Method for preparing lithium iron phosphate nanopowder

Patent metadata

Field	Value
Publication number	US-9865875-B2
Application number	US-201414510370-A
Country	US
Kind code	B2
Filing date	Oct 9, 2014
Priority date	Jan 10, 2013
Publication date	Jan 9, 2018
Grant date	Jan 9, 2018

Abstract

The present invention relates to a method for preparing a lithium iron phosphate nanopowder, including the steps of (a) preparing a mixture solution by adding a lithium precursor, an iron precursor and a phosphorus precursor in a glycerol solvent, and (b) putting the mixture solution into a reactor and heating to prepare the lithium iron phosphate nanopowder under pressure conditions of 1 bar to 10 bar, and a lithium iron phosphate nanopowder prepared by the method. When compared to a common hydrothermal synthesis method, a supercritical hydrothermal synthesis method and a glycothermal synthesis method, a reaction may be performed under a relatively lower pressure. Thus, a high temperature/high pressure reactor is not necessary and process safety and economic feasibility may be secured. In addition, a lithium iron phosphate nanopowder having uniform particle size and effectively controlled particle size distribution may be easily prepared.

First claim

What is claimed is:

1. A method for preparing a lithium iron phosphate nanopowder, comprising the steps of: (a) preparing a non-aqueous mixture solution by adding a lithium precursor, an iron precursor and a phosphorus precursor in a glycerol solvent; and (b) putting the non-aqueous mixture solution into a reactor and heating to prepare the lithium iron phosphate nanopowder under pressure conditions of 1 bar to 10 bar, wherein the reactor is an open reactor or a closed reactor connected to a reflux, and wherein a particle diameter of the lithium iron phosphate nanopowder is from 30 nm to 300 nm,
wherein the lithium iron phosphate nanopowder prepared in Step (b) is sequentially conducted a washing step and a drying step.

2. The method for preparing a lithium iron phosphate nanopowder of claim 1 , further comprising the step of (c) heat treating the lithium iron phosphate nanopowder thus prepared to form a coating layer at a portion or a whole of a surface of an individual particle of the nanopowder.

3. The method for preparing a lithium iron phosphate nanopowder of claim 1 , wherein Step (b) is performed at a temperature less than or equal to a boiling point of the glycerol solvent.

4. The method for preparing a lithium iron phosphate nanopowder of claim 1 , wherein Step (b) is performed at a temperature range of 150° C. to 290° C.

5. The method for preparing a lithium iron phosphate nanopowder of claim 1 , wherein Step (b) is performed for 1 to 72 hours.

6. The method for preparing a lithium iron phosphate nanopowder of claim 1 , wherein the lithium precursor is at least one selected from lithium acetate dihydrate (CH 3 COOLi.2H 2 O), lithium hydroxide monohydrate (LiOH.H 2 O), lithium hydroxide (LiOH), lithium carbonate (Li 2 CO 3 ), lithium phosphate (Li 3 PO 4 ), lithium phosphate dodecahydrate (Li 3 PO 4 .12H 2 O), lithium oxalate (Li 2 C 2 O 4 ), or a mixture thereof.

7. The method for preparing a lithium iron phosphate nanopowder of claim 1 , wherein the iron precursor is at least one selected from iron citrate (FeC 6 H 5 O 7 ), iron citrate hydrate (FeC 6 H 5 O 7 .nH 2 O), ferrous sulfate heptahydrate (FeSO 4 .7H 2 O), iron(II) oxalate dihydrate (FeC 2 O 4 .2H 2 O), iron acetyl acetonate (Fe(C 5 H 7 O 2 ) 3 ), iron phosphate dihydrate (FePO 4 .2H 2 O), ferric hydroxide (FeO(OH)), or a mixture thereof.

8. The method for preparing a lithium iron phosphate nanopowder of claim 1 , wherein the phosphorus precursor is at least one selected from tri-ammonium phosphate trihydrate ((NH 4 ) 3 PO 4 .3H 2 O), ammonium phosphate ((NH 4 ) 2 HPO 4 ), ammonium dihydrogen phosphate (NH 4 H 2 PO 4 ), phosphoric acid (H 3 PO 4 ), or a mixture thereof.

9. The method for preparing a lithium iron phosphate nanopowder of claim 2 , wherein the heat treating is performed by heating to a temperature range of 400° C. to 900° C.

10. The method for preparing a lithium iron phosphate nanopowder of claim 1 , wherein the washing step is performed by sequentially using acetone and methanol.

11. A lithium iron phosphate nanopowder comprising the lithium iron phosphate nanopowder prepared according to claim 1 and having an olivine crystal structure.

12. The lithium iron phosphate nanopowder of claim 11 , wherein a particle size distribution of the lithium iron phosphate nanopowder is less than or equal to 50% of an average value of the particle diameter.

13. The lithium iron phosphate nanopowder of claim 11 , further comprising a carbon coating layer or a glassy lithium compound coating layer on a surface of a particle of the lithium iron phosphate nanopowder.

14. The lithium iron phosphate nanopowder of claim 13 , wherein a thickness of the carbon coating layer is less than or equal to 10 nm.

15. A cathode active material comprising the lithium iron phosphate nanopowder according to claim 11 .

16. The cathode active material of claim 15 , further comprising a conductive agent, a binder and a filler.

17. A cathode for a lithium secondary battery comprising the cathode active material of claim 15 .

18. A lithium secondary battery comprising the cathode of claim 17 , an anode, a separator and a non-aqueous electrolyte comprising a lithium salt.

Assignees

• Lg Chemical Ltd

Inventors

• Jun In Kook
• Cho Seung Beom
• Oh Myoung Hwan

Classifications

• C01P2002/30

  Three-dimensional structures · CPC title

• H01M2004/028

  Positive electrodes · CPC title

• C01P2004/51

  Particles with a specific particle size distribution · CPC title

• H01M4/587

  for inserting or intercalating light metals · CPC title

• H01M10/052

  Li-accumulators · CPC title