Method of preparing inorganic particles and inorganic particles prepared using the same

Abstract

Disclosed is a method of preparing inorganic particles using a hydrothermal synthesis device, including introducing a precursor liquid or slurry stream including a reaction precursor for preparation of an inorganic material into a hydrothermal synthesis reactor, introducing a supercritical liquid stream including water into the hydrothermal synthesis reactor, preparing an inorganic slurry by hydrothermal reaction in the hydrothermal synthesis reactor and discharging the inorganic slurry therefrom, and filtering the discharged inorganic slurry, wherein the precursor liquid or slurry stream includes an NH.sub.3 source at a high temperature of the supercritical liquid stream and thus clogging of the stream in the hydrothermal synthesis reactor is inhibited by pH changes in the hydrothermal reaction.

Claims

1. A method of preparing inorganic particles using a hydrothermal synthesis device, the method comprising: introducing a precursor liquid or slurry stream comprising a reaction precursor for preparation of an inorganic material into a hydrothermal synthesis reactor; introducing at least one supercritical liquid stream comprising high temperature and high pressure water into the hydrothermal synthesis reactor; preparing an inorganic slurry by hydrothermal reaction in the hydrothermal synthesis reactor and discharging the inorganic slurry therefrom; and filtering the discharged inorganic slurry to obtain a filtrate, wherein the precursor liquid or slurry stream comprises an NH.sub.3 source at the high temperature of the supercritical liquid stream and the NH.sub.3 source adjusts the pH of the inorganic slurry to within a range of 3.5 to 8 to inhibit clogging of the stream in the hydrothermal synthesis reactor.

2. The method according to claim 1, wherein the hydrothermal synthesis device comprises a structure in which a precursor liquid or slurry stream containing a precursor for preparation of an inorganic material is included, and a supercritical liquid stream containing high-temperature and high-pressure water is included, and the precursor liquid or slurry stream and the supercritical liquid stream are introduced into the hydrothermal synthesis reactor to undergo hydrothermal reaction and an inorganic slurry as a reaction product is discharged therefrom.

3. The method according to claim 1, wherein an inorganic material of the inorganic slurry is at least one selected from the group consisting of CO.sub.2O.sub.3, Fe.sub.2O.sub.3, LiMn.sub.2O.sub.4, MO.sub.x where M is Fe, Ni, Co, Mn, or Al and x is a number satisfying electroneutrality, MOOH where M is at least one selected from the group consisting of Fe, Ni, Co, Mn, and Al, and A.sub.aM.sub.mX.sub.xO.sub.oS.sub.sN.sub.nF.sub.f where A is at least one selected from the group consisting of Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, and Ba; M comprises at least one transition metal and optionally comprises at least one selected from the group consisting of B, Al, Ga, and In; X is at least one selected from the group consisting of P, As, Si, Ge, Se, Te, and C; O is oxygen; S is sulfur; N is nitrogen; F is fluorine; and a, m, x, o, s, n, and f are each independently a number of 0 or more, satisfying electroneutrality.

4. The method according to claim 3, wherein the inorganic material is Li.sub.aM.sub.bM′.sub.cPO.sub.4 where M is at least one selected from the group consisting of Fe, Ni, Co, and Mn; M′ is at least one selected from the group consisting of Ca, Ti, S, C, and Mg; and a, b, and c are each independently a number of 0 or more, satisfying electroneutrality.

5. The method according to claim 4, wherein the inorganic material is LiFePO.sub.4.

6. The method according to claim 1, wherein a material causing the clogging is γ-Fe.sub.2O.sub.3.

7. The method according to claim 1, wherein the NH.sub.3 source is urea.

8. The method according to claim 1, wherein the hydrothermal synthesis device further comprises a pre-mixer for preparation of a precursor to provide the precursor liquid or slurry stream.

9. The method according to claim 1, wherein an injection direction of the precursor liquid or slurry stream into the reactor forms an angle of 0° to 60° based on a discharge direction of an inorganic slurry stream comprising the inorganic slurry.

10. The method according to claim 9, wherein the injection direction of the precursor liquid or slurry stream forms an angle of 0° to 45° based on the discharge direction of the inorganic slurry stream comprising the inorganic slurry.

11. The method according to claim 1, wherein a ratio of flow rates per hour of the precursor liquid or slurry stream and the supercritical liquid stream is 1:2 to 1:50 (precursor liquid or slurry stream: supercritical liquid stream) on a weight ratio basis.

