KR20210119905A - Positive electrode active material, positive electrode including the same, and lithium secondary battery employing the positive electrode - Google Patents

Abstract

Provided are a positive electrode active material, a positive electrode including the same, and a lithium secondary battery including the positive electrode, a negative electrode and an electrolyte interposed therebetween, wherein the positive electrode active material includes a lithium cobalt-based active material and a lithium nickel cobalt-based active material, the size and content of the lithium cobalt-based active material are larger than the size and content of the lithium nickel cobalt-based active material, respectively, and the lithium nickel cobalt-based active material is a single particle type.

Description

Positive electrode active material, positive electrode including the same, and lithium secondary battery employing the positive electrode}

It relates to a positive electrode active material, a positive electrode including the same, and a lithium secondary battery employing the positive electrode.

In order to meet the miniaturization and high performance of various devices, in addition to miniaturization and weight reduction of lithium secondary batteries, high energy density is becoming more important. In addition, in order to be applied to fields such as electric vehicles, high capacity, high temperature and high voltage stability of lithium secondary batteries are becoming important.

In order to implement a lithium secondary battery suitable for the above use, various positive electrode active materials are being studied.

As the positive electrode active material, a nickel-based active material or a cobalt-based active material is used. However, the nickel-based active material has a high intrinsic capacity, but has a large average particle size and a hard spherical shape. And since the cobalt-based positive electrode active material is expensive, it is required to lower the manufacturing cost.

One aspect is to provide a positive electrode active material having improved capacity characteristics by improving the mixture density of the positive electrode.

Another aspect is to provide a positive electrode including the above-described positive electrode active material.

Another aspect is to provide a lithium secondary battery having improved cell performance by employing the positive electrode.

According to one aspect,

A positive electrode active material comprising a lithium cobalt-based active material and a lithium nickel cobalt-based active material, wherein the size and content of the lithium cobalt-based active material are respectively larger than the size and content of the lithium nickel cobalt-based active material, and the lithium nickel cobalt-based active material is a single particle A positive active material, which is a one body type active material, is provided.

According to another aspect, a positive electrode including the above-described positive active material is provided.

According to another aspect, there is provided a lithium secondary battery including a positive electrode, a negative electrode, and an electrolyte interposed therebetween.

According to one aspect, a positive electrode active material having improved high voltage characteristics is provided. By using such a positive active material, it is possible to manufacture a positive electrode for a lithium secondary battery with improved positive electrode slurry stability and electrode plate mixture density in the electrode plate manufacturing process. In addition, when the positive electrode is employed, a lithium secondary battery with improved reliability and safety can be manufactured by reducing gas generation at high voltage.

1 is a scanning electron microscope (SEM) photograph showing a state after rolling of an anode according to Example 1;
2 to 5 are SEM photographs showing the state of the positive electrode of Comparative Examples 1 to 4 after rolling, respectively.
6a and 6b show the SEM analysis results of the positive active material obtained according to Preparation Example 1.
7 is a schematic diagram of a lithium secondary battery according to an embodiment.
8 is a graph showing the change in discharge capacity according to the number of cycles in the lithium secondary batteries prepared in Example 1 and Comparative Examples 1 and 3;

Hereinafter, a positive electrode active material according to exemplary embodiments, a method for manufacturing the same, and a positive electrode and a lithium secondary battery including the same will be described in more detail.

A positive electrode active material comprising a lithium cobalt-based active material and a lithium nickel cobalt-based active material, wherein the size and content of the lithium cobalt-based active material is larger than that of the lithium nickel cobalt-based active material, respectively, and the lithium nickel cobalt-based active material is a single particle A positive active material, which is a one body type active material, is provided.

If the size of the lithium cobalt-based active material in the positive electrode active material is smaller than the size of the lithium nickel cobalt-based active material, the active material particles are severely cracked after rolling during the production of the positive electrode. . In addition, when the content of the lithium cobalt-based active material is smaller than that of the lithium nickel cobalt-based active material, the capacity characteristics of a lithium secondary battery employing a positive electrode containing such a positive active material are deteriorated. In addition, if the lithium nickel cobalt-based active material is not of a single body type, the strength of the positive electrode active material is weak, so that the positive electrode active material may be broken during the pressurization process, and the high temperature resistance property is deteriorated due to the generation of gas, which is not preferable.

In the present specification, the term “size” refers to an average particle diameter (D50) when the particles of the lithium cobalt-based active material and the lithium nickel cobalt-based active material are spherical. And when the lithium cobalt-based active material and the lithium nickel cobalt-based active material are not spherical, the term “size” indicates a major axis length.

The average particle diameter can be measured using a PSD (Particle Size Distribution) measuring device or it can be measured through SEM. The major axis length can be measured through SEM or the like.

In this specification, "D50" is analyzed with a particle size analyzer (HORIBA, LA-950 Laser Particle Size Analyzer) to measure the particle size of the particles and when the volume is accumulated from small particles, it means a particle size corresponding to 50% of the total volume. .

When only nickel-based active materials are used as positive electrode active materials, nickel-based active materials have high intrinsic capacity, but particles are hard and spherical. capacity is smaller than expected. In addition, since the nickel-based active material is very hard, it is difficult to improve the volume density of the electrode plate even when press molding is performed during the production of the electrode plate. In addition, the nickel-based active material has a low discharge capacity, which is a problem with a general nickel-based positive electrode active material, and the safety when driven at a high voltage is deteriorated.

Accordingly, the present inventors mixed a lithium-nickel-cobalt-based active material having a small average particle size with a lithium-cobalt-based active material having a large average particle size in order to solve the above-described problem of the nickel-based active material. The space between the lithium cobalt-based active materials, which are particles, can be filled with a lithium-nickel-cobalt-based active material having a small average particle size, thereby effectively improving the mixing density of the positive electrode and the electrode plate volume density.

The lithium cobalt-based active material may have, for example, a spherical shape.

In addition, when a lithium cobalt-based active material is used alone as a positive electrode active material, the positive mix density of the positive electrode is excellent, but the lithium cobalt-based active material is expensive, thus increasing the manufacturing cost. However, the positive electrode active material according to one embodiment uses a lithium cobalt-based active material having a large particle diameter and a lithium nickel cobalt-based active material having a small particle diameter, but using a lithium cobalt-based active material as a main component of the positive electrode active material and a lithium cobalt-based active material alone By solving the problems in the case of manufacturing a positive electrode using can do.

The lithium nickel cobalt-based active material has a single particle form.

As used herein, the term “single particle” is made by increasing the size of the primary particles, which is different from the general shape of the nickel-based positive electrode active material, that is, the primary particles having an average particle diameter of 1 μm or less to form secondary particles. “Single particle” refers to a structure in which particles exist as independent phases in which particles are not agglomerated with each other as a morphology. The particle structure as opposed to such a single particle may include a structure in which small-sized particles (primary particles) are physically and/or chemically aggregated to form relatively large particles (secondary particles). A positive active material having a single particle shape is a positive electrode active material mainly composed of single particles. 90% or more, 95% or more, 99% or more, for example, 99 to 100% of the positive active material is composed of single particles.

When the positive electrode active material having a single particle shape is used, the stability of the positive electrode slurry and the electrode plate mixture density in the positive electrode manufacturing process are improved. And by using such a positive electrode, it is possible to manufacture a lithium secondary battery with reduced gas generation at high voltage and improved reliability and safety.

As the lithium nickel cobalt-based active material has a single particle shape as described above, a movement path for lithium ions to reach the surface of the positive electrode active material becomes longer. Accordingly, lithium ions that have moved to the surface of the positive electrode active material _{react with moisture or CO 2} in the air to obtain Li ₂ CO ₃ , LiOH, etc., and the Li ₂ CO ₃ , LiOH, etc. are adsorbed on the surface of the positive electrode active material Formation of surface impurities can be minimized. In addition, it is possible to prevent problems that may occur due to surface impurities, i.e., decrease in battery capacity, increase in interfacial resistance due to obstruction of lithium ion movement, gas generation due to decomposition of impurities, and swelling of the battery due to this. . As a result, it is possible to improve the capacity characteristics, high temperature stability and charge/discharge characteristics when the positive electrode active material is applied to a battery.

