JP4651960B2 - Method for producing positive electrode active material for lithium battery, positive electrode active material for lithium battery, positive electrode material for lithium battery, and lithium battery - Google Patents

Description

  The present invention relates to a method for producing a positive electrode active material for a lithium battery, a positive electrode active material for a lithium battery, a positive electrode material for a lithium battery, and a lithium battery, and more particularly, a lithium metal phosphate having a highly crystalline and fine olivine structure. It is related with the technique which can obtain easily.

In recent years, secondary batteries have been developed as batteries for use in portable electronic devices, hybrid automobiles, and the like.
As typical secondary batteries, lead storage batteries, alkaline storage batteries, lithium batteries, and the like are generally known. In particular, lithium batteries can be reduced in size, weight, capacity, and output. Because of its high energy density, it is highly anticipated and research is being actively promoted.
This lithium battery is composed of a positive electrode having an active material capable of reversibly inserting and removing lithium ions, a negative electrode, and a non-aqueous electrolyte.

The positive electrode itself is composed of an electrode material containing a positive electrode active material, a conductive additive, and a binder, and is formed into a positive electrode by applying this electrode material to the surface of a metal foil called a current collector.
As the positive electrode active material, a metal oxide, a metal sulfide, a polymer, or the like is used. For example, titanium sulfide (TiS ₂ ), molybdenum sulfide (MoS ₂ ), niobium selenide (NbSe ₂ ), vanadium oxide (V Lithium-free compounds such as ₂ O ₅ ) or lithium composite oxides such as LiMO ₂ (M = Co, Ni, Mn, Fe, etc.) and LiMn ₂ O ₄ are known.

Conventionally, lithium cobalt oxide (LiCoO ₂ ) has been generally used as a positive electrode active material for lithium batteries because it is possible to form a battery having a high energy density and a high voltage.
However, because Co is unevenly distributed on the earth and is a scarce resource, there are problems that it is costly and that it is difficult to stably supply, so there are abundant resources on the earth as an alternative to Co. Positive electrode materials using inexpensive positive electrode active materials based on Ni or Mn, for example, lithium nickelate (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), etc., have been proposed and put into practical use. It was.

However, although the positive electrode material using LiNiO ₂ has the advantages of a large theoretical capacity and a high discharge potential, the crystal structure of LiNiO ₂ collapses as the charge / discharge cycle is repeated. As a result, problems such as a decrease in discharge capacity and deterioration in thermal stability have occurred.
On the other hand, since LiMn ₂ O ₄ has a positive spinel structure and has a space group Fd 3 m, it has a high potential equivalent to 4 V class LiCoO ₂ with respect to the lithium electrode, and is easy to synthesize. Since it has excellent characteristics such as battery capacity, it is considered as a very promising material and has been put into practical use.
Although this LiMn ₂ O ₄ is such an excellent material, the battery using this LiMn ₂ O ₄ has a large capacity deterioration during high-temperature storage, and Mn is dissolved in the electrolytic solution. However, there remains a problem that the chargeability and charge / discharge cycle characteristics are not sufficient.

Accordingly, a lithium battery using a transition metal phosphate compound such as Fe, Mn, Co, or Ni having an olivine structure as a positive electrode active material has been proposed (see Patent Document 1), and a transition metal phosphate having this olivine structure. As a compound, a lithium battery using LiFePO ₄ using Fe, which is a resource-rich and inexpensive metal, as a positive electrode active material has been proposed (see Patent Document 2).
This LiFePO ₄ exhibits a potential of about 3.3 V with respect to metallic lithium (Li), and can be used as a chargeable / dischargeable positive electrode material.
Conventionally, a so-called solid phase method has been used for a phosphate-based material such as a lithium transition metal phosphate.
JP-A-9-134724 Japanese Patent Laid-Open No. 9-171827

However, since lithium metal phosphate compounds such as conventional lithium transition metal phosphates are synthesized by the solid-phase method, it is necessary to repeat firing and pulverization in an inert gas atmosphere, which is a complicated operation. There was a problem that it was necessary.
In the solid phase method, in order to reduce the particle size, it is better to fire at a lower temperature and in a shorter time. In this case, since the firing temperature at the time of synthesis is low, the crystallinity and grain size at the time of synthesis are reduced. It is difficult to control the diameter, and the obtained lithium metal phosphate compound has a structure in which small crystallites are arranged randomly. Therefore, the crystal phase of the lithium metal phosphate compound is not sufficiently generated / developed, the crystallinity is low, the diffusibility of ions in the particles and the electron conductivity are lowered, and the polarization during charge / discharge is increased. There was a problem.

