Method for producing negative electrode active material, negative electrode and secondary battery

Abstract

The present invention provides a method for producing a mixture of green coke particles, calcined coke particles, and a binder, the method comprising the steps of: mixing green coke particles, calcined coke particles, and a binder to obtain a mixture; and heat-treating the mixture to graphitize it, thereby forming artificial graphite particles in the form of secondary particles in which primary artificial graphite particles are bonded to each other; and the average particle size (D 50 ) is the average particle size of the calcined coke particles (D 50 The present invention relates to a method for producing a negative electrode active material, the method being characterized in that the capacitance of the negative electrode active material is larger than that of the negative electrode active material.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0121303 dated September 10, 2021, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference. The present invention relates to a method for producing a negative electrode active material, a negative electrode, and a secondary battery. [Background technology]

[0002] With the depletion of fossil fuels causing rising energy prices and increasing concerns about environmental pollution, alternative, environmentally friendly energy sources have become an essential factor for future life.

[0003] In particular, with the development of technology and increasing demand for mobile devices, the demand for secondary batteries as an environmentally friendly alternative energy source is rapidly increasing.

[0004] In addition, with the recent growing interest in environmental issues, much research is being conducted into electric vehicles (EVs) and hybrid electric vehicles (HEVs) that can replace vehicles that use fossil fuels such as gasoline and diesel, which are one of the main causes of air pollution. Lithium secondary batteries, which have high energy density, high discharge voltage, and stable output, are being primarily researched and used as the power source for such electric vehicles (EVs) and hybrid electric vehicles (HEVs).

[0005] In the secondary battery, lithium metal has traditionally been used as the negative electrode. However, as the risk of short circuiting of the battery due to the formation of dendrites and the resulting explosion has become an issue, the use of carbon-based active materials, which allow reversible intercalation and deintercalation of lithium ions and maintain structural and electrical properties, is gaining popularity.

[0006] The carbon-based active material has been applied in various forms, such as artificial graphite, natural graphite, and hard carbon, among which graphite-based active materials are the most widely used because they have excellent reversibility and can ensure the life characteristics of lithium secondary batteries. Because the graphite-based active material has a low discharge voltage of -0.2 V relative to lithium, batteries using the graphite-based active material can exhibit a high discharge voltage of 3.6 V, providing many advantages in terms of the energy density of lithium batteries.

[0007] Among these, artificial graphite has advantages over natural graphite, such as superior swelling prevention and excellent high-temperature properties. However, artificial graphite has fewer voids than natural graphite, resulting in lower output characteristics. Therefore, it is known to use artificial graphite in the form of secondary particles in which primary particles are aggregated or bonded together to improve output characteristics and form voids within the particles.

[0008] However, artificial graphite assembled from secondary particles is likely to have an irregular and uneven shape due to the assembly of primary particles. When used in a negative electrode, such artificial graphite has problems such as poor electrode adhesion, which reduces processability due to the reduced electrode adhesion, and the occurrence of active material detachment during operation of the negative electrode, which reduces long-term cycle performance.

[0009] Japanese Patent No. 4403327 discloses graphite powder for the negative electrode of a lithium ion secondary battery, but fails to provide an alternative to the above-mentioned problems. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Patent No. 4403327 Summary of the Invention [Problem to be solved by the invention]

[0011] An object of the present invention is to provide a method for manufacturing an anode active material containing artificial graphite in the form of secondary particles, which has excellent adhesive strength and improved fast charging performance.

[0012] Another object of the present invention is to provide a negative electrode including a negative electrode active material produced by the above-described method for producing a negative electrode active material.

[0013] Another object of the present invention is to provide a secondary battery including the above-mentioned negative electrode. [Means for solving the problem]

[0014] The present invention includes a step of mixing green coke particles, calcined coke particles, and a binder, and a step of graphitizing the mixture by heat treating the mixture to form artificial graphite particles in the form of secondary particles in which primary artificial graphite particles are bonded to each other, and the average particle size (D 50 ) is the average particle size (D 50 The present invention provides a method for producing a negative electrode active material characterized in that the capacitance is larger than that of the negative electrode active material.

[0015] The present invention also provides a negative electrode comprising: a negative electrode current collector; and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes the negative electrode active material produced by the method for producing a negative electrode active material described above. The present invention also provides a secondary battery including the above-described negative electrode, a positive electrode facing the negative electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte. [Effects of the Invention]

[0016] The method for producing an anode active material according to the present invention includes the steps of: producing an anode active material containing artificial graphite in the form of secondary particles; using green coke particles and calcined coke particles as raw materials for primary particles; and 50 ) is the average particle size (D 50) The negative electrode including the negative electrode active material prepared by the method for preparing the negative electrode active material of the present invention can have improved adhesive strength and fast charging performance at the same time. DETAILED DESCRIPTION OF THE INVENTION

[0017] The terms and words used in this specification and claims should not be interpreted as being limited to their ordinary and dictionary meanings, but should be interpreted as meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that an inventor can appropriately define the concepts of terms in order to best explain his or her invention.

