Negative electrode for rechargeable lithium battery and rechargeable lithium battery including same

Abstract

The invention relates to a negative electrode for a rechargeable lithium battery and a rechargeable lithium battery including the same. The negative electrode includes a current collector and a negative electrode active material layer formed on at least one surface of the current collector, in which the negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer sequentially disposed on the current collector, expression 1 is satisfied: the average tilt angle t of the first negative electrode active material layer; and an average tilt angle of the second negative electrode active material layer.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority and benefit to Korean Patent Application No. 10-2024-0111521, filed on August 20, 2024, with the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] One or more embodiments of this disclosure relate to a negative electrode for a rechargeable lithium battery and a rechargeable lithium battery including the thereof. Background Technology

[0004] Recently, with the rapid proliferation of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles, the demand for rechargeable batteries with high energy density and high capacity has increased significantly. In response, research and development to improve the performance of such rechargeable batteries (especially rechargeable lithium-ion batteries) is actively underway.

[0005] A rechargeable lithium-ion battery typically includes a positive electrode and a negative electrode, each of which contains an active material capable of inserting and deintercalating lithium ions; and an electrolyte. Electrical energy is generated through oxidation and reduction reactions as lithium ions insert / deintercalate between the positive and negative electrodes. For example, electrical energy is generated during discharge when lithium ions insert into the positive electrode and / or deintercalate from the negative electrode. Summary of the Invention

[0006] One or more aspects of embodiments of this disclosure relate to a negative electrode for a rechargeable lithium battery, having a high adhesion of the active material layer to the current collector and ensuring fast charging.

[0007] One or more aspects of embodiments of this disclosure relate to a rechargeable lithium battery, which includes a negative electrode for the rechargeable lithium battery.

[0008] Other aspects will be set forth in part in the description which follows, and in part will be obvious from the description or may be learned by practicing the embodiments presented in this disclosure.

[0009] According to one or more embodiments of the present disclosure, a negative electrode for a rechargeable lithium battery includes: a current collector; and a negative electrode active material layer on (e.g., formed on) at least one surface of the current collector, wherein the negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer sequentially disposed on the current collector, and satisfies Expression 1.

[0010] Expression 1

[0011] The average tilt angle of the first negative electrode active material layer is less than the average tilt angle of the second negative electrode active material layer.

[0012] According to one or more embodiments of this disclosure, a rechargeable lithium battery includes the aforementioned negative electrode and positive electrode.

[0013] The negative electrode for a rechargeable lithium battery according to one or more embodiments can have high adhesion to the current collector and provide high fast charging performance. Attached Figure Description

[0014] The accompanying drawings are included to provide a further understanding of this disclosure, and are incorporated in and constitute a part of this disclosure. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the disclosure. Certain embodiments of the present disclosure and other aspects, features, and advantages will become more apparent from the following description taken in conjunction with the accompanying drawings.

[0015] Figure 1 This is a schematic cross-sectional view of a negative electrode for a rechargeable lithium battery according to one or more embodiments of the present disclosure.

[0016] Figure 2 This is a schematic cross-sectional view of a negative electrode for a rechargeable lithium battery according to one or more embodiments of the present disclosure.

[0017] Figure 3A An example of the tilt angle of the first negative electrode active material layer and the second negative electrode active material layer before rolling is shown according to one or more embodiments of the present disclosure, wherein the X-axis (horizontal axis) represents the tilt angle (in degrees) and the Y-axis (vertical axis) represents the amount ratio of active material with the tilt angle (in wt%), ■ represents the second negative electrode active material layer, and □ represents the first negative electrode active material layer. The stated "~10°" may mean a range of tilt angles or an average tilt angle range of "greater than 0 and less than or equal to 10°".

[0018] Figure 3B Examples of the tilt angles of the first and second negative electrode active material layers after rolling are shown according to one or more embodiments of the present disclosure, wherein the X-axis (horizontal axis) represents the tilt angle (in degrees) and the Y-axis (vertical axis) represents the percentage of active material having the tilt angle (in wt%), ■ represents the second negative electrode active material layer, and □ represents the first negative electrode active material layer. The stated term "~10°" may mean a range of tilt angles or an average tilt angle range that is "greater than 0 and less than or equal to 10°".

[0019] Figure 4AAnother example is shown of the tilt angle of the first negative electrode active material layer and the second negative electrode active material layer before rolling, according to one or more embodiments of the present disclosure, wherein the X-axis (horizontal axis) represents the tilt angle (in degrees) and the Y-axis (vertical axis) represents the amount ratio of active material with the tilt angle (in wt%), ■ represents the second negative electrode active material layer, and □ represents the first negative electrode active material layer. The stated "~10°" may mean a range of tilt angles or an average tilt angle range of "greater than 0 and less than or equal to 10°".

[0020] Figure 4B Another example is shown of the tilt angle of the first and second negative electrode active material layers after rolling, according to one or more embodiments of the present disclosure, wherein the X-axis (horizontal axis) represents the tilt angle (in degrees) and the Y-axis (vertical axis) represents the percentage of active material having the tilt angle (in wt%), ■ represents the second negative electrode active material layer, and □ represents the first negative electrode active material layer. The stated "~10°" may mean a range of tilt angles or an average tilt angle range that is "greater than 0 and less than or equal to 10°".

[0021] Figure 5 Examples of porosity changes of a first negative electrode active material layer and a second negative electrode active material layer before and after rolling are shown according to one or more embodiments of the present disclosure, where I represents the result of the first negative electrode active material layer, II represents the result of the second negative electrode active material layer, the Y-axis (vertical axis) represents porosity (in %), ■ represents the result before rolling, and □ represents the result after rolling.

[0022] Figure 6 Another example is shown of the porosity changes of the first negative electrode active material layer and the second negative electrode active material layer before and after rolling according to one or more embodiments of the present disclosure, where I represents the result of the first negative electrode active material layer, II represents the result of the second negative electrode active material layer, the Y-axis (vertical axis) represents the porosity (in %), ■ represents the result before rolling, and □ represents the result after rolling.

[0023] Figures 7-10 Each is a schematic diagram illustrating a rechargeable lithium battery according to one or more embodiments of the present disclosure.

[0024] Explanation of reference numerals in the attached figures

[0025] 100: Rechargeable lithium battery; 10: Positive electrode

[0026] 11: Positive electrode lead connector 12: Positive electrode terminal

[0027] 20: Negative electrode 23: Negative electrode lead connector

[0028] 24: Negative electrode terminal; 30: Diaphragm

[0029] 40: Electrode assembly; 50: Housing

[0030] 60: Sealing component; 70: Electrode terminal piece

[0031] 71: Positive electrode connector; 72: Negative electrode connector Detailed Implementation

[0032] In the following description, one or more embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. However, these are provided by way of example only, and the present disclosure is not limited thereto, but is defined only by the scope of the claims and their equivalents.

[0033] Unless otherwise specifically described in this disclosure, when a portion of a layer, film, region, plate, etc., is referred to as being "on" another portion, this includes not only embodiments in which the portion is "directly" "on" the other portion, but also embodiments in which one or more intervening portions are inserted therebetween. In contrast, when a portion (such as a layer, film, region, or plate) is described as being "directly" "on" another portion (such as a layer, film, region, or plate), there is no intervening portion.