  In addition, there is a method of pulverizing after firing as a method of reducing the particle size, but this method cannot pulverize to a sufficiently small particle size, and excessive force is applied to the particles themselves during pulverization. , Distortion and cracking occur, and crystallinity also decreases. Therefore, when the lithium metal phosphate compound obtained by this method is used in a lithium battery, the volume change of the active material occurs due to the insertion / extraction of lithium ions by charging / discharging, and the particles are cracked by repeating this. Then, cracks progress and the particles are destroyed and refined. As a result, the ion diffusibility in the particles and the impedance between the particles increase, and the polarization during discharge increases. It was.

Therefore, it has been attempted to apply a hydrothermal method capable of synthesizing a material having high crystallinity at a relatively low temperature to a lithium metal phosphate compound such as a lithium transition metal phosphate. When the thermal method is applied to a lithium metal phosphate compound, Li ₃ PO ₄ and Fe ₃ (PO ₄ ) ₂ having low solubility are generated when the raw materials are mixed, and the purity of the lithium metal phosphate compound is lowered. there were.
Therefore, in order to completely react Li ₃ PO ₄ and Fe ₃ (PO ₄ ) ₂ , it is necessary to increase the reaction temperature, extend the reaction time, etc. In this case, the particles are likely to be coarsened. Thus, there is a problem that the advantages of the hydrothermal method cannot always be obtained, such as difficulty in making fine particles.
This decrease in the purity of the lithium metal phosphate compound and the coarsening of the particles decrease the current density during charge and discharge, and as a result, hinder the increase in output.

  The present invention has been made to solve the above-mentioned problems, and by using inexpensive and resource-rich elements, high discharge capacity, stable charge / discharge cycle characteristics, high fillability and high output can be achieved. An object of the present invention is to provide a method for producing a positive electrode active material for a lithium battery, a positive electrode active material for a lithium battery, a positive electrode material for a lithium battery, and a lithium battery.

As a result of intensive studies, the present inventors have found that the lithium metal phosphate compound (Li _x A _y D _z PO ₄ ) has a low electronic conductivity compared to a conventionally used electrode material such as LiCoO ₂ , This point is considered to be one of the reasons why the current density during charging and discharging is low and it is difficult to increase the output, and in order to allow more current to flow, increase the specific surface area of the material, That is, it is considered effective to make fine particles. Therefore, when a lithium metal phosphate compound (Li _x A _y D _z PO ₄ ) is synthesized by a hydrothermal method, N-methyl-2-pyrrolidinone is contained in the reaction system. It is found that a highly crystalline and fine-particle lithium metal phosphate compound (Li _x A _y D _z PO ₄ ) can be obtained by adding a polar organic substance that is soluble in water as described above, and the present invention has been completed. It was.

That is, the manufacturing method of the positive electrode active material for a lithium battery of the present invention is Li _x A _y D _z PO ₄ (where A is one selected from Co, Ni, Mn, Fe, Cu, Cr, and D is Mg , Ca, Fe, Ni, Co, Mn, Zn, Ge, Cu, Cr, Ti, Sr, Ba, Sc, Y, Al, Ga, In, Si, B, one or two selected from rare earth elements A method for producing a positive electrode active material for a lithium battery represented by 0 <x <2, 0 <y <1.5, 0 ≦ z <1.5, which is different from the above A, wherein water is mainly used. A step of preparing a solution by adding a lithium salt, phosphoric acid or ammonium hydrogen phosphate, a metal salt containing A, and N-methyl-2-pyrrolidinone to a solvent as a component, or containing water as a main component Add a metal salt containing D together with the above components to the solvent Preparing a solution by Rukoto, by heating the solution prepared under pressure, said Li _x A _y D _z average primary particle diameter and having a step of generating PO _4, the Is a method for producing a positive electrode active material for a lithium battery having a thickness of 0.02 μm or more and 1 μm or less.

The polar organic substance is preferably N-methyl-2-pyrrolidinone.
The A is preferably one selected from Co, Ni, Mn, and Fe.
The D is preferably one or more selected from Mg, Ca, Ni, Co, Mn, Zn, Ti, and Al.

