Negative electrode active material, negative electrode containing the same, and secondary battery

Abstract

The present invention relates to a negative electrode active material containing artificial graphite particles. Among them, when measuring a sample containing the negative electrode active material and water with a torque rheometer, the solid content value of the negative electrode active material at the maximum torque value of the sample measured by a specific method is at least 69.5% by weight. If, when performing the torque rheometer measurement, the solid content value at the maximum torque value satisfies this range, the powder fluidity of the negative electrode active material can be evaluated as excellent. If the negative electrode active material is included in the negative electrode slurry, the dispersibility and phase stability can be improved. Therefore, the productivity and quality of the negative electrode slurry containing the negative electrode active material of the present invention, the negative electrode manufactured therefrom, and the secondary battery can be improved.

Description

Technical Field

[0001] Cross - reference to related applications

[0002] This application claims the priority of Korean Patent Application No. 10-2021-0184259, filed on December 21, 2021, the disclosure of which is incorporated herein by reference. Technical Field

[0004] The present invention relates to a negative electrode active material, a negative electrode including the same, and a secondary battery. Background Art

[0005] As environmental concerns have grown, extensive research has been conducted on electric vehicles (EVs) and hybrid electric vehicles (HEVs), which can replace vehicles using fossil fuels, such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution. As a power source for these electric vehicles (EVs) and hybrid electric vehicles (HEVs), lithium secondary batteries having a high energy density, a high discharge voltage, and high output stability have been mainly studied and used.

[0006] Generally, a lithium secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive electrode or the negative electrode is prepared by mixing a positive electrode active material or a negative electrode active material with a binder, dispersing the mixture in a solvent to prepare a slurry, and forming an electrode active material layer by coating the slurry on the surface of an electrode current collector and drying.

[0007] As the negative electrode active material, carbon-based active materials capable of reversibly inserting and extracting lithium ions and maintaining structural and electrical properties can be used. Various types of carbon-based materials, such as artificial graphite, natural graphite, and hard carbon, have been used as the carbon-based active materials. Among them, graphite-based active materials can ensure the life characteristics of lithium secondary batteries due to their excellent reversibility, and thus have been most widely used. Since the graphite-based active materials have a low discharge voltage of -0.2 V with respect to lithium, a battery using the graphite-based active materials can exhibit a high discharge voltage of 3.6 V. Therefore, it provides many advantages in terms of the energy density of lithium batteries.

[0008] Among the graphite-based active materials, artificial graphite has an advantage in that it has excellent fast charging performance of the battery because it has a relatively low degree of orientation during electrode rolling compared to natural graphite, and thus has good lithium ion insertion / extraction characteristics, and has excellent life characteristics because of a low degree of swelling caused by charge and discharge.

[0009] However, since artificial graphite exhibits hydrophobicity, when water is used as the solvent for the negative electrode slurry, there are problems of difficult dispersion and reduced phase stability of the slurry. In particular, due to reasons such as increasing the negative electrode loading amount, improving the efficiency during the drying process, and improving the binder migration, attempts have been made to increase the solid content of the negative electrode slurry. Therefore, the above problems of reduced dispersibility of artificial graphite and slurry phase stability become more significant as the solid content increases. In addition, due to the dispersion problem, a filter clogging problem is caused during the transportation of the negative electrode slurry in the negative electrode preparation process, so there is a problem of reducing the efficiency and quality of the overall preparation process of the secondary battery.

[0010] Japanese Patent No. 4403327 discloses graphite powder for the negative electrode of a lithium ion secondary battery, but does not provide an alternative solution to the above problems.

[0011] [Prior Art Documents]

[0012] [Patent Documents]

[0013] Japanese Patent No. 4403327 Summary of the Invention

[0014] Technical Problem

[0015] One aspect of the present invention provides a negative electrode active material that can have excellent dispersibility even when the solid content of the negative electrode slurry increases and can improve the phase stability of the negative electrode slurry.

[0016] Another aspect of the present invention provides a negative electrode slurry containing the above negative electrode active material.

[0017] Another aspect of the present invention provides a negative electrode containing the above negative electrode active material.

[0018] Another aspect of the present invention provides a secondary battery containing the above negative electrode.

[0019] Technical Solution

[0020] According to one aspect of the present invention, there is provided a negative electrode active material containing artificial graphite particles, wherein during the measurement of the torque rheometer of a sample composed of the negative electrode active material and water, the solid content value when the sample has the maximum torque value is 69.5% by weight or more, and the solid content value when the sample has the maximum torque value is measured by a method including the following steps (a) to (c).

[0021] (a) Put the negative electrode active material into the sample container of the torque rheometer;

[0022] (b) While injecting water into the sample container of the torque rheometer at a constant rate, operate the torque rheometer and measure the torque value of the sample generated according to the solid content value; and

[0023] (c) When the sample has the maximum torque value in step (b), derive the solid content value.

[0024] According to another aspect of the present invention, there is provided a negative electrode paste comprising the above-mentioned negative electrode active material, a negative electrode binder, a negative electrode conductive agent, and a solvent.

[0025] According to another aspect of the present invention, there is provided a negative electrode comprising a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer contains the above-mentioned negative electrode active material.

[0026] According to another aspect of the present invention, there is provided a secondary battery comprising the above-mentioned negative electrode, a positive electrode opposite to the negative electrode, a separator provided between the negative electrode and the positive electrode, and an electrolyte.

[0027] Advantageous Effects

[0028] The present invention relates to a negative electrode active material containing artificial graphite particles. During the measurement of the torque rheometer of a sample formed by the negative electrode active material and water, the solid content value when the sample (measured by a specific method) has the maximum torque value is 69.5% by weight or more. When the sample has the maximum torque value during the measurement of the torque rheometer, if the solid content value satisfies the above range, the powder fluidity of the negative electrode active material can be evaluated as excellent, and when the negative electrode active material is included in the negative electrode paste, the dispersibility and phase stability can be improved. Therefore, the negative electrode paste containing the negative electrode active material of the present invention, the negative electrode prepared therefrom, and the secondary battery can improve the productivity and quality. Brief Description of the Drawings

[0029] Figure 1 A graph showing the torque value and solid content value of a sample formed by the negative electrode active material and water according to Example 1.

