Negative electrode for rechargeable battery and electrode assembly comprising the same

Abstract

A negative electrode for a rechargeable battery and an electrode assembly including the negative electrode are provided. The negative electrode includes a substrate, a first active material layer formed on the substrate, and a second active material layer formed on the first active material layer. The porosity of the first active material layer is greater than the porosity of the second active material layer.

Description

Technical Field

[0001] This disclosure relates to a negative electrode for a rechargeable battery and an electrode assembly including the negative electrode. Background Technology

[0002] With the technological advancements in portable devices, the demand for rechargeable batteries as an energy source is increasing. Unlike primary batteries, rechargeable batteries are batteries that can be repeatedly charged and discharged.

[0003] This rechargeable battery can be formed into a cylindrical or core-shaped electrode assembly by stacking and then winding the positive electrode, separator, and negative electrode, or by stacking the positive electrode, separator, and negative electrode after separating them into sheets.

[0004] Meanwhile, with the development of electronic products, there is a demand for miniaturized rechargeable batteries with high capacity. Although capacity can be increased by adding silicon, silicon exhibits large volume changes during the charging and discharging process due to its material properties.

[0005] Thus, if the contraction and expansion of the active material layer are large during the charging and discharging process (when the contraction and expansion of the active material layer are large during the charging and discharging process), cracks may appear in the active material layer, which not only degrades the performance of the rechargeable battery, but also increases the risk of fire.

[0006] The information disclosed in this background section is only intended to enhance the understanding of the background of this disclosure and may therefore include information that does not constitute prior art. Summary of the Invention

[0007] This disclosure aims to provide a negative electrode and an electrode assembly including the negative electrode that can reduce the performance degradation of a rechargeable battery due to shrinkage and expansion while increasing the capacity of the rechargeable battery.

[0008] A negative electrode according to an example embodiment of the present disclosure includes: a substrate; a first active material layer formed on the substrate; and a second active material layer formed on the first active material layer, wherein the porosity of the first active material layer is greater than the porosity of the second active material layer.

[0009] The porosity of the first active material layer is in the range of about 15% to about 18%, and the porosity of the second active material layer is in the range of about 10% to about 12%.

[0010] Each or at least one of the first active material layer and the second active material layer may include a first active material and a second active material, wherein artificial graphite and silicon particles are mixed together in the first active material, and the second active material includes natural graphite.

[0011] The ratio of the first active substance to the second active substance in the first active substance layer may differ from the ratio of the first active substance to the second active substance layer.

[0012] The first and second active substances in the first active substance layer can be mixed in a ratio of approximately 25wt%:75wt%.

[0013] The particle size of artificial graphite can range from about 11 μm to about 15 μm.

[0014] The particle size of natural graphite can be in the range of about 7 μm or smaller.

[0015] The particle size of silicon particles can be in the range of about 20 μm or smaller.

[0016] The first active material layer can be formed to have a mixture density in the range of about 1.60 g / cc to about 1.65 g / cc.

[0017] The first and second active material layers can be oriented.

[0018] The first and second active material layers of the negative electrode include carbon-based negative electrode active materials. The first and second active material layers of the negative electrode have DD (divergence) values ​​as defined by Equation 1 below, and the DD value can be equal to about 30 or greater.

[0019] Equation 1: DD (divergence) = (Ia / Itotal) × 100.

[0020] In Equation 1, Ia is the sum of peak intensities appearing at non-planar angles during XRD measurements using CuKα rays, and I is always the sum of peak intensities appearing at all angles during XRD measurements using CuKα rays.

[0021] An electrode assembly according to another exemplary embodiment of this disclosure includes: a negative electrode; a positive electrode; and a separator located between the positive electrode and the negative electrode. The negative electrode includes a substrate and a first active material layer and a second active material layer stacked on the substrate, wherein the porosity of the first active material layer may be greater than the porosity of the second active material layer.

[0022] The porosity of the first active material layer can be in the range of about 15% to about 18%, and the porosity of the second active material layer can be in the range of about 10% to about 12%.

[0023] The first active material layer may include a first active material composed of a mixture of artificial graphite and silicon particles, and the second active material layer may include a second active material containing natural graphite.

[0024] The first and second active substances in the first active substance layer can be mixed in a ratio different from that in the second active substance layer.

[0025] The first and second active substances in the first active substance layer can be mixed in a ratio of approximately 25wt%:75wt%.

[0026] The first and second active material layers can be oriented.

[0027] In this disclosure, by forming pores in the active material layer, high-capacity negative electrodes and electrode assemblies for rechargeable batteries can be provided while using silicon by reducing or minimizing the occurrence of cracks due to volume expansion. Attached Figure Description

[0028] The accompanying drawings illustrate exemplary embodiments of the present disclosure and, together with the detailed description of the disclosure to be described below, are used to further understand the technical features of the present disclosure. Therefore, the present disclosure should not be construed as being limited to the contents described in these drawings.

[0029] Figure 1 This is a schematic perspective view of a rechargeable battery according to an example embodiment of the present disclosure.

