Method for producing negative electrode active material, negative electrode, and secondary battery
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- LG ENERGY SOLUTION LTD
- Filing Date
- 2022-09-06
- Publication Date
- 2026-07-10
Smart Images
Figure GDA0004657368750000241
Abstract
Description
Technical Field
[0001] Cross-reference to related applications
[0002] This application claims the benefit of Korean Patent Application No. 10-2021-0121303, filed with the Korean Intellectual Property Office on September 10, 2021, the disclosure of which is incorporated herein by reference in its entirety. Technical Field
[0004] This invention relates to a method for preparing a negative electrode active material, a negative electrode, and a secondary battery. Background Technology
[0005] As fossil fuel depletion leads to rising energy prices and growing concerns about environmental pollution, environmentally friendly alternative energy sources have become a top priority for future living.
[0006] In particular, with the continuous development of mobile device technology and the increasing demand for mobile devices, the demand for secondary batteries as an environmentally friendly alternative energy source has increased dramatically.
[0007] Furthermore, in recent years, increasing concern about environmental issues has spurred extensive research into electric vehicles (EVs) and hybrid electric vehicles (HEVs), which can replace fossil fuel-powered vehicles such as gasoline and diesel vehicles, a major contributor to air pollution. Lithium-ion batteries, with their high energy density, high discharge voltage, and high output stability, have been the primary focus of research and application as the power source for these EVs and HEVs.
[0008] In the aforementioned secondary batteries, lithium metal is typically used as the negative electrode, but due to the short circuit caused by dendrite formation and the resulting explosion risk, carbon-based active materials for reversibly inserting and de-intercalating lithium ions while maintaining structural and electrical properties have emerged as alternatives.
[0009] Various types of carbon-based active materials, such as artificial graphite, natural graphite, and hard carbon, have been used as carbon-based active materials. Among these, graphite-based active materials, which ensure the lifespan characteristics of lithium-ion batteries due to their excellent reversibility, have been the most widely used. Because graphite-based active materials have a low discharge voltage of -0.2V relative to lithium, batteries using these materials can exhibit a high discharge voltage of 3.6V. Therefore, graphite-based active materials offer many advantages in terms of energy density for lithium-ion batteries.
[0010] In particular, compared with natural graphite, synthetic graphite offers advantages such as superior anti-swelling properties and excellent high-temperature properties. However, synthetic graphite has fewer pores than natural graphite, and therefore exhibits lower output characteristics. In response, to improve output characteristics and form pores within the particles, it is known to use synthetic graphite in the form of secondary particles, in which primary particles are aggregated or bonded.
[0011] However, depending on the shape and assembly of the primary particles, artificial graphite assembled in the form of secondary particles is highly likely to have an irregular and uneven shape. When such artificial graphite is used as a negative electrode, it results in poor electrode adhesion, leading to deterioration in processability, and the active material detaches during the driving of the negative electrode, causing long-term cycling performance degradation.
[0012] Japanese Patent No. 4403327 discloses graphite powder for use as the negative electrode in lithium-ion secondary batteries, but does not provide an alternative to the above task.
[0013] [Related Technical Documents]
[0014] [Patent Literature]
[0015] Japanese Patent No. 4403327 Summary of the Invention
[0016] Technical issues
[0017] One aspect of the present invention (in a method for manufacturing an anode active material comprising artificial graphite in the form of secondary particles) provides a method for preparing an anode active material having excellent adhesion and improved fast charging performance.
[0018] Furthermore, another aspect of the present invention provides a negative electrode comprising a negative electrode active material prepared by the above-described method for preparing negative electrode active materials.
[0019] Furthermore, another aspect of the present invention provides a secondary battery comprising the aforementioned negative electrode.
[0020] Technical solution
[0021] According to one aspect of the present invention, a method for preparing a negative electrode active material is provided, the method comprising: mixing raw coke particles, calcined coke particles and a binder to obtain a mixture; and graphitizing the mixture by heat treatment to form artificial graphite particles in the form of secondary particles wherein primary artificial graphite particles are bonded together, wherein the average particle size (D) of the raw coke particles is... 50 The average particle size (D) of the calcined coke particles is greater than that of the average particle size of the calcined 50 (It is larger.)
[0022] Furthermore, according to another aspect of the present invention, a negative electrode is provided, the negative electrode comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material prepared by the above-described method for preparing negative electrode active material.
[0023] Furthermore, according to another aspect of the present invention, a secondary battery is provided, comprising the aforementioned negative electrode; a positive electrode facing the negative electrode; a separator disposed between the negative electrode and the positive electrode; and an electrolyte.
[0024] Beneficial effects
[0025] The method for preparing the negative electrode active material of the present invention is characterized in that, in preparing the negative electrode active material containing artificial graphite in the form of secondary particles, raw coke particles and calcined coke particles are used as raw materials for primary particles, wherein the average particle size (D) of the raw coke particles is... 50 The average particle size (D) of the calcined coke particles is greater than that of the average particle size of the calcined 50 (The negative electrode containing the negative electrode active material prepared by the method of the present invention can have improved adhesion and fast charging performance.) Detailed Implementation
[0026] It should be understood that the words or terms used in the specification and claims should not be interpreted as having the meanings defined in common dictionaries, and it should also be understood that, based on the principle that the inventors may appropriately define the meanings of the words or terms to best interpret the invention, the words or terms should be interpreted as having meanings consistent with their meanings in the context of the related technology and the technical concept of the invention.
