JP2018032567A - Method for manufacturing lithium phosphate-based positive electrode active material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a lithium phosphate-based positive electrode active material, by which superior battery characteristics can be developed without a hydrothermal reaction step.SOLUTION: A method for manufacturing a lithium phosphate-based positive electrode active material without a hydrothermal reaction step comprises the steps of (I) mixing a solution A and a solution B to obtain a mixture solution X, provided that (the solution A) is a solution containing a lithium compound, a phosphate compound and water A, in which the mole ratio (Li:P) of lithium to phosphorus is 1:x(x=1-3), and the mole ratio (water A:Li) of the water A to lithium is 80:1 to 1400:1, and (the solution B) is a solution containing a manganese compound and/or an iron compound, and water B, in which the mole ratio (water B:(Mn+Fe)) of a quantity of the water B to a total quantity of manganese and iron is 13:1 to 100:1, (II) adding an alkali to the resultant mixture solution X to obtain a slurry liquid Y of which the mole ratio (Alkali:(Mn+Fe)) of a quantity of the alkali to a total quantity of manganese and iron is 3:2 to 4:1; and (III) separating the resultant slurry liquid Y and firing a solid content.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a lithium phosphate-based positive electrode active material that can provide a lithium phosphate-based positive electrode active material capable of exhibiting high battery properties without going through a hydrothermal reaction step.

  Conventionally, highly conductive substances have been used as positive electrode materials and negative electrode materials in order to improve battery performance. In recent years, next-generation batteries such as lithium ion batteries have been increasingly used, and various positive electrode materials for such batteries have been developed. Lithium manganese phosphate is one of them. Phosphoric acid, manganese compound and water are mixed to make an acidic solution, and lithium hydroxide is added dropwise to make it alkaline and subjected to hydrothermal reaction. An obtained method is known (see Non-Patent Document 1).

Under these circumstances, lithium phosphate compounds such as lithium manganese phosphate have low electrical conductivity, so that they can be sufficiently refined to ensure good battery properties for effective use as a positive electrode active material. Various manufacturing methods for obtaining this as a positive electrode active material are known. For example, in Patent Document 1, a solution containing lithium and a solution containing phosphorus are mixed, formed into a weakly alkaline mixed solution, dropped into a solution containing manganese and the like, and subjected to hydrothermal synthesis. A method for producing a composite oxide containing a metal is disclosed. Patent Document 2 discloses that a precursor mixture containing a Li ⁺ source, a PO ₄ ³⁻ source, a manganese source, and the like is generated, and subjected to a dispersion treatment or the like to react under hydrothermal conditions (hydrothermal reaction). To obtain a LiMPO ₄ compound (M is at least one metal from the first transition series).

JP 2012-211072 A JP 2007-511458 A

Hongmei Ji et al, Elestrochimica Acta 56 (2011), p3093-3100

  However, in any of the methods described above, in order to obtain a positive electrode active material through a hydrothermal reaction, at least two steps of a hydrothermal reaction step and a subsequent firing step are allowed to reach a high temperature range. Therefore, it is necessary to prepare a processing apparatus required for this, and the manufacturing process is inevitable. For these reasons, it is desired to realize a manufacturing method that can omit the heat treatment step as much as possible without degrading the performance of the obtained positive electrode active material.

  Therefore, the subject of this invention is providing the manufacturing method of the lithium phosphate type | system | group positive electrode active material which can express the outstanding battery characteristic, without passing through a hydrothermal reaction process.

  Accordingly, the present inventors have made various studies and found that a specific solution containing a lithium compound, a phosphoric acid compound, and water, a manganese compound and / or an iron compound, and a specific solution containing water were used, and an alkaline solution was used. Through the process of adding a specific amount of lithium phosphate-based positive electrode active material capable of exhibiting excellent battery characteristics without going through a hydrothermal reaction process, the present invention is completed. It came to.

