Positive electrode slurry composition, positive electrode, method of manufacturing positive electrode, and rechargeable lithium battery

Abstract

The invention relates to a positive electrode slurry composition, a positive electrode, a method of manufacturing a positive electrode, and a rechargeable lithium battery. The positive electrode slurry composition includes a positive electrode active material including secondary particles of a lithium nickel-based composite oxide, carbon nanotubes, and a cellulose-based additive.

Description

[0001] This disclosure relates to research conducted in 2024 with funding from the Korean government (Ministry of Trade, Industry and Energy) and supported by the Korea Institute for Industrial Technology Promotion (RS-2024-00419413, 2024 Industrial Innovation Talent Development Support Project). Technical Field

[0002] This disclosure relates to a positive electrode slurry composition, a positive electrode, a method for manufacturing a positive electrode, and a rechargeable lithium battery. Background Technology

[0003] Portable information devices (such as cellular phones, laptops, smartphones, or electric vehicles) typically use rechargeable lithium-ion batteries as their power source. Rechargeable lithium-ion batteries have relatively high energy density and are portable. Research is actively underway to utilize rechargeable lithium-ion batteries with their relatively high energy density as a power source for hybrid or electric vehicles, or as an energy storage source.

[0004] Various positive electrode active materials have been studied. Among them, lithium nickel oxides, lithium nickel manganese cobalt composite oxides, lithium nickel cobalt aluminum composite oxides, and lithium cobalt oxides have emerged as the main candidates. Positive electrode active materials with a nickel content of approximately equal to or greater than 80 mol% can provide this relatively high energy density and have therefore been actively developed. However, some limitations exist (such as structural degradation due to charging and discharging, surface side reactions with the electrolyte, and degradation due to particle cracking). Accordingly, there is a need to develop positive electrode active materials that achieve this relatively high energy density and have a relatively long cycle life.

[0005] This background section is intended to provide a general understanding of the background of this disclosure, and therefore may contain information that does not constitute related technology (or prior art). Summary of the Invention

[0006] By adding cellulose-based additives to the positive electrode slurry composition, the dispersibility of carbon nanotubes is improved, thereby inhibiting the aggregation of carbon nanotubes in a portion of the positive electrode and potentially forming a carbon nanotube film, even during drying during positive electrode fabrication. The carbon nanotubes can be uniformly dispersed within the positive electrode and can be selectively and uniformly coated onto the surface of the positive electrode active material during positive electrode fabrication, without the need for separate coating of carbon nanotubes onto the positive electrode active material.

[0007] Embodiments of this disclosure provide a positive electrode slurry composition comprising a positive electrode active material, carbon nanotubes, and cellulose-based additives, wherein the positive electrode active material comprises secondary particles of lithium-nickel composite oxides.

[0008] Embodiments of the present disclosure provide a positive electrode paste composition, comprising: a positive electrode active material, the positive electrode active material comprising secondary particles of a lithium nickel-based composite oxide; carbon nanotubes; and a cellulose-based additive.

[0009] In some embodiments, the lithium nickel-based composite oxide is represented by Chemical Formula 1:

[0010] [Chemical Formula 1]

[0011] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1 ,

[0012] where 0.9 ≤ a1 ≤ 1.2, 0.8 ≤ x1 < 1, 0 < y1 ≤ 0.2, 0 ≤ z1 ≤ 0.2, 0.9 ≤ x1 + y1 + z1 ≤ 1.1 and 0 ≤ b1 ≤ 0.1, where M 1 and M 2 are each independently one or more elements selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn and Zr, and where X is one or more elements selected from F, P and S.

[0013] In some embodiments, based on 100 mol% of the total metals other than lithium, the lithium nickel-based composite oxide has a nickel content equal to or greater than about 80 mol%.

[0014] In some embodiments, multiple primary particles are aggregated in the secondary particles and the average particle diameter (D 50 ) of the secondary particles is about 2 μm to about 20 μm, and where the average particle diameter (D 50 ) of the primary particles is less than or equal to about 6 μm.

[0015] In some embodiments, the carbon nanotubes include single-walled carbon nanotubes, multi-walled carbon nanotubes or a combination thereof.

[0016] In some embodiments, the average diameter of the carbon nanotubes is about 0.8 nm to about 100 nm, and where the average aspect ratio of the carbon nanotubes is about 100 to about 500,000. In some embodiments, the cellulose-based additive includes ethyl cellulose, cellulose acetate, carboxymethyl cellulose, hydroxypropyl cellulose, methyl cellulose, nitrocellulose or a combination thereof.

[0017] In some embodiments, based on the total solids content of 100 wt% of the positive electrode slurry composition, the content of lithium nickel composite oxide is about 90 wt% to about 99 wt%, wherein based on the total solids content of 100 wt% of the positive electrode slurry composition, the content of carbon nanotubes is about 0.1 wt% to about 5 wt%, and wherein based on the total solids content of 100 wt% of the positive electrode slurry composition, the content of cellulose additives is about 0.01 wt% to about 5 wt%.

[0018] In some embodiments, the weight ratio of carbon nanotubes to cellulose-based additives is about 10:1 to about 1:5.

[0019] In some embodiments, the positive electrode paste composition further includes a binder, a conductive material, or a combination thereof.

[0020] Embodiments of this disclosure provide a positive electrode, comprising: a positive electrode current collector; and a positive electrode active material layer disposed on the positive electrode current collector and comprising a positive electrode active material and carbon nanotubes, the positive electrode active material comprising a lithium-nickel composite oxide in the form of secondary particles in which a plurality of primary particles are aggregated.

[0021] Embodiments of this disclosure provide a positive electrode, comprising: a positive electrode current collector; and a positive electrode active material layer disposed on the positive electrode current collector and comprising secondary particles comprising lithium nickel composite oxides; carbon nanotubes; and cellulose derivatives, amorphous carbon, or combinations thereof.

[0022] Embodiments of this disclosure provide a method for manufacturing a positive electrode, the method comprising: preparing a positive electrode slurry composition, the positive electrode slurry composition comprising a positive electrode active material, carbon nanotubes and cellulose-based additives, the positive electrode active material comprising a lithium-nickel composite oxide in the form of secondary particles in which a plurality of primary particles are aggregated; coating the positive electrode slurry composition onto a positive electrode current collector and drying the positive electrode slurry composition; and performing heat treatment.

[0023] Embodiments of this disclosure provide a method for manufacturing a positive electrode, comprising: preparing a positive electrode slurry composition, the positive electrode slurry composition comprising a positive electrode active material, carbon nanotubes and cellulose-based additives, the positive electrode active material comprising secondary particles of lithium-nickel composite oxides; coating the positive electrode slurry composition onto a positive electrode current collector and drying the positive electrode slurry composition; and performing heat treatment.

[0024] In some embodiments, the preparation of the positive electrode slurry composition includes mixing secondary particles of lithium-nickel composite oxides, carbon nanotubes, and cellulose-based additives in a solvent.

[0025] In some embodiments, preparing a positive electrode slurry composition includes: adding carbon nanotubes and cellulose-based additives to a solvent to form a pre-dispersion, and adding the pre-dispersion to a slurry comprising secondary particles of lithium-nickel composite oxides.

[0026] In some embodiments, drying is carried out at a temperature of about 60°C to about 160°C.

[0027] In some embodiments, the heat treatment is performed at a temperature of about 180°C to about 300°C.

[0028] In some implementations, the heat treatment is performed for approximately 10 to approximately 60 minutes.

[0029] In some embodiments, the heat treatment is performed under a vacuum or in an atmosphere containing gas.

[0030] In some implementations, the gas includes oxygen, argon, air, or nitrogen.

[0031] Embodiments of this disclosure provide a rechargeable lithium battery, including a positive electrode, a negative electrode, and an electrolyte.

[0032] Embodiments of this disclosure provide a rechargeable lithium battery, including a positive electrode, a negative electrode, and an electrolyte.

[0033] The positive electrode slurry composition improves the dispersibility of carbon nanotubes by adding cellulose-based additives, thereby inhibiting the aggregation of carbon nanotubes in a portion of the positive electrode and potentially forming a carbon nanotube film, even during drying during the manufacturing process of the positive electrode. During the manufacturing of the positive electrode, carbon nanotubes can be selectively and uniformly coated onto the surface of the positive electrode active material, without the need for separate coating of carbon nanotubes onto the positive electrode active material. Attached Figure Description

[0034] The accompanying drawings illustrate embodiments of the present disclosure and, together with the specific embodiments thereof, further describe aspects and features of the present disclosure. Therefore, this disclosure should not be construed as limited to the drawings.

[0035] Figure 1 A rechargeable lithium battery according to an embodiment of the present disclosure is illustrated schematically.

[0036] Figure 2 A rechargeable lithium battery according to an embodiment of the present disclosure is illustrated schematically.

[0037] Figure 3 A rechargeable lithium battery according to an embodiment of the present disclosure is illustrated schematically.

[0038] Figure 4 A rechargeable lithium battery according to an embodiment of the present disclosure is illustrated schematically.

[0039] Figure 5 The photographs, taken using a scanning electron microscope (SEM), illustrate the dispersion of carbon nanotubes in a sample manufactured according to an embodiment of the present disclosure, depending on the presence or absence of cellulose-based additives.

[0040] Figure 6 Photographs of the surface of the positive electrode of Embodiment 1 and Reference Example 1 according to the present disclosure, taken using SEM.