[0018] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise.

[0019] In this specification, terms such as "comprises," "comprises," or "has" are to be understood as specifying the presence of embodied features, numbers, steps, components, or combinations thereof, without precluding the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0020] In this specification, the average particle size (D 50 The average particle size (D) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. 50 ) can be measured, for example, by using a laser diffraction method. The laser diffraction method generally enables measurement of particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0021] The present invention will be specifically described below.

[0022] Method for producing negative electrode active material The present invention relates to a method for producing a negative electrode active material, and more particularly to a method for producing a negative electrode active material for a lithium secondary battery.

[0023] Specifically, the method for preparing a negative electrode active material according to the present invention includes the steps of mixing green coke particles, calcined coke particles, and a binder, and graphitizing the mixture by heat treating the mixture to form secondary particles of artificial graphite particles in which primary artificial graphite particles are bonded to each other, and the average particle size (D 50 ) is the average particle size (D 50 ) is characterized by being larger than

[0024] Conventionally, artificial graphite in the form of secondary particles is likely to have an irregular and non-smooth shape due to the shape of primary particles and the assembly of these particles. When used in a negative electrode, such artificial graphite has problems such as poor electrode adhesion, which reduces processability due to the reduced electrode adhesion, and problems such as the occurrence of active material detachment during negative electrode operation, resulting in poor long-term cycle performance. Furthermore, in the case of artificial graphite in the form of secondary particles, as the size of the primary particles increases, adhesion tends to improve, but fast charging performance tends to decrease. Conversely, in the case of artificial graphite in the form of secondary particles, as the size of the primary particles decreases, fast charging performance tends to improve, but adhesion tends to decrease.

[0025] In order to solve this problem, the present invention provides a method for producing artificial graphite particles in the form of secondary particles in which primary artificial graphite particles are bonded to each other, by mixing green coke particles, calcined coke particles, and a binder, and by heat-treating the mixture to graphitize it, and the average particle size (D 50 ) is the average particle size (D 50 The green coke particles have round and gentle characteristics, and have a larger average particle size (D) than the calcined coke particles. 50) is larger, which helps to improve the overall adhesive strength of the negative electrode active material. Meanwhile, the calcined coke particles have a larger average particle size (D 50 ) is small, which contributes to improving fast charging performance and excellent capacity retention. Therefore, the negative electrode active material produced by the method for producing a negative electrode active material of the present invention can simultaneously improve fast charging performance and adhesive strength.

[0026] The method for preparing a negative electrode active material of the present invention includes a step of mixing green coke particles, calcined coke particles, and a binder. 50 ) is the average particle size (D 50 ) is larger than

[0027] The green coke particles and the calcined coke particles may be graphitized to form primary particle-type artificial graphite particles, and the primary artificial graphite particles derived from the green coke particles and the calcined coke particles may be bonded to each other to form secondary particle-type artificial graphite particles.

[0028] The green coke particles can be obtained by coking coal or petroleum residues, or processed pitch, under high pressure and high temperature conditions. The green coke particles are obtained immediately after the coking process and may contain volatile components (e.g., sulfur) because they are not subjected to heat treatments such as calcination or carbonization.

[0029] The green coke particles may have a smoother surface and a more gradual shape than the calcined coke particles described below. Therefore, when the green coke particles are converted into secondary particles, they can smooth the surface of the entire particle and contribute to improving the uniformity of the shape, thereby contributing to improving the adhesive strength of the negative electrode active material. In particular, since the green coke particles have a larger average particle size than the calcined coke particles, the adhesive strength of the negative electrode active material produced therefrom can be further improved.

[0030] The average particle size of the green coke particles (D 50 ) may be 9 μm to 15 μm, specifically 10 μm to 13 μm. When the diameter is within this range, the effect of improving the adhesive strength of the negative electrode active material can be maximized while preventing a decrease in fast charging performance due to excessively large green coke particles.

[0031] The true density of the green coke particles may be 1.20 g / cc to 1.60 g / cc, specifically 1.3 g / cc to 1.5 g / cc. In this specification, the true density may refer to the density of only the particles, excluding the gaps between the particles to be measured. The true density can be measured using a gas pycnometer.

[0032] The green coke particles may contain 1,000 ppm to 5,000 ppm, specifically 1,500 ppm to 3,000 ppm, of sulfur (S). The sulfur content may be measured by inductively coupled plasma (ICP) analysis.

[0033] The calcined coke particles may refer to coke obtained by calcining coal or petroleum-based residues, or processed pitch, under high pressure and high temperature conditions. The calcined coke particles may contain no or only a trace amount of volatile matter due to the calcination process.