That is, the present invention provides (I) the following solution A and solution B:
(Solution A) A lithium compound, a phosphoric acid compound, and water A are contained, the molar ratio of lithium to phosphorus (Li: P) is 1: x (x = 1 to 3), and water A and lithium A solution having a molar ratio (water A: Li) of 80: 1 to 1400: 1 (solution B) containing a manganese compound and / or an iron compound, and water B, and a total amount of water B, manganese and iron; A step of obtaining a mixed solution X by mixing a solution having a molar ratio (water B: (Mn + Fe)) of 13: 1 to 100: 1,
(II) An alkali is added to the obtained mixed liquid X, and a slurry liquid Y in which the molar ratio of the alkali and the total amount of manganese and iron (alkali: (Mn + Fe)) is from 3: 2 to 4: 1. Obtaining step,
(III) A method for producing a lithium phosphate-based positive electrode active material that does not involve a hydrothermal reaction step, comprising a step of separating the obtained slurry liquid Y and firing the solid content.

  According to the method for producing a lithium phosphate-based positive electrode active material of the present invention, it is not necessary to go through a hydrothermal reaction step, and the heat treatment for reaching only the firing step in the final step to a high temperature range is excellent. Since a lithium phosphate-based positive electrode active material that can exhibit battery physical properties can be obtained, simplification of the manufacturing method can be effectively achieved. Further, since the amount of the lithium compound used as the lithium source can be reduced, the efficiency of the manufacturing method can be improved.

Hereinafter, the present invention will be described in detail.
The manufacturing method of the lithium phosphate positive electrode active material of the present invention includes (I) the following solution A and solution B:
(Solution A) A lithium compound, a phosphoric acid compound, and water A are contained, the molar ratio of lithium to phosphorus (Li: P) is 1: x (x = 1 to 3), and water A and lithium A solution having a molar ratio (water A: Li) of 80: 1 to 1400: 1 (solution B) containing a manganese compound and / or an iron compound, and water B, and a total amount of water B, manganese and iron; A step of obtaining a mixed solution X by mixing a solution having a molar ratio (water B: (Mn + Fe)) of 13: 1 to 100: 1,
(II) An alkali is added to the obtained mixed liquid X, and a slurry liquid Y in which the molar ratio of the alkali and the total amount of manganese and iron (alkali: (Mn + Fe)) is from 3: 2 to 4: 1. Obtaining step,
(III) A manufacturing method that does not involve a hydrothermal reaction step, including a step of separating the obtained slurry Y and firing the solid content.
As described above, the active material precursor can be efficiently and effectively obtained by adding a specific alkali while using a solution in which a predetermined raw material compound is well dissolved. At least, it becomes possible to manufacture a lithium phosphate-based positive electrode active material, a processing apparatus required for heat treatment for reaching a high temperature region can be omitted, and the manufacturing method can be simplified.

In step (I), the following solution A and solution B:
(Solution A) A lithium compound, a phosphoric acid compound, and water A are contained, the molar ratio of lithium to phosphorus (Li: P) is 1: x (x = 1 to 3), and water A and lithium A solution having a molar ratio (water A: Li) of 80: 1 to 1400: 1 (solution B) containing a manganese compound and / or an iron compound, and water B, and a total amount of water B, manganese and iron; A solution having a molar ratio (water B: (Mn + Fe)) of 13: 1 to 100: 1 is mixed to obtain a mixed solution X.

  The solution A used in the step (I) contains a lithium compound, a phosphoric acid compound, and water A. The solution A means that the lithium compound as a solute and the phosphoric acid compound are completely dissolved in water as a solvent, and a highly transparent solution without causing suspended matters or precipitates in the solution, It is a liquid substance different from so-called slurry. By using such a solution, it is only necessary to add a specific amount of alkali to the mixed solution obtained by mixing with the solution B described later, without the need for heat treatment to reach the high temperature range, A slurry liquid containing the precursor can be effectively obtained.

Examples of the lithium compound include lithium hydroxide (for example, LiOH.H ₂ O), lithium carbonate (for example, LiCO ₃ ), lithium sulfate, lithium acetate, and hydrates thereof. Of these, lithium carbonate is preferable from the viewpoint of solubility in water and reduction of production costs.

Examples of the phosphoric acid compound include orthophosphoric acid (H ₃ PO ₄ , phosphoric acid), metaphosphoric acid, pyrophosphoric acid, triphosphoric acid, tetraphosphoric acid, ammonium phosphate, and ammonium hydrogen phosphate. Of these, phosphoric acid is preferably used, and is preferably used as an aqueous solution having a concentration of 70 to 90% by mass.

