Manufacturing method of lithium iron manganese phosphate

Abstract

To provide a manufacturing method of lithium iron manganese phosphate that can reduce costs and suppress waste.SOLUTION: A manufacturing method of lithium iron manganese phosphate comprises the steps of mixing, stirring, and grinding metal powder comprising iron and manganese and a phosphate compound to obtain first precursor particles, mixing, stirring, and grinding the first precursor particles and a lithium source to obtain second precursor particles, and firing the second precursor particles to obtain lithium iron manganese phosphate.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing lithium iron manganese phosphate. [Background technology]

[0002] Japanese Patent Application Laid-Open No. 2014-65641 (Patent Document 1) discloses a method for producing iron phosphate by reacting iron with phosphorus to produce a precipitate and then washing the precipitate, and also discloses a method for producing lithium iron phosphate 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] Japanese Patent Application Laid-Open No. 2014-65641 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-81866 Summary of the Invention [Problem to be solved by the invention]

[0005] Lithium iron phosphate and lithium manganese iron phosphate are used as positive electrode active materials. As disclosed in Patent Document 1, iron phosphate exists as a suitable precursor for lithium iron phosphate. On the other hand, there is no suitable precursor for lithium manganese iron phosphate, and no low-cost production method has been established.

[0006] Furthermore, as disclosed in Patent Document 2, lithium manganese iron phosphate can be produced by a hydrothermal reaction. However, this production method requires the use of sulfates and the like, which must be discarded after the reaction.

[0007] An object of the present disclosure is to provide a method for producing lithium manganese iron phosphate at low cost, which can reduce waste. [Means for solving the problem]

[0008] [1] A step of mixing, stirring, and pulverizing a metal powder containing iron and manganese with a phosphate compound to obtain first precursor particles; mixing, stirring, and grinding the first precursor particles and a lithium source to obtain second precursor particles; and calcining the second precursor particles to obtain lithium manganese iron phosphate.

[0009] By using metal powder containing iron and manganese as raw materials and mixing, stirring, and grinding it with a phosphate compound, lithium iron manganese phosphate can be produced at low cost via phosphate (precursor). Furthermore, the manufacturing process does not require the use of sulfates, etc., which reduces waste. Furthermore, it is expected that low energy consumption will be achieved throughout the entire process.

[0010] [2] The method for producing lithium manganese iron phosphate according to [1], wherein the molar ratio of iron and manganese to phosphorus in the second precursor particles is 5:4.

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

[0012] [4] The method for producing lithium manganese iron phosphate according to any one of [1] to [3], wherein in the step of obtaining the second precursor particles, a carbon source is further added, followed by stirring and pulverization. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic flow chart of a method for producing lithium manganese iron phosphate in this embodiment. [Figure 2] FIG. 2 is an explanatory diagram illustrating steps in the method for producing lithium manganese iron phosphate of this embodiment. [Figure 3] Figure 3 shows an example of an SEM image of No. 1 lithium manganese iron phosphate. [Figure 4] Figure 4 shows an example of an SEM image of No. 2 lithium manganese iron phosphate. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment of the present disclosure (hereinafter may be abbreviated as "the present embodiment") and an example of the present disclosure (hereinafter may be abbreviated as "the present example") will be described. However, the present embodiment and the example do not limit the technical scope of the present disclosure.

[0015] The lithium manganese iron phosphate produced in this embodiment is suitable for use, 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 of manufacturing lithium manganese iron phosphate> FIG. 1 is a schematic flowchart of a method for producing lithium manganese iron phosphate according to this embodiment. Hereinafter, "a method for producing lithium manganese iron phosphate according to this embodiment" may be abbreviated as "this production method." This production method includes at least (a) a first precursor particle production step, (b) a second precursor particle production step, and (c) a calcination step. Each step will be described below with reference to FIG. 2.

[0017] (a) First precursor particle production step In the first precursor particle production step, a metal powder containing iron and manganese and a phosphate compound are mixed, stirred, and pulverized to obtain the first precursor particles.

[0018] Examples of the metal powder containing iron and manganese include a powder obtained by mixing iron powder and manganese powder, an iron-manganese alloy powder, and the like. In the metal powder containing iron and manganese, when the number of moles of iron is a and the number of moles of manganese is b, it is preferable that 0 < a < 0.5 and 0.5 < b < 1. Lithium iron manganese phosphate produced by using such a metal powder is expected to contribute to improving the characteristics of a secondary battery.

[0019] As the iron-manganese alloy powder, ferromanganese is preferably used. 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 a low cost, and has an advantage that its composition of iron and manganese is close to that of lithium iron manganese phosphate currently used as a positive electrode active material (iron:manganese = 20 - 30:70 - 80 (molar ratio)).