[0034] The calcined coke particles generally tend to be flatter and sharper in shape than the green coke particles, but have excellent volume retention characteristics. 50 ) is the average particle size (D 50 ) it is possible to realize a negative electrode active material with excellent capacity retention and fast charging characteristics without reducing adhesive strength.

[0035] The average particle size of the calcined coke particles (D 50 ) may be 3 μm to 8 μm, specifically 6 μm to 8 μm. When it is in this range, it may be possible to improve the rapid charging performance of the negative electrode active material while preventing a decrease in adhesive strength due to excessively large calcined coke particles.

[0036] The calcined coke particles may have a true density of 1.80 g / cc to 2.25 g / cc, specifically 1.9 g / cc to 2.2 g / cc.

[0037] The calcined coke particles may also contain sulfur (S) in an amount of 50 ppm to 1,000 ppm, specifically 80 ppm to 200 ppm.

[0038] In the present invention, the average particle size (D 50 ) is the average particle size (D 50 The green coke particles have a smooth and gentle surface and a larger average particle size (D 50 ) is larger than that of the green coke particles, which can help improve the overall adhesive strength of the negative active material. 50 ) is small, which contributes to improved fast charging performance and excellent capacity retention. Therefore, the negative electrode active material prepared by the method for preparing a negative electrode active material of the present invention can simultaneously improve fast charging performance and adhesive strength.

[0039] The average particle size of the green coke particles (D 50 ) is the average particle size (D 50 ) or the average particle size (D 50 ), not only is the effect of improving adhesive strength by the green coke particles not improved, but rapid charging performance is also not improved as the particle size of the calcined coke particles becomes larger than that of the green coke particles.

[0040] Specifically, the average particle size (D 50 ) compared to the average particle size of the calcined coke particles (D 50 ) is 0.3 or more and less than 1, specifically 0.5 to 0.8, and when it is in this range, the effect of simultaneously improving the fast charging performance and adhesive strength can be maximized.

[0041] The green coke particles and the calcined coke particles may be mixed in a weight ratio of 10:90 to 90:10, specifically 25:75 to 75:25, which is preferable because the green coke particles can maximize the adhesive strength of the negative active material while improving fast charging performance.

[0042] The green coke particles and the calcined coke particles may each be mixed as a plurality of particles of two or more.

[0043] The binder may serve to bind or bond the green coke particles and the calcined coke particles to each other. By binding the green coke particles and the calcined coke particles using the binder and then performing heat treatment and graphitization, the green coke particles and the calcined coke particles can be produced as primary artificial graphite particles, and at the same time, secondary particle-type artificial graphite particles in which the primary artificial graphite particles are bound to each other can be produced.

[0044] The binder may include at least one selected from the group consisting of a polymer resin and a pitch. Specifically, the polymer resin may include at least one selected from the group consisting of sucrose, phenol resin, naphthalene resin, polyvinyl alcohol resin, furfuryl alcohol resin, polyacrylonitrile resin, polyamide resin, furan resin, cellulose resin, styrene resin, polyimide resin, epoxy resin, vinyl chloride resin, and polyvinyl chloride. The pitch may include at least one selected from the group consisting of coal-based pitch, petroleum-based pitch, and mesophase pitch.

[0045] The binder may be mixed in an amount of 1 to 10 wt %, specifically 4 to 8 wt %, based on the total weight of the green coke particles, the calcined coke particles, and the binder. The green coke particles contain volatile matter and have a low true density, so a binder may not be necessary when producing secondary particle-form artificial graphite from the green coke particles alone. However, the calcined coke particles have their volatile matter removed and have a high true density, so a binder may be essential when producing secondary particle-form artificial graphite from the calcined coke particles alone. In the present invention, when the binder is added to a mixture of the green coke particles and the calcined coke particles in an amount within this range, the coke particles are densely packed together, thereby further improving fast charging performance and adhesive strength.

[0046] The present invention includes a step of graphitizing the mixture by heat treating it, thereby forming artificial graphite particles in the form of secondary particles in which the primary artificial graphite particles are bonded to each other.

[0047] The artificial graphite particles in the form of secondary particles can be graphitized by heat-treating a mixture of the green coke particles, the calcined coke particles, and the binder. Specifically, the mixture of the green coke particles, the calcined coke particles, and the binder is introduced into a reactor, and the reactor is operated to combine the mixture by centrifugal force to form secondary particles in which primary particles are combined, which can then be graphitized by heat-treating the secondary particles.

[0048] The heat treatment can be carried out at 2,500° C. to 3,500° C., preferably 2,700° C. to 3,200° C., and within this temperature range, smooth graphitization of the green coke particles and the calcined coke particles is possible.

[0049] The heat treatment may be performed for 40 to 60 hours, and within this range, the green coke particles and the calcined coke particles can be sufficiently graphitized through the heat treatment within the aforementioned temperature range.

