WO2014017729A1 - Method for preparing electrode material using hydrothermal synthesis process - Google Patents

Method for preparing electrode material using hydrothermal synthesis process Download PDF

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WO2014017729A1
WO2014017729A1 PCT/KR2013/003554 KR2013003554W WO2014017729A1 WO 2014017729 A1 WO2014017729 A1 WO 2014017729A1 KR 2013003554 W KR2013003554 W KR 2013003554W WO 2014017729 A1 WO2014017729 A1 WO 2014017729A1
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electrode material
pressure
containing stream
mixture
temperature
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PCT/KR2013/003554
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French (fr)
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Ki Taeg Jung
Kyu Ho Song
Kee Do Han
Wan Jae Myeong
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Hanwha Chemical Corporation
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0471—Processes of manufacture in general involving thermal treatment, e.g. firing, sintering, backing particulate active material, thermal decomposition, pyrolysis
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
    • H01B1/02—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors mainly consisting of metals or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/049—Manufacturing of an active layer by chemical means
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a method of preparing an electrode material and, more particularly, to a method of preparing an electrode material using a hydrothermal synthesis process.
  • a dry burning method and a wet precipitation method are widely known to be conventional methods of preparing an electrode material.
  • the dry burning method is used to prepare an electrode material by mixing an oxide or hydroxide of a transition metal such as cobalt (Co), etc., with a lithium source, that is, lithium carbonate or lithium hydroxide, under dry conditions, and then burning the mixture at a high temperature of 700 ⁇ 1000°C for 5 ⁇ 48 hr.
  • the dry burning method has typically mainly been utilized to prepare the metal oxide and is advantageous in terms of it being a relatively easy approach, but it is difficult to uniformly mix feed materials, making it difficult to obtain a single-phase product. Furthermore, in the case of a multi-component electrode material comprising two or more transition metals, it is difficult to uniformly arrange two or more elements at an atom level. Moreover, the case of doping with or substitution with a specific metal component to improve electrochemical performance is problematic because it is difficult to uniformly mix the specific metal component added in a small amount, and also because pollution may be caused in the course of grinding and sorting to obtain particles having a desired size.
  • the wet precipitation method is used to prepare an electrode material by dissolving a salt containing a transition metal such as cobalt (Co), etc., in water, adding an alkali to the salt solution so that the salt solution is precipitated into a transition metal hydroxide, and filtering and drying the precipitate, which is then mixed with a lithium source, that is, lithium carbonate or lithium hydroxide, under dry conditions, and then burned at a high temperature of 700 ⁇ 1000°C for 1 ⁇ 48 hr.
  • a lithium source that is, lithium carbonate or lithium hydroxide
  • the wet precipitation method is known to easily obtain a uniform mixture by co-precipitating two or more transition metal elements, but is problematic because a precipitation reaction requires a long period of time, the preparation process is complicated, and waste acids and the like are generated as byproducts.
  • a variety of methods including a sol-gel method, a hydrothermal method, a spray pyrolysis method, an ion exchange method, etc., have been proposed as methods of preparing an electrode material for a lithium secondary battery.
  • a batch type hydrothermal synthesis method cannot accomplish continuous production, undesirably making it difficult to achieve mass production and increasing the production cost.
  • energy is consumed in a large amount relative to the throughput, and particles produced in the synthesis process equipment may accumulate, undesirably decreasing equipment efficiency, making it difficult to obtain nano-sized particles, and lowering crystallinity.
  • the particle size of a cell material has a great influence on cell performance and cell fabrication, it is required to obtain nano-sized primary particles and to narrow the particle size distribution in the synthesis process.
  • an object of the present invention is to provide a method of continuously synthesizing an electrode material using a hydrothermal synthesis process, wherein synthesis conditions are maintained stable, operation stability of the synthesis process is ensured, and mass production and energy saving are possible.
  • the present invention provides a method of preparing an electrode material using a hydrothermal synthesis process, comprising (a) mixing an electrode material precursor and high-temperature, high-pressure water so as to react with each other, thus producing an electrode material-containing stream, (b) cooling the electrode material-containing stream through a heat exchanger including a plurality of shell sides or a plurality of heat exchangers connected in series, (c) reducing the pressure of the cooled electrode material-containing stream using a pressure reducer, and (d) concentrating the electrode material-containing stream at the reduced pressure using a concentrator, thus producing a concentrated electrode material.
  • heat may be recovered from the stream in (b) by the heat exchanger, and may be used to preheat the water in order to make the high-temperature, high-pressure water in (a).
  • (a) to (d) may be performed using a continuous synthesis process.
  • (a) may comprise (a-1) preparing a first mixture comprising at least one metal precursor selected from the group consisting of Group 2 elements, transition metals, Group 12 elements, and Group 13 elements, (a-2) preparing a second mixture comprising a lithium precursor and an alkalizing agent, and (a-3) mixing the first mixture, the second mixture, and the high-temperature, high-pressure water so as to react with each other, thus producing the electrode material-containing stream.
  • (a-3) may be performed by simultaneously mixing the first mixture, the second mixture, and the high-temperature, high-pressure water.
  • (a-3) may comprise (a-3-1) mixing the first mixture and the second mixture, and (a-3-2) mixing the mixture obtained in (a-3-1) with the high-temperature, high-pressure water.
  • (a-3) may be performed at a pressure of 150 ⁇ 700 bar and at a temperature of 200 ⁇ 700°C.
  • (a-3) may be performed under subcritical or supercritical conditions.
  • the high-temperature, high-pressure water in (a-3) may be subcritical water or supercritical water.
  • a precursor of iron (Fe) which is the transition metal may be at least one selected from the group consisting of FeSO 4 , Fe(NO 3 ) 2 , FeC 2 O 4 ⁇ 2H 2 O, and FeCl 2 .
  • the first mixture may further include a multi-acid compound.
  • the multi-acid compound may be at least one selected from the group consisting of H 3 PO 4 , NH 4 H 2 PO 4 , (NH 4 ) 2 HPO 4 and P 2 O 5 .
  • the lithium (Li) precursor may be at least one selected from the group consisting of Li 2 CO 3 , Li(OH), Li(OH) ⁇ xH 2 O, LiCl and LiNO 3 .
  • the alkalizing agent may be at least one selected from the group consisting of alkali metal hydroxides, alkaline earth metal hydroxides, and ammonia compounds.
  • the first mixture may further include a reducing agent.
  • the reducing agent may be at least one selected from the group consisting of oxalic acid, sugar, fructose, glucose, formic acid, and ascorbic acid (Vitamin C).
  • (c) may be performed so that the pressure is reduced to 1 ⁇ 100 bar.
  • the concentrated electrode material using the concentrator in (d) may have a concentration of 1 ⁇ 60 wt%.
  • the electrode material may be any one selected from the group consisting of an anode active material and a cathode active material.
  • an electrode material can be prepared using a hydrothermal synthesis process at high temperature and high pressure, thereby stably maintaining a continuous synthesis process, enabling mass production and ensuring the operation stability of the synthesis process.
  • a concentrator is disposed downstream of a pressure reducer, a low-pressure concentrator can be applied, thus reducing the preparation cost, and heat recovery efficiency can be increased using a plurality of heat exchangers, thus exhibiting energy saving effects.
