Negative electrode and lithium secondary battery comprising the same

Abstract

This invention relates to a negative electrode comprising a negative electrode current collector; a first negative electrode active material layer disposed on the negative electrode current collector; and a second negative electrode active material layer disposed on the first negative electrode active material layer, wherein the volume of pores contained in the first negative electrode active material layer is 20% to 49% of the total volume of pores contained in the first and second negative electrode active material layers, the first negative electrode active material layer contains a first negative electrode active material, the first negative electrode active material contains natural graphite and a first silicon-based negative electrode active material, the second negative electrode active material layer contains a second negative electrode active material, the second negative electrode active material contains artificial graphite and a second silicon-based negative electrode active material, and the content of the first silicon-based negative electrode active material contained in the first negative electrode active material layer is greater than the content of the second silicon-based negative electrode active material contained in the second negative electrode active material layer.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2024-0153034, filed on October 31, 2024, and Korean Patent Application No. 10-2025-0159607, filed on October 29, 2025, the disclosures of which are incorporated herein by reference. Technical Field

[0003] This invention relates to a negative electrode and a lithium secondary battery containing the same. Background Technology

[0004] In recent years, lithium-ion batteries have been gaining attention as an energy source for electric vehicles. With the continued expansion of electric vehicle adoption, the demand for lithium-ion batteries that can provide longer driving range and shorter charging times on a single charge is constantly increasing.

[0005] Lithium-ion secondary batteries are typically fabricated by placing a separator between a positive electrode containing a positive electrode active material made of a lithium-containing transition metal oxide and a negative electrode containing a negative electrode active material capable of storing lithium ions, thus forming an electrode assembly. After inserting the electrode assembly into a battery casing, a non-aqueous electrolyte, which serves as the lithium-ion transport medium, is injected, and then the battery casing is sealed. The non-aqueous electrolyte typically consists of a lithium salt and an organic solvent capable of dissolving the lithium salt. Carbon-based materials, such as natural or artificial graphite, are commonly used as the negative electrode active material in lithium-ion secondary batteries. However, due to the slow reaction and low capacity of carbon-based negative electrode active materials with lithium, secondary batteries using these materials have limitations in achieving high capacity and fast charging characteristics.

[0006] Therefore, in recent years, people have been trying to apply silicon-based anode active materials with higher capacity per unit weight than graphite. However, because silicon-based active materials undergo volume expansion of up to 400% during charging and discharging, there are problems such as damage to the solid electrolyte interphase (SEI) layer on the anode surface, degradation of the active material, reduced lifetime characteristics, and higher resistance than carbon-based anode active materials.

[0007] Therefore, there is a need to develop a negative electrode that achieves high capacity while also exhibiting excellent resistance and lifetime characteristics during fast charging. Summary of the Invention

[0008] Technical issues

[0009] One aspect of the present invention provides a negative electrode that exhibits excellent capacity, resistance and lifespan characteristics during fast charging, and also provides a lithium secondary battery comprising the negative electrode.

[0010] Technical solution

[0011] [1] The present invention provides a negative electrode comprising: a negative electrode current collector; a first negative electrode active material layer disposed on the negative electrode current collector; and a second negative electrode active material layer disposed on the first negative electrode active material layer, wherein the volume of the pores contained in the first negative electrode active material layer is 11% to 49% of the total volume of the pores contained in the first negative electrode active material layer and the second negative electrode active material layer, the first negative electrode active material layer contains a first negative electrode active material, the first negative electrode active material contains natural graphite and a first silicon-based negative electrode active material, the second negative electrode active material layer contains a second negative electrode active material, the second negative electrode active material contains artificial graphite and a second silicon-based negative electrode active material, and the content of the first silicon-based negative electrode active material contained in the first negative electrode active material layer is greater than the content of the second silicon-based negative electrode active material contained in the second negative electrode active material layer.

[0012] [2] The present invention provides the negative electrode described in [1] above, wherein the ratio (X1 / X2) of the content of the first silicon-based negative electrode active material in the first negative electrode active material layer to the content of the second silicon-based negative electrode active material in the second negative electrode active material layer is greater than 1 and less than or equal to 10.

[0013] [3] The present invention provides a negative electrode as described in at least one of [1] or [2] above, wherein the content of the first silicon-based negative electrode active material is from 5% to 30% by weight based on the total weight of the first negative electrode active material.

[0014] [4] The present invention provides at least one of the above [1] to [3] negative electrode, wherein the content of the second silicon-based negative electrode active material is 1% to 20% by weight based on the total weight of the second negative electrode active material.

[0015] [5] The present invention provides a negative electrode as described in at least one of [1] to [4] above, wherein the porosity of the first negative electrode active material layer is 15% to 30%.

[0016] [6] The present invention provides a negative electrode according to at least one of [1] to [5] above, wherein the porosity of the second negative electrode active material layer is 20% to 35%.

[0017] [7] The present invention provides a negative electrode according to at least one of [1] to [6] above, wherein the thickness of the first negative electrode active material layer is 35% to 50% of the total thickness of the first negative electrode active material layer and the second negative electrode active material layer.

[0018] [8] The present invention provides at least one of the above [1] to [7] negative electrodes, wherein the first silicon-based negative electrode active material and the second silicon-based negative electrode active material each comprise a Si / C composite.

[0019] [9] The present invention provides a lithium secondary battery comprising: an electrode assembly comprising a negative electrode, a positive electrode and a separator disposed between the negative electrode and the positive electrode as described in any one of [1] to [8] above; an electrolyte; and a battery case containing the electrode assembly and the electrolyte.

[0020]

[10] The present invention provides a lithium secondary battery according to at least one of [1] to [9] above, wherein the lithium secondary battery is a cylindrical lithium secondary battery in which the ratio of the diameter (R) of the lithium secondary battery to the height (h) of the lithium secondary battery is 0.4 or more.

[0021]

[11] The present invention provides a lithium secondary battery according to at least one of [1] to

[10] above, wherein the lithium secondary battery is a 46110 cell, a 48110 cell, a 4880 cell or a 4680 cell.

[0022]

[12] The present invention provides a lithium secondary battery according to at least one of [1] to

[11] above, wherein the positive electrode and the negative electrode each include an uncoated portion in which an active material layer is not formed, and at least a portion of the uncoated portion of the positive electrode and the uncoated portion of the negative electrode define an electrode tab.

[0023]

[13] The present invention provides a lithium secondary battery according to at least one of [1] to

[12] above, wherein a current collector is respectively coupled to the uncoated portion of the positive electrode and the uncoated portion of the negative electrode, and the current collector is connected to the electrode terminal.

[0024]

[14] The present invention provides a lithium secondary battery according to at least one of [1] to

[13] above, wherein the uncoated portion of the positive electrode and the uncoated portion of the negative electrode are processed into a plurality of independently bendable segmented pieces, and at least a portion of the plurality of segmented pieces bends toward the winding center of the electrode assembly.

[0025] Beneficial effects

[0026] In this invention, the negative electrode is designed with a two-layer structure, comprising: a first negative electrode active material layer disposed on a current collector and comprising natural graphite and a first silicon-based negative electrode active material; and a second negative electrode active material layer disposed on the first negative electrode active material layer and comprising artificial graphite and a second silicon-based negative electrode active material. The volume of pores in the first negative electrode active material layer and the volume of pores in the second negative electrode active material layer are controlled at an appropriate ratio, and the first negative electrode active material layer contains a higher content of silicon-based negative electrode active material than the second negative electrode active material layer. Therefore, the negative electrode of this invention exhibits excellent capacity and resistance characteristics, as well as excellent lifespan characteristics during battery fast charging.

[0027] Specifically, by designing the volume of the pores contained in the first negative electrode active material layer and the volume of the pores contained in the second negative electrode active material layer to be in an appropriate ratio, the electrolyte wettability of the first and second negative electrode active material layers is ensured while suppressing the increase in internal resistance, and lithium ions can diffuse smoothly through the second negative electrode active material layer, thereby suppressing the reverse polarity phenomenon.

[0028] Meanwhile, by including a higher content of silicon-based anode active material in the first anode active material layer compared to the second anode active material layer, the volume expansion of the silicon-based anode active material in the upper second anode active material layer during charge and discharge can be effectively mitigated. Therefore, even with repeated charge and discharge cycles, the degradation of the anode active material and the damage to the solid electrolyte interphase (SEI) layer caused by the silicon-based anode active material can be suppressed, thus preventing degradation of lifetime characteristics even during fast charging.

[0029] As a result, the negative electrode of the present invention can have excellent resistance characteristics by reducing the interface resistance and surface resistance of the negative electrode, and can have excellent fast charging performance by improving the lifetime characteristics during the fast charging process. Attached Figure Description

[0030] Figure 1 This is a diagram showing the stacked state of the electrode assembly before winding according to the present invention.

[0031] Figure 2 This is a cross-sectional view showing the electrode structure of an electrode assembly according to one embodiment of the present invention.

[0032] Figure 3 This is a diagram illustrating the structure of an electrode assembly according to one embodiment of the present invention.

[0033] Figure 4 This is a cross-sectional view showing the structure of a lithium secondary battery according to one embodiment of the present invention.

[0034] Figure 5This is a cross-sectional view showing the structure of a lithium secondary battery according to another embodiment of the present invention.

[0035] Figure 6 This is a diagram illustrating the battery pack of the present invention. Detailed Implementation

[0036] The invention will be described in more detail below.

[0037] It should be understood that the words or terms used in the specification and claims should not be interpreted as having the meaning defined in a commonly used dictionary, and it should also be understood that, based on the principle that the inventors may appropriately define the meaning of words or terms to best interpret the invention, the words or terms should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and in the technical concept of the invention.

[0038] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. Unless otherwise stated, singular terms may include plural forms.

[0039] In this specification, it should also be understood that the terms “comprising,” “including,” or “having” specify the presence of the stated features, numbers, steps, elements, or combinations thereof, but do not exclude the presence or addition of more than one other feature, number, step, element, or combination thereof.

[0040] In this invention, "pore volume" refers to the volume of pores contained in the electrode active material layer. In this case, the pores contained in the electrode active material can be disregarded. After cutting the cross-section of the electrode, the pore volume is calculated using the nitrogen adsorption isotherm obtained from the cut electrode cross-section under a liquid nitrogen atmosphere at 77 K using BELSORP-MAX (MicrotracBEL corp.). For pores with diameters from 2 nm to 185 nm, the calculation is performed using the BJH (Barrett-Joyner-Halenda) plot.

[0041] For example, for a negative electrode comprising a first negative electrode active material layer and a second negative electrode active material layer disposed on the first negative electrode active material layer, the pore volume of the first negative electrode active material layer and the pore volume of the second negative electrode active material layer can be measured by the following method.

[0042] (1) Using Ar +(1) The cross-section of the negative electrode was cut using an ion milling system (manufacturer: Hitachi High-Tech, product name: Arblade 5000, accelerating voltage: 6 kV, ion beam current: 350 μA). (2) The first negative electrode active material layer and the second negative electrode active material layer were distinguished in the scanning electron microscope (SEM) image of the cross-section of the cut negative electrode based on the brightness difference of the first negative electrode active material layer and the second negative electrode active material layer caused by the content of silicon-based active material, as well as the thickness of the first negative electrode active material layer and the second negative electrode active material layer. (3) Subsequently, the pore volume of the first negative electrode active material layer and the second negative electrode active material layer was calculated using nitrogen adsorption isotherms obtained by BELSORP-MAX (MicrotracBEL corp.) at 77 K liquid nitrogen atmosphere.

[0043] In this invention, "porosity" refers to the percentage of pore volume relative to the total volume of the electrode active material layer. Porosity can be measured by methods known in the art. For example, for a negative electrode comprising a first negative electrode active material layer and a second negative electrode active material layer disposed on the first negative electrode active material layer, the porosity can be measured by method 1 or method 2.

[0044] [Method 1]

[0045] (1) Using Ar + (1) An ion milling system for an ion beam (manufacturer: Hitachi High-Tech, product name: Arblade 5000, accelerating voltage: 6 kV, ion beam current: 350 μA) was used to cut a cross-section of the negative electrode. (2) In the scanning electron microscope (SEM) image of the cut cross-section of the negative electrode, the first negative electrode active material layer and the second negative electrode active material layer were distinguished based on the brightness difference of the first negative electrode active material layer and the second negative electrode active material layer caused by the content of silicon-based active material, as well as the thickness of the first negative electrode active material layer and the second negative electrode active material layer. (3) The volume of each layer was calculated from the cross-sectional area of ​​the first negative electrode active material layer and the second negative electrode active material layer. (4) Subsequently, for the first negative electrode active material layer and the second negative electrode active material layer, the percentage of pore volume relative to the total volume was calculated, thereby allowing the porosity of the first negative electrode active material layer and the second negative electrode active material layer to be measured. In this case, the pore volume can be measured by the method described above.

