JP2010168230A - Lithium phosphate powder, slurry containing lithium phosphate, method for producing electrode active material and lithium ion battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide lithium phosphate powders useful as a raw material for an electrode active material in a lithium ion battery having high electric conductivity and high current density at the time of charge and discharge, a slurry containing lithium phosphate where the lithium phosphate powders are dispersed in a dispersion medium, a method for producing an electrode active material using the slurry containing lithium phosphate and the lithium ion battery using the electrode active material obtained by the method for producing the electrode active material. <P>SOLUTION: The lithium phosphate powders contain one or more elements selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and a rare earth element by 0.1 mass% or more and 0.5 mass% or less in total. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a lithium phosphate powder, a lithium phosphate-containing slurry, a method for producing an electrode active material, and a lithium ion battery, and particularly useful as a raw material for an electrode active material suitably used for a positive electrode active material of a lithium ion battery. Lithium phosphate powder, lithium phosphate-containing slurry obtained by dispersing this lithium phosphate powder in a dispersion medium, method for producing electrode active material using this lithium phosphate-containing slurry, method for producing this electrode active material The present invention relates to a lithium ion battery including, as a positive electrode, an electrode formed using the electrode active material obtained by the above.

In recent years, various secondary batteries have been developed as batteries for use in portable electronic devices and hybrid vehicles.
As typical secondary batteries, lead storage batteries, alkaline storage batteries, lithium ion batteries, and the like are known. In particular, lithium ion batteries can be reduced in size, weight, capacity, and output. Because of its high energy density, it is highly anticipated and research has been activated.

Conventionally, lithium cobalt oxide (LiCoO ₂ ) has been generally used as a positive electrode active material for lithium ion batteries because of its high energy density and high voltage.
However, since cobalt (Co) is unevenly distributed on the earth and is a scarce resource, there are problems such as high costs and difficulty in stable supply. Therefore, a new alternative to lithium cobaltate (LiCoO ₂ ) As positive electrode active materials, for example, positive electrode active materials such as lithium nickelate (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium ferrate (LiFeO ₂ ), and lithium iron phosphate (LiFePO ₄ ) have been developed. It is being advanced.

Among them, lithium iron phosphate (LiFePO ₄ ) is rich in iron (Fe) resources as a main raw material, is inexpensive, and a battery having a large theoretical capacity of 170 mAh / g can be obtained. It is expected as a positive electrode active material for a new lithium ion battery replacing lithium (LiCoO ₂ ). For example, lithium iron phosphate (LiFePO ₄ ) or a part of iron (Fe) is replaced with another metal (M) Lithium ion batteries using lithium iron phosphate (LiFe _1-x M _x PO ₄ ) as a positive electrode active material have been proposed (see, for example, Patent Documents 1 and 2).

By the way, lithium iron phosphates such as LiFePO ₄ and LiFe _1-x M _x PO ₄ have a lower electric conductivity than LiCoO ₂ and a lower current density at the time of charge and discharge. In order to fabricate, it is necessary to increase the specific surface area of lithium iron phosphate, that is, to make fine particles.
However, in a general method for synthesizing an electrode active material, for example, a solid phase method, since the raw materials are mixed and then fired for a long time at a high temperature, the generated electrode active material particles are likely to be coarsened. In addition to the above, there is a problem of coarsening and a problem that a large amount of energy is required at the time of firing.
Therefore, in order to make the electrode active material into fine particles, (1) the raw material is made fine particles to increase the reactivity, and the low-temperature baking method in which baking is performed at a low temperature and in a short time; (2) the baking powder obtained by baking A pulverization method using a ball mill or the like is used.

Moreover, the manufacturing method of the electrode active material using a hydrothermal method is also proposed (for example, refer patent documents 3-7 etc.).
This hydrothermal method can synthesize the electrode active material at a lower temperature than the solid phase method in order to synthesize the electrode active material under high pressure. Moreover, the obtained electrode active material has the characteristic that it is excellent in monodispersity.
Furthermore, a method for producing an electrode active material using a spray pyrolysis method has also been proposed (see, for example, Patent Documents 8 and 9).
This spray pyrolysis method is an electrode active material having a uniform composition with a uniform particle size in order to thermally decompose fine droplets generated by spraying a slurry containing a precursor of an electrode active material in a very short time. Is obtained.

JP 2000-294238 A JP 2001-110414 A JP 2002-151082 A JP 2004-095385 A JP 2005-276476 A JP 2007-035358 A JP 2008-159495 A JP 2004-014340 A JP 2004-259471 A

However, in the conventional low-temperature firing method, the crystal phase of lithium iron phosphate (LiFePO ₄ ), which is an electrode active material, cannot be sufficiently generated and grown, so that the obtained lithium iron phosphate (LiFePO ₄ ) There was a problem that the crystallinity was low and the electrical conductivity was not high.
Further, in the conventional pulverization method, since it is mechanically pulverized, it is difficult to pulverize to a sufficiently fine particle diameter, and the electrical conductivity of the obtained lithium iron phosphate (LiFePO ₄ ) does not increase. There was a problem.