  • FIG. 1 is a flowchart illustrating a process of preparing an electrode material using a hydrothermal synthesis process according to the present invention
  • FIG. 2 is a schematic view illustrating an apparatus for preparing an electrode material using a hydrothermal synthesis process according to the present invention
  • FIG. 3 is a schematic view illustrating a plurality of heat exchangers in which a double pipe type heat exchanger (a) and a shell-and-tube type heat exchanger (b) are connected in series;
  • FIG. 4 is a schematic view illustrating a plurality of heat exchangers in which two shell-and-tube type heat exchangers (a, b) are connected in series;
  • FIG. 5 is a schematic view illustrating a plurality of heat exchangers in which two double pipe type heat exchangers (a, b) are connected in series;
  • FIG. 6 is a schematic view illustrating a shell-and-tube type heat exchanger in which the shell side of the heat exchanger is divided into two;
  • FIG. 7 is a schematic view illustrating a shell-and-tube type heat exchanger in which the shell side of the heat exchanger is divided into two;
  • FIG. 8 is XRD data illustrating the crystalline structure of LiFePO 4 synthesized in Example 1.
  • the present invention may be variously modified, and may have a variety of embodiments, and is intended to illustrate specific embodiments. However, the following description does not limit the present invention to specific embodiments, and should be understood to include all variations, equivalents or substitutions within the spirit and scope of the present invention. Furthermore, in the description of the present invention, when it is determined that the detailed description of the related art would obscure the gist of the present invention, the description thereof will be omitted.
  • first a first component
  • second a second component
  • first component a first component
  • first component a second component
  • first component a first component
  • second component a second component
  • the singular expression includes a plural expression.
  • the terms “include” or “have” are used to designate the presence of features, numbers, steps, operations, components, parts or combinations thereof described in the specification, and should be understood so as not to exclude the presence or additional probability of one or more different features, numbers, steps, operations, components, parts or combinations thereof.
  • FIGS. 1 and 2 a method of preparing an electrode material using a hydrothermal synthesis process according to the present invention is described with reference to FIGS. 1 and 2.
  • the method of preparing an electrode material using a hydrothermal synthesis process includes (a) mixing an electrode material precursor and high-temperature, high-pressure water so as to react with each other, thus producing an electrode material-containing stream; (b) cooling the electrode material-containing stream through a heat exchanger including a plurality of shell sides or through a plurality of heat exchangers connected in series; (c) reducing the pressure of the cooled electrode material-containing stream using a pressure reducer; and (d) concentrating the electrode material-containing stream at the reduced pressure using a concentrator, thus producing a concentrated electrode material.
  • Step (a) may include (a-1) preparing a first mixture comprising at least one metal precursor selected from the group consisting of Group 2 elements, transition metals, Group 12 elements, and Group 13 elements; (a-2) preparing a second mixture comprising a lithium precursor and an alkalizing agent; and (a-3) mixing the first mixture, the second mixture, and the high-temperature, high-pressure water so as to react with each other, thus producing the electrode material-containing stream.
  • the metal precursor may include a precursor of a Group 2 element, a transition metal, a Group 12 element, or a Group 13 element, which may be used alone or in mixtures of two or more.
  • the transition metal may also include zinc (Zn), cadmium (Cd), and mercury (Hg), as Group 12 elements.
  • the transition metal precursor includes any one or a mixture of two or more selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo precursors and combinations thereof.
  • any compound may be used without particular limitation so long as it is a salt including the above metal and is able to be ionized.
  • a water-soluble compound Preferably useful is a water-soluble compound.
  • the transition metal precursor compound include salts, such as alkoxides, nitrates, acetates, halides, hydroxides, oxides, carbonates, oxalates, sulfates, and combinations thereof, each of which has the above metal.
  • Particularly useful is a nitrate, sulfate, or acetate.
  • compounds e.g. Ni-Mn, Ni-Co, Ni-Mn-Co and the like
  • Ni-Mn, Ni-Co, Ni-Mn-Co and the like including any one or a combination of two or more of the above transition metals may be used.
  • the first mixture, the second mixture, and the high-temperature, high-pressure water are mixed using a mixer 1 and reacted using a reactor 2, thus producing the electrode material-containing stream (a-3).
  • (a-3) producing the electrode material-containing stream preferably includes (a-3-1) mixing the first mixture and the second mixture; and (a-3-2) mixing the mixture obtained in (a-3-1) with the high-temperature, high-pressure water.
  • the mixer 1 and the reactor 2 are separated, so that mixing and reaction are separately performed, but the scope of the present invention is not limited thereto. In some cases, these two devices are provided integratedly, so that mixing and reaction may be simultaneously carried out, and also may be conducted using a continuous synthesis process.
  • the high-temperature, high-pressure water is preferably subcritical water or supercritical water, and the high-temperature, high-pressure water may include another material, such as an additive, etc., within a range that is adapted for purposes of the present invention.
  • (a-3) may be performed at a pressure of 150 ⁇ 700 bar, preferably 200 ⁇ 400 bar, and a temperature of 200 ⁇ 700°C, preferably 250 ⁇ 500°C. If the pressure is less than 150 bar, reactivity may decrease, undesirably making it difficult to obtain single-phase particles having uniform quality. In contrast, if the pressure exceeds 700 bar, the material cost for the preparation apparatus may increase, undesirably excessively increasing the equipment cost. In addition, if the temperature is lower than 200°C, it is difficult to synthesize the nano-sized particles. In contrast, if the temperature is higher than 700°C, the material cost for the equipment becomes too high.
  • (a-3) may be performed under subcritical or supercritical conditions.
  • the supercritical point of water is reached when the temperature is 374°C and the pressure is 220 bar.
  • supercritical water preferably indicates water under conditions of 374°C or higher and 220 bar or more.
  • subcritical water preferably indicates water under conditions of 250°C or higher and 200 bar or more.
  • the first mixture may further include a multi-acid compound, and the multi-acid compound may be at least one selected from the group consisting of H 3 PO 4 , NH 4 H 2 PO 4 , (NH 4 ) 2 HPO 4 and P 2 O 5 .
  • the multi-acid compound is preferably a phosphoric acid compound, and the phosphoric acid compound is preferably used as a feed upon preparing an olivine structured electrode material.
  • the first mixture may further include a reducing agent to prevent oxidation of the electrode material precursor, etc., during the hydrothermal synthesis process, and also to prevent oxidation of the produced electrode material.
  • the reducing agent may be at least one selected from the group consisting of formic acid, oxalic acid, sugar, fructose, and ascorbic acid (Vitamin C).
  • the carbonaceous material such as sugar may be used in an amount of 2 ⁇ 30 wt% based on the weight of the metal precursor.
  • the lithium (Li) precursor may be at least one selected from the group consisting of Li 2 CO 3 , Li(OH), Li(OH) ⁇ xH 2 O, LiCl and LiNO 3 .
  • the amount of the lithium precursor is set at a molar ratio of 1.0 ⁇ 20 times, and preferably 1.0 ⁇ 10 times relative to the amount of the metal precursor. If the amount of the lithium precursor is smaller than 1.0 times, the metal precursor that does not react with the metal lithium, for example, impurities such as oxides and the like, may be produced and thus the purity of the product may decrease. In contrast, if the amount of the lithium precursor is greater than 20 times, lithium may remain and thus should be recovered from the discharged solution or should be disposed of as waste, undesirably lowering profitability.
  • the alkalizing agent may be at least one selected from the group consisting of alkali metal hydroxides, alkaline earth metal hydroxides, and ammonia compounds.
  • the alkalizing agent facilitates at least one transition metal compound to be hydrolyzed with a hydroxide and precipitated, and any compound may be used without particular limitation so long as it makes the reaction solution alkaline.
  • Non-limited examples of the alkalizing agent may include alkali metal hydroxides (NaOH, KOH, etc.), alkaline earth metal hydroxides (Ca(OH) 2 , Mg(OH) 2 , etc.), ammonia compounds (aqueous ammonia, ammonium nitrate, etc.), and mixtures thereof. Particularly useful is the case where the metal compound is a nitrate and the alkalizing agent is an ammonia compound.