[0034] Unless otherwise specifically stated in this disclosure, singular expressions may include plural expressions. For example, the singular forms “a,” “an,” “one,” and “the” are intended to also include the plural forms, unless the context clearly indicates otherwise. Furthermore, unless otherwise specifically stated, “A or B,” “A and / or B,” or “A / B” may mean “including A, including B, or including A and B.” Expressions such as “at least one of…,” “one of…,” and “selected from…” modify the entire list of elements without modifying any individual element of the list when placed before or after a list of elements. For example, “at least one of a, b, and c,” “selected from at least one of a, b, and c,” “selected from at least one of a to c” may indicate only a, only b, only c, both a and b (e.g., both a and b simultaneously), both a and c (e.g., both a and c simultaneously), both b and c (e.g., both b and c simultaneously), all a, b, and c, or variations thereof. Furthermore, when describing embodiments of this disclosure, the use of "may" refers to "one or more embodiments of this disclosure".

[0035] In this disclosure, "combination thereof" can refer to mixtures, laminates, composites, copolymers, alloys, blends, and reaction products of the components.

[0036] Unless otherwise specified in this disclosure, particle size / size can be the average particle size / average size. Furthermore, particle size / size refers to the average particle size / average size corresponding to a cumulative volume percentage (D) of 50% of the particle size distribution. 50 Average particle size / average size (D) 50 The average particle size / average size (D) can be measured using methods well known in the art (e.g., using a particle size analyzer, transmission electron microscopy, or scanning electron microscopy). In one or more embodiments, the average particle size / average size (D) is... 50 The average particle size (Dsize) can be obtained by using a dynamic light scattering method to measure and analyze data with a measuring instrument to count the number of particles in each particle size range, and calculating the average particle size / average size based on the results. In one or more embodiments, a laser diffraction method can be used for measurement. For example, when using a laser diffraction method, the particles to be measured are dispersed in a dispersion medium, and then ultrasonic waves are irradiated at a frequency of approximately 28 kHz with an output power of 60 W using a commercially available laser diffraction particle size measuring instrument (e.g., MT 3000 from Microtrac) at a frequency of approximately 28 kHz, and the average particle size / average size (Dsize) corresponding to 50% by volume in the particle size distribution of the measuring instrument is calculated. 50 In this disclosure, D 50 The term "diameter" refers to the average diameter (or size) of 50% by volume of particles in a particle size distribution (e.g., a cumulative distribution), and in a distribution curve accumulating in order from smallest to largest particle size, when the total number of particles is 100%, the value from smallest to largest particle size corresponds to 50% of the particle size. In this disclosure, when the particles are spherical, "diameter" indicates the particle size or average particle size, and when the particles are non-spherical, "diameter" indicates the major axis length or average major axis length.

[0037] In this disclosure, "tilt angle" refers to the angle at which the negative electrode active material in the negative electrode active material layer is tilted relative to (e.g., relative to) a current collector set to 0°, such as the angle at which the current collector on which the negative electrode active material layer is formed is tilted (this surface is a reference plane set to 0°). The tilt angle can be measured by the method described below.

[0038] In this disclosure, "porosity" refers to the ratio of pore area in any cross-section of the negative electrode active material layer (i.e., the percentage of total pore area in any cross-sectional area of ​​the negative electrode active material layer). Porosity can be measured by the methods described below.

[0039] According to one or more embodiments of the present disclosure, a negative electrode for a rechargeable lithium battery includes: a current collector; and a negative electrode active material layer on (e.g., formed on) at least one surface of the current collector, wherein the negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer sequentially disposed on the current collector (e.g., the first negative electrode active material layer is disposed between the current collector and the second negative electrode active material layer), and satisfies Expression 1.

[0040] Expression 1

[0041] The average tilt angle of the first negative electrode active material layer is less than the average tilt angle of the second negative electrode active material layer.

[0042] Expression 1 can be a criterion for determining whether a negative electrode active material layer can simultaneously provide high adhesion to the current collector and fast charging effect. If (e.g., when) different negative electrode active material layers are stacked on the current collector, the negative electrode active material layers can simultaneously provide high adhesion to the current collector and fast charging effect by satisfying Expression 1. In one or more embodiments, a first negative electrode active material layer can provide high adhesion to the current collector, and a second negative electrode active material layer can provide fast charging effect.

[0043] According to one or more embodiments, the average tilt angle of the second negative electrode active material layer may differ from the average tilt angle of the first negative electrode active material layer by about 2° or more (e.g., about 2° to about 10°, about 2° to about 7°, about 3° to about 7°, or about 4.5° to about 7°). Within the above range, fast charging effect and improved adhesion to the current collector can be provided, and the first negative electrode active material layer and the second negative electrode active material layer can be easily manufactured simultaneously.

[0044] According to one or more embodiments, the second negative electrode active material layer may have an average tilt angle of about 35° or greater (e.g., about 35° to about 45°, about 35° to about 40°, or about 37° to about 40°). Within the above range, Expression 1 can be easily satisfied, the fast charging effect can be further increased, and the second negative electrode active material layer can be easily manufactured.

[0045] According to one or more embodiments, the first negative electrode active material layer may have an average tilt angle of about 30° or greater (e.g., about 30° to about 40° or about 30° to about 35°). Within the above range, Expression 1 can be easily satisfied, and adhesion to the current collector can be increased.

[0046] In one or more embodiments, the negative electrode active material layer may further satisfy Expression 2. Although there may be some embodiments in which Expression 1 is satisfied but Expression 2 is not, a negative electrode active material layer that satisfies both Expression 1 and Expression 2 can increase the fast charging effect and improve adhesion.

[0047] Expression 2

[0048] The porosity of the first negative electrode active material layer is less than the porosity of the second negative electrode active material layer.

[0049] According to one or more embodiments, the porosity of the second negative electrode active material layer may differ from that of the first negative electrode active material layer by about 3% or more (e.g., about 3% to about 10%, about 3% to about 8%, or about 6% to about 8%). Within these ranges, the battery characteristics of the negative electrode can also be improved.

[0050] According to one or more embodiments, the second negative electrode active material layer may have a porosity of about 15% or greater (e.g., about 15% to about 25%, about 15% to about 20%, or about 17% to about 20%). Within the above range, the second negative electrode active material layer can be readily fabricated.

[0051] According to one or more embodiments, the first negative electrode active material layer may have a porosity of about 10% or greater (e.g., about 10% to about 20% or about 10% to about 15%). Within the above range, the first negative electrode active material layer can be readily fabricated.

[0052] According to one or more embodiments, a first negative electrode active material layer can be directly formed on the current collector, and a second negative electrode active material layer can be directly formed on the first negative electrode active material layer. Here, "directly formed" means that no other layer (e.g., other negative electrode active material layers) is inserted between the current collector and the first negative electrode active material layer, or between the first negative electrode active material layer and the second negative electrode active material layer. In other words, there is no intermediary layer inserted between the current collector and the first negative electrode active material layer, or between the first negative electrode active material layer and the second negative electrode active material layer.

