JP6389773B2 - Method for producing positive electrode material for lithium secondary battery - Google Patents

Description

  The present invention relates to a method for producing a positive electrode material for a lithium secondary battery.

  Among positive electrode materials used for lithium secondary batteries, lithium manganese phosphate (hereinafter referred to as “LMP” as appropriate) that is excellent in stability and can be reduced in cost by being composed of resource-rich elements. Materials such as lithium iron phosphate (hereinafter referred to as “LFP” where appropriate) are attracting attention as potential candidates for future positive electrode materials.

  When this LMP and LFP are compared, the operating voltage of the lithium secondary battery can be increased by using LMP. Therefore, by selecting LMP as the positive electrode material, it is possible to increase the voltage and energy density of the lithium secondary battery.

However, LMP is a yarn teller ion in which Mn ³⁺ generated after charging is unstable and has lower lithium ion conductivity and electronic conductivity than LFP. Therefore, when LMP is selected as the positive electrode material, there is a problem that cycle characteristics and charge / discharge stability are not good.

Therefore, a technique has been proposed in which part of Mn constituting LMP is replaced with Fe to solve the above-mentioned problems.
For example, Patent Document 1 includes a general formula Li _{1 + x} Mn _y Fe _z PO ₄ (wherein x, y, and z are 0 <x <0.1, 0.5 <y <0.95, 0.9, respectively). A positive electrode material comprising a compound represented by <y + z ≦ 1) is disclosed.

JP 2002-151072 A

  Here, a method for producing lithium manganese iron phosphate (hereinafter referred to as “LMFP” as appropriate) in which a part of Mn constituting LMP is replaced with Fe is roughly divided into “solid phase method” and “hydrothermal method”. Can be divided.

  The hydrothermal method is advantageous in that it is excellent in crystallinity and can produce uniform particles. However, when LMFP, which is a Fe—Mn solid solution, is produced by the hydrothermal method, it is difficult to precipitate Fe and Mn at the same time. Therefore, it is expected that phase separation into LMP and LFP occurs. When such phase separation occurs, the synergistic effect of LMP and LFP is not exhibited, and only the respective defects appear.

  On the other hand, in the solid phase method, LMFP in which Fe and Mn are appropriately dissolved can be produced by mixing, pulverizing, and firing the precursor. Furthermore, in order to increase the density of energy, it is necessary to set the Fe content in LLMP to about 10 to 30 mol%. In the case of the solid phase method, the content of each precursor to be prepared first is set. By doing so, it is possible to appropriately control the content ratio of Fe in the LMFP.

  However, simply adopting the solid-phase method does not mean that it is possible to produce a high-performance LFP. For example, in order to improve performance such as charge / discharge capacity, various conditions at the time of manufacture are examined and appropriate conditions are set. Need to find out.

  Then, this invention makes it a subject to provide the manufacturing method of the positive electrode material for lithium secondary batteries excellent in charge / discharge capacity.

  In order to solve the above-mentioned problems, the inventors of the present invention can manufacture a positive electrode material having excellent charge / discharge capacity by specifying a predetermined LMF precursor and mixing and grinding using a wet bead mill. And found the present invention.

That is, in the method for producing a positive electrode material for a lithium secondary battery according to the present invention, the element ratio of Li: Mn: Fe: P is 1 to 1.1: 1-x: x: 1 (0 <x <1). as will be, and the manganese phosphate, lithium hydroxide, and iron phosphate, and phosphoric acid, as well as blending, mixing pulverizing step of pulverizing a mixture of slurry formulated with carbon compounds by wet bead mill, the mixed A firing step for firing the pulverized product after the grinding step, and the firing step comprises firing at 350 ° C. to 500 ° C. for 4 hours to 12 hours in an inert gas atmosphere. And a secondary firing step in which firing is performed at 650 ° C. to 780 ° C. for 4 hours to 12 hours in an inert gas atmosphere .

Also, method for producing a cathode material for lithium secondary battery according to the present invention, between the front Symbol primary firing step and the second firing step, preferably contains carbon mixing step of mixing a carbon material.

In the method for producing a positive electrode material for a lithium secondary battery according to the present invention, it is preferable that a specific surface area of the manganese phosphate used in the mixing and pulverizing step is 15 m ² / g or more.

