KR100975875B1 - Cathode active material, method of preparing the same, and cathode and lithium battery containing the material - Google Patents

Abstract

A composite positive electrode active material having a ratio of the average particle diameter D50 of the small diameter active material to the large diameter active material is 6: 1 to 100: 1.

The composite positive electrode active material includes a large diameter positive electrode active material and a small diameter positive electrode active material, and it is possible to improve the filling density by mixing them in a constant particle size and weight ratio, and improved compared to the conventional positive electrode active material including high stability material and high conductivity material It is possible to obtain volume density, discharge capacity, thermal stability, high rate discharge capacity and the like.

Description

Cathode active material, method of preparing the same, and cathode and lithium battery containing the material}

1 is a graph showing the theoretical value of the fractional density according to the ratio of particle size of particles having two different average particle diameters.

2 is a schematic view showing a change in packing density according to a mixing ratio of particles having two different average particle diameters.

3 is a graph showing the results of scanning differential calorimetry (DSC) measurement of the positive electrode obtained in Example 8 and Comparative Example 4. FIG.

The present invention relates to a positive electrode active material, a method for manufacturing the same, and a positive electrode and a lithium battery employing the same. More particularly, the present invention relates to a positive electrode active material having a high volume density, a method of manufacturing the same, and the positive electrode active material, thereby providing high voltage stability, thermal stability, and excellent high rate. A positive electrode and a lithium battery exhibiting discharge characteristics.

The lithium secondary battery has a higher voltage and a higher capacity than a conventional nickel cadmium secondary battery, and the like, and specifically, a lithium transition metal composite oxide represented by LiCoO ₂ , LiNiO ₂ , or LiMn ₂ O ₄ is used as the cathode active material. When carbon, such as graphite and carbon fiber, is used as a cathode, high voltage and high capacity of 4V or more can be obtained, and there is no side effect such as short circuit, and thus it is widely used as a power source for mobile electronic devices such as mobile phones, laptop personal computers, and digital cameras.

However, as mobile devices continue to be lighter, smaller, and become more functional, such as being endowed with various functions, higher levels of capacitance, charge and discharge characteristics, and stability are required, such as use at high or low temperatures. Therefore, there is a problem in that a conventional lithium battery using a certain type of LiCoO ₂ powder as a positive electrode active material cannot obtain the battery characteristics required above, and various conventional technologies have been proposed to satisfy these requirements.

For example, a method of coating the positive electrode active material particles has been proposed, but this causes a complicated process and has a problem that it is difficult to actually apply, and thus a method of improving the packing density of the active material particles has been proposed.

Japanese Patent Laid-Open No. 2000-082466 discloses a positive electrode active material in which the average particle diameter of lithium cobalt composite oxide particles is 0.1 to 50 µm and two peaks are present in the particle distribution. Korean Patent Laid-Open No. 2002-0057825 discloses a cathode active material in which a cathode active material having an average particle diameter of 7 to 25 µm and a cathode active material having an average particle diameter of 2 to 6 µm are mixed. Japanese Patent Laid-Open No. 2004-119218 discloses a positive electrode active material in which a positive electrode active material having an average particle diameter of 7 to 20 µm and a positive electrode active material having an average particle diameter of 10 to 30% of the active material are mixed.

The conventional techniques are to mix two or more kinds of positive electrode active materials having different average particle diameters or to use two or more positive electrode active materials having a maximum average particle size to densify the positive electrode active material to improve battery capacity. However, the positive electrode volume density manufactured by using the positive electrode active material obtained by the prior art was 3.4 g / cm ³ or less, and the use of the positive electrode alone has limitations in improving the high voltage stability, thermal stability, and high rate discharge characteristics of the lithium battery. there was.

Therefore, there is still a need to obtain a composite cathode active material capable of providing a lithium battery having a more adequate mixing and filling of two or more kinds of cathode active materials to improve volume density and improved physical properties such as high voltage stability, thermal stability, and high rate discharge characteristics. to be.

The first technical problem to be achieved by the present invention is to provide a composite cathode active material having improved volume density, high voltage stability, thermal stability and high rate discharge characteristics.

It is a second object of the present invention to provide a cathode and a lithium battery including the composite cathode active material.

The present invention to achieve the first technical problem,

At least one large-diameter active material selected from the group consisting of compounds of Formulas (1) and (2) and at least one small-diameter active material selected from the group consisting of compounds of formulas (2), (3), (4), and carbon-based materials, It provides a composite positive electrode active material having a ratio of the average particle diameter D50 of the small-diameter active material to 6: 1 to 100: 1.

