Method of preparing positive electrode active material comprising coating layer, method of preparing positive electrode comprising the same

Abstract

The present invention relates to a method for manufacturing a positive electrode active material comprising a coating layer, comprising the steps of: preparing a mixture by solid-state mixing a positive electrode active material comprising a lithium transition metal oxide, a silicon compound, and boric acid; and preparing a coating layer by heat-treating the mixture.

Description

Technology Field

[0001] The present invention relates to a method for manufacturing an anode active material comprising a coating layer and a method for manufacturing an anode comprising the same. More specifically, the invention relates to a method for manufacturing an anode active material comprising a coating layer capable of minimizing the amount of gas generated by side reactions such as surface corrosion of the anode active material and decomposition of a non-aqueous electrolyte, and a method for manufacturing an anode comprising the same. Background Technology

[0003] With the increasing technological development and demand for mobile devices, the demand for rechargeable batteries as an energy source is rapidly rising. Among these rechargeable batteries, lithium-ion batteries, which possess high energy density and voltage, long cycle life, and low self-discharge rates, have been commercialized and are widely used.

[0004] Lithium transition metal oxides are used as cathode active materials for lithium-ion batteries; among these, lithium cobalt oxides such as LiCoO2 are primarily used due to their high operating voltage and excellent capacity characteristics. However, lithium cobalt oxide exhibits poor thermal properties due to the instability of its crystal structure caused by lithium delithiation. Furthermore, since lithium cobalt oxide is expensive, there are limitations to its mass use as a power source in fields such as electric vehicles.

[0005] As materials to replace lithium cobalt oxide, lithium manganese oxides such as LiMnO2 and LiMn2O4, lithium iron phosphate compounds such as LiFePO4, and lithium nickel oxides such as LiNiO2 have been developed. Among these, research and development on lithium nickel oxide is actively underway, as it has a high reversible capacity of about 200 mA·h / g, making it easy to implement large-capacity batteries. However, lithium nickel oxide has a problem in that it does not have excellent thermal stability compared to lithium cobalt oxide, and if an internal short circuit occurs due to external pressure or other factors while charged, the positive electrode active material itself decomposes, causing rupture and ignition of the battery.

[0006] Accordingly, lithium transition metal oxides have been developed in which a portion of the nickel is replaced with transition metals such as cobalt, manganese, and aluminum as a method to improve the low thermal stability of lithium nickel oxide while maintaining its excellent reversible capacity. However, in the case of lithium secondary batteries using such lithium transition metal oxides, particularly those containing a high amount of nickel, as the cathode active material, there is a problem of reduced stability due to side reactions such as surface corrosion of the cathode active material caused by direct contact between the electrolyte and the cathode active material, and gas generation resulting from the decomposition of the non-aqueous electrolyte. Prior art literature

[0008] KR2012-0129926A The problem to be solved

[0009] The objective of the present invention is to provide a method for manufacturing an anode active material comprising a coating layer capable of minimizing the amount of gas generated by side reactions such as surface corrosion of the anode active material and decomposition of a non-aqueous electrolyte, and a method for manufacturing an anode comprising the same. means of solving the problem

[0011] To solve the above-mentioned problem, the present invention provides a method for manufacturing a positive electrode active material comprising a coating layer, comprising the steps of: (1) preparing a mixture by solid-state mixing a positive electrode active material comprising a lithium transition metal oxide, a silicon compound represented by the following chemical formula 1, and boric acid; and heat-treating the mixture to prepare a coating layer.

[0012] <Chemical Formula 1>

[0013]

[0014] In the above chemical formula 1

[0015] R 1 to R 4 Each independently, a halogen group, a hydroxyl group, an amine group, a vinyl group, C1 to C 10 alkyl group of, C6 to C 20 The aryl group of, C1 to C10 The alkoxy group or C1 to C 10 It is an acyloxy group of, but R 1 to R 4 At least one of C1 to C 10 It is the alkoxy group.

[0016] In addition, (2) the present invention provides a method for manufacturing an anode active material comprising a coating layer, wherein, in the step of manufacturing the coating layer in (1), the heat treatment temperature is 171 to 400 ℃.

[0017] In addition, (3) the present invention provides a method for manufacturing an anode active material comprising a coating layer in which the weight ratio of the silicon compound to the boric acid in (1) or (2) is 1.0:1.0 to 5.0.

