Method for manufacturing graphite, negative electrode active material and secondary battery including the same

Abstract

The present invention relates to a method for manufacturing graphite, a negative electrode active material, and a secondary battery comprising the same. It aims to provide graphite with improved process productivity and economic efficiency by utilizing fine particles generated during the process, and with excellent rapid charging performance.

Description

Technology Field

[0001] The present invention relates to a method for manufacturing graphite, a negative electrode active material, and a secondary battery containing the same. Background Technology

[0002] The rapid increase in the use of fossil fuels has led to a growing demand for alternative and clean energy. In response to this demand, one of the most actively researched fields is power generation and energy storage utilizing electrochemical reactions. Currently, secondary batteries are a representative example of electrochemical devices that utilize such electrochemical energy, and their scope of application is steadily expanding.

[0003] Among secondary batteries, lithium-ion batteries, which possess high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used; graphite is primarily used as the negative electrode active material for lithium-ion batteries. Graphite has established itself as one of the most commercially widely used negative electrode active materials due to its advantages of providing excellent electrochemical properties and stable charge-discharge cycles.

[0004] Recently, as technology development and demand for electric vehicles have increased, the demand for secondary battery performance, particularly fast charging performance, has been growing significantly. If fast charging performance is improved so that the battery in an electric vehicle can be charged to 80% and used smoothly in a short time of about 10 minutes, moving from a state where the remaining capacity is almost discharged to 10% and the device is difficult to use, it can be considered to have convenience comparable to internal combustion engines. Therefore, attempts are being made to develop various types or combinations of materials to improve fast charging performance. The problem to be solved

[0005] The present specification aims to provide a method for manufacturing graphite capable of solving the aforementioned problems, a negative electrode active material, and a secondary battery including the same. means of solving the problem

[0006] One embodiment of the present specification provides a method for manufacturing graphite, comprising: (S1) a step of grinding a carbon-based raw material to produce primary particles and fine powder; (S2) a step of mixing the primary particles and the fine powder to produce single particles; and (S3) a step of graphitizing the single particles, wherein the average particle size (D50) of the fine powder is 3 μm or less, and in (S1), the carbon-based raw material is petroleum coke, or in (S2), pitch is mixed together in an amount greater than 0 parts by weight and less than or equal to 3 parts by weight based on 100 parts by weight of the total content of the primary particles and the fine powder.

[0007] Another embodiment of the present specification provides a negative electrode active material comprising graphite produced by the method for producing graphite.

[0008] Another embodiment of the present specification provides a cathode comprising the cathode active material.

[0009] Another embodiment of the present specification provides a secondary battery comprising the negative electrode.

[0010] Another embodiment of the present specification provides a battery module or battery pack including the secondary battery.

[0011] Finally, a battery pack including the above-mentioned battery module is provided. Effects of the invention

[0012] According to one embodiment of the present invention, a method for manufacturing graphite with improved productivity and economic efficiency can be provided by simplifying the process conditions of graphite.

[0013] According to one embodiment of the present invention, a method for manufacturing graphite with improved productivity and economic efficiency can be provided by utilizing fine particles generated during the process within the process without removing them.

[0014] According to one embodiment of the present invention, graphite with improved rapid charging performance can be provided.

[0015] Further scopes of the applicability of the present invention will become apparent from the following detailed description. However, since various changes and modifications within the spirit and scope of the present invention are clearly understood by those skilled in the art, specific embodiments, such as the detailed description and preferred embodiments of the present invention, should be understood as being given merely as examples. Brief explanation of the drawing

[0016] Figure 1 is an SEM image of the pulverized primary particle (top) and single particle (bottom) of Example 1. Figure 2 is an SEM image of the crushed primary particles (top) and secondary particles (bottom) of Reference Example 2. Figure 3 is a graph of the particle size of the crushed primary particles and the single particles of Example 1. Figure 4 is a particle size graph of the crushed primary particles and the secondary particles of Reference Example 2. Specific details for implementing the invention

[0017] Before describing the present invention, we will first define some terms.

[0018] The present invention may be embodied in various different forms and is not limited to the embodiments described herein. In this case, terms or words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0019] In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should not be understood as precluding the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0020] Furthermore, when it is said that one part is "above" or "on" another part, this includes not only the case where it is "directly above" the other part, but also the case where there is another part in between. Conversely, when it is said that one part is "directly above" another part, it means that there is no other part in between. Also, saying that one is "above" or "on" a reference part means that one is located above or below the reference part, and it does not necessarily mean that one is located "above" or "on" facing the opposite direction of gravity.

[0021] In this specification, "p to q" means a range of p or more and q or less.

[0022] In this specification, "Dn" refers to the particle size distribution and represents the particle size at the n% point of the cumulative distribution of the number of particles according to particle size. That is, D50 is the particle size at the 50% point of the cumulative distribution of the number of particles according to particle size (central particle size), D90 is the particle size at the 90% point of the cumulative distribution of the number of particles according to particle size, and D10 is the particle size at the 10% point of the cumulative distribution of the number of particles according to particle size. Meanwhile, the central particle size can be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) and the difference in diffraction patterns according to particle size is measured as the particles pass through the laser beam to calculate the particle size distribution.

