Method for producing ferromanganese phosphate particles

Abstract

Provided is a method for producing ferromanganese phosphate particles, the method comprising: a step for obtaining a slurry containing ferromanganese phosphate particles by mixing and stirring a metal powder containing carbon, iron, and manganese and a phosphoric acid compound in a protonic solvent; and a step for drying the slurry to obtain the ferromanganese phosphate particles.

Description

Technical Field

[0001] This disclosure relates to a method for manufacturing ferromanganese phosphate particles. Background Technology

[0002] Japanese Patent Application Publication No. 2014-65641 discloses a method for producing iron phosphate by reacting iron with phosphorus to form a precipitate and then washing the precipitate. Furthermore, it discloses a method for producing lithium iron phosphate by reacting the aforementioned iron phosphate with a lithium compound.

[0003] A method for producing lithium manganese iron phosphate via hydrothermal reaction is disclosed in Japanese Patent Application Publication No. 2016-81866. Summary of the Invention

[0004] Lithium iron phosphate and lithium manganese iron phosphate are used as positive electrode active materials. As disclosed in Japanese Patent Application Publication No. 2014-65641, iron phosphate is a suitable precursor for lithium iron phosphate. On the other hand, there is no suitable precursor for lithium manganese iron phosphate, and a method for its low-cost manufacture has not yet been established.

[0005] Furthermore, as disclosed in Japanese Patent Application Publication No. 2016-81866, lithium manganese iron phosphate can be manufactured via a hydrothermal reaction. On the other hand, the lithium manganese iron phosphate obtained by this manufacturing method has a large particle size, and it must be further pulverized in order to be used as a positive electrode active material, which takes time.

[0006] The purpose of this invention is to provide a method for manufacturing manganese iron phosphate particles that can shorten the crushing time.

[0007] [1] A method for manufacturing ferromanganese phosphate particles, comprising: a step of mixing and stirring a metal powder containing carbon, iron, and manganese and a phosphoric acid compound in a protic solvent to obtain a slurry containing ferromanganese phosphate particles; and

[0008] The process of drying the slurry to obtain the manganese iron phosphate particles.

[0009] By mixing and stirring metal powders containing carbon, iron, and manganese with phosphoric acid compounds in a protic solvent, hydrocarbon gases such as hydrogen, methane, and ethane are generated. Manganese iron phosphate particles synthesized using this gas-generating method spontaneously atomize due to gasification, thus eliminating the need for pulverization. As a result, pulverization time is expected to be reduced. Furthermore, as a suitable precursor to lithium manganese iron phosphate, it is anticipated to contribute to cost reduction.

[0010] [2] According to the method for manufacturing manganese iron phosphate particles described in [1], the molar ratio of iron to manganese in the metal powder is 20-30:70-80.

[0011] [3] The method for manufacturing manganese iron phosphate particles according to [1] or [2], wherein the metal powder is manganese iron.

[0012] [4] The method for manufacturing 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.

[0013] The above and other objects, features, aspects and advantages of the present invention will become apparent from the following detailed description of the invention, which will be understood in conjunction with the accompanying drawings. Attached Figure Description

[0014] Figure 1 This is a simplified flowchart of the manufacturing method of lithium manganese iron phosphate in this embodiment.

[0015] Figure 2 This is an example of a SEM image of No. 1 manganese iron phosphate particles.

[0016] Figure 3 This is an example of a SEM image of manganese iron phosphate particles No. 2.

[0017] Figure 4 This is an example of a SEM image of manganese iron phosphate particles No. 3.

[0018] Figure 5 This is an example of a SEM image of manganese phosphate particles No. 4.

[0019] Figure 6 This is an example of a SEM image of iron phosphate particles No. 5.

[0020] Figure 7 This is an example of a SEM image of manganese iron phosphate particles No. 6. Detailed Implementation

[0021] The embodiments of this disclosure (hereinafter referred to as "this embodiment") and the examples of this disclosure (hereinafter referred to as "this example") will be described below. However, this embodiment and the examples do not limit the technical scope of this disclosure.

[0022] The manganese iron phosphate particles manufactured in this embodiment can be used to manufacture lithium manganese iron phosphate. Furthermore, lithium manganese iron phosphate is suitable, for example, as an electrode active material for secondary batteries, and particularly suitable as a positive electrode active material for non-aqueous electrolyte secondary batteries.

[0023] <Method for manufacturing manganese iron phosphate particles>

[0024] Figure 1This is a simplified flowchart of the method for manufacturing ferromanganese phosphate particles according to this embodiment. Hereinafter, "the method for manufacturing ferromanganese phosphate particles according to this embodiment" may be simply referred to as "this manufacturing method". This manufacturing method includes at least (a) a slurry preparation step and (b) a drying step.