[Formula 1] Li _x Co _1-y M _y O _2-α X _α

Li _x Co _1-yz Ni _y M _z O _2-α X _α

Li _x Mn _2-y M _y O _4-α X _α

[Formula 4] Li _x Co _2-y M _y O _4-α X _α

Wherein 0.90 ≦ x ≦ 1.1, 0 ≦ y ≦ 0.9, 0 ≦ z ≦ 0.5, 0 ≦ α ≦ 2, and M is composed of Al, Ni, Mn, Cr, Fe, Mg, Sr, V and rare earth elements At least one element selected from the group, X is an element selected from the group consisting of O, F, S and P.

According to one embodiment of the present invention, the ratio of the average particle diameter D50 of the small diameter active material to the large diameter active material is preferably 6: 1 to 20: 1.

According to an embodiment of the present invention, the weight ratio of the large-diameter active material and the small-diameter active material is preferably (60 / M _w1 : 40 / M _w2 ) to (90 / M _w1 : 10 / M _w2 ), wherein , M _w1 is the molecular weight of the large diameter active material, M _w2 is It is the molecular weight of a small diameter active material, and W1 and W2 are non-zero integers.

According to an embodiment of the present invention, the weight ratio of the large-diameter active material and the small-diameter active material is preferably (70 / M _w1 : 30 / M _w2 ) to (80 / M _w1 : 20 / M _w2 ), wherein , M _w1 is the molecular weight of the large diameter active material, M _w2 is It is the molecular weight of a small diameter active material, and W1 and W2 are non-zero integers.

According to an embodiment of the present invention, the carbonaceous material is preferably graphite, hard carbon, carbon black, carbon fiber, carbon nanotube (CNT), or the like.

According to an embodiment of the present invention, the press density of each of the large-diameter active material and the small-diameter active material is preferably 2.5 to 4.0 g / cm ³ and 1.0 to 4.0 g / cm ³ .

According to one embodiment of the present invention, it is preferable that the average particle diameter D50 of the large diameter active material is 1 to 25 μm.

According to one embodiment of the present invention, it is preferable that the average particle diameter D50 of the small diameter active material is 0.05 to 5 μm.

The present invention provides a cathode including the composite cathode active material and a lithium battery employing the same in order to achieve the second technical problem.

Hereinafter, the present invention will be described in more detail.

The composite positive electrode active material of the present invention includes a large diameter positive electrode active material and a small diameter positive electrode active material, and includes them in a specific particle size and weight ratio to improve the bulk density compared to the conventional positive electrode active material including the active material while maintaining high safety and It is possible to manufacture a positive electrode and a lithium battery using high conductivity materials with improved high voltage stability, thermal stability and high rate discharge characteristics.

One of the methods for improving the capacitance of a positive electrode for a lithium battery is to optimize the distribution of single or heterogeneous powders. For example, when filling a single type of powder, a certain void is formed between the particles. Therefore, in the case of a hard spherical particle, the filling rate theoretically cannot exceed 64% and the volume density is 3.2g. There is a limit to optimization as it cannot exceed / cm ³ . Therefore, it is preferable to fill the empty space between large diameter particles with small diameter particles by using two kinds of particles having different sizes for denser filling. In this case the ratio of the sizes between these particles becomes important.

In the present invention, the fractional density was calculated according to the ratio of the particle size of the particles having two different average particle diameters. The particles in this calculation were assumed to be hard spherical isotropic particles that did not change shape by filling and the calculations (simulations) used methods common in the art.

As shown in FIG. 1, when the particle size ratio is 1, the density fraction is about 0.6, but as the ratio of the particle size increases, the density fraction continues to increase to 0.8, and when the particle size ratio is 7 or more, it is near 0.85. The pattern converges by value. When the particle size ratio is 7, the point becomes a size at which one small-diameter particle can be filled in a triangular pore size generated between three large-diameter particles. Therefore, when the ratio of the particle size is 7 or more, the small-diameter particles can be filled in the space between the large-diameter particles, so that the effective use of the space can be achieved and an excellent density fraction can be obtained.

Accordingly, in the composite cathode active material of the present invention, at least one element selected from the group consisting of compounds of the following formulas 2, 3, and 4 and carbon-based materials for at least one large-diameter active material selected from the group consisting of the compounds of Formulas 1 and 2 The ratio of the average particle diameter D50 of the caliber active material is 6: 1 to 100: 1. The ratio of the average particle diameter D50 is preferably 6: 1 to 50: 1, more preferably 6: 1 to 20: 1 and most preferably 7: 1 to 20: 1.