Further, the conventional hydrothermal method has a problem that the amount of the electrode active material obtained by one operation is small and the productivity is low. Therefore, if the reaction concentration of the precursor of the electrode active material is increased in order to increase the productivity, the viscosity of the precursor becomes high and it becomes difficult to stir, resulting in a temperature distribution due to poor stirring in the raw material components. As a result, there arises a new problem that the generation of an impurity phase and the coarsening of particles are likely to occur.
Therefore, since the reaction concentration of the precursor of the electrode active material cannot be increased, the productivity cannot be increased and the production cost of the electrode active material is increased.

  In addition, in the conventional spray pyrolysis method, in order to perform stable spraying without losing fluidity, it is necessary to suppress an increase in viscosity at the time of spraying the slurry containing the precursor of the electrode active material. It is necessary to keep the concentration of the precursor at a certain level or less, and as a result, the productivity of the electrode active material cannot be increased, and the production cost of the electrode active material is increased.

  The present invention has been made in view of the above circumstances, and is a lithium phosphate powder useful as a raw material for an electrode active material of a lithium ion battery having high electrical conductivity and high current density during charge and discharge. A lithium phosphate-containing slurry obtained by dispersing lithium acid powder in a dispersion medium, an electrode active material manufacturing method using the lithium phosphate-containing slurry, and an electrode active material obtained by the electrode active material manufacturing method It aims at providing the used lithium ion battery.

The present inventors have selected a result of extensive studies to solve the above problems, the formula _{Li x A y B z PO 4} ( provided that, A is Cr, Mn, Fe, Co, Ni, from the group of Cu One or more selected from the group consisting of Mg, Ca, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y, and rare earth elements As a raw material of the electrode active material represented by 2 or more, 0 <x <2, 0 <y <1.5, 0 ≦ z <1.5), the content of a specific element is within a predetermined range Using lithium phosphate powder, a lithium phosphate-containing slurry having an average dispersed particle size in a specific range in the dispersion medium of the lithium phosphate powder is prepared, and the lithium phosphate-containing slurry is used to produce the above-described slurry. if fabricate an electrode active material represented by the formula _{Li x a y B z PO 4} , It is possible to prevent the generation of a pure phase and the coarsening of the electrode active material particles. Therefore, if this electrode active material is used, a lithium ion battery having stable charge / discharge characteristics can be obtained. Knowing that the concentration of the precursor in the lithium-containing slurry and the concentration of the precursor in the slurry at the time of spraying can be increased to increase productivity, and the production cost of the electrode active material can be greatly reduced. The invention has been completed.

  That is, the lithium phosphate powder according to claim 1 of the present invention is selected from the group of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and rare earth elements. It is characterized by containing one or more elements in a total of 0.1 mass% or more and 0.5 mass% or less.

  A lithium phosphate-containing slurry according to claim 2 is a lithium phosphate-containing slurry obtained by dispersing the lithium phosphate powder according to claim 1 of the present invention in a dispersion medium. The average dispersed particle size in the dispersion medium is 5 μm or more and 500 μm or less.

The method for producing an electrode active material according to claim 3 has the formula Li _x A _y B _z PO ₄ (where A is one or more selected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu) , B is one or more selected from the group consisting of Mg, Ca, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y, and rare earth elements, and 0 <x < A method for producing an electrode active material represented by 2, 0 <y <1.5, 0 ≦ z <1.5), wherein the lithium phosphate-containing slurry according to claim 2 contains the element A. A first step of obtaining a precursor slurry by adding a B raw material containing the A raw material and, if necessary, the B element, and heat treatment of the precursor slurry, and an electrode represented by the formula Li _x A _y B _z PO ₄ And a second step of obtaining an active material.

  According to a fourth aspect of the present invention, there is provided a lithium ion battery comprising an electrode formed using the electrode active material obtained by the method for producing an electrode active material according to the third aspect as a positive electrode.

  According to the lithium phosphate powder according to claim 1 of the present invention, it is selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and rare earth elements. Since one or two or more elements in total are contained in an amount of 0.1% by mass or more and 0.5% by mass or less, the lithium phosphate powder and the dispersion medium are stirred and mixed in a ball mill, a pin mill, or the like By performing the stirring and mixing treatment using the means, the average dispersed particle size in the dispersion medium of the lithium phosphate powder can be controlled to 5 μm or more and 500 μm or less.

According to the lithium phosphate-containing slurry according to claim 2, since the average dispersed particle diameter in the dispersion medium of the lithium phosphate powder is set to 5 μm or more and 500 μm or less, the average dispersed particle diameter in the dispersion medium is increased. Thus, the concentration of the lithium phosphate powder in the slurry can be increased.
Therefore, in this lithium phosphate-containing slurry, A raw material containing one or more selected from the group of Cr, Mn, Fe, Co, Ni, Cu, and Mg, Ca, Sr, Ba, Ti as necessary , Zn, B, Al, Ga, In, Si, Ge, Sc, Y, by adding a B raw material containing one or more selected from the group of rare earth elements, the formula Li _x A _y B _z The concentration of the precursor slurry of the electrode active material represented by PO ₄ can be increased.

