KR20230154698A - Method of preparing positive electrode active material comprising coating layer, method of preparing positive electrode comprising the same - Google Patents

Abstract

The present invention includes the steps of preparing a mixture by solid-phase mixing a positive electrode active material containing lithium transition metal oxide, a silicon compound, and boric acid; and heat-treating the mixture to produce a coating layer. It relates to a method of producing a positive electrode active material including a coating layer.

Description

Method for manufacturing a positive electrode active material including a coating layer, and a method for manufacturing a positive electrode including the same {METHOD OF PREPARING POSITIVE ELECTRODE ACTIVE MATERIAL COMPRISING COATING LAYER, METHOD OF PREPARING POSITIVE ELECTRODE COMPRISING THE SAME}

The present invention relates to a method of manufacturing a positive electrode active material including a coating layer, and a method of manufacturing a positive electrode including the same. More specifically, the present invention relates to a method of manufacturing a positive electrode active material including the same, and more specifically, to a method of manufacturing a positive electrode active material that can minimize the amount of gas generated by side reactions such as surface corrosion of the positive electrode active material and decomposition of the non-aqueous electrolyte. It relates to a method of manufacturing a positive electrode active material including a coating layer and a method of manufacturing a positive electrode including the same.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

Lithium transition metal oxide is used as a positive electrode active material for lithium secondary batteries, and among these, lithium cobalt oxide such as LiCoO ₂ , which has a high operating voltage and excellent capacity characteristics, is mainly used. However, lithium cobalt oxide has poor thermal properties due to destabilization of the crystal structure due to delithiation. Additionally, lithium cobalt oxide is expensive, so there are limits to its mass use as a power source in fields such as electric vehicles.

As materials to replace lithium cobalt oxide, lithium manganese oxides such as LiMnO ₂ and LiMn ₂ O ₄ , lithium iron phosphate compounds such as LiFePO ₄ , and lithium nickel oxides such as LiNiO ₂ have been developed. Among these, research and development on lithium nickel oxide, which has a high reversible capacity of about 200 ㎃·h/g and is easy to implement as a large-capacity battery, is being actively conducted. However, lithium nickal oxide does not have excellent thermal stability compared to lithium cobalt oxide, and when an internal short circuit occurs due to external pressure during charging, the positive electrode active material itself decomposes, resulting in rupture and ignition of the battery.

Accordingly, as a method to improve the low thermal stability of lithium nickel oxide while maintaining its excellent reversible capacity, lithium transition metal oxide was developed in which some of the nickel was replaced with transition metals such as cobalt, manganese, and aluminum. In the case of a lithium secondary battery that uses lithium transition metal oxide, especially lithium transition metal oxide containing a high content of nickel, as a positive electrode active material, surface corrosion of the positive electrode active material and damage to the non-aqueous electrolyte occur due to direct contact between the electrolyte and the positive electrode active material. There is a problem that the stability of lithium secondary batteries is reduced, such as gas generation due to side reactions such as decomposition.

KR2012-0129926A

The object of the present invention is to provide a method for manufacturing a positive electrode active material including a coating layer that can minimize the amount of gas generated by side reactions such as surface corrosion of the positive electrode active material and decomposition of non-aqueous electrolyte, and a method for manufacturing a positive electrode including the same.

In order to solve the above-described problem, (1) the present invention includes the steps of preparing a mixture by solid-phase mixing a positive electrode active material containing lithium transition metal oxide, a silicon compound represented by the following Chemical Formula 1, and boric acid; and heat-treating the mixture to produce a coating layer. A method for producing a positive electrode active material including a coating layer is provided:

<Formula 1>

In Formula 1 above,

R ¹ to R ⁴ are each independently a halogen group, a hydroxy group, an amine group, a vinyl group, a C ₁ to C ₁₀ alkyl group, a C ₆ to C ₂₀ aryl group, a C ₁ to C ₁₀ alkoxy group, or a C ₁ to C 10 alkyl group. It is a C ₁₀ acyloxy group, and at least one of R ¹ to R ⁴ is a C ₁ to C ₁₀ alkoxy group.