[0046] [Method 2]

[0047] (1) After coating the first negative electrode active material layer onto the negative electrode current collector with a slurry and drying it, the actual density of the first negative electrode active material layer is measured. Then, the porosity of the first negative electrode active material layer is measured by substituting the theoretical electrode density and the actual density of the first negative electrode active material layer into Equation 1 below. (2) After coating the second negative electrode active material layer onto the first negative electrode active material layer with a slurry and drying it, the actual density of the entire negative electrode active material layer is measured. Then, the actual density of the second negative electrode active material layer is calculated by excluding the actual density of the first negative electrode active material layer. The porosity of the second negative electrode active material layer is measured by substituting the theoretical electrode density and the actual density of the second negative electrode active material layer into Equation 1 below. In this case, the theoretical electrode density of the negative electrode active material layer refers to the value calculated from the mass of all solid components (e.g., negative electrode active material, negative electrode binder, and negative electrode conductive agent) in the negative electrode active material layer and their respective true densities.

[0048] [Equation 1] Porosity (%) of the negative electrode active material layer = [1 - (Actual density of the negative electrode active material layer / Theoretical electrode density of the negative electrode active material layer)] × 100

[0049] In this invention, the term "single-particle type" refers to a particle composed of 50 or fewer nodules, which includes the concept of a single particle composed of one nodule and a compound of 2 to 50 nodules.

[0050] "Nodule" is a sub-particle unit that makes up a single particle or a particle-like particle. A nodule can be a single crystal without grain boundaries, or a polycrystalline material that does not appear to have grain boundaries when viewed with a scanning electron microscope at a field of view of 5,000 to 20,000 times.

[0051] In this invention, the term "secondary particle" refers to a particle formed by the aggregation of multiple (e.g., dozens to hundreds) primary particles. Specifically, a secondary particle can be an aggregate of more than 50 primary particles.

[0052] In this invention, the term "particle" is used to refer to any one or all of the following concepts: single particle, quasi-single particle, primary particle, nodule, and secondary particle.

[0053] In this invention, "load capacity" (La, unit: mg / 25cm) 2 ) refers to every 25 cm 2 The total mass (mg) of the target negative electrode active material layer contained in the area. Specifically, the loading amount (L) of the first negative electrode active material layer. a1The following method can be used to measure the negative electrode: with only the first negative electrode active material layer formed on one surface of the negative electrode current collector, the negative electrode is punched into a size of 5cm×5cm, the weight W1 of the punched area and the weight W2 of the negative electrode current collector are measured, and then the measured values ​​are substituted into the following [Equation 2-1].

[0054] [Equation 2-1] Loading amount L of the first negative electrode active material layer a1 (g / 25 cm 2 = (W1-W2)

[0055] In addition, the loading amount (L) of the second negative electrode active material layer a2 The following method can be used to measure the negative electrode: With a first negative electrode active material layer formed on one surface of the negative electrode current collector and a second negative electrode active material layer formed on top of the first negative electrode active material layer, the negative electrode is punched into a size of 5 cm × 5 cm. The weight W3 of the punched area is measured. Then, the measured weight W3 is compared with the weight W2 of the negative electrode current collector and the load L of the first negative electrode active material layer obtained when measuring the load of the first negative electrode active material layer. a1 Substitute them together into the following [Equation 2-2].

[0056] [Equation 2-2] Loading amount L of the second negative electrode active material layer a2 (g / 25 cm 2 )=(W3-W2-L a1 )

[0057] The invention will be described in more detail below.

[0058] The negative electrode and / or the lithium secondary battery containing the negative electrode of the present invention comprises at least one of the following disclosed constructions, and may include any combination of technically feasible constructions among the following constructions.

[0059] negative electrode

[0060] The negative electrode of the present invention comprises: a negative electrode current collector; a first negative electrode active material layer disposed on the negative electrode current collector; and a second negative electrode active material layer disposed on the first negative electrode active material layer. The volume of pores contained in the first negative electrode active material layer is 11% to 49% of the total volume of pores contained in the first and second negative electrode active material layers. The first negative electrode active material layer contains a first negative electrode active material, which comprises natural graphite and a first silicon-based negative electrode active material. The second negative electrode active material layer contains a second negative electrode active material, which comprises artificial graphite and a second silicon-based negative electrode active material. The content of the first silicon-based negative electrode active material in the first negative electrode active material layer is greater than the content of the second silicon-based negative electrode active material in the second negative electrode active material layer.

[0061] Conversely, even if the content of the first silicon-based negative electrode active material in the first negative electrode active material layer is greater than the content of the second silicon-based negative electrode active material in the second negative electrode active material layer, if the volume of pores in the first negative electrode active material layer does not meet the requirement of 11% to 49% of the total volume of pores in the first and second negative electrode active material layers, the inflow of lithium ions into the second negative electrode active material layer in contact with the electrolyte may be difficult. Therefore, since the capacity and efficiency of the negative electrode may not be fully realized during charging and discharging, a reverse polarity phenomenon may occur when this negative electrode is used in a lithium secondary battery, resulting in a potential difference opposite to that of the positive electrode. Furthermore, due to the unfavorable structure for electrolyte penetration into the second negative electrode active material layer, electrolyte wettability may be reduced, potentially leading to poor fast-charging characteristics.

[0062] Therefore, in the negative electrode of the present invention, since the volume of pores contained in the first negative electrode active material layer is 11% to 49% of the total volume of pores contained in the first and second negative electrode active material layers, and the content of the first silicon-based negative electrode active material contained in the first negative electrode active material layer is greater than the content of the second silicon-based negative electrode active material contained in the second negative electrode active material layer, the lithium-ion mobility is improved and the resistivity characteristics of the negative electrode are enhanced. Furthermore, even with repeated charge and discharge at high charging rates, the degradation of lifetime characteristics can be suppressed, thus exhibiting excellent fast charging characteristics.

[0063] The components of the negative electrode of the present invention will be described in detail below.

[0064] As the negative electrode current collector, any negative electrode current collector commonly used in the art can be used, such as copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys. The negative electrode current collector typically has a thickness from 3 μm to 500 μm, and similar to the positive electrode current collector, fine irregularities can be formed on its surface to improve the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in various shapes such as films, sheets, foils, meshes, porous bodies, foams, nonwoven fabrics, etc.

[0065] The first negative electrode active material layer includes a first negative electrode active material, which includes natural graphite and a first silicon-based negative electrode active material.

[0066] Generally, carbon-based negative electrode active materials have been used alone as negative electrode active materials. However, due to the low capacity of carbon-based negative electrode active materials and the slow reaction rate with lithium, lithium secondary batteries using such materials have limitations in achieving high capacity characteristics and fast charging performance. Therefore, in the present invention, since the silicon-based negative electrode active material with high theoretical capacity and fast reaction rate with lithium is included together with natural graphite in the first negative electrode active material layer, the capacity characteristics and fast charging characteristics of the lithium secondary battery using the negative electrode are improved.

[0067] Furthermore, since natural graphite has relatively higher structural flexibility and lower strength than artificial graphite, it can alleviate the volume expansion of the silicon-based negative electrode active material. Therefore, even if the first negative electrode active material layer contains a higher content of the silicon-based negative electrode active material than the second negative electrode active material layer, problems caused by the volume expansion of the silicon-based negative electrode active material can be suppressed. In addition, since natural graphite has a relatively high tap density, the volume of pores included in the first negative electrode active material layer can be set within a desired range, and the adhesion to the current collector can be improved.

[0068] Based on the total weight of the first negative electrode active material, the content of natural graphite may be 70 wt% to 95 wt%, 75 wt% to 92 wt%, or 80 wt% to 90 wt%. When the above range is satisfied, a balance can be achieved among capacity characteristics, fast charging characteristics and lifespan characteristics.

[0069] The first silicon-based negative electrode active material may be selected from silicon (Si), silicon oxide (may be expressed as SiO x (0 < x < 2)) and Si / C composites, and may preferably include a Si / C composite. Furthermore, the first silicon-based negative electrode active material may be a Si / C composite.

[0070] The Si / C composite may include silicon particles embedded in a carbon matrix, instead of being in a state where Si and carbon (C) are simply agglomerated or mixed. The carbon matrix may be a porous carbon matrix.

[0071] When the first silicon-based negative electrode active material includes a Si / C composite, since the degree of volume expansion during charging and discharging can be smaller than that of pure silicon, the deterioration of lifespan characteristics during charging and discharging can be suppressed, and since silicon and carbon exist in a mechanically bonded state, the capacity characteristics and conductivity can be superior to those of silicon oxide. Therefore, when the first silicon-based negative electrode active material includes a Si / C composite, it has the advantage of achieving the high capacity characteristic of a lithium secondary battery while improving the cycle performance during fast charging.

[0072] Si / C composites can contain silicon (Si) and carbon (C) in weight ratios of 2:8 to 8:2, 3:7 to 7:3, or 4:6 to 6:4. Meeting these ranges allows for improved conductivity of the anode active material while achieving high capacity.

[0073] The first silicon-based anode active material D 50 The diameter can be 5 μm to 15 μm, 6 μm to 11 μm, or 7 μm to 9 μm. When these ranges are met, high energy density can be achieved due to the increased negative electrode density.

[0074] The first negative electrode active material layer contains a greater amount of the first silicon-based negative electrode active material than the second negative electrode active material layer contains a greater amount of the second silicon-based negative electrode active material. In this case, the content of the first silicon-based negative electrode active material in the first negative electrode active material layer refers to the content of the first silicon-based negative electrode active material measured as a percentage of weight based on the total weight of the first negative electrode active material layer, and the content of the second silicon-based negative electrode active material in the second negative electrode active material layer refers to the content of the second silicon-based negative electrode active material measured as a percentage of weight based on the total weight of the second negative electrode active material layer.

[0075] When the content of the first silicon-based negative electrode active material in the first negative electrode active material layer is greater than the content of the second silicon-based negative electrode active material in the second negative electrode active material layer, this helps to appropriately control the ratio of the volume of pores in the first negative electrode active material layer to the volume of pores in the second negative electrode active material layer. Therefore, the electrolyte wettability of the second negative electrode active material layer can be improved, and the lithium-ion mobility can be improved. Furthermore, by including a relatively small amount of silicon-based negative electrode active material in the second negative electrode active material layer, which is in direct contact with the electrolyte, the increase in negative electrode resistance caused by repeated damage and reforming of the SEI (solid electrolyte interface) layer due to the volume expansion of the silicon-based negative electrode active material can be suppressed. As a result, excellent fast-charging characteristics can be achieved because lifetime characteristics can be improved during repeated charge-discharge cycles at high charging rates.

[0076] The ratio (X1 / X2) of the content of the first silicon-based anode active material in the first anode active material layer (X1) to the content of the second silicon-based anode active material in the second anode active material layer (X2) can be greater than 1 and less than or equal to 10. Specifically, X1 / X2 tThe pore size can be greater than 1, greater than 1.2, greater than 1.5, greater than 1.7, greater than 2.0, greater than 2.2, greater than 2.5, greater than 2.7, greater than 3.0, less than 10, less than 9, less than 8, less than 7, less than 6, less than 5, less than 5.5, less than 5, less than 4.5, less than 4, less than 3.7, less than 3.5, less than 3.2, or less than 3. For example, X1 / X2 can be in the range of greater than 1 and less than or equal to 10, 1.2 to 8, 1.5 to 6, 2 to 4, or 2.5 to 3.5. When the above ranges are met, the volume of pores contained in the first negative electrode active material layer and the second negative electrode active material layer can be appropriately controlled, and the effect of improving electrolyte wettability, lithium-ion mobility, and fast charging characteristics can be maximized.

[0077] The weight of the first silicon-based anode active material can be greater than the weight of the second silicon-based anode active material. That is, the weight of the silicon-based anode active material contained in the first anode active material layer can be greater than the weight contained in the second anode active material layer.

[0078] By enabling the first anode active material layer, which serves as the lower layer, to contain a larger amount of silicon-based anode active material, the increase in anode resistance caused by the repeated damage and reforming of the SEI (solid electrolyte interface) layer due to the volume expansion of the silicon-based anode active material can be suppressed, while simultaneously achieving sufficiently high capacity characteristics. Furthermore, it can promote the migration of lithium ions in the second anode active material layer. As a result, high energy density can be achieved while providing excellent fast charging characteristics.

[0079] Based on the total weight of the first negative electrode active material, the content of the first silicon-based negative electrode active material can be from 5% to 30% by weight. Specifically, based on the total weight of the first negative electrode active material, the content of the first silicon-based negative electrode active material can be 5% or more, 5.5% or more, 6% or more, 6.5% or more, 7% or more, 7.5% or more, 8% or more, 8.5% or more, 9% or more, 9.5% or more, 10% or more, 10.5% or more, 11% or more, 11.5% or more, 12% or more, 12.5% ​​or more, 1... The content of the first silicon-based anode active material can be in the range of 3% to 30% by weight or more, 13.5% to 14% by weight or more, 14.5% to 14.5% by weight or more, 15% to 15% by weight or more, less than 30% by weight, less than 29% by weight, less than 28% by weight, less than 27% by weight, less than 26% by weight, less than 25% by weight, less than 24% by weight, less than 23% by weight, less than 22% by weight, less than 21% by weight, less than 20% by weight, less than 19% by weight, less than 18% by weight, less than 17% by weight, less than 16% by weight, or less than 15% by weight, based on the total weight of the first anode active material. When the above ranges are met, a balance can be achieved between capacity characteristics, fast charging characteristics, and lifetime characteristics.