[0030] Figure 2 Is included Figure 1 A schematic cross-sectional view of the stacked electrode assemblies.

[0031] Figure 3 This is a diagram used to illustrate the orientation of the negative electrode active material. Detailed Implementation

[0032] The exemplary embodiments of this disclosure are described in detail below with reference to the accompanying drawings. The terms or words used in this specification and claims should not be construed as limited to their ordinary or dictionary meanings. Rather, based on the principle that the inventor can appropriately define the concepts of terms to best describe his / her own disclosure, such terms or words should be interpreted as having meanings and concepts consistent with the technical features of this disclosure. Therefore, it should be understood that the exemplary embodiments described in this specification and the constructions shown in the accompanying drawings are merely some exemplary embodiments of this disclosure and do not represent all the technical features of this disclosure. Therefore, various equivalents and modifications may exist that can replace the exemplary embodiments at the time of filing this application.

[0033] Furthermore, when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of the mentioned shapes, quantities, steps, operations, components, elements, and / or groups thereof, without excluding the presence or addition of one or more other shapes, quantities, steps, operations, components, elements, and / or groups thereof.

[0034] Furthermore, to aid in understanding the disclosure, the dimensions of some components may be exaggerated rather than shown to scale in the accompanying drawings. Additionally, the same reference numerals may be assigned to the same components in different example embodiments.

[0035] Although terms like "first," "second," etc., are used to describe various components, it will be understood that these components are not limited by these terms. These terms are only used to distinguish one component from another, and unless otherwise specified, it will be understood that a first component can also be a second component.

[0036] Throughout this instruction manual, unless otherwise specified, each component may be singular or plural.

[0037] For ease of description, spatial relative terms such as "below," "under," "lower," "above," and "upper" may be used herein to describe the relationship between one element or feature and another element(s) shown in the accompanying drawings. Spatial relative position is understood to encompass not only the orientation depicted in the figures but also the different orientations of the device during use or operation. For example, if the device in the figures is flipped (when the device in the figures is flipped), an element described as "below" or "under" other elements will subsequently be understood as "above" or "on" said other elements. Thus, the term "below" can encompass both above and below orientations.

[0038] Furthermore, when an element is described as being “connected to” or “combined to” another element, these elements may be directly connected or directly connected to each other, but it should be understood that the other element may be “placed” between each element, or each element may be “connected,” “combined,” or “linked” through another element.

[0039] Unless otherwise defined in this specification, particle size can refer to the average particle diameter. Furthermore, particle size refers to the average particle diameter (D50), which represents the diameter of particles having a cumulative volume of 50% of the total volume in a particle size distribution. The average particle diameter (D50) can be measured by methods known to those skilled in the art, for example, by a particle size analyzer or by transmission electron microscopy (TEM) or scanning electron microscopy (SEM) photographs. Alternatively, it can be measured using a measuring device utilizing dynamic light scattering, and the average particle diameter (D50) value can be obtained based on the count after data analysis to count the number of particles for each particle size range. Optionally, the average particle diameter (D50) value can be measured using laser diffraction. For example, when measuring by laser diffraction, after dispersing the particles to be measured in a dispersion medium, the particles are introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000) and irradiated with ultrasound at an output of 60W at approximately 28kHz. The average particle size (D50) based on a 50% standard of particle size distribution in the measuring device can then be calculated.

[0040] In one example embodiment, the average particle size can be measured by the various methods described above, such as by a particle size analyzer.

[0041] In one example embodiment, the thickness can be measured by a cross-sectional SEM image or TEM image, but is not limited to this, and can be measured by any method in the art capable of measuring thickness. The thickness can be the average thickness.

[0042] In this specification, soft carbon refers to graphitizable carbon materials that can be graphitized by heat treatment at high temperatures (e.g., about 2800°C), while hard carbon refers to non-graphitizable carbon materials that cannot be graphitized by heat treatment. Soft carbon and hard carbon are well known in the art.

[0043] In one example embodiment, crystalline carbon and amorphous carbon can be classified by X-ray diffraction analysis. Crystalline carbon includes natural graphite and artificial graphite. Natural graphite refers to naturally occurring graphite obtained by separation from minerals and has a d002 of 3.350 Å to 3.360 Å in X-ray diffraction analysis; artificial graphite refers to graphite produced through graphitization and has a d002 of 3.355 Å to 3.365 Å in X-ray diffraction analysis. Amorphous carbon has a d002 of 3.34 Å or less in X-ray diffraction analysis. X-ray diffraction (XRD) analysis can be performed using CuKα rays as the target ray and an X-ray diffractometer (e.g., X'Pert (manufacturer: Malvern Panalytical)), and to improve peak intensity resolution, the monochromator device can be removed for measurement. Measurement conditions can be 2θ = 10° to 80°, scanning speed (° / s) = 0.044 to 0.089, and step size (° / step) = 0.013 to 0.039.

[0044] In one example embodiment, the weight-average molecular weight can be measured, for example, by gel permeation chromatography.

