JP2002222648A - Positive electrode active material, its manufacturing method, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material, capable of realizing a secondary battery, which combines high safety level and superior capacity characteristic, when it is used as the positive electrode material of the battery, its manufacturing method, and the lithium ion secondary battery. SOLUTION: It consists of compound oxide particles, which has a composition expressed by the general formula Li1+xNi1-y-zCoyAlzO2 (where, 0<=x<=0.1, 0.1<=y<=0.4, 0.02<=z<=0.1). The difference in the Bragg angles of the (110) face and (018) face in the X-ray diffraction pattern of the powder of the compound oxide particles is [0.29×(y+z)+0.172] degree or more, and its 10% cumulative frequency of the particle diameters is 1 μm or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode active material, a method for producing the same, and a lithium ion secondary battery using the active material. Particularly, when used as a positive electrode material for a battery, high safety and excellent capacity characteristics are obtained. The present invention relates to a positive electrode active material capable of realizing a secondary battery having both of the above, a method for manufacturing the same, and a lithium ion secondary battery.

[0002]

2. Description of the Related Art In recent years, relatively safe anode materials have been developed, and non-aqueous electrolytes having a higher decomposition voltage have been developed.
High voltage non-aqueous electrolyte secondary batteries have been put to practical use. In particular, lithium-ion-based secondary batteries have a high discharge potential, are lightweight, and have high energy density. It is expanding to.

[0003] This lithium ion secondary battery comprises a positive electrode and a negative electrode capable of reversibly occluding and releasing lithium ions,
And a non-aqueous electrolyte in which a lithium salt is dissolved in a non-aqueous solvent.

Examples of the positive electrode active material for the lithium ion secondary battery include lithium cobalt composite oxides such as LiCoO ₂ , lithium nickel composite oxides such as LiNiO _2, and lithium manganese composite oxides such as LiMn ₂ O ₄ . Metal oxides are commonly used.

[0005]

However, in a battery using a metal oxide such as the above-mentioned lithium-cobalt composite oxide, the discharge potential becomes higher than that in a battery using the other two composite oxides. There is a disadvantage that the discharge capacity in a potential range where the non-aqueous electrolyte does not decompose is reduced to about 1/2 of the theoretical capacity. In addition, there is a problem that the production cost is increased because cobalt, which is a scarce resource, is used as a material.

On the other hand, a battery using a lithium nickel composite oxide has a problem that the theoretical capacity is large and an appropriate discharge potential is obtained, but the stability of the battery is insufficient.

That is, in the charged state of the battery, a deoxygenation reaction from the positive electrode active material and an oxidation reaction of the electrolytic solution occur. These reactions are exothermic, and the reaction rate increases as the temperature increases. The calorific value also increases rapidly. Therefore, thermal runaway in which the exothermic reaction proceeds rapidly at a specific temperature is likely to occur, and the safety of the battery is likely to be impaired. This tendency is due to the differential thermal analysis (DTA) of the active material in the charged state.
And thermal analysis using differential scanning calorimetry (DSC) or the like. As described above, the higher the temperature (exothermic peak temperature) at which the exothermic peak due to the above-mentioned reaction in the thermal analysis of the charged active material is, the higher the safety of the battery can be evaluated.

However, the heat generation peak temperature of the conventional positive electrode active material is as low as about 160 to 190 ° C., and a battery having sufficiently high safety cannot be obtained. On the other hand, although a positive electrode active material having an exothermic peak temperature of about 300 to 350 ° C. has been obtained, there is a problem that the battery capacity characteristics are significantly reduced.

On the other hand, for the purpose of improving the safety of a battery which is easily hindered by the above-mentioned exothermic reaction, it has been attempted to replace a part of the Ni component constituting the positive electrode active material with a metal element such as Mn, Co and Al. ing. However, although the safety of the battery is improved by introducing these substitution elements, there is a problem that the battery capacity is easily reduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to realize a secondary battery having both high safety and excellent capacity characteristics particularly when used as a positive electrode material of a battery. It is an object of the present invention to provide a possible positive electrode active material, a method for producing the same, and a lithium ion secondary battery using the active material.

[0011]

Means for Solving the Problems In order to achieve the above object, the present inventors have prepared positive electrode active materials having various compositions.
The effects of the composition, particle size distribution, and mixed state of the constituent elements of the obtained positive electrode active material on the safety and capacity characteristics of the battery were prepared by using various physicochemical methods. As a result, it has been found that excellent battery characteristics can be obtained when the degree of substitution of the constituent elements is appropriately controlled and the particle size distribution of the active material particles is adjusted to a more appropriate range.

Specifically, the general formula Li _{1 + x} Ni
_{1-y-z Co y Al} z O 2 ( where, 0 ≦ x ≦ 0.1,
(0.1 ≦ y ≦ 0.4, 0.02 ≦ z ≦ 0.1). The composite oxide particles have a (110) plane in the powder X-ray diffraction pattern. A positive electrode active material having a difference in Bragg angle with the (018) plane of a predetermined value or more and a 10% cumulative frequency particle size of 1 μm or more can realize a secondary battery satisfying both safety and capacity characteristics. I got the knowledge.

[0013] Further, by spray-drying a mixture of raw material components constituting the positive electrode active material, pulverizing the raw material mixture by a shock wave or an ultrasonic wave, or allowing a co-precipitation reaction to proceed with a raw material suspension, It was also found that the mixing state of the active material raw material components was improved, and that a positive electrode active material having an appropriate particle size distribution of the active material was obtained.

The present invention has been completed based on the above findings. That is, the positive electrode active material according to the present invention have the general formula _{Li 1 + x Ni 1-y} -z Co y Al z O 2 ( where,
0 ≦ x ≦ 0.1, 0.1 ≦ y ≦ 0.4, 0.02 ≦ z ≦
0.1), and the difference in Bragg angle between the (110) plane and the (018) plane in the powder X-ray diffraction pattern of the composite oxide particles is [0.29 × (y + z) +0.172] degrees and a 10% cumulative frequency particle size of 1 μm or more.