[0053] In the negative electrode, the total thickness of the first negative electrode active material layer can be from about 80 micrometers (μm) to about 800 μm. The total thickness of the first negative electrode active material layer can be about 80% or less of the total thickness of the negative electrode active material layer (e.g., about 20% to about 80%). When the thickness ratio of the first negative electrode active material layer falls within the above range, not only can the impregnation of the electrolyte be improved, but also the electron transfer of the active material layer in the negative electrode can be improved.

[0054] In the negative electrode, the total thickness of the second negative electrode active material layer can be approximately 20 μm to approximately 200 μm. When the thickness of the second negative electrode active material layer falls within this range, it is beneficial to impregnate the negative electrode with the electrolyte, thus increasing ion transfer within the negative electrode. The total thickness of the second negative electrode active material layer can be approximately 20% or greater (e.g., approximately 20% to approximately 80%) of the total thickness of the negative electrode active material layer. Within this range, not only is the impregnationability of the electrolyte improved, but electron transfer in the active material layer of the negative electrode is also improved.

[0055] The total thickness of the negative electrode active material layer, i.e., the sum of the total thickness of the first negative electrode active material layer and the total thickness of the second negative electrode active material layer, can be approximately 100 μm to approximately 1000 μm. As described above, the negative electrode active material layer according to one or more embodiments can be formed to have a maximum thickness of 1000 μm, which is much higher than the maximum thickness of a typical negative electrode active material layer (200 μm). In one or more embodiments, since the divergence (DD) of the first negative electrode active material layer (calculated by Expression 3) and the divergence (DD) of the second negative electrode active material layer are adjusted to improve the impregnation of the electrolyte, fast charging and discharging can be effectively performed even when the negative electrode active material layer is formed as thick as described above, and accordingly, it can be effectively applied to high-output batteries. According to one or more embodiments, the first negative electrode active material layer can have a DD of approximately 24 or greater, and the second negative electrode active material layer can have a DD of approximately 24 or greater.

[0056] Expression 3

[0057] Divergence (DD) = (I a / I total )*100

[0058] In expression 3,

[0059] I a It is the sum of peak intensities at non-planar angles measured by X-ray diffraction (XRD) using CuKα radiation, and

[0060] I total It is the sum of peak intensities at all angles measured by XRD using CuKα radiation.

[0061] According to one or more embodiments, the negative electrode includes: a current collector; and an upper negative electrode active material layer on (e.g., formed on) one surface of the current collector and a lower negative electrode active material layer on (e.g., formed on) another surface of the current collector, wherein the upper negative electrode active layer and the lower negative electrode active layer may each satisfy Expression 1, and optionally further satisfy Expression 2. The other surface of the current collector, as used herein, is the surface of the current collector opposite to one surface of the current collector.

[0062] Figure 1 This is a schematic cross-sectional view of a negative electrode for a rechargeable lithium battery according to one or more embodiments of the present disclosure.

[0063] refer to Figure 1 The negative electrode may include a current collector 1, an upper negative electrode active material layer 2 on (e.g., formed on) one surface of the current collector 1, and a lower negative electrode active material layer 3 on (e.g., formed on) another surface of the current collector 1.

[0064] The upper negative electrode active material layer 2 may include a first negative electrode active material layer 21 and a second negative electrode active material layer 22 sequentially formed on the current collector 1. The lower negative electrode active material layer 3 may include a first negative electrode active material layer 31 and a second negative electrode active material layer 32 sequentially formed on the current collector 1.

[0065] The upper negative electrode active material layer 2 and the lower negative electrode active material layer 3 may each satisfy Expression 1, and their average tilt angles may be the same or different. In one or more embodiments, the upper negative electrode active material layer 2 and the lower negative electrode active material layer 3 may optionally further satisfy Expression 2, and their porosities may be the same or different.

[0066] According to one or more embodiments, the negative electrode includes: a current collector; and an upper negative electrode active material layer only (e.g., formed on) one surface of the current collector, and the upper negative electrode active material layer may satisfy expression 1, and optionally further satisfy expression 2.

[0067] Figure 2 This is a schematic cross-sectional view of a negative electrode for a rechargeable lithium battery according to one or more embodiments of the present disclosure.

[0068] refer to Figure 2 The negative electrode includes a current collector 1 and an upper negative electrode active material layer 2 formed only on one surface of the current collector 1 (e.g., on).

[0069] The upper negative electrode active material layer 2 may include a first negative electrode active material layer 21 and a second negative electrode active material layer 22 sequentially formed on the current collector 1.

[0070] The first negative electrode active material layer and the second negative electrode active material layer will be described in detail below.

[0071] First negative electrode active material layer

[0072] The first negative electrode active material layer may include a carbon-based negative electrode active material (e.g., a carbon-based negative electrode active material in particulate form). The carbon-based negative electrode active material may suitably satisfy Expression 1 and Expression 2. In one or more embodiments, the carbon-based negative electrode active material may include one or more selected from natural graphite and artificial graphite.

[0073] Natural graphite is a crystalline carbon material, and because the crystallographic properties of graphite particles are further developed compared to amorphous carbon active materials, the orientation characteristics of the carbon material within the electrode plate relative to an external magnetic field can be further improved. Since natural graphite is relatively softer than synthetic graphite, if (for example, when) a first negative electrode active material layer and a second negative electrode active material layer are formed simultaneously, it is advantageous to obtain a lower average tilt angle and lower porosity.

[0074] Natural graphite can have any shape, such as irregular shape, plate shape, flake shape, spherical shape, fibrous shape, or a combination thereof. In one or more embodiments, natural graphite can have a spherical shape. Spherical natural graphite can readily achieve the aforementioned average tilt angle and porosity.

[0075] Natural graphite can have a higher powder compaction density than synthetic graphite. This higher powder compaction density can further increase the adhesion of the first negative electrode active material layer to the current collector. The powder compaction density can be from about 1.5 g / cc to about 2.5 g / cc (e.g., from about 1.5 g / cc to about 2.0 g / cc or from about 1.6 g / cc to about 2.0 g / cc). Within these ranges, the aforementioned average tilt angle and porosity can be readily obtained.

[0076] Artificial graphite can have any shape, such as irregular shape, plate shape, flake shape, spherical shape, fibrous shape, or a combination thereof. In one or more embodiments, artificial graphite can have a plate shape. Plate-shaped artificial graphite can readily obtain the aforementioned average tilt angle and porosity.

[0077] Artificial graphite can have a lower powder compaction density than natural graphite. Compared to natural graphite, this powder compaction density is beneficial for ensuring surface pores in the negative electrode active material layer, thus increasing the fast charging effect. For example, artificial graphite can have a powder compaction density of about 1.0 g / cc to about 2.0 g / cc (e.g., about 1.0 g / cc to about 1.8 g / cc). Within this range, the aforementioned average tilt angle and porosity can be easily obtained.

[0078] In this disclosure, the term "powder compaction density" refers to the density of particles produced by feeding 1g of negative electrode active material into a mold and pressing it for 30 seconds while maintaining a pressure of 2 tons.

