. A method for preparing the lithium iron phosphate according to claim 1 comprising:
(a′) primarily mixing a lithium precursor, an iron (Fe) precursor and a phosphorus precursor as starting materials, wherein the lithium precursor is Li 2 CO 3 , Li(OH), Li(OH)H 2 O or LiNO 3 , wherein the iron precursor is FeSO 4 , FeC 2 O 4 .2H 2 O or FeCl 2 , wherein the phosphorus precursor is H 3 PO 4 , NH 4 H 2 PO 4 , (NH 4 ) 2 HPO 4 , P 2 O 5 ;
(b′) secondarily mixing the mixture obtained in step (a′) with supercritical or subcritical water to synthesize lithium iron phosphate, followed by drying;
(c′) heating a synthesized lithium iron phosphate; and
(d′) milling the lithium iron phosphate and a carbon powder.

9. The method according to claim 7 , wherein the heating is carried out under an inert gas atmosphere.

10. The method according to claim 7 , wherein the synthesis of the lithium iron phosphate is carried out by a continuous reaction process.

11. The method according to claim 8 , wherein the heating is carried out under an inert gas atmosphere.

12. The method according to claim 8 , wherein the synthesis of the lithium iron phosphate is carried out by a continuous reaction process.

13. A method for preparing the lithium iron phosphate according to claim 1 comprising:
(a″) synthesizing lithium iron phosphate using a lithium precursor, an iron (Fe) precursor and a phosphorus precursor as starting materials by a coprecipitation or solid phase reaction, wherein the lithium precursor is Li 2 CO 3 , Li(OH), Li(OH)H 2 O or LiNO 3 , wherein the iron precursor is FeSO 4 , FeC 2 O 4 .2H 2 O or FeCl 2 , wherein the phosphorus precursor is H 3 PO 4 , NH 4 H 2 PO 4 , (NH 4 ) 2 HPO 4 , P 2 O 5 ;
(b″) adding a synthesized lithium iron phosphate to a dispersion chamber containing a sulfur-containing compound, followed by stirring;
(c″) drying a mixture obtained in step (b″), followed by baking; and
(d″) mixing a dried/baked lithium iron phosphate with a carbon powder, followed by milling, or mixing a dried/baked lithium iron phosphate and carbon precursor with a solvent, followed by drying and baking, wherein the carbon precursor is a polyol-type carbon-containing precursor.

14. The lithium iron phosphate according to claim 4 , wherein the carbon is coated on the particle surface of the lithium iron phosphate to a thickness of 3 to 10 nm.

15. The lithium iron phosphate according to claim 1 , wherein the precursor is an iron precursor of FeSO 4 .

Assignees

• Lg Chemical Ltd

Inventors

• Noh Hyun Kuk
• Park Hong Kyu
• Park Cheol-Hee
• Park su-min
• Lee Jieun

Classifications

• Y02E60/10

  Energy storage using batteries · CPC title

• C01B25/26

  Phosphates (perphosphates C01B15/16) · CPC title

• C01B25/45

  containing plural metal, or metal and ammonium · CPC title

• H01M4/1397

  of electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy · CPC title

• H01M4/0416

  involving impregnation with a solution, dispersion, paste or dry powder (H01M4/0438 takes precedence) · CPC title