  According to the method for producing an electrode active material according to claim 3, the lithium phosphate-containing slurry having an average dispersed particle size of the lithium phosphate powder in the dispersion medium of 5 μm to 500 μm is added to Cr, Mn, Fe, Co. A raw material containing one or more selected from the group of Ni, Cu, and Mg, Ca, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, if necessary Since the B raw material containing one or more selected from the group of Y and rare earth elements is added to form a precursor slurry, the viscosity of the reaction solution when synthesizing this precursor slurry can be kept low. Therefore, the stirring failure does not occur, and the concentration of the obtained precursor slurry can be increased. Further, by increasing the concentration of the precursor slurry, the production efficiency when synthesizing the electrode active material can be improved, and the manufacturing cost of the electrode active material can be reduced.

Further, by heat-treating this precursor slurry, the formula Li _x A _y B _z PO ₄ (where A is one or more selected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu, B is one or more selected from the group consisting of Mg, Ca, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y, and rare earth elements, and 0 <x <2 , 0 <y <1.5, 0 ≦ z <1.5), there is no possibility that coarse particles or impurity phases are generated, and the electrode active material is made into fine particles composed of a single phase. be able to.

  According to the lithium ion battery according to claim 4, since the electrode formed using the electrode active material obtained by the method for producing an electrode active material is provided as a positive electrode, the electrical conductivity can be increased, The current density at the time of charging / discharging can be increased, and thus the charge / discharge characteristics can be stabilized.

An embodiment for carrying out a lithium phosphate powder, a lithium phosphate-containing slurry, a method for producing an electrode active material, and a lithium ion battery according to the present invention will be described.
This embodiment is specifically described for better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

"Lithium phosphate powder"
The lithium phosphate (Li ₃ PO ₄ ) powder of this embodiment is selected from the group of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and rare earth elements. One or more elements are contained in a total of 0.1% by mass to 0.5% by mass, preferably 0.2% by mass to 0.4% by mass.

In this lithium phosphate (Li ₃ PO ₄ ) powder, one kind selected from the group of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and rare earth elements Alternatively, two or more elements generally exist as a coprecipitate of a salt containing this element and the above lithium phosphate (Li ₃ PO ₄ ).

Here, the reason why the total content of the above elements is limited to 0.1% by mass or more and 0.5% by mass or less is that the total content of the above elements is less than 0.1% by mass. In the “lithium phosphate (Li ₃ PO ₄ ) -containing slurry” described later, the average dispersed particle diameter in the dispersion medium of the lithium phosphate (Li ₃ PO ₄ ) powder is less than 5 μm. In the “active material production method”, the lithium phosphate-containing slurry contains A raw material containing one or more selected from the group consisting of Cr, Mn, Fe, Co, Ni, and Cu, and, if necessary, Mg, Ca Precursor slurry by adding B raw material containing one or more selected from the group of Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y, and rare earth elements When synthesizing the viscosity of the reaction solution As a result, the stirring becomes poor and the progress of the uniform reaction is hindered. As a result, the electrode active material may be coarsened or an impurity phase may be generated.

On the other hand, when the total content of the above elements exceeds 0.5% by mass, in the “lithium phosphate (Li ₃ PO ₄ ) -containing slurry” described later, the above lithium phosphate (Li ₃ PO ₄ ) In the dispersion medium of the powder, the average dispersed particle diameter is less than 5 μm, and in the “electrode active material production method” described later, the lithium phosphate (Li ₃ PO ₄ ) -containing slurry is mixed with Cr, Mn, Fe, Co, A raw material containing one or more selected from the group of Ni and Cu, and Mg, Ca, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y as necessary When a precursor raw material containing one or more selected from the group of rare earth elements is added to synthesize the precursor slurry, the viscosity of the reaction solution increases, resulting in poor stirring and uniform reaction. Inhibit the progression of , And consequently, or the electrode active material are coarsened, there is a possibility that impurities are generated.

  When the total content of the above elements exceeds 0.5% by mass, beryllium (Be), magnesium (Mg), calcium is contained in the electrode active material obtained by the “method for producing electrode active material” described later. One or more of (Ca), strontium (Sr), barium (Ba), and rare earth elements will be contained, reducing the active ingredient as an electrode active material and reducing the capacity of the lithium ion battery. This is because the absolute value may decrease.

As the lithium phosphate _(Li 3 PO ₄₎ manufacturing method of a powder, is not particularly limited, for example, lithium hydroxide (LiOH), lithium carbonate _(Li 2 _CO 3), lithium acetate (LiCH ₃ COO) and Li sources such as, phosphoric acid _(H 3 _PO 4), phosphoric acid dihydrogen ammonium _{(NH 4} H 2 PO4), monohydrogen phosphate diammonium _{((NH 4)} PO 4, such as 2 HPO ₄₎ Source, hydroxide of one or more elements selected from the group of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and rare earth elements, oxidation The product, sulfate, nitrate, acetate, and chloride are mixed in water to form a precipitate, and the precipitate can be obtained by solid-liquid separation.

According to this lithium phosphate (Li ₃ PO ₄ ) powder, 1 selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and rare earth elements Since the seed or two or more elements are contained in a total amount of 0.1% by mass or more and 0.5% by mass or less, the lithium phosphate powder and the dispersion medium are mixed with a stirring / mixing means such as a ball mill or a pin mill. By carrying out the stirring and mixing treatment using, the average dispersed particle size in the dispersion medium of this lithium phosphate (Li ₃ PO ₄ ) powder can be controlled to 5 μm or more and 500 μm or less.