[0030] Figure 2 A graph showing the torque value and solid content value of a sample formed by the negative electrode active material and water according to Example 2.

[0031] Figure 3 A graph showing the torque value and solid content value of a sample formed by the negative electrode active material and water according to Comparative Example 1.

[0032] Figure 4A graph showing the torque value and solid content value of a sample formed from the negative electrode active material and water according to Comparative Example 2.

[0033] Figure 5 A graph showing the change in shear viscosity according to the shear rate for Example A, Example B, Example C, Comparative Example A, Comparative Example B, and Comparative Example C. Detailed Description

[0034] It will be understood that the words or terms used in the specification and claims should not be construed as having the meanings defined in a common dictionary. It will be further understood that the words or terms should be construed as having meanings consistent with their meanings in the relevant technical background and the technical idea of the present invention, based on the principle that the inventor can appropriately define the meanings of the said words or terms to best explain the present invention.

[0035] The terms used herein are for the purpose of describing specific exemplary embodiments only and are not intended to limit the present invention. In this specification, unless otherwise indicated, the singular forms of terms may include the plural forms.

[0036] It will be further understood that when the terms "comprising", "including" or "having" are used in this specification, they specify the presence of the stated features, numbers, steps, elements or combinations thereof, but do not exclude the presence or addition of one or more other features, numbers, steps, elements or combinations thereof.

[0037] The average particle size (D 50 ) in this specification can be defined as the particle size at which the cumulative volume is 50% in the particle size distribution curve of the particles. The average particle size (D 50 ) can be measured, for example, using the laser diffraction method. The laser diffraction method can generally measure particle sizes in the range from the sub-micron level to several mm and can obtain results with high reproducibility and high resolution.

[0038] The expression 'primary particle' in this specification refers to a single particle, i.e., one particle, while the expression'secondary particle' refers to an aggregate in which a plurality of primary particles are aggregated through an intentional assembly or bonding process.

[0039] The present invention will be described in detail below.

[0040] Negative electrode active material

[0041] The present invention relates to a negative electrode active material, and specifically, to a negative electrode active material for a lithium secondary battery.

[0042] Specifically, the negative electrode active material is characterized in that it is a negative electrode active material containing artificial graphite particles, wherein, during the measurement of a sample composed of the negative electrode active material and water by a torque rheometer, the solid content value when the sample has the maximum torque value is 69.5% by weight or more, and the solid content value when the sample has the maximum torque value is measured by a method including the following steps (a) to (c).

[0043] (a) Put the negative electrode active material into the sample container of the torque rheometer;

[0044] (b) While injecting water into the sample container of the torque rheometer at a constant rate, operate the torque rheometer and measure the torque value of the sample generated according to the solid content value; and

[0045] (c) When the sample has the maximum torque value in step (b), derive the solid content value.

[0046] Conventionally, since artificial graphite exhibits hydrophobicity, when water is used as the solvent for the negative electrode paste, there are problems of poor dispersibility and reduced phase stability of the paste. In addition, due to the dispersibility problem, a filter clogging problem is caused during the transportation of the negative electrode paste in the negative electrode preparation process, so there is a problem of reducing the efficiency and quality of the overall preparation process of the secondary battery.

[0047] To solve these problems, the present invention relates to a negative electrode active material containing artificial graphite particles, wherein, during the measurement of a sample formed by the negative electrode active material and water by a torque rheometer, the solid content value when the sample (measured by a specific method) has the maximum torque value is 69.5% by weight or more. During the measurement by the torque rheometer, when the sample has the maximum torque value, if the solid content value satisfies the above range, the powder fluidity of the negative electrode active material can be evaluated as excellent, and when the negative electrode active material is contained in the negative electrode paste, the dispersibility and phase stability can be improved. Therefore, the negative electrode paste containing the negative electrode active material of the present invention, the negative electrode prepared therefrom, and the secondary battery can improve the productivity and quality.

[0048] The negative electrode active material contains artificial graphite particles. Artificial graphite is prepared by heat-treating amorphous carbon at a high temperature (for example, 2,500 °C to 3,200 °C), and the difference between the artificial graphite and natural graphite is that it is synthetic graphite.

[0049] The artificial graphite particles may be in the form of primary particles or may have a secondary particle structure in which two or more primary particles are assembled. More specifically, the artificial graphite particles may have a secondary particle structure in which two or more primary particles are assembled, and in this case, it is ideal in terms of slurry dispersibility and phase stability.

[0050] In the case where the artificial graphite particles are in the form of secondary particles, voids may be formed in the artificial graphite particles. The voids may be blank spaces formed between the primary particles, may be amorphous, and two or more voids may exist.

[0051] In the present invention, there is no particular limitation on the method for preparing artificial graphite particles as long as it satisfies the "solid content value when the sample has the maximum torque value" described later.

[0052] Specifically, in the case where the artificial graphite particles are in the form of secondary particles, the artificial graphite particles can be prepared as follows: mixing a carbon precursor and a binder material (such as pitch), performing a spheroidization and assembly process to prepare an intermediate in the form of secondary particles, and graphitizing the intermediate by performing heat treatment at a temperature of 2,500 °C or higher, specifically 3,000 °C or higher. In this case, the carbon precursor may be at least one selected from the group consisting of coal-based heavy oil, petroleum-based heavy oil, tar, pitch, or coke, and specifically may be at least one selected from the group consisting of coke and pitch. In this case, a spheroidization process may be additionally performed on the carbon precursor. In this case, the surface of the artificial graphite primary particles can be further smoothed, so that the wettability of the artificial graphite particles formed by secondary particle formation can be improved, the fluidity of the negative electrode active material powder can be improved, and the solid content value when the sample formed by the negative electrode active material and water has the maximum torque value described later can be improved to a desired level. The spheroidization process performed on the carbon precursor can be carried out using, for example, a jet mill, specifically a counter jet mill. The rotational speed of the jet mill may be 8 Hz or higher, particularly 10 Hz or higher, more particularly 15 Hz or higher, and may be 50 Hz or lower, particularly 40 Hz or lower, more particularly 30 Hz or lower. In addition, the spheroidization process performed on the carbon precursor can be carried out for 3 minutes to 60 minutes, specifically 5 minutes to 15 minutes.

