KR101706487B1 - Lithium-ion battery positive electrode active material, lithium-ion battery positive electrode, and lithium-ion battery - Google Patents

Abstract

The present invention provides a positive electrode active material for a lithium ion battery in which cracking of particles is satisfactorily suppressed to improve battery characteristics such as battery life and the coating performance and fixability of a positive electrode mixture using a positive electrode active material at the time of manufacturing a battery .
Composition formula: Li _x Ni _1-y M _y O _{2 + α}
(In the above formula, M is a metal, 0.9? X? 1.2, 0 <y? 0.7, and -0.1?? 0.1)
An average particle diameter D50 of 7 占 퐉 or more and 12 占 퐉 or less,
In the micro compression test, the average mechanical strength when loaded up to a set load of 49 mN at a load speed of 2.67 mN / sec by a diamond impregnator was 10 MPa or more and 60 MPa or less, Wherein an average displacement when the displacement of the indenter from the position where the indenter contacts the indenter to the position where the indenter is pressed to the fired position is in the range of 0.2 占 퐉 or more to 1 占 퐉 or less.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode active material for a lithium ion battery, a positive electrode for a lithium ion battery, and a lithium ion battery. BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]

The present invention relates to a positive electrode active material for a lithium ion battery, a positive electrode for a lithium ion battery, and a lithium ion battery.

Lithium-containing transition metal oxide is generally used for the positive electrode active material of a lithium ion battery. Concretely, it is possible to improve the characteristics (high capacity, cycle characteristics, storage characteristics, internal resistance reduction, rate characteristics) of lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ) In order to increase safety, it is progressing to composite them. Lithium ion batteries in large-sized applications such as automobile use and load leveling are required to have characteristics different from those of conventional cellular phones and personal computers.

The lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or lithium manganese oxide (LiMn ₂ O ₄ ) as described above is a typical example of the positive electrode active material used in the positive electrode active material Material, but each has its advantages and disadvantages. Lithium cobalt oxide is a balanced material such as capacity and safety, but cobalt is a very rare metal, rare metal, which is expensive. Lithium nickel oxide has a considerable battery capacity, but lacks safety. Lithium manganese oxide is very thermally stable, but its capacity has been reported to be low.

Japanese Laid-Open Patent Publication No. 2006-004724

In recent years, ternary positive electrode active materials typified by NiMnCo and NiCoAl have been used in terms of high capacity, safety and cost. For example, when the ternary positive electrode active material has a high nickel ratio, lithium ions It has been reported that the secondary battery is charged and discharged to cause cracks (cracks) in the particles of the positive electrode active material, thereby deteriorating the life of the battery. Generally, a positive electrode mixture is prepared by mixing a positive electrode active material with a conductive auxiliary agent and a binder, and the negative electrode active material is coated on one surface or both surfaces of a current collector made of aluminum foil or the like to produce a positive electrode. When the positive electrode mixture is applied to the current collector, a pressure is applied to the particles of the positive electrode active material, so that the particles may be elastically or plastically deformed. The deformation of the particles of the positive electrode active material causes a problem that the performance of the positive electrode mixture using the positive electrode mixture is deteriorated.

Disclosure of the Invention The present invention is to provide a lithium ion battery capable of satisfactorily suppressing cracking of particles and improving cell characteristics such as battery life and the like and also having good applicability and fixability of a positive electrode mixture using a positive electrode active material at the time of battery production And to provide a positive electrode active material.

The present inventors have focused on the strength of the particles of the positive electrode active material in order to suppress the generation of cracks in the particles of the positive electrode active material caused by charging and discharging of the lithium ion secondary battery and to improve the coating property and fixability of the positive electrode mixture , It is possible to control the hardness of one particle of the positive electrode active material, that is, the micro-compression hardness to a predetermined range, rather than the simple strength, to reduce the cracks of the particles after charging and discharging, Which is very effective in suppressing the deformation of the particles. Further, it has been found that these characteristics are further improved by making the composition of the positive electrode active material a predetermined composition and making the particle diameter of the positive electrode active material uniform.