[0041] Figure 7 The photographs are taken using SEM to show the cross-section of the positive electrode in Embodiment 2 and Reference Example 2 according to the present disclosure.

[0042] Figure 8 Photographs illustrating the adhesive strength of carbon nanotubes using positive electrode active materials extracted from the positive electrodes manufactured in Example 1 and Reference Example 3. According to embodiments of this disclosure, each positive electrode active material was added to an N-methyl-2-pyrrolidone solvent and sonicated in an ultrasonic processor for 0 minutes, 1 minute, 3 minutes, and 5 minutes.

[0043] Figure 9 A graph showing the cycle life of rechargeable lithium battery cells manufactured in Embodiment 1, Reference Example 3, and Comparative Examples 1 and 2 according to the present disclosure.

[0044] <Description of important figure markers>

[0045] 100: Rechargeable lithium battery; 10: Positive electrode

[0046] 11: Positive electrode lead connector 12: Positive electrode terminal

[0047] 20: Negative electrode 21: Negative electrode lead connector

[0048] 22: Negative electrode terminal; 30: Diaphragm

[0049] 40: Electrode assembly; 50: Housing

[0050] 60: Sealing component; 70: Electrode terminal piece

[0051] 71: Positive electrode connector; 72: Negative electrode connector Detailed Implementation

[0052] In this document, some embodiments of the present disclosure will be described in further detail with reference to the accompanying drawings. The terms or words used in this specification and claims should not be construed as limited to their ordinary or dictionary meanings, and should be interpreted as having meanings and concepts consistent with the technical concept of the present disclosure, based on the principle that the inventor, as a lexicographer, may appropriately define the terms and concepts.

[0053] The embodiments described in this specification and the configurations shown in the accompanying drawings are provided as some exemplary embodiments of this disclosure and do not represent all technical concepts, aspects, and features of this disclosure. Accordingly, it should be understood that various equivalents and modifications may exist at the time of filing this application, and the embodiments described herein may be substituted or modified.

[0054] It should be understood that when an element or layer is described as being "on" another element or layer, "connected to," or "linked to" another element or layer, it may be directly on, directly connected to, or directly linked to the other element or layer, or one or more intermediary elements or layers may be present. When an element or layer is described as being "directly on" another element or layer, "directly connected to," or "directly linked to" another element or layer, no intermediary element or layer is present. For example, when a first element is described as being "linked to" or "connected to" a second element, the first element may be directly linked to or directly connected to the second element, or the first element may be indirectly linked to or connected to the second element via one or more intermediary elements.

[0055] In the figures, for clarity of explanation, the dimensions of various elements, layers, etc., may be magnified. The same reference numerals label the same or identical elements. As used herein, the term "and / or" includes any and all combinations of one or more of the associated enumerated items. Furthermore, when describing embodiments of this disclosure, the use of "may" refers to "one or more embodiments of this disclosure." Expressions such as "at least one of..." and "any one of...", when used after a list of elements, modify the entire list of elements and not individual elements in the list. When phrases such as "at least one of A, B, and C," "at least one selected from the group of A, B, and C," or "at least one selected from A, B, and C" are used to label a list of elements A, B, and C, the phrase may refer to any and all suitable combinations or subsets of A, B, and C, such as A, B, C, A and B, A and C, B and C, or A, B, and C. As used herein, the terms “use,” “using,” and “used” are to be regarded as synonyms with the terms “utilize,” “utilizing,” and “utilized,” respectively. As used herein, the terms “substantially,” “about,” and similar terms are used as approximations and not as terms of degree, and are intended to take into account the inherent changes in measurements or calculations that would be recognized by one of ordinary skill in the art.

[0056] It should be understood that although the terms “first,” “second,” “third,” etc., may be used herein to describe various elements, components, areas, layers, and / or portions, these elements, components, areas, layers, and / or portions should not be limited by these terms. These terms are used to distinguish one element, component, area, layer, or portion from another element, component, area, layer, or portion. Therefore, without departing from the teachings of the exemplary embodiments, the first element, component, area, layer, or portion discussed below may be referred to as the second element, component, area, layer, or portion.

[0057] For ease of description, spatial relative terms (such as "below," "below," "down," "above," "up," etc.) may be used herein to describe the relationship between one element or feature and another element or feature illustrated in the figures. It should be understood that, in addition to the orientation depicted in the figures, spatial relative terms are intended to encompass different orientations of the device in use or operation. For example, if the device in the figures is flipped, an element described as "below" or "below" other elements or features will then be oriented "above" or "on top" other elements or features. Thus, the term "below" can encompass both above and below orientations. The device may be oriented in other ways (e.g., rotated 90 degrees or otherwise), and the spatial relative descriptors used herein should be interpreted accordingly.

[0058] The terminology used herein is for the purpose of describing embodiments of this disclosure and is not intended to limit this disclosure. Unless the context clearly indicates otherwise, the singular forms “a” and “an” as used herein are intended to include the plural forms as well. It should be further understood that, when used in this specification, the terms “includes,” “including,” “comprises,” and / or “comprising” indicate the presence of the described features, integers, steps, operations, elements, components, and / or groups thereof, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0059] Furthermore, any numerical range disclosed and / or set forth herein is intended to include all subranges with the same numerical precision falling within the set forth range. For example, the range “1.0 to 10.0” is intended to include (and inclusive) the minimum value of 1.0 and the maximum value of 10.0, i.e., all subranges having a minimum value equal to or greater than 1.0 and a maximum value equal to or less than 10.0 (such as, for example, 2.4 to 7.6). Any maximum numerical limit set forth herein is intended to include all lower numerical limits falling within it, and any minimum numerical limit set forth in this specification is intended to include all higher numerical limits falling within it. Accordingly, the applicant reserves the right to amend this specification (including the claims) to expressly set forth any subranges falling within the range expressly set forth herein.

[0060] Referring to two compared elements, features, etc., as "identical" can mean that they are "substantially identical." Therefore, the phrase "substantially identical" can include cases considered in the art to have small deviations, for example, 5% or less. Additionally, when a particular parameter is said to be uniform in a given region, it can mean that it is uniform in terms of average value.

[0061] Throughout the manual, unless otherwise stated, each element may be single or multiple.

[0062] When any element is referred to as being arranged (or positioned or placed) "above (or below)" or "over (or under)" an assembly, it can mean that the element is positioned to contact the upper (or lower) surface of the assembly, and it can also mean that another assembly can be inserted between the assembly and any element arranged (or positioned or placed) above (or below) the assembly.

[0063] Furthermore, it should be understood that when an element is referred to as "connected," "linked," or "attached" to another element, these elements may be directly "connected," "linked," or "attached" to each other, or one or more intermediary elements may exist between them, through which the element may be "connected," "linked," or "attached" to the other element. Additionally, when a part is referred to as "electrically connected" to another part, that part may be directly electrically connected to the other part, or one or more intermediary parts may exist between them, such that the part and the other part are indirectly electrically connected to each other.

[0064] Unless otherwise stated, throughout the specification, when “A and / or B” is stated, it means A, B, or A and B. That is, “and / or” includes any or all combinations of the listed items. Unless otherwise indicated, when “C~D” is stated, it means C or greater and D or less.

[0065] As used herein, “combination of” can refer to mixtures of components, laminates, composites, copolymers, alloys, blends, or reaction products.

[0066] In the accompanying drawings, the thicknesses of layers, films, panels, areas, etc., are enlarged for clarity. It will be understood that when an element (such as a layer, film, area, or substrate) is referred to as being "on" another element, it may be directly on the other element, or an intermediary element may be present. In contrast, when an element is referred to as being "directly on" another element, no intermediary element is present.

[0067] In addition, the term "layer" in this document includes not only shapes that form across the entire surface when viewed from a plan view, but also shapes that form on a portion of the surface.

[0068] The average particle size can be measured using methods well known to those skilled in the art, such as by a particle size analyzer or by transmission electron microscopy or scanning electron microscopy images. Alternatively, the average particle size value can be obtained by measuring using dynamic light scattering methods, performing data analysis, counting the number of particles in each particle size range, and thereby calculating. Unless otherwise specified, the average particle size (D...) 50 The term "average particle size" can refer to the diameter of particles that constitute 50% of the total volume in the particle size distribution. As used herein, unless otherwise specified, the average particle size (D) refers to the diameter of particles that constitute 50% of the total volume in the particle size distribution. 50 This refers to the diameter of particles that constitute 50% of the total volume in a particle size distribution obtained by randomly measuring the size (diameter or major axis length) of approximately 20 particles in a scanning electron microscope image.

[0069] As used herein, the term "metal" refers to common metals, transition metals, and metalloids (semi-metals).

[0070] The terminology used in this specification is for describing embodiments of this disclosure and is not intended to limit this disclosure.

[0071] As used herein, the term "primary particle" refers to particles of a given material that have not undergone aggregation.

[0072] As used herein, the term "secondary particle" refers to particles of a given material that have undergone aggregation.

[0073] Positive electrode slurry composition

[0074] In some embodiments, the positive electrode slurry composition includes a positive electrode active material, carbon nanotubes, and cellulose-based additives, wherein the positive electrode active material includes secondary particles of lithium-nickel composite oxides.