[0050] The present invention may further include forming an amorphous carbon coating layer on the artificial graphite particles in the form of secondary particles.

[0051] The amorphous carbon coating layer may improve the structural stability of the artificial graphite particles in the form of secondary particles and contribute to preventing side reactions between the negative electrode active material and the electrolyte.

[0052] The amorphous carbon coating layer may be formed in an amount of 0.1 wt % to 10 wt %, preferably 1 wt % to 5 wt %, based on the total weight of the negative electrode active material. The presence of the amorphous carbon coating layer can improve the structural stability of the negative electrode active material, but excessive formation of the amorphous carbon coating layer can increase the specific surface area during rolling of the negative electrode, thereby reducing initial efficiency and high-temperature storage performance. Therefore, it is preferable to form the carbon coating layer in an amount within the above range.

[0053] The amorphous carbon coating layer may be formed by providing a carbon coating layer precursor to the artificial graphite particles in the form of secondary particles and then heat treating the resulting mixture.

[0054] The carbon coating layer precursor may include at least one selected from the group consisting of a polymer resin and a pitch. Specifically, the polymer resin may include at least one selected from the group consisting of sucrose, phenol resin, naphthalene resin, polyvinyl alcohol resin, furfuryl alcohol resin, polyacrylonitrile resin, polyamide resin, furan resin, cellulose resin, styrene resin, polyimide resin, epoxy resin, vinyl chloride resin, and polyvinyl chloride. The pitch may include at least one selected from the group consisting of coal-based pitch, petroleum-based pitch, and mesophase pitch.

[0055] The heat treatment process for forming the amorphous carbon coating layer may be performed at 1,000 to 1,500° C. in order to achieve a uniform formation of the amorphous carbon coating layer.

[0056] According to the present invention, a negative electrode active material can be formed that includes artificial graphite particles in the form of secondary particles formed by bonding primary artificial graphite particles together. Here, the primary artificial graphite particles are derived from graphitization of the green coke particles and the calcined coke particles. The secondary artificial graphite particles can be formed by bonding and assembling the primary artificial graphite particles.

[0057] negative electrode The present invention also provides a negative electrode, more specifically, a negative electrode for a lithium secondary battery, including the negative electrode active material produced by the method for producing the negative electrode active material described above.

[0058] The negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material manufactured by the above-described method for manufacturing a negative electrode active material layer.

[0059] The negative electrode current collector may be any negative electrode current collector commonly used in the art, and is not particularly limited as long as it has high conductivity and does not induce chemical changes in the lithium secondary battery. For example, the negative electrode current collector may include at least one selected from copper, stainless steel, aluminum, nickel, titanium, sintered carbon, and an aluminum-cadmium alloy, and preferably copper.

[0060] The negative electrode current collector may have fine irregularities on its surface to strengthen the binding force of the negative electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, or a nonwoven fabric.

[0061] The negative electrode current collector can generally have a thickness of 3 μm to 500 μm.

[0062] The negative electrode active material layer is stacked on the negative electrode current collector and includes the negative electrode active material prepared from the above-described negative electrode active material.

[0063] The average particle size (D 50 ) may be 10 μm to 30 μm, specifically 14 μm to 25 μm, more specifically 15 μm to 20 μm. In particular, when the negative electrode active material produced by the production method of the present invention has an average particle size within this range, the effects of improving adhesive strength due to the green coke particles and improving fast charging performance due to the calcined coke having a smaller average particle size than the green coke particles can be further improved.

[0064] The tap density of the negative electrode active material may be 1.08 g / cc to 1.17 g / cc, specifically 1.10 g / cc to 1.16 g / cc. When the tap density is within this range, a negative electrode active material having a smooth and uniform surface can be realized, and high electrode adhesion strength can be realized, which is preferable.

[0065] The negative electrode active material may be contained in the negative electrode active material layer in an amount of 80 to 99% by weight, preferably 93 to 98% by weight.

[0066] The negative electrode active material layer may further include a negative electrode binder, a negative electrode conductive material, and / or a thickener in addition to the negative electrode active material.

[0067] The negative electrode binder is a component that aids in bonding between the active material and / or the current collector, and may be contained in the negative electrode active material layer in an amount of 1 wt % to 30 wt %, preferably 1 wt % to 10 wt %.

[0068] The negative electrode binder may include at least one selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, and preferably at least one selected from polyvinylidene fluoride and styrene-butadiene rubber.

[0069] As the thickener, any thickener that has been used in the past for lithium secondary batteries may be used, and an example thereof is carboxymethyl cellulose (CMC).

[0070] The negative electrode conductive material is a component for further improving the conductivity of the negative electrode active material, and may be contained in the negative electrode active material layer in an amount of 1 wt % to 30 wt %, preferably 1 wt % to 10 wt %.