According to one aspect of the present invention, which is completed on the basis of the above finding, the present invention provides a composition represented by a composition formula: Li _x Ni _1-y M _y O _{2 +}

(In the above formula, M is a metal, 0.9? X? 1.2, 0 <y? 0.7, and -0.1?? 0.1)

An average particle diameter D50 of not less than 7 mu m and not more than 12 mu m and having an average mechanical load at a loading speed of 2.67 mN / sec to a set load of 49 mN by a diamond impregnator to one particle of the secondary particles of the positive electrode active material in the micro compression test The average displacement when the displacement is the moving distance of the indenter from the position where the indenter abuts on the particle to the position where the pressing is started to the split point is 0.2 Lt; RTI ID = 0.0 &gt; 1 &lt; / RTI &gt;

The positive electrode active material for a lithium ion battery according to the present invention has a better average mechanical strength of 15 MPa or more and 60 MPa or less in one embodiment.

In another embodiment, the positive electrode active material for a lithium ion battery according to the present invention is at least one selected from Mn, Co, Cu, Al, Zn, Mg and Zr.

In another embodiment of the positive electrode active material for a lithium ion battery according to the present invention, M is one or more selected from Mn and Co.

In the positive electrode active material for a lithium ion battery according to another embodiment of the present invention, the average mechanical strength and the average displacement of the positive electrode active material for a lithium ion battery are set such that, in the micro compression test, The load is less than 2.67 mN / sec and the load is applied to 49 mN.

The present invention is, in another aspect, a positive electrode for a lithium ion battery using the positive electrode active material for a lithium ion battery according to the present invention.

The present invention is, in another aspect, a lithium ion battery using a positive electrode for a lithium ion battery according to the present invention.

INDUSTRIAL APPLICABILITY According to the present invention, cracks in particles are satisfactorily suppressed, whereby battery characteristics such as battery life are improved, and a positive electrode mixture prepared by using a positive electrode active material at the time of battery manufacturing is excellent in coating properties and fixability. A positive electrode active material can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram showing the relationship between the mechanical strength CS and the displacement in the micro compression test according to the third embodiment. Fig.
2 is a graph showing the relationship between mechanical strength (CS) and displacement in the micro compression test of Comparative Example 2. Fig.

(Constitution of positive electrode active material for lithium ion battery)

As a material of the positive electrode active material for a lithium ion battery of the present invention, a compound useful as a positive electrode active material for a general lithium ion battery positive electrode can be widely used. In particular, lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ) It is preferable to use a lithium-containing transition metal oxide such as lithium (LiMn ₂ O ₄ ). The positive electrode active material for a lithium ion battery of the present invention, which is manufactured using such a material,

Composition formula: Li _x Ni _1-y M _y O _{2 + α}

(In the above formula, M is a metal, 0.9? X? 1.2, 0 <y? 0.7, and -0.1?? 0.1).

M is preferably at least one element selected from Mn, Co, Cu, Al, Zn, Mg, and Zr, and more preferably at least one element selected from Mn and Co.

The positive electrode active material for a lithium ion battery of the present invention is composed of primary particles, secondary particles formed by aggregation of primary particles, or a mixture of primary particles and secondary particles. The average particle diameter D50 of the primary particles, the secondary particles formed by aggregation of the primary particles, or the mixture of the primary particles and the secondary particles is 7 占 퐉 or more and 12 占 퐉 or less. When the average particle diameter D50 is in the range of 7 탆 or more and 12 탆 or less, it is possible to uniformly coat the positive electrode material mixture containing the positive electrode active material at the time of manufacturing the electrode of the lithium ion battery, Can be suppressed. Therefore, when used in a lithium ion battery, battery characteristics such as rate characteristics and cycle characteristics are improved. The average particle diameter D50 is preferably 7 占 퐉 or more and 9 占 퐉 or less.

