Method for producing manganese iron phosphate particles
By mixing metal powders with phosphate compounds in a protic solvent to generate hydrocarbon gases, the method addresses the lack of a low-cost precursor for lithium manganese iron phosphate, achieving finer particles and reduced grinding time, thus improving battery performance.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- TOYOTA JIDOSHA KK
- Filing Date
- 2024-11-11
- Publication Date
- 2026-05-21
AI Technical Summary
There is no suitable precursor for producing lithium manganese iron phosphate at low cost, and the existing hydrothermal method results in large particle sizes requiring additional pulverization, which is time-consuming.
A method involving mixing metal powders containing carbon, iron, and manganese with a phosphate compound in a protic solvent, generating hydrocarbon gases that facilitate spontaneous gasification and micronization of manganese iron phosphate particles, eliminating the need for grinding.
The method reduces grinding time and production costs while producing finer manganese iron phosphate particles suitable for lithium manganese iron phosphate, enhancing battery performance.
Smart Images
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Abstract
Description
Technical Field
[0001] The present disclosure relates to a method for producing manganese iron phosphate particles.
Background Art
[0002] Japanese Patent Application Laid-Open No. 2014-65641 (Patent Document 1) discloses a method for producing iron phosphate by reacting iron and phosphorus to form a precipitate and washing the precipitate. Further, it is also disclosed that lithium iron phosphate is produced by reacting the obtained iron phosphate with a lithium compound.
[0003] Japanese Patent Application Laid-Open No. 2016-81866 (Patent Document 2) discloses a method for producing lithium manganese iron phosphate by a hydrothermal reaction.
Prior Art Documents
Patent Documents
[0004]
Patent Document 1
Patent Document 2
Summary of the Invention
Problems to be Solved by the Invention
[0005] As a cathode active material, lithium iron phosphate or lithium manganese iron phosphate is used. As disclosed in Patent Document 1, with respect to lithium iron phosphate, iron phosphate exists as a suitable precursor. On the other hand, with respect to lithium manganese iron phosphate, no suitable precursor exists, and a method for producing it at low cost has not been established.
[0006] Furthermore, as disclosed in Patent Document 2, lithium manganese iron phosphate can be produced by a hydrothermal reaction. However, the lithium manganese iron phosphate obtained by this production method has a large particle size and must be further pulverized in order to be used as a positive electrode active material, which requires time for pulverization.
[0007] The object of this disclosure is to provide a method for producing manganese iron phosphate particles that can shorten the grinding time. [Means for solving the problem]
[0008] [1] A step of mixing a metal powder containing carbon, iron, and manganese with a phosphate compound in a protic solvent and stirring to obtain a slurry containing iron manganese phosphate particles, A method for producing manganese iron phosphate particles, comprising the step of drying the slurry to obtain the manganese iron phosphate particles.
[0009] By mixing metal powders containing carbon, iron, and manganese with phosphate compounds in a protic solvent and stirring, hydrocarbon gases such as hydrogen, methane, and ethane are generated. Manganese iron phosphate particles synthesized using this gas generation method spontaneously become finer through gasification, eliminating the need for grinding. As a result, grinding time is expected to be reduced. Furthermore, it is expected to contribute to cost reduction as a suitable precursor for lithium manganese iron phosphate.
[0010] [2] The method for producing manganese iron phosphate particles according to [1], wherein the molar ratio of iron to manganese in the metal powder is 20-30:70-80.
[0011] [3] The method for producing manganese iron phosphate particles according to [1] or [2], wherein the metal powder is ferromanganese.
