Lithium-ion secondary battery negative electrode and lithium-ion secondary battery including the negative electrode
By employing a multilayer structure of artificial and natural graphite in the negative electrode of lithium secondary batteries, the pollution problem of calendering equipment has been solved, and the improvement of high energy density and fast charging performance has been achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SK ON CO LTD
- Filing Date
- 2025-12-02
- Publication Date
- 2026-06-02
Smart Images
Figure CN122136279A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery including the negative electrode. Background Technology
[0002] In recent years, there has been active research into electric vehicles (EVs), which can replace fossil fuel-based vehicles as one of the main causes of air pollution. As the primary power source for these EVs, lithium-ion batteries with high discharge voltage and power stability are used, and high-performance lithium-ion batteries are needed to improve the performance of EVs.
[0003] With the increasing demand for such high-performance lithium secondary batteries, there is also a need for the development of technologies that can improve the performance of components such as the negative electrode in lithium secondary batteries, such as energy density. Summary of the Invention
[0004] (a) Technical problems to be solved One aspect of the present invention aims to provide a negative electrode for lithium secondary batteries with high energy density.
[0005] Another aspect of the present invention aims to provide a negative electrode for a lithium secondary battery with improved fast charging performance.
[0006] Another aspect of the present invention aims to improve the productivity of negative electrodes for lithium secondary batteries.
[0007] (II) Technical Solution A negative electrode for a lithium secondary battery according to one embodiment includes: a negative electrode current collector; and a negative electrode mixture layer disposed on at least one side of the negative electrode current collector and comprising a graphite-based negative electrode active material, wherein the negative electrode mixture layer comprises: a first negative electrode mixture layer disposed on the negative electrode current collector; and a second negative electrode mixture layer disposed on the first negative electrode mixture layer, wherein the graphite-based negative electrode active material comprises artificial graphite and natural graphite, wherein in the graphite-based negative electrode active material contained in the first negative electrode mixture layer, the weight of artificial graphite is greater than the weight of natural graphite, and in the graphite-based negative electrode active material contained in the second negative electrode mixture layer, the weight of natural graphite is greater than the weight of artificial graphite.
[0008] In some specific implementations, the content of artificial graphite can be greater than 50% by weight, based on the total weight of the graphite-based negative electrode active material contained in the first negative electrode mixture layer.
[0009] In some specific implementations, the first negative electrode mixture layer may not contain natural graphite.
[0010] In some specific implementations, the graphite-based negative electrode active material contained in the first negative electrode mixture layer can be artificial graphite.
[0011] In some specific implementations, the content of natural graphite can be greater than 50% by weight, based on the total weight of the graphite-based negative electrode active material contained in the second negative electrode mixture layer.
[0012] In some specific implementations, the second negative electrode mixture layer may not contain artificial graphite.
[0013] In some specific implementations, the graphite-based negative electrode active material contained in the second negative electrode mixture layer can be natural graphite.
[0014] In some specific embodiments, the total weight of artificial graphite contained in the negative electrode mixture layer may be greater than the total weight of natural graphite.
[0015] In some specific embodiments, based on the graphite-based negative electrode active material contained in the entire negative electrode mixture layer including the first negative electrode mixture layer and the second negative electrode mixture layer, the content of artificial graphite can be more than 60% by weight and less than 90% by weight.
[0016] In some specific embodiments, the content of natural graphite can be more than 10% by weight and less than 40% by weight, based on the graphite-based negative electrode active material contained in the entire negative electrode mixture layer including the first negative electrode mixture layer and the second negative electrode mixture layer.
[0017] In some specific implementations, the load weight of the first negative electrode mixture layer can be greater than the load weight of the second negative electrode mixture layer.
[0018] In some specific implementations, the ratio of the load weight of the first negative electrode mixture layer to the total load weight of the first negative electrode mixture layer and the second negative electrode mixture layer can be 70% to 95%.
[0019] In some specific implementations, the ratio of the load weight of the second negative electrode mixture layer to the total load weight of the first negative electrode mixture layer and the second negative electrode mixture layer can be 5% to 30%.
[0020] In some specific embodiments, the thickness of the second negative electrode mixture layer can be 10% to 50% of the total thickness of the negative electrode mixture layer.
[0021] A lithium secondary battery according to a specific embodiment includes a negative electrode for a lithium secondary battery according to any of the above-described specific embodiments.
[0022] A method for manufacturing a negative electrode for a lithium secondary battery according to a specific embodiment includes the following steps: coating a first negative electrode mixture slurry containing a graphite-based negative electrode active material onto at least one side of a negative electrode current collector; coating a second negative electrode mixture slurry containing a graphite-based negative electrode active material onto the coated first negative electrode mixture slurry; drying the coated first negative electrode mixture slurry and second negative electrode mixture slurry to form a first negative electrode mixture layer and a second negative electrode mixture layer; and calendering the first negative electrode mixture layer and the second negative electrode mixture layer, wherein the graphite-based negative electrode active material comprises artificial graphite and natural graphite, wherein in the graphite-based negative electrode active material contained in the first negative electrode mixture layer, the weight of artificial graphite is greater than the weight of natural graphite, and in the graphite-based negative electrode active material contained in the second negative electrode mixture layer, the weight of natural graphite is greater than the weight of artificial graphite.
[0023] In some specific implementations, the calendering step can be carried out at a linear pressure of 0.50 tons / cm to 1.20 tons / cm.
[0024] (III) Beneficial Effects According to a specific embodiment of the present invention, the phenomenon of contamination on the surface of calendering equipment such as calendering rolls can be suppressed.
[0025] According to another specific embodiment of the invention, equipment downtime for cleaning the surfaces of calendering equipment can be minimized.
[0026] According to another specific embodiment of the present invention, the rolling processability can be improved and the electrode productivity can be increased.
[0027] According to another specific embodiment of the present invention, the pressure applied to the electrode during the rolling process in the electrode manufacturing process can be increased, thereby achieving a high energy density electrode.
[0028] According to another specific embodiment of the present invention, the fast charging performance of the battery can be improved.
[0029] The electrodes of this invention can be widely used as negative electrodes in green technology fields such as electric vehicles, battery charging stations, and other battery-powered solar and wind power generation. Furthermore, the electrodes of this invention can be used in eco-friendly electric vehicles and hybrid vehicles to prevent climate change by suppressing air pollution and greenhouse gas emissions. Attached Figure Description
[0030] Figure 1 This is a conceptual cross-sectional view of a negative electrode for a lithium secondary battery according to a specific embodiment.
