JP4209646B2 - Method for producing lithium cobalt composite oxide for positive electrode of secondary battery - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention includes a method for producing a lithium cobalt composite oxide for a positive electrode of a lithium secondary battery having a large volumetric capacity density, high safety, and excellent charge / discharge cycle durability, and the produced lithium cobalt composite oxide. The present invention relates to a positive electrode for a lithium secondary battery and a lithium secondary battery.
[0002]
[Prior art]
In recent years, as devices become more portable and cordless, demands for non-aqueous electrolyte secondary batteries such as lithium secondary batteries that are small, lightweight, and have high energy density are increasing. The positive electrode active material for such a non-aqueous electrolyte secondary battery includes LiCoO.₂, LiNiO₂, LiNi_0.8Co_0.2O₂, LiMn₂O_FourLiMnO₂There are known composite oxides of lithium and transition metals.
[0003]
Among these, lithium cobalt composite oxide (LiCoO₂) Is used as a positive electrode active material, and lithium secondary batteries using carbon such as lithium alloy, graphite, and carbon fiber as negative electrodes are widely used as batteries having high energy density because a high voltage of 4V is obtained. Yes.
[0004]
However, LiCoO₂In the case of a non-aqueous secondary battery using as a positive electrode active material, further improvement in the capacity density per unit volume and safety of the positive electrode layer is desired, and the battery discharge capacity can be increased by repeating the charge / discharge cycle. There are problems such as deterioration of cycle characteristics in which the gradual decrease, weight capacity density, and large decrease in discharge capacity at low temperatures.
[0005]
In order to solve some of these problems, Japanese Patent Laid-Open No. 6-243897 discloses LiCoO which is a positive electrode active material.₂2θ measured by X-ray diffraction using CuKα as a radiation source is set to about 19 °, and an average particle size of 3 to 9 μm, and a volume occupied by a particle group having a particle size of 3 to 15 μm is 75% or more of the total volume. It has been proposed to make the active material excellent in coating characteristics, self-discharge characteristics, and cycleability by setting the 45 ° diffraction peak intensity ratio to a specific value. Further, the publication includes LiCoO₂It has been proposed as a preferred embodiment that substantially does not have a particle size distribution of 1 μm or less or 25 μm or more. However, such a positive electrode active material has improved coating characteristics and cycle characteristics, but has not been sufficiently satisfactory in safety, volume capacity density, and weight capacity density.
[0006]
In order to improve the weight capacity density and charge / discharge cycleability of the positive electrode, Japanese Patent Application Laid-Open No. 2000-82466 discloses that the lithium composite oxide particles have an average particle size of 0.1 to 50 μm and a particle size distribution. A positive electrode active material having two or more peaks is proposed. In addition, it has also been proposed to mix two kinds of positive electrode active materials having different average particle diameters to obtain a positive electrode active material having two or more peaks in the particle size distribution. In such a proposal, the weight capacity density of the positive electrode and the charge / discharge cycleability may be improved, but there is a troublesome production of the positive electrode raw material powder having two kinds of particle size distributions, and the positive electrode volume capacity density, safety No material satisfying all of the properties, coating uniformity, weight capacity density, and cycleability has been obtained.
[0007]
In order to solve the problem related to battery characteristics, Japanese Patent Laid-Open No. 3-201368 proposes replacing 5 to 35% of Co atoms with W, Mn, Ta, Ti or Nb for improving cycle characteristics. ing. JP-A-10-31805 discloses a hexagonal LiCoO in which the c-axis length of the lattice constant is not more than 14.051 mm and the crystallite diameter in the (110) direction is 45 to 100 nm.₂It has been proposed to improve cycle characteristics by using as a positive electrode active material.
[0008]
Further, JP-A-10-72219 discloses the formula Li_xNi_1-yN_yO₂(Where 0 <x <1.1, 0 ≦ y ≦ 1), and the primary particles are plate-like or columnar, and (volume-based cumulative 95% diameter−volume-based cumulative 5% diameter) ) / Volume-based cumulative 5% diameter) is 3 or less, and a lithium composite oxide having an average particle diameter of 1 to 50 μm is proposed to have a high initial discharge capacity per weight and excellent charge / discharge cycle durability. ing.
[0009]
However, the conventional technology described above sufficiently satisfies all of volume capacity density, safety, coating uniformity, cycle characteristics, and low temperature characteristics in a lithium secondary battery using a lithium composite oxide as a positive electrode active material. We still haven't got what to do.
[0010]
[Problems to be solved by the invention]
The present invention includes a method for producing a lithium cobalt composite oxide for a lithium secondary battery positive electrode having a large volumetric capacity density, high safety, and excellent charge / discharge cycle durability, and a produced lithium cobalt composite oxide. An object is to provide a positive electrode for a lithium secondary battery and a lithium secondary battery.
[0011]
[Means for Solving the Problems]
As a raw material for producing lithium cobalt composite oxide, the present inventor has continued research to achieve the above-mentioned problems, and has low crystallinity, relatively high specific surface area, low press density, and dense primary particles. Using cobalt tetroxide having specific physical properties formed by agglomeration to form secondary particles, and calcining a mixture of the cobalt tetroxide and lithium source to give lithium cobalt composite oxide as the specific temperature We have found that this problem can be achieved by adopting a range.
