JP2015038848A - Method for manufacturing lithium manganese phosphate positive electrode active material precursor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a lithium manganese phosphate positive electrode active material precursor which can obtain the lithium manganese phosphate positive electrode active material precursor capable of exhibiting an excellent battery physical property as a positive electrode material of a lithium ion battery, and a method for manufacturing a lithium manganese phosphate positive electrode active material.SOLUTION: A method for manufacturing a lithium manganese phosphate positive electrode active material precursor comprises: a step (I) of obtaining a mixed slurry liquid having a pH of 9 to 11 by stirring a slurry liquid containing lithium hydroxide in an amount exceeding solubility to water, while dropping phosphoric acid to the slurry liquid; and a step (II) of obtaining the lithium manganese phosphate positive electrode active material precursor as a precursor slurry liquid by purging nitrogen to the resulting mixed slurry liquid and completing the reaction in the mixed slurry liquid.

Description

  The present invention relates to a method for producing a lithium manganese phosphate positive electrode active material precursor capable of obtaining a lithium manganese phosphate positive electrode active material capable of expressing high battery properties, and a lithium manganese phosphate positive electrode active material obtained therefrom.

  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 manganese phosphate itself has low conductivity, and therefore, in order to effectively use it as a positive electrode active material, it is necessary to sufficiently refine the particles to ensure good battery properties. Various production methods are known for obtaining the substance. For example, in Patent Document 1, a lithium-containing composite oxide is manufactured by mixing a solution containing lithium and a solution containing phosphorus, forming a weakly alkaline mixed solution, and dropping the solution into a solution that can contain manganese or the like. A method is disclosed. In Patent Document 2, a precursor mixture containing a Li ⁺ source, a PO ₄ ³⁻ source, a manganese source, and the like is generated, and the obtained precursor mixture is dispersed or pulverized to obtain a LiMPO ₄ compound. A method is disclosed.

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 in any of the above documents, there is still room for improvement, including what solution should be prepared or what procedure should be mixed, and the like. I haven't come to get.

  Accordingly, an object of the present invention is to provide a method for producing a lithium manganese phosphate positive electrode active material precursor for obtaining a lithium manganese phosphate positive electrode active material capable of expressing excellent battery properties as a positive electrode material of a lithium ion battery, and from this It is in providing the obtained lithium manganese phosphate positive electrode active material.

  Accordingly, the present inventors have made various studies, and by using a slurry process containing a specific amount of lithium hydroxide and including a specific process, a lithium manganese phosphate positive electrode formed with extremely fine dispersed particles. In addition to finding out that a slurry liquid of an active material precursor can be obtained, it has also been found that by using this, a very fine particle lithium manganese phosphate positive electrode active material can be obtained, and the present invention has been completed.

That is, the present invention is a step (I) of obtaining a mixed slurry liquid having a pH of 9 to 11 by stirring the slurry water while dropping phosphoric acid into slurry water containing an amount of lithium hydroxide exceeding the solubility in water. And a step of purging nitrogen with respect to the obtained mixed slurry liquid to complete the reaction in the mixed slurry liquid to obtain a lithium manganese phosphate positive electrode active material precursor as a precursor slurry liquid (II)
The manufacturing method of the lithium manganese phosphate positive electrode active material precursor containing this is provided.
In addition, the present invention is obtained by adding a transition metal compound containing at least a manganese compound to the lithium manganese phosphate positive electrode active material precursor obtained by the above production method, and then subjecting it to a hydrothermal reaction. A lithium manganese phosphate positive electrode active material is provided.

  According to the method for producing a lithium manganese phosphate positive electrode active material precursor of the present invention, a slurry liquid in which the lithium manganese phosphate positive electrode active material precursor is present as extremely fine dispersed particles can be obtained, and such a slurry liquid is used. Also in the lithium manganese phosphate positive electrode active material obtained in this way, the particles can be sufficiently miniaturized. If the lithium manganese phosphate positive electrode active material thus obtained is used, a lithium ion battery having good battery properties can be easily realized.

The schematic of the steam heating type autoclave used by this invention is shown. The SEM image of the lithium manganese phosphate positive electrode active material precursor obtained in Example 1 is shown. The SEM image of the lithium manganese phosphate positive electrode active material obtained in Example 1 is shown. The SEM image of the lithium manganese phosphate positive electrode active material obtained by the comparative example 1 is shown. The charging / discharging capacity | capacitance curve of the lithium ion battery produced using the lithium manganese phosphate positive electrode active material obtained in Example 1 is shown. The charging / discharging capacity | capacitance curve of the lithium ion battery produced using the lithium manganese phosphate positive electrode active material obtained by the comparative example 2 is shown. It is a Nyquist plot which shows the impedance measurement result of the lithium ion battery produced using the lithium manganese phosphate positive electrode active material obtained in Example 1 and Comparative Example 2.