[0080] The first silicon-based anode active material and natural graphite can be contained in a weight ratio of 5:95 to 30:70, 8:92 to 25:75, 10:90 to 20:80, or 13:87 to 17:83. When these ranges are met, excellent capacity characteristics, fast charging characteristics, and lifespan characteristics can be achieved.

[0081] Based on the total weight of the first negative electrode active material layer, the content of the first negative electrode active material can be 80% to 99.9% by weight, 90% to 99.7% by weight, 93% to 99.5% by weight, or 95% to 99% by weight. When the content of the first negative electrode active material meets the above range, excellent energy density can be achieved.

[0082] The first negative electrode active material layer may also include a first negative electrode conductive agent and / or a first negative electrode binder.

[0083] The first negative electrode conductive agent is used to provide conductivity to the negative electrode. Any conductive agent can be used without particular limitation, as long as it has electronic conductivity and does not cause chemical changes in the battery. Specific examples of the first negative electrode conductive agent can be carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermally cracked carbon black, carbon fibers, and carbon nanotubes; powders or fibers of metals such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and any one or a mixture of two or more of these can be used.

[0084] Based on the total weight of the first negative electrode active material layer, the content of the first negative electrode conductive agent can be from 0.1 wt% to 10 wt%, from 0.1 wt% to 8 wt%, or from 0.1 wt% to 5 wt%.

[0085] The first negative electrode binder improves the adhesion between negative electrode active material particles and the adhesion between the negative electrode active material and the negative electrode current collector. Specific examples of the first negative electrode binder can be polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber and various copolymers thereof, and any one or a mixture of two or more of them can be used.

[0086] Based on the total weight of the first negative electrode active material layer, the content of the first negative electrode binder can be from 0.1% to 10% by weight, from 0.5% to 10% by weight, or from 1% to 8% by weight.

[0087] The volume of pores contained in the first negative electrode active material layer can be smaller than the volume of pores contained in the second negative electrode active material layer.

[0088] The volume of pores contained in the first negative electrode active material layer is 11% to 49% of the total volume of pores contained in the first negative electrode active material layer and the second negative electrode active material layer. Specifically, the volume of pores contained in the first negative electrode active material layer is 11% or more, 12% or more, 13% or more, 14% or more, 15% or more, 16% or more, 17% or more, 19% or more, 20% or more, 21% or more, 22% or more, 23% or more, 24% or more, 25% or more, 26% or more, 27% or more, 28% or more, 29% or more, 30% or more, less than 49% or less, less than 48% or less, less than 47% or less, less than 46% or less, less than 45% or less, less than 44% or less, less than 43% or less, less than 42% or less, less than 41% or less, less than 40% or less, less than 39% or less, less than 38% or less, less than 37% or less, less than 36% or less, less than 35% or less, less than 34% or less, less than 33% or less, less than 32% or less, less than 31% or less, of the total volume of pores contained in the first negative electrode active material layer and the second negative electrode active material layer. For example, the volume of pores contained in the first negative electrode active material layer is 11% to 49%, 20% to 49%, 22% to 40%, 25% to 35%, or 28% to 32% of the total volume of pores contained in the first negative electrode active material layer and the second negative electrode active material layer.

[0089] When the volume of pores in the first negative electrode active material layer is less than 11% of the total volume of pores in both the first and second negative electrode active material layers, insufficient pores may not form in the first negative electrode active material layer. This could reduce electrolyte wettability, leading to decreased lithium-ion conductivity, deteriorated capacity characteristics, and increased internal resistance. Furthermore, when the volume of pores in the first negative electrode active material layer exceeds 49% of the total volume of pores in both the first and second negative electrode active material layers, lithium-ion inflow into the second negative electrode active material layer in contact with the electrolyte may be difficult. Consequently, the negative electrode's capacity and efficiency may not be fully realized during charge and discharge, potentially resulting in reverse polarity when this negative electrode is used in a lithium-ion secondary battery, with the potential difference reversing that of the positive electrode. Additionally, the unfavorable structure hindering electrolyte penetration into the second negative electrode active material layer may reduce electrolyte wettability, potentially leading to poor fast-charging characteristics.

[0090] Under the aforementioned conditions, since the electrolyte can readily wet the second negative electrode active material layer in contact with the electrolyte, and lithium ion migration can be promoted by including a larger number of pores in the upper part of the two-layer negative electrode active material layer, lithium ions can be rapidly inserted into and extracted from the negative electrode active material during charging and discharging. Therefore, even under high charging and discharging rates, sufficient capacity can be maintained, and lifetime characteristics can be improved. Furthermore, by relatively reducing the pore distribution in the lower first negative electrode active material layer, adhesion to the current collector can be improved, and the contact area between the negative electrode active materials contained in the first negative electrode active material layer can be increased to reduce the negative electrode resistance. In addition, since the occurrence of binder migration in the upper second negative electrode active material layer can be suppressed, lithium ion mobility and adhesion to the negative electrode current collector can be improved, lifetime characteristics can be enhanced, and the SEI layer can be uniformly formed.

[0091] The volume of pores contained in the first negative electrode active material layer, as well as the total volume of pores contained in the first and second negative electrode active material layers as a whole, can be controlled by the porosity and thickness of the first and second negative electrode active material layers, the composition of the negative electrode active material, or the rolling conditions. That is, the volume of pores depends not only on the porosity of each negative electrode active material layer, but can also be controlled by organically adjusting various factors inside the negative electrode.

[0092] The porosity of the first negative electrode active material layer can be from 15% to 30%. Specifically, the porosity of the first negative electrode active material layer can be above 15%, above 15.5%, above 16%, above 16.5%, above 17%, above 17.5%, above 18%, above 18.5%, above 19%, above 19.5%, above 20%, above 20.5%, above 21%, above 21.5%, above 22%, below 30%, below 29%, below 28%, below 27%, below 26%, below 25.5%, below 25%, below 24.5%, below 24%, below 23.5%, below 23%, below 22.5%, or below 22%. For example, the porosity of the first negative electrode active material layer can be from 15% to 30%, from 18% to 28%, from 20% to 24%, or from 21% to 23%. Under the above conditions, smooth contact between negative electrode active materials can be ensured, and high energy density can be achieved.

[0093] The thickness of the first negative electrode active material layer can be 35% to 50% of the total thickness of the first and second negative electrode active material layers. Specifically, the thickness of the first negative electrode active material layer can be more than 35%, more than 36%, more than 37%, more than 38%, more than 39%, more than 40%, more than 41%, more than 42%, more than 43%, more than 44%, more than 45%, less than 50%, less than 49%, less than 48%, less than 47%, less than 46%, less than 45%, less than 44%, less than 43%, less than 42%, less than 41%, or less than 40% of the total thickness of the first and second negative electrode active material layers. For example, the thickness of the first negative electrode active material layer can be 35% to 50%, 37% to 48%, 39% to 46%, or 41% to 45% of the total thickness of the first and second negative electrode active material layers. If the above range is met, the volume of pores contained in the first negative electrode active material layer and the second negative electrode active material layer, as well as the porosity of each negative electrode active material layer, can be controlled within the required range. This is advantageous in terms of energy density and can improve fast charging characteristics.

[0094] The thickness of the first negative electrode active material layer can be in the range of 20 μm to 90 μm, 35 μm to 75 μm, or 45 μm to 65 μm. Within these ranges, pores can be appropriately formed in the first negative electrode active material layer while achieving high energy density.

[0095] The loading of the first negative electrode active material layer can be 50 mg / 25 cm⁻¹ 2 Up to 160 mg / 25 cm 2 65 mg / 25cm 2 Up to 145 mg / 25 cm 2 Or 85 mg / 25 cm 2 Up to 130 mg / 25 cm 2 Within the aforementioned range, the first negative electrode active material layer can exhibit sufficient capacity while possessing appropriately sized pores.

[0096] The second negative electrode active material layer contains a second negative electrode active material, which includes artificial graphite and a second silicon-based negative electrode active material.

[0097] Generally, carbon-based negative electrode active materials have been used alone as negative electrode active materials. However, due to the low capacity and slow reaction rate with lithium of carbon-based negative electrode active materials, lithium secondary batteries using such materials have limitations in achieving high capacity characteristics and fast charging performance. Therefore, in the present invention, since the silicon-based negative electrode active material with high theoretical capacity and fast reaction rate with lithium is included together with natural graphite in the first negative electrode active material layer, the capacity characteristics and fast charging characteristics of the lithium secondary battery using the negative electrode are improved.

[0098] In addition, artificial graphite has a lower tap density than natural graphite, and has lower structural flexibility and higher strength. Therefore, when artificial graphite is included in the second negative electrode active material layer, since pore clogging is not prone to occur during the rolling process of the negative electrode, it is favorable for forming a well-developed pore volume, thereby allowing the volume of pores included in the second negative electrode active material layer to be set within a desired range.

[0099] Based on the total weight of the second negative electrode active material, the content of artificial graphite may be 80 wt% to 99 wt%, 85 wt% to 98.5 wt%, or 90 wt% to 98 wt%. When the above range is satisfied, a balance among capacity characteristics, fast charging characteristics and lifespan characteristics can be achieved.

[0100] The second silicon-based negative electrode active material may comprise at least one selected from the group consisting of silicon (Si), silicon oxide (which can be expressed as SiO x (0<x<2)) and Si / C composites, and may preferably comprise a Si / C composite. In addition, the second silicon-based negative electrode active material may be a Si / C composite.

[0101] The Si / C composite may comprise silicon particles embedded in a carbon matrix, rather than being in a state of simple agglomeration or mixing of Si and carbon (C). The carbon matrix may be a porous carbon matrix.

[0102] In the case where the second silicon-based negative electrode active material comprises a Si / C composite, since the degree of volume expansion during charge and discharge can be smaller than that of silicon, deterioration of lifespan characteristics during charge and discharge can be suppressed, and the capacity characteristics and electrical conductivity can be superior to those of silicon oxide. Therefore, when the second silicon-based negative electrode active material comprises a Si / C composite, it has the advantage of achieving high capacity characteristics of a lithium secondary battery while improving cycle performance during fast charging.

[0103] D of the second silicon-based negative electrode active material 50 may be 5 μm to 15 μm, 6 μm to 11 μm, or 7 μm to 9 μm. When the above range is satisfied, high energy density can be achieved due to the increased negative electrode density.

[0104] Based on the total weight of the second anode active material, the content of the second silicon-based anode active material can be from 1% to 20% by weight. Specifically, based on the total weight of the second anode active material, the content of the second silicon-based anode active material can be 1% or more by weight, 1.3% or more by weight, 1.5% or more by weight, 1.8% or more by weight, 2% or more by weight, 2.3% or more by weight, 2.5% or more by weight, 2.8% or more by weight, 3% or more by weight, 3.3% or more by weight, 3.5% or more by weight, 3.8% or more by weight, 4% or more by weight, 4.3% or more by weight, 4.5% or more by weight, 4.8% or more by weight, 5% or more by weight, less than 20% by weight, less than 19% by weight, less than 18% by weight, less than 17% by weight, less than 16% by weight, less than 15% by weight, less than 14% by weight, less than 13% by weight, less than 12% by weight, less than 11% by weight, less than 10% by weight, less than 9% by weight, less than 8% by weight, less than 7% by weight, less than 6% by weight, or less than 5% by weight. For example, based on the total weight of the second anode active material, the content of the second silicon-based anode active material can be in the range of 1 wt% to 20 wt%, 1.5 wt% to 15 wt%, 2 wt% to 10 wt%, or 3 wt% to 7 wt%. By satisfying these ranges, sufficient porosity in the second anode active material layer is ensured to mitigate lifetime degradation caused by the volume expansion of the silicon-based anode active material, resulting in excellent conductivity and preventing lifetime degradation even during fast charging.

[0105] The second silicon-based anode active material and artificial graphite can be contained in a weight ratio of 1:99 to 20:80, 1.5:98.5 to 15:85, 2:98 to 10:90, or 3:97 to 7:93. When these ranges are met, excellent capacity characteristics, fast charging characteristics, and lifetime characteristics can be achieved.

[0106] Based on the total weight of the second negative electrode active material layer, the content of the second negative electrode active material can be from 80% to 99.9% by weight, preferably from 90% to 99.7% by weight, more preferably from 93% to 99.5% by weight, or from 95% to 99% by weight. When the content of the second negative electrode active material meets the above range, excellent energy density can be achieved.

[0107] The second negative electrode active material layer may also contain a second negative electrode conductive agent and / or a second negative electrode binder.

[0108] The second negative electrode conductive agent is used to provide conductivity to the negative electrode. Any conductive agent can be used without particular limitation, as long as it has electronic conductivity and does not cause chemical changes in the battery. Specific examples of the first negative electrode conductive agent can be carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermally cracked carbon black, carbon fibers, and carbon nanotubes; powders or fibers of metals such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and any one or a mixture of two or more of these can be used.

[0109] Based on the total weight of the second negative electrode active material layer, the content of the second negative electrode conductive agent can be from 0.1 wt% to 10 wt%, from 0.1 wt% to 8 wt%, or from 0.1 wt% to 5 wt%.