[0012]
Although it is not necessarily clear why the above problem is achieved by adopting such a configuration in the present invention, when the crystallinity of cobalt trioxide is high, the specific surface area is low, and the press density is high, The reaction rate of the lithiation is slow, and therefore the growth of the primary particles of the obtained lithium cobalt composite oxide is slow, so that the lithium cobalt composite oxide composed of dense secondary particles is not formed, and the filling property is reduced. It will not be high. However, in the present invention, the progress of lithiation of tribasic cobalt oxide is fast, and as a result, the growth of primary particles of the lithium cobalt composite oxide is promoted, the density of secondary particles is improved, and the filling property of the whole powder is improved. As a result, it is assumed that the above-mentioned characteristics are achieved.
[0013]
  Thus, the gist of the present invention is as follows.
(1) A general formula in which a mixture of cobalt trioxide, a lithium source and, if necessary, the following M element source is fired in an oxygen-containing atmosphere.
Li_pCo_xM_yO_zF_a(However, M is a transition metal element or alkaline earth metal element other than Co. 0.9 ≦ p ≦ 1.1, 0.980 ≦ x ≦ 1.0, 0 ≦ y ≦ 0.02, 9 ≦ z ≦ 2.1, x + y = 1, 0 ≦ a ≦ 0.02), wherein the cobalt cobalt tetroxide is X The half-value width of the diffraction peak of the (220) plane at 2θ = 31 ± 1 ° measured by line diffraction is 0.14 to 0.45, and the half-value width of the diffraction peak of the (311) plane at 2θ = 37 ± 1 °. 0.14 to 0.45, specific surface area 3 to 25m²/ G, and cobalt trioxide having an average secondary particle size of 5 to 25 μm, and the mixture, Oxygen-containing atmosphere, atmospheric pressure,800-1050 ° C5-20 hours,A method for producing a lithium cobalt composite oxide for a positive electrode of a lithium secondary battery, characterized by firing.
(2)The particle powder of lithium cobalt composite oxide is 0.3 t / cm. ² When press compressed withPress density is 3.15 to 3.40 g / cm^ThreeThe manufacturing method of the lithium cobalt complex oxide for lithium secondary battery positive electrodes as described in said (1) which is.
(3) The manufacturing method of the lithium cobalt composite oxide for lithium secondary battery positive electrodes as described in said (1) or 2 whose residual alkali amount contained is 0.03 mass% or less.
(4) The half width of the diffraction peak of the (001) plane of 2θ = 19 ± 1 ° measured by X-ray diffraction using CuKα as the radiation source is 0.18 to 0.35, The full width at half maximum of the diffraction peak of (101) plane at 2θ = 38 ± 1 ° is 0.15 to 0.35, the average particle size of primary particles is 0.1 to 1.2 μm, and the specific surface area is 5 to 50 m.²/ G, and (1), (2) or (3) above, which is obtained by firing substantially spherical cobalt hydroxide having an average secondary particle size of 5 to 25 μm at 300 to 700 ° C. in an oxygen-containing atmosphere. ) For producing a lithium cobalt composite oxide for a positive electrode of a lithium secondary battery.
(5) of the cobalt trioxideParticle powder 0.3t / cm ² When press compressed withPress density is 2.0 to 3.2 g / cm^ThreeThe manufacturing method of the lithium cobalt complex oxide for lithium secondary battery positive electrodes as described in said (4) which is.
(6) In the above general formula (1), M is at least one selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Mn, Mg, Ca, Sr, Ba, and Al. The manufacturing method of the lithium cobalt complex oxide for lithium secondary battery positive electrodes in any one of-(5).
(7The above (4), wherein the average particle diameter D50 after the secondary particles of cobalt hydroxide are dispersed in pure water is ¼ or less of the original average particle diameter D50.)The manufacturing method of lithium cobalt complex oxide of description.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The lithium cobalt composite oxide for a lithium secondary battery positive electrode produced in the present invention has a general formula Li._pCo_xM_yO_zF_aIt is represented by In such general formula, M, p, x, y, z and a are defined above. Among these, p, x, y, z and a are preferably as follows. 0.97 ≦ p ≦ 1.03, 0.990 ≦ x ≦ 1.0, 0.0005 ≦ y ≦ 0.01, 1.95 ≦ z ≦ 2.05, x + y = 1, 0.001 ≦ a ≦ 0.01. Here, when a is larger than 0, a part of oxygen atoms becomes a composite oxide in which fluorine atoms are substituted. In this case, the safety of the obtained positive electrode active material is improved.
[0015]
M is a transition metal element or alkaline earth metal excluding Co, and the transition metal element is Group 4, Group 6, Group 7, Group 8, Group 9, Group 10, Group 11 of the periodic table. Represents a transition metal. Among these, M is at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Mn, Mg, Ca, Sr, Ba, and Al. Among these, Ti, Zr, Hf, Mg, or Al is preferable from the viewpoint of capacity development, safety, cycle durability, and the like.
[0016]
In the present invention, when M and / or F is contained, both M and F are preferably present on the surface of the lithium cobalt oxide particles. It is not preferable that the particles exist inside the particles because not only the effect of improving the battery characteristics due to the particles is small but also the battery characteristics may be deteriorated. By being present on the surface, it is possible to improve important battery characteristics such as safety and charge / discharge cycle characteristics by adding a small amount without causing deterioration of battery performance. Whether or not it exists on the surface can be determined by performing spectroscopic analysis such as XPS analysis on the positive electrode particles.
