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

Abstract

The present invention relates to an anode active material containing artificial graphite particles, the anode active material having a solid content of 69.5% by weight or more when a sample consisting of the anode active material and water has a maximum torque value measured by a specific method during torque rheometer measurement. When the solid content value during torque rheometer measurement satisfies the above range, the anode active material can be evaluated as having excellent powder fluidity, and when the anode active material is included in an anode slurry, dispersibility and phase stability can be improved. Therefore, the productivity and quality of the anode slurry containing the anode active material of the present invention, and the anode and secondary battery manufactured therefrom can be improved.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0184259 filed on Dec. 21, 2021, and all the contents disclosed in the literature of the Korean patent application are incorporated herein by reference in their entirety.

[0002] The present invention relates to a negative electrode active material, a negative electrode including the same, and a secondary battery.

Background Art

[0003] As interest in environmental issues increases, many studies have been conducted on electric vehicles (EVs), hybrid electric vehicles (HEVs), etc., 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 power sources for such electric vehicles (EVs), hybrid electric vehicles (HEVs), etc., lithium secondary batteries with high energy density, high discharge voltage, and output stability have been mainly studied and used.

[0004] Generally, a lithium secondary battery is composed of a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode or the negative electrode is manufactured by mixing a positive electrode active material or a negative electrode active material with a binder or the like, dispersing it in a solvent to produce a slurry, applying the slurry to the surface of an electrode current collector, and drying it to form an electrode active material layer.

[0005] On one hand, as the negative electrode active material, a carbon-based active material capable of reversible insertion and desorption of lithium ions and maintaining its structural and electrical properties is used. As the carbon-based active material, various forms of carbon-based materials such as artificial graphite, natural graphite, and hard carbon are applied. Among them, graphite-based active materials, which can ensure the life characteristics of lithium secondary batteries due to their excellent reversibility, are most widely used. Since the graphite-based active material has a discharge voltage as low as -0.2V compared to lithium, a battery using the graphite-based active material can exhibit a high discharge voltage of 3.6V, providing many advantages in terms of the energy density of lithium batteries.

[0006] Among them, artificial graphite has a relatively low degree of orientation during the rolling of the electrode compared to natural graphite and good lithium ion insertion / extraction characteristics. Therefore, it has the advantages of excellent rapid charging performance of the battery, low degree of expansion due to charge and discharge, and excellent life characteristics.

[0007] However, in the case of artificial graphite, since it exhibits hydrophobicity, when water is used as the solvent of the negative electrode slurry, dispersion is not easy, and there is a problem of reduced phase stability of the slurry. In particular, due to reasons such as an increase in the negative electrode loading amount, improvement in efficiency during the drying process, and improvement in binder migration, attempts have been made to increase the solid content of the negative electrode slurry. In terms of such an increase in the solid content, the above-mentioned problems of reduced dispersibility of artificial graphite and phase stability of the slurry have become more prominent. In addition, such a dispersion problem causes a problem of filter clogging during the transfer of the negative electrode slurry during the manufacturing process of the negative electrode, and reduces the efficiency and quality of the overall secondary battery manufacturing process.

[0008] Japanese Patent No. 4403327 discloses graphite powder for a negative electrode of a lithium ion secondary battery, but it could not present an alternative solution to the above problems.

Prior Art Documents

Patent Documents

[0009] Patent Document 1 Japanese Patent No. 4403327 Summary of the Invention Problems to be Solved by the Invention

[0010] One problem of the present invention is to provide a negative electrode active material that has excellent dispersibility and can improve the phase stability of the negative electrode slurry even when the solid content of the negative electrode slurry increases.

[0011] Another problem of the present invention relates to a negative electrode slurry containing the above-described negative electrode active material.

[0012] Still another problem of the present invention relates to a negative electrode containing the above-described negative electrode active material.

[0013] Still another problem of the present invention relates to a secondary battery containing the above-described negative electrode. Means for Solving the Problems

[0014] The present invention provides a negative electrode active material containing artificial graphite particles, wherein when measuring the sample consisting of the negative electrode active material and water with a torque rheometer, the value of the solid content when the sample has the maximum torque value is 69.5% by weight or more, and the value of the solid content when the sample has the maximum torque value is measured by a method including the following steps (a) to (c). (a) A step of putting the negative electrode active material into a sample container of a torque rheometer, (b) A step of operating the torque rheometer while injecting water into the sample container of the torque rheometer at a predetermined speed to measure the torque value according to the value of the solid content of the sample, and (c) A step of deriving the value of the solid content when the sample has the maximum torque value in step (b).

[0015] The present invention also provides a negative electrode slurry containing the above-described negative electrode active material, a negative electrode binder, a negative electrode conductive material, and a solvent.

[0016] The present invention also provides a negative electrode including 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 contains the above-described negative electrode active material.

[0017] 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.