[0027] The terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to limit the invention. Unless the context clearly indicates otherwise, the singular form is intended to include the plural form as well.
[0028] It should also be understood that, when used in this specification, the terms “comprising,” “including,” or “having” specify the presence of the said features, quantities, steps, elements, or combinations thereof, but do not exclude the presence or addition of one or more other features, quantities, steps, elements, or combinations thereof.
[0029] As used in this article, the term "average particle size (D)" 50 The average particle size (D) can be defined as the particle size at which the cumulative volume in the particle size distribution curve is 50%. 50 For example, this can be measured using laser diffraction. Laser diffraction can typically measure particle sizes ranging from submicron to millimeters and can yield highly repeatable and high-resolution results.
[0030] The present invention will be described in detail below.
[0031] Preparation method of negative electrode active material
[0032] This invention relates to a method for preparing a negative electrode active material, and more particularly, to a method for preparing a negative electrode active material for lithium secondary batteries.
[0033] Specifically, the method for preparing the negative electrode active material is characterized by comprising: mixing raw coke particles, calcined coke particles, and a binder to obtain a mixture; and graphitizing the mixture by heat treatment to form artificial graphite particles in the form of secondary particles in which primary artificial graphite particles are bonded together, wherein the average particle size (D) of the raw coke particles is... 50 The average particle size (D) of the calcined coke particles is greater than that of the average particle size of the calcined 50 (It is larger.)
[0034] In existing technologies, depending on the shape and assembly of the primary particles, artificial graphite in the form of secondary particles is highly likely to have an irregular and uneven shape. When such artificial graphite is used as a negative electrode, poor electrode adhesion leads to deteriorated processability, and the active material detaches during negative electrode driving, resulting in deterioration of long-term cycling characteristics. Furthermore, the larger the primary particles, the better the adhesion of artificial graphite in the form of secondary particles, but tends to have lower fast-charging performance. Conversely, the smaller the primary particles, the better the fast-charging performance of artificial graphite in the form of secondary particles, but tends to have lower adhesion.
[0035] To overcome these limitations, the present invention is characterized by: mixing raw coke particles, calcined coke particles, and a binder to obtain a mixture; and graphitizing the mixture by heat treatment to form artificial graphite particles in the form of secondary particles in which primary artificial graphite particles are bonded together, wherein the average particle size (D) of the raw coke particles is... 50 The average particle size (D) of the calcined coke particles is greater than that of the average particle size of the calcined 50 The raw coke particles are larger. They are round and have a smooth surface, and have a larger average particle size (D) than the calcined coke particles. 50 This helps improve the overall adhesion of the negative electrode active material. On the other hand, the calcined coke particles have a smaller average particle size (D0) than the raw coke particles. 50 This method helps improve fast-charging performance and exhibits excellent capacity retention. Consequently, the negative electrode active material prepared by the method of this invention possesses improved fast-charging performance and adhesion.
[0036] The method for preparing the negative electrode active material of the present invention includes mixing raw coke particles, calcined coke particles, and a binder. In this case, the average particle size (D) of the raw coke particles is... 50 The average particle size (D) of the calcined coke particles is greater than that of the average particle size of the calcined 50 (It is larger.)
[0037] The raw coke particles and the calcined coke particles can each be processed through a graphitization process to form primary artificial graphite particles. Furthermore, the primary artificial graphite particles from the raw coke particles and the calcined coke particles can be combined to form secondary artificial graphite particles.
[0038] The raw coke particles can be obtained by coking coal or petroleum residues or bitumen as a processed product under high pressure and high temperature. In this case, the raw coke particles are coke particles obtained immediately after the coking process and do not undergo heat treatment such as calcination or carbonization, and therefore may contain volatile substances (e.g., sulfur).
[0039] The raw coke particles can have a smoother and more even surface than the calcined coke particles, which will be described later. Therefore, when forming secondary particles, the raw coke particles can help smooth the entire surface of the particles and improve the uniformity of their shape, thereby contributing to improved adhesion of the negative electrode active material. In particular, in this invention, the raw coke particles have a larger average particle size than the calcined coke particles, thus the negative electrode active material prepared thereby can have further improved adhesion.
[0040] The raw coke particles may have an average particle size (D) of 9 μm to 15 μm, specifically 10 μm to 13 μm. 50 When the average particle size of the raw coke particles is within the above range, the degradation of fast charging performance due to excessively large raw coke particles can be prevented, and the adhesion of the negative electrode active material can be improved to the maximum extent.
[0041] The raw coke particles may have a true density of 1.20 g / cc to 1.60 g / cc, specifically 1.3 g / cc to 1.5 g / cc. As used herein, the true density may refer to the density of the particles alone, excluding the gaps between the particles being measured. The true density can be measured using a gas specific gravity bottle.
[0042] Furthermore, the raw coke particles may contain 1000 ppm to 5000 ppm, specifically 1500 ppm to 3000 ppm of sulfur (S). The amount of sulfur can be measured by inductively coupled plasma (ICP) analysis.
[0043] The calcined coke particles can refer to coke that has been calcined after undergoing a coking reaction of coal or petroleum residues or asphalt as a processed product under high pressure and high temperature. Due to the calcination process, the calcined coke particles may be free of volatile substances or contain trace amounts of volatile substances.