[0017]
The lithium cobalt composite oxide of the present invention can be obtained by firing a mixture of tribasic cobalt oxide, a lithium source and, if necessary, the following M element source in an oxygen-containing atmosphere. Is measured by X-ray diffraction using CuKα as a radiation source, the half-value width of the diffraction peak of (220) plane at 2θ = 31 ± 1 ° is 0.14 to 0.45, and 2θ = 37 ± 1 ° ( 311) The half width of the diffraction peak of the surface is 0.14 to 0.45, and the specific surface area is 3 to 25 m.²/ G and cobalt trioxide having an average secondary particle size of 5 to 25 μm, and the mixture needs to be fired at 800 to 1050 ° C.
[0018]
Half-width of diffraction peak of (220) plane of 2θ = 31 ± 1 ° and (311) plane of 2θ = 37 ± 1 ° measured by X-ray diffraction using CuKα of cobalt trioxide used as a radiation source If the half-value width of the diffraction peak is outside the range defined in the present invention, the press density of the positive electrode decreases, the initial internal capacity decreases, and the safety decreases. Cannot be achieved. The above half-value width is, in particular, that of the diffraction peak of the (311) plane where the half-value width of the (220) plane at 2θ = 31 ± 1 ° is 0.16 to 0.35, and 2θ = 37 ± 1 °. The full width at half maximum is preferably 0.16 to 0.40.
[0019]
The specific surface area of cobalt tetroxide is 3m.²If it is smaller than / g, the safety is lowered or the initial capacity is lowered. Conversely, 25m²When the amount exceeds / g, the powder is so high that productivity is lowered. In particular, the specific surface area is 4 to 20 m.²/ G is preferred. Furthermore, when the average particle diameter of secondary particles of cobalt tetroxide is smaller than 5 μm, it becomes difficult to form a dense electrode shape or the press density is lowered. On the other hand, when it exceeds 25 μm, the large current discharge characteristics deteriorate. In particular, the average particle size of the secondary particles is preferably 8 to 20 μm.
[0020]
In the present invention, the temperature at which the mixture of cobalt tetroxide, lithium source and, if necessary, the following M element source is calcined in an oxygen-containing atmosphere is important. When the firing temperature is lower than 800 ° C., the lithiation is incomplete, and when it exceeds 1050 ° C., the discharge characteristics / cycle characteristics are deteriorated. In particular, the firing temperature is preferably 900 to 1000 ° C.
[0021]
The cobalt tetroxide having the specific physical properties used for the production of the lithium cobalt composite oxide of the present invention is produced by various methods. In particular, the half-value width of the diffraction peak on the (001) plane of 2θ = 19 ± 1 ° measured by X-ray diffraction using CuKα as a radiation source is 0.18 to 0.35, and 2θ = 38 ± 1 °. The full width at half maximum of the (101) plane diffraction peak is 0.15 to 0.35, the average primary particle size is 0.1 to 1.2 μm, and the specific surface area is 5 to 50 m.²/ G and substantially spherical cobalt hydroxide having an average secondary particle diameter (D50) of 5 to 25 μm is preferably fired at 300 to 700 ° C. in an oxygen-containing atmosphere.
[0022]
The half width of the diffraction peak on the (001) plane of 2θ = 19 ± 1 ° and 2θ = 38 ± 1 ° measured by X-ray diffraction using CuKα of cobalt hydroxide as a raw material for cobalt tetraoxide. When the half-value width of the diffraction peak of the (101) plane is outside the range defined in the present invention, the powder becomes sublime, the press density of the positive electrode decreases, the safety decreases, and the present invention The goal of cannot be achieved. The half width of the diffraction peak on the (220) plane at 2θ = 19 ± 1 ° is 0.22 to 0.30, and the diffraction on the (101) plane at 2θ = 38 ± 1 ° is the above half width. It is preferable that the half width of the peak is 0.18 to 0.30.
[0023]
Further, when the average particle size of the primary particles of cobalt hydroxide is smaller than 0.1 μm, the powder becomes higher. On the other hand, when the average particle size exceeds 1.2 μm, the safety is lowered or the initial capacity or discharge is reduced. Rate characteristics are degraded. In particular, the average particle size of the primary particles is preferably 0.3 to 0.9 μm. The specific surface area of cobalt hydroxide is 5m.²If it is smaller than / g, the specific surface area of cobalt tetroxide will be too low, so the initial capacity and rate characteristics will be reduced.²If it exceeds / g, the powder becomes sublime. In particular, the specific surface area is 10 to 25 m.²/ G is preferred. Further, when the average particle diameter of the secondary particles of cobalt hydroxide is smaller than 5 μm, the density of the electrode is lowered, and conversely, when it exceeds 25 μm, the large current discharge characteristics are lowered. In particular, the average particle diameter of the secondary particles is preferably 8 to 20 μm.
[0024]
The shape of the secondary particles of cobalt hydroxide is preferably substantially spherical. The substantially spherical shape of the particle includes a spherical shape, a rugby ball shape, a polygonal shape and the like, and the major axis / minor axis thereof is preferably 2/1 to 1/1, particularly 1.5 / 1 to 1 /. 1 is preferred. Among them, it is preferable to have a spherical shape as much as possible.
[0025]
In addition, cobalt hydroxide used as a raw material for cobalt trioxide in the present invention can provide a lithicobalt composite oxide having excellent properties as a positive electrode active material when the cohesion between the secondary particles is small. There was found. The cohesive force between the secondary particles is defined by the size of the average particle size D50 after the cobalt hydroxide secondary particles are dispersed in pure water with respect to the original average particle size D50. The particles are dispersed in pure water while being irradiated with ultrasonic waves (42 KHz, 40 W) for 3 minutes. When the cohesive force between the secondary particles is large, the average particle size after the dispersion as described above is the same as the original average particle size, but becomes small when the cohesive force is small. In the present invention, the average particle size after the dispersion is preferably ¼ or less, particularly ８ or less of the original average particle size.