In the method for producing a positive electrode active material according to the present invention, a metal salt containing an active material component is dispersed in a dispersion medium, and the 99% cumulative frequency particle size of the metal salt in the slurry is 5%.
a step of preparing a metal salt slurry having a particle size of not more than μm, a step of preparing an aggregated particle by spray-drying the metal salt slurry, and baking the aggregated particle to have a 10% cumulative frequency particle size of 1 μm or more. And forming an active material particle.

In the above production method, the metal salt preferably has insolubility or poor solubility in a dispersion medium. Further, in the step of preparing the metal salt slurry, the metal salt slurry is supplied to the dispersion nozzle at a pressure of 10 MPa or more, and the metal salt slurry is subjected to a shock wave or ultrasonic vibration generated by the metal salt slurry flowing in a turbulent state. Is preferably crushed.

Further, another method for producing a positive electrode active material according to the present invention includes a step of forming a nickel-cobalt composite hydroxide by advancing a coprecipitation reaction between a nickel component and a cobalt component in a suspension of an aluminum salt. And a step of adding a lithium salt to the obtained nickel-cobalt composite hydroxide and calcining to form active material particles having a 10% cumulative frequency particle size of 1 μm or more.

Further, the lithium ion secondary battery according to the present invention have the general formula _{Li 1 + x Ni 1-y} -z Co y Al z O
₂ (however, 0 ≦ x ≦ 0.1, 0.1 ≦ y ≦ 0.4, 0.
02 ≦ z ≦ 0.1), and the difference in the Bragg angle between the (110) plane and the (018) plane in the powder X-ray diffraction pattern of the composite oxide particles is as follows: A positive electrode containing a positive electrode active material having a degree of [0.29 × (y + z) +0.172] degrees or more and a 10% cumulative frequency particle diameter of 1 μm or more; a negative electrode arranged with the positive electrode and a separator interposed therebetween; A battery container accommodating the positive electrode, the separator, and the negative electrode, and a non-aqueous electrolyte filled in the battery container are provided.

In the general formula Li _{1 + x} Ni _1-yz Co _y Al _z O ₂ representing the composition of the positive electrode active material according to the present invention, the reason why the excess addition ratio x of Li is defined as 0 ≦ x ≦ 0.1 Is as follows. This is because, when the value x is negative, the arrangement of metal ions is disturbed, a component having a rock salt structure is easily formed, and a desired capacity cannot be obtained. On the other hand, when the x value exceeds 0.4, the capacity is reduced.

On the other hand, Co and Al are added in order to increase the peak heat generation temperature of the active material and enhance the safety of the battery.
The reason why the range of the Co addition ratio y is defined as 0.1 ≦ y ≦ 0.4 is that if the y value is less than 0.1, it becomes difficult to ensure the safety of the battery. This is because no gain in capacity can be found if it exceeds. Further, the range of the addition ratio z of Al is defined as 0.02 ≦ z ≦ 0.1 because the z value is 0.0
If it is less than 2, it is difficult to ensure safety, while if it exceeds 0.1, the capacity is reduced.

Further, in the positive electrode active material according to the present invention, since the components are oriented to a state of being finer and more uniformly mixed,
The difference (Δ) between the Bragg angles of the (110) plane and the (018) plane in the powder X-ray diffraction pattern of the composite oxide particles constituting the active material is expressed in relation to the component ratios y and z of Co and Al [ 0.29 × (y + z) +0.172] degrees or more.

The above Bragg angle is measured using an X-ray diffractometer using Cu X-rays. Difference of the above Bragg angle (Δ)
Is an index indicating the degree to which the Co component and the Al component are uniformly substituted in the Li-Ni structure, and Co, Al
When the component occupies a certain amount in the tissue, it can take a value within the above range.

It is known that when nickel is replaced with cobalt and aluminum as in the active material composition of the present invention, the a-axis shrinks and the c-axis elongates. The lattice constant obtained from powder X-ray diffraction is measured temperature, mechanical accuracy of the optical system,
Strong dependence on parameters used for analysis. On the other hand, the Bragg angle difference Δ defined in the present invention directly reflects the a-axis and c-axis ratios, and has little dependence on measurement conditions or analysis parameters. It is possible to grasp. When the Bragg angle difference Δ is within the above range, the substitution state of each component element is improved, the bonding force between Ni and oxygen is increased, and the safety of the crystal is improved. 160 with increasing
High capacity characteristics of mAh / g or more can be obtained.

The 10% cumulative frequency particle size (D10 value) of the positive electrode active material according to the present invention is 1 μm or more. This one
Since the positive electrode active material for a lithium ion secondary battery having a 0% cumulative frequency particle size of 1 μm or more has a small amount of fine particles, the reaction with the electrolytic solution is limited in the battery, and the exothermic peak temperature is 220 ° C. or more, preferably 240 ° C. or more. Thus, a highly safe secondary battery can be realized.

The 10% cumulative frequency particle size (D10 value) defined in the present invention is obtained by measuring the particle size distribution by a microtrack method and integrating the volume of particles having a small particle size into 10%.
Shall indicate the particle size of the particles that have reached. The D99 value indicates the particle size of the particle when the integrated volume of the particle reaches 99%.

The measurement of the particle size distribution is performed as follows. That is, a laser light scattering type particle size distribution meter (for example, MICR manufactured by LEEDS & NOTHRUP)
OTRAC II PARTICLE-SIZE AN
ALYZER) is used to measure the particle size distribution. This utilizes a light scattering phenomenon that occurs when laser light is applied to particles as a measurement principle. Since the intensity and the scattering angle of the scattered light greatly depend on the size of the particles, the particle size distribution of the powder can be obtained by measuring the intensity and the scattering angle of the scattered light with an optical detector and processing them by computer. .

In measuring the 10% cumulative frequency particle size (D10 value), a laser light scattering type particle size distribution meter capable of measuring a wet sample can be suitably used. Specifically, it is preferable to prepare a slurry by suspending the active material in an appropriate solvent, disperse the slurry sufficiently with ultrasonic waves, and then measure. The ultrasonic device is preferably of a type in which a metal chip connected by an ultrasonic oscillator is directly immersed in slurry. This structure has the advantages that the ultrasonic waves are transmitted directly to the slurry so that they can be efficiently dispersed and the reproducibility of the dispersion is excellent.