Hereinafter, the present invention will be described in detail.
In the method for producing a lithium manganese phosphate positive electrode active material precursor of the present invention, the slurry water is stirred while dropping phosphoric acid into slurry water containing lithium hydroxide in an amount exceeding the solubility in water. 11 to obtain the mixed slurry liquid of 11 and the reaction with the mixed slurry liquid is completed by purging nitrogen to the obtained mixed slurry liquid to obtain a lithium manganese phosphate positive electrode active material precursor. Step to obtain as precursor slurry (II)
including.

  In the step (I), slurry water containing lithium hydroxide in an amount exceeding the solubility in water (g number of lithium hydroxide dissolved in 100 g of the saturated aqueous solution) is used. As described above, by using slurry water containing lithium hydroxide in an excessive amount exceeding the solubility in water, the lithium manganese phosphate positive electrode active material precursor is finely combined with the process described later. It can be obtained as dispersed particles.

  In order to prepare such slurry water, water and lithium hydroxide in an amount exceeding the solubility in water may be mixed. Such slurry water preferably contains 1.5 to 3.5 times the amount of lithium hydroxide, based on the solubility of lithium hydroxide in water, and 2.2 to 3.3 times the amount of hydroxide. It is more preferable to contain lithium, and it is more preferable to contain lithium hydroxide in an amount of 2.5 to 3.2 times. Moreover, it is preferable to contain 20-50 mass parts lithium hydroxide with respect to 100 mass parts of water, It is more preferable to contain 25-48 mass parts lithium hydroxide, 30-45 mass parts hydroxylation More preferably, it contains lithium.

More specifically, for example, in the case of slurry water containing 100 g of water at 20 ° C., it is preferable to contain 21 to 49 g of lithium hydroxide and 30 to 46 g of lithium hydroxide in the slurry water. More preferably, it contains 35 to 44 g of lithium hydroxide. In the case of slurry water containing 100 g of 40 ° C. water, it is preferable to contain 22 to 51 g of lithium hydroxide, more preferably 31 to 47 g of lithium hydroxide, and 36 to 45 g of lithium hydroxide. It is preferable to do this.
As the lithium hydroxide, for example, it may be used a hydrate of such LiOH · H ₂ O, in this case, the content is a value obtained by converting the lithium hydroxide (LiOH) content.

In step (I), the slurry water is stirred while dropping phosphoric acid into the slurry water to obtain a mixed slurry liquid having a pH of 9 to 11. In this way, dispersed particles of lithium manganese phosphate positive electrode active material precursor by stirring while adding phosphoric acid dropwise to a slurry liquid in which an excessive amount of lithium hydroxide is present while being in a saturated state. Can be effectively miniaturized by effectively suppressing the aggregation.
Phosphoric acid is so-called orthophosphoric acid (H ₃ PO ₄ ) and is preferably used as an aqueous solution having a concentration of 70 to 90% by mass. The dropping rate of phosphoric acid into the slurry water is preferably 15 to 50 mL / min, more preferably 20 to 45 mL / min, and further preferably 28 to 40 ml / min.
In the step (I), when stirring the slurry water while dropping phosphoric acid, the stirring speed of the slurry water is preferably 250 to 600 rpm, more preferably 300 to 550 rpm, further preferably 350 to 500 rpm. It is.

The temperature of the slurry water when stirring slurry water while dropping phosphoric acid depends on the dropping rate of phosphoric acid, but is preferably 20 to 90 ° C, more preferably 20 to 70 ° C. .
In addition, when stirring slurry water, although it depends also on the dripping speed | rate of phosphoric acid, it is preferable to cool to below the boiling point temperature of slurry water. Specifically, cooling to 80 ° C. or lower is preferable, and cooling to 20 to 60 ° C. is more preferable.

  The mixed slurry obtained in the step (I) preferably contains 0.28 to 0.38 mol of phosphoric acid, more preferably 0.30 to 0.36 mol, per 1 mol of lithium hydroxide. The content is preferably 0.32 to 0.34 mol. Moreover, it is preferable to contain 115-155 mass parts of phosphoric acid with respect to 100 mass parts of lithium hydroxide, It is more preferable to contain 123-147 mass parts, It is preferable to contain 131-139 mass parts.