[0044] The calcined coke particles are generally flatter and sharper in shape than the raw coke particles, but have excellent capacity retention properties. Furthermore, in this invention, due to the average particle size (D) of the calcined coke particles... 50 The particle size was adjusted to be larger than the average particle size (D) of the raw coke particles. 50 The smaller size allows for the production of negative electrode active materials with excellent capacity retention and fast charging performance without compromising adhesion.
[0045] The calcined coke particles may have an average particle size of 3 μm to 8 μm, specifically 6 μm to 7 μm (D). 50 When the average particle size of the calcined coke particles is within the above-mentioned range, it can prevent the degradation of adhesion caused by excessively large calcined coke particles, and can also improve the fast charging performance of the negative electrode active material.
[0046] The calcined coke particles may have a true density of 1.80 g / cc to 2.25 g / cc, specifically 1.9 g / cc to 2.2 g / cc.
[0047] In addition, the calcined coke particles may contain sulfur (S) in amounts of 50 ppm to 1000 ppm, specifically 80 ppm to 200 ppm.
[0048] In this invention, the average particle size (D) of the raw coke particles 50 The average particle size (D) of the calcined coke particles is greater than that of the average particle size of the calcined 50 The raw coke particles have a smooth and gentle surface and a larger average particle size (D) than the calcined coke particles. 50 This helps improve the overall adhesion of the negative electrode active material. On the other hand, the calcined coke particles have a smaller average particle size (D0) than the raw coke particles. 50 This method helps improve fast-charging performance and exhibits excellent capacity retention. Consequently, the negative electrode active material prepared by the method of this invention possesses improved fast-charging performance and adhesion.
[0049] When the average particle size of the raw coke particles (D) 50 The average particle size (D) of the calcined coke particles is equal to that of the calcined coke particles. 50 (), or smaller than the average particle size (D) of the calcined coke particles. 50When the calcined coke particles are used, the improved adhesion due to the raw coke particles may not be improved, and the fast charging performance may not be improved because the calcined coke particles have a larger particle size than the raw coke particles.
[0050] Specifically, the average particle size (D) of the calcined coke particles 50 The average particle size (D) of the raw coke particles 50 The ratio can be greater than 0.3 and less than 1, specifically 0.5 to 0.8. When the ratio is within the above range, the above fast charging performance and adhesion can be improved to the maximum extent.
[0051] The raw coke particles and the calcined coke particles can be mixed in a weight ratio of 10:90 to 90:10, specifically in a weight ratio of 25:75 to 75:25. When the weight ratio is within the above range, the improved adhesion of the negative electrode active material brought about by the raw coke particles can be maximized, and the fast charging performance can be improved, which is therefore desirable.
[0052] The raw coke particles and the calcined coke particles can each be mixed as two or more particles.
[0053] The adhesive can be used to bind or tether the raw coke particles and the calcined coke particles together. By binding the raw coke particles and the calcined coke particles together with the adhesive, and then subjecting them to heat treatment and graphitization, the raw coke particles and the calcined coke particles can be prepared into artificial graphite primary particles, and artificial graphite particles in the form of secondary particles in which the artificial graphite primary particles are bonded together can also be prepared.
[0054] The adhesive may contain at least one selected from polymer resins and asphalt. Specifically, the polymer resin may contain at least one selected from the group consisting of sucrose, phenolic resin, naphthalene resin, polyvinyl alcohol resin, furfuryl alcohol resin, polyacrylonitrile resin, polyamide resin, furan resin, cellulose resin, styrene resin, polyimide resin, epoxy resin, vinyl chloride resin, and polyvinyl chloride. The asphalt may contain at least one selected from the group consisting of coal-based asphalt, petroleum-based asphalt, and mesophase asphalt.
[0055] The binder may be mixed in an amount of 1% to 10% by weight, specifically 4% to 8% by weight, relative to the total weight of the raw coke particles, the calcined coke particles, and the binder. The raw coke particles contain volatile substances and have a low true density; therefore, a binder may not be necessary when using the raw coke particles alone to prepare artificial graphite in the form of secondary particles. However, the calcined coke particles are coke particles from which volatile substances have been removed and have a high true density; therefore, a binder may be essential when using the calcined coke particles alone to prepare artificial graphite in the form of secondary particles. In this invention, when the binder is added to the mixture of the raw coke particles and the calcined coke particles in the amounts within the above range, the individual coke particles are tightly assembled, thereby further improving fast-charging performance and adhesion.
[0056] The present invention includes graphitizing the mixture by heat treatment to form artificial graphite particles in the form of secondary particles in which primary artificial graphite particles are bonded together.
[0057] The artificial graphite particles in the form of secondary particles can be graphitized by heat treatment of a mixture of the raw coke particles, the calcined coke particles, and the binder. Specifically, the mixture of the raw coke particles, the calcined coke particles, and the binder can be placed in a reactor, and the reactor can be operated to bind the mixture together by centrifugal force to form secondary particles in which the primary particles are bonded together, and the secondary particles can be graphitized by heat treatment.
[0058] The heat treatment can be carried out at 2500°C to 3500°C, preferably 2700°C to 3200°C, within which the raw coke particles and the calcined coke particles can be well graphitized.