[0079] The content of artificial graphite can be less than that of natural graphite. Because the compacted density of natural graphite powder is higher than that of artificial graphite powder, artificial graphite needs to be included in a smaller amount than natural graphite, thereby relatively reducing the average tilt angle and porosity of the first negative electrode active material layer.

[0080] According to one or more embodiments, the first negative electrode active material layer includes a negative electrode active material, and based on the total weight of 100 wt% of the negative electrode active material, the negative electrode active material may include a mixture of about 60 wt% to 100 wt% of natural graphite and 0 wt% to about 40 wt% of artificial graphite.

[0081] According to one or more embodiments, the mixture may include 100 wt% of natural graphite and 0 wt% of artificial graphite.

[0082] According to one or more embodiments, the mixture may include about 60 wt% or more and less than 100 wt% (e.g., about 65 wt% to about 95 wt% or about 70 wt% to about 90 wt%) of natural graphite and more than 0 wt% and about 40 wt% or less (e.g., about 5 wt% to about 35 wt% or about 10 wt% to about 30 wt%) of synthetic graphite. Within the above ranges, the aforementioned average tilt angle and porosity can be readily obtained.

[0083] In one or more embodiments, the first negative electrode active material layer may further include at least one of Si-based negative electrode active materials (e.g., Si-based negative electrode active materials in particulate form), Sn-based negative electrode active materials (e.g., Sn-based negative electrode active materials in particulate form), and lithium vanadium oxide negative electrode active materials (e.g., lithium vanadium oxide negative electrode active materials in particulate form). When the first negative electrode active material layer further includes one or more of those listed above, that is, when it includes one or more of the carbon-based negative electrode active materials as the first negative electrode active material and the negative electrode active materials listed above as the second negative electrode active material, the mixing ratio of the first negative electrode active material to the second negative electrode active material may be 50:50 to 99:1 by weight.

[0084] In addition to the negative electrode active material, the first negative electrode active material layer may further include one or more of a conductive material and a binder.

[0085] For example, in one or more embodiments, based on the total weight of 100 wt% of the first negative electrode active material layer, the first negative electrode active material layer may include about 90 wt% to about 99.5 wt% of negative electrode active material, about 0.5 wt% to about 5 wt% of binder, and 0 wt% to about 5 wt% (e.g., about 0.1 wt% to about 5 wt%) of conductive material.

[0086] The binder is used to bond the negative electrode active material particles and adhere the negative electrode active material to the current collector. As a binder, non-aqueous (e.g., water-insoluble) binders, aqueous (e.g., water-soluble) binders, dry binders, or combinations thereof can be used.

[0087] The non-aqueous adhesive may be polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or a combination thereof.

[0088] Waterborne adhesives may be selected from styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepoxychloropropane, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0089] When an aqueous binder is used as a binder in the negative electrode active material layer, it may further include a cellulose-based compound capable of imparting viscosity. As a cellulose-based compound, one or more mixtures of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and their alkali metal salts may be used. As an alkali metal, Na, K, or Li may be used.

[0090] Dry binders are polymeric materials capable of being fibrous, and can be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or combinations thereof.

[0091] Conductive materials (e.g., electrically conductive materials) are used to impart conductivity to electrodes, and any material can be used as long as it does not cause undesirable chemical changes in the battery and is electronically conductive. Non-limiting 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, carbon nanotubes, etc.; metallic materials, including copper, nickel, aluminum, silver, etc., and in the form of metal powders or metal fibers; conductive polymers, such as polyphenylene derivatives, etc.; and mixtures thereof.

[0092] According to one or more embodiments, the first negative electrode active material layer may be a layer manufactured by applying a slurry for the first negative electrode active material layer onto a current collector, drying the slurry to prepare a film for the first negative electrode active material layer, and rolling the film. In other words, the first negative electrode active material layer manufactured by rolling the film can satisfy Expression 1, and optionally further satisfy Expression 2.

[0093] According to one or more embodiments, the first negative electrode active material layer may be a layer manufactured by applying a slurry for the first negative electrode active material layer onto a current collector, drying the slurry to prepare a film for the first negative electrode active material layer, and then rolling and vacuum drying the film. In other words, the first negative electrode active material layer manufactured by rolling and vacuum drying the film can satisfy Expression 1, and optionally further satisfy Expression 2.

[0094] The average tilt angle and porosity of the first negative electrode active material layer can be achieved by adjusting the characteristics of the negative electrode active material included in the first negative electrode active material layer (such as the type of negative electrode active material and powder compaction density, rolling degree, and the orientation of the magnetic field, which will be described below). In one or more embodiments, a magnetic field can be applied when the slurry for the first negative electrode active material is applied. This will be described in detail below.

[0095] Second negative electrode active material layer

[0096] The second negative electrode active material layer may include a carbon-based negative electrode active material (e.g., a carbon-based negative electrode active material in particulate form). The carbon-based negative electrode active material may suitably satisfy Expression 1 and Expression 2. The carbon-based negative electrode active material may include one or more selected from natural graphite and artificial graphite.

[0097] Natural graphite and artificial graphite may each have a configuration substantially the same as that described for the first negative electrode active material layer (e.g., powder compaction density, shape, etc.).

[0098] According to one or more embodiments, the second negative electrode active material layer may include artificial graphite as a carbon-based negative electrode active material. Artificial graphite is a crystalline carbon material, and because the crystallographic properties of graphite particles are further developed compared to amorphous carbon active materials, the orientation characteristics of the carbon material within the electrode plate relative to an external magnetic field can be further improved. Because artificial graphite is relatively hard compared to natural graphite, if (e.g., when) the first and second negative electrode active material layers are formed simultaneously, it is advantageous to obtain a higher average tilt angle and higher porosity.

[0099] According to one or more embodiments, the second negative electrode active material layer includes a negative electrode active material, and based on the total weight of the negative electrode active material, the negative electrode active material may include a mixture of about 60 wt% to 100 wt% artificial graphite and 0 wt% to about 40 wt% natural graphite.

[0100] According to one or more embodiments, the mixture may include 100 wt% of artificial graphite and 0 wt% of natural graphite.

[0101] According to one or more embodiments, the mixture may include about 60 wt% or more and less than 100 wt% (e.g., about 65 wt% to about 95 wt% or about 70 wt% to about 90 wt%) of artificial graphite and more than 0 wt% and about 40 wt% or less (e.g., about 5 wt% to about 35 wt% or about 10 wt% to about 30 wt%) of natural graphite. Within the above ranges, the aforementioned average tilt angle and porosity can be readily obtained.

[0102] In one or more embodiments, the second negative electrode active material layer may further include at least one of Si-based negative electrode active materials (e.g., Si-based negative electrode active materials in particulate form), Sn-based negative electrode active materials (e.g., Sn-based negative electrode active materials in particulate form), and lithium vanadium oxide negative electrode active materials (e.g., lithium vanadium oxide negative electrode active materials in particulate form). When the second negative electrode active material layer further includes one or more of those listed above, that is, when it includes one or more of the carbon-based negative electrode active materials as the first negative electrode active material and the negative electrode active materials listed above as the second negative electrode active material, the mixing ratio of the first negative electrode active material to the second negative electrode active material may be 50:50 to 99:1 by weight.