12. The method according to claim 1, wherein the supercritical liquid stream comprising high-temperature and high-pressure water has a temperature of 100° C. to 700° C. and a pressure of 10 to 550 bar.

13. The method according to claim 1, wherein the introducing at least one supercritical liquid stream comprising high temperature and high pressure water into the hydrothermal synthesis reactor comprises: introducing a first supercritical liquid stream in a first injection direction; and introducing a second supercritical liquid stream in a second injection direction.

14. The method according to claim 13, wherein the first injection direction is facing the second injection direction with respect to an injection direction of the precursor liquid or slurry stream.

15. The method according to claim 13, wherein the first and second injection directions of the first supercritical liquid stream and the second supercritical liquid stream forms an angle of greater than 0° to less than 180° based on a discharge direction of the inorganic slurry stream.

16. The method according to claim 15, wherein each injection direction forms an angle of 10° to 170° based on the discharge direction of the inorganic slurry stream.

17. The method according to claim 1, wherein an injection direction of the precursor liquid or slurry stream and a discharge direction of the inorganic slurry stream are arranged in a straight line.

18. The method according to claim 1, wherein an injection direction of the precursor liquid or slurry stream and a discharge direction of an inorganic slurry stream are not arranged in a straight line.

19. An inorganic slurry prepared using the method according to claim 1.

20. An inorganic material obtained by drying the inorganic slurry according to claim 19.

21. The inorganic material according to claim 20, wherein the inorganic material is used as a cathode active material for a secondary battery.

22. A method of preparing inorganic particles using a hydrothermal synthesis device, the method comprising: introducing a precursor liquid or slurry stream comprising LiOH, FeSO.sub.4, phosphoric acid and an NH3 source introducing at least one supercritical liquid stream comprising high-temperature and high-pressure water into the hydrothermal synthesis reactor; preparing an inorganic slurry by hydrothermal reaction in the hydrothermal synthesis reactor and discharging the inorganic slurry therefrom; and filtering the discharged inorganic slurry; adding sucrose to the filtered discharged inorganic slurry; spray-drying the filtered discharged inorganic slurry to obtain a sucrose-coated LiFePO4 powder; heat treating the sucrose-coated powder to obtain carbon-coated LiFePO.sub.4 that has a substantially pure LiFePO.sub.4 crystal structure; wherein the NH.sub.3 source is at a high temperature of the supercritical liquid stream and adjusts the slurry to a pH between 4 and 9.

23. The method according to claim 1, wherein the NH.sub.3 source adjusts the pH of the inorganic slurry to within a range of 3.5 to 7.8.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawing, in which:

(2) FIG. 1 is a schematic view of a hydrothermal synthesis device according to an embodiment of the present invention;

(3) FIG. 2 is a schematic view of a hydrothermal synthesis device according to another embodiment of the present invention;

(4) FIGS. 3 and 4 are schematic views illustrating a structure of a hydrothermal synthesis device further including a pre-mixer according to another embodiment of the present invention.

BEST MODE

(5) Now, the present invention will be described in more detail with reference to the following examples. These examples are provided only for illustration of the present invention and should not be construed as limiting the scope and spirit of the present invention.

(6) According to the present invention, first, LiOH as a Li precursor, FeSO.sub.4 as an Fe precursor, and H.sub.3PO.sub.4 as a P precursor are mixed in a pre-mixer M.sub.1, hydrothermal synthesis reaction thereamong occurs in a hydrothermal synthesis reactor M.sub.2, and a reaction product is obtained via filtration after a cooling process. In these processes, supercritical water having a high temperature and a high pressure participates in reaction prior to the filtering process and thus it is very difficult to measure pH. Thus, pH of the filtrate may be measured and adjusted to control clogging occurring in the manufacturing processes.

(7) FIG. 1 is a schematic view of a hydrothermal synthesis device according to an embodiment of the present invention. FIG. 2 is a schematic view of a hydrothermal synthesis device according to another embodiment of the present invention.

(8) Referring to FIG. 1, a precursor liquid or slurry stream is introduced into a hydrothermal synthesis reactor 100 in a direction substantially the same as a discharge direction of an inorganic slurry stream and supercritical liquid streams facing each other are introduced from opposite sides into the reactor 100 in a direction perpendicular to the injection direction of the precursor liquid or slurry stream.

