Positive electrode and rechargeable lithium battery including same

Abstract

Disclosed are a positive electrode and a rechargeable lithium battery including the same. The positive electrode includes a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector and including a positive electrode active material and a conductive material. The positive electrode active material includes a layered lithium nickel manganese-based composite oxide. The positive electrode may obtain a reduced amount of a required conductive material using only information of a positive electrode active material, thereby achieving high capacity and low mixture resistance, thereby enabling a long cycle life.

Description

Technical Field

[0001] A positive electrode and a rechargeable lithium battery including the positive electrode are disclosed. Background Technology

[0002] Portable information devices (such as cellular phones, laptops, and smartphones) or electric vehicles and other devices typically use rechargeable lithium batteries with high energy density and portability as their power source. Therefore, it may be advantageous to produce rechargeable lithium batteries with high energy density as a power source or energy storage source for hybrid or electric vehicles.

[0003] Various positive electrode active materials and conductive materials have been studied to produce rechargeable lithium batteries for the applications discussed above. Here, the desired amount of conductive material can be determined by measuring the resistance of an electrode plate obtained by coating a slurry onto a substrate and pressing it, or by solidifying the slurry into powder and measuring the resistance of the powder. However, determining the resistance of the electrode plate or powder each time a slurry is prepared is typically inefficient.

[0004] Therefore, it may be advantageous to obtain the desired amount of conductive material by using only the basic information of the positive electrode active material. Summary of the Invention

[0005] A method is provided for obtaining a minimum or reduced amount of a desired conductive material using only information about the positive electrode active material, and a positive electrode and a rechargeable lithium battery using the method are also provided.

[0006] In some example embodiments, the positive electrode includes a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector and comprising a positive electrode active material and a conductive material. The positive electrode active material comprises a layered lithium-nickel-manganese composite oxide, and in the positive electrode active material layer, the positive electrode active material and the conductive material satisfy the following Equation 1.

[0007] Equation 1: y=1.0923x 2 +0.102x+0.7471.

[0008] In Equation 1, x is the specific surface area of ​​the positive electrode active material, 0.13≤x≤0.63, and y is the content of conductive material based on 100wt% of the positive electrode active material layer.

[0009] In some example embodiments, the method for manufacturing a positive electrode includes the following steps: i) measuring the average particle size (D0) of the positive electrode active material comprising layered lithium-nickel-manganese composite oxides using a particle size analyzer. 50 ); ii) Assuming the positive electrode active material is spherical, use the average particle size (D).50 iii) Calculate the specific surface area of ​​the positive electrode active material; iv) Substitute the specific surface area of ​​the positive electrode active material into Equation 1 to obtain the minimum or reduced content of the conductive material; and iv) Form a positive electrode active material layer on the positive electrode current collector, including the positive electrode active material and the minimum or reduced content of the conductive material.

[0010] Equation 1: y=1.0923x 2 +0.102x+0.7471.

[0011] In Equation 1, x is the specific surface area of ​​the positive electrode active material, 0.13≤x≤0.63, and y is the content of conductive material based on 100wt% of the positive electrode active material layer.

[0012] An example embodiment includes a rechargeable lithium battery comprising a positive electrode, a negative electrode, and an electrolyte solution.

[0013] According to some example embodiments, the positive electrode can use only information about the positive electrode active material to obtain a minimum or reduced amount of the desired conductive material, thereby achieving high capacity and low mixture resistance, and enabling long cycle life. Attached Figure Description

[0014] Figures 1 to 4 This is a schematic diagram illustrating a lithium rechargeable battery according to some example embodiments.

[0015] Figure 5 This is a graph showing the particle size distribution of a particle size analyzer (PSA) based on the content of conductive material in Example 2.

[0016] Figure 6 This is a graph showing the PSA particle size distribution based on the content of conductive material in Example 3.

[0017] Figure 7 This is a graph showing the PSA particle size distribution based on the content of conductive material in Example 4.

[0018] Figure 8 It is a graph showing the amount of conductive material with the expected specific surface area of ​​the positive electrode active material according to Examples 1 to 6.

[0019] Figure 9 This is a flowchart illustrating a method for manufacturing a positive electrode according to an example embodiment. Detailed Implementation

[0020] Example embodiments are described in detail below to enable those skilled in the art to readily implement them. However, this disclosure may be implemented in many different forms and is not to be construed as limited to the example embodiments set forth herein.

[0021] The terminology used herein is for describing exemplary embodiments only and is not intended to limit this disclosure. Unless the context clearly specifies otherwise, singular expressions include plural expressions.

[0022] As used herein, “combination of them” refers to mixtures, laminates, complexes, copolymers, alloys, blends, reaction products, etc. of the components.

[0023] It is understood here that terms such as “comprising,” “including,” or “having” are intended to indicate the presence of features, quantities, steps, elements, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, quantities, steps, elements, or combinations thereof.

[0024] In the accompanying drawings, for clarity, the thickness of layers, films, panels, regions, etc., may be exaggerated, and the same reference numerals denote the same elements throughout the specification. It is understood that when an element such as a layer, film, region, or substrate is referred to as being "on" another element, the element may be "directly on" the other element, or an intervening element may be present. Conversely, when an element is referred to as being "directly on" another element, no intervening element is present.

[0025] The term "layer" here 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.

[0026] The average particle size can be measured using methods known to those skilled in the art (e.g., by a particle size analyzer or by transmission electron microscopy or scanning electron microscopy images). Alternatively, it can be measured using dynamic light scattering, performing data analysis, counting the number of particles in each particle size range, and thereby calculating the average particle size value. Unless otherwise defined, the average particle size (D...) 50 The particle size distribution (D) can represent the diameter of particles having a cumulative volume of 50% of the total volume. As used herein, unless otherwise defined, the average particle size (D) is... 50 () represents the diameter of particles with a cumulative volume of 50% 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.

[0027] Here, "or" is not interpreted as having an exclusive meaning. For example, "A or B" is interpreted as including A, B, A+B, etc.

[0028] The term "metal" is interpreted as encompassing common metals, transition metals, and metalloids (semi-metals).

[0029] When the terms “about” or “substantially” are used in conjunction with numerical values ​​in this specification, it is intended that the relevant numerical value include a tolerance of ±10% around the stated value. When a range is specified, the range includes all values ​​within it, such as increments of 0.1%.

[0030] positive electrode In some example embodiments, the positive electrode includes: a positive electrode current collector; and a positive electrode active material layer located on the positive electrode current collector and comprising the positive electrode active material and a conductive material. The positive electrode active material comprises a layered lithium-nickel-manganese composite oxide, and in the positive electrode active material layer, the positive electrode active material and the conductive material satisfy Equation 1 below.

[0031] Equation 1: y=1.0923x 2 +0.102x+0.7471.

[0032] In Equation 1, x is the specific surface area (m²) of the active material of the positive electrode. 2 / g), 0.13≤x≤0.63, and y is based on the content of conductive material in the 100wt% positive electrode active material layer (wt%).