"Lithium phosphate-containing slurry"
The lithium phosphate (Li ₃ PO ₄ ) -containing slurry of the present embodiment is a lithium phosphate-containing slurry obtained by dispersing the above lithium phosphate (Li ₃ PO ₄ ) powder in a dispersion medium. The average dispersed particle diameter of the lithium (Li ₃ PO ₄ ) powder in the dispersion medium is preferably 5 μm or more and 500 μm or less, more preferably 15 μm or more and 100 μm or less, and further preferably 15 μm or more and 30 μm or less.
Here, “average dispersed particle size” means “volume average dispersed particle size”, and this average dispersed particle size can be measured with a laser diffraction / scattering particle size distribution analyzer.

In this lithium phosphate (Li ₃ PO ₄ ) -containing slurry, the lithium phosphate (Li ₃ PO ₄ ) powder and dispersion medium are subjected to a stirring and mixing process using a stirring and mixing means such as a ball mill and a pin mill. Thus, it can be easily obtained.
As this dispersion medium, for example, water, alcohols, ethers, polar organic solvents, or a mixed solution containing one or more of these solvents are suitable.

Examples of the alcohols include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol and the like.
Examples of ethers include diethyl ether, ethylene glycol monomethyl ether (methyl cellosolve), ethylene glycol monoethyl ether (ethyl cellosolve), and ethylene glycol monobutyl ether (butyl cellosolve).
Examples of the polar organic solvent include acetonitrile, tetrahydrofuran, dimethyl sulfoxide and the like.

According to the lithium phosphate (Li ₃ PO ₄ ) -containing slurry, the average dispersed particle size in the dispersion medium of the lithium phosphate (Li ₃ PO ₄ ) powder is 5 μm or more and 500 μm or less. The concentration of the lithium phosphate (Li ₃ PO ₄ ) powder can be increased.
Therefore, in the “electrode active material manufacturing method” described later, this lithium phosphate (Li ₃ PO ₄ ) -containing slurry is added to one or two selected from the group consisting of Cr, Mn, Fe, Co, Ni, and Cu. One or two selected from the group consisting of A raw materials including the above, and Mg, Ca, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y, and rare earth elements as necessary The concentration of the precursor slurry of the electrode active material represented by the formula Li _x A _y B _z PO ₄ can be increased by adding the B raw material including the above.

"Method for producing electrode active material"
The method for producing the electrode active material of the present embodiment has the formula Li _x A _y B _z PO ₄ (where A is one or more selected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu, B is one or more selected from the group consisting of Mg, Ca, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y, and rare earth elements, and 0 <x <2 , 0 <y <1.5, 0 ≦ z <1.5), wherein the element A is added to the lithium phosphate (Li ₃ PO ₄ ) -containing slurry. The first step of obtaining a precursor slurry by adding the A raw material containing B and, if necessary, the B raw material containing the above B element, and heat treating the precursor slurry, the above formula Li _x A _y B _z PO ₄ A second step of obtaining an electrode active material represented by

As said A raw material, the metal salt containing 1 type, or 2 or more types of elements selected from the group of Cr, Mn, Fe, Co, Ni, Cu is used suitably.
As said B raw material, 1 type, or 2 or more types selected from the group of Mg, Ca, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y, and rare earth elements A metal salt containing an element or a compound containing the above element is preferably used.
Here, the rare earth elements are La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

The ratio of the raw material components in the precursor slurry is not limited as long as impurities are not generated. For example, Li ions are 1 to 4 mol and PO ₄ ions are 1 mol with respect to 1 mol of A ions. However, it is preferable because impurities can be generated and particles can be coarsened.
In addition, in order to adjust the concentration of the precursor in this precursor slurry, for example, water, alcohols, ethers, acetonitrile, tetrahydrofuran, dimethyl sulfoxide or other polar organic solvents, or a mixture containing two or more of these A solution may be added.

As the heat treatment method for the precursor slurry, any one of (1) hydrothermal synthesis method, (2) spray pyrolysis method, and (3) spray drying / pyrolysis method is suitably used.
Next, each of these methods will be described in detail.

(1) Hydrothermal synthesis method In this method, the precursor slurry is placed in a pressure vessel and heated, a synthesis reaction is performed at a predetermined temperature for a predetermined time, and then natural cooling or rapid cooling is performed.
The reaction conditions for the hydrothermal reaction are appropriately selected according to the type of the dispersion medium or the substance to be synthesized. When the dispersion medium is water, the heating temperature is 120 to 250 ° C, more preferably 150 to 220 ° C. Yes, the reaction time is 1 to 24 hours.

After completion of the synthesis reaction, the synthesized product is subjected to solid-liquid separation by suction filtration or the like, and the separated solid is recovered, washed with water and dried to obtain the formula Li _x A _y B _z PO ₄ (where A is One or more selected from the group of Cr, Mn, Fe, Co, Ni, Cu, B is Mg, Ca, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, An electrode active material represented by one or more selected from the group of Sc, Y and rare earth elements, 0 <x <2, 0 <y <1.5, 0 ≦ z <1.5) can get.