Advantages of the Invention

[0018] The present invention relates to a negative electrode active material containing artificial graphite particles, wherein when measuring the sample composed of the negative electrode active material and water with a torque rheometer, the solid content value when having the maximum torque value of the sample measured by a specific method is 69.5% by weight or more. When the solid content value when having the maximum torque value satisfies the above range during the torque rheometer measurement, it can be evaluated that the powder fluidity of the negative electrode active material is excellent. When the negative electrode active material is contained in a negative electrode slurry, the dispersibility and phase stability can be improved. Therefore, the negative electrode slurry containing the negative electrode active material of the present invention, the negative electrode and the secondary battery manufactured therefrom have improved productivity and quality.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Best Mode for Carrying Out the Invention

[0020] The terms and words used in this specification and the claims should not be construed as being limited to their ordinary or dictionary meanings. The inventor should interpret them in accordance with the principle that the concept of the terms can be appropriately defined in order to explain his or her invention in the best way, and should interpret them in a meaning and concept that conforms to the technical idea of the present invention.

[0021] The terms used in this specification are merely used to illustrate exemplary embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly has a different meaning.

[0022] In this specification, terms such as "including", "comprising", or "having" are used to specify the presence of implemented features, numbers, steps, components, or combinations thereof, and it should be understood that they do not preclude the presence or possibility of addition of one or more different features, numbers, steps, components, or combinations thereof.

[0023] In this specification, the average particle size (D 50 ) can be defined as the particle size corresponding to 50% of the volume cumulative amount 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 submicron region to about several millimeters, and can obtain highly reproducible and highly resolved results.

[0024] In this specification, "primary particle" means a single particle, i.e., one particle (single particle), and "secondary particle" means an aggregate in which a plurality of the primary particles are aggregated by an intentional granulation or binding process.

[0025] Hereinafter, the present invention will be specifically described.

[0026] Negative electrode active material The present invention relates to a negative electrode active material, specifically, a negative electrode active material for a lithium secondary battery.

[0027] Specifically, the negative electrode active material is a negative electrode active material containing artificial graphite particles, and when measuring the torque rheometer of a sample composed of the negative electrode active material and water, the value of the solid content when having the maximum torque value of the sample is 69.5% by weight or more, and the value of the solid content when having the maximum torque value of the sample is measured by a method including the following steps (a) to (c).

[0028] (a) A step of putting the negative electrode active material into a sample container of a torque rheometer. (b) A step of operating the torque rheometer while injecting water into the sample container of the torque rheometer at a predetermined speed to measure the torque value according to the value of the solid content of the sample, and (c) A step of deriving the value of the solid content when having the maximum torque value of the sample in step (b).

[0029] Conventionally, since artificial graphite exhibits hydrophobicity, when adding it to water as a negative electrode slurry solvent, there has been a problem that the dispersibility is not good and the slurry phase stability is reduced. Further, such a problem of dispersibility causes a problem of filter clogging during the transfer of the negative electrode slurry during the manufacturing process of the negative electrode, and there is a problem of reducing the efficiency and quality of the overall manufacturing process of the secondary battery.

[0030] To solve such problems, the present invention relates to a negative electrode active material containing artificial graphite particles, wherein the value of the solid content when the maximum torque value of a sample composed of the negative electrode active material and water is measured by a torque rheometer in a specific method is 69.5% by weight or more. When the value of the solid content when having the maximum torque value satisfies the above range during the torque rheometer measurement, it can be evaluated that the powder fluidity of the negative electrode active material is excellent. When the negative electrode active material is included in a negative electrode slurry, the dispersibility and phase stability can be improved. Therefore, the negative electrode slurry containing the negative electrode active material of the present invention, the negative electrode and the secondary battery manufactured therefrom have improved productivity and quality.

[0031] The negative electrode active material contains artificial graphite particles. Artificial graphite is manufactured by heat-treating amorphous carbon at a high temperature (for example, 2,500 °C to 3,200 °C), and is distinguished from natural graphite in that it is artificially synthesized graphite.

[0032] The artificial graphite particles can be in the form of primary particles, or can be in the form of secondary particles in which two or more primary particles are granulated. More specifically, the artificial graphite particles can be in the form of secondary particles in which two or more primary particles are granulated, and in this case, it is preferable in terms of slurry dispersibility and phase stability.

[0033] When the artificial graphite particles are in the form of secondary particles, voids can be formed in the artificial graphite particles. The voids can be the empty spaces formed between the primary particles, can be amorphous, and can be present in two or more.

[0034] In the present invention, as long as the "value of the solid content when having the maximum torque value" described later is satisfied, the manufacturing method of the artificial graphite particles is not particularly limited.

[0035] Specifically, when the artificial graphite particles are in the form of secondary particles, the artificial graphite particles can be produced by mixing a carbon precursor and a binder material (e.g., pitch), performing a spheroidization and granulation process to produce an intermediate in the form of secondary particles, and heat-treating the intermediate at a temperature of 2,500 °C or higher, specifically 3,000 °C or higher, to graphitize it. Here, the carbon precursor can be coal-based heavy oil, petroleum-based heavy oil, tar, pitch, coke, etc., and specifically, it can be at least one selected from the group consisting of coke and pitch. Here, furthermore, a spheroidization process can be performed on the carbon precursor. In this case, the surface of the primary artificial graphite particles can be made smoother, thereby improving the wettability of the secondary-particle artificial graphite particles and improving the fluidity of the negative electrode active material powder. The value of the solid content when having the maximum torque value of the sample composed of the negative electrode active material and water described later can be improved to a preferable level. The spheroidization process performed on the carbon precursor can be performed, for example, using a jet mill, specifically a counter jet mill. Here, the rotational speed of the jet mill can be 8 Hz or higher, specifically 10 Hz or higher, more specifically 15 Hz or higher, and 50 Hz or lower, specifically 40 Hz or lower, even more specifically 30 Hz or lower. Also, the spheroidization process performed on the carbon precursor can be performed for 3 minutes to 60 minutes, specifically 5 minutes to 15 minutes.