[0103] Based on the total weight of 100 wt% of the second negative electrode active material layer, the second negative electrode active material layer may include an amount of about 90 wt% to about 99.5 wt% (e.g., about 95 wt% to about 99 wt%) of carbon-based negative electrode active material.

[0104] In addition to the carbon-based negative electrode active material, the second negative electrode active material layer may further include one or more of a conductive material and a binder.

[0105] For example, in one or more embodiments, based on the total weight of 100 wt% of the second negative electrode active material layer, the second negative electrode active material layer may include about 90 wt% to about 99.5 wt% of negative electrode active material, about 0.5 wt% to about 5 wt% of binder, and 0 wt% to about 5 wt% of conductive material.

[0106] The binder and conductive material are substantially the same as those described for the first negative electrode active material layer.

[0107] According to one or more embodiments, the second negative electrode active material layer can be a layer manufactured by applying a slurry for the second negative electrode active material layer onto a current collector, drying the slurry to prepare a film for the second negative electrode active material layer, and rolling the film. In other words, the second negative electrode active material layer manufactured by rolling the film can satisfy Expression 1, and optionally further satisfy Expression 2.

[0108] According to one or more embodiments, the second negative electrode active material layer can be a layer manufactured by applying a slurry for the second negative electrode active material layer onto a current collector, drying the slurry to prepare a membrane for the second negative electrode active material layer, and then rolling and vacuum drying the membrane. In other words, the second negative electrode active material layer manufactured by rolling and vacuum drying the membrane can satisfy Expression 1, and optionally further satisfy Expression 2.

[0109] The average tilt angle and porosity of the second negative electrode active material layer can be achieved by adjusting the characteristics of the negative electrode active material included in the second negative electrode active material layer, such as the type of negative electrode active material and powder compaction density, rolling degree, and the orientation of the magnetic field, which will be described below. In one or more embodiments, a magnetic field can be applied when the slurry for the second negative electrode active material is applied. This will be described in detail below.

[0110] Manufacturing of the first negative electrode active material layer and the second negative electrode active material layer

[0111] The first negative electrode active material layer can be formed by a method including applying a magnetic field when a slurry for the first negative electrode active material layer is applied to a current collector. The second negative electrode active material layer can be formed by a method including applying a magnetic field when a slurry for the second negative electrode active material layer is applied to the first negative electrode active material layer.

[0112] For example, in one or more embodiments, a current collector is located below a magnet, and then a slurry for a first negative electrode active material layer is applied to the current collector. After applying the slurry for the first negative electrode active material layer, the slurry is dried to form the first negative electrode active material layer. Subsequently, a slurry comprising the negative electrode active material for a second negative electrode active material layer is applied to the first negative electrode active material layer and dried to form the second negative electrode active material layer.

[0113] The first and second negative electrode active material layers can be formed by separately applying slurries for the first and second negative electrode active material layers. In this regard, the drying process is performed simultaneously with the application of the slurries for the first and second negative electrode active material layers. Accordingly, since the slurries for the first and second negative electrode active material layers are dried simultaneously with their application, the first and second negative electrode active material layers can be formed as independent layers, rather than as single layers without boundaries.

[0114] In one or more embodiments, when applying a slurry for a first negative electrode active material layer to both surfaces of the current collector, and then applying a slurry for a second negative electrode active material layer onto the slurry of the first negative electrode active material layer, the process can be performed as follows: forming a first negative electrode active material layer on one surface of the current collector, forming a first negative electrode active material layer on another surface of the current collector (the other surface of the current collector is opposite to the surface on which the first negative electrode active material layer is formed, and is the surface on which the first negative electrode active material layer is not formed), and forming a second negative electrode active material layer on each of the two first negative electrode active material layers. In one or more embodiments, the process can be performed as follows: sequentially forming a first negative electrode active material layer and a second negative electrode active material layer on one surface of the current collector, and then sequentially forming a first negative electrode active material layer and a second negative electrode active material layer on the other surface of the current collector.

[0115] The magnetic field generated by the magnet can be from approximately 1000 Gauss to approximately 10000 Gauss. Furthermore, after being applied to the current collector, the slurry used for the negative electrode active material layer can be maintained for approximately 1 second to approximately 9 seconds, that is, it can be exposed to the magnetic field for approximately 1 second to approximately 9 seconds.

[0116] Because a magnetic field is applied, especially when the coating process is performed while the current collector is moving, a magnetic field (magnetic flux) is formed by a magnet in a direction perpendicular to the current collector. However, depending on the coating speed (the current collector's moving speed), the actual direction of the magnetic field is formed at a constant angle in the form of a vector function. Therefore, the negative electrode active material included in the slurry for the first negative electrode active material layer and the negative electrode active material included in the slurry for the second negative electrode active material layer can be tilted at their respective constant angles based on the current collector surface, i.e., they can be oriented.

[0117] In this regard, in the case of a negative electrode active material layer, the ratio of the peak intensity of the (002) plane to the (110) plane in the XRD pattern can be about 200 or greater (e.g., about 200 to about 300).

[0118] In one or more embodiments, drying may include vacuum drying. Vacuum drying may be performed at a pressure of about 0.03 atm to about 0.06 atm and a temperature of about 100°C to about 160°C.

[0119] The first and second negative electrode active material layers can be manufactured by rolling after drying.

[0120] Rolling can affect the average tilt angle and porosity of each of the first and second negative electrode active material layers. Rolling can be performed under suitable conditions in the art. Within the above range, the aforementioned average tilt angle and porosity can be readily obtained.

[0121] Figure 3A The following are illustrated according to one or more embodiments: Figure 1 An example of the tilt angle of the first and second negative electrode active material layers in the upper negative electrode active material layer before rolling. Figure 3B The following are illustrated according to one or more embodiments: Figure 1 An example of the tilt angle of the first and second negative electrode active layers in the upper negative electrode active material layer after rolling.

[0122] refer to Figure 3A and Figure 3B It can be seen that the trends of the tilt angle before and after roller pressing are different.

[0123] Figure 4A The following are illustrated according to one or more embodiments: Figure 1 Another example of the tilt angle of the first and second negative electrode active layers in the lower negative electrode active material layer before rolling. Figure 4B The following are illustrated according to one or more embodiments: Figure 1 Another example of the tilt angle of the first and second negative electrode active material layers after rolling.

[0124] refer to Figure 4A and Figure 4B It can be seen that the trends of the tilt angle before and after roller pressing are different.

[0125] Figure 5 The following are illustrated according to one or more embodiments: Figure 1 The porosity changes of the first and second negative electrode active material layers in the upper negative electrode active material layer before and after rolling. Figure 6 The following are illustrated according to one or more embodiments: Figure 1 The porosity changes of the first and second negative electrode active material layers in the lower negative electrode active material layer before and after rolling.

[0126] refer to Figure 5 and Figure 6 It can be seen that the porosity trends before and after roller pressing are different.

[0127] current collector

[0128] The current collector can be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and combinations thereof.

[0129] According to one or more embodiments of this disclosure, a rechargeable lithium battery may include a negative electrode and a positive electrode for a rechargeable lithium battery according to one or more embodiments.