The ultrasonic output is desirably 100 W or more. If it is less than 100 W, the mechanical energy is insufficient even if the ultrasonic wave is applied for a long time, and the aggregation between the fine structures cannot be destroyed. Conversely, when energy of 200 W or more is input, the slurry temperature rises rapidly, and it is difficult to obtain reproducibility of the dispersed state.

The ultrasonic oscillator having a frequency of about 20 kHz is used. It is particularly preferable to provide a control system capable of tracking the frequency.

The slurry concentration is desirably 0.001-1% by mass. At a concentration higher than this, the probability of association between the particles increases, and the crushed fine particles re-aggregate, making it impossible to grasp the state of crushing accurately. If the concentration is below this range, the absorption efficiency of the ultrasonic energy by the particles is reduced, and the S / N ratio is reduced due to the restriction of the measuring device for optically detecting the scattering, and the noise is increased.

The above ultrasonic irradiation time is desirably within 5 minutes. Irradiation beyond this increases the slurry temperature and changes the amplitude of the ultrasonic waves, resulting in poor reproducibility.

In order to obtain a positive electrode active material for a lithium ion secondary battery having a uniform structure and particle size distribution as described above, lithium salt, nickel salt,
Disperse metal salts such as cobalt salts and aluminum salts in a dispersion medium to prepare metal salt slurries, and spray-dry the slurries or treat them by coprecipitation to properly control the mixing state of the component elements. is important. Then, by firing the obtained product, the positive electrode active material of the present invention is obtained.

As the lithium salt, lithium carbonate and lithium hydroxide are preferably used. Nickel salts include nickel hydroxide, nickel oxide, nickel carbonate,
Nickel oxalate or the like is used. As the cobalt salt, not only oxides of CoO, Co ₂ O ₃ , and Co ₃ O ₄ , but also cobalt hydroxide or a nickel-cobalt composite hydroxide compounded with nickel can be suitably used. Alumina, hydrates of alumina, and alumina hydroxide are used as the aluminum salt.

As a dispersion medium used in the metal salt slurry, an organic solvent such as various alcohols and ketone solvents can be used in addition to water. At this time, it is desirable to make a combination such that the metal salt is insoluble or hardly soluble in the dispersion medium.

The following method can be applied as a specific method for controlling the mixed state of the constituent elements when producing the positive electrode active material according to the present invention. That is, the metal salt containing the active material component is dispersed in a dispersion medium,
A step of preparing a metal salt slurry in which the 99% cumulative frequency particle size (D99) of the metal salt in the slurry is 5 μm or less; a step of spray-drying the metal salt slurry to prepare aggregated particles; A firing method can be applied.

As the measuring instrument for the 99% cumulative frequency particle size (D99), the above-mentioned laser light scattering type particle size distribution meter which can be used for a wet type sample can be used. As described above, 99 of the metal salt particles constituting the metal salt slurry
By making the% cumulative frequency particle size (D99) into a fine particle of 5 μm or less, the diffusion of the component elements proceeds easily and quickly during firing, and a uniform active material composition can be obtained. The D99 value is 5
When a coarse metal salt is contained so as to exceed μm, a uniform and fine mixed state of the component elements in the active material cannot be obtained.

In order to effectively control the particle size of the metal salt particles constituting the metal salt slurry, the metal salt mixed slurry is sent to a dispersion nozzle at a pressure of 100 MPa or more.
It is preferable that the metal salt is pulverized by a shock wave or ultrasonic vibration caused by the turbulent flow generated in the dispersion nozzle portion. The supply pressure of the metal salt slurry to the dispersion nozzle is 100MP.
If it is less than a, the pulverizing effect of the metal salt is insufficient, and it becomes difficult to obtain a predetermined D99 value. The above pulverizing operation is extremely effective because the surface of the pulverized metal salt particles greatly increases the reaction activity and promotes the synthesis reaction during firing.

By spray-drying the thus obtained metal salt slurry, a uniform composition in the form of aggregated particles can be obtained. As the spray drying method, a disk type or nozzle type spray dry in which a metal salt slurry is dropped and dispersed on a disk rotating in a drying air flow can be employed. By firing the uniform composition in the form of aggregated particles, a desired positive electrode active material for a lithium ion secondary battery is obtained.

As another method for producing the positive electrode active material according to the present invention, a method in which a lithium salt is added to a nickel-cobalt composite hydroxide obtained by a coprecipitation reaction in a suspension of an aluminum salt, followed by firing is also employed. can do. That is, a step of promoting a coprecipitation reaction between a nickel component and a cobalt component in an aluminum salt suspension to produce a nickel cobalt composite hydroxide, and adding a lithium salt to the obtained nickel cobalt composite hydroxide. And baking to form active material particles having a 10% cumulative frequency particle diameter of 1 μm or more.

In the above production method, alumina, various types of alumina hydrate, and alumina hydroxide can be used as the aluminum salt. As the lithium salt, lithium carbonate, lithium hydroxide or the like is used. In addition, a known coprecipitation process can be used. For example, an alkali component such as caustic soda can be added to an aqueous solution of a water-soluble salt of nickel cobalt to cause a coprecipitation reaction. The resulting precipitate is separated by filtration and dried to obtain a composite hydroxide having a desired composition. By adding a lithium salt to the composite hydroxide and firing it, the positive electrode active material of the present invention is prepared.

It is preferable to perform firing in an atmosphere having a high oxygen partial pressure. 50-100% as oxygen partial pressure,
More preferably, it is 80-100%. The firing temperature is 650-800 ° C., more preferably 700-800 ° C.
780 ° C. is preferred. The temperature drop rate after firing was 1 ° C /
It is desirable that it be less than minutes.

The lithium ion secondary battery according to the present invention
A positive electrode, which is prepared by mixing and pressing the positive electrode active material and the conductive auxiliary prepared as described above together with a binder and the like,
A negative electrode having a negative electrode active material is disposed so as to face the inside of the battery can with a separator and a non-aqueous electrolyte interposed therebetween.