[0023] In this specification, particle size or particle diameter may refer to the average diameter or representative diameter of each individual grain constituting the particle powder.

[0024] In this specification, "particle size (or particle diameter)" may refer to the average diameter or representative diameter of a particle. The particle may be in the form of a single particle or in the form of a secondary particle formed by the aggregation of multiple primary particles. Additionally, the central particle diameter of a particle may be used interchangeably with the average particle diameter, D50, or particle diameter, and the central particle diameter may refer to the size of a particle.

[0025] In this specification, "particle" may be in the form of a single particle, a pseudo-single particle, or a single particle.

[0026] In this specification, "single particle" may mean one primary particle and may include a pseudo-single particle formed by aggregating, combining, or assembling 30 or fewer primary particles.

[0027] The term "secondary particles" as used in this specification refers to particles formed by the aggregation of dozens to hundreds, for example, more than 30 primary particles, by combining, combining, or assembling.

[0028] The terms used in this specification are used merely to describe exemplary embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0029] The present invention is described in detail below so that those skilled in the art can easily practice it. However, the present invention may be embodied in various different forms and is not limited to the description below.

[0030] One embodiment of the present specification provides a method for manufacturing graphite, comprising: (S1) a step of grinding a carbon-based raw material to produce primary particles and fine powder; (S2) a step of mixing the primary particles and the fine powder to produce single particles; and (S3) a step of graphitizing the single particles, wherein the average particle size (D50) of the fine powder is 3 μm or less, and in (S1), the carbon-based raw material is petroleum coke, or in (S2), pitch is mixed together in an amount of 3 parts by weight or less based on 100 parts by weight of the total content of the primary particles and the fine powder.

[0031] The graphite manufacturing method according to the aforementioned embodiments of the present invention can provide graphite with excellent rapid charging performance and improved process productivity and economic efficiency, as it overcomes the disadvantages of existing processes by simplifying process conditions and does not include a separate process for removing fine particles generated during the process.

[0032] In other words, according to the embodiments of the present invention, the productivity of the process is maximized by not including a separate fine powder removal process after the grinding of carbon-based raw materials, while economic efficiency is improved by applying the generated fine powder within the process instead of discarding it. Furthermore, the fine powder can improve the binding strength between the primary particles, thereby reducing the amount of pitch used in the process, and the graphite produced through the above manufacturing method can provide excellent rapid charging performance. Specifically, the graphite produced by the above method is a single particle smaller than the D50 of the secondary particles; when used as an active material for an electrode, the lithium ion migration distance is short, and additionally, if it has a carbon coating layer, it can suppress the decomposition reaction of the electrolyte and provide excellent rapid charging performance due to the reduction of RCT (Charge Transfer Resistance).

[0033] The above fine powder is discharged during the grinding process of carbon-based raw materials and has an average particle size that is relatively smaller than that of primary particles; conventionally, it was considered an impurity and was removed through a granulation process or a deironing process.

[0034] However, the present invention is characterized by eliminating the assembly process and forming single particles by attaching the fine powder as an additive to the surface of primary particles, thereby improving productivity and economic efficiency, and providing graphite with excellent rapid charging performance as a single particle itself that is similar in size to the primary particles. In the present invention, in order to form single particles by attaching the fine powder as an additive to the surface of primary particles, petroleum coke is used as a carbon-based raw material in (S1), or a small amount of pitch is mixed in in (S2).

[0035] Below, each step is described in detail.

[0036] A method for manufacturing graphite according to one embodiment of the present invention includes (S1) a step of grinding a carbon-based raw material to produce primary particles and fine powder.

[0037] According to one embodiment of the present invention, the step of grinding the carbon-based raw material may be carried out using a grinder such as a jet mill, a fin mill, or an impact mill, and a circulating grinding facility combining a grinder and a classifier may also be applied. When grinding the carbon-based raw material, grinding conditions and a grinder may be appropriately selected by paying attention to the grinding characteristics of the carbon-based raw material, such as high abrasiveness, hygroscopicity, lubricity, and impact strength, and low specific gravity and elastic modulus.

[0038] According to one embodiment of the present invention, the carbon-based raw material may be coke. Specifically, the carbon-based raw material may be coal-based coke or petroleum-based coke.

[0039] According to one embodiment of the present invention, the carbon-based raw material may be petroleum coke. Specifically, the carbon-based raw material may be petroleum green coke, petroleum calcined coke, or petroleum needle coke. It is preferable that the carbon-based raw material be petroleum coke, as using petroleum coke with a volatile content of 5% or more results in relatively high self-adhesion of the raw material, which allows for excellent adhesion between primary particles and fine particles in (S2) described later. The volatile content in the petroleum coke is inherent to the raw material itself and may include moisture, organic compounds, or gaseous components. The amount of volatile content in the petroleum coke affects the properties of the raw material, final quality, production efficiency, etc. The amount of volatile matter in the above petroleum coke can be measured through thermal decomposition at high temperatures, and generally, it can be calculated by heating a sample of 1 to 2 g at a high temperature of about 950°C for about 7 minutes and measuring the change in weight of the sample (difference in weight before and after heating).

