Negative electrode and lithium secondary battery comprising same

Abstract

The present invention relates to a negative electrode comprising: a negative electrode current collector; a first negative electrode active material layer located on the negative electrode current collector; and a second negative electrode active material layer located on the first negative electrode active material layer, wherein: the volume of pores included in the first negative electrode active material layer is 20% to 49% of the total volume of pores included in the entire first and second negative electrode active material layers; the first negative electrode active material layer includes a first negative electrode active material including natural graphite and a first silicon-based negative electrode active material; the second negative electrode active material layer includes a second negative electrode active material including artificial graphite and a second silicon-based negative electrode active material; and the content of the first silicon-based negative electrode active material included in the first negative electrode active material layer is greater than the content of the second silicon-based negative electrode active material included in the second negative electrode active material layer.

Description

Negative electrode and lithium secondary battery including the same

[0001] Cross-citation with related applications

[0002] The present application claims the benefit of priority based on 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, and all contents disclosed in said Korean patent application documents are incorporated into this specification.

[0003] Technology field

[0004] The present invention relates to a negative electrode and a lithium secondary battery including the same.

[0005]

[0006] Recently, lithium-ion batteries have been gaining attention as an energy source for electric vehicles. As the adoption of electric vehicles expands, there is an increasing demand for lithium-ion batteries that offer a longer driving range on a single charge and shorter charging times.

[0007] A lithium secondary battery is generally manufactured by forming an electrode assembly by interposing a separator between a positive electrode, which contains a positive active material composed of a transition metal oxide containing lithium, and a negative electrode, which contains a negative active material capable of storing lithium ions; inserting the electrode assembly into a battery case; injecting a non-aqueous electrolyte that serves as a medium for transmitting lithium ions; and then sealing the case. The non-aqueous electrolyte is generally composed of a lithium salt and an organic solvent capable of dissolving the lithium salt. Conventionally, carbon-based materials such as natural graphite or synthetic graphite have been primarily used as negative active materials for lithium secondary batteries. However, such carbon-based negative active materials have slow reactivity with lithium and low capacity, which limits the realization of high capacity and rapid charging characteristics in secondary batteries utilizing them.

[0008] Accordingly, there have been continuous attempts recently to apply silicon-based anode active materials, which have a higher capacity per unit weight compared to graphite. However, silicon-based active materials have a problem in that their volume expands by up to 400% during charging and discharging, which destroys the SEI film on the anode surface, degrades the active material, and results in inferior lifespan characteristics, as well as higher resistance compared to carbon-based anode active materials.

[0009] Therefore, there is a need to develop a cathode that achieves high capacity while exhibiting excellent resistance characteristics and superior lifespan characteristics during rapid charging.

[0010]

[0011] The present invention aims to solve the above-mentioned problems by providing a negative electrode with excellent capacity characteristics, resistance characteristics, and lifespan characteristics during rapid charging, and a lithium secondary battery including the same.

[0012]

[0013] [1] The present invention provides a cathode comprising: a cathode current collector; a first cathode active material layer located on the cathode current collector; and a second cathode active material layer located on the first cathode active material layer; wherein the volume of pores included in the first cathode active material layer is 11% to 49% of the total volume of pores included in the first cathode active material layer and the second cathode active material layer, the first cathode active material layer includes a first cathode active material including natural graphite and a first silicon-based cathode active material, and the second cathode active material layer includes a second cathode active material including artificial graphite and a second silicon-based cathode active material, and the content of the first silicon-based cathode active material included in the first cathode active material layer is greater than the content of the second silicon-based cathode active material included in the second cathode active material layer.

[0014] [2] The present invention provides a cathode in which the ratio (X1 / X2) of the content of the first silicon-based cathode active material (X1) included in the first cathode active material layer and the content of the second silicon-based cathode active material (X2) included in the second cathode active material layer is greater than 1 and less than or equal to 10.

[0015] [3] The present invention provides a cathode in which, in at least one of [1] or [2], the first silicon-based cathode active material is included in an amount of 5 to 30 weight% based on the total weight of the first cathode active material.

[0016] [4] The present invention provides a cathode in which, in at least one of [1] to [3], the second silicon-based cathode active material is included in an amount of 1 to 20 weight% based on the total weight of the second cathode active material.

[0017] [5] The present invention provides a cathode in which, in at least one of [1] to [4], the first cathode active material layer has a porosity of 15 to 30%.

[0018] [6] The present invention provides a cathode in which, in at least one of [1] to [5], the second cathode active material layer has a porosity of 20 to 35%.

[0019] [7] The present invention provides a cathode in which, in at least one of [1] to [6], the thickness of the first cathode active material layer is 35% to 50% of the total thickness of the first cathode active material layer and the second cathode active material layer.

[0020] [8] The present invention provides a cathode in which, in at least one of [1] to [7], the first silicon-based cathode active material and the second silicon-based cathode active material each comprise a Si / C composite.

[0021] [9] The present invention provides a lithium secondary battery comprising: an electrode assembly including a cathode, an anode, and a separator interposed between the cathode and the anode according to at least one of [1] to [8]; an electrolyte; and a battery case in which the electrode assembly and the electrolyte are housed.

[0022]

[0010] The present invention provides a lithium secondary battery, wherein, in at least one of [1] to [9], the ratio of the diameter (R) of the lithium secondary battery to the height (h) of the lithium secondary battery is 0.4 or greater.

[0023]

[0011] The present invention provides a lithium secondary battery, wherein, in at least one of [1] to

[0010] , the lithium secondary battery is a 46110 cell, a 48110 cell, a 4880 cell, or a 4680 cell.

[0024]

[0012] The present invention provides a lithium secondary battery in which, in at least one of [1] to

[0011] , the positive electrode and the negative electrode each include a non-active portion in which an active material layer is not formed, and at least a portion of the non-active portion of the positive electrode and the non-active portion of the negative electrode defines an electrode tab.