Here, acetylene black, carbon black, graphite or the like is used as the conductive assistant. As the binder, for example, polyterafluoroethylene (PTFE), polyvinylidene fluoride (P
VDF), ethylene-propylene-diene copolymer (E
PDM), styrene-butadiene rubber (SBR) and the like can be used.

The above-mentioned positive electrode is manufactured by, for example, suspending the above-mentioned positive electrode active material and binder in a suitable solvent, applying the suspension to a current collector, drying and then press-pressing. Here, as the current collector, for example, an aluminum foil, a stainless steel foil, a nickel foil, or the like is preferably used.

In producing the positive electrode, from the viewpoint of controlling the contact state between the active material and the electrolyte,
It is preferable to provide holes of an appropriate amount and an appropriate size in the active material in the electrode sheet. That is, when there are no vacancies, the contact ratio between the electrolyte and the active material is reduced and the high-temperature characteristics are improved, but the battery reaction itself does not easily occur and the rate characteristics of the battery are reduced. Conversely, when the porosity becomes excessive, the contact ratio between the electrolyte and the active material increases, and the battery reaction easily occurs, and the capacity characteristics of the battery, particularly the rate characteristics, are improved, but the high-temperature characteristics cannot be maintained. There is.

The porosity is set in the range of 5 to 80% from the above viewpoint, and more preferably in the range of 10 to 60%. Furthermore, the range of 10 to 50% is preferable. The porosity can be adjusted by controlling the degree of dispersion of the active material layer by adjusting the molding pressure at the time of forming an electrode by applying pressure after forming the active material on the current collector surface. The porosity can also be adjusted by appropriately adjusting the amount of the binder added to the active material. That is, it has been confirmed that when the binder amount increases, the porosity decreases and the battery reaction itself does not easily occur, whereas when the binder amount decreases, the porosity increases and the high temperature characteristics of the battery tend not to be maintained. The appropriate amount of the binder varies depending on the type of the binder, the particle size of the positive electrode active material, and the like, and it is difficult to uniformly define the amount. The porosity and vacancy distribution of the active material can be determined, for example, by using a mercury-injected vacancy distribution measuring device (autopore)
And the like.

On the other hand, as the active material of the negative electrode, for example, a carbon material that absorbs and releases lithium ions, a material containing a chalcogen compound, or an active material made of a light metal can be used. It is particularly preferable to use a negative electrode containing a carbon substance or a chalcogen compound that inserts and extracts lithium ions, since battery characteristics such as cycle life of a secondary battery are improved.

Examples of the carbon material that occludes and releases lithium ions include coke, carbon dioxide fiber, pyrolysis gas phase carbon material, graphite, resin fired body, mesophase pitch-based carbon fiber (MCF) and mesophase spherical carbon. A fired body or the like is used. In particular, heavy oil at a temperature of 250
By using mesophase pitch-based carbon fibers and mesophase spherical carbon in the form of liquid crystal which are graphitized at 0 ° C. or higher, the electrode capacity of the battery can be increased.

In addition, the carbon material is particularly useful in differential thermal analysis.
It has an exothermic peak at 00 ° C. or higher, more preferably 800 ° C. or higher, and has a graphite structure (10%) by X-ray diffraction (XRD).
1) and diffraction peak _{(P 101)} (100) intensity ratio _{P 10} 1 _{/ P 100} of a diffraction peak _{(P 100)} is 0.7
It is desirably within the range of 2.2. Since a negative electrode containing a carbon material having such a diffraction peak intensity ratio can rapidly absorb and release lithium ions, a combination with a positive electrode containing the positive electrode active material that directs rapid charge and discharge is particularly effective. It is.

Further, as the chalcogen compound capable of inserting and extracting lithium ions, titanium disulfide (Ti)
S ₂ ), molybdenum disulfide (MoS ₂ ), niobium selenide (NbSe ₂ ), or the like can be used. When such a chalcogen compound is used for the negative electrode, the voltage of the secondary battery is reduced, but the capacity of the negative electrode is increased, so that the capacity of the secondary battery is improved. Further, since the diffusion rate of lithium ions in the negative electrode increases, the combination with the positive electrode active material used in the present invention is particularly effective.

Examples of the light metal used for the negative electrode include aluminum, aluminum alloy, magnesium alloy, lithium metal, lithium alloy and the like.

Further, for the negative electrode containing an active material that absorbs and releases lithium ions, for example, the negative electrode active material and the binder are suspended in an appropriate solvent, and this suspension is applied to a current collector and dried. It is manufactured by press bonding afterwards. Examples of the current collector include copper foil, stainless steel foil,
One formed from nickel foil or the like is used. As the binder, for example, polytetrafluoroethylene (PT
FE), polyvinylidene fluoride (PVDF), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and the like can be used.

The separator is formed of, for example, a synthetic resin nonwoven fabric, a polyethylene porous film, a polypropylene porous film, or the like.

As the non-aqueous electrolyte, a solution in which an electrolyte (lithium salt) is dissolved in a non-aqueous solvent is used.

Examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC), dimethyl carbonate (DMC), and the like.
Chain carbonates such as methyl ethyl carbonate (MEC) and diethyl carbonate (DEC), chain ethers such as dimethoxyethane (DME), diethoxyethane (DEE) and ethoxymethoxyethane, tetrahydrofuran (THF), 2-methyltetrahydrofuran ( 2-M
eTHF) and other cyclic ethers and crown ethers, γ-
Fatty acid esters such as butyrolactone (γ-BL), nitrogen compounds such as acetonitrile (AN), and sulfolane (S
L) and sulfides such as dimethylsulfoxide (DMSO).

The above-mentioned non-aqueous solvents may be used alone or as a mixture of two or more. In particular, E
DMC, MEC, DEC, DME, DEE, TH with at least one selected from C, PC, and γ-BL, and at least one selected from EC, PC, and γ-BL
It is desirable to use a mixed solvent comprising at least one selected from F, 2-MeTHF and AN.