[0130] Since the negative electrode for rechargeable lithium batteries has already been described above, its detailed description will not be repeated for the sake of brevity.

[0131] positive electrode

[0132] The positive electrode for a rechargeable lithium battery may include a positive electrode current collector and a layer of positive electrode active material on the positive electrode current collector. The positive electrode active material layer may include positive electrode active material (e.g., positive electrode active material in particulate form) and may further include a binder and / or a conductive material (e.g., an electrically conductive material).

[0133] In one or more embodiments, the positive electrode may further include a component that can be used as a sacrificial positive electrode.

[0134] Based on the total weight of 100 wt% of the positive electrode active material layer, the amount of positive electrode active material can be from about 90 wt% to about 99 wt%. Based on the total weight of 100 wt% of the positive electrode active material layer, the amounts of binder and conductive material can each be from about 0.5 wt% to about 5 wt%.

[0135] In one or more embodiments, the positive electrode active material may include a compound capable of intercalating and deintercalating lithium (lithiation intercalation compound). For example, in one or more embodiments, at least one of lithium and a composite oxide of a metal selected from cobalt, manganese, nickel and combinations thereof may be used.

[0136] The composite oxide can be a lithium transition metal composite oxide. Non-limiting examples of lithium transition metal composite oxides may include lithium nickel oxides, lithium cobalt oxides, lithium manganese oxides, lithium iron phosphate compounds, cobalt-free nickel manganese oxides, or combinations thereof.

[0137] In one or more embodiments, one or more compounds represented by any of the following chemical formulas may be used: Li a A 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5 and 0≤c≤0.05); Li a Mn 2-b X b O4-c D c (0.90≤a≤1.8, 0≤b≤0.5 and 0≤c≤0.05); Li a Ni 1-b-c Co b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5 and 0<α<2); Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5 and 0<α<2); Li a Ni b Co c L 1 d G e O2 (0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5 and 0≤e≤0.1); Li a NiG b O2(0.90≤a≤1.8 and 0.001≤b≤0.1); Li a CoG b O2(0.90≤a≤1.8 and 0.001≤b≤0.1); Li a Mn 1-b G b O2(0.90≤a≤1.8 and 0.001≤b≤0.1); Li a Mn2G b O4 (0.90≤a≤1.8 and 0.001≤b≤0.1); Li a Mn 1-g G g PO4 (0.90≤a≤1.8 and 0≤g≤0.5); Li (3-f) Fe2(PO4)3 (0≤f≤2); and Li a FePO4 (0.90≤a≤1.8).

[0138] In the preceding chemical formulas, A is nickel (Ni), cobalt (Co), manganese (Mn), or a combination thereof; X is aluminum (Al), Ni, Co, Mn, chromium (Cr), iron (Fe), magnesium (Mg), strontium (Sr), vanadium (V), rare earth elements, or a combination thereof; D is oxygen (O), fluorine (F), sulfur (S), phosphorus (P), or a combination thereof; G is Al, Cr, Mn, Fe, Mg, lanthanum (La), cerium (Ce), Sr, V, or a combination thereof; and L1 It is Mn, Al, or a combination thereof.

[0139] In one or more embodiments, the positive electrode active material can be, for example, a high-nickel positive electrode active material, based on 100 mol% of the total metals other than lithium in the lithium transition metal complex oxide, having a nickel content greater than or equal to about 80 mol%, greater than or equal to about 85 mol%, greater than or equal to about 90 mol%, greater than or equal to about 91 mol%, or greater than or equal to about 94 mol% and less than or equal to about 99 mol%. High-nickel positive electrode active materials can achieve high capacity and can be applied to high-capacity, high-density rechargeable lithium batteries.

[0140] The binder is used to ensure good adhesion between the positive electrode active material particles and also to ensure good adhesion between the positive electrode active material and the positive electrode current collector. Examples of binders may include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers including ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylate resin, polyester resin, nylon, etc., as non-limiting examples.

[0141] Conductive materials can be used to impart conductivity (e.g., electrical conductivity) to electrodes. Any material that does not cause chemical changes (e.g., does not cause undesirable chemical changes in rechargeable lithium batteries) and conducts electrons can be used in the battery. Non-limiting examples of conductive materials may include: carbon-based materials such as natural graphite, synthetic graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and / or carbon nanotubes; metallic materials, including copper, nickel, aluminum, silver, etc., and in the form of metal powders or metal fibers; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0142] In one or more embodiments, the Al foil can be used as a positive electrode current collector, but the embodiments of this disclosure are not limited thereto.

[0143] Rechargeable lithium batteries may further include an electrolyte.

[0144] electrolyte

[0145] Electrolytes used in rechargeable lithium batteries may include non-aqueous organic solvents and lithium salts.

[0146] Non-aqueous organic solvents can be used as media for transporting ions that participate in the electrochemical reactions of rechargeable lithium batteries.

[0147] Non-aqueous organic solvents may include carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, aprotic solvents, or combinations thereof.

[0148] Carbonate solvents can 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), butyl carbonate (BC), etc.

[0149] Ester solvents can include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanoic acid lactone, mevalonate lactone, caprolactone, etc.

[0150] Ether solvents can include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. Ketone solvents can include cyclohexanone, etc. Alcohol solvents can include ethanol, isopropanol, etc. Aprotic solvents can include: nitrile solvents, such as R-CN (where R is a C2-C20 straight-chain, branched, or cyclic hydrocarbon group, and may include double bonds, aromatic rings, ether bonds, etc.); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane, 1,4-dioxolane, etc.; sulfolane, etc.

[0151] Non-aqueous organic solvents can be used alone or in combination of two or more.

[0152] In one or more embodiments, when using carbonate solvents, cyclic carbonates and chain carbonates can be mixed and used, and the cyclic carbonates and chain carbonates can be mixed in a volume ratio of about 1:1 to about 1:9.

[0153] Lithium salts dissolved in non-aqueous organic solvents supply lithium ions to rechargeable lithium batteries, ensuring basic operation and improving lithium ion transport between the positive and negative electrodes. Non-limiting examples of lithium salts include those selected from LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide, LiFSI), LiC4F9SO3, and LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2 (where x and y are each integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFBOP), and lithium bis(oxalate)borate (LiBOB).

[0154] Rechargeable lithium batteries may further include a separator.

[0155] diaphragm

[0156] 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 film of two or more layers thereof (such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator, etc.).

[0157] The diaphragm may include a porous substrate and a coating on one or both surfaces of the porous substrate, the coating comprising an organic material, an inorganic material, or a combination thereof.

[0158] The porous substrate may be a polymer membrane formed from any one of the following polymers or copolymers or mixtures thereof: polyolefins (such as polyethylene and / or polypropylene), polyesters (such as polyethylene terephthalate and / or 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).

[0159] Organic materials may include polymers such as polyvinylidene fluoride or (meth)acrylic acid polymers.

[0160] Inorganic materials may include 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, but the embodiments disclosed herein are not limited thereto.

[0161] Organic and inorganic materials can be mixed in a single coating, or they can exist in the form of a stacked coating containing organic materials and a coating containing inorganic materials.