[0018] In addition, (4) the present invention provides a method for manufacturing a positive electrode active material comprising a coating layer in which, in any one of (1) to (3), the total content of the silicon compound and boric acid is 0.1 to 1.50 parts by weight per 100 parts by weight of the positive electrode active material.

[0019] In addition, (5) the present invention provides a method for manufacturing an anode active material comprising a coating layer in which, in any one of (1) to (4), the silicon compound is one or more selected from the group consisting of tetramethoxysilane, tetraethoxysilane, dimethoxydimethylsilane, methoxytrimethylsilane, trimethoxy(vinyl)silane and methoxydimethyl(phenyl)silane.

[0020] In addition, (6) the present invention provides a method for manufacturing an anode active material comprising a coating layer, wherein, in any one of (1) to (5), the step of manufacturing the mixture is performed at 15 to 30 ℃.

[0021] In addition, (7) the present invention provides a method for manufacturing an anode active material comprising a coating layer, wherein, in any one of (1) to (6), the step of manufacturing the mixture does not use a solvent.

[0022] In addition, (8) the present invention provides a method for manufacturing an anode active material comprising a coating layer in which, in any one of (1) to (7), the lithium transition metal oxide is represented by the following chemical formula 2:

[0023] <Chemical Formula 2>

[0024] Li 1+a Ni b Co c M 1 d M 2 e O2

[0025] In the above chemical formula 2,

[0026] M 1 It is one or more selected from Mn and Al, and

[0027] M 2 is one or more selected from W, Mo, Cr, Zr, Ti, Mg, Ta, and Nb, and

[0028] 0.00≤a≤0.30, 0.60≤b<1.00, 0.00 <c<0.40, 0.00<d<0.40, 0.00≤e≤0.10이다.

[0029] In addition, (9) the present invention provides a method for manufacturing an anode active material comprising a coating layer wherein the coating layer comprises a unit represented by the following chemical formula 3:

[0030] <Chemical Formula 3>

[0031] *-SiO x -B y O z -*

[0032] In the above chemical formula 3,

[0033] x, y, and z are the number of moles per 1 mole of Si, and each can be independently 1 to 20.

[0034] In addition, (10) the present invention provides a method for manufacturing an anode comprising a method for manufacturing an anode active material including a coating layer according to any one of (1) to (9). Effects of the invention

[0036] An anode active material comprising a coating layer manufactured by the manufacturing method according to the present invention can minimize the amount of gas generated due to side reactions such as surface corrosion of the anode active material and decomposition of the non-aqueous electrolyte.

[0037] The thermal stability of the anode active material comprising a coating layer prepared by the manufacturing method according to the present invention can be significantly improved.

[0038] The positive electrode active material comprising a coating layer manufactured by the manufacturing method according to the present invention minimizes the breakdown of the coating layer, thereby improving the long-term lifespan of the lithium secondary battery.

[0039] The conductivity of lithium ions is improved due to the positive active material including a coating layer manufactured by the manufacturing method according to the present invention, thereby improving the capacity of the lithium secondary battery. Specific details for implementing the invention

[0042] Terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0043] The terms used in this invention are used merely to describe specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this invention, terms such as "comprising" or "having" are to be understood as specifying the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and not as precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0044] In this specification, the term "on" means not only cases where one configuration is formed on the immediate upper surface of another configuration, but also cases where a third configuration is interposed between these configurations.

[0046] 1. Method for manufacturing an anode active material including a coating layer

[0048] A method for manufacturing a positive electrode active material comprising a coating layer according to one embodiment of the present invention comprises: a step of preparing a mixture by solid-state mixing a positive electrode active material comprising a lithium transition metal oxide, a silicon compound represented by the following chemical formula 1, and boric acid; and a step of preparing a coating layer by heat-treating the mixture.

[0049] <Chemical Formula 1>

[0050]

[0051] In the above chemical formula 1

[0052] R 1 to R 4 Each independently, a halogen group, a hydroxyl group, an amine group, a vinyl group, C1 to C 10 alkyl group of, C6 to C 20 The aryl group of, C1 to C 10 The alkoxy group or C1 to C 10 It is an acyloxy group of, but R 1 to R4 At least one of C1 to C 10 It is the alkoxy group.