In addition, the above-mentioned lithium ions are stored in the negative electrode.
When a negative electrode active material containing a carbon material to be released is used, from the viewpoint of improving the cycle life of a secondary battery including the negative electrode, EC and PC and γ-BL, EC and PC and MEC, EC
And PC and DEC, EC and PC and DEE, EC and AN, E
C and MEC, PC and DMC, PC and DEC, or EC
It is particularly preferable to use a mixed solvent consisting of and DEC.

As the electrolytic solution, for example, lithium perchlorate
(LiClO₄), Lithium hexafluoride (LiPF)
₆), Lithium borofluoride (LiBF₄), Hexafluoride
Lithium (LiAsF)₆), Trifluorometasulf
Lithium sulphonate (LiCF₃SO₃), Bistrifluo
Limethylsulfonylimide lithium [LiN (CF ₃
SO₂)₂] And the like. In particular, Li
PF₆, LiBF₄, LiN (CF₃SO₂)₂Using
This is desirable because conductivity and safety are improved.

It is desirable that the amount of these electrolytes dissolved in the non-aqueous solvent be set in the range of 0.1 to 3.0 mol / l. If the concentration of the electrolyte exceeds 3.0 mol / l, the reaction between the positive electrode active material and the electrolyte becomes active in a high temperature range, which is not preferable because the safety of the battery is reduced.

According to the positive electrode active material, the method for producing the same, and the lithium ion secondary battery using the active material according to the above constitution, the mixed state of each component in the active material is improved, and the particle size of the active material is reduced. Since it is defined in the predetermined range, when used as a positive electrode material of a battery, it becomes possible to realize a secondary battery having both high safety and excellent capacity characteristics.

[0061]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described more specifically with reference to the following examples. The present invention is not limited to the following examples,
The present invention can be implemented with appropriate modifications without departing from the scope defined by the gist of the present invention and the elements described in the claims.

In accordance with the following procedures, lithium ion secondary batteries for positive electrode evaluation according to each of Examples and Comparative Examples as shown in FIG. 1 were prepared, and their characteristics were compared and evaluated.

[Preparation of Positive Electrode Active Material] Example 1 The composition of the positive electrode active material was adjusted to the composition shown in the left column of Table 1.
0.98 moles of _{(Ni 0 .9 Co 0.1) (} OH) 2 and 0.02 moles of boehmite [AlO (OH)], 0 .
05 mol of Li ₂ CO ₃ was dispersed in pure water to prepare a metal salt slurry having a solid concentration of 15% by mass. The metal salt slurry was supplied to a wet pulverizer (nano maker: manufactured by Nanomizer Co., Ltd.) while being pressurized to 100 MPa to pulverize the metal salt and adjust the particle size.

The wet mill has a pair of opposing injection nozzles, injects the metal salt slurry at a predetermined pressure from the injection nozzles at a very high speed, and the impact caused by the collision of the opposing injected metal salt slurries. This is a device that crushes metal salts by force. Then, the 50% cumulative frequency particle diameter (D
50 value) and 99% cumulative frequency particle size (D99 value)
The D50 value was 1.0 μm as measured by EEDS & NORTHRUP Microtrack II.
Nine values were 5.0 μm.

The crushed metal salt slurry is spray-dried by a spray-drying apparatus to prepare aggregated particles, and the obtained aggregated particles are further calcined at a temperature of 750 ° C. for 10 hours, and then cooled at a rate of 1 ° C. per minute. By cooling with
A positive electrode active material for a lithium ion secondary battery according to Example 1 was prepared.

Example 2 The same treatment as in Example 1 was carried out except that each metal salt was blended so as to have the active material composition shown in Table 1, while pulverization was performed five times by a wet pulverizer. Thus, the positive electrode active material according to Example 2 was prepared.

Example 3 The same treatment as in Example 1 was carried out except that each metal salt was blended so as to have the active material composition shown in Table 1, while pulverization was performed 10 times with a wet pulverizer. Thus, the positive electrode active material according to Example 3 was prepared.

Example 4 After dispersing and stirring 0.02 mol of boehmite [AlO (OH)] in 1 liter of pure water, 0.88 mol of boehmite [AlO (OH)] was further added.
A mole of nickel nitrate and 0.1 mole of cobalt nitrate were added and sufficiently stirred to prepare a metal salt slurry. A 0.1 M caustic soda solution was added to this metal salt slurry at a slow rate until the pH value reached 9, and the coprecipitation reaction was allowed to proceed to give N
A precipitate of the i-Co composite hydroxide was produced. Next, the precipitated product was separated by filtration, washed and dried. The resulting dry powder is
The metal component ratio (molar ratio) of Ni: Co: Al is 0.88:
The composite oxide was 0.10: 0.02. Lithium hydroxide was added to the composite oxide, and the temperature was increased to 700
After sintering at 10 ° C. for 10 hours, the mixture was cooled at a cooling rate of 1 ° C. per minute to prepare a positive electrode active material for a lithium ion secondary battery according to Example 4.

Comparative Example 1 The positive electrode active material prepared in Example 3 was further pulverized using a planetary ball mill to obtain a positive electrode active material according to Comparative Example 1.
The D10 value of the active material according to Comparative Example 1 was 0.9 μm.

Comparative Example 2 As shown in Table 1, the metal composition ratio of the positive electrode active material was Li: N
i: Co: Al = 1.0: 0.90: 0.09: 0.0
A positive electrode active material according to Comparative Example 2 was prepared by treating under the same conditions as in Example 4 except that the metal salt was blended so as to be 1.

Comparative Example 3 As shown in Table 1, the metal composition ratio of the positive electrode active material was Li: N
i: Co: Al = 1.0: 0.48: 0.41: 0.1
A positive electrode active material according to Comparative Example 3 was prepared by blending a metal salt so as to be 1, firing at a temperature of 720 ° C. for 10 hours, and cooling at a rate of 1 ° C./min.

[0072] except that it does not implement the pulverized by a wet pulverizer in Comparative Example 4 Example 1 by treatment under the same conditions as in Example 1 to prepare a positive electrode active material according to Comparative Example 4.