  Further, in the method for producing a positive electrode material for a lithium secondary battery according to the present invention, the volume-based particle size distribution of the pulverized product after the mixing and pulverizing step is (1) D50 <0.2 μm and (2) D97 <2. It is preferable to satisfy 0.0 μm.

  In the method for producing a positive electrode material for a lithium secondary battery according to the present invention, the carbon compound used in the mixing and pulverizing step is preferably a saccharide or an organic acid.

  In the method for producing a positive electrode material for a lithium secondary battery according to the present invention, it is preferable that the carbon compound used in the mixing and grinding step is ascorbic acid.

  In the method for producing a positive electrode material for a lithium secondary battery according to the present invention, the carbon raw material used in the carbon mixing step is preferably a coal pitch.

According to the method for producing a positive electrode material for a lithium secondary battery according to the present invention, by specifying the precursor of LMFP to a predetermined one (manganese phosphate, lithium hydroxide, iron phosphate, phosphoric acid, carbon compound), During mixing in the mixing and pulverizing step, a pre-reaction occurs between manganese phosphate and lithium hydroxide, and iron phosphate and lithium hydroxide. In this preliminary reaction, the reaction between the main substances is advanced to some extent before the reaction in the firing, so that the crystallinity is improved and the charge / discharge capacity of the finally obtained positive electrode material is improved. . Furthermore, a pulverized product in which each raw material is appropriately mixed can be obtained by pulverization using a wet bead mill in the mixing and pulverizing step.
As mentioned above, according to the manufacturing method of the positive electrode material for lithium secondary batteries which concerns on this invention, the positive electrode material excellent in charging / discharging capacity | capacitance can be manufactured.

It is a flowchart of the manufacturing method of the positive electrode material for lithium secondary batteries which concerns on this embodiment. It is a graph which shows the charging / discharging curve at the time of implementing a grinding | pulverization process using a wet bead mill or a dry-type bead mill. It is image data of the positive electrode material measured using a scanning electron microscope (SEM). It is a graph which shows the charging / discharging curve (0.1, 0.2, 1, 3, 5C) at the time of using a citric acid and PVA as a carbon raw material. It is a graph which shows the charging / discharging curve (0.1, 0.2, 1, 3, 5C) at the time of using a citric acid, PVA, and coal pitch as a carbon raw material. It is a graph which shows the charging / discharging curve (0.1, 0.2, 1, 3, 5C) at the time of using coal pitch as a carbon raw material. It is a graph which shows the charging / discharging curve (0.1, 0.2, 1, 3, 5C) at the time of using manganese phosphate whose specific surface area is 13.0 m < ² > / g as a raw material. It is a graph which shows the charging / discharging curve (0.1, 0.2, 1, 3, 5C) at the time of using manganese phosphate whose specific surface area is 18.4 m < ² > / g as a raw material.

  Hereinafter, an embodiment for carrying out a method for producing a positive electrode material for a lithium secondary battery according to the present invention (hereinafter referred to as “positive electrode material” as appropriate) will be described with reference to the drawings.

[Positive electrode material for lithium secondary batteries]
First, the “positive electrode material” manufactured by the method for manufacturing a positive electrode material according to the present embodiment will be described.
The application target of the positive electrode material is a “lithium secondary battery”. This lithium secondary battery is a battery in which lithium ions (Li ⁺ ) are responsible for ion conduction during charge and discharge, such as a positive electrode, a negative electrode, an electrolyte, etc. It is comprised including the member of. And the lithium secondary battery used as application object is not specifically limited about the material, structure, etc. of members other than a positive electrode.
For example, lithium secondary batteries using various materials such as a carbon-based material, a metal oxide-based material, a silicon-based material, and a tin-based alloy material are applicable as the negative electrode. Further, lithium secondary batteries using various electrolytes such as an organic electrolyte system, an ionic liquid system, and a solid electrolyte system are also applicable.

The positive electrode material is configured to include a fine positive electrode active material having a uniform primary particle size. Then, the positive electrode active material, lithium manganese iron phosphate (hereinafter, appropriately referred to as "LMFP setting"), this LMFP _{is, Li n Mn 1-x Fe} x PO 4 (n is 0 <n ≦ 1, X is 0 <X ≦ 1).
Note that the positive electrode active material is preferably coated with a carbon compound because LMFP has low electronic conductivity. In addition to the positive electrode active material, the positive electrode material may contain a known binder, a conductive agent (conductive auxiliary agent), and the like. Furthermore, the positive electrode material may further include a positive electrode active material different from the positive electrode active material described above.