[0033] The positive electrode active material layer includes a positive electrode active material and a conductive material, wherein the conductive material can be included in a desired amount relative to the content of the positive electrode active material, and is used to reduce the resistance of the positive electrode, thereby achieving high capacity and long cycle life. At this point, the desired amount of conductive material can be determined by measuring the resistance of the electrode plate obtained by coating the slurry onto a substrate and pressing it, or by curing the slurry into powder and measuring the resistance of the powder. However, determining the powder resistance or electrode plate resistance each time a slurry is prepared may be inefficient.

[0034] According to some example embodiments, the positive electrode can enable the desired minimum or reduced content of conductive material to be obtained by using information about the positive electrode active material alone, thereby achieving high capacity and low mixture resistance for long cycle life.

[0035] Furthermore, because the desired minimum or reduced content of conductive material varies depending on the type of positive electrode active material applied to the positive electrode, obtaining the desired content of conductive material each time can be challenging based on the composition or characteristics of the positive electrode active material. In positive electrodes employing positive electrode active materials including layered lithium-nickel-manganese composite oxides, some example embodiments involve simply obtaining a minimum or reduced content of conductive material and adding it to maximize or improve capacity and energy density while reducing resistance, thereby improving the overall performance of the positive electrode. Some example embodiments can reduce or prevent problems such as deterioration of electronic conductivity or increased resistance due to insufficient conductive material content in the positive electrode, and also effectively reduce or prevent another problem of capacity and energy density deterioration due to excessive or excessive addition of conductive material, preventing the positive electrode active material from being included at its maximum content.

[0036] Positive electrode active material The recent sharp rise in the price of the rare metal cobalt has created a demand for the development of positive electrode active materials that exclude or reduce cobalt content. Among these, positive electrode active materials with olivine crystal structures (such as lithium iron phosphate (LFP), lithium manganese phosphate (LMP), and lithium manganese iron phosphate (LMFP)) or spinel crystal structures (such as lithium manganese oxide (LMO)) are limited in achieving high capacities due to their low available lithium content. Layered lithium-nickel-manganese positive electrode active materials, due to their high available lithium content, exhibit desirable or improved capacity and efficiency characteristics, making them suitable as materials for high-capacity batteries. However, removing cobalt, which plays a crucial role in the layered structure, reduces structural stability, increases resistance, and makes it difficult to ensure long cycle life characteristics. Furthermore, layered lithium-nickel-manganese positive electrode active materials that exclude cobalt may exhibit accelerated side reactions with the electrolyte under high voltage and high temperature conditions, resulting in increased gas generation and deterioration of cycle life characteristics.

[0037] Therefore, in some example embodiments, a method is proposed to improve capacity and cycle life characteristics by using lithium nickel manganese composite oxides as positive electrode active materials and by measuring the specific surface area of ​​the positive electrode active materials to obtain the minimum or reduced amount of the desired conductive material.

[0038] In layered lithium-nickel-manganese composite oxides, based on 100 mol% of total metals excluding lithium, the nickel content can be greater than or equal to about 60 mol%, for example, about 60 mol% to about 80 mol%, about 65 mol% to about 80 mol%, about 70 mol% to about 80 mol%, about 60 mol% to about 79 mol%, about 60 mol% to about 78 mol%, or about 60 mol% to about 75 mol%. When the nickel content meets the above range, high capacity can be achieved and structural stability can be increased even when the cobalt content is reduced.

[0039] Based on 100 mol% of total metals other than lithium in layered lithium-nickel-manganese composite oxides, the manganese content can be, for example, greater than or equal to about 15 mol%, such as about 15 mol% to about 40 mol%, about 15 mol% to about 35 mol%, about 15 mol% to about 30 mol%, or about 20 mol% to about 30%. When the manganese content meets the above range, the positive electrode active material can improve structural stability while achieving high capacity.

[0040] Lithium-nickel-manganese composite oxides can be lithium-nickel-manganese-aluminum composite oxides, which include aluminum in addition to nickel and manganese. When the composite oxide includes aluminum, it is beneficial to maintain a stable layered structure even when cobalt is excluded from the structure. The aluminum content of 100 mol% lithium-nickel-manganese-aluminum composite oxides can be greater than or equal to about 0.1 mol%, greater than or equal to about 0.5 mol%, or greater than or equal to about 1 mol%, for example, about 1 mol% to about 3 mol%, about 1 mol% to about 2.5 mol%, about 1 mol% to about 2 mol%, or about 1.5 mol% to about 2.5 mol%. When the aluminum content meets the above ranges, a stable layered structure can be maintained even when cobalt is excluded, which can reduce or suppress the problem of structural collapse due to charging and discharging, and can achieve long cycle life characteristics of the positive electrode active material.

[0041] According to some example embodiments, the aluminum concentration in particles comprising lithium nickel manganese-based composite oxides can be substantially uniform. In other words, this indicates that there is essentially no aluminum concentration gradient from the center to the surface within the particle, or that the aluminum concentration on the outside of the particle is neither higher nor lower than the aluminum concentration on the inside, and that the aluminum within the particle is substantially uniformly distributed. This can be a structure obtained by using an aluminum feedstock during precursor production to synthesize a composite oxide using nickel manganese aluminum hydroxide as a precursor, without additional aluminum doping during the synthesis of the lithium nickel manganese-based composite oxide. The particles can take the form of secondary particles in which multiple primary particles are aggregated, and the aluminum content within the primary particles can be identical or similar, regardless of the location of the primary particles. In other words, when a primary particle can be selected at any location on the profile of the secondary particle to measure the aluminum content inside the primary particle rather than on the surface of the primary particle, the aluminum content can be expressed as identical / similar / uniform, regardless of the location of the primary particle (i.e., whether the primary particle is near the center or near the surface of the secondary particle). In this structure, a stable layered structure can be maintained even when cobalt is absent or present in very small amounts, and no aluminum byproducts or aluminum aggregates are generated, which can improve the capacity, efficiency and cycle life characteristics of the positive electrode active material.

[0042] Layered lithium-nickel-manganese composite oxides can be represented by chemical formula 1.

[0043] Chemical Formula 1: Li a1 Ni x1 Mn y1 Al z1 M 1 w1 O 2-b1 X b1 .

[0044] In chemical formula 1, 0.9 ≤ a1 ≤ 1.8, 0.6 ≤ x1 ≤ 0.8, 0.1 ≤ y1 ≤ 0.4, 0 ≤ z1 ≤ 0.03, 0 ≤ w1 ≤ 0.3, 0.9 ≤ x1 + y1 + z1 + w1 ≤ 1.1, and 0 ≤ b1 ≤ 0.1, M 1 X is or includes one or more of B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zr, and Zn, and X is or includes one or more of F, P, and S.