[0053] In addition, in the case where the artificial graphite particles are in the form of secondary particles, the artificial graphite particles can be prepared by the following method: mixing artificial graphite particles in the form of primary particles with a binder material (such as pitch), spheronizing, aggregating, and heat-treating to aggregate the artificial graphite particles in the form of primary particles into secondary particles. In this case, the artificial graphite particles in the form of primary particles can be prepared by heat-treating a carbon precursor at a temperature of 2,500 °C or higher, specifically 3,000 °C or higher, to graphitize it. The carbon precursor can be at least one selected from the group consisting of coal heavy oil, petroleum heavy oil, tar, pitch, or coke, and specifically can be at least one selected from the group consisting of coke and pitch. In this case, a spheronization process can be additionally performed on the artificial graphite particles in the form of primary particles, or the carbon precursor used during the preparation of the artificial graphite particles in the form of primary particles. In this case, the surface of the artificial graphite primary particles can be further smoothed. Therefore, the wettability of the secondary particle artificial graphite particles can be improved, the fluidity of the negative electrode active material powder can be improved, and the solid content value when the sample formed by the negative electrode active material and water described later has the maximum torque value can be improved to a desired level. The spheronization process performed on the artificial graphite particles in the form of primary particles, or the carbon precursor used during the preparation of the artificial graphite particles in the form of primary particles, can be performed using, for example, a jet mill, specifically a counter jet mill. The rotational speed of the jet mill can be 8 Hz or higher, particularly 10 Hz or higher, more particularly 15 Hz or higher, and can be 50 Hz or lower, particularly 40 Hz or lower, more particularly 30 Hz or lower. In addition, the spheronization process performed on the artificial graphite particles in the form of primary particles, or the carbon precursor used during the preparation of the artificial graphite particles in the form of primary particles, can be performed for 3 minutes to 60 minutes, specifically 5 minutes to 15 minutes.

[0054] In the present invention, during the measurement of the torque rheometer of the sample composed of the negative electrode active material and water, the solid content value when the sample has the maximum torque value is 69.5% by weight or more.

[0055] The solid content value when the sample has the maximum torque value can be measured by a method including the following steps (a) to (c).

[0056] (a) Put the negative electrode active material into the sample container of the torque rheometer;

[0057] (b) While injecting water into the sample container of the torque rheometer at a constant rate, operate the torque rheometer and measure the torque value of the sample generated according to the solid content value; and

[0058] (c) When the sample has the maximum torque value in the step (b), derive the solid content value.

[0059] The torque rheometer is a device that measures rheological properties based on the flow generated by rotating fluids, etc. For example, the torque rheometer can measure the viscosity-related torque generated by the fluid resistance formed by shear action and various rheological properties resulting therefrom. An example of the torque rheometer can be a measuring mixer of Brabender.

[0060] Specifically, in the present invention, the negative electrode active material is put into the sample container of the torque rheometer, and while water is injected into the sample container at a constant rate, the sample in the sample container is stirred using two blades, so that the torque value can be measured according to the solid content value of the sample formed by the negative electrode active material and water. Through the analysis device of the torque rheometer, a graph showing the torque value corresponding to the solid content value of the sample can be obtained.

[0061] By measuring the solid content value of the negative electrode active material when the sample has the maximum torque value using the torque rheometer, the phase stability and dispersibility of the negative electrode paste containing the negative electrode active material can be predicted. When the solid content value of the sample formed by the negative electrode active material and water is 69.5% by weight or more when the sample has the maximum torque value, the negative electrode active material can be evaluated as having excellent wettability to water and excellent fluidity of the negative electrode active material powder. When the negative electrode active material having the above characteristics is added to the negative electrode paste, the advantages are that it has excellent dispersibility, can improve the phase stability of the paste, and can improve the productivity and quality of the negative electrode preparation process. For example, when the solid content value of the sample formed by the negative electrode active material and water is less than 69.5% by weight when the sample has the maximum torque value, due to the poor fluidity of the powder, the dispersibility and phase stability of the negative electrode paste are reduced, so there is a concern that the productivity and quality of the negative electrode may be reduced, for example, causing blockage of the filter during the transportation of the negative electrode paste.

[0062] In the step (a), the volume of the negative electrode active material put into the sample container can be 55 mL.

[0063] In the step (b), the rate of water injection can be 1 mL / min. In addition, the stirring speed of the sample container or the rotational speed of the two blades in the sample container can be 50 rpm. The temperature of the sample container during the operation of the torque rheometer can be 25 °C.

[0064] The solid content value when the sample formed by the negative electrode active material according to the present invention and water has the maximum torque value can be obtained by adjusting the shape or surface roughness in the process of preparing the negative electrode active material. For example, it can be obtained by adjusting the spheroidization speed or spheroidization time during the preparation of the artificial graphite. For example, the solid content value when the sample according to the present invention has the maximum torque value can be achieved by increasing the spheroidization speed (in terms of smoothing the shape of the negative electrode active material). More specifically, it can be achieved by performing a spheroidization process on the artificial graphite primary particles or the carbon precursor to be the artificial graphite primary particles during the preparation of the artificial graphite in the form of secondary particles and appropriately adjusting the spheroidization speed and time, but the present invention is not limited thereto.

[0065] The tapped density of the negative electrode active material measured by powder flow analysis (powder flow test) can be in the range of 850 kg / m 3 to 1,200 kg / m 3 , specifically 900 kg / m 3 to 950 kg / m 3 . When the tapped density of the negative electrode active material measured by powder flow analysis satisfies the above range, the negative electrode active material can be evaluated as having a shape close to a sphere, and thus the fluidity and dispersibility of the negative electrode active material can be further improved.