  In such a solution A, the molar ratio of lithium to phosphorus (Li: P) may be 1: x (x = 1 to 3), from the viewpoint of securing excellent battery characteristics and from the viewpoint of productivity. These molar ratios (Li: P) are preferably 1: x (x = 1 to 2), more preferably 1: x (x = 1 to 1.5).

  The molar ratio of water A to lithium (water A: Li) may be 80: 1 to 1400: 1, avoiding unnecessary aggregation when alkali is added in step (II) described later. From the viewpoint of obtaining a highly uniform slurry Y, the ratio is preferably 90: 1 to 1300: 1, more preferably 100: 1 to 1200: 1.

  Furthermore, for example, the content of the lithium compound in the solution A is preferably 1.5 to 26 g / L, and more preferably 1.7 to 20 g / L. Moreover, the total content of the lithium compound and the phosphate compound in the solution A is preferably 6 to 270 g / L, and more preferably 6.5 to 250 g / L.

  In preparing the solution A, the order of addition of the lithium compound, phosphoric acid and water A is not particularly limited, but from the viewpoint of efficiently dissolving the lithium compound and phosphoric acid, the lithium compound and phosphoric acid are added to the water A. It is preferable to add. Moreover, after adding these, it is preferable to stir the solution A, the stirring time is preferably 5 to 120 minutes, more preferably 5 to 90 minutes, and the temperature of the solution A during stirring is preferably Is 5-80 degreeC, More preferably, it is 10-70 degreeC.

  The solution B used in the step (I) contains a manganese compound and / or an iron compound and water B. The solution B means that the manganese compound and / or the iron compound is a solute, which is completely dissolved in water as a solvent, and does not cause suspended matters or precipitates in the solution, and thus has a high transparency. However, like the solution A, it is a liquid substance different from the so-called slurry. By using such a solution, after obtaining a mixed solution using the above solution A, only by adding a specific amount of alkali to the mixed solution, without requiring a heat treatment to reach a high temperature range, A slurry liquid containing the precursor of the target product can be obtained effectively.

  The manganese compound may be a divalent manganese compound or a hydrate thereof, such as a halide such as manganese halide; a sulfate such as manganese sulfate; an organic acid salt such as manganese oxalate or manganese acetate. As well as hydrates thereof. Especially, it is preferable to use manganese sulfate or its hydrate from a viewpoint of obtaining solid content efficiently in process (III), and a viewpoint of improving battery physical property.

  The iron compound may be a divalent iron compound or a hydrate thereof, such as a halide such as iron halide; a sulfate such as iron sulfate; an organic acid salt such as iron oxalate or iron acetate. As well as hydrates thereof. Especially, it is preferable to use iron sulfate or its hydrate from a viewpoint of obtaining solid content efficiently in process (III), and a viewpoint of improving battery physical property.

  As transition metal (M) compounds other than manganese compounds or iron compounds (M represents Mg, Ca, Sr, Y, Zr, Co, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd) From the viewpoint of enhancing battery physical properties, for example, halides; organic acid salts such as oxalate and acetate; and hydrates thereof may be used.

  In such solution B, the molar ratio of water B to the total amount of manganese and iron (water B: (Mn + Fe)) may be 13: 1 to 100: 1, and an alkali is added in step (II) described later. In view of obtaining a highly uniform slurry liquid Y by avoiding unnecessary agglomeration, the precursor of the obtained lithium phosphate-based positive electrode active material is refined to ensure excellent battery characteristics and production From the viewpoint of considering the properties, the molar ratio (water B: (Mn + Fe)) is preferably 14: 1 to 80: 1, and more preferably 15: 1 to 60: 1.

  Moreover, the molar ratio (Mn: Fe) of manganese and iron in the solution B is not particularly limited, and may be y: 1-y (0 ≦ y ≦ 1).

  Furthermore, for example, the total content of the manganese compound and the iron compound in the solution B is preferably 130 to 1200 g / L, more preferably 140 to 1150 g / L.