  The mixed slurry is finally adjusted to pH 9-11, preferably pH 9.5 to 11.0. Thereby, the growth of by-products and particles can be effectively suppressed. Under the present circumstances, you may use pH adjusters, such as sodium hydroxide and a sulfuric acid, as needed.

In the step (II), the mixed slurry liquid obtained in the above step (I) is purged with nitrogen to complete the reaction in the mixed slurry liquid, whereby the lithium manganese phosphate positive electrode active material precursor is precursor. Obtained as body slurry liquid. When nitrogen is purged, the reaction can proceed in a state where the dissolved oxygen concentration in the mixed slurry liquid is reduced, and the dissolved oxygen concentration in the resulting precursor slurry liquid is also effectively reduced. Oxidation of the transition metal (M) compound added in the next step can be suppressed. In such a precursor slurry liquid, a lithium manganese phosphate positive electrode active material precursor (trilithium phosphate: Li ₃ PO ₄ ) exists as fine dispersed particles.

The pressure in the step (II) is preferably 0.1 to 0.2 MPa, more preferably 0.1 to 0.15 MPa. Moreover, the temperature of a mixed slurry liquid becomes like this. Preferably it is 20-80 degreeC, More preferably, it is 20-60 degreeC. The reaction time is preferably 5 to 60 minutes, more preferably 15 to 45 minutes.
Moreover, when purging nitrogen, it is preferable to stir a mixed slurry liquid from a viewpoint of making reaction progress favorable. The stirring speed at this time is preferably 250 to 600 rpm, more preferably 350 to 500 rpm.

  Further, in the step (II), the dissolved oxygen concentration in the mixed slurry liquid is reduced from the viewpoint of more effectively suppressing the oxidation of the lithium manganese phosphate positive electrode active material precursor on the surface of the dispersed particles and miniaturizing the dispersed particles. 0.5 mg / L or less is preferable, and 0.2 mg / L or less is more preferable.

  By passing through the said process (I) and process (II), the precursor slurry liquid in which a lithium manganese phosphate positive electrode active material precursor exists as a fine dispersed particle can be obtained. The dissolved oxygen concentration in the precursor slurry is preferably adjusted to 0.5 mg / L or less, and more preferably adjusted to 0.2 mg / L or less.

The average dispersed particle diameter of the lithium manganese phosphate positive electrode active material precursor (Li ₃ PO ₄ ) in the obtained precursor slurry is preferably 30 to 5000 nm, more preferably 30 to 4000 nm, and still more preferably. 30-3500 nm.
The average dispersed particle diameter of the lithium manganese phosphate positive electrode active material precursor means a value measured using a dynamic light scattering nanotrack particle size analyzer (manufactured by Nikkiso Co., Ltd.).

The step (I) and step (II) is obtained by passing through the precursor slurry while the slurry liquid, used as the lithium manganese phosphate positive electrode active material precursor (Li ₃ PO _4), comprising at least manganese compound By including a step of adding a transition metal (M) compound and then subjecting it to a hydrothermal reaction, a lithium manganese phosphate compound that is very fine particles and is very useful as a positive electrode active material can be obtained.

  As the transition metal compound (M), at least a manganese compound is used. The manganese compound may be a divalent manganese compound, and examples thereof include manganese halide, manganese sulfate, and manganese acetate. These may be used alone or in combination of two or more. Among these, manganese sulfate is preferably used from the viewpoint of improving battery physical properties.

  Examples of other transition metal (M) compounds include iron compounds. The iron compound may be a divalent iron compound or a hydrate thereof, for example, 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. Among these, iron sulfate is preferably used from the viewpoint of improving battery physical properties.

When a manganese compound and an iron compound are used as the transition metal (M) compound, the molar ratio used (manganese compound: iron compound) is preferably 99: 1 to 51:49, more preferably 95: 5 to 70. : 30, and more preferably 90:10 to 80:20. The total addition amount of these transition metal compounds is preferably 0.99 to 1.01 with respect to 1 mol of lithium manganese phosphate positive electrode active material precursor (Li ₃ PO ₄ ) contained in the precursor slurry. Mol, more preferably 0.995 to 1.005 mol.

The amount of water used for the hydrothermal reaction is selected from the viewpoints of the solubility of the transition metal compound, the ease of stirring, the efficiency of synthesis, etc., and the lithium manganese phosphate positive electrode contained in the precursor slurry liquid to phosphate ion 1 mole of the active material precursor (Li ₃ PO _4), preferably 10 to 30 moles, more preferably 12.5 to 25 mol.