[0059] The heat treatment can be carried out for 40 to 60 hours, within which the raw coke particles and the calcined coke particles can be fully graphitized by heat treatment within the above temperature range.
[0060] The present invention may also include forming an amorphous carbon coating on the artificial graphite particles in the form of secondary particles.
[0061] The amorphous carbon coating can help improve the structural stability of the artificial graphite particles in the form of secondary particles and prevent side reactions between the negative electrode active material and the electrolyte.
[0062] The amorphous carbon coating can be formed in an amount of 0.1% to 10% by weight, preferably 1% to 5% by weight, relative to the total amount of the negative electrode active material. The presence of the amorphous carbon coating can improve the structural stability of the negative electrode active material; however, since there is concern that excessive formation of the amorphous carbon coating could lead to a decrease in initial efficiency due to increased specific surface area during negative electrode calendering and a deterioration in high-temperature storage performance, it is desirable to form the carbon coating within the above-mentioned content range.
[0063] The amorphous carbon coating can be formed by providing a carbon coating precursor to artificial graphite particles in the form of secondary particles, followed by heat treatment.
[0064] The carbon coating precursor may comprise at least one selected from polymer resins and bitumen. Specifically, the polymer resin may comprise at least one selected from the group consisting of sucrose, phenolic resin, naphthalene resin, polyvinyl alcohol resin, furfuryl alcohol resin, polyacrylonitrile resin, polyamide resin, furan resin, cellulose resin, styrene resin, polyimide resin, epoxy resin, vinyl chloride resin, and polyvinyl chloride. The bitumen may comprise at least one selected from the group consisting of coal-based bitumen, petroleum-based bitumen, and mesophase bitumen.
[0065] In order to promote the uniform formation of the amorphous carbon coating, a heat treatment process for forming the amorphous carbon coating can be performed at 1000°C to 1500°C.
[0066] According to the present invention, a negative electrode active material can be formed comprising artificial graphite particles in the form of secondary particles in which primary artificial graphite particles are bonded together. In this case, the primary artificial graphite particles are obtained by graphitizing the raw coke particles and the calcined coke particles. The artificial graphite in the form of secondary particles can be formed by bonding and assembling the primary artificial graphite particles.
[0067] negative electrode
[0068] Furthermore, the present invention provides a negative electrode comprising a negative electrode active material prepared by the above-described method for preparing negative electrode active materials, and more particularly, provides a negative electrode for lithium secondary batteries.
[0069] The negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer contains a negative electrode active material prepared by the above-described method for preparing negative electrode active material.
[0070] The negative electrode current collector commonly used in the art can be used without limitation as the negative electrode current collector. For example, the negative electrode current collector is not particularly limited, as long as it has high conductivity and will not cause chemical changes in the lithium secondary battery. For example, the negative electrode current collector may contain at least one selected from copper, stainless steel, aluminum, nickel, titanium, sintered carbon, and aluminum-cadmium alloys, preferably copper.
[0071] The negative electrode current collector may have fine irregularities on its surface to improve the bonding strength of the negative electrode active material, and the negative electrode current collector may be used in various forms, such as membrane, sheet, foil, mesh, porous body, foam and non-woven fabric.
[0072] The negative electrode current collector can typically have a thickness of 3μm to 500μm.
[0073] The negative electrode active material layer is stacked on the negative electrode current collector and comprises the negative electrode active material prepared by the method described above.
[0074] The negative electrode active material may have an average particle size (D) of 10 μm to 30 μm, specifically 14 μm to 25 μm, more specifically 15 μm to 20 μm. 50 In particular, when the average particle size of the negative electrode active material prepared by the method of the present invention is within the above-mentioned range, the effects of improving adhesion by the raw coke particles and improving fast charging performance by the calcined coke particles having a smaller average particle size than the raw coke particles can be further improved.
[0075] The negative electrode active material can have a tap density of 1.08 g / cc to 1.17 g / cc, specifically 1.10 g / cc to 1.16 g / cc. When the above tap density range is met, a negative electrode active material with a smooth and uniform surface can be obtained, and high electrode adhesion can be achieved, which is desirable.
[0076] The negative electrode active material may be included in the negative electrode active material layer in an amount of 80% to 99% by weight, preferably 93% to 98% by weight.
[0077] In addition to the aforementioned negative electrode active material, the negative electrode active material layer may also include a negative electrode binder, a negative electrode conductive material, and / or a thickener.
[0078] The negative electrode binder is a component that facilitates bonding between the active material and / or the current collector, and is typically included in the negative electrode active material layer in an amount of 1% to 30% by weight, preferably 1% to 10% by weight.
[0079] The negative electrode adhesive may contain at least one selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, preferably at least one selected from polyvinylidene fluoride and styrene-butadiene rubber.
[0080] As the thickener, any thickener used in typical lithium secondary batteries can be used, an example being carboxymethyl cellulose (CMC).
[0081] The negative electrode conductive material is a component used to further improve the conductivity of the negative electrode active material, and can be included in the negative electrode active material layer in an amount of 1% to 30% by weight, preferably 1% to 10% by weight.