[0075] Lithium-nickel composite oxides are secondary particles within which primary particles aggregate. With repeated charge / discharge cycles, the crystal structure of lithium-nickel composite oxides undergoes volume expansion, leading to widening of the gaps between primary particles and resulting in misalignment of the primary particles. This alters the degree of contraction and expansion of the secondary particles, as well as the degree of contraction and expansion of the positive electrode containing the secondary particles. Structural breakage and / or destruction may occur in the secondary particles and / or the positive electrode, resulting in a broken electrochemical charge transfer network, charge imbalance, increased area for side reactions with the electrolyte, and deterioration of charge / discharge cycle life.

[0076] Existing techniques attempt to uniformly coat the surface of a positive electrode active material with carbon-based materials (such as graphene or carbon nanotubes). However, this requires a multi-step process to uniformly coat the carbon-based material onto the surface of the positive electrode active material. Each step incurs various costs, leading to increased manufacturing costs.

[0077] On the other hand, carbon nanotubes have been added to the positive electrode as a conductive material to improve its conductivity and reduce the amount of conductive material. However, carbon nanotubes cannot be uniformly dispersed. Even so, when the solvent dries after forming the positive electrode, the carbon nanotubes can concentrate in the upper part of the positive electrode, leading to adverse results when applied to relatively high-load electrodes. Because the carbon nanotubes are not selectively located on the surface of the active material of the positive electrode, they cannot improve the conductivity of the positive electrode, nor can they reduce the amount of conductive material.

[0078] A positive electrode paste composition to which a cellulose-based additive is added to improve the dispersion of carbon nanotubes can suppress the aggregation of carbon nanotubes in a certain part of the positive electrode and potentially form a carbon nanotube film even after subsequent drying. The carbon nanotubes are uniformly dispersed in the positive electrode and uniformly coated on the surface of the positive electrode active material without separately coating the carbon nanotubes on the positive electrode active material. Accordingly, the positive electrode paste composition can prevent particle cracks caused by the shrinkage and expansion of the positive electrode active material due to repeated charging and discharging, thereby improving the battery cycle life. In particular, when carbon nanotubes are used instead of other known conductive materials, electrons can be easily transferred within the positive electrode, demonstrating excellent conductivity. By connecting the carbon nanotubes on the surface of the primary particles of the positive electrode active material, a stable conduction network can be formed.

[0079] Positive electrode active material

[0080] The positive electrode active material includes a lithium nickel-based composite oxide. According to some embodiments, the positive electrode active material can achieve a relatively high energy density by including a lithium nickel-based composite oxide.

[0081] The lithium nickel-based composite oxide can be represented, for example, by Chemical Formula 1.

[0082] [Chemical Formula 1]

[0083] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1

[0084] In Chemical Formula 1, 0.9 ≤ a1 ≤ 1.2, 0.8 ≤ x1 < 1, 0 < y1 ≤ 0.2, 0 ≤ z1 ≤ 0.2, 0.9 ≤ x1 + y1 + z1 ≤ 1.1 and 0 ≤ b1 ≤ 0.1, M 1 and M 2 are each independently one or more elements selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from F, P, and S. M 1 and M 2 can be different elements.

[0085] In Chemical Formula 1, 0.85 ≤ x1 < 1, 0 < y1 ≤ 0.15 and 0 ≤ z1 ≤ 0.15; or 0.9 ≤ x1 < 1, 0 < y1 ≤ 0.1 and 0 ≤ z1 ≤ 0.1.

[0086] As a specific example, the lithium nickel-based composite oxide can be represented by Chemical Formula 2 or Chemical Formula 3.

[0087] [Chemical Formula 2]

[0088] Li a2 Ni x2 Co y2 M 3 z2 O 2-b2 X b2

[0089] In Chemical Formula 2, 0.9 ≤ a2 ≤ 1.2, 0.8 ≤ x2 < 1, 0 < y2 ≤ 0.2, 0 ≤ z2 ≤ 0.2, 0.9 ≤ x2 + y2 + z2 ≤ 1.1 and 0 ≤ b2 ≤ 0.1, M 3 is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn and Zr, and X is F, P, S or a combination thereof.

[0090] In Chemical Formula 2, 0.9 ≤ x2 ≤ 0.99, 0.01 ≤ y2 ≤ 0.1 and 0 ≤ z2 ≤ 0.1.

[0091] [Chemical Formula 3]

[0092] Li a3 Ni x3 Co y3 M 4 z3 M 5 w3 O 2-b3 X b3

[0093] In Chemical Formula 3, 0.9 ≤ a3 ≤ 1.2, 0.8 ≤ x3 ≤ 0.98, 0.01 ≤ y3 ≤ 0.19, 0.01 ≤ z3 ≤ 0.19, 0 ≤ w3 ≤ 0.19, 0.9 ≤ x3 + y3 + z3 + w3 ≤ 1.1 and 0 ≤ b3 ≤ 0.1, M 4 is Al, Mn or a combination thereof, M 5 is one or more elements selected from B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn and Zr, and X is F, P, S or a combination thereof.

[0094] In Chemical Formula 3, 0.9 ≤ x3 ≤ 0.98, 0.01 ≤ y3 ≤ 0.09, 0.01 ≤ z3 ≤ 0.09 and 0 ≤ w3 ≤ 0.09.

[0095] In lithium-nickel composite oxides, based on 100 mol% of total metals excluding lithium, the nickel content can be greater than or equal to about 80 mol%, for example, greater than or equal to about 85 mol%, greater than or equal to about 90 mol%, greater than or equal to about 91 mol%, greater than or equal to about 94 mol%, and less than or equal to about 99 mol%. This allows for relatively high capacity and relatively high energy density.

[0096] Lithium-nickel composite oxides can exist as secondary particles within which multiple primary particles aggregate. The secondary particles can be spherical, ellipsoidal, polyhedral, or irregular in shape, and the primary particles can be spherical, ellipsoidal, or plate-like.

[0097] The average particle size of secondary particles (D) 50 The particle size can range from approximately 2 μm to approximately 20 μm, for example, from approximately 3 μm to approximately 18 μm or from approximately 4 μm to approximately 15 μm. The particle size distribution can be obtained by randomly measuring the size (diameter or major axis length) of approximately 20 particles from a scanning electron microscope image of lithium-nickel composite oxide particles in secondary particle form, and the average particle size (D) is obtained by taking the diameter of the particles with a cumulative volume of 50% from the particle size distribution as the average particle size. 50 Thus, relatively high capacity and relatively high energy density can be achieved, and the electrochemical performance of the positive electrode can be improved because carbon nanotubes are advantageously and selectively located on the surface of the secondary particles.

[0098] The average particle size (D) of the primary particles forming secondary particles of lithium-nickel composite oxides 50 The primary particle size can be less than or equal to about 6 μm, for example, about 100 nm to about 4 μm, about 100 nm to about 2 μm, about 200 nm to about 800 nm, or about 300 nm to about 700 nm. The particle size distribution can be obtained by randomly measuring the size (diameter or major axis length) of about 20 primary particles from scanning electron microscopy or transmission electron microscopy images of the surface of the secondary particles, and the average particle size (Dm) of the primary particles is obtained by taking the diameter of the particles having a cumulative volume of 50% from the particle size distribution as the average particle size. 50 Thus, the positive electrode active material can achieve high initial charge / discharge capacity and efficiency, as well as excellent output characteristics and cycle life characteristics.

[0099] carbon nanotubes

[0100] The positive electrode slurry composition according to some embodiments includes carbon nanotubes. When graphene is coated using a known graphene coating technique, graphene, as a 2D material, can cover the entire surface of a lithium-nickel composite oxide, preventing lithium ions from moving between the positive electrode active material surface and the electrolyte, thereby degrading the relatively high capacity, high power, and long cycle life characteristics of the rechargeable lithium battery. Carbon nanotubes, being essentially a 1D material, can connect primary particles together on the surface of the lithium-nickel composite oxide and can maintain the geometry of secondary particles without obstructing lithium ion movement, even without covering the entire surface of the lithium-nickel composite oxide. This suppresses the shrinkage and expansion of secondary particles and the positive electrode, thereby improving the battery's cycle life characteristics.

[0101] Carbon nanotubes are highly crystalline carbon materials in which carbon atoms are arranged in a hexagonal pattern to form a tube shape. Carbon nanotubes possess excellent electrical conductivity and lithium-ion conductivity. Therefore, by maintaining a uniform current and voltage distribution within the positive electrode during charge / discharge cycles, cycle characteristics can be significantly improved, and the battery's output characteristics can be enhanced due to the improved conductivity. Because carbon nanotubes are composed of carbon atoms with strong covalent bonds, they exhibit excellent tensile strength and high resistance to damage, thus improving battery safety.

[0102] Carbon nanotubes (CNTs) may include single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), or combinations thereof. According to some embodiments, the carbon nanotubes may be multi-walled carbon nanotubes. Among the different types of carbon nanotubes, multi-walled carbon nanotubes are relatively cheaper than single-walled carbon nanotubes, thus ensuring price competitiveness.

