JPH07326356A - Lithium transition metal composite oxide powder and manufacture thereof, lithium secondary battery positive electrode and lithium secondary battery - Google Patents

Abstract

PURPOSE:To provide composite oxide powder for a lithium secondary battery positive electrode having a steep grain size distribution and displaying an excellent discharge characteristic as well as a method for manufacturing the powder, and also provide a positive electrode for a lithium secondary battery as well as a lithium secondary battery. CONSTITUTION:This lithium transition metal composite oxide powder for the positive electrode of a lithium ion secondary battery is obtained by adding a compound giving a liquid phase at a baking temperature to a lithium compound and a transition metal compound, and, then, applying a baking process thereto. In this case, when 10% grain sizes available by totalling the measurement results of a grain size distribution from the side of fine grains on a volume basis is expressed as D10, and 90% grain sizes as D90, the ratio of D90 to D10 is kept equal to or less than six.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium transition metal composite oxide powder, a method for producing the same, a lithium secondary battery positive electrode including the same, and a lithium secondary battery.

[0002]

2. Description of the Related Art Recently, as seen in VTRs, mobile phones, laptop personal computers, etc., portable electronic devices and cordless electronic devices have been rapidly developed. Currently, the mainstream of these driving power supplies is nickel-cadmium batteries,
Along with higher functionality, expectations for lithium secondary batteries, which are smaller, lighter, and have higher capacity, are increasing. The positive electrode active material of the lithium secondary battery uses a composite oxide of lithium and a transition metal such as lithium cobalt oxide and lithium nickel oxide, which can be electrochemically doped and undoped with lithium ions. Is common.

Usually, a composite oxide of lithium and a transition metal is prepared by mixing a lithium compound such as lithium carbonate as a raw material with a transition metal compound such as cobalt carbonate,
A method of firing in an atmosphere such as air or oxygen is widely used. The firing temperature varies depending on each transition metal, but in consideration of charge / discharge characteristics, a relatively narrow temperature range is selected in each case. In such a manufacturing method, since the starting material undergoes large volume contraction when thermally decomposed, uneven firing is likely to occur, and as a result, partial sintering of the composite oxide particles proceeds, and the obtained powder is sintered. Will be a collection of things with different degrees. Generally, when the composite oxide powder is used as a positive electrode active material for a lithium secondary battery, it is thinly applied together with a conductive material and a binder onto a current collector such as a metal foil to form a sheet. At this time, if a complex oxide powder having a large degree of irregularity in particle size, that is, a complex oxide powder having a steep particle size distribution is used, the mixed state with the conductive material and the binder becomes non-uniform, and overvoltage increases, and charging is increased. There is a problem that the active material is likely to fall off due to the expansion and contraction of the volume accompanying the discharge.

Therefore, in the conventional manufacturing method, it was necessary to grind coarse agglomerated particles produced by partial sintering in a subsequent step. However, it is difficult to control the particle size distribution by pulverization, and there is a decrease in performance due to the inclusion of impurities from the pulverizing medium, the distortion of crystals introduced by the impact during pulverization, and the irregular shape of the particles caused by pulverization. The problem remained. Classification is a means for achieving a sharp particle size distribution without using crushing. However, this operation deteriorates the production yield and is industrially disadvantageous. Attempts have been made to use special starting materials in order to solve the above problems. For example, in JP-A-5-54888, a cobalt source of lithium cobalt oxide is synthesized by using a cobalt oxide composed of an agglomerate of a plurality of primary particles having a substantially spherical or ellipsoidal shape and having an average particle size of 1 μm or less. By doing so, a method of obtaining lithium cobalt oxide having a uniform particle size and a fine particle shape is disclosed.

Further, in Japanese Patent Laid-Open No. 5-29083, the particle size of one or several metals selected from Co, Ni, Fe and Mn or their alloy powders is 0.2 to 9 μm.
A method is disclosed in which the particle size distribution of the positive electrode active material is made constant without adding a pulverizing step by aligning the particles with m and heat-treating this with a lithium compound. However, these all require the use of raw materials prepared by a special method, and are not industrially simple and efficient methods.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a composite oxide powder for a lithium secondary battery positive electrode having a sharp particle size distribution and exhibiting excellent charge / discharge characteristics, a method for producing the same, and a lithium secondary battery positive electrode. And to provide a lithium secondary battery.