Next, a method for producing a positive electrode material for a lithium secondary battery according to this embodiment will be described with reference to FIG.
[Method for producing positive electrode material for lithium secondary battery]
The method for producing a positive electrode material according to the present embodiment includes a mixing and grinding step S1 and firing steps S2 and S4. And the manufacturing method of the positive electrode material which concerns on this embodiment has a baking process consisting of primary baking process S2 and secondary baking process S4, and carbon mixing process S3 between primary baking process S2 and secondary baking process S4. May be included. Furthermore, the manufacturing method of the positive electrode material according to the present embodiment may include a classification step S5 after the secondary firing step S4.

In addition, in the manufacturing method of the positive electrode material according to the present embodiment, it is possible to perform the baking treatment at a time. However, the firing steps S2 and S4 are divided into two steps, a primary firing step S2 and a secondary firing step S4, and a carbon mixing step S3 is performed between the two steps to produce a positive electrode material excellent in electronic conductivity. It is preferable in that it can be performed.
Therefore, in the following, the manufacturing method of the positive electrode material when the firing treatments S2 and S4 are performed in two steps and the carbon mixing step S3 is included between the two steps will be described for each step.

(Mixing and grinding process)
The mixing and pulverizing step S1 is a step of mixing and pulverizing a slurry containing manganese phosphate, lithium hydroxide, iron phosphate, phosphoric acid, and a carbon compound by a wet bead mill. Here, the slurry is an aqueous slurry using water as a solvent in detail.
In the mixing and grinding step S1, the order of mixing the respective raw materials before the grinding treatment is not particularly limited. For example, after mixing manganese phosphate and iron phosphate, lithium hydroxide is added and mixed, and then, What is necessary is just to implement in the flow of adding and mixing phosphoric acid, and finally adding and mixing a carbon compound.

(Mixing and grinding process: raw material)
The raw materials (LMFP raw materials, carbon compounds) used in the mixing and grinding step S1 are as follows in detail.
Regarding the raw material (precursor) of LMFP, the raw material for introducing lithium is lithium hydroxide (LiOH), and the raw material for introducing manganese is manganese phosphate (eg, manganese phosphate: Mn ₃ (PO ₄ )). ₂ ), the raw material for introducing iron is iron phosphate (for example, ferric phosphate: FePO ₄ .nH ₂ O), and the raw material for introducing phosphoric acid is phosphoric acid (H ₃ PO ₄ ) It is.

By specifying the raw material of LMFP used in the mixing and grinding step S1 as described above, at the stage of the mixing process in the mixing and grinding step S1, between manganese phosphate and lithium hydroxide, iron phosphate and lithium hydroxide, Pre-reaction occurs. Although the detailed phenomenon in this pre-reaction has not been clearly clarified, the crystallinity is increased by promoting the reaction between the main substances to some extent before the reaction in the firing steps S2 and S4, and the uniform primary It is considered that the charge / discharge capacity of the finally obtained positive electrode material is improved by forming the particle group.
In addition, since the LMFP raw material used in the mixing and pulverizing step S1 does not include ammonium phosphate that has been conventionally used as a raw material for introducing phosphoric acid, generation of harmful gas can be avoided.

Regarding the raw material (precursor) of LMFP, the manganese phosphate that is a raw material for introducing manganese preferably has a specific surface area of 15 m ² / g or more, and more preferably 18 m ² / g or more. By using manganese phosphate having a large specific surface area as a raw material in this way, the specific surface area of the obtained positive electrode active material is also increased, and finally the charge / discharge capacity of the positive electrode material can be increased.
The specific surface area can be measured based on a gas adsorption method (BET method).

  A carbon compound is a compound containing carbon as a component and acts as a reducing agent. The carbon compound is preferably a water-soluble saccharide or organic acid, and more preferably ascorbic acid, from the viewpoint that the slurry is easy to handle without increasing the viscosity of the slurry. If a polymer carbon compound such as polyvinyl alcohol (PVA) is used, the viscosity of the slurry increases, and the handling property of the slurry becomes poor.