Comparative Example 5 A sealed reaction vessel was charged with 420 ml of a 4.0 mol / l sodium hydroxide solution and filled with nitrogen gas. Ni:
2.0 m so that the molar ratio of Co: Al becomes 8: 1: 1
ol / l of an aqueous solution of nickel nitrate, cobalt nitrate and aluminum nitrate were mixed.
The mixture was added dropwise at room temperature over 30 minutes while flowing nitrogen gas. The obtained reaction solution was filtered under a nitrogen atmosphere, washed with water, and then suspended in water to form Ni _0.8 Co _0.1 Al.
A basic salt slurry of _0.1 was obtained. The atomic ratio of the slurry to (Ni + Co + Al) is Li / (Ni + C).
After adding a 3 mol / l aqueous lithium hydroxide solution in an amount corresponding to (o + Al) = 1.05 to the slurry, spray drying was performed by a closed system spray dryer filled with nitrogen. The obtained spray-dried product is put on an alumina board, pre-baked in a tubular furnace (TF-630 type manufactured by Yamada Electric Co., Ltd.) at 350 ° C. for 1 hour under nitrogen flow, and then at 725 ° C. under oxygen flow.
For 15 hours to prepare a positive electrode active material according to Comparative Example 5. The chemical composition of the obtained fired product is Li _1.03 Ni
_{Although it was 0.799} Co _0.103 Al _0.097 O ₂ , the Li-Al-O phase was partially mixed.

Comparative Example 6 Lithium hydroxide, LiNi _0.85 Al _0.05 Co _0.10 O ₂ was obtained so that an active material having a composition of
Nickel hydroxide, aluminum hydroxide, and cobalt hydroxide were mixed at a predetermined molar ratio, fired in air at 650 ° C. for 20 hours, and fired in oxygen at 750 ° C. for 20 hours.
Was prepared. It was confirmed from the X-ray diffraction pattern that the crystals of the positive electrode active material thus obtained were in a single phase.

Comparative Example 7 An aqueous solution of a mixture of nickel nitrate, cobalt nitrate and aluminum nitrate as a nickel salt aqueous solution containing a cobalt salt and an aluminum salt was used. Each using an aqueous sodium hydroxide solution,
A positive electrode active material was prepared as follows.

That is, when the salt concentration is 100 m
1. adjusted to S / cm and containing 0.6 mol / l cobalt sulphate, 0.3 mol / l aluminum sulphate
300 mol / mi of 0 mol / l nickel sulfate aqueous solution
n and an aqueous solution of 6 mol / l ammonium sulfate
50 ml / min was simultaneously and continuously charged. On the other hand, 10m
ol / l aqueous sodium hydroxide solution at pH in the reactor
Was automatically maintained at 12.5. The temperature in the reaction vessel was maintained at 45 ° C., and was constantly stirred by a stirrer. The generated nickel hydroxide was taken out of the overflow tube by overflowing, and was washed with water, dehydrated, and dried to obtain a three-element (Al-Co-Ni) coprecipitated hydroxide.

Next, lithium hydroxide monohydrate and the above-mentioned Al—Co—Ni coprecipitated nickel hydroxide were mixed with (Li: (N
i + Co + Al)) = 1.03: 1.00 at a molar ratio, and heated in oxygen at 650 ° C. for 4 hours.
Li (Ni _0.70 Co
_A positive electrode active material according to Comparative Example 7 including lithium _0.20 Al _0.10 ) O ₂ (aluminum-cobalt-nickel) was synthesized. Li ₂ SO ₄ was used as the obtained positive electrode active material.
A peak was observed, and no single-phase state was obtained.

Comparative Example 8 Lithium hydroxide, nickel hydroxide, cobalt hydroxide, and aluminum hydroxide were each weighed at a molar ratio of 105: 80: 15: 5, and then pulverized and mixed with a ball mill to obtain a mixture. The mixed powder was subjected to pressure molding under a pressure of 1 ton / cm ² , and the obtained molded body was used as a raw material for firing.

This raw material was fired (primary firing) at 700 ° C. for 10 hours in an air stream. The obtained calcined product and pure water were mixed at a weight ratio of 40:60, and then mixed with a wet bead mill.
The slurry was pulverized and dispersed for a time to obtain a slurry having an average particle diameter of 0.4 micron, and was dried and granulated in a spherical shape by a spray dryer. This granulated powder is fired (secondary firing) at 850 ° C. for 2 hours in an oxygen stream, pulverized by a mortar-type pulverizer, and then sized by a screen-type classifier to obtain Comparative Example 8. A positive electrode active material was prepared.

The positive electrode active materials according to Examples and Comparative Examples prepared as described above were subjected to a powder X-ray diffractometer (Ri
nt2000, manufactured by Rigaku Corporation) using (110)
The difference Δ in the Bragg angle between the plane and the (018) plane was measured. In addition, an NMP 0.05% slurry of each positive electrode active material was prepared, and an ultrasonic wave having an output of 100 W and an oscillator frequency of 20 Hz was applied to one slurry.
After irradiation for 10 minutes, the 10% cumulative frequency particle size of the active material was measured using the Microtrack. Table 1 shows the measurement results.

[Preparation of Positive Electrode] The above positive electrode active material powder, acetylene black as a conductive additive, and Teflon (registered trademark) powder as a binder were mixed at a weight ratio of 80: 1.
Each was mixed at a ratio of 7: 3 to form a positive electrode mixture. Next, each positive electrode mixture was attached to a current collector (stainless steel) to prepare a positive electrode having a size of 10 mm × 0.5 mm. The subsequent battery preparation work was performed in a glove box filled with argon gas.

[Preparation of Negative Electrode] A negative electrode was prepared by integrally attaching a lithium metal foil to a stainless steel current collector.

[Preparation of Reference Electrode] A lithium metal foil was integrally attached to a stainless steel current collector,
A 10 mm square reference electrode was prepared.