[0031] Figure 2 This is a conceptual cross-sectional view of a negative electrode for a lithium secondary battery according to embodiments and comparative examples. A is a negative electrode of an embodiment having a dual-layer structure comprising a second negative electrode mixture layer containing natural graphite. B is a negative electrode of an embodiment having a dual-layer structure comprising natural graphite and artificial graphite in a second negative electrode mixture layer. C is a negative electrode of a comparative example having a single-layer structure comprising natural graphite and artificial graphite in a negative electrode mixture layer.
[0032] Figure 3 During the manufacturing process of the negative electrodes of Examples 1, 2, and Comparative Examples 1 to 4, each with a diameter of 500m, the blackness and whiteness of the calender roll surface were measured every 50m unit, and a graph showing the changes was displayed.
[0033] [Explanation of reference numerals in the attached figures] 2: Negative electrode current collector 4: Negative electrode mixture layer 6: First negative electrode mixture layer 8: Second negative electrode mixture layer 10: Negative electrode Detailed Implementation
[0034] As described above, there is a need to develop a technology to improve the performance of negative electrodes for lithium-ion batteries. A manufacturing process for a negative electrode for lithium-ion batteries according to one specific embodiment may include a calendering process to increase the energy density of the secondary battery. Specifically, the calendering process may be a process of physically calendering a negative electrode mixture layer formed on a negative electrode current collector and containing negative electrode active material using calendering equipment such as calendering rolls. By calendering the negative electrode mixture layer using the calendering equipment, the thickness of the negative electrode can be reduced and the amount of active material per unit volume can be increased, thereby improving the energy density of the secondary battery including the negative electrode.
[0035] However, when increasing the pressure during the calendering process to improve the energy density of the secondary battery, particles constituting the negative electrode mixture layer may adhere to the surface of the calendering equipment, potentially causing contamination of the calendering equipment. Furthermore, as the amount of particles adhering to the surface of the calendering equipment increases and forms agglomerates, these agglomerates create unevenness on the calendering rolls, leading to surface defects on the negative electrode, such as depressions.
[0036] Furthermore, if the amount of binder in the negative electrode mixture layer is reduced in order to improve the fast-charging performance of the lithium secondary battery, the adhesion of the negative electrode active material in the negative electrode mixture layer may decrease. In this case, the negative electrode active material particles may detach from the negative electrode and adhere to the surface of the calendering equipment, thereby exacerbating the aforementioned surface quality defects of the negative electrode.
[0037] To address the electrode quality defects caused by surface contamination of the calendering equipment as described above, a cleaning unit can be installed on the calendering equipment surface to remove contaminants adhering to the equipment during operation. However, even with this contaminant removal equipment, it may be difficult to completely remove particles adhering to the calendering equipment surface.
[0038] The cleaning unit may include equipment such as a doctor blade, non-woven fabric, and a cleaning fluid spraying device. To improve the cleaning effect on the surface of the calendering equipment, the equipment of the cleaning unit can be improved or the operating conditions can be strengthened. However, in this case, it may be necessary to periodically stop the operation of the electrode production equipment to clean the calendering equipment and other operations. Therefore, the cessation of the operation of the electrode production equipment may reduce the productivity of the electrodes.
[0039] Furthermore, if the surface contamination of the calendering equipment is so severe that electrode production is impossible, the density of the electrode mixture can be reduced by performing a calendering process, thereby mitigating the contamination on the calendering equipment surface. However, in this case, it may be difficult to achieve high energy density electrodes and secondary batteries.
[0040] Therefore, one specific embodiment of the present invention aims to provide a negative electrode for a lithium secondary battery that can alleviate the above-mentioned problems, and a lithium secondary battery including the negative electrode. Hereinafter, various specific embodiments of the present invention will be described in more detail with reference to the accompanying drawings. However, these are merely exemplary embodiments, and the present invention is not limited to the specific embodiments described exemplarily.
[0041] According to a specific embodiment of the present invention, a negative electrode for a lithium secondary battery includes: a negative electrode current collector; and a negative electrode mixture layer disposed on at least one side of the negative electrode current collector and comprising a graphite-based negative electrode active material, wherein the negative electrode mixture layer comprises: a first negative electrode mixture layer disposed on the negative electrode current collector; and a second negative electrode mixture layer disposed on the first negative electrode mixture layer, wherein the graphite-based negative electrode active material comprises artificial graphite and natural graphite, wherein in the graphite-based negative electrode active material contained in the first negative electrode mixture layer, the weight of artificial graphite is greater than the weight of natural graphite, and in the graphite-based negative electrode active material contained in the second negative electrode mixture layer, the weight of natural graphite is greater than the weight of artificial graphite.
[0042] The negative electrode 10 includes a negative electrode current collector 2 and a negative electrode mixture layer 4 disposed on at least one side of the negative electrode current collector 2, the negative electrode mixture layer 4 having a multilayer structure. Figure 1 The cross-sectional structure of the negative electrode according to a specific embodiment is schematically shown. For example... Figure 1 As shown, the negative electrode mixture layer 4 can be a multilayer structure including a first negative electrode mixture layer 6 disposed on both sides of the negative electrode current collector 2 and a second negative electrode mixture layer 8 disposed on the first negative electrode mixture layer 6.
[0043] Furthermore, although not shown in the accompanying drawings, as another example, the negative electrode of the present invention may further include one or more additional negative electrode mixture layers (third negative electrode mixture layers) between the first negative electrode mixture layer and the second negative electrode mixture layer. The third negative electrode mixture layer may be a mixture of natural graphite and artificial graphite as negative electrode active materials, but is not particularly limited thereto. More specifically, the weight of natural graphite contained in the third negative electrode mixture layer may be greater than the weight of natural graphite contained in the first negative electrode mixture layer, and may be less than the weight of natural graphite contained in the second negative electrode mixture layer.
[0044] In the negative electrode, the second negative electrode mixture layer may have the same or smaller thickness as the first negative electrode mixture layer, but is not limited thereto. Specifically, the thickness of the second negative electrode mixture layer may be 10-50% of the total thickness of the negative electrode mixture layer.
[0045] The thickness of the first negative electrode mixture layer can be 10 μm or more, or 300 μm or less, but is not limited thereto. As an example, the thickness of the first negative electrode mixture layer can be 10 μm or more, 20 μm or more, 30 μm or more, or 50 μm or more, and can be less than 300 μm, 250 μm or less, 200 μm or less, 180 μm or less, 150 μm or less, 120 μm or less, or 100 μm or less.
[0046] The negative electrode mixture layer provided in this invention comprises artificial graphite and natural graphite. The artificial graphite has a sheet-like structure. Due to the structural characteristics described above, the sheet-like artificial graphite has an amorphous sheet structure with exposed edges, thus providing a larger exposed surface area compared to spherical natural graphite, and facilitating the insertion and extraction of lithium ions. Therefore, when artificial graphite is included as the negative electrode active material, the diffusion coefficient of lithium ions can be increased, thereby improving fast charging performance and fast charging capacity retention.
