KR101657742B1 - Positive electrode for secondary battery and the method for manufacturing the same - Google Patents

Abstract

The present invention relates to a method of manufacturing a positive electrode for a secondary battery having improved dispersibility of a conductive material bonded to a surface of a positive electrode active material by including dry mixing of the positive electrode active material particles and conductive material particles and a positive electrode for a secondary battery produced by such a method .

Description

TECHNICAL FIELD [0001] The present invention relates to a positive electrode for a secondary battery and a method for manufacturing the same,

The present invention relates to a method of manufacturing a positive electrode for a secondary battery and a positive electrode for a secondary battery produced by such a method.

As technology development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. Among secondary batteries, lithium secondary batteries having high energy density and voltage have been commercialized and widely used.

The lithium secondary battery generally comprises a cathode in which a cathode active material layer made of a metal oxide (LiCoO ₂ ) is formed on at least one surface of a cathode current collector, a cathode in which a cathode active material layer made of a carbon material is formed on at least one surface of the anode current collector, And a separator interposed between the anode and the cathode to electrically insulate the cathode and the cathode, and an electrolyte.

On the other hand, the portion having the greatest influence on the capacity of the lithium secondary battery can be referred to as a positive electrode and a negative electrode in which an electrochemical reaction takes place substantially.

The positive electrode or the negative electrode may be prepared by directly applying and drying an electrode slurry in which electrode active material particles, binder resin, and conductive material particles are mixed and dried, or applying the electrode slurry to an upper portion of another support and drying the electrode slurry, And then the laminated film is laminated on the current collector.

However, when the electrode active material slurry is prepared, the conductive material particles 13 are dispersed unevenly due to the difference in size and specific gravity of the particles of the cathode active material particles and the conductive material, and are mainly distributed between the cathode active material particles 11 Therefore, there is a problem that the stability of the electrode is deteriorated due to the increase of the current due to the decrease of the electrical resistance between the cathode active material particles (see FIG. 1).

Therefore, there is a high need for a method of manufacturing a bipolar electrode with a new structure capable of fundamentally solving such problems.

The present invention also provides a method of manufacturing a positive electrode for a secondary battery, comprising the step of dry mixing the positive electrode active material particles and the conductive material particles to improve the dispersibility of the conductive material bonded to the surface of the positive electrode active material.

The present invention also provides a positive electrode for a secondary battery manufactured by the above method and a secondary battery comprising the same.

Hereinafter, the present invention will be described in detail.

In the present invention,

Dry mixing the cathode active material particles and the conductive material particles;

Dispersing a binder resin in the mixture to prepare a cathode active material slurry;

Applying the positive electrode active material slurry on the positive electrode collector; And

And drying the cathode current collector coated with the cathode active material slurry.

In the present invention,

Dry mixing the cathode active material particles and the conductive material particles;

Dispersing a binder resin in the mixture to prepare a cathode active material slurry;

Applying the positive electrode active material slurry to a support;

Drying the cathode active material slurry applied on the support to produce a cathode active material film; And

And laminating the positive electrode active material film on the positive electrode current collector.

In the method of the present invention, the step of dry-mixing the cathode active material particles and the conductive material particles is performed by a mechano chemical method.

The present invention also provides a cathode for a secondary battery produced by the above method.

The present invention also provides a secondary battery including the anode for the secondary battery, the cathode, the separator, and the electrolyte.

In the method of the present invention, it is possible to prepare a positive electrode having improved stability and a secondary battery with improved capacity by providing the positive electrode active material slurry containing the conductive material particles separated and bonded to the surface of the positive electrode active material particles at a uniform interval have.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention and together with the description of the invention serve to further the understanding of the technical idea of the invention, It is not limited.
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an enlarged view of a surface of a cathode active material particle produced by a conventional method;
2 is an enlarged photograph of the surface of the cathode active material particles produced by the mechanochemical method of the present invention.
3 (a) to 3 (c) are enlarged photographs of the surface of the cathode active material layer produced according to one embodiment of the present invention and a comparative example.

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention. Herein, terms and words used in the present specification and claims should not be construed to be limited to ordinary or dictionary meanings, and the inventor may appropriately define the concept of the term to describe its own invention in the best way. It should be construed as meaning and concept consistent with the technical idea of the present invention.