In this hydrothermal synthesis method, the precursor concentration (reaction concentration) is 0.5 mol / kg or more in terms of Li _x A _y B _z PO ₄ , for example, 1 mol / kg to 1.5 mol / kg can be achieved, and therefore, an increase in viscosity of the precursor slurry during the hydrothermal reaction can be suppressed, and fluidity is not lost even when the concentration of the precursor slurry is high. A uniform reaction is possible.
As a result, productivity is improved, and thus the manufacturing cost of the electrode active material represented by the formula Li _x A _y B _z PO ₄ can be reduced.
The electrode active material thus obtained can be suitably used as a positive electrode material for lithium ion batteries because the particle diameter is small, the dispersibility of the particle diameter is controlled, and the crystallinity is good. .

In order to increase the conductivity of the electrode active material, a step of coating the surface of the electrode active material with a conductive film may be added.
As this process, for example, the electrode active material and a conductive material or a precursor of a conductive material are mixed, and this mixture is mixed in a non-oxidizing atmosphere such as a nitrogen atmosphere at 600 ° C. to 800 ° C., The process of heat-processing for 30 minutes-120 minutes is mentioned.

As the conductive material, in addition to carbon, a metal, particularly a noble metal such as Au, Pt, Ag, Pd, Ru, Rh, and Ir, is preferably used, and Ag is particularly preferable.
In addition, the precursor of the conductive substance becomes a conductive substance by heating, and as the precursor of the conductive substance, in addition to the organic compound, the above-mentioned metal, particularly a salt containing a noble metal, the above-mentioned A metal alkoxide, a complex of the above metal, and the like are preferably used.

As the carbon described above, simple carbon or a carbon compound is used. As the carbon simple substance, for example, carbon black, acetylene black, graphite or the like can be used, and either carbon black or acetylene black is preferable. The primary particle diameter of these carbon simple substance is preferably 1 to 1000 nm, more preferably 10 nm to 200 nm.
The primary particle diameter of carbon simple substance can be measured using a laser diffraction particle size distribution meter.

(2) Spray pyrolysis method The above precursor slurry is made into fine droplets by using droplet generation means such as an ultrasonic atomizer, and the droplets are sprayed in a high-temperature non-oxidizing atmosphere. It is a method of disassembling.
The average particle size of the droplets is preferably in the range of 0.05 μm to 500 μm.

The thermal decomposition temperature of the droplets varies depending on the raw material used, but is preferably 500 to 1000 ° C, more preferably 650 to 800 ° C.
The reason for this is that when the thermal decomposition temperature is lower than 500 ° C., the decomposition and reaction of the droplets do not proceed sufficiently, the crystallinity of the obtained product is also lowered, and in some cases it becomes amorphous. This is because there is a possibility, and when the thermal decomposition temperature exceeds 1000 ° C., the obtained product may be melted and vitrified.
The atmosphere for spray pyrolysis is preferably an inert atmosphere such as N ₂ or Ar when the element A is Fe, and a reducing gas such as H ₂ is used to suppress oxidation more. A reducing atmosphere is preferred.

Thereafter, by recovering the resulting product of the formula _{Li x A y B z PO 4} ( provided that, A is Cr, Mn, Fe, Co, Ni, 1 or more kinds selected from the group of Cu , B is one or more selected from the group consisting of Mg, Ca, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y, and rare earth elements, and 0 <x < An electrode active material represented by 2, 0 <y <1.5, 0 ≦ z <1.5) is obtained.
The electrode active material thus obtained can be suitably used as a positive electrode material for lithium ion batteries because the particle diameter is small, the dispersibility of the particle diameter is controlled, and the crystallinity is good. .

In this spray pyrolysis method, by using the precursor slurry, the precursor concentration (reaction concentration) is 0.5 mol / kg or more in terms of Li _x A _y B _z PO ₄ , for example, 1 mol / kg to Thus, it is possible to suppress the increase in the viscosity of the droplet during spraying, and even if the droplet has a high concentration, fluidity is not lost and stable spraying is achieved. It becomes possible.
As a result, productivity is improved, and thus the manufacturing cost of the electrode active material represented by the formula Li _x A _y B _z PO ₄ can be reduced.

Also in this electrode active material, in order to improve conductivity, a conductive material or a conductive material precursor may be added to the precursor slurry.
As the conductive material or the precursor of the conductive material, the same materials as those used in the hydrothermal synthesis method can be used.

(3) Spray drying / pyrolysis method The above precursor slurry is made into fine droplets using droplet generating means such as an ultrasonic atomizer, and these droplets are sprayed into a high-temperature atmosphere and dried. Thus, a granulated powder is obtained, and this granulated powder is fired in a non-oxidizing atmosphere.
The average particle size of these droplets is preferably in the range of 0.05 μm to 50 μm.

The drying temperature of the droplets varies depending on the raw material used, but is preferably 100 to 300 ° C, more preferably 150 to 250 ° C.
The reason for this is that when the drying temperature is lower than 100 ° C., the drying of the droplets does not proceed sufficiently, the obtained particles are aggregated, and the particles are likely to become coarse during the subsequent pyrolysis step. In addition, when the drying temperature exceeds 300 ° C., the oxidation of the droplet proceeds, and an electrode active material represented by the formula Li _x A _y B _z PO ₄ is obtained in the subsequent thermal decomposition step. It is because it becomes impossible.
The atmosphere at the time of spray drying may be ordinary air, and a non-oxidizing atmosphere or reducing atmosphere as in the spray pyrolysis method is not necessary.