[0040] According to one embodiment of the present invention, the average particle size (D50) of the primary particles is greater than 3 μm and less than or equal to 15 μm. Specifically, the average particle size (D50) of the primary particles may be greater than 3 μm, greater than or equal to 5 μm, greater than or equal to 6 μm, greater than or equal to 7 μm, less than or equal to 15 μm, less than or equal to 14 μm, less than or equal to 13 μm, less than or equal to 12 μm, less than or equal to 11 μm, less than or equal to 10 μm, less than or equal to 9 μm, less than or equal to 8 μm, less than or equal to 8.5 μm, or less than or equal to 8 μm. When the average particle size (D50) of the primary particles falls within the above range, they can be evenly dispersed within the negative electrode active material layer when applied as a negative electrode active material.

[0041] According to one embodiment of the present invention, the average particle size (D50) of the primary particles is preferably 7 μm or more and 15 μm or less, for example, 9 μm or more and 13 μm or less. When the average particle size (D50) of the primary particles falls within the above range, the discharge capacity is not low, and the BET can be controlled with an appropriate specific surface area, and high-temperature storage performance and long-term cycle life can be secured.

[0042] According to one embodiment of the present invention, the average particle size (D50) of the fine powder is 3 μm or less. Specifically, the average particle size (D50) of the fine powder may be 2.5 μm or less or 2 μm or less.

[0043] A method for manufacturing graphite according to one embodiment of the present invention comprises the step of (S1) grinding a carbon-based raw material to produce primary particles and fine powder, and then (S2) mixing the primary particles and the fine powder to produce single particles, wherein in (S1), the carbon-based raw material is petroleum coke, or pitch is mixed together in an amount greater than 0 parts by weight and less than or equal to 3 parts by weight based on 100 parts by weight of the total content of the primary particles and the fine powder.

[0044] One feature of the present invention is that, after step (S1), step (S2) is performed without including a separate fine particle removal process through a separate iron removal or assembly process, and includes the fine particles generated during the process as they are. This configuration is characterized by the ability to significantly reduce the amount of pitch used compared to existing processes while exhibiting results equivalent to or superior to those in terms of battery performance.

[0045] In the above (S1), petroleum coke is used as a carbon-based raw material, or in the above (S2), a small amount of pitch is mixed. Even if pitch is absent or included in a small amount in the above (S2) step, an excellent binding effect is achieved through the synergistic action between the primary particles and the fine powder, or between the fine powder and the pitch. In particular, the fine powder plays a role in improving the bonding strength between the primary particles, thereby replacing the role of pitch. As a result, while reducing the amount of pitch used during the process, the manufactured single particles maintain sufficient strength and stability, and have the advantage of not being easily pulverized in subsequent processes such as grinding and powder treatment.

[0046] In one embodiment of the present invention, the pitch may be a solid pitch or a liquid pitch. The solid pitch may be obtained by grinding coal tar pitch, petroleum pitch, synthetic pitch, wood tar pitch, etc., and the liquid pitch may be prepared by dissolving a liquid resin or a solid pitch in a solvent, coating it, and then carbonizing it. In this case, the solvent may be hexane, toluene, tetrahydrofuran (THF), quinoline, N-methylpyrrolidone (NMP), ethanol, etc.

[0047] According to one embodiment of the present invention, the softening point of the pitch may be 80 to 300 ℃, for example 90 to 280 ℃, 95 to 250 ℃, 100 to 280 ℃, 105 to 260 ℃, 105 to 240 ℃, or 110 to 220 ℃. When the softening point satisfies the above range, thermal deformation of the composition within the process can be prevented.

[0048] A method for manufacturing graphite according to one embodiment of the present invention (S3) includes the step of graphitizing the single particles. That is, the single particles manufactured as above can be graphitized by heat-treating them at a high temperature.

[0049] According to one embodiment of the present invention, the processing temperature for graphitization is not particularly limited, but graphitization can be performed in a range of, for example, 2,000 to 3,500°C, or 2,500 to 3,500°C, or 2,800 to 3,500°C, or 2,800 to 3,200°C. When the graphitization treatment satisfies the above temperature range, crystallization of the graphite proceeds, and the artificial graphite obtained has ductility and can be easily processed, and since sublimation of the graphite surface is minimal, the temperature can be easily raised.

[0050] The above graphitization step can be carried out using devices such as an Etchison graphitization furnace, a box-type graphitization furnace, or a lengthwise graphitization furnace.

[0051] The above method of graphitization is not limited to, but may utilize an Acheson furnace in which the assembled product is embedded in a furnace and heat is generated by passing an electric current from an electrode to the sintered body, or an induction furnace in which heat is generated by passing an induced current through an induction coil to the sintered body.

[0052] According to one embodiment of the present invention, the method for manufacturing the graphite further includes the step of (S4) providing a carbon coating layer on the single particle.

[0053] In one embodiment of the present invention, the above (S4) may be performed after the above (S2) and before the above (S3), or may be performed after the above (S3).

[0054] In one embodiment of the present invention, the above (S4) may be performed after the above (S2) and before the above (S3).