(9) In addition, referring to FIG. 2, a precursor liquid or slurry stream is introduced into a hydrothermal synthesis reactor 100 in a direction substantially the same as a discharge direction of an inorganic slurry stream and supercritical liquid streams facing each other are introduced from opposite sides at a predetermined angle θ with respect to the discharge direction of the inorganic slurry stream. The angle θ may be appropriately adjusted within greater than 0 to less than 180 degrees with respect to the discharge direction of the inorganic slurry stream, according to desired reaction atmosphere.

(10) Referring to FIGS. 1 and 2, since the injection direction of the precursor liquid or slurry stream and the discharge direction of the inorganic slurry stream are substantially arranged in a straight line, the precursor liquid or slurry stream considerably maintaining the injection direction reacts with the supercritical stream and an inorganic slurry is thus discharged as a reaction product. Thus, high resistance is not applied near an inlet and a phenomenon in which the edge of the inlet begins to clog may be reduced. Consequently, such configuration may help adjust pH and minimize clogging of the inlet. In addition, in the process of introducing the precursor liquid or slurry stream into the reactor, there is almost no loss of movement in the preceding direction and the amount of the inorganic material in the reaction product is larger than that of a conventional device.

(11) FIGS. 3 and 4 are schematic views illustrating a structure of a hydrothermal synthesis device further including a pre-mixer according to another embodiment of the present invention.

(12) Referring to FIGS. 3 and 4, in another embodiment, a structure of a hydrothermal synthesis device further including a pre-mixer 200 is schematically shown. The present hydrothermal synthesis device has the same basic configuration as that of the devices illustrated in FIGS. 1 and 2, but is different therefrom in that the present hydrothermal synthesis device further includes the pre-mixer 200 for preparing the precursor liquid or slurry stream.

(13) This device prepares a LiFePO.sub.4 inorganic slurry, for example, by mixing a Li precursor, an Fe precursor, a P precursor, and NH.sub.3 in the pre-mixer 200, introducing a precursor liquid or slurry stream obtained therefrom into a reactor, and performing the reaction described with reference to FIGS. 1 and 2.

(14) Hereinafter, the present invention will be described in more detail with reference to the following examples. These examples are provided for illustrative purposes only and should not be construed as limiting the scope and spirit of the present invention.

EXAMPLE 1

(15) 481 g of LiOH—H.sub.2O, 258 g of urea, and 8270 g of distilled water were mixed and dissolved to prepare aqueous solution A. Similarly, 1581 g of FeSO.sub.4-7H.sub.2O, 159 g of sucrose, 661 g of phosphoric acid (85 wt %), and 6640 g of distilled water were mixed and dissolved to prepare aqueous solution B. Subsequently, supercritical water having a pressure of 250 bar and a temperature of 450° C. flowed into a continuous tube-type reactor at a flow rate of 100 g/min under increased temperature and pressure conditions and each of the aqueous solutions A and B flowed thereinto at a flow rate of 15 g/min so as to contact the supercritical water for several seconds and be mixed therewith to induce reaction therebetween. In this regard, reaction occurs such that the aqueous solutions A and B contact to prepare a slurry and then the slurry contacts the supercritical water.

(16) The prepared LiFePO.sub.4 reaction slurry was cooled and filtered at an edge portion of the tube-type reactor to obtain a concentrated LiFePO.sub.4 slurry. In this regard, pH of the filtrate was 7.8 in a normal state. 7 hours after reaction, a difference (P1−P3) between a pressure P3 of a supercritical water tube and a pressure P1 of a raw material injection tube was 0 bar, from which it was confirmed that there was no clogging phenomenon.

(17) Thereafter, the concentration of water in the slurry was adjusted to prepare a slurry containing a solid content of 15 wt %, and sucrose was added thereto in an amount of 15 wt % based on the weight of the solid content and dissolved therein. The obtained slurry was spray-dried to obtain a sucrose-coated LiFePO.sub.4 powder.

(18) The prepared powder was heat-treated at about 700° C. for 10 hours in nitrogen atmosphere to finally obtain a carbon-coated LiFePO.sub.4 powder. As a result of XRD/Rietveld analysis, it was confirmed that the carbon-coated LiFePO.sub.4 powder had a pure LiFePO.sub.4 crystal structure.

EXAMPLE 2

(19) A LiFePO.sub.4 slurry was prepared in the same manner as in Example 1, except that 474 g of LiOH—H.sub.2O, 180 g of urea, and 8350 g of distilled water were mixed and dissolved to prepare aqueous solution A.