(Mixing and crushing process: mixing ratio of raw materials)
The blending ratio of the LMFP raw material (precursor) used in the mixing and grinding step S1 is not particularly limited. For example, the element ratio of “Li: Mn: Fe: P” is “1 to 1.1: 1−x: The above-mentioned raw materials may be blended so that “x: 1” (0 ≦ x <1).
The blending ratio of the carbon compound is not particularly limited, but may be blended so as to be 0 to 10 wt% with respect to the total weight (LMFP raw material weight + carbon compound weight).

(Mixing and grinding process: grinding process)
The pulverization process in the mixing and pulverizing step S1 is performed by a wet bead mill. Note that a wet bead mill is, for example, a method in which a plurality of beads (grinding media) and a slurry to be crushed (and a solvent such as water) are put into a container called a grinding chamber, and the whole container or beads are rotated. By this, the beads crush the solid matter in the slurry to form a fine pulverized product. The wet bead mill includes what is called a wet ball mill (a grinding media is a ball).
In the present invention, the pulverization process is carried out with a wet bead mill. However, by using this “wet bead mill”, the pulverization process can be performed with each raw material suitably dispersed in a solvent. it can. As a result, it is considered that a pulverized product in which each raw material is appropriately mixed can be obtained and finally the charge / discharge capacity of the positive electrode material can be increased as compared with the case where the pulverization treatment is performed by “dry”. In addition, the reaction proceeds between lithium hydroxide and manganese phosphate or iron phosphate, but by using a wet bead mill, coarse parts such as lithium phosphate generated by a partial reaction proceed and As a result of the progress of the reaction on the surface newly appeared by crushing, a more uniform and fine firing precursor can be produced.

Various conditions (diameter / number of beads, rotation speed, pulverization time, etc.) relating to the wet bead mill are not particularly limited, but the pulverization process using the wet bead mill is based on the volume basis of the pulverized product (primary particles) after the pulverization process. It is preferable that the particle size distribution satisfy (1) D50 <0.2 μm and (2) D97 <2.0 μm. By carrying out the pulverization treatment in this way, the obtained positive electrode active material can be made fine and uniform, and finally the charge / discharge capacity of the positive electrode material can be increased.
The volume-based particle size distribution of the pulverized product can be measured based on a laser diffraction / scattering method. “D50, D97” are so-called 50% particle diameter and 97% particle diameter, and in a volume-based cumulative particle size distribution curve (horizontal axis: particle diameter (μm), vertical axis: cumulative frequency (%)). It is a particle diameter showing a cumulative frequency of 50% and 97%. Moreover, this particle diameter is a sphere equivalent diameter.

(Primary firing process)
The primary firing step S2 is a step of performing primary firing (temporary firing) on the pulverized product obtained in the mixing and grinding step S1.
The primary firing step S2 is a step in which the pulverized product is heated to react to an intermediate state before reaching the final positive electrode active material. Accompanied by outbreaks. Therefore, the firing temperature (final temperature) of the primary firing is a temperature at which most of the gas has been released and the reaction leading to the positive electrode active material does not proceed completely, that is, the second stage two in a higher temperature range. A temperature that leaves room for re-diffusion / homogenization of constituent elements in the positive electrode active material during the next firing may be selected.
Specifically, the firing temperature (attainment temperature) in the primary firing step S2 is preferably 300 ° C. or higher and 600 ° C. or lower, and more preferably 350 ° C. or higher and 500 ° C. or lower.

The firing time in the primary firing step S2 (the retention time after reaching the ultimate temperature) is not particularly limited, but is preferably a time during which the above reaction occurs sufficiently, for example, 4 hours to 12 hours.
In addition, the firing atmosphere in the primary firing step S2 is not particularly limited, but in the absence of oxygen gas (in an inert gas atmosphere) in order to prevent the formation of oxidants as impurities and promote the reduction of remaining oxidants. Preferably there is.

(Carbon mixing process)
The carbon mixing step S3 is a step of mixing a carbon raw material into the fired product after the primary firing step S2 in order to coat the positive electrode active material with carbon. In the carbon mixing step S3, the pulverization process may be performed while mixing the carbon compound.