The order of addition of the transition metal (M) compound is not particularly limited. Moreover, while adding a transition metal compound, you may add antioxidant as needed. As such an antioxidant, sodium sulfite (Na ₂ SO ₃ ), hydrosulfite sodium (Na ₂ S ₂ O ₄ ), aqueous ammonia and the like can be used. The addition amount of the antioxidant is preferably 0.01 to 1 mol with respect to 1 mol of the transition metal compound, from the viewpoint of preventing the generation of the lithium manganese phosphate compound from being excessively added. Yes, more preferably 0.03 to 0.5 mol.

A mixed liquid obtained by adding a transition metal compound to the precursor slurry and adding an antioxidant or the like as required is a lithium manganese phosphate positive electrode active material precursor (trilithium phosphate: Li ₃ PO ₄ ) In a large amount. Thus, by subjecting a mixed liquid containing a large amount of lithium manganese phosphate positive electrode active material precursor formed by forming fine dispersed particles to a hydrothermal reaction, phosphorous of extremely fine particles useful as a positive electrode active material is obtained. A lithium manganese oxide compound can be obtained. The content of the lithium manganese phosphate positive electrode active material precursor in the mixed solution is preferably 10 to 50% by mass, more preferably 15 to 45% by mass, and further preferably 20 to 40% by mass. .

  In subjecting the obtained mixed solution to a hydrothermal reaction, it is preferable to use a steam heating autoclave, for example, as shown in FIG. 1 from the viewpoint of effectively preventing oxidation of the transition metal compound. Steam-heated autoclaves receive saturated steam and pressurize and heat, so the interior of the autoclave is filled with saturated steam and can effectively prevent oxidation of transition metals in the autoclave during hydrothermal synthesis. it can. Moreover, since saturated steam does not generate anything other than water (drain water) even when cooled, it is possible to suppress oxidation of the transition metal even in the process. When the saturated steam is introduced into the autoclave and heating is started, it is preferable to further reduce the oxygen remaining in the autoclave by performing an operation to push out (replace) the air in the autoclave with the saturated steam.

  The saturated steam is produced by heating water, but it is preferable to deoxidize the water used in the boiler for heating the water. The water for producing the steam preferably has a dissolved oxygen concentration of 0.5 mg / L or less, more preferably a dissolved oxygen concentration of 0.2 mg / L or less. Such deoxidized water can be easily produced by, for example, bubbling nitrogen gas in water or using a membrane separation device.

  The reaction temperature in hydrothermal reaction should just be 100 degreeC or more, Preferably it is 130-250 degreeC, More preferably, it is 140-230 degreeC. When using a steam-heated autoclave, it is only necessary to seal in the autoclave and heat with steam. When the reaction is performed at 130 to 250 ° C, the pressure is 0.3 to 1.5 MPa, and the reaction is performed at 140 to 230 ° C. When performing, it will be 0.4-1.0 MPa. The reaction time is preferably 10 minutes to 3 hours, more preferably 10 to 1 hour.

  After completion of the hydrothermal reaction, the produced lithium manganese phosphate compound is preferably collected by filtration and washed. Washing is preferably performed with water using a filtration device having a cake washing function. The obtained crystals are dried if necessary. Examples of the drying means include spray drying, vacuum drying, freeze drying and the like.

The obtained lithium manganese phosphate compound can be used as a positive electrode active material for a lithium ion battery, and contains at least manganese (Mn) as a transition metal (M). Specifically, for example, it is represented by the following formula (A).
Li ₂ Fe _a Mn _1-a PO ₄ (A)
(In the formula, a represents a number satisfying 0 ≦ a <0.5.)
A in the formula (A) is preferably 0.05 to 0.4, more preferably 0.075 to 0.35, from the viewpoint of obtaining a lithium manganese phosphate compound having higher battery properties. More preferably, it is 0.1-0.3.

  The obtained lithium manganese phosphate compound is preferably supported on carbon and then fired to form a positive electrode active material. For carbon loading, a carbon source such as glucose, fructose, polyethylene glycol, polyvinyl alcohol, carboxymethylcellulose, saccharose, starch, dextrin, citric acid and water may be added to a lithium manganese phosphate compound by a conventional method and then fired. . The firing conditions are 400 ° C. or higher, preferably 400 to 800 ° C. for 10 minutes to 3 hours, preferably 0.5 to 1.5 hours under an inert gas atmosphere or reducing conditions. By such treatment, a positive electrode active material in which carbon is supported on the particle surface of the lithium manganese phosphate compound can be obtained. 3-15 mass parts is preferable as carbon contained in a carbon source with respect to 100 mass parts of lithium manganese phosphate compounds, and, as for the usage-amount of a carbon source, 5-10 mass parts is more preferable as carbon contained in a carbon source.