In addition, (2) the present invention provides a method for producing a positive electrode active material including a coating layer in (1) above, wherein in the step of manufacturing the coating layer, the heat treatment temperature is 171 to 400 ° C.

Additionally, (3) the present invention provides a method for producing a positive electrode active material including a coating layer according to (1) or (2) above, wherein the weight ratio of the silicon compound and boric acid is 1.0:1.0 to 5.0.

In addition, (4) the present invention includes the coating layer according to any one of (1) to (3) above, wherein the total content of the silicon compound and boric acid is 0.1 to 1.50 parts by weight based on 100 parts by weight of the positive electrode active material. Provides a method for manufacturing a positive electrode active material.

In addition, (5) the present invention according to any one of (1) to (4) above, wherein the silicone compound is tetramethoxysilane, tetraethoxysilane, dimethoxydimethylsilane, methoxytrimethylsilane, trimethoxy ( Provided is a method for producing a positive electrode active material including a coating layer of at least one selected from the group consisting of vinyl) silane and methoxydimethyl (phenyl) silane.

In addition, (6) the present invention provides a method for producing a positive electrode active material including a coating layer according to any one of (1) to (5) above, wherein the step of preparing the mixture is performed at 15 to 30 ° C. .

Additionally, (7) the present invention provides a method for producing a positive electrode active material including a coating layer according to any one of (1) to (6) above, wherein the step of preparing the mixture does not use a solvent.

Additionally, (8) the present invention provides a method for producing a positive electrode active material including a coating layer according to any one of (1) to (7) above, wherein the lithium transition metal oxide is represented by the following formula (2):

<Formula 2>

Li _1+a Ni _b Co _c M ¹ _d M ² _e O ₂

In Formula 2,

M ¹ is one or more selected from Mn and Al,

M ² is one or more selected from W, Mo, Cr, Zr, Ti, Mg, Ta and Nb,

0.00≤a≤0.30, 0.60≤b<1.00, 0.00<c<0.40, 0.00<d<0.40, 0.00≤e≤0.10.

Additionally, (9) the present invention provides a method for producing a positive electrode active material including a coating layer, wherein the coating layer includes a unit represented by the following formula (3):

<Formula 3>

*-SiO _x -B _y O _z -*

In Formula 3 above,

x, y, and z are the number of moles per mole of Si, and may each independently be 1 to 20.

Additionally, (10) the present invention provides a method for producing a positive electrode, including a method for producing a positive electrode active material including the coating layer according to any one of (1) to (9) above.

The positive electrode active material including the coating layer manufactured by the manufacturing method according to the present invention can minimize the amount of gas generated by side reactions such as surface corrosion of the positive electrode active material and decomposition of the non-aqueous electrolyte solution.

The thermal stability of a positive electrode active material including a coating layer manufactured by the manufacturing method according to the present invention can be significantly improved.

The cathode active material including the coating layer manufactured by the manufacturing method according to the present invention can minimize the collapse of the coating layer, thereby improving the long-term lifespan of the lithium secondary battery.

The conductivity of lithium ions can be improved due to the positive electrode active material including the coating layer manufactured by the manufacturing method according to the present invention, thereby improving the capacity of the lithium secondary battery.

Terms or words used in this specification and claims should not be construed as limited to their common or dictionary meanings, and the inventor may appropriately define the concept of terms in order to explain his or her invention in the best way. It must be interpreted with meaning and concept consistent with the technical idea of the present invention based on the principle that it is.

The terms used in the present invention are only used to describe specific embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In the present invention, terms such as 'include' or 'have' do not designate the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, but rather mean that one or more other It should be understood that this does not exclude in advance the presence or addition of features, numbers, steps, operations, components, parts, or combinations thereof.

In this specification, the term ‘on’ means not only the case where a certain component is formed directly on top of another component, but also the case where a third component is interposed between these components.