[0025]

[0013] The present invention provides a lithium secondary battery in which, in at least one of [1] to

[0012] , a current collecting plate is coupled to each of the non-existent portion of the positive electrode and the non-existent portion of the negative electrode, and the current collecting plate is connected to an electrode terminal.

[0026]

[0014] The present invention provides a lithium secondary battery in which, in at least one of [1] to

[0013] , the uncoated portion of the positive electrode and the uncoated portion of the negative electrode are independently bendable but processed into a plurality of segmented portions, and at least some of the plurality of segmented portions are bent toward the winding center of the electrode assembly.

[0027]

[0028] The present invention is designed with a two-layer structure comprising: a first negative electrode active material layer comprising natural graphite and a first silicon-based negative electrode active material located on a current collector; and a second negative electrode active material layer comprising artificial graphite and a second silicon-based negative electrode active material located on the first negative electrode active material layer. The volume of pores contained in the first negative electrode active material layer and the volume of pores contained in the second negative electrode active material layer are controlled in 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. Accordingly, the negative electrode according to the present invention has excellent capacity and resistance characteristics and excellent lifespan characteristics during rapid charging of the battery.

[0029] Specifically, by designing the volume of pores included in the first negative electrode active material layer and the volume of pores included in the second negative electrode active material layer in an appropriate ratio, electrolyte impregnation in the first negative electrode active material layer and the second negative electrode active material layer is secured, and while suppressing the increase in internal resistance, lithium ions can be smoothly diffused through the second negative electrode active material layer to suppress the reversal phenomenon.

[0030] At the same time, by making the first negative electrode active material layer contain a larger amount of silicon-based negative electrode active material than the second negative electrode active material layer, the volume expansion of the silicon-based negative electrode active material during charging and discharging in the upper second negative electrode active material layer can be sufficiently mitigated. Accordingly, even if charging and discharging are repeated, the destruction of the SEI film and degradation of the negative electrode active material caused by the silicon-based negative electrode active material can be suppressed, thereby preventing a decrease in lifespan characteristics even during rapid charging.

[0031] As a result, the cathode according to the present invention reduces the interfacial resistance and sheet resistance of the cathode, thereby having excellent resistance characteristics, and improves lifespan characteristics during rapid charging, so that the rapid charging performance can be excellent.

[0032]

[0033] FIG. 1 is a drawing showing the stacked state of an electrode assembly before winding according to the present invention.

[0034] FIG. 2 is a cross-sectional view showing the structure of an electrode of an electrode assembly according to one embodiment of the present invention.

[0035] FIG. 3 is a drawing for explaining the structure of an electrode assembly according to one embodiment of the present invention.

[0036] FIG. 4 is a cross-sectional view showing the structure of a lithium secondary battery according to one embodiment of the present invention.

[0037] FIG. 5 is a cross-sectional view showing the structure of a lithium secondary battery according to another embodiment of the present invention.

[0038] FIG. 6 is a drawing for explaining a battery pack according to the present invention.

[0039]

[0040] The present invention will be described in more detail below.

[0041] Terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0042] The terms used in this specification are used merely to describe exemplary embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0043] In this specification, terms such as “comprising,” “having,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0044] In the present invention, “pore volume” refers to the volume of pores contained in the electrode active material layer. At this time, pores contained within the electrode active material may not be considered. The pore volume is calculated from the nitrogen adsorption isotherm under a 77K liquid nitrogen atmosphere obtained using BELSORP-MAX (MicrotracBEL corp.) on the cut electrode cross-section after cutting the electrode cross-section, and is calculated using a BJH (Barrett-Joyner-Halenda) plot for pores with a diameter of 2 nm to 185 nm.

[0045] For example, in the case of a cathode comprising a first cathode active material layer and a second cathode active material layer located on the first cathode active material layer, the volume of the pores of the first cathode active material layer and the volume of the pores of the second cathode active material layer can be measured by the following method.

[0046] (1) The cathode is cut in cross-section using an ion milling device using an Ar+ ion beam (Manufacturer: Hitachi, Product name: Ar blade5000, Acceleration voltage: 6 kV, Ion beam current: 350 μA). (2) The first cathode active material layer and the second cathode active material layer are distinguished from the first cathode active material layer and the second cathode active material layer by the difference in brightness between the first cathode active material layer and the second cathode active material layer according to the content of silicon-based active material, and the thickness of the first cathode active material layer and the second cathode active material layer in the scanning electron microscope (SEM) image of the cut cathode cross-section. (3) Afterwards, the first cathode active material layer and the second cathode active material layer are each calculated from the nitrogen adsorption isotherm under a 77 K liquid nitrogen atmosphere obtained using BELSORP-MAX (MicrotracBEL corp.).

[0047] In the present invention, “porosity” refers to the percentage of the volume of pores relative to the total volume of the electrode active material layer. The porosity can be measured by methods known in the art. For example, in the case of a cathode comprising a first negative active material layer and a second negative active material layer located on the first negative active material layer, the porosity can be measured by the following method 1 or method 2.

[0048] [Method 1]

[0049] (1) The cathode is cut in cross-section using an ion milling device using an Ar+ ion beam (Manufacturer: Hitachi, Product name: Ar blade5000, Acceleration voltage: 6 kV, Ion beam current: 350 μA). (2) The first cathode active material layer and the second cathode active material layer are distinguished from the first cathode active material layer and the second cathode active material layer by the difference in brightness between the first cathode active material layer and the second cathode active material layer according to the content of the silicon-based active material, and the thickness of the first cathode active material layer and the second cathode active material layer, in the scanning electron microscope (SEM) image of the cut cathode cross-section. (3) The volume of each layer is calculated from the cross-sectional area of ​​the first cathode active material layer and the second cathode active material layer. (4) Afterwards, the percentage of the volume of pores relative to the total volume is calculated for each of the first cathode active material layer and the second cathode active material layer, and the porosity of the first cathode active material layer and the porosity of the second cathode active material layer can be measured. At this time, the volume of the above pore can be measured by the method described above.