[0012] [4] The method for producing manganese iron phosphate particles according to any one of [1] to [3], wherein the carbon content in the metal powder is 4% by mass or more and 7% by mass or less. [Brief explanation of the drawing]
[0013] [Figure 1] Figure 1 is a schematic flowchart of the method for producing lithium manganese iron phosphate in this embodiment. [Figure 2] Figure 2 shows an example of a SEM image of manganese iron phosphate particle No. 1. [Figure 3] Figure 3 is an example of a SEM image of manganese iron phosphate particles No. 2. [Figure 4] Figure 4 shows an example of an SEM image of manganese iron phosphate particle No. 3. [Figure 5] Figure 5 shows an example of a SEM image of manganese phosphate particle No. 4. [Figure 6] Figure 6 shows an example of an SEM image of iron phosphate particles No. 5. [Figure 7] Figure 7 shows an example of a SEM image of manganese iron phosphate particle No. 6. [Modes for carrying out the invention]
[0014] Embodiments of the present disclosure (hereinafter abbreviated as "Embodiments") and examples of the present disclosure (hereinafter abbreviated as "Examples") are described below. However, these embodiments and examples do not limit the technical scope of the present disclosure.
[0015] The manganese iron phosphate particles produced in this embodiment can be used to produce lithium manganese iron phosphate. Furthermore, lithium manganese iron phosphate is suitably used, for example, as an electrode active material for secondary batteries, and particularly as a positive electrode active material for non-aqueous electrolyte secondary batteries.
[0016] <Method for producing manganese phosphate iron particles> Figure 1 is a schematic flowchart of the method for producing manganese iron phosphate particles in this embodiment. Hereinafter, "the method for producing manganese iron phosphate particles in this embodiment" may be abbreviated as "this manufacturing method." This manufacturing method includes at least (a) a slurry preparation step and (b) a drying step.
[0017] 《(a) Slurry Preparation Process》 In the slurry preparation process, a metal powder containing carbon, iron, and manganese and a phosphoric acid compound are mixed in a protic solvent and stirred to obtain a slurry containing manganese iron phosphate particles.
[0018] Examples of the metal powder containing carbon, iron, and manganese include a powder obtained by mixing carbon powder, iron powder, and manganese powder, an iron-manganese alloy powder containing carbon, etc. In the metal powder containing carbon, iron, and manganese, the molar ratio of iron to manganese is preferably 0 to 50:50 to 100, more preferably 20 to 30:70 to 80. The manganese iron phosphate particles obtained by using such a metal powder are expected to contribute to the improvement of the characteristics of the secondary battery.
[0019] Ferromanganese is preferably used as the iron-manganese alloy powder containing carbon. Ferromanganese is an iron-manganese alloy containing a high volume of manganese and is classified into high-carbon ferromanganese, medium-carbon ferromanganese, low-carbon ferromanganese, etc. according to the carbon content (see JIS standard G2301). Ferromanganese is mass-produced worldwide and is available at low cost, and has the advantage that its composition of iron and manganese is close to that of lithium manganese iron phosphate currently used as a positive electrode active material (iron:manganese = 20 to 30:70 to 80 (molar ratio)).
[0020] The carbon content in the metal powder containing carbon, iron, and manganese may be 0.5 mass% or more and 10 mass% or less. When the carbon content in the metal powder containing carbon, iron, and manganese is within the above range, the micronization of the obtained manganese iron phosphate particles is promoted. The carbon content in the metal powder containing carbon, iron, and manganese may be 1 mass% or more and 8 mass% or less, or may be 4 mass% or more and 7 mass% or less.
[0021] Examples of phosphoric acid compounds include phosphoric acid, ammonium dihydrogen phosphate, and ammonium dihydrogen phosphate. Among these, phosphoric acid is preferred from the viewpoint of improving battery characteristics, and it is preferable to use it as a 70-90% by mass aqueous solution of phosphoric acid.
[0022] Examples of protic solvents include water, alcohols such as methanol and ethanol, etc. Of these, water is preferred from a cost standpoint.
[0023] In this process, metal powders containing carbon, iron, and manganese are mixed with a phosphate compound in a protic solvent and stirred. Mixing and stirring these metal powders in a protic solvent generates hydrocarbon gases such as hydrogen, methane, and ethane. Manganese iron phosphate particles synthesized using this gas generation method spontaneously become finer through gasification, eliminating the need for grinding. As a result, a reduction in grinding time is expected.