First, a temporary example of the present invention provides a method of manufacturing a positive electrode for a secondary battery. More specifically, in one embodiment of the present invention

Dry mixing the active material particles and conductive material particles;

Dispersing a binder resin in the mixture to prepare a cathode active material slurry;

Applying the positive electrode active material slurry on the positive electrode collector; And

And drying the cathode current collector coated with the cathode active material slurry.

In another embodiment of the present invention,

Dry mixing the cathode active material particles and the conductive material particles;

Dispersing a binder resin in the mixture to prepare a cathode active material slurry;

Applying the positive electrode active material slurry to a support;

Drying the cathode active material slurry applied on the support to produce a cathode active material film; And

And laminating the positive electrode active material film on the positive electrode current collector.

At this time, the method of the present invention may further include a step of drying a cathode active material slurry or a cathode active material on the current collector to form a film, followed by rolling.

In the method of the present invention, the step of preferentially dry mixing the cathode active material particles and the conductive material particles may be performed by a mechano chemical method to secure a kinetic balance between the positive and negative electrodes do. By such a processing method, the dispersibility of the particles is improved, and the conductive material particles can be bonded to the surface of the cathode active material at uniform intervals.

Specifically, the mechanochemical method can be carried out using a Nobilta machine under a dry process without any binder including a solvent such as NMP or an additive such as a binder. Under conditions of room temperature, 10 to 20 A, specifically 16 A current, 2 to 3 W, specifically 2.5 W power and 1500 to 1550 rpm.

Also, the step of mixing the cathode active material particles coated with the conductive material particles and the binder to prepare the active material slurry is performed by a wet mixing process using an organic solvent such as N-methylpyrrolidone (NMP).

The present invention also provides a cathode for a secondary battery manufactured by the method of the present invention.

Specifically, the anode of the present invention comprises an electrode collector; And a positive electrode active material layer formed on the current collector, wherein the positive electrode active material layer comprises positive electrode active material particles (21), conductive material particles (23) coated on the surface of the positive electrode active material particles; And a binder (25) for binding the cathode active material coated with the conductive material particles (see Fig. 2).

Specifically, in the positive electrode of the present invention, the positive electrode active material is _{LiCoO 2, LiNiO 2, LiMnO 2} , LiMn 2 O 4, LiFePO 4, LiNi x Co x -1 O 2 (0 <x <2) , and LiNi _{1 - x- y} Co _x Mn _y O ₂ (0? X? 0.5, 0? Y? 0.5) can be used as the transition metal oxide.

The average particle diameter of the cathode active material particles may be 10 to 20 占 퐉. If the particle diameter is too large or too small, there is a problem that the slurry stability is poor and the kinetic balance of the positive and negative electrodes is not matched.

The conductive material is not particularly limited as long as it is a material ordinarily used in a lithium secondary battery. Examples of the conductive material include natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, channel black, perneic black, lamp black, Black, and may be carbon black, preferably carbon black.

The average particle diameter of the conductive material may be 30 to 50 nm. If the average particle diameter of the conductive material exceeds 50 nm, the performance of the battery may deteriorate. Conversely, if the particle diameter is less than 30 nm, the conductive material may be aggregated between the conductive materials during production of the carbon solution, .

Also, the content of the conductive material particles may be 1 to 1.5 wt% based on the total weight of the anode. If the content of the conductive material particles is more than 1.5% by weight or less than 1% by weight, the lithium metal is produced on the cathode because the kinetic balance of the cathode and the anode is not matched.

Further, in the anode of the present invention, the conductive material particles may be bonded to the surfaces of the respective cathode active material particles at intervals. If the spacing distance between the conductive material particles is large, the performance of the battery may deteriorate. Conversely, if the distance between the conductive material particles is close to each other, the conductive material may aggregate between the conductive materials.

The binder may be selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polymethylmethacrylate, polyvinylpyrrolidone Polyacrylonitrile, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), tetrafluoroethylene, styrene butylene rubber (SBR), carboxymethyl cellulose (CMC), hydroxypropyl Cellulose, regenerated cellulose, starch, sulfonated EPDM, and fluorine rubber, or a mixture of two or more thereof.

The binder content may be in a range usually used in a lithium secondary battery, for example, 1.5 to 2.5% by weight based on the total weight of the cathode active material composition.