[Formula 1] Li _x Co _1-y M _y O _2-α X _α

Li _x Co _1-yz Ni _y M _z O _2-α X _α

Li _x Mn _2-y M _y O _4-α X _α

[Formula 4] Li _x Co _2-y M _y O _4-α X _α

Wherein 0.90 ≦ x ≦ 1.1, 0 ≦ y ≦ 0.9, 0 ≦ z ≦ 0.5, 0 ≦ α ≦ 2, and M is composed of Al, Ni, Mn, Cr, Fe, Mg, Sr, V or rare earth elements At least one element selected from the group, X is an element selected from the group consisting of O, F, S and P. The above Chemical Formulas 1, 2, 3, 4 and carbon-based materials will be described in detail in relation to thermal stability.

In the present invention, in order to effectively fill the space, the ratio of the average particle size between the active material particles having different sizes of the average particle diameter is also important, but in order to increase the final packing ratio of the space, the weight ratio of the particles is also important. As shown in FIG. 2, when two kinds of particles having different particle diameters are mixed, there is a specific range of weight composition ratio showing the highest packing density. In other words, in order to densely fill particles with small particle sizes in the empty spaces between the particles having large particle sizes, they must be mixed in an appropriate weight ratio. In the present invention, the theoretical maximum packing fraction is 0.86 when the particle size ratio is 7: 1 and the weight ratio is 73:27 when two kinds of particles are used, and 0.64 is used when one type of particle is used. appear. Therefore, in the present invention, the ratio of the average particle diameter D50 of the large-diameter active material and the small-diameter active material is 7: 1 to 100: 1, and the mixing ratio of the large-diameter active material and the small-diameter active material is 60:40 to 90:10 by weight ratio. It is preferably in the weight ratio of 70:30 to 80:20.

However, the weight ratio is when the two particles differ only in size and have the same molecular weight. Therefore, when the molecular weight of the particles are different from each other, the weight ratio of the large-diameter active material and the small-diameter active material is preferably (60 / M _w1 : 40 / M _w2 ) to (90 / M _w1 : 10 / M _w2 ), more preferably. Is (70 / M _w1 : 30 / M _w2 ) to (80 / M _w1 : 20 / M _w2 ). _Wherein M _w1 is the molecular weight of the large diameter active material, M _w2 is It is the molecular weight of a small diameter active material, and W1 and W2 are non-zero integers. When the mixing ratio is out of the range, the filling density decreases, thereby making it impossible to achieve the object of the present invention.

Although only two kinds of particles are assumed in the above, it is also possible to use three or more kinds of particles. In this case, it is possible to obtain more improved volume density by having the above average particle diameter ratio and weight ratio between the particles. For example, if the above three kinds of particles are present, a theoretical maximum filling ratio of 0.95 is obtained when the average particle size ratio between them is 49: 7: 1 and the weight ratio between them is 75:14:11, and four kinds of particles are present. And the theoretical maximum filling rate of 0.98 is obtained when the ratio of the average particle diameter between them is 343: 49: 7: 1 and the weight ratio between them is 73: 14; 10: 3. Therefore, in order to further improve the volume density, it is preferable to mix three or more kinds of positive electrode active materials in a constant average particle diameter ratio and weight ratio in a range close to the above ratio.

By increasing the volume density by including the positive electrode active material in a specific particle diameter and weight ratio as described above it is possible to obtain further increased electric capacity. However, in addition to the improved volume density, when the high-safety material and the high-conductivity material are used as the small-diameter positive electrode active material of the composite positive electrode active material, improved thermal safety and high rate discharge characteristics can be obtained. As a result, both volumetric capacity and charge / discharge characteristics are improved. A battery can be obtained.

Therefore, among the compounds of Chemical Formulas 1, 2, 3, 4 and carbon-based materials of the present invention, it is preferable to first use the positive electrode active material having a high capacity as the compound of Chemical Formulas 1 and 2 to improve the electric capacity of the positive electrode. Examples of such materials include, but are not limited to, LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , LiNiO ₂ , LiNi _0.9 Co _0.1 O ₂ , LiNi _0.9 Co _0.1 Al _0.1 O ₂ , but are not limited thereto. All compounds known to be available.