The micro compression test according to the present invention can be carried out using a micro compression test apparatus. The micro compression testing apparatus is provided with a flat base on which particles to be tested are placed and a diamond indenter having a pressing surface of, for example, 50 to 500 탆 in diameter for compressing and pressing the particles placed on the platform . The micro compression test apparatus is capable of applying a load of, for example, 9.8 to 4903 mN to the particles from the indenter by an electromagnetic force (electromagnetic force). By this, for example, particles having diameters of 1 to 500 탆, That is, one particle can be compressed. The sample is confirmed to be secondary particles of the positive electrode active material by a microscope, and this is regarded as a particle to be measured. The positive electrode active material for a lithium ion battery of the present invention has an average mechanical strength of not less than 10 MPa and not more than 60 MPa when load of 49 mN is applied to one particle of secondary particles of the positive electrode active material at a load speed of 2.67 mN / Hereinafter, the average displacement is 0.2 mu m or more and 1 mu m or less. In the micro compression test according to the present invention, several tens to several hundreds of particles of the positive electrode active material to be tested are sampled and tested by one particle, and the mechanical strength and displacement are measured. The average value of the measurement results is obtained, Mechanical strength and average displacement. The particle is subjected to a load displacement of 2.67 mN / sec to a set load of 49 mN to compressively displace the particle, and the point at which the displacement increases sharply (the point at which the test force required for compression is constant) The mechanical strength and the displacement in the machine direction.

That is, the displacement represents the moving distance of the indenter of the micro compression testing apparatus. More specifically, the particle is compressed and displaced from the position where the indenter abuts against the particle placed on the platform to start the pressing, (I.e., the position at which the indenter is moved).

Further, the mechanical strength CS is obtained from the following formula (1) from JIS R 1639-5.

CS (㎫) = 2.48 × P / πd 2 (1)

[P: test force (N), d: particle diameter (nm)]

Since the secondary particles of the positive electrode active material are formed by aggregation of minute particles (primary particles), when the load is suddenly increased in the micro compression test apparatus, abrupt deformation or the like occurs and the average mechanical strength and average It becomes difficult to accurately measure the displacement. Thus, in the present invention, accurate average mechanical strength and average displacement are measured by applying a load to a particle of the secondary particles of the positive electrode active material at a slow speed of 2.67 mN / sec. The average mechanical strength and average displacement of the positive electrode active material for a lithium ion battery of the present invention were measured in a micro compression test by using a diamond insulator to set a load of 2.67 mN / The load may be up to 49 mN. In the present invention, the minimum load speed which was found to be in the range of the average mechanical strength and the average displacement was 0.446 mN / sec.

When the mechanical strength of one particle of the secondary particles of the positive electrode active material is 10 to 60 MPa and the average displacement is 0.2 to 1 μm, The generation of cracks in the substrate is suppressed. In addition, the coating property and fixability of the positive electrode mixture using such a positive electrode active material are improved. If the mechanical strength is less than 10 MPa, the strength of the positive electrode active material is insufficient and the cracks of particles after charging and discharging are increased. If the mechanical strength exceeds 60 MPa, there is a possibility that the resin becomes hard as the AS resin and is rather fragile (the impact strength is weak). If the displacement is less than 0.2 탆, the strength of the positive electrode active material is insufficient and the cracks of the particles after charging and discharging are increased. If the displacement is more than 1 占 퐉, there is a possibility that soft particles, such as insufficient calcination and sintering, may not be crushed due to insufficient fracture strength and poor crystallinity. The present invention aims at controlling the mechanical strength and displacement of one particle of the positive electrode active material within the above range by examining the entire positive electrode active material rather than the strength of the whole positive electrode active material to reduce the cracks of the particles after charging and discharging, The present invention is based on the knowledge that it is very effective in suppressing particle deformation of the positive electrode active material. By controlling the mechanical strength and displacement of one particle of the secondary particles in this manner, it becomes possible to produce a cathode active material having good crystallinity and good battery characteristics. The average mechanical strength is preferably 10 to 60 MPa, and the average mechanical strength is preferably 15 to 60 MPa.

(Configuration of Positive Electrode for Lithium Ion Battery and Lithium Ion Battery Using It)

The positive electrode for a lithium ion battery according to the embodiment of the present invention can be produced, for example, by mixing the positive electrode active material for a lithium ion battery having the above-described constitution, the positive electrode active material prepared by mixing a conductive auxiliary agent and a binder with one another on one surface or both surfaces . The lithium ion battery according to the embodiment of the present invention is provided with a positive electrode for a lithium ion battery having such a structure.

(Method for producing positive electrode active material for lithium ion battery)

Next, a method for producing a positive electrode active material for a lithium ion battery according to an embodiment of the present invention will be described in detail.