[0110] The second negative electrode binder improves the adhesion between negative electrode active material particles and the adhesion between the negative electrode active material and the negative electrode current collector. Specific examples of the first negative electrode binder can be polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber and various copolymers thereof, and any one or a mixture of two or more of them can be used.

[0111] Based on the total weight of the second negative electrode active material layer, the content of the second negative electrode binder can be from 0.1% to 10% by weight, 0.5% to 10% by weight, or 1% to 8% by weight.

[0112] The porosity of the second negative electrode active material layer can be between 20% and 35%. Specifically, the porosity of the second negative electrode active material layer can be above 20%, above 21%, above 22%, above 23%, above 24%, above 25%, above 25.5%, above 26%, above 26.5%, above 27%, above 27.5%, above 28%, above 28.5%, above 29%, above 29.5%, above 30%, above 30.5%, above 31%, above 31.5%, above 32%, below 35%, below 34.5%, below 34%, below 33.5%, below 33%, below 32.5%, below 32%, below 31.5%, below 31%, below 30.5%, below 30%, below 29.5%, below 29%, below 28.5%, or below 28%. For example, the porosity of the second negative electrode active material layer can be 20% to 35%, 22% to 33%, 24% to 31%, 26% to 30%, or 27% to 29%. When the above ranges are met, the second negative electrode active material layer has well-developed pores, which are sufficient to promote electrolyte wetting. Therefore, due to the promotion of lithium ion migration, lithium ions can be repeatedly and rapidly inserted into and extracted from the negative electrode active material, thereby improving fast charging characteristics.

[0113] The overall porosity of the first and second anode active material layers can be 20% to 30%, 23% to 27%, or 24% to 26%. Within these ranges, the overall density of the anode is appropriate, and it can exhibit sufficient capacity characteristics.

[0114] The thickness of the second negative electrode active material layer can be in the range of 40 μm to 110 μm, 55 μm to 95 μm, or 65 μm to 85 μm. Within these ranges, high energy density can be achieved while appropriately forming pores in the second negative electrode active material layer.

[0115] The loading of the second negative electrode active material layer can be 95 mg / 25 cm⁻¹ 2 Up to 205 mg / 25 cm 2 Within the range, preferably 110 mg / 25 cm 2 Up to 190 mg / 25 cm 2 More preferably 130 mg / 25 cm 2 Up to 175 mg / 25 cm 2 Under the aforementioned conditions, the second negative electrode active material layer can exhibit sufficient capacity while possessing appropriate porosity.

[0116] The negative electrode can be prepared by: coating a first negative electrode active material layer slurry onto one or both sides of a sheet-like negative electrode current collector; coating a second negative electrode active material layer slurry onto the first negative electrode active material layer slurry; removing the solvent from the first and second negative electrode active material layer slurries through a drying process; and then rolling. A negative electrode containing an uncoated portion can be prepared by: when coating the first and second negative electrode active material layer slurries, not coating a portion of the negative electrode current collector, such as one end of the negative electrode current collector.

[0117] The first negative electrode active material layer slurry and the second negative electrode active material layer slurry can be prepared by dispersing the first negative electrode active material or the second negative electrode active material in a solvent such as distilled water, ethanol, methanol or isopropanol.

[0118] In addition, the negative electrode can be prepared by casting the first negative electrode active material layer slurry and the second negative electrode active material layer slurry onto a separate support, and then stacking the membrane layer separated from the support onto the negative electrode current collector.

[0119] Lithium secondary batteries

[0120] The lithium secondary battery of the present invention comprises: an electrode assembly including the aforementioned negative electrode, a positive electrode and a separator disposed between the negative electrode and the positive electrode; an electrolyte; and a battery casing housing the electrode assembly and the electrolyte.

[0121] The lithium secondary battery of the present invention is not limited to pouch-type secondary batteries, cylindrical secondary batteries or prismatic secondary batteries, but may preferably be a cylindrical secondary battery.

[0122] The components of the lithium secondary battery of the present invention will be described in detail below.

[0123] (1) Electrode assembly

[0124] The electrode assembly includes the aforementioned negative electrode, positive electrode, and a diaphragm disposed between the negative electrode and the positive electrode.

[0125] Electrode assemblies can be formed by stacking a positive electrode, a separator, and a negative electrode in sequence, and the positive and negative electrodes can be insulated from each other by the separator.

[0126] Specifically, the electrode assembly can be formed by stacking a positive electrode, a separator, and a negative electrode in sequence and winding them in one direction.

[0127] Figure 1 The following is an illustration of the stacked structure of the electrode assembly before winding, according to one embodiment of the present invention. Figure 2 The cross-sectional structure of an electrode plate (positive or negative electrode) according to one embodiment of the present invention is shown. Figure 3 The structure of an electrode assembly according to one embodiment of the present invention is shown.

[0128] Reference Figure 1 and Figure 2 The electrode assembly A of the present invention can be prepared by winding a stack formed by sequentially stacking a diaphragm 12, a positive electrode 10, a diaphragm 12 and a negative electrode 11 at least once in one direction X.

[0129] In this case, the positive electrode 10 and the negative electrode 11 each have a structure in which an active material layer 21 is formed on the sheet current collector 20, and may include an uncoated portion 22 in a portion of the current collector 20 in which the active material layer 21 is not formed.

[0130] If the positive electrode 10 and negative electrode 11, which include the uncoated portion 22 as described above, are used, a battery with a structure that does not include separate electrode tabs and at least a portion of the uncoated portion of the positive electrode 10 and negative electrode 11 defines the electrode tabs can be realized.

[0131] Specifically, the uncoated portion 22 can be formed by extending along the winding direction X at one end of the current collector 20, and by connecting the current collector plate to the uncoated portion of the positive electrode and the uncoated portion of the negative electrode respectively and connecting the current collector plate to the electrode terminal, the uncoated portion can function as an electrode tab.

[0132] For example, a battery in which the uncoated portions of the positive and negative electrodes serve as electrode tabs can be fabricated using the following method. First, a separator, a positive electrode, another separator, and a negative electrode are stacked sequentially, with the uncoated portions of the positive and negative electrodes positioned in opposite directions. Then, the electrodes are wound in one direction to fabricate a wound-core electrode assembly. Next, after bending the uncoated portions of the positive and negative electrodes towards the winding center C, current collectors are welded and bonded to the uncoated portions of the positive and negative electrodes, respectively. The battery is then fabricated by connecting the current collectors to the electrode terminals. Since the cross-sectional area of ​​the current collector is larger than that of the strip-shaped electrode tabs, and the resistance is inversely proportional to the cross-sectional area of ​​the current-carrying channel, the cell resistance can be significantly reduced when a secondary battery is formed using the above structure.

[0133] The uncoated portions of the positive and negative electrodes can be processed into multiple independently bendable segmented pieces, and at least a portion of the multiple segmented pieces can be bent toward the winding center C of the electrode assembly.

[0134] Segmented sheets can be formed by processing the current collectors of the positive and negative electrodes using metal foil cutting processes such as laser grooving, ultrasonic cutting, and punching.

[0135] When the uncoated portions of the positive and negative electrodes are processed into multiple segmented pieces, deformation or damage to the uncoated portions can be prevented by reducing the stress applied to the uncoated portions during bending, and the welding characteristics with the current collector can be improved.

[0136] The current collector and the uncoated portion are typically joined by welding. To improve welding characteristics, strong pressure must be applied to the welded area of ​​the uncoated portion to bend it as flat as possible. However, during this bending process, the shape of the uncoated portion may irregularly twist and deform, and the deformed portion may come into contact with electrodes of opposite polarity, causing internal short circuits or microcracks in the uncoated portion. However, if the uncoated portions of the positive and negative electrodes are machined into multiple independently bendable segments, the stress applied to the uncoated portion during bending can be alleviated, thereby minimizing deformation and damage to the uncoated portion.

[0137] Furthermore, when the uncoated portion is processed into segmented pieces as described above, overlap occurs between multiple segments during bending. As a result, the weld strength of the current collector is increased, and the problem of laser beams penetrating into the electrode assembly to ablate the diaphragm or active material when using modern technologies such as laser welding is prevented. Preferably, at least a portion of the multiple bent segments can overlap at the upper and lower ends of the electrode assembly, and the current collector can be bonded to the overlapping segments.

[0138] like Figure 3 As shown, the electrode assembly of the present invention can be configured such that an insulating layer 24 is additionally formed on the positive electrode 10. Specifically, the insulating layer 24 can be configured to cover a portion of the positive electrode active material layer and a portion of the uncoated portion along a direction parallel to the winding direction of the electrode assembly.

[0139] For a tabless battery that uses the uncoated portion 22c of the positive electrode 10 and the uncoated portion 22a of the negative electrode 11 as electrode tabs, the electrode assembly is formed such that the positive electrode 10 protrudes above the separator 12 and the negative electrode 11 protrudes below the separator 12, and the protruding positive electrode 10 and / or negative electrode 11 are bent and then bonded to the current collector. When the positive electrode 10 or negative electrode 11 is bent as described above, the current collector of the positive electrode 10 or negative electrode 11 passes through the separator and is positioned close to the electrode of opposite polarity. As a result, there is a possibility of internal short circuit caused by electrical contact between the positive and negative electrodes. However, as... Figure 3 As shown, when an insulating layer 24 is formed that covers the positive electrode active material layer and a portion of the uncoated portion, short circuits in the battery can be prevented because electrical contact between the positive electrode 10 and the negative electrode 11 can be prevented through the insulating layer 24.

[0140] Preferably, the insulating layer 24 can be disposed on at least one side of the current collector of the positive electrode 10, and more preferably, it can be disposed on both sides of the positive electrode 10.

[0141] Furthermore, the insulating layer 24 can be formed in the region of the active material layer 21a of the positive electrode 10 that may face the negative electrode 11. For example, on the surface of the uncoated portion 22c of the positive electrode 10 facing the negative electrode 11 after bending, the insulating layer 24 can extend to the end of the uncoated portion 22c. However, for the surface opposite to the surface facing the negative electrode 11 after bending, it is advantageous that the insulating layer 24 is formed only on a portion of the uncoated portion 22c, for example, before the bending point of the uncoated portion 22c. The reason for this is that if the insulating layer 24 is formed over the entire region of the uncoated portion on the surface opposite to the negative electrode 11, it cannot make electrical contact with the current collector and therefore cannot function as an electrode tab.

[0142] Insulating layer 24 can be used, as long as it can adhere to the positive electrode while ensuring insulation performance, and its material or composition is not particularly limited. For example, the insulating layer can be an insulating coating or an insulating tape, and the insulating coating can contain organic adhesives and inorganic particles. In this case, the organic adhesive can be, for example, styrene-butadiene rubber (SBR), and the inorganic particles can be alumina, but are not limited thereto.

[0143] The components of the electrode assembly of the present invention will be described in more detail below. Since the negative electrode is the same as described above, its detailed description will be omitted.

[0144] 1) Positive electrode

[0145] The positive electrode may include a positive current collector and a positive active material layer, and the positive active material layer may include a positive active material.

[0146] As the positive electrode current collector, various positive electrode current collectors used in the art can be used. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc., can be used as the positive electrode current collector. The thickness of the positive electrode current collector can typically be from 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to improve the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various shapes such as membranes, sheets, foils, meshes, porous bodies, foams, nonwoven fabrics, etc.

[0147] The positive electrode active material layer can be disposed on the positive electrode current collector, and specifically, it can be disposed on one or both sides of the positive electrode current collector. The positive electrode active material layer can have a single-layer structure or a multi-layer structure with two or more layers.

[0148] The positive electrode active materials commonly used in this field can be used as the above-mentioned positive electrode active materials, and there is no particular limitation on their type. The positive electrode active material is a compound capable of reversibly inserting and de-intercalating lithium, wherein the positive electrode active material may specifically include a lithium transition metal composite oxide comprising lithium and at least one transition metal selected from the group consisting of nickel, cobalt, manganese and aluminum, preferably a lithium transition metal composite oxide comprising lithium and a transition metal containing nickel, cobalt and manganese.

[0149] Preferably, the positive electrode active material may comprise a lithium nickel oxide. The nickel content in the total metals excluding lithium in the lithium nickel oxide may be 80 mol% or more. Specifically, the nickel content in the total metals excluding lithium in the positive electrode active material may be 80 mol% or more, preferably 85 mol% or more, more preferably 90 mol% or more, more preferably 91 mol% or more, more preferably 92 mol% or more, and more preferably 93 mol% or more. Meeting the above ranges allows for better capacity characteristics.

[0150] Lithium-nickel oxides can contain nickel, cobalt, manganese, and aluminum. In this case, they can be stable at high potentials and, while exhibiting excellent capacity and output characteristics, can also possess excellent structural and thermal stability.

[0151] Specifically, lithium nickel oxides can be represented by the following formula 1.