  The positive electrode active material for a lithium battery of the present invention is obtained by the method for producing a positive electrode active material for a lithium battery of the present invention.

  The positive electrode material for a lithium battery of the present invention is characterized by containing the positive electrode active material for a lithium battery of the present invention.

  The lithium battery of the present invention is characterized by using the positive electrode material for a lithium battery of the present invention.

According to the method for producing a positive electrode active material for a lithium battery of the present invention, Li _x A _y D _z PO ₄ (where A is one selected from Co, Ni, Mn, Fe, Cu, Cr, and D is Mg , Ca, Fe, Ni, Co, Mn, Zn, Ge, Cu, Cr, Ti, Sr, Ba, Sc, Y, Al, Ga, In, Si, B, one or two selected from rare earth elements When producing a positive electrode active material for a lithium battery, which is different from A and represented by 0 ≦ x <2, 0 <y <1.5, 0 ≦ z <1.5), water is the main component. Li component, P component, A component, D component and water-soluble polar organic substance are added to the solvent, and then this solution is heated under pressure, so that Li component, P component, A component and to control the crystal growth of the _Li x _a y _D z PO ₄ in an aqueous solution containing a component D Can, therefore, to produce a fine particle by hydrothermal method from the aqueous solution, it is possible to produce Li _x A _y D _z PO ₄ of highly crystalline and fine.

According to the positive electrode active material for a lithium battery of the present invention, Li _x A _y D _z PO ₄ which is the main component of the positive electrode active material for a lithium battery is obtained by the method for producing a positive electrode active material for a lithium battery of the present invention. Can be highly crystallized and finely divided, the charge / discharge capacity can be greatly improved, and stable charge / discharge cycle characteristics can be realized.

  According to the positive electrode material for a lithium battery of the present invention, since the positive electrode active material for a lithium battery of the present invention is contained, the charge / discharge capacity can be greatly improved, and stable charge / discharge cycle characteristics can be realized. Further, the quality and size of the lithium battery electrode can be reduced.

  According to the lithium battery of the present invention, since the positive electrode material for a lithium battery of the present invention is used, the charge / discharge capacity can be greatly improved, and stable charge / discharge cycle characteristics can be realized. The output can be increased. Therefore, it is possible to provide a lithium battery excellent in various electric characteristics.

The manufacturing method of the positive electrode active material for lithium batteries of this invention, the positive electrode active material for lithium batteries, the positive electrode material for lithium batteries, and the best form of a lithium battery are demonstrated.
This embodiment is specifically described for better understanding of the gist of the invention and does not limit the present invention unless otherwise specified.

The method for producing a positive electrode active material for a lithium battery of the present invention is Li _x A _y D _z PO ₄ (where A is one selected from Co, Ni, Mn, Fe, Cu, Cr, and D is Mg, Ca Fe, Ni, Co, Mn, Zn, Ge, Cu, Cr, Ti, Sr, Ba, Sc, Y, Al, Ga, In, Si, B, one or more selected from rare earth elements and A method for producing a positive electrode active material for a lithium battery, which is different from A and represented by 0 ≦ x <2, 0 <y <1.5, 0 ≦ z <1.5), wherein water is a main component. A lithium (Li) component, a phosphorus (P) component, the A component, the D component, and a water-soluble polar organic substance are added to the solvent, and then the solution is heated under pressure to thereby add the Li a method of generating _x a _y D _z PO _4.

As the polar organic substance, N-methyl-2-pyrrolidinone is preferable.
A is preferably one selected from Co, Ni, Mn, and Fe.
D is preferably one or more selected from Mg, Ca, Ni, Co, Mn, Zn, Ti, and Al.

When Li _x A _y D _z PO ₄ is generated by the hydrothermal method, a lithium (Li) component, a phosphorus (P) component, an A component and a D component are added to a solvent containing water as a main component. For example, a hardly soluble substance such as Li ₃ PO ₄ or Fe ₃ (PO ₄ ) ₂ is generated.
These hardly soluble substances are dissolved as the temperature rises when heated in a pressure resistant container, and the generated Li ⁺ , Fe ²⁺ , PO ₄ ^{3− and} other ions react to form LiFePO ₄ crystal nuclei. Generate and grow. At this time, if the temperature is increased or the heating time is extended in order to completely dissolve Li ₃ PO ₄ or Fe ₃ (PO ₄ ) ₂ , the LiFePO ₄ crystal nucleus grows abnormally.