[0055] In one embodiment of the present invention, the above (S4) may be performed after the above (S3).

[0056] The step of providing the carbon coating layer may, for example, involve mixing the result of the previous step with pitch and carbonizing it at a temperature of 1,000 to 2,600°C, or 1,500 to 2,000°C, or 1,500 to 1,600°C to form a carbon coating. That is, the step of forming the carbon coating layer may include (S41) homogeneously mixing the surface of the result particles of the previous step, for example, the single particles or the graphitized particles, with pitch, which is a carbon coating material, and (S42) subsequently carbonizing it.

[0057] The above (S41) is for attaching a carbon coating material to the surface of the particles of the previous step product, and the mixing method is not particularly limited and can be performed by a method commonly known in the art. For example, it can be performed by using a mechanochemical method such as a two-roll kneader, blade, meccano micro system, extruder, ball mill, planetary mill, meccano fusion system, Novilta, hydridation, rotary ball mill, etc., or by using a spray drying method, emulsion method, etc.

[0058] The above (S42) is for forming a carbon coating layer on the surface of the previous step product particles, and may involve homogeneously mixing the carbon coating material and the previous step product particles and then carbonizing them at a temperature of 1,100 to 1,600°C, and the carbonizing treatment may be performed for 18 to 30 hours.

[0059] According to one embodiment of the present invention, the above (S42) may be performed at a temperature of 1,400 to 1,600°C for 20 to 26 hours.

[0060] The formed carbon coating layer may consist of amorphous or crystalline carbon. When the above carbonization treatment conditions are satisfied, the stabilization of the carbon coating material proceeds sufficiently, impurities within the carbon coating material are almost completely removed, the deterioration of the coated surface characteristics of the carbon coating material at excessively high temperatures can be prevented, and the swelling of the battery due to an increased negative electrode expansion rate can be suppressed.

[0061] According to one embodiment of the present invention, the pitch used in (S4) may be the same as or different from the pitch used in (S2).

[0062] According to one embodiment of the present invention, the fine powder may be used in an amount of 1 to 30 parts by weight based on 100 parts by weight of the primary particle. Specifically, the fine powder may be used in an amount of 1 part by weight or more, 3 parts by weight or more, 5 parts by weight or more, or 7 parts by weight or more based on 100 parts by weight of the primary particle. The above fine powder may be used in an amount of 30 parts by weight or less, or 25 parts by weight or less, based on 100 parts by weight of the above primary particle.

[0063] According to one embodiment of the present invention, the pitch may not be used in step (S2), or the pitch may be used in an amount greater than 0 parts by weight and less than or equal to 3 parts by weight based on 100 parts by weight of the total of the primary particles and the fine powder. Conventionally, the pitch introduced during the assembly process of secondary particles is at a level of about 15% by weight, but in the present invention, even if the pitch is introduced at half or less as described above, the waste fine powder can be sufficiently attached to the surface of the primary particles.

[0064] In one example, a pitch having a volatile content of 5 weight% or more may be used as the pitch. Since a high volatile content implies a high molecular weight, it implies a high content of beta resin (b-resin). When there is a high amount of beta resin, the adhesiveness is high, so self-adhesion is achieved even when using a small amount of pitch, which has the advantage of enabling sufficient adhesion between particles. Furthermore, beta resin is self-adhesive, making it easy to create a uniform coating layer. Here, as previously mentioned, the volatile content can be measured through thermal decomposition at high temperatures; generally, it can be calculated by heating a sample of 1 to 2 g at a high temperature of about 950°C for about 7 minutes and measuring the change in weight of the sample (the difference in weight before and after heating).

[0065] As the volatile content increases, the softening point and beta resin content tend to increase, but the levels of volatile content, softening point, and beta resin may vary depending on the type of coke. In the present invention, it is advantageous to use a coke with a high volatile content, for example, 5% by weight or more, and a high beta resin content, for example, 5% by weight or more, or 10% by weight or more. For example, when the beta resin content is 10% by weight, the growth of mesophase can be promoted with a polymer and a ring-like arrangement, and as described above, it has self-adhesive properties and has the characteristic of clumping (sticking) well even when a small amount of pitch is added.

[0066] Graphite produced according to one embodiment of the present invention has an average particle size (D50) of 15 μm or less, 14 μm or less, 13 μm or less, 12 μm or less, and 11 μm or less. That is, graphite produced according to one embodiment of the present invention is characterized by having a smaller average particle size (D50) compared to conventional graphite by using a small amount of pitch during the manufacturing process, thereby improving dispersibility.

[0067] Graphite produced according to one embodiment of the present invention is artificial graphite.

[0068] According to one embodiment of the present invention, a negative electrode active material comprising graphite produced by the above manufacturing method is provided. That is, the graphite is applicable as a negative electrode active material for a secondary battery, and the graphite is a graphite for a secondary battery.

[0069] According to one embodiment of the present invention, a cathode comprising the cathode active material is provided.

[0070] According to one embodiment of the present invention, a cathode is provided comprising: a cathode current collector; and a cathode active material layer provided on one or both sides of the cathode current collector, wherein the cathode active material layer comprises a cathode active material according to one embodiment of the present invention.