[0066] The measurement of the tapped density of the negative electrode active material can be carried out by a powder flow analysis device. For example, it can be carried out by the following method: putting the negative electrode active material into the powder flow analysis device and repeating the process of applying vertical stress and shear stress to the negative electrode active material with a lid five times to measure the density of the negative electrode active material after compression. The measurement of the tapped density of the negative electrode active material can be carried out using a powder flow analysis device (device name: PFT) manufactured by Brookfield Engineering Laboratories, Inc. in Middleborough, Massachusetts, USA. The tapped density can be carried out in accordance with ASTM D6128.

[0067] The sphericity of the negative electrode active material can be 0.75 to 1, specifically 0.78 to 0.95. When the sphericity is within the above range, the fluidity and dispersibility of the negative electrode active material can be further improved. However, merely increasing the sphericity of the negative electrode active material may not achieve the effect of improving the fluidity and dispersibility of the negative electrode active material, and it is also necessary to satisfy the above-mentioned "solid content value when the sample formed by the negative electrode active material and water has the maximum torque value".

[0068] The sphericity can be measured using a particle shape analysis device (e.g., Morphologi M4 manufactured by Malvern Panalytical).

[0069] The average particle diameter (D 50 ) of the negative electrode active material can be 14 μm to 20 μm, specifically 14 μm to 20 μm. When the average particle diameter is within the above range, since the specific surface area is adjusted to an appropriate level, the amount of dispersant to be added during the preparation of the negative electrode paste can be minimized, and because aggregation and reduction in phase stability caused by excessive increase in the average particle diameter (D 50 ) of the negative electrode active material can be prevented, it is ideal in terms of improving processability and the resulting battery performance.

[0070] The Brunauer - Emmett - Teller (BET) specific surface area of the negative electrode active material can be 0.1 m 2 / g to 2.0 m 2 / g, particularly 0.6 m 2 / g to 1.2 m 2 / g, more particularly 0.6 m 2 / g to 0.9 m 2 / g. When the BET specific surface area is within the above range, since the specific surface area is adjusted to an appropriate level, the amount of dispersant to be added during the preparation of the negative electrode paste can be minimized, thus being ideal in terms of improving processability and the resulting battery performance. The BET specific surface area can be measured using a BEL Sorption instrument (manufactured by BEL Japan Co., Ltd.).

[0071] The negative electrode active material may further include an amorphous carbon coating provided on the surface of the artificial graphite particles. The amorphous carbon coating can contribute to improving the structural stability of the artificial graphite particles and preventing side reactions between the negative electrode active material and the electrolyte.

[0072] The amorphous carbon coating can be formed in an amount in the range of 0.1 wt% to 10 wt%, preferably in the range of 1 wt% to 5 wt% based on the total weight of the negative electrode active material. The presence of the amorphous carbon coating can improve the structural stability of the negative electrode active material. However, due to concerns about a decrease in initial efficiency caused by an increase in specific surface area during negative electrode calendering and deterioration of high - temperature storage performance due to excessive formation of the amorphous carbon coating, it is ideal to form the carbon coating within the above content range.

[0073] The amorphous carbon coating can be formed by performing heat treatment after providing a carbon - coating precursor for the artificial graphite particles.

[0074] The carbon coating precursor may include at least one selected from polymer resins and pitch. Specifically, the polymer resin may include at least one selected from the group consisting of sucrose, phenolic 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 tar pitch, petroleum pitch, and mesophase pitch. In terms of promoting the uniform formation of the amorphous carbon coating, the heat treatment process for forming the amorphous carbon coating may be carried out at 1000 °C to 1500 °C.

[0075] Negative electrode paste

[0076] In addition, the present invention provides a negative electrode paste. The negative electrode paste may be a negative electrode paste for preparing a negative electrode of a lithium secondary battery.

[0077] The negative electrode paste contains the above-mentioned negative electrode active material. Specifically, the negative electrode paste may contain the above-mentioned negative electrode active material, a negative electrode binder, a negative electrode conductive agent, and a solvent.

[0078] The negative electrode paste according to the present invention can have excellent dispersibility and improved phase stability by containing the above-mentioned negative electrode active material. In particular, since the negative electrode paste according to the present invention exhibits excellent dispersibility and phase stability even when the solid content of the negative electrode paste increases, the productivity and quality of high-capacity negative electrodes and secondary batteries can be improved.

[0079] Based on the weight of the solid component of the negative electrode paste, the content of the negative electrode active material in the negative electrode paste may be in the range of 80% by weight to 99% by weight, preferably in the range of 88% by weight to 98% by weight.

[0080] In addition, the description of the negative electrode active material is as described above.

[0081] The negative electrode binder is a component that helps the binding between the negative electrode active material and / or the current collector. Based on the weight of the solid component of the negative electrode paste, the content of the negative electrode binder in the negative electrode paste may be in the range of 1% by weight to 30% by weight, preferably in the range of 1% by weight to 10% by weight.

[0082] 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 monomer (EPDM), sulfonated EPDM, styrene butadiene rubber, and fluororubber. Preferably, it includes at least one selected from polyvinylidene fluoride and styrene butadiene rubber.

[0083] The negative electrode conductive agent is a component for further improving the conductivity of the negative electrode active material. Based on the weight of the solid component of the negative electrode slurry, the content of the negative electrode conductive agent in the negative electrode slurry may be in the range of 1% by weight to 30% by weight, preferably in the range of 1% by weight to 10% by weight.

[0084] Any negative electrode conductive agent can be used without particular limitation as long as it has conductivity and does not cause adverse chemical changes in the battery. For example, conductive materials such as graphite, such as natural graphite or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking carbon black; conductive fibers, such as carbon fibers or metal fibers; fluorocarbons; metal powders, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxides; or polyphenylene derivatives can be used. Specific examples of commercial conductive agents can be acetylene black-based products (Chevron Chemical Company, Denka Black (Denka Singapore Pte. Ltd.), or Gulf Oil Corporation), Ketjen black, EC-based products (Armak Company), Vulcan XC-72 (Cabot Corporation), and Super P (Timcal Graphite & Carbon Company).