  • the alkalizing agent may be used in a catalytic amount.
  • the electrode material-containing stream produced in (a) is transferred into the heat exchangers 3, 4, 6, and cooled by means of a heat medium such as cooling water, etc.
  • the heat exchangers may include i) a plurality of heat exchangers connected in series or ii) a heat exchanger having a plurality of shell sides, which may be used alone or in combinations of two or more.
  • the heat exchangers 3, 4, 6 may be a plurality of heat exchangers connected in series.
  • the plurality of heat exchangers connected in series may be exemplified by two heat exchangers in which a double pipe type heat exchanger (a) and a shell-and-tube type heat exchanger (b) are connected in series, but the present invention is not limited thereto, and two or more types of three or more heat exchangers may be connected in series.
  • the plurality of heat exchangers connected in series may be exemplified by a plurality of heat exchangers in which two shell-and-tube type heat exchangers (a, b) are connected in series, but the present invention is not limited thereto, and a plurality of heat exchanges in which three or more shell-and-tube type heat exchangers are connected in series may be used.
  • a plurality of heat exchangers may be configured such that two double pipe type heat exchangers (a, b) are connected in series, wherein different fluids (cooling water) are fed into the outer pipes of the double pipe type heat exchangers, and the outer pipe of the double pipe type heat exchanger corresponds to the shell side of the shell-and-tube type heat exchanger.
  • a plurality of heat exchangers in which two double pipe type heat exchangers are connected may be provided, but the present invention is not limited thereto, and a plurality of heat exchangers in which three or more double pipe type heat exchangers are connected may be provided.
  • a heat exchanger including a plurality of shell sides
  • FIGS. 6 and 7 illustrate different examples of a heat exchanger whose shell side is divided into two. As illustrated in these drawings, one heat exchanger whose shell side is divided into two may be used, but the present invention is not limited thereto, and two or more heat exchangers may be used together, or it may be combined with a different type of heat exchanger. Furthermore, a heat exchanger whose shell side is divided into three or more may be used.
  • the arrow in the vertical direction is the direction of transfer of a cooling medium, preferably water, and the arrow in the horizontal direction is the direction of transfer of the electrode material-containing stream.
  • the heat exchangers 3, 4, 6 may be the same or different types of heat exchangers, and the double pipe type heat exchanger or the shell-and-tube type heat exchanger may be applied but the type of heat exchanger is not limited thereto.
  • one heat exchanger in which a plurality of shell sides is separated in series may be applied, and thus, the same effects in which the electrode material-containing stream is cooled two or more times as in the case of using the plurality of heat exchangers 3, 4, 6 may be exhibited.
  • the electrode material-containing stream in a subcritical or supercritical phase may be cooled through the heat exchangers, so that the temperature thereof may be decreased to 10 ⁇ 200°C, and preferably 40 ⁇ 90°C.
  • Heat which is sequentially recovered using the medium such as cooling water by means of the heat exchangers 3, 4, 6, may be used to preheat water that is to be used in the reaction of (a).
  • the recovered medium such as cooling water may be additionally heated to a required temperature using a furnace 5.
  • the medium used to recover heat in one heat exchanger may be reused as a heat recovery medium in another heat exchanger.
  • the electrode material-containing stream cooled in (b) is transferred into the pressure reducer to reduce the pressure thereof.
  • the pressure may be set to 1 ⁇ 100 bar, and preferably 1 ⁇ 30 bar.
  • the electrode material-containing stream at the reduced pressure using the pressure reducer 7 is transferred into the concentrator 8 so that it is concentrated (Step d).
  • the electrode material-containing stream is concentrated such that the concentration of particles for preparing the electrode material is 1 ⁇ 60 wt%, and preferably 10 ⁇ 40 wt%.
  • Steps (a) and (d) may be performed using a continuous synthesis process.
  • the electrode material in a slurry form prepared using the method of the invention may be obtained downstream of the preparation apparatus.
  • the electrode material may be an anode active material or a cathode active material, and preferably is an anode active material or an electrode material for a lithium secondary battery.
  • Iron sulfate (FeSO 4 ⁇ 7H 2 O) and phosphoric acid (H 3 PO 4 ) were weighted at a molar ratio of 1 : 1, and sugar was weighed in an amount of 10 wt% relative to iron sulfate, thus preparing an aqueous solution.
  • aqueous ammonia and lithium hydroxide (LiOH ⁇ H 2 O) were respectively weighed at molar ratios of 1 : 1.1 and 1 : 2 relative to iron sulfate, thus preparing an aqueous solution.
  • the above two aqueous solutions were pumped at a pressure of 250 bar at room temperature at a flow rate of 8 g/min, and mixed using a mixer, thus producing a lithium iron phosphate (LiFePO 4 ) precursor.
  • deionized water heated at about 450°C was pumped at a pressure of 250 bar at a flow rate of 96 g/min, and mixed with the above precursor using the mixer.
  • the final mixture solution was produced into lithium iron phosphate (LiFePO 4 ) in a reactor at 386°C and 250 bar, and the resulting LiFePO 4 -containing stream was fed into a first double pipe type heat exchanger so as to be primarily cooled, and was fed into a second shell-and-tube type heat exchanger having one shell side so as to be cooled, whereby the stream was at 200°C and 250 bar.
  • the cooling water discharged after having been used for cooling in the second heat exchanger was fed into the first heat exchanger so as to be recycled.
  • the LiFePO 4 -containing stream secondarily cooled by means of the second heat exchanger was fed into a third shell-and-tube type heat exchanger having one shell side so as to be cooled to 50°C.
  • the tertiarily cooled LiFePO 4 -containing stream was transferred into the pressure reducer so that its pressure was reduced to 3 ⁇ 30 bar, and then transferred into the concentrator and thus concentrated so that the concentration of LiFePO 4 particles was 20 wt%, thus preparing a LiFePO 4 anode active material.
  • the LiFePO 4 anode active material was analyzed using XRD, and was thus confirmed to be defect-free single-phase LiFePO 4 crystals as illustrated in FIG. 8.
  • Iron sulfate (FeSO 4 ⁇ 7H 2 O) and phosphoric acid (H 3 PO 4 ) were weighted at a molar ratio of 1 : 1, and sugar was weighed in an amount of 10 wt% relative to iron sulfate, thus preparing an aqueous solution.
  • aqueous ammonia and lithium hydroxide (LiOH ⁇ H 2 O) were respectively weighed at molar ratios of 1 : 1.1 and 1 : 2 relative to iron sulfate, thus preparing an aqueous solution.
  • the above two aqueous solutions were pumped at a pressure of 250 bar at room temperature at a flow rate of 8 g/min, and mixed using a mixer, thus producing a lithium iron phosphate (LiFePO 4 ) precursor.
  • deionized water heated at about 450°C was pumped at a pressure of 250 bar at a flow rate of 96 g/min, and mixed with the above precursor using the mixer.
  • the final mixture solution was produced into lithium iron phosphate (LiFePO 4 ) in a reactor at 386°C and 250 bar, and the resulting LiFePO 4 -containing stream was fed into a first shell-and-tube type heat exchanger having two shell sides so as to be cooled, so that the stream was at 200°C and 250 bar.
  • the cooling water discharged after having been used for cooling in the first heat exchanger was additionally heated using a heater and then fed into the mixer.
  • the LiFePO 4 -containing stream primarily cooled by means of the first heat exchanger was fed into a second shell-and-tube type heat exchanger having one shell side so as to be cooled to 50°C.
