KR100566915B1 - Positive electrode for lithium secondary battery with enhanced electrode?s adhesion using lithium manganese oxide - Google Patents

Abstract

The present invention relates to a positive electrode active material composition for a lithium secondary battery having improved the electrode adhesion of the positive electrode, a method for manufacturing the same, and a positive electrode including the same. More specifically, a small amount of a lithium transition metal complex in a lithium manganese oxide having a spinel structure The positive electrode active material composition for the lithium secondary battery containing the oxide increases the adhesive force between the positive electrode active material inside the electrode without affecting the adhesive force between the positive electrode active material and the current collector, thereby improving the adhesion of the electrode and the life of the battery at high temperature. Can be extended.

Lithium secondary battery, lithium manganese oxide, lithium transition metal complex oxide, adhesion

Description

Positive electrode for lithium secondary battery with enhanced electrode's adhesion using lithium manganese oxide}

Figure 1 shows a method for testing the degree of electrode breakage of the anode prepared according to the present invention,

Figure 2 shows the life effect of the battery at a high temperature of the Examples and Comparative Examples prepared according to the present invention.

<Description of Major Symbols in Drawing>

1-current collector; 2-anode; 3-schematic diagram of the appearance of the electrode not broken;

4-Schematic when the electrode is broken

The present invention relates to a positive electrode active material composition for a lithium secondary battery, and more particularly, to a lithium secondary battery using lithium manganese oxide as a positive electrode active material, a small amount of a lithium transition metal composite oxide is added as a positive electrode active material to improve electrode adhesion of the positive electrode. One relates to a cathode active material composition for a lithium secondary battery.

Recently, with the rapid development of the electric, electronic, communication and computer industries, the demand for high-performance, high-safety lithium secondary batteries is gradually increasing. In particular, as the miniaturization, thinning, and lightening of electronic devices are rapidly spreading, The demand for miniaturization and thinning is increasing day by day.

In addition, a lithium manganese composite oxide having a spinel structure is a material that has been studied a lot recently because it has advantages in terms of safety and price compared to other positive electrode active materials of lithium or lithium secondary batteries having a 4 V (volt) potential, and especially safety It is a material that is being actively researched in the field of large-capacity secondary batteries for automobiles, which are the most important characteristics. However, this material has a disadvantage in that its life characteristics are poor because its capacity decreases severely as the charge / discharge cycle proceeds. In particular, in order to actually manufacture a large capacity battery, when the electrode plate is made thick, the adhesive force of the electrode is considerably inferior.

In order to solve these disadvantages, until now, researches on the maintenance of lifespan characteristics have mainly been made mainly related to the properties of the materials themselves. For example, Korean Laid-Open Patent Publication No. 1999-0018077 discloses a lithium secondary battery in which lithium manganese oxide is prepared as a lithium manganese oxide fine powder in which the particles of the powder are octahedral and used as a cathode active material.

Meanwhile, Korean Laid-Open Patent Publication No. 2001-0018401 discloses a lithium secondary battery employing lithium nickel oxide as a cathode active material. However, the addition of a small amount of lithium transition metal composite oxide to lithium manganese oxide as described in the present invention is not disclosed at all, and the excessive use of lithium nickel oxide causes a problem that the adhesion between the electrode and the current collector is inferior.

However, there is almost no research on the positive electrode active material in which a small amount of lithium transition metal complex oxide is added to lithium manganese oxide in the electrode plate manufacturing process of the electrode, in particular, regarding the adhesion of the electrode.

Therefore, in the process of studying the method for improving the performance of a lithium secondary battery using a lithium manganese oxide having a spinel structure, the present inventors have a large amount of lithium manganese oxide having a spinel structure on the plate to produce a large capacity battery. It was confirmed that the coating strength of the electrode is significantly reduced when coating with, and the active material in the electrode without affecting the adhesion between the electrode and the current collector by adding a small amount of lithium transition metal complex oxide having a high pH while looking for a solution to solve this problem It was confirmed that the adhesion between the liver is improved, and based on this, the present invention was completed.

In order to solve the above problems, the present invention improves the adhesion of the electrode, that is, the adhesion between the active material and the current collector by adding a small amount of a high pH lithium transition oxide to the lithium manganese oxide having a spinel structure To improve the life characteristics of the lithium secondary battery.

In order to achieve the above object, the present invention is a positive electrode active material composition for a lithium secondary battery comprising a positive electrode active material, a binder, a conductive material and a solvent, the positive electrode active material is lithium manganese oxide 97 to 99 having a spinel (spinel) structure It provides a cathode active material composition for a lithium secondary battery comprising a weight% and 1 to 3% by weight of the lithium transition metal composite oxide.