The average particle diameter of the lithium cobalt-based active material is 10 to 20㎛, and the average particle diameter of the lithium nickel cobalt-based active material is 3 to 8㎛.

The lithium cobalt-based active material may be at least one secondary particle or a single particle including an aggregate of two or more primary particles. According to one embodiment, the lithium cobalt-based active material has a single particle form.

When the lithium cobalt-based active material is a secondary particle, the average particle diameter of the lithium cobalt-based active material represents the average particle diameter of the secondary particles. And when the lithium cobalt-based active material is a single particle, the average particle diameter of the lithium cobalt-based active material represents the average particle diameter of a single particle obtained by increasing the size of the primary particles. According to one embodiment, the average particle diameter of the lithium nickel cobalt-based active material refers to the average particle diameter of a single particle obtained by increasing the size of the primary particles.

The average particle diameter of the lithium cobalt-based active material is, for example, 11 to 18 μm, for example, 12 to 17 μm, 12.5 to 17 μm, 13 to 17 μm, 13.5 to 17 μm, 14 to 16.5 μm, or 14 to 16 μm. am. The lithium nickel cobalt-based active material has an average particle diameter of 3 to 8 μm, 3.5 to 7.5 μm, 3.5 to 7 μm, 4 to 7 μm, 4.5 to 6.5 μm, for example, 5 to 6 μm. When the average particle diameter of the lithium cobalt-based active material having a large particle diameter is within the above range, the high-rate characteristic is not deteriorated and the electrode plate mixture density is excellent. In addition, when the average particle diameter of the lithium nickel cobalt-based active material (secondary particles) having a small particle diameter is within the above range, the electrode plate mixture density is excellent without deteriorating the safety of the lithium secondary battery.

The mixing weight ratio of the lithium cobalt-based active material and the lithium nickel cobalt-based active material is 6:4 to 8:2 (1.5; 1 to 4:1), for example, 7:3 to 6:2 (2.3:1 to 3:1). )am. According to one embodiment, the mixing weight ratio of the lithium cobalt-based active material and the lithium nickel cobalt-based active material is 7:3. When the mixing weight ratio of the lithium cobalt-based active material and the lithium nickel cobalt-based active material is within the above range, a positive electrode having excellent capacity per volume characteristics can be manufactured without deterioration of swelling characteristics due to gas generation at high voltage and high temperature.

The positive electrode active material according to one embodiment overcomes the limit of capacity per volume, and thus it is possible to obtain a high-capacity cell while maintaining an excellent positive electrode plate mixture density. According to one embodiment, the anode mixture density is 4.0 g/cc or more, 4.1 g/cc or more, 4.1 to 4.2 g/cc, or 4.15 to 4.2 g/cc.

The porosity of the positive electrode according to one embodiment is 10.0% to 12.1%, 10.3% to 12%, or 10.5% to 11.5%. In the present specification, the porosity of the positive electrode is expressed as a ratio of the volume occupied by the pores to the total volume of the positive electrode.

And according to one embodiment, the compressibility of the positive electrode is less than 42.7%, 42.68% or less, 20 to 42.86%, 22 to 42.5%, 23 to 42%, 24 to 41%, or 25 to 40%. In order to obtain the compressibility of the positive electrode, the coating thickness (d1) of the positive electrode before rolling the positive electrode is measured. Then, after the positive electrode is rolled, the thickness (d2) of the positive electrode is measured. Here, the positive electrode represents a combination of the positive electrode active material layer and the positive electrode current collector.

After the positive electrode is cut to a size of 30 mm X 30 mm, the thickness and weight are measured to obtain the mixture density, and the positive electrode having the same loading level is rolled to calculate the compressibility of the positive electrode according to Equation 1 below.

<Equation 1>

Compressibility (%) = {(d1 - current collector thickness) - (d2 - current collector thickness)}/(d1 - current collector thickness)

The specific surface area of the lithium-cobalt-based active material is 0.1 to 0.3 m ² / g, 0.15 to 0.25 m ² / g, 0.1 to 0.2 m ² / g, 0.15 to 0.18 m ² / g, or 0.160 to 0.165m ² / g a specific surface area of the lithium-nickel-cobalt-based active material is 0.4 to 0.8m ² / g, 0.5 to 0.7m ² / g or 0.60 to 0.65m ² / g. The specific surface area is the BET specific surface area measured by the Brunauer-Emmett-Teller (BET) method.

The lithium cobalt-based active material is a compound represented by the following formula (1), a compound represented by the following formula (2), or a combination thereof.

<Formula 1>

Li _x Co _1-y M _y A ₂

In formula 1, 0.9≤x≤1.2, 0≤y≤0.5, M is Mn, Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al, Si, Cr, Fe, V, A rare earth element or a combination thereof, A is O, F, S, P or a combination thereof,

<Formula 2>

Li _x Co _1-y M _y O _2-z X _z

In Formula 2, 0.9≤x≤1.2, 0≤y≤0.5, 0≤z≤0.5, M is Mn, Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al, Si, Cr, Fe, V, a rare earth element or a combination thereof, and X is F, S, P or a combination thereof.

The lithium nickel cobalt-based active material of the positive electrode active material according to one embodiment is a compound represented by the following Chemical Formula 3, a compound represented by Chemical Formula 4, or a combination thereof.

<Formula 3>

Li _x Ni _1-y Co _y O _2-z X _z

In Formula 3, 0.9≤x≤1.2, 0<y≤0.5, 0≤z≤0.5,

X is F, S, P or a combination thereof,

<Formula 4>

Li _x Ni _1-yz Co _y M _z O _2-a X _a

In Formula 4, 0.9≤x≤1.2, 0<y≤0.5, 0<1-yz, 0≤z≤0.5, 0≤a<2,

M is Mn, Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al, Si, Cr, Fe, V, a rare earth element or a combination thereof, and X is F, S, P or a combination thereof It is a combination.

In Formulas 3 and 4, x is 1 to 1.05, 1 to 1.03, or 1 to 1.02, and y is, for example, 0.05 to 0.2. And in Formula 4, M is Al, and z is, for example, 0.005 to 0.05.

The lithium cobalt-based compound is, for example, a compound represented by the following formula (5).

<Formula 5>

Li _x Co _a O _2+α

In Formula 5, 0.9≤x≤1.2, 0.98≤a≤1.00, and -0.1≤α≤0.1.

The lithium cobalt-based compound according to an embodiment is, for example, LiCoO ₂ .

The lithium nickel cobalt-based active material according to an embodiment is a compound represented by the following Chemical Formula 7 or a compound represented by the following Chemical Formula 8.

<Formula 7>

Li _x Co _a Ni _b Mn _c O ₂

In formula 7, 0.9<x<1.2, 0<a<0.5, 0<b<1, 0<c<1, a+b+c=1,

<Formula 8>

Li _x Co _a Ni _b Al _c O ₂

In Formula 8, 0.9<x<1.2, 0<a<0.5, 0<b<1, 0<c<1, a+b+c=1.

In Formulas 7 and 8, x is 1.0 to 1.2, or 1.0 to 1.1, a is 0.001 to 0.45, 0.01 to 0.4, 0.01 to 0.3, 0.01 to 0.2, 0.01 to 0.1, or 0.01 to 0.02, and b is 0.6 to 0.99, 0.7 to 0.98, or 0.75 to 0.95. c is 0.001 to 0.3, 0.001 to 0.2, 0.001 to 0.1, 0.001 to 0.05 or 0.001 to 0.01.

The lithium nickel cobalt-based active material is, for example, LiNi _0.9 Co _0.09 Al _0.01 O ₂ , LiNi _0.9 Co _0.09 Mn _0.01 O ₂ , Li _1.05 Ni _0.9 Co _0.09 Al _0.01 O ₂ , Li _1.05 Ni _0.9 Co _0.09 Mn _0.01 O ₂ , Li _1.05 Ni _0.5 Co _0.2 Mn _0.3 O ₂ , Li _1.1 Ni _0.5 Co _0.2 Mn _0.3 O ₂ , Li _1.05 Ni _0.6 Co _0.2 Mn _0.2 O ₂ , Li _1.1 Ni _0.6 Co _0.2 Mn _0.2 O ₂ , and the like.