  In preparing the solution B, the order of addition of the manganese compound and / or the iron compound and the water B is not particularly limited. From the viewpoint of efficiently dissolving the manganese compound and / or the iron compound, the manganese compound and / or the water B are dissolved. Or it is preferable to add an iron compound. Moreover, after adding these, it is preferable to stir the solution B, the stirring time is preferably 5 to 120 minutes, more preferably 5 to 90 minutes, and the temperature of the solution B during stirring is preferably Is 5-50 degreeC, More preferably, it is 10-40 degreeC.

  Next, in step (I), the solution A and the solution B are mixed to obtain a mixed solution X. Although the addition order of these solutions A and B is not particularly limited, it is preferable to add the solution B to the solution A from the viewpoint of improving the uniformity of the mixed solution X. After adding these, it is preferable to stir the mixed solution X, the stirring time is preferably 5 to 120 minutes, more preferably 5 to 90 minutes, and the temperature of the mixed solution X during stirring is preferably Is 5-50 degreeC, More preferably, it is 10-40 degreeC.

  The molar ratio (lithium: (water A + water B)) between lithium and water A and water B in the mixed solution X is preferably 1:90 from the viewpoint of promoting the formation of the precursor in the mixed solution X. -1: 1500, more preferably 1: 100-1: 1400. Further, for example, the content of the lithium compound in the mixed solution X is preferably 1 to 23 g / L, more preferably 1.5 to 21 g / L. Furthermore, the total content of the manganese compound and the iron compound in the mixed solution X is preferably 8 to 170 g / L, more preferably 9 to 155 g / L.

  In the step (II), an alkali is added to the mixed solution X obtained in the step (I), and the molar ratio between the alkali and the total amount of manganese and iron (alkali: (Mn + Fe)) is 3: 2-4. A slurry liquid Y of 1 is obtained.

  Examples of the alkali added to the mixed solution X include sodium hydroxide, potassium hydroxide, and aqueous ammonia. Especially, it is preferable to use sodium hydroxide from a viewpoint of improving the collection rate of solid content in the process (III) mentioned later, and a viewpoint of the improvement of the battery characteristic by the positive electrode active material obtained. As such sodium hydroxide, either solid (granular or flaky) or aqueous solution may be used.

  The addition amount of the alkali may be an amount such that the molar ratio of the alkali and the total amount of manganese and iron (alkali: (Mn + Fe)) is 3: 2 to 4: 1. Formation of the precursor in the mixed solution X From the viewpoint of promoting the above, the molar ratio (alkali: (Mn + Fe)) is preferably 3: 2 to 3: 1, more preferably 2: 1 to 5: 2. Moreover, from the viewpoint of enhancing the uniformity of the obtained slurry liquid Y, the alkali addition rate is preferably 10 to 100 mL / min, and more preferably 20 to 80 mL / min.

  When adding an alkali, it is preferable to stir, the stirring time is preferably 5 to 120 minutes, more preferably 10 to 90 minutes, and the temperature of the slurry Y during stirring is preferably 5 to 50. It is 10 degreeC, More preferably, it is 10-40 degreeC.

  The resulting slurry liquid Y is a liquid material in which a precursor of a lithium phosphate-based positive electrode active material is uniformly dispersed as a solid content. The pH of the slurry Y is preferably 7-11, more preferably 8-10.

  In step (III), the slurry liquid Y obtained in step (II) is separated and the solid content is baked. In order to obtain the solid content by separating the slurry liquid Y, an apparatus usually used for solid-liquid separation may be used. Examples of such apparatuses include a filter press machine, a centrifugal filter, a vacuum filter, and a Buchner funnel. . The obtained solid content is a precursor of the lithium phosphate-based positive electrode active material, and can be obtained as a powder by subsequent washing and drying.

  It is preferable to use water for washing the solid content. Specifically, it is preferable to use 3 to 10 times the amount of water, more preferably 5 to 10 times the amount of water relative to the solid content. . As a means for drying the solid content, freeze drying or vacuum drying is preferable.