[0082] The negative electrode conductive material is not particularly limited in its use, as long as it is conductive and will not cause chemical changes in the battery. For example, conductive materials such as: graphite, including natural and artificial graphite; carbon black, including acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking black; conductive fibers, such as carbon fibers and metal fibers; fluorocarbons; metal powders, such as aluminum and nickel powders; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxides; or polyphenylene derivatives, etc. Specific examples of commercially available conductive materials may include acetylene black series such as products manufactured by Chevron Chemicals or Denka black manufactured by Denka Singapore Pte Ltd, products manufactured by Gulf Oil, Ketjen black, the EC series manufactured by Armak, Vulcan XC-72 manufactured by Cabot Corporation, and Super P manufactured by Timcal Corporation.
[0083] The above-mentioned negative electrode active material and at least one selected from the negative electrode binder, the negative electrode conductive material and the thickener can be mixed in a solvent to prepare a negative electrode slurry. The negative electrode slurry can be applied to the negative electrode current collector and calendered and dried to prepare the negative electrode active material layer.
[0084] The solvent may comprise water or an organic solvent such as N-methyl-2-pyrrolidone (NMP), and may be used in an amount such that a desired viscosity is obtained when the negative electrode active material, optionally the negative electrode binder, and the negative electrode conductive material are included. For example, the solvent content may be such that the concentration of the solid component comprising the negative electrode active material and optionally at least one selected from the negative electrode binder, the thickener, and the negative electrode conductive material is in the range of 50% to 95% by weight, preferably 70% to 90% by weight.
[0085] The negative electrode can have an orientation index I(004) / I(110) of 8.5 or less, specifically 4.0 to 8.5. When the area ratio I(004) / I(110) is within the above range, the active material particles can be arranged to minimize the diffusion path of lithium ions, thereby improving fast charging performance. The orientation index can be achieved by using the negative electrode active material prepared by the above-described method for preparing negative electrode active material as the negative electrode.
[0086] The orientation index represents the degree to which the crystal structure inside the negative electrode is aligned in a specific direction, indicating the orientation direction of the crystal in the electrode, and can be measured by X-ray diffraction (XRD). More specifically, the orientation index is the area ratio ((004) / (110)) obtained by integrating the peak intensities of the surfaces (110) and (004) of the negative electrode active material contained in the negative electrode after XRD measurement. More specifically, the XRD measurement conditions are as follows.
[0087] Target: Cu (Kα ray) graphite monochromator
[0088] Slits: Diverging slit = 1 degree, Receiving slit = 0.1 mm, Scattering slit = 1 degree
[0089] Measurement area and step angle / measurement time:
[0090] Face (110): 76.5 degrees < 2θ < 78.5 degrees, 0.01 degrees / 3 seconds
[0091] Face (004): 53.5 degrees < 2θ < 56.0 degrees, 0.01 degrees / 3 seconds
[0092] In the above text, 2θ represents the diffraction angle.
[0093] XRD measurement is one example; other measurement methods can also be used.
[0094] Secondary batteries
[0095] Furthermore, the present invention provides a secondary battery comprising the above-mentioned negative electrode, and more particularly, a lithium secondary battery.
[0096] The secondary battery may include the above-described negative electrode, a positive electrode facing the negative electrode, a separator disposed between the negative electrode and the positive electrode, and an electrolyte.
[0097] The positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector.
[0098] As the positive electrode current collector, a positive electrode current collector commonly used in the art may be used without limitation. For example, the positive electrode current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes in the secondary battery. For example, the positive electrode current collector may include at least one selected from copper, stainless steel, aluminum, nickel, titanium, fired carbon, and an aluminum-cadmium alloy, and preferably includes aluminum.
[0099] The positive electrode current collector may have fine irregularities on its surface to improve the bonding strength of the positive electrode active material, and the positive electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous body, foam body, and non-woven fabric body.
[0100] The positive electrode current collector generally may have a thickness of 3 μm to 500 μm.
[0101] The positive electrode active material layer may include a positive electrode active material.
[0102] The positive electrode active material is a compound capable of reversibly inserting and extracting lithium, and the positive electrode active material may specifically include a lithium composite metal oxide, which includes lithium and at least one metal, such as cobalt, manganese, nickel, or aluminum. More specifically, the lithium composite metal oxide may include lithium-manganese-based oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium-cobalt-based oxides (e.g., LiCoO2, etc.), lithium-nickel-based oxides (e.g., LiNiO2, etc.), lithium-nickel-manganese-based oxides (e.g., LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-z Ni z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt-based oxides (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), lithium-manganese-cobalt-based oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-z1 Co z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt-based oxides (e.g., Li(Ni p Co q Mn r1)O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, and p + q + r1 = 1) or Li(Ni p1 O q1 Mn r2 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, and p1 + q1 + r2 = 2), etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r3 M S2 )O2 (where M is selected from the group consisting of aluminum (Al), iron (Fe), vanadium (V), chromium (Cr), titanium (Ti), tantalum (Ta), magnesium (Mg), and molybdenum (Mo), and p2, q2, r3, and s2 are the atomic fractions of the respective independent elements, where 0 < p2 < 1, 0 < q2 < 1, 0 < r3 < 1, 0 < s2 < 1, and p2 + q2 + r3 + s2 = 1), etc.), and may include any one or a mixture of two or more thereof. Among these materials, in terms of improving the capacity characteristics and stability of the battery, the lithium composite metal oxide may include 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), or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.), and, considering the significant improvement due to the control of the type and content ratio of the elements constituting the lithium composite metal oxide, the lithium composite metal oxide may include 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, and any one or a mixture of two or more thereof may be used.