[0050] [Method 2]

[0051] (1) After applying a first cathode active material layer slurry onto a cathode current collector and drying it, the actual density of the first cathode active material layer is measured, and then the porosity of the first cathode active material layer is measured by substituting the theoretical electrode density of the first cathode active material layer and the actual density of the first cathode active material layer into Equation 1 below. (2) After applying a second cathode active material layer slurry onto the first cathode active material layer and drying it, the actual density of the entire cathode active material layer is measured, and then the actual density of the second cathode active material layer is calculated by subtracting the actual density of the first cathode active material layer, and then the porosity of the second cathode active material layer is measured by substituting the theoretical electrode density of the second cathode active material layer and the actual density of the second cathode active material layer into Equation 1 below. At this time, the theoretical electrode density of the cathode active material layer refers to a value calculated from the mass of all solid components such as the cathode active material, cathode binder, and cathode conductive material within the cathode active material layer and their respective true densities.

[0052] [Equation 1] Porosity (%) of the cathode active material layer = [1 - (Actual density of the cathode active material layer / Theoretical electrode density of the cathode active material layer)] × 100

[0053] In the present invention, "single particle type" refers to a particle composed of 50 or fewer nodules, and is a concept that includes a single particle composed of one nodule and a pseudo-single particle which is a complex of 2 to 50 nodules.

[0054] The above “nodule” is a sub-grain unit constituting a single particle and a pseudo-single particle, and may be a single crystal that does not have crystalline grain boundaries, or a polycrystalline one in which no grain boundaries appear to exist when observed at a field of view of 5,000 to 20,000 times using a scanning electron microscope.

[0055] In the present invention, "secondary particle" refers to a particle formed by the aggregation of a plurality of primary particles, for example, tens to hundreds of primary particles. Specifically, the secondary particle may be an aggregate of more than 50 primary particles.

[0056] In the present invention, the term “particle” is a concept that includes any one or all of a single particle, a pseudo-single particle, a primary particle, a nodule, and a secondary particle.

[0057] In the present invention, “loading amount” (La, unit: mg / 25cm 2 ) is 25cm 2 It refers to the total mass (mg) of the target cathode active material layer included per area. Specifically, the loading amount (L of the first cathode active material layer) a1 ) can be measured by forming a cathode with a size of 5 cm × 5 cm while only the first cathode active material layer is formed on one side of the cathode current collector, measuring the weight W1 of the formed area and the weight W2 of the cathode current collector, and then substituting them into the following [Equation 2-1].

[0058] [Equation 2-1] Loading amount L of the first cathode active material layer a1 (g / 25cm 2) = (W1-W2)

[0059] Or, the loading amount of the second cathode active material layer (L a2 ) is the weight W2 of the cathode current collector and the loading amount L of the first cathode active material layer obtained when measuring the loading amount of the first cathode active material layer, after the cathode is punched to a size of 5cm × 5cm while a first cathode active material layer is formed on one surface of the cathode current collector and a second cathode active material layer is formed on the first cathode active material layer, and the weight W3 of the punched area is measured. a1 The value of can be measured by substituting it into [Equation 2-2] below.

[0060] [Equation 2-2] Loading amount L of the second cathode active material layer a2 (g / 25cm 2 ) = (W3-W2-L a1 )

[0061]

[0062] The present invention will be described in detail below.

[0063] The negative electrode and / or lithium secondary battery including the same according to the present invention comprises at least one of the configurations disclosed below, and may include any combination of technically feasible configurations among the configurations below.

[0064]

[0065] cathode

[0066] A cathode according to the present invention comprises: a cathode current collector; a first cathode active material layer located on the cathode current collector; and a second cathode active material layer located on the first cathode active material layer. The volume of pores included in the first cathode active material layer is 11% to 49% of the total volume of pores included in the first cathode active material layer and the second cathode active material layer. The first cathode active material layer comprises a first cathode active material comprising natural graphite and a first silicon-based cathode active material. The second cathode active material layer comprises a second cathode active material comprising artificial graphite and a second silicon-based cathode active material. The content of the first silicon-based cathode active material included in the first cathode active material layer is greater than the content of the second silicon-based cathode active material included in the second cathode active material layer.

[0067] Conversely, even if the content of the first silicon-based negative electrode active material included in the first negative electrode active material layer is greater than the content of the second silicon-based negative electrode active material included in the second negative electrode active material layer, if the volume of pores included in the first negative electrode active material layer does not satisfy 11% to 49% of the total volume of pores included in the first negative electrode active material layer and the second negative electrode active material layer, it may be difficult for lithium ions to flow into the second negative electrode active material layer in contact with the electrolyte. Accordingly, the capacity and efficiency of the negative electrode are not sufficiently expressed during charging and discharging, and when the negative electrode is applied to a lithium secondary battery, a reversal phenomenon may occur in which the potential difference with the positive electrode is reversed. In addition, there is a problem that the rapid charging characteristics may be inferior due to the structure being unfavorable for the electrolyte to penetrate the second negative electrode active material layer, which reduces electrolyte impregnation.

[0068] Accordingly, the cathode according to the present invention has a volume of pores included in the first cathode active material layer that is 11% to 49% of the total volume of pores included in the first cathode active material layer and the second cathode active material layer, and at the same time, the content of the first silicon-based cathode active material included in the first cathode active material layer is greater than the content of the second silicon-based cathode active material included in the second cathode active material layer, thereby improving the mobility of lithium ions and enhancing the resistance characteristics of the cathode. In addition, the degradation of lifespan characteristics is suppressed even when charging and discharging are repeated at a high charging speed, and the rapid charging characteristics are excellent.

[0069]

[0070] Hereinafter, each component of the cathode according to the present invention will be described in detail.

[0071]

[0072] As the above-mentioned negative current collector, negative current collectors generally used in the relevant technical field may be used, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. The above-mentioned negative current collector may typically have a thickness of 3 μm to 500 μm, and, similar to the anode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding force of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0073]

[0074] The first cathode active material layer comprises a first cathode active material including natural graphite and a first silicon-based cathode active material.