  • the secondarily cooled LiFePO 4 -containing stream was transferred into the pressure reducer so that its pressure was reduced to 3 ⁇ 30 bar, and then transferred into the concentrator and thus concentrated so that the concentration of LiFePO 4 particles was 20 wt%, thus preparing a LiFePO 4 anode active material.
  • Iron sulfate (FeSO 4 ⁇ 7H 2 O) and phosphoric acid (H 3 PO 4 ) were weighted at a molar ratio of 1 : 1, and sugar was weighed in an amount of 10 wt% relative to iron sulfate, thus preparing an aqueous solution.
  • aqueous ammonia and lithium hydroxide (LiOH ⁇ H 2 O) were respectively weighed at molar ratios of 1 : 1.1 and 1 : 2 relative to iron sulfate, thus preparing an aqueous solution.
  • the above two aqueous solutions were pumped at a pressure of 250 bar at room temperature at a flow rate of 8 g/min, and mixed using a mixer, thus producing a lithium iron phosphate (LiFePO 4 ) precursor.
  • deionized water heated at about 450°C was pumped at a pressure of 250 bar at a flow rate of 96 g/min, and mixed with the above precursor using the mixer.
  • the final mixture solution was produced into lithium iron phosphate (LiFePO 4 ) in a reactor at 386°C and 250 bar, and the resulting LiFePO 4 -containing stream was fed into a first shell-and-tube type heat exchanger having one shell side so as to be cooled, so that the stream was at 200°C and 250 bar.
  • the cooling water discharged after having been used for cooling in the first heat exchanger was additionally heated using a heater and then fed into the mixer.
  • the LiFePO 4 -containing stream primarily cooled by means of the first heat exchanger was fed into a second shell-and-tube type heat exchanger having one shell side so as to be cooled to 50°C.
  • the secondarily cooled LiFePO 4 -containing stream was transferred into the pressure reducer so that its pressure was reduced to 3 ⁇ 30 bar, and then transferred into the concentrator and thus concentrated so that the concentration of LiFePO 4 particles was 20 wt%, thus preparing a LiFePO 4 anode active material.
  • a LiFePO 4 anode active material was prepared using the same apparatus and method as in Example 1, with the exception that the pressure reducer and the concentrator were positioned vice versa, and thus concentrating and then pressure reducing were conducted.
  • a high-pressure concentrator is required. Accordingly, a concentrating process was performed using a metal filter type concentrator.
  • Iron sulfate (FeSO 4 ⁇ 7H 2 O) and phosphoric acid (H 3 PO 4 ) were weighted at a molar ratio of 1 : 1, and sugar was weighed in an amount of 10 wt% relative to iron sulfate, thus preparing an aqueous solution.
  • aqueous ammonia and lithium hydroxide (LiOH ⁇ H 2 O) were respectively weighed at molar ratios of 1 : 1.1 and 1 : 2 relative to iron sulfate, thus preparing an aqueous solution.
  • the above two aqueous solutions were pumped at a pressure of 250 bar at room temperature at a flow rate of 8 g/min, and mixed using a mixer, thus producing a lithium iron phosphate (LiFePO 4 ) precursor.
  • deionized water heated at about 450°C was pumped at a pressure of 250 bar at a flow rate of 96 g/min, and mixed with the above precursor using the mixer.
  • the final mixture solution was produced into lithium iron phosphate (LiFePO 4 ) in a reactor at 386°C and 250 bar, and the resulting LiFePO 4 -containing stream was fed into a first shell-and-tube type heat exchanger having one shell side so as to be cooled, whereby the stream was at 90°C and 250 bar.
  • the primarily cooled LiFePO 4 -containing stream was transferred into the pressure reducer so that its pressure was reduced to 3 ⁇ 30 bar, and then transferred into the concentrator and thus concentrated so that the concentration of LiFePO 4 particles was 20 wt%, thus preparing a LiFePO 4 anode active material.
  • Comparative Example 1 the pressure of the stream used in the concentrating process is excessively high, making it difficult to manufacture large-scale production equipment, and the manufacturing cost of the production equipment is higher by 2 ⁇ 10 times compared to Example 1 wherein the pressure is reduced and then concentrating is performed, and also maintenance and repair are difficult.
  • the type of concentrator should be changed depending on the properties of the particles, the concentrator usable in Comparative Example 1 is limited to a metal filter type, which may rapidly increase the pressure of the concentrator during operation, making it difficult to achieve continuous operation.
  • Comparative Example 2 it is impossible to recover heat due to cooling using a single heat exchanger. In this case, 3 ⁇ 4 times more energy is required compared to Example 1, in addition to the recovered energy, and excessive use of energy results in remarkably increased energy production equipment cost and related costs.
  • the devices disposed downstream of equipment should be those at high temperatures, thus increasing the equipment cost, and this comparative example is difficult to apply to a large-scale production process.
  • energy necessary for cooling up to the temperature adapted to recover the anode active material is increased by 3 ⁇ 4 times compared to when using the process of Example 1. Also, a cooling water system and a cooling tower are additionally required.
  • an electrode material can be prepared using a hydrothermal synthesis process at high temperature and high pressure, thereby stably maintaining a continuous synthesis process, enabling mass production and ensuring the operation stability of the synthesis process.
  • a concentrator is disposed downstream of a pressure reducer, a low-pressure concentrator can be applied, thus reducing the preparation cost, and heat recovery efficiency can be increased using a plurality of heat exchangers, thus exhibiting energy saving effects.

Abstract

Disclosed is a method of preparing an electrode material using a hydrothermal synthesis process, including (a) mixing an electrode material precursor and high-temperature, high-pressure water so as to react with each other, thus producing an electrode material-containing stream, (b) cooling the electrode material-containing stream through heat exchangers, (c) reducing the pressure of the cooled electrode material-containing stream using a pressure reducer, and (d) concentrating the electrode material-containing stream at the reduced pressure using a concentrator, thus producing a concentrated electrode material. According to this invention, synthesis conditions are maintained stable, continuous mass production is possible, and operation stability of the synthesis process can be ensured. Particularly, the concentrator is disposed downstream of the pressure reducer and thus a low-pressure concentrator can be applied, thereby lowering the preparation cost, and increasing heat recovery efficiency by using a plurality of heat exchangers to thus attain energy saving effects.

Description

METHOD FOR PREPARING ELECTRODE MATERIAL USING HYDROTHERMAL SYNTHESIS PROCESS
The present invention relates to a method of preparing an electrode material and, more particularly, to a method of preparing an electrode material using a hydrothermal synthesis process.
A dry burning method and a wet precipitation method are widely known to be conventional methods of preparing an electrode material. The dry burning method is used to prepare an electrode material by mixing an oxide or hydroxide of a transition metal such as cobalt (Co), etc., with a lithium source, that is, lithium carbonate or lithium hydroxide, under dry conditions, and then burning the mixture at a high temperature of 700 ~ 1000℃ for 5 ~ 48 hr.
The dry burning method has typically mainly been utilized to prepare the metal oxide and is advantageous in terms of it being a relatively easy approach, but it is difficult to uniformly mix feed materials, making it difficult to obtain a single-phase product. Furthermore, in the case of a multi-component electrode material comprising two or more transition metals, it is difficult to uniformly arrange two or more elements at an atom level. Moreover, the case of doping with or substitution with a specific metal component to improve electrochemical performance is problematic because it is difficult to uniformly mix the specific metal component added in a small amount, and also because pollution may be caused in the course of grinding and sorting to obtain particles having a desired size.