(Carbon mixing process: raw material)
Examples of the carbon raw material to be mixed in the carbon mixing step S3 include bitumen and the like, preferably a coal pitch having a softening point of 300 ° C. or lower, particularly preferably a coal pitch having a softening point of 200 ° C. or lower. By using a coal pitch having a low softening point, the positive electrode active material is appropriately carbon-coated, the particle group of the product becomes uniform, and finally the charge / discharge capacity of the positive electrode material can be increased.

  The carbon raw material is 2 wt% or more and 8 wt% or less with respect to the total weight (weight of the fired product after the primary firing step S2 + weight of the carbon raw material) so that the positive electrode active material can be appropriately carbon coated. It is preferable to add such that 3 wt% or more and 6 wt% or less is more preferable.

(Secondary firing process)
The secondary firing step S4 is a step of performing secondary firing (main firing) on the fired product after the carbon mixing step S3.
And in secondary baking process S4, it is necessary to advance reaction which reaches the positive electrode material of a final product completely. Therefore, what is necessary is just to select the temperature which the said reaction advances completely as a calcination temperature (attainment temperature) of secondary calcination.
Specifically, the firing temperature (attainment temperature) in the secondary firing step S4 is preferably 600 ° C. or higher and 800 ° C. or lower, and more preferably 650 ° C. or higher and 780 ° C. or lower.

  In the secondary firing step S4, unlike the primary firing step S2, the generation of gas hardly occurs. Therefore, the carbon mixed in the carbon mixing step S3 can be easily coated on the positive electrode active material.

The firing time in the secondary firing step S4 (holding time after reaching the reached temperature) is not particularly limited, but is preferably a time during which the above reaction occurs sufficiently, for example, 4 hours or more and 12 hours or less.
Further, the firing atmosphere in the secondary firing step S4 is not particularly limited, but in the absence of oxygen gas (in an inert gas atmosphere) in order to prevent the formation of oxidized oxidants and promote the reduction of remaining oxidants. Is preferred.

(Classification process)
The classification step S5 is a step of performing classification in order to exclude coarse particles from the fired product obtained in the secondary firing step S4.
For example, in the classification step S5, classification is performed using a sieve or the like so as to exclude particles having a diameter of 30 μm or more.

  The manufacturing method of the positive electrode material for a lithium secondary battery according to the present embodiment is as described above, but includes other steps between or before and after each step within a range that does not adversely affect each step. May be. For example, a drying step of drying the pulverized product may be included after the mixing and pulverizing step S1. Moreover, a cooling step for cooling the fired product may be included after the primary firing step S2 and the secondary firing step S4. Furthermore, after the classification step S5, a slurrying step of mixing a known binder, a conductive agent (conductive auxiliary agent) or the like may be included in order to apply the positive electrode material to the current collector.

  In addition, as for conditions that are not clearly shown in the respective steps, it is sufficient to use conventionally known conditions, and it is needless to say that the conditions can be appropriately changed as long as the effects obtained by the processing in the respective steps are exhibited.

Next, the manufacturing method of the positive electrode material for a lithium secondary battery according to the present invention will be specifically described by comparing an example satisfying the requirements of the present invention with a comparative example not satisfying the requirements of the present invention.
In Example 1, the influence of the pulverization method (wet / dry) on the charge / discharge capacity of the positive electrode material will be described.

[Method for producing positive electrode material]
(Sample 1)
The manufacturing method of the positive electrode material of the test material 1 is shown below.
First, as a positive electrode active material precursor, 29.13 g of lithium hydroxide (LiOH · H ₂ O, manufactured by Toyo Chemical Co., Ltd.) and manganese phosphate (Mn ₃ (PO ₄ ) ₂ · 2H ₂ O, manufactured by Budenheim) 63.29 g, ferric phosphate (FePO ₄ .2H ₂ O, Budenheim) 38.91 g and phosphoric acid (H ₃ PO ₄ , Kishida Chemical Co.) 18.67 g were prepared. The granular lithium hydroxide was pulverized until D50 (volume-based 50% particle diameter measured based on laser diffraction / scattering method) was 100 μm or less. And the specific surface area of manganese phosphate was 18.4 m < ² > / g.
As a carbon compound, 6 g of ascorbic acid (manufactured by Kishida Chemical Co., Ltd.) was prepared.