[0162] Rechargeable lithium batteries

[0163] Depending on their shape, rechargeable lithium batteries can be classified as cylindrical batteries, prismatic batteries, pouch batteries, or coin-shaped batteries, etc. Figures 7-10 Each of the following is a schematic diagram illustrating a rechargeable lithium battery according to one or more embodiments of the present disclosure. Figure 7 A cylindrical battery is shown. Figure 8 A prismatic battery is shown, and Figure 9 and Figure 10A pouch-shaped battery is shown. (Reference) Figures 7-10 The rechargeable lithium battery 100 may include an electrode assembly 40 and a housing 50. The electrode assembly 40 includes a separator 30 between a positive electrode 10 and a negative electrode 20, and the housing 50 houses the electrode assembly 40. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte. In one or more embodiments, such as Figure 7 As shown, the rechargeable lithium battery 100 may include a sealing member 60 of a sealed housing 50. In one or more embodiments, such as Figure 8 As shown, the rechargeable lithium battery 100 may include a positive electrode lead connector 11, a positive electrode terminal 12, a negative electrode lead connector 23, and a negative electrode terminal 24. In one or more embodiments, such as Figure 9 and Figure 10 As shown, the rechargeable lithium battery 100 may include electrode terminals 70, which may serve as electrical paths for guiding current formed in the electrode assembly 40 to the outside, such as positive electrode terminal 71 and negative electrode terminal 72.

[0164] As a non-limiting example, rechargeable lithium batteries according to one or more embodiments can be used in automobiles, mobile phones and / or various types of electronic devices.

[0165] Embodiments and comparative examples of this disclosure will be described below. The examples below are for illustrative purposes only and are not intended to limit the scope of this disclosure.

[0166] Example 1:

[0167] A slurry for the first negative electrode active material layer was prepared by mixing 75 wt% natural graphite (with a spherical shape and a powder compaction density of 1.7 g / cc), 22.5 wt% artificial graphite (with a plate shape and a powder compaction density of 1.5 g / cc), 1.7 wt% styrene-butadiene rubber, and 0.8 wt% carboxymethyl cellulose in water.

[0168] A slurry for the second negative electrode active material layer was prepared by mixing 75 wt% artificial graphite (with a plate shape and a powder compaction density of 1.5 g / cc), 22.5 wt% natural graphite (with a spherical shape and a powder compaction density of 1.7 g / cc), 1.7 wt% styrene-butadiene rubber, and 0.8 wt% carboxymethyl cellulose in water.

[0169] A copper foil is placed beneath a magnet with a magnetic field strength of 5000 Gauss. While moving the copper foil, slurries for the first negative electrode active material layer and slurries for the second negative electrode active material layer are sequentially applied to one surface of the copper foil, and then dried for single-sided coating. For example, slurry for the first negative electrode active material layer is applied to one surface of the copper foil, and slurry for the second negative electrode active material layer is sequentially applied over the slurry for the first negative electrode active material layer, and then dried for single-sided coating.

[0170] Subsequently, the slurry for the first negative electrode active material layer and the slurry for the second negative electrode active material layer are applied sequentially to another surface of the copper foil in the same manner as described above, and then dried for single-sided coating.

[0171] The copper foil obtained is subjected to a roll forming process to manufacture a negative electrode, wherein a first negative electrode active material layer (comprising 75 wt% natural graphite and 22.5 wt% artificial graphite) and a second negative electrode active material layer (comprising 75 wt% artificial graphite and 22.5 wt% natural graphite) are sequentially formed on one surface of the copper foil, and the same process is repeated on the other surface of the copper foil.

[0172] A positive electrode active material slurry was prepared by mixing 96 wt% LiCoO2 as the positive electrode active material, 2 wt% carbon black as the conductive material, and 2 wt% polyvinylidene fluoride as the binder in an N-methylpyrrolidone solvent. The positive electrode active material slurry was applied to an Al substrate, dried, and rolled to fabricate the positive electrode.

[0173] A battery with a capacity of 550 mAh and a flux density of 4.70 mAh / cm³ was fabricated using a negative electrode, a positive electrode, and an electrolyte. 2 A cylindrical rechargeable lithium-ion battery of type 18650 with a full cell capacity. The electrolyte is prepared by dissolving 1M LiPF6 in a mixed solvent of ethylene carbonate and diethyl carbonate (50:50 volume ratio).

[0174] Example 2

[0175] The negative electrode and battery were manufactured in essentially the same manner as in Example 1, except that the amounts of natural graphite and artificial graphite in the first negative electrode active material layer were changed to 86 wt% and 11.5 wt%, respectively, and the amounts of natural graphite and artificial graphite in the second negative electrode active material layer were changed to 11.5 wt% and 86 wt%, respectively.

[0176] Example 3

[0177] The negative electrode and battery were manufactured in essentially the same manner as in Example 1, except that the amounts of natural graphite and artificial graphite in the first negative electrode active material layer were changed to 97.5 wt% and 0 wt%, respectively, and the amounts of natural graphite and artificial graphite in the second negative electrode active material layer were changed to 0 wt% and 97.5 wt%, respectively.

[0178] Comparative Example 1

[0179] The negative electrode and battery were manufactured in essentially the same manner as in Example 1, except that the amounts of natural graphite and artificial graphite in the first negative electrode active material layer were changed to 48.75 wt% and 48.75 wt%, respectively, and the amounts of natural graphite and artificial graphite in the second negative electrode active material layer were changed to 48.75 wt% and 48.75 wt%, respectively.

[0180] The average tilt angle and porosity of each of the manufactured negative electrodes were measured.

[0181] (1) Tilt Angle: The cross-sectional SEM image of the negative electrode plate was measured and confirmed using ImageJ software (commercially available). The cross-sectional SEM image of the electrode plate was loaded into ImageJ software, and the area for measuring the tilt angle was selected. The tilt degree of the holes in the cross-section of the electrode plate within the selected area was measured (when the angle of the current collector is set to 0°, the tilt angle of the holes is (e.g., = ) the tilt angle of the negative electrode active material layer), and the average tilt angle was calculated. The average tilt angle can be confirmed using ImageJ software.

[0182] (2) Porosity: The cross-sectional SEM image of the negative electrode plate was measured and verified using ImageJ software (commercially available). The cross-sectional SEM image of the electrode plate was loaded into ImageJ software, the area to be measured for porosity was selected, and the ratio of the area of ​​the pores in the selected area to the total area of ​​the selected area was measured to determine the porosity. The porosity can be verified using ImageJ software.

[0183] The adhesion and fast-charging performance of each of the manufactured batteries were evaluated.

[0184] (3) Adhesion (unit: gf / 25mm): To measure adhesion, adhesive tape was attached to a glass slide, and then the electrode plate to be measured was attached to the tape. Air bubbles between the slide and tape were then removed by pressing the attachment surfaces, and a roller was used to ensure tight contact between the electrode plate and the tape to prepare the sample. The adhesion at 90° was then measured three times using an adhesion measuring device, and the average value was calculated.

[0185] (4) Fast charging performance (unit: Ω): Symmetrical battery cells were fabricated, and the ion resistance of the electrode plates was calculated by electrochemical impedance spectroscopy (EIS) to predict fast charging performance. The lower the ion resistance, the better the fast charging performance at high C-rates.