[0071] The above-mentioned cathode active material layer may further include other types of graphite in addition to the graphite as an additional cathode active material. For example, the above-mentioned cathode active material layer may include artificial graphite of one embodiment of the present invention and may further include natural graphite as an additional cathode active material.

[0072] When natural graphite is further included as the additional cathode active material, the weight ratio of artificial graphite to natural graphite according to one embodiment of the present invention may be 9.99 : 0.01 to 0.01 : 9.99, or 9.7 : 0.3 to 7:3. When satisfying this weight ratio range, superior output can be exhibited.

[0073] The above negative electrode active material layer may further include a silicon-based active material as an additional negative electrode active material in addition to the graphite for the purpose of increasing capacity, etc. For example, the above negative electrode active material layer may include Si, SiOx(0) as an additional negative electrode active material. <x≤2), Si-alloy 및 Si / C로 이루어진 군에서 선택되는 1 이상을 포함할 수 있다.

[0074] When a silicon-based active material is further included as the additional negative electrode active material, the silicon-based active material may be included in an amount of 0.1 to 30 parts by weight based on 100 parts by weight of the total negative electrode active material. For example, it may be included in an amount of 0.1 parts by weight or more, 1 part by weight or more, 5 parts by weight or more, or 6 parts by weight or more, and may be included in an amount of 30 parts by weight or less, 25 parts by weight or less, 20 parts by weight or less, 15 parts by weight or less, 10 parts by weight or less, or 9 parts by weight or less. When the silicon-based active material is included within the above range, a secondary battery having high energy density and excellent rapid charging performance can be provided.

[0075] In one embodiment of the present invention, the cathode active material layer may include a cathode conductive material and a cathode binder.

[0076] The content of the negative active material in the above negative active material layer may be 70 parts by weight or more based on 100 parts by weight of the negative active material layer. For example, it may be 70 parts by weight or more, 75 parts by weight or more, 80 parts by weight or more, 90 parts by weight or more, 98 parts by weight or more, or 99 parts by weight or more, and may be 100 parts by weight or less, less than 100 parts by weight, 99 parts by weight or less, 97 parts by weight or less, or 96 parts by weight or less.

[0077] In one embodiment of the present invention, the cathode conductive material may include one or more selected from the group consisting of point conductive materials, planar conductive materials, and linear conductive materials.

[0078] In one embodiment of the present invention, the point-shaped conductive material can be used to improve conductivity of the cathode and refers to a spherical or point-shaped conductive material that has conductivity without causing chemical changes. Specifically, the point-shaped conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, Farnes black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably may include carbon black in terms of achieving high conductivity and excellent dispersibility.

[0079] In one embodiment of the present invention, the planar conductive material may comprise at least one selected from the group consisting of plate-shaped graphite, graphene, graphene oxide, and graphite flakes, and preferably may be plate-shaped graphite.

[0080] In one embodiment of the present invention, the linear conductive material may be a carbon nanotube. The carbon nanotube may be a bundled carbon nanotube. The bundled carbon nanotube may include a plurality of carbon nanotube units. Specifically, "bundle type" refers to a secondary shape in the form of a bundle or rope, in which a plurality of carbon nanotube units are arranged in parallel or intertwined with a substantially identical orientation along the axis of the carbon nanotube unit length direction, unless otherwise noted. The carbon nanotube unit has a graphite sheet having a cylindrical shape with a nano-sized diameter and an sp2 bonding structure. Depending on the angle and structure in which the graphite sheet is rolled, it may exhibit conductive or semiconductor properties. The bundled carbon nanotubes mentioned above can be uniformly dispersed during cathode manufacturing compared to entangled type carbon nanotubes, and can smoothly form a conductive network within the cathode, thereby improving the conductivity of the cathode.

[0081] The content of the cathode conductive material in the above cathode active material layer may be 0.01 to 10 parts by weight, preferably 0.03 to 8 parts by weight, relative to 100 parts by weight of the cathode active material layer.

[0082] The cathode conductive material according to the present invention has a completely separate composition from the anode conductive material applied to the anode. That is, the cathode conductive material according to the present invention serves to hold the contact points between silicon-based active materials, which undergo significant volume expansion of the electrodes due to charging and discharging, whereas the anode conductive material serves as a buffer during rolling and provides partial conductivity; thus, their composition and roles are completely different from those of the cathode conductive material of the present invention.

[0083] In one embodiment of the present invention, the cathode binder may comprise at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, polyacrylamide (PAM), and materials in which hydrogens thereof are substituted with Li, Na, or Ca, and may also comprise various copolymers thereof.

[0084] A cathode binder according to one embodiment of the present invention serves to hold the active material and the conductive material to prevent distortion or structural deformation of the cathode structure, and any general binder that satisfies the above role can be applied.

[0085] In one embodiment of the present invention, the cathode composition is provided in which the cathode binder comprises 1 part by weight or more and 10 parts by weight or less of the cathode binder based on 100 parts by weight of the cathode active material layer.

