JP2002151082A - Iron phosphate lithium, its manufacturing method, and secondary battery using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery has little variation of a particle diameter and a particle size distribution between manufacturing lots, iron phosphate lithium having characteristic of being especially used suitably as a part of positive pole material of a secondary battery, a manufacturing method that can compounds this with sufficient reproducibility, high capacity, and a stable secondary-battery characteristic are shown. SOLUTION: The iron phosphate lithium has a particle size distribution, which measured with laser diffraction/dispersion method is a normal distribution mathematically, a median of the above particle size distribution of 5.3 μm or less, and the particle diameter from the minimum particle diameter to 10%, of 2.2 μm or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithium iron phosphate which is particularly preferably used as a positive electrode material for a secondary battery which can be repeatedly charged and discharged, a method for producing the same, and a method using the lithium iron phosphate. Related to secondary batteries.

[0002]

2. Description of the Related Art Lithium iron phosphate having a chemical composition of LiFePO ₄ and a secondary battery using the same as a cathode material are disclosed in, for example, US Pat. No. 5,910,382 and Journal of Electrochemical Society,
144, 1188, 1997 (J. Electr
ochem. Soc. , 144, 1188, 199
7), Journal of Electrochemical Society, 144, 1609, 1997 (J. El.
electrochem. Soc. , 144, 1609, 1
997). Further, analogous compounds of the above lithium compounds are also disclosed in JP-A-9-134724, JP-A-9-171827, and the like.

According to the above publications, nitrogen and argon are prepared from lithium compounds such as lithium carbonate and phosphate compounds such as divalent iron compounds such as iron oxalate and iron acetate and ammonium dihydrogen phosphate. A method for obtaining a lithium compound represented by LiFePO ₄ by firing at a high temperature of about 650 ° C. to 800 ° C. in an inert gas stream such as that described above. In addition, a technique for forming a secondary battery using the obtained lithium compound as a part of a positive electrode material is also described.

[0004]

However, the above-mentioned conventional method has a problem that the particle size and the particle size distribution of the obtained lithium iron phosphate vary from one production lot to another even if the calcination temperature is controlled. are doing. For this reason, it is difficult to produce the desired lithium iron phosphate with good reproducibility by the above-mentioned conventional production method, which is not suitable for mass production. Therefore, the LiFePO obtained by the above production method
Lithium iron phosphate represented by No. ₄ has a problem that it cannot be put to practical use as a positive electrode material of a secondary battery.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to reduce variation in particle size and particle size distribution among manufacturing lots, and to provide at least a part of a positive electrode material of a secondary battery as: In particular, it is an object of the present invention to provide lithium iron phosphate having characteristics particularly suitably used, a production method capable of synthesizing the same with good reproducibility, and a secondary battery exhibiting high capacity and stable secondary battery characteristics.

[0006]

Means for Solving the Problems The inventors of the present application have made intensive studies to achieve the above object. As a result, it has been found that lithium iron phosphate having a chemical composition of LiFePO ₄ has excellent characteristics as a positive electrode material of a secondary battery when the particle size distribution is within a predetermined range, thereby completing the present invention. Reached.

That is, in order to solve the above problems, the lithium iron phosphate according to the first aspect has a chemical composition of Li
A lithium iron phosphate represented by FePO ₄ , wherein the particle size distribution measured by a laser diffraction / scattering method is mathematically a normal distribution, and the median value of the particle size distribution is 5.3 μm.
m or less, and the particle diameter from the minimum particle diameter to 10% is 2.2 μm or less.

[0008] lithium iron phosphate according to claim 2 is the lithium iron phosphate chemical composition represented by LiFePO _4, in the particle size distribution measured by the laser diffraction scattering method, of 10% from the minimum particle size Is characterized by having a particle size of 0.7 μm or less.

According to the above configuration, since the lithium iron phosphate exhibits the particle size distribution in the above-mentioned predetermined range, the variation in the particle size among the production lots is small, and the lithium iron phosphate exhibits excellent characteristics as a positive electrode material of a secondary battery. Lithium iron phosphate can be obtained stably.