  The lithium manganese phosphate positive electrode active material precursor obtained by the above method using the lithium manganese phosphate positive electrode active material precursor obtained by the production method of the present invention has a fine and uniform particle size. Useful as a material. Specifically, the average particle diameter of the lithium manganese phosphate positive electrode active material is preferably 10 to 100 nm, and more preferably 10 to 50 nm.

Next, a lithium ion battery containing the lithium manganese phosphate positive electrode active material 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 that is 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 by using the lithium manganese phosphate positive electrode active material of the present invention exhibits very high performance battery properties, and has effective polarization (voltage loss) when charged and discharged at a constant current density. Can be suppressed. Specifically, for example, charge and discharge conditions of the current 0.1CA (17mA / g), when the charging voltage V _c when the discharge capacity is 60 mAh / g, and the discharge voltage is V _d, phosphorus of the present invention In the lithium ion battery obtained using the lithium manganese oxide positive electrode active material, the value of these ratios (V _c / V _d ) is preferably 1.000 to 1.028, more preferably 1.000 to 1. .025. That is, assuming that polarization does not occur during charge / discharge, the value of V _c / V _d becomes 1, but the lithium ion battery obtained using the lithium manganese phosphate positive electrode active material of the present invention has a V _c / V The value of V _d shows a value very close to 1, and it is an excellent battery in which polarization is effectively suppressed.

Moreover, if the lithium manganese phosphate positive electrode active material of the present invention is used, a lithium ion battery with effectively reduced impedance can be obtained. Specifically, for example, as shown in FIG. 7, the AC impedance method is used, the horizontal axis represents the real part of the impedance (Z _re , unit: Ω), and the vertical axis represents the imaginary part of the impedance (Z _im , unit: In the Nyquist plot of Ω), the semicircular diameter D indicating the bulk resistance of lithium manganese phosphate can be reduced. More specifically, the lithium ion battery obtained by using the lithium manganese phosphate positive electrode active material of the present invention has an inflection where ΔZ _im = 0 in a Nyquist plot produced under conditions of a frequency of 0.1 to 1000000 Hz. the value of Z _re at the point P (the end point of the semicircular arc S) is preferably a 10～200Omu, more preferably 10～150Omu. That is, if the value of Z _re at the inflection point P is within such a range, it means that the diameter D of the semicircle showing the bulk resistance of lithium manganese phosphate is small, and the lithium manganese phosphate of the present invention It means that the lithium ion battery obtained using the positive electrode active material is a battery having a very low impedance.

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

[Example 1]
<< Preparation of precursor slurry liquid >>
4.9 kg of LiOH · H ₂ O and 11.7 kg of water were mixed to obtain slurry water. Subsequently, the obtained slurry water was stirred at a stirring speed of 400 rpm while maintaining the temperature at 25 ° C., and then 5.09 kg of a 70% phosphoric acid aqueous solution was dropped at 35 mL / min to obtain a mixed slurry liquid. . The pH of the mixed slurry was 10.0 and contained 0.33 mol of phosphoric acid with respect to 1 mol of lithium hydroxide.

Next, the obtained slurry mixture was purged with nitrogen while stirring at a speed of 400 rpm for 30 minutes to complete the reaction with the slurry mixture, and the precursor adjusted to a dissolved oxygen concentration of 0.5 mg / L. A body slurry liquid was obtained.
The average dispersed particle size of trilithium phosphate (Li ₃ PO ₄ ) in the obtained precursor slurry was 3000 nm as measured with a dynamic light scattering nanotrack particle size analyzer (manufactured by Nikkiso Co., Ltd.). .
An SEM image of dispersed particles of trilithium phosphate (Li ₃ PO ₄ ) in the precursor slurry is shown in FIG.