The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. Examples of the positive electrode current collector include stainless steel, aluminum, nickel, titanium, sintered carbon or a surface of aluminum or stainless steel Treated with carbon, nickel, titanium, silver or the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible. The cathode current collector is generally formed to a thickness of 3 to 300 mu m.

The positive electrode of the present invention may further include, in addition to the above-described components, other additives such as fillers known in the art. For example, the filler is optionally used as a component for suppressing the expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery. For example, the filler may be an oligomeric polymer such as polyethylene, My; Fibrous materials such as glass fibers and carbon fibers are used.

In addition, the present invention provides a secondary battery comprising a positive electrode produced by the above method, a negative electrode, a separator, and a nonaqueous electrolyte solution containing a lithium salt.

As described above, in the present invention, at the time of preparing the slurry of the positive electrode active material, the positive electrode active material and the conductive material particles are dry-mixed preferentially by using a mechanochemical method in order to secure the kinetic balance between the positive and negative electrodes, The dispersibility of the conductive material particles in the anode active material particles can be improved, and the cathode active material particles containing the conductive material particles coated at a uniform interval can be produced. As a result, the electronic conductivity of the cathode active material surface is reduced, and the electrical resistance is increased (inversely proportional to the resistance and conductivity), thereby reducing the short-circuit current in the electrode. That is, the conductivity pass between the cathode active materials decreases, the electrode resistance increases, and the output characteristic at a high-rate is reduced, so that the stability of the anode can be secured.

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. It should be noted, however, that the examples are for illustrative purposes only and are not intended to limit the scope of the invention.

Example

(Example 1)

1) Manufacture of anode

LiCoO ₂ cathode active material (96.5%) and carbon black conductive material (super P) particles (1.5%) were injected into a mechanochemical equipment (nobilta equipment, manufactured by hosokawa micron corporation) And the reactor were stirred and mixed at a rotation speed of 1520 to 1530 rpm to obtain particles-coated cathode active material particles (see Fig. 3 (a)).

Next, the cathode active material particles coated with the conductive material particles and a binder (polyvinylidene fluoride) (2%) were added to the N-methylpyrrolidone solution and then mixed to prepare a cathode active material slurry.

 Subsequently, the above-mentioned positive electrode active material slurry was coated on an aluminum foil having a thickness of 15 μm, hot air dried, and then rolled using a roll press equipment.

Then, one end of the positive electrode lead was bonded to produce a positive electrode.

2) Manufacture of cathode

The negative electrode active material (98% by weight), CMC (1% by weight) and SBR binder (2% by weight) mixed with artificial graphite and natural graphite (mixing weight ratio = 5: 5) To prepare an anode slurry. The negative electrode slurry was applied to a copper current collector and then dried in a vacuum oven at 120 DEG C to prepare a negative electrode.

3) Manufacture of batteries

A cylindrical secondary battery was fabricated by injecting an electrolyte consisting of the anode, ethylene carbonate (EC) and ethylmethyl carbonate (EMC) solution having a volume ratio of 1: 2 in which the anode and 1M of LiPF ₆ were dissolved.

(Comparative Example 1)

A cylindrical rechargeable battery was prepared in the same manner as in Example 1, except that the LiCoO ₂ cathode active material and the conductive material were mixed in the presence of N-methylpyrrolidone solution at the time of preparing the anode.

Experimental Example : Evaluation of stability

First, the surface of the cathode active material obtained in Example 1 and Comparative Example 1 was observed to be coated with the conductive material particles uniformly spaced on the surface of the cathode active material of Example 1 (see FIG. 2) It can be seen that the conductive material particles were not uniformly applied to the surface of the positive electrode active material produced in Example 1, and coagulation occurred (see Fig. 1).

Thus, the voltage and temperature changes of the secondary battery of Example 1 and the secondary battery of Comparative Example 1 in which the distribution of the conductive material was non-uniform were measured at room temperature and 45 ° C with time, and the results are shown in Table 1 .

At this time, the nail evaluation was conducted through the center of the cell using a nail having a sharp tip at a speed of from 7 m / min, which is the most stable environment, to 0.8 m / min, which is the worst environment.