[0045] The terminology used herein is for the purpose of describing exemplary embodiments and is not intended to limit this disclosure.

[0046] When the terms “about” or “substantially” are used in conjunction with numerical values ​​in this specification, it is intended that the relevant numerical values ​​include a tolerance of ±10% around the stated value. When a range is specified, the range includes all values ​​within that range, such as increments of 0.1%.

[0047] Figure 1 This is a schematic perspective view of a rechargeable battery according to an example embodiment of the present disclosure. Figure 2 yes Figure 1 A schematic cross-sectional view of the stacked electrode assembly of the rechargeable battery shown.

[0048] like Figure 1 and Figure 2 As shown, a rechargeable battery 1000 according to an example embodiment of the present disclosure includes an electrode assembly 400 and a housing 500 that houses the electrode assembly 400 and an electrolyte (not shown).

[0049] Electrode assembly 400 is a stacked electrode assembly 400 formed by repeatedly layering a positive electrode 100 and a negative electrode 200 with a diaphragm 300 placed between them. For ease of description, Figure 2 The diagram shows a positive electrode 100, a negative electrode 200, and a diaphragm 300.

[0050] The positive electrode 100 includes a positive electrode substrate 10 and a positive electrode active material layer 12 formed on the positive electrode substrate 10. The positive electrode substrate 10 is formed of or includes a thin conductive metal foil and serves as a current collector, and may be, for example, aluminum.

[0051] The positive electrode substrate 10 includes an electrode active portion DA1 on which a positive electrode active material layer 12 is formed, and an electrode uncoated area of ​​the positive electrode substrate 10 where the positive electrode active material layer 12 is not formed, thereby exposing the positive electrode substrate 10. The positive electrode substrate 10 provides a movement path for the charge generated in the positive electrode active material layer 12 and supports the positive electrode active material layer 12.

[0052] The uncoated area of ​​the electrode can be located around the active portion DA1 of the electrode and can have the form of extending from the active portion DA1 of the electrode.

[0053] like Figure 1 and Figure 2 As shown, a portion of the uncoated electrode area protruding from one side of the active electrode portion DA1 can be connected to a positive electrode tab 91 for leading current to the outside, and the positive electrode tab 91 can be made of the same material as the substrate (e.g., aluminum) or include the same material as the substrate (e.g., aluminum). In the following description, for ease of description, the protruding uncoated electrode area connected to the positive electrode tab 91 is referred to as the tab uncoated area DA2. The tab uncoated areas DA2 of the repeatedly stacked positive electrodes 100 can be electrically connected by soldering or similar methods.

[0054] The positive electrode active material layer 12 can be formed on one surface (not shown) or both surfaces of the positive electrode substrate 10. The positive electrode active material layer 12 includes a positive electrode active material and may also include a binder and / or a conductive material. The positive electrode may also include additives that can constitute a sacrificial positive electrode.

[0055] Based on the total weight of the positive electrode active material layer, the content of the positive electrode active material can be in the range of about 90 wt% to about 99.5 wt%, and based on the total weight of the positive electrode active material layer, the content of the binder and the conductive material can be in the range of about 0.5 wt% to about 5 wt%, respectively.

[0056] Positive electrode active material As a positive electrode active material, compounds capable of reversibly inserting and deintercalating lithium (lithium-intercalating compounds) can be used. For example, one or more types of composite oxides of lithium and metals (such as or including at least one of cobalt, manganese, nickel, and combinations thereof) can be used.

[0057] The composite oxide can be or includes lithium transition metal composite oxides, and examples include at least one of lithium nickel oxides, lithium cobalt oxides, lithium manganese oxides, lithium iron phosphate compounds, cobalt-free lithium nickel manganese oxides, or combinations thereof.

[0058] As an example, a compound represented by any of the following chemical formulas can be used. Li a A 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a Mn 2-b X b O 4-c D c (0.90≤a≤1.8, 0≤b≤0.5, 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, 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, 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, 0≤e≤0.1); Li a NiG b O2 (0.90≤a≤1.8, 0.001≤b≤0.1); Li a CoG b O2 (0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-b G b O2 (0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn2G b O4 (0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn1-g G g PO4 (0.90≤a≤1.8, 0≤g≤0.5); Li (3-f) Fe2(PO4)3 (0≤f≤2); Li a FePO4 (0.90≤a≤1.8).

[0059] In the above chemical formulas, A is or includes at least one of Ni, Co, Mn, or combinations thereof; X is or includes at least one of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, or combinations thereof; D is or includes at least one of O, F, S, P, or combinations thereof; G is or includes at least one of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or combinations thereof; and L 1 It is or includes at least one of Mn, Al, or combinations thereof.

[0060] As an example, the positive electrode active material can be or includes a high-nickel positive electrode active material, in which the nickel content is 80 mol% or greater, 85 mol% or greater, 90 mol% or greater, 91 mol% or greater, or 94 mol% or greater and 99 mol% or less, relative to 100 mol% of the metals other than lithium in the lithium transition metal composite oxide. High-nickel positive electrode active materials can achieve high capacity and therefore can be used in high-capacity, high-density lithium rechargeable batteries.