The granulated powder thus obtained is collected and then fired using an electric furnace or the like.
This firing temperature varies depending on the composition of the granulated powder and the raw materials used, but is preferably 500 to 1000 ° C, more preferably 650 to 800 ° C.
The reason is that if the firing temperature is lower than 500 ° C., the decomposition and reaction of the granulated powder does not proceed sufficiently, the crystallinity becomes low, and in some cases, it may become amorphous. In addition, if the firing temperature exceeds 1000 ° C., the fired product may be melted and vitrified.

Thereafter, the obtained product is recovered to obtain the formula Li _x A _y B _z PO ₄ (where A is one or more selected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu) , B is one or more selected from the group consisting of Mg, Ca, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y, and rare earth elements, and 0 <x < An electrode active material represented by 2, 0 <y <1.5, 0 ≦ z <1.5) is obtained.
The electrode active material thus obtained can be suitably used as a positive electrode material for lithium ion batteries because the particle diameter is small, the dispersibility of the particle diameter is controlled, and the crystallinity is good. .

In this spray drying / pyrolysis method, the precursor concentration (reaction concentration) is 0.5 mol / kg or more in terms of Li _x A _y B _z PO ₄ , for example, 1 mol / kg, by using the precursor slurry. kg-1.5 mol / kg can be achieved, and therefore the viscosity increase of the droplets during spray drying can be suppressed, and even if these droplets have a high concentration, the fluidity is not lost and is stable. Spraying is possible.
As a result, productivity is improved, and thus the manufacturing cost of the electrode active material represented by the formula Li _x A _y B _z PO ₄ can be reduced.

Also in this electrode active material, in order to improve conductivity, a conductive material or a conductive material precursor may be added to the precursor slurry.
As the conductive material or the precursor of the conductive material, the same materials as those used in the hydrothermal synthesis method can be used.

"Lithium-ion battery"
The lithium ion battery of the present embodiment has a positive electrode as an electrode formed using the electrode active material obtained by the above-described method for producing an electrode active material, and further includes a negative electrode, an electrolyte, and a separator.
In order to produce this positive electrode, first, for example, the electrode active material, a binder resin (binder), and a solvent are mixed to prepare a paint or paste for forming a positive electrode. At this time, a conductive aid such as carbon black may be added as necessary.

  Next, the positive electrode-forming paint or paste is applied to one surface of the metal foil, and then dried to obtain a metal foil in which the positive electrode active material is held in layers on one surface. Next, the layered positive electrode active material held on one surface of the metal foil is pressure-bonded by pressurization, and then dried to form a positive electrode to produce a current collector (positive electrode).

Said binder resin can be selected as needed. For example, polytetrafluoroethylene (PTFE) resin, polyvinylidene fluoride (PVdF) resin, or the like is used. These resins may be used alone or in combination of two or more.
The ratio between the electrode active material and the binder resin is not particularly limited. For example, the binder resin is 3 parts by mass to 20 parts by mass with respect to 100 parts by mass of the electrode active material.
The shape, size, etc. of the positive electrode are appropriately selected as necessary.
Further, the negative electrode, electrolyte, separator, battery shape, etc. are also particularly limited, and may be appropriately selected as necessary.

  In the lithium ion battery of this embodiment, the positive electrode is a fine spherical powder having a uniform particle diameter, and is formed of a high-purity electrode active material composed of a single phase that does not contain an impurity phase. Therefore, the discharge capacity in high-speed charge / discharge is large, and therefore, it has sufficient charge / discharge performance, stable charge / discharge cycle performance, high output, and low cost.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited by these Examples.

"Example 1"
6 mol of lithium hydroxide (LiOH) and 0.0203 mol of calcium hydroxide (Ca (OH) ₂ ) were added to 5 L of pure water and stirred sufficiently, and then 2 mol of phosphoric acid (H ₃ PO ₄ ). Was dripped. At this time, the generated precipitate was precipitated. This precipitate was filtered and then washed with pure water to obtain a cake having a solid content.
A part of the cake was dried to obtain a measurement sample, and the Ca content in the measurement sample was measured by ICP spectroscopy. The measurement results are shown in Table 1.
Further, when the sample for measurement was identified by X-ray diffraction (XRD), it was found that it was composed of single-phase lithium phosphate (Li ₃ PO ₄ ).

Then, lithium phosphate (Li 3 _{PO 4)} of the cake made of, 1.5 molar, it was dispersed in water and dispersed in a ball mill to a solid concentration of 42 wt%, phosphoric acid A lithium (Li ₃ PO ₄ ) -containing slurry was obtained.
The average dispersion particle diameter of the lithium phosphate (Li ₃ PO ₄ ) powder in the lithium phosphate (Li ₃ PO ₄ ) -containing slurry is changed to a laser diffraction / scattering particle size distribution analyzer SALD-2000J (manufactured by Shimadzu Corporation). Measured. The measurement results are shown in Table 1.

Next, 1.4 mol of lithium phosphate (Li ₃ PO ₄ ) is taken out from the lithium phosphate (Li ₃ PO ₄ ) -containing slurry, and 1.4 mol of chloride is added to the lithium phosphate (Li ₃ PO ₄ ). ferrous and (FeCl ₂₎ was added, further the 1kg the total amount added to pure water, phosphate lithium iron concentration of lithium iron phosphate (LiFePO ₄₎ Convert 1.4 mol / kg of (LiFePO ₄₎ A precursor slurry was obtained.
Next, this precursor slurry was put into a pressure-resistant airtight container and reacted at 190 ° C. for 6 hours. The obtained precipitate was washed with 10 L of pure water and then dried to obtain a powder of an electrode active material.