[0103] The positive electrode active material may be included in the positive electrode active material layer in an amount of 80% to 99% by weight.
[0104] The positive electrode active material layer may further include at least one selected from positive electrode binder and positive electrode conductive material, in addition to the positive electrode active material.
[0105] The positive electrode binder is a component that facilitates the bonding between the active and conductive materials and with the current collector, and is typically added in an amount of 1% to 30% by weight relative to the total weight of the positive electrode material mixture. Examples of the positive electrode binder may be at least one selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber.
[0106] The positive electrode binder may be included in the positive electrode active material layer in an amount of 1% to 30% by weight.
[0107] The conductive material can be used without particular restriction, as long as it is conductive and will not cause chemical changes in the battery. For example, conductive materials such as: graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermally cracked black; conductive fibers such as carbon fibers or metal fibers; fluorocarbons; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or polyphenylene derivatives. Specific examples of commercially available conductive materials may include acetylene black series such as products manufactured by Chevron Chemicals or Danka Black manufactured by Danka Singapore Pte Ltd, products manufactured by Gulf Oil, Ketjen black, the EC series manufactured by Armak, Vulcan XC-72 manufactured by Cabot Corporation, and Super P manufactured by Timcal Corporation.
[0108] The positive electrode conductive material can be added to the positive electrode active material layer in an amount of 1% to 30% by weight.
[0109] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator can be used without particular limitation, as long as it is typically used in secondary batteries. Specifically, separators with high electrolyte retention capacity and low resistance to electrolyte ion transfer can be used. More specifically, porous polymer membranes can be used, for example, porous polymer membranes made from polyolefin polymers (such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers), or laminates of two or more layers thereof. Furthermore, typical porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Additionally, coated separators containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and can be selectively used in single-layer or multi-layer structures.
[0110] Furthermore, the electrolyte used in this invention can be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc., all of which can be used to manufacture lithium secondary batteries, but are not limited thereto.
[0111] Specifically, the electrolyte may contain an organic solvent and a lithium salt.
[0112] As the organic solvent, any organic solvent can be used without particular limitation, as long as it can serve as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, as the organic solvent, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone can be used; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic solvents such as benzene and fluorobenzene; or carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN (where R is a linear, branched, or cyclic C2-C20 hydrocarbon group and may contain a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolane such as 1,3-dioxolane; or sulfolane. Among these solvents, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constants with linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) with low viscosity are more preferred as they can improve the charge / discharge performance of the battery. In this case, the electrolyte performance can be excellent when cyclic carbonates and linear carbonates are mixed in a volume ratio of about 1:1 to about 1:9.
[0113] The lithium salt can be used without particular restriction, as long as it is a compound capable of providing lithium ions for use in lithium secondary batteries. Specifically, as the lithium salt, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2 can be used. The lithium salt can preferably be used in a concentration range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has suitable conductivity and viscosity, thus exhibiting excellent performance, and lithium ions can move efficiently.
[0114] As described above, since the lithium secondary battery according to the present invention stably exhibits excellent discharge capacity, fast charging characteristics, and capacity retention, it is suitable for portable devices such as mobile phones, laptops, and digital cameras; and electric vehicles such as hybrid electric vehicles (HEVs). In particular, it can be preferably used as a constituent battery in medium-to-large-sized battery modules. Therefore, the present invention also provides medium-to-large-sized battery modules comprising the above-described secondary battery as a unit cell.
[0115] The medium-to-large battery modules are preferably used in power sources that require high output and large capacity, such as electric vehicles, hybrid electric vehicles, and energy storage systems.
[0116] In the following, embodiments of the invention will be described in detail in a manner readily apparent to those skilled in the art. However, the invention may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein.
[0117] Example
[0118] <Preparation of Negative Electrode Active Materials>
[0119] Example 1: Preparation of negative electrode active material
[0120] The sulfur content was 2009 ppm, the true density was 1.4 g / cc, and the average particle size (D) was... 50 The sample contains 11 μm raw coke particles and has a sulfur content of 115 ppm, a true density of 2.1 g / cc, and an average particle size (D). 50Calcined coke particles with a diameter of 7 μm and a petroleum-based pitch binder were placed in a reactor. The raw coke particles and the calcined coke particles were mixed at a weight ratio of 30:70. The pitch binder was mixed in an amount of 7% by weight relative to the total weight of the raw coke particles, the calcined coke particles, and the petroleum-based pitch. The raw coke particles, the calcined coke particles, and the petroleum-based pitch binder were heat-treated at 3000°C for 50 hours to graphitize, thereby preparing artificial graphite particles in the form of secondary particles in which the primary artificial graphite particles are bonded together. In this case, the primary artificial graphite particles are derived from the raw coke particles and the calcined coke particles.
[0121] The artificial graphite particles in the secondary particle form are mixed with petroleum-based bitumen and heat-treated in a roller kiln at 1300°C to form an amorphous carbon coating on the artificial graphite particles in the secondary particle form.
[0122] The prepared negative electrode active material has a tap density of 1.13 g / cc and an average particle size of 18 μm (D 50 The amorphous carbon coating is formed in an amount of 3.5% by weight relative to the weight of the negative electrode active material.