Among typical methods of preparing an electrode material, the wet precipitation method is exemplified. The wet precipitation method is used to prepare an electrode material by dissolving a salt containing a transition metal such as cobalt (Co), etc., in water, adding an alkali to the salt solution so that the salt solution is precipitated into a transition metal hydroxide, and filtering and drying the precipitate, which is then mixed with a lithium source, that is, lithium carbonate or lithium hydroxide, under dry conditions, and then burned at a high temperature of 700 ~ 1000℃ for 1 ~ 48 hr.
The wet precipitation method is known to easily obtain a uniform mixture by co-precipitating two or more transition metal elements, but is problematic because a precipitation reaction requires a long period of time, the preparation process is complicated, and waste acids and the like are generated as byproducts. In addition, a variety of methods, including a sol-gel method, a hydrothermal method, a spray pyrolysis method, an ion exchange method, etc., have been proposed as methods of preparing an electrode material for a lithium secondary battery.
A batch type hydrothermal synthesis method cannot accomplish continuous production, undesirably making it difficult to achieve mass production and increasing the production cost. Upon hydrothermal synthesis, energy is consumed in a large amount relative to the throughput, and particles produced in the synthesis process equipment may accumulate, undesirably decreasing equipment efficiency, making it difficult to obtain nano-sized particles, and lowering crystallinity.
In particular, because the particle size of a cell material has a great influence on cell performance and cell fabrication, it is required to obtain nano-sized primary particles and to narrow the particle size distribution in the synthesis process.
Meanwhile, in addition to the above methods, methods of preparing an inorganic compound for an electrode material through a hydrothermal synthesis process using high-temperature, high-pressure water are being employed. In the case of the electrode material for a lithium secondary battery, when using a hydrothermal synthesis process at high temperature and high pressure, particle crystallinity is greatly increased, and the average size of the primary particles may be controlled to the level ranging from tens of to hundreds of nanometers. By virtue of the advantages of the hydrothermal synthesis process, nano-sized particles may be formed and crystal stability may be improved upon synthesizing the cell material. Also, a continuous synthesis method of an electrode material using the hydrothermal synthesis process enables mass production, thus increasing profitability.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and an object of the present invention is to provide a method of continuously synthesizing an electrode material using a hydrothermal synthesis process, wherein synthesis conditions are maintained stable, operation stability of the synthesis process is ensured, and mass production and energy saving are possible.
In order to accomplish the above object, the present invention provides a method of preparing an electrode material using a hydrothermal synthesis process, comprising (a) mixing an electrode material precursor and high-temperature, high-pressure water so as to react with each other, thus producing an electrode material-containing stream, (b) cooling the electrode material-containing stream through a heat exchanger including a plurality of shell sides or a plurality of heat exchangers connected in series, (c) reducing the pressure of the cooled electrode material-containing stream using a pressure reducer, and (d) concentrating the electrode material-containing stream at the reduced pressure using a concentrator, thus producing a concentrated electrode material.
In the method of the present invention, heat may be recovered from the stream in (b) by the heat exchanger, and may be used to preheat the water in order to make the high-temperature, high-pressure water in (a).
In the method of the present invention, (a) to (d) may be performed using a continuous synthesis process.
In the method of the present invention, (a) may comprise (a-1) preparing a first mixture comprising at least one metal precursor selected from the group consisting of Group 2 elements, transition metals, Group 12 elements, and Group 13 elements, (a-2) preparing a second mixture comprising a lithium precursor and an alkalizing agent, and (a-3) mixing the first mixture, the second mixture, and the high-temperature, high-pressure water so as to react with each other, thus producing the electrode material-containing stream.
In an embodiment of the present invention, (a-3) may be performed by simultaneously mixing the first mixture, the second mixture, and the high-temperature, high-pressure water.
In the method of the present invention, (a-3) may comprise (a-3-1) mixing the first mixture and the second mixture, and (a-3-2) mixing the mixture obtained in (a-3-1) with the high-temperature, high-pressure water.
As such, (a-3) may be performed at a pressure of 150 ~ 700 bar and at a temperature of 200 ~ 700℃.
Also, (a-3) may be performed under subcritical or supercritical conditions.
The high-temperature, high-pressure water in (a-3) may be subcritical water or supercritical water.
In an embodiment of the present invention, a precursor of iron (Fe) which is the transition metal may be at least one selected from the group consisting of FeSO4, Fe(NO3)2, FeC2O4·2H2O, and FeCl2.
In an embodiment of the present invention, the first mixture may further include a multi-acid compound.
As such, the multi-acid compound may be at least one selected from the group consisting of H3PO4, NH4H2PO4, (NH4)2HPO4 and P2O5.
In an embodiment of the present invention, the lithium (Li) precursor may be at least one selected from the group consisting of Li2CO3, Li(OH), Li(OH)·xH2O, LiCl and LiNO3.
Also, the alkalizing agent may be at least one selected from the group consisting of alkali metal hydroxides, alkaline earth metal hydroxides, and ammonia compounds.
The first mixture may further include a reducing agent.
The reducing agent may be at least one selected from the group consisting of oxalic acid, sugar, fructose, glucose, formic acid, and ascorbic acid (Vitamin C).
In the method of the present invention, (c) may be performed so that the pressure is reduced to 1 ~ 100 bar.
In the method of the present invention, the concentrated electrode material using the concentrator in (d) may have a concentration of 1 ~ 60 wt%.
In the method of the present invention, the electrode material may be any one selected from the group consisting of an anode active material and a cathode active material.
According to the present invention, an electrode material can be prepared using a hydrothermal synthesis process at high temperature and high pressure, thereby stably maintaining a continuous synthesis process, enabling mass production and ensuring the operation stability of the synthesis process. In particular, because a concentrator is disposed downstream of a pressure reducer, a low-pressure concentrator can be applied, thus reducing the preparation cost, and heat recovery efficiency can be increased using a plurality of heat exchangers, thus exhibiting energy saving effects.
FIG. 1 is a flowchart illustrating a process of preparing an electrode material using a hydrothermal synthesis process according to the present invention;
FIG. 2 is a schematic view illustrating an apparatus for preparing an electrode material using a hydrothermal synthesis process according to the present invention;
FIG. 3 is a schematic view illustrating a plurality of heat exchangers in which a double pipe type heat exchanger (a) and a shell-and-tube type heat exchanger (b) are connected in series;
FIG. 4 is a schematic view illustrating a plurality of heat exchangers in which two shell-and-tube type heat exchangers (a, b) are connected in series;
FIG. 5 is a schematic view illustrating a plurality of heat exchangers in which two double pipe type heat exchangers (a, b) are connected in series;
FIG. 6 is a schematic view illustrating a shell-and-tube type heat exchanger in which the shell side of the heat exchanger is divided into two;
FIG. 7 is a schematic view illustrating a shell-and-tube type heat exchanger in which the shell side of the heat exchanger is divided into two; and
FIG. 8 is XRD data illustrating the crystalline structure of LiFePO4 synthesized in Example 1.
The present invention may be variously modified, and may have a variety of embodiments, and is intended to illustrate specific embodiments. However, the following description does not limit the present invention to specific embodiments, and should be understood to include all variations, equivalents or substitutions within the spirit and scope of the present invention. Furthermore, in the description of the present invention, when it is determined that the detailed description of the related art would obscure the gist of the present invention, the description thereof will be omitted.
Also, in the following description, the terms “first,” “second” and the like are used to differentiate a certain component from other components, but the configuration of such components should not be construed to be limited by the terms. For example, a first component may be referred to as a second component, and also, a second component may be referred to as a first component, within the scope of the present invention.
Unless otherwise stated, the singular expression includes a plural expression. In this application, the terms “include” or “have” are used to designate the presence of features, numbers, steps, operations, components, parts or combinations thereof described in the specification, and should be understood so as not to exclude the presence or additional probability of one or more different features, numbers, steps, operations, components, parts or combinations thereof.