1. Method of manufacturing a positive electrode active material including a coating layer

A method of manufacturing a positive electrode active material including a coating layer according to an embodiment of the present invention includes the steps of solid-phase mixing a positive electrode active material containing lithium transition metal oxide, a silicon compound represented by the following Chemical Formula 1, and boric acid to prepare a mixture; and a method for producing a positive electrode active material including a coating layer, including the step of heat-treating the mixture to produce a coating layer:

<Formula 1>

In Formula 1 above,

R ¹ to R ⁴ are each independently a halogen group, a hydroxy group, an amine group, a vinyl group, a C ₁ to C ₁₀ alkyl group, a C ₆ to C ₂₀ aryl group, a C ₁ to C ₁₀ alkoxy group, or a C ₁ to C 10 alkyl group. It is a C ₁₀ acyloxy group, and at least one of R ¹ to R ⁴ is a C ₁ to C ₁₀ alkoxy group.

Hereinafter, a method for manufacturing a positive electrode active material including a coating layer according to an embodiment of the present invention will be described in detail.

1) Preparation of mixture

First, a positive electrode active material containing lithium transition metal oxide, a silicon compound represented by Chemical Formula 1, and boric acid are mixed in solid phase to prepare a mixture.

The lithium transition metal oxide may be represented by the following formula 2:

<Formula 2>

Li _1+a Ni _b Co _c M ¹ _d M ² _e O ₂

In Formula 1,

M ¹ is one or more selected from Mn and Al,

M ² is one or more selected from W, Mo, Cr, Zr, Ti, Mg, Ta and Nb,

0.00≤a≤0.30, 0.60≤b<1.00, 0.00<c<0.40, 0.00<d<0.40, 0.00≤e≤0.10.

The 1+a represents the molar ratio of lithium in the lithium transition metal oxide, and may be 0.00≤a≤0.30, preferably 0.00≤a≤0.20.

The b represents the molar ratio of nickel among all transition metals, and may be 0.60≤b<1.00, 0.60≤b≤0.99, or 0.60≤b≤90. When the nickel content satisfies the above-mentioned range, excellent capacity characteristics can be achieved.

The c represents the molar ratio of cobalt among all transition metals, and may be 0.00<c<0.40, 0.01≤c≤0.35, or 0.05≤c≤0.35.

The d represents the molar ratio of M ¹ among all transition metals, and may be 0.00<d<0.40, 0.01≤d≤0.35, or 0.05≤d≤0.35.

The e represents the molar ratio of M ² among all transition metals, and may be 0.00≤w≤0.10, or 0.00≤w≤0.05.

The silicon compound can undergo a condensation reaction with the hydroxyl group on the surface of the lithium transition metal oxide through a hydrolysis reaction, allowing it to chemically bond with the surface of the positive electrode active material. Through this chemical bond, a coating layer can be easily manufactured on the surface of the positive electrode active material.

In Formula 1, R ¹ to R ⁴ are each independently a vinyl group, a C ₁ to C ₁₀ alkyl group, ^a C ₆ to C ₂₀ aryl group, or a ^C ₁ to C ₁₀ alkoxy group. At least one is preferably a C ₁ to C ₁₀ alkoxy group.

Additionally, in Formula 1, R ¹ to R ⁴ may each independently be a C ₁ to C ₁₀ alkoxy group; C ₁ to C ₁₀ alkyl group or C ₁ to C ₁₀ alkoxy group, where at least one of R ¹ to R ⁴ may be a C ₁ to C ₁₀ alkoxy group; A vinyl group or a C ₁ to C ₁₀ alkoxy group, where at least one of R ¹ to R ⁴ may be a C ₁ to C ₁₀ alkoxy group; It may be a C ₁ to C ₁₀ alkyl group, a C ₆ to C ₂₀ aryl group, or a C ₁ to C ₁₀ alkoxy group, and at least one of R ¹ to R ⁴ may be a C ₁ to C ₁₀ alkoxy group.