[0061] adhesive The binder effectively adheres the positive electrode active material particles to each other and effectively adheres the positive electrode active material to the substrate (or current collector). Representative examples of binders 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, polymers containing 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.

[0062] conductive materials Conductive materials impart conductivity to electrodes, and any electrically conductive material can be used in the constructed battery, as long as it does not cause adverse chemical changes within the battery. Examples of conductive materials include: carbon-based materials, such as at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials, including at least one of copper, nickel, aluminum, silver, etc., in the form of metal powder or metal fibers; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0063] The negative electrode 200 includes a negative electrode substrate 20 and negative electrode active material layers 22 and 24 formed on the negative electrode substrate 20. The negative electrode substrate 20 is formed of or includes a thin conductive metal foil and serves as a current collector. For example, at least one of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and combinations thereof can be used.

[0064] The negative electrode substrate 20 includes an electrode active portion DB1 on which negative electrode active material layers 22 and 24 are formed, and an electrode uncoated area where negative electrode active material layers 22 and 24 are not formed and the negative electrode substrate 20 is exposed. The negative electrode substrate 20 provides a movement path for the charge generated in the negative electrode active material layers 22 and 24, and supports the negative electrode active material layers 22 and 24.

[0065] The uncoated area of ​​the electrode can be located around the active portion DB1 of the electrode and can have the form of extending from the active portion DB1 of the electrode.

[0066] like Figure 1 and Figure 2 As shown, the negative electrode tab 92 for leading current to the outside can be connected to a portion of the uncoated electrode area protruding from one side of the active electrode portion DB1. In the following text, for ease of description, the protruding uncoated electrode area connected to the negative electrode tab 92 is referred to as the tab uncoated area DB2. The tab uncoated areas DB2 of the repeatedly stacked negative electrodes 200 can be electrically connected by soldering.

[0067] Although the uncoated areas DA2, DB2 of the positive and negative electrodes are shown to protrude in opposite directions, this disclosure is not limited thereto. The uncoated areas DA2, DB2 may protrude in the same direction (not shown) when the positive and negative electrodes are spaced apart from each other.

[0068] The negative active material layer may be formed on one surface (not shown) of the negative electrode current collector 20, or may be respectively formed on both surfaces of the negative electrode current collector 20. Relative to the total weight of the negative active material layer, the content of the negative active material in the negative active material layer may be in the range of about 95 wt% to about 99 wt%.

[0069] Negative electrode active material The negative active material includes a first active material and a second active material capable of reversibly intercalating / deintercalating lithium ions, and a third active material capable of doping and dedoping lithium.

[0070] The first active material and the second active material are or include carbon-based negative active materials, and may be or include, for example, crystalline carbon, and examples of the crystalline carbon may be amorphous, plate-shaped, flake-shaped, spherical or fibrous graphite. In this case, the first active material may be or include artificial graphite, and the second active material may be or include natural graphite.

[0071] The first active material may further include a Si-based negative active material or a Sn-based negative active material. The Si-based negative active material may be or include silicon, a silicon-carbon composite, silicon oxide (SiO x , 0<x≤2), a Si-Q alloy (Q is or includes at least one selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements (excluding Si), Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof), or at least one of combinations thereof. The Sn-based negative active material may be or include at least one selected from Sn, SnO₂, Sn-based alloys, and combinations thereof.

[0072] The silicon-carbon composite may be or include a composite of silicon and amorphous carbon. According to an example embodiment, the silicon-carbon composite may be in a form where silicon particles are coated with amorphous carbon on the surfaces of the silicon particles. For example, the silicon-carbon composite may include secondary particles (core) assembled from silicon primary particles and an amorphous carbon coating layer (shell) located on the surfaces of the secondary particles. Amorphous carbon may also be located between the silicon primary particles, such that for example the silicon primary particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0073] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the surface of the core.

[0074] adhesive The binder causes the negative active material particles to adhere to each other, and also causes the negative active material to adhere to the current collector (or the negative electrode substrate). As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof may be used.

[0075] Non-aqueous adhesives may include at least one of polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0076] The waterborne adhesive may be or include at least one of 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.

[0077] When using an aqueous binder as the negative electrode binder, the aqueous binder may also include a cellulose-based compound capable of imparting viscosity. As a cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or their alkali metal salts may be mixed together. As an alkali metal, at least one of Na, K, or Li may be used.

[0078] Dry adhesives are polymeric materials capable of being fibrous and may be or include at least one of, for example, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or combinations thereof.

[0079] conductive materials Conductive materials impart conductivity to electrodes, and any electrically conductive material can be used in the constructed battery, as long as it does not cause adverse chemical changes within the battery. Examples of conductive materials may include: carbon-based materials, such as at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials, including at least one of copper, nickel, aluminum, silver, etc., in the form of metal powder or metal fibers; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0080] Meanwhile, the first active material layer 22 may include active materials that are different from those in the second active material layer 24. These different active materials may include not only active materials made of different materials, but also structures containing the same active material mixed in different proportions.