[0054] Hereinafter, a method for manufacturing an anode active material including a coating layer according to one embodiment of the present invention will be described in detail.

[0056] 1) Preparation of a mixture

[0058] First, a mixture is prepared by solid-state mixing of a positive electrode active material containing a lithium transition metal oxide, a silicon compound represented by Chemical Formula 1, and boric acid.

[0059] The above lithium transition metal oxide can be represented by the following chemical formula 2:

[0060] <Chemical Formula 2>

[0061] Li 1+a Ni b Co c M 1 d M 2 e O2

[0062] In the above chemical formula 1,

[0063] M 1 It is one or more selected from Mn and Al, and

[0064] M 2 is one or more selected from W, Mo, Cr, Zr, Ti, Mg, Ta, and Nb, and

[0065] 0.00≤a≤0.30, 0.60≤b<1.00, 0.00 <c<0.40, 0.00<d<0.40, 0.00≤e≤0.10이다.

[0067] The above 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.

[0068] The above b represents the molar ratio of nickel among the total 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-described range, excellent capacitance characteristics can be achieved.

[0069] The above c represents the molar ratio of cobalt among the total transition metals, 0.00 <c<0.40, 0.01≤c≤0.35, 또는 0.05≤c≤0.35일 수 있다.

[0070] The above d is M among the total transition metals. 1 Representing the molar ratio of, 0.00 <d<0.40, 0.01≤d≤0.35, 또는 0.05≤d≤0.35일 수 있다.

[0071] The above e is M among the total transition metals 2 It represents the molar ratio of , which can be 0.00≤w≤0.10 or 0.00≤w≤0.05.

[0073] The above silicon compound can undergo a condensation reaction with hydroxyl groups on the surface of the lithium transition metal oxide through a hydrolysis reaction, thereby enabling chemical bonding with the surface of the positive electrode active material. Through this chemical bonding, a coating layer can be easily prepared on the surface of the positive electrode active material.

[0074] In the above chemical formula 1, R 1 to R 4 Each independently has a vinyl group, C1 to C 10 alkyl group of, C6 to C 20 The aryl group of or C1 to C 10 It is the alkoxy group of, but R 1 to R 4 At least one of C1 to C 10 It is desirable that it be an alkoxy group.

[0075] In addition, in the above Chemical Formula 1, R 1 to R 4 Each independently C1 to C 10 It may be an alkoxy group; C1 to C 10alkyl group of or C1 to C 10 It is the alkoxy group of, but R 1 to R 4 At least one of C1 to C 10 It may be an alkoxy group; a vinyl group or C1 to C 10 It is the alkoxy group of, but R 1 to R 4 At least one of C1 to C 10 It may be an alkoxy group; C1 to C 10 alkyl group of, C6 to C 20 The aryl group of or C1 to C 10 It is the alkoxy group of, but R 1 to R 4 At least one of C1 to C 10 It can be an alkoxy group.

[0076] The above silicon compound may be one or more selected from the group consisting of tetramethoxysilane, tetraethoxysilane, dimethoxydimethylsilane, methoxytrimethylsilane, trimethoxy(vinyl)silane, and methoxydimethyl(phenyl)silane, and among these, tetraethoxysilane and dimethoxydimethylsilane are preferred as they are commercially available and react easily with the cathode active material.

[0078] When the above boric acid is used as a raw material for the coating layer of the positive electrode active material, the conductivity of lithium ions in the positive electrode active material is improved, and the capacity of the lithium secondary battery can be significantly improved.

[0080] When the above-mentioned positive electrode active material, silicon compound, and boric acid are mixed in a solid state, compared to the case of mixing in a liquid state, the process is simple and does not require facilities such as expensive explosion-proof equipment required when using organic solvents, thereby reducing process costs. In addition, since the lithium in the positive electrode active material can be dissolved in organic solvents, specifically in alcohol solvents such as ethanol, the capacity may decrease; however, by mixing in a solid state, the decrease in capacity can be prevented.

[0082] The weight ratio of the silicon compound to the boric acid may be 1.0:1.0 to 5.0, and 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, or 1.0:1.0 to 3.5. If the above conditions are satisfied, the problem of capacitance reduction due to increased resistance may not occur.