<< Manufacture of lithium manganese phosphate cathode active material >>
Then, with respect to the precursor slurry _{21.7kg, FeSO 4 · 7H 2 O1.63kg} , added MnSO ₄ · H ₂ O 5.60kg, stirring speed 400rpm further added Na ₂ SO ₃ 46.8 g The mixture was obtained by stirring and mixing. At this time, the added FeSO ₄ and MnSO ₄ molar ratio (manganese compound: iron compound) was 85:15, and the content of lithium manganese phosphate positive electrode active material precursor (Li ₃ PO ₄ ) in the mixed solution Was 24 mass%.
Next, the mixed solution was put into a synthesis container installed in the steam heating autoclave of FIG. The inside of the autoclave was heated at 170 ° C. for 1 hour using saturated steam obtained by heating water with a dissolved oxygen concentration of less than 0.5 mg / L using a membrane separator. During the heating, stirring of the mixed slurry in the container was continued. The pressure in the autoclave was 0.8 MPa. The formed crystals were filtered and then washed with water. The washed crystal was vacuum dried at 60 ° C. and 1 Torr. 10 g of the obtained powder was taken, mixed with 2.7 g of glucose, and put into a container equipped in a planetary ball mill (P-5, manufactured by Fritsch), and 90 g of ethanol and 10 g of water were mixed therewith. The solvent was added. Next, 100 g of φ100 μm ZrO ₂ balls were used and mixed for 1 hour at a rotational speed of 400 rpm. The obtained mixture was filtered, the solvent was distilled off using an evaporator, and then calcined at 700 ° C. for 1 hr in a reducing atmosphere to obtain a lithium manganese phosphate positive electrode active material.
The average particle diameter of the obtained lithium manganese phosphate positive electrode active material (Li ₂ Fe _0.15 Mn _0.85 PO ₄ ) was 50 nm. An SEM image of such a lithium manganese phosphate positive electrode active material is shown in FIG.

<Manufacture of lithium ion batteries>
The obtained lithium manganese phosphate positive electrode active material, ketjen black (conducting agent), and polyvinylidene fluoride (binding agent) were mixed at a weight ratio of 75: 20: 5, and this was mixed with N-methyl-2- Pyrrolidone was added and sufficiently kneaded to prepare a positive electrode slurry. 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 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 having a dew point of −50 ° C. or lower to produce a coin-type lithium ion battery (CR-2032).

A charge / discharge test at a constant current density was performed using the manufactured lithium ion battery. The charging conditions at this time were constant current charging with a current of 0.1 CA (17 mAg) and a voltage of 4.5 V, and the discharging conditions were constant current discharging with a current of 0.1 CA and a final voltage of 2.0 V. All temperatures were 30 ° C.
The charge / discharge capacity curve at this time is shown in FIG.
In addition, when the discharge capacity in Example 1 was 60 mAh / g, the ratio (V _c / V _d ) between the charge pressure V _c and the discharge voltage V _d was 1.020. In addition, when the charge / discharge conditions were a current of 0.5 CA (85 mA / g), the charge / discharge capacity when 50 cycles of charge / discharge were performed was 143 mAh / g.

[Comparative Example 1]
A precursor slurry was prepared in the same manner as in Example 1 except that 4.31 kg of Li ₂ CO ₃ was used instead of 4.9 kg of LiOH.H ₂ O, and this was used to prepare a phosphorous solution in the same manner as in Example 1. A lithium manganese oxide positive electrode active material was produced.
The average particle diameter of the obtained lithium manganese phosphate positive electrode active material (Li ₂ Fe _0.15 Mn _0.85 PO ₄ ) was 150 nm. The SEM image of this lithium manganese phosphate positive electrode active material is shown in FIG.

[Comparative Example 2]
Li ₂ SO ₄ 6.45kg, was obtained _{(NH 4) 2 HPO 4 5.16kg} , FeSO 4 · 7H 2 O1.63kg, MnSO 4 · H 2 O 5.60kg, mixture was mixed solution of distilled water 13L . At this time, the molar ratio of FeSO ₄ and MnSO ₄ added (manganese compound: iron compound) was 85:15.
Next, the mixed solution was put into a synthesis container installed in the steam heating autoclave of FIG. The inside of the autoclave was heated at 200 ° C. for 1 hour using saturated steam obtained by heating water having a dissolved oxygen concentration of less than 0.5 mg / L using a membrane separator. During the heating, stirring of the mixed slurry in the container was continued. The pressure in the autoclave was 1.5 MPa. The formed crystals were filtered and then washed with water. The washed crystal was vacuum dried at 60 ° C. and 1 Torr. 10 g of the obtained powder was taken, mixed with 2.7 g of glucose, and put into a container equipped in a planetary ball mill (P-5, manufactured by Fritsch), and 90 g of ethanol and 10 g of water were mixed therewith. The solvent was added. Next, 100 g of φ100 μm ZrO ₂ balls were used and mixed for 1 hour at a rotational speed of 400 rpm. The obtained mixture was filtered, the solvent was distilled off using an evaporator, and then fired at 700 ° C. for 1 hr in a reducing atmosphere to produce a lithium manganese phosphate positive electrode active material.
The average particle diameter of the obtained lithium manganese phosphate positive electrode active material (Li ₂ Fe _0.15 Mn _0.85 PO ₄ ) was 50 nm.
Next, a coin-type lithium ion battery (CR-2032) was produced in the same manner as in Example 1, and a charge / discharge test at a constant current density was performed.
The charge / discharge capacity curve at this time is shown in FIG.
Note that the ratio (V _c / V _d ) between the charge pressure V _c and the discharge voltage V _d when the discharge capacity in Comparative Example 2 was 60 mAh / g was 1.030.