According to one embodiment, by adjusting the size of single particles of the lithium nickel cobalt-based active material, when implementing a lithium secondary battery using the same, low-temperature characteristics, rate characteristics improvement, and gas generation at high voltage are reduced, and reliability and safety can be secured. .

In the lithium nickel cobalt-based active material according to an embodiment, the mixture molar ratio of the transition metal of the lithium nickel cobalt-based active material precursor and lithium of the lithium precursor is adjusted in the manufacturing process of the positive electrode active material, and heat treatment conditions (heat treatment temperature, atmosphere and time), etc. are controlled. By adjusting the size of the primary and secondary particles of the positive electrode active material, the specific surface area is reduced and residual lithium is removed as much as possible to suppress the surface side reaction between the residual lithium and the electrolyte. In addition, by controlling the manufacturing process as described above, it is possible to obtain a positive electrode active material having improved crystallinity and securing stability at high voltage. _{The content of 2} CO ₃ is 0.05 to 0.1% by weight. Here, the content of LiOH and Li ₂ CO ₃ is measured through a titration method.

The content of lithium carbonate through GC-MS analysis in the lithium nickel cobalt-based active material is 0.01 to 0.05 wt% based on 100 wt% of the lithium nickel cobalt-based active material.

As described above, when the content of the residual lithium is small, the side reaction between the residual lithium and the electrolyte can be suppressed to suppress gas generation at high voltage and high temperature, and thus the safety of the positive electrode active material is excellent. In addition, when the content of LiOH is small, the pH value of the slurry is lowered in the positive electrode slurry manufacturing process to make the positive electrode slurry in a stable state so that a uniform electrode plate coating operation is possible. This reduction in LiOH ensures slurry stability in the slurry manufacturing process for coating the positive electrode plate.

The positive active material has an onset point temperature of 250 to 270 °C in differential scanning calorimetry analysis, which is higher than that of a conventional commercial NCM, and has a characteristic that the instantaneous calorific value of the main peak is reduced. By exhibiting these characteristics, the high temperature stability of the lithium ion secondary battery using the positive electrode active material is excellent.

If the above-described positive active material is used, side reactions of the electrolyte may be suppressed, and thermal stability and structural stability of the positive active material may be improved, thereby improving stability and charge/discharge characteristics of a lithium secondary battery including the positive active material.

The manufacturing method of the single particle lithium nickel cobalt-based active material will be described in more detail as follows.

The lithium nickel cobalt-based active material precursor 300 to 800 ℃, 320 to 780 ℃, for example, 350 to 750 ℃, 400 to 700 ℃, for example, a step of primary heat treatment at 400 to 600 ℃, lithium nickel cobalt-based active material precursor The mixing molar ratio of transition metal of lithium and lithium precursor

The resultant of the first heat treatment and the lithium precursor are mixed so as to be 1:1.05 or more, and the resultant is mixed at 900 to 1200 °C, 920 to 1150 °C, 930 to 1130 °C, 950 to 1100 °C, 1000 °C to 1100 °C, 1000 °C to 1050 °C. , 1010 °C to 1050 °C, or 1020 °C to 1045 °C comprising the step of secondary heat treatment.

As described above, the lithium content of the lithium precursor is excessively used compared to the transition metal of the lithium nickel cobalt-based active material precursor. The mixing molar ratio of the transition metal of the lithium nickel cobalt-based active material precursor and lithium of the lithium precursor is, for example, 1:1.05 to 1:1.1, or 1:1.05 to 1:1.08.

The primary heat treatment and the secondary heat treatment are performed in an oxidizing gas atmosphere.

The oxidizing gas atmosphere refers to an atmosphere or a gas atmosphere containing oxygen. The oxygen content in the oxygen-containing gas atmosphere is 20 to 40% by volume.

The primary heat treatment is performed in an oxidizing gas atmosphere for 1 to 5 hours, and the secondary heat treatment is performed in an oxidizing gas atmosphere for 5 to 10 hours.

When the first heat treatment is within the above range, a uniform lithium nickel cobalt-based active material may be formed. And when the secondary heat treatment is within the above range, there is no problem in that the electrochemical properties such as capacity and efficiency are rapidly lowered due to excessive grain growth, and the crystallinity is poor due to insufficient grain growth, entering or scattering inside the structure As the amount of lithium decreases, a positive electrode active material having excellent performance may be obtained without a problem in that the residual lithium content on the surface of the positive electrode active material increases.

The mixing molar ratio of the transition metal of the lithium nickel cobalt-based active material precursor and lithium of the lithium precursor is controlled to be 1:1.05 or more, 1:1.05 to 1:1.1, or 1:1.05 to 1:1.08. If the mixing molar ratio of lithium to transition metal is less than the above range, a deficiency of lithium required at the same temperature occurs, which makes cation mixing, crystallinity reduction, and granular growth difficult. In the lithium nickel cobalt-based active material precursor, the transition metal is the sum of all metals except lithium.

The lithium nickel cobalt-based active material precursor may be prepared by co-precipitating a nickel precursor and a precursor of another transition metal. For example, the lithium nickel cobalt-based active material precursor may be a hydroxide including nickel, cobalt, and other metals.

The lithium nickel cobalt-based active material precursor may be prepared by, for example, mixing a nickel precursor, a cobalt precursor, and a manganese precursor with a first solvent.

The nickel precursor, cobalt precursor, and manganese precursor may be any material that can be used in the art.

Nickel sulfate, nickel chloride, nickel nitrate, etc. are used as the nickel precursor.

Cobalt sulfate, cobalt chloride, cobalt nitrate, etc. are used as the cobalt precursor, and manganese sulfate, manganese chloride, manganese nitrate, etc. are used as the manganese precursor.

Contents of the nickel precursor, the cobalt precursor, and the manganese precursor are stoichiometrically controlled to obtain a desired lithium nickel cobalt-based active material precursor.

As the first solvent, water, ethanol, propanol, butanol, and the like are used. And the content of the first solvent is 100 to 2000 parts by weight based on 100 parts by weight of the total weight of the nickel precursor, the cobalt precursor, and the manganese precursor.

When mixing the lithium nickel cobalt-based active material precursor and the lithium precursor, a second solvent may be used. As the second solvent, water, ethanol, butanol, propanol, etc. are used in the same manner as in the above-described first solvent, and the content of the second solvent is 100 to 2000 parts by weight based on 100 parts by weight of the lithium precursor.

A complexing agent and a pH adjusting agent are added and mixed to the mixture containing the lithium nickel cobalt-based active material precursor and the lithium precursor.

The lithium nickel cobalt-based active material precursor is, for example, a compound represented by the following Chemical Formula 3-1.

<Formula 3-1>

Ni _1-yz Co _y M _z (OH) ₂

In Formula 3-1, 0<y≤0.5, 0<1-yz, 0≤z≤0.5,

M is Mn, Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al, Si, Cr, Fe, V, a rare earth element or a combination thereof.

The lithium precursor uses at least one selected from lithium hydroxide, lithium carbonate, lithium sulfate, lithium nitrate, and lithium fluoride.

As an example of a complexing agent, aqueous ammonia is used as an ammonium ion supplying agent, As an example of a pH adjusting agent, sodium hydroxide solution etc. are used.

The pH of the resultant is controlled in the range of 11 to 13 by adjusting the content of the pH adjusting agent.

A lithium nickel cobalt-based active material can be obtained by obtaining a precipitate from the resultant and performing washing and secondary heat treatment using pure water.

In the manufacturing method, the mixing process may be performed by a wet or dry method.

The single-particle lithium cobalt-based active material was performed in the same manner as in the above-described method for preparing a single-particle lithium nickel cobalt-based active material, except that a lithium cobalt-based active material precursor was used instead of a lithium nickel cobalt-based active material precursor. A system active material can be prepared.

The lithium cobalt-based active material precursor is, for example, a compound represented by the following formula (6).

<Formula 6>

Co _1-y M _y (OH) ₂

In Formula 6, 0≤y≤0.5, M is Mn, Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al, Si, Cr, Fe, V, rare earth element or a combination thereof. .

The lithium cobalt-based active material precursor according to the embodiment may be obtained by performing the same method as the above-described method for preparing the lithium-nickel-cobalt-based active material precursor, except that the nickel precursor is not used.