[0086] In one embodiment of the present invention, the negative current collector has a thickness of 1 μm to 100 μm. Such a negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy may be used. In addition, fine irregularities may be formed on the surface to strengthen the bonding strength of the negative active material, and it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0087] In one embodiment of the present invention, a cathode is provided in which the thickness of the cathode current collector is 1 μm to 100 μm or less, and the thickness of the cathode active material layer is 5 μm to 500 μm.

[0088] However, the thickness of the above-mentioned cathode current collector and cathode active material layer may vary depending on the type and application of the cathode used and is not limited thereto.

[0089] One embodiment of the present invention provides a secondary battery comprising a positive electrode; a negative electrode according to one embodiment of the present invention; a separator; and a positive electrode.

[0090] A secondary battery according to one embodiment of the present specification may particularly include the negative electrode described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the negative electrode is identical to the negative electrode described above. Since the negative electrode has been described above, a detailed description thereof is omitted.

[0091] The above positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and comprising the positive electrode active material.

[0092] In the above-mentioned positive electrode, the positive current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the above-mentioned positive current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0093] The above-mentioned positive electrode active material may be a commonly used positive electrode active material. Specifically, the above-mentioned positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; or a compound with the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4 (0≤c1≤0.33), LiMnO3, LiMn2O3, LiMnO2, etc.; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7, etc.; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented by O2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, satisfying 0.01≤c2≤0.3); chemical formula LiMn 2-c3 M c3Examples include lithium manganese composite oxides represented by O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn and Ta, satisfying 0.01≤c3≤0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu and Zn); and LiMn2O4 in which a portion of the Li in the chemical formula is substituted with alkaline earth metal ions, but are not limited thereto. The anode may also be Li-metal.

[0094] The above-described positive active material layer may include a positive conductive material and a positive binder together with the positive active material described above.

[0095] At this time, the positive electrode conductive material is used to impart conductivity to the electrode, and in the battery being constructed, any material that has electronic conductivity without causing chemical changes can be used without special limitations. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used.

[0096] In addition, the anode binder serves to improve adhesion between anode active material particles and adhesion between the anode active material and the anode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0097] The above separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. Any separator commonly used in secondary batteries can be used without special limitations, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte moisture retention capacity. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure.

[0098] Examples of the above electrolytes that can be used in the manufacture of lithium secondary batteries include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., but are not limited to these.

[0099] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0100] As the above-mentioned non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyl lactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolone, formamide, dimethylformamide, dioxolone, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolone derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate, etc. may be used.

[0101] In particular, among the above carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants that effectively dissociate lithium salts, so they can be used preferably. Furthermore, if low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate are mixed with these cyclic carbonates in appropriate proportions, an electrolyte with high electrical conductivity can be produced, making it even more preferable to use.

[0102] The metal salt mentioned above may be a lithium salt, and the lithium salt is a substance that dissolves well in the non-aqueous electrolyte; for example, as the anion of the lithium salt, F - , Cl - , I - , NO3 -, N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more types selected from the group consisting of can be used.

[0103] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0104] One embodiment of the present invention provides a battery module including a secondary battery according to one embodiment of the present invention.

[0105] One embodiment of the present invention provides a battery pack including a secondary battery according to one embodiment of the present invention.

[0106] One embodiment of the present invention provides a battery pack including a battery module according to one embodiment of the present invention.

[0107] One embodiment of the present invention provides a battery module comprising the secondary battery as a unit cell and a battery pack comprising the secondary battery or the battery module. Since the battery module and the battery pack include the secondary battery having high capacity, high rate capability and cycle capability, they can be used as a power source for a medium-to-large device selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0108] Hereinafter, preferred embodiments are presented to aid in understanding the present invention; however, the above embodiments are merely illustrative of the description, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of the description, and that such variations and modifications fall within the scope of the appended claims.

[0109] <Preparation Example>

[0110] Example 1

[0111] 1) Preparation of cathode active material

[0112] The coke raw material was ground using an ACM (Air Classifier Mill), an impact mill, a shaping mill, a roll grinder, etc. As a result, it was produced in the form of primary particles (average particle size (D50): 7-9㎛) and fine powder (average particle size (D50): 3㎛ or less). At this time, the primary particles and fine powder were mixed in a weight ratio of approximately 8:2.

[0113] Subsequently, the primary particles and the fine powder were mixed with 3 parts by weight of pitch per 100 parts by weight of the total content of the primary particles and the fine powder to produce single particles. Due to the presence of the fine powder, the D50 did not increase as in the secondary particle assembly process, and the D50 of the produced single particles was at the level of the primary particles' D50; therefore, the above method is different from the assembly process for producing secondary particles and can be referred to as a method for treating the surface shape of primary particles. The average particle size (D50) of the produced single particles was at the level of 10 μm.

[0114] The above product was graphitized by heating it to a temperature of 2,800°C to 3,000°C using a graphitization furnace device and heat-treating it for 400 hours, including cooling time.

[0115] Subsequently, the graphitized product under the above conditions was mixed with pitch to form a carbon coating layer, and an artificial graphite cathode active material was manufactured by carbonizing it at a temperature of 1,500°C for 24 hours.