The precursor of the lithium phosphate-based positive electrode active material obtained in the step (III) is effective by using the solution A and the solution B and through a so-called liquid-liquid reaction without going through a hydrothermal reaction step. It can be obtained as a fine powder.
Specifically, the precursor (powder) of the lithium phosphate positive electrode active material is represented by, for example, the following formula (I).
LiFe _a Mn _b M _c PO ₄ (I)
(In the formula (I), M is Mg, Ca, Sr, Y, Zr, Co, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd, 0 ≦ a ≦ 1, 0 ≦ b ≦ 1, and 0 ≦ c ≦ 0.3, and a and b are not 0 at the same time)

The precursor (powder) of the lithium phosphate-based positive electrode active material is amorphous, and the BET specific surface area is preferably 5 to 100 m ² / g, more preferably 10 to 90 m ² / g.

  The precursor of the obtained lithium phosphate-based positive electrode active material is preferably subjected to a treatment for supporting carbon before firing. Carbon support may be carried out by adding a carbon source such as glucose, fructose, polyethylene glycol, polyvinyl alcohol, carboxymethyl cellulose, saccharose, starch, dextrin, citric acid and water to the precursor in a conventional manner. The amount of the carbon source used is preferably 3 to 15 parts by mass as carbon contained in the carbon source, and more preferably 5 to 10 parts by mass as carbon contained in the carbon source with respect to 100 parts by mass of the precursor. Moreover, the usage-amount of a carbon source is as a carbon atom conversion amount in the lithium phosphate type positive electrode active material obtained, Preferably it is 0.3-10 mass%, More preferably, it is 0.5-7 mass%. .

  Next, the solid content is fired to obtain a positive electrode active material. The firing conditions are preferably an inert gas atmosphere or reducing conditions. In particular, from the viewpoint of promoting the decomposition of the carbon source when carbon is supported and effectively increasing the conductivity, the firing temperature is preferably It is 600-900 degreeC, More preferably, it is 650-800 degreeC, A baking time becomes like this. Preferably it is 0.1-12 hours, More preferably, it is 0.3-6 hours.

Next, a lithium ion battery containing the lithium phosphate positive electrode active material obtained by the method of the present invention as a positive electrode material will be described.
The lithium ion battery to which the positive electrode material of the present invention can be applied is not particularly limited as long as it has a positive electrode, a negative electrode, an electrolytic solution, and a separator as essential components.

  Here, as long as lithium ions can be occluded at the time of charging and released at the time of discharging, the material structure is not particularly limited, and a known material structure can be used. For example, a carbon material such as lithium metal, graphite, or amorphous carbon. It is preferable to use an electrode formed of an intercalating material capable of electrochemically inserting and extracting lithium, particularly a carbon material.

  The electrolytic solution is obtained by dissolving a supporting salt in an organic solvent. The organic solvent is not particularly limited as long as it is an organic solvent usually used for an electrolyte solution of a lithium ion secondary battery. For example, carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones An oxolane compound or the like can be used.

The type of the supporting salt is not particularly limited, but an inorganic salt selected from LiPF ₆ , LiBF ₄ , LiClO ₄ and LiAsF ₆ , a derivative of the inorganic salt, LiSO ₃ CF ₃ , LiC (SO ₃ CF ₃ ) ₂ and LiN (SO ₃ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ and LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), and organic salt derivatives It is preferable that it is at least 1 type of these.

The separator plays a role of electrically insulating the positive electrode and the negative electrode and holding the electrolytic solution. For example, a porous synthetic resin film, particularly a polyolefin polymer (polyethylene, polypropylene) porous film may be used.
The lithium ion battery obtained in this way has an S source that is effectively reduced and contains a refined lithium phosphate-based positive electrode active material as a positive electrode material, so that no volatile gas is generated. It is a high-performance battery with safety.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.