[0085] The solvent may include water or an organic solvent such as N-methyl-2-pyrrolidone (NMP), and more specifically, it may be water. For the negative electrode slurry according to the present invention, problems such as reduced dispersibility and reduced phase stability caused by using a negative electrode active material containing artificial graphite particles can be significantly prevented.

[0086] In terms of improving dispersibility, the negative electrode slurry may further include a thickening agent.

[0087] Any thickening agent used in conventional lithium secondary batteries can be used as the thickening agent, and an example thereof is carboxymethyl cellulose (CMC).

[0088] Based on the total weight of the negative electrode slurry, the solid content of the negative electrode slurry may be 46% by weight or more, specifically in the range of 47% by weight to 56% by weight.

[0089] According to the present invention, due to the use of the above-mentioned negative electrode active material, the dispersibility and phase stability of the negative electrode slurry are improved. Therefore, even when the negative electrode slurry is prepared with a solid content within the above-mentioned range, excellent dispersibility and phase stability can be ensured.

[0090] When the solid content of the negative electrode slurry is 46% by weight or more, specifically in the range of 47% to 56% by weight, the viscosity at 23°C can be in the range of 4,500 cP to 10,000 cP, specifically 4,800 cP to 7,800 cP.

[0091] When the solid content of the negative electrode slurry is 46% by weight or more, specifically in the range of 47% to 56% by weight, the shear thickening slope obtained when measuring the shear viscosity according to the shear rate can be a negative (-) value.

[0092] In the case where the shear thickening slope of the negative electrode slurry is a negative (-) slope, it is easy to pass through the filter. Specifically, since it can pass through a 125-mesh filter, filter clogging does not occur when the negative electrode slurry passes through the filter. The smaller the shear thickening, the easier it is for the negative electrode slurry to pass through the filter. A negative electrode active material slurry that exhibits significant thickening when strong shear is applied by the filter is likely to clog the filter, and this tendency can be quantitatively evaluated by the value of the shear thickening slope.

[0093] When using a rheometer to measure the shear viscosity of the negative electrode active material slurry according to the shear rate and converting the viscosity values in the interval showing shear thickening in the measured shear viscosity into logarithmic values, a straight-line graph can be drawn by performing linear fitting from the starting point to the ending point of the shear thickening, thereby determining the shear thickening slope.

[0094] Negative electrode

[0095] In addition, the present invention provides a negative electrode, specifically, a negative electrode for a lithium secondary battery. The negative electrode can be a negative electrode containing the above-mentioned negative electrode active material.

[0096] Specifically, the negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, and the negative electrode active material layer contains the above-mentioned negative electrode active material.

[0097] The negative electrode current collector commonly used in the art can be used as the negative electrode current collector without limitation. For example, there is no particular limitation on the negative electrode current collector as long as it has high conductivity and does not cause adverse chemical changes in the lithium secondary battery. For example, the negative electrode current collector can include at least one selected from the following: copper, stainless steel, aluminum, nickel, titanium, fired carbon, and aluminum cadmium alloy, preferably copper.

[0098] The negative electrode current collector may have minute surface irregularities to improve the bonding strength with the negative electrode active material, and the negative electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam body, non-woven fabric body, etc.

[0099] The negative electrode current collector generally may have a thickness in the range of 3 μm to 500 μm.

[0100] The negative electrode active material layer is provided on at least one surface of the negative electrode current collector. Specifically, the negative electrode active material layer may be provided on one surface or both surfaces of the negative electrode current collector.

[0101] The negative electrode active material layer contains the above-mentioned negative electrode active material.

[0102] The content of the negative electrode active material in the negative electrode active material layer may be in the range of 80% by weight to 99% by weight, preferably in the range of 88% by weight to 98% by weight.

[0103] In addition, the description of the negative electrode active material is as described above.

[0104] On the basis of containing the above-mentioned negative electrode active material, the negative electrode active material layer may further contain a negative electrode binder, a negative electrode conductive agent, and / or a thickening agent.

[0105] The negative electrode binder is a component that helps the bonding between the active material and / or the current collector. The content of the negative electrode binder in the negative electrode active material layer generally may be in the range of 1% by weight to 30% by weight, preferably in the range of 1% by weight to 10% by weight.

[0106] In addition, the description of the negative electrode binder is as described above.

[0107] Any thickening agent used in a conventional lithium secondary battery may be used as the thickening agent, and an example thereof is carboxymethyl cellulose (CMC).

[0108] The negative electrode conductive agent is a component for further improving the conductivity of the negative electrode active material. The content of the negative electrode conductive agent in the negative electrode active material layer may be in the range of 1% by weight to 30% by weight, preferably in the range of 1% by weight to 10% by weight.

[0109] In addition, the description of the negative electrode conductive agent is as described above.

[0110] The thickness of the negative electrode active material layer may be in the range of 10 μm to 150 μm, specifically in the range of 50 μm to 100 μm, but is not limited thereto.

[0111] The negative electrode active material layer can be prepared by coating the negative electrode current collector with the negative electrode paste, and calendering and drying the coated negative electrode current collector.

[0112] Secondary battery

[0113] Furthermore, the present invention provides a secondary battery including the above-mentioned negative electrode, and more particularly, a lithium secondary battery.

[0114] The secondary battery may include the above-mentioned negative electrode, a positive electrode opposite to the negative electrode, a separator disposed between the negative electrode and the positive electrode, and an electrolyte.

[0115] The positive electrode may be opposite to the negative electrode.

[0116] The positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector.

[0117] The positive electrode current collector commonly used in the art can be used as the positive electrode current collector without limitation. For example, there is no particular limitation on the positive electrode current collector as long as it has high conductivity and does not cause adverse chemical changes in the secondary battery. For example, the positive electrode current collector may include at least one selected from the following: copper, stainless steel, aluminum, nickel, titanium, fired carbon, and aluminum-cadmium alloy, preferably aluminum.