[0117] 2) Preparation of cathode slurry and electrode

[0118] A cathode active material layer composition was prepared by mixing the cathode active material (graphite) prepared above, and carbon black, CMC, and SBR as cathode conductive materials in a weight ratio of 95.6:1:1.1:2.3, and a cathode slurry was prepared by adding distilled water as a solvent for forming the cathode slurry. (Solid content 50%)

[0119] As a mixing method, the above conductive material and binder and water were dispersed using a homo mixer at 2500 rpm for 30 minutes, then the cathode active material was added, and the mixture was further dispersed at 2500 rpm for 30 minutes to produce a cathode slurry.

[0120] As a cathode current collector, the above cathode slurry is applied to a copper current collector at 3.6 Ah / cm 2A cathode was formed by applying a loading amount, rolling it with roll-pressing, and then vacuum drying it in a vacuum oven at 130°C for 8 hours.

[0122] 3) Manufacturing of cathode half-cell

[0123] Using the cathode prepared above as the working electrode and the counter electrode, 1.7671 cm 2 An electrode assembly was manufactured by using a lithium metal thin film cut into a circular shape and interposing a polyethylene separator between the working electrode and the counter electrode.

[0124] Ethylene carbonate (EC) and ethyl carbonate (EMC) were mixed in a volume ratio of 2:8, and a non-aqueous electrolyte was prepared by adding 0.5 wt% of vinylene carbonate (VC) and 1 M of LiPF6 as non-aqueous electrolyte additives to the mixed solvent.

[0125] A coin-type half-cell lithium secondary battery was manufactured by embedding the above electrode assembly in a coin-type case and injecting the prepared non-aqueous electrolyte.

[0127] Example 2

[0128] The procedure was carried out in the same manner as Example 1, except that the amount of pitch mixed with the primary particles and the fine powder was 1 part by weight per 100 parts by weight of the total content of the primary particles and the fine powder.

[0130] Example 3

[0131] The procedure was carried out in the same manner as Example 1, except that pitch was not used when mixing the primary particles and the fine powder.

[0133] Reference Example 1

[0134] A secondary battery was manufactured in the same manner as Example 1, except that the negative electrode active material in 1) above was manufactured in the following manner.

[0135] 1) Preparation of cathode active material

[0136] The coke raw material was ground using an ACM (Air Classifier Mill), impact mill, shaping mill, roll grinder, etc., as in Example 1. The fine powder generated at this time (average particle size (D50): 3㎛ or less) was removed.

[0137] Primary particles (average particle size (D50): 7-9㎛) from which fine particles have been removed using a horizontal and vertical assembly device were heated to a temperature of 2,800℃ to 3,000℃ using a graphitization furnace device and graphitized by heat treatment for 400 hours including cooling time.

[0138] Subsequently, the graphitized product under the above conditions was mixed with pitch to form a carbon coating layer, and an artificial graphite cathode active material was manufactured by carbonizing it at a temperature of 1,500°C for 24 hours.

[0140] Reference Example 2

[0141] A secondary battery was manufactured in the same manner as Example 1, except that the negative electrode active material in 1) above was manufactured in the following manner.

[0142] 1) Preparation of cathode active material

[0143] The coke raw material was ground using an ACM (Air Classifier Mill), impact mill, shaping mill, roll grinder, etc., as in Example 1. The fine powder generated at this time (average particle size (D50): 3㎛ or less) was removed.

[0144] Primary particles from which fine particles have been removed (average particle size (D50): 7-9㎛) and pitch (15 parts by weight based on 100 parts by weight of the primary particles) were mixed using a horizontal and vertical assembly device, and secondary particles were formed by assembly at a high temperature (500℃ to 700℃).

[0145] The assembled secondary particles were graphitized by heating them to a temperature of 2,800°C to 3,000°C using a graphitization furnace device and heat-treating them for 400 hours, including cooling time.

[0146] Subsequently, the graphitized product under the above conditions was mixed with pitch to form a carbon coating layer, and an artificial graphite cathode active material was manufactured by carbonizing it at a temperature of 1,500°C for 24 hours.

[0148] <Experimental Example>

[0149] Experimental Example 1: Evaluation of Initial Capacity and Initial Efficiency

[0150] The coin half-cell capacity / efficiency of the cathodes prepared in the above examples and reference examples was evaluated and is shown in Table 1. Specifically, the capacity / efficiency of the first cycle of the secondary battery was measured using an electrochemical charge / discharger. The test was conducted using lithium metal as the counter electrode of the cathode, and

[0151] Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off)

[0152] Discharge condition: CC (constant current) condition 1.5V

[0153] Discharge capacity (mAh / g) = {(3rd cycle discharge capacity (mAh)) / (Cathode active material weight (g))}

[0154] Initial efficiency (%) = {(Discharge capacity in 1st cycle) / (Charge capacity in 1st cycle)} * 100%

[0156] Experimental Example 2: Li plating evaluation

[0157] For the secondary batteries prepared in the above examples and reference examples, the Li plating timing was evaluated and is shown in Table 1. The first and second cycles were charged and discharged at 0.1C, and from the third cycle onwards, the cell resistance was measured while charging and discharging at a rate of 3C.