[0036] Also, when the artificial graphite particles are in the form of secondary particles, the artificial graphite particles can be produced by a method in which artificial graphite particles in the form of primary particles are mixed with a binder material (e.g., pitch), spheronized, aggregated, and heat-treated to aggregate the artificial graphite particles in the form of primary particles into secondary particles. Here, the artificial graphite particles in the form of primary particles can be produced 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 coal-based heavy oil, petroleum-based heavy oil, tar, pitch, coke, etc., and specifically, it can be at least one selected from the group consisting of coke and pitch. Here, further, a spheronization step can be performed on the artificial graphite particles in the form of primary particles; or the carbon precursor used in the production of the artificial graphite particles in the form of primary particles; in this case, the surface of the primary artificial graphite particles can be made smoother, thereby improving the wettability of the secondary-particle artificial graphite particles and improving the fluidity of the negative electrode active material powder, and the value of the solid content when having the maximum torque value of the sample composed of the negative electrode active material and water described later can be improved to a preferable level. The spheronization step performed on the artificial graphite particles in the form of primary particles; or the carbon precursor used in the production of the artificial graphite particles in the form of primary particles; can be performed, for example, using a jet mill, specifically a counter jet mill. Here, the rotation speed of the jet mill can be 8 Hz or higher, specifically 10 Hz or higher, more specifically 15 Hz or higher, and can be 50 Hz or lower, specifically 40 Hz or lower, and more specifically 30 Hz or lower. Also, the spheronization step performed on the artificial graphite particles in the form of primary particles; or the carbon precursor used in the production 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.

[0037] In the present invention, when measuring the torque of a sample composed of the negative electrode active material and water with a torque rheometer, the value of the solid content when the sample has the maximum torque value is characterized by being 69.5% by weight or more.

[0038] The value of the solid content when the sample has the maximum torque value can be measured by a method including the following steps (a) to (c).

[0039] (a) A step of charging the negative electrode active material into the sample container of the torque rheometer. (b) A step of operating the torque rheometer while injecting water into the sample container of the torque rheometer at a predetermined speed to measure the torque value according to the value of the solid content of the sample, and (c) A step of deriving the value of the solid content when the sample has the maximum torque value in the step (b).

[0040] The torque rheometer is a device that measures the rheological properties due to the flow generated by rotating a fluid or the like. For example, it can measure the viscosity-related torque generated by the resistance of the fluid formed from the shearing action, various rheological properties due to this, and the like. As the torque rheometer, the Measuring Mixers device manufactured by Brabender is cited as an example.

[0041] Specifically, in the present invention, the negative electrode active material is charged into the sample container of the torque rheometer, and while injecting water into the sample container at a predetermined speed, the sample in the sample container is stirred using two blades, and the torque value according to the value of the solid content of the sample composed of the negative electrode active material and water can be measured. A graph in which the torque value according to the value of the solid content of the sample is shown can be obtained by the analyzer of the torque rheometer.

[0042] By measuring the solid content value when the sample has the maximum torque value by means of a torque rheometer for the negative electrode active material, the phase stability and dispersibility of the negative electrode slurry containing the negative electrode active material can be predicted. When the solid content value when the sample composed of the negative electrode active material and water has the maximum torque value is 69.5% by weight or more, it can be evaluated that the negative electrode active material has excellent wettability with respect to water and excellent fluidity of the negative electrode active material powder. The negative electrode active material having the above-described characteristics has the advantage that when added to the negative electrode slurry, it has excellent dispersibility and can improve the phase stability of the slurry, and can improve the productivity and quality of the negative electrode manufacturing process. For example, when the solid content value when the sample composed of the negative electrode active material and water has the maximum torque value is less than 69.5% by weight, the fluidity of the powder is not good, which reduces the dispersibility and phase stability of the negative electrode slurry, and may cause clogging of the filter during the transfer process of the negative electrode slurry, etc., which may reduce the productivity and quality of the negative electrode.

[0043] In step (a), the volume of the negative electrode active material charged into the sample container can be 55 mL.

[0044] In step (b), the injection rate of the water can be 1 mL / min. Also, the stirring rate 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 when the torque rheometer is driven can be 25°C.