The silicone compound may be one or more selected from the group consisting of tetramethoxysilane, tetraethoxysilane, dimethoxydimethylsilane, methoxytrimethylsilane, trimethoxy(vinyl)silane, and methoxydimethyl(phenyl)silane, , Among these, tetraethoxysilane and dimethoxydimethylsilane are preferable as they are commercially available and easily react with the positive electrode active material.

When the boric acid is used as a raw material for the coating layer of the positive electrode active material, the conductivity of lithium ions of the positive electrode active material is improved, and the capacity of the lithium secondary battery can be significantly improved.

When the positive electrode active material, silicon compound, and boric acid are mixed in solid phase, the process is simple compared to liquid phase mixing, and facilities such as expensive explosion-proof equipment required when using organic solvents are not required, thereby reducing process costs. . In addition, lithium in the positive electrode active material can be dissolved in organic solvents, specifically in alcohol solvents such as ethanol, so the capacity may decrease, but solid-phase mixing can prevent the capacity from decreasing.

The weight ratio of the silicone compound and boric acid may be 1.0:1.0 to 5.0, preferably 1.0:1.0 to 4.5, 1.0:1.0 to 3.5, 1.0:1.0 to 3.0, 1.0:1.0 to 2.5, 1.0:1.0 to 2.0, It may be 1.0:1.0 to 3.5. If the above-mentioned conditions are satisfied, the problem of capacity degradation due to increased resistance may not occur.

With respect to 100 parts by weight of the positive electrode active material, the total content of the silicon compound and boric acid may be 0.10 to 1.50 parts by weight, preferably 0.20 parts by weight or more, 0.30 parts by weight or more, 0.40 parts by weight, or 0.50 parts by weight or more; It may be 0.75 parts by weight or less, 0.80 parts by weight or less, 0.90 parts by weight or less, 1.00 parts by weight or less, 1.10 parts by weight or less, 1.20 parts by weight or less, 1.30 parts by weight or less, and 1.40 parts by weight or less. If the above-mentioned conditions are satisfied, the problem of capacity degradation due to increased resistance may not occur.

The step of preparing the mixture may be performed at 15 to 30° C., preferably 20 to 25° C. If the above-mentioned conditions are met, mixing can be performed without separate heat treatment, thereby simplifying the process and improving manufacturing efficiency.

2) Preparation of coating layer

Next, the mixture is heat treated to prepare a coating layer.

The heat treatment temperature is 171 to 400 ℃, preferably 171 ℃ or higher, 180 ℃ or higher, 190 ℃ or higher, 200 ℃ or higher, 210 ℃ or higher, 220 ℃ or higher, 230 ℃ or higher, 240 ℃ or higher, 250 ℃ or higher, 260 ℃ or higher. The coating layer is prepared by heat treatment at 270 ℃ or higher, 280 ℃ or higher, 390 ℃ or lower, 380 ℃ or lower, 370 ℃ or lower, 360 ℃ or lower, 350 ℃ or lower, 340 ℃ or lower, 330 ℃ or lower, 320 ℃ or lower.

Since boric acid becomes liquid under the above-described heat treatment temperature conditions, it easily chemically reacts with the positive electrode active material and the silicon compound without a separate solvent, and a coating layer containing boron oxide can be produced on the positive electrode active material. Specifically, the liquid silicon compound undergoes a hydrolysis reaction due to moisture on the surface of the positive electrode active material and undergoes a condensation polymerization reaction with liquid boric acid and hydroxyl groups on the surface of the positive electrode active material to form a coating layer. In addition, it is possible to prevent the initial discharge capacity of the lithium secondary battery from decreasing due to lithium moving inside the positive electrode crystal and being oxidized on the positive electrode surface.

Since no separate solvent is used in the step of manufacturing the coating layer, a drying process to remove the solvent is not required, and energy efficiency can be significantly improved.

The coating layer may include a unit represented by the following formula (3):

<Formula 3>

*-SiO _x -B _y O _z -*

In Formula 3 above,

x, y, and z are the number of moles per mole of Si, and may each independently be 1 to 20.