[0081] The first active material may further include silicon (e.g., silicon particles) together with artificial graphite. The silicon included in the first active material may range from about 6 wt% to about 10 wt% relative to the total weight of the active materials in the first active material layer 22 and the second active material layer 24, and may be included in the first active material layer 22 and the second active material layer 24 in the same proportion. The first active material layer may be formed to have a mixture density in the range of about 1.60 g / cc to about 1.65 g / cc.

[0082] The ratio of the first active substance to the second active substance in the first active substance layer 22 can be 25wt%:75wt%.

[0083] The second active material layer 24 may include the first active material and the second active material in a different proportion than the first active material layer 22, but is not limited thereto, and may be made of different negative electrode active materials or include different negative electrode active materials. The second active material layer 24 may also include a third active material in addition to artificial graphite, silicon, and natural graphite, which are referred to as the first and second active materials, or may be composed of only silicon and the third active material.

[0084] The third active material may be or include amorphous carbon, and may be or include at least one of the following: soft carbon, hard carbon, mesophase pitch carbon, calcined coke, etc.

[0085] Meanwhile, the porosity of the first active material layer 22 and the porosity of the second active material layer 24 can be different from each other.

[0086] Porosity refers to the ratio of the volume occupied by pores to the volume of the active material layer. Porosity can be measured using, for example, nitrogen adsorption or mercury infiltration. Alternatively, porosity can be measured using, for example, gases and BELSORP (BET equipment) from BEL JAPAN, or it can be measured by image analysis methods (such as FE-SEM) after dyeing specific components (such as binders) in the electrode.

[0087] The porosity of the first active material layer 22 can be in the range of about 15% to about 18%.

[0088] Porosity can be obtained by changing the particle size of artificial graphite, silicon and natural graphite included in the first active material and the second active material and adjusting the mixing ratio.

[0089] The particle size can increase in the order of natural graphite, artificial graphite, and silicon. For example, the particle size (D50) of natural graphite can be about 7 μm or smaller, the particle size of artificial graphite can be in the range of about 11 μm to about 15 μm, and the particle size of silicon can be about 20 μm or smaller.

[0090] The porosity of the second active material layer 24 may be less than that of the first active material layer 22, and the second active material layer 24 may have a porosity in the range of, for example, about 10% to about 12%.

[0091] As described above, the active material of the second active material layer 24 may be different from the active material of the first active material layer 22. When the second active material layer 24 includes both the first and second active materials, the second active material layer 24 may include natural graphite, artificial graphite, and silicon having the same particle size as the active material of the first active material layer 22 and mixed in a different proportion than the active material of the first active material layer 22.

[0092] To increase capacity and achieve uniform or substantially uniform expansion, silicon can be incorporated in the first active material layer 22 and the second active material layer 24 with the same particle size and proportion. In this case, the silicon particle size can be about 20 μm or smaller.

[0093] Regarding volume expansion during charging and discharging, cracking and deformation of the active material layer may occur more significantly in the portion closer to the substrate. That is, volume expansion in the first active material layer 22 can be transmitted to the second active material layer 24, causing deformation of the entire active material layer. Therefore, in this disclosure, by increasing the porosity of the relatively lower first active material layer 22, the pores absorb the volume expansion caused by silicon, thereby alleviating stress and reducing volume expansion and cracking throughout the active material layer, which can reduce electrode deformation.

[0094] Meanwhile, the first active material layer 22 and the second active material layer 24 according to an example embodiment of the present disclosure may be oriented.

[0095] The first active material layer 22 and the second active material layer 24 may have a divergence (DD) value as defined by the following Equation 1.

[0096] Equation 1: DD (divergence) = (Ia / Itotal) × 100.

[0097] In Equation 1 above, Ia is the sum of peak intensities appearing at non-planar angles during XRD measurements using CuKα rays, and I is always the sum of peak intensities appearing at all angles during XRD measurements using CuKα rays.

[0098] In this case, when measured using CuKα rays by XRD, the non-planar angles exhibit 2θ values ​​of 42.4±0.2°, 43.4±0.2°, 44.6±0.2°, and 77.5±0.2°, respectively, corresponding to the (100) plane, (101)R plane, (101)H plane, and (110) plane. Generally, based on the stacking order of graphene layers, graphite is classified into hexagonal structures and rhombic structures with an ABAB-type stacking order; the R plane refers to the rhombic structure, and the H plane refers to the hexagonal structure.

[0099] Furthermore, all angles refer to 2θ = 26.5 ± 0.2°, 42.4 ± 0.2°, 43.4 ± 0.2°, 44.6 ± 0.2°, 54.7 ± 0.2°, and 77.5 ± 0.2° during XRD measurements using CuKα rays, i.e., representing the (002) plane, (100) plane, (101)R plane, (101)H plane, (004) plane, and (110) plane. The peak appearing at 2θ = 43.4 ± 0.2° can be considered as the result of the overlap between the peak corresponding to the (101)R plane of carbonaceous materials and the peak corresponding to the (111) plane of current collectors (e.g., Cu).