[Example 1]
To 100 g of distilled water A, 1.847 g of LiCO ₃ (manufactured by Kanto Chemical Co., Ltd., 0.025 mol) and 5.765 g of H ₃ PO ₄ (primary grade, purity 85%, 0.05 mol, manufactured by Wako Pure Chemical Industries, Ltd.) The solution A was obtained by stirring at 20 ° C. for 30 minutes. On the other hand, distilled water _{B 30g MnSO 4 · 5H 2 O} 8.438g ( Kanto Chemical Co. special grade, 0.035 mol), and FeSO ₄ · 7H ₂ O 4.17g (Kanto Chemical Co. special grade, 0.015 mol) and And stirred for 15 minutes at 20 ° C. to obtain solution B. Next, after adding the solution B to the solution A and stirring at 20 ° C. for 5 minutes to obtain a mixed solution X, 8.333 g of NaOH (Asahi Glass General Industrial concentration 48 mass%, 0.1 mol) was added to the mixed solution X. Was added at a rate of 50 mL / min. Crystals were precipitated simultaneously with the addition, and the mixture was further stirred at 30 ° C. for 10 minutes to obtain slurry liquid Y (pH 8.5).

After the obtained slurry liquid Y was solid-liquid separated using a Buchner funnel, the solid content obtained was washed with water (10 times the solid content) and dried in a constant temperature bath at 80 ° C. for 12 hours to obtain a powder. (LiFe _0.3 Mn _0.7 PO ₄ ) was obtained.
The average crystallite diameter of the obtained powder was calculated by Scherrer's formula based on the half-width of the XRD diffraction line of 10 ° to 80 ° (2θ-Cukα). Was not. Moreover, it was 22.4 m < ² > / g when the BET specific surface area was measured.

Further, 3 g of the obtained powder was fractionated and put into a planetary mill (P-5 manufactured by Fritsch, ZrO ₂ φ1 ball: 30 g), and 0.15 g of glucose (carbon atom equivalent amount in active material: 5) (Corresponding to mass%) and 10 mL of distilled water were added and treated at 400 rpm for 1 hour. Subsequently, it was fired in a reducing atmosphere under N ₂ flow at 700 ° C. for 1 hour to obtain a carbon-coated lithium manganese phosphate positive electrode active material.

[Example 2]
Instead of LiCO ₃ 1.847 g (0.025 mol), LiOH.H ₂ O (Kanto Chemical Co., Ltd. deer grade, 2.098 g (0.05 mol) was used in the same manner as in Example 1 except that powder (LiFe _0.3 Mn _0.7 PO ₄ ) was obtained, and then a carbon-coated lithium manganese phosphate positive electrode active material was obtained.
Table 1 shows the measurement results of the average crystallite diameter and the BET specific surface area, together with the results of confirming the presence or absence of heterogeneous phases by XRD of the obtained powder.

[Example 3]
A powder (LiFe _0.3 Mn _0.7 PO ₄ ) was obtained in the same manner as in Example 1 except that NaOH added to the mixed solution X was changed to 16.666 g (0.2 mol), and then carbon-coated lithium manganese phosphate positive electrode An active material was obtained.
Table 1 shows the measurement results of the average crystallite diameter and the BET specific surface area, together with the results of confirming the presence or absence of heterogeneous phases by XRD of the obtained powder.

[Example 4]
A powder (LiFe _0.3 Mn _0.7 PO ₄ ) was obtained in the same manner as in Example 1 except that 6.25 g (0.075 mol) of NaOH was added to the mixed solution X, and then carbon-coated lithium manganese phosphate positive electrode An active material was obtained.
Table 1 shows the measurement results of the average crystallite diameter and the BET specific surface area, together with the results of confirming the presence or absence of heterogeneous phases by XRD of the obtained powder.

[Example 5]
In obtaining the solution B, a powder (as in Example 1) except that MnSO ₄ .5H ₂ O was changed to 10.4949 g (0.045 mol) and FeSO ₄ .7H ₂ O was changed to 1.39 g (0.005 mol). LiFe _0.1 Mn _0.9 PO ₄ ) was obtained, and then a carbon-coated lithium manganese phosphate positive electrode active material was obtained.
Table 1 shows the measurement results of the average crystallite diameter and the BET specific surface area, together with the results of confirming the presence or absence of heterogeneous phases by XRD of the obtained powder.

[Example 6]
In obtaining Solution B, a powder (as in Example 1) except that 1.205 g (0.005 mol) of MnSO ₄ .5H ₂ O and 12.51 g (0.045 mol) of FeSO ₄ .7H ₂ O were used. LiFe _0.1 Mn _0.9 PO ₄ ) was obtained, and then a carbon-coated lithium manganese phosphate positive electrode active material was obtained.
Table 1 shows the measurement results of the average crystallite diameter and the BET specific surface area, together with the results of confirming the presence or absence of heterogeneous phases by XRD of the obtained powder.