[0045] In Chemical Formula 1, 0.9 ≤ a1 ≤ 1.5 or 0.9 ≤ a1 ≤ 1.2. Additionally, Chemical Formula 1 may include aluminum, and in this case, 0.6 ≤ x1 ≤ 0.8, 0.1 ≤ y1 ≤ 0.39, 0.01 ≤ z1 ≤ 0.03, and 0 ≤ w1 ≤ 0.29 may be satisfied, or for example, 0.6 ≤ x1 ≤ 0.8, 0.1 ≤ y1 ≤ 0.39, 0.01 < z1 ≤ 0.03, and 0 ≤ w1 ≤ 0.29 may be satisfied.

[0046] In Chemical Formula 1, for example, 0.6 ≤ x1 ≤ 0.79, 0.6 ≤ x1 ≤ 0.78, 0.6 ≤ x1 ≤ 0.75, 0.65 ≤ x1 ≤ 0.8 or 0.7 ≤ x1 ≤ 0.79, 0.1 ≤ y1 ≤ 0.35, 0.1 ≤ y1 ≤ 0.30, 0.1 ≤ y1 ≤ 0.29, 0.15 ≤ y1 ≤ 0.39 or 0.2 ≤ y1 ≤ 0.3, 0.01 ≤ z1 ≤ 0.025, 0.01 < z1 ≤ 0.02 or 0.01 < z1 ≤ 0.019, 0 ≤ w1 ≤ 0.28, 0 ≤ w1 ≤ 0.27, 0 ≤ w1 ≤ 0.25, 0 ≤ w1 ≤ 0.24, 0 ≤ w1 ≤ 0.2, 0 ≤ w1 ≤ 0.15, 0 ≤ w1 ≤ 0.1 or 0 ≤ w1 ≤ 0.09.

[0047] For example, the lithium nickel manganese composite oxide may not include or may include a small amount of cobalt, and based on 100 mol% of the total metals except lithium, the cobalt content may be less than or equal to about 2 mol%, less than or equal to about 1 mol%, or about 0 mol% to about 0.01 mol%.

[0048] Particles including the layered lithium nickel manganese composite oxide may be in the form of secondary particles formed by the aggregation of a plurality of primary particles. Here, the secondary particles may be substantially spherical, substantially elliptical, substantially polyhedral, or irregular in shape, and the primary particles may be substantially spherical, substantially elliptical, substantially plate-shaped, or a combination thereof.

[0049] Some exemplary embodiments include a positive electrode active material including: a first positive electrode active material including a layered lithium nickel manganese composite oxide; and a second positive electrode active material including a layered lithium nickel manganese composite oxide.

[0050] The first positive electrode active material has an average particle diameter (D 50 ) in the range of about 10 μm to about 25 μm (for example, about 11 μm to about 20 μm or about 12 μm to about 18 μm). The second positive electrode active material may have an average particle diameter (D 50Here, the mixed positive electrode active material can have an average particle size (D) in the range of about 3 μm to about 15 μm (e.g., about 4 μm to about 14 μm or about 5 μm to about 12 μm). 50 As included herein, unless otherwise defined, the average particle size (D) 50 () represents the diameter of particles with a cumulative volume of 50% 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 of the positive electrode active material.

[0051] The first positive electrode active material and the second positive electrode active material can be mixed in a weight ratio ranging from about 80:20 to about 10:90 (e.g., about 80:20 to about 20:80 or about 80:20 to about 30:70). When mixed in the above proportions, high capacity can be achieved while maximizing energy density.

[0052] conductive materials The term "conductive material" includes materials that provide electrode conductivity. Any electrically conductive material can be included as a conductive material unless it causes a chemical change. Examples of conductive materials may include: carbonaceous materials, such as at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, carbon nanotubes, etc.; metallic materials, such as metal powders or metal fibers, including at least one of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0053] Conductive materials may include, for example, linear conductive materials, spherical conductive materials, or mixtures of linear and spherical conductive materials. Linear conductive materials may have a fibrous or tubular shape, for example, a conductive material having an aspect ratio equal to or greater than about 2 or equal to or greater than about 10. For example, linear conductive materials may be or include at least one of carbon nanofibers, carbon nanotubes, and combinations thereof. Spherical conductive materials may be or include particulate conductive materials that can be understood to include spherical shapes, near-spherical ellipsoidal shapes, or polygonal shapes. Spherical conductive materials may have an aspect ratio in the range of about 0.8 to about 1.2 or about 0.9 to about 1.1, for example, at least one of carbon black, acetylene black, Ketjen black, and combinations thereof.

[0054] When the conductive material comprises linear and spherical conductive materials, the linear and spherical conductive materials can be mixed in a weight ratio ranging from about 10:90 to about 90:10 (e.g., about 20:80 to about 80:20, about 30:70 to about 70:30, or about 40:60 to about 60:40). When the weight ratio of linear to spherical conductive materials falls within the above range, high conductivity can be achieved by reducing the content of conductive materials, thereby increasing capacity and reducing electrode plate resistance.

[0055] In the positive electrode active material layer according to some example embodiments, the positive electrode active material and the conductive material satisfy Equation 1.

[0056] Equation 1: y=1.0923x 2 +0.102x+0.7471.

[0057] In Equation 1, x is the specific surface area (m²) of the active material of the positive electrode. 2 / g), 0.13≤x≤0.63, and y is based on the content of conductive material in the 100wt% positive electrode active material layer (wt%).

[0058] In Equation 1, based on a 100 wt% positive electrode active material layer, the content of the conductive material can be expressed in "wt%", and the specific surface area of ​​the positive electrode active material can be expressed in "m²". 2 / g”.

[0059] Furthermore, in Equation 1, the specific surface area of ​​the positive electrode active material can be obtained through the following steps: measuring the average particle size (D) of the positive electrode active material using a particle size analyzer. 50 Given the amount of 4πr and the quantity of the positive electrode active material, and assuming the positive electrode active material is spherical, calculate 4πr. 2 The surface area of ​​the positive electrode active material is calculated by multiplying the surface area by the amount of positive electrode active material, and then dividing the product by the weight of the positive electrode active material in the positive electrode active material layer. Here, the particle size analyzer can be, for example, a laser diffraction particle size measurement device (e.g., MT 3000, Microtrac Inc.).

[0060] The specific surface area (x) of the positive electrode active material according to some example embodiments can be approximately 0.13 m². 2 / g to approximately 0.63m 2 / g (e.g., approximately 0.2m) 2 / g to approximately 0.6m 2 / g, approximately 0.25m 2 / g to approximately 0.58m 2 / g, approximately 0.3m 2 / g to approximately 0.55m 2 / g, approximately 0.35m 2 / g to approximately 0.52m 2 / g or approximately 0.4m 2 / g to approximately 0.5m 2 The content (y) of the conductive material, based on a total positive electrode active material layer of 100 wt%, can be in the range of about 0.6 wt% to about 1.5 wt% (e.g., about 0.7 wt% to about 1.3 wt% or about 0.8 wt% to about 1.2 wt%) according to some example embodiments. A positive electrode including a positive electrode active material having a specific surface area within the above range and a conductive material having a content within the above range can achieve high capacity and high energy density by using a reduced content of conductive material.