[0103] Carbon nanotubes can include bare carbon nanotubes (untreated), surface-treated carbon nanotubes, or combinations thereof. Bare carbon nanotubes refer to carbon nanotubes having surface functional groups (CO, CH, C-OOH, etc.) typically present on the surface of carbon nanotubes. These functional groups are generated during the synthesis of carbon nanotubes. Surface-treated carbon nanotubes refer to carbon nanotubes that have additional functional groups attached by disrupting and oxidizing the carbon ring structure on the surface of the carbon nanotube (more specifically, the surface of bare carbon nanotubes) using an acid (such as nitric acid). These additional functional groups include carboxylic acids, amines, or polyethylene glycols, and surface-treated carbon nanotubes having such additional functional groups include COOH-functionalized CNTs, amine-functionalized CNTs, and polyethylene glycol-functionalized CNTs. Carbon nanotubes can include, but are not limited to, bare carbon nanotubes or surface-treated carbon nanotubes.

[0104] The average diameter of carbon nanotubes can range from approximately 0.8 nm to approximately 100 nm. For example, it can be approximately 1 nm to approximately 90 nm, approximately 2 nm to approximately 80 nm, approximately 3 nm to approximately 70 nm, or approximately 2 nm to approximately 100 nm. The average diameter of the carbon nanotubes can be the average of the diameters of the thickest portions measured by observing 10 or more carbon nanotubes using a scanning electron microscope (SEM). In this way, a suitable amount of electrons can be moved, thereby forming a stable conductive network.

[0105] The average aspect ratio of carbon nanotubes can range from approximately 100 to approximately 500,000. For example, it can be approximately 200 to approximately 300,000, approximately 200 to approximately 15,000, approximately 1,000 to approximately 100,000, or approximately 2,000 to approximately 50,000. The average aspect ratio of carbon nanotubes is the ratio of average length to average diameter (average length / average diameter ratio). The average aspect ratio of carbon nanotubes can be calculated by measuring the average diameter and average length and dividing the average length by the average diameter. The average diameter can be measured in the same way, and the average length can be the average of the lengths measured by observing 10 or more carbon nanotubes using a scanning electron microscope (SEM). Thus, when fabricating a positive electrode using a positive electrode paste, a sufficient conductive network can be formed using only a small amount of carbon nanotubes.

[0106] Cellulose additives

[0107] The positive electrode slurry composition according to some embodiments includes a cellulose-based additive. By including the cellulose-based additive, the dispersibility of carbon nanotubes is improved, and the carbon nanotubes can be selectively and uniformly coated onto the surface of the positive electrode active material. The selective coating of carbon nanotubes onto the surface of the positive electrode active material prevents particle breakage due to shrinkage and expansion of the positive electrode active material caused by repeated charging and discharging, and improves battery cycle life.

[0108] Cellulose additives include alkyl groups, and their types are not limited, as long as they include functional groups capable of forming hydrogen bonds. For example, cellulose additives may include ethyl cellulose, cellulose acetate, carboxymethyl cellulose, hydroxypropyl cellulose, methyl cellulose, nitrocellulose, or combinations thereof.

[0109] Based on the solid content of the 100 wt% positive electrode slurry composition, the amount of lithium nickel composite oxide included may be about 60 wt% to about 99.9 wt%, about 70 wt% to about 99.8 wt%, about 80 wt% to about 99 wt%, about 90 wt% to about 99 wt%, or about 95 wt% to about 99 wt%.

[0110] Based on the solid content of 100 wt% of the positive electrode slurry composition, the amount of carbon nanotubes included may be from about 0.1 wt% to about 5 wt%, for example, from about 0.1 wt% to about 4 wt%, from about 0.1 wt% to about 3 wt%, from about 0.1 wt% to about 2 wt%, or from about 0.1 wt% to about 1 wt%.

[0111] Based on the solids content of the 100 wt% positive electrode slurry composition, the amount of cellulose additives included can be from about 0.01 wt% to about 5 wt%, for example, from about 0.05 wt% to about 4 wt%, from about 0.1 wt% to about 3 wt%, from about 0.1 wt% to about 2 wt%, or from about 0.1 wt% to about 1 wt%. In this way, the cellulose additives can be uniformly dispersed in the solvent and can interact appropriately with the carbon nanotubes.

[0112] The weight ratio of carbon nanotubes to cellulose-based additives can be approximately 10:1 to approximately 1:5, approximately 9:1 to approximately 1:4, approximately 8:1 to approximately 1:3, or approximately 7:1 to approximately 1:2. This maximizes the interaction between the cellulose-based additives and the carbon nanotubes, effectively dispersing the carbon nanotubes and reducing the resistance of the positive electrode, thereby effectively generating the positive electrode.

[0113] other

[0114] In addition to the positive electrode active material, carbon nanotubes, and cellulose-based additives, the positive electrode slurry composition may optionally include a binder, a conductive material, or a combination thereof.

[0115] The binder improves the adhesion properties between the positive electrode active material particles and between the positive electrode active material particles and the positive electrode current collector. Examples of binders may include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylate resin, polyester resin, or nylon.

[0116] Conductive materials are included to provide electrode conductivity. Any electrically conductive material may be used as a conductive material unless it causes harmful chemical changes. Examples of conductive materials may include carbon-based materials (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, or carbon nanotubes); metallic materials including metal powders or fibers of copper, nickel, aluminum, or silver; conductive polymers (such as polyphenylene derivatives); or mixtures thereof.

[0117] Based on a 100 wt% positive electrode paste composition, the amount of binder in the positive electrode paste composition may be from about 0.1 wt% to about 5 wt%, and based on a 100 wt% positive electrode paste composition, the amount of conductive material may be from about 0.1 wt% to about 5 wt%.

[0118] The positive electrode paste composition may include a solvent, and the solvent may be, for example, a non-aqueous organic solvent. The solvent may include, for example, cycloaliphatic hydrocarbons (such as cyclopentane and cyclohexane); aromatic hydrocarbons (such as toluene, xylene, and ethylbenzene); ketones (such as acetone, ethyl methyl ketone, diisopropyl ketone, cyclohexanone, methylcyclohexane, and ethylcyclohexane); chlorinated aliphatic hydrocarbons (such as dichloromethane, chloroform, and carbon tetrachloride); esters (such as ethyl acetate, butyl acetate, γ-butyrolactone, and ε-caprolactone); acetonitrs (such as acetonitrile and propionitrile); ethers (such as tetrahydrofuran and ethylene glycol diethyl ether); alcohols (such as methanol, ethanol, isopropanol, ethylene glycol, and ethylene glycol monomethyl ether); or amides (such as N-methyl-2-pyrrolidone and N,N-dimethylformamide). The solvent may be a single solvent or a mixture of two or more solvents.

[0119] The positive electrode slurry composition may include a positive electrode active material, which may include secondary particles of lithium nickel composite oxides, and may also include single particles of lithium nickel composite oxides.

[0120] Individual particles of the positive electrode active material may include lithium-nickel composite oxides. Individual particles of the positive electrode active material may be represented by chemical formulas 1 to 3, and based on 100 mol% of total metals other than lithium, the nickel content may be greater than or equal to about 80 mol%. Individual particles of the positive electrode active material may be primary particles separate from the secondary particles of the positive electrode active material.

[0121] The average particle size (D) of a single particle 50 The particle size can range from approximately 1 μm to approximately 12 μm, for example, from approximately 2 μm to approximately 11 μm or from approximately 3 μm to approximately 8 μm. The particle size distribution can be obtained by randomly measuring the size (diameter or major axis length) of approximately 20 particles from a scanning electron microscope image of a single particle of the positive electrode active material, and the average particle size (D) is obtained by taking the diameter of the particles having a cumulative volume of 50% from the particle size distribution as the average particle size. 50 This allows for relatively high initial charge / discharge capacity and efficiency, as well as excellent output and cycle life characteristics.

[0122] When secondary particles of positive electrode active material and single particles of positive electrode active material are mixed (hereinafter referred to as "mixed positive electrode active material"), the mixing weight ratio of secondary particles of positive electrode active material to single particles of positive electrode active material can be about 1:9 to about 9:1, for example, about 2:8 to about 9:1, about 3:7 to about 9:1, about 4:6 to about 9:1, about 5:5 to about 8:2 or about 6:4 to about 7:3.

[0123] When secondary particles of positive electrode active material are mixed with single particles of positive electrode active material, the average particle size (D) of the mixed positive electrode active material is... 50 The particle size can range from approximately 1 μm to approximately 20 μm, for example, from approximately 3 μm to approximately 18 μm or from approximately 4 μm to approximately 15 μm. The particle size distribution can be obtained by randomly measuring the size (diameter or major axis length) of approximately 20 particles from a scanning electron microscope image of the mixed positive electrode active material, and the average particle size (D) is obtained by taking the diameter of the particles with a cumulative volume of 50% of the particle size distribution as the average particle size. 50 Thus, because carbon nanotubes are advantageously and selectively located on the surface of secondary particles, relatively high capacity and energy density can be achieved, and the electrochemical performance of the positive electrode can be improved.

[0124] positive electrode

[0125] The positive electrode includes a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer is disposed on the positive electrode current collector and includes positive electrode active material and carbon nanotubes. The positive electrode active material includes secondary particles of lithium-nickel composite oxides. The positive electrode active material layer further includes cellulose derivatives, amorphous carbon, or combinations thereof. According to some embodiments, the positive electrode can achieve relatively high capacity and relatively long cycle life while suppressing structural degradation and cracking caused by charging / discharging.

[0126] Positive electrode current collector

[0127] The positive electrode current collector is not specifically limited, as long as it is conductive and does not cause harmful chemical changes in the rechargeable lithium battery. The positive electrode current collector may include aluminum foil or stainless steel foil with a thickness of about 10 μm to about 15 μm.