[0025] (a) Slurry preparation process)

[0026] In the slurry preparation process, metal powders containing carbon, iron, and manganese are mixed and stirred with phosphate compounds in a protic solvent to obtain a slurry containing manganese iron phosphate particles.

[0027] Examples of metal powders containing carbon, iron, and manganese include powders composed of a mixture of carbon, iron, and manganese powders, and iron-manganese alloy powders containing carbon. In these carbon-, iron-, and manganese-containing metal powders, the molar ratio of iron to manganese is preferably 0–50:50–100, more preferably 20–30:70–80. The manganese-iron phosphate particles obtained by using such metal powders are expected to contribute to improved characteristics of secondary batteries.

[0028] Ferromanganese is suitable as a carbon-containing iron-manganese alloy powder. Ferromanganese is an iron-manganese alloy with high manganese content, and is classified according to carbon content into high-carbon ferromanganese, medium-carbon ferromanganese, and low-carbon ferromanganese, etc. (refer to JIS standard G2301). Ferromanganese is mass-produced worldwide and can be obtained at low cost. It also has the advantage of having an iron and manganese composition close to that of lithium iron phosphate, which is currently used as a positive electrode active material (iron:manganese = 20-30:70-80 (molar ratio)).

[0029] The carbon content in the metal powder containing carbon, iron, and manganese can be 0.5% by mass or more and 10% by mass or less. When the carbon content in the metal powder containing carbon, iron, and manganese is within the above range, it promotes the micronization of the obtained ferromanganese phosphate particles. The carbon content in the metal powder containing carbon, iron, and manganese can be either 1% by mass or more and 8% by mass or 4% by mass or more and 7% by mass or less.

[0030] Examples of phosphoric acid compounds include phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate. Among these, from the viewpoint of improving battery performance, phosphoric acid is preferred, and it is especially preferred to use it in the form of a 70-90% by mass aqueous solution.

[0031] Examples of protic solvents include water, methanol, and ethanol. Among these, water is preferred from a cost perspective.

[0032] In this process, metal powders containing carbon, iron, and manganese are mixed and stirred with a phosphate compound in a protic solvent. By mixing and stirring the metal powders containing carbon, iron, and manganese with the phosphate compound in a protic solvent, hydrocarbon gases such as hydrogen, methane, and ethane are generated. The manganese-iron phosphate particles synthesized using this method spontaneously atomize due to gasification, thus eliminating the need for pulverization. As a result, a reduction in pulverization time is expected.

[0033] Stirring can be performed, for example, by adding metal powders containing carbon, iron, and manganese to a protic solvent to prepare a slurry, while simultaneously dripping the phosphoric acid compound. The stirring speed during the dripping of the phosphoric acid compound can be, for example, 100 to 1000 rpm. There is no particular limitation on the stirring time, but it is preferable to continue stirring until the generation of gas ceases.

[0034] This process forms ferric manganese phosphate particles in the slurry. After stirring, the slurry can be filtered.

[0035] After stirring, the resulting slurry can be pulverized. By pulverizing the slurry, manganese iron phosphate particles with the desired particle size can be obtained. Pulverization can be carried out using, for example, ball mills, bead mills, planetary mills, jet mills, homogenizers, etc. There is no particular limitation on the pulverization time; for example, it can be 5 to 60 minutes. After pulverization, the slurry can be filtered.

[0036] (b) Drying process)

[0037] In the drying process, the slurry containing ferromanganese phosphate particles is dried to obtain ferromanganese phosphate particles.

[0038] Drying can be carried out by any method. For example, slurry can be dried using a spray dryer or hot air.

[0039] The primary particle size of the ferromanganese phosphate particles obtained by this manufacturing method can be, for example, less than 800 nm, less than 600 nm, or less than 400 nm. The particle size of the ferromanganese phosphate particles obtained by this manufacturing method can be, for example, greater than 50 nm, greater than 100 nm, or greater than 200 nm.

[0040] The ferromanganese phosphate particles obtained by this manufacturing method can be spherical, columnar, blocky, or flaky. The spherical shape is preferred. Spherical ferromanganese phosphate particles are expected to contribute to improved characteristics of secondary batteries.

[0041] [Example]

[0042] <No.1>

[0043] High-carbon ferromanganese was added to water. Then, 75% by mass of phosphoric acid was added dropwise while stirring to obtain a slurry. Stirring continued for 1 hour until gas generation ceased. The slurry was dried using hot air at 80°C to obtain No. 1 ferromanganese phosphate particles. Furthermore, 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 in a molar ratio of iron and manganese in the high-carbon ferromanganese to phosphorus in the phosphoric acid of 1:1.