[0071] The negative electrode conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. Specific examples of commercially available conductive materials include acetylene black series products manufactured by Chevron Chemical Company, Denka Black (manufactured by Denka Singapore Private Limited), Gulf Oil Company products, Ketjenblack, EC series products (manufactured by Armak Company), Vulcan XC-72 (manufactured by Cabot Company), and Super P (manufactured by Timcal).

[0072] The negative electrode active material layer may be manufactured by mixing the negative electrode active material, a negative electrode binder, a negative electrode conductive material, and at least one selected from a thickener, in a solvent to prepare a negative electrode slurry, and then applying the negative electrode slurry to the negative electrode current collector, rolling, and drying the slurry.

[0073] The solvent may include water or an organic solvent such as N-methyl-2-pyrrolidone (NMP), and may be used in an amount that provides a desired viscosity when the negative electrode active material and, optionally, a negative electrode binder and a negative electrode conductive material are included. For example, the solvent may be included so that the concentration of solids including the negative electrode active material and, optionally, at least one selected from the negative electrode binder, the thickener, and the negative electrode conductive material is 50 wt % to 95 wt %, preferably 70 wt % to 90 wt %.

[0074] The orientation index I(004) / I(110) of the negative electrode may be 8.5 or less, specifically 4.0 to 8.5. When the ratio is within this range, the active material may be particle-aligned to minimize the diffusion path of lithium ions, thereby improving fast charging performance. Achieving this orientation index may be achieved by using a negative electrode active material prepared by the above-described method for preparing a negative electrode active material in the negative electrode.

[0075] The orientation index indicates the degree to which the crystalline structure within the negative electrode is aligned in a specific direction, and can be used to evaluate the orientation of the crystals within the electrode. This may be measured by X-ray diffraction (XRD). More specifically, the orientation index is the area ratio (004) / (110) obtained by measuring the (110) and (004) planes of the negative electrode active material included in the negative electrode by XRD and then integrating the peak intensities of the (110) and (004) planes. More specifically, the XRD measurement conditions are as follows:

[0076] - Target: Cu (Kα line) graphite monochromator -Slit: Divergence slit = 1 degree, Receiving slit = 0.1 mm, Scattering slit = 1 degree -Measurement area and step angle / measurement time: (110) plane: 76.5 degrees < 2θ < 78.5 degrees, 0.01 degrees / 3 seconds (004) plane: 53.5 degrees < 2θ < 56.0 degrees, 0.01 degrees / 3 seconds, In the above, 2θ represents the diffraction angle. The XRD measurement is just one example, but other measurement methods may also be used.

[0077] secondary battery The present invention also provides a secondary battery, more specifically a lithium secondary battery, including the above-described negative electrode.

[0078] The secondary battery may include the negative electrode, a positive electrode facing the negative electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte.

[0079] The positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector.

[0080] The positive electrode current collector may be used without limitation as a negative electrode current collector commonly used in the art. For example, it is not particularly limited as long as it has high conductivity without inducing chemical changes in the secondary battery. For example, the positive electrode current collector may include at least one selected from copper, stainless steel, aluminum, nickel, titanium, fired carbon, and an aluminum-cadmium alloy, preferably aluminum.

[0081] The positive electrode current collector may also form fine irregularities on its surface to strengthen the binding force of the positive electrode active material, and can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven bodies, etc.

[0082] Generally, the positive electrode current collector can have a thickness of 3 μm to 500 μm. The positive electrode active material layer may include a positive electrode active material.

[0083] The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium. Specifically, it may include a lithium composite metal oxide containing one or more metals such as cobalt, manganese, nickel, or aluminum and lithium. More specifically, the lithium composite metal oxide is a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (e.g., LiNiO2, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese-based oxide (e.g., LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-z Ni z O4 (where 0 < Z < 2), etc.), a lithium-nickel-cobalt-based oxide (e.g., LiNi 1-Y1 Co Y1O2 (where 0 < Y1 < 1, etc.), lithium-manganese-cobalt-based oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-z1 Co z1 O4 (where 0 < Z1 < 2, etc.), lithium-nickel-manganese-cobalt-based oxides (e.g., Li(Ni p Co q Mn r1 )O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, p + q + r1 = 1) or Li(Ni p1 Co q1 Mn r2 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2, etc.), or lithium-nickel-cobalt-transition metal (M) oxides (e.g., Li(Ni p2 Co q2 Mn r3 M S2 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are atomic fractions of independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, and p2 + q2 + r3 + s2 = 1, etc.), etc. Any one or two or more of these compounds may be included. Among them, in terms of being able to enhance the capacity characteristics and stability of the battery, the lithium composite metal oxide is LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxide (e.g., Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05)O2, etc.), and in consideration of the remarkable improvement effect by controlling the types and content ratios of constituent elements forming the lithium composite metal oxide, the lithium composite metal oxide may be Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2, or Li(Ni 0.8 n 0.1 Co 0.1 )O2, etc., and any one or a mixture of two or more of these may be used.