A positive electrode according to another embodiment includes the above-described positive electrode active material.

The positive electrode is a current collector; and a positive electrode active material layer containing the positive electrode active material according to an embodiment disposed on the current collector.

The positive electrode may be manufactured by, for example, a method in which a positive active material composition including the positive active material and a binder is molded into a predetermined shape, or the positive active material composition is applied to a current collector such as an aluminum foil.

Specifically, a cathode active material composition in which the cathode active material, a conductive material, a binder, and a solvent are mixed is prepared. The positive electrode active material composition is directly coated on a metal current collector to manufacture a positive electrode plate. Alternatively, the positive electrode active material composition may be cast on a separate support, and then a film peeled from the support may be laminated on a metal current collector to manufacture a positive electrode plate. The positive electrode is not limited to the above-listed shapes and may be in a shape other than the above-mentioned shapes.

The positive electrode may additionally include a conventional positive electrode active material known in the art.

The conventional positive electrode active material may include at least one selected from the group consisting of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium manganese oxide, but is not necessarily limited thereto. Any positive electrode active material available in the technical field may be additionally used.

For example, Li _a A _1-b B _b D ₂ (in the above formula, 0.90≤a≤1.8, and 0≤b≤0.5); Li _a E _1-b B _b O _2-c D _c (in the above formula, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); LiE _2-b BbO _4-c D _c (wherein 0≤b≤0.5, 0≤c≤0.05); Li _a Ni _1-bc Co _b B _c D _α (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li _a Ni _1-bc Co _b B _c O _2-α F _α (in the above formula, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li _a Ni _1-bc Co _b B _c O _2-α F ₂ (in the above formula, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li _a Ni _1-bc Mn _b B _c D _α (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li _a Ni _1-bc Mn _b B _c O _2-α F _α (in the above formula, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li _a Ni _1-bc Mn _b B _c O _2-α F ₂ (in the above formula, 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, 0<α<2); Li _a Ni _b E _c G _d O ₂ (in the above formula, 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0.001≤d≤0.1); Li _a Ni _b Co _c Mn _d G _e O ₂ (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); Li _a NiG _b O ₂ (in the above formula, 0.90≤a≤1.8, 0.001≤b≤0.1); Li _a CoG _b O ₂ (in the above formula, 0.90≤a≤1.8, 0.001≤b≤0.1); Li _a MnG _b O ₂ (in the above formula, 0.90≤a≤1.8, 0.001≤b≤0.1); Li _a Mn ₂ GbO ₄ (in the above formula, 0.90≤a≤1.8, 0.001≤b≤0.1); QO ₂ ; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiIO ₂ ; LiNiVO ₄ ; Li _(3-f) J ₂ (PO ₄ ) ₃ (0≤f≤2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0≤f≤2); And LiFePO ₄ A compound represented by any one of the formulas may be used.

In the above formula, A is Ni, Co, Mn, or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn, or a combination thereof; F is F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; I is Cr, V, Fe, Sc, Y, or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.

Of course, a compound having a coating layer on the surface of the compound may be used, or a mixture of the compound and a compound having a coating layer may be used. The coating layer may include a coating element compound of oxide or hydroxide of the coating element, oxyhydroxide of the coating element, oxycarbonate of the coating element, or hydroxycarbonate of the coating element. The compound constituting these coating layers may be amorphous or crystalline. As the coating element included in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof may be used. In the coating layer forming process, any coating method may be used as long as it can be coated by a method that does not adversely affect the physical properties of the positive electrode active material by using these elements in the compound (eg, spray coating, immersion method, etc.). Since the content can be well understood by those engaged in the field, a detailed description thereof will be omitted.

For example, LiNiO ₂ , LiCoO ₂ , LiMn _x O _2x (x=1, 2), LiNi _1-x Mn _x O ₂ (0<x<1), LiNi _1-xy Co _x Mn _y O ₂ (0 ≤x≤0.5, 0≤y≤0.5), LiFeO ₂ , V ₂ O ₅ , TiS, MoS, etc. may be used.

Carbon black, graphite fine particles, etc. may be used as the conductive material, but are not limited thereto, and any conductive material that can be used as a conductive material in the art may be used. For example, graphite, such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum and nickel powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; A conductive material such as a polyphenylene derivative may be used.

The binder includes vinylidene fluoride/hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene and mixtures thereof, or styrene butadiene rubber-based polymer, etc. may be used, but is not limited thereto, and any binder that can be used as a binder in the art may be used.

As the solvent, N-methylpyrrolidone, acetone, or water may be used, but the solvent is not limited thereto and any solvent that can be used in the art may be used.

The content of the positive active material, the conductive agent, the binder, and the solvent is a level commonly used in a lithium secondary battery. At least one of the conductive agent, the binder, and the solvent may be omitted depending on the use and configuration of the lithium secondary battery.

The true density of the positive electrode active material according to an embodiment means the intrinsic density of the electrode active material without pores. The true density of the positive active material is 4.76 to 5.10 g/cc, 4.8 to 5.05 g/cc, or 4.9 to 5.0 g/cc.

A lithium secondary battery according to another embodiment employs a positive electrode including the positive electrode active material, a negative electrode, and an electrolyte interposed therebetween. The lithium secondary battery may be manufactured in the following way.

First, a positive electrode is manufactured according to the above method of manufacturing the positive electrode.

Next, a negative electrode active material composition is prepared by mixing the negative electrode active material, the conductive material, the binder and the solvent. The negative electrode active material composition is directly coated and dried on a metal current collector to prepare a negative electrode plate. Alternatively, the negative electrode active material composition may be cast on a separate support, and then a film peeled from the support may be laminated on a metal current collector to manufacture a negative electrode plate.

The negative active material is not particularly limited to those generally used in the art, but more specifically, lithium metal, a metal alloyable with lithium, a transition metal oxide, a transition metal sulfide, a material capable of doping and dedoping lithium, A material capable of reversibly intercalating and deintercalating lithium ions, a conductive polymer, and the like may be used.

The transition metal oxide may be, for example, tungsten oxide, molybdenum oxide, titanium oxide, lithium titanium oxide, vanadium oxide, lithium vanadium oxide, or the like. For example, Group 1 metal compounds such as _{CuO, Cu 2} O, Ag ₂ O, CuS, CuSO _{4 , TiS 2} , Group 4 metal compounds such as SnO, V ₂ O ₅ , V ₆ O ₁₂ , VO _x (0 <x<6), Nb ₂ O ₅ , Bi ₂ O ₃ , Group 5 metal compounds such as _{Sb 2} O _{3 , CrO 3} , Cr ₂ O ₃ , MoO ₃ , MoS ₂ , WO ₃ , Group 4 such as _{SeO 2} Metal compounds, Group 7 metal compounds such as _{MnO 2} , Mn ₂ O _{3 , Fe 2} O ₃ , FeO, Fe ₃ O ₄ , Ni ₂ O ₃ Group 8 metal compounds such as NiO, CoO _{3 , CoO General formula} Li _x MN _y X ₂ (M, N is a metal of Groups 1 to 8, X is oxygen, sulfur, 0.1≤x≤2, 0≤y≤1), etc., and, for example, Li _y TiO ₂ ( 0≤y≤1), Li _4+y Ti ₅ O ₁₂ (0≤y≤1), Li _4+y Ti ₁₁ O ₂₀ (0≤y≤1), etc. may be lithium titanate.

The material capable of doping and dedoping lithium is, for example, Si, SiOx (0<x≤2), Si-Y alloy (wherein Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal) , a rare earth element or a combination element thereof, but not Si), Sn, SnO ₂ , Sn-Y' alloy (wherein Y' is an alkali metal, alkaline earth metal, group 13 to 16 element, transition metal, rare earth element, or these It is a combination element of , not Sn) and the like, and at least one of these and SiO ₂ may be mixed and used. The element Y includes Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, or a combination thereof.

The material capable of reversibly intercalating and deintercalating lithium ions is a carbon-based material, and any carbon-based negative active material generally used in lithium secondary batteries may be used. For example, crystalline carbon, amorphous carbon, or mixtures thereof. The crystalline carbon is, for example, amorphous, plate-like, flake-like, spherical or fibrous natural graphite; or artificial graphite, and the amorphous carbon may be, for example, soft carbon (low temperature calcined carbon) or hard carbon, mesophase pitch carbide, calcined coke, or the like.