[0020] Examples of the phosphoric acid compound include phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and the like. Among these, from the viewpoint of enhancing battery characteristics, phosphoric acid is preferable, and it is preferably used as an aqueous phosphoric acid solution of 70 - 90% by mass.

[0021] In this step, a metal powder containing iron and manganese and a phosphoric acid compound are mixed, stirred, and pulverized. <

[0022] Stirring may be performed, for example, by adding a metal powder containing iron and manganese to water to prepare a slurry, followed by adding a phosphate compound dropwise. By adding the phosphate compound dropwise to the slurry, a layer of the metal powder containing iron and manganese (first layer 11) and a layer of the phosphate compound (second layer 12) are first formed (FIG. 2(a)). Next, by stirring, a coating of manganese iron phosphate (third layer 13) is formed between the first layer 11 and the second layer 12 by phosphorylating the first layer 11 (FIG. 2(b)). The stirring speed when adding the phosphate compound dropwise may be, for example, 100 to 1000 rpm. The stirring time is not particularly limited, but adding ferromanganese to water generates hydrogen. Therefore, it is preferable to continue stirring until hydrogen generation is complete.

[0023] After stirring, the resulting slurry is pulverized. By pulverizing the resulting slurry, peeling of the second layer 12 and phosphorylation of the first layer 11 occur repeatedly (FIG. 2(c)). As a result, first precursor particles are formed in the slurry. The pulverization may be performed using, for example, a ball mill, a bead mill, a planetary mill, a jet mill, a planetary mixer, a homogenizer, or the like. There is no particular limitation on the pulverization time, and it may be, for example, 5 to 60 minutes. After pulverization, the slurry may be filtered.

[0024] (b) Second precursor particle production step In the second precursor particle production step, the first precursor particles and a lithium source are mixed, stirred, and pulverized to obtain the second precursor particles.

[0025] Examples of the lithium source include lithium carbonate, lithium hydroxide, and lithium nitrate.

[0026] In this step, the first precursor particles and a lithium source are mixed, stirred, and pulverized.

[0027] Stirring may be performed, for example, while adding a lithium source to the slurry containing the first precursor particles obtained in the first precursor particle production step. By stirring the slurry while adding the lithium source, a lithium phosphate layer (second layer 14) is formed (FIG. 2(d)). The stirring speed when adding the lithium source may be, for example, 100 to 500 rpm. Meanwhile, this step is thought to involve heat generation due to the neutralization reaction and foaming due to the use of the lithium source. Therefore, it is preferable to slow the stirring speed to suppress heat generation and foaming. There is no particular limitation on the stirring time, but it is preferable to continue stirring until the reaction is complete. To avoid a sudden increase in pH, the lithium source is preferably added over a period of 15 minutes or more, more preferably 30 minutes or more.

[0028] After stirring, the slurry is pulverized. By pulverizing the slurry, peeling of the second' layer 14 and phosphorylation of the first layer 11 occur repeatedly. As a result, second precursor particles are formed in the slurry (FIG. 2(e)). The pulverization may be performed using, for example, a ball mill, a bead mill, a planetary mill, a jet mill, a planetary mixer, a homogenizer, or the like. There is no particular limitation on the pulverization time, and it may be, for example, 30 to 120 minutes. After pulverization, the slurry may be filtered.

[0029] The molar ratio (iron + manganese:phosphorus) of iron and manganese to phosphorus (phosphate) in the second' layer 14 of the second precursor particle is, for example, 5:4, 3:2, or 1:1, and preferably 5:4. When the molar ratio is 5:4, it is expected that lithium manganese iron phosphate having a small particle size and a high density will be obtained.

[0030] In this step, a carbon source may be further added, followed by stirring and pulverization. The lithium manganese iron phosphate produced in this embodiment is expected to be a highly safe and suitable positive electrode active material for obtaining a high-power non-aqueous electrolyte secondary battery. However, there is room for improvement in electrical conductivity and lithium ion diffusibility. From this perspective, it is preferable to coat the surface of the lithium manganese iron phosphate with carbon. This is expected to further improve battery characteristics.

[0031] Examples of the carbon source include sugars such as glucose, fructose, starch, cellulose, etc. The amount of the carbon source added may be, for example, 0.5 to 15 parts by mass with respect to 100 parts by mass of the metal powder containing iron and manganese.

[0032] 《(c) Firing process》 In the calcination step, the second precursor particles are calcined to obtain lithium manganese iron phosphate 20 (FIG. 2(f)).

[0033] The firing temperature may be, for example, 500 to 1000° C. If the firing temperature is too low, unreacted second precursor particles may remain, or the crystallinity of the resulting lithium manganese iron phosphate may be insufficient. If the firing temperature is too high, the amount of amorphous lithium manganese iron phosphate may increase.

[0034] The temperature increase rate may be, for example, 1 to 10° C. / min. When the temperature increase rate is within the above range, the reaction proceeds evenly, and the crystallinity of the obtained lithium manganese iron phosphate is stable.