[0045] The value of the solid content when the sample composed of the negative electrode active material and water according to the present invention has the maximum torque value can be obtained by adjusting the shape, surface roughness, etc. in the manufacturing process of the negative electrode active material. For example, it can be obtained by adjusting the spheroidization rate, spheroidization time, etc. during the production of artificial graphite. For example, the value of the solid content when the sample according to the present invention has the maximum torque value can be realized by making the shape of the negative electrode active material smooth and gentle, such as increasing the spheroidization rate. More specifically, during the production of artificial graphite in the form of secondary particles, a spheroidization process is performed on primary artificial graphite particles or carbon precursors that become primary artificial graphite particles, and it can be achieved by appropriately adjusting the spheroidization rate and time, but it is not limited thereto.

[0046] The compression density measured by the powder flow analysis (Powder flow test) of the negative electrode active material is 850 kg / m 3 ~1,200 kg / m 3 , specifically 900 kg / m 3 ~950 kg / m 3 It can be. When the compression density measured by the powder flow analysis (Powder flow test) of the negative electrode active material satisfies the above range, it can be evaluated that the negative electrode active material is close to a spherical shape, whereby the fluidity and dispersibility of the negative electrode active material are further improved.

[0047] The measurement of the compression density of the negative electrode active material can be performed by a powder flow analyzer. For example, the negative electrode active material is put into a powder flow analyzer, and the process of applying a normal stress and a shear stress to the negative electrode active material with a lid is repeated 5 times to measure the density of the compressed negative electrode active material. The measurement of the compression density of the negative electrode active material can be performed using a powder flow analyzer (equipment name: PFT) manufactured by Brookfield Engineering Laboratories, Inc., located in Middleborough, Massachusetts, USA. The compression density can be performed in accordance with ASTM D6128.

[0048] The sphericity of the negative electrode active material can be 0.75 to 1, specifically 0.78 to 0.95. When within the above range, the fluidity and dispersibility of the negative electrode active material can be further improved. However, simply increasing the sphericity of the negative electrode active material cannot achieve the effect of improving the fluidity and dispersibility of the negative electrode active material, and it is necessary to satisfy up to the "value of the solid content when having the maximum torque value" of the sample composed of the above-mentioned negative electrode active material and water.

[0049] The sphericity can be measured using a particle shape analyzer (for example, Morphologi M4 equipment manufactured by Malvern Panalytical).

[0050] The average particle diameter (D 50 ) of the negative electrode active material can be 14 μm to 20 μm. When within the above range, the specific surface area is adjusted to an appropriate level and reduced, and the amount of dispersant that must be added during the production of the negative electrode slurry can be minimized. The problem of aggregation and reduction of phase stability due to the excessive increase of the average particle diameter (D 50 ) of the negative electrode active material can be prevented, which is preferable in terms of improving processability and thereby improving battery performance.

[0051] The BET specific surface area of the negative electrode active material is 0.1 m 2 / g to 2.0 m 2 / g, specifically 0.6 m 2 / g to 1.2 m 2 / g, more specifically 0.6 m 2 / g to 0.9 m 2 / g, and when within the above range, the specific surface area is adjusted to an appropriate level and reduced, and the amount of dispersant that must be added during the production of the negative electrode slurry can be minimized. It is preferable in terms of improving processability and thereby improving battery performance. The BET specific surface area can be measured using a BEL Sorption instrument (manufactured by BEL Japan).

[0052] The negative electrode active material can further include an amorphous carbon coating layer located on the surface of the artificial graphite particles. The amorphous carbon coating layer can improve the structural stability of the artificial graphite particles and help prevent side reactions between the negative electrode active material and the electrolyte solution.

[0053] The amorphous carbon coating layer can be formed at 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. However, excessive formation of the amorphous carbon coating layer may cause a decrease in the initial efficiency due to an increase in the specific surface area during negative electrode rolling, and the high-temperature storage performance may deteriorate. Therefore, it is preferable to form the carbon coating layer within the above-mentioned range of content.

[0054] The amorphous carbon coating layer can be formed by providing a carbon coating layer precursor to the artificial graphite particles and then performing heat treatment.

[0055] The carbon coating layer precursor can include at least one selected from a polymer resin and pitch. Specifically, the polymer resin can 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 can include at least one selected from the group consisting of coal-based pitch, petroleum-based pitch, and mesophase pitch. The heat treatment step for forming the amorphous carbon coating layer can be carried out at 1,000 °C to 1,500 °C in terms of achieving uniform formation of the amorphous carbon coating layer.

[0056] Negative electrode slurry Further, the present invention provides a negative electrode slurry. The negative electrode slurry can be a negative electrode slurry for manufacturing a negative electrode of a lithium secondary battery.

[0057] The negative electrode slurry includes the above-described negative electrode active material. Specifically, the negative electrode slurry can include the above-described negative electrode active material, a negative electrode binder, a negative electrode conductive material, and a solvent.

[0058] The negative electrode slurry according to the present invention includes the above-described negative electrode active material, has excellent dispersibility, and can improve phase stability. In particular, the negative electrode slurry according to the present invention exhibits excellent dispersibility and phase stability even when the solid content of the negative electrode slurry increases, so that it is possible to improve the productivity and quality of high-capacity negative electrodes and secondary batteries.

[0059] The negative electrode active material can be contained in the negative electrode slurry at 80% to 99% by weight, preferably 88% to 98% by weight, based on the solid content of the negative electrode slurry.