[0047] Furthermore, synthetic graphite has a lower swelling ratio than natural graphite. Typically, during battery charge-discharge cycles, if the solid electrolyte interface (SEI) film formed on the negative electrode surface is damaged due to expansion, electrolyte is continuously consumed, leading to gas generation within the battery. However, when synthetic graphite, with its low swelling ratio, is used as the negative electrode active material, the amount of electrolyte consumed due to SEI film damage is reduced, gas generation is decreased, and the internal pressure of the battery can be lowered.
[0048] Furthermore, natural graphite is shaped into spheres, while artificial graphite is amorphous and sheet-like. Therefore, the contact points between active material particles are small, resulting in lower adhesion strength for artificial graphite compared to natural graphite. Consequently, when artificial graphite is widely distributed on the electrode surface, it may detach from the electrode surface and adhere to the calender rolls during the calendering process, contaminating the rolls and potentially causing a decrease in the surface quality of the negative electrode after calendering.
[0049] Therefore, in a multilayer negative electrode that simultaneously contains artificial graphite and natural graphite as negative electrode active materials, by controlling the distribution of artificial graphite and natural graphite, it is possible to provide an electrode that can ensure battery safety and fast charging characteristics through artificial graphite while improving calendering processability through natural graphite.
[0050] The negative electrode provided by this invention contains a large amount of artificial graphite in the first negative electrode mixture layer and a large amount of natural graphite in the second negative electrode mixture layer. According to one specific embodiment, in the negative electrode, based on the total amount of graphite-based negative electrode active material contained in the first negative electrode mixture layer, the first negative electrode mixture layer contains more than 50% by weight of artificial graphite, and based on the total content of graphite-based negative electrode active material contained in the second negative electrode mixture layer, the second negative electrode mixture layer contains more than 50% by weight of natural graphite.
[0051] Specifically, based on the total weight of the graphite-based negative electrode active material contained in the first negative electrode mixture layer, the content of artificial graphite can be greater than 50% by weight, and based on the total weight of the graphite-based negative electrode active material contained in the second negative electrode mixture layer, the content of natural graphite can be greater than 50% by weight.
[0052] More specifically, based on the total weight of the graphite-based negative electrode active material contained in the first negative electrode mixture layer, the first negative electrode mixture layer may contain more than 60% by weight, more than 70% by weight, more than 80% by weight, or more than 90% by weight of artificial graphite.
[0053] According to one specific embodiment, the first negative electrode mixture layer may not contain natural graphite. Specifically, the graphite-based negative electrode active material contained in the first negative electrode mixture layer may be artificial graphite. That is, 100% by weight of the graphite-based negative electrode active material contained in the first negative electrode mixture layer may be artificial graphite.
[0054] Furthermore, based on the total weight of the graphite-based negative electrode active material contained in the second negative electrode mixture layer, the second negative electrode mixture layer may contain natural graphite with a content of 60% or more, 70% or more, 80% or more, or 90% or more.
[0055] According to one specific embodiment, the second negative electrode mixture layer may not contain artificial graphite. Specifically, the graphite-based negative electrode active material contained in the second negative electrode mixture layer may be natural graphite. That is, 100% by weight of the graphite-based negative electrode active material contained in the second negative electrode mixture layer may be natural graphite.
[0056] As described above, when natural graphite is distributed in large quantities in the upper layer (second negative electrode mixture layer) serving as the negative electrode surface, it can suppress or mitigate the phenomenon of negative electrode active material particles adhering to the calender roll surface and contaminating the calender roll during the calendering process, thereby helping to improve calendering processability and increase the productivity of the negative electrode. Furthermore, when artificial graphite is distributed in large quantities in the lower layer (first negative electrode mixture layer) serving as the negative electrode current collector side, it can suppress contamination on the calender roll surface while improving the fast charging performance and energy density of the lithium secondary battery.
[0057] As one implementation, the total weight of artificial graphite contained in the negative electrode mixture layer can be greater than the total weight of natural graphite. Specifically, based on the graphite-based negative electrode active material contained in the entire negative electrode mixture layer, including the first negative electrode mixture layer and the second negative electrode mixture layer, the negative electrode can contain more than 50% by weight, more than 60% by weight, or more than 65% by weight of artificial graphite, and can contain less than 90% by weight, less than 80% by weight, or less than 75% by weight of artificial graphite.
[0058] Furthermore, based on the graphite-based negative electrode active material contained in the entire negative electrode mixture layer, including the first negative electrode mixture layer and the second negative electrode mixture layer, the negative electrode may contain less than 50% by weight, less than 40% by weight, or less than 35% by weight of natural graphite, and may contain more than 10% by weight, more than 20% by weight, or more than 25% by weight of natural graphite.
[0059] When the content of the artificial graphite is less than 50% by weight, the improvement in electrode performance by using artificial graphite may be insufficient. Furthermore, when the content of the artificial graphite is greater than 90% by weight, the amount of artificial graphite exposed on the outermost surface of the negative electrode increases, thus increasing the likelihood of artificial graphite detaching from the electrode surface during the calendering process. Consequently, the effect of reducing contamination on the calender roll surface may be halved.
[0060] The content of artificial graphite in the first negative electrode mixture layer may be 50% or more, 70% or more, 90% or more, 99% or more, or 100% by weight of the artificial graphite in the entire negative electrode mixture layer, but is not limited thereto. Furthermore, the content of natural graphite in the second negative electrode mixture layer may be 50% or more, 70% or more, 90% or more, 99% or more, or 100% by weight of the natural graphite in the entire negative electrode mixture layer.
[0061] In some specific embodiments, the thickness of the first negative electrode mixture layer may be equal to or greater than the thickness of the second negative electrode mixture layer. As an example, based on the thickness of the entire negative electrode including the first and second negative electrode mixture layers, the thickness of the second negative electrode mixture layer may be 10-50%. For example, the thickness ratio of the first negative electrode mixture layer to the second negative electrode mixture layer may be 9:1 to 5:5 or 9:1 to 7:3.
[0062] In some specific implementations, the load weight of the first negative electrode mixture layer can be greater than the load weight of the second negative electrode mixture layer. As an example, based on the total load weight of the first and second negative electrode mixture layers, the load weight ratio of the first negative electrode mixture layer can be 70-95%, and based on the total load weight of the first and second negative electrode mixture layers, the load weight ratio of the second negative electrode mixture layer can be 5-30%.
[0063] In some specific embodiments, the loading weight of the first negative electrode mixture layer can be 5-15 mg / cm³. 2 Specifically, the loading weight of the first negative electrode mixture layer can be 7 mg / cm³. 2 Above or 9mg / cm 2 The above, and can be 12 mg / cm³ 2 Below or 10 mg / cm 2 the following.