[0158] Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off)

[0159] Discharge condition: CC (constant current) condition 1.5V

[0160] The point at which the cell's resistance drops sharply and a rapid change in the current value occurs was calculated as the point at which lithium plating (Li Plating) occurs.

[0161] Pitch content mixed before graphitization Average particle size (D50) (㎛) Discharge capacity (mAh / g) Initial efficiency (%) Li Plating Time (SOC %) Example 1 3 10.2 349.0 92.7 40 Example 2 1 10.1 348.7 92.8 39 Example 3 0 10.0 348.5 92.8 39 Reference Example 1 0 10.0 348.5 92.5 34 Reference Example 2 15 16.0 349.3 92.3 37

[0162] According to Table 1, although Examples 1 to 3 simplified process conditions and reduced the amount of pitch used compared to Reference Examples 1 and 2, they achieved discharge capacity and initial efficiency equivalent to Reference Examples 1 and 2. Furthermore, since the Li plating timing was delayed under the same 3C conditions and appeared at a higher SOC %, it can be seen that the SOC % at which Li precipitation occurs is higher when evaluated at the same output, and thus it can be confirmed that this is advantageous for rapid charging performance.

[0164] Experimental Example 3: SEM Analysis

[0165] To confirm the difference between the single particles of Example 1 and the secondary particles of Reference Example 2, the morphology of the ground primary particles, the single particles of Example 1, and the secondary particles of Reference Example 2 was observed using a scanning electron microscope (SEM). The results are shown in Figures 1 and 2.

[0166] Figure 1 compares the pulverized primary particles of Example 1 (top) and the single particles of Example 1 (bottom), and Figure 2 compares the pulverized primary particles of Reference Example 2 (top) and the secondary particles of Reference Example 2 (bottom).

[0167] Through this, it can be confirmed that the single particle of Example 1 in Fig. 1 does not change in size significantly, and the secondary particle of Reference Example 2 in Fig. 2 shows a large change in size.

[0169] Experimental Example 4: Change in Particle Size

[0170] Based on the crushed primary particles, the change in particle size before and after assembly for the single particles of Example 1 and the secondary particles of Reference Example 2 was confirmed.

[0171] As a result, graphs are shown in Figures 3 and 4, and based on Figure 3, D10, D50, D90, and Span are indicated in Table 2 below, and based on Figure 4, D10, D50, D90, and Span are indicated in Table 3.

[0172] Particle size (μm) Primary particles Single particle of Example 1 rate of change D10 5.6 5 -10% D50 10 10.2 2% D90 30 32 6% Span(D90-D10) / D50 2.44 2.65 -

[0173] Particle size (μm) Primary particles Secondary particles of Reference Example 2 rate of change D10 5.5 9.8 78% D50 11.0 16.0 45% D90 23.9 27.5 15% Span(D90-D10) / D50 1.67 1.09 -

[0174] Through this, it can be confirmed that the single particle of Example 1 is a different particle from the secondary particle of Reference Example 2, and is manufactured as a particle with little change in size from the primary particle.

[0175] Although the present invention has been described with reference to embodiments thereof, those skilled in the art will be able to make various applications and modifications within the scope of the present invention based on the above description.

Claims

Claim 1 (S1) a step of grinding a carbon-based raw material to produce primary particles and fine powder; (S2) a step of mixing the primary particles and the fine powder to produce single particles; and (S3) a step of graphitizing the single particles, wherein the average particle size (D50) of the fine powder is 3 μm or less, and in (S1), the carbon-based raw material is petroleum coke, or in (S2), pitch is mixed together in an amount greater than 0 parts by weight and less than or equal to 3 parts by weight based on 100 parts by weight of the total content of the primary particles and the fine powder. Claim 2 A method for manufacturing graphite according to claim 1, further comprising the step of (S4) providing a carbon coating layer on the single particle; wherein (S4) is performed after (S2) and before (S3) or after (S3). Claim 3 A method for manufacturing graphite according to claim 1, wherein the fine powder is included in an amount of 1 to 30 parts by weight based on 100 parts by weight of the primary particle. Claim 4 A method for manufacturing graphite according to claim 1, wherein the average particle size (D50) of the primary particles is 7 μm or more and 15 μm or less. Claim 5 A method for manufacturing graphite according to claim 1, wherein the average particle size (D50) of the graphite is 15 μm or less. Claim 6 A method for manufacturing graphite according to claim 1, wherein the carbon-based raw material is petroleum-based coke having a volatile content of 5% or more. Claim 7 A method for manufacturing graphite according to claim 1, wherein the graphite is artificial graphite. Claim 8 A negative electrode active material comprising graphite produced by the manufacturing method of any one of claims 1 to 7. Claim 9 A cathode comprising a cathode active material according to claim 8. Claim 10 A secondary battery comprising a negative electrode according to claim 9; a separator; and a positive electrode. Claim 11 A battery module comprising a secondary battery according to claim 10. Claim 12 A battery pack comprising a secondary battery according to claim 10. Claim 13 A battery pack comprising a battery module according to claim 11.

Images