[0024] Stirring may be performed, for example, by adding metal powders containing carbon, iron, and manganese to a protic solvent to prepare a slurry, and then adding the phosphate compound dropwise. The stirring speed when adding the phosphate compound dropwise may be, for example, 100 to 1000 rpm. There are no particular restrictions on the stirring time, but it is preferable to continue stirring until gas generation stops.
[0025] This process forms manganese iron phosphate particles in the slurry. After stirring, the slurry may be filtered.
[0026] After stirring, the resulting slurry may be pulverized. By pulverizing the slurry, manganese iron phosphate particles with the desired particle size can be obtained. Pulverization may be carried out using, for example, a ball mill, bead mill, planetary mill, jet mill, planetary mixer, homogenizer, etc. There are no particular restrictions on the pulverization time, and it may be, for example, 5 to 60 minutes. After pulverization, the slurry may be filtered.
[0027] 《(b) Drying process》 In the drying process, the slurry containing manganese iron phosphate particles is dried to obtain manganese iron phosphate particles.
[0028] Drying can be carried out by any method. For example, the slurry may be dried using a spray dryer or hot air.
[0029] The particle size of the primary particles of the manganese iron phosphate particles obtained by this manufacturing method may be, for example, 800 nm or less, 600 nm or less, or 400 nm or less. The particle size of the manganese iron phosphate particles obtained by this manufacturing method may be, for example, 50 nm or more, 100 nm or more, or 200 nm or more.
[0030] The shape of the manganese iron phosphate particles obtained by this manufacturing method may be, for example, spherical, columnar, lumpy, or flaky. The shape of the manganese iron phosphate particles obtained by this manufacturing method is preferably spherical. Spherical manganese iron phosphate particles are expected to contribute to improving the characteristics of secondary batteries. [Examples]
[0031] <No.1> High-carbon ferromanganese was added to water. Then, 75% by mass of phosphoric acid was added dropwise while stirring to obtain a slurry. Stirring was continued for 1 hour until gas generation ceased. The obtained slurry was dried with hot air at 80°C to obtain manganese iron phosphate particles No. 1. The high-carbon ferromanganese contained 6.8% by mass of carbon, and the molar ratio of iron to manganese in the high-carbon ferromanganese was 8:2. The high-carbon ferromanganese and phosphoric acid were mixed so that the molar ratio of iron and manganese in the high-carbon ferromanganese to phosphorus in the phosphoric acid was 1:1.
[0032] 《No.2》 Medium carbon ferromanganese was added to water. Then, 75% by mass of phosphoric acid was added dropwise while stirring to obtain a slurry. Stirring was continued for 1 hour until gas generation ceased. The obtained slurry was dried with hot air at 80°C to obtain manganese iron phosphate particles No. 2. The medium carbon ferromanganese contained 1.8% by mass of carbon, and the molar ratio of iron to manganese in the medium carbon ferromanganese was 8:2. The medium carbon ferromanganese and phosphoric acid were mixed so that the molar ratio of iron and manganese in the medium carbon ferromanganese to phosphorus in the phosphoric acid was 1:1.
[0033] 《No.3》 Low-carbon ferromanganese was added to water. Then, 75% by mass of phosphoric acid was added dropwise while stirring to obtain a slurry. Stirring was continued for 1 hour until gas generation ceased. The obtained slurry was dried with hot air at 80°C to obtain manganese iron phosphate particles No. 3. The low-carbon ferromanganese contained 0.8% by mass of carbon, and the molar ratio of iron to manganese in the low-carbon ferromanganese was 8:2. The low-carbon ferromanganese and phosphoric acid were mixed so that the molar ratio of iron and manganese in the low-carbon ferromanganese to phosphorus in the phosphoric acid was 1:1.