Additionally, * may be a site that combines with the remaining components of the coating layer and/or with the positive electrode active material.

Due to the unit represented by Formula 3, the thermal stability of the positive electrode active material including the coating layer can be significantly improved.

2. Manufacturing method of anode

A method of manufacturing a positive electrode according to another embodiment of the present invention includes a method of manufacturing a positive electrode active material including the coating layer described above. Specifically, manufacturing a positive electrode active material including a coating layer according to an embodiment of the present invention; and applying a positive electrode active material slurry prepared by dissolving or dispersing the positive electrode active material including the coating layer in a solvent onto the positive electrode current collector, followed by drying and rolling.

In addition to the positive electrode active material including the coating layer, a binder and a conductive material may be dissolved or dispersed in a solvent.

The binder serves to improve adhesion between positive electrode active material particles and adhesion between the positive active material and the current collector. The binder is polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, and carboxymethyl cellulose (CMC). ), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber. It may be one or more selected from the group consisting of (SBR) and fluororubber. The content of the binder may be 1 to 30 parts by weight based on 100 parts by weight of the positive electrode active material including the coating layer.

The conductive material is used to provide conductivity to the electrode, and can be used without particular limitation as long as it does not cause chemical change and has electronic conductivity in the battery being constructed. The conductive materials include natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, copper, nickel, aluminum, silver, zinc oxide, potassium titanate, and titanium oxide. and polyphenylene derivatives. The content of the conductive material may be 1 to 30 parts by weight based on 100 parts by weight of the positive electrode active material including the coating layer.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes in the battery. The positive electrode current collector is stainless steel; aluminum; nickel; titanium; calcined carbon; aluminum; carbon; nickel; titanium; It may be one or more types selected from the group consisting of stainless steel surface treated with silver, etc. In addition, the positive electrode current collector may typically have a thickness of 3 ㎛ to 500 ㎛, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive electrode active material including the coating layer. For example, it can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven materials.

Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention may be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described in detail below. Examples of the present invention are provided to more completely explain the present invention to those with average knowledge in the art.

Manufacturing Example 1

A negative electrode active material slurry (solid concentration: 50% by weight) was prepared by adding the negative electrode active material (graphite), the conductive material (carbon black), and the binder (polyvinylidene fluoride) to distilled water at a weight ratio of 96.0:0.5:3.5. The negative electrode active material slurry was applied to one side of a negative electrode current collector (Cu thin film) with a thickness of 8 ㎛, dried, and rolled to prepare a negative electrode.

Production example 2

A non-aqueous electrolyte solution was prepared by adding 1.5 parts by weight of vinylene carbonate (VC) to 98.5 parts by weight of an organic solvent in which 1.0 M LiPF ₆ was dissolved (ethylene carbonate (EC):ethylmethyl carbonate (EMC) = 3:7 volume ratio).

Example 1

<Manufacture of positive electrode active material including coating layer>

100 parts by weight of a positive electrode active material containing a lithium transition metal oxide having a composition expressed as LiNi _0.8 Co _0.1 Mn _0.1 O ₂ and having an average particle diameter (D50) of 10 ㎛, 0.25 parts by weight of tetraethoxysilane, and 0.25 parts by weight of boric acid at 25 ° C. It was stirred with a planetary mixer (MJ Research, AR-100) for 1 minute. Afterwards, heat treatment was performed at 300°C for 3 hours in an air atmosphere to prepare a positive electrode active material including a coating layer.

The positive electrode active material containing the coating layer was heated at a rate of 10 ℃/min from 30 ℃ to 800 ℃ using a thermogravimetric analyzer (Mettler-Toledo, TGA2) and the weight change was measured (N ₂ flow: 50 ml /minute). As a result of the measurement, the content of the coating layer was 0.5 parts by weight compared to 100 parts by weight of the positive electrode active material.