Then, as a small diameter positive electrode active material corresponding to the compounds of Formulas 2, 3, and 4, it is preferable to use a compound which can achieve the stability through structural thermal stability or surface treatment even at a high voltage of 4.2V or higher with respect to lithium metal. Do. When using such a compound, it is possible to charge the battery at a high potential, so that the discharge capacity can be relatively increased, thereby achieving high capacity and being thermally stable, thereby reducing the volume change due to thermal expansion even in many charge and discharge cycles. Overall battery performance is improved. More specifically, the compounds corresponding to Chemical Formulas 2, 3, and 4 may be more specifically LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiMn ₂ O ₄ , LiNi _0.5 Mn _0.5 O ₂ , LiCo _0.95 Mg _0.05 0 ₂ , LiCoPO ₄ and LiNi _1/2 Mn _3/2 O ₄ and the like are preferred, but not limited thereto, and any compound known in the art to be structurally and thermally stable at high voltage may be used.

In addition, the compound that can be used in the small diameter cathode active material corresponding to the carbon-based material is preferably a carbon-based material having excellent conductivity. When these compounds are used, a large amount of electrons can be simultaneously occluded and released, and since their resistance is low, the movement of electrons occurs reversibly. Therefore, even when the discharge current is flowed at a high rate, the voltage does not change so as a stable driving power source. To be able to work, resulting in a wider variety of environments. More specifically, the compound corresponding to the carbonaceous material is preferably graphite, hard carbon, carbon black, carbon fiber, carbon nanotube (CNT), etc. And all carbon-based compounds known in the art to be excellent in conductivity may be used.

In the present invention, the press density of each of the large-diameter active material and the small-diameter active material is preferably 2.5 to 4.0 g / cm ³ and 1.0 to 4.0 g / cm ³ . In the present invention, the press density refers to the appearance press density when the particle powder is pressed by a pressure of 0.3 t / cm ³ . If the press density of the large-diameter particles and the small-diameter particles is smaller than the above range, there is a problem in that the press density of the mixture is lowered, and in the case of a large diameter, the high rate discharge characteristics are lowered.

The press density of the composite cathode active material in which the large-diameter active material and the small-diameter active material are mixed is different depending on the type and density of the electrode plate compressed with the active material when press-pressed at a pressure of 0.3 t / cm ³ . Preference is given to 3.2 to 4.0 g / cm ³ . If it is less than 3.2 g / cm ^{3 It} is difficult to obtain a high battery capacity because the volume density is low, and when it exceeds 4.0 g / cm ³ generally not only out of the obtained density range, there is a problem of fracture of the active material particles.

In the present invention, it is preferable that the average particle diameter D50 of the large diameter active material is 1 to 25 μm. If the average particle diameter D50 is less than 1 μm, there is a problem in that dispersion becomes difficult during electrode forming, and when the average particle diameter D50 exceeds 25 μm, there is a problem that the internal resistance becomes high.

In addition, in the present invention, the average particle diameter D50 of the small diameter active material is preferably 0.05 to 5 μm. When the average particle diameter D50 is less than 0.05 μm, there is a problem in that dispersion becomes difficult during electrode forming, and when the average particle diameter D50 exceeds 5 μm, there is a problem that the internal resistance becomes high.

Next, the positive electrode of the present invention is characterized by being produced including the composite positive electrode active material described above.

For example, the electrode may be formed by forming a positive electrode mixed material including the composite positive electrode active material and a binder into a predetermined shape, or manufactured by applying the positive electrode mixed material to a current collector such as aluminum foil or mesh. Do.

More specifically, a cathode material composition may be prepared and coated directly on an aluminum foil or a mesh current collector, or the cathode active material film cast on a separate support and peeled from the support may be laminated on an aluminum foil or a mesh current collector to form a cathode electrode plate. Get In addition, the anode of this invention is not limited to the form enumerated above, The form other than the enumerated form is possible.

In order to increase the capacity of the battery, it is necessary to charge and discharge a large amount of current, and for this purpose, a material having low electrical resistance of the electrode is required. Therefore, in order to reduce the resistance of the electrode, the addition of various conductive materials is common, and mainly used conductive materials include carbon black and graphite fine particles.

In addition, the lithium battery of the present invention is characterized by being manufactured including the positive electrode. The lithium battery of the present invention can be produced as follows.