[0026]
The cobalt tetroxide produced as described above preferably has a secondary particle press density of 2.0 to 3.2 g / cm.^ThreeIt is preferable to have. The press density in the present invention is such that the particle powder is 0.3 t / cm unless otherwise specified.²The apparent press density when press-compressed at a pressure of. Press density of tribasic cobalt oxide is 2.0 g / cm^ThreeIs smaller, the press density of the positive electrode is reduced, while 3.2 g / cm.^ThreeIf it exceeds 1, the press density of the positive electrode is lowered, which is not preferable. Among these, the press density is 2.1 to 3.0 g / cm.^ThreeIs preferred.
[0027]
The present invention is characterized in that the cobalt trioxide having the specific structure and a lithium source are mixed and calcined. However, when a part of the cobalt trioxide having the specific structure is replaced with another cobalt source, further battery characteristics or In some cases, the balance of positive electrode manufacturing productivity and the like can be improved. Examples of other cobalt sources include cobalt hydroxide or cobalt oxyhydroxide having a particle size, specific surface area, crystallinity, and the like different from those of cobalt trioxide having the specific structure of the present invention. In any case, in order to achieve the above-described effects of the present invention, it is preferable that the cobalt trioxide having the specific structure of the present invention is contained in an amount of preferably 10 mol% or more of the total cobalt source. If the content is 10 mol% or less, the effect of the present invention is reduced, which is not preferable. In particular, the content is preferably 30% or more.
[0028]
When a lithium cobalt composite oxide is produced using the above-described tribasic cobalt oxide, various methods can be used as the production method. For example, lithium carbonate or lithium hydroxide is preferably used as the lithium source. Further, hydroxides, oxides, carbonates, and the like are selected as raw materials for the element M used as necessary. As the fluorine source when a fluorine atom is contained, lithium fluoride or magnesium fluoride is preferably used. A mixed powder of cobalt trioxide, a lithium source, and, if necessary, a raw material of element M and a fluorine source is calcined at 800 to 1050 ° C. in an oxygen-containing atmosphere for 5 to 20 hours as described above, and obtained calcined Lithium cobalt composite oxide particles are produced by pulverizing and classifying the product after cooling.
[0029]
The lithium cobalt composite oxide thus produced has an average particle diameter D50 of preferably 5 to 15 μm, particularly preferably 8 to 12 μm, and a specific surface area of preferably 0.3 to 0.7 m.²/ G, particularly preferably 0.4 to 0.6 m²/ 110, (110) plane diffraction peak half width of 2θ = 66.5 ± 1 ° measured by X-ray diffraction using CuKα as a radiation source is preferably 0.07 to 0.14 °, particularly preferably 0.08. ˜0.12 ° and the press density is preferably 3.15 to 3.40 g / cm^Three, Particularly preferably 3.20 to 3.35 g / cm^ThreePreferably there is. In the lithium cobalt composite oxide of the present invention, the amount of residual alkali contained therein is preferably 0.03% by mass or less, and particularly preferably 0.01% by mass or less.
[0030]
When producing a positive electrode for a lithium secondary battery from such a lithium cobalt composite oxide, the composite oxide powder is mixed with a carbon-based conductive material such as acetylene black, graphite, and Ketchen black and a binder. It is formed by. For the binder, polyvinylidene fluoride, polytetrafluoroethylene, polyamide, carboxymethyl cellulose, acrylic resin, or the like is preferably used.
[0031]
The lithium cobalt composite oxide powder, conductive material and binder of the present invention are made into a slurry or kneaded material using a solvent or dispersion medium, and this is supported on a positive electrode current collector such as an aluminum foil or a stainless steel foil by coating or the like. Thus, a positive electrode for a lithium secondary battery is manufactured.
[0032]
In the lithium secondary battery using the lithium cobalt composite oxide of the present invention as the positive electrode active material, a porous polyethylene film, a porous polypropylene film, or the like is used as the separator. Various solvents can be used as the solvent for the electrolyte solution of the battery, and among them, carbonate ester is preferable. The carbonate ester can be either cyclic or chain. Examples of the cyclic carbonate include propylene carbonate and ethylene carbonate (EC). Examples of the chain carbonate ester include dimethyl carbonate, diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate, methyl isopropyl carbonate and the like.
[0033]
In this invention, the said carbonate ester can be used individually or in mixture of 2 or more types. Moreover, you may mix and use with another solvent. Moreover, depending on the material of the negative electrode active material, when a chain carbonate ester and a cyclic carbonate ester are used in combination, discharge characteristics, cycle durability, and charge / discharge efficiency may be improved.
[0034]
Further, in the lithium secondary battery using the lithium cobalt composite oxide of the present invention as the positive electrode active material, a vinylidene fluoride-hexafluoropropylene copolymer (for example, product name Kyner manufactured by Atchem Co.) or vinylidene fluoride-perfluoro is used. A gel polymer electrolyte containing a propyl vinyl ether copolymer may be used. Solutes added to the electrolyte solvent or polymer electrolyte include ClO._Four-, CF_ThreeSO_Three-, BF_Four-, PF₆-, AsF₆-, SbF₆-, CF_ThreeCO₂-, (CF_ThreeSO₂)₂Any one or more of lithium salts having N- or the like as an anion is preferably used. It is preferable to add at a concentration of 0.2 to 2.0 mol / l (liter) with respect to the electrolyte solvent or polymer electrolyte made of the lithium salt. If it deviates from this range, the ionic conductivity is lowered and the electrical conductivity of the electrolyte is lowered. Of these, 0.5 to 1.5 mol / l is particularly preferable.