[0128] Positive electrode active material layer

[0129] The positive electrode active material layer includes a positive electrode active material and carbon nanotubes, wherein the positive electrode active material includes secondary particles of lithium-nickel composite oxides. The positive electrode active material layer further includes cellulose derivatives, amorphous carbon, or combinations thereof.

[0130] Based on a 100 wt% positive electrode active material layer, the amount of positive electrode active material can be approximately 60 wt% to approximately 99.9 wt%, approximately 70 wt% to approximately 99.8 wt%, approximately 80 wt% to approximately 99 wt%, approximately 90 wt% to approximately 99 wt%, or approximately 95 wt% to approximately 99 wt%. Thus, due to the relatively large amount of positive electrode active material, the energy density can be improved.

[0131] Carbon nanotubes can be uniformly dispersed in the positive electrode active material layer and can also be disposed on the surface of the positive electrode active material.

[0132] When carbon nanotubes are uniformly dispersed in the positive electrode active material and disposed on the surface of the positive electrode active material, the carbon nanotubes are randomly arranged on the surface of the secondary particles of the lithium-nickel composite oxide and connected between the primary particles. For example, carbon nanotubes can exist on the surface of the secondary particles in a three-dimensional network or spider web shape.

[0133] Carbon nanotubes are crystalline carbon materials in which carbon atoms are arranged in a hexagonal pattern to form a tube shape. Carbon nanotubes exhibit excellent electrical conductivity and lithium-ion conductivity. By maintaining a uniform current and voltage distribution within the positive electrode during charge and discharge cycles, cycle characteristics can be significantly improved, and the battery's output characteristics can be enhanced due to the improved conductivity. Because carbon nanotubes consist of carbon atoms with strong covalent bonds, they possess excellent tensile strength and resistance to damage, thus improving battery safety.

[0134] Carbon nanotubes can be provided independently as individual fibers or fiber bundles, and can be provided through point contacts or point-to-surface connections. Furthermore, the carbon nanotubes on the surface of the positive electrode active material can be spaced apart from each other. The arrangement of the carbon nanotubes on the surface of the positive electrode active material is designed to leave sufficient space for lithium ions to move freely between the surface of the positive electrode active material and the electrolyte, thereby ensuring relatively high capacity, high output, and long cycle life characteristics.

[0135] Carbon nanotubes can cover approximately 30% to approximately 80% of the total area of ​​the positive electrode active material. For example, carbon nanotubes can cover approximately 35% to approximately 75%, approximately 40% to approximately 70%, or approximately 45% to approximately 65% ​​of the total area of ​​the positive electrode active material. The area of ​​carbon nanotubes based on the total area of ​​the positive electrode active material can be quantitatively calculated by setting a specific pixel intensity (threshold) in an image of the positive electrode active material taken by a scanning electron microscope, selecting pixels with pixel intensities higher than the specific pixel intensity, and considering the selected pixels as the areas where carbon nanotubes are placed. If the area of ​​carbon nanotubes based on the total area of ​​the positive electrode active material is within this range, dislocation of primary particles (such as gaps between primary particles due to charging and discharging) can be prevented without hindering the movement of lithium ions between the positive electrode active material and the electrolyte. The shape of secondary particles can be maintained, and the shrinkage and expansion of secondary particles and the positive electrode can be suppressed, thereby improving battery cycle life characteristics. For example, if carbon nanotubes cover less than about 30% of the total surface area of ​​the positive electrode active material, the adhesive force of the carbon nanotubes adhering to the surface of the positive electrode active material to maintain its particle shape can be weakened, thereby degrading the battery cycle life characteristics and preventing the formation of a proper conductive network. If carbon nanotubes cover more than 80% of the total surface area of ​​the positive electrode active material, the carbon nanotubes can cover most of the surface of the positive electrode active material, hindering lithium-ion movement and thus degrading battery performance.

[0136] Based on a 100 wt% positive electrode active material layer, the amount of carbon nanotubes included can be from about 0.1 wt% to about 5 wt%. For example, the amount of carbon nanotubes included can be from about 0.1 wt% to about 4 wt%, from about 0.1 wt% to about 3 wt%, from about 0.1 wt% to about 2 wt%, or from about 0.1 wt% to about 1 wt%. Compared with the amount of graphene in known graphene coatings, the amount of carbon nanotubes used according to some embodiments is relatively small, thereby reducing the amount of conductive material in the positive electrode compared to graphene coatings. Advantageously, the energy density of the positive electrode can be improved, and the battery cycle life characteristics can be improved.

[0137] Based on a 100 wt% positive electrode active material layer, the total amount of cellulose derivatives, amorphous carbon, or combinations thereof may be from about 0.01 wt% to about 5 wt%, for example, from about 0.05 wt% to about 4 wt%, from about 0.1 wt% to about 3 wt%, from about 0.1 wt% to about 2 wt%, or from about 0.1 wt% to about 1 wt%. The cellulose derivatives, amorphous carbon, or combinations thereof may be derived from cellulose-based additives in the positive electrode slurry composition used to form the positive electrode active material layer. The total amount may be equal to the amount of cellulose-based additives included in the positive electrode slurry composition.

[0138] Cellulose derivatives can be cellulose additives that do not carbonize even after heat treatment and retain their integrity. Cellulose derivatives contain alkyl groups, and their type is not limited, as long as they contain functional groups capable of hydrogen bonding. Cellulose derivatives may include, for example, ethyl cellulose, cellulose acetate, carboxymethyl cellulose, hydroxypropyl cellulose, methyl cellulose, nitrocellulose, or combinations thereof.

[0139] Amorphous carbon is carbon with no crystallinity or very low crystallinity, and is different from crystalline carbon or graphitic carbon.

[0140] Amorphous carbon can include soft carbon, mesophase pitch carbonization products, and carbides of cellulose derivatives. Soft carbon refers to graphitizable carbon materials, specifically those that have been graphitized by heat treatment at high temperatures (e.g., about 2800°C). Carbides of cellulose derivatives are amorphous carbon materials formed when cellulose-based additives undergo heat treatment or carbonization processes.

[0141] According to some embodiments, amorphous carbon may include carbides of cellulose derivatives. The type of cellulose derivative carbides is not limited, as long as they include alkyl groups and functional groups capable of forming hydrogen bonds. For example, cellulose derivative carbides may include carbides of ethyl cellulose, cellulose acetate, carboxymethyl cellulose, hydroxypropyl cellulose, methyl cellulose, nitrocellulose, or combinations thereof.

[0142] Amorphous carbon can be disposed between lithium-nickel composite oxides and carbon nanotubes. The amorphous carbon acts as a binder, ensuring that the carbon nanotubes can attach to the surface of the lithium-nickel composite oxide, thereby firmly attaching the carbon nanotubes to the lithium-nickel composite oxide, further maintaining the shape of the secondary particles, and inhibiting the shrinkage and expansion of the secondary particles and the positive electrode.

[0143] When both cellulose derivatives and amorphous carbon are included, the weight ratio of cellulose derivatives and amorphous carbon can be about 1:1 to about 1:30, for example, about 1:2 to about 1:20, about 1:3 to about 1:15, or about 1:5 to about 1:10.

[0144] The positive electrode active material layer may optionally include a binder, a conductive material, or a combination thereof.

[0145] Methods for manufacturing positive electrodes

[0146] Embodiments of this disclosure provide a method for manufacturing a positive electrode, the method comprising preparing a positive electrode slurry composition comprising a positive electrode active material, carbon nanotubes and cellulose-based additives, the positive electrode active material comprising secondary particles of lithium-nickel composite oxides; coating the positive electrode slurry composition onto a positive electrode current collector and drying the positive electrode slurry composition; and performing heat treatment.

[0147] A positive electrode slurry composition comprising a positive electrode active material, carbon nanotubes, and cellulose-based additives was prepared. The positive electrode active material included secondary particles of lithium-nickel composite oxides.

[0148] The positive electrode slurry composition can be prepared by mixing secondary particles of lithium nickel composite oxide, carbon nanotubes and cellulose additives in a solvent; or by adding carbon nanotubes and cellulose additives to a solvent to prepare a pre-dispersion, and then adding the pre-dispersion to a slurry containing secondary particles of lithium nickel composite oxide to prepare the positive electrode slurry composition.

[0149] The solvent for the predispersant can be a solvent commonly used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropanol, N-methyl-2-pyrrolidone (NMP), acetone or water, and may use one of them alone or a mixture of two or more of them.

[0150] The positive electrode slurry composition is coated onto the positive electrode current collector and then dried. During the drying step, the solvent in the positive electrode slurry composition can be removed by evaporation. The drying can be carried out at a temperature of about 60°C to about 160°C, for example, about 90°C to about 160°C, about 100°C to about 160°C, or about 100°C to about 140°C.

[0151] Heat treatment is performed.

[0152] The heat treatment can be performed for 10 to 60 minutes at a temperature of approximately 180°C to approximately 300°C under vacuum or in a specific gas atmosphere, where the gas may include oxygen, argon, air, or nitrogen. Through heat treatment, the cellulose-based additives are partially carbonized to form carbides, allowing carbon nanotubes to firmly attach to the surface of the positive electrode active material. Consequently, particle breakage due to the contraction and expansion of the positive electrode active material is prevented even during repeated charge / discharge cycles, thereby improving battery cycle life.