First, a negative electrode active material composition is prepared by mixing a negative electrode active material, a conductive material, a binder, and a solvent. The negative electrode active material composition is directly coated and dried on a metal current collector to prepare a negative electrode plate. It is also possible to produce a negative electrode plate by casting the negative electrode active material composition on a separate support and then laminating the film obtained by peeling from the support onto a metal current collector.

Examples of the negative electrode active material include a lithium metal, a lithium alloy, a carbon material, oxides, carbon compounds, carbon silicon compounds, silicon oxide compounds, titanium sulfides, boron carbide compounds, and carbon metal composites mainly composed of metals of the Periodic Tables 14 and 15. Can be mentioned. As the carbon material, those obtained by pyrolysing organic substances under various pyrolysis conditions, artificial graphite, natural graphite, soil graphite, expanded graphite, scaly graphite, and the like can be used.

Carbon black is used as the conductive material, and vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene, and carboxymethyl Cellulose and mixtures thereof, styrene butadiene rubber-based polymers are used, and N-methylpyrrolidone, acetone, water and the like are used as the solvent. At this time, the content of the negative electrode active material, the conductive material, the binder, and the solvent is at a level commonly used in lithium batteries.

As the separator, any one commonly used in lithium batteries can be used. In particular, it is preferable that it is low resistance with respect to the ion migration of electrolyte, and is excellent in electrolyte-moisture capability. More specifically, the material selected from glass fiber, polyester, teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), and combinations thereof may be nonwoven or woven. In more detail, a lithium ion battery uses a rollable separator made of a material such as polyethylene or polypropylene, and a lithium ion polymer battery uses a separator having excellent organic electrolyte impregnation ability. It can be manufactured according to the method.

That is, a separator composition is prepared by mixing a polymer resin, a filler, and a solvent, and the separator composition is directly coated and dried on an electrode to form a separator film, or the separator composition is cast and dried on a support, and then the support The separator film peeled off can be laminated on the electrode and formed.

The polymer resin is not particularly limited, and any material used for the binder of the electrode plate may be used. For example, vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate and mixtures thereof can be used.

Examples of the electrolyte include propylene carbonate, ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butylene carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, and dioxo Column, 4-methyldioxolane, N, N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, dimethyl carbonate LiPF ₆ , LiBF ₄ in a solvent such as methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, dipropyl carbonate, dibutyl carbonate, diethylene glycol or dimethyl ether, or a mixed solvent thereof. , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiSbF ₆ , LiAlO ₄ , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO2) (C _y F _{2y + 1} SO ₂ ) (where x and y are natural waters), one or more electrolytes consisting of lithium salts such as LiCl and LiI or a mixture of two or more thereof are dissolved Can be used.

The separator is disposed between the negative electrode plate and the positive electrode plate as described above to form a battery structure. The battery structure is wound or folded, placed in a cylindrical battery case or a square battery case, and then the organic electrolyte solution of the present invention is injected to complete a lithium ion battery.

In addition, after stacking the battery structure in a bi-cell structure, it is impregnated in an organic electrolyte, and the resultant is placed in a pouch and sealed to complete a lithium ion polymer battery.

The present invention will be described in more detail with reference to the following examples and comparative examples. However, an Example is for illustrating this invention and does not limit the scope of the present invention only by these.

Composite Cathode Active Material and Cathode Manufacturing

Example 1

1.4 g of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ powder having an average particle diameter of 14 μm, 0.6 g of LiCoO ₂ powder having an average particle diameter of 2 μm, 0.6 g of acetylene black powder having an average diameter of 6 μm as a conductive material, and polyvinylidene fluoride as a binder ( PVdF) 0.045g was mixed and 5mL of N-methyl-pyrrolidone was added thereto, followed by stirring for 30 minutes using a mechanical stirrer to prepare a slurry.

The slurry was applied to an aluminum (Al) current collector using a doctor blade to a thickness of about 200 μm, dried, and dried again under vacuum and 110 ° C. to prepare a positive electrode plate. The positive electrode plate was rolled by roll press to form a sheet.

Example 2

The experiment was carried out under the same conditions as in Example 1 except that LiNi _0.8 Co _0.1 Mn _0.1 O ₂ powder having an average particle diameter of 14 μm and LiCoO ₂ powder having an average particle diameter of 1.3 μm were used.

Example 3

The experiment was carried out under the same conditions as in Example 1 except that LiNi _0.8 Co _0.1 Mn _0.1 O ₂ powder having an average particle diameter of 14 μm and LiCoO ₂ powder having an average particle diameter of 0.7 μm were used.