[0044] <No.2>

[0045] Medium-carbon ferromanganese was added to water. Then, 75% by mass of phosphoric acid was added dropwise while stirring to obtain a slurry. Stirring continued for 1 hour until gas generation ceased. The slurry was dried using hot air at 80°C to obtain No. 2 ferromanganese phosphate particles. 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 in a molar ratio of iron and manganese in the medium-carbon ferromanganese to phosphorus in the phosphoric acid of 1:1.

[0046] <No.3>

[0047] Low-carbon ferromanganese was added to water. Then, 75% by mass phosphoric acid was added dropwise while stirring to obtain a slurry. Stirring continued for 1 hour until gas generation ceased. The slurry was dried using hot air at 80°C to obtain No. 3 ferromanganese phosphate particles. Additionally, 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 in a molar ratio of iron and manganese in the low-carbon ferromanganese to phosphorus in the phosphoric acid of 1:1.

[0048] <No.4>

[0049] 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 resulting slurry was fed into a ball mill and pulverized for 30 minutes using 5 mm balls. The pulverized slurry was dried using 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. In addition, the manganese powder did not contain carbon.

[0050] <No.5>

[0051] 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 resulting slurry was fed into a ball mill and pulverized for 30 minutes using 5 mm balls. The pulverized slurry was dried using hot air at 80°C to obtain iron phosphate particles No. 5. The iron powder and phosphoric acid were mixed in a 1:1 molar ratio of iron to phosphorus in the phosphoric acid. Furthermore, the iron powder contained no carbon.

[0052] <No.6>

[0053] Manganese and iron powders were 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. The resulting slurry was then fed into a ball mill and pulverized for 30 minutes using 5mm balls. The pulverized slurry was dried using 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. Furthermore, the manganese and iron powders contained no carbon.

[0054] <Observation>

[0055] Particles No. 1 through No. 6 were observed using SEM (Scanning Electron Microscope) at 5000x magnification. The SEM images of each No. are shown below. Figures 2-7 .

[0056] In addition, the particle size and shape of the primary particles for particles No. 1 to No. 6 were calculated and confirmed. The primary particle size was calculated as the average distance between the two furthest points on the contour lines of more than 10 primary particles randomly extracted from each SEM image. The average particle size and shape of the primary particles for particles No. 1 to No. 6 are shown in Table 1.

[0057] [Table 1]

[0058]

[0059] Depend on Figures 2-4 Table 1 confirms that the manganese iron phosphate particles No. 1 to No. 3 are micronized even without being crushed. On the other hand, the particles No. 4 to No. 6 are micronized through a separate crushing process.

[0060] The manganese iron phosphate particles No. 1 to No. 3 are spherical in shape. When using lithium manganese iron phosphate as the positive electrode active material for secondary batteries, it is believed that the spherical shape contributes to improved battery characteristics. Furthermore, it is generally believed that smaller particle sizes of positive electrode active materials contribute to improved secondary battery characteristics compared to larger particle sizes. Therefore, the manganese iron phosphate particles No. 1 to No. 3 are considered suitable as precursors for lithium manganese iron phosphate. Moreover, it is desirable to manufacture these precursors at low cost.

[0061] This embodiment and example are illustrative in all respects. This embodiment and example are not restrictive. The scope of this disclosure includes the meaning equivalent to the claims and all modifications within that scope. For example, it was originally conceived that arbitrary structures be extracted from this embodiment and example and combined arbitrarily.

[0062] The embodiments of the present invention have been described above, but it should be considered that the embodiments disclosed herein are illustrative in all respects and not limiting. The scope of the present invention is defined by the claims, including all modifications within the meaning and scope equivalent to the claims.

Claims

1. A method for manufacturing ferromanganese phosphate particles, comprising: The process of mixing and stirring metal powders containing carbon, iron, and manganese with a phosphate compound in a protic solvent to obtain a slurry containing ferric manganese phosphate particles; and The process of drying the slurry to obtain the manganese iron phosphate particles.

2. The method for manufacturing manganese iron phosphate particles according to claim 1, wherein, The molar ratio of iron to manganese in the metal powder is 20-30:70-80.

3. The method for manufacturing manganese iron phosphate particles according to claim 1 or 2, wherein, The metal powder is ferromanganese.

4. The method for manufacturing manganese iron phosphate particles according to claim 1 or 2, wherein, The carbon content in the metal powder is more than 4% by mass and less than 7% by mass.

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