[0064] In some specific embodiments, the loading weight of the second negative electrode mixture layer can be 0.5-5 mg / cm³. 2Specifically, the loading weight of the second negative electrode mixture layer can be 0.7 mg / cm³. 2 Above or 1 mg / cm 2 The above, and can be 4 mg / cm³ 2 Below or 2mg / cm 2 the following.
[0065] Based on the total load weight of the first negative electrode mixture layer and the second negative electrode mixture layer, the ratio of the load weight of the first negative electrode mixture layer to the load weight of the second negative electrode mixture layer can be 70:30 to 95:5 or 70:30 to 90:10.
[0066] By increasing the loading of the first negative electrode mixture layer containing a large amount of artificial graphite as described above, the diffusion coefficient of lithium ions can be increased, thereby improving fast charging performance and cycle performance. Furthermore, by including a second negative electrode mixture layer containing a large amount of natural graphite on the outer surface of the electrode, even during the high-pressure calendering process to achieve a high-density negative electrode, the high adhesion results in fewer active material particles detaching from the negative electrode surface, reducing contamination on the calendering roll surface. Moreover, due to the high adhesion, the same negative electrode density can be achieved even with lower pressure during the calendering process.
[0067] Figure 2 This illustrates an example of a negative electrode in which the negative electrode mixture layer comprises natural graphite and artificial graphite as the negative electrode active material. Figure 2 Examples of various forms of negative electrodes are shown on the negative electrode current collector 2 having a negative electrode mixture layer 4 containing natural graphite and artificial graphite, and exemplary negative electrodes are shown in which the ratio of natural graphite to artificial graphite in the negative electrode mixture layer 4 is the same, but the distribution patterns of artificial graphite and natural graphite are different.
[0068] Specifically, Figure 2 Figure A illustrates one embodiment of a multilayer negative electrode where the negative electrode mixture layer 4 has a first negative electrode mixture layer 6 formed of artificial graphite and a second negative electrode mixture layer 8 formed of natural graphite. Figure 2 B illustrates one embodiment of the negative electrode mixture layer 4, comprising a first negative electrode mixture layer formed of artificial graphite and a second negative electrode mixture layer formed of a mixture of artificial graphite and natural graphite. Figure 2 The negative electrodes shown in A and B contain a large amount of artificial graphite, which improves fast-charging performance and enhances battery cycle performance. Furthermore, because the outer surface layer contains a large amount of natural graphite, contamination of the calendering rolls can be suppressed during the calendering process in the manufacture of the negative electrode, thereby improving the surface quality of the negative electrode.
[0069] Figure 2C shows a comparative example of a negative electrode having a negative electrode mixture layer 4 formed by mixing artificial graphite and natural graphite, which has a content ratio of artificial graphite to natural graphite similar to that of the negative electrodes shown in A and B of the Figure 2 However, in the negative electrode, a large amount of artificial graphite is distributed on the outer surface of the negative electrode active material layer. Therefore, during the calendering process, the artificial graphite may adhere to the surface of the calendering roller and cause contamination of the calendering roller surface, which may reduce the surface quality of the negative electrode.
[0070] In addition to the graphite-based negative electrode active material as described above, the negative electrode mixture layer may further include a silicon-based negative electrode active material. By including the silicon-based negative electrode active material, higher capacity characteristics can be provided, and the silicon-based negative electrode active material may be included in at least one of the first negative electrode mixture layer and the second negative electrode mixture layer. For example, it may be included in the first negative electrode mixture layer.
[0071] The silicon-based negative electrode active material may include, for example, Si, SiOx (0 < x < 2), metal-doped SiOx, silicon-carbon composites, etc. The metal in the metal-doped SiOx may include lithium and / or magnesium, and the metal-doped SiOx may include metal silicates.
[0072] The content of the silicon-based negative electrode active material may be 3-40% by weight of the total weight of the negative electrode mixture layer, but is not limited thereto.
[0073] In addition to the graphite-based negative electrode active material and the silicon-based negative electrode active material, the negative electrode mixture layer may further include a third negative electrode active material. For example, it may include carbon-based materials such as hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers (MPCF), carbon composites, etc.; lithium metal; lithium alloy; or tin (Sn)-containing substances, etc.
[0074] The lithium metal may be listed as pure lithium metal or lithium metal formed with a protective layer for inhibiting dendrite growth, etc. The elements included in the lithium alloy may include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium, etc.
[0075] For example, the first negative electrode mixture slurry for forming the first negative electrode mixture layer and the second negative electrode mixture slurry for forming the second negative electrode mixture layer may be prepared by mixing the negative electrode active materials in a solvent. The first negative electrode mixture slurry and the second negative electrode mixture slurry may be coated / deposited on the negative electrode current collector, and then dried and calendered to prepare the first negative electrode mixture layer and the second negative electrode mixture layer.
[0076] The negative electrode current collector is the negative electrode current collector commonly used in the process of manufacturing the negative electrode of a secondary battery. As long as it does not cause chemical changes inside the battery and has conductivity, there are no special restrictions on its use.
[0077] For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or copper or stainless steel, aluminum-cadmium alloys with surface treatments of carbon, nickel, titanium, silver, etc., can be used as the negative electrode current collector. Furthermore, the negative electrode current collector can have fine irregularities formed on its surface to enhance the adhesion of the negative electrode active material, and can be in various forms such as films, sheets, foils, meshes, porous materials, foams, and non-woven fabrics. The thickness of the negative electrode current collector 2 can be, for example, 10-50 μm, but is not limited to this.
[0078] The process of coating the negative electrode mixture slurry onto the negative electrode current collector can be carried out by methods such as gravure coating, slot extrusion coating, multi-layer simultaneous die coating, embossing, doctor blade coating, dip coating, bar coating, casting, etc., and is not limited to these methods.
[0079] In some implementations, the negative electrode may include a layer of negative electrode active material in the form of lithium metal formed by a deposition / coating process.
[0080] Specifically, the coating can be performed by simultaneously coating the first negative electrode mixture slurry and the second negative electrode mixture slurry and then drying them, or by coating the first negative electrode mixture slurry and then coating and drying the second negative electrode mixture slurry.
[0081] Non-limiting examples of solvents used for the negative electrode mixture slurry include water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, tert-butanol, etc.
[0082] The negative electrode mixture slurry may further contain a binder, and may optionally further contain additives such as conductive materials, thickeners, or dispersants.
[0083] The adhesive may include polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) copolymer, polyacrylonitrile, polymethyl methacrylate, nitrile rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. In one embodiment, as the negative electrode adhesive, styrene-butadiene rubber (SBR) based adhesive, carboxymethyl cellulose (CMC), polyacrylic acid based adhesive, poly(3,4-ethylenedioxythiophene) (PEDOT) based adhesive, etc.