[0152] [Formula 1]

[0153] Li 1+a1 [Ni x1 Co y1 Mn z1 Al w1 M 1 r1 O2

[0154] In Equation 1, M 1 This can correspond to dopants that partially replace transition metal elements in lithium nickel oxides, and can improve structural stability by suppressing nickel ion migration, thus preventing the valence state of nickel (Ni) from 2+ to 4+ and the problem of cation mixing. Specifically, M 1may be at least one doping element selected from the group consisting of tungsten (W), copper (Cu), iron (Fe), vanadium (V), chromium (Cr), titanium (Ti), zirconium (Zr), zinc (Zn), indium (In), tantalum (Ta), yttrium (Y), lanthanum (La), strontium (Sr), gallium (Ga), scandium (Sc), gadolinium (Gd), samarium (Sm), calcium (Ca), cerium (Ce), niobium (Nb), magnesium (Mg), boron (B) and molybdenum (Mo), and may preferably be at least one doping element selected from the group consisting of W, Y, barium (Ba), Ca, Ti, Mg, Ta and Nb.

[0155] 1+a1 may refer to the molar ratio of lithium (Li) in the lithium-nickel-based oxide, wherein a1 may satisfy 0≤a1≤0.5, 0≤a1≤0.2, 0≤a1≤0.1 or 0≤a1≤0.05. When the above range is satisfied, the positive electrode active material can form a stable layered crystal structure.

[0156] x1 may refer to the molar ratio of nickel in the total metals other than lithium in the lithium-nickel-based oxide particles, wherein x1 may satisfy 0.8≤x1<1, 0.85≤x1<1, 0.9≤x1<1, 0.92≤x1<1 or 0.93≤x1<1. When the above range is satisfied, a higher capacity can be achieved because a sufficient amount of nickel (Ni) that contributes to charging and discharging is ensured in the lithium-nickel-based oxide.

[0157] y1 may refer to the molar ratio of cobalt in the total metals other than lithium in the lithium-nickel-based oxide particles, wherein y1 may satisfy 0<y1<0.20, 0<y1≤0.10 or 0<y1≤0.08. When the above range is satisfied, good resistance characteristics and output characteristics can be achieved while obtaining cost advantages by reducing the content of cobalt (Co), and the structural stability of the positive electrode active material can be improved by relatively increasing the proportion of manganese (Mn).

[0158] z1 may refer to the molar ratio of Mn in the total metals other than lithium in the lithium-nickel-based oxide particles, wherein z1 may satisfy 0<z1<0.20, 0<z1≤0.15, 0.001≤z1≤0.10 or 0.01≤z1≤0.08. When the above range is satisfied, the structural stability of the positive electrode active material can be improved.

[0159] w1 represents the molar ratio of aluminum (Al) in the total metals other than lithium in the lithium-nickel-based oxide, wherein w1 may satisfy 0<w1≤0.2, 0<w1≤0.10 or 0.01≤w1≤0.08. When the above range is satisfied, the structural stability and thermal stability of the positive electrode active material can be further improved.

[0160] r1 represents the molar ratio of element M in the total metals other than lithium in the lithium-nickel-based oxide1 The molar ratio, where r1 can satisfy 0 ≤ r1 ≤ 0.1, specifically 0 ≤ r1 ≤ 0.07, and more specifically 0 ≤ r1 ≤ 0.05. When the above range is satisfied, it can promote particle growth during the sintering process of the positive electrode active material, or improve the stability of the crystal structure.

[0161] There are no particular limitations on the form of lithium nickel oxides, and they can be in the form of secondary particles composed of more than 50 primary particles, or in the form of single particles containing fewer than 50 nodules. If necessary, a mixture of positive electrode active materials containing secondary particle lithium nickel oxides and positive electrode active materials containing single particle lithium nickel oxides can be used. Positive electrode active materials containing secondary particle lithium nickel oxides exhibit excellent resistance and capacity characteristics, while positive electrode active materials containing single particle lithium nickel oxides exhibit excellent high-temperature / high-voltage stability and lifetime characteristics. Therefore, the appropriate form of lithium nickel oxide can be selected and used considering the performance and specifications of the lithium secondary battery to be prepared.

[0162] According to one embodiment, lithium nickel oxides can be lithium nickel oxides in the form of single particles containing fewer than 50 nodules.

[0163] For single-particle lithium nickel oxides, less particle breakage due to rolling during cathode preparation compared to secondary-particle lithium nickel oxides, and superior structural stability under high temperature and / or high voltage conditions, the use of single-particle lithium nickel oxides reduces cathode degradation under high temperature / high voltage conditions and suppresses the generation of fine particles after cathode preparation. Consequently, less gas generation occurs due to side reactions between fine particles and the electrolyte. Therefore, using single-particle lithium nickel oxides is advantageous for preparing lithium secondary batteries with long lifespan characteristics.

[0164] The single-particle form of lithium nickel oxide can contain fewer than 50 nodules, preferably fewer than 30 nodules, more preferably 1 to 25 nodules, and even more preferably 1 to 15 nodules. This is because if the single-particle form of lithium nickel oxide contains too many nodules, particle breakage during electrode fabrication may increase, and the formation of internal cracks due to the volume expansion / contraction of nodules during charge / discharge may increase, thus potentially resulting in poor high-temperature lifetime and high-temperature storage characteristics.

[0165] Considering that the positive electrode active material exhibits sufficient capacity, the content of the positive electrode active material can be from 80% to 99% by weight, preferably from 92% to 98.5% by weight, based on the total weight of the positive electrode active material layer.

[0166] The positive electrode active material layer may optionally further comprise at least one of a positive electrode conductive agent and a positive electrode binder.

[0167] A positive electrode conductive agent is used to provide conductivity to the electrode. Any conductive agent can be used without particular limitation, as long as it has electronic conductivity and does not cause chemical changes in the battery. Specific examples of positive electrode conductive agents can be graphite, such as natural or artificial graphite; carbon materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermally cracked carbon black, carbon fibers, and carbon nanotubes; powders or fibers of metals such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and any one or a mixture of two or more of these can be used. Based on the total weight of the positive electrode active material layer, the content of the positive electrode conductive agent is typically from 1% to 30% by weight, preferably from 1% to 20% by weight, and more preferably from 1% to 10% by weight.

[0168] The positive electrode binder improves the adhesion between positive electrode material particles and the adhesion between the positive electrode material and the positive electrode current collector. Specific examples of the positive electrode binder can be fluoropolymer binders, including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber binders, including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, or styrene-isoprene rubber; cellulose binders, including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; polyol binders, including polyvinyl alcohol; polyolefin binders, including polyethylene or polypropylene; polyimide binders; polyester binders; and silane binders, and any one or a mixture of two or more of these can be used. Based on the total weight of the positive electrode active material layer, the content of the positive electrode binder can be from 1% to 30% by weight, preferably from 1% to 20% by weight, and more preferably from 1% to 10% by weight.

[0169] The positive electrode can be prepared by coating a positive electrode slurry onto one or both sides of a sheet-like positive electrode current collector, removing the solvent from the positive electrode slurry through a drying process, and then rolling it. A positive electrode containing an uncoated portion can be prepared by not coating a portion of the positive electrode current collector, such as one end of the current collector, with the positive electrode slurry not applied during coating.

[0170] Furthermore, the positive electrode slurry can be prepared by dispersing the positive electrode material of the present invention in a solvent such as dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone or water.

[0171] 2) Diaphragm

[0172] The diaphragm is positioned between the positive and negative electrodes.

[0173] The separator separates the negative and positive electrodes and provides a migration path for lithium ions. Any separator can be used without particular limitation, as long as it is commonly used in lithium-ion secondary batteries. Specifically, porous polymer membranes can be used as separators, such as porous polymer membranes prepared from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers. Alternatively, porous polymer membranes having a laminated structure with two or more layers can be used as separators. Furthermore, conventional porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers or polyethylene terephthalate fibers. Additionally, coated separators containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength.

[0174] (2) Electrolytes

[0175] The electrolyte of the present invention may contain lithium salt and organic solvent.

[0176] Lithium salts can be used without particular limitations, as long as they are compounds capable of providing lithium ions for use in lithium secondary batteries. Specifically, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiFSI, or LiB(C2O4)2 can be used as lithium salts. The concentration of the lithium salt is preferably in the range of 0.1M to 5.0M, more preferably 0.1M to 3.0M. Since the electrolyte can have suitable conductivity and viscosity when the concentration of the lithium salt is within the above range, excellent electrolyte performance can be obtained, and lithium ions can migrate efficiently.

[0177] Organic solvents may include at least one of cyclic carbonate organic solvents, linear carbonate organic solvents, linear ester organic solvents, and cyclic ester organic solvents.

[0178] Cyclic carbonate organic solvents are high-viscosity organic solvents. Cyclic carbonate organic solvents typically include at least one organic solvent selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butyl carbonate, 2,3-butyl carbonate, 1,2-pentane carbonate, 2,3-pentane carbonate and vinylene carbonate.

[0179] In addition, linear carbonate organic solvents are organic solvents with low viscosity and low dielectric constant. Typical examples of linear carbonate organic solvents may be at least one organic solvent selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate and ethyl propyl carbonate, and linear carbonate organic solvents may specifically include ethyl methyl carbonate (EMC).

[0180] Specific examples of linear ester organic solvents may be at least one organic solvent selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate and butyl propionate.

[0181] Cyclic ester organic solvents may include at least one organic solvent selected from the group consisting of butyrolactone, valproic acid and caprolactone.

[0182] Preferably, the electrolyte of the present invention may contain ethylene carbonate and dimethyl carbonate as organic solvents.

[0183] In order to improve battery life characteristics, suppress battery capacity reduction and improve battery discharge capacity, in addition to electrolyte components, the electrolyte may also contain other additives.

[0184] Typical examples of these other additives may include at least one other additive selected from the group consisting of cyclic carbonates, halogen-substituted carbonates, sulfonyl lactones, sulfates / salts, borates / salts, nitriles, benzenes, amines, silanes, and lithium salts that are different from the lithium salts contained in the electrolyte.

[0185] Specifically, other additives may include one or more compounds selected from the group consisting of: vinylene carbonate (VC), vinyl ethylene carbonate, fluoroethylene carbonate (FEC), 1,3-propane sulpholactone (PS), 1,4-butane sulpholactone, ethane sulpholactone, 1,3-propene sulpholactone (PRS), 1,4-butene sulpholactone, 1-methyl-1,3-propene sulpholactone, ethylene sulfate (Esa), trimethylene sulfate (TMS), methyltrimethylene sulfate (MTMS), tetraphenylborate, lithium difluorooxalate borate, and succinic anhydride. Adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, octanoic acid, heptanonitrile, cyclopentanonitrile, cyclohexanoic acid, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, fluorobenzene, triethanolamine, ethylenediamine, tetravinylsilane, LiN(SO2F)2 (lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF3)2 (lithium bis(trifluoromethanesulfonyl)imide, LiTFSI), LiPO2F2, LiODFB, LiBOB (lithium bis(oxalate)borate, LiB(C2O4)2) and LiBF4.

[0186] Based on the total weight of the electrolyte, the content of other additives can be from 0.01 wt% to 20 wt%, and preferably from 0.05 wt% to 5.0 wt%. If the content of other additives is less than 0.01 wt%, the effect of improving the battery's low-temperature output, high-temperature storage characteristics, and high-temperature lifespan characteristics is not significant, and if the content of other additives is greater than 20 wt%, excessive side reactions may occur in the electrolyte during battery charging and discharging. In particular, when an excessive amount of additives for SEI layer formation is added, since other additives may not decompose sufficiently at high temperatures, they may exist in the electrolyte as unreacted substances or precipitates at room temperature. Therefore, side reactions that degrade the lifespan or resistance characteristics of the secondary battery may occur.

[0187] (3) Battery casing

[0188] The battery casing can be a can-type battery casing or a pouch-type battery casing as used in this field.

[0189] Specifically, the battery casing can be a can-shaped battery casing. The can-shaped battery casing can be a prismatic battery casing or a cylindrical battery casing. More specifically, the battery casing can be a cylindrical battery casing. However, the invention is not limited to this, and the lithium secondary battery of the present invention can use various battery casings as appropriate.

[0190] Specifically, the lithium secondary battery of the present invention can be a cylindrical lithium secondary battery in which the ratio of the diameter (R) to the height (h) of the lithium secondary battery is 0.4 or more, 0.4 to 0.8, or 0.5 to 0.8. When the ratio meets the above range, high capacity characteristics can be achieved. In the following, the ratio of the diameter (R) to the height (h) of the lithium secondary battery is referred to as the shape factor.

[0191] For example, the lithium secondary battery of the present invention can be a 46110 cell (diameter 46 mm, height 110 mm, shape factor ratio 0.418), a 4875 cell (diameter 48 mm, height 75 mm, shape factor ratio 0.640), a 48110 cell (diameter 48 mm, height 110 mm, shape factor ratio 0.436), a 4880 cell (diameter 48 mm, height 80 mm, shape factor ratio 0.600), or a 4680 cell (diameter 46 mm, height 80 mm, shape factor ratio 0.575). In the shape factor, the first two digits represent the diameter of the lithium secondary battery, and the following two or three digits represent the height of the lithium secondary battery.

[0192] Next, one embodiment of the lithium secondary battery of the present invention will be described.