The present invention also relates to a cathode for a lithium secondary battery including the cathode active material composition.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention provides a positive electrode plate of a positive electrode for a lithium secondary battery by inserting a small amount of lithium nickel oxide or a lithium transition metal composite oxide having a corresponding pH into a lithium manganese oxide having a spinel structure in a mixing process before coating To manufacture, and the present invention also relates to a lithium secondary battery comprising a positive electrode produced by the above production method.

LiMn _2-x M _x O ₄

In Chemical Formula 1,

M is Al, Li, Co, Cr, Sn, Ti, Ui, Si or B,

x is 0 to 0.1.

The lithium transition metal composite oxide used in the present invention uses a compound represented by the following formula (2), and the pH measured by dissolving 0.5 g of the lithium transition metal composite oxide in 50 ml of water is preferably 10.8-12.0. In addition, the lithium transition metal composite oxide is preferably included in an amount of 1 to 3% by weight when the total content of the lithium manganese oxide having a spinel structure and the lithium transition metal composite oxide is 100.

LiM _1-x A _x O ₂

In Chemical Formula 2,

M is Ni or Co,

A is Al, Li, Co, Cr, Sn, Ti, Ui, Si or B,

x is 0 to 0.5.

More specifically, the positive electrode for a lithium secondary battery uses lithium manganese oxide having a spinel structure as a positive electrode active material, and a binder and a conductive material are added thereto, wherein the lithium transition metal composite oxide is a lithium manganese oxide and a lithium transition metal composite oxide. A slurry prepared by mixing 1 to 3% by weight based on a total content of 100 is prepared by coating on a current collector and rolling. The slurry is preferably coated with a content of 1.8-3.5 mAh / ㎠ on the current collector.

The binder may be polyvinylidene dichloride (PVDF), styrene butadiene rubber (SBR) or polytetrafluoroethylene (PTFE), and the conductive material may be carbon black. , Acetylene black or graphite can be used.

The lithium transition metal composite oxide is preferably coated with 1 to 3% by weight based on the total content of lithium manganese oxide and lithium transition metal composite oxide 100.

In addition, the present invention relates to a lithium secondary battery comprising a cathode, an anode, a separator, and an electrolyte for a lithium secondary battery prepared as described above.

The negative electrode may be prepared by applying and drying a slurry of a negative electrode active material, a binder, and a conductive material on a current collector. In this case, as the negative electrode active material, artificial graphite containing natural carbon, natural graphite, fibrous graphite, crystalline carbon, or amorphous carbon may be used.

The separator is preferably used consisting of polyethylene, polypropylene or a porous membrane of polyethylene and polypropylene.

It is preferable that the said electrolyte solution uses the liquid electrolyte which melt | dissolved lithium salt in the organic solvent, or uses a carbonate type electrolyte solution. The organic solvent is N-methylpyrrolidone (NMP), ethylene carbonate (EC), propylene carbonate (PC), gamma-butyrolacton (GBL), di Mixed solvents such as ethyl carbonate (DEC), dimethyl carbonate (DMC), or ethylmethyl carbonate (EMC) can be used. Lithium salts include LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ or CF ₃ SO ₃ Li and the like can be used.

A battery having a lithium manganese oxide including a lithium transition metal composite oxide prepared according to the present invention as a positive electrode not only has good adhesion between the active materials in the electrode, but also maintains the adhesion between the electrode and the current collector, while improving the high temperature life. give.

Hereinafter, preferred examples are provided to help understanding of the present invention, but the following examples are merely to illustrate the present invention, and the scope of the present invention is not limited to the following examples.

<Example 1>

Assuming that the cathode active material is 100, a cathode active material including 99% by weight of lithium manganese oxide and 1% by weight of lithium nickel composite oxide having a pH of 11.8 as a lithium transition metal composite oxide was prepared. 85% by weight of the positive electrode active material prepared previously for coating the positive electrode plate, 5% by weight of polyvinylidene dichloride (PVDF) as a binder, and 10% by weight of graphite as a conductive material were used as an organic solvent, N-methylpyrrolidone (N-methylpyrrolidone). , NMP) was mixed with a solvent to prepare a slurry. The slurry was coated on an aluminum electrode plate in an amount of 2.0 mAh / cm ² and then dried. After drying, rolling was performed to prepare a positive electrode. In addition, to measure the pH of the electrode, 0.5 g of a material mixed with lithium manganese oxide, a lithium nickel composite oxide, and graphite used as a conductive material in the same ratio as above was dissolved in 50 ml of water to measure pH. The results are shown in Table 1.

<Example 2>

Except for using 98% by weight of lithium manganese oxide and 2% by weight of the lithium nickel composite oxide in Example 1 was carried out in the same manner as in Example 1.

<Example 3>

Except for using 97% by weight of lithium manganese oxide and 3% by weight of lithium nickel composite oxide in Example 1 was carried out in the same manner as in Example 1.

Comparative Example 1

Example 1 was carried out in the same manner as in Example 1 except that 100% by weight of lithium manganese oxide, and not using a lithium nickel composite oxide.