[Preparation of Nonaqueous Electrolyte] A predetermined amount of LiClO ₄ as an electrolyte was dissolved in a mixed solvent composed of propylene carbonate and dimethoxyethane so as to have a concentration of 1 mol / l. An electrolytic solution was prepared.

[Preparation of Battery for Positive Electrode Evaluation] Battery members such as the positive electrode, the negative electrode, the reference electrode, and the sufficiently dried nonaqueous electrolyte solution prepared as described above were placed in an argon atmosphere, and these battery members were removed. The batteries for evaluation of the lithium ion secondary batteries according to Examples and Comparative Examples each having a beaker-type glass cell as shown in FIG. 1 were respectively assembled.

As shown in FIG. 1, each of the batteries for evaluation 1 includes a glass cell 2 as a battery container, and contains 20 ml of the non-aqueous electrolyte 3 in the glass cell 2. The positive electrode 4 and the negative electrode 6 housed in the bag-shaped separator 5 are laminated with the separator 5 interposed therebetween, and this laminated body is immersed in the non-aqueous electrolyte 3 in the glass cell 2. ing. The two holding plates 7 sandwich and fix the laminate between them. The reference electrode 8 housed in the bag-shaped separator 5 is immersed in the non-aqueous electrolyte 3 in the glass cell 2.

One end of each of the three electrode wires 9 penetrates through the upper surface of the glass cell 2 and is led out, while the other end is connected to the positive electrode 4, the negative electrode 6 and the reference electrode 8. Connected to each other. Such a glass cell 2 is subjected to a sealing treatment so that the air does not enter inside during the charge / discharge test.

[Evaluation of Battery] (Initial Capacity) With respect to the batteries for evaluation of the lithium ion secondary batteries according to Examples and Comparative Examples prepared as described above, the current between the reference electrode and the positive electrode was measured at a current value of 1 mA. The battery was charged until the potential difference reached 4.2 V, and the battery was charged at a constant voltage for 4 hours, and then the current was stopped for 30 minutes. Then 1m
The discharge was performed at the current value of A until the potential difference between the positive electrode reference electrode became 3 V, and the amount of discharge electricity during this time was examined.

(Safety test) Subsequently, charging was performed at a current value of 1 mA until the potential difference between the positive electrode and the reference electrode reached 4.2 V, and then constant voltage charging was performed for 4 hours. This was disassembled in a glove box, and the positive electrode was recovered. About 20 mg of the positive electrode was placed in an Al cell, and the upper pig was swaged. The swine was then taken out into the atmosphere, and the DSC was measured at a heating rate of 5 ° C. per minute to measure the exothermic peak temperature. Table 1 below shows the measurement results.
Shown in

[0090]

[Table 1]

As is clear from the results shown in Table 1 above,
In each of the batteries using the positive electrode active material in which the composition of the positive electrode active material, the 10% cumulative frequency particle size (D10 value), and the difference Δ of the Bragg angle were set in appropriate ranges, the initial capacity was 160 mAh / g. High and the exothermic peak temperature is 2
It was found to be as high as 20 to 280 ° C. and to have both excellent capacity characteristics and safety.

On the other hand, it was reconfirmed that in Comparative Example 1 in which the D10 value of the active material particles was too small and contained fine active material particles, the capacity was reduced, the peak heat generation temperature was low, and the safety as a battery was lowered. did it. In the battery of Comparative Example 2 in which the composition of the active material is out of the range specified in the present invention, the capacity is secured to some extent, but the peak heat generation temperature is low and the safety is poor. On the other hand, in Comparative Example 3, the exothermic peak temperature was 370.
° C and high safety, but there is a drawback that the capacity is reduced. In Comparative Example 4, the exothermic peak temperature was low, and it can be reconfirmed that the safety was not sufficient.

Further, using each of the positive electrode active materials prepared as described above, lithium ion secondary batteries 10 having the structure shown in FIG. 2 according to each of Examples and Comparative Examples were manufactured. Note that, as the negative electrode active material constituting the secondary battery, graphitized MCF (mesoface pitch-based carbon fiber) was used. In addition, as a binder for the positive electrode and the negative electrode,
PVDF was used. Further, an aluminum foil was used as a positive electrode current collector, and a copper foil was used as a negative electrode current collector.

That is, each lithium ion secondary battery 10
, A cylindrical battery container 1 having a bottom made of stainless steel
4 has an insulator 18 at the bottom. Electrode group 15
Are stored in the battery container 14. The electrode group 1
Reference numeral 5 is formed in a structure in which a strip formed by laminating a positive electrode 12, a separator 13, and a negative electrode 11 in this order is spirally wound so that the negative electrode 11 is located outside. The separator 13 is formed of, for example, a nonwoven fabric or a porous polypropylene film. An electrolyte is contained in the battery container 14. The insulating sealing plate 19 having a central portion opened is disposed in the upper opening of the battery container 14, and the vicinity of the upper opening is caulked to make the insulating sealing plate 19 liquid-tight to the battery container 14. Fixed. The positive electrode terminal 20 is fitted in the center of the insulating sealing plate 19. One end of the positive electrode lead 17 is connected to the positive electrode 12.
The other end is connected to the positive electrode terminal 20, respectively. The negative electrode 11 is connected to a battery container 14 serving as a negative electrode terminal via a negative electrode lead (not shown).

With respect to the lithium ion secondary batteries according to Examples and Comparative Examples prepared as described above, the discharge capacity was measured, and a nail penetration test was performed to evaluate battery characteristics and safety. The above discharge capacity was charged at a current value of 1 mA until the potential difference reached 4.2 V, and further discharged at a current value of 1 mA until the potential difference reached 3 V, and the discharge capacity was measured during this period. Note that this discharge capacity is determined by comparing the discharge capacity of the battery according to the first embodiment with a reference value (1).
00).

The nail penetration test was conducted at 4.2 V and 4.
The safety of each cylindrical battery when a large current was passed by forcibly generating a short circuit by inserting a nail having a diameter of 2.5 mm into the battery in a charged state of 3 V and evaluated by the following evaluation criteria.
In other words, regarding the damage level of the battery pierced by nails, those that did not generate liquid leakage were evaluated as ○, those that generated liquid leakage were evaluated as Δ, and the Joule heat due to the large current exceeded a certain critical temperature. Those which caused a runaway reaction and resulted in ignition were evaluated as x. The measurement and evaluation results are shown in Table 1 above.