The conductive polymer may be disulfide, polypyrrole, polyaniline, polyparaphenylene, polyacetylene, polyacene-based material, or the like.

In the negative active material composition, the conductive material, binder, and solvent may be the same as in the positive active material composition. Meanwhile, it is also possible to form pores in the electrode plate by further adding a plasticizer to the positive electrode active material composition and/or the negative electrode active material composition.

The content of the negative electrode active material, the conductive material, the binder and the solvent is the level normally used in the lithium secondary battery. At least one of the conductive material, the binder, and the solvent may be omitted depending on the use and configuration of the lithium secondary battery.

Next, a separator to be inserted between the positive electrode and the negative electrode is prepared. Any of the separators may be used as long as they are commonly used in lithium secondary batteries. Those having low resistance to ion movement of the electrolyte and excellent in the electrolyte moisture content may be used. For example, it is selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and may be in the form of a nonwoven fabric or a woven fabric. For example, a separator that can be wound up such as polyethylene or polypropylene is used for a lithium ion battery, and a separator having an excellent organic electrolyte impregnation ability may be used for a lithium ion polymer battery. For example, the separator may be manufactured according to the following method.

A separator composition is prepared by mixing a polymer resin, a filler, and a solvent. The separator composition may be directly coated on the electrode and dried to form a separator. Alternatively, after the separator composition is cast and dried on a support, a separator film peeled from the support is laminated on an electrode to form a separator.

The polymer resin used for manufacturing the separator is not particularly limited, and all materials used for the bonding material of the electrode plate may be used. For example, vinylidene fluoride/hexafluoropropylene copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, or mixtures thereof may be used.

Next, the electrolyte is prepared.

For example, the electrolyte may be an organic electrolyte. The organic electrolyte may be prepared by dissolving a lithium salt in an organic solvent.

The organic solvent may be used as long as it can be used as an organic solvent in the art. For example, propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate , benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N,N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide , dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether, or mixtures thereof.

The lithium salt may also be used as long as it can be used as a lithium salt in the art. For example, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li(CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ) (where x and y are natural numbers), LiCl, LiI, or a mixture thereof.

In addition, the electrolyte may be a solid electrolyte such as an organic solid electrolyte or an inorganic solid electrolyte. When a solid electrolyte is used, the solid electrolyte may also serve as a separator.

Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, A polymer containing an ionic dissociation group or the like can be used.

The inorganic solid electrolyte may be, for example, boron oxide, lithium oxynitride, etc., but is not limited thereto, and any solid electrolyte that can be used in the art may be used. The solid electrolyte may be formed on the negative electrode by a method such as sputtering. The inorganic solid electrolyte may be, for example, Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ and the like.

As shown in FIG. 7 , the lithium secondary battery 1 includes a positive electrode 3 , a negative electrode 2 , and a separator 4 . The positive electrode 3 , the negative electrode 2 and the separator 4 described above are wound or folded and accommodated in the battery case 5 . Then, an organic electrolyte is injected into the battery case 5 and sealed with a cap assembly 6 to complete the lithium secondary battery 1 . The battery case may have a cylindrical shape, a prismatic shape, or a thin film type. For example, the lithium secondary battery may be a thin film battery. The lithium secondary battery may be a lithium ion secondary battery.

A separator may be disposed between the positive electrode and the negative electrode to form a battery structure. After the battery structure is laminated in a bi-cell structure, impregnated with an organic electrolyte, and the obtained result is accommodated and sealed in a pouch, a lithium ion polymer battery is completed.

In addition, a plurality of the battery structure is stacked to form a battery pack connected in series, and the battery pack can be used in any device requiring high capacity and high output. For example, it can be used in a laptop, a smartphone, a power tool, an electric vehicle, and the like.

In particular, since the lithium secondary battery has excellent high-temperature cycle characteristics and high-temperature stability, it is suitable for medium and large-sized energy storage devices. For example, it is suitable as a power source for an electric vehicle (EV). For example, it is suitable as a power source for a hybrid electric vehicle such as a plug-in hybrid electric vehicle (PHEV).

The present invention will be described in more detail through the following examples and comparative examples, but the present invention is not limited to the following examples.

Preparation Example 1: One body type NCA (LiNi) _0.9 Co _0.09 Al _0.01 O ₂₎ manufacture of

NiSO ₄ as a nickel precursor, CoSO _{4 as a} cobalt precursor, and Al ₂ (SO ₄ ) ₃ as an aluminum precursor are added to water in a molar ratio of Ni:Co:Al of 90:9:1 to prepare a lithium-nickel-cobalt-based hydroxide precursor aqueous solution did. While stirring the aqueous solution, an aqueous sodium hydroxide solution was slowly added dropwise thereto, and the precursor aqueous solution was neutralized by stirring and reacting the reaction mixture for 5 hours to precipitate _{Ni 0.9} Co _0.09 Al _0.01 (OH) _{2 .} The precipitate was filtered and washed with water, and the resultant product was dried at 80° C. in an atmospheric atmosphere to prepare _{Ni 0.9} Co _0.09 Al _0.01 (OH) _{2 powder having an average particle diameter of about 4 μm.}

The Ni _0.9 Co _0.09 Al _0.01 (OH) ₂ powder was heat treated at a heat treatment temperature (T1) of 700° C. in an atmospheric atmosphere for 1 hour to obtain nickel cobalt aluminum hydroxide, a lithium nickel cobalt-based precursor.

The transition metal of the nickel cobalt aluminum hydroxide (the total of nickel, cobalt, and manganese and the lithium precursor Li ₂ CO ₃ were prepared so that the mixing molar ratio of lithium was 1: 1.05.

After mixing the prepared precursors in a mortar, put them in a furnace, and _{while flowing O 2} , a secondary heat treatment was performed at a heat treatment temperature (T2) of 1040° C. for 10 hours to prepare a cathode active material.

The positive electrode active material obtained according to the manufacturing method was NCA (LiNi _0.9 Co _0.09 Al _0.01 O ₂ ), and the average particle diameter of primary particles in the form of one body particles of the positive electrode active material was 4 μm.

The average particle diameter of the primary particles of the positive active material was measured through a particle size analyzer [Beckman Coulter LS13 320].

Preparation Example 2: One body type NCM (LiNi) _0.9 Co _0.09 Mn _0.01 O ₂ ) manufacturing

_{MnSO 4} as a manganese precursor instead of Al ₂ (SO ₄ ) _{3 as an aluminum precursor} Except for using, it was carried out in the same manner as in Preparation Example 1 to prepare a single-body type NCM (LiNi _0.9 Co _0.09 Mn _0.01 O ₂ ).

The positive active material obtained according to the above preparation method was NCM (LiNi _0.9 Co _0.09 Mn _0.01 O ₂ ), and the average particle diameter of primary particles in the form of one body particles of the positive active material was 4 μm.

The average particle diameter of the primary particles of the positive active material was measured through a particle size analyzer [Beckman Coulter LS13 320].

Preparation Example 3: Preparation of single particle NCA

_{NCA (LiNi 0.9} Co _0.09 Al _0.01 O ₂ ) was carried out in the same manner as in Preparation Example 1, except that the heat treatment temperature (T1) was changed by 650° C. so that the average particle diameter of the primary particles of the positive electrode active material was about 3 μm. was obtained, and the average particle diameter of the primary particles of the positive electrode active material was about 3 μm.

The average particle diameter of the primary particles of the positive active material was measured through a particle size analyzer [Beckman Coulter LS13 320].

Preparation Example 4: Preparation of single particle NCA

The heat treatment temperature (T1) was changed to 750° C. so that the average particle diameter of the primary particles of the positive electrode active material was about 5 μm, and the mixing molar ratio _{of the transition metal of nickel cobalt aluminum hydroxide and lithium of the lithium precursor Li 2} CO _{3 was 1:1.1} Except that it was changed to be this, it was carried out in the same manner as in Preparation Example 1 to obtain NCA (LiNi _0.9 Co _0.09 Al _0.01 O ₂ ) in the form of single particles having an average particle diameter (D50) of about 5 μm, and the primary of the positive electrode active material The average particle diameter of the particles is about 5 μm. The average particle diameter of the primary particles of the positive active material was measured through a particle size analyzer [Beckman Coulter LS13 320].