[0084] With respect to 100 parts by weight of the above positive 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 more, 0.50 parts by weight or more; 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, 1.40 parts by weight or less. If the above conditions are satisfied, a problem of capacity reduction due to increased resistance may not occur.

[0086] The step of preparing the above mixture can be performed at 15 to 30°C, preferably 20 to 25°C. If the above conditions are satisfied, mixing can be performed without separate heat treatment, so the process is simplified and manufacturing efficiency can be improved.

[0088] 2) Preparation of the coating layer

[0090] Next, the above mixture is heat-treated to produce a coating layer.

[0092] The above 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, 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, and 320 ℃ or lower to produce a coating layer by heat treatment.

[0093] Under the heat treatment temperature conditions described above, boric acid becomes liquid, so it can easily chemically react with the positive electrode active material and the silicon compound without a separate solvent, thereby enabling the preparation of a coating layer containing boron oxide on the positive electrode active material. Specifically, the liquid silicon compound can form a coating layer by undergoing a hydrolysis reaction by moisture on the surface of the positive electrode active material, followed by a condensation polymerization reaction with the liquid boric acid and the hydroxyl groups on the surface of the positive electrode active material. Furthermore, this prevents the phenomenon in which the initial discharge capacity of a lithium secondary battery decreases due to lithium moving within the positive electrode crystal and oxidizing on the positive electrode surface.

[0095] Since no separate solvent is used in the step of manufacturing the above coating layer, a drying process to remove the solvent is not required, so energy efficiency can be significantly improved.

[0097] The above coating layer may comprise a unit represented by the following chemical formula 3:

[0098] <Chemical Formula 3>

[0099] *-SiO x -B y O z -*

[0100] In the above chemical formula 3,

[0101] x, y, and z are the number of moles per 1 mole of Si, and each can be independently 1 to 20.

[0102] In addition, * may be a site that combines with the remaining composition of the coating layer and / or combines with the positive active material.

[0104] Due to the unit represented by the above chemical formula 3, the thermal stability of the positive active material including the coating layer can be significantly improved.

[0106] 2. Method for manufacturing the anode

[0108] A method for manufacturing a positive electrode according to another embodiment of the present invention includes a method for manufacturing a positive electrode active material comprising the coating layer described above. Specifically, it includes the steps of: manufacturing a positive electrode active material comprising a coating layer according to one embodiment of the present invention; and applying a positive electrode active material slurry, prepared by dissolving or dispersing the positive electrode active material comprising the coating layer in a solvent, onto a positive electrode current collector, and then drying and rolling.

[0109] In addition to the positive active material including the above coating layer, a binder and a conductive material can be dissolved or dispersed in a solvent.

[0110] The binder serves to improve adhesion between positive active material particles and adhesion between the positive active material and the current collector. The binder may be one or more selected from the group consisting of polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), and fluororubber. The content of the binder may be 1 to 30 parts by weight per 100 parts by weight of the positive active material including the coating layer.

[0111] The above conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it may be used without special limitations as long as it has electronic conductivity without causing chemical changes. The above conductive material may be one or more selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, copper, nickel, aluminum, silver, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives. The content of the above conductive material may be 1 to 30 parts by weight per 100 parts by weight of the positive electrode active material including the coating layer.

[0113] The above positive current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery. The above positive current collector may be one or more selected from the group consisting of stainless steel; aluminum; nickel; titanium; calcined carbon; aluminum; carbon; nickel; titanium; and stainless steel surface-treated with silver, etc. Additionally, the above positive current collector may typically have a thickness of 3 μm to 500 μm, and may form fine irregularities on the surface of the current collector to increase the adhesion of the positive active material including a coating layer. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0115] Hereinafter, the present invention will be described in detail with reference to examples to specifically explain the invention. However, the embodiments according to the present invention may be modified in various different forms, and the scope of the present invention should not be interpreted as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the invention to those with average knowledge in the art.

[0117] Preparation Example 1

[0118] A negative electrode active material slurry (solid content concentration: 50 wt%) was prepared by adding a negative electrode active material (graphite), a conductive material (carbon black), and a binder (polyvinylidene fluoride) to distilled water in a weight ratio of 96.0:0.5:3.5. The negative electrode active material slurry was coated on one surface of a negative electrode current collector (Cu thin film) with a thickness of 8 μm, and a negative electrode was manufactured by drying and rolling.