[0075] Conventionally, carbon-based negative electrode active materials were used exclusively as negative electrode active materials; however, because carbon-based negative electrode active materials have low capacity and slow reaction rates with lithium, lithium secondary batteries utilizing them had limitations in realizing high capacity characteristics and rapid charging performance. Accordingly, the present invention improves the capacity characteristics and rapid charging characteristics of a lithium secondary battery by including a silicon-based negative electrode active material, which has a high theoretical capacity and a fast reaction rate with lithium, together with natural graphite in the first negative electrode active material layer.

[0076] Furthermore, natural graphite has relatively higher structural flexibility and lower strength compared to artificial graphite, which can mitigate the volume expansion of silicon-based negative electrode active materials. Accordingly, even if 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, problems caused by the volume expansion of silicon-based negative electrode active materials can be suppressed. Additionally, natural graphite has a relatively high tap density, which allows the volume of pores included in the first negative electrode active material layer to be set to a desired range and improves adhesion to the current collector.

[0077]

[0078] The above natural graphite may be included in an amount of 70 to 95 weight%, 75 to 92 weight%, or 80 to 90 weight% based on the total weight of the first negative electrode active material. If the above range is satisfied, a balance can be achieved between capacity characteristics, rapid charging characteristics, and lifespan characteristics.

[0079]

[0080] The first silicon-based negative electrode active material is silicon (Si) and silicon oxide (SiO₂). x (0 <x<2)로 표시될 수 있음) 및 Si / C 복합체(Si / C Composite)로 이루어진 군에서 선택된 적어도 1종을 포함할 수 있고, 바람직하게는 Si / C 복합체를 포함할 수 있다. 또는, 상기 제1 실리콘계 음극 활물질은 Si / C 복합체일 수 있다.

[0081] The above Si / C composite may include silicon particles embedded within a carbon matrix, rather than in a state where Si and carbon (C) are simply aggregated or mixed. The carbon matrix may be a porous carbon matrix.

[0082] When the first silicon-based negative electrode active material includes a Si / C composite, the degree of volume expansion during charging and discharging may be smaller compared to silicon, thereby suppressing the degradation of lifespan characteristics during charging and discharging; furthermore, since silicon and carbon exist in a mechanically bonded state, the capacity characteristics and electrical conductivity may be superior compared to silicon oxide. Therefore, when the first silicon-based negative electrode active material includes a Si / C composite, it has the advantage of improving cycle performance during rapid charging while realizing high capacity characteristics of the lithium secondary battery.

[0083]

[0084] The above Si / C composite may contain silicon (Si) and carbon (C) in a weight ratio of 2:8 to 8:2, 3:7 to 7:3, or 4:6 to 6:4. When the above ranges are satisfied, it is possible to achieve high capacity while improving the electrical conductivity of the negative electrode active material.

[0085] The above first silicon-based negative electrode active material is D 50 This can be 5㎛ to 15㎛, 6㎛ to 11㎛, or 7㎛ to 9㎛. When the above range is satisfied, the cathode electrode density is increased, and high energy density can be achieved.

[0086]

[0087] The content of the first silicon-based negative electrode active material included in the first negative electrode active material layer is greater than the content of the second silicon-based negative electrode active material included in the second negative electrode active material layer. At this time, the content of the first silicon-based negative electrode active material included in the first negative electrode active material layer refers to the content of the first silicon-based negative electrode active material measured in 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 included in the second negative electrode active material layer refers to the content of the second silicon-based negative electrode active material measured in weight% based on the total weight of the second negative electrode active material layer.

[0088] When the content of the first silicon-based negative electrode active material included in the first negative electrode active material layer is greater than the content of the second silicon-based negative electrode active material included in the second negative electrode active material layer, it can contribute to appropriately adjusting the ratio of the volume of pores included in the first negative electrode active material layer to the volume of pores included in the second negative electrode active material layer, thereby improving the electrolyte impregnation of the second negative electrode active material layer and improving the mobility of lithium ions. In addition, by ensuring that the silicon-based negative electrode active material is included in a relatively small amount in the second negative electrode active material layer that is in direct contact with the electrolyte, it is possible to suppress the increase in the resistance of the negative electrode caused by the repeated destruction and regeneration of the SEI film (Solid electrolyte Interphase Layer) due to the volume expansion of the silicon-based negative electrode active material. As a result, when charging and discharging are repeated at a high charging rate, the lifespan characteristics can be improved, and the rapid charging characteristics can be excellent.

[0089]

[0090] The ratio (X1 / X2) of the content (X1) of the first silicon-based negative electrode active material included in the first negative electrode active material layer and the content (X2) of the second silicon-based negative electrode active material included in the second negative electrode active material layer may be greater than 1 and less than or equal to 10. Specifically, the X1 / X tIt may be greater than 1, 1.2 or more, 1.5 or more, 1.7 or more, 2.0 or more, 2.2 or more, 2.5 or more, 2.7 or more, 3.0 or more, 10 or less, 9 or less, 8 or less, 7 or less, 6 or less, 5 or less, 5.5 or less, 5 or less, 4.5 or less, 4 or less, 3.7 or less, 3.5 or less, 3.2 or less, or 3 or less. For example, the above X1 / X2 may be greater than 1 and 10 or less, 1.2 or more and 8 or less, 1.5 or more and 6 or less, 2 or more and 4 or less, or 2.5 or more and 3.5 or less. When the above range is satisfied, the volume of pores included 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 impregnation, lithium ion mobility, and rapid charging characteristics can be maximized.

[0091]

[0092] The weight of the first silicon-based negative electrode active material may be greater than the weight of the second silicon-based negative electrode active material. That is, the silicon-based active material may be included in the first negative electrode active material layer in greater weight than in the second negative electrode active material layer.