[0100] Typically, peak intensity value refers to the height of the peak or the integral area of ​​the peak, and according to an example embodiment, peak intensity value refers to the integral area of ​​the peak.

[0101] In one example embodiment of this disclosure, CuKα rays are used as the target rays for XRD measurements. To improve peak intensity resolution, the target rays are extracted using a monochromator before measurement. Furthermore, the measurements are performed under the following conditions: 2θ is in the range of about 10° to about 80°, the scan rate (° / s) is in the range of about 0.044 to about 0.089, and the step size is about 0.026° / step.

[0102] According to an example embodiment of this disclosure, the DD value is obtained by XRD of the negative electrode obtained by disassembling the battery in a fully discharged state after charging and discharging the lithium rechargeable battery including the negative electrode. In this case, the charging and discharging conditions are performed once or twice in the range of about 0.1C to about 0.2C.

[0103] During XRD measurements using CuKα rays, the peak intensity ratio of the (004) plane of the negative electrode to the peak intensity of the (002) plane (i.e., I(004) / I(002)) can be 0.04 or greater, approximately 0.04 or greater and approximately 0.07 or less. When I(004) / I(002) of the negative electrode is approximately 0.04 or greater, the DC internal resistance does not increase, rate performance (especially high-rate performance) can be improved, and cycle life characteristics can be improved.

[0104] Such a DD value is a physical property value that is maintained even during charging and discharging, and represents the degree to which the negative electrode active material is oriented at a given angle. For ease of description, carbonaceous active materials (e.g., graphite particles) are shown as negative electrode active materials in the accompanying drawings.

[0105] According to exemplary embodiments of this disclosure, the DD value can be equal to or greater than about 30, and can be about 30 or greater and about 60 or less. When the DD value is about 30 or greater, it means that the negative electrode active material is not placed horizontally on one surface of the substrate, but is sufficiently oriented to facilitate the movement of Li ions within the negative electrode.

[0106] This orientation can be achieved using a magnetic field.

[0107] Figure 3 This is a diagram showing the orientation of the negative electrode active material.

[0108] Reference Figure 3 After the negative electrode active material is applied to the substrate, a magnetic field is used to orient the negative electrode active material. Graphite is shown as a representative example of the negative electrode active material.

[0109] According to an example embodiment of this disclosure, the magnet is an electromagnet, and a magnetic field can be easily applied or removed as needed. In this case, the degree of orientation can be controlled by adjusting the strength of the magnetic field, the exposure time of the magnetic field, and the viscosity of the negative electrode active material composition.

[0110] After positioning a substrate made of or including Cu foil for the negative electrode on top of the magnet, a negative electrode active material slurry can be applied to the substrate and exposed to the magnetic field. In this case, the DD value of the active material layer formed by exposure to the magnetic field can be about 30 or greater.

[0111] Reference Figure 3 A negative electrode can be formed by continuously coating a negative electrode active material while moving the negative electrode substrate. In this case, the magnetic flux generated by the magnet can be formed in a direction perpendicular to the negative electrode substrate, or the direction of the magnetic flux formation can have a given angle as a vector function dependent on the coating speed (i.e., the moving speed of the negative electrode substrate). Therefore, the negative electrode active material in the active material layer can have a shape in which the negative electrode active material stands at a given angle relative to the surface of the negative electrode substrate; that is, the negative electrode active material is oriented.

[0112] Again, refer to Figure 1 and Figure 2 The diaphragm 300 may include a porous substrate and a coating layer located on one or both surfaces of the porous substrate, the coating layer including organic materials, inorganic materials or combinations thereof.

[0113] The porous substrate may be or include a polymer membrane, which is formed of any polymer or copolymer or mixture thereof, such as 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, polyetherimide, polyamide-imide, polybenzimidazole, polyethersulfone, polyphenylene ether, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fiber, and polytetrafluoroethylene (such as Teflon).

[0114] Organic materials may include polyvinylidene fluoride polymers or (meth)acrylic acid polymers.

[0115] Inorganic materials may include inorganic particles such as or containing at least one of Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof, but inorganic materials are not limited thereto.

[0116] Organic and inorganic materials can exist as a mixture in a coating layer, or a coating layer containing organic materials and a coating layer containing inorganic materials can exist in a stacked form.

[0117] The electrode assembly 400, together with the electrolyte, can be housed in a pouch-type housing 500 or a prismatic housing (not shown) in the form of a can and used as a rechargeable battery, and the electrolyte comprises a non-aqueous organic solvent and a lithium salt.

[0118] Non-aqueous organic solvents constitute the medium through which ions participating in the electrochemical reactions of the battery can move.

[0119] Non-aqueous organic solvents may be or include at least one of carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, aprotic solvents, or combinations thereof.

[0120] As a carbonate solvent, at least one of the following can be used: 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).

[0121] As an ester solvent, at least one of the following can be used: methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, decanoic acid lactone, mevalonate lactone, caprolactone, etc.