[Example 7]
In obtaining the solution A, a powder (LiFe _0.3 Mn _0.7 PO ₄ ) was obtained in the same manner as in Example 1 except that the amount of distilled water A was 1000 g, and then a carbon-coated lithium manganese phosphate positive electrode active material was obtained. .
Table 1 shows the measurement results of the average crystallite diameter and the BET specific surface area, together with the results of confirming the presence or absence of heterogeneous phases by XRD of the obtained powder.

[Example 8]
In obtaining Solution B, powder (LiFe _0.3 Mn _0.7 PO ₄ ) was obtained in the same manner as in Example 1 except that distilled water B was changed to 15 g, and then a carbon-coated lithium manganese phosphate positive electrode active material was obtained. .
Table 1 shows the measurement results of the average crystallite diameter and the BET specific surface area, together with the results of confirming the presence or absence of heterogeneous phases by XRD of the obtained powder.

[Comparative Example 1]
In obtaining the solution A, a powder (LiFe _0.3 Mn _0.7 PO ₄ ) was obtained in the same manner as in Example 1 except that 10 g of distilled water A was used, and then a carbon-coated lithium manganese phosphate positive electrode active material was obtained. .
Table 1 shows the measurement results of the average crystallite diameter and the BET specific surface area, together with the results of confirming the presence or absence of heterogeneous phases by XRD of the obtained powder.

[Comparative Example 2]
In obtaining the solution B, powder (LiFe _0.3 Mn _0.7 PO ₄ ) was used in the same manner as in Example 1 except that distilled water B was 15 g and NaOH added to the mixed solution X was 4.167 g (0.05 mol). Then, a carbon-coated lithium manganese phosphate positive electrode active material was obtained.
Table 1 shows the measurement results of the average crystallite diameter and the BET specific surface area, together with the results of confirming the presence or absence of heterogeneous phases by XRD of the obtained powder.

[Comparative Example 3]
In obtaining the solution B, a powder (LiFe _0.3 Mn _0.7 PO ₄ ) was obtained in the same manner as in Example 1 except that 10 g of distilled water B was used, and then a carbon-coated lithium manganese phosphate positive electrode active material was obtained. .
Table 1 shows the measurement results of the average crystallite diameter and the BET specific surface area, together with the results of confirming the presence or absence of heterogeneous phases by XRD of the obtained powder.

[Comparative Example 4]
After adding 6.249 g of LiOH.H ₂ O to 30 g of distilled water and stirring for 5 minutes, 5.765 g of H ₃ PO ₄ was added and stirred for 30 minutes to obtain a Li ₃ PO ₄ -containing slurry. Next, 8.438 g (0.035 mol) of MnSO ₄ .5H ₂ O and 4.170 g (0.015 mol) of FeSO ₄ .7H ₂ O were added and stirred for 15 minutes to obtain a precursor slurry. The obtained precursor slurry was put into a 200 mL pressure-resistant autoclave, heated and maintained at 170 ° C. for 1 hour, and a hydrothermal reaction was performed. After cooling this naturally, solid-liquid separation and washing were performed using a Buchner funnel. Then dried in a thermostatic bath at 80 ° C. 12 hours to obtain LiMn _0.7 Fe _0.3 PO ₄ powder.

Further, 3 g of the obtained powder was fractionated and put into a planetary mill (P-5 manufactured by Fritsch, ZrO ₂ φ1 ball: 30 g), and 0.15 g of glucose (carbon atom equivalent amount in active material: 5) (Corresponding to mass%) and 10 mL of distilled water were added and treated at 400 rpm for 1 hour. Subsequently, it was fired in a reducing atmosphere under N ₂ flow at 700 ° C. for 1 hour to obtain a carbon-coated lithium manganese phosphate positive electrode active material.
Table 1 shows the measurement results of the average crystallite diameter and the BET specific surface area, together with the results of confirming the presence or absence of heterogeneous phases by XRD of the obtained powder.