[0007]

[Means for Solving the Problems] In view of such circumstances,
As a result of intensive studies by the present inventors, the lithium compound and the transition metal compound, which are the raw materials, are added with the third component that is in the liquid phase at the firing temperature and fired without adding a pulverization or classification step. Furthermore, they have found that a complex oxide powder having a sharp particle size distribution and exhibiting excellent charge / discharge characteristics when used as a positive electrode for a lithium secondary battery is obtained, and completed the present invention.

That is, the present invention comprises the following inventions. (I) A lithium compound and a transition metal compound, which are obtained by adding a compound that is in a liquid phase at a firing temperature and firing the mixture, wherein the particle size distribution measurement results are integrated from the fine particle side on a volume basis. 10% particle size is D ₁₀ , 90% particle size is D
_{When 90} , the ratio of D ₉₀ / D ₁₀ is 6 or less, and the lithium transition metal composite oxide powder for a lithium secondary battery positive electrode. (II) The lithium-transition metal composite oxide powder according to (I), wherein the compound that becomes a liquid phase at the firing temperature is lithium halide. (III) A 10% particle obtained by adding a compound that is in a liquid phase at a firing temperature to a lithium compound and a transition metal compound and firing the mixture, where the particle size distribution measurement results are integrated from the fine grain side on a volume basis. If D _10, 90% particle diameter of the diameter is D _90, the value of the ratio D ₉₀ / D ₁₀ is 6 or less, the manufacturing method of a lithium secondary battery positive electrode for a lithium transition metal composite oxide powder. (IV) The method for producing a lithium-transition metal composite oxide powder according to (III), wherein the compound that becomes a liquid phase at the firing temperature is lithium halide. (V) A lithium secondary battery positive electrode containing the lithium-transition metal composite oxide powder according to (I) or (II). (VI) A positive electrode containing a material capable of doping and dedoping lithium ions as an active material, a negative electrode made of lithium metal, a lithium alloy, or a material capable of doping and dedoping lithium ions, and a liquid or solid electrolyte. A lithium secondary battery having the lithium secondary battery including the lithium transition metal composite oxide powder according to (I) or (II) as an active material of the positive electrode.

The present invention will be described in more detail below. The lithium transition metal composite oxide powder for a lithium secondary battery positive electrode of the present invention (hereinafter sometimes referred to as the composite oxide powder of the present invention) is a composite oxide powder of lithium and a transition metal. As Ni, Co, Fe or Mn
At least one selected from the above is preferable, and Ni and Co are more preferable. However, it is preferable to use Fe together with other transition metals. The composite oxide powder of the present invention has a ratio D ₉₀ / when the 10% particle size is D ₁₀ and the 90% particle size is D ₉₀ when the particle size distribution measurement results of the powder are integrated from the fine particle side on a volume basis. The value of D ₁₀ is 6 or less. If the ratio D ₉₀ / D ₁₀ exceeds 6, the lithium ion secondary battery positive electrode may have a non-uniform mixed state with a conductive material or a binder, resulting in increased overvoltage or volume accompanying charge / discharge. The active material is likely to fall off due to the expansion and contraction of, which is not preferable. Here, the powder particle size distribution measuring method in the present invention means a laser scattering type particle size distribution measuring method. The median diameter in the present invention also depends on the measuring method.

A method for producing the composite oxide powder of the present invention will be described. As the raw material, a lithium compound, a transition metal compound, and a compound that becomes a liquid phase at the firing temperature (hereinafter, may be referred to as a third component) are used. These raw materials are mixed and fired by a known method at an appropriate temperature depending on the combination of the lithium compound and the transition metal compound. Examples of the lithium compound as a raw material include lithium carbonate, lithium nitrate, lithium hydroxide and the like. These can be used as commercial products without any particular pretreatment. Similarly, the transition metal compound as a raw material is a transition metal, preferably a carbonate, nitrate, hydroxide, oxide or the like of at least one transition metal selected from Ni, Co, Fe or Mn, or a mixture thereof. Is mentioned. These can be used as commercial products without any special pretreatment. It is preferable that each has high purity.