[0035] The firing time may be, for example, 1 to 12 hours. If the firing time is too short, unreacted second precursor particles may remain, or the crystallinity of the resulting lithium manganese iron phosphate may be insufficient. If the firing time is too long, the amount of amorphous lithium manganese iron phosphate may increase. Note that the firing time in this disclosure refers to the time from the start of heating until the maximum temperature is reached until heating at the maximum temperature, excluding the time until the maximum temperature is reached (heating time) and the time until cooling to room temperature (30°C) after heating at the maximum temperature (cooling time).

[0036] The firing atmosphere may be, for example, an inert atmosphere containing argon, nitrogen, or the like.

[0037] Other processes The present production method may include a drying step after the second precursor particle production step. Any drying method may be used in the present production method. For example, the slurry may be dried using a spray dryer or hot air. [Example]

[0038] <No.1> 35.2 g of ferromanganese was added to 400 g of water. Then, 73 g of 85% by mass phosphoric acid was added dropwise while stirring at 200 rpm to obtain a slurry. Stirring was continued for 1 hour until hydrogen generation ceased.

[0039] The resulting slurry was placed in a planetary mill and pulverized for 15 minutes using 5 mm beads, and the pulverized slurry was filtered using a filter with 75 μm openings.

[0040] To the filtered slurry, 23.5 g of lithium carbonate was added over 30 minutes while stirring at 200 rpm, followed by adding 9 g of fructose and stirring for 30 minutes to dissolve the fructose, yielding a slurry.

[0041] The obtained slurry was placed in a bead mill (Super Apex Mill, Metal & Machinery Co., Ltd.) and pulverized for 90 minutes using 0.1 mm beads. The pulverized slurry was filtered using a filter with 75 μm openings.

[0042] The filtered slurry was dried using a spray dryer.

[0043] The dried second precursor particles were calcined for 3 hours in an argon atmosphere at a temperature of 680°C with a temperature increase rate of 5°C / min. The calcined particles were sieved through a filter with a mesh size of 75 μm to obtain No. 1 lithium manganese iron phosphate (positive electrode active material).

[0044] No.2 No. 2 lithium manganese iron phosphate (positive electrode active material) was obtained using the same materials and method as No. 1, except that 23.5 g of lithium carbonate was added all at once.

[0045] <Analysis> The second precursor particles Nos. 1 and 2 after drying with the spray dryer were irradiated with X-rays using an X-ray diffraction (XRD) device to confirm the molar ratio of iron and manganese to phosphorus (iron + manganese:phosphorus) in the second precursor particles. In No. 1, the ratio of iron + manganese:phosphorus was 5:4, and in No. 2, the ratio of iron + manganese:phosphorus was 3:2.

[0046] <Observation> The lithium manganese iron phosphate samples No. 1 and No. 2 were observed under a scanning electron microscope (SEM) (magnification: 10,000 times). SEM images of each sample are shown in Figures 3 and 4.

[0047] As shown in Figures 3 and 4, No. 1 lithium manganese iron phosphate was a fine particle with a smaller particle size than No. 2 lithium manganese iron phosphate. In general, a positive electrode active material with a smaller particle size is thought to contribute more to improving the performance of secondary batteries than a positive electrode active material with a larger particle size. In other words, No. 1 lithium manganese iron phosphate is expected to contribute more to improving the performance of secondary batteries than No. 2 lithium manganese iron phosphate.

[0048] Furthermore, the lithium manganese iron phosphate obtained above is obtained via a phosphate (precursor), and is expected to be produced at low cost. Furthermore, since no sulfate or other salts are used in the production process, waste can be reduced.

[0049] The present embodiment and examples are illustrative in all respects. The present embodiment and examples are not limiting. The technical scope of the present disclosure encompasses all modifications within the meaning and scope equivalent to the claims. For example, it is also intended from the beginning that any configuration may be extracted from the present embodiment and examples and that they may be combined in any desired manner. [Explanation of symbols]

[0050] 11 1st layer, 12 2nd layer, 13 3rd layer, 14 2'th layer, 20 Lithium manganese iron phosphate.

Claims

1. a step of mixing, stirring, and pulverizing a metal powder containing iron and manganese with a phosphate compound to obtain first precursor particles; mixing, stirring, and grinding the first precursor particles and a lithium source to obtain second precursor particles; and calcining the second precursor particles to obtain lithium manganese iron phosphate.

2. 2. The method for producing lithium manganese iron phosphate according to claim 1, wherein the molar ratio of iron and manganese to phosphorus in the second precursor particles is 5:

4.

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

4. 3. The method for producing lithium manganese iron phosphate according to claim 1, wherein in the step of obtaining the second precursor particles, a carbon source is further added, followed by stirring and pulverization.

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