[0118] The positive electrode current collector may have fine surface irregularities to improve the bonding strength with the positive electrode active material, and the positive electrode current collector can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and non-woven fabric bodies.

[0119] The positive electrode current collector generally may have a thickness of 3 μm to 500 μm.

[0120] The positive electrode active material layer may include a positive electrode active material.

[0121] The positive electrode active material is a compound capable of reversibly inserting and extracting lithium, and specifically, the positive electrode active material may include a lithium composite metal oxide, and the lithium composite metal oxide includes lithium and at least one metal such as cobalt, manganese, nickel, or aluminum. More specifically, the lithium composite metal oxide may include: lithium manganese-based oxides (such as LiMnO2, LiMn2O4, etc.), lithium cobalt-based oxides (such as LiCoO2, etc.), lithium nickel-based oxides (such as LiNiO2, etc.), lithium nickel manganese-based oxides (such as LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-Z Ni z O4 (where 0 < Z < 2), etc.), lithium nickel cobalt-based oxides (such as LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1, etc.), lithium manganese cobalt oxides (such as 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 oxides (such as Li(Ni p Co q Mn r1 )O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1 and p + q + r1 = 1) or Li(Ni p1 Co q1 Mn r2 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2 and p1 + q1 + r2 = 2, etc.), or lithium nickel cobalt transition metal (M) oxides (such as Li(Ni p2 Co q2 Mn r3 M S2 )O2 (where M is selected from the group consisting of aluminum (Al), iron (Fe), vanadium (V), chromium (Cr), titanium (Ti), tantalum (Ta), magnesium (Mg) and molybdenum (Mo), and p2, q2, r3 and s2 are atomic fractions of each independent element, where 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < S2 < 1 and p2 + q2 + r3 + S2 = 1), etc.), and may contain any one or a mixture of two or more thereof. Among these materials, in terms of improving the capacity characteristics and stability of the battery, the lithium composite metal oxide may contain LiCoO2, LiMnO2, LiNiO2, lithium nickel manganese cobalt oxides (such as 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), or lithium nickel cobalt aluminum oxides (such as LiNi 0.8 Co 0.15 Al 0.05 O2, etc.), and, considering the significant improvement brought about by controlling the type and content ratio of the elements constituting the lithium composite metal oxide, the lithium composite metal oxide may contain Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2 or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, and any one of them or a mixture of two or more of them can be used.

[0122] The content of the positive electrode active material in the positive electrode active material layer can be in the range of 80% to 99% by weight.

[0123] On the basis of containing the positive electrode active material, the positive electrode active material layer can further contain at least one selected from a binder and a conductive agent.

[0124] The binder is a component that helps the binding between the active material and the conductive agent and the binding with the current collector. Usually, the binder is added in an amount in the range of 1% to 30% by weight based on the total weight of the positive electrode material mixture. Examples of the binder can be 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 monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber.

[0125] The content of the binder in the positive electrode active material layer can be in the range of 1% to 30% by weight.

[0126] As the conductive agent, any conductive agent can be used without particular limitation as long as it has conductivity and does not cause adverse chemical changes in the battery, and conductive materials such as graphite; carbon materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking carbon black; conductive fibers such as carbon fiber or metal fiber; fluorocarbons; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or polyphenylene derivatives can be used. Specific examples of commercial conductive agents can be acetylene black products (Chevron Chemical Company, Denka Black (Denka Singapore Pte. Ltd.), or Gulf Oil Corporation), Ketjen black, EC products (Armak Corporation), Vulcan XC-72 (Cabot Corporation), and Super P (Timcal Graphite & Carbon Corporation).

[0127] The addition amount of the conductive agent in the positive electrode active material layer can be 1% to 30% by weight.

[0128] The separator separates the negative electrode and the positive electrode and provides a path for the movement of lithium ions. Any separator can be used as the separator without particular limitation as long as it is commonly used in secondary batteries. In particular, a separator with a high moisture-holding capacity for the electrolyte and a low resistance to the movement of electrolyte ions can be used. Specifically, a porous polymer membrane can be used, for example, a porous polymer membrane prepared from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or a laminated structure of two or more layers thereof. Additionally, ordinary porous non-woven fabrics can be used, such as non-woven fabrics formed from high-melting-point glass fibers or polyethylene terephthalate fibers. Furthermore, a coated separator containing a ceramic component or a polymer component can be used to ensure heat resistance or mechanical strength, and a separator having a single-layer or multi-layer structure can be selectively used.

[0129] In addition, the electrolyte used in the present invention can include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten-type inorganic electrolyte that can be used in the preparation of lithium secondary batteries, but the present invention is not limited thereto.

[0130] Specifically, the electrolyte can contain an organic solvent and a lithium salt.

[0131] Any organic solvent can be used as the organic solvent without particular limitation as long as it can act as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, as the organic solvent, the following can be used: ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; or carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN (where R is a linear, branched, or cyclic C2 to C20 hydrocarbon group and may contain a double bond, an aromatic ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolane. Among these solvents, the carbonate solvents can be used. For example, a mixture of a cyclic carbonate (such as ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant and a linear carbonate compound (such as ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) having low viscosity, which can improve the charge-discharge performance of the battery, can be used. In this case, when the cyclic carbonate and the linear carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte can be excellent.

[0132] The lithium salt can be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, as the lithium salt, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2 can be used. The lithium salt can be used within a concentration range of 0.1 M to 2.0 M. When the concentration of the lithium salt is included within the above range, since the electrolyte can have appropriate conductivity and viscosity, excellent electrolyte performance can be obtained, and lithium ions can move effectively.

[0133] As described above, since the lithium secondary battery according to the present invention stably exhibits excellent discharge capacity, output characteristics, and life characteristics, the lithium secondary battery is suitable for portable devices such as mobile phones, laptop computers, and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs), and in particular, can preferably be used as a battery constituting a medium- to large-sized battery module. Therefore, the present invention also provides a medium- to large-sized battery module including the above secondary battery as a unit cell.