[0084] Based on the total weight of the negative electrode mixture layer, the content of the adhesive can be from about 1.2% by weight to about 5% by weight.
[0085] The conductive material can be added to enhance the conductivity and / or the mobility of lithium ions or electrons in the negative electrode mixture layer. For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), and carbon fiber, and / or metal-based conductive materials containing perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3, but is not limited thereto.
[0086] In one embodiment, the content of the conductive material can be from about 0.05% by weight to about 3% by weight, based on the total weight of the negative electrode mixture layer.
[0087] Depending on the requirements, the negative electrode mixture layer may further contain thickeners and / or dispersants, etc. As one embodiment, the negative electrode mixture layer may contain thickeners such as carboxymethyl cellulose (CMC).
[0088] After coating the negative electrode current collector with a negative electrode mixture slurry, a calendering process is performed, which can be carried out, for example, by calendering rolls.
[0089] As described above, in the negative electrode according to one embodiment of the present invention, the negative electrode mixture layer disposed outside the negative electrode mixture layer is a layer containing a large amount of natural graphite with excellent adhesion. This results in less detachment from the negative electrode during the calendering process, thus suppressing contamination of the calendering rolls. Therefore, higher pressure can be provided during the calendering process, thereby enabling the manufacture of a higher density negative electrode.
[0090] Furthermore, as mentioned above, natural graphite, due to its high binding strength, can reduce contamination of the calendering rolls, but achieving the same mixture density may require a calendering process with higher pressure than that using artificial graphite. However, if natural graphite is predominantly distributed on the surface of the negative electrode mixture layer and artificial graphite is predominantly distributed within the negative electrode mixture layer, the same mixture density can be achieved with lower pressure during calendering.
[0091] Therefore, as shown in one specific embodiment of the present invention, by distributing natural graphite on the electrode surface in contact with the calendering roll, the roll can be prevented from being contaminated due to the properties of natural graphite that provide high adhesion. At the same time, the linear pressure (tons / cm) can be reduced during calendering, thereby improving the economics of the process and reducing the generation of negative electrode surface defects that may result from applying high pressure to achieve high mixture density.
[0092] According to another aspect of the present invention, a lithium secondary battery including the above-described negative electrode can be provided. Specifically, a lithium secondary battery according to one embodiment includes a negative electrode for a lithium secondary battery according to any of the above embodiments.
[0093] For example, the lithium secondary battery may include a positive electrode in addition to the negative electrode described above, and a separator may be included between the negative electrode and the positive electrode.
[0094] The positive electrode may include a positive electrode current collector and a positive electrode mixture layer disposed on at least one side of the positive electrode current collector.
[0095] The positive electrode current collector may contain stainless steel, nickel, aluminum, titanium, or alloys thereof. It may also contain aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. The thickness of the positive electrode current collector is not limited thereto; for example, it may be 10-50 µm.
[0096] The positive electrode mixture layer may contain a positive electrode active material. The positive electrode active material may contain compounds that enable reversible insertion and extraction of lithium ions.
[0097] According to some embodiments, the positive electrode active material may comprise a lithium-nickel metal oxide. The lithium-nickel metal oxide may further comprise at least one of cobalt (Co), manganese (Mn), and aluminum (Al).
[0098] In some embodiments, the positive electrode active material or the lithium-nickel metal oxide may comprise a layered structure or a crystal structure represented by the following chemical formula 1.
[0099] [Chemical Formula 1] Li x Ni a M b O 2+z In chemical formula 1, the values can be 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b≤0.4, or -0.5≤z≤0.1. As mentioned above, M can contain Co, Mn, and / or Al.
[0100] The chemical structure represented by Formula 1 indicates the bonding relationships contained in the layered or crystalline structure of the positive electrode active material, and does not exclude other additional elements. For example, M may contain Co and / or Mn, and Co and / or Mn may be provided together with Ni as the main active element of the positive electrode active material. Formula 1 is provided to represent the bonding relationships of the main active elements, and it should be understood that Formula 1 includes the introduction and substitution of additional elements.
[0101] In one embodiment, in addition to the primary active element, auxiliary elements may be further included to enhance the chemical stability of the positive electrode active material or the layered / crystal structure. These auxiliary elements may be incorporated into the layered / crystal structure to form a bond, and this should be understood to also include the chemical structures represented by Formula 1.
[0102] The auxiliary element may include at least one of, for example, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, and Zr. The auxiliary element may function as an auxiliary active element, together with Co or Mn, to contribute to the capacity / power activity of the positive electrode active material; for example, Al.
[0103] For example, the positive electrode active material or the lithium-nickel metal oxide may contain a layered structure or a crystal structure represented by the following chemical formula 1-1.
[0104] [Chemical Formula 1-1] Li x Ni a M1 b1 M2 b2 O 2+z In chemical formula 1-1, M1 may contain Co, Mn, and / or Al. M2 may contain the aforementioned auxiliary elements. In chemical formula 1-1, the values can be 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b1+b2≤0.4, and -0.5≤z≤0.1.
[0105] The positive electrode active material may further include coating elements or doping elements. For example, elements that are substantially the same as or similar to the auxiliary elements described above can be used as coating elements or doping elements. For example, one or more combinations of the elements described above can be used as coating elements or doping elements.
[0106] The coating element or dopant element may exist on the surface of the lithium-nickel metal oxide particles or penetrate through the surface of the lithium-nickel metal oxide particles and be contained in the bonding structure represented by chemical formula 1 or chemical formula 1-1.
[0107] The positive electrode active material may contain nickel-cobalt-manganese (NCM)-based lithium oxide. In this case, NCM-based lithium oxide with increased nickel content can be used.
[0108] Ni can be provided as a transition metal related to the power and capacity of lithium secondary batteries. Therefore, as described above, by using a high-content (High-Ni) composition for the positive electrode active material, a high-capacity positive electrode and a high-capacity lithium secondary battery can be provided.
[0109] However, with increasing Ni content, the long-term storage stability and lifetime stability of the cathode or secondary battery may relatively decrease, and side reactions with the electrolyte may also increase. However, according to an exemplary embodiment, conductivity can be maintained by including Co, while lifetime stability and capacity retention characteristics can be improved by including Mn.
[0110] The Ni content in the NCM-based lithium oxide (e.g., the mole fraction of nickel in the total moles of nickel, cobalt, and manganese) can be 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the Ni content can be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95.
[0111] In some embodiments, the positive electrode active material may further comprise lithium cobalt oxide-based active material, lithium manganese oxide-based active material, lithium nickel oxide-based active material, or lithium iron phosphate (LFP)-based active material (e.g., LiFePO4).