In the production method of the present invention, a polar organic substance soluble in water such as N-methyl-2-pyrrolidinone is further added to the Li component, P component, A component and D component, and this water-soluble polarity is added. The organic substance is adsorbed on the Li _x A _y D _z PO ₄ crystal nucleus generated in the solution, thereby suppressing the growth of the Li _x A _y D _z PO ₄ crystal nucleus.
In addition, the water-soluble polar organic substance forms a network structure in the solution, thereby generating a minute reaction field surrounded by the polar organic substance, and mass transfer only in the minute reaction field. Will occur. Therefore, crystal growth of Li _x A _y D _z PO ₄ is suppressed.

Thus, after the heating temperature is increased or the heating time is extended in order to completely dissolve insoluble materials such as Li ₃ PO ₄ and Fe ₃ (PO ₄ ) ₂ generated during the synthesis in the solution. However, excessive growth of Li _x A _y D _z PO ₄ crystal nuclei such as LiFePO ₄ is suppressed. Accordingly, highly crystalline and fine particles can be synthesized, and the average primary particle diameter of the particles can be controlled.

Next, the manufacturing method of the positive electrode active material for lithium batteries of this invention is demonstrated more concretely.
First, in a solvent containing water as a main component, a Li component, a P component, and an A component (where A is one selected from Co, Ni, Mn, Fe, Cu, and Cr), a D component (where D is One or two selected from Mg, Ca, Fe, Ni, Co, Mn, Zn, Ge, Cu, Cr, Ti, Sr, Ba, Sc, Y, Al, Ga, In, Si, B, rare earth elements The starting material is prepared by adding more than seeds and different from A). Here, the rare earth elements are 15 elements of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu which are lanthanum series.

Here, a polar organic substance soluble in water is further added to the starting material.
Examples of the Li component include lithium inorganic acid salts such as lithium hydroxide (LiOH), lithium carbonate (Li ₂ CO ₃ ), lithium phosphate (Li ₃ PO ₄ ), lithium acetate (LiCH ₃ COO), lithium oxalate ( Examples include lithium organic acid salts such as (COOLi) ₂ ).

Examples of the phosphorus component include phosphoric acid such as orthophosphoric acid (H ₃ PO ₄ ) and metaphosphoric acid (HPO ₃ ), diammonium hydrogen phosphate ((NH ₄ ) ₂ HPO ₄ ), and ammonium dihydrogen phosphate (NH ₄ Examples thereof include ammonium hydrogen phosphate such as H ₂ PO ₄ ), and orthophosphoric acid, diammonium hydrogen phosphate, and ammonium dihydrogen phosphate are preferable because of relatively high purity and easy composition control.

As the A component, one of metal salts of Co, Ni, Mn, Fe, Cu, and Cr is used. For example, as the Fe salt, iron (II) sulfate (FeSO ₄ ), iron (II) acetate. (Fe (CH ₃ COO) ₂ ), iron chloride (II) (FeCl ₂ ) and the like are preferable.
As D component, Mg, Ca, Fe, Ni, Co, Mn, Zn, Ge, Cu, Cr, Ti, Sr, Ba, Sc, Y, Al, Ga, In, Si, B, each of rare earth elements One or more metal salts of elements different from the component A are used, for example, sulfates such as Al ₂ (SO ₄ ) ₃ , MgSO ₄ , Ti (SO ₄ ) ₂ , Al (CH ₃ COO ) ₃ , metal salts such as acetates such as Mg (CH ₃ COO) ₂ and chlorides such as AlCl ₃ , CaCl ₂ and TiCl ₄ are preferred.

Here, a polar organic substance that is soluble in water is an organic substance that is soluble in water and has polarity in the molecule, and has a large dipole moment in the whole molecule or in the molecule, so that the ion reactivity is high. Therefore, it is possible to suppress the growth of Li _x A _y D _z PO ₄ crystal nuclei such as LiFePO ₄ generated during the synthesis.

  The polar organic substance soluble in water is not particularly limited, but N-methyl-2-pyrrolidinone (NMP), polycarboxylic acid polymer, polyether polymer, glycols such as ethylene glycol and propylene glycol, glycerin Trivalent alcohols such as polyglycerin, polyethyleneimine, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, and the like, or copolymers thereof are preferably used.