[Production of Nyquist plot]
Using the coin-type lithium ion battery manufactured in Example 1 and Comparative Example 2, a Nyquist plot was prepared based on the AC impedance method. Specifically, using a VersaSTAT device manufactured by Princeton Applied, the impedance was measured under the condition of a frequency of 0.1 to 1000000 Hz, and a Nyquist plot with the horizontal axis Z _re (Ω) and the vertical axis Z _im (Ω). The value of Z _re at the inflection point P (end point of the semicircular arc S) where ΔZ _im = 0 is obtained.
The obtained Nyquist plot is shown in FIG.
The value of Z _re at the inflection point P in the first embodiment is 54 Ohm, the value of Z _re at the inflection point P in Comparative Example 2 was 64Omu.

S: Semicircular arc in the Nyquist plot of Example 1 D: Diameter of the semicircle in the Nyquist plot of Example 1 P: Inflection point D (end point of the semicircular arc) where ΔZ _im = 0 in the Nyquist plot of Example 1

The obtained lithium manganese phosphate compound can be used as a positive electrode active material for a lithium ion battery, and contains at least manganese (Mn) as a transition metal (M). Specifically, for example, it is represented by the following formula (A).
Li Fe _a Mn _1-a PO ₄ (A)
(In the formula, a represents a number satisfying 0 ≦ a <0.5.)
A in the formula (A) is preferably 0.05 to 0.4, more preferably 0.075 to 0.35, from the viewpoint of obtaining a lithium manganese phosphate compound having higher battery properties. More preferably, it is 0.1-0.3.

<< Manufacture of lithium manganese phosphate cathode active material >>
Then, with respect to the precursor slurry _{21.7kg, FeSO 4 · 7H 2 O1.63kg} , added MnSO ₄ · H ₂ O 5.60kg, stirring speed 400rpm further added Na ₂ SO ₃ 46.8 g The mixture was obtained by stirring and mixing. At this time, the added FeSO ₄ and MnSO ₄ molar ratio (manganese compound: iron compound) was 85:15, and the content of lithium manganese phosphate positive electrode active material precursor (Li ₃ PO ₄ ) in the mixed solution Was 24 mass%.
Next, the mixed solution was put into a synthesis container installed in the steam heating autoclave of FIG. The inside of the autoclave was heated at 170 ° C. for 1 hour using saturated steam obtained by heating water with a dissolved oxygen concentration of less than 0.5 mg / L using a membrane separator. During the heating, stirring of the mixed slurry in the container was continued. The pressure in the autoclave was 0.8 MPa. The formed crystals were filtered and then washed with water. The washed crystal was vacuum dried at 60 ° C. and 1 Torr. 10 g of the obtained powder was taken, mixed with 2.7 g of glucose, and put into a container equipped in a planetary ball mill (P-5, manufactured by Fritsch), and 90 g of ethanol and 10 g of water were mixed therewith. The solvent was added. Next, 100 g of φ100 μm ZrO ₂ balls were used and mixed for 1 hour at a rotational speed of 400 rpm. The obtained mixture was filtered, the solvent was distilled off using an evaporator, and then calcined at 700 ° C. for 1 hr in a reducing atmosphere to obtain a lithium manganese phosphate positive electrode active material.
The average particle diameter of the obtained lithium manganese phosphate positive electrode active material _{(Li Fe 0.15 Mn 0.85 PO 4} ) was 50nm. An SEM image of such a lithium manganese phosphate positive electrode active material is shown in FIG.

[Comparative Example 1]
A precursor slurry was prepared in the same manner as in Example 1 except that 4.31 kg of Li ₂ CO ₃ was used instead of 4.9 kg of LiOH.H ₂ O, and this was used to prepare a phosphorous solution in the same manner as in Example 1. A lithium manganese oxide positive electrode active material was produced.
The average particle diameter of the obtained lithium manganese phosphate positive electrode active material _{(Li Fe 0.15 Mn 0.85 PO 4} ) was 150 nm. The SEM image of this lithium manganese phosphate positive electrode active material is shown in FIG.