Example 4

The experiment was carried out under the same conditions as in Example 1 except that LiNi _0.8 Co _0.1 Mn _0.1 O ₂ powder having an average particle diameter of 14 μm and LiCoO ₂ powder having an average particle diameter of 0.28 μm were used.

Example 5

1.2 g of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ powder having an average particle diameter of 14 μm and _0.8 g of LiCoO ₂ powder having an average particle diameter of 2 μm were used under the same conditions as in Example 1.

Example 6

1.4 g of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ powder having an average particle diameter of 14 μm and 0.5 g of LiCoO ₂ powder having an average particle diameter of 2 μm were used under the same conditions as in Example 1.

Example 7

1.8 g of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ powder having an average particle diameter of 14 μm and 0.2 g of LiCoO ₂ powder having an average particle diameter of 2 μm were used under the same conditions as in Example 1.

Example 8

Experiment was carried out under the same conditions as in Example 1 except that 1.6 g of LiCoO ₂ powder having an average particle diameter of 12 μm and 0.4 g of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ powder having an average particle diameter of 1 μm were used. .

Example 9

The experiment was carried out under the same conditions as in Example 1, except that 1.6 g of LiCoO ₂ powder having an average particle diameter of 12 μm and 0.4 g of LiMn ₂ O ₄ powder having an average particle diameter of 1 μm were used.

Example 10

The experiment was carried out under the same conditions as in Example 1, except that 1.4 g of LiCoO ₂ powder having an average particle diameter of 14 μm and 0.6 g of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ powder having an average particle diameter of 1 μm were used. .

Example 11

The experiment was carried out under the same conditions as in Example 1 except that 1.4 g of LiCoO ₂ powder having an average particle diameter of 14 μm and 0.6 g of LiNi _0.5 Mn _0.5 O ₂ powder having an average particle diameter of 1 μm were used.

Example 12

The experiment was carried out under the same conditions as in Example 1 except that 1 g of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ powder having an average particle diameter of 7 μm and 1 g of graphite powder having an average particle diameter of 1 μm were used.

Example 13

The experiment was carried out under the same conditions as in Example 1 except that 1 g of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ powder having an average particle diameter of 6 μm and 1 g of graphite powder having an average particle diameter of 1 μm were used.

Example 14

The experiment was carried out under the same conditions as in Example 1 except that 1 g of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ powder having an average particle diameter of 7 μm and 1 g of graphite powder having an average particle diameter of 0.4 μm were used.

Comparative Example 1

The experiment was carried out under the same conditions as in Example 1 except that LiNi _0.8 Co _0.1 Mn _0.1 O ₂ powder having an average particle diameter of 14 μm and LiCoO ₂ powder having an average particle diameter of 10 μm were used.

Comparative Example 2

The experiment was carried out under the same conditions as in Example 1, except that 1 g of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ powder having an average particle diameter of 14 μm and 1 g of LiCoO ₂ powder having an average particle diameter of 2 μm were used.

Comparative Example 3

Except that 2g of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ powder having an average particle diameter of 14 μm was used and LiCoO ₂ powder was not used.

Comparative Example 4

The experiment was carried out under the same conditions as in Example 8 except that only 2 g of LiCoO ₂ powder having an average particle diameter of 12 μm and no LiNi _1/3 Co _1/3 Mn _1/3 O ₂ powder were used.

Comparative Example 5

The experiment was carried out under the same conditions as in Example 12 except that only ₂ g of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ powder having an average particle diameter of 7 μm and no graphite powder were used.

Experimental Example 1 electrode density measurement

The electrode densities of the anodes prepared in Examples 1 to 14 and Comparative Examples 1 to 5 were measured and shown in Table 1 below.

Kinds Example Comparative example One 2 3 4 5 6 7 8 9 10 11 12 13 14 One 2 3 4 5 density
(g / cm ³⁾ 3.55 3.57 3.59 3.60 3.53 3.58 3.52 3.68 3.65 3.7 3.64 3.25 3.22 3.27 3.32 3.39 3.29 3.47 3.30

As shown in Table 1, when the ratio of the average particle diameter between the large-diameter particles and the small-diameter particles is 6: 1 to 100: 1 and the mixing ratio of the particles is 60:40 to 90:10, the embodiments are out of the range. The electrode density was relatively improved compared to the comparative examples. However, Examples 12 to 14 should be compared with Comparative Example 5 as using graphite. This improved electrode density is believed to be due to the more densely packed positive electrode active materials in this range.

