Solvothermal method for making lithium iron phosphate

Patent metadata

Field	Value
Publication number	US-2017320737-A1
Application number	US-201715658392-A
Country	US
Kind code	A1
Filing date	Jul 25, 2017
Priority date	Jan 27, 2015
Publication date	Nov 9, 2017
Grant date	—

Abstract

A solvothermal method for making a lithium iron phosphate is disclosed. The waste liquid of a solvothermal reaction is treated synthetically by flash evaporation and a centrifugal separation to separate the water, the organic solvent, and the lithium sulfate, which is a byproduct from each other. One part of the separated organic solvent is reused as a reaction material of the solvothermal reaction to form a organic solvent recycle circuit. The other part of the separated organic solvent is mixed with the separated water to be used as a washing liquid. The washing liquid is retreated by flash evaporation and centrifugal separation to obtain the water and the organic solvent again to form a washing liquid circuit.

First claim

What is claimed is:

1 . A solvothermal method for making lithium iron phosphate, comprising:
providing a precursor solution for synthesizing lithium iron phosphate, wherein the precursor solution comprises a solvent mixture comprising an organic solvent and water; solvothermal reacting the precursor solution to obtain a first suspension liquid; filtering the first suspension liquid to obtain a wet lithium iron phosphate material and a filtrate, wherein the filtrate comprises the organic solvent, the water, and a byproduct of the solvothermal reacting; flash evaporating the filtrate to respectively obtain the water and a second suspension liquid, wherein the second suspension liquid comprises the organic solvent and the byproduct suspended in the organic solvent; separating the byproduct from the organic solvent of the second suspension liquid; mixing the water obtained from flash evaporating the filtrate and a part of the organic solvent obtained from separating the byproduct from the organic solvent of the second suspension liquid to obtain a first washing liquid, and countercurrent washing the wet lithium iron phosphate material by using the first washing liquid to obtain a purified wet lithium iron phosphate material and a second washing liquid; and drying the purified wet lithium iron phosphate material to obtain the lithium iron phosphate.

2 . The solvothermal method of claim 1 further comprising reintroducing the second washing liquid and flash evaporating the second washing liquid together with the filtrate.

3 . The solvothermal method of claim 2 , wherein the second washing liquid and the filtrate have the same composition.

4 . The solvothermal method of claim 1 , wherein the providing a precursor solution for synthesizing lithium iron phosphate comprises:
providing the organic solvent, ferrous sulfate, lithium hydroxide, and a phosphoric acid solution, wherein the phosphoric acid solution comprises water and phosphoric acid; mixing the organic solvent, the ferrous sulfate, the lithium hydroxide, and the phosphoric acid solution to obtain the precursor solution.

5 . The solvothermal method of claim 4 , wherein the organic solvent and the water are miscible with each other, the ferrous sulfate and the lithium hydroxide are dissolvable in the organic solvent, and the byproduct is insoluble in the organic solvent.

6 . The solvothermal method of claim 4 , wherein the organic solvent is selected from the group consisting of ethanol, ethylene glycol, glycerol, diethylene glycol, triethylene glycol, tetraethylene glycol, butanetriol, n-butanol, isobutanol, and combinations thereof.

7 . The solvothermal method of claim 4 , wherein a molar ratio of the lithium hydroxide to the ferrous sulfate in the precursor solution is equal to or larger than 3:1.

8 . The solvothermal method of claim 4 , wherein the byproduct is lithium sulfate.

9 . The solvothermal method of claim 4 , wherein the mixing the organic solvent, the ferrous sulfate, the lithium hydroxide, and the phosphoric acid solution comprises:
mixing one part of the organic solvent and the ferrous sulfate to form a first mixture solution; mixing another part of the organic solvent and the lithium hydroxide to form a second solution; and mixing the first mixture solution, the second mixture solution, and the phosphoric acid solution to form the precursor solution.

10 . The solvothermal method of claim 1 , wherein in the solvothermal reacting the precursor solution to obtain a first suspension liquid, the solvothermal reacting is carried out at a temperature in a range from about 120° C. to about 300° C., and under a pressure in a range from about 0.2 MPa to about 2.0 Mpa for about 0.5 hours to about 10 hours.

11 . The solvothermal method of claim 1 , wherein in the filtering the first suspension liquid to obtain a wet lithium iron phosphate material and a filtrate, the first suspension liquid is filtered at a temperature in a range from about 80° C. to about 180° C.

12 . The solvothermal method of claim 11 , wherein the first suspension liquid is filtered at a temperature in a range from about 100° C. to about 140° C.

13 . The solvothermal method of claim 1 , wherein the flash evaporating the filtrate to respectively obtain the water and a second suspension liquid comprises:
preheating the filtrate under atmospheric pressure to a temperature in a range from about 100° C. to about 160° C.; and transferring the filtrate preheated to the temperature in the range from about 100° C. to about 160° C. into a liquid-vapor separator with a pressure in a range from about 3 kPa to about 60 kPa.

14 . The solvothermal method of claim 1 , wherein in the separating the byproduct from the organic solvent of the second suspension liquid, the lithium sulfate is separated from the organic solvent by a centrifugal separation method.

15 . The solvothermal method of claim 1 , wherein in the mixing the water obtained from flash evaporating the filtrate and a part of the organic solvent obtained from separating the byproduct from the organic solvent of the second suspension liquid, the wet lithium iron phosphate material is washed by a three-stage countercurrent washing method.

16 . The solvothermal method of claim 1 , wherein the second suspension liquid further comprises lithium phosphate.

17 . The solvothermal method of claim 1 , wherein the organic solvent separated from the second suspension liquid is reused in the precursor solution.

Assignees

• Jiangsu Huadong Inst Of Li-Ion Battery Co Ltd
• Univ Tsinghua

Inventors

• He xiang-ming
• Xu cheng-hao
• Wang Li
• Li Jian-Jun
• Shang yu-ming
• Gao Jian
• Wang yao-wu

Classifications

• C01B25/45 Primary

  containing plural metal, or metal and ammonium · CPC title

• H01M2004/028

  Positive electrodes · CPC title

• H01M10/0525

  Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries · CPC title

• H01M4/5825

  Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines · CPC title

• Y02E60/10

  Energy storage using batteries · CPC title