[Comparative Example 2]
Li ₂ SO ₄ 6.45kg, was obtained _{(NH 4) 2 HPO 4 5.16kg} , FeSO 4 · 7H 2 O1.63kg, MnSO 4 · H 2 O 5.60kg, mixture was mixed solution of distilled water 13L . At this time, the molar ratio of FeSO ₄ and MnSO ₄ added (manganese compound: iron compound) was 85:15.
Next, the mixed solution was put into a synthesis container installed in the steam heating autoclave of FIG. The inside of the autoclave was heated at 200 ° C. for 1 hour using saturated steam obtained by heating water having a dissolved oxygen concentration of less than 0.5 mg / L using a membrane separator. During the heating, stirring of the mixed slurry in the container was continued. The pressure in the autoclave was 1.5 MPa. The formed crystals were filtered and then washed with water. The washed crystal was vacuum dried at 60 ° C. and 1 Torr. 10 g of the obtained powder was taken, mixed with 2.7 g of glucose, and put into a container equipped in a planetary ball mill (P-5, manufactured by Fritsch), and 90 g of ethanol and 10 g of water were mixed therewith. The solvent was added. Next, 100 g of φ100 μm ZrO ₂ balls were used and mixed for 1 hour at a rotational speed of 400 rpm. The obtained mixture was filtered, the solvent was distilled off using an evaporator, and then fired at 700 ° C. for 1 hr in a reducing atmosphere to produce a lithium manganese phosphate positive electrode active material.
The average particle diameter of the obtained lithium manganese phosphate positive electrode active material _{(Li Fe 0.15 Mn 0.85 PO 4} ) was 50nm.
Next, a coin-type lithium ion battery (CR-2032) was produced in the same manner as in Example 1, and a charge / discharge test at a constant current density was performed.
The charge / discharge capacity curve at this time is shown in FIG.
Note that the ratio (V _c / V _d ) between the charge pressure V _c and the discharge voltage V _d when the discharge capacity in Comparative Example 2 was 60 mAh / g was 1.030.

Claims (11)

Step (I) of stirring slurry water while dropping phosphoric acid into slurry water containing an amount of lithium hydroxide exceeding the solubility in water to obtain a mixed slurry liquid having a pH of 9 to 11, and the obtained mixing A step of purging nitrogen with respect to the slurry liquid to complete the reaction in the mixed slurry liquid to obtain a lithium manganese phosphate positive electrode active material precursor as a precursor slurry liquid (II)
The manufacturing method of the lithium manganese phosphate positive electrode active material precursor containing this.   2. The lithium manganese phosphate positive electrode active material according to claim 1, wherein the slurry water in step (I) contains 1.5 to 3.5 times as much lithium hydroxide based on the solubility of lithium hydroxide in water. A method for producing a precursor.   3. The method for producing a lithium manganese phosphate positive electrode active material precursor according to claim 1, wherein in the step (I), the slurry water is stirred while dropping the phosphoric acid, and then cooled to the boiling point temperature of the slurry water or lower.   4. The lithium manganese phosphate according to claim 1, wherein the mixed slurry obtained in step (I) contains 0.28 to 0.38 mol of phosphoric acid with respect to 1 mol of lithium hydroxide. A method for producing a positive electrode active material precursor.   The method for producing a lithium manganese phosphate positive electrode active material precursor according to any one of claims 1 to 4, wherein in step (II), the dissolved oxygen concentration in the precursor slurry liquid is adjusted to 0.5 mg / L or less. .   A lithium manganese phosphate positive electrode active material precursor obtained by the production method according to claim 1.   A lithium manganese phosphate positive electrode active material obtained by adding a transition metal compound containing at least a manganese compound to the lithium manganese phosphate positive electrode active material precursor according to claim 6 and then subjecting it to a hydrothermal reaction. .   The lithium manganese phosphate positive electrode active material according to claim 7, wherein the transition metal compound contains a manganese compound and an iron compound.   The lithium manganese phosphate positive electrode active material according to claim 7 or 8, wherein a steam heating autoclave is used in the step of subjecting to a hydrothermal reaction.   The lithium manganese phosphate positive electrode active material according to claim 8 or 9, wherein the molar ratio of the manganese compound to the iron compound is 100: 0 to 51:49.   The lithium ion battery containing the lithium manganese phosphate positive electrode active material of any one of Claims 7-10 as positive electrode material.