[0093] By including a larger amount of silicon-based anode active material in the lower first anode active material layer, sufficient high-capacity characteristics can be achieved, while suppressing the increase in anode resistance caused by the repeated destruction and regeneration of the SEI (Solid Electrolyte Interphase Layer) due to the volume expansion of the silicon-based anode active material. Additionally, the movement of lithium ions in the second anode active material layer can be facilitated. As a result, excellent rapid charging characteristics can be achieved while realizing high energy density.

[0094]

[0095] The first silicon-based negative electrode active material may be included in an amount of 5 to 30 weight percent based on the total weight of the first negative electrode active material. Specifically, the first silicon-based negative electrode active material is, based on the total weight of the first negative electrode active material, 5 wt% or more, 5.5 wt% or more, 6 wt% or more, 6.5 wt% or more, 7 wt% or more, 7.5 wt% or more, 8 wt% or more, 8.5 wt% or more, 9 wt% or more, 9.5 wt% or more, 10 wt% or more, 10.5 wt% or more, 11 wt% or more, 11.5 wt% or more, 12 wt% or more, 12.5 wt% or more, 13 wt% or more, 13.5 wt% or more, 14 wt% or more, 14.5 wt% or more, 15 wt% or more, 30 wt% or less, 29 wt% or less, 28 wt% or less, 27 wt% or less, 26 wt% or less, 25 wt% or less, 24 wt% or less, 23 wt% or less, 22 wt% or less, It may be 21 wt% or less, 20 wt% or less, 19 wt% or less, 18 wt% or less, 17 wt% or less, 16 wt% or less, or 15 wt% or less. For example, the first silicon-based negative electrode active material may be 5 to 30 wt%, 8 to 25 wt%, 10 to 20 wt%, or 13 to 17 wt% based on the total weight of the first negative electrode active material. If the above range is satisfied, a balance can be achieved between capacity characteristics, rapid charging characteristics, and lifespan characteristics.

[0096]

[0097]

[0098] The first silicon-based negative electrode active material and the natural graphite may be included 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 the above ranges are satisfied, the capacity characteristics, rapid charging characteristics, and lifespan characteristics may all be excellent.

[0099]

[0100] The first negative electrode active material may be included in an amount of 80 to 99.9 wt%, 90 to 99.7 wt%, 93 to 99.5 wt%, or 95 to 99 wt% based on the total weight of the first negative electrode active material layer. When the content of the first negative electrode active material satisfies the above range, excellent energy density can be achieved.

[0101]

[0102] The first cathode active material layer may further include a first cathode conductive material and / or a first cathode binder.

[0103] The first cathode conductive material is used to impart conductivity to the cathode, and in the battery being constructed, any material that has electronic conductivity without causing chemical changes can be used without special limitations. Specific examples include carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, carbon nanotube; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used.

[0104] The first cathode conductive material may be included in an amount of 0.1 to 10 weight%, 0.1 to 8 weight%, or 0.1 to 5 weight% based on the total weight of the first cathode active material layer.

[0105] The first cathode binder described above serves to improve adhesion between cathode active material particles and adhesion between the cathode active material and the cathode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0106] The first cathode binder may be included in an amount of 0.1 to 10 weight%, 0.5 to 10 weight%, or 1 to 8 weight% based on the total weight of the first cathode active material layer.

[0107]

[0108] The volume of the pores included in the first cathode active material layer may be smaller than the volume of the pores included in the second cathode active material layer.

[0109] The volume of pores included in the first negative electrode active material layer is 11% to 49% of the total volume of pores included in the first negative electrode active material layer and the second negative electrode active material layer. Specifically, the volume of pores included 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, 49% or less, 48% or less, 47% or less, 46% or less, 45% or less, 44% or less, 43% or less, 42% or less, 41% or less, 40% or less, 39% or less, 38% or less, 37% or less, 36% or less, 35% It is less than or equal to 34%, less than or equal to 33%, less than or equal to 32%, less than or equal to 31%, or less than or equal to 30%. For example, the volume of pores included 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 included in the first negative electrode active material layer and the second negative electrode active material layer.

[0110] If the volume of pores included in the first negative active material layer is less than 11% of the total volume of pores included in the first negative active material layer and the second negative active material layer, sufficient pores may not be formed in the first negative active material layer, which may reduce electrolyte impregnation. Consequently, the conductivity of lithium ions may decrease, capacity characteristics may deteriorate, and internal resistance may increase. Furthermore, if the volume of pores included in the first negative active material layer exceeds 49% of the total volume of pores included in the first negative active material layer and the second negative active material layer, it may be difficult for lithium ions to flow into the second negative active material layer in contact with the electrolyte. Consequently, the capacity and efficiency of the negative electrode are not sufficiently expressed during charging and discharging, and when the negative electrode is applied to a lithium secondary battery, a reversal phenomenon may occur in which the potential difference with the positive electrode is reversed. In addition, there is a problem in that the structure is unfavorable for the electrolyte to penetrate the second negative electrode active material layer, which reduces electrolyte impregnation and may result in inferior rapid charging characteristics.

[0111] When the above range is satisfied, by including more pores in the upper layer of the two-layer cathode active material layer, the electrolyte can be smoothly impregnated into the second cathode active material layer in contact with the electrolyte, and the movement of lithium ions can be facilitated, allowing lithium ions to be rapidly inserted into and extracted from the cathode active material during charging and discharging. Accordingly, sufficient capacity can be achieved even when charging and discharging at high charging speeds, and lifespan characteristics can be excellent. In addition, by distributing relatively fewer pores in the lower layer, the first cathode active material layer, adhesion to the current collector can be improved, and the contact area between the cathode active materials included in the first cathode active material layer can be increased, thereby reducing cathode resistance. Furthermore, binder migration to the upper layer, the second cathode active material layer, can be suppressed, thereby improving lithium ion mobility and adhesion to the cathode current collector, enhancing lifespan characteristics, and allowing the SEI film to be formed uniformly.