(20) In this regard, pH of the filtrate was 5.8 in a normal state. 7 hours after reaction, the difference (P1−P3) between the pressure P3 of the supercritical water tube and the pressure P1 of the raw material injection tube was 0 bar, from which it was confirmed that there was no clogging phenomenon.

(21) Thereafter, the concentration of water in the slurry was adjusted to prepare a slurry containing a solid content of 15 wt %, and sucrose was added thereto in an amount of 15 wt % based on the weight of the solid content and dissolved therein. The obtained slurry was spray-dried to obtain a sucrose-coated LiFePO.sub.4 powder.

(22) The prepared powder was heat-treated at about 700° C. for 10 hours in nitrogen atmosphere to finally obtain a carbon-coated LiFePO.sub.4 powder. As a result of XRD/Rietveld analysis, it was confirmed that the carbon-coated LiFePO.sub.4 powder had a pure LiFePO.sub.4 crystal structure.

Comparative Example 1

(23) A LiFePO.sub.4 slurry was prepared in the same manner as in Example 1, except that 601 g of LiOH—H.sub.2O, 519 g of ammonia water (29 wt %), and 7890 g of distilled water were mixed and dissolved to prepare aqueous solution A.

(24) In this regard, pH of the filtrate was 9.8 in a normal state. 7 hours after reaction, the difference (P1−P3) between the pressure P3 of the supercritical water tube and the pressure P1 of the raw material injection tube was 12 bar, from which it was confirmed that clogging severely occurred.

(25) Thereafter, the concentration of water in the slurry was adjusted to prepare a slurry containing a solid content of 15 wt %, and sucrose was added thereto in an amount of 15 wt % based on the weight of the solid content and dissolved therein. The obtained slurry was spray-dried to obtain a sucrose-coated LiFePO.sub.4 powder.

(26) The prepared powder was heat-treated at about 700° C. for 10 hours in nitrogen atmosphere to finally obtain a carbon-coated LiFePO.sub.4 powder. As a result of XRD/Rietveld analysis, it was confirmed that approximately 10 wt % of Fe.sub.2O.sub.3 (maghemite) phase in addition to the LiFePO.sub.4 phase was present.

Comparative Example 2

(27) A LiFePO.sub.4 slurry was prepared in the same manner as in Example 1, except that 474 g of LiOH—H.sub.2O, 347 g of urea, and 8175 g of distilled water were mixed and dissolved to prepare aqueous solution A.

(28) In this regard, pH of the filtrate was 10.1 in a normal state. 7 hours after reaction, the difference (P1−P3) between the pressure P3 of the supercritical water tube and the pressure P1 of the raw material injection tube was 14 bar, from which it was confirmed that clogging severely occurred.

(29) Thereafter, the concentration of water in the slurry was adjusted to prepare a slurry containing a solid content of 15 wt %, and sucrose was added thereto in an amount of 15 wt % based on the weight of the solid content and dissolved therein. The obtained slurry was spray-dried to obtain a sucrose-coated LiFePO.sub.4 powder.

(30) The prepared powder was heat-treated at about 700° C. for 10 hours in nitrogen atmosphere to finally obtain a carbon-coated LiFePO.sub.4 powder. As a result of XRD/Rietveld analysis, it was confirmed that approximately 10 wt % of Fe.sub.2O.sub.3 (maghemite) phase in addition to the LiFePO.sub.4 phase was present.

Comparative Example 3

(31) A LiFePO.sub.4 slurry was prepared in the same manner as in Example 1, except that 415 g of LiOH—H.sub.2O, 159 g of urea, and 8425 g of distilled water were mixed and dissolved to prepare aqueous solution A.

(32) In this regard, pH of the filtrate was 3.3 in a normal state. 7 hours after reaction, the difference (P1−P3) between the pressure P3 of the supercritical water tube and the pressure P1 of the raw material injection tube was 0 bar, from which it was confirmed that there was no clogging phenomenon.

(33) Thereafter, the concentration of water in the slurry was adjusted to prepare a slurry containing a solid content of 15 wt %, and sucrose was added thereto in an amount of 15 wt % based on the weight of the solid content and dissolved therein. The obtained slurry was spray-dried to obtain a sucrose-coated LiFePO.sub.4 powder.

(34) The prepared powder was heat-treated at about 700° C. for 10 hours in nitrogen atmosphere to finally obtain a carbon-coated LiFePO.sub.4 powder. As a result of XRD/Rietveld analysis, it was confirmed that a considerable amount of other impurities in addition to the LiFePO.sub.4 phase were present.

(35) Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.