[0061] According to Equation 1, a mathematical relationship can be obtained between the specific surface area of ​​the positive electrode active material and the minimum or reduced content of the conductive material. The content of the positive electrode active material can be calculated through this mathematical relationship. Therefore, a positive electrode with the positive electrode active material and the minimum or reduced content of the conductive material can be obtained in terms of conductivity, energy density, and cycle life performance.

[0062] A method for obtaining the mathematical relationship between the specific surface area of ​​the positive electrode active material and the minimum or reduced content of the conductive material can be performed by the following steps: preparing positive electrode slurry samples with different contents of conductive material to measure their PSA particle size distribution, and specifying the content of conductive material in the range of about 0.01 μm to about 0.1 μm as the minimum or reduced content, and using data on the surface area of ​​the positive electrode active material and the minimum or reduced content of the conductive material.

[0063] Peaks appearing in the range of about 0.01 μm to about 0.1 μm may be due to conductive materials, but PSA particle size distribution of slurries containing conductive materials in amounts smaller than specified in the range of about 0.01 μm to about 0.1 μm will not show peaks, which confirms that the amount of conductive material is present to the extent that it is adsorbed on the surface of the positive electrode active material.

[0064] On the other hand, the PSA particle size distribution of a slurry containing a higher content of conductive material than specified can exhibit a peak in the range of approximately 0.01 μm to approximately 0.1 μm. This indicates that the conductive material is present in large or excessive amounts beyond the extent to which it is adsorbed onto the surface of the positive electrode active material, forming conductive pathways between the active materials. This confirms that the large or excessive use of conductive material reduces the electrode plate resistance. Therefore, the content of conductive material in which a peak begins to appear in the range of approximately 0.01 μm to approximately 0.1 μm can be specified as the desired minimum amount or the amount reduced of the conductive material.

[0065] When a positive electrode using a positive electrode active material comprising a layered lithium nickel manganese composite oxide satisfies Equation 1, it is understood that the positive electrode includes a minimum or reduced amount of conductive material as desired. This can reduce or prevent degradation of electronic conductivity or increase of resistance due to insufficient conductive material content in the positive electrode, and can also reduce or prevent degradation of capacity and energy density due to a large or excessive amount of conductive material without increasing the content of the positive electrode active material. According to some example embodiments, the positive electrode comprising a layered lithium nickel manganese composite oxide includes a minimum or reduced amount of conductive material to improve or maximize capacity and energy density, and to reduce resistance and improve electronic conductivity, thereby improving overall battery performance, such as cycle life characteristics.

[0066] adhesive The binder is configured to improve the adhesion properties between the positive electrode active material particles and the adhesion properties between the positive electrode active material particles and the current collector. Examples of binders may include, but are not limited to, at least one of the following: 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, and nylon.

[0067] Based on a 100wt% positive electrode active material layer, the content of each or at least one of the binder and conductive material can range from about 0.5wt% to about 5wt%.

[0068] The positive electrode current collector may include, but is not limited to, Al, etc.

[0069] Methods for manufacturing positive electrodes In some example embodiments, the method for manufacturing a positive electrode includes the following steps: i) measuring the average particle size (D0) of the positive electrode active material comprising layered lithium-nickel-manganese composite oxides using a particle size analyzer.50 ); ii) Assuming the positive electrode active material is substantially spherical, use the average particle size (D 50 iii) Calculate the specific surface area of ​​the positive electrode active material; iv) Substitute the specific surface area of ​​the positive electrode active material into Equation 1 to obtain the reduced content of the conductive material; and iv) Form a positive electrode active material layer comprising the positive electrode active material and the reduced content of the conductive material on the positive electrode current collector.

[0070] Equation 1: y=1.0923x 2 +0.102x+0.7471.

[0071] In Equation 1, x is the specific surface area (m²) of the active material of the positive electrode. 2 / g), 0.13≤x≤0.63, and y is based on the content of conductive material in the 100wt% positive electrode active material layer (wt%).

[0072] The above positive electrode can be manufactured using this method. The active material, conductive material, and Equation 1 for the positive electrode are the same as those described above, and will not be described in detail again.

[0073] The average particle size (D) of the positive electrode active material 50 The specific surface area of ​​the positive electrode active material can be measured using, for example, a laser diffraction particle size analyzer (e.g., MT 3000, Microtrac Inc.). The average particle size (D0.05) of the positive electrode active material can be obtained by measuring, for example, a particle size analyzer. 50 =2r) and count the number of positive electrode active materials, calculating 4πr under the assumption that the positive electrode active materials are spherical. 2 The surface area of ​​the positive electrode active material is calculated by multiplying the surface area by the amount of positive electrode active material and then dividing the product by the weight of the positive electrode active material in the positive electrode active material layer.

[0074] According to this manufacturing method, a positive electrode incorporating a positive electrode active material including a layered lithium nickel manganese composite oxide can be manufactured, comprising a reduced amount of conductive material as desired. Therefore, the positive electrode can reduce or prevent drawbacks such as deterioration of electronic conductivity and increased resistance caused by insufficient conductive material, as well as other drawbacks (such as capacity and energy density degradation due to insufficient or excessive conductive material resulting in no significant increase in the content of the positive electrode active material). A positive electrode comprising a layered lithium nickel manganese composite oxide manufactured according to the method of some example embodiments can include a reduced amount of conductive material as desired, thereby increasing or maximizing capacity and energy density, and reducing resistance and improving electronic conductivity, thereby enhancing overall battery performance (such as cycle life characteristics).

[0075] In other example embodiments, a method for obtaining the reduction in the amount of conductive material in the positive electrode includes the following steps: mixing a positive electrode active material comprising a layered lithium nickel manganese composite oxide and a conductive material in a solvent to prepare a positive electrode slurry; varying the content of the conductive material in the range of about 0.1 wt% to about 3 wt% based on a 100 wt% solids content in the positive electrode slurry to prepare multiple positive electrode slurry samples; analyzing the particle size in the slurry from the positive electrode slurry sample with a low conductive material content using a particle size analyzer; and specifying the content of conductive material in the positive electrode slurry sample at points where a peak appears in the particle size analysis in the particle size range of about 0.01 μm to about 0.1 μm as the reduction in the desired amount of conductive material in the positive electrode. This method, which does not require the fabrication of an electrode plate, is simpler and more accurate than conventional methods that measure the resistance of the electrode plate to obtain the desired amount of conductive material.

[0076] Based on the 100wt% solids content of each sample, the preparation of the positive electrode slurry sample can be performed by changing the content of the conductive material to, for example, about 0.1wt%, about 0.2wt%, 0.3wt%, about 0.4wt%, about 0.5wt%, about 0.6wt%, about 0.7wt%, about 0.8wt%, about 0.9wt%, about 1.0wt%, about 1.1wt%, about 1.2wt%, about 1.3wt%, about 1.4wt%, and about 1.5wt%.