As is evident from the results shown in Table 1, each of the examples using the positive electrode active material in which the composition of the positive electrode active material has a 10% cumulative frequency particle diameter (D10) and the difference Δ in the Bragg angle are in appropriate ranges. In the example batteries, the capacities are all high,
Even if a nail penetration test is performed, there is no ignition, and excellent safety is provided.

On the other hand, none of the batteries according to the comparative examples satisfy both the safety and the high capacity in the nail penetration test. In particular, in Comparative Example 5 in which a lithium hydroxide solution was spray-dried to prepare a positive electrode active material, as the water was removed from the slurry during the spray-drying, the lithium hydroxide moved with the water. Is formed. In other words, lithium and aluminum react with each other to form a different phase of a Li-Al-O phase, so that battery characteristics deteriorate. On the other hand, in each of the examples, since a combination of metal salts insoluble in the solvent is employed, the composition of the dried product is uniform, and Li-Al-
No O phase is formed.

In Comparative Example 6, since a general synthesis method in which solid-phase raw materials were mixed and fired was used, a composition in which each raw material was uniformly dispersed was not obtained, and the active material was not dispersed. It has been found that the difference Δ in Bragg angle is small and the peak heat generation temperature is also low.

On the other hand, in Comparative Example 7, since the aluminum component was carbonized by coprecipitation, the sulfate groups remained without being completely removed by washing. Since this sulfate group combines with lithium to form a different phase (Li ₂ SO ₄ ), an active material having a predetermined uniform composition was not obtained, and the capacity was significantly reduced.
Further, due to the above-mentioned heterophase, uniform LiNiCoAlO ₂ is not formed, and there are many Li-deficient oxides and a rock salt structure is mixed. Therefore, there is no point in measuring the Bragg angle difference Δ.

On the other hand, in Comparative Example 8, when the raw material mixture was pulverized with a wet bead mill, lithium ions were eluted, and only a heterogeneous composition having a different phase was obtained as in Comparative Example 5. The characteristics deteriorated.

[0102]

As described above, according to the positive electrode active material, the method for producing the same, and the lithium ion secondary battery of the present invention, the mixing state of each component in the active material is improved.
In addition, since the particle diameter of the active material is defined in a predetermined range, when used as a positive electrode material of a battery, it is possible to realize a secondary battery having both high safety and excellent capacity characteristics. .

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a structure of a lithium ion secondary battery for evaluating a positive electrode.

FIG. 2 is a half sectional view showing a structural example of a lithium ion secondary battery according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 Evaluation (lithium ion secondary) battery 2 Glass cell (battery container) 3 Nonaqueous electrolyte 4 Positive electrode 5 Separator 6 Negative electrode 7 Holding plate 8 Reference electrode 9 Electrode wiring 10 Lithium ion secondary battery 11 Negative electrode 12 Positive electrode 13 Separator 14 Battery container 15 Electrode group 16 Insulating paper 17 Positive electrode lead 18 Insulator 19 Insulating sealing plate 20 Positive electrode terminal

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yasuhiro Shirakawa 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture F-term (reference) 5H029 AJ03 AJ12 AK03 AL06 AL07 AM03 AM04 AM05 AM07 CJ02 CJ08 CJ12 HJ02 HJ05 HJ13 5H050 AA08 AA15 BA17 CA08 CB05 CB07 CB08 DA02 EA10 EA24 FA19 GA02 GA05 GA06 GA10 GA12 HA02 HA05 HA13

Claims (6)

[Claims] 1. The general formula Li _{1 + x} Ni _1-yz Co _y
Al _z O ₂ (provided that 0 ≦ x ≦ 0.1, 0.1 ≦ y ≦ 0.
4,0.02 ≦ z ≦ 0.1), and a powder X of the composite oxide particles
The difference in the Bragg angle between the (110) plane and the (018) plane in the line diffraction pattern is [0.29 × (y + z) +0.1
72] degree or more, and a 10% cumulative frequency particle size is 1 μm or more. 2. A step of dispersing a metal salt containing an active material component in a dispersion medium to prepare a metal salt slurry in which the 99% cumulative frequency particle size of the metal salt in the slurry is 5 μm or less; A step of spray-drying the salt slurry to prepare aggregated particles, and baking the aggregated particles to obtain 1
Forming active material particles having a 0% cumulative frequency particle size of 1 μm or more. 3. The method according to claim 2, wherein the metal salt is insoluble or hardly soluble in a dispersion medium. 4. In the step of preparing the metal salt slurry, the metal salt slurry is supplied to a dispersion nozzle at a pressure of 10 MPa or more, and a shock wave or ultrasonic vibration generated by the metal salt slurry flowing in a turbulent state through the dispersion nozzle. 3. The method for producing a positive electrode active material according to claim 2, wherein the metal salt is pulverized by the method. 5. A step of promoting a coprecipitation reaction between a nickel component and a cobalt component in an aluminum salt suspension to produce a nickel-cobalt composite hydroxide, and adding lithium to the obtained nickel-cobalt composite hydroxide. A step of forming active material particles having a 10% cumulative frequency particle diameter of 1 μm or more by adding a salt and firing the mixture. 6. The formula Li _{1 + x} Ni _1-yz Co _y
Al _z O ₂ (provided that 0 ≦ x ≦ 0.1, 0.1 ≦ y ≦ 0.
4,0.02 ≦ z ≦ 0.1), and a powder X of the composite oxide particles
The difference in the Bragg angle between the (110) plane and the (018) plane in the line diffraction pattern is [0.29 × (y + z) +0.1
72] degrees or more, and a positive electrode containing a positive electrode active material having a 10% cumulative frequency particle size of 1 μm or more, a negative electrode arranged with the positive electrode and a separator interposed therebetween, and the positive electrode, the separator, and the negative electrode housed therein. And a non-aqueous electrolyte filled in the battery container.