[0120] Preparation Example 2

[0121] A non-aqueous electrolyte was prepared by adding 1.5 parts by weight of vinylene carbonate (VC) to 98.5 parts by weight of an organic solvent (ethylene carbonate (EC):ethylmethyl carbonate (EMC) = 3:7 volume ratio) in which 1.0 M LiPF6 was dissolved.

[0123] Example 1

[0124] <Preparation of a positive electrode active material including a coating layer>

[0125] LiNi 0.8 Co 0.1 Mn 0.1 100 parts by weight of a positive electrode active material containing a lithium transition metal oxide having a composition represented by O2 and having an average particle size (D50) of 10 μm, 0.25 parts by weight of tetraethoxysilane, and 0.25 parts by weight of boric acid were stirred in a planetary mixer (MJ Research, AR-100) at 25°C for 1 minute. Then, the mixture was heat-treated in an air atmosphere at 300°C for 3 hours to produce a positive electrode active material including a coating layer.

[0126] The change in weight of the positive electrode active material including the coating layer was measured using a thermogravimetric analyzer (Mettler-Toledo, TGA2) while increasing the temperature from 30 ℃ to 800 ℃ at a rate of 10 ℃ / min (N2 flow: 50 ml / min). As a result of the measurement, the content of the coating layer was 0.5 parts by weight relative to 100 parts by weight of the positive electrode active material.

[0128] Manufacturing of the anode

[0129] A positive active material slurry (solid content: 60 wt%) was prepared by adding a positive active material including the above coating layer, a conductive material (carbon black), and a binder (polyvinylidene fluoride) to N-methyl-2-pyrrolidone (NMP) in a weight ratio of 97.5:1.0:1.5. The positive active material slurry was applied to one surface of a positive current collector (Al thin film) with a thickness of 15 μm, and a positive electrode was manufactured by drying and rolling.

[0131] Manufacture of Lithium Secondary Batteries

[0132] An electrode assembly was prepared by placing a porous polyethylene separator between the anode and the cathode of Preparation Example 1, placing the assembly in a battery case, injecting the non-aqueous electrolyte of Preparation Example 2, and sealing it to produce a pouch-type lithium secondary battery (battery capacity: 6.24 mA·h).

[0134] Example 2

[0135] In the preparation of a positive electrode active material including a coating layer, a positive electrode and a lithium secondary battery 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.

[0136] Meanwhile, the content of the coating layer was 0.5 parts by weight relative to 100 parts by weight of the positive active material.

[0138] Example 3

[0139] In the preparation of a positive electrode active material including a coating layer, 0.50 parts by weight of dimethoxydimethylsilane was added instead of 0.25 parts by weight of tetraethoxysilane, and a positive electrode active material, a positive electrode, and a lithium secondary battery were prepared in the same manner as in Example 1.

[0140] Meanwhile, the content of the coating layer was 0.75 parts by weight relative to 100 parts by weight of the positive active material.

[0142] Comparative Example 1

[0143] Manufacturing of the anode

[0144] LiNi 0.8 Co 0.1 Mn 0.1 A positive electrode active material slurry (solid content: 60 wt%) was prepared by adding a positive electrode active material containing a lithium transition metal oxide having a composition represented by O2 and an average particle size (D50) of 10 μm, a conductive material (carbon black), and a binder (polyvinylidene fluoride) to N-methyl-2-pyrrolidone (NMP) in a weight ratio of 97.5:1.0:1.5. The positive electrode active material slurry was coated on one surface of a positive electrode current collector (Al thin film) with a thickness of 15 μm, and a positive electrode was manufactured by drying and rolling.

[0146] Manufacture of Lithium Secondary Batteries

[0147] An electrode assembly was prepared by placing a porous polyethylene separator between the anode and the cathode of Preparation Example 1, placing the assembly in a battery case, injecting the non-aqueous electrolyte of Preparation Example 2, and sealing it to produce a pouch-type lithium secondary battery (battery capacity: 6.24 mA·h).