[0084] The positive electrode active material may be contained in the positive electrode active material layer in an amount of 80% by weight to 99% by weight. The positive electrode active material layer may further include at least one selected from the group consisting of a positive electrode binder and a positive electrode conductive material in addition to the positive electrode active material.

[0085] The positive electrode binder is a component that aids in bonding the active material and conductive material and the current collector, and is typically added in an amount of 1 to 30 wt % based on the total weight of the positive electrode mixture. Examples of such positive electrode binders include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber.

[0086] The positive electrode binder may be contained in the positive electrode active material layer in an amount of 1 wt % to 30 wt %.

[0087] The positive electrode conductive material is not particularly limited as long as it is conductive without inducing chemical changes in the battery, and examples thereof include carbon-based materials such as graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; carbon fluoride; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. Specific examples of commercially available conductive materials include acetylene black products manufactured by Chevron Chemical Company, Denka Singapore Private Limited, and Gulf Oil Company, as well as Ketjenblack, EC series products (manufactured by Armak Company), Vulcan XC-72 (manufactured by Cabot Company), and Super P (manufactured by Timcal).

[0088] The positive electrode conductive material may be added to the positive electrode active material layer in an amount of 1% by weight to 30% by weight.

[0089] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitation. In particular, a separator that exhibits low resistance to electrolyte ion movement and excellent electrolyte humidification is preferred. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material may also be used, and may be selectively used in a single-layer or multi-layer structure.

[0090] Furthermore, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the production of lithium secondary batteries, but are not limited to these.

[0091] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0092] The organic solvent may be used without any particular limitation as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specific examples of the organic solvent that may be used include ester-based solvents such as methyl acetate, ethyl acetate, gamma-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether and hydrofuran; ketone-based solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a C2 to C20 linear, branched, or cyclic hydrocarbon group that may contain a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; and sulfolanes. Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of a battery, and a low-viscosity chain carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, the cyclic carbonate and the chain carbonate can be mixed in a volume ratio of about 1:1 to about 1:9 to achieve excellent electrolyte performance.

[0093] The lithium salt may be any compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be LiPF, LiClO, LiAsF, LiBF, LiSbF, LiAlO, LiAlCl, LiCF, SO, LiCF, SO, LiN(CF, SO), LiN(CF, SO), LiN(CF, SO), LiCl, LiI, or LiB(CO) . The lithium salt concentration is preferably in the range of 0.1 to 2.0 M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0094] As described above, the lithium secondary battery according to the present invention exhibits excellent discharge capacity, fast charge characteristics, and stable capacity retention, and is therefore useful in fields such as mobile phones, laptops, and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs), and is particularly suitable as a component battery of medium- to large-sized battery modules. Accordingly, the present invention also provides a medium- to large-sized battery module including the above-described secondary battery as a unit cell.

[0095] Such a medium- to large-sized battery module can be suitably applied to power sources that require high output and large capacity, such as electric vehicles, hybrid electric vehicles, and power storage devices.

[0096] Although the present invention may be embodied in many different forms, it is to be understood that the invention is not limited to the embodiments set forth herein, and that the invention may be embodied in various different forms, rather than in a limited manner, as defined by the appended claims. [Example]

[0097] Example <Production of negative electrode active material> Example 1: Preparation of negative electrode active material The sulfur content is 2,009 ppm, the true density is 1.4 g / cc, and the average particle size (D 50 The green coke particles have a mean particle size (D) of 11 μm, a sulfur content of 115 ppm, a true density of 2.1 g / cc, and 50 Calcined coke particles with a particle size of 7 μm and a petroleum-based pitch binder were charged into a reactor. The green coke particles and the calcined coke particles were mixed in a weight ratio of 30:70. The pitch binder was mixed at 7 wt% based on the total weight of the green coke particles, the calcined coke particles, and the petroleum-based pitch. The green coke particles, the calcined coke particles, and the petroleum-based pitch binder were heat-treated at 3,000°C for 50 hours to be graphitized, thereby producing artificial graphite particles in the form of secondary particles in which primary artificial graphite particles were bonded to each other. The primary artificial graphite particles were derived from the green coke particles and the calcined coke particles.

[0098] The secondary particle-type artificial graphite particles and petroleum-based pitch were mixed and heat-treated at 1,300° C. in a roller hearth kiln to form an amorphous carbon coating layer on the secondary particle-type artificial graphite particles.

[0099] The tap density of the negative electrode active material prepared above was 1.13 g / cc, and the average particle size (D 50 The thickness of the amorphous carbon coating layer was 18 μm. The amorphous carbon coating layer was formed in an amount of 3.5 wt % based on the weight of the negative electrode active material.