[0193] Figure 4 and Figure 5 Examples of the lithium secondary battery of the present invention have been disclosed. In the following, reference will be made to... Figure 4 and Figure 5 The lithium secondary battery of the present invention is described. However, Figure 4 and Figure 5 Only one embodiment of the present invention has been shown, and the structure of the battery of the present invention is not limited to this. Figure 4 and Figure 5 The scope of public disclosure.

[0194] Figure 4 A cross-sectional view of a lithium secondary battery according to one embodiment of the present invention is shown.

[0195] Reference Figure 4 The lithium secondary battery 140 of the present invention includes an electrode assembly 141, a battery can 142 containing the electrode assembly 141 and an electrolyte (not shown), and a sealing body 143 sealing the open end of the battery can 142.

[0196] In this case, the electrode assembly is formed by sequentially stacking a positive electrode, a separator, and a negative electrode and winding them in one direction. Furthermore, both the positive and negative electrodes of the electrode assembly include uncoated portions without an active material layer, and they can be stacked and wound such that the uncoated portions of the positive and negative electrodes are respectively located at the upper and lower ends of the electrode assembly. Since the electrode assembly has already been described above, only components other than the electrode assembly will be described below.

[0197] The battery can 142 is a can-shaped container with an open top end, which is formed of a conductive metal material such as aluminum or steel. The battery can houses the electrode assembly 141 in the internal space through the open top end, and also houses the electrolyte (not shown).

[0198] Advantageously, the lithium secondary battery 140 of the present invention does not include a current interruption device (CID).

[0199] like Figure 4 As shown, the battery canister 142 is electrically connected to the uncoated portion 146b of the negative electrode and can be used as a contact point with an external power source to transfer current applied from the external power source to the negative terminal of the negative electrode.

[0200] If necessary, a rolled edge 147 and a crimped portion 148 may be included at the upper end of the battery can 142. The rolled edge 147 can be formed by pressing the outer peripheral surface of the battery can 142 by a distance D1. The rolled edge 147 prevents the electrode assembly 141 housed inside the battery can 142 from escaping from the upper opening of the battery can 142, and can also serve as a support for the sealing body 143 to be stably placed thereon.

[0201] The crimping portion 148 may be formed on the upper part of the rolled edge portion 147 and has an extended and curved shape to surround the outer peripheral surface of the cover plate 143a provided on the rolled edge portion 147 and a portion of the upper surface of the cover plate 143a.

[0202] Next, the sealing body 143 is used to seal the open end of the battery can 142, wherein it includes a cover plate 143a and a first gasket 143b that provides airtightness and has insulating properties between the cover plate 143a and the battery can 142, and may also include a connecting plate 143c that is electrically and mechanically connected to the cover plate 143a if necessary. The cover plate 143a can be pressed onto the rolled edge 147 formed in the battery can 142 and can be fixed by the crimping part 148.

[0203] The cover 143a is a component formed of a conductive metal material, which covers the upper opening of the battery can 142. The cover 143a is electrically connected to the positive electrode of the electrode assembly 141 and electrically insulated from the battery can 142 by a first gasket 143b. Therefore, the cover 143a can function as the positive terminal of a lithium secondary battery. The cover 143a may include a protrusion 143d projecting upward from the center C, and the protrusion 143d can contact an external power source to allow current to be applied from an external power source.

[0204] The first gasket 143b can be disposed between the cover plate 143a and the crimping part 148 to ensure the airtightness of the battery can 142 and to electrically insulate the battery can 142 and the cover plate 143a.

[0205] If necessary, the lithium secondary battery 140 of the present invention may also include current collectors 144 and 145. The current collectors are respectively coupled to the uncoated portion 146a of the positive electrode and the uncoated portion 146b of the negative electrode, and are connected to the electrode terminals (i.e., the positive terminal and the negative terminal).

[0206] Specifically, the lithium secondary battery 140 of the present invention may include a first current collector 144 attached to the upper part of the electrode assembly 141 and a second current collector 145 attached to the lower part of the electrode assembly 141.

[0207] It may also include a first collector plate 144 and / or a second collector plate 145.

[0208] A first current collector 144 is attached to the upper part of the electrode assembly 141. The first current collector 144 is formed of a conductive metal material such as aluminum, copper, and nickel, and is electrically connected to the uncoated portion 146a of the positive electrode. A lead 149 can be connected to the first current collector 144. The lead 149 can extend upward from the electrode assembly 141 and can be attached to a connecting plate 143c or directly to the lower surface of the cover plate 143a. The lead 149 and other components can be joined by welding. Preferably, the first current collector 144 can be integrally formed with the lead 149. In this case, the lead 149 can have a plate-like shape extending outward from the center of the first current collector 144.

[0209] The first current collector 144 is bonded to the end of the uncoated portion 146a of the positive electrode, and the bonding can be performed, for example, by methods such as laser welding, resistance welding, ultrasonic welding and brazing.

[0210] The second current collector 145 is attached to the lower part of the electrode assembly 141. The second current collector 145 is formed of a conductive metal material such as aluminum, copper, or nickel, and is electrically connected to the uncoated portion 146b of the negative electrode. One surface of the second current collector 145 can be attached to the uncoated portion 146b of the negative electrode, and the opposite surface can be attached to the inner bottom surface of the battery canister 142. In this case, the attachment can be performed by methods such as laser welding, resistance welding, ultrasonic welding, and brazing.

[0211] If necessary, the lithium secondary battery 140 of the present invention may also include an insulator 146. The insulator 146 may be configured to cover the upper surface of the first current collector 144. Since the insulator 146 covers the first current collector 144, direct contact between the first current collector 144 and the inner peripheral surface of the battery canister 142 can be prevented.

[0212] The insulator 146 includes a lead hole 151 so that a lead 149 extending upward from the first current collector 144 can be led out. The lead 149 is led out upward through the lead hole 151 and is attached to the lower surface of the connecting plate 143c or the lower surface of the cover plate 143a.

[0213] Insulator 146 may be formed from insulating polymer resins, such as polyethylene, polypropylene, polyimide, or polybutylene terephthalate.

[0214] If necessary, the lithium secondary battery 140 of the present invention may further include a vent 152 formed on the lower surface of the battery can 142. The vent 152 corresponds to a region on the lower surface of the battery can 142 that is thinner than the surrounding region. Because the vent 152 is thinner, it is structurally weaker than the surrounding region. Therefore, if the pressure inside the lithium secondary battery 140 increases to a certain level, the vent 152 ruptures, and the gas inside the battery can be released to the outside to prevent the battery from exploding.

[0215] Figure 5 A cross-sectional view of a lithium secondary battery according to another embodiment of the present invention is shown.

[0216] Reference Figure 5 ,and Figure 4 Compared to the lithium secondary battery 140 shown, the lithium secondary battery 170 of another embodiment of the present invention has a different battery case and sealing structure, and the configuration of the electrode assembly and electrolyte is basically the same.

[0217] Specifically, in another embodiment of the present invention, a lithium secondary battery 170 includes a battery canister 171, through which a rivet terminal 172 is mounted. The rivet terminal 172 is mounted on a partially closed surface (the upper surface in the figure) at one end of the battery canister 171. The rivet terminal 172 is riveted to a through-hole (the first opening at the first end) of the battery canister 171 with an insulating second gasket 173 disposed therebetween. The rivet terminal 172 is exposed to the outside in a direction opposite to the direction of gravity.

[0218] The rivet terminal 172 includes a terminal exposure portion 172a and a terminal insertion portion 172b. The terminal exposure portion 172a is exposed to the outside of the closed surface of the battery can 171. The terminal exposure portion 172a may be located approximately at the center of a portion of the closed surface of the battery can 171. The maximum diameter of the terminal exposure portion 172a may be larger than the maximum diameter of the through hole formed in the battery can 171. The terminal insertion portion 172b may be electrically connected to the uncoated portion 146a of the positive electrode through approximately the center of the closed surface of the battery can 171. The terminal insertion portion 172b may be riveted to the inner surface of the battery can 171. That is, the end of the terminal insertion portion 172b may have a shape that bends toward the inner surface of the battery can 171. The maximum diameter of the end of the terminal insertion portion 172b may be larger than the maximum diameter of the through hole of the battery can 171.

[0219] The lower end face of the terminal insertion portion 172b can be welded to the first current collector 144, which is connected to the uncoated portion 146a of the positive electrode. An insulating cap 174, formed of insulating material, can be disposed between the first current collector 144 and the inner surface of the battery canister 171. The insulating cap 174 covers the upper part of the first current collector 144 and the upper edge of the electrode assembly 141. Therefore, it can prevent the uncoated portion B3 of the outer periphery of the electrode assembly 141 from contacting the inner surface of the battery canister 171, which has a different polarity, and thus preventing a short circuit. The terminal insertion portion 172b of the rivet terminal 172 can pass through the insulating cap 174 to be welded to the first current collector 144.

[0220] A second gasket 173 is disposed between the battery can 171 and the rivet terminal 172 to prevent electrical contact between the battery can 171 and the rivet terminal 172, which have opposite polarities. Therefore, the upper surface of the battery can 171, which has a substantially flat shape, can be used as the negative terminal of the lithium secondary battery 170.

[0221] The second gasket 173 includes a gasket exposure portion 173a and a gasket insertion portion 173b. The gasket exposure portion 173a is disposed between the terminal exposure portion 172a of the rivet terminal 172 and the battery canister 171. The gasket insertion portion 173b is disposed between the terminal insertion portion 172b of the rivet terminal 172 and the battery canister 171. The gasket insertion portion 173b can be tightly attached to the inner surface of the battery canister 171 by deforming together with the terminal insertion portion 172b during the riveting process. For example, the second gasket 173 can be formed of a polymer resin with insulating properties.

[0222] The gasket exposure portion 173a of the second gasket 173 may have an extended shape to cover the outer peripheral surface of the terminal exposure portion 172a of the rivet terminal 172. With the second gasket 173 covering the outer peripheral surface of the rivet terminal 172, short circuits can be prevented during the process of attaching electrical connection components such as busbars to the upper surface of the battery canister 171 and / or the rivet terminal 172. Although not shown in the figures, the gasket exposure portion 173a may have an extended shape to cover not only the outer peripheral surface of the terminal exposure portion 172a, but also a portion of its upper surface.

[0223] When the second gasket 173 is formed of polymer resin, it can be thermally bonded to the battery canister 171 and the rivet terminal 172. This enhances the airtightness of the bonding interface between the second gasket 173 and the rivet terminal 172, as well as the bonding interface between the second gasket 173 and the battery canister 171. When the gasket exposure portion 173a of the second gasket 173 has a shape extending to the upper surface of the terminal exposure portion 172a, the rivet terminal 172 can be integrally bonded to the second gasket 173 via insert injection molding.

[0224] The area 175 on the upper surface of the battery can 171, excluding the area occupied by the rivet terminal 172 and the second gasket 173, corresponds to the negative terminal having the opposite polarity to the rivet terminal 172.

[0225] The second current collector 176 is attached to the lower part of the electrode assembly 141. The second current collector 176 is formed of a conductive metal material such as aluminum, steel, copper and nickel, and is electrically connected to the uncoated portion 146b of the negative electrode.

[0226] Preferably, the second current collector 176 is electrically connected to the battery canister 171. For this purpose, at least a portion of the edge of the second current collector 176 can be fixed by being disposed between the inner surface of the battery canister 171 and the first gasket 178b. In one example, at least a portion of the edge of the second current collector 176 can be fixed to the rolled edge 180 by welding while being supported on the lower end face of the rolled edge 180 formed at the lower end of the battery canister 171. In a modified example, at least a portion of the edge of the second current collector 176 can be directly welded to the inner wall surface of the battery canister 171.

[0227] The second manifold 176 may have a plurality of radially formed irregularities (not shown) on the surface facing the uncoated portion 146b. When irregularities are formed, the second manifold 176 may be pressed to press the irregularities into the uncoated portion 146b.

[0228] Preferably, the ends of the second manifold 176 and the uncoated portion 146b can be joined by welding (e.g., laser welding).

[0229] The sealing body 178 at the lower open end of the sealed battery can 171 includes a cover plate 178a and a first gasket 178b. The first gasket 178b electrically separates the cover plate 178a and the battery can 171. A crimping portion 181 secures the edge of the cover plate 178a and the first gasket 178b together. The cover plate 178a includes a venting portion 179. The structure of the venting portion 179 is substantially the same as that of the embodiment described above.

[0230] Preferably, the cover plate 178a is formed of a conductive metal material. However, since the first gasket 178b is disposed between the cover plate 178a and the battery canister 171, the cover plate 178a has no electrode polarity. The seal 178 serves to seal the lower opening of the battery canister 171 and to release gas when the internal pressure of the battery cell 170 increases above a critical value.

[0231] Preferably, the rivet terminal 172, electrically connected to the uncoated portion 146a of the positive electrode, serves as the positive terminal. Furthermore, the portion 175 of the upper surface of the battery canister 171, excluding the rivet terminal 172, is electrically connected to the uncoated portion 146b of the negative electrode via a second current collector 176, serving as the negative terminal. As described above, with both electrode terminals located at the top of the lithium secondary battery, electrical connection components such as busbars can be arranged only on one side of the lithium secondary battery 170. This simplifies the battery pack structure and increases energy density. Furthermore, since the portion 175 serving as the negative terminal has a substantially flat shape, sufficient contact area can be ensured for connecting electrical connection components such as busbars. Therefore, the lithium secondary battery 170 can reduce the resistance at the contact points of the electrical connection components to the desired level.