[0122] As an ether solvent, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. can be used.

[0123] In addition, cyclohexanone and the like can be used as ketone solvents. Ethanol, isopropanol, and the like can be used as alcohol solvents. At least one of the following can be used as an aprotic solvent: nitriles, such as R-CN (R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to about 20 carbon atoms, and may include double bonds, aromatic rings, or ether groups); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane and 1,4-dioxolane; sulfolane, etc.

[0124] Non-aqueous organic solvents can be used alone or in mixtures of two or more types.

[0125] Furthermore, when using carbonate solvents, cyclic carbonates and chain carbonates can be mixed together, and the cyclic carbonates and chain carbonates can be mixed in a volume ratio ranging from about 1:1 to about 1:9.

[0126] Lithium salts dissolve in organic solvents and constitute the lithium-ion source in batteries, enabling the basic operation of lithium rechargeable batteries and facilitating the movement of lithium ions between the positive and negative electrodes. Representative examples of lithium salts can include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO2C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide (LiFSI)), LiC4F9SO3, and LiN(C x F 2x +1SO2)(C y F 2y +1SO2) (x and y are integers in the range of 1 to about 20), lithium trifluoromethane sulfonate, lithium tetrafluoroethane sulfonate, lithium difluoro(oxalate)borate (LiDFOB), lithium difluorobis(oxalate)phosphate (LiDFBOP), and lithium bis(oxalate)borate (LiBOB) are one or more of these.

[0127] The housing 500 is bag-shaped and may be formed of or comprise a laminated external material, which may be formed of or comprise a multilayer structure having, for example, a first insulating layer 2, a metal layer 3, and a second insulating layer 4. Various other adhesive layers or functional layers may be further added.

[0128] The second insulating layer 4 is formed of a material with insulating and thermally adhesive properties as the inner surface of the laminated outer material, and can be sealed by heat sealing the edges while accommodating the electrode assembly 400. Furthermore, the second insulating layer 4 is formed on one surface of the metal layer 3 and forms the inner surface of the laminated outer material facing the electrode assembly 400. The second insulating layer 4 can be formed of or include cast polypropylene (CPP) or its equivalents that do not react with the electrolyte.

[0129] Thus, in this disclosure, by adjusting the particle size of the active material in the first active material layer 22 and the second active material layer 24 of the negative electrode so that the porosity of the first active material layer 22 is greater than that of the second active material layer 24, even when silicon is included to achieve high capacity (when silicon is included to achieve high capacity), cracks in the active material layer due to volume expansion are mitigated, thereby providing a rechargeable battery with improved electrical properties such as lifetime retention.

[0130] The following describes comparative examples and illustrations of this disclosure. These examples are merely exemplary embodiments of this disclosure, and this disclosure is not limited to these examples.

[0131] Example 1 An active material is prepared by mixing a first active material comprising artificial graphite with a particle size (D50) of 15 μm and silicon with a particle size of 20 μm with a second active material comprising natural graphite with a particle size of 7 μm in a ratio of 25 wt%: 75 wt%, and coating it onto a substrate at a mixture density (compacted density) of 1.6 g / cc to form a first active material layer.

[0132] Then, an active material is prepared by mixing a first active material comprising artificial graphite with a particle size of 15 μm and silicon with a particle size of 20 μm with a second active material comprising natural graphite with a particle size of 7 μm in a ratio of 75 wt%: 25 wt%, and coating the mixture onto the first active material layer at a mixture density of 1.6 g / cc to form the second active material layer.

[0133] Combined with the manufactured negative electrode, it is manufactured using conventional methods. Figure 1 The lithium rechargeable battery shown.

[0134] Example 2 The active material is manufactured in the same manner as in Example 1, except that the size of the artificial graphite is 11 μm.

[0135] Example 3 The active substance was manufactured in the same manner as in Example 2, except that the density of the mixture was 1.65 g / cc.

[0136] Comparison Example 1 The active material is manufactured in the same manner as in Example 1, except that the size of the natural graphite is 16 μm.

[0137] Comparison Example 2 The active material is manufactured in the same manner as in Example 1, except that the size of the artificial graphite is 16 μm.

[0138] Comparison Example 3 Except that the ratio of the first active material to the second active material in the first active material layer is 65wt%:35wt%, the active material is manufactured in the same manner as in Example 1.

[0139] The lifetime retention characteristics and swelling rates of Examples 1 to 3 and Comparative Examples 1 to 3 were measured and are shown in Table 1 below.

[0140] Evaluation Example 1: Lifetime Retention Rate (%) Measurement The lithium rechargeable batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 3 were charged at 25°C with a constant current of 0.33C until reaching 4.25V, and then charged once with a constant voltage of 4.3V until the charging current reached 0.05C (charging cutoff 0.05C). Afterward, after placing the lithium rechargeable batteries in the environment for 30 minutes, they were discharged once with a constant current of 0.33C until reaching 2.8V to measure the discharge capacity. This is referred to as one cycle, and the lifetime retention was measured after 100 cycles.