Comparative Example 2

The same process as in Example 1 was performed except that 95 wt% of lithium manganese oxide and 5 wt% of lithium nickel composite oxide were used in Example 1.

Experimental Example 1 Electrode Adhesion Test

Electrode adhesion experiment of the positive electrode prepared in Examples 1 to 3 and Comparative Examples 1 to 2 was performed. In the test method, a strong double-sided tape was attached to the electrode surface and the tensile force was measured using a tensile tester. As a result, the degree of tensile force is shown in Table 1.

In addition, in order to examine the adhesive force between the active materials in the electrode, the electrode was cut into a rectangular shape of 6 cm x 1 cm, and the center portion was folded at an angle of 60 degrees as shown in FIG. 1, and the degree of breakage of the electrode was examined in Table 1 below. Indicated.

In addition, the following experiment was conducted to confirm the life at high temperatures of the positive electrode.

First, the anodes prepared in Examples 1 to 3 and Comparative Examples 1 and 2 were used as the anode, lithium metal was used as the cathode, and ethylene carbonate (EC) and ethylmethyl carbonate (EMC) were 1: 2 as the electrolyte. A lithium secondary battery was prepared using a solution in which 1 mol of LiPF 6 was dissolved in a solvent mixed at a volume ratio of.

In order to measure the life characteristics of the lithium secondary battery at 50 ° C., the voltage range of the charge discharge was 3.4V to 4.3V, and the charge rate and discharge rate were the same at 0.2 C (0.5 mAh / cm 2) rate. Is the same as FIG.

pH Electrode Adhesion (Adhesion / g) Degree of breakage of electrode Other Example 1 9.05 4.596 none Example 2 9.19 4.582 none Example 3 9.30 4.321 none Comparative Example 1 8.84 4.545 fracture Electrode Desorption During Rolling Comparative Example 2 9.64 2.54 none

As shown in Table 1, no breakage of the electrode was observed in the case of the electrode manufactured in Example, but in the case of Comparative Example 1, not only the breakage of the electrode was observed, but also the phenomenon of the electrode detaching when the electrode was rolled. In addition, as shown in Figure 2, in the case of Comparative Example 1 was confirmed that the results are significantly poor in the actual high temperature life test. This is a problem caused by the extremely low adhesion between the active material in the electrode.

In addition, as shown in Table 1, in the case of Comparative Example 2 contained a substance having a high pH, the breakage phenomenon of the electrode was not observed, but it was confirmed that the adhesive strength between the electrode and the current collector is poor because of the addition of excess. In addition, as shown in Figure 2, it was observed that the high temperature life is worse than the embodiment.

On the other hand, in the case of Example, there was no breakage of the electrode at all, and it was found that the service life at a high temperature was also good. In other words, when the lithium transition metal composite oxide containing a small amount of high pH was added to make the positive electrode, not only the adhesion of the electrode was improved, but also the high temperature life was confirmed.

As described above, a positive electrode prepared according to the present invention, that is, a positive electrode including a positive electrode active material composition in which a small amount of lithium transition metal having a high pH is added to a lithium manganese oxide having a spinel structure may not only increase adhesion between active materials in the electrode. In addition, there is an excellent effect in improving the life characteristics, in particular in improving the life characteristics at a high temperature of 45 ℃ or more.

Claims (7)

In the positive electrode active material composition for a lithium secondary battery comprising a positive electrode active material, a binder, a conductive material and a solvent, the positive electrode active material is 97 to 99% by weight lithium manganese oxide having a spinel structure and the lithium transition metal composite oxide 1 to 3 A cathode active material composition for a lithium secondary battery comprising a weight%. The method of claim 1, The lithium manganese oxide is a cathode active material composition, characterized in that the compound represented by the formula (1). <Formula 1> LiMn _2-x M _x O ₄ In Chemical Formula 1, M is Al, Li, Co, Cr, Sn, Ti, Ui, Si or B, x is 0 to 0.1 The method of claim 1, The lithium transition metal composite oxide has a pH of 10.8-12.0, the cathode active material composition, characterized in that the compound represented by the formula (2). <Formula 2> LiM _1-x A _x O ₂ In the formula (2), M is Ni or Co, A is Al, Li, Co, Cr, Sn, Ti, Ui, Si, or B, x is 0 to 0.5. A cathode for a lithium secondary battery, comprising the cathode active material composition of any one of claims 1 to 3. Mixing 97 to 99% by weight of lithium manganese oxide having a spinel structure and 1 to 3% by weight of a lithium transition metal composite oxide (first step); Preparing a slurry by adding and mixing a binder, a conductive material, and an organic solvent to the mixture (second step); And coating the slurry on a current collector and then rolling the third slurry (third step). The method of claim 5, wherein the slurry is coated on a current collector in a content of 1.8 to 3.5 mAh / ㎠. A lithium secondary battery comprising the positive electrode active material composition of any one of claims 1 to 3.

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