According to a third aspect of the present invention, there is provided a method for producing lithium iron phosphate, which comprises solving a lithium compound, a divalent iron compound and a phosphate compound with at least divalent iron ion. And the molar ratio of phosphate ions is approximately 1: 1
And the mixture is heated at 100 ° C. or higher to 250 ° C.
It is characterized in that a polar solvent and an inert gas are sealed and reacted in a temperature range of not more than ° C and in a sealed container.

According to a fourth aspect of the present invention, there is provided a method for producing lithium iron phosphate, wherein the chemical composition is Li
It is characterized by subjecting lithium iron phosphate represented by FePO ₄ to physical pulverization.

According to the above configuration, lithium iron phosphate having a particle size distribution in the above-mentioned predetermined range can be synthesized with good reproducibility, so that there is little variation in the particle size between production lots, and the positive electrode material of the secondary battery can be synthesized. As a result, lithium iron phosphate exhibiting excellent characteristics can be stably provided.

A secondary battery according to a fifth aspect is characterized in that, in order to solve the above-mentioned problem, the lithium iron phosphate according to the first or second aspect is used as at least a part of a positive electrode material. And According to the above configuration, by using the lithium iron phosphate as at least a part of the positive electrode material, a secondary battery having excellent characteristics can be stably obtained.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

The lithium iron phosphate of the present invention is a lithium iron phosphate having a chemical composition represented by LiFePO ₄ ,
The particle size distribution measured by the laser diffraction / scattering method is mathematically a normal distribution, the median of the particle size distribution is 5.3 μm or less, and the particle size from the minimum particle size to 10% is 2. 2 μm or less.

The lithium iron phosphate of the present invention is a lithium iron phosphate having a chemical composition represented by LiFePO ₄ , which has a particle size distribution ranging from the minimum particle size to 10% in the particle size distribution measured by a laser diffraction / scattering method. Particle size 0.7
μm or less.

According to the present invention, the chemical composition is LiFePO ₄
As a raw material for synthesizing lithium iron phosphate represented by the formula, various lithium compounds, a divalent iron compound and a phosphate compound are appropriately used in combination. Examples of the lithium compound include lithium fluoride, lithium chloride, lithium bromide, lithium iodide, lithium carbonate, lithium hydroxide, lithium phosphate and the like.

Examples of the divalent iron compound include iron fluoride, iron chloride, iron bromide, iron iodide, iron sulfate, iron phosphate, iron oxalate, and iron acetate. Examples of the phosphoric acid compound include orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, triphosphate, tetraphosphate, ammonium phosphate, ammonium dihydrogenphosphate, lithium phosphate, iron phosphate, and the like.

As a method for producing lithium iron phosphate having a chemical composition represented by LiFePO ₄ , the lithium compound exemplified above, a divalent iron compound, and a phosphoric acid compound are used in an appropriate combination, and the lithium compound to be used is A method in which a divalent iron compound and a phosphoric acid compound are mixed so as to have a stoichiometric ratio of lithium iron phosphate, which is the target substance, and placed in a sealed container (pressure-resistant container) to react. Is mentioned. More specifically, a lithium compound, a divalent iron compound, and a phosphate compound are mixed such that the molar ratio of at least divalent iron ions to phosphate ions is approximately 1: 1.

At this time, it is particularly preferable that various polar solvents and inert gases are both sealed in the above-mentioned sealed container so that the reaction is carried out under high pressure. As the polar solvent, for example, water, methanol, ethanol, 2-propanol, ethylene glycol, propylene glycol,
Acetone, cyclohexanone, 2-methylpyrrolidone,
Ethyl methyl ketone, 2-ethoxyethanol, propylene carbonate, ethylene carbonate, dimethyl carbonate, dimethylformamide, dimethylsulfoxide; etc. are used alone, or a mixture of two or more solvents is used. As the inert gas, for example, nitrogen, argon, carbon dioxide, carbon monoxide or the like can be used alone or as a mixture of two or more.