[0077] For example, when a peak in the particle size range of about 0.01 μm to about 0.1 μm does not appear in a positive electrode slurry sample having a conductive material content of about 0.1 wt% to about 0.7 wt%, but appears in a positive electrode slurry sample having a conductive material content of about 0.8 wt%, the corresponding reduction in the desired conductive material content of the positive electrode can be specified as about 0.8 wt%.

[0078] The positive electrode paste may also include a binder, wherein the positive electrode active material, conductive material, binder, etc. are the same as described above and will not be described in further detail. The solvent may be or include general solvents used in the manufacture of the positive electrode (e.g., N-methylpyrrolidone (NMP)).

[0079] Rechargeable lithium batteries Some example embodiments include a rechargeable lithium battery comprising the aforementioned positive electrode, negative electrode, and electrolyte. As an example, a rechargeable lithium battery may include a positive electrode, a negative electrode, a separator between the positive and negative electrodes, and an electrolyte solution.

[0080] Based on their shape, rechargeable lithium batteries can be classified into cylindrical, prismatic, pouch-shaped, coin-shaped, etc. Figures 1 to 4 This is a schematic diagram illustrating a rechargeable lithium battery according to some example embodiments, wherein, Figure 1 It is a cylindrical battery. Figure 2 It is a prismatic battery. Figure 3 and Figure 4 It's a pouch battery. (See reference) Figures 1 to 4 The rechargeable lithium battery 100 includes an electrode assembly 40 and a housing 50. The electrode assembly 40 has a separator 30 disposed between a positive electrode 10 and a negative electrode 20. The electrode assembly 40 is housed within the housing 50. An electrolyte solution (not shown) may be impregnated in the positive electrode 10, the negative electrode 20, and the separator 30. Figure 1 As shown, the rechargeable lithium battery 100 may include a sealing member 60 of a sealed housing 50. Additionally, in 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 Figure 4 The electrode connector 70 shown is or Figure 3 The positive electrode terminal 71 and negative electrode terminal 72 shown herein form an electrical path for guiding the current generated in the electrode assembly 40 to the outside of the rechargeable lithium battery 100.

[0081] negative electrode The negative electrode may include a current collector and a negative electrode active material layer on the current collector, and the negative electrode active material layer may include a negative electrode active material, and may also include a binder, a conductive material, or a combination thereof.

[0082] Negative electrode active material 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.

[0083] 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 or sheet-like, flake-like, spherical, or fibrous natural or artificial graphite. Amorphous carbon can be or includes at least one of soft carbon, hard carbon, mesophase pitch carbonization products, calcined coke, etc.

[0084] The lithium metal alloy includes an alloy of lithium and a metal (such as or including at least one of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn).

[0085] The material capable of doping / dedoping lithium can be or include 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, a silicon-carbon composite, SiO x (where 0 < x ≤ 2), a Si-Q alloy (where Q is or includes at least one of an alkali metal, an alkaline earth metal, a Group-13 element, a Group-14 element (excluding Si), a Group-15 element, a Group-16 element, a transition metal, a rare earth element, and a combination thereof, for example, at least one of 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 a combination thereof), and a combination thereof. The Sn-based negative electrode active material can be or include at least one of Sn, SnO2, a Sn alloy, and a combination thereof.

[0086] The silicon-carbon composite can be or include a composite of silicon and amorphous carbon. The average particle size (D 50 ) can be, for example, in the range of about 0.5 μm to about 20 μm. According to some example embodiments, the silicon-carbon composite can be in the form of silicon particles and an amorphous carbon coating on the surface of the silicon particles. For example, the silicon-carbon composite can include secondary particles (cores) in which primary silicon particles are assembled and an amorphous carbon coating layer (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 an amorphous carbon matrix.

[0087] The silicon-carbon composite can also include crystalline carbon. For example, the silicon-carbon composite can include a core containing crystalline carbon and silicon particles and an amorphous carbon coating layer on the surface of the core. The crystalline carbon can be or include artificial graphite, natural graphite, or a combination thereof. The amorphous carbon can include at least one of soft carbon, hard carbon, mesophase pitch carbonized products, and calcined coke.

[0088] When the silicon-carbon composite includes silicon and amorphous carbon, based on 100 wt% of the silicon-carbon composite, the content of silicon can be in the range of about 10 wt% to about 50 wt%, and the content of amorphous carbon can be in the range of about 50 wt% to about 90 wt%. Additionally, when the silicon-carbon composite includes silicon, amorphous carbon, and crystalline carbon, based on 100 wt% of the silicon-carbon composite, the content of silicon can be in the range of about 10 wt% to about 50 wt%, the content of crystalline carbon can be in the range of about 10 wt% to about 70 wt%, and the content of amorphous carbon can be in the range of about 20 wt% to about 40 wt%.

[0089] Additionally, the thickness of the amorphous carbon coating layer can be in the range of about 5 nm to about 100 nm. The average particle size (D 50 ) of the silicon particles (primary particles) can be in the range of about 10 nm to about 1 μm or about 10 nm to about 200 nm. The silicon particles can exist as elemental silicon, in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon can be represented by SiO x (0 < x < 2). At this time, the atomic content ratio of Si:O representing the degree of oxidation can be in the range of about 99:1 to about 33:67. As included herein, when no other definition is provided, the average particle size (D 50 ) represents the particle at which the cumulative volume in the particle size distribution is about 50 volume%.

[0090] Si-based negative electrode active materials or Sn-based negative electrode active materials can be mixed with carbon-based negative electrode active materials. When the Si-based negative electrode active materials or Sn-based negative electrode active materials are mixed with the included carbon-based negative electrode active materials, the mixing ratio can be a weight ratio in the range of about 1:99 to about 90:10.

[0091] adhesive The binder is configured to adhere the negative electrode active material particles to each other and adhere the negative electrode active material to the current collector. The binder can be a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0092] 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.

[0093] Waterborne adhesives may include styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepoxygenated alcohol, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, or combinations thereof.

[0094] When an aqueous binder is included as the negative electrode binder, a cellulose compound capable of imparting viscosity may be further included. As a cellulose compound, a mixture may be included, and may include one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and their alkali metal salts. The alkali metal may be Na, K, or Li.

[0095] The dry binder can be a polymeric material that can be turned into fibers, and can be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0096] conductive materials The term "conductive material" includes materials that provide electrical conductivity to electrodes, and any electrically conductive material can be included as a conductive material unless it causes a chemical change. Examples of conductive materials include: carbon-based materials such as natural graphite, synthetic graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, carbon nanotubes, etc.; metallic materials such as metal powders or metal fibers, including copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0097] Based on a 100wt% negative electrode active material layer, the content of the negative electrode active material can be from about 95wt% to about 99.5wt%, and the content of the binder can be from about 0.5wt% to about 5wt%. For example, the negative electrode active material layer may include about 90wt% to about 99wt% of negative electrode active material, about 0.5wt% to about 5wt% of binder, and about 0.5wt% to about 5wt% of conductive material.