In addition, saccharides, for example, sugar alcohols, sugar esters, celluloses such as ethyl cellulose, various water-soluble organic surfactants such as sorbitan ester and polyoxyethylene sorbitan can be used.
Among these polar organic substances, in particular, N-methyl-2-pyrrolidinone can effectively suppress the growth of Li _x A _y D _z PO ₄ crystal nuclei such as LiFePO ₄ , and has a low viscosity. Excellent in terms of easy workability.
These polar organic substances may be added simultaneously with these components when adjusting the starting materials by adding the Li component, P component, A component and D component, or may be added after mixing these components. Good.

Examples of the solvent containing water as a main component include pure water, a water-alcohol solution, a water-ketone solution, and a water-ether solution. Among these, pure water is preferable.
The reason is that water is inexpensive and exhibits a large change in dielectric constant near the critical point, so that it is possible to easily control solvent physical properties such as solubility in each substance by manipulating temperature and pressure.

The starting material solution is then heated under pressure. The method of heating under pressure is not particularly limited, but it is usually performed by storing the starting material solution in a pressure resistant container and heating.
The starting material adjusted as described above is stored in a pressure vessel, and then heated to raise the temperature to a predetermined maximum holding temperature, and the synthesis reaction proceeds by holding at this maximum holding temperature for a predetermined time. Thereafter, the temperature is lowered to room temperature (25 ° C.).

  The reaction conditions are appropriately selected according to the type of solvent and the substance to be synthesized. In the production method of the present invention, when the lithium metal phosphate compound fine particles are synthesized, the reaction temperature is increased or the reaction is performed for a long time. However, the reaction conditions can be set relatively freely because there is no risk of coarsening of the particles. For example, when the solvent is pure water, it is possible to synthesize lithium metal phosphate fine particles having excellent crystallinity with a maximum holding temperature of 120 to 200 ° C. and a holding time (reaction time) of about 1 to 12 hours.

Next, the product in the pressure vessel is separated and recovered by filtration, washed with water, and dried to obtain Li _x A _y D _z PO ₄ (where A is selected from Co, Ni, Mn, Fe, Cu, Cr). D is selected from Mg, Ca, Fe, Ni, Co, Mn, Zn, Ge, Cu, Cr, Ti, Sr, Ba, Sc, Y, Al, Ga, In, Si, B, and rare earth elements The positive electrode active material for a lithium battery represented by one or two or more of the above and different from A is represented by 0 ≦ x <2, 0 <y <1.5, 0 ≦ z <1.5) is obtained. .

  This positive electrode active material for a lithium battery is synthesized at a relatively low temperature as compared with the solid phase method, and the conditions for dissolution and precipitation can be controlled. For example, the average primary particle diameter is 0.01 to 10 μm. The positive electrode active material fine particles for lithium battery can be obtained. By further controlling the synthesis conditions, for example, positive electrode active material fine particles for lithium batteries having an average primary particle size of 0.02 to 1 μm can be obtained.

If the average primary particle size of the positive electrode active material fine particles for lithium batteries is smaller than 0.01 μm, the particles break down due to structural changes accompanying Li insertion / desorption, and the surface area is too large, so a large amount of binder is required. As a result, the conductivity of the positive electrode mixture is lowered, and the packing density of the positive electrode is significantly reduced. Further, if the average primary particle diameter is larger than 10 μm, the internal resistance of the positive electrode active material is increased, and the mass transfer of Li ions is also delayed, so that the utilization rate is lowered and the specific surface area of the obtained particles is small. Thus, the charge / discharge capacity per unit weight is reduced. In addition, there are problems such as repeated destruction of the particles and destruction of the particles, resulting in a decrease in battery capacity.
Thereby, in order to obtain a higher output, particles of 0.02 to 1 μm that are less affected by the internal resistance of the active material are preferable.

In general, in the case of the solid phase method, in order to increase crystallinity, it is necessary to increase the heating temperature or extend the heating time. In this case, the particles are fused with each other in the heating process, or the particles are not bonded. Abnormal grain growth may cause coarse particles, and control of the particle size is not easy.
In the production method of the present embodiment, synthesis can be performed at a relatively low temperature compared to the solid phase method, and the dissolution and precipitation conditions can be controlled. For example, the average primary particle size is 0.01 to 10 μm. In addition, it is possible to obtain positive electrode active material fine particles for lithium battery, preferably having a high crystallinity of 0.02 to 1 μm, and therefore the surface area of the positive electrode active material fine particles for lithium battery can be increased.