[0149] Comparative Example 2

[0150] In the preparation of a positive electrode active material including a coating layer, 0.50 parts by weight of tetraethoxysilane was added instead of 0.25 parts by weight of tetraethoxysilane, and boric acid was not added; except for this, a positive electrode active material including a coating layer, a positive electrode, and a lithium secondary battery were prepared in the same manner as in Example 1.

[0151] Meanwhile, the content of the coating layer was 0.5 parts by weight relative to 100 parts by weight of the positive active material.

[0153] Comparative Example 3

[0154] In the preparation of a positive electrode active material including a coating layer, a positive electrode and a lithium secondary battery were prepared in the same manner as in Example 1, except that 0.50 parts by weight of boric acid was added instead of tetraethoxysilane.

[0155] Meanwhile, the content of the coating layer was 0.5 parts by weight relative to 100 parts by weight of the positive active material.

[0157] Comparative Example 4

[0158] <Preparation of a positive electrode active material including a coating layer>

[0159] LiNi 0.8 Co 0.1 Mn 0.1 100 parts by weight of a positive active material having a composition represented by O2 and containing a lithium transition metal oxide with an average particle size (D50) of 10 μm, 0.25 parts by weight of tetraethoxysilane, and 0.25 parts by weight of boric acid were added to 100 parts by weight of ethanol, stirred for 4 hours, and then adsorption was induced in a vacuum oven at 70°C while removing the ethanol to produce a positive active material including a coating layer.

[0160] The change in weight of the positive electrode active material including the coating layer was measured using a thermogravimetric analyzer (Mettler-Toledo, TGA2) while increasing the temperature from 30 ℃ to 800 ℃ at a rate of 10 ℃ / min (N2 flow: 50 ml / min). As a result of the measurement, the content of the coating layer was 0.5 parts by weight relative to 100 parts by weight of the positive electrode active material.

[0162] Manufacturing of the anode

[0163] A positive active material slurry (solid content: 60 wt%) was prepared by adding a positive active material including the above coating layer, a conductive material (carbon black), and a binder (polyvinylidene fluoride) to N-methyl-2-pyrrolidone (NMP) in a weight ratio of 97.5:1.0:1.5. The positive active material slurry was applied to one surface of a positive current collector (Al thin film) with a thickness of 15 μm, and a positive electrode was manufactured by drying and rolling.

[0165] Manufacture of Lithium Secondary Batteries

[0166] An electrode assembly was prepared by placing a porous polyethylene separator between the anode and the cathode of Preparation Example 1, placing the assembly in a battery case, injecting the non-aqueous electrolyte of Preparation Example 2, and sealing it to produce a pouch-type lithium secondary battery (battery capacity: 6.24 mA·h).

[0168] Experimental Example

[0169] The physical properties of each lithium secondary battery prepared in the examples and comparative examples were evaluated using the method described below.

[0171] (1) Evaluation of initial discharge capacity

[0172] After activating the lithium secondary battery at 25°C with a constant current (CC) of 0.1 C, it was charged to 4.2 V with a constant current of 0.33 C under constant current-constant voltage (CC-CV) charging conditions, followed by a 0.05 C current cut, and then discharged to 2.5 V with a constant current of 0.33 C under CC conditions. The above charging and discharging was counted as one cycle, and three cycles were performed. Subsequently, the initial discharge capacity was measured using a PNE-0506 charger / discharger (PNE Solution Co., Ltd., 5V, 6A), and the results are shown in Tables 1 and 2 below.

[0174] (2) CO 2 Specific gas generation amount

[0175] Each lithium secondary battery was charged to 4.2 V at 25 ℃ with a constant current of 0.1 C. Afterward, it was discharged to 3 V with a constant current of 0.1 C (1 cycle), and then 200 cycles of charge and discharge were performed at 45 ℃ with 0.33 C in the range of 2.5 V to 4.2 V.

[0176] The lithium secondary battery that has been charged and discharged once and the lithium secondary battery that has been charged and discharged twice, respectively, were each perforated in a vacuum chamber to vent the gas inside the battery and collect it inside the vacuum chamber. The amount of CO2 gas generated (μl) was quantitatively analyzed using a gas chromatograph-flame ionization detector (GC-FID), and the results are shown in Tables 1 and 2 below.