<Manufacture of anode>

The positive electrode active material including the coating layer, the conductive material (carbon black), and the binder (polyvinylidene fluoride) were added to N-methyl-2-pyrrolidone (NMP) at a weight ratio of 97.5:1.0:1.5 to create a positive electrode active material slurry ( Solid concentration: 60% by weight) was prepared. The positive electrode active material slurry was applied to one side of a positive electrode current collector (Al thin film) with a thickness of 15 ㎛, dried, and rolled to prepare a positive electrode.

<Manufacture of lithium secondary batteries>

After manufacturing the electrode assembly by placing a porous polyethylene separator between the positive electrode and the negative electrode of Preparation Example 1, it was placed in a battery case, the non-aqueous electrolyte of Preparation Example 2 was injected, and the pouch-type lithium secondary battery (battery capacity: 6.24) was sealed. ㎃·h) was prepared.

Example 2

In the production of a positive electrode active material including a coating layer, a positive electrode active material, positive electrode, and lithium secondary battery including a coating layer were prepared in the same manner as in Example 1, except that 0.25 parts by weight of dimethoxydimethylsilane was added instead of 0.25 parts by weight of tetraethoxysilane. was manufactured.

Meanwhile, the content of the coating layer was 0.5 parts by weight compared to 100 parts by weight of the positive electrode active material.

Example 3

In the production of a positive electrode active material including a coating layer, a positive electrode active material, positive electrode, and lithium secondary battery including a coating layer were prepared in the same manner as in Example 1, except that 0.50 parts by weight of dimethoxydimethylsilane was added instead of 0.25 parts by weight of tetraethoxysilane. was manufactured.

Meanwhile, the content of the coating layer was 0.75 parts by weight compared to 100 parts by weight of the positive electrode active material.

Comparative Example 1

<Manufacture of anode>

A positive electrode active material containing a lithium transition metal oxide having a composition expressed as LiNi _0.8 Co _0.1 Mn _0.1 O ₂ and having an average particle diameter (D50) of 10 ㎛, a conductive material (carbon black), and a binder (polyvinylidene fluoride) were prepared at 97.5: A positive electrode active material slurry (solid concentration: 60% by weight) was prepared by adding N-methyl-2-pyrrolidone (NMP) at a weight ratio of 1.0:1.5. The positive electrode active material slurry was applied to one side of a positive electrode current collector (Al thin film) with a thickness of 15 ㎛, dried, and rolled to prepare a positive electrode.

<Manufacture of lithium secondary batteries>

After manufacturing the electrode assembly by placing a porous polyethylene separator between the positive electrode and the negative electrode of Preparation Example 1, it was placed in a battery case, the non-aqueous electrolyte of Preparation Example 2 was injected, and the pouch-type lithium secondary battery (battery capacity: 6.24) was sealed. ㎃·h) was prepared.

Comparative Example 2

In the production of a positive electrode active material including a coating layer, a positive electrode active material including a coating layer was prepared in the same manner as in Example 1, except that 0.50 parts by weight of tetraethoxysilane was added instead of 0.25 parts by weight of tetraethoxysilane and boric acid was not added. A positive electrode and lithium secondary battery were manufactured.

Meanwhile, the content of the coating layer was 0.5 parts by weight compared to 100 parts by weight of the positive electrode active material.

Comparative Example 3

In the production of a positive electrode active material including a coating layer, a positive electrode active material including a coating layer, a positive electrode, and a lithium secondary battery were manufactured in the same manner as Example 1, except that 0.50 parts by weight of boric acid was added instead of tetraethoxysilane. did.

Meanwhile, the content of the coating layer was 0.5 parts by weight compared to 100 parts by weight of the positive electrode active material.

Comparative Example 4

<Manufacture of positive electrode active material including coating layer>

100 parts by weight of a positive electrode active material containing a lithium transition metal oxide having a composition expressed as LiNi _0.8 Co _0.1 Mn _0.1 O ₂ and having an average particle diameter (D50) of 10 ㎛, 0.25 parts by weight of tetraethoxysilane, and 0.25 parts by weight of boric acid are mixed with 100 parts by weight of ethanol. After the mixture was added to the reactor and stirred for 4 hours, ethanol was removed in a vacuum oven at 70° C., and adsorption was induced to prepare a positive electrode active material including a coating layer.