[0112] The volume of pores included in the first cathode active material layer and the total volume of pores included in the first cathode active material layer and the second cathode active material layer can be controlled by the porosity, thickness, composition of the cathode active material, rolling conditions, etc. of the first cathode active material layer and the second cathode active material layer. That is, the volume of the pores does not depend solely on the porosity of each cathode active material layer, but can be controlled by organically adjusting various factors within the cathode.

[0113]

[0114] The first negative active material layer may have a porosity of 15 to 30%. Specifically, the first negative active material layer may have a porosity of 15% or more, 15.5% or more, 16% or more, 16.5% or more, 17% or more, 17.5% or more, 18% or more, 18.5% or more, 19% or more, 19.5% or more, 20% or more, 20.5% or more, 21% or more, 21.5% or more, 22% or more, 30% or less, 29% or less, 28% or less, 27% or less, 26% or less, 25.5% or less, 25% or less, 24.5% or less, 24% or less, 23.5% or less, 23% or less, 22.5% or less, or 22% or less. For example, the first negative electrode active material layer may have a porosity of 15 to 30%, 18 to 28%, 20 to 24%, or 21 to 23%. When the above range is satisfied, the negative electrode active materials can make smooth contact with each other and achieve high energy density.

[0115]

[0116] The thickness of the first cathode active material layer may be 35% to 50% of the total thickness of the first cathode active material layer and the second cathode active material layer. Specifically, the thickness of the first cathode active material layer may be 35% or more, 36% or more, 37% or more, 38% or more, 39% or more, 40% or more, 41% or more, 42% or more, 43% or more, 44% or more, 45% or more, 50% or less, 49% or less, 48% or less, 47% or less, 46% or less, 45% or less, 44% or less, 43% or less, 42% or less, 41% or less, or 40% or less. For example, the thickness of the first negative electrode active material layer may be 35% to 50%, 37% to 48%, 39% to 46%, or 41% to 45% with respect to the total thickness of the first negative electrode active material layer and the second negative electrode active material layer. When the above range is satisfied, the volume of pores included in the first negative electrode active material layer and the second negative electrode active material layer and the porosity of each negative electrode active material layer can be controlled to a desired range, which is advantageous in terms of energy density and can improve rapid charging characteristics.

[0117] The thickness of the first cathode active material layer may be 20 to 90 μm, 35 to 75 μm, or 45 to 65 μm. When the above range is satisfied, pores can be appropriately formed in the first cathode active material layer while achieving high energy density.

[0118]

[0119] The loading amount of the first negative electrode active material layer is 50 mg / 25 cm 2 Up to 160 mg / 25 cm 2 , 65mg / 25cm 2 Up to 145 mg / 25 cm 2 , or 85mg / 25cm 2 Up to 130 mg / 25 cm 2 It may be possible. If the above range is satisfied, the first cathode active material layer may have pores of an appropriate volume while exhibiting sufficient capacity.

[0120]

[0121] The second cathode active material layer comprises a second cathode active material including artificial graphite and a second silicon-based cathode active material.

[0122] Conventionally, carbon-based negative electrode active materials were used exclusively as negative electrode active materials; however, because carbon-based negative electrode active materials have low capacity and slow reaction rates with lithium, lithium secondary batteries utilizing them had limitations in realizing high capacity characteristics and rapid charging performance. Accordingly, the present invention improves the capacity characteristics and rapid charging characteristics of a lithium secondary battery by including a silicon-based negative electrode active material with a high theoretical capacity and a fast reaction rate with lithium in the second negative electrode active material layer.

[0123] In addition, artificial graphite has a lower tap density, lower structural flexibility, and higher strength compared to natural graphite. Accordingly, when artificial graphite is included in the second cathode active material layer, pore clogging occurs less frequently during the cathode rolling process, which is advantageous for the development of pore volume; thus, the volume of pores included in the second cathode active material layer can be set to a desired range.

[0124] The artificial graphite may be included in an amount of 80 to 99 weight%, 85 to 98.5 weight%, or 90 to 98 weight% based on the total weight of the second negative electrode active material. If the above range is satisfied, a balance can be achieved between capacity characteristics, rapid charging characteristics, and lifespan characteristics.

[0125]

[0126] The above second silicon-based negative electrode active material is silicon (Si) and silicon oxide (SiO₂). x (0 <x<2)로 표시될 수 있음) 및 Si / C 복합체(Si / C Composite)로 이루어진 군에서 선택된 적어도 1종을 포함할 수 있고, 바람직하게는 Si / C 복합체를 포함할 수 있다. 또는 상기 제2 실리콘계 음극 활물질은 Si / C 복합체일 수 있다.

[0127] The above Si / C composite may include silicon particles embedded within a carbon matrix, rather than in a state where Si and carbon (C) are simply aggregated or mixed. The carbon matrix may be a porous carbon matrix.

[0128] When the second silicon-based negative electrode active material includes a Si / C composite, the degree of volume expansion during charging and discharging may be smaller compared to silicon, thereby suppressing the degradation of lifespan characteristics during charging and discharging, and the capacity characteristics and electrical conductivity may be superior compared to silicon oxide. Therefore, when the second silicon-based negative electrode active material includes a Si / C composite, it has the advantage of improving cycle performance during rapid charging while realizing high capacity characteristics of the lithium secondary battery.

[0129] The above second silicon-based negative electrode active material is D 50 This can be 5㎛ to 15㎛, 6㎛ to 11㎛, or 7㎛ to 9㎛. When the above range is satisfied, the cathode electrode density is increased, and high energy density can be achieved.