Comparative Preparation Example 1: LiNi in the form of secondary particles _0.9 Co _0.09 Mn _0.01 O ₂ Preparation of (NCM)

_{In order to obtain LiNi 0.9} Co _0.09 Mn _0.01 O ₂ (NCM) in the form of secondary particles having an average particle diameter (D50) of about 12 μm, the heat treatment temperature (T1) was changed to 1050°C and the heat treatment temperature (T2) to 900°C, and the nickel A secondary having an average particle diameter (D50) of about 12 μm was carried out in the same manner as in Preparation Example 2, except that the mixture molar ratio of the transition metal of cobalt manganese hydroxide and lithium of Li ₂ CO _{3 , a lithium precursor, was changed to 1:1.03. LiNi 0.9} Co _0.09 Mn _0.01 O ₂ (NCM) in particle form was obtained.

Comparative Preparation Example 2: LiNi in the form of secondary particles _0.9 Co _0.09 Al _0.01 O ₂ Preparation of (NCA)

_{Except for using an NCA precursor instead of an NCM precursor to obtain LiNi 0.9} Co _0.09 Al _0.01 O ₂ (NCA) in the form of secondary particles having an average particle diameter (D50) of about 12 μm, it was carried out in the same manner as in Comparative Preparation Example 1, and the average _{LiNi 0.9} Co _0.09 Mn Al _0.01 O ₂ (NCA) in the form of secondary particles having a particle diameter (D50) of about 12 μm was obtained.

(Manufacture of lithium secondary battery)

Example 1

_{LiCoO 2} (CM15V, Samsung SDI Co., Ltd.) having an average particle diameter of 16 _{μm in the form of single particles and LiNi 0.9} Co _0.09 Al _0.01 O ₂ in the form of single particles having an average particle diameter (D50) of about 4 μm prepared according to Preparation Example 1 It was mixed in a weight ratio of 7:3 to prepare a positive electrode active material.

The positive active material, carbon conductive agent (Super P), and PVDF (polyvinylidene fluoride) binder solution were added and mixed to prepare an active material slurry. The mixing weight ratio of the active material: the conductive agent: the binder in the active material slurry is 98:1:1. The slurry was coated on an aluminum current collector having a thickness of 12 μm using a thick film coater so that the loading level was 36 mg/cm ² , dried at 120° C. for at least 1 hour, and then rolled (pressed) to prepare a positive electrode. . Rolling is carried out using a rolling roll at 25°C, the linear pressure of the rolling roll is controlled to about 2.3 tons, and the gap between the upper and lower rolls constituting the rolling roll is adjusted to 0, and the anode is rolled to the maximum after rolling. The thickness of the anode was minimized and the density of the mixture was formed to be high.

A negative electrode active material slurry was prepared by mixing a mixture of graphite powder (japan carbon), which is an anode active material, SBR (styrene butadiene rubber) and CMC (carboxymethyl cellulose) in a weight ratio of 1:1 at a weight ratio of 98:2.

The prepared negative active material slurry was coated on a copper foil current collector having a thickness of 8 μm at a ^{level of 19.5 mg/cm 2 .} The coated electrode plate was dried at 100° C. for at least 1 hour, and then rolled to prepare a negative electrode having a mixture density of 1.66 g/cm 3 .

Using the positive electrode and the negative electrode, using a polyethylene separator (separator, STAR 20, Asahi) as a separator, EC (ethylene carbonate): EMC (ethylmethyl carbonate): DMC (dimethyl carbonate) (3: 3: 4 volume ratio) A lithium secondary battery having a capacity _{of 2000 mAh was prepared by using 1.15 M LiPF 6 dissolved in a mixed solvent.}

Example 2

_{LiNi 0.9} Co _0.09 Al _0.01 O ₂ (NCA) in the form of single particles having an average particle diameter (D50) of about 4 μm prepared according to Preparation Example 1 instead of an average particle diameter (D50) prepared according to Preparation Example 2 of about 4 μm _{A lithium secondary} battery was manufactured in the same manner as in Example 1, except that _{LiNi 0.9} Co _0.09 Mn _0.01 O 2 (NCM) in the form of single particles was used.

Example 3

_{LiNi 0.9} Co _0.09 Al _0.01 O ₂ having an average particle diameter of 16 μm LiCoO ₂ (CM15V, Samsung SDI Co., Ltd.) and single particle LiNi 0.9 Co 0.09 Al 0.01 O 2 having an average particle diameter (D50) of about 4 μm prepared according to Preparation Example 1 in a 6:4 weight ratio A lithium secondary battery was manufactured in the same manner as in Example 1, except that it was changed to .

Example 4

_{LiNi 0.9} Co _0.09 Al _0.01 O ₂ having an average particle diameter of 16㎛ LiCoO ₂ (CM15V, Samsung SDI Co., Ltd.) and LiNi 0.9 Co 0.09 Al 0.01 O 2 in the form of single particles having an average particle diameter (D50) of about 4 μm prepared according to Preparation Example 1 in an 8:2 weight ratio A lithium secondary battery was manufactured in the same manner as in Example 1, except that it was changed to .

Example 5-7

_{A lithium secondary} battery was manufactured in the same manner as in Example 1, except that LiCoO 2 and NCA having an average particle diameter as shown in Table 1 were used, respectively.

division Average particle diameter of single particle LiCoO _{2 (㎛)} Average particle diameter of single particle NCA (㎛) Example 5 13 4 Example 6 17 4 Example 7 14 3 Example 8 14 5

Comparative Example 1

Secondary particles having an average particle diameter (D50) of about 12 μm obtained according to Comparative Preparation Example 2 instead _{of LiNi 0.9} Co _0.09 Al _0.01 O _{2 in the} form of single particles having an average particle diameter (D50) of about 4 μm prepared according to Preparation Example 1 A _{lithium secondary} battery was prepared in the same manner as in Example 1, except that _{LiNi 0.9} Co _0.09 Al _0.01 O 2 was used. The positive active material used in Comparative Example 1 was LiCoO _{2 (CM15V, Samsung SDI Co., Ltd.) having an average particle diameter of 16 μm in the form of single particles and LiNi 0.9} Co _0.09 Al _0.01 O in the form of secondary particles having an average particle diameter (D50) of about 12 μm. ₂ was mixed in a 7:3 weight ratio.

Comparative Example 2

A lithium secondary battery was prepared in the same manner as in Example 1, except that only _{LiNi 0.9} Co _0.09 Al _0.01 O _{2 in the} form of single particles having an average particle diameter (D50) of about 4 μm was used as the positive electrode active material according to Preparation Example 1 prepared. The mixture density of the positive electrode was about 3.6 g/cc.

Comparative Example 3

_{LiCoO 2} (CM15V, Samsung SDI) with an average particle diameter of 16 _{μm in the form of single particles and LiNi 0.9} Co _0.09 Al _0.01 O _{2 in} the form of single particles having an average particle diameter (D50) of about 4 μm prepared according to Preparation Example 1 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the mixing weight ratio was changed to 3:7. The positive active material of Comparative Example 3 was LiCoO _{2 (CM15V, Samsung SDI) having an average particle diameter of 16 μm in the form of single particles and LiNi 0.9 in the} form of single particles having an average particle diameter (D50) of about 4 μm prepared according to Preparation Example 1 Co _0.09 Al _0.01 O ₂ is mixed in a weight ratio of 3:7.

Comparative Example 4

_{A lithium secondary} battery was manufactured in the same manner as in Example 1, except that only LiCoO 2 having an average particle diameter (D50) of about 16 μm was used as the positive electrode active material.

Comparative Example 5

_{LiNi 0.9} Co _0.09 Mn _0.01 O _{2 In the} same manner as in Example 1, except that only LiNi 0.9 Co 0.09 Mn 0.01 O 2 in the form of single particles having an average particle diameter (D50) of about 4 μm, prepared according to Preparation Example 2, was used as the positive electrode active material. paper was prepared.