Then, after mixing manganese phosphate and ferric phosphate, lithium hydroxide after pulverization was added and mixed, then phosphoric acid was added and mixed, and ascorbic acid was added and mixed. And the slurry obtained by mixing each raw material was grind | pulverized using the wet bead mill (super apex mill SAM-05 type | mold, Kotobuki Kogyo company make).
Details of the grinding treatment are shown in Table 1.

The pulverized product was heated to 450 ° C. and held for 6 hours under N ₂ gas atmosphere (primary firing: implementation on a lab scale). Then, 4 wt% of coal pitch (MCP-200D: softening point 200 ° C., manufactured by JFE Chemical Co.) was added to the fired product after the primary firing, and pulverized for 5 minutes with a dry pulverizer. Thereafter, the pulverized product was heated to 680 ° C. and held for 4 hours under N ₂ gas atmosphere (secondary firing: implementation on a lab scale). Then, the fired product after the secondary firing was cooled and then crushed and classified (excluding those having a diameter of 30 μm or more by sieving).
And the baked material after crushing and classification, acetylene black (Denka Black (registered trademark), manufactured by Denki Kagaku Kogyo Co., Ltd., 75% press product), polyvinylidene fluoride (manufactured by Kureha Battery Materials Japan, # 9100) , 86: 7: 7 (mass ratio). Next, the obtained mixture was stirred and mixed in N-methylpyrrolidone to obtain a positive electrode mixture slurry (positive electrode material).

(Sample 2)
About the manufacturing method of the positive electrode material of the test material 2, only a different point from the manufacturing method of the positive electrode material of the test material 1 is shown below.
First, as a positive electrode active material precursor, 29.13 g of lithium hydroxide (LiOH · H ₂ O, manufactured by Toyo Chemical Co., Ltd.) and manganese phosphate (Mn ₃ (PO ₄ ) ₂ · 2H ₂ O, manufactured by Budenheim) 63.29 g, ferric phosphate (FePO ₄ .2H ₂ O, Budenheim) 38.91 g and phosphoric acid (H ₃ PO ₄ , Kishida Chemical Co.) 18.67 g were prepared. The granular lithium hydroxide was pulverized until D50 (volume-based 50% particle diameter measured based on laser diffraction / scattering method) was 100 μm or less. And the specific surface area of manganese phosphate was 18.4 m < ² > / g.
Moreover, 6 g of sucrose (Kishida Chemical Co., Ltd.) was prepared as a carbon compound.

Then, after mixing manganese phosphate and ferric phosphate, lithium hydroxide after pulverization was added and mixed, then phosphoric acid was added and mixed, and sucrose was added and mixed. And the mixture of each raw material was grind | pulverized using the dry table crusher crusher (made by Sansho Industry Co., Ltd.).
Details of the grinding treatment are shown in Table 1.

[Method for producing lithium secondary battery]
The positive electrode material obtained by the above-described manufacturing method was applied to the surface of an aluminum foil as a current collector (application amount: 8 mg / cm ² ). And after application | coating, the positive electrode was manufactured by making it dry.
Then, using a metal aluminum plate and a metal SUS plate as positive and negative electrode current collectors respectively in a stainless steel coin battery case (model number CR2032), the positive electrode and the metal lithium foil negative electrode are assembled via a separator (manufactured by Celgard), and an electrolyte solution And filled with a 7/3 mixed electrolyte solution (produced by Kishida Chemical Co., Ltd.) of ethyl methyl carbonate / ethylene carbonate in which 1M LiPF ₆ was dissolved to produce a coin-type lithium secondary battery.
In addition, a series of battery assemblies such as positive and negative electrodes, a diaphragm, and an electrolyte solution were performed in a glove box substituted with argon.

[Evaluation of charge / discharge characteristics]
The lithium secondary batteries of the test materials 1 and 2 were evaluated for charge / discharge characteristics at room temperature (25 ° C.).
Specifically, a discharge curve (0.1 C discharge) showing the relationship between the charge / discharge capacity and the battery voltage was created. The discharge curve is obtained when discharging is performed at 0.1 C. Here, “1 C” is a current value for discharging the entire capacity of the battery in one hour. Is a current value 1/10 of the current value.
In FIG. 2, the solid line is the charge / discharge curve of the specimen 1, and the dotted line is the charge / discharge curve of the specimen 2.