When this powder was identified by X-ray diffraction (XRD), it was found to be composed of single-phase lithium iron phosphate (LiFePO ₄ ).
Further, the specific surface area (BET value) of the powder was measured by the BET method. The measurement results are shown in Table 2.

"Example 2"
A cake was obtained in the same manner as in Example 1 except that the addition amount of calcium hydroxide (Ca (OH) ₂ ) was changed to 0.016 mol. A part of the cake was dried to obtain a measurement sample, and the Ca content in the measurement sample was measured by ICP spectroscopy. The measurement results are shown in Table 1.
Further, when the sample for measurement was identified by X-ray diffraction (XRD), it was found that it was composed of single-phase lithium phosphate (Li ₃ PO ₄ ).

Next, in the same manner as in Example 1, a lithium phosphate (Li ₃ PO ₄ ) -containing slurry was obtained.
The average dispersion particle diameter of the lithium phosphate (Li ₃ PO ₄ ) powder in the lithium phosphate (Li ₃ PO ₄ ) -containing slurry is changed to a laser diffraction / scattering particle size distribution analyzer SALD-2000J (manufactured by Shimadzu Corporation). Measured. The measurement results are shown in Table 1.

Next, an electrode active material powder was obtained in the same manner as in Example 1.
When this powder was identified by X-ray diffraction (XRD), it was found to be composed of single-phase lithium iron phosphate (LiFePO ₄ ).
Further, the specific surface area (BET value) of the powder was measured by the BET method. The measurement results are shown in Table 2.

"Example 3"
1.4 mol of lithium phosphate (Li ₃ PO ₄ ) was taken out from the lithium phosphate (Li ₃ PO ₄ ) -containing slurry of Example 1, and 1.4 mol of lithium phosphate (Li ₃ PO ₄ ) was added to this lithium phosphate (Li ₃ PO ₄ ). Ferrous phosphate (Fe ₃ (PO ₄ ) ₂ ) is added, pure water is added to make the total amount 1 kg, and the concentration in terms of lithium iron phosphate (LiFePO ₄ ) is 1.4 mol / kg. A precursor slurry of iron lithium (LiFePO ₄ ) was obtained.

Next, an electrode active material powder was obtained in the same manner as in Example 1, except that this lithium iron phosphate (LiFePO ₄ ) precursor slurry was used.
When this powder was identified by X-ray diffraction (XRD), it was found to be composed of single-phase lithium iron phosphate (LiFePO ₄ ).
Further, the specific surface area (BET value) of the powder was measured by the BET method. The measurement results are shown in Table 2.

“Comparative Example 1”
6 mol of lithium hydroxide (LiOH) was added to 5 L of pure water and stirred sufficiently, and then 2 mol of phosphoric acid (H ₃ PO ₄ ) was added dropwise. At this time, the generated precipitate was precipitated. This precipitate was filtered and then washed with pure water to obtain a cake having a solid content.
A part of the cake was dried to obtain a measurement sample, and the Ca content in the measurement sample was measured by ICP spectroscopy. The measurement results are shown in Table 1.
Further, when the sample for measurement was identified by X-ray diffraction (XRD), it was found that it was composed of single-phase lithium phosphate (Li ₃ PO ₄ ).

Next, in the same manner as in Example 1, a lithium phosphate (Li ₃ PO ₄ ) -containing slurry was obtained.
The average dispersion particle diameter of the lithium phosphate (Li ₃ PO ₄ ) powder in the lithium phosphate (Li ₃ PO ₄ ) -containing slurry is changed to a laser diffraction / scattering particle size distribution analyzer SALD-2000J (manufactured by Shimadzu Corporation). Measured. The measurement results are shown in Table 1.

Next, an electrode active material powder was obtained in the same manner as in Example 1.
When this powder was identified by X-ray diffraction (XRD), it was found to be composed of single-phase lithium iron phosphate (LiFePO ₄ ).
Further, the specific surface area (BET value) of the powder was measured by the BET method. The measurement results are shown in Table 2.

“Comparative Example 2”
A cake was obtained in the same manner as in Example 1, except that the amount of calcium hydroxide (Ca (OH) ₂ ) was changed to 0.0348 mol.
A part of the cake was dried to obtain a measurement sample, and the Ca content in the measurement sample was measured by ICP spectroscopy. The measurement results are shown in Table 1.
Further, when the sample for measurement was identified by X-ray diffraction (XRD), it was found that it was composed of single-phase lithium phosphate (Li ₃ PO ₄ ).

Next, in the same manner as in Example 1, a lithium phosphate (Li ₃ PO ₄ ) -containing slurry was obtained.
The average dispersion particle diameter of the lithium phosphate (Li ₃ PO ₄ ) powder in the lithium phosphate (Li ₃ PO ₄ ) -containing slurry is changed to a laser diffraction / scattering particle size distribution analyzer SALD-2000J (manufactured by Shimadzu Corporation). Measured. The measurement results are shown in Table 1.