First, a metal salt solution is prepared. The metal is Ni and metal M. The metal M is preferably at least one element selected from Mn, Co, Cu, Al, Zn, Mg and Zr, and more preferably at least one element selected from Mn and Co. The metal salt is preferably a sulfate, a chloride, a nitrate, an acetate or the like, particularly a nitrate. This is because the cleaning process can be omitted because nitric acid salt functions as an oxidizing agent and promotes oxidation of metal in the firing raw material since firing can be performed as it is even if mixed as impurities in the firing raw material. Each metal contained in the metal salt is adjusted so as to have a desired molar ratio. Thereby, the molar ratio of each metal in the positive electrode active material is determined.

Next, lithium carbonate is suspended in pure water, and then a metal salt solution of the metal is added to prepare a metal carbonate slurry. At this time, the lithium-containing carbonate of fine particles precipitates in the slurry. When the lithium compound does not react with a metal salt such as sulfate or chloride during the heat treatment, the precipitate is washed with a saturated lithium carbonate solution and separated by filtration. When the lithium compound reacts as a lithium source during the heat treatment, such as nitrate or acetate, it can be used as a calcination precursor by washing with water without washing and drying it.

Next, the lithium-containing carbonate that has been separated by filtration is dried to obtain a powder of a lithium salt complex (precursor for a lithium ion battery positive electrode material).

Next, a firing vessel having a predetermined capacity is prepared, and the firing vessel is filled with the powder of the precursor for the lithium ion battery cathode material. Next, the firing vessel filled with the powder of the precursor for the lithium ion battery positive electrode is transferred to the firing furnace, and firing is performed. The firing is carried out at a heating rate of 140 to 170 占 폚 / h to 850 to 1000 占 폚 in the temperature raising step, and then kept at the temperature for a predetermined time. In the temperature lowering step, the temperature is cooled from the holding temperature to 300 DEG C at a cooling rate of 70 to 90 DEG C / h, and at that time, air is supplied at 10 m &lt; 3 &gt; / h or more, or oxygen is supplied at 10 m & By this firing condition, heat is uniformly introduced in the temperature raising step, and the conductivity of the heat between the particles becomes good. Further, in the cooling step, cooling is carried out to a predetermined temperature at an appropriate cooling rate, and by appropriate supply of air or oxygen, structural changes such as rearrangement of atoms in the transition metal layer, formation of lamination defects in the transition metal layer, So that the average mechanical strength of the secondary particles can be controlled to 10 to 60 MPa and the average displacement to 0.2 to 1 mu m.

Further, if firing is performed under pressure at 101 to 202 KPa, the amount of oxygen in the composition is further increased, which is preferable.

In the method for producing the positive electrode active material for a lithium ion battery of the present invention, the crystallization is promoted by increasing the firing temperature to control the average particle diameter D50 to 7 mu m or more and 12 mu m or less.

Example

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples.

(Examples 1 to 11)

First, a prescribed amount of lithium carbonate was suspended in 3.2 liters of pure water, and 4.8 liters of a metal salt solution was added. Here, the hydrate of each metal nitrate was adjusted so that each metal had a composition ratio shown in Table 1, and the total metal mole number was 14 mol.

By this treatment, lithium-containing carbonate of fine particles was precipitated in the solution, and this precipitate was separated by filtration using a filter press.

Subsequently, the precipitate was dried to obtain a lithium-containing carbonate (a precursor for lithium ion battery positive electrode material).

Next, a firing vessel was prepared, and the firing vessel was filled with the lithium-containing carbonate. Next, firing was carried out under the firing conditions shown in Table 2. Subsequently, the mixture was cooled to room temperature and then pulverized to obtain a lithium ion secondary battery positive electrode material powder.

(Comparative Examples 1 to 3)

As Comparative Examples 1 to 3, the same treatment as in Examples 1 to 11 was carried out by firing each metal of the raw material in the composition shown in Table 1 under the firing conditions shown in Table 2.

(evaluation)

- Evaluation of Positive Electrode Reconstruction -

The metal content in each of the positive electrode materials was measured by an inductively coupled plasma emission spectrochemical analyzer (ICP-OES), and the composition ratio (molar ratio) of each metal was calculated. It was confirmed that the composition ratios of the respective metals were as shown in Table 1. The oxygen content was measured by the LECO method to calculate?.