[0112] In some embodiments, the positive electrode active material may include, for example, an Mn-rich based active material having a chemical structure or crystal structure represented by Chemical Formula 2, a Li rich layered oxide (LLO) / Over Lithiated Oxide (OLO) based active material, and a Co-less based active material.
[0113] [Chemical Formula 2] p[Li2MnO3]·(1-p)[Li q JO2] In Chemical Formula 2, 0 < p < 1, 0.9 ≤ q ≤ 1.2, and J may include at least one element selected from Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, and B.
[0114] For example, the positive electrode active material may be mixed in a solvent to prepare a positive electrode mixture slurry. The positive electrode mixture slurry may be coated on a positive electrode current collector and then dried and calendered to prepare a positive electrode mixture layer.
[0115] The coating process may be performed by methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, knife coating, dip coating, rod coating, casting, etc., and is not limited thereto.
[0116] As non-limiting examples of the solvent for preparing the positive electrode mixture, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc. may be cited.
[0117] The positive electrode mixture layer may further include an adhesive. The adhesive may include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (poly(vinylidene fluoride-co-hexafluoropropylene)), polyacrylonitrile, polymethyl methacrylate, nitrile rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. In one embodiment, a PVDF-based adhesive may be used as the positive electrode adhesive.
[0118] The positive electrode mixture layer may selectively further include a conductive material. The conductive material may be added to enhance the conductivity of the positive electrode mixture layer and / or the mobility of lithium ions or electrons. For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, vapor grown carbon fibers (VGCF), carbon fibers, etc. and / or metal-based conductive materials including perovskite minerals such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3, etc., but is not limited thereto.
[0119] The positive electrode mixture layer may optionally further include additives such as thickeners or dispersants. As an example, the positive electrode mixture layer may include a thickener such as carboxymethyl cellulose (CMC).
[0120] An electrode assembly can be manufactured by placing a diaphragm between the positive and negative electrodes. The diaphragm can be configured to prevent short circuits between the positive and negative electrodes and to allow ion flow.
[0121] For example, the diaphragm may comprise a porous polymer membrane or a porous nonwoven fabric. The porous polymer membrane may comprise polyolefin-based polymers such as ethylene polymers, propylene polymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers. The porous nonwoven fabric may comprise high-melting-point glass fibers, polyethylene terephthalate fibers, etc. The diaphragm may also comprise ceramic-based materials. For example, inorganic particles may be coated on or dispersed within the polymer membrane to improve heat resistance.
[0122] The diaphragm may have a single-layer or multi-layer structure comprising the aforementioned polymer membrane and / or nonwoven fabric. Depending on the specific embodiment, the thickness of the diaphragm may be from 10 μm to 20 μm, but the invention is not limited thereto.
[0123] According to an exemplary embodiment, the electrode assembly formed by repeatedly setting the positive electrode, negative electrode and the separator can be of the winding type, stacking type, z-folding type, or stack-folding type.
[0124] The electrode assembly and electrolyte are housed together in a casing, thereby defining a lithium secondary battery. According to an exemplary embodiment, a non-aqueous electrolyte can be used.
[0125] The non-aqueous electrolyte may contain a lithium salt as the electrolyte and an organic solvent, wherein the lithium salt may be, for example, Li. + X - This indicates that the anion (X) of the lithium salt is... - ), can be exemplified by F - Cl - ,Br - I - NO3 - N(CN)2 - BF4- 、ClO4 - 、PF6 - 、(CF3)2PF4 - 、(CF3)3PF3 - 、(CF3)4PF2 - 、(CF3)5PF - 、(CF3)6P - 、CF3SO3 - 、CF3CF2SO3 - 、(CF3SO2)2N - 、(FSO2)2N - 、CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、(SF5)3C - 、(CF3SO2)3C - 、CF3(CF2)7SO3 - 、CF3CO2 - 、CH3CO2 - 、SCN - and (CF3CF2SO2)2N - etc.
[0126] The organic solvent may contain an organic compound that has sufficient solubility for the lithium salt and additives and is non-reactive within the battery. For example, the organic solvent may include at least one of carbonate-based solvents, ester-based solvents, ether-based solvents, ketone-based solvents, alcohol-based solvents, and aprotic solvents. As the organic solvent, for example, propylene carbonate (PC), ethylene carbonate (EC), butene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, vinylene carbonate, methyl acetate (MA), ethyl acetate (EA), n-propylacetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), ethyl fluoroacetate (FEA), ethyl difluoroacetate (DFEA), ethyl trifluoroacetate (TFEA), dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), and diethylene glycol dimethyl ether can be used. Dimethyl ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), 2-methyltetrahydrofuran, ethyl alcohol, isopropyl alcohol, dimethyl sulfoxide, acetonitrile, diethoxyethane, sulfolane, γ-butyrolactone, and propylene sulfite, etc. These can be used alone or in combination of two or more.
[0127] The non-aqueous electrolyte may further comprise additives. These additives may include, for example, cyclic carbonate compounds, fluorinated carbonate compounds, sulopentalide compounds, cyclic sulfate compounds, cyclic sulfite compounds, phosphate compounds, and borate compounds.
[0128] The cyclic carbonate-based compound may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), etc.
[0129] The fluorinated carbonate compounds may include fluoroethylene carbonate (FEC), etc.
[0130] The sulfonyl compounds may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, etc.
[0131] The cyclic sulfate-based compounds may include 1,2-ethylene sulfate, 1,2-propylene sulfate, etc.
[0132] The cyclic sulfite-based compound may include ethylene sulfite, butylene sulfite, etc.
[0133] The phosphate-based compounds may include lithium difluorobis-oxalato phosphate, lithium difluorophosphate, etc.
[0134] The borate-based compounds may include lithium bis(oxalate) borate, etc.
[0135] According to another aspect of the present invention, a method for manufacturing a negative electrode for a lithium secondary battery can be provided, the method comprising the steps of: coating a first negative electrode mixture slurry comprising a graphite-based negative electrode active material onto at least one side of a negative electrode current collector; coating a second negative electrode mixture slurry comprising a graphite-based negative electrode active material onto the coated first negative electrode mixture slurry; drying the coated first negative electrode mixture slurry and the second negative electrode mixture slurry to form a first negative electrode mixture layer and a second negative electrode mixture layer; and calendering the first negative electrode mixture layer and the second negative electrode mixture layer, wherein the graphite-based negative electrode active material comprises artificial graphite and natural graphite, wherein in the graphite-based negative electrode active material contained in the first negative electrode mixture layer, the weight of artificial graphite is greater than the weight of natural graphite, and in the graphite-based negative electrode active material contained in the second negative electrode mixture layer, the weight of natural graphite is greater than the weight of artificial graphite.