[0134] The medium- to large-sized battery module can preferably be used for power sources that require high output and large capacity, such as electric vehicles, hybrid electric vehicles, and power storage systems.

[0135] Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily implement it. However, the present invention can be embodied in many different forms and should not be construed as limited to the embodiments presented herein.

[0136] Examples and Comparative Examples

[0137] (1) Preparation of negative electrode active material

[0138] Prepare the negative electrode active materials of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 shown in Table 1 below.

[0139] Example 1: Preparation of negative electrode active material

[0140] After crushing, air-classifying, and spheronizing a coke raw material to prepare a carbon precursor in the form of primary particles, the carbon precursor is mixed with pitch and spheronized to prepare an intermediate in the form of secondary particles, and the intermediate is heat-treated at 3,000 °C to graphitize it, thereby preparing artificial graphite particles in the form of secondary particles aggregated from two or more artificial graphite primary particles. In this case, the spheronization during the preparation of the carbon precursor is carried out for 10 minutes using a counter-jet mill (rotation speed: 10 Hz).

[0141] After mixing the artificial graphite particles with pitch, heat treatment is carried out at 1,200 °C to form an amorphous carbon coating on the surface of the artificial graphite particles, thereby preparing a negative electrode active material. The content of the amorphous carbon coating in the negative electrode active material is 3% by weight.

[0142] The sphericity of the negative electrode active material is 0.79, and the average particle diameter (D 50 ) is 18 μm, and the BET specific surface area is 0.7 m 2 / g.

[0143] Example 2: Preparation of negative electrode active material

[0144] A negative electrode active material was prepared in the same manner as in Example 1, except that the rotation speed of the counter-jet mill was adjusted to 25 Hz during the spheronization step in the preparation of the carbon precursor.

[0145] The sphericity of the negative electrode active material is 0.79, and the average particle diameter (D 50 ) is 18 μm, and the BET specific surface area is 0.8 m 2 / g.

[0146] Comparative Example 1: Preparation of negative electrode active material

[0147] The negative electrode active material of Comparative Example 1 was prepared in the same manner as in Example 1, except that the spheronization step was not carried out during the preparation of the carbon precursor.

[0148] The sphericity of the negative electrode active material is 0.74, and the average particle diameter (D 50 ) is 18 μm, and the BET specific surface area is 0.8 m 2 / g.

[0149] Comparative Example 2: Preparation of negative electrode active material

[0150] A negative electrode active material was prepared in the same manner as in Example 1, except that the rotation speed of the counter-jet mill was adjusted to 5 Hz and the spheronization time was 20 minutes during the spheronization step in the preparation of the carbon precursor.

[0151] The sphericity of the negative electrode active material is 0.81, and the average particle diameter (D 50 ) is 18 μm, and the BET specific surface area is 0.8 m 2 / g.

[0152] [Table 1]

[0153]

[0154] 1) The solid content value when the sample has the maximum torque value

[0155] As the torque rheometer, a measuring mixer manufactured by Brabender is used.

[0156] The "solid content value at the maximum torque value" is measured by the following method.

[0157] Step (a): First, 55 mL of the negative electrode active material of Example 1 is put into the sample container of the torque rheometer.

[0158] Step (b): While injecting water into the sample container at a rate of 1 mL / minute, operate the torque rheometer to rotate the two blades in the sample container at 50 rpm to stir the sample. During this process, run the analysis software of the torque rheometer to measure the torque value according to the solid content value, and thus draw a graph with the solid content value (unit: wt%) on the X-axis and the torque value (unit: N·m) on the Y-axis, as Figure 1 shown.

[0159] Step (c): Analyze the graph obtained above to obtain the "solid content value at the maximum torque value" of the sample formed by the negative electrode active material and water.

[0160] The "solid content value at the maximum torque value" of Example 2, Comparative Example 1, and Comparative Example 2 is obtained in the same manner as above. Figure 2 , 3 and 4 respectively show the graphs of the solid content value and the torque value of the samples formed by the negative electrode active materials of Example 2, Comparative Example 1, and Comparative Example 2 and water.

[0161] 2) Sphericity

[0162] The sphericity of the negative electrode active material is measured using Morphologi M4 manufactured by Malvern Panalytical. Specifically, after preparing a sample of the negative electrode active material and measuring the sphericity of the particles in the sample with the above instrument, the average value is taken as the sphericity of the negative electrode active material.

[0163] 3) Average particle diameter (D 50 )

[0164] After obtaining the particle size distribution curve of the particles by the laser diffraction method, the particle size at 50% of the cumulative volume is obtained, and the particle size is defined as the average particle size (D 50 ) of the negative electrode active material.

[0165] 4) BET specific surface area

[0166] The BET specific surface area of the negative electrode active material is measured using a BEL Sorption instrument (manufactured by BEL Japan Co., Ltd.).

[0167] (2) Preparation of the negative electrode slurry

[0168] Example A

[0169] The negative electrode active material of Example 1, styrene-butadiene rubber (SBR) as a binder, carbon black as a conductive agent, and carboxymethyl cellulose (CMC) as a thickener are added to water as a solvent at a weight ratio of 96:1:1:2 to obtain a negative electrode slurry.

[0170] The solid content of the negative electrode slurry is adjusted to 48% by weight based on the total weight of the negative electrode slurry.

[0171] The viscosity of the negative electrode slurry at 25 °C is 7,500 cP.

[0172] Example B

[0173] The negative electrode active material of Example 2, styrene-butadiene rubber (SBR) as a binder, carbon black as a conductive agent, and carboxymethyl cellulose (CMC) as a thickener are added to water as a solvent at a weight ratio of 96:1:1:2 to obtain a negative electrode slurry.

[0174] The solid content of the negative electrode slurry is adjusted to 53% by weight based on the total weight of the negative electrode slurry.

[0175] The viscosity of the negative electrode slurry at 25 °C is 6,000 cP.