[0100] At this time, the tap density was determined by filling 40 g of the negative electrode active material into a container, vibrating it up and down 1,000 times, measuring the final volume, and then measuring the apparent density.

[0101] Example 2: Preparation of negative electrode active material A negative active material was prepared in the same manner as in Example 1, except that the green coke particles and the calcined coke particles were mixed in a weight ratio of 70:30. The tap density of the negative electrode active material prepared above was 1.15 g / cc, and the average particle size (D 50 ) was 18 μm.

[0102] Comparative Example 1: Production of negative electrode active material A negative electrode active material was prepared in the same manner as in Example 1, except that only green coke particles were used instead of calcined coke particles. The tap density of the negative electrode active material prepared above was 1.05 g / cc, and the average particle size (D 50 ) was 18 μm.

[0103] Comparative Example 2: Production of negative electrode active material A negative electrode active material was prepared in the same manner as in Example 1, except that only calcined coke particles were used instead of green coke particles. The tap density of the negative electrode active material prepared above was 0.87 g / cc, and the average particle size (D 50 ) was 18 μm.

[0104] Comparative Example 3: Production of negative electrode active material A negative electrode active material was prepared in the same manner as in Example 1, except that no binder was used. The tap density of the negative electrode active material prepared above was 1.18 g / cc, and the average particle size (D 50 ) was 12 μm.

[0105] Comparative Example 4: Production of negative electrode active material The negative active material prepared in Comparative Example 1 and the negative active material prepared in Comparative Example 2 were mixed in a weight ratio of 30:70 to prepare a negative active material. The tap density of the negative electrode active material prepared above was 0.98 g / cc, and the average particle size (D 50 ) was 18 μm.

[0106] Comparative Example 5: Production of negative electrode active material The negative active material prepared in Comparative Example 1 and the negative active material prepared in Comparative Example 2 were mixed in a weight ratio of 70:30 to prepare a negative active material. The tap density of the negative electrode active material prepared above was 1.04 g / cc, and the average particle size (D 50 ) was 18 μm.

[0107] Comparative Example 6: Production of negative electrode active material The green coke particles have a sulfur content of 2,009 ppm, a true density of 1.4 g / cc, and an average particle size (D 50 The calcined coke particles had a sulfur content of 115 ppm, a true density of 2.1 g / cc, and an average particle size (D 50 ) was prepared as 11 μm.

[0108] A negative active material was prepared in the same manner as in Example 1, except that the green coke particles and calcined coke particles were used. The tap density of the negative electrode active material prepared above was 1.02 g / cc, and the average particle size (D 50 ) was 18 μm.

[0109] Comparative Example 7: Production of negative electrode active material The green coke particles have a sulfur content of 2,009 ppm, a true density of 1.4 g / cc, and an average particle size (D 50 The calcined coke particles had a sulfur content of 115 ppm, a true density of 2.1 g / cc, and an average particle size (D 50 ) was prepared.

[0110] A negative active material was prepared in the same manner as in Example 1, except that the green coke particles and calcined coke particles were used. The tap density of the negative electrode active material prepared above was 1.05 g / cc, and the average particle size (D 50 ) was 18 μm.

[0111] <Production of negative electrodes> The negative electrode active material prepared in Example 1, carbon black as a conductive material, styrene-butadiene rubber as a binder, and carboxymethyl cellulose as a thickener were mixed in a weight ratio of 95.9:0.5:2.5:1.1, and water was added to prepare a negative electrode slurry.

[0112] The negative electrode slurry was applied to a copper negative electrode current collector (thickness: 15 μm), vacuum dried at about 130° C. for 8 hours, and rolled to form a negative electrode active material layer (thickness: 55 μm), thereby preparing the negative electrode of Example 1. At this time, the negative electrode loading was 3.3 mAh / cm 2 It was manufactured so that

[0113] Negative electrodes of Example 2 and Comparative Examples 1 to 7 were prepared in the same manner as in Example 1, except that the negative electrode active materials prepared in Example 2 and Comparative Examples 1 to 7 were used, respectively.

[0114] The orientation index of the negative electrodes of the Examples and Comparative Examples was determined by measuring the (004) and (110) planes by XRD and integrating the measured XRD peaks to obtain the area ratio I(004) / I(110). The XRD measurement conditions were as follows. The results are shown in Table 1 below.

[0115] - Target: Cu (Kα line) graphite monochromator -Slit: Divergence slit = 1 degree, Receiving slit = 0.1 mm, Scattering slit = 1 degree -Measurement area and step angle / measurement time: (110) plane: 76.5 degrees < 2θ < 78.5 degrees, 0.01 degrees / 3 seconds (004) plane: 53.5 degrees < 2θ < 56.0 degrees, 0.01 degrees / 3 seconds

[0116] [Table 1]

[0117] Experimental Example Experimental Example 1: Evaluation of adhesive strength The negative electrode of Example 1 was punched out to a size of 20 mm x 150 mm and fixed to the center of a 25 mm x 75 mm slide glass using double-sided tape, and then the 90-degree peel strength was measured while peeling the negative electrode active material layer from the negative electrode current collector using a UTM (manufacturer: LLOYD Instrument LTD., equipment name: LF Plus). Five identical negative electrodes of Example 1 were prepared, and the 90-degree peel strength was measured five times using the same method. The average value was taken as the adhesive strength (unit: gf / 10 mm) of the negative electrode of Example 1.