Moreover, the lithium secondary battery which has a high charging / discharging rate is realizable by applying this positive electrode active material microparticle for lithium batteries to a lithium secondary battery.
Further, in the case of the solid phase method, it is necessary to hold for a predetermined time at a relatively high temperature. However, in the case of the manufacturing method of the present embodiment, the reaction can proceed with less energy than the solid phase method, so that the running cost is reduced. This is also advantageous.

As described above, according to the manufacturing method of the present embodiment, the hardly soluble substance, which is a by-product substance generated in the initial stage of the reaction, is dissolved in the reaction process, and this reaction is performed when Li _x A _y D _z PO ₄ is precipitated. Occurs in a narrow reaction field surrounded by a network of polar organic substances, and mass transfer occurs only in this reaction field, thereby suppressing crystal growth.

Therefore, in order to completely react the poorly soluble substances such as Li ₃ PO ₄ and Fe ₃ (PO ₄ ) ₂ generated in the reaction process, the reaction temperature is increased and the reaction time is extended. Further, excessive growth of Li _x A _y D _z PO ₄ crystal nuclei such as LiFePO ₄ can be suppressed. Therefore, highly crystalline and fine particles can be synthesized, and the average primary particle diameter of the particles can be controlled.
Furthermore, in the reaction process, once dissolved, the particles are formed by precipitation, so that the direction of crystal growth can be controlled, fine particles with the same direction of crystal growth can be synthesized, and the shape of the particles can also be controlled. Is possible.

EXAMPLES Hereinafter, although an Example and Comparative Examples 1 and 2 demonstrate this invention concretely, this invention is not limited by these Examples.
(Example)
0.2 mol / L lithium acetate (LiCH ₃ COO), 0.1 mol / L iron (II) sulfate (FeSO ₄ ), 0.1 mol / L orthophosphoric acid (H ₃ PO ₄ ) 0.02 L each, The resultant was housed in a pressure-resistant airtight container having a capacity of 0.3 L together with 0.12 L of N-methyl-2-pyrrolidinone and allowed to react at 170 ° C. for 6 hours. Thereafter, the product in the pressure tight sealed container was separated and collected by filtration, washed with water and dried to obtain Sample 1.

(Comparative Example 1)
Sample 2 was obtained in the same manner as in Example except that 0.12 L of pure water was added instead of N-methyl-2-pyrrolidinone.
(Comparative Example 2)
Sample 3 was obtained in the same manner as in Comparative Example 1 except that the reaction time was 3 hours.

FIG. 1 shows powder X-ray diffraction patterns of Cu Kα rays of Samples 1 to 3 obtained in Examples and Comparative Examples 1 and 2, respectively. Note that the diffraction line (2θ °) of LiFePO ₄ described on the JCPDS card (# 81-1173) is shown at the lower end of FIG.
Moreover, the scanning electron microscope image (SEM image) of the sample 1 obtained in the Example is shown in FIG. 2, and the scanning electron microscope image (SEM image) of the sample 2 obtained in Comparative Example 1 is shown in FIG.

(Production of lithium battery)
The lithium batteries of Examples and Comparative Examples 1 and 2 were produced based on Samples 1 to 3 obtained in Examples and Comparative Examples 1 and 2, respectively.
Here, 85 parts by weight of each of Samples 1 to 3, 10 parts by weight of carbon black (CB) having an average primary particle diameter of 14 nm and a specific surface area of 290 m ² / g as a conductive assistant, and 5 parts by weight of polyvinylidene fluoride (PVdF) Together with 70 parts by weight of N-methyl-2-pyrrolidinone, kneaded and pasted using a three-roll or the like, coated on an aluminum foil having a thickness of 30 μm, dried, and compacted at a pressure of 40 MPa, did.

Next, these positive electrodes were vacuum-dried using a vacuum dryer, and then batteries of Examples and Comparative Examples 1 and 2 were fabricated using 2016 type coin cells in a dry argon atmosphere.
Here, metal Li was used as the negative electrode, a porous polypropylene film was used as the separator, and a 1 mol / L LiPF ₆ solution was used as the electrolyte solution.
As the solvent used in this LiPF ₆ solution, 1 ethylene carbonate and methyl ethyl carbonate in a volume%: was a mixture in 1.