[0141] The lifetime retention rate (%) is calculated using the following Equation 2.

[0142] Equation 2: Lifetime retention rate (%) = (100-cycle discharge capacity / 1-cycle discharge capacity) × 100%.

[0143] Evaluation Example 2: Measurement of Swelling Rate (%) The swelling rate (%) is calculated using the following Equation 3.

[0144] Equation 3: Swelling rate (%) = (Thickness of electrode plate at SOC 100 / Thickness of electrode plate at SOC 0) × 100% Table 1:

[0145] Referring to Table 1, it can be seen that the porosity of the first active material layer in Examples 1 to 3 is 15% or greater, which is significantly greater than the 14% or less porosity of Comparative Examples 1 to 3. It can also be seen that Examples 1 to 3 have a swelling rate of 8.5% or less, which is less than the 9% or greater swelling rate of Comparative Examples 1 to 3. Specifically, it can be seen that Example 2 has a swelling rate of 6.5%, which is significantly less than the 10% swelling rate of Comparative Example 3.

[0146] As can be seen, Examples 1 and 2 have a lifetime retention rate of 95% or greater, which is an improvement compared to Comparative Examples 1 to 3. Examples 3 and Comparative Examples 3 have similar lifetime retention rates, but Comparative Example 3 has a larger swelling rate than Example 3, which may increase the probability of crack initiation.

[0147] Although exemplary embodiments of the present disclosure have been described above, the present disclosure is not limited thereto, and various modifications can be made and implemented within the scope of the claims, the detailed description of the present disclosure and the accompanying drawings, and these modifications naturally fall within the scope of the present disclosure.

Claims

1. A negative electrode for a rechargeable battery, the negative electrode comprising: substrate; A first active material layer is formed on the substrate; as well as A second active material layer is formed on the first active material layer; The porosity of the first active material layer is greater than that of the second active material layer.

2. The negative electrode for a rechargeable battery according to claim 1, wherein: The porosity of the first active material layer is in the range of 15% to 18%, and The porosity of the second active material layer is in the range of 10% to 12%.

3. The negative electrode for a rechargeable battery according to claim 1, wherein: Both the first active material layer and the second active material layer include a first active material and a second active material. The first active material is formed by mixing artificial graphite and silicon particles, and The second active substance includes natural graphite.

4. The negative electrode for a rechargeable battery according to claim 3, wherein, The ratio of the first active substance to the second active substance in the first active substance layer is different from the ratio of the first active substance to the second active substance in the second active substance layer.

5. The negative electrode for a rechargeable battery according to claim 4, wherein, The first active substance and the second active substance in the first active substance layer are mixed in a ratio of 25wt%:75wt%.

6. The negative electrode for a rechargeable battery according to claim 3, wherein, The particle size of the artificial graphite is in the range of 11 μm to 15 μm.

7. The negative electrode for a rechargeable battery according to claim 3, wherein, The natural graphite has a particle size of 7 μm or smaller.

8. The negative electrode for a rechargeable battery according to claim 3, wherein, The silicon particles have a particle size of 20 μm or smaller.

9. The negative electrode for a rechargeable battery according to claim 1, wherein, The first active material layer is formed to have a mixture density in the range of 1.60 g / cc to 1.65 g / cc.

10. The negative electrode for a rechargeable battery according to claim 1, wherein, The first active material layer and the second active material layer are oriented.

11. The negative electrode for a rechargeable battery according to claim 10, wherein: The first and second active material layers of the negative electrode comprise carbon-based negative electrode active materials, and The first active material layer and the second active material layer of the negative electrode have a divergence value DD defined by Equation 1, wherein the DD value is equal to 30 or greater; Equation 1: DD (divergence) = (Ia / Itotal) × 100; in: Ia is the sum of peak intensities appearing at non-planar angles during XRD measurements using CuKα rays, and I is always the sum of the peak intensities that appear at all angles during XRD measurements using CuKα rays.

12. An electrode assembly, the electrode assembly comprising: negative electrode; Positive electrode; as well as A diaphragm is located between the positive electrode and the negative electrode. The negative electrode includes a substrate and a first active material layer and a second active material layer stacked on the substrate, and The porosity of the first active material layer is greater than that of the second active material layer.

13. The electrode assembly according to claim 12, wherein: The porosity of the first active material layer is in the range of 15% to 18%, and The porosity of the second active material layer is in the range of 10% to 12%.

14. The electrode assembly according to claim 12, wherein: Both the first active material layer and the second active material layer include a first active material and a second active material. The first active material is formed by mixing artificial graphite and silicon particles, and The second active substance includes natural graphite.

15. The electrode assembly of claim 14, wherein, The ratio of the first active substance to the second active substance in the first active substance layer is different from the ratio of the first active substance to the second active substance in the second active substance layer.

16. The electrode assembly of claim 15, wherein, The first active substance and the second active substance in the first active substance layer are mixed in a ratio of 25wt%:75wt%.

17. The electrode assembly according to claim 12, wherein, The first active material layer and the second active material layer are oriented.

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