More specifically, a pressure-resistant container filled with an appropriate combination of the above three kinds of synthesis raw materials, a polar solvent and an inert gas is sealed, and at a temperature of 100 ° C. or more and 250 ° C. or less,
The contents are exposed for 12 hours to 100 hours, preferably 12 hours to 50 hours. Next, the pressure-resistant container is allowed to cool to room temperature, and the contents are taken out. As a result, lithium iron phosphate having a particle size distribution within the above-mentioned predetermined range and a chemical composition represented by LiFePO ₄ is obtained.

The lithium iron phosphate is, for example, 0.5
When the particle size and the particle size distribution are measured by a laser diffraction / scattering method using water containing sodium hexametaphosphate by weight as a dispersion medium, the particle size distribution is mathematically a normal distribution, the median is 5.3 μm or less, and the minimum particle size is It can be confirmed that the chemical composition having a particle size of from 2.2 to 10% and a particle size of 2.2 μm or less is a lithium compound represented by LiFePO ₄ . The measurement of the particle size and the particle size distribution by the laser diffraction / scattering method can be performed using, for example, LA-910 manufactured by Horiba, Ltd.

On the other hand, lithium iron phosphate having a chemical composition of LiFePO _4, which is 10% lower than the minimum particle size in the particle size distribution measured by a laser diffraction / scattering method.
The lithium iron phosphate of the present invention having a particle diameter of 0.7 μm or less can be obtained by appropriately physically pulverizing lithium iron phosphate having a chemical composition of LiFePO ₄ .

That is, the lithium iron phosphate is Li
The lithium iron phosphate shows the chemical composition of the FePO _4, a method of particle diameter is physically grinding to be within the predetermined range; or, a lithium iron phosphate shows the chemical composition of LiFePO _4, the physical And then appropriately classifying such that the particle size falls within the above-mentioned predetermined range; As the physical pulverization method, for example, a commonly used method such as pulverization using a ball mill or the like can be used.

When the particle size and the particle size distribution of the physically pulverized lithium iron phosphate are measured in the same manner as described above, the particle size distribution may not be normal. The particle size from the minimum particle size to 10% of the physically pulverized lithium iron phosphate is 0.7 μm.
In the following cases, when this is used as a part of the positive electrode material of a secondary battery, it exhibits good secondary battery characteristics as described below.

The secondary battery (lithium ion secondary battery) of the present invention can be obtained, for example, by the following method. That is, the lithium iron phosphate of the present invention obtained as described above is used as at least a part of a positive electrode material for a secondary battery. In this case, first, the lithium iron phosphate of the present invention and various conductive auxiliaries and binders (conductive binders) are used according to a normal secondary battery electrode manufacturing method.
To form a positive electrode. In addition to the above positive electrode, a commonly used nonaqueous secondary battery such as propylene carbonate or ethylene carbonate containing a commonly used negative electrode material such as metallic lithium or a layered carbon compound such as graphite and a lithium salt such as LiBF ₄ or LiPF ₆ A secondary battery can be manufactured using the electrolyte for use as a main component.

FIG. 5 is a schematic diagram showing a configuration of a lithium ion secondary battery cell, which is a secondary battery according to an embodiment of the present invention. As shown in FIG. 5, the lithium ion secondary battery cell includes a SUS cell including a cell container 304, a cell lid 305, and an insulating member 306, a positive electrode 301 manufactured in the cell, and a metal lithium foil. Negative electrode 3
02 and a glass filter paper 303 impregnated with a mixed solvent (1: 1 volume ratio) of propylene carbonate and ethylene carbonate containing 1 mol / L LiBF ₄ . The positive electrode 301 is prepared by mixing, for example, 50% by weight of the lithium iron phosphate powder of the present invention with 50% by weight of ketchin black as a conductive binder in a mortar,
A positive electrode having a diameter of 13 mm can be produced by pressure molding on an S network.

[0028]

EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited to these examples.

Example 1 Lithium phosphate as a lithium compound and a phosphate compound according to the present invention 1.158
g, and 1.988 g of divalent iron chloride tetrahydrate as the divalent iron compound according to the present invention were placed in distilled water in a pressure vessel.
The mixture was charged together with 00 ml, and the atmosphere was replaced with argon gas, followed by sealing. Put this pressure vessel in a 180 ° C oil bath,
Allowed to react for hours. After cooling to room temperature, the contents were taken out and dried at 100 ° C. to obtain a powder sample. The X-ray diffraction pattern of the obtained powder sample is shown in FIG. From the X-ray diffraction pattern, the obtained powder sample was identified to be LiFePO ₄ having an orthorhombic olivine structure.