[0153] Rechargeable lithium batteries

[0154] Embodiments of this disclosure provide a rechargeable lithium battery, including a positive electrode, a negative electrode, and an electrolyte. The rechargeable lithium battery may include a positive electrode, a negative electrode, a separator between the positive and negative electrodes, and an electrolyte.

[0155] Depending on their shape, rechargeable lithium batteries can be classified as cylindrical, prismatic, pouch-shaped, or coin-shaped. Figures 1-4 To illustrate a schematic diagram of a rechargeable lithium battery, where Figure 1 Refers to cylindrical batteries. Figure 2 Prismatic battery, and Figure 3 and Figure 4Refers to a pouch-shaped battery. (Reference) Figures 1-4 The rechargeable lithium battery 100 includes an electrode assembly 40 and a housing 50 therein housing the electrode assembly 40. The electrode assembly 40 has a separator 30 inserted between a positive electrode 10 and a negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). Figure 1 As shown, the rechargeable lithium battery 100 may include a sealing member 60 of a sealed housing 50. Figure 2 In this context, the rechargeable lithium battery 100 may include a positive electrode lead connector 11, a positive electrode terminal 12, a negative electrode lead connector 21, and a negative electrode terminal 22. For example... Figure 3 and Figure 4 As shown, the rechargeable lithium battery 100 includes electrode terminals 70, namely, positive electrode terminal 71 and negative electrode terminal 72, which serve as electrical paths for guiding current formed in the electrode assembly 40 to the outside.

[0156] By including a positive electrode, rechargeable lithium batteries can suppress cycle life degradation and improve battery performance.

[0157] negative electrode

[0158] The negative electrode for a rechargeable lithium battery includes a negative electrode current collector and a layer of negative electrode active material on the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material and may optionally include a binder, a conductive material, or a combination thereof.

[0159] The negative electrode current collector is not specifically limited, as long as it is conductive and does not cause harmful chemical changes in the rechargeable lithium battery. The negative electrode current collector may include copper foil with a thickness of about 10 μm to about 15 μm.

[0160] The negative electrode active material may include materials that can reversibly insert / deintercalate lithium ions, lithium metal, lithium metal alloys, materials that can be doped / dedoped with lithium, or transition metal oxides.

[0161] Materials that can reversibly insert / deintercalate lithium ions can include, for example, crystalline carbon, amorphous carbon, or combinations thereof as carbon-based negative electrode active materials. Crystalline carbon can be irregular natural or artificial graphite, or can be in the form of flakes, sheets, spheres, or fibers. Amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbonization products, or calcined coke.

[0162] Lithium metal alloys include alloys of lithium with metals selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0163] The material capable of doping / de-doping lithium can be a Si-based negative electrode active material or a Sn-based negative electrode active material. The Si-based negative electrode active material can include silicon, silicon-carbon composite, SiO x (0 < x ≤ 2, for example, SiO2), Si-Q alloy (where Q is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements (excluding Si), Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, such as Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof) or combinations thereof. The Sn-based negative electrode active material can be Sn, SnO x (0 < x ≤ 2, for example, SnO2), Sn alloy, or combinations thereof.

[0164] The silicon-carbon composite can be a composite of silicon and amorphous carbon. The average particle size (D 50 ) of the silicon-carbon composite particles can be, for example, about 0.5 μm to about 20 μm. According to some embodiments, the silicon-carbon composite can be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, it can include secondary particles (cores) in which primary silicon particles are aggregated and an amorphous carbon coating (shell) on the surface of the secondary particles. Amorphous carbon can also be present between the primary silicon particles. For example, the primary silicon particles can be coated with amorphous carbon. The secondary particles can be dispersed in the amorphous carbon matrix.

[0165] The silicon-carbon composite can include crystalline carbon. For example, the silicon-carbon composite can include: a core including crystalline carbon and silicon particles and an amorphous carbon coating on the surface of the core. The crystalline carbon can be artificial graphite, natural graphite, or combinations thereof. The amorphous carbon can include soft carbon, hard carbon, mesophase pitch carbonized products, and calcined coke.

[0166] When the silicon-carbon composite includes silicon and amorphous carbon, based on 100 wt% of the silicon-carbon composite, the silicon content can be about 10 wt% to about 50 wt%, and the amount of amorphous carbon can be about 50 wt% to about 90 wt%. When the silicon-carbon composite includes silicon, amorphous carbon, and crystalline carbon, based on 100 wt% of the silicon-carbon composite, the silicon content can be about 10 wt% to about 50 wt%, the amount of crystalline carbon can be about 10 wt% to about 70 wt%, and the amount of amorphous carbon can be about 20 wt% to about 40 wt%.

[0167] The thickness of the amorphous carbon coating can be about 5 nm to about 100 nm. The average particle size (D50 It can be from about 10 nm to about 1 μm or from about 10 nm to about 200 nm. The silicon particles can exist alone as silicon, in the form of a silicon alloy, or in the oxidized form of silicon. The oxidized form of silicon can be represented by SiO x (0 < x ≤ 2). The atomic content ratio of Si:O indicating the degree of oxidation can be from about 99:1 to about 33:67. As used herein, when not otherwise limited, the average particle size (D 50 ) indicates the diameter of the particles in the particle distribution where the cumulative volume is about 50% by volume.

[0168] The Si-based negative electrode active material or the Sn-based negative electrode active material can be mixed with the carbon-based negative electrode active material. When mixing and using the Si-based negative electrode active material or the Sn-based negative electrode active material and the carbon-based negative electrode active material, the mixing ratio can be a weight ratio of from about 1:99 to about 90:10.

[0169] Based on 100 wt% of the negative electrode active material layer, the amount of the negative electrode active material included can be from about 90 wt% to about 99.8 wt% or from about 94 wt% to about 99 wt%.

[0170] The binder is used to bond the negative electrode active material particles to each other and to bond the negative electrode active material to the negative electrode current collector. The binder can be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0171] The non-aqueous binder can include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0172] The aqueous binder can include styrene-butadiene rubber, (meth)acrylate-modified styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, epichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, or a combination thereof.

[0173] When the aqueous binder is used as the electrode binder in the negative active material layer, a cellulose-based compound capable of imparting viscosity can be further included. As the cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and their alkali metal salts can be mixed and used. The alkali metal can be Na, K, or Li.

[0174] Dry adhesives can be polymeric materials that can be turned into fibers, and can be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or combinations thereof.

[0175] This includes conductive materials to provide electrode conductivity, and any conductive material can be used as a conductive material unless it causes a chemical change. Examples of conductive materials include carbon-based materials (such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, carbon nanotubes, etc.); metallic materials including metal powders or fibers of copper, nickel, aluminum, or silver; conductive polymers (such as polyphenylene derivatives); or mixtures thereof.

[0176] Based on a 100 wt% negative electrode active material layer, the amount of binder can be from about 0.1 wt% to about 5 wt%, and based on a 100 wt% negative electrode active material layer, the amount of conductive material can be from about 0.1 wt% to about 5 wt%.

[0177] electrolyte

[0178] Electrolytes used in rechargeable lithium batteries may be electrolytes that include non-aqueous organic solvents and lithium salts.

[0179] Non-aqueous organic solvents are used as media for transporting ions that participate in the electrochemical reactions of a battery. Non-aqueous organic solvents may include carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, aprotic solvents, or combinations thereof.

[0180] Carbonate solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate (BC). Ester solvents may include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolactone, mevalonolactone, valproic acid lactone, or caprolactone. Ether solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, or tetrahydrofuran. Ketone solvents may include cyclohexanone. Alcohol solvents may include ethanol or isopropanol. Aprotic solvents may include nitriles (such as R-CN, where R is a C2-C20 straight-chain hydrocarbon group, branched hydrocarbon group, or cyclic hydrocarbon group, and may include double bonds, aromatic rings, or ether bonds); amides (such as dimethylformamide); dioxolane (such as 1,3-dioxolane or 1,4-dioxolane); or sulfolane.

[0181] A single non-aqueous organic solvent or a mixture of two or more types of non-aqueous organic solvents may be used. When using two or more types in a mixture, the mixing ratio may be appropriately adjusted according to the desired battery performance.

[0182] When using carbonate solvents, cyclic carbonates and chain carbonates can be mixed and used. Cyclic carbonates and chain carbonates can be mixed in a volume ratio of about 1:1 to about 1:9.

[0183] Non-aqueous organic solvents may include aromatic hydrocarbon organic solvents. For example, carbonate solvents and aromatic hydrocarbon organic solvents may be mixed in a volume ratio of about 1:1 to about 30:1.

[0184] Electrolytes may include vinyl ethylene carbonate, vinylene carbonate, or ethylene carbonate compounds to improve battery cycle life.

[0185] Examples of ethylene carbonate compounds may include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, or cyanoethylene carbonate.

[0186] Lithium salts dissolved in non-aqueous organic solvents supply lithium ions in batteries, ensuring basic operation of rechargeable lithium batteries and improving lithium ion transport between the positive and negative electrodes. Examples of lithium salts may include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide; LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 (SO2) (where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFBOP) or lithium bis(oxalate)borate (LiBOB).

[0187] The concentration of lithium salt can be in the range of about 0.1 M to about 2.0 M. This results in an electrolyte with suitable ionic conductivity and viscosity, thus enabling excellent performance and efficient movement of lithium ions.