- Evaluation of average particle diameter D50 -

The particle cross-section was cut out by FIB, and a SIM image was directly obtained using an FIB apparatus (SMI3050SE) manufactured by ASE Nanotechnology Co., An average particle diameter D50 was calculated by measuring the diameter of a straight direction of only the particles existing on an arbitrary straight line on the SIM image.

- Evaluation of average mechanical strength and average displacement -

A micro compression test using a micro compression test apparatus MCT-211 manufactured by Shimadzu Corporation was carried out. In the micro compression test, first of all, one particle of the secondary particles was compressed and deformed by a diamond impregnator at a loading speed of 2.67 mN / sec and a set load of 49 mN to obtain a point at which the displacement increased sharply The point at which the test force is constant) was determined as the point at which the particles were fired, and the mechanical strength and the displacement at the point were determined.

The mechanical strength (CS) was obtained from the following formula (1) from JIS R 1639-5.

CS (㎫) = 2.48 × P / πd 2 (1)

[P: test force (N), d: particle diameter (nm)]

This measurement was carried out for 20 particles, and the average value thereof was determined.

- Evaluation of Discharge Capacity and Charge / Discharge Efficiency -

Each positive electrode active material, the conductive material and the binder were weighed at a ratio of 90: 5: 5, and the binder was dissolved in an organic solvent (N-methylpyrrolidone). The positive electrode active material and the conductive material were mixed to form a slurry, This was applied to an aluminum foil, dried and pressed to form a positive electrode. Subsequently, a 2032-type coin cell for evaluation in which Li was used as the counter electrode was prepared, and 1 M-LiPF6 was dissolved in EC-DMC (1: 1) as an electrolytic solution. Was measured. The charge-discharge efficiency was calculated from the initial discharge capacity and initial charge capacity obtained by the battery measurement.

These results are shown in Tables 1 to 3.

From Table 3, it can be seen that in Examples 1 to 11, the average particle diameter D50 was not less than 7 mu m and not more than 12 mu m, the average mechanical strength was not less than 10 Mpa and not more than 60 Mpa, and the average displacement was not less than 0.2 mu m and not more than 1 mu m, Discharge capacity and charge / discharge efficiency were good. In addition, the positive electrode material mixture containing the positive electrode active material had good applicability to the current collector.

In Comparative Examples 1 to 3, the average mechanical strength was less than 10 MPa, and in Comparative Examples 1 and 3, the average displacement exceeded 1 占 퐉.

Figs. 1 and 2 show the relationship between the mechanical strength CS and the displacement in the micro compression test of Example 3 and Comparative Example 2, respectively.

Claims (7)

Composition formula: Li _x Ni _1-y M _y O _{2 + α}
Wherein M is at least one selected from Mn, Co, Cu, Al, Zn, Mg and Zr, 0.9? X? 1.2, 0 <y? 0.7 and 0.02? ),
An average particle diameter D50 of 7 占 퐉 or more and 12 占 퐉 or less,
In the micro compression test, one particle of the secondary particles of the positive electrode active material was loaded to a load of 49 mN at a load speed of 2.67 mN / sec by a diamond impregnator, and the mechanical strength obtained by measuring 20 particles was 20 Wherein the average displacement of the 20 particles is 0.2 占 퐉 or more and 1 占 퐉 or less when the moving distance of the indenter from the position where the indenter is in contact with the particles to the position where the pressing is started to the fired position is referred to as the displacement, Positive electrode active material for ion battery. The method according to claim 1,
Wherein the average mechanical strength is 15 MPa or more and 60 MPa or less. delete The method according to claim 1,
Wherein M is at least one selected from Mn and Co. The method according to any one of claims 1, 2, and 4,
Wherein the average mechanical strength and the average displacement are obtained by applying a load of 49 mN to a particle of the secondary particles of the positive electrode active material under a load speed of less than 2.67 mN / Positive electrode active material for lithium ion battery. A positive electrode for a lithium ion battery using the positive electrode active material for a lithium ion battery according to any one of claims 1, 2, and 4. A lithium ion battery using the positive electrode for a lithium ion battery according to claim 6.

Images