Comparative Example 6

_{LiNi 0.9} Co _0.09 Mn _0.01 O ₂ (NCM) in the form of single particles having an average particle diameter (D50) of about 4 μm prepared according to Preparation Example 2 instead of an average particle diameter (D50) obtained according to Comparative Preparation Example 1 of about 12 μm A lithium secondary battery was prepared in the same manner as in Example 2, except that _{LiNi 0.9} Co _0.09 Mn _0.01 O ₂ (NCM) in the form of secondary particles was used.

Evaluation Example 1: Mixture density of positive electrode

The mixture density of the positive electrodes prepared according to Examples 1-5 and Comparative Examples 1-4 was investigated, and the results are shown in Table 2 below.

division Mixture density (g/cc) Example 1 4.19 Example 2 4.13 Example 3 4.10 Example 4 4.17 Comparative Example 1 4.09 Comparative Example 2 3.60 Comparative Example 3 3.85 Comparative Example 4 4.19 Comparative Example 5 3.60

Referring to Table 2, it can be seen that the positive active material of Examples 1 to 4 has an increase in the density of the mixture as compared to the case of Comparative Example 3. As such, when the density of the mixture is increased, an effect of increasing the capacity can be obtained. The positive active material of Comparative Example 4 has excellent mixture density characteristics, but as shown in Evaluation Example 3 below due to the implementation of excessive mixture density, many cracks of the LCO opposition were observed, resulting in increased electrolyte side reactions, poor high-temperature storage characteristics, and poor electrode plate flexibility.

In addition, the mixing density of the positive electrode of Examples 5-8 was investigated. The positive electrode of Examples 5-8 exhibited the same level of mixing density as that of Example 1.

Evaluation Example 2: Scanning Electron Microscopy (SEM) Analysis

An SEM image of the positive active material obtained according to Preparation Example 1 was measured. The SEM measuring device (FEI, USA) used a model name (Sirion). The results of the SEM analysis are shown in FIGS. 6A and 6B . In Figure 6b, some small particles are fragments generated during the analysis process. 6A and 6B , it was found that the positive active material of Preparation Example 1 was a primary particle having a single particle shape and had a uniform size.

Evaluation Example 3: Anode thickness, mixture density, adhesive force, true density and porosity

The thickness (d1) of the positive electrode prepared according to Example 1 and Comparative Examples 1 to 4 was measured. Then, after the positive electrode active material layer was rolled, the thickness (d2) of the positive electrode was measured.

After the positive electrode was cut to a size of 30 mm X 30 mm, the thickness and weight were measured to obtain a mixture density, and the positive electrode having the same loading level was rolled to calculate the compressibility of the positive electrode according to Equation 1 below.

<Equation 1>

Compressibility (%) = {(d1 - current collector thickness) - (d2 - current collector thickness)}/(d1 - current collector thickness)

In addition, SEM photographs showing cross-sections after rolling the positive electrodes of Example 1 and Comparative Examples 1 to 4 are shown in FIGS. 1 to 5, and the crack test results confirmed through this are shown. The SEM measuring device (FEI, USA) used a model name (Sirion).

Through the SEM photograph, the press (rolling) roll gap for each positive electrode is fixed to 0, which is the minimum value, and the degree of pulverization of the active material can be confirmed after the rolling is carried out at 25° C. by pressing with a pressure of about 2.5 tons. Pressurization is pressurized by a hydraulic method, and the roll size is Φ500x550mm (W). The rolling conditions are the same as the anode rolling conditions of Example 1.

In addition, the adhesive strength of each positive electrode was evaluated using UTM equipment, and the porosity of each positive electrode was calculated according to Equation 2.

<Equation 2>

P = {A-(B/T)}/AХ100

In Equation 2, P represents the porosity of the cathode, A represents the actual volume of the cathode active material layer in the cathode, B represents the weight of the active material in the cathode, and T represents the true density of the cathode active material in the cathode excluding the cathode current collector. The true density uses the one disclosed in the literature (Principle and Application of Lithium Secondary Battery - Refer to the author's document, Jeonggi Park).

The evaluation results of each characteristic are shown in Tables 3 and 4 below.

division cathode active material Thickness (㎛) after press adhesion
(gf/mm) coating (d1) press (d2) mix density
(g/cc) compressibility(%) Example 1 LCO: single particle NCA
(7:3 weight ratio) 169 102 4.19 42.68 0.72 Comparative Example 1 LCO: Secondary particle NCA (7:3 weight ratio) 173 104 4.09 42.86 0.50 Comparative Example 2 single particle NCA 197 118 3.60 42.70 0.20 Comparative Example 3 LCO: single particle NCA (3:7 weight ratio) 187 113 3.85 42.29 0.43 Comparative Example 4 LCO 170 102 4.19 43.04 0.73

In Table 3, “after press” refers to the case of maximally pressurizing the gap of the press equipment to the minimum. In Table 3, the press is the same as the rolling of Example 1, and the conditions are the same.

division cathode active material True density (g/cc) crack test
(crack test) Porosity (%) Example 1 LCO: single particle NCA (7:3 weight ratio) 4.96 Good 10.08 Comparative Example 1 LCO: Secondary particle NCA (7:3 weight ratio) 4.96 Bad (pinhole) 12.15 Comparative Example 2 single particle NCA 4.76 Bad (pinhole) 19.43 Comparative Example 3 LCO: single particle NCA (3:7 weight ratio) 4.85 Good 15.67 Comparative Example 4 LCO 5.10 Good 12.50

The true density in Table 4 refers to the principle and application of a lithium secondary battery (author Park Jung-ki).

Referring to Table 3, the coating thickness of the positive electrode at the same loading level was the lowest in Example 1. In addition, the compression ratio of the positive electrode of Example 1 was smaller than that of the positive electrode of Comparative Examples 1 to 4 when the pressing was performed with the same gap. From this, it can be seen that the positive electrode of Example 1 has improved electrode plate flexibility compared to the positive electrode of Comparative Examples 1 to 4, and is advantageous for increasing the density of the mixture, and there is no cracking of the active material after rolling as shown in FIG. 1 .

As shown in Table 3, the mixture density of the positive electrode of Example 1 shows the same level as that of the positive electrode (LCO alone) of Comparative Example 4, but as shown in Table 4, the compressibility of the positive electrode of Example 1 is the same as that of Comparative Example 4 It is smaller than the compressibility of the positive electrode. The positive electrode of Example 1 had a low compressibility when the electrode plate was rolled, so there was little stress on the electrode plate. The plate quality is also excellent.

As shown in FIG. 5, in the positive electrode of Comparative Example 4, many cracks in the LCO opposition were observed after pressing due to the implementation of excessive mixture density.

When a positive electrode was manufactured using secondary particles NCA according to Comparative Example 1, the compressibility of the positive electrode was disadvantageous compared to that of Example 1, and as shown in FIG. As this is repeated, there is a high possibility that gas is generated. And, as shown in Table 3, the positive electrode of Comparative Example 1 exhibited unfavorable results compared to the positive electrode of Example 1 in density and adhesive strength.

The positive electrode of Comparative Example 3 had a higher ratio of NCA in the form of single particles in the positive electrode active material compared to LCO, and the positive electrode of Comparative Example 2 was a case where single particle NCA was used as the positive electrode active material, and the thickness of the coated electrode plate was high and the compressibility was high. It is disadvantageous in terms of packing. In addition, the adhesive strength is too low, so it is necessary to add more binder when blending an excessive amount of single-particle type NCA. In addition, the positive electrode of Comparative Example 2 contained only NCA in the form of a single particle as a positive electrode active material, so that pinholes were generated in the electrode plate during winding.

Referring to Table 4, the positive electrode of Example 1 has a smaller porosity than the positive electrode of Comparative Examples 1 to 3. As such, since the porosity is small, contact between the active materials is advantageous, thereby reducing the resistance. In addition, the positive electrode of Example 1 does not have cracks and has characteristics of high density and high capacity.

On the other hand, the positive electrode of Comparative Example 1 was not dense compared to the positive electrode of Example 1, so the porosity in the electrode plate was high, and a defect in which a pinhole was generated in the electrode plate was observed due to excessive pressing. And the positive electrode of Comparative Example 1 has a high possibility of dropping the active material during winding, and thus the possibility of cell failure is very high.