Lithium battery manufacturers

Examples 8 to 14 and Comparative Example 4, the graphite electrode to the positive electrode manufactured to 5 as a counter electrode, and a PE separator (separator), and 1 M LiPF ₆ EC (ethylene carbonate) + DEC (diethyl carbonate) (3 The solution dissolved in (7) was used as an electrolyte to prepare a 2000 mAh 18650 cylindrical lithium battery.

Experimental Example 2 Discharge Capacity Measurement

1000 mA until the Li electrode reached 4.2, 4.3, and 4.5 V, respectively, at a current of about 70 mA per gram of the active material using the lithium batteries employing the positive electrodes prepared in Examples 8-14 and Comparative Examples 4-5. The constant current was charged with a current of. After the charging was completed, the cell was subjected to a rest period of about 30 minutes, and then a constant current discharge was performed at a current of about 70 mA per gram of active material until the voltage reached 3.0 V to obtain a discharge capacity per gram. The discharge capacity test results are shown in Table 2 below.

After charging 4.2V
Discharge Capacity (mAh / g) After charging 4.3V
Discharge Capacity (mAh / g) 4.5V after charging
Discharge Capacity (mAh / g) Example 8 143 158 187 Example 9 139 156 183 Example 10 144 159 191 Example 11 138 155 182 Comparative Example 4 145 159 179

As shown in Table 2, in Examples 8 to 11 using the high safety material LiNi _1/3 Co _1/3 Mn _1/3 O ₂ powder, the discharge capacity of about 140mAh / g when charged to 4.2V However, only a high discharge capacity of about 160mAh / g and about 190mAh / g was obtained when charging to 4.3V and 4.5V, respectively.

On the contrary, in the case of Comparative Example 4, there was a problem in that irreversible capacity increased when charging to 4.3V and 4.5V.

Experimental Example 3 Measurement of Thermal Stability

After completion of the initial charge capacity experiment, the lithium batteries employing the positive electrodes of Examples 8 to 11 and Comparative Example 4 were taken out, and the charged positive electrode sheet was taken out and washed, sealed with an aluminum capsule together with an electrolyte, and a scanning differential calorimeter ( The DSC: Differential Scanning Calorimeter was heated at a rate of 5 ° C / min to measure the exothermic onset temperature and calorific value. Exothermic onset temperatures of the above Examples and Comparative Examples are shown in Table 3 and FIG.

Exothermic onset temperature (℃) after 4.3V charging Exothermic onset temperature (℃) after 4.5V charging Example 8 241 221 Example 9 233 218 Example 10 244 225 Example 11 231 218 Comparative Example 4 220 195

As shown in Table 3, Examples 8 to 11 had an exotherm onset temperature of 230 to 245 ° C. when charged to 4.3V and an exotherm onset temperature of 218 to 225 ° C when charged to 4.5V. On the contrary, in the case of Comparative Example 4, the exothermic onset temperatures were 220 and 195 ° C., which were lower than those of the above Examples. In addition, as shown in FIG. 3, the amount of heat generated in Example 8 was also lower than in Comparative Example 4. This is considered to be because the exothermic reaction is suppressed by maintaining a stable chemical state even at high voltage using LiNi _1/3 Co _1/3 Mn _1/3 O ₂ powder which is a high safety material.

Experimental Example 4 Measurement of High Rate Discharge Capacity

Using lithium batteries employing the positive electrodes prepared in Examples 12 to 14 and Comparative Example 5, constant current was charged at a current of 1000 mA until the graphite electrodes reached 4.2 V, respectively. After the battery was fully charged, the battery was subjected to a rest period of about 30 minutes, and then subjected to constant current discharge under conditions of 1C to 10C to measure high rate discharge capacity. Table 4 shows the results of the high rate discharge capacity of the Examples and Comparative Examples.

At 1C
Discharge Capacity (mAh) At 2C
Discharge capacity (mAh) At 5C
Discharge capacity (mAh) At 10C
Discharge Capacity (mAh) Example 12 2010 1980 1860 1703 Example 13 2011 1983 1866 1713 Example 14 2013 1986 1869 1729 Comparative Example 5 2013 1950 1804 1618

As shown in Table 4, in the case of 12 to 14, the discharge capacity decreases as the amount of current increases, but in the case of high-rate discharge such as 10C, the decrease in discharge capacity is less than 15% based on the discharge capacity at 1C. In Comparative Example 5, however, the discharge capacity was reduced by about 20%. In the case of the embodiment, the graphite powder, which is a highly conductive material, is used as the small-diameter particles, so that the electrons are easy to move even when a large amount of current is flowed. It is considered that it is not easy.