[Examination of results]
In FIG. 2, when the discharge curves of the specimen 1 and the specimen 2 are compared, it can be confirmed that the battery voltage of the specimen 1 is higher. In addition, when the charge curves and discharge curves of the test material 1 and the test material 2 are compared, it can be confirmed that the capacity of the test material 1 is larger.
From these results, it was found that the test material 1 which was pulverized using a wet bead mill can increase the charge / discharge capacity.

  Next, Example 2 demonstrates the influence which the kind of carbon raw material has on the charging / discharging capacity | capacitance of positive electrode material.

[Method for producing positive electrode material]
(Sample 3)
Compared with the manufacturing method of the positive electrode material of the test material 1, the manufacturing method of the positive electrode material of the test material 3 uses citric acid (made by Kishida Chemical Co., Ltd.) with respect to the whole weight as a carbon raw material in the baked product after the primary baking. The point of adding 3.3 wt% and PVA (manufactured by Kuraray Co., Ltd.) 2.3% was different from the scale of primary firing (implemented on a pilot scale of 20 kg level), and the conditions of other production methods were the same.

(Sample 4)
Compared with the manufacturing method of the positive electrode material of the test material 3, the manufacturing method of the positive electrode material of the test material 4 uses 2% of coal pitch (MCP200D, manufactured by JFE Chemical Co.) as a carbon raw material in the fired product after the primary firing. Only the difference was made, and the conditions of the other production methods were the same.

(Sample 5)
Compared with the manufacturing method of the positive electrode material of the test material 3, the manufacturing method of the positive electrode material of the test material 5 uses coal pitch (MCP200D: softening point 200 degreeC, JFE Chemical Co., Ltd.) as a carbon raw material in the baked product after primary baking. ) Was added only 5 wt% with respect to the total weight, and the conditions of the other production methods were the same.

[Method for producing lithium secondary battery]
About the manufacturing method of a lithium secondary battery, it carried out on the same conditions as Example 1. FIG.

[Confirmation of positive electrode material shape]
About the test materials 3-5, the shape of the positive electrode material was confirmed.
Specifically, about the positive electrode material after pulverizing and classifying the fired product after the secondary firing, the scanning electron microscope (S-3400N, manufactured by Hitachi High-Technologies Corp.) is used to increase 30,000 times or 20,000 times. The shape was observed at a magnification.
3A shows the image data of the specimen 3 (30,000 times), FIG. 3B shows the image data of the specimen 4 (30,000 times), and FIG. ) Is image data (20,000 times) of the specimen 5.

[Evaluation of charge / discharge characteristics]
About the lithium secondary battery of the test materials 3-5, the charge / discharge characteristic was evaluated in room temperature (25 degreeC).
Specifically, discharge curves (0.1C, 0.2C, 1C, 3C, 5C discharge) showing the relationship between the charge / discharge capacity and the battery voltage were created.
4 is a charge / discharge curve of the test material 3, FIG. 5 is a charge / discharge curve of the test material 4, and FIG. 6 is a charge / discharge curve of the test material 5.

[Examination of results]
In FIG. 3, when the states of the test materials 3 to 5 are compared, in the test material 3 and the test material 4, the aggregation of primary particles is stronger than that of the test material 5. It can be confirmed that No. 5 is a more uniform and more dispersible particle group.
From this result, it was found that the test material 5 using coal pitch as a carbon raw material is suitable for producing particles having uniform and good dispersibility.
4, 5, and 6, when the discharge curves of the specimens 3 to 5 are compared, it can be confirmed that the battery voltage of the specimen 5 is higher. In addition, when the charge curves and discharge curves of the test materials 3 to 5 are compared, it can be confirmed that the capacity of the test material 5 is increased.
From these results, it was found that the charge / discharge capacity can be increased by using coal pitch as the carbon raw material.

  Next, Example 3 demonstrates the influence which the specific surface area of the manganese phosphate which is a raw material has on the charging / discharging capacity | capacitance of positive electrode material.