As shown in the following Table 1, when the secondary batteries of Example 1 and Comparative Example 1 were tested at room temperature three times, it was found that all the batteries were stable without ignition up to 1 m / min, It was found that there was no large charge by ignition. However, after storing the battery at 45 ° C for 2 hours, the secondary battery of Comparative Example 1 ignited all three times even at a stable environment of 5 m / min, whereas the secondary battery of Example 1 had a poorer environment of 3 m / min. &lt; / RTI &gt;

speed
(meter / min) 4.35 V, room temperature After storage at 4.35 V, 45 ° C for 2 hours Comparative Example 1 Example 1 Comparative Example 1 Example 1 7 m / min ㅡ ㅡ 0/3 ㅡ 5 m / min 0/3 ㅡ 3/3 0/3 3 m / min 0/3 ㅡ ㅡ 3/3 1 m / min 0/3 0/3 ㅡ ㅡ 0.8 m / min 3/3 3/3 ㅡ ㅡ

11, 21: Cathode active material
13, 23: Conductive material
25: binder

Claims (18)

Preparing a mixture by dry-mixing the cathode active material particles and the conductive material particles;
Dispersing a binder resin in the mixture to prepare a cathode active material slurry;
Applying the positive electrode active material slurry on the positive electrode collector; And
And drying the cathode current collector coated with the cathode active material slurry,
The cathode active material is LiCoO ₂ , the conductive material is carbon black,
The average particle diameter of the conductive material particles is 30 to 50 nm,
In the step of preparing the mixture, the conductive material particles are bonded to the surface of the cathode active material particles at a uniform interval by a mechanochemical method,
Wherein the mechanochemical method is carried out under a condition of room temperature while stirring the reactor at a current of 10 to 20 A, a power of 2 to 3 W and a rotating speed of 1500 to 1550 rpm. The method according to claim 1,
Wherein the method further comprises a step of drying and then rolling the cathode current collector coated with the cathode active material slurry. delete delete The method according to claim 1,
Wherein the step of preparing the cathode active material slurry is performed by a wet mixing method using an organic solvent. Preparing a mixture by dry-mixing the cathode active material particles and the conductive material particles;
Dispersing a binder resin in the mixture to prepare a cathode active material slurry;
Applying the positive electrode active material slurry to a support;
Drying the cathode active material slurry applied on the support to produce a cathode active material film; And
And laminating the positive electrode active material film on the positive electrode current collector,
The cathode active material is LiCoO ₂ , the conductive material is carbon black,
The average particle diameter of the conductive material particles is 30 to 50 nm,
In the step of preparing the mixture, the conductive material particles are bonded to the surface of the cathode active material particles at a uniform interval by a mechanochemical method,
Wherein the mechanochemical method is carried out under a condition of room temperature while stirring the reactor at a current of 10 to 20 A, a power of 2 to 3 W and a rotation speed of 1500 to 1550 rpm. The method of claim 6,
Wherein the method further comprises a step of laminating the cathode active material film on the current collector and then rolling the anode active material film. delete delete The method of claim 6,
Wherein the step of preparing the cathode active material slurry is performed by a wet mixing method using an organic solvent. Electrode collector; And
And a cathode active material layer formed on the current collector,
The positive electrode active material layer includes a positive electrode active material particle;
A conductive material particle bonded to the surface of the positive electrode active material at a uniform interval; And
And a binder for bonding the cathode active material coated with the conductive material particles to each other,
The anode for a secondary battery according to claim 1, wherein the conductive material has an average particle diameter of 30 nm to 50 nm. Electrode collector; And
And a cathode active material layer formed on the current collector,
The positive electrode active material layer includes a positive electrode active material particle;
A conductive material particle bonded to the surface of the positive electrode active material at a uniform interval; And
And a binder for binding the cathode active material to which the conductive material particles are bound,
The anode for a secondary battery according to claim 6, wherein the conductive material has an average particle diameter of 30 nm to 50 nm. The method according to claim 11 or 12,
Wherein the average particle diameter of the positive electrode active material particles is 10 占 퐉 to 20 占 퐉. delete The method according to claim 11 or 12,
Wherein the content of the conductive material particles is 1 wt% to 1.5 wt% based on the total weight of the positive electrode. The method according to claim 11 or 12,
Wherein the content of the binder is 1.5 wt% to 2.5 wt% based on the total weight of the cathode active material composition. A secondary battery comprising: the positive electrode according to claim 11; and a non-aqueous electrolyte containing a negative electrode, a separator, and a lithium salt. A secondary battery comprising: the positive electrode according to claim 12; and a non-aqueous electrolyte containing a negative electrode, a separator, and a lithium salt.

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