[0098] current collector The negative electrode current collector may include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or alloys thereof, and may be in the form of foil, sheet, or foam. The thickness of the negative electrode current collector may be, for example, about 1 μm to about 20 μm, about 5 μm to about 15 μm, or about 7 μm to about 10 μm.

[0099] electrolytes For example, the electrolyte used in rechargeable lithium batteries can be an electrolyte solution that may include non-aqueous organic solvents and lithium salts.

[0100] Non-aqueous organic solvents are configured as media for transporting ions that participate in the electrochemical reactions of a battery. Non-aqueous organic solvents can be or include at least one of carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, aprotic solvents, and combinations thereof.

[0101] Carbonate solvents may include at least one of 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 at least one of methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolactone, mevalonolactone, valproic acid lactone, caprolactone, etc. Ether solvents may include at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. Additionally, ketone solvents may include cyclohexanone, etc. Alcohol solvents may include at least one of ethanol, isopropanol, etc. Aprotic solvents may include at least one of the following: nitriles, such as R-CN (wherein R is a C2 to C20 straight chain, branched chain, and may include cyclic hydrocarbon groups, double bonds, aromatic rings, or ether groups); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane, 1,4-dioxolane, etc.; sulfolane, etc.

[0102] Non-aqueous organic solvents may be included alone or in a mixture of two or more types of solvents. When a mixture includes two or more types, the mixing ratio may be adjusted according to the desired battery performance, as may be known to those skilled in the art.

[0103] When using carbonate solvents, cyclic carbonates and chain carbonates can be mixed and include each other, and the cyclic carbonates and chain carbonates can be mixed in a volume ratio ranging from about 1:1 to about 1:9.

[0104] Non-aqueous organic solvents may also include aromatic hydrocarbon organic solvents. For example, carbonate solvents and aromatic hydrocarbon organic solvents may be mixed and included in a volume ratio ranging from about 1:1 to about 30:1.

[0105] The electrolyte solution may also include at least one of vinyl ethyl carbonate, vinylene carbonate, and ethylene carbonate compounds to improve battery cycle life.

[0106] Examples of ethylene carbonate compounds may include at least one of fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, and cyanoethylene carbonate.

[0107] Lithium salts dissolved in organic solvents are configured to supply lithium ions in a battery to enable basic operation of the rechargeable lithium battery and improve 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 At least one of the following: (SO2) (where x and y are integers in the range of 1 to 20), lithium trifluoromethane sulfonate, lithium tetrafluoroethane sulfonate, lithium difluoro(oxalate)borate (LiDFOB), lithium difluorobis(oxalate)phosphate (LiDFBOP), and lithium bis(oxalate)borate (LiBOB).

[0108] The concentration of lithium salt can range from about 0.1 M to about 2.0 M. When the concentration of lithium salt is within this range, the electrolyte solution has the desired ionic conductivity and viscosity, thus achieving the desired or improved performance and allowing lithium ions to move more efficiently.

[0109] diaphragm Depending on the type of rechargeable lithium battery, a separator may be present between the positive and negative electrodes. The separator may include at least one of polyethylene, polypropylene, polyvinylidene fluoride, and multilayer films of two or more layers thereof, as well as mixed multilayer films (such as polyethylene / polypropylene bilayer separators, polyethylene / polypropylene / polyethylene trilayer separators, polypropylene / polyethylene / polypropylene trilayer separators, etc.).

[0110] The membrane may include a porous substrate and a coating layer on one or both surfaces of the porous substrate, the coating layer comprising an organic material, an inorganic material, or a combination thereof.

[0111] The porous substrate may be or include a polymer membrane formed of or comprising at least one of the following: polyolefins (such as polyethylene and polypropylene), polyesters (such as polyethylene terephthalate and polybutylene terephthalate), polyacetal, polyamide, polyimide, polycarbonate, polyetherketone, polyaryletherketone, polyetherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene ether, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fiber, TEFLON and polytetrafluoroethylene, and copolymers or mixtures of two or more thereof.

[0112] The porous substrate may have a thickness ranging from about 1 μm to about 40 μm (e.g., 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).

[0113] Organic materials may include (meth)acrylic acid copolymers, which include a first structural unit and a second structural unit derived from (meth)acrylamide, wherein 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.

[0114] Inorganic materials may include inorganic particles, such as or including Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof, but are not limited thereto. The average particle size (D) of the inorganic particles... 50 It can be in the range of about 1nm to about 2000nm (e.g., about 100nm to about 1000nm or about 100nm to about 700nm).

[0115] Organic and inorganic materials can be mixed in a coating layer, or a coating layer containing organic materials and a coating layer containing inorganic materials can be stacked together.

[0116] The thickness of the coating can be in the range of about 0.5 μm to about 20 μm (e.g., about 1 μm to about 10 μm or about 1 μm to about 5 μm).

[0117] Figure 9 This is a flowchart illustrating a method for manufacturing a positive electrode according to an example embodiment. Figure 9 In method 900, operation 910 includes measuring the average particle size (D0) of the positive electrode active material comprising layered lithium nickel manganese composite oxides using a particle size analyzer. 50 Operation 920 includes assuming the positive electrode active material is spherical and using the average particle size (D).50 Calculate the specific surface area of ​​the positive electrode active material; Operation 930 includes substituting the specific surface area of ​​the positive electrode active material into Equation 1 to obtain the reduced or minimum content of the conductive material, in Equation 1, y = 1.0923x 2 +0.102x+0.7471, where x is the specific surface area of ​​the positive electrode active material, 0.13≤x≤0.63, and y is the content of conductive material in the positive electrode active material layer based on 100wt%; and operation 940, comprising forming a positive electrode active material layer on the positive electrode current collector comprising the positive electrode active material and a reduced content of conductive material.

[0118] Examples and comparative examples of this disclosure are described below. However, the following examples are merely examples of this disclosure, and this disclosure is not limited to these examples.

[0119] Example 1 (1) Manufacturing of the positive electrode By mixing Li in a weight ratio of 80:20, the particles were in secondary particle form with a particle size of approximately 13.6 μm and Li 1.05 Ni 0.75 Mn 0.23 Al 0.02 The composition of O2 is the first positive electrode active material and has a secondary particle form with a particle size of approximately 3.12 μm and Li 1.05 Ni 0.75 Mn 0.25 The positive electrode active material was prepared by mixing a second positive electrode active material composed of O2. Here, when measured using a particle size analyzer (MT 3000, Microtrac Inc.), the positive electrode active material had an average particle size (D) of 12.3 μm. 50 ) and 0.243m 2 The specific surface area is calculated as / g, where the surface area of ​​the sphere is calculated by assuming the positive electrode active material has a spherical shape, multiplying the surface area by the amount of positive electrode active material, and dividing the product by the weight of the positive electrode active material. The parameter "y" of the conductive material content is calculated to be 0.8 by replacing the parameter "x" in Equation 1 discussed above with 0.243.