[0123] In this case, the tap density is obtained by loading 40g of the negative electrode active material into a container and measuring the final volume obtained by vibrating it up and down 1000 times to measure the apparent density.
[0124] Example 2: Preparation of negative electrode active material
[0125] The negative electrode active material was prepared in the same manner as in Example 1, except that the raw coke particles and the calcined coke particles were mixed in a weight ratio of 70:30.
[0126] The prepared negative electrode active material has a tap density of 1.15 g / cc and an average particle size of 18 μm (D 50 ).
[0127] Comparative Example 1: Preparation of Negative Electrode Active Materials
[0128] The negative electrode active material was prepared in the same manner as in Example 1, except that the calcined coke particles were not used as coke particles, but only the raw coke particles were used.
[0129] The prepared negative electrode active material has a tap density of 1.05 g / cc and an average particle size of 18 μm (D 50 ).
[0130] Comparative Example 2: Preparation of Negative Electrode Active Materials
[0131] The negative electrode active material was prepared in the same manner as in Example 1, except that the raw coke particles were not used as coke particles, but only the calcined coke particles were used.
[0132] The prepared negative electrode active material has a tap density of 0.87 g / cc and an average particle size of 18 μm (D 50 ).
[0133] Comparative Example 3: Preparation of Negative Electrode Active Materials
[0134] The negative electrode active material was prepared in the same manner as in Example 1, except that no binder was used.
[0135] The prepared negative electrode active material has a tap density of 1.18 g / cc and an average particle size of 12 μm (D). 50 ).
[0136] Comparative Example 4: Preparation of Negative Electrode Active Materials
[0137] The negative electrode active material was prepared by mixing the negative electrode active material prepared in Comparative Example 1 and the negative electrode active material prepared in Comparative Example 2 at a weight ratio of 30:70.
[0138] The prepared negative electrode active material has a tap density of 0.98 g / cc and an average particle size of 18 μm (D 50 ).
[0139] Comparative Example 5: Preparation of Negative Electrode Active Materials
[0140] The negative electrode active material was prepared by mixing the negative electrode active material prepared in Comparative Example 1 and the negative electrode active material prepared in Comparative Example 2 at a weight ratio of 70:30.
[0141] The prepared negative electrode active material has a tap density of 1.04 g / cc and an average particle size of 18 μm (D 50 ).
[0142] Comparative Example 6: Preparation of Negative Electrode Active Materials
[0143] Prepare particles with a sulfur content of 2009 ppm, a true density of 1.4 g / cc, and an average particle size (D). 50 Raw coke particles with a diameter of 7 μm were prepared. The sulfur content was 115 ppm, the true density was 2.1 g / cc, and the average particle size (D) was... 50 The calcined coke particles are 11 μm in size.
[0144] The negative electrode active material was prepared in the same manner as in Example 1, except that the raw coke particles and the calcined coke particles were used.
[0145] The prepared negative electrode active material has a tap density of 1.02 g / cc and an average particle size of 18 μm (D 50 ).
[0146] Comparative Example 7: Preparation of Negative Electrode Active Materials
[0147] Prepare particles with a sulfur content of 2009 ppm, a true density of 1.4 g / cc, and an average particle size (D). 50 Raw coke particles with a diameter of 9 μm were prepared. The sulfur content was 115 ppm, the true density was 2.1 g / cc, and the average particle size (D) was [missing information]. 50 The calcined coke particles are 9 μm in size.
[0148] The negative electrode active material was prepared in the same manner as in Example 1, except that the raw coke particles and the calcined coke particles were used.
[0149] The prepared negative electrode active material has a tap density of 1.05 g / cc and an average particle size of 18 μm (D 50 ).
[0150] <Preparation of the negative electrode>
[0151] The negative electrode active material prepared in Example 1, carbon black as a conductive material, styrene-butadiene rubber as a binder, and carboxymethyl cellulose as a thickener were mixed in a weight ratio of 95.9:0.5:2.5:1.1, and water was added to prepare a negative electrode slurry.
[0152] The negative electrode slurry was applied to a copper negative electrode current collector (thickness: 15 μm), vacuum dried at approximately 130°C for 8 hours, and then calendered to form a negative electrode active material layer (thickness: 55 μm), thereby preparing the negative electrode of Example 1. In this case, the negative electrode was prepared such that the loading of the negative electrode was 3.3 mAh / cm³. 2 .
[0153] The negative electrodes of Examples 2 and Comparative Examples 1 to 7 were prepared in the same manner as in Example 1, except that the negative electrode active materials prepared in Examples 2 and Comparative Examples 1 to 7 were used respectively.
[0154] The orientation index of each negative electrode in the examples and comparative examples was obtained as an area ratio I(004) / I(110), which was obtained by measuring the (004) and (110) surfaces by XRD and integrating the measured XRD peaks. The XRD measurement conditions are as follows. The results are presented in Table 1 below.