[0060] In addition, the description of the negative electrode active material is as described above.

[0061] The negative electrode binder is a component that helps bind the negative electrode active material and / or the current collector, and can be contained in the negative electrode slurry at 1% to 30% by weight, preferably 1% to 10% by weight, based on the solid content of the negative electrode slurry.

[0062] The negative electrode binder can include at least one selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, and fluorine rubber, preferably at least one selected from polyvinylidene fluoride and styrene-butadiene rubber.

[0063] The negative electrode conductive material can be contained in the negative electrode slurry at 1% to 30% by weight, preferably 1% to 10% by weight, based on the solid content of the negative electrode slurry, as a component for further improving the conductivity of the negative electrode active material.

[0064] The negative electrode conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers and metal fibers; 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; conductive materials such as polyphenylene derivatives can be used. Specific examples of commercially available conductive materials include acetylene black-based (manufactured by Chevron Chemical Company, Denka Singapore Private Limited, or Gulf Oil Company, etc.), Ketjenblack, EC-based (manufactured by Armak Company), Vulcan XC-72 (manufactured by Cabot Company), and Super P (manufactured by Timcal), etc.

[0065] The solvent can include water or an organic solvent such as NMP (N-methyl-2-pyrrolidone), and more specifically, it can be water. The negative electrode slurry according to the present invention can prevent problems such as a significant decrease in dispersibility and a decrease in phase stability caused by using a negative electrode active material containing artificial graphite particles to a remarkable level.

[0066] The negative electrode slurry can further include a thickener in terms of improving dispersibility.

[0067] As the thickener, all thickeners conventionally used in lithium secondary batteries can be used. As an example, there is carboxymethyl cellulose (CMC), etc.

[0068] The solid content of the negative electrode slurry can be 46% by weight or more, specifically 47% to 56% by weight, based on the total weight of the negative electrode slurry.

[0069] According to the present invention, by using the above-described negative electrode active material, the dispersibility and phase stability of the negative electrode slurry are improved. Therefore, even when the negative electrode slurry is produced with a solid content within the above range, excellent levels of dispersibility and phase stability can be ensured.

[0070] When the solid content of the negative electrode slurry is 46% by weight or more, specifically 47% to 56% by weight, the viscosity at 23°C can be 4,500 cP to 10,000 cP, specifically 4,800 cP to 7,800 cP.

[0071] On the other hand, when the solid content of the negative electrode slurry is 46% by weight or more, specifically 47% to 56% by weight, the slope of the shear thickening slope obtained when measuring the shear viscosity according to the shear rate can have a negative value.

[0072] When the slope of the thickening slope of the negative electrode slurry has a negative slope, the passage through the filter is smooth. Specifically, it is possible to pass through a 125 mesh filter, and no clogging of the filter occurs when passing through it. The negative electrode slurry becomes smoother in passing through the filter as the shear thickening phenomenon decreases. When strong shear acts on the filter, the negative electrode active material slurry that shows a large thickening is highly likely to clog the filter, and such a tendency can be quantitatively evaluated by the thickening slope value.

[0073] The thickening slope can be determined by measuring the shear viscosity of the negative electrode active material slurry according to the shear rate using a rheometer, and linearly approximating (linear fitting) the start point to the end point of the section showing the shear thickening phenomenon with the measured shear viscosity transformed into log values of the viscosity values to draw a straight-line graph.

[0074] Negative electrode Further, 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-described negative electrode active material.

[0075] Specifically, the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, and the negative electrode active material layer contains the above-described negative electrode active material.

[0076] The negative electrode current collector can be used without limitation any negative electrode current collector generally used in the art. For example, it is not particularly limited as long as it does not cause a chemical change in the lithium secondary battery and has high conductivity. For example, the negative electrode current collector can contain at least one selected from copper, stainless steel, aluminum, nickel, titanium, fired carbon, and an aluminum-cadmium alloy, preferably copper.

[0077] The negative electrode current collector can also form fine irregularities on the surface to strengthen the binding force of the negative electrode active material, and can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric body.

[0078] Generally, the negative electrode current collector can have a thickness of 3 μm to 500 μm.

[0079] The negative electrode active material layer is disposed on at least one surface of the negative electrode current collector. Specifically, the negative electrode active material layer can be disposed on one surface or both surfaces of the negative electrode current collector.

[0080] The negative electrode active material layer contains the above-described negative electrode active material.

[0081] The negative electrode active material can be contained in the negative electrode active material layer at 80% to 99% by weight, preferably 88% to 98% by weight.

[0082] Other descriptions regarding the negative electrode active material are as described above.

[0083] In addition to the above-described negative electrode active material, the negative electrode active material layer can further contain a negative electrode binder, a negative electrode conductive material, and / or a thickener.

[0084] The negative electrode binder can usually be contained in the negative electrode active material layer at 1% to 30% by weight, preferably 1% to 10% by weight, as a component that helps bind the active material and / or the current collector.

[0085] Other descriptions regarding the negative electrode binder are as described above.

[0086] As the thickener, all thickeners conventionally used in lithium secondary batteries can be used, and examples include carboxymethyl cellulose (CMC).