[0120] A positive electrode composition was prepared by mixing 97.7 wt% of the prepared positive electrode active material, 1.5 wt% of the binder PVDF, and 0.8 wt% of the conductive material CNT in NMP solvent. The prepared positive electrode composition was coated onto an aluminum current collector. The coated aluminum current collector was dried and pressed to manufacture a positive electrode in which the current collector and the positive electrode active material layers were sequentially stacked.

[0121] (2) Manufacturing of the negative electrode A negative electrode active material slurry was prepared by mixing 97.3 wt% graphite (as the negative electrode active material), 0.5 wt% denka black (superconducting acetylene black), 0.9 wt% carboxymethyl cellulose, and 1.3 wt% styrene-butadiene rubber in an aqueous solvent. The prepared negative electrode active material slurry was coated onto copper foil, then dried and pressed to manufacture the negative electrode.

[0122] (3) Manufacturing of battery cells A positive electrode, a separator with a multilayer structure of polyethylene / polypropylene, and a negative electrode are sequentially stacked to manufacture a pouch-type battery cell. Then, an electrolyte solution prepared by adding 1.0 M of LiPF6 lithium salt to a solvent of ethylene carbonate and diethyl carbonate mixed in a 50:50 volume ratio is injected to manufacture a rechargeable lithium battery cell.

[0123] Example 2 The rechargeable lithium-ion battery cell was manufactured in essentially the same manner as in Example 1, except that the weight ratio of the first positive electrode active material to the second positive electrode active material was changed from 80:20 to 70:30, and the positive electrode active material was prepared using 97.7 wt% positive electrode active material, 1.4 wt% PVDF binder, and 0.9 wt% CNT conductive material. Here, when measured in the same manner as in Example 1, the positive electrode active material has an average particle size (D) of 11.0 μm. 50 ) and 0.298m 2 Specific surface area per g.

[0124] Example 3 The rechargeable lithium-ion battery cell was manufactured in essentially the same manner as in Example 1, except that the weight ratio of the first positive electrode active material to the second positive electrode active material was changed from 80:20 to 50:50, and the positive electrode active material was prepared using 97.7 wt% positive electrode active material, 1.4 wt% PVDF binder, and 0.9 wt% conductive material CNTs. Here, when measured in the same manner as in Example 1, the positive electrode active material has an average particle size (D) of 6.13 μm. 50 ) and 0.409m 2 Specific surface area per g.

[0125] Example 4 The rechargeable lithium-ion battery cell was manufactured in essentially the same manner as in Example 1, except that the weight ratio of the first positive electrode active material to the second positive electrode active material was changed from 80:20 to 30:70, and the positive electrode active material was prepared using 97.7 wt% positive electrode active material, 1.1 wt% PVDF binder, and 1.2 wt% CNT conductive material. Here, when measured in the same manner as in Example 1, the positive electrode active material has an average particle size (D) of 3.41 μm. 50 ) and 0.519m 2 Specific surface area per g.

[0126] Example 5 The rechargeable lithium-ion battery cell was manufactured in essentially the same manner as in Example 1, except that the weight ratio of the first positive electrode active material to the second positive electrode active material was changed from 80:20 to 10:90, and the positive electrode active material was prepared using 97.7 wt% positive electrode active material, 1.1 wt% PVDF binder, and 1.2 wt% conductive material CNTs. Here, when measured in the same manner as in Example 1, the positive electrode active material has an average particle size (D) of 3.14 μm. 50 ) and 0.629m 2 Specific surface area per g.

[0127] Example 6 The rechargeable lithium-ion battery cell was manufactured in essentially the same manner as in Example 1, except that a separate first positive electrode active material was used instead of the positive electrode active material prepared by mixing the first and second positive electrode active materials in a weight ratio of 80:20, in the absence of a second positive electrode active material. Here, when measured in the same manner as in Example 1, the positive electrode active material has an average particle size (D) of 13.6 μm. 50 ) and 0.133m 2 Specific surface area per g.

[0128] Comparison Example 1 The rechargeable lithium battery cell was manufactured in essentially the same manner as in Example 2, except that 97.7 wt% of positive electrode active material, 1.8 wt% of binder PVDF and 0.5 wt% of conductive material CNT were used.

[0129] Comparison Example 2 The rechargeable lithium battery cell was manufactured in essentially the same manner as in Example 4, except that 97.7 wt% of positive electrode active material, 1.8 wt% of binder PVDF and 0.5 wt% of conductive material CNT were used.

[0130] Compare Example 3 The rechargeable lithium-ion battery cell is manufactured in essentially the same manner as in Example 1, except that Li1Ni is used. 0.91 Co 0.07 Al 0.01 Mn 0.01 O2 is used as the positive electrode active material. Here, when measured in the same manner as in Example 1, the positive electrode active material has an average particle size of 2.35 μm (D). 50 ) and 3.5m 2 Specific surface area per g.

[0131] Evaluation Example 1: Calculate the minimum amount of conductive material required. The Do of the positive electrode active material included in the rechargeable lithium-ion battery cell according to Examples 1 to 6 was measured using a PSA device. 50 The results are shown in Table 1 below. Subsequently, the D of the positive electrode active material was measured using the assumption that the positive electrode active material is spherical. 50 The surface area and specific surface area of ​​the positive electrode active material were calculated, and the results are shown in Table 1 below.

[0132] Subsequently, after varying the conductive material content of the rechargeable lithium battery cells of Examples 1 to 6 to prepare positive electrode active material slurries, the PSA particle size distribution of the positive electrode active material slurry was measured to specify the minimum content of conductive material by obtaining the conductive material content in the range of 0.01 μm to 0.1 μm. The minimum conductive material content was then used together with the specific surface area of ​​the positive electrode active material to obtain an equation.

[0133] Reference Figure 5 In the positive electrode active material of Example 2, when the conductive material content is 0.8 wt% or less, no peak appears in the PSA particle size distribution in the range of 0.01 μm to 0.1 μm, confirming that the conductive material is present to the extent that it is adsorbed on the surface of the positive electrode active material. Conversely, when the conductive material content is 0.9 wt% or greater, a peak appears in the PSA particle size distribution in the range of 0.01 μm to 0.1 μm. This means that from this point onwards, an excess of conductive material is detected, and it is understood that conductive pathways have been successfully formed between the active materials. In fact, from this point onwards, the resistance of the electrode plate begins to decrease. The conductive material content at which the corresponding peak begins to appear is defined as the minimum required content of conductive material.