The powder sample was dispersed in water containing 0.5% by weight of sodium hexametaphosphate, and the particle size distribution was measured with LA-910 manufactured by HORIBA, Ltd. The results are shown in FIG. 10% from the median and minimum particle size of the powder sample
Table 1 shows the particle diameters up to.

After mixing 50% by weight of the powder sample and 50% by weight of ketchin black as a conductive binder in a mortar,
A positive electrode having a diameter of 13 mm was produced by pressure molding on a US net. Next, the above-prepared positive electrode, metallic lithium foil as a negative electrode, and 1 mol / L LiB were placed in a SUS cell.
A glass filter paper impregnated with a mixed solvent (1: 1 volume ratio) of propylene carbonate and ethylene carbonate containing F4 was arranged to produce a secondary battery of the present invention. FIG. 6 shows charge / discharge characteristics of the fabricated secondary battery when charged / discharged at 0.2 mA / cm ² , with Cell Voltage (V) as the vertical axis and Time (hr) as the horizontal axis. Table 1 shows the discharge capacity (mAh).

Example 2 0.370 g of lithium carbonate
And 1.799 g of iron oxalate and 1.150 g of ammonium dihydrogen phosphate at 650 ° C. under a stream of argon gas.
It was fired in a temperature range of -800 ° C. The compound obtained after the calcination was placed in a sealed container together with water and zirconia beads, subjected to a physical crushing treatment by shaking overnight, and a powder sample was obtained after drying.

The powder sample was dispersed in water containing 0.5% by weight of sodium hexametaphosphate, and the particle size distribution was measured by LA-910 manufactured by HORIBA, Ltd. The results are shown in FIG. 10% from the median and minimum particle size of the powder sample
Table 1 shows the particle diameters up to.

After mixing 50% by weight of the powder sample and 50% by weight of ketchin black as a conductive binder in a mortar,
A positive electrode having a diameter of 13 mm was produced by pressure molding on a US net. Next, the above-prepared positive electrode, metallic lithium foil as a negative electrode, and 1 mol / L LiB were placed in a SUS cell.
F ₄ mixed solvent of propylene carbonate and ethylene carbonate containing (1: 1 by volume) to place the glass filter paper impregnated with, to prepare a secondary battery of the present invention. FIG. 7 shows charge / discharge characteristics when the produced secondary battery was charged / discharged at 0.2 mA / cm ² . Table 1 shows the discharge capacity (mAh).

Comparative Example 1 0.370 g of lithium carbonate
And 1.799 g of iron oxalate and 1.150 g of ammonium dihydrogen phosphate at 650 ° C. under a stream of argon gas.
It was fired in a temperature range of -800 ° C. The compound obtained after the firing was used as a powder sample for comparison. The powder sample for comparison was dispersed in water containing 0.5% by weight of sodium hexametaphosphate, and its particle size distribution was measured by LA-9 manufactured by HORIBA, Ltd.
Measured at 10. The results are shown in FIG. Table 1 shows the median value and the particle size from the minimum particle size to 10% of the powder sample for comparison.

After mixing 50% by weight of the powder sample for comparison and 50% by weight of ketchin black as a conductive binder in a mortar, a positive electrode having a diameter of 13 mm was prepared by press-molding on a SUS net. Next, a SUS cell was impregnated with the above-prepared positive electrode, metallic lithium foil as a negative electrode, and a mixed solvent (1: 1 volume ratio) of propylene carbonate and ethylene carbonate containing 1 mol / L LiBF ₄ . A glass filter paper was arranged, and a secondary battery for comparison was produced. FIG. 8 shows charge / discharge characteristics when the prepared secondary battery was charged / discharged at 0.2 mA / cm ² . In addition, the discharge capacity (mA)
h) is shown in Table 1.