Hereinafter, a method of preparing an electrode material using a hydrothermal synthesis process according to the present invention is described with reference to FIGS. 1 and 2.
The method of preparing an electrode material using a hydrothermal synthesis process according to the present invention includes (a) mixing an electrode material precursor and high-temperature, high-pressure water so as to react with each other, thus producing an electrode material-containing stream; (b) cooling the electrode material-containing stream through a heat exchanger including a plurality of shell sides or through a plurality of heat exchangers connected in series; (c) reducing the pressure of the cooled electrode material-containing stream using a pressure reducer; and (d) concentrating the electrode material-containing stream at the reduced pressure using a concentrator, thus producing a concentrated electrode material.
Respective steps of the method of the present invention are specified below.
Step (a): Mixing an electrode material precursor and high-temperature, high-pressure water so as to react with each other, thus producing an electrode material-containing stream
Step (a) may include (a-1) preparing a first mixture comprising at least one metal precursor selected from the group consisting of Group 2 elements, transition metals, Group 12 elements, and Group 13 elements; (a-2) preparing a second mixture comprising a lithium precursor and an alkalizing agent; and (a-3) mixing the first mixture, the second mixture, and the high-temperature, high-pressure water so as to react with each other, thus producing the electrode material-containing stream.
Metal precursor
The metal precursor may include a precursor of a Group 2 element, a transition metal, a Group 12 element, or a Group 13 element, which may be used alone or in mixtures of two or more. The transition metal may also include zinc (Zn), cadmium (Cd), and mercury (Hg), as Group 12 elements.
Preferably, the transition metal precursor includes any one or a mixture of two or more selected from the group consisting of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo precursors and combinations thereof.
As the metal precursor compound, any compound may be used without particular limitation so long as it is a salt including the above metal and is able to be ionized. Preferably useful is a water-soluble compound. Examples of the transition metal precursor compound include salts, such as alkoxides, nitrates, acetates, halides, hydroxides, oxides, carbonates, oxalates, sulfates, and combinations thereof, each of which has the above metal. Particularly useful is a nitrate, sulfate, or acetate. Also, compounds (e.g. Ni-Mn, Ni-Co, Ni-Mn-Co and the like) including any one or a combination of two or more of the above transition metals may be used.
With reference to FIG. 2, the first mixture, the second mixture, and the high-temperature, high-pressure water are mixed using a mixer 1 and reacted using a reactor 2, thus producing the electrode material-containing stream (a-3).
Also, (a-3) producing the electrode material-containing stream preferably includes (a-3-1) mixing the first mixture and the second mixture; and (a-3-2) mixing the mixture obtained in (a-3-1) with the high-temperature, high-pressure water. As seen in FIG. 2, the mixer 1 and the reactor 2 are separated, so that mixing and reaction are separately performed, but the scope of the present invention is not limited thereto. In some cases, these two devices are provided integratedly, so that mixing and reaction may be simultaneously carried out, and also may be conducted using a continuous synthesis process.
High-temperature, high-pressure water
The high-temperature, high-pressure water is preferably subcritical water or supercritical water, and the high-temperature, high-pressure water may include another material, such as an additive, etc., within a range that is adapted for purposes of the present invention.
Also, (a-3) may be performed at a pressure of 150 ~ 700 bar, preferably 200 ~ 400 bar, and a temperature of 200 ~ 700℃, preferably 250 ~ 500℃. If the pressure is less than 150 bar, reactivity may decrease, undesirably making it difficult to obtain single-phase particles having uniform quality. In contrast, if the pressure exceeds 700 bar, the material cost for the preparation apparatus may increase, undesirably excessively increasing the equipment cost. In addition, if the temperature is lower than 200℃, it is difficult to synthesize the nano-sized particles. In contrast, if the temperature is higher than 700℃, the material cost for the equipment becomes too high.
Also, (a-3) may be performed under subcritical or supercritical conditions. The supercritical point of water is reached when the temperature is 374℃ and the pressure is 220 bar. In the present invention, supercritical water preferably indicates water under conditions of 374℃ or higher and 220 bar or more. Also, in the present invention, subcritical water preferably indicates water under conditions of 250℃ or higher and 200 bar or more.
According to an embodiment of the present invention, the first mixture may further include a multi-acid compound, and the multi-acid compound may be at least one selected from the group consisting of H3PO4, NH4H2PO4, (NH4)2HPO4 and P2O5.
The multi-acid compound is preferably a phosphoric acid compound, and the phosphoric acid compound is preferably used as a feed upon preparing an olivine structured electrode material.
According to an embodiment of the present invention, the first mixture may further include a reducing agent to prevent oxidation of the electrode material precursor, etc., during the hydrothermal synthesis process, and also to prevent oxidation of the produced electrode material.
The reducing agent may be at least one selected from the group consisting of formic acid, oxalic acid, sugar, fructose, and ascorbic acid (Vitamin C). The carbonaceous material such as sugar may be used in an amount of 2 ~ 30 wt% based on the weight of the metal precursor.
Lithium precursor
The lithium (Li) precursor may be at least one selected from the group consisting of Li2CO3, Li(OH), Li(OH)·xH2O, LiCl and LiNO3.
The amount of the lithium precursor is set at a molar ratio of 1.0 ~ 20 times, and preferably 1.0 ~ 10 times relative to the amount of the metal precursor. If the amount of the lithium precursor is smaller than 1.0 times, the metal precursor that does not react with the metal lithium, for example, impurities such as oxides and the like, may be produced and thus the purity of the product may decrease. In contrast, if the amount of the lithium precursor is greater than 20 times, lithium may remain and thus should be recovered from the discharged solution or should be disposed of as waste, undesirably lowering profitability.
Alkalizing agent
The alkalizing agent may be at least one selected from the group consisting of alkali metal hydroxides, alkaline earth metal hydroxides, and ammonia compounds.
The alkalizing agent facilitates at least one transition metal compound to be hydrolyzed with a hydroxide and precipitated, and any compound may be used without particular limitation so long as it makes the reaction solution alkaline. Non-limited examples of the alkalizing agent may include alkali metal hydroxides (NaOH, KOH, etc.), alkaline earth metal hydroxides (Ca(OH)2, Mg(OH)2, etc.), ammonia compounds (aqueous ammonia, ammonium nitrate, etc.), and mixtures thereof. Particularly useful is the case where the metal compound is a nitrate and the alkalizing agent is an ammonia compound. This is because the nitrate ion produced as a byproduct may be mostly decomposed in the same process, and the residual ion may be easily removed via washing with water, drying or burning after the synthesis process. The alkalizing agent may be used in a catalytic amount.
Step (b): Cooling the electrode material-containing stream through heat exchangers
With reference to FIG. 2, the electrode material-containing stream produced in (a) is transferred into the heat exchangers 3, 4, 6, and cooled by means of a heat medium such as cooling water, etc.
As such, the heat exchangers may include i) a plurality of heat exchangers connected in series or ii) a heat exchanger having a plurality of shell sides, which may be used alone or in combinations of two or more.
In FIG. 2, the heat exchangers 3, 4, 6 may be a plurality of heat exchangers connected in series.
i) A plurality of heat exchangers connected in series
With reference to FIG. 3, the plurality of heat exchangers connected in series may be exemplified by two heat exchangers in which a double pipe type heat exchanger (a) and a shell-and-tube type heat exchanger (b) are connected in series, but the present invention is not limited thereto, and two or more types of three or more heat exchangers may be connected in series.