[0134] Reference Figure 6 When the conductive material content is 0.8 wt% or less, the positive electrode active material of Example 3 does not exhibit a peak in the PSA particle size distribution in the range of 0.01 μm to 0.1 μm. Conversely, when the conductive material content is 0.9 wt% or greater, a peak appears in the PSA particle size distribution in the range of 0.01 μm to 0.1 μm. Therefore, 0.9 wt% is defined as the minimum required content of the conductive material.

[0135] Reference Figure 7 When the conductive material content is 1.2 wt% or greater, the positive electrode active material of Example 4 exhibits a peak in the PSA particle size distribution in the range of 0.01 μm to 0.1 μm. Therefore, 1.2 wt% is defined as the minimum required content of conductive material.

[0136] The minimum amount of each conductive material required for the rechargeable lithium-ion battery cells of Examples 1 to 6 is shown in Table 1 below.

[0137] Table 1:

[0138] In Table 1, "Total Surface Area" represents the total surface area obtained by multiplying the surface area of ​​a single positive electrode active material particle by the number of positive electrode active material particles. Approximate values ​​for the required amount of conductive material in Examples 2 to 4 can be obtained by... Figures 5 to 7 The approximate value found.

[0139] exist Figure 8 The figure shows the relationship between the specific surface area of ​​the positive electrode active material for Examples 1 to 6 and the various required minimum amounts of conductive material. If we derive an approximate function using the specific surface area and the required amount of conductive material, we can confirm that we have obtained the relationship in Equation 1.

[0140] Reference Figure 8 As the specific surface area increases, the minimum required content of conductive material increases, which confirms Equation 1, which describes the relationship between specific surface area and the minimum required content of conductive material.

[0141] Evaluation Example 2: Evaluation of the resistance of electrode plate mixtures The resistivity of the mixture of positive electrodes included in the rechargeable lithium battery cells according to Examples 1 to 6 was measured, and the results are shown in Table 2.

[0142] Table 2:

[0143] Referring to Table 2, compared with the comparative examples, Examples 1 to 5, in which the relationship between the specific surface area of ​​the positive electrode active material and the minimum required content of the conductive material satisfies Equation 1, exhibit a reduced mixture resistivity.

[0144] Conversely, compared to the examples, Comparative Examples 1 and 2, where the relationship between the specific surface area of ​​the respective positive electrode active materials and the respective minimum required content of the respective conductive materials does not satisfy Equation 1, or Comparative Example 3, which does not use cobalt-free positive electrode active materials as positive electrode active materials, all exhibit increased mixture resistivity. This increased mixture resistivity can be explained by the fact that it does not include the desired amount of conductive material.

[0145] While this disclosure has been described in conjunction with exemplary embodiments now considered practical, it will be understood that the disclosure is not limited to the disclosed exemplary embodiments. Rather, the disclosure is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

[0146] Explanation of reference numerals in the attached figures: 100: Rechargeable lithium battery; 10: Positive electrode 11: Positive electrode lead connector 12: Positive electrode terminal 20: Negative electrode 21: Negative electrode lead connector 22: Negative electrode terminal; 30: Diaphragm 40: Electrode assembly; 50: Housing 60: Sealing component; 70: Electrode terminal piece 71: Positive electrode connector; 72: Negative electrode connector

Claims

1. A positive electrode, the positive electrode comprising: a positive electrode current collector; and a positive electrode active material layer on the positive electrode current collector and including a positive electrode active material and a conductive material; wherein the positive electrode active material includes a layered lithium nickel manganese-based composite oxide, and in the positive electrode active material layer, the positive electrode active material and the conductive material satisfy Equation 1: Equation 1: y = 1.0923x 2 + 0.102x + 0.7471, wherein, in Equation 1, x is a specific surface area of the positive electrode active material, 0.13 ≤ x ≤ 0.63, and y is a content of the conductive material based on 100 wt% of the positive electrode active material layer.

2. The positive electrode according to claim 1, wherein y is in a range of 0.8 wt% to 1.2 wt% based on 100 wt% of the positive electrode active material layer.

3. The positive electrode of claim 1, wherein, The layered lithium nickel manganese-based composite oxide has a nickel content in a range of 60 mol% to 80 mol% and a manganese content equal to or greater than 15 mol% based on 100 mol% of total metals other than lithium.

4. The positive electrode of claim 1, wherein, In the layered lithium nickel manganese-based composite oxide, a cobalt content is in a range of 0 mol% to 0.01 mol% based on 100 mol% of total metals other than lithium.

5. The positive electrode of claim 1, wherein, The layered lithium nickel manganese-based composite oxide is represented by Chemical Formula 1: Chemical Formula 1: Li a1 Ni x1 Mn y1 Al z1 M 1 w1 O 2-b1 X b1 , wherein, in Chemical Formula 1, 0.9≤a1≤1.8, 0.6≤x1≤0.8, 0.1≤y1≤0.4, 0≤z1≤0.03, 0≤w1≤0.3, 0.9≤x1+y1+z1+w1≤1.1, and 0≤b1≤0.1, M 1 includes one or more of B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zr, and Zn, and X includes one or more of F, P, and S.

6. The positive electrode of claim 1, wherein, The positive electrode active material includes secondary particles in which a plurality of primary particles are aggregated.

7. The positive electrode of claim 1, wherein, The positive electrode active material includes: a first positive electrode active material having an average particle diameter D in a range of 10 μm to 25 μm 50 ; and A second positive electrode active material having an average particle diameter D in the range of 0.1 μm to 5 μm 50 .

8. The positive electrode of claim 7, wherein, a weight ratio of the first positive electrode active material to the second positive electrode active material is in a range of 80:20 to 30:

70.

9. The positive electrode of claim 1, wherein, The positive electrode active material has an average particle diameter in a range of 3 μm to 15 μm.

10. The positive electrode of claim 1, wherein, The conductive material includes linear conductive material and spherical conductive material.

11. The positive electrode of claim 10, wherein, A weight ratio of the linear conductive material to the spherical conductive material is in a range of 10:90 to 90:

10. 12.A method for manufacturing a positive electrode, the method comprising the steps of: The average particle diameter D of the positive electrode active material including the layered lithium nickel manganese-based complex oxide is measured using a particle size analyzer 50 ; Assuming that the positive electrode active material is spherical, the average particle diameter D 50 The specific surface area of the positive electrode active material is calculated; substituting the specific surface area of the positive electrode active material into Equation 1 to obtain a reduced content of conductive material; and forming a positive electrode active material layer including the positive electrode active material and the reduced content of conductive material on a positive electrode current collector; Equation 1: y = 1.0923x 2 + 0.102x + 0.7471, wherein, in Equation 1, x is the specific surface area of the positive electrode active material, 0.13 ≤ x ≤ 0.63, and y is a content of the conductive material based on 100 wt% of the positive electrode active material layer. 13.A rechargeable lithium battery, the rechargeable lithium battery comprising: the positive electrode according to any one of claims 1 to 11; a negative electrode; and an electrolyte solution. ​

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