[0034] 《No.4》 Manganese powder was added to water. Then, 75% by mass of phosphoric acid was added dropwise while stirring to obtain a slurry. Stirring was carried out for 1 hour. The obtained slurry was placed in a ball mill and ground using 5 mm balls for 30 minutes. The ground slurry was dried with hot air at 80°C to obtain manganese phosphate particles No. 4. The manganese powder and phosphoric acid were mixed so that the molar ratio of manganese to phosphorus in the phosphoric acid was 1:1. Note that the manganese powder did not contain carbon.
[0035] 《No.5》 Iron powder was added to water. Then, 75% by mass of phosphoric acid was added dropwise while stirring to obtain a slurry. Stirring was carried out for 1 hour. The obtained slurry was placed in a ball mill and ground using 5 mm balls for 30 minutes. The ground slurry was dried with hot air at 80°C to obtain iron phosphate particles No. 5. The iron powder and phosphoric acid were mixed so that the molar ratio of iron to phosphorus in the phosphoric acid was 1:1. Note that the iron powder did not contain carbon.
[0036] 《No.6》 Manganese powder and iron powder were added to water. Then, 75% by mass of phosphoric acid was added dropwise while stirring to obtain a slurry. Stirring was carried out for 1 hour. The obtained slurry was placed in a ball mill and ground using 5 mm balls for 30 minutes. The ground slurry was dried with hot air at 80°C to obtain manganese iron phosphate particles No. 6. The manganese powder, iron powder, and phosphoric acid were mixed so that the molar ratio of manganese and iron to phosphorus in the phosphoric acid was 1:1. Note that the manganese powder and iron powder did not contain carbon.
[0037] <Observation> Each particle from No. 1 to 6 was observed using a Scanning Electron Microscope (SEM) (magnification: 5000x). SEM images for each particle number are shown in Figures 2 to 7.
[0038] Furthermore, the particle diameter and shape of the primary particles of each particle from No. 1 to 6 were calculated. The primary particle diameter was calculated as the average distance between the two furthest points on the contour line of 10 or more primary particles randomly selected from each SEM image. Table 1 shows the average particle diameter and shape of the primary particles of each particle from No. 1 to 6.
[0039] [Table 1]
[0040] Figures 2-4 and Table 1 confirm that manganese iron phosphate particles No. 1-3 were already micronized without the need for grinding. On the other hand, particles No. 4-6 were micronized through a separate grinding process.
[0041] The shape of manganese iron phosphate particles No. 1-3 was spherical. When lithium manganese iron phosphate is used as a positive electrode active material for secondary batteries, its spherical shape is thought to contribute to improving the characteristics of the secondary battery. In addition, generally speaking, positive electrode active materials with smaller particle sizes are thought to contribute to improving the characteristics of secondary batteries more than positive electrode active materials with larger particle sizes. Thus, manganese iron phosphate particles No. 1-3 are considered suitable for use as a precursor for lithium manganese iron phosphate. Furthermore, it is expected that they can be manufactured at low cost as a precursor for lithium manganese iron phosphate.
[0042] These embodiments and examples are illustrative in all respects. These embodiments and examples are not restrictive. The technical scope of this disclosure includes all modifications in the sense and scope equivalent to the claims. For example, it is intended from the outset that any configuration may be extracted from these embodiments and examples and combined in any way.
Claims
1. A step of mixing metal powder containing carbon, iron, and manganese with a phosphate compound in a protic solvent and stirring to obtain a slurry containing iron manganese phosphate particles, A method for producing manganese iron phosphate particles, comprising the step of drying the slurry to obtain the manganese iron phosphate particles.
2. The method for producing manganese iron phosphate particles according to claim 1, wherein the molar ratio of iron to manganese in the metal powder is 20 to 30:70 to 80.
3. The method for producing manganese iron phosphate particles according to claim 1 or 2, wherein the metal powder is ferromanganese.
4. The method for producing manganese iron phosphate particles according to claim 1 or 2, wherein the carbon content in the metal powder is 4% by mass or more and 7% by mass or less.