Also, with reference to FIG. 4, the plurality of heat exchangers connected in series may be exemplified by a plurality of heat exchangers in which two shell-and-tube type heat exchangers (a, b) are connected in series, but the present invention is not limited thereto, and a plurality of heat exchanges in which three or more shell-and-tube type heat exchangers are connected in series may be used.
Also, with reference to FIG. 5, a plurality of heat exchangers may be configured such that two double pipe type heat exchangers (a, b) are connected in series, wherein different fluids (cooling water) are fed into the outer pipes of the double pipe type heat exchangers, and the outer pipe of the double pipe type heat exchanger corresponds to the shell side of the shell-and-tube type heat exchanger. In the preparation method according to the present invention, a plurality of heat exchangers in which two double pipe type heat exchangers are connected may be provided, but the present invention is not limited thereto, and a plurality of heat exchangers in which three or more double pipe type heat exchangers are connected may be provided.
ii) A heat exchanger including a plurality of shell sides
FIGS. 6 and 7 illustrate different examples of a heat exchanger whose shell side is divided into two. As illustrated in these drawings, one heat exchanger whose shell side is divided into two may be used, but the present invention is not limited thereto, and two or more heat exchangers may be used together, or it may be combined with a different type of heat exchanger. Furthermore, a heat exchanger whose shell side is divided into three or more may be used.
In FIGS. 3 to 7, the arrow in the vertical direction is the direction of transfer of a cooling medium, preferably water, and the arrow in the horizontal direction is the direction of transfer of the electrode material-containing stream.
In FIG. 2, the heat exchangers 3, 4, 6 may be the same or different types of heat exchangers, and the double pipe type heat exchanger or the shell-and-tube type heat exchanger may be applied but the type of heat exchanger is not limited thereto.
For the sake of description, the case where three heat exchangers 3, 4, 6 are connected in series is illustrated in FIG. 2, but the present invention may include all cases where two or more heat exchangers are connected in series.
On the other hand, one heat exchanger in which a plurality of shell sides is separated in series may be applied, and thus, the same effects in which the electrode material-containing stream is cooled two or more times as in the case of using the plurality of heat exchangers 3, 4, 6 may be exhibited.
The electrode material-containing stream in a subcritical or supercritical phase may be cooled through the heat exchangers, so that the temperature thereof may be decreased to 10 ~ 200℃, and preferably 40 ~ 90℃.
Heat, which is sequentially recovered using the medium such as cooling water by means of the heat exchangers 3, 4, 6, may be used to preheat water that is to be used in the reaction of (a). As such, in order to obtain the preheated water under subcritical or supercritical conditions, the recovered medium such as cooling water may be additionally heated to a required temperature using a furnace 5.
Moreover, the medium used to recover heat in one heat exchanger may be reused as a heat recovery medium in another heat exchanger.
Step (c): Reducing pressure of the electrode material-containing stream cooled in (b) using a pressure reducer
The electrode material-containing stream cooled in (b) is transferred into the pressure reducer to reduce the pressure thereof. As such, the pressure may be set to 1 ~ 100 bar, and preferably 1 ~ 30 bar.
Step (d): Concentrating the electrode material-containing stream at reduced pressure using a concentrator
With reference to FIG. 2, the electrode material-containing stream at the reduced pressure using the pressure reducer 7 is transferred into the concentrator 8 so that it is concentrated (Step d).
As such, the electrode material-containing stream is concentrated such that the concentration of particles for preparing the electrode material is 1 ~ 60 wt%, and preferably 10 ~ 40 wt%.
Steps (a) and (d) may be performed using a continuous synthesis process.
The electrode material in a slurry form prepared using the method of the invention may be obtained downstream of the preparation apparatus.
The electrode material may be an anode active material or a cathode active material, and preferably is an anode active material or an electrode material for a lithium secondary battery.
A better understanding of the present invention may be obtained through the following examples which are set forth to illustrate, but are not to be construed as limiting the present invention.
[Example]
Example 1
Iron sulfate (FeSO4·7H2O) and phosphoric acid (H3PO4) were weighted at a molar ratio of 1 : 1, and sugar was weighed in an amount of 10 wt% relative to iron sulfate, thus preparing an aqueous solution. Separately, aqueous ammonia and lithium hydroxide (LiOH·H2O) were respectively weighed at molar ratios of 1 : 1.1 and 1 : 2 relative to iron sulfate, thus preparing an aqueous solution. The above two aqueous solutions were pumped at a pressure of 250 bar at room temperature at a flow rate of 8 g/min, and mixed using a mixer, thus producing a lithium iron phosphate (LiFePO4) precursor.
Also, deionized water heated at about 450℃ was pumped at a pressure of 250 bar at a flow rate of 96 g/min, and mixed with the above precursor using the mixer. The final mixture solution was produced into lithium iron phosphate (LiFePO4) in a reactor at 386℃ and 250 bar, and the resulting LiFePO4-containing stream was fed into a first double pipe type heat exchanger so as to be primarily cooled, and was fed into a second shell-and-tube type heat exchanger having one shell side so as to be cooled, whereby the stream was at 200℃ and 250 bar. The cooling water discharged after having been used for cooling in the second heat exchanger was fed into the first heat exchanger so as to be recycled.
Subsequently, the LiFePO4-containing stream secondarily cooled by means of the second heat exchanger was fed into a third shell-and-tube type heat exchanger having one shell side so as to be cooled to 50℃.
Subsequently, the tertiarily cooled LiFePO4-containing stream was transferred into the pressure reducer so that its pressure was reduced to 3 ~ 30 bar, and then transferred into the concentrator and thus concentrated so that the concentration of LiFePO4 particles was 20 wt%, thus preparing a LiFePO4 anode active material.
The LiFePO4 anode active material was analyzed using XRD, and was thus confirmed to be defect-free single-phase LiFePO4 crystals as illustrated in FIG. 8.
Example 2
Iron sulfate (FeSO4·7H2O) and phosphoric acid (H3PO4) were weighted at a molar ratio of 1 : 1, and sugar was weighed in an amount of 10 wt% relative to iron sulfate, thus preparing an aqueous solution. Separately, aqueous ammonia and lithium hydroxide (LiOH·H2O) were respectively weighed at molar ratios of 1 : 1.1 and 1 : 2 relative to iron sulfate, thus preparing an aqueous solution. The above two aqueous solutions were pumped at a pressure of 250 bar at room temperature at a flow rate of 8 g/min, and mixed using a mixer, thus producing a lithium iron phosphate (LiFePO4) precursor.
Also, deionized water heated at about 450℃ was pumped at a pressure of 250 bar at a flow rate of 96 g/min, and mixed with the above precursor using the mixer. The final mixture solution was produced into lithium iron phosphate (LiFePO4) in a reactor at 386℃ and 250 bar, and the resulting LiFePO4-containing stream was fed into a first shell-and-tube type heat exchanger having two shell sides so as to be cooled, so that the stream was at 200℃ and 250 bar. The cooling water discharged after having been used for cooling in the first heat exchanger was additionally heated using a heater and then fed into the mixer.
Subsequently, the LiFePO4-containing stream primarily cooled by means of the first heat exchanger was fed into a second shell-and-tube type heat exchanger having one shell side so as to be cooled to 50℃.
Subsequently, the secondarily cooled LiFePO4-containing stream was transferred into the pressure reducer so that its pressure was reduced to 3 ~ 30 bar, and then transferred into the concentrator and thus concentrated so that the concentration of LiFePO4 particles was 20 wt%, thus preparing a LiFePO4 anode active material.