[0232] When a lithium secondary battery is formed into a tabless structure as described above, the battery with a tabless structure has less current concentration than a conventional battery with electrode tabs. Therefore, it can effectively reduce the heat generated in the battery, thereby improving the thermal stability of the battery.

[0233] Next, a battery pack incorporating the lithium secondary battery of the present invention as a single cell will be described.

[0234] The lithium secondary battery of the present invention, as described above, can be used as a single cell to prepare a battery pack. Figure 6 The structure of a battery pack according to one embodiment of the present invention is illustrated schematically. (Refer to...) Figure 6 In one embodiment of the present invention, the battery pack 3 includes an assembly electrically connected to a lithium secondary battery 1 and a battery pack shell 2 housing the assembly. The lithium secondary battery 1 is the lithium secondary battery of the above embodiment. In the figures, for ease of explanation, components such as busbars, cooling units, and external terminals for electrically connecting the lithium secondary battery 1 are omitted.

[0235] Battery pack 3 can be installed in a vehicle. The vehicle can be, for example, an electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. The vehicle can be a four-wheeled vehicle or a two-wheeled vehicle.

[0236] The invention will be described in more detail below with reference to specific embodiments.

[0237] Examples and Comparative Examples

[0238] Example 1

[0239] A first negative electrode active material slurry was prepared by mixing a first negative electrode active material, a negative electrode conductive agent, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water at a weight ratio of 98.15:0.05:0.9:0.9. In this case, a mixture of Si / C composite and natural graphite at a weight ratio of 15:85 was used as the first negative electrode active material, and single-walled carbon nanotubes were used as the negative electrode conductive agent.

[0240] Next, a slurry of the second negative electrode active material, negative electrode conductive agent, styrene-butadiene rubber (SBR), and carboxymethyl cellulose was prepared by mixing them in water at a weight ratio of 98.1:0.1:0.9:0.9. In this case, a mixture of Si / C composite and artificial graphite at a weight ratio of 5:95 was used as the second negative electrode active material, and single-walled carbon nanotubes were used as the negative electrode conductive agent.

[0241] The first negative electrode active material layer slurry prepared above was coated onto a copper current collector and dried at 80°C to form the first negative electrode active material layer. Then, the second negative electrode active material layer slurry prepared above was coated onto the formed first negative electrode active material layer, dried at 80°C, and then rolled to prepare the negative electrode. In this negative electrode, the thickness of the first negative electrode active material layer is 60 µm and the porosity is 22%, while the thickness of the second negative electrode active material layer is 70 µm and the porosity is 28%. In this case, the ratio of the volume of pores contained in the first negative electrode active material layer to the volume of pores contained in the second negative electrode active material layer was measured to be 30:70.

[0242] Example 2

[0243] A first negative electrode active material slurry was prepared by mixing a first negative electrode active material, a negative electrode conductive agent, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water at a weight ratio of 98.15:0.05:0.9:0.9. In this case, a mixture of Si / C composite and natural graphite at a weight ratio of 15:85 was used as the first negative electrode active material, and single-walled carbon nanotubes were used as the negative electrode conductive agent.

[0244] Next, a slurry of the second negative electrode active material, negative electrode conductive agent, styrene-butadiene rubber (SBR), and carboxymethyl cellulose was prepared by mixing them in water at a weight ratio of 98.1:0.1:0.9:0.9. In this case, a mixture of Si / C composite and artificial graphite at a weight ratio of 5:95 was used as the second negative electrode active material, and single-walled carbon nanotubes were used as the negative electrode conductive agent.

[0245] The first negative electrode active material layer slurry prepared above was coated onto a copper current collector, and the second negative electrode active material layer slurry prepared above was coated onto the first negative electrode active material layer slurry. The mixture was dried at 80°C and then rolled to prepare the negative electrode. In this negative electrode, the thickness of the first negative electrode active material layer was 64 µm and the porosity was 26%, while the thickness of the second negative electrode active material layer was 66 µm and the porosity was 24%. In this case, the ratio of the volume of pores contained in the first negative electrode active material layer to the volume of pores contained in the second negative electrode active material layer was measured to be 24:76.

[0246] Comparative Example 1

[0247] A first negative electrode active material slurry was prepared by mixing a first negative electrode active material, a negative electrode conductive agent, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water at a weight ratio of 98.125:0.075:0.9:0.9. In this case, a mixture of Si / C composite and natural graphite at a weight ratio of 10:90 was used as the first negative electrode active material, and single-walled carbon nanotubes were used as the negative electrode conductive agent.

[0248] Next, a slurry of the second negative electrode active material, negative electrode conductive agent, styrene-butadiene rubber (SBR), and carboxymethyl cellulose was prepared by mixing them in water at a weight ratio of 98.125:0.075:0.9:0.9. In this case, a mixture of Si / C composite and artificial graphite at a weight ratio of 10:90 was used as the second negative electrode active material, and single-walled carbon nanotubes were used as the negative electrode conductive agent.

[0249] The first negative electrode active material layer slurry prepared above was coated onto a copper current collector, and the second negative electrode active material layer slurry prepared above was coated onto the coated first negative electrode active material layer slurry. The mixture was dried at 80°C and then rolled to prepare the negative electrode. In this negative electrode, the thickness of the first negative electrode active material layer was 65 µm and the porosity was 25%, and the thickness of the second negative electrode active material layer was also 65 µm and the porosity was 25%. In this case, the ratio of the volume of pores contained in the first negative electrode active material layer to the volume of pores contained in the second negative electrode active material layer was measured to be 50:50.

[0250] Comparative Example 2

[0251] A first negative electrode active material slurry was prepared by mixing a first negative electrode active material, a negative electrode conductive agent, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water at a weight ratio of 98.1:0.1:0.9:0.9. In this case, a mixture of Si / C composite and natural graphite at a weight ratio of 5:95 was used as the first negative electrode active material, and single-walled carbon nanotubes were used as the negative electrode conductive agent.

[0252] Next, a slurry of the second negative electrode active material, negative electrode conductive agent, styrene-butadiene rubber (SBR), and carboxymethyl cellulose was prepared by mixing them in water at a weight ratio of 98.15:0.05:0.9:0.9. In this case, a mixture of Si / C composite and artificial graphite at a weight ratio of 15:85 was used as the second negative electrode active material, and single-walled carbon nanotubes were used as the negative electrode conductive agent.

[0253] The first negative electrode active material layer slurry prepared above was coated onto a copper current collector, and the second negative electrode active material layer slurry prepared above was coated onto the coated first negative electrode active material layer slurry. The mixture was dried at 98°C and then rolled to prepare the negative electrode. In this negative electrode, the thickness of the first negative electrode active material layer was 70 µm and the porosity was 28%, while the thickness of the second negative electrode active material layer was 60 µm and the porosity was 22%. In this case, the ratio of the volume of pores contained in the first negative electrode active material layer to the volume of pores contained in the second negative electrode active material layer was measured to be 70:30.

[0254] Comparative Example 3

[0255] A first negative electrode active material slurry was prepared by mixing a first negative electrode active material, a negative electrode conductive agent, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water at a weight ratio of 98.15:0.05:0.9:0.9. In this case, a mixture of Si / C composite and natural graphite at a weight ratio of 15:85 was used as the first negative electrode active material, and single-walled carbon nanotubes were used as the negative electrode conductive agent.

[0256] Next, a slurry of the second negative electrode active material, negative electrode conductive agent, styrene-butadiene rubber (SBR), and carboxymethyl cellulose was prepared by mixing them in water at a weight ratio of 98.1:0.1:0.9:0.9. In this case, a mixture of Si / C composite and artificial graphite at a weight ratio of 5:95 was used as the second negative electrode active material, and single-walled carbon nanotubes were used as the negative electrode conductive agent.

[0257] The first negative electrode active material layer slurry prepared above was coated onto a copper current collector, and the second negative electrode active material layer slurry prepared above was coated onto the coated first negative electrode active material layer slurry. The mixture was dried at 80°C and then rolled to prepare the negative electrode. In this negative electrode, the thickness of the first negative electrode active material layer was 60 µm and the porosity was 28%, while the thickness of the second negative electrode active material layer was 70 µm and the porosity was 22%. In this case, the ratio of the volume of pores contained in the first negative electrode active material layer to the volume of pores contained in the second negative electrode active material layer was measured to be 70:30.

[0258] Comparative Example 4

[0259] A first negative electrode active material slurry was prepared by mixing a first negative electrode active material, a negative electrode conductive agent, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water at a weight ratio of 98.15:0.05:0.9:0.9. In this case, a mixture of Si / C composite and natural graphite at a weight ratio of 15:85 was used as the first negative electrode active material, and single-walled carbon nanotubes were used as the negative electrode conductive agent.

[0260] Next, a slurry of the second negative electrode active material, negative electrode conductive agent, styrene-butadiene rubber (SBR), and carboxymethyl cellulose was prepared by mixing them in water at a weight ratio of 98.1:0.1:0.9:0.9. In this case, a mixture of Si / C composite and artificial graphite at a weight ratio of 5:95 was used as the second negative electrode active material, and single-walled carbon nanotubes were used as the negative electrode conductive agent.

[0261] The first negative electrode active material layer slurry prepared above was coated onto a copper current collector, and the second negative electrode active material layer slurry prepared above was coated onto the coated first negative electrode active material layer slurry. The mixture was dried at 80°C and then rolled to prepare the negative electrode. In this negative electrode, the thickness of the first negative electrode active material layer was 55 µm and the porosity was 20%, while the thickness of the second negative electrode active material layer was 75 µm and the porosity was 30%. In this case, the ratio of the volume of pores contained in the first negative electrode active material layer to the volume of pores contained in the second negative electrode active material layer was measured to be 10:90.

[0262] Comparative Example 5

[0263] A first negative electrode active material slurry was prepared by mixing a first negative electrode active material, a negative electrode conductive agent, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water at a weight ratio of 98.15:0.05:0.9:0.9. In this case, a mixture of Si / C composite and natural graphite at a weight ratio of 5:95 was used as the first negative electrode active material, and single-walled carbon nanotubes were used as the negative electrode conductive agent.

[0264] Next, a slurry of the second negative electrode active material, negative electrode conductive agent, styrene-butadiene rubber (SBR), and carboxymethyl cellulose was prepared by mixing them in water at a weight ratio of 98.1:0.1:0.9:0.9. In this case, a mixture of Si / C composite and artificial graphite at a weight ratio of 15:85 was used as the second negative electrode active material, and single-walled carbon nanotubes were used as the negative electrode conductive agent.

[0265] The first negative electrode active material layer slurry prepared above was coated onto a copper current collector, and the second negative electrode active material layer slurry prepared above was coated onto the coated first negative electrode active material layer slurry. The mixture was dried at 80°C and then rolled to prepare the negative electrode. In this negative electrode, the thickness of the first negative electrode active material layer was 60 µm and the porosity was 22%, while the thickness of the second negative electrode active material layer was 70 µm and the porosity was 28%. In this case, the ratio of the volume of pores contained in the first negative electrode active material layer to the volume of pores contained in the second negative electrode active material layer was measured to be 30:70.

[0266] Comparative Example 6: Satisfying main configurations 2 and 3+, the first layer contains artificial graphite and the second layer contains natural graphite.

[0267] A slurry for the first negative electrode active material was prepared by mixing the first negative electrode active material, the negative electrode conductive agent, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water at a weight ratio of 98.15:0.05:0.9:0.9. In this case, a mixture of Si / C composite and artificial graphite at a weight ratio of 15:85 was used as the first negative electrode active material, and single-walled carbon nanotubes were used as the negative electrode conductive agent.

[0268] Next, a slurry of the second negative electrode active material, negative electrode conductive agent, styrene-butadiene rubber (SBR), and carboxymethyl cellulose was prepared by mixing them in water at a weight ratio of 98.1:0.1:0.9:0.9. In this case, a mixture of Si / C composite and natural graphite at a weight ratio of 5:95 was used as the second negative electrode active material, and single-walled carbon nanotubes were used as the negative electrode conductive agent.

[0269] The first negative electrode active material layer slurry prepared above was coated onto a copper current collector, and the second negative electrode active material layer slurry prepared above was coated onto the coated first negative electrode active material layer slurry. The mixture was dried at 80°C and then rolled to prepare the negative electrode. In this negative electrode, the thickness of the first negative electrode active material layer was 60 µm and the porosity was 22%, while the thickness of the second negative electrode active material layer was 70 µm and the porosity was 28%. In this case, the ratio of the volume of pores contained in the first negative electrode active material layer to the volume of pores contained in the second negative electrode active material layer was measured to be 28:72.

[0270] The characteristics of the negative electrodes prepared in the examples and comparative examples are shown in Table 1 below. In this case, the pore volume of the first negative electrode active material layer, the pore volume of the second negative electrode active material layer, and the porosity in the negative electrodes prepared in the examples and comparative examples were measured by the following methods.