[Method for producing positive electrode material]
(Sample 6)
Compared with the manufacturing method of the positive electrode material of Specimen 1, the manufacturing method of the positive electrode material of Specimen 6 is different from that of the wet bead mill in that the specific surface area of the manganese phosphate used was 13.0 m ² / g. The only difference was the use of SC220 made by Coke Co., Ltd. and the scale of secondary firing (scale of 10 kg level), and the conditions of other production methods were the same.

(Sample 7)
The manufacturing method of the positive electrode material of the test material 7 differs from the manufacturing method of the positive electrode material of the test material 6 only in that the specific surface area of the manganese phosphate used was 18.4 m ² / g. The conditions of the manufacturing method were the same.

[Method for producing lithium secondary battery]
About the manufacturing method of a lithium secondary battery, it carried out on the same conditions as Example 1. FIG.

[Confirmation of specific surface area of positive electrode material]
For the test materials 6 and 7, the specific surface area of the positive electrode material was confirmed.
Specifically, the positive electrode material after pulverizing and classifying the fired product after the secondary firing was performed by the BET method (BELSORP-mini, manufactured by Nippon Bell Co., Ltd.).
The specific surface area of manganese phosphate is also a value measured by the same method.

[Evaluation of charge / discharge characteristics]
The lithium secondary batteries of the test materials 6 and 7 were evaluated for charge / discharge characteristics.
Specifically, discharge curves (0.1C, 0.2C, 1C, 3C, 5C discharge) showing the relationship between the charge / discharge capacity and the battery voltage were created.
7 is a charge / discharge curve of the test material 6, and FIG. 8 is a charge / discharge curve of the test material 7.

[Examination of results]
In Table 2, when the results of the test material 6 and the test material 7 are compared, it can be confirmed that the specific surface area of the positive electrode material of the test material 7 is increased.
From this result, it was found that the specific surface area of the finally obtained positive electrode material can be increased by increasing the specific surface area of the raw material manganese phosphate.

7 and 8, when the discharge curves of the test materials 6 and 7 are compared, it can be confirmed that the battery voltage of the test material 7 is higher. In addition, when the charge curves and discharge curves of the test materials 6 and 7 are compared, it can be confirmed that the capacity of the test material 7 is increased.
From these results, it was found that the charge / discharge capacity can be increased by using manganese phosphate having a large specific surface area as a raw material.

S1 mixing and grinding step S2 primary firing step (firing step)
S3 Carbon mixing process S4 Secondary firing process (firing process)
S5 classification process

Claims (7)

Manganese phosphate, lithium hydroxide, and iron phosphate so that the element ratio of Li: Mn: Fe: P is 1 to 1.1: 1-x: x: 1 (0 <x <1) And a mixing and pulverizing step of mixing and pulverizing the slurry containing the carbon compound with a wet bead mill, and
A firing step for firing the pulverized product after the mixing and grinding step ,
The firing step includes a primary firing step in which firing is performed at 350 ° C. to 500 ° C. for 4 hours to 12 hours in an inert gas atmosphere, and 650 ° C. to 780 ° C. for 4 hours to 12 hours in an inert gas atmosphere. And a secondary firing step of firing for a period of time or less . A method for producing a positive electrode material for a lithium secondary battery. Between the front Symbol primary firing step the secondary firing step, method for producing a cathode material for lithium secondary battery according to claim 1, characterized in that it comprises a carbon mixture step of mixing a carbon material. 3. The method for producing a positive electrode material for a lithium secondary battery according to claim 1, wherein a specific surface area of the manganese phosphate used in the mixing and pulverizing step is 15 m ² / g or more. 4. The volume-based particle size distribution of the pulverized product after the mixing and pulverizing step satisfies the following (1) and (2): 4. Manufacturing method of positive electrode material for lithium secondary battery.
(1) D50 <0.2 μm
(2) D97 <2.0 μm   The method for producing a positive electrode material for a lithium secondary battery according to any one of claims 1 to 4, wherein the carbon compound used in the mixing and pulverizing step is a saccharide or an organic acid.   The said carbon compound used in the said mixing and grinding | pulverization process is ascorbic acid, The manufacturing method of the positive electrode material for lithium secondary batteries of any one of Claims 1-5 characterized by the above-mentioned.   The said carbon raw material used in the said carbon mixing process is a coal pitch, The manufacturing method of the positive electrode material for lithium secondary batteries of Claim 2 characterized by the above-mentioned.