The third component is selected individually because the appropriate firing temperature varies depending on the combination of the lithium compound and the transition metal compound. For example, when the transition metal is Co, 600 ° C. or more and 1000 ° C. or less is preferable, when Ni is 350 ° C. or more and 800 ° C. or less, and when Mn is 350 ° C. or more and 900 ° C. or less, respectively. If the vapor pressure of the third component is high at the firing temperature, it may be volatilized during firing and a sufficient effect may not be obtained. Therefore, the vapor pressure at the firing temperature is preferably low. Lithium halide is preferred as the third component, and lithium chloride is particularly preferred. Although the role of the third component has not been clarified yet, it is considered that a certain amount of liquid phase is maintained during firing to provide a uniform firing environment and prevent uneven firing.

The amount of the third component to be added may be such that a sufficient amount of liquid phase can be secured, and it is preferably 1 mol% or more with respect to the lithium compound as a raw material. Since it is disadvantageous in characteristics, the molar ratio to the lithium compound as a raw material is preferably 1/3 or less, more preferably 1/4 or less.
It is preferable to adopt a method capable of adding more uniformly, such as adding by dissolving in a solvent such as water, since the addition amount can be further reduced.

After firing, it is preferable to wash with a solvent in order to remove the compound which becomes a liquid phase at the remaining firing temperature. Examples of the solvent include methanol, ethanol, acetone, ether and the like. Further, in order to improve the efficiency in the washing step, crushing with a weak force that does not usually break the agglomerated particles can be performed before the washing.

Next, the lithium secondary battery of the present invention will be described in detail. The positive electrode of the lithium secondary battery of the present invention is
It contains the above-mentioned lithium-transition metal composite oxide powder of the present invention as an active material. Specific examples of the positive electrode include those containing the lithium transition metal composite oxide powder, a carbonaceous material as a conductive material, and a thermoplastic resin as a binder. As the carbonaceous material, natural graphite,
Examples include artificial graphite and cokes. Examples of the thermoplastic resin include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene and the like.

For the negative electrode of the lithium secondary battery of the present invention, a lithium metal, a lithium alloy, or a material capable of being doped / dedoped with lithium ions is used. Examples of the material capable of doping / dedoping with lithium ions include carbonaceous materials such as natural graphite, artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers, and organic polymer compound fired bodies. The carbonaceous material may be in the form of flakes, spheres, fibers, or an aggregate of fine powder, and a thermoplastic resin as a binder may be added if necessary. Examples of the thermoplastic resin include polyvinylidene fluoride, polyethylene, polypropylene and the like.

As the electrolyte of the lithium secondary battery of the present invention
Is a non-aqueous electrolyte solution prepared by dissolving a lithium salt in an organic solvent.
A well-known material selected from either liquid or solid electrolytes
Is used. As the lithium salt, LiClO_Four,
LiPF₆, LiAsF₆, LiSbF₆, LiB
F_Four, LiCF₃SO₃, LiN (CF₃SO₂)₂,
Li ₂B_TenCl_Ten, Lower aliphatic carboxylic acid lithium salt,
LiAlCl_FourOr a mixture of two or more
Things can be mentioned.

As the organic solvent, carbonates such as propylene carbonate, ethylene carbonate, dimethyl carbonate and diethyl carbonate; ethers such as 1,2-dimethoxyethane, 1,3-dimethoxypropane, tetrahydrofuran and 2-methyltetrahydrofuran; methyl formate , Esters such as methyl acetate and γ-butyrolactone; nitriles such as acetonitrile and butyronitrile; N, N-dimethylformamide,
Amides such as N, N-dimethylacetamide; carbamates such as 3-methyl-2-oxazolidone; sulfur-containing compounds such as sulfolane, dimethylsulfoxide, and 1,3-propanesultone, but of these, usually Two or more of these are mixed and used. Among them, a mixed solvent containing a carbonate is preferable, and a mixed solvent of a cyclic carbonate and an acyclic carbonate, or a mixed solvent of a cyclic carbonate and an ether is more preferable.