[0188] diaphragm

[0189] Depending on the type of rechargeable lithium battery, a separator may be present between the positive and negative electrodes. The separator may include a polyethylene separator, a polypropylene separator, a polyvinylidene fluoride separator, or a multilayer membrane of two or more layers thereof (such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polypropylene three-layer separator, a polypropylene / polypropylene / polypropylene three-layer separator, etc.).

[0190] The diaphragm may include a porous substrate and a coating on one or both surfaces of the porous substrate, comprising organic materials, inorganic materials or combinations thereof.

[0191] The porous substrate may be made of a material selected from polyolefins (such as polyethylene and polypropylene), polyesters (such as polyethylene terephthalate and polybutylene terephthalate), polyacetal, polyamide, polyimide, polycarbonate, polyetherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene ether, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fiber, and polytetrafluoroethylene (e.g., TEFLON). ® Polymer films formed from any one of the polymers or copolymers or mixtures thereof.

[0192] The porous substrate may have a thickness of about 1 μm to about 40 μm, for example, about 1 μm to about 30 μm, about 1 μm to about 20 μm, about 5 μm to about 15 μm or about 10 μm to about 15 μm.

[0193] Organic materials may include (meth)acrylic acid copolymers, which include a first structural unit and a second structural unit, wherein the first structural unit is derived from (meth)acrylamide, and the second structural unit includes at least one structural unit derived from (meth)acrylic acid or (meth)acrylate and a structural unit derived from (meth)acrylamide sulfonic acid or a salt thereof.

[0194] Inorganic materials may include, but are not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof. The average particle size (D) of the inorganic particles... 50 The range can be approximately 1 nm to approximately 2000 nm, for example, approximately 100 nm to approximately 1000 nm or approximately 100 nm to approximately 700 nm.

[0195] Organic and inorganic materials can be mixed in a coating, or coatings containing organic materials and coatings containing inorganic materials can be stacked.

[0196] The coating thickness can be from about 0.5 μm to about 20 μm, for example, from about 1 μm to about 10 μm or from about 1 μm to about 5 μm.

[0197] Example

[0198] The following embodiments are merely examples of this disclosure, and this disclosure is not limited to the following embodiments.

[0199] Example 1

[0200] (1) Manufacturing of the positive electrode

[0201] The positive electrode active material comprises particles with an average particle size (D) of approximately 700 nm. 50 The primary particles formed include lithium-nickel composite oxides LiNi. 0.91 Co 0.08 Al 0.01 O2 and has an average particle size of approximately 15 μm (D 50 Secondary particles of lithium-nickel composite oxide were used. Multi-walled carbon nanotubes with an average aspect ratio of approximately 15,000 and an average diameter of approximately 5 nm were used as carbon nanotubes. Ethyl cellulose was used as a cellulose-based additive. Polyvinylidene fluoride was used as a binder. The lithium-nickel composite oxide, carbon nanotubes, cellulose-based additive, and binder were mixed in a weight ratio of 98.5:0.25:0.25:1 to obtain a mixture. The mixture was added to an N-methyl-2-pyrrolidone solvent and mixed using a centrifugal mixer to prepare a positive electrode slurry composition.

[0202] The positive electrode slurry composition was adjusted to have a solids content of approximately 70%.

[0203] The positive electrode slurry composition was coated onto aluminum foil using a scraper and dried in a convection oven at 120°C for 20 minutes to remove N-methyl-2-pyrrolidone.

[0204] The electrode was obtained by removing the solvent through heat treatment at 250°C using a tube furnace. The specific details of this heat treatment are as follows: heat treatment was carried out in an argon atmosphere by increasing the temperature at 5°C / min and maintaining the temperature at 250°C for 10 minutes.

[0205] The electrode was compressed at a slurry density of 3 g / cc to fabricate a positive electrode with a positive electrode active material layer formed on an aluminum foil. The positive electrode active material contained 98.5 wt% carbon nanotubes, 0.25 wt% amorphous carbon, 0.225 wt% cellulose derivatives, and 1 wt% binder. The slurry was compressed at approximately 5 mg / cm³. 2 The loading level forms the positive electrode active material layer.

[0206] (2) Manufacturing of rechargeable lithium battery cells

[0207] Using the aforementioned positive electrode, lithium metal as the negative electrode, and glass fiber filter paper as the separator, the separator is inserted between the two electrodes to create an electrode assembly inserted into the casing. Electrolyte is injected into the casing to manufacture a 2032-coin cell as a rechargeable lithium battery cell. The electrolyte is prepared by adding 3 wt% VC (ethylene carbonate) to a mixed solvent of EC (ethylene carbonate):MEC (methyl ethyl carbonate):DMC (dimethyl carbonate) in a volume ratio of 3:3:4, and dissolving 1 M LiPF6 therein.

[0208] Example 2

[0209] The positive electrode and rechargeable lithium battery cell were manufactured in a similar manner to those in Example 1, except that the positive electrode active material layer of Example 1 had a concentration of 25 mg / cm³. 2 The load level.

[0210] Comparative Example 1

[0211] The positive electrode and rechargeable lithium battery cell were manufactured in a similar manner to those in Example 1, except that the positive electrode slurry composition was prepared by mixing the same positive electrode active material, Super P as a conductive material, and polyvinylidene fluoride as a binder in a weight ratio of 98.75:0.25:1.

[0212] Comparative Example 2

[0213] The positive electrode and rechargeable lithium battery cell were manufactured in a manner similar to that in Comparative Example 1, except that they were dried but not subjected to heat treatment after drying.

[0214] Reference Example 1

[0215] The positive electrode and rechargeable lithium battery cell were manufactured in a similar manner to that in Example 1, except that the positive electrode active material, carbon nanotubes and binder were mixed in a weight ratio of 98.75:0.25:1 without the addition of cellulose-based additives.

[0216] See Example 2

[0217] The positive electrode and rechargeable lithium battery cell are manufactured in a similar manner to those in Reference Example 1, except that the positive electrode active material layer of Reference Example 1 has a concentration of 25 mg / cm³. 2 The load level.

[0218] See Example 3

[0219] The positive electrode and rechargeable lithium battery cell were manufactured in a manner similar to that in Example 1, except that they were dried but without post-drying heat treatment. The positive electrode active material layer comprises 98.5 wt% positive electrode active material, 0.25 wt% carbon nanotubes, 0.25 wt% cellulose derivatives, and 1 wt% binder.

[0220] Evaluation Example 1: Evaluation of the Dispersibility of Carbon Nanotubes

[0221] To evaluate the dispersibility of carbon nanotubes dependent on cellulose-based additives, each slurry composition was prepared in a manner similar to that in Example 1 and Reference Example 1, except that no positive electrode active material was added. The slurry compositions were coated onto aluminum foil and then dried and heat-treated. SEM images of the samples were taken to evaluate the dispersibility of the carbon nanotubes.

[0222] Figure 5 SEM images of the sample are shown. Figure 5 a) and b) show samples with added cellulose additives, and Figure 5 c) and d) show samples without added cellulose additives.

[0223] refer to Figure 5 In the sample with added cellulose additives ( Figure 5 a) and the sample without added cellulose additives ( Figure 5 In c), carbon nanotube aggregation was observed on the surface. Figure 5 b) shows a magnified image of a), confirming that the carbon nanotubes are relatively uniformly dispersed across the entire surface of the aluminum foil. Figure 5 Image d) shows a magnified image of image c), confirming that the carbon nanotubes were not uniformly dispersed but rather aggregated on the surface of the aluminum foil. Correspondingly, it was confirmed that the dispersibility of the carbon nanotubes was improved by adding cellulose-based additives. The carbon nanotubes were uniformly dispersed on the surface of the positive electrode.

[0224] Evaluation Example 2: Evaluation of the surface and cross-section of the positive electrode

[0225] SEM images of the surfaces of the positive electrodes according to Example 1 and Reference Example 1 were taken to evaluate how carbon nanotubes adhere to the surface of the positive electrode active material. SEM images of cross-sections of the positive electrodes of Example 2 and Reference Example 2 were taken to evaluate how carbon nanotubes adhere to the surface of the positive electrode active material.

[0226] Figure 6 A photograph showing the surface of the positive electrode according to Example 1 and Reference Example 1. Figure 6 a) and Figure 6 b) shows the surface of the positive electrode of Example 1 at different magnifications. Figure 6 c) and Figure 6d) shows the surface of the positive electrode of Reference Example 1 at different magnifications.

[0227] refer to Figure 6 a) and Figure 6 Example 1 (b) illustrates the selective adhesion of carbon nanotubes to the surface of the positive electrode active material using a positive electrode slurry composition with added cellulose additives. (See reference...) Figure 6 c) and Figure 6 (d) Reference Example 1, without the addition of cellulose-based additives, shows that carbon nanotubes did not selectively adhere to the surface of the positive electrode active material. Example 1 demonstrates that a greater amount of carbon nanotubes than in Reference Example 1 adhered to the surface of the positive electrode active material. Accordingly, it is confirmed that the cellulose-based additives played a role in selectively coating the carbon nanotubes.

[0228] Figure 7 These are cross-sectional photographs of the positive electrode of Example 2 and Reference Example 2 at different magnifications. Figure 7 a) and Figure 7 b) shows the cross-section of the positive electrode of Example 2 at different magnifications, and Figure 7 The two lower images show the cross-section of the positive electrode of Reference Example 2 at different magnifications.