Example 3
Iron sulfate (FeSO4·7H2O) and phosphoric acid (H3PO4) were weighted at a molar ratio of 1 : 1, and sugar was weighed in an amount of 10 wt% relative to iron sulfate, thus preparing an aqueous solution. Separately, aqueous ammonia and lithium hydroxide (LiOH·H2O) were respectively weighed at molar ratios of 1 : 1.1 and 1 : 2 relative to iron sulfate, thus preparing an aqueous solution. The above two aqueous solutions were pumped at a pressure of 250 bar at room temperature at a flow rate of 8 g/min, and mixed using a mixer, thus producing a lithium iron phosphate (LiFePO4) precursor.
Also, deionized water heated at about 450℃ was pumped at a pressure of 250 bar at a flow rate of 96 g/min, and mixed with the above precursor using the mixer. The final mixture solution was produced into lithium iron phosphate (LiFePO4) in a reactor at 386℃ and 250 bar, and the resulting LiFePO4-containing stream was fed into a first shell-and-tube type heat exchanger having one shell side so as to be cooled, so that the stream was at 200℃ and 250 bar. The cooling water discharged after having been used for cooling in the first heat exchanger was additionally heated using a heater and then fed into the mixer.
Subsequently, the LiFePO4-containing stream primarily cooled by means of the first heat exchanger was fed into a second shell-and-tube type heat exchanger having one shell side so as to be cooled to 50℃.
Subsequently, the secondarily cooled LiFePO4-containing stream was transferred into the pressure reducer so that its pressure was reduced to 3 ~ 30 bar, and then transferred into the concentrator and thus concentrated so that the concentration of LiFePO4 particles was 20 wt%, thus preparing a LiFePO4 anode active material.
Table 1
Position of pressure reducer Type and number of heat exchangers
Concentrator disposed downstream of pressure reducer Pressure reducer disposed downstream of concentrator Use of a plurality of heat exchangers Use of a single heat exchanger Number of heat exchangers
Ex.1 ○ - ○ - 3
Ex.2 ○ - ○ - 2 (1 with two shell sides, 1 with one shell side)
Ex.3 ○ - ○ - 2
Comp.Ex.1 - ○ ○ - 3
Comp.Ex.2 ○ - - ○ 1
Comparative Example 1
A LiFePO4 anode active material was prepared using the same apparatus and method as in Example 1, with the exception that the pressure reducer and the concentrator were positioned vice versa, and thus concentrating and then pressure reducing were conducted.
Because the stream has to be concentrated before the pressure thereof is reduced using the pressure reducer, a high-pressure concentrator is required. Accordingly, a concentrating process was performed using a metal filter type concentrator.
Comparative Example 2
Iron sulfate (FeSO4·7H2O) and phosphoric acid (H3PO4) were weighted at a molar ratio of 1 : 1, and sugar was weighed in an amount of 10 wt% relative to iron sulfate, thus preparing an aqueous solution. Separately, aqueous ammonia and lithium hydroxide (LiOH·H2O) were respectively weighed at molar ratios of 1 : 1.1 and 1 : 2 relative to iron sulfate, thus preparing an aqueous solution. The above two aqueous solutions were pumped at a pressure of 250 bar at room temperature at a flow rate of 8 g/min, and mixed using a mixer, thus producing a lithium iron phosphate (LiFePO4) precursor.
Also, deionized water heated at about 450℃ was pumped at a pressure of 250 bar at a flow rate of 96 g/min, and mixed with the above precursor using the mixer. The final mixture solution was produced into lithium iron phosphate (LiFePO4) in a reactor at 386℃ and 250 bar, and the resulting LiFePO4-containing stream was fed into a first shell-and-tube type heat exchanger having one shell side so as to be cooled, whereby the stream was at 90℃ and 250 bar.
Subsequently, the primarily cooled LiFePO4-containing stream was transferred into the pressure reducer so that its pressure was reduced to 3 ~ 30 bar, and then transferred into the concentrator and thus concentrated so that the concentration of LiFePO4 particles was 20 wt%, thus preparing a LiFePO4 anode active material.
In Comparative Example 1, the pressure of the stream used in the concentrating process is excessively high, making it difficult to manufacture large-scale production equipment, and the manufacturing cost of the production equipment is higher by 2 ~ 10 times compared to Example 1 wherein the pressure is reduced and then concentrating is performed, and also maintenance and repair are difficult. Although the type of concentrator should be changed depending on the properties of the particles, the concentrator usable in Comparative Example 1 is limited to a metal filter type, which may rapidly increase the pressure of the concentrator during operation, making it difficult to achieve continuous operation.
Also, in Comparative Example 2, it is impossible to recover heat due to cooling using a single heat exchanger. In this case, 3 ~ 4 times more energy is required compared to Example 1, in addition to the recovered energy, and excessive use of energy results in remarkably increased energy production equipment cost and related costs. The devices disposed downstream of equipment should be those at high temperatures, thus increasing the equipment cost, and this comparative example is difficult to apply to a large-scale production process. Furthermore, energy necessary for cooling up to the temperature adapted to recover the anode active material is increased by 3 ~ 4 times compared to when using the process of Example 1. Also, a cooling water system and a cooling tower are additionally required.
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.
According to the present invention, an electrode material can be prepared using a hydrothermal synthesis process at high temperature and high pressure, thereby stably maintaining a continuous synthesis process, enabling mass production and ensuring the operation stability of the synthesis process. In particular, because a concentrator is disposed downstream of a pressure reducer, a low-pressure concentrator can be applied, thus reducing the preparation cost, and heat recovery efficiency can be increased using a plurality of heat exchangers, thus exhibiting energy saving effects.

Claims (11)

  1. A method of preparing an electrode material using a hydrothermal synthesis process, comprising:
    (a) mixing an electrode material precursor and high-temperature, high-pressure water so as to react with each other, thus producing an electrode material-containing stream;
    (b) cooling the electrode material-containing stream through a heat exchanger including a plurality of shell sides or a plurality of heat exchangers connected in series;
    (c) reducing a pressure of the cooled electrode material-containing stream using a pressure reducer; and
    (d) concentrating the electrode material-containing stream at the reduced pressure using a concentrator, thus producing a concentrated electrode material.
  2. The method of claim 1, wherein heat is recovered from the stream in (b) by the heat exchanger, and is used to preheat the water in order to make the high-temperature, high-pressure water in (a).
  3. The method of claim 1, wherein (a) to (d) are performed using a continuous synthesis process.
  4. The method of claim 1, wherein (a) comprises:
    (a-1) preparing a first mixture comprising at least one metal precursor selected from the group consisting of Group 2 elements, transition metals, Group 12 elements, and Group 13 elements;
    (a-2) preparing a second mixture comprising a lithium precursor and an alkalizing agent; and
    (a-3) mixing the first mixture, the second mixture, and the high-temperature, high-pressure water so as to react with each other, thus producing the electrode material-containing stream.
  5. The method of claim 4, wherein (a-3) comprises:
    (a-3-1) mixing the first mixture with the second mixture; and
    (a-3-2) mixing the mixture obtained in (a-3-1) with the high-temperature, high-pressure water.
  6. The method of claim 4, wherein (a-3) is performed at a pressure of 150 ~ 700 bar and at a temperature of 200 ~ 700℃.
  7. The method of claim 4, wherein (a-3) is performed under subcritical or supercritical conditions.
  8. The method of claim 4, wherein the high-temperature, high-pressure water in (a-3) is subcritical water or supercritical water.
  9. The method of claim 1, wherein (c) is performed so that the pressure is reduced to 1 ~ 100 bar.
  10. The method of claim 1, wherein the concentrated electrode material using the concentrator in (d) has a concentration of 1 ~ 60 wt%.
  11. The method of claim 1, wherein the electrode material is any one selected from the group consisting of an anode active material and a cathode active material.
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