Polyethylene oxide as the solid electrolyte
De-based, polyorganosiloxane chain or polyoxya
A polymer compound containing at least one or more alkylene chains
Which polyelectrolyte, or Li₂S-SiS₂, Li₂
S-GeS₂, Li₂SP ₂S_Five, Li₂S-B₂S
₃Sulfide-based electrolyte such as, or Li₂S-SiS₂−
Li₃PO_Four, Li₂S-SiS₂-Li₂SO_FourSuch
Inorganic compound-based electrolytes containing sulfides of Well
In addition, a so-called gel in which a non-aqueous electrolyte solution is held in a polymer is used.
It is also possible to use the red type. In addition, according to the present invention
The shape of the lithium secondary battery is not particularly limited.
Type, coin type, cylindrical type, square type, etc.
Yes.

[0019]

EXAMPLES The present invention will now be described in more detail by way of examples, which should not be construed as limiting the invention thereto. Unless otherwise specified, the electrodes for charge / discharge test and the flat battery were manufactured by the following method. 1 of polyvinylidene fluoride (hereinafter sometimes referred to as PVDF) as a binder is added to a mixture of an active material composed of a lithium transition metal composite oxide and a conductive material acetylene black.
-Methyl-2-pyrrolidone solution (hereinafter, sometimes referred to as NMP), active material: conductive material: binder = 91:
A paste was prepared by adding and kneading the mixture to give a composition of 6: 3 (weight ratio), applying the paste to # 200 stainless steel mesh serving as a current collector, and vacuum drying at 150 ° C. for 8 hours to form an electrode. Obtained. The electrode thus obtained, as an electrolyte solution, propylene carbonate (hereinafter,
Sometimes called a PC. ) And 1,2-dimethoxyethane (hereinafter sometimes referred to as DME) in a 1: 1 mixture of lithium perchlorate at a concentration of 1 mol / liter, and a polypropylene porous membrane as a separator. Further, a plate type battery was produced by combining metallic lithium as a counter electrode (negative electrode).

[0020] Example 1 Lithium nitrate (manufactured by Wako Pure Chemical Industries, Ltd., reagent special grade) 1.815G, nickel carbonate [NiCO ₃ · 2N
_{i (OH) 2 · 4H 2} O: Wako Pure Chemical Industries, Ltd., reagent grade] 3.136G, (manufactured by Wako Pure Chemical Industries, Ltd., reagent special grade) lithium chloride 0.223g well in an agate mortar mixtures After that, it was placed in a tubular furnace using an alumina core tube, and fired at 700 ° C. for 15 hours in an oxygen stream having an oxygen flow rate of 50 cm ³ / min. The molar ratio of lithium nitrate to lithium chloride is 1: 0.2. After cooling to room temperature, the lithium chloride was removed by washing with methanol (Wako Pure Chemical Industries, Ltd., special grade reagent).

Particle size of the obtained lithium nickelate powder
Laser scattering type particle size distribution measuring device (Shimadzu Corporation)
Manufactured by SALD1100) and the distribution shown in FIG.
The curve was obtained. In addition, as a powder dispersion medium, a trade name Da
rvan821A (RT Vanderbilt, Inc.
(Manufactured by Japan) was used. From the fine particle side based on volume
10% particle size D when integrated_TenAnd 90% particle size D
₉₀Are 0.25 and 1.11 μm, respectively, particle size distribution
Ratio D that represents the steepness of₉₀/ D_TenThe value of was 4.4. Well
The median diameter is 0.47 μm, coarse particles of 2.6 μm or more
The component was 3.2%. Table 1 summarizes these results.
It was The obtained lithium nickel oxide powder is processed into an electrode,
After making a flat-type battery, charge maximum voltage 4.2V, discharge maximum
Small voltage 2.5V, 0.17mA / cm²Charged with a constant current of
An electric test was carried out. The discharge capacity is 162 mAh / g
It was

Example 2 14.48 g of lithium nitrate (manufactured by Wako Pure Chemical Industries, Ltd., reagent special grade) and lithium chloride (Wako Pure Chemical Industries, Ltd. reagent special grade) 1.78 g, 20.9 g
Of dissolved in water, further nickel carbonate [NiCO ₃ · 2
_{Ni (OH) 2 · 4H 2} O: manufactured by Wako Pure Chemical Industries, Ltd., was dispersed well by the addition of reagent grade] 25.08g,
It was dried to obtain a mixed powder. The molar ratio of lithium nitrate to lithium chloride is 1: 0.2. This was put into a tubular furnace using an alumina core tube, and the oxygen flow rate was 50 cm ³ /
It was fired at 700 ° C. for 15 hours in an oxygen stream of min. After cooling to room temperature, the lithium chloride was removed by washing with methanol (Wako Pure Chemical Industries, Ltd., special grade reagent). The particle size distribution of the obtained lithium nickelate powder was measured in the same manner as in Example 1. The results are shown in FIG. 1 and Table 1. The value of the ratio D ₉₀ / D ₁₀ representing the steepness of the particle size distribution was 5.5, and the median diameter was 0.32 μm, and the coarse particle component of 2.6 μm or more was 0%. Example 1 using the obtained lithium nickel oxide powder
A charge / discharge test was carried out in the same manner as in. Discharge capacity is 156mA
It was h / g.