Next, an electrode active material powder was obtained in the same manner as in Example 1.
When this powder was identified by X-ray diffraction (XRD), it was found to be composed of single-phase lithium iron phosphate (LiFePO ₄ ).
Further, the specific surface area (BET value) of the powder was measured by the BET method. The measurement results are shown in Table 2.

“Production and evaluation of lithium-ion batteries”
The following processes were performed on the electrode active materials of Examples 1 to 3 and Comparative Examples 1 and 2, and lithium ion batteries of Examples 1 to 3 and Comparative Examples 1 and 2 were produced.
First, the electrode active material was ground using an mortar and 85 parts by weight of the ground electrode active material, and 10 parts by weight of carbon black having an average primary particle size of 14 nm and a specific surface area of 290 m ² / g as a conductive auxiliary agent. Then, it was kneaded using a three roll together with 5 parts by mass of polyvinylidene fluoride to form a paste, and this paste was applied onto an aluminum foil having a thickness of 30 μm and then dried to obtain a positive electrode.

Subsequently, this positive electrode was vacuum-dried using a vacuum dryer, and a lithium ion battery was produced using a cell in a dry argon atmosphere.
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. Moreover, as a solvent used for this LiPF ₆ solution, what mixed ethylene carbonate and diethyl carbonate 1: 1 by volume% was used.

Next, a battery charge / discharge test was performed using the lithium ion batteries of Examples 1 to 3 and Comparative Examples 1 and 2.
Here, the cut-off voltage was 2 V to 4.5 V, and the charge / discharge current was changed from 0.1 C to 3 C. However, a constant current was always used during one cycle of charge / discharge. The evaluation results are shown in Table 2.

According to Table 1, the following was found.
(1) Since the lithium phosphate (Li ₃ PO ₄ ) powders of Examples 1 to 3 contain 0.1 mass% to 0.5 mass% of Ca element, the average when dispersed in water The dispersed particle diameter is in the range of 5 μm to 500 μm.
(2) On the other hand, the lithium phosphate (Li ₃ PO ₄ ) powders of Comparative Examples 1 and 2 do not contain Ca element or contain more than 0.5% by mass. The average dispersed particle size is outside the range of 5 μm to 500 μm.

Moreover, according to Table 2, the following was found.
(3) Although the electrode active materials of Examples 1 to 3 have a precursor concentration in the synthesis process as high as 1 mol / kg in terms of LiFePO ₄ , the electrode active materials of Comparative Examples 1 and 2 In comparison, the specific surface area is large.
Furthermore, the lithium ion battery including the positive electrode formed using the electrode active material of Examples 1 to 3 has a discharge capacity of both low rate (0.1 C) and high rate (3 C) charge and discharge. The decrease was small, and the discharge capacity was 129 mAh / g or more, particularly in charge / discharge at a high rate (3C).

(4) On the other hand, the electrode active materials of Comparative Examples 1 and 2 are compared with the electrode active materials of Examples 1 to 5 because the precursor concentration in the synthesis process is as high as 1 mol / kg in terms of LiFePO _4. The specific surface area is small.
Furthermore, the lithium ion battery including the positive electrode formed using the electrode active material of Comparative Examples 1 and 2 has a discharge capacity of 117 mAh / g or 110 mAh / g in charge / discharge at a high rate (3C). The decrease in discharge capacity was significant.

The lithium phosphate (Li ₃ PO ₄ ) powder of the present invention is selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and rare earth elements. This lithium phosphate (Li ₃ PO ₄ ) particles have an average dispersed particle size of 5 μm or more and 500 μm or less by containing seeds or two or more elements in total of 0.1% by weight or more and 0.5% by weight or less. Lithium having a high electrical conductivity and a high current density during charge and discharge can be synthesized using a precursor slurry dispersed within the range of An ion battery can be realized, and the precursor slurry concentration and the precursor slurry concentration at the time of spraying can be increased to increase the productivity. Because as it can greatly reduce the significance of the industry is extremely large.

Claims (4)

  0.1% by mass or more in total of one or more elements selected from the group of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and rare earth elements And a lithium phosphate powder containing 0.5% by mass or less. A lithium phosphate-containing slurry obtained by dispersing the lithium phosphate powder according to claim 1 in a dispersion medium,
The lithium phosphate-containing slurry, wherein an average dispersed particle size of the lithium phosphate powder in the dispersion medium is 5 μm or more and 500 μm or less. Wherein _{Li x A y B z PO 4} ( provided that, A is Cr, Mn, Fe, Co, Ni, 1 or more kinds selected from the group of Cu, B is Mg, Ca, Sr, Ba, Ti, One or more selected from the group consisting of Zn, B, Al, Ga, In, Si, Ge, Sc, Y and rare earth elements, 0 <x <2, 0 <y <1.5, 0 ≦ z <1.5) A method for producing an electrode active material represented by
A first step of obtaining a precursor slurry by adding the A raw material containing the A element and, if necessary, the B raw material containing the B element to the lithium phosphate-containing slurry according to claim 2;
A second step of heat-treating the precursor slurry to obtain an electrode active material represented by the formula Li _x A _y B _z PO ₄ ;
A method for producing an electrode active material, comprising:   A lithium ion battery comprising, as a positive electrode, an electrode formed using an electrode active material obtained by the method for producing an electrode active material according to claim 3.