[0136] Detailed descriptions of the negative electrode current collector 2, graphite-based negative electrode active material, first negative electrode mixture slurry, second negative electrode mixture slurry, first negative electrode mixture layer 6, second negative electrode mixture layer 8, artificial graphite and natural graphite are repeated above and therefore omitted.
[0137] According to one specific implementation, the calendering step can be carried out at a linear pressure of 0.50-1.20 tons / cm.
[0138] Specifically, the calendering step can be carried out with a linear pressure of 0.55 tons / cm or more than 0.60 tons / cm, and can also be carried out with a linear pressure of 0.80 tons / cm or less than 0.60 tons / cm.
[0139] Example The embodiments of the present invention will be further described below with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples are only for illustrating the present invention and are not intended to limit the claims. Various changes and modifications can be made to the embodiments within the scope and technical concept of the present invention, which will be obvious to those skilled in the art, and such variations and modifications are naturally within the scope of the claims.
[0140] Example 1 (First negative electrode mixture layer) The first negative electrode mixture was prepared by mixing artificial graphite (AG) as the negative electrode active material, carbon black (CB) as the conductive material, and carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) as the binders in the weight ratios shown in Table 1.
[0141] The first negative electrode mixture was added to water to prepare a first negative electrode mixture slurry with a solid content of 48%. The first negative electrode mixture slurry was coated onto both sides of a copper foil (thickness: 8 μm) negative electrode current collector and dried to produce a loading weight of 9.18 mg / cm³. 2 The first negative electrode mixture layer.
[0142] (Second negative electrode mixture layer) A second negative electrode mixture was prepared by mixing natural graphite (NG) as the negative electrode active material, carbon black (CB) as the conductive material, and carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) as binders in the weight ratios shown in Table 1.
[0143] The second negative electrode mixture was added to water to prepare a second negative electrode mixture slurry with a solid content of 48%. The second negative electrode mixture slurry was coated onto the first negative electrode mixture layer and dried to produce a loading weight of 1.02 mg / cm³. 2 The second negative electrode mixture layer (the ratio of the load weight of the first negative electrode mixture layer to the second negative electrode mixture layer is 9:1).
[0144] (Manufacturing of the negative electrode) The material, manufactured by the above method, has a total load weight of 10.2 mg / cm² using calendering rolls. 2 The negative electrode of the negative electrode mixture layer is rolled to produce a thickness of 128 μm and a density of 1.7 g / cm³. 3 The negative electrode has a multi-layer (double-layer) structure.
[0145] (evaluate) Linear pressure during calendering The results of measuring the linear pressure (force per unit length of the calender roll in the axial direction) required for the calendering process are shown in Table 1.
[0146] Contamination level of calender rolls To evaluate the contamination level of the calender rolls according to the calendering process, the results of measuring the blackness / whiteness (ΔL) of the calender roll surface after the calendering process are shown in Table 1 and... Figure 3 Show.
[0147] The blackness / whiteness of the calender roll was measured at the same location using a colorimeter (VISKO CR-400). Specifically, while manufacturing 500m of negative electrode, the blackness / whiteness was measured at the same location on the surface of the calender roll every 50m (refer to...). Figure 3 When measuring black and white color, the colorimeter device is attached to the calender roll for measurement. The black and white color values of the calender roll when calendering 500m of negative electrode are shown in Table 1.
[0148] Example 2 The double-layer negative electrode was manufactured using the same method as in Example 1, except that the load weights of the first negative electrode mixture layer and the second negative electrode mixture layer were adjusted as shown in Table 1.
[0149] The linear pressure and blackness / whiteness of the manufactured negative electrode during calendering were measured, and the results are shown in Table 1 and 2. Figure 3 .
[0150] Comparative Example 1 The double-layer negative electrode as shown in Table 1 was manufactured using the same method as in Example 1, except that the second negative electrode mixture slurry of Example 1 was used to manufacture the first negative electrode mixture layer, and the first negative electrode mixture slurry of Example 1 was used to manufacture the second negative electrode mixture layer.
[0151] The linear pressure and blackness / whiteness of the manufactured negative electrode during calendering were measured, and the results are shown in Table 1 and 2. Figure 3 .
[0152] Comparative Examples 2 to 4 A negative electrode mixture was prepared by mixing a mixture of natural graphite (NG) and artificial graphite (AG) as the negative electrode active material, carbon black (CB) as the conductive material, and carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) as the binder in the weight ratios shown in Table 1.
[0153] The negative electrode mixture is added to water to prepare a negative electrode mixture slurry with a solid content of 48%. The negative electrode mixture slurry is coated on both sides of the negative electrode current collector of copper foil (thickness: 8μm) and dried to create a single-layer negative electrode mixture layer.
[0154] The negative electrode having the single-layer negative electrode mixture layer is calendered using calendering rolls to produce a negative electrode with a thickness of 128 μm and a density of 1.7 g / cm³. 3 A single-layer negative electrode.
[0155] The linear pressure and blackness / whiteness of the manufactured negative electrode during calendering were measured, and the results are shown in Table 1 and 2. Figure 3 .
[0156] [Table 1] The percentages (%) in Table 1 represent the proportion of each layer in the total load weight of the first negative electrode mixture layer and the second negative electrode mixture layer.
[0157] See Table 1 and Figure 3Compared with the negative electrodes of Comparative Examples 1 to 4, the calender rolls of the negative electrodes of Examples 1 and 2, in which the weight of artificial graphite in the graphite-based negative electrode active material contained in the first negative electrode mixture layer is greater than the weight of natural graphite and the weight of natural graphite in the graphite-based negative electrode active material contained in the second negative electrode mixture layer is greater than the weight of artificial graphite, have low black and white color. Therefore, it can be confirmed that the phenomenon of surface contamination of calender rolls and other calendering equipment can be improved, and higher electrode density can be achieved.
[0158] Specifically, refer to Figure 3 As the calendering process was repeated, the contamination level on the roll surface increased. However, even after calendering for 500m, the negative electrodes of Examples 1 and 2 exhibited a lower black-and-white value on the calendering roll compared to the negative electrode of Comparative Example 3 after calendering for 300m. Therefore, it can be concluded that the negative electrodes of Examples 1 and 2 effectively improved the contamination level of the calendering roll, thereby significantly enhancing the productivity of the negative electrode.
[0159] In this regard, referring to the negative electrodes of Comparative Examples 2 to 4, which have a single-layer structure, it can be confirmed that the more artificial graphite with relatively low electrode adhesion is contained, the more serious the contamination of the calender roll is (Comparative Example 4 > Comparative Example 2 > Comparative Example 3), and the more natural graphite with relatively high expansion rate is contained, the higher the linear pressure required during calendering is (Comparative Example 3 > Comparative Example 2 > Comparative Example 4).