[0087] The negative electrode conductive material can be contained in the negative electrode active material layer at 1% to 30% by weight, preferably 1% to 10% by weight, as a component for further improving the conductivity of the negative electrode active material.

[0088] Other descriptions regarding the negative electrode conductive material are as described above.

[0089] The thickness of the negative electrode active material layer can be 10 μm to 150 μm, specifically 50 μm to 100 μm, but is not limited thereto.

[0090] The negative electrode active material layer can be manufactured by applying, rolling, and drying the above-described negative electrode slurry onto the negative electrode current collector.

[0091] Secondary battery Further, the present invention provides a secondary battery including the above-described negative electrode, and more specifically, a lithium secondary battery.

[0092] The secondary battery may include 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.

[0093] The positive electrode can face the negative electrode.

[0094] The positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector.

[0095] The positive electrode current collector can be any positive electrode current collector commonly used in the art without limitation. For example, it is not particularly limited as long as it does not cause chemical changes in the secondary battery and has high conductivity. For example, the positive electrode current collector can be at least one selected from copper, stainless steel, aluminum, nickel, titanium, fired carbon, and an aluminum-cadmium alloy, and preferably includes aluminum.

[0096] The positive electrode current collector can 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 a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric.

[0097] Generally, the positive electrode current collector can have a thickness of 3 μm to 500 μm.

[0098] The positive electrode active material layer can include a positive electrode active material.

[0099] The positive electrode active material can include a compound capable of reversible intercalation and deintercalation of lithium, specifically, 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., LiCoO2, 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 Y1 O2 (where 0 < Y1 < 1), etc.), a lithium-manganese-cobalt-based oxide (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-z1 Co z1 O4 (where 0 < Z1 < 2), etc.), a lithium-nickel-manganese-cobalt-based oxide (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 a lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r3 M S2O2 (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, as atomic fractions of independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, and p2 + q2 + r3 + s2 = 1), etc.), and one or more of these compounds can 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 Mn 0.15 Co 0.05 )O2, etc.), and considering the significance of the improvement effect by controlling the types and content ratios of the constituent elements forming the lithium composite metal oxide, the lithium composite metal oxide can 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 Mn 0.1 Co 0.1 )O2, etc., and one or more mixtures of these can be used.

[0100] The positive electrode active material can be contained in the positive electrode active material layer in an amount of 80% to 99% by weight.

[0101] The positive electrode active material layer may further include at least one selected from the group consisting of a binder and a conductive material, together with the positive electrode active material.

[0102] The binder is usually added in an amount of 1 to 30% by weight based on the total weight of the positive electrode mixture as a component that facilitates the bonding of the active material and the conductive material, etc. and the bonding to the current collector. Examples of such a binder include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluorine rubber.

[0103] The binder can be contained in the positive electrode active material layer in an amount of 1% to 30% by weight.

[0104] The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers and metal fibers; 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; conductive materials such as polyphenylene derivatives, etc. can be used. Specific examples of commercially available conductive materials include acetylene black-based (manufactured by Chevron Chemical Company, Denka Singapore Private Limited, or Gulf Oil Company, etc.), Ketjenblack, EC-based (manufactured by Armak Company), Vulcan XC-72 (manufactured by Cabot Company), and Super P (manufactured by Timcal), etc.

[0105] The conductive material can be added in an amount of 1% to 30% by weight in the positive electrode active material layer.

[0106] The separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions. Usually, in a lithium secondary battery, any separator can be used without particular limitation as long as it can be used as a separator. In particular, those with low resistance to the ion migration of the electrolyte and excellent electrolyte moisture retention ability are preferred. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as a polyethylene homopolymer, a polypropylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof can be used. Also, a normal porous nonwoven fabric, for example, a nonwoven fabric made of high-melting glass fibers, polyethylene terephthalate fibers, etc. can also be used. Further, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer substance can also be used, and optionally, it can be used in a single-layer or multilayer structure.

[0107] In addition, examples of the electrolyte used in the present invention include, but are not limited to, 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 manufacture of lithium secondary batteries.

[0108] Specifically, the electrolyte can contain an organic solvent and a lithium salt.

[0109] As the organic solvent, any solvent can be used without particular limitation as long as it serves as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include 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; 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 ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain a double bond aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes. Among them, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having a high ionic conductivity and a high dielectric constant, which can enhance the charge-discharge performance of the battery, and a linear carbonate compound having a low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, the cyclic carbonate and the linear carbonate can be mixed and used at a volume ratio of about 1:1 to about 1:9, so that the electrolyte can exhibit excellent performance.

[0110] 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, examples of the lithium salt include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc., which can be used. The concentration of the lithium salt is preferably in the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0111] As described above, the lithium secondary battery according to the present invention stably exhibits excellent discharge capacity, rapid charging characteristics, and capacity retention rate. Therefore, it is useful in portable devices such as mobile phones, notebook computers, digital cameras, etc., and in the field of electric vehicles such as hybrid electric vehicles (HEV). In particular, it can be preferably used as a constituent battery of a medium and large-sized battery module. Accordingly, the present invention also provides a medium and large-sized battery module including the secondary battery as described above as a unit battery.