[0155] Target: Cu (Kα ray) graphite monochromator
[0156] Slits: Diverging slit = 1 degree, Receiving slit = 0.1 mm, Scattering slit = 1 degree
[0157] Measurement area and step angle / measurement time:
[0158] Face (110): 76.5 degrees < 2θ < 78.5 degrees, 0.01 degrees / 3 seconds
[0159] Face (004): 53.5 degrees < 2θ < 56.0 degrees, 0.01 degrees / 3 seconds
[0160] [Table 1]
[0161] Negative electrode orientation index I(004) / I(110) Example 1 8 Example 2 8 Comparative Example 1 9 Comparative Example 2 15 Comparative Example 3 22 Comparative Example 4 13 Comparative Example 5 11 Comparative Example 6 18 Comparative Example 7 15
[0162] Experimental Example
[0163] Experimental Example 1: Adhesion Force Evaluation
[0164] The negative electrode of Example 1 was stamped into a size of 20mm × 150mm and fixed to the center of a 25mm × 75mm glass slide using double-sided tape. Then, using a UTM (manufacturer: Lloyd Instrument LTD., device name: LF Plus), the 90° peel strength was measured while peeling the negative electrode active material layer from the negative electrode current collector. Five identical negative electrodes of Example 1 were prepared, and the 90° peel strength was measured five times in the same manner. The average value was taken as the adhesion force (unit: gf / 10mm) of the negative electrode of Example 1.
[0165] The 90° peel strength of Examples 2 and Comparative Examples 1 to 7 was measured in the same manner as in Example 1. The results are presented in Table 2 below.
[0166] Experiment Example 2: Evaluation of Fast Charging Performance
[0167] <Preparation of Secondary Batteries>
[0168] Prepare a lithium metal counter electrode as the positive electrode.
[0169] After arranging a polyolefin separator between each negative electrode prepared in the examples and the aforementioned positive electrode, an electrolyte was injected to prepare the secondary batteries of the examples and comparative examples. As the electrolyte, an electrolyte prepared by means of adding vinylene carbonate (VC) in an amount of 0.5% by weight relative to the solvent to a non-aqueous electrolyte solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 2:8, and dissolving LiPF6 in 1M solution.
[0170] <Evaluation of Fast Charging Performance>
[0171] Using the prepared secondary battery, the battery was charged and discharged three times at 1C, then charged at 3C for 15 minutes, and the curve was differentiated once. In this case, the inflection point shown in dQ / dV was determined to quantify the lithium plating SOC (Li plating SOC, %), which is the SOC when Li plating occurs on the surface of the negative electrode. The results are presented in Table 2 below.
[0172] [Table 2]
[0173]
[0174] Referring to Table 2, it can be seen that, compared with the negative electrode and secondary battery of Comparative Examples 1 to 7, the negative electrode and secondary battery of Examples 1 and 2 have improved negative electrode adhesion and fast charging performance.
Claims
1. A method for preparing a negative electrode active material, the method comprising: A mixture is obtained by mixing raw coke particles, calcined coke particles, and a binder; and The mixture is graphitized by heat treatment to form artificial graphite particles in the form of secondary particles, in which primary artificial graphite particles are bonded together. The average particle size D of the raw coke particles is 50 The average particle size D of the calcined coke particles 50 Larger.
2. The method according to claim 1, wherein the raw coke particles have an average particle size D of 9 μm to 15 μm. 50 ,and The calcined coke particles have an average particle size D of 3 μm to 8 μm. 50 .
3. The method according to claim 1, wherein the average particle size D of the calcined coke particles 50 The average particle size D of the raw coke particles 50 The ratio is greater than 0.3 and less than 1.
4. The method according to claim 1, wherein the raw coke particles have a true density of 1.20 g / cc to 1.60 g / cc.
5. The method according to claim 1, wherein the calcined coke particles have a true density of 1.80 g / cc to 2.25 g / cc.
6. The method of claim 1, wherein the raw coke particles contain sulfur in an amount of 1,000 ppm to 5,000 ppm.
7. The method of claim 1, wherein the calcined coke particles contain 50 ppm to 1000 ppm of sulfur.
8. The method according to claim 1, wherein the raw coke particles and the calcined coke particles are mixed in a weight ratio of 10:90 to 90:
10.
9. The method according to claim 8, wherein the raw coke particles and the calcined coke particles are mixed in a weight ratio of 25:75 to 75:
25.
10. The method of claim 1, wherein the binder is mixed in an amount of 1% to 10% by weight relative to the total weight of the raw coke particles, the calcined coke particles and the binder.
11. The method according to claim 1, wherein the heat treatment is performed at 2500°C to 3500°C.
12. The method of claim 1, wherein the heat treatment is performed for 40 to 60 hours.
13. The method of claim 1, further comprising forming an amorphous carbon coating on the artificial graphite particles in the form of secondary particles.
14. The method of claim 13, wherein the amorphous carbon coating is formed in an amount of 0.1 to 10% by weight relative to the total amount of the negative electrode active material.
15. A negative electrode comprising: Negative current collector; and A negative electrode active material layer is disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer comprises a negative electrode active material prepared by the method for preparing a negative electrode active material according to any one of claims 1 to 14.
16. The negative electrode according to claim 15, wherein the negative electrode active material has a tap density of 1.08 g / cc to 1.17 g / cc.
17. The negative electrode according to claim 15, wherein the negative electrode has an orientation index I(004) / I(110) of 8.5 or less.
18. A secondary battery, comprising: The negative electrode according to any one of claims 15 to 17; Positive electrode, the positive electrode facing the negative electrode; A diaphragm is disposed between the negative electrode and the positive electrode; and Electrolytes.