[0130]

[0131] The second silicon-based negative electrode active material may be included in an amount of 1 to 20 weight percent based on the total weight of the second negative electrode active material. Specifically, the second silicon-based negative electrode active material is, based on the total weight of the second negative electrode active material, 1 wt% or more, 1.3 wt% or more, 1.5 wt% or more, 1.8 wt% or more, 2 wt% or more, 2.3 wt% or more, 2.5 wt% or more, 2.8 wt% or more, 3 wt% or more, 3.3 wt% or more, 3.5 wt% or more, 3.8 wt% or more, 4 wt% or more, 4.3 wt% or more, 4.5 wt% or more, 4.8 wt% or more, 5 wt% or more, 20 wt% or less, 19 wt% or less, 18 wt% or less, 17 wt% or less, 16 wt% or less, 15 wt% or less, 14 wt% or less, 13 wt% or less, 12 wt% or less, 11 wt% or less, 10 wt% or less, 9 wt% or less, 8 wt% or less, 7 wt% or less, It may be included in an amount of 6% by weight or less, or 5% by weight or less. For example, the second silicon-based negative electrode active material may be included in an amount of 1 to 20% by weight, 1.5 to 15% by weight, 2 to 10% by weight, or 3 to 7% by weight based on the total weight of the second negative electrode active material. When the above range is satisfied, sufficient pores within the second negative electrode active material layer are secured to mitigate lifespan degradation caused by volume expansion of the silicon-based negative electrode active material, excellent conductivity, and prevention of degradation of lifespan characteristics even during rapid charging.

[0132]

[0133]

[0134] The second silicon-based negative electrode active material and the artificial graphite may be included 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 the above ranges are satisfied, the capacity characteristics, rapid charging characteristics, and lifespan characteristics may all be excellent.

[0135]

[0136] The second negative electrode active material may be included in an amount of 80 to 99.9 weight%, more preferably 90 to 99.7 weight%, more preferably 93 to 99.5 weight%, or 95 to 99 weight% based on the total weight of the second negative electrode active material layer. When the content of the negative electrode active material satisfies the above range, excellent energy density can be achieved.

[0137]

[0138] The second cathode active material layer may further include a second cathode conductive material and / or a second cathode binder.

[0139] The second cathode conductive material is used to impart conductivity to the cathode, and in the battery being constructed, it may be used without special limitations as long as it has electronic conductivity without causing chemical changes. Specific examples include carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, carbon nanotube; metal powders or metal fibers such as copper, nickel, aluminum, silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used.

[0140] The second cathode conductive material may be included in an amount of 0.1 to 10 weight%, 0.1 to 8 weight%, or 0.1 to 5 weight% based on the total weight of the second cathode active material layer.

[0141] The second cathode binder described above serves to improve adhesion between cathode active material particles and adhesion between the cathode active material and the cathode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0142] The second cathode binder may be included in an amount of 0.1 to 10 weight%, 0.5 to 10 weight%, or 1 to 8 weight% based on the total weight of the second cathode active material layer.

[0143]

[0144] The above second negative electrode active material layer may have a porosity of 20% to 35%. Specifically, the second negative electrode active material layer has a porosity of 20% or more, 21% or more, 22% or more, 23% or more, 24% or more, 25% or more, 25.5% or more, 26% or more, 26.5% or more, 27% or more, 27.5% or more, 28% or more, 28.5% or more, 29% or more, 29.5% or more, 30% or more, 30.5% or more, 31% or more, 31.5% or more, 32% or more, 35% or less, 34.5% or less, 34% or less, 33.5% or less, 33% or less, 32.5% or less, 32% or less, 31.5% or less, 31% or less, 30.5% or less, 30% or less, 29.5% or less, 29% or less, 28.5% or less, Or it may be 28% or less. For example, the porosity of the second negative electrode active material layer may be 20% to 35%, 22% to 33%, 24% to 31%, 26% to 30%, or 27% to 29%. When the above range is satisfied, pores are sufficiently developed within the second negative electrode active material layer, making electrolyte impregnation easy. Accordingly, the movement of lithium ions is facilitated, allowing lithium ions to rapidly insert and extract from the negative electrode active material repeatedly, thereby improving rapid charging characteristics.

[0145] The entire first cathode active material layer and the second cathode active material layer may have a porosity of 20 to 30%, 23% to 27%, or 24% to 26%. When the above range is satisfied, the density of the entire cathode is appropriate, and sufficient capacitance characteristics can be exhibited.

[0146]

[0147] The thickness of the second cathode active material layer may be 40 to 110 μm, 55 to 95 μm, or 65 to 85 μm. When the above range is satisfied, pores can be appropriately formed in the second cathode active material layer while achieving high energy density.

[0148]

[0149] The loading amount of the second negative electrode active material layer is 95 mg / 25 cm 2 Up to 205 mg / 25 cm 2 , preferably 110 mg / 25 cm 2 Up to 190 mg / 25 cm 2 , more preferably 130mg / 25cm 2 Up to 175 mg / 25 cm 2 It may be possible. If the above range is satisfied, the second negative active material layer may have pores of an appropriate volume while exhibiting sufficient capacity.

[0150]

[0151] The above-mentioned cathode can be manufactured by applying a first cathode active material layer slurry to one or both sides of a sheet-shaped cathode current collector, applying a second cathode active material layer slurry on the first cathode active material layer slurry, removing the solvent of the first cathode active material layer slurry and the second cathode active material layer slurry through a drying process, and then rolling. Meanwhile, a cathode including an uncoated portion can be manufactured by not applying the first cathode active material layer slurry and the second cathode active material layer slurry to a portion of the cathode current collector, for example, to one end of the cathode current collector, when applying the first cathode active material layer slurry and the second cathode active material layer slurry.

[0152] The first cathode active material layer slurry and the second cathode active material layer slurry can be prepared by dispersing the first cathode active material or the second cathode active material in a solvent such as distilled water, ethanol, methanol, or isopropyl alcohol.

[0153] Alternatively, the cathode may be manufactured by casting the first cathode active material layer slurry and the second cathode active material layer slurry onto separate supports, and then laminating the film obtained by peeling off from the supports onto a cathode current collector.

[0154]

[0155] lithium secondary battery

[0156] A lithium secondary battery according to the present invention comprises: an electrode assembly comprising the aforementioned negative electrode, a positive electrode, and a separator interposed between the negative electrode and the positive electrode; an electrolyte; and a battery case in which the electrode assembly and the electrolyte are housed.