The positive electrode active material containing the coating layer was heated at a rate of 10 ℃/min from 30 ℃ to 800 ℃ using a thermogravimetric analyzer (Mettler-Toledo, TGA2) and the weight change was measured (N ₂ flow: 50 ml /minute). As a result of the measurement, the content of the coating layer was 0.5 parts by weight compared to 100 parts by weight of the positive electrode active material.

<Manufacture of anode>

The positive electrode active material including the coating layer, the conductive material (carbon black), and the binder (polyvinylidene fluoride) were added to N-methyl-2-pyrrolidone (NMP) at a weight ratio of 97.5:1.0:1.5 to create a positive electrode active material slurry ( Solid concentration: 60% by weight) was prepared. The positive electrode active material slurry was applied to one side of a positive electrode current collector (Al thin film) with a thickness of 15 ㎛, dried, and rolled to prepare a positive electrode.

<Manufacture of lithium secondary batteries>

After manufacturing the electrode assembly by placing a porous polyethylene separator between the positive electrode and the negative electrode of Preparation Example 1, it was placed in a battery case, the non-aqueous electrolyte of Preparation Example 2 was injected, and the pouch-type lithium secondary battery (battery capacity: 6.24) was sealed. ㎃·h) was prepared.

Experiment example

The physical properties of each lithium secondary battery manufactured in Examples and Comparative Examples were evaluated by the method described below.

(1) Initial discharge capacity evaluation

After activating the lithium secondary battery with 0.1 C constant current (CC) at 25 ° C, it was charged with 0.33 C constant current up to 4.2 V under constant current-constant voltage (CC-CV) charging conditions, then 0.05 C current cut was performed, and under CC conditions. Discharged at 0.33 C until 2.5 V. The charging and discharging was regarded as 1 cycle, and 3 cycles were performed. Subsequently, the initial discharge capacity was measured using a PNE-0506 charger/discharger (PNE Solutions Co., Ltd., 5V, 6A), and the results are shown in Tables 1 and 2 below.

(2) C.O. ₂ Specific gas generation amount

Each lithium secondary battery was charged to 4.2 V at 25°C with a constant current of 0.1 C. Afterwards, discharge was performed to 3 V at a constant current of 0.1 C (1 cycle), and then 200 cycles of charge and discharge were performed in the range of 2.5 V to 4.2 V at 0.33 C at 45°C.

The lithium secondary battery that has been charged and discharged for 1 cycle and the lithium secondary battery that has been charged and discharged for 200 cycles are each drilled in a chamber in a vacuum atmosphere, the gas inside the battery is discharged and collected inside the vacuum chamber, and the gas in the chamber is subjected to gas chromatography-flame. The amount of CO ₂ gas generated (μl) was quantitatively analyzed using an ionization detector (Gas Chromatograph-Flame Ionizaiton detector, GC-FID), and the results are shown in Tables 1 and 2 below.

division Example 1 Example 2 Example 3 Cathode active material (parts by weight) 100 100 100 Tetraethoxysilane (parts by weight) 0.25 0.00 0.00 Dimethoxydimethylsilane (parts by weight) 0.00 0.25 0.50 Boric acid (parts by weight) 0.25 0.25 0.25 Ethanol (parts by weight) 0.00 0.00 0.00 Heat treatment temperature (℃) 300 300 300 Initial discharge capacity (㎃·h/g) 214 215 195 CO ₂ gas generation amount (㎕) 90 88 85

division Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Cathode active material (parts by weight) 100 100 100 100 Tetraethoxysilane (parts by weight) 0.00 0.50 0.00 0.25 Dimethoxydimethylsilane (parts by weight) 0.00 0.00 0.00 0.00 Boric acid (parts by weight) 0.00 0.00 0.50 0.25 Ethanol (parts by weight) 0.00 0.00 0.00 100 Heat treatment temperature (℃) 300 300 300 70 Initial discharge capacity (㎃·h/g) 198 200 214 201 CO ₂ gas generation amount (㎕) 177 97 116 110

Referring to Table 1, Examples 1 to 3 using a positive electrode active material including a coating layer prepared by solid-phase mixing a positive electrode active material, a silicon compound, and boric acid, compared to Comparative Example 1 using a positive electrode active material without a coating layer, CO ₂ The amount of gas generated was significantly reduced.