[0035]
In the lithium battery using the lithium cobalt composite oxide of the present invention as the positive electrode active material, a material capable of inserting and extracting lithium ions is used as the negative electrode active material. The material for forming the negative electrode active material is not particularly limited. For example, an oxide, a carbon compound, a silicon carbide compound, or a silicon oxide compound mainly composed of lithium metal, lithium alloy, carbon material, periodic table 14 or group 15 metal. , Titanium sulfide, boron carbide compounds and the like. As the carbon material, those obtained by pyrolyzing an organic substance under various pyrolysis conditions, artificial graphite, natural graphite, soil graphite, expanded graphite, flake graphite, and the like can be used. As the oxide, a compound mainly composed of tin oxide can be used. As the negative electrode current collector, a copper foil, a nickel foil, or the like is used. Such a negative electrode is preferably produced by kneading the active material with an organic solvent to form a slurry, and applying the slurry to a metal foil current collector, drying, and pressing.
[0036]
There is no restriction | limiting in particular in the shape of the lithium battery which uses the lithium cobalt complex oxide of this invention for a positive electrode active material. A sheet shape, a film shape, a folded shape, a wound-type bottomed cylindrical shape, a button shape, or the like is selected depending on the application.
[0037]
【Example】
EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In the following, Examples 1 to 2 and Examples 5 to 8 are examples of the present invention, and Examples 3 and 4 are comparative examples.
[0038]
[Example 1]
Cobalt hydroxide powder is mixed continuously with a caustic soda solution and a cobalt hydroxide slurry is continuously synthesized by a known method, followed by agglomeration, filtration and drying processes. Got. The obtained cobalt hydroxide had a diffraction peak half-width of (001) plane near 2θ = 19 ° of 0.27 ° in powder X-ray diffraction using CuKα ray, and (101 ) Plane diffraction peak half-width was 0.23 °. As a result of volume-based particle size distribution analysis obtained from image analysis under scanning electron microscope observation, the average particle size D50 was 17.5 μm, D10 was 7.1 μm, and D90 was 26.4 μm. The specific surface area is 17.1m.²/ G and the press density is 1.75 g / cm.^ThreeThe ratio of the major axis to the minor axis was 1.2: 1, which was a substantially spherical cobalt hydroxide powder formed by aggregation of primary particles.
[0039]
This cobalt hydroxide easily collapsed secondary particles in water. As a result of measuring the particle size distribution of this powder after irradiating ultrasonic waves (42 KHz, 40 W) with pure water as a dispersion medium for 3 minutes using a laser scattering type particle size distribution measuring device, the average particle size D50 is 0.75 μm and D10 is 0.35 μm. D90 was 1.6 μm, and the average particle diameter D50 (0.75 μm) was about 1/23 of the original particle D50 (17.5 μm). The slurry after the measurement was dried, and as a result of observation with a scanning electron microscope, the secondary particle shape before the measurement was not observed.
[0040]
This cobalt hydroxide powder was calcined at 600 ° C. for 12 hours in the atmosphere to synthesize cobalt trioxide. The synthesized cobalt tetroxide has a diffraction peak half-width of (220) plane near 2θ = 31 ° is 0.17 ° in powder X-ray diffraction using CuKα ray, and is around 2θ = 37 ± 1 °. The diffraction peak half-value width of the (311) plane is 0.17 °. As a result of volume-based particle size distribution analysis obtained from image analysis under scanning electron microscope observation, the average particle size D50 is 16 μm, D10 is 3 μm, and D90 is 23 μm and specific surface area of 5.8 m²/ G and the press density is 2.96 g / cm.^ThreeIt was a substantially spherical cobalt tetroxide powder formed by agglomeration of primary particles.
[0041]
This cobalt trioxide and the specific surface area is 1.2m²/ G lithium carbonate powder was dry mixed. Mixing ratio is LiCoO after firing₂It mix | blended so that it might become. A mixture of these two types of powders was fired in air at 950 ° C. for 12 hours. LiCoO formed by agglomerating primary particles by crushing the fired product₂A powder was obtained. As a result of measuring the particle size distribution using a laser scattering type particle size distribution measuring device, the average particle size D50 was 11.8 μm, D10 was 12.7 μm, D90 was 22.7 μm, and the specific surface area determined by the BET method was 0. .48m²/ G of substantially spherical particles. LiCoO₂An X-ray diffraction spectrum was obtained for the powder using an X diffraction device (RINT 2100 type, manufactured by Rigaku Corporation). In powder X-ray diffraction using CuKα ray, the half value width of the diffraction peak of (110) plane in the vicinity of 2θ = 66.5 ± 1 ° was 0.093 °. LiCoO₂Press density of powder is 3.36 g / cm^ThreeMet. This LiCoO₂10 g of the powder was dispersed in 100 g of pure water, filtered, and potentiometrically titrated with 0.1 N HCl to determine the residual alkali amount, which was 0.02% by mass.
[0042]
LiCoO above₂Powder, acetylene black, and polyvinylidene fluoride powder are mixed at a mass ratio of 90/5/5, N-methylpyrrolidone is added to prepare a slurry, and a doctor blade is used on a 20 μm thick aluminum foil. One side was coated. The positive electrode sheet for lithium batteries was produced by drying and performing roll press rolling 5 times.