[0177] division Example 1 Example 2 Example 3 positive 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 (°C) 300 300 300 Initial discharge capacity (mA·h / g) 214 215 195 CO2 gas generation amount (µl) 90 88 85

[0178] division Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 positive 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 (°C) 300 300 300 70 Initial discharge capacity (mA·h / g) 198 200 214 201 CO2 gas generation amount (µl) 177 97 116 110

[0179] Referring to Table 1 above, Examples 1 to 3, which use a positive electrode active material comprising a coating layer prepared by solid-state mixing of a positive electrode active material, a silicon compound, and boric acid, showed a significantly reduced amount of CO2 gas generation compared to Comparative Example 1, which uses a positive electrode active material without a coating layer.

[0180] In addition, Examples 1 to 3 showed a significantly reduced amount of CO2 gas compared to Comparative Example 2, which used a cathode active material comprising a coating layer made solely of tetraethoxysilane.

[0181] In addition, Examples 1 to 3 showed a significantly reduced amount of CO2 gas compared to Comparative Example 2, which used a positive electrode active material containing a coating layer made only of boric acid.

[0182] In addition, Examples 1 to 3 showed significantly improved initial discharge capacity and significantly reduced CO2 gas generation compared to Comparative Example 4 using ethanol. In the case of Comparative Example 4, it was confirmed that the initial discharge capacity decreased and the amount of CO2 gas generated increased because the lithium contained in the cathode active material dissolved in the ethanol.

Claims

Claim 1 A method for manufacturing a positive electrode active material comprising: a step of preparing a mixture by solid-state mixing a positive electrode active material comprising a lithium transition metal oxide, a silicon compound represented by the following Chemical Formula 1, and boric acid; and a step of preparing a coating layer by heat-treating the mixture, wherein the weight ratio of the silicon compound represented by the following Chemical Formula 1 to the boric acid is 1.0:1.0 to 5.0; a coating layer comprising: <Chemical Formula 1> R in Chemical Formula 1 above 1 to R 4 Each independently, a halogen group, a hydroxyl group, an amine group, a vinyl group, C1 to C 10 alkyl group of, C6 to C 20 The aryl group of, C1 to C 10 The alkoxy group or C1 to C 10 It is an acyloxy group of, but R 1 to R 4 At least one of C1 to C 10 It is the alkoxy group. Claim 2 A method for manufacturing an anode active material comprising a coating layer according to claim 1, wherein the heat treatment temperature in the step of manufacturing the coating layer is 171 to 400 ℃. Claim 3 delete Claim 4 A method for manufacturing an anode active material according to claim 1, comprising a coating layer wherein, with respect to 100 parts by weight of the anode active material, the total content of the silicon compound and boric acid is 0.1 to 1.50 parts by weight. Claim 5 A method for manufacturing an anode active material according to claim 1, wherein the silicon compound is one or more selected from the group consisting of tetramethoxysilane, tetraethoxysilane, dimethoxydimethylsilane, methoxytrimethylsilane, trimethoxy(vinyl)silane, and methoxydimethyl(phenyl)silane, comprising a coating layer. Claim 6 A method for manufacturing an anode active material comprising a coating layer according to claim 1, wherein the step of manufacturing the mixture is performed at 15 to 30 ℃. Claim 7 A method for manufacturing an anode active material comprising a coating layer, wherein the step of manufacturing the mixture according to claim 1 does not use a solvent. Claim 8 Method for manufacturing an anode active material according to claim 1, comprising a coating layer wherein the lithium transition metal oxide is represented by the following chemical formula 2: <Chemical Formula 2>Li 1+a Ni b Co c M 1 d M 2 e In the above chemical formula 2, O2, M 1 is one or more selected from Mn and Al, and M 2 is one or more selected from W, Mo, Cr, Zr, Ti, Mg, Ta, and Nb, and 0.00≤a≤0.30, 0.60≤b<1.00, 0.00 <c<0.40, 0.00<d<0.40, 0.00≤e≤0.10이다. Claim 9 Method for manufacturing an anode active material according to claim 1, wherein the coating layer comprises a unit represented by the following chemical formula 3: <Chemical Formula 3>*-SiO x -B y O z -*In the above chemical formula 3, x, y, and z are the number of moles per 1 mole of Si, and each can be independently 1 to 20. Claim 10 A method for manufacturing an anode comprising a method for manufacturing an anode active material including a coating layer according to claim 1.

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