[0157] The lithium secondary battery according to the present invention is not limited to the type of secondary battery, such as a pouch-type secondary battery, a cylindrical secondary battery, or a prismatic secondary battery, and preferably may be a cylindrical secondary battery.

[0158]

[0159] Hereinafter, each component of the lithium secondary battery according to the present invention will be described in detail.

[0160]

[0161] (1) Electrode assembly

[0162] The electrode assembly described above includes the aforementioned cathode, a positive electrode, and a separator interposed between the cathode and the positive electrode.

[0163] The above electrode assembly can be formed by sequentially stacking an anode, a separator, and a cathode, and the anode and cathode can be mutually insulated by the separator.

[0164] Specifically, the electrode assembly may be one in which an anode, a separator, and a cathode are sequentially stacked and wound in one direction.

[0165]

[0166] FIG. 1 illustrates a pre-winding laminated structure of an electrode assembly according to one embodiment of the present invention, FIG. 2 illustrates a cross-sectional structure of an electrode plate (anode or cathode) according to one embodiment of the present invention, and FIG. 3 illustrates a structure of an electrode assembly according to one embodiment of the present invention.

[0167] Referring to FIGS. 1 and 2, the electrode assembly (A) of the present invention can be manufactured by winding a laminate formed by sequentially stacking a separator (12), an anode (10), a separator (12), and a cathode (11) at least once in one direction (X).

[0168] At this time, the positive electrode (10) and the negative electrode (11) have a structure in which an active material layer (21) is formed on a sheet-shaped current collector (20), and may include a non-active portion (22) in which the active material layer (21) is not formed in a part of the current collector (20).

[0169] By using the positive electrode (10) and negative electrode (11) including the non-electrode portion (22) as described above, a battery structure can be implemented in which at least a portion of the non-electrode portion of the positive electrode (10) and negative electrode (11) defines the electrode tab without having a separate electrode tab.

[0170] Specifically, the above-mentioned non-circular portion (22) can be formed lengthwise along the winding direction (X) at one end of the current collector (20), and by attaching a current collecting plate to each of the positive non-circular portion and the negative non-circular portion and connecting the current collecting plate to an electrode terminal, it can function as an electrode tab.

[0171] For example, a battery in which the positive and negative electrode non-existent sections function as electrode tabs can be manufactured through the following method. First, a separator, a positive electrode, a separator, and a negative electrode are sequentially stacked so that the positive and negative electrode non-existent sections are positioned in opposite directions, and then wound in one direction to manufacture a jelly-roll type electrode assembly. Then, the positive and negative electrode non-existent sections are folded in the direction of the winding center (C), and current collection plates are welded to the positive and negative electrode non-existent sections, respectively, to join them. The battery is then manufactured by connecting the current collection plates to electrode terminals. Since the current collection plates have a larger cross-sectional area compared to strip-type electrode tabs and resistance is inversely proportional to the cross-sectional area of ​​the current flow path, the cell resistance can be significantly reduced when the secondary battery is formed with such a structure.

[0172] Meanwhile, the above-mentioned positive and negative electrode uncoated portions may be processed into a plurality of segmented portions that can be independently bent, and at least some of the plurality of segmented portions may be bent toward the winding center (C) of the electrode assembly.

[0173] The above segments can be formed by processing the current collectors of the anode and cathode through metal foil cutting processes such as laser notching, ultrasonic cutting, and stamping.

[0174] When the uncoated portions of the anode and cathode are processed into multiple segmented forms, the stress applied to the uncoated portions during bending can be reduced, thereby preventing deformation or damage to the uncoated portions and improving welding characteristics with the current collector plate.

[0175] The current collector plate and the non-current portion are generally joined by welding; however, to improve welding characteristics, strong pressure must be applied to the weld area of ​​the non-current portion to bend it as flat as possible. During this bending process, the shape of the non-current portion may become irregularly distorted and deformed, and the deformed area may come into contact with the electrode of opposite polarity, causing an internal short circuit or inducing microcracks in the non-current portion. However, if the non-current portions of the positive and negative electrodes are processed into multiple segments that can be bent independently, the stress applied to the non-current portion during bending is alleviated, thereby minimizing deformation and damage to the non-current portion.

[0176] In addition, when the uncoated portion is processed into a segmented form as described above, overlap occurs between multiple segmented pieces during bending, which increases the welding strength with the current collection plate and prevents the problem of the laser penetrating into the electrode assembly and melting the separator or active material when using the latest technology such as laser welding. Preferably, at least some of the bent multiple segmented pieces may overlap on the upper and lower ends of the electrode assembly, and a current collection plate may be coupled on the overlapped multiple segmented pieces.

[0177] Meanwhile, the electrode assembly according to the present invention may be formed with a structure in which an insulating layer (24) is additionally formed on the anode (10), as shown in FIG. 3. Specifically, the insulating layer (24) may be formed to cover a part of the anode active material layer and a part of the uncoated portion along a direction parallel to the winding direction of the electrode assembly.

[0178] In the case of a tap-less battery structure using the non-existent portion (22c) of the positive electrode (10) and the non-existent portion (22a) of the negative electrode (11) as electrode tabs, an electrode assembly is formed so 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 combined with a current collector plate. However, 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) is positioned close to the electrode of the opposite polarity beyond the separator, and as a result, the positive electrode and the negative electrode come into electrical contact, which may cause an internal short circuit. However, as shown in FIG. 3, if an insulating layer (24) covering a portion of the positive active material layer and the uninsulated portion is formed, the positive electrode (10) and the negative electrode (11) can be prevented from coming into electrical contact by the insulating layer (24), thereby preventing a short circuit from occurring inside the battery.

[0179] Preferably, the insulating layer (24) may be provided on at least one surface of the positive electrode (10) current collector, and preferably, may be provided on both surfaces of the positive electrode (10).

[0180] Additionally, the insulating layer (24) may be formed in an area of ​​the positive electrode (10) that