[0043]
The positive electrode sheet is punched out as a positive electrode, a metal lithium foil having a thickness of 500 μm is used as a negative electrode, a nickel foil of 20 μm is used as a negative electrode current collector, and a porous polypropylene having a thickness of 25 μm is used as a separator. In addition, the electrolyte contains LiPF with a concentration of 1M.₆/ EC + DEC (1: 1) solution (LiPF₆Means a mixed solution of EC and DEC in a mass ratio (1: 1). The solvent described later also conforms to this. ) Were used to assemble two stainless steel simple sealed cell type lithium batteries in an argon glove box.
[0044]
For one battery using an EC + DEC (1: 1) solution as the electrolyte, the battery was charged at a load current of 75 mA / g of the positive electrode active material at 25 ° C. to 4.3 V, and a load of 75 mA / g of the positive electrode active material. The initial discharge capacity was determined by discharging to 2.5 V with current. Further, the volume capacity density was determined from the density of the electrode layer and the capacity per weight. Moreover, about this battery, the charging / discharging cycle test was done 30 times continuously. As a result, the initial volume capacity density of the positive electrode layer at 25 ° C. and 2.5 to 4.3 V was 556 mAh / cm.^ThreeThe electrode layer has an initial weight capacity density of 162 mAh / g-LiCoO.₂The capacity retention rate after 30 charge / discharge cycles was 97.3%.
[0045]
On the other hand, the remaining battery using the EC + DEC (1: 1) solution as the electrolyte was charged at 4.3 V for 10 hours, disassembled in an argon glove box, and charged positive electrode sheet. The positive electrode sheet was washed, punched out to a diameter of 3 mm, sealed in an aluminum capsule together with EC, and heated at a rate of 5 ° C./min with a scanning differential calorimeter to measure the heat generation start temperature. As a result, the heat generation start temperature of the 4.3V charged product was 166 ° C.
[0046]
[Example 2]
Cobalt tetroxide was synthesized in the same manner as in Example 1 except that the calcining temperature of cobalt hydroxide was set to 400 ° C. in Example 1. The synthesized cobalt tetroxide has a diffraction peak half-value width of (220) plane near 2θ = 31 ° is 0.31 ° in powder X-ray diffraction using CuKα ray, and it is around 2θ = 37 ± 1 °. The (311) plane has a diffraction peak half width of 0.36 °, an average particle diameter D50 of 17 μm, D10 of 5 μm, D90 of 23 μm, and a specific surface area of 16.6 m.²/ G and the press density is 2.08 g / cm.^ThreeIt was a substantially spherical cobalt tetroxide powder formed by agglomeration of primary particles.
[0047]
Except for using this cobalt tetroxide powder, the same procedure as in Example 1 was followed.₂A powder was synthesized. The average particle diameter D50 is 13.5 μm, D10 is 4.7 μm, D90 is 22.6 μm, and the specific surface area determined by the BET method is 0.38 m.²/ G of substantially spherical LiCoO₂A powder was obtained. LiCoO₂An X-ray diffraction spectrum was obtained for the powder using an X-ray diffractometer (RINT 2100 type, manufactured by Rigaku Corporation). In powder X-ray diffraction using CuKα ray, the half value width of the diffraction peak of (110) plane in the vicinity of 2θ = 66.5 ± 1 ° was 0.095 °. Obtained LiCoO₂The press density of the powder is 3.31 g / cm^ThreeMet.
[0048]
Such LiCoO₂A positive electrode sheet was prepared in the same manner as in Example 1 except that powder was used, and two simple sealed cell type lithium batteries were assembled, and the initial weight capacity density was charged 30 times under the same conditions as in Example 1. When the capacity retention ratio after the discharge cycle and the heat generation start temperature were measured, they were 161 mAh / g, 97.4%, and 165 ° C., respectively.
[0049]
[Example 3]
Cobalt tetroxide was synthesized in the same manner as in Example 1 except that the calcining temperature of cobalt hydroxide was 800 ° C. in Example 1. The synthesized cobalt tetroxide has a diffraction peak half-width of (220) plane near 2θ = 31 ° is 0.094 ° in powder X-ray diffraction using CuKα ray, and is around 2θ = 37 ± 1 °. The (311) plane has a diffraction peak half width of 0.093 °, an average particle diameter D50 of 14 μm, D10 of 4 μm, D90 of 22 μm and a specific surface area of 1.43 m.²/ G and the press density is 3.45 g / cm.^ThreeIt was a substantially spherical cobalt tetroxide powder formed by agglomeration of primary particles.
[0050]
Except for using this cobalt tetroxide powder, the same procedure as in Example 1 was followed.₂A powder was synthesized. The average particle diameter D50 is 10.7 μm, D10 is 3.0 μm, D90 is 23.3 μm, and the specific surface area determined by the BET method is 0.54 m.²/ G of substantially spherical LiCoO₂A powder was obtained. LiCoO₂An X-ray diffraction spectrum was obtained for the powder using an X-ray diffractometer (RINT 2100 type, manufactured by Rigaku Corporation). In powder X-ray diffraction using CuKα ray, the half value width of the diffraction peak of (110) plane in the vicinity of 2θ = 66.5 ± 1 ° was 0.093 °. Obtained LiCoO₂The press density of the powder is 3.08 g / cm^ThreeMet.