[0112] Such a medium and large-sized battery module can be preferably applied as a power source that requires high output and large capacity, such as in electric vehicles, hybrid electric vehicles, power storage devices, etc.

[0113] Hereinafter, embodiments of the present invention will be described in detail so that those having ordinary knowledge in the technical field to which the present invention pertains can easily implement it. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0114] Examples and comparative examples (1) Preparation of the negative electrode active material The negative electrode active materials of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 as shown in Table 1 below were prepared.

[0115] Example 1: Production of Negative Electrode Active Material After crushing the coke raw material, classifying it by air flow, and spheroidizing it to produce a carbon precursor in the form of primary particles, the carbon precursor and pitch were mixed and spheroidized to produce an intermediate in the form of secondary particles. The intermediate was heat-treated at 3,000 °C to graphitize it, thereby producing artificial graphite particles in the form of secondary particles in which two or more primary artificial graphite particles were aggregated. Here, the spheroidization during the production of the carbon precursor was performed for 10 minutes using a counter jet mill (rotation speed: 10 Hz).

[0116] After mixing the artificial graphite particles and pitch, they were heat-treated at 1,200 °C to form an amorphous carbon coating layer on the surface of the artificial graphite particles, thereby producing a negative electrode active material. The amorphous carbon coating layer was contained in the negative electrode active material at 3% by weight.

[0117] The sphericity of the negative electrode active material was 0.79, and the average particle size (D 50 ) was 18 μm, and the BET specific surface area was 0.7 m 2 / g.

[0118] Example 2: Production of Negative Electrode Active Material A negative electrode active material was produced in the same manner as in Example 1, except that the rotation speed of the counter jet mill was adjusted to 25 Hz in the spheroidization step during the production of the carbon precursor.

[0119] The sphericity of the negative electrode active material was 0.81, and the average particle size (D 50 ) was 18 μm, and the BET specific surface area was 0.8 m 2 / g.

[0120] Comparative Example 1: Production of Negative Electrode Active Material The negative electrode active material of Comparative Example 1 was produced in the same manner as in Example 1, except that the spheroidization step was not performed during the production of the carbon precursor.

[0121] The sphericity of the negative electrode active material was 0.74, and the average particle size (D 50 ) was 18 μm, and the BET specific surface area was 0.8 m 2 / g.

[0122] Comparative Example 2: Production of negative electrode active material A negative electrode active material was produced in the same manner as in Example 1, except that the rotational speed of the counter jet mill was adjusted to 5 Hz and the spheroidization time was set to 20 minutes in the spheroidization step during the production of the carbon precursor.

[0123] The sphericity of the negative electrode active material was 0.81, and the average particle size (D 50 ) was 18 μm, and the BET specific surface area was 0.8 m 2 / g.

[0124]

Table 1

[0125] 1) Value of solid content when the sample has the maximum torque value As the torque rheometer, a Measuring Mixers device manufactured by Brabender was used.

[0126] The "value of solid content when having the maximum torque value" was measured by the following method.

[0127] Step (a): 55 mL of the negative electrode active material of Example 1 was charged into the sample container of the torque rheometer. Step (b): While injecting water into the sample container at a rate of 1 mL / min, the torque rheometer was operated to rotate two blades in the sample container at 50 rpm to stir the sample. During this process, the analysis software of the torque rheometer was driven to measure the torque value according to the value of the solid content, and thereby, a graph of the value of the solid content on the X-axis (unit: wt%) and the torque value on the Y-axis (unit: N·m) was illustrated as shown in FIG. 1. Step (c): The graph obtained in step (b) was analyzed to determine the "value of the solid content when the maximum torque value" of the sample composed of the negative electrode active material and water.

[0128] The "value of the solid content when the sample has the maximum torque value" for Example 2, Comparative Example 1, and Comparative Example 2 was determined by the method described above. Graphs of the solid content values and torque values of the samples composed of the negative electrode active material and water for Example 2, Comparative Example 1, and Comparative Example 2 are shown in FIGS. 2, 3, and 4, respectively.

[0129] 2) Sphericity The sphericity of the negative electrode active material was measured using a Morphologi M4 instrument manufactured by Malvern Panalyrical. Specifically, a sample of the negative electrode active material was prepared, and after measuring the sphericity of the powder in the sample using the instrument, the average value of these was taken as the sphericity of the negative electrode active material.

[0130] 3) Average particle diameter (D 50 ) The average particle diameter (D 50 ) of the negative electrode active material was obtained by using the laser diffraction method to obtain a particle size distribution curve of the particles, and then determining the particle diameter corresponding to 50% of the volume cumulative amount, which was defined as the average particle diameter (D 50 ) of the negative electrode active material.

[0131] 4) BET specific surface area The BET specific surface area of the negative electrode active material was measured using a BEL Sorption instrument (manufactured by BEL Japan).

[0132] (2) Preparation of negative electrode slurry Example A The negative electrode active material of Example 1, styrene-butadiene rubber (SBR) as a binder, carbon black as a conductive material, 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.

[0133] The solid content of the negative electrode slurry was adjusted to 48% by weight based on the total weight of the negative electrode slurry.