[0186] Table 1

[0187]

[0188] As shown in Table 1, each of the negative electrodes in Examples 1 to 3 exhibits excellent adhesion to the current collector and provides excellent fast charging performance.

[0189] However, compared with Examples 1 to 3, the negative electrode of Comparative Example 1, which does not satisfy Expression 1 of this disclosure, exhibits low adhesion and low fast charging effect.

[0190] As used herein, the term "group" refers to a group in the periodic table of elements according to the International Union of Pure and Applied Chemistry ("IUPAC") grouping system 1–18.

[0191] In this disclosure, it will be understood that the terms “comprise(s)”, “include(s)”, or “have / has / having” indicate the presence of the described features, integers, steps, operations, elements, components, and / or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. Furthermore, the terms “comprise(s)”, “include(s)”, or “have / has / having”, or other similar terms that include or support the terms “consisting of” and “substantially constitute” indicate the presence of the described features, integers, steps, operations, elements, components, and / or groups thereof, while other features, integers, steps, operations, elements, components, and / or groups thereof are absent or substantially absent.

[0192] The terms “substantially,” “about,” and similar terms used herein are used as terms of approximation and not as terms of degree, and are intended to describe inherent biases in measured or calculated values ​​that would be recognized by a person skilled in the art. “About” or “approximately” as used herein also includes stated values ​​and means within an acceptable range of deviation for a particular value, determined by a person skilled in the art taking into account the measurement in question and the errors associated with the measurement of the particular quantity (i.e., limitations of the measurement system). For example, “about” may mean within one or more standard deviations, or within ±30%, ±20%, ±10%, or ±5% of the stated value. Furthermore, it should be understood that even if the terms “about,” “approximately,” or “substantially” are not explicitly stated in a given element (e.g., a claim element), the scope of that element is intended to include non-substantial variations or variations within the understanding of a person skilled in the art. For example, the numerical values ​​and ranges provided herein are intended to include tolerances and measurement uncertainties that would be recognized by a person skilled in the art, and these elements (e.g., claim elements) should be interpreted accordingly to include these equivalents.

[0193] In the context of this disclosure, unless otherwise specified, “use,” “using,” and “used” are to be regarded as synonymous with the terms “utilize,” “utilizing,” and “utilized,” respectively.

[0194] Any numerical range set forth herein is intended to include all subranges of 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 stated minimum value of 1.0 and the stated maximum value of 10.0, that is, 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.

[0195] The battery (e.g., dry electrode) manufacturing apparatus, battery pack, battery management system (BMS) apparatus, and / or any other related apparatus or components described herein according to embodiments of this disclosure may be implemented using any suitable hardware, firmware (e.g., application-specific integrated circuits), software, or a combination of software, firmware, and hardware. For example, various components of the apparatus may be formed on an integrated circuit (IC) chip or on a separate IC chip. Furthermore, various components of the apparatus may be implemented on a flexible printed circuit film, tape-on-a-carrier package (TCP), or printed circuit board (PCB), or formed on a substrate. Furthermore, various components of the apparatus may be processes or threads that run on one or more processors in one or more computing devices, execute computer program instructions, and interact with other system components to perform the various functions described herein. The computer program instructions are stored in memory, which may be implemented in the computing device using standard memory devices (such as, for example, random access memory (RAM)). The computer program instructions may also be stored in other non-transitory computer-readable media (such as, for example, CD-ROMs or flash drives). Furthermore, those skilled in the art will recognize that, without departing from the scope of this disclosure, the functions of various computing devices can be combined or integrated into a single computing device, or the functions of a dedicated computing device can be distributed across one or more other computing devices.

[0196] Those skilled in the art, in view of the entirety of this disclosure, will recognize that each suitable feature of the various embodiments of this disclosure may be combined in part or in whole, or combined with one another, and may be technically interlocked and operated in various suitable ways, and that, unless otherwise stated or implied, each embodiment may be implemented independently of one another or may be implemented in any suitable way in combination with one another.

[0197] Example embodiments of this disclosure have been described, but this disclosure is not limited thereto. Various other modifications may be made within the scope of the claims, and the detailed description and accompanying drawings of this disclosure are also included within its scope. Therefore, the technical scope of this disclosure is not limited to what is described in the detailed description of this disclosure, but should be determined by the claims and their equivalents.

Claims

1. A negative electrode for a rechargeable lithium battery, the negative electrode comprising: current collector; and A layer of negative electrode active material on at least one surface of the current collector. The negative electrode active material layer comprises a first negative electrode active material layer and a second negative electrode active material layer sequentially arranged on the current collector, and satisfies expression 1: Expression 1 The average tilt angle of the first negative electrode active material layer is less than the average tilt angle of the second negative electrode active material layer.

2. The negative electrode according to claim 1, wherein the average tilt angle of the second negative electrode active material layer differs from the average tilt angle of the first negative electrode active material layer by 2° or more.

3. The negative electrode according to claim 1, wherein the second negative electrode active material layer has an average tilt angle of 35° or greater, and the first negative electrode active material layer has an average tilt angle of 30° or greater.

4. The negative electrode according to claim 1, wherein the active material layer of the negative electrode further satisfies expression 2: Expression 2 The porosity of the first negative electrode active material layer is less than that of the second negative electrode active material layer.

5. The negative electrode according to claim 4, wherein the porosity of the second negative electrode active material layer differs from the porosity of the first negative electrode active material layer by 3% or more.

6. The negative electrode according to claim 5, wherein the second negative electrode active material layer has a porosity of 15% or greater, and the first negative electrode active material layer has a porosity of 10% or greater.

7. The negative electrode according to claim 1, wherein the first negative electrode active material layer comprises a carbon-based negative electrode active material.

8. The negative electrode according to claim 7, wherein, based on the total weight of 100 wt% of the carbon-based negative electrode active material, the carbon-based negative electrode active material comprises a mixture of 60 wt% to 100 wt% of natural graphite and 0 wt% to 40 wt% of artificial graphite.

9. The negative electrode according to claim 8, wherein the natural graphite has a powder compaction density of 1.5 g / cc to 2.5 g / cc, and the artificial graphite has a powder compaction density of 1.0 g / cc to 2.0 g / cc.

10. The negative electrode according to claim 9, wherein the natural graphite has a spherical shape and the artificial graphite has a plate shape.

11. The negative electrode according to claim 1, wherein the second negative electrode active material layer comprises a carbon-based negative electrode active material.

12. The negative electrode according to claim 11, wherein, based on the total weight of 100 wt% of the carbon-based negative electrode active material, the carbon-based negative electrode active material comprises a mixture of 60 wt% to 100 wt% artificial graphite and 0 wt% to 40 wt% natural graphite.

13. The negative electrode according to claim 12, wherein the natural graphite has a powder compaction density of 1.5 g / cc to 2.5 g / cc, and the artificial graphite has a powder compaction density of 1.0 g / cc to 2.0 g / cc.

14. The negative electrode according to claim 13, wherein the natural graphite has a spherical shape and the artificial graphite has a plate shape.

15. A rechargeable lithium battery comprising a negative electrode and a positive electrode according to any one of claims 1 to 14.

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