[0271] Pore ​​volume: using Ar +Cross-sections of the anodes prepared in the examples and comparative examples were captured using an ion milling system (manufacturer: Hitachi High-Tech, product name: Ar blade 5000, accelerating voltage: 6 kV, ion beam current: 350 µA). In the scanning electron microscope (SEM) images of the anodes with captured cross-sections, the first and second anode active material layers were distinguished by considering both the brightness difference in silicon-based active material content and the thickness of the first and second anode active material layers. Subsequently, for both the first and second anode active material layers, the pore volume was calculated using the nitrogen adsorption isotherm at 77 K under liquid nitrogen atmosphere obtained by BELSORP-MAX (MicrotracBEL corp.). In this case, the pore volume was calculated using the BJH (Barrett–Joyner–Halenda) plot for pores with diameters ranging from 2 nm to 185 nm.

[0272] Porosity: The first and second negative electrode active material layers are distinguished in the same manner as the pore volume measurement, and the volume of each layer is calculated from the cross-sectional area of ​​the first and second negative electrode active material layers. Subsequently, for both the first and second negative electrode active material layers, the percentage of pore volume relative to the total volume is calculated.

[0273] [Table 1]

[0274] Experimental Example 1: Negative Electrode Performance Evaluation

[0275] (1) Measurement of tortuosity

[0276] After preparing two negative electrodes each of Examples 1 and 2 and Comparative Examples 1 to 6, an electrode assembly was fabricated by placing a separator between the two negative electrodes. This electrode assembly was placed in a battery case, an electrolyte solution without lithium salt (ethylene carbonate: ethyl methyl carbonate = 3:7 volume ratio) was injected, and the battery case was aged for 24 hours to prepare a symmetrical coin cell (symmetrical cell). Subsequently, a current with a frequency of 0.1 to 1,000,000 Hz and an amplitude of 10 mV was applied to the symmetrical coin cell, and the tortuosity was measured according to Equation A using a graph obtained by electrochemical impedance spectroscopy (EIS). The results are shown in Table 2 below.

[0277] Equation A: Torque (τ) = R / R th

[0278] In equation A, R is the x-intercept value calculated by extrapolating the linear region of the graph obtained from EIS measurements. th It is a value defined by the following equation B.

[0279] Equation B: R th =(Thickness of the first negative electrode active material layer + Thickness of the second negative electrode active material layer)(µm) / (Ionic conductivity of electrolyte solution (S / cm) × Negative electrode area (cm²) 2 ) × Negative electrode porosity (%)

[0280] (2) MP resistance measurement

[0281] The overall sheet resistance and the interfacial resistance between the first negative electrode active material layer and the current collector were measured using an MP resistance meter (product name: RM2610, manufacturer: HIOKI) for the negative electrodes prepared in Examples 1 and 2 and Comparative Examples 1 to 6. The results are shown in Table 2 below.

[0282] (3) Electrolyte infiltration assessment

[0283] Electrolyte wettability was evaluated for the negative electrodes prepared in Examples 1 and 2, and Comparative Examples 1 to 6. Specifically, each negative electrode was punched to a size of 5 cm × 5 cm, then adhered to a glass plate with tape to ensure it was flat and in close contact with the glass plate, and a 10 μL syringe was completely filled with electrolyte without air bubbles. Subsequently, 1 μL of electrolyte was dropped onto the negative electrode adhered to the glass plate, and the time for the negative electrode surface to dry was measured to evaluate the electrolyte wettability of each negative electrode.

[0284] In this case, the electrolyte was prepared by adding 0.5 M LiPF6 and 0.5 M LiFSI to an organic solvent consisting of an ethylene carbonate: ethyl carbonate: dimethyl carbonate mixture in a volume ratio of 20:5:75, and adding 3 wt% ethylene carbonate, 1 wt% propanesulfonyl lactone, 0.2 wt% succinic anionyl, 0.2 wt% methylprop-2-yn-1-yl carbonate, and 0.2 wt% propargyl 1H-imidazolium-1-carboxylic acid ester as additives. The results are shown in Table 2 below.

[0285] [Table 2]

[0286] Referring to Table 2, it can be confirmed that the tortuosity, overall thin-film resistance, interfacial resistance and electrolyte wettability of the negative electrodes prepared in Examples 1 and 2 are significantly better than those prepared in Comparative Examples 1 to 6.

[0287] Experimental Example 2: Initial Discharge Capacity Assessment

[0288] In Examples 1 and 2 and Comparative Examples 1 to 6, a separator was provided between each negative electrode and the positive electrode to prepare an electrode assembly. After the assembly was placed inside a battery case, an electrolyte solution was injected into the battery case to prepare a lithium secondary battery (coin cell).

[0289] The positive electrode is prepared by the following method: lithium nickel oxide as the positive electrode active material, single-walled carbon nanotubes as the conductive agent, and polyvinylidene fluoride (PVDF) as the binder are mixed in N-methyl-2-pyrrolidone solvent at a weight ratio of 97.6:0.6:1.8 to prepare a positive electrode slurry. The positive electrode slurry is coated onto an aluminum current collector, the coated positive electrode slurry is dried, and then the dried aluminum current collector is rolled. In this case, the nickel content in the total metals other than lithium in the lithium nickel oxide is 93 mol%. The lithium nickel oxide contains nickel, cobalt, manganese, and aluminum, and is in single-crystal form.

[0290] The electrolyte used was prepared by adding 0.5 M LiPF6 and 0.5 M LiFSI to an organic solvent in which ethylene carbonate, ethyl carbonate, and dimethyl carbonate were mixed in a volume ratio of 20:5:75, and 3 wt% ethylene carbonate, 1 wt% propane sulpholol, 0.2 wt% succinate, 0.2 wt% methylprop-2-yn-1-yl carbonate, and 0.2 wt% propargyl 1H-imidazol-1-carboxylic acid ester were added as additives.

[0291] The lithium secondary battery prepared above was charged to 4.2V at a C rate of 0.2C, and then discharged to 2.5V for formation. Subsequently, the lithium secondary battery was charged to 4.2V (cutoff 0.005C) at a C rate of 0.2C in constant current-constant voltage (CCCV) mode, and then discharged to 2.5V at 0.2C. The capacity of the first discharge cycle was measured as the initial capacity. The results are shown in Table 3 below.

[0292] Experiment Example 3: Initial Resistance Evaluation

[0293] The lithium secondary batteries prepared in Experimental Example 2, containing the negative electrodes of Examples 1 and 2 and Comparative Examples 1 to 6, were charged at 0.2C to 4.2 V at 25°C, and then discharged to 2.5 V for formation. Subsequently, the batteries were charged at 0.5C (reference capacity 1C = 6.3 mAh / g) under CC-CV conditions at 25°C to 4.2 V (0.005C cutoff) to reach 100% state of charge (SOC). Then, the coin half-cell, discharged to 50% SOC, was discharged at a constant current of 0.5C for 10 seconds at 25°C, and the resulting voltage drop was measured. The initial resistance (DCIR) was calculated using Ohm's law based on the measurements. The results are shown in Table 3 below.

[0294] Experiment Example 4: Fast Charging Characteristics Evaluation

[0295] The lithium secondary batteries prepared in Experimental Example 2, containing the negative electrodes of Examples 1 and 2 and Comparative Examples 1 to 6, were charged to 4.2 V (0.005C cutoff) at 25°C under CC-CV conditions, and then discharged to 2.5 V at a constant current of 1.0C for 124 charge-discharge cycles. The discharge capacity after one cycle and the discharge capacity after 124 cycles were measured. Then, the capacity retention rate was measured according to the following equation C. The results are shown in Table 3 below.

[0296] Equation C: Capacity retention (%) = {Discharge capacity after 124 cycles / Discharge capacity after 1 cycle} × 100

[0297] [Table 3]

[0298] Referring to Table 3, it can be confirmed that, compared with the lithium secondary batteries prepared using the negative electrodes prepared in Comparative Examples 1 to 6, the lithium secondary batteries prepared using the negative electrodes prepared in Examples 1 and 2 have higher initial capacity, lower initial resistance, and higher capacity retention during fast charging.

[0299] (Explanation of reference numerals in the attached diagram)

[0300] 1: Lithium secondary battery

[0301] 2: Battery pack casing

[0302] 3: Battery Pack

[0303] 10: Positive electrode

[0304] 11: Negative electrode

[0305] 12: Diaphragm

[0306] 20: Current collector

[0307] 21: Active material layer

[0308] 21a: Negative electrode active material layer

[0309] 22: Uncoated area

[0310] 22a: Uncoated portion of the negative electrode

[0311] 22c: Uncoated portion of the positive electrode

[0312] 24: Insulation layer

[0313] C: Winding center

[0314] 140: Lithium secondary battery

[0315] 141: Electrode assembly

[0316] 142: Battery Canister

[0317] 143: Sealing body

[0318] 143a: Cover plate

[0319] 143b: First gasket

[0320] 143c: Connector

[0321] 143d: Protrusion

[0322] 144: First manifold

[0323] 145: Second manifold

[0324] 146: Insulator

[0325] 146a: Uncoated portion of the positive electrode

[0326] 146b: Uncoated portion of the negative electrode

[0327] 147: Rolled edge

[0328] 148: Crimping section

[0329] 149: Lead wire

[0330] 151: Lead hole

[0331] 152: Exhaust section

[0332] 170: Lithium secondary battery

[0333] 171: Battery Canister

[0334] 172: Rivet Terminal

[0335] 172a: Exposed terminal portion

[0336] 172b: Terminal insertion part

[0337] 173: Second gasket

[0338] 173a: Exposed part of gasket

[0339] 173b: Gasket insertion part

[0340] 174: Insulating Cap

[0341] 176: Second manifold

[0342] 178: Sealing body

[0343] 178a: Cover plate

[0344] 178b: First gasket

[0345] 179: Exhaust section

[0346] 180: Rolled edge

[0347] 181: Crimping section

Claims

1. A negative electrode comprising: A negative electrode current collector; a first negative electrode active material layer disposed on the negative electrode current collector; and a second negative electrode active material layer disposed on the first negative electrode active material layer. in, The volume of pores contained in the first negative electrode active material layer is 11% to 49% of the total volume of pores contained in the first negative electrode active material layer and the second negative electrode active material layer. The first negative electrode active material layer comprises a first negative electrode active material, which includes natural graphite and a first silicon-based negative electrode active material. The second negative electrode active material layer comprises a second negative electrode active material, which includes artificial graphite and a second silicon-based negative electrode active material. The content of the first silicon-based negative electrode active material in the first negative electrode active material layer is greater than the content of the second silicon-based negative electrode active material in the second negative electrode active material layer.

2. The negative electrode as described in claim 1, wherein, The ratio X1 / X2 of the content of the first silicon-based negative electrode active material in the first negative electrode active material layer to the content of the second silicon-based negative electrode active material in the second negative electrode active material layer is greater than 1 and less than or equal to 10.

3. The negative electrode as described in claim 1, wherein, Based on the total weight of the first negative electrode active material, the content of the first silicon-based negative electrode active material is 5% to 30% by weight.

4. The negative electrode as described in claim 1, wherein, Based on the total weight of the second negative electrode active material, the content of the second silicon-based negative electrode active material is from 1% to 20% by weight.

5. The negative electrode as described in claim 1, wherein, The porosity of the first negative electrode active material layer is 15% to 30%.

6. The negative electrode as described in claim 1, wherein, The porosity of the second negative electrode active material layer is 20% to 35%.

7. The negative electrode as described in claim 1, wherein, The thickness of the first negative electrode active material layer is 35% to 50% of the total thickness of the first negative electrode active material layer and the second negative electrode active material layer.

8. The negative electrode as described in claim 1, wherein, The first silicon-based anode active material and the second silicon-based anode active material each contain a Si / C composite.

9. A lithium secondary battery, comprising: An electrode assembly comprising a negative electrode, a positive electrode, and a separator disposed between the negative electrode and the positive electrode, as described in any one of claims 1 to 8; an electrolyte; and a battery case housing the electrode assembly and the electrolyte.

10. The lithium secondary battery as described in claim 9, wherein, The lithium secondary battery is a cylindrical lithium secondary battery in which the ratio of the diameter R to the height h is 0.4 or more.

11. The lithium secondary battery as described in claim 9, wherein, The lithium secondary battery is a 46110 cell, a 48110 cell, a 4880 cell, or a 4680 cell.

12. The lithium secondary battery as described in claim 9, wherein, The positive electrode and the negative electrode each include an uncoated portion where no active material layer is formed, and The uncoated portion of the positive electrode and at least a portion of the uncoated portion of the negative electrode define the electrode tab.

13. The lithium secondary battery as described in claim 12, wherein, The current collector is coupled to the uncoated portions of the positive electrode and the uncoated portions of the negative electrode, respectively, and The current collector is connected to the electrode terminals.

14. The lithium secondary battery as described in claim 12, wherein, The uncoated portions of the positive electrode and the uncoated portions of the negative electrode are processed into multiple independently bendable segmented pieces, and At least a portion of the plurality of segmented pieces bends toward the winding center of the electrode assembly.

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