Comparative Example 1 18.10 g of lithium nitrate (Wako Pure Chemical Industries, Ltd. special grade reagent) and nickel carbonate [NiCO ₃ .2Ni]
_{(OH) 2 · 4H 2 O} : Wako Pure Chemical Industries, Ltd., was mixed well and reagent grade] 31.34g in an agate mortar, charged in a tubular furnace having an alumina core tube, the oxygen flow rate 50 cm ³ / min In an oxygen stream at 700 ℃
It was baked for 5 hours. The particle size distribution of the obtained lithium nickelate powder was measured in the same manner as in Example 1. The result is shown in Figure 1.
And shown in Table 1. The particle size distribution is non-uniform, and the ratio D ₉₀ / D ₁₀ indicating steepness is 130, and the median diameter is 1.2.
The proportion of coarse particles having a particle size of 2 μm or more than 2.6 μm was 44%.

The obtained lithium nickel oxide powder was put into an alumina pot together with alumina balls, and ball milling was performed for 11 hours. The particle size distribution of the pulverized lithium nickel oxide powder was measured in the same manner as in Example 1. The results are shown in FIG. 1 and Table 1. Although a reduction in the coarse particle content was recognized by the pulverization and the steepness of the particle size distribution was improved (D ₉₀ / D ₁₀ value was 7.3), the discharge capacity measured by the same method as in Example 1 was 126 mAh / g. Has fallen to.

[0025]

[Table 1]

[0026]

The lithium-transition metal composite oxide powder for a lithium secondary battery positive electrode of the present invention has a sharp particle size distribution,
The positive electrode of a lithium secondary battery using the composite oxide powder has a low overvoltage, less loss of active material, and excellent charge / discharge characteristics, and therefore has an extremely large industrial value.

[Brief description of drawings]

FIG. 1 is a particle size distribution diagram of composite oxides obtained in Examples of the present invention and Comparative Examples.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomo Sato 6 Kitahara, Tsukuba, Ibaraki Sumitomo Chemical Co., Ltd.

Claims (6)

[Claims] 1. A lithium compound and a transition metal compound, which are obtained by adding a compound that is in a liquid phase at a baking temperature and baking the mixture, and the particle size distribution measurement results are integrated from the fine particle side on a volume basis. In this case, when the 10% particle size is D ₁₀ and the 90% particle size is D ₉₀ , the lithium transition metal composite oxide powder for a lithium secondary battery positive electrode has a ratio D ₉₀ / D ₁₀ of 6 or less. 2. The lithium-transition metal composite oxide powder according to claim 1, wherein the compound which becomes a liquid phase at the firing temperature is lithium halide. 3. A lithium compound and a transition metal compound, wherein a compound which is in a liquid phase at a firing temperature is added, and the mixture is fired. % Particle size is D ₁₀ , 90% particle size is D ₉₀
And the ratio D ₉₀ / D ₁₀ is 6 or less, the method for producing a lithium transition metal composite oxide powder for a lithium secondary battery positive electrode. 4. The method for producing a lithium-transition metal composite oxide powder according to claim 3, wherein the compound which is in a liquid phase at the firing temperature is lithium halide. 5. A lithium secondary battery positive electrode containing the lithium-transition metal composite oxide powder according to claim 1. 6. A positive electrode containing a material capable of doping and dedoping lithium ions as an active material, a negative electrode made of lithium metal, a lithium alloy, or a material capable of doping and dedoping lithium ions, and a liquid or solid electrolyte. A lithium secondary battery comprising: a lithium secondary battery containing the lithium-transition metal composite oxide powder according to claim 1 or 2 as an active material of the positive electrode.