[0051]
Such LiCoO₂A positive electrode sheet was prepared in the same manner as in Example 1 except that powder was used, and two simple sealed cell type lithium batteries were assembled, and the initial weight capacity density was charged 30 times under the same conditions as in Example 1. When the capacity retention rate after the discharge cycle and the heat generation start temperature were measured, they were 158 mAh / g, 95.3%, and 157 ° C., respectively.
[0052]
[Example 4]
LiCoO was prepared in the same manner as in Example 1 except that commercially available cobalt tetroxide was used.₂Was synthesized. As a result of investigating the physical properties of cobalt tetroxide, in the powder X-ray diffraction using CuKα ray, the half value width of the diffraction peak of (220) plane near 2θ = 31 ° is 0.11 °, and 2θ = 37 ± 1. The half-value width of the diffraction peak of (311) plane near 0.1 ° is 0.12 °, the average particle diameter D50 is 2.8 μm, D10 is 1.6 μm, D90 is 4.0 μm and the specific surface area is 1.2 m.²/ G and the press density is 3.45 g / cm.^ThreeIt was a cage-shaped cobalt tetroxide powder formed by agglomeration of primary particles.
[0053]
Except for using this cobalt tetroxide powder, the same procedure as in Example 1 was followed.₂A powder was synthesized. The average particle diameter D50 is 7.3 μm, D10 is 3.3 μm, D90 is 15.0 μm, and the specific surface area determined by the BET method is 0.55 m.²/ G of substantially spherical LiCoO₂I got the end. LiCoO₂An X-ray diffraction spectrum was obtained for the powder using an X-ray diffractometer (RINT 2100 type, manufactured by Rigaku Corporation). In the powder X-ray diffraction using CuKα ray, the half value width of the diffraction peak of (110) plane around 2θ = 66.5 ± 1 ° was 0.099 °. Obtained LiCoO₂The press density of the powder is 2.71 g / cm^ThreeMet.
[0054]
Such LiCoO₂A positive electrode sheet was prepared in the same manner as in Example 1 except that powder was used, and two simple sealed cell type lithium batteries were assembled. The initial volume capacity density and initial weight capacity were the same as in Example 1. When the density, the capacity retention rate after 30 charge / discharge cycles, and the heat generation start temperature were measured, 440 mAh / cm, respectively.^Three, 160 mAh / g, 97.0%, and 159 ° C.
[0055]
[Example 5]
In Example 1, a positive electrode active material was synthesized in the same manner as in Example 1 except that titanium oxide powder and lithium fluoride powder were further added when mixing cobalt hydroxide and lithium carbonate. As a result of elemental analysis, LiCo_0.997Ti_0.003O_1.995F_0.005Met. LiCo made by agglomerating primary particles obtained by crushing the fired product_0.997Ti_0.003O_1.995F_0.005As a result of measuring the particle size distribution of the powder using a laser scattering type particle size distribution measuring apparatus with water as a dispersion medium, the average particle size D50 is 10.7 μm, D10 is 2.6 μm, D90 is 20.7 μm, and the ratio obtained by the BET method Surface area is 0.55m²/ G of substantially spherical LiCoO₂A powder was obtained.
[0056]
LiCo_0.997Ti_0.003O_1.995F_0.005An X-ray diffraction spectrum was obtained for the powder using an X-ray diffractometer (RINT 2100 type, manufactured by Rigaku Corporation). In powder X-ray diffraction using CuKα ray, the half value width of the diffraction peak of (110) plane in the vicinity of 2θ = 66.5 ± 1 ° was 0.095 °. LiCo_0.997Ti_0.003O_1.995F_0.005The density of the powder is 3.35 g / cm^ThreeMet. As a result of spectroscopic analysis, titanium and fluorine were localized on the surface.
[0057]
LiCo above_0.997Ti_0.003O_1.995F_0.005Powder, acetylene black, and polyvinylidene fluoride powder are mixed at a mass ratio of 90/5/5, N-methylpyrrolidone is added to prepare a slurry, and a doctor blade is used on a 20 μm thick aluminum foil. One side was coated. The positive electrode sheet for lithium batteries was produced by drying and roll press rolling.
[0058]
The positive electrode sheet is punched out as a positive electrode, a metal lithium foil having a thickness of 500 μm is used as a negative electrode, a nickel foil of 20 μm is used as a negative electrode current collector, and a porous polypropylene having a thickness of 25 μm is used as a separator. In addition, the electrolyte contains LiPF with a concentration of 1M.₆/ EC + DEC (1: 1) solution (LiPF₆Means a mixed solution of EC and DEC in a mass ratio (1: 1). The solvent described later also conforms to this. ) Were used to assemble two stainless steel simple sealed cell type lithium batteries in an argon glove box.
[0059]
For one battery using an EC + DEC (1: 1) solution as the electrolyte, the battery was charged at a load current of 75 mA / g of the positive electrode active material at 25 ° C. to 4.3 V, and a load of 75 mA / g of the positive electrode active material. The initial discharge capacity was determined by discharging to 2.5 V with current. Further, the volume capacity density was determined from the density of the electrode layer and the capacity per weight. Moreover, about this battery, the charging / discharging cycle test was done 30 times continuously.