<Evaluation of charge / discharge characteristics>
Each of the obtained positive electrode active materials, ketjen black, and polyvinylidene fluoride were mixed at a weight ratio of 90: 3: 7, and N-methyl-2-pyrrolidone was added and kneaded sufficiently to prepare a positive electrode slurry. did. The positive electrode slurry was applied to a current collector made of an aluminum foil having a thickness of 20 μm using a coating machine, and vacuum dried at 80 ° C. for 12 hours. Thereafter, it was punched into a disk shape of φ14 mm and pressed at 16 MPa for 2 minutes using a hand press to obtain a positive electrode.

Next, a coin-type lithium ion secondary battery was constructed using the positive electrode. A lithium foil punched to φ15 mm was used for the negative electrode. As the electrolytic solution, a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1: 1 was used. As the separator, a known one such as a polymer porous film such as polypropylene was used. These battery components were assembled and housed in a conventional manner in an atmosphere with a dew point of −50 ° C. or lower to produce a coin-type lithium secondary battery (CR-2032).

A charge / discharge test at a constant current density was performed using the manufactured lithium secondary battery. The charging conditions at this time were constant current charging with a current of 0.1 CA (170 mAh / g) and a voltage of 4.5V. The discharge conditions were a current of 0.1 CA and a constant current discharge with a final voltage of 2.0V. All temperatures were 30 ° C.
Table 1 shows the results of the obtained discharge capacity.

  Comparative Example 1 in which the amount of water A is insufficient when obtaining Solution A, Comparative Example 2 in which the amount of alkali added is insufficient, and Comparative Example in which the amount of water B is insufficient when obtaining Solution B Compared to 3, in Examples 1 to 8, it was possible to obtain a positive electrode active material capable of expressing battery characteristics comparable to those of Comparative Example 4 through the hydrothermal reaction step.

Claims (6)

(I) Next solution A and solution B:
(Solution A) A lithium compound, a phosphoric acid compound, and water A are contained, the molar ratio of lithium to phosphorus (Li: P) is 1: x (x = 1 to 3), and water A and lithium A solution having a molar ratio (water A: Li) of 80: 1 to 1400: 1 (solution B) containing a manganese compound and / or an iron compound, and water B, and a total amount of water B, manganese and iron; A step of obtaining a mixed solution X by mixing a solution having a molar ratio (water B: (Mn + Fe)) of 13: 1 to 100: 1,
(II) An alkali is added to the obtained mixed liquid X, and a slurry liquid Y in which the molar ratio of the alkali and the total amount of manganese and iron (alkali: (Mn + Fe)) is from 3: 2 to 4: 1. Obtaining step,
(III) A method for producing a lithium phosphate-based positive electrode active material that does not involve a hydrothermal reaction step, comprising a step of separating the obtained slurry liquid Y and firing the solid content.   2. The lithium phosphate according to claim 1, wherein in the mixed solution X, the molar ratio of lithium to the total molar amount of water A and water B (lithium: (water A + water B)) is 1:90 to 1: 1500. Of manufacturing a positive electrode active material.   3. The method for producing a lithium phosphate-based positive electrode active material according to claim 1, wherein a molar ratio of manganese to iron (Mn: Fe) in the solution B is y: 1-y (0 ≦ y ≦ 1).   The method for producing a lithium phosphate-based positive electrode active material according to any one of claims 1 to 3, wherein the alkali is selected from sodium hydroxide, potassium hydroxide, or aqueous ammonia.   The method for producing a lithium phosphate-based positive electrode active material according to any one of claims 1 to 4, wherein the firing temperature in step (III) is 600 to 900 ° C. The lithium phosphate-based positive electrode active material has the formula (I):
LiFe _a Mn _b M _c PO ₄ (I)
(In the formula (I), M is Mg, Ca, Sr, Y, Zr, Co, Mo, Ba, Pb, Bi, La, Ce, Nd or Gd, 0 ≦ a ≦ 1, 0 ≦ b ≦ 1, and 0 ≦ c ≦ 0.3, and a and b are not 0 at the same time)
The manufacturing method of the lithium-phosphate type positive electrode active material of any one of Claims 1-5 represented by these.