[0229] refer to Figure 7 a) and Figure 7 Example 2, using a positive electrode slurry composition prepared by adding cellulose-based additives, demonstrates that carbon nanotubes are selectively coated onto the surface of the positive electrode active material without agglomerating on the upper part of the electrode. This is because the carbon nanotubes are bound to the binder, which inhibits their arrangement. (See reference...) Figure 7 c) and Figure 7 (d) Reference Example 2, without the addition of cellulose-based additives, shows that carbon nanotubes were not selectively coated on the surface of the positive electrode active material, but rather aggregated on the upper part of the electrode. Accordingly, it was confirmed that cellulose-based additives selectively coated carbon nanotubes even at relatively high loading levels, increasing the dispersibility of the carbon nanotubes.

[0230] Evaluation Example 3: Evaluation of the adhesive strength of heat-treated carbon nanotubes

[0231] The adhesiveness of the carbon nanotubes of the positive electrodes of Example 1 and Reference Example 3 was evaluated before ultrasonic treatment and after ultrasonic treatment for 1 minute, 3 minutes and 5 minutes by using a scraper or knife to extract the positive electrode active material and adding the extracted positive electrode active material to N-methyl-2-pyrrolidone solvent to prepare a solution.

[0232] Figure 8A photograph shows the adhesion of carbon nanotubes to the positive electrode active material extracted from the positive electrodes of Example 1 and Reference Example 3. Figure 8 From left to right, the tests are shown in sequence: no sonication (after standing for 30 minutes), 1 minute of sonication, 3 minutes of sonication, and 5 minutes of sonication. In each test, samples were prepared by adding the positive electrode active material extracted from the positive electrode of Reference Example 3 to an N-methyl-2-pyrrolidone solvent, and by adding the positive electrode active material extracted from the positive electrode of Example 1 to an N-methyl-2-pyrrolidone solvent.

[0233] refer to Figure 8 In Example 1, the surface of the heat-treated positive electrode active material was firmly bonded with carbon nanotubes, preventing them from separating even under ultrasonic treatment. In contrast, the untreated positive electrode active material according to Reference Example 3 showed that, when using an ultrasonic processor, the carbon nanotubes further separated over time and gradually turned black.

[0234] Evaluation Example 4: Evaluation of the cycle life of a rechargeable lithium battery cell

[0235] The cycle life of the rechargeable lithium battery cells of Example 1, Reference Example 3, Comparative Example 1 and Comparative Example 2 was evaluated.

[0236] At 25°C, a rechargeable lithium-ion battery cell is charged to 4.3 V at a constant current of 0.1 C, and then continuously charged to 0.05 C while maintaining a constant voltage of 4.3 V. The rechargeable lithium-ion battery cell is then discharged to 3 V at 0.1 C, and this charge-discharge cycle is repeated twice.

[0237] Under the same conditions, the cycle life was evaluated by repeating the charge and discharge cycles 100 times with the current changed to 1 C only, and the discharge capacity retention rate was measured. The results are shown in... Figure 9 middle.

[0238] refer to Figure 9Compared to Reference Example 3 using carbon nanotubes, Comparative Example 2 using Super P showed a rapid decrease in discharge capacity (38.09%) over cycling. Even with the same amount of carbon nanotubes and Super P, when Super P was used as the conductive material, the conductive network could not be adequately maintained during cycling, leading to a rapid decrease in capacity. That is, to achieve a conductive network comparable to that formed by carbon nanotubes, a larger amount of Super P is required when using Super P as the conductive material. As a result, compared to Comparative Example 2 using the same amount of Super P, Reference Example 3 using the same amount of carbon nanotubes as Comparative Example 2 showed an improvement in cycle life characteristics equal to or greater than about 25% based on 100 cycles, presumably because a stable conductive network was formed even with a relatively small amount of carbon nanotubes compared to the amount of Super P.

[0239] Even under heat treatment conditions, Comparative Example 1, which used Super P as the conductive material, exhibited a rapid decrease in discharge capacity (41.25%) as cycling progressed. This is presumably because the amount of Super P was too low, leading to rapid degradation, and also because the absence of ethyl cellulose (a cellulose-based additive) hindered the effective enhancement of the conductive material's adhesion by heat treatment.

[0240] On the other hand, compared with Reference Example 3 (66.68%) which did not undergo heat treatment, Example 1 (81.61%) which underwent heat treatment showed an improvement of approximately 15% in cycle life characteristics. This is presumably because when carbon nanotubes are used as conductive materials, heat treatment causes the carbon nanotubes to adhere more firmly to the surface of the positive electrode active material, thereby maintaining a stable conductive network even as cycling progresses.

[0241] Although this disclosure has been described in conjunction with embodiments now regarded as practice, it should be understood that the invention is not limited to the disclosed embodiments, but rather is intended to cover various modifications and equivalent arrangements included within the spirit and scope of this disclosure.

Claims

1. A positive electrode paste composition, comprising: A positive electrode active material, comprising secondary particles of a lithium nickel-based composite oxide; Carbon nanotubes; And A cellulose-based additive.

2. The positive electrode paste composition according to claim 1, wherein the lithium nickel-based composite oxide is represented by Chemical Formula 1: Chemical Formula 1 Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1 , in, 0.9 ≤ a1 ≤ 1.2, 0.8 ≤ x1 < 1, 0 < y1 ≤ 0.2, 0 ≤ z1 ≤ 0.2, 0.9 ≤ x1 + y1 + z1 ≤ 1.1 and 0 ≤ b1 ≤ 0.1, Where M 1 and M 2 Each is independently selected from one or more elements chosen from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr. where X is one or more elements selected from F, P, and S.

3. The positive electrode paste composition according to claim 1, wherein based on 100 mol% of the total metals other than lithium, the lithium nickel-based composite oxide has a nickel content of 80 mol% or more.

4. The positive electrode slurry composition according to claim 1, wherein the secondary particles aggregate a plurality of primary particles and the average particle size D of the secondary particles is... 50 The size ranges from 2 μm to 20 μm, and The average particle size D of the primary particles 50 Less than or equal to 6 μm.

5. The positive electrode paste composition according to claim 1, wherein the carbon nanotubes include single-walled carbon nanotubes, multi-walled carbon nanotubes, or a combination thereof.

6. The positive electrode paste composition according to claim 1, wherein the average diameter of the carbon nanotubes is 0.8 nm to 100 nm, and where the average aspect ratio of the carbon nanotubes is 100 to 500,000.

7. The positive electrode paste composition according to claim 1, wherein the cellulose-based additive includes ethyl cellulose, cellulose acetate, carboxymethyl cellulose, hydroxypropyl cellulose, methyl cellulose, nitrocellulose, or a combination thereof.

8. The positive electrode paste composition according to claim 1, wherein based on 100 wt% of the total solid content of the positive electrode paste composition, the content of the lithium nickel-based composite oxide is 90 wt% to 99 wt%, where based on 100 wt% of the total solid content of the positive electrode paste composition, the content of the carbon nanotubes is 0.1 wt% to 5 wt%, and where based on 100 wt% of the total solid content of the positive electrode paste composition, the content of the cellulose-based additive is 0.01 wt% to 5 wt%.

9. The positive electrode paste composition according to claim 1, wherein the weight ratio of the carbon nanotubes to the cellulose-based additive is 10:1 to 1:

5.

10. The positive electrode paste composition according to claim 1, further comprising a binder, a conductive material, or a combination thereof.

11. A positive electrode, comprising: A positive electrode current collector; And A positive electrode active material layer provided on the positive electrode current collector and comprising: A positive electrode active material containing secondary particles of a lithium nickel-based composite oxide; Carbon nanotubes; and A cellulose derivative, amorphous carbon, or a combination thereof.

12. A method for manufacturing a positive electrode, comprising: Preparing a positive electrode paste composition, the positive electrode paste composition comprising a positive electrode active material, carbon nanotubes, and a cellulose-based additive, the positive electrode active material comprising secondary particles of a lithium nickel-based composite oxide; Coating the positive electrode paste composition on a positive electrode current collector and drying the positive electrode paste composition; and Performing a heat treatment.

13. The method of claim 12, wherein preparing the positive electrode slurry composition comprises: The secondary particles of the lithium-nickel composite oxide, the carbon nanotubes, and the cellulose-based additives are mixed in a solvent.

14. The method of claim 12, wherein the preparation of the positive electrode slurry composition comprises; The carbon nanotubes and the cellulose-based additives are added to a solvent to form a pre-dispersion, and The pre-dispersion is added to the slurry comprising the secondary particles of the lithium-nickel composite oxide.

15. The method according to claim 12, wherein the drying is performed at a temperature of 60°C to 160°C.

16. The method according to claim 12, wherein the heat treatment is performed at 180°C to 300°C.

17. The method according to claim 12, wherein the heat treatment is performed for 10 to 60 minutes.

18. The method of claim 12, wherein the heat treatment is performed under vacuum or in an atmosphere comprising gas.

19. The method of claim 18, wherein the gas comprises oxygen, argon, air or nitrogen.

20. A rechargeable lithium battery, comprising: A positive electrode prepared using the positive electrode slurry composition according to any one of claims 1 to 10, a positive electrode according to claim 11, or a positive electrode prepared by the method according to any one of claims 12 to 19; negative electrode; and Electrolyte.

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