In addition, in Examples 1 to 3, the amount of CO ₂ gas generated was significantly reduced compared to Comparative Example 2 using a positive electrode active material including a coating layer made only of tetraethoxysilane.

In addition, in Examples 1 to 3, the amount of CO ₂ gas generated was significantly reduced compared to Comparative Example 2 using a positive electrode active material including a coating layer made only of boric acid.

In addition, in Examples 1 to 3, the initial discharge capacity was significantly improved and the amount of CO ₂ gas generated was significantly reduced compared to Comparative Example 4 using ethanol. In Comparative Example 4, it was confirmed that the initial discharge capacity decreased and the amount of CO ₂ gas generated increased because the lithium contained in the positive electrode active material dissolved in ethanol.

Claims (10)

Preparing a mixture by solid-phase mixing a positive electrode active material containing lithium transition metal oxide, a silicon compound represented by the following formula (1), and boric acid; and
Method for producing a positive electrode active material including a coating layer comprising the step of heat treating the mixture to produce a coating layer:
<Formula 1>

In Formula 1 above,
R ¹ to R ⁴ are each independently a halogen group, a hydroxy group, an amine group, a vinyl group, a C ₁ to C ₁₀ alkyl group, a C ₆ to C ₂₀ aryl group, a C ₁ to C ₁₀ alkoxy group, or a C ₁ to C 10 alkyl group. It is a C ₁₀ acyloxy group, and at least one of R ¹ to R ⁴ is a C ₁ to C ₁₀ alkoxy group.
In claim 1,
A method of producing a positive electrode active material including a coating layer, wherein in the step of manufacturing the coating layer, the heat treatment temperature is 171 to 400 ° C.
In claim 1,
A method for producing a positive electrode active material including a coating layer wherein the weight ratio of the silicon compound and boric acid is 1.0:1.0 to 5.0.
In claim 1,
A method for producing a positive electrode active material including a coating layer, wherein the total content of the silicon compound and boric acid is 0.1 to 1.50 parts by weight based on 100 parts by weight of the positive electrode active material.
In claim 1,
The silicone compound is one or more selected from the group consisting of tetramethoxysilane, tetraethoxysilane, dimethoxydimethylsilane, methoxytrimethylsilane, trimethoxy(vinyl)silane, and methoxydimethyl(phenyl)silane. Method for manufacturing a positive electrode active material including a coating layer.
In claim 1,
A method of producing a positive electrode active material including a coating layer, wherein the step of preparing the mixture is performed at 15 to 30 ° C.
In claim 1,
A method of producing a positive electrode active material including a coating layer in which the step of preparing the mixture does not use a solvent.
In claim 1,
The lithium transition metal oxide is a method of producing a positive electrode active material including a coating layer represented by the following formula (2):
<Formula 2>
Li _1+a Ni _b Co _c M ¹ _d M ² _e O ₂
In Formula 2,
M ¹ is one or more selected from Mn and Al,
M ² is one or more selected from W, Mo, Cr, Zr, Ti, Mg, Ta and Nb,
0.00≤a≤0.30, 0.60≤b<1.00, 0.00<c<0.40, 0.00<d<0.40, 0.00≤e≤0.10.
In claim 1,
A method of producing a positive electrode active material including a coating layer, wherein the coating layer includes a unit represented by the following formula (3):
<Formula 3>
*-SiO _x -B _y O _z -*
In Formula 3 above,
x, y, and z are the number of moles per mole of Si, and may each independently be 1 to 20.
A method of manufacturing a positive electrode including a method of manufacturing a positive electrode active material including the coating layer according to claim 1.