The composite positive electrode active material according to the present invention includes a large diameter positive electrode active material and a small diameter positive electrode active material, and it is possible to improve the filling density by mixing them at a constant particle size ratio and weight ratio, and includes a conventional positive electrode active material including a high stability material and a high conductivity material. Compared with the above, it is possible to obtain improved volume density, discharge capacity, thermal stability and high rate discharge capacity.

Claims (12)

At least one large-diameter active material selected from the group consisting of compounds of Formulas (1) and (2) and at least one small-diameter active material selected from the group consisting of compounds of formulas (2), (3), (4) and carbon-based materials, As a composite positive electrode active material having a ratio of the average particle diameter D50 of the small-diameter active material to 6: 1 to 20: 1, The press density of the composite cathode active material is 3.2 to 4.0 g / cm ³ , A composite positive electrode active material wherein the large diameter active material and the small diameter active material are different from each other: [Formula 1] Li _x Co _1-y M _y O _2-α X _α Li _x Co _1-yz Ni _y M _z O _2-α X _α Li _x Mn _2-y M _y O _4-α X _α [Formula 4] Li _x Co _2-y M _y O _4-α X _α Wherein 0.90 ≦ x ≦ 1.1, 0 ≦ y ≦ 0.9, 0 ≦ z ≦ 0.5, 0 ≦ α ≦ 2, and M is composed of Al, Ni, Mn, Cr, Fe, Mg, Sr, V or rare earth elements At least one element selected from the group, X is an element selected from the group consisting of O, F, S and P. The composite cathode active material according to claim 1, wherein a weight ratio of the large-diameter active material and the small-diameter active material is (60 / M _w1 : 40 / M _w2 ) to (90 / M _w1 : 10 / M _w2 ), wherein M _w1 is the molecular weight of the large diameter active material, M _w2 is It is the molecular weight of a small diameter active material, W1 and W2 are nonzero integers, The composite positive electrode active material characterized by the above-mentioned. The composite cathode active material of claim 1, wherein a weight ratio of the large-diameter active material to the small-diameter active material is (70 / M _w1 : 30 / M _w2 ) to (80 / M _w1 : 20 / M _w2 ). _Wherein M _w1 is the molecular weight of the large diameter active material, M _w2 is It is the molecular weight of a small diameter active material, W1 and W2 are nonzero integers, The composite positive electrode active material characterized by the above-mentioned. The method of claim 1, wherein the large-diameter active material is at least one compound selected from the group consisting of LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , LiCoO ₂ , LiNiO ₂ , LiNi _0.9 Co _0.1 O ₂ and LiNi _0.9 Co _0.1 Al _0.1 O ₂ . , The small-diameter active material is LiCoO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiMnO ₂ , LiNi _0.5 Mn _0.5 O ₂ , LiCo _0.95 Mg _0.05 O ₂ , LiCoPO ₄ , LiNi _1/2 Mn _{2 /} Composite active material, characterized in that at least one compound selected from the group consisting of ₃ O ₄ and a carbon-based material. The composite cathode active material of claim 1, wherein the large diameter active material is LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , and the small diameter active material is at least one compound selected from the group consisting of LiCoO ₂ and a carbon-based material. . The method of claim 1, wherein the large diameter active material is LiCoO ₂ , The small diameter active material is at least one compound selected from the group consisting of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiMnO ₂ , LiNi _0.5 Mn _0.5 O ₂ , and a carbon-based material Positive electrode active material The method of claim 1, wherein the carbon-based material is characterized in that at least one selected from the group consisting of graphite, hard carbon, carbon black, carbon fiber and carbon nanotubes (CNT). Composite cathode active material. The composite cathode active material according to claim 1, wherein the press densities of the large-diameter active material and the small-diameter active material are 2.5 to 4.0 g / cm ³ and 1.0 to 4.0 g / cm ³ , respectively. The composite cathode active material according to claim 1, wherein the large diameter active material has an average particle diameter D50 of 1 to 25 µm. The composite positive electrode active material according to claim 1, wherein an average particle diameter D50 of the small diameter active material is 0.05 to 5 µm. A positive electrode comprising the composite positive electrode active material according to any one of claims 1 to 10. A lithium battery comprising the positive electrode according to claim 11.

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