[0060]
As a result, the initial volume capacity density of the positive electrode layer at 25 ° C. and 2.5 to 4.3 V was 558 mAh / cm.^ThreeThe electrode layer has an initial weight capacity density of 160 mAh / g-LiCoO.₂The capacity retention rate after 30 charge / discharge cycles was 99.5%. On the other hand, the remaining battery using the EC + DEC (1: 1) solution as the electrolyte was charged at 4.3 V for 10 hours, disassembled in an argon glove box, and charged positive electrode sheet. The positive electrode sheet was washed, punched out to a diameter of 3 mm, sealed in an aluminum capsule together with EC, and heated at a rate of 5 ° C./min with a scanning differential calorimeter to measure the heat generation start temperature. As a result, the heat generation start temperature of the 4.3V charged product was 174 ° C.
[0061]
[Example 6]
In Example 5, a positive electrode active material was synthesized in the same manner as in Example 5 except that aluminum hydroxide was used instead of titanium oxide. As a result of chemical analysis, LiCo_0.997Al_0.003O_1.995F_0.005The press density of this powder is 3.34 g / cm^ThreeMet. The battery characteristics and heat generation start temperature were measured in the same manner as in Example 1. As a result, the initial capacity was 160 mAH / g, the capacity retention after 30 cycles was 99.5%, and the heat generation start temperature was 179 ° C.
[0062]
[Example 7]
A positive electrode active material was synthesized in the same manner as in Example 5 except that magnesium hydroxide was used instead of titanium oxide. As a result of chemical analysis, LiCo_0.997Mg_0.003O_1.995F_0.005The press density of this powder is 3.35 g / cm^ThreeMet. The battery characteristics and heat generation start temperature were measured in the same manner as in Example 1. As a result, the initial capacity was 160 mAH / g, the capacity retention rate after 30 cycles was 99.6%, and the heat generation start temperature was 185 ° C.
[0063]
[Example 8]
In Example 5, a positive electrode active material was synthesized in the same manner as in Example 5 except that zirconium oxide was used instead of titanium oxide. As a result of chemical analysis, LiCo_0.997Zr_0.003O_1.995F_0.005The press density of this powder is 3.36 g / cm^ThreeMet. As a result of measuring the battery characteristics and the heat generation start temperature in the same manner as in Example 1, the initial capacity was 161 mAH / g, the capacity retention rate after 30 cycles was 99.5%, and the heat generation start temperature was 173 ° C.
[0064]
【The invention's effect】
According to the present invention, the volumetric capacity density is large, the safety is high, the charge / discharge cycle durability, the method for producing a lithium cobalt composite oxide for a lithium secondary battery positive electrode, A positive electrode for a secondary battery and a lithium secondary battery are provided.

Claims (7)

Tricobalt tetroxide, calcined in an oxygen-containing atmosphere a mixture of the following M element source if lithium source and required the general formula _{Li p Co x M y O z} F a ( where, M is or transition metal elements other than Co An alkaline earth metal element, 0.9 ≦ p ≦ 1.1, 0.980 ≦ x ≦ 1.000, 0 ≦ y ≦ 0.02, 1.9 ≦ z ≦ 2.1, x + y = 1, 0 ≦ a ≦ 0.02), which is measured by X-ray diffraction using CuKα as a radiation source as the above-described cobalt trioxide, 2θ = 31 ± 1 The full width at half maximum of the diffraction peak on the (220) plane at 0.1 ° is 0.14 to 0.45, and the full width at half maximum of the diffraction peak on the (311) plane at 2θ = 37 ± 1 ° is 0.14 to 0.45. the average particle diameter D50 of 3~25m ² / g and a secondary particle is 5~25μm trimanganese cobaltite Using, and the mixture, an oxygen-containing atmosphere, atmospheric pressure, 5 to 20 hours at 800 to 1050 ° C., a manufacturing method of a lithium secondary battery positive electrode for a lithium-cobalt composite oxide and firing. 2. The lithium cobalt composite oxide according to claim 1, which has a press density of 3.15 to 3.40 g / cm ³ when the powder powder of the lithium cobalt composite oxide is pressed at a pressure of 0.3 t / cm ² . Production method.   The method for producing a lithium cobalt composite oxide for a lithium secondary battery positive electrode according to claim 1 or 2, wherein the residual alkali content is 0.03% by mass or less. When the cobalt trioxide is measured by X-ray diffraction using CuKα as a radiation source, the half-value width of the diffraction peak of the (001) plane at 2θ = 19 ± 1 ° is 0.18 to 0.35, 2θ = 38. The half-width of the diffraction peak on the (101) plane of ± 1 ° is 0.15 to 0.35, the average primary particle size is 0.1 to 1.2 μm, the specific surface area is 5 to 50 m ² / g, and 2 The lithium secondary battery positive electrode according to claim 1, 2, or 3, wherein substantially spherical cobalt hydroxide having an average particle diameter of 5 to 25 µm is fired at 300 to 700 ° C in an oxygen-containing atmosphere. Method for producing lithium cobalt composite oxide. 5. The lithium cobalt composite oxide according to claim 4, which has a press density of 2.0 to 3.2 g / cm ³ when the powder powder of cobalt trioxide is press-compressed at a pressure of 0.3 t / cm ² . Production method. In the general formula, one M is Ti, Zr, Hf, V, Nb, Ta, Mn, Mg, Ca, Sr, Ba, and at least one is selected from the group consisting of Al of claims 1-5 A method for producing a lithium cobalt composite oxide for a positive electrode of a lithium secondary battery according to claim 1. 5. The lithium cobalt composite oxide according to claim 4, wherein an average particle diameter D50 after the secondary particles of cobalt hydroxide are dispersed in pure water is ¼ or less of the original average particle diameter D50. Production method.