[0176] Example C

[0177] The negative electrode active material of Example 2, styrene-butadiene rubber (SBR) as a binder, carbon black as a conductive agent, and carboxymethyl cellulose (CMC) as a thickener are added to water as a solvent at a weight ratio of 96:1:1:2 to obtain a negative electrode slurry.

[0178] The solid content of the negative electrode slurry is adjusted to 48% by weight based on the total weight of the negative electrode slurry.

[0179] The viscosity of the negative electrode slurry at 25 °C is 5,000 cP.

[0180] Comparative Example A

[0181] The negative electrode active material of Comparative Example 1, styrene-butadiene rubber (SBR) as a binder, carbon black as a conductive agent, and carboxymethyl cellulose (CMC) as a thickener were added to water as a solvent at a weight ratio of 96:1:1:2 to obtain a negative electrode slurry.

[0182] The solid content of the negative electrode slurry was adjusted to 46% by weight based on the total weight of the negative electrode slurry.

[0183] The viscosity of the negative electrode slurry at 25 °C is 8,000 cP.

[0184] Comparative Example B

[0185] The negative electrode active material of Comparative Example 1, styrene-butadiene rubber (SBR) as a binder, carbon black as a conductive agent, and carboxymethyl cellulose (CMC) as a thickener were added to water as a solvent at a weight ratio of 96:1:1:2 to obtain a negative electrode slurry.

[0186] The solid content of the negative electrode slurry was adjusted to 48% by weight based on the total weight of the negative electrode slurry.

[0187] The viscosity of the negative electrode slurry at 25 °C is 9,500 cP.

[0188] Comparative Example C

[0189] The negative electrode active material of Comparative Example 2, styrene-butadiene rubber (SBR) as a binder, carbon black as a conductive agent, and carboxymethyl cellulose (CMC) as a thickener were added to water as a solvent at a weight ratio of 96:1:1:2 to obtain a negative electrode slurry.

[0190] The solid content of the negative electrode slurry was adjusted to 48% by weight based on the total weight of the negative electrode slurry.

[0191] The viscosity of the negative electrode slurry at 25 °C is 8,000 cP.

[0192] Experimental Example

[0193] Experimental Example 1: Filter Test

[0194] The negative electrode slurries prepared in Example A, Example B, Example C, Comparative Example A, Comparative Example B, and Comparative Example C were each passed through a 125-mesh filter for a filter test. If the filter was clogged with the negative electrode slurry, it was marked as "×", and if no clogging of the filter was found, it was marked as "○". The results are shown in Table 2 below.

[0195] Experimental Example 2: Measurement of Shear Thickening Slope Value

[0196] The shear viscosity according to the shear rate of the negative electrode slurries prepared in Example A, Example B, Example C, Comparative Example A, Comparative Example B, and Comparative Example C was measured using a Hakke rheometer (manufactured by Thermo Scientific). The change in the shear viscosity (unit: Pa·s) according to the shear rate (unit: 1 / s) is as Figure 5 shown.

[0197] The viscosity values in the range showing shear thickening in the measured shear viscosity were converted to logarithmic values to determine whether the slope value (linear fitting value) was positive (+) or negative (-). The results are shown in Table 2.

[0198] [Table 2]

[0199] Filter test Shear thickening slope Example A ○ Negative (-) Example B ○ Negative (-) Example C ○ Negative (-) Comparative Example A × Positive (+) Comparative Example B × Positive (+) Comparative Example C × Positive (+)

[0200] Referring to Table 2, for the negative electrode slurries of Example A, Example B, and Example C containing the negative electrode active material according to the present invention, it can be confirmed that the phase stability is excellent and the dispersibility of the negative electrode active material is significantly improved compared to the negative electrode slurries of Comparative Example A, Comparative Example B, and Comparative Example C.

Claims

1. A negative electrode active material comprising artificial graphite particles, Among them, during the measurement by a torque rheometer of a sample composed of the negative electrode active material and water, the solid content value at the time when the sample has the maximum torque value is 69.5% by weight or more, and wherein the solid content value at the time when the sample has the maximum torque value is measured by a method including the following steps (a) to (c): (a) Putting the negative electrode active material into the sample container of the torque rheometer; (b) Operating the torque rheometer while injecting water into the sample container of the torque rheometer at a constant rate, and measuring the torque value of the sample generated according to the solid content value; and (c) When the sample has the maximum torque value in the step (b), deriving the solid content value, wherein the sphericity of the negative electrode active material is in the range of 0.75 to 1, wherein the average particle size D of the negative electrode active material 50 is from 14 μm to 20 μm, and wherein the BET specific surface area of the negative electrode active material is 0.1 m 2 / g to 2.0 m 2 / g.

2. The negative electrode active material according to claim 1, wherein the tapped density of the negative electrode active material measured by powder flow analysis is in the range of 850 kg / m 3 to 1,200 kg / m 3 .

3. The negative electrode active material according to claim 1, wherein the artificial graphite particles have a secondary particle structure in which two or more primary particles are assembled.

4. The negative electrode active material according to claim 1, further comprising an amorphous carbon coating provided on the surface of the artificial graphite particles.

5. The negative electrode active material according to claim 4, wherein the content of the amorphous carbon coating in the negative electrode active material is in the range of 0.01% by weight to 10% by weight.

6. A negative electrode paste, the negative electrode paste comprising: the negative electrode active material according to claim 1; a negative electrode binder; a negative electrode conductive agent; and a solvent.

7. The negative electrode paste according to claim 6, wherein the solid content of the negative electrode paste is 46% by weight or more relative to the total weight of the negative electrode paste.

8. The negative electrode paste according to claim 6, wherein, When the solid content of the negative electrode paste is 46% by weight or more, the shear thickening slope obtained when measuring the shear viscosity according to the shear rate is a negative value.

9. A negative electrode, the negative electrode comprising: a negative electrode current collector; and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer comprises the negative electrode active material according to claim 1.

10. A secondary battery, the secondary battery comprising: the negative electrode according to claim 9; a positive electrode opposite to the negative electrode; a separator provided between the negative electrode and the positive electrode; and an electrolyte.

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