(Battery charge / discharge test)
A battery charge / discharge test was performed at room temperature (25 ° C.) for each of the batteries of Examples and Comparative Examples 1 and 2.
In this battery charge / discharge test, the cut-off voltage is set to 2 to 4.5 V, and the current density of discharge / discharge is a constant current with a current amount (rate: 1C) for both discharge and charge, and the charge / discharge cycle is 1 hour. And charging in 1 hour.

The charge / discharge test results of the above Examples and Comparative Example 1 are shown in FIG. In Comparative Example 2, the charge / discharge test could not be performed because it contained a large amount of impurity phase such as Li ₃ PO ₄ .
Table 1 shows the crystal phases, average primary particle diameters, and discharge capacities of Examples and Comparative Examples 1 and 2, respectively.

According to these results, in the examples, by adding N-methyl-2-pyrrolidinone, particle coarsening is suppressed even after sufficient reaction time, and the discharge capacity at high output is greatly improved. I found out that
On the other hand, in Comparative Example 2, since the reaction was insufficient, it was found that Li ₃ PO ₄ and reaction intermediate produced during mixing of the raw materials remained in the sample 3.

In this example, in order to reflect the behavior of the electrode material itself in the data, metal Li was used for the negative electrode, but the negative electrode material may be, for example, a carbon material, a Li alloy, Li ₄ Ti other than metal Li. ₅ O ₁₂ or the like may be used. A solid electrolyte may be used instead of the electrolyte solution and the separator.

In the present invention, when synthesizing positive electrode active material fine particles for a lithium battery, a highly crystalline and fine particle Li _x A _y D is added by adding a polar organic substance soluble in water such as N-methyl-2-pyrrolidinone. _z PO ₄ can be obtained, so further improvement in charge / discharge capacity of lithium batteries, stabilization of charge / discharge cycle, higher output, as well as further reduction in size, weight and capacity are expected. It can be applied to the field of secondary batteries.

It is a figure which shows the powder X-ray-diffraction figure of each of the samples 1-3 obtained by the Example of this invention and Comparative Examples 1 and 2. FIG. It is a figure which shows the scanning electron microscope image (SEM image) of the sample 1 obtained by the Example of this invention. It is a figure which shows the scanning electron microscope image (SEM image) of the sample 2 obtained by the comparative example 1. FIG. It is a figure which shows the charging / discharging characteristic of each battery of the Example and comparative example 1 of this invention.

Claims (6)

Li _x A _y D _z PO ₄ (where A is one selected from Co, Ni, Mn, Fe, Cu, Cr, D is Mg, Ca, Fe, Ni, Co, Mn, Zn, Ge, Cu) , Cr, Ti, Sr, Ba, Sc, Y, Al, Ga, In, Si, B, one or more selected from rare earth elements and different from A, 0 <x <2, 0 <y <1.5, 0 ≦ z <1.5), a method for producing a positive electrode active material for a lithium battery,
A step of preparing a solution by adding a lithium salt, phosphoric acid or ammonium hydrogen phosphate, a metal salt containing A, and N-methyl-2-pyrrolidinone to a solvent containing water as a main component, or the water Preparing a solution by adding a metal salt containing D together with each of the components to a solvent having a main component;
Producing the Li _x A _y D _z PO ₄ by heating the prepared solution under pressure;
A method for producing a positive electrode active material for a lithium battery having an average primary particle diameter of 0.02 μm or more and 1 μm or less.   2. The method for producing a positive electrode active material for a lithium battery according to claim 1, wherein A is one selected from Co, Ni, Mn, and Fe.   3. The positive electrode active material for a lithium battery according to claim 1, wherein the D is one or more selected from Mg, Ca, Ni, Co, Mn, Zn, Ti, and Al. 4. Production method.   A positive electrode active material for a lithium battery, which is obtained by the method for producing a positive electrode active material for a lithium battery according to any one of claims 1 to 3.   A positive electrode material for a lithium battery, comprising the positive electrode active material for a lithium battery according to claim 4.   A lithium battery comprising the positive electrode material for a lithium battery according to claim 5.

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