[0134] The viscosity of the negative electrode slurry at 25 °C was 7,500 cP.

[0135] Example B The negative electrode active material of Example 2, styrene-butadiene rubber (SBR) as a binder, carbon black as a conductive material, 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.

[0136] The solid content of the negative electrode slurry was adjusted to 53% by weight based on the total weight of the negative electrode slurry.

[0137] The viscosity of the negative electrode slurry at 25 °C was 6,000 cP.

[0138] Example C The negative electrode active material of Example 2, styrene-butadiene rubber (SBR) as a binder, carbon black as a conductive material, 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.

[0139] The solid content of the negative electrode slurry was adjusted to 48% by weight based on the total weight of the negative electrode slurry.

[0140] The viscosity of the negative electrode slurry at 25 °C was 5,000 cP.

[0141] Comparative example A The negative electrode active material of Comparative Example 1, styrene-butadiene rubber (SBR) as a binder, carbon black as a conductive material, 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.

[0142] The solid content of the negative electrode slurry was adjusted to 46% by weight based on the total weight of the negative electrode slurry.

[0143] The viscosity of the negative electrode slurry at 25 °C was 8,000 cP.

[0144] Comparative example B The negative electrode active material of Comparative Example 1, styrene-butadiene rubber (SBR) as a binder, carbon black as a conductive material, 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.

[0145] The solid content of the negative electrode slurry was adjusted to 48% by weight based on the total weight of the negative electrode slurry.

[0146] The viscosity of the negative electrode slurry at 25 °C was 9,500 cP.

[0147] Comparative example C The negative electrode active material of Comparative Example 2, styrene-butadiene rubber (SBR) as a binder, carbon black as a conductive material, 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.

[0148] The solid content of the negative electrode slurry was adjusted to 48% by weight based on the total weight of the negative electrode slurry.

[0149] The viscosity of the negative electrode slurry at 25 °C was 8,000 cP.

[0150] Experimental example Experimental Example 1: Filter Test The negative electrode slurries manufactured 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 to conduct a filter test. When the filter was clogged by the negative electrode slurry, it was marked with "×", and when no filter clogging phenomenon was found, it was marked with "○". The results are shown in Table 2 below.

[0151] Experimental Example 2: Measurement of thickening slope value Using a Hakke Rheometer (manufactured by Thermo Scientific), the shear viscosity according to the shear rate of the negative electrode slurries manufactured in Example A, Example B, Example C, Comparative Example A, Comparative Example B, and Comparative Example C was measured. The change in shear viscosity (unit: Pa·s) according to the shear rate (unit: 1 / s) is shown in Figure 5.

[0152] The viscosity values in the section showing the shear thickening phenomenon with the measured shear viscosity were transformed into log values, and it was determined whether the slope of the slope value (linear fitting value) was positive (+) or negative (-), which is shown in Table 2.

[0153]

Table 2

[0154] Referring to Table 2, it can be confirmed that the negative electrode slurries of Example A, Example B, and Example C containing the negative electrode active material according to the present invention are superior in phase stability 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 containing artificial graphite particles, when measuring the torque rheometer of a sample composed of the negative electrode active material and water, the value of the solid content when the sample has the maximum torque value is 69.5% by weight or more, the value of the solid content when the sample has the maximum torque value is determined by the following steps (a) to (c): (a) A step of putting the negative electrode active material into a sample container of a torque rheometer, (b) A step of operating the torque rheometer while injecting water into the sample container of the torque rheometer at a predetermined speed to measure the torque value according to the value of the solid content of the sample, and (c) A step of deriving the value of the solid content when the sample has the maximum torque value in step (b), is measured by a method including, a negative electrode active material, wherein the negative electrode active material is used in a negative electrode slurry using water as a solvent.

2. The negative electrode active material according to claim 1, wherein the sphericity of the negative electrode active material is 0.75 to 1.

3. The compression density measured by the powder flow test of the negative electrode active material is 850 kg / m ３ to 1,200 kg / m ３ The negative electrode active material according to claim 1, wherein the negative electrode active material is as described above.

4. The negative electrode active material according to claim 1, wherein the artificial graphite particles are in the form of secondary particles obtained by granulating two or more primary particles.

5. The average particle size (D ５０ ) of the negative electrode active material is 14 μm to 20 μm, and the negative electrode active material according to claim 1.

6. The BET specific surface area of the negative electrode active material is 0.1 m ２ / g to 2.0 m ２ / g, and the negative electrode active material according to claim 1.

7. The negative electrode active material according to claim 1, further including an amorphous carbon coating layer located on the surface of the artificial graphite particles.

8. The negative electrode active material according to claim 7, wherein the amorphous carbon coating layer is contained in the negative electrode active material in an amount of 0.01% by weight to 10% by weight.

9. A negative electrode slurry containing the negative electrode active material according to any one of claims 1 to 8, a negative electrode binder, a negative electrode conductive material, and a solvent, wherein the solvent is water.

10. The negative electrode slurry according to claim 9, wherein the solid content of the negative electrode slurry is 46% by weight or more based on the total weight of the negative electrode slurry.

Images