[0160] On the other hand, the negative electrodes of Examples 1 and 2 are multi-layer (double-layer) negative electrodes with a second negative electrode mixture layer comprising natural graphite as the negative electrode active material on the negative electrode surface (upper layer) and a first negative electrode mixture layer comprising artificial graphite as the negative electrode active material on the negative electrode interior (lower layer) serving as the negative electrode current collector side. The ratio of negative electrode active material in the entire negative electrode is the same as that of Comparative Examples 2 and 3, respectively. However, in terms of the contamination degree of the calender roll, the blackness and whiteness values of Examples 1 and 2 are 31.2 and 33.9, respectively, which are significantly improved compared to 41.5 and 37.1 of Comparative Examples 2 and 3.
[0161] Therefore, it was determined that even if the negative electrode mixture contained artificial graphite and natural graphite, as in Comparative Examples 2 to 4, the design of a single-layer negative electrode made it difficult to suppress the contamination phenomenon on the surface of the calendering equipment and to design a high-density electrode.
[0162] In addition, the negative electrode of Comparative Example 1, which has a multilayer (double-layer) structure, is the opposite of that of Embodiment 1 of the present invention. On the negative electrode current collector side, which is the inner (lower layer), it includes a first negative electrode mixture layer that separately contains natural graphite as the negative electrode active material, and on the surface (upper layer) of the negative electrode, it includes a second negative electrode mixture layer that separately contains artificial graphite as the negative electrode active material.
[0163] However, the negative electrode of Comparative Example 1 required a significantly high linear pressure of 0.83 tons / cm² to manufacture a negative electrode with the same thickness and calendering density, and the black-and-white ratio of the calendering roll was 47.3, indicating severe contamination of the calendering equipment surface. This was determined to be due to the fact that a first negative electrode mixture layer containing only natural graphite with a relatively high expansion rate as the negative electrode active material was placed on the negative electrode current collector side (the inner layer), while a second negative electrode mixture layer containing only artificial graphite with relatively low electrode adhesion was placed on the negative electrode surface (the upper layer).
[0164] Therefore, when the negative electrode is designed to have the same composition and structure as in Examples 1 and 2, the contamination on the surface of the calendering equipment can be effectively improved, and a high-density negative electrode for lithium secondary batteries can be provided.
Claims
1. A negative electrode for a lithium secondary battery, the negative electrode for the lithium secondary battery comprising: Negative electrode current collector; And a negative electrode mixture layer, the negative electrode mixture layer being disposed on at least one side of the negative electrode current collector and comprising a graphite-based negative electrode active material. The negative electrode mixture layer comprises: a first negative electrode mixture layer disposed on the negative electrode current collector; and a second negative electrode mixture layer disposed on the first negative electrode mixture layer. The graphite-based negative electrode active material includes artificial graphite and natural graphite. In the graphite-based negative electrode active material contained in the first negative electrode mixture layer, the weight of artificial graphite is greater than the weight of natural graphite. In the graphite-based negative electrode active material contained in the second negative electrode mixture layer, the weight of natural graphite is greater than that of artificial graphite.
2. The negative electrode for a lithium secondary battery according to claim 1, wherein, Based on the total weight of the graphite-based negative electrode active material contained in the first negative electrode mixture layer, the content of artificial graphite is greater than 50% by weight.
3. The negative electrode for a lithium secondary battery according to claim 1, wherein, The first negative electrode mixture layer does not contain natural graphite.
4. The negative electrode for a lithium secondary battery according to claim 1, wherein, The graphite-based negative electrode active material contained in the first negative electrode mixture layer is artificial graphite.
5. The negative electrode for a lithium secondary battery according to claim 1, wherein, Based on the total weight of the graphite-based negative electrode active material contained in the second negative electrode mixture layer, the content of natural graphite is greater than 50% by weight.
6. The negative electrode for a lithium secondary battery according to claim 1, wherein, The second negative electrode mixture layer does not contain artificial graphite.
7. The negative electrode for a lithium secondary battery according to claim 1, wherein, The graphite-based negative electrode active material contained in the second negative electrode mixture layer is natural graphite.
8. The negative electrode for a lithium secondary battery according to claim 1, wherein, The total weight of the artificial graphite contained in the negative electrode mixture layer is greater than the total weight of the natural graphite.
9. The negative electrode for a lithium secondary battery according to claim 1, wherein, Based on the graphite-based negative electrode active material contained in the entire negative electrode mixture layer including the first negative electrode mixture layer and the second negative electrode mixture layer, the content of artificial graphite is 60% by weight or more and 90% by weight or less.
10. The negative electrode for a lithium secondary battery according to claim 1, wherein, Based on the graphite-based negative electrode active material contained in the entire negative electrode mixture layer including the first negative electrode mixture layer and the second negative electrode mixture layer, the content of natural graphite is more than 10% by weight and less than 40% by weight.
11. The negative electrode for a lithium secondary battery according to claim 1, wherein, The load weight of the first negative electrode mixture layer is greater than the load weight of the second negative electrode mixture layer.
12. The negative electrode for a lithium secondary battery according to claim 11, wherein, Based on the total load weight of the first negative electrode mixture layer and the second negative electrode mixture layer, the ratio of the load weight of the first negative electrode mixture layer is 70% to 95%.
13. The negative electrode for a lithium secondary battery according to claim 11, wherein, Based on the total load weight of the first negative electrode mixture layer and the second negative electrode mixture layer, the load weight ratio of the second negative electrode mixture layer is 5% to 30%.
14. The negative electrode for a lithium secondary battery according to claim 1, wherein, The thickness of the second negative electrode mixture layer is 10% to 50% of the total thickness of the negative electrode mixture layer.
15. A lithium secondary battery comprising the negative electrode for a lithium secondary battery as described in claim 1.
16. A method for manufacturing a negative electrode for a lithium secondary battery, comprising the following steps: A first negative electrode mixture slurry containing a graphite-based negative electrode active material is coated on at least one side of the negative electrode current collector; A second negative electrode mixture slurry containing a graphite-based negative electrode active material is coated onto the first negative electrode mixture slurry that has been coated; The coated first negative electrode mixture slurry and second negative electrode mixture slurry are dried to form a first negative electrode mixture layer and a second negative electrode mixture layer; and The first negative electrode mixture layer and the second negative electrode mixture layer are calendered. The graphite-based negative electrode active material includes artificial graphite and natural graphite. In the graphite-based negative electrode active material contained in the first negative electrode mixture layer, the weight of artificial graphite is greater than the weight of natural graphite. In the graphite-based negative electrode active material contained in the second negative electrode mixture layer, the weight of natural graphite is greater than that of artificial graphite.
17. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 16, wherein, The calendering step is carried out at a linear pressure of 0.50 tons / cm to 1.20 tons / cm.