[0037]

[Table 1]

As is clear from the results of the discharge capacities shown in FIGS. 6 and 7 and Table 1, the secondary battery produced with the positive electrode using lithium iron phosphate of the present invention has a high capacity,
It can be seen that the battery has a flat operating voltage in the vicinity of 3.4 to 3.5 V, and exhibits stable rechargeable rechargeable battery characteristics. Also, from the results of the median value and the 10% particle size value in FIG. 2 and Table 1, the lithium iron phosphate obtained in Example 1 has a mathematically normal particle size distribution, The value is 5.3 μm or less, and 10% from the minimum particle size.
It can be seen that the particle size up to is within a range of 2.2 μm or less. Further, from the results of the median value and the 10% particle size value in FIG. 3 and Table 1, the lithium iron phosphate obtained in Example 2 was
It can be seen that the particle size from the minimum particle size to 10% is within the range of 0.7 μm or less.

[0039]

As described above, according to the present invention, it is possible to obtain a positive electrode material having a certain level of characteristics or more with good reproducibility and to obtain a secondary battery having high operation reliability.

[Brief description of the drawings]

FIG. 1 is a graph showing an X-ray diffraction pattern of lithium iron phosphate having a synthesized chemical composition represented by LiFePO ₄ .

FIG. 2 is a graph showing a particle size distribution of lithium iron phosphate according to one embodiment of the present invention.

FIG. 3 is a graph showing a particle size distribution of lithium iron phosphate according to another embodiment of the present invention.

FIG. 4 is a graph showing a particle size distribution of lithium iron phosphate for comparison.

FIG. 5 is a schematic diagram showing a configuration of a cell of the secondary battery of the present invention.

FIG. 6 is a graph showing charge / discharge characteristics of a lithium ion secondary battery manufactured using lithium iron phosphate according to one embodiment of the present invention.

FIG. 7 is a graph showing charge and discharge characteristics of a lithium ion secondary battery manufactured using lithium iron phosphate according to another embodiment of the present invention.

FIG. 8 is a graph showing charge / discharge characteristics of a lithium ion secondary battery manufactured using lithium iron phosphate for comparison.

[Explanation of symbols]

 301 Positive electrode 302 Negative electrode 303 Glass filter paper 304 Cell container 305 Cell lid 306 Insulating member

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Toshikazu Uegakiuchi 17 Kanodera Minamicho, Shimogyo-ku, Kyoto-shi, Kyoto Inside Kansai New Technology Research Institute Co., Ltd. 17 Minamicho Inside Kansai New Technology Research Institute Co., Ltd. (72) Inventor Makoto Kobayashi 1-13-1 Nihonbashi, Chuo-ku Tokyo HJ02 HJ05 5H050 AA08 AA19 BA17 CA01 FA17 GA05 GA28 HA02 HA05

Claims (5)

[Claims] 1. A lithium iron phosphate having a chemical composition represented by LiFePO ₄ , wherein a particle size distribution measured by a laser diffraction / scattering method is mathematically a normal distribution, and a median of the particle size distribution is 5 Lithium iron phosphate having a particle size of not more than 0.3 μm and a particle size from the minimum particle size to 10% of not more than 2.2 μm. 2. A lithium iron phosphate having a chemical composition of LiFePO ₄ , wherein a particle size from a minimum particle size to 10% is 0.7 μm or less in a particle size distribution measured by a laser diffraction / scattering method. Lithium iron phosphate. 3. A lithium compound, a divalent iron compound,
A phosphate compound is mixed so that the molar ratio of at least divalent iron ions to phosphate ions is approximately 1: 1. The mixture is mixed within a temperature range of 100 ° C. or more and 250 ° C. or less.
And, the chemical composition is characterized in that a polar solvent and an inert gas are sealed and reacted in a sealed container.
_{4. A} method for producing lithium iron phosphate represented by ₄ . 4. The method for producing lithium iron phosphate according to claim 2, wherein the lithium iron phosphate having a chemical composition of LiFePO ₄ is subjected to physical pulverization. 5. A secondary battery, wherein the lithium iron phosphate according to claim 1 or 2 is used as at least a part of a positive electrode material.