[0118] The 90-degree peel strength of Example 2 and Comparative Examples 1 to 7 was measured in the same manner as in Example 1. The results are shown in Table 2 below.

[0119] Experimental example 2: Evaluation of rapid charging performance <Secondary battery manufacturing> A lithium metal counter electrode was prepared as the positive electrode. Secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 4 were fabricated by inserting a polyolefin separator between the negative and positive electrodes and injecting an electrolyte solution into the electrodes. The electrolyte solution was prepared by adding 0.5 wt % vinylene carbonate (VC) to a non-aqueous electrolyte solvent made by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 2:8, and dissolving LiPF6 at 1M.

[0120] <Evaluation of rapid charging performance> The secondary battery prepared above was charged and discharged for three cycles at 1 C, and then charged at 3 C for 15 minutes. The charging and discharging profiles were first differentiated. The inflection point of dQ / dV was identified, and the lithium plating SOC (Li-Plating SOC, %), which is the SOC at which lithium deposition occurs on the surface of the negative electrode, was quantified. The results are shown in Table 2 below.

[0121] [Table 2]

[0122] Referring to Table 2, it can be seen that the negative electrodes and secondary batteries of Examples 1 and 2 can simultaneously improve the negative electrode adhesion and fast charging performance compared to the negative electrodes and secondary batteries of Comparative Examples 1 to 7.

Claims

1. mixing the green coke particles, the calcined coke particles, and the binder to obtain a mixture; and heat-treating the mixture to graphitize it, thereby forming artificial graphite particles in the form of secondary particles in which particles of primary artificial graphite are bonded to each other; The average particle size (D ５０ ) is the average particle size (D ５０ ) is larger than The green coke particles have an average particle size (D 50 ) of 9 μm to 15 μm; The calcined coke particles have an average particle size (D50) of 3 μm to 8 μm; The method for manufacturing a negative electrode active material, wherein the green coke particles and the calcined coke particles are mixed in a weight ratio of 10:90 to 90:

10.

2. The average particle size (D ５０ ) compared to the average particle size (D ５０ 2. The method for producing a negative electrode active material according to claim 1, wherein the ratio of (a) to (b) is 0.3 or more and less than 1.

3. The method for producing a negative electrode active material according to claim 1 , wherein the true density of the green coke particles is 1.20 g / cc to 1.60 g / cc.

4. The method for producing a negative electrode active material according to claim 1 , wherein the calcined coke particles have a true density of 1.80 g / cc to 2.25 g / cc.

5. The method for producing a negative electrode active material according to claim 1 , wherein the green coke particles contain sulfur (S) in an amount of 1,000 ppm to 5,000 ppm.

6. The method for producing a negative electrode active material according to claim 1 , wherein the calcined coke particles contain sulfur (S) in an amount of 50 ppm to 1,000 ppm.

7. The method of claim 1 , wherein the binder is mixed in an amount of 1 wt % to 10 wt % based on the total weight of the green coke particles, the calcined coke particles, and the binder.

8. The method for producing a negative electrode active material according to claim 1 , wherein the heat treatment is performed at 2,500° C. to 3,500° C.

9. The method for producing a negative electrode active material according to claim 1 , wherein the heat treatment is performed for 40 to 60 hours.

10. a negative electrode current collector; and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the negative electrode active material layer includes a negative electrode active material including artificial graphite particles in the form of secondary particles formed by bonding primary artificial graphite particles to each other, The artificial graphite particles are graphitized from a mixture including green coke particles, calcined coke particles, and a binder; The average particle size (D ５０ ) is the average particle size (D ５０ ) is larger than The green coke particles have an average particle size (D 50 ) of 9 μm to 15 μm; The calcined coke particles have an average particle size (D50) of 3 μm to 8 μm; The negative electrode is characterized in that the green coke particles and the calcined coke particles are mixed in a weight ratio of 10:90 to 90:

10.

11. 11. The anode of claim 10, wherein the anode active material has a tap density of 1.08 g / cc to 1.17 g / cc.

12. 11. The negative electrode according to claim 10, wherein the orientation index I(004) / I(110) of the negative electrode is 8.5 or less.

13. The negative electrode according to any one of claims 10 to 12; a positive electrode facing the negative electrode; a separator interposed between the negative electrode and the positive electrode; and A secondary battery comprising: an electrolyte;

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