In the positive electrode of Comparative Example 2, since the positive electrode active material is composed of only small particles, true density and mixing density are low, which is disadvantageous in packing. And, as shown in Table 4, the porosity in the positive electrode plate is very high.

The positive electrode of Comparative Example 3 had a high specific gravity of small particles in the positive electrode active material, so that the true density was low and the porosity of the electrode plate was high compared to the positive electrode of Example 1. And the positive electrode of Comparative Example 4 was composed of only LCO, and had a high true density and a low porosity of the electrode plate, but as shown in FIG.

Evaluation Example 4: Discharge capacity, efficiency, rate characteristics, room temperature life and high temperature life

The lithium secondary batteries prepared in Example 1 and Comparative Examples 1 and 3 were charged with a constant current at 25° C. with a current of 0.5 C at a voltage of 4.35 V, and while maintaining 4.35 V, the lithium secondary batteries were charged at a constant voltage until the current reached 0.1 C. . Then, it was discharged at a constant current of 0.7C until the voltage reached 2.75V during discharge. (Mars stage)

Then, constant current charging was performed with a current of 0.5C until the voltage reached 4.35V, and constant voltage charging was performed until the current reached 0.02C while maintaining 4.35V. Then, it was discharged with a constant current of 0.2C until the voltage reached 2.75V at the time of discharge (standard step).

The lithium secondary battery, which had undergone the chemical formation and standard steps, was charged with a constant current at 25° C. with a current of 0.7C, respectively, until the voltage reached 4.35V, and was charged with a constant voltage until the current reached 0.05C while maintaining 4.35V. Then, a cycle of discharging at a constant current of 0.5C until the voltage reached 3.0V during discharging was repeated 300 times.

In addition, the charge-discharge experiment was performed in the same manner as the charge-discharge experiment at 25°C, except that the charge/discharge experiment was changed from 25°C to 45°C, and a total of 300 charge/discharge cycles were repeated. For the rate characteristics, each lithium secondary battery was charged with a constant current of 4.35V with a current of 0.5C at 25°C, and charged with a constant voltage until the current reached 0.05C while maintaining 4.35V. After discharging at a constant current of 0.2C, 0.5C, 1.0C, and 2.0C until it reaches 3.0V, the discharge capacity at 2.0C compared to the discharge capacity at c-rate of 0.2C is given by the following equation It was calculated according to the ratio and shown in Table 5 below.

<Equation 3>

Rate characteristic (%) = (discharge capacity at 2.0C / discharge capacity at 0.2C) × 100

Some of the results of the charging and discharging experiments are shown in Table 5 and FIG. 8 below. The capacity retention rate is expressed by the following formula (4).

<Equation 4>

Capacity retention rate (%) = (discharge capacity at ^{300 th cycle/1 discharge capacity at st} cycle] x 100

division Discharge capacity (mAh/g) Charging/discharging efficiency (%) Rate characteristics (%)
(2.0C/0.2C) at 300 ^th cycle
Capacity retention rate (%] 25℃ 45℃ Example 1 184 91.3% 91.9 92.6 89.0 Comparative Example 1 182 89.6% 90.6 89.6 84.7 Comparative Example 3 194 88.1% 88.7 81.9 77.7

As shown in Table 5 and FIG. 8, it was found that the lithium secondary battery of Example 1 has improved charge/discharge efficiency, rate characteristics, room temperature life and high temperature life compared to the lithium secondary batteries of Comparative Examples 1 and 3.

In addition, the charging and discharging efficiency, rate characteristics, room temperature life, and high temperature life of the lithium secondary batteries of Examples 2 to 7 are the same as the charging and discharging efficiency, rate characteristics, room temperature life and high temperature life evaluation method of the lithium secondary battery of Example 1 described above. and evaluated.

As a result of the evaluation, the charge/discharge efficiency, rate characteristics, room temperature life and high temperature life of the lithium secondary batteries of Examples 2 to 7 were equivalent to those of the lithium secondary batteries of Example 1.

1: lithium secondary battery 2: negative electrode
3: positive electrode 4: separator
5: Battery case 6: Cap assembly

Claims (12)

It is a positive electrode active material comprising a lithium cobalt-based active material and a lithium nickel cobalt-based active material,
The size and content of the lithium cobalt-based active material is larger than the size and content of the lithium nickel cobalt-based active material, respectively,
The lithium nickel cobalt-based active material is a positive active material of a single body type active material. According to claim 1,
The average particle diameter of the lithium cobalt-based active material is 10 μm to 20 μm,
The lithium nickel cobalt-based active material has an average particle diameter of 3 μm to 8 μm. According to claim 1,
The lithium cobalt-based active material is a positive active material of a single body type active material. According to claim 1,
The lithium cobalt-based active material is a compound represented by the following formula (1), a compound represented by the following formula (2), or a positive active material of a combination thereof:
<Formula 1>
Li _x Co _1-y M _y A ₂
In Formula 1, 0.9≤x≤1.2, 0≤y≤0.5,
M is Mn, Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al, Si, Cr, Fe, V, a rare earth element or a combination thereof;
A is 0, F, S, P or a combination thereof,
<Formula 2>
Li _x Co _1-y M _y O _2-z X _z
In Formula 2, 0.9≤x≤1.2, 0≤y≤0.5, 0≤z≤0.5,
M is Mn, Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al, Si, Cr, Fe, V, a rare earth element or a combination thereof, and X is F, S, P or a combination thereof It is a combination. According to claim 1,
The lithium nickel cobalt-based active material is a compound represented by the following formula (3), a compound represented by the formula (4), or a positive active material a combination thereof:
<Formula 3>
Li _x Ni _1-y Co _y O _2-z X _z
In Formula 3, 0.9≤x≤1.2, 0<y≤0.5, 0≤z≤0.5,
X is F, S, P or a combination thereof,
<Formula 4>
Li _x Ni _1-yz Co _y M _z O _2-a X _a
In Formula 5, 0.9≤x≤1.2, 0<y≤0.5, 0<1-yz, 0≤z≤0.5, 0≤a<2,
M is Ni, Co, Mn, Mg, Ca, Sr, Ba, Ti, Zr, Nb, Mo, W, Zn, Al, Si, Cr, Fe, V, a rare earth element or a combination thereof;
X is F, S, P or a combination thereof. The cathode active material according to claim 1, wherein the lithium cobalt-based compound is a compound represented by the following formula (5):
<Formula 5>
Li _x Co _a O _2+α
In Formula 5, 0.9≤x≤1.2, 0.98≤a≤1.00, and -0.1≤α≤0.1. The cathode active material according to claim 1, wherein the lithium nickel cobalt-based active material is a compound represented by the following Chemical Formula 7 or a compound represented by the following Chemical Formula 8:
<Formula 7>
Li _x Co _a Ni _b Mn _c O ₂
In formula 7, 0.9<x<1.2, 0<a<0.5, 0<b<1, 0<c<1, a+b+c=1,
<Formula 8>
Li _x Co _a Ni _b Al _c O ₂
In Formula 8, 0.9<x<1.2, 0<a<0.5, 0<b<1, 0<c<1, a+b+c=1. According to claim 1,
The lithium cobalt-based active material is LiCoO ₂ ,
The lithium nickel cobalt-based active material is LiNi _0.9 Co _0.09 Al _0.01 O ₂ , LiNi _0.9 Co _0.09 Mn _0.01 O ₂ , Li _1.05 Ni _0.9 Co _0.09 Al _0.01 O ₂ , Li _1.05 Ni _0.9 Co _0.09 Mn _0.01 O ₂ , Li _1.05 Ni _0.5 Co _0.2 Mn _0.3 O ₂ , Li _1.1 Ni _0.5 Co _0.2 Mn _0.3 O ₂ , Li _1.05 Ni _0.6 Co _0.2 Mn _0.2 O ₂ , Li _1.1 Ni _0.6 Co _0.2 Mn _0.2 O ₂ , or a combination thereof. A positive electrode comprising the positive active material of any one of claims 1 to 8. 10. The method of claim 9,
The positive electrode mixture density of the positive electrode is 4.0 g / cc or more. 10. The method of claim 9,
A positive electrode having a porosity of 10.0% to 12.1% of the positive electrode. A lithium secondary battery comprising the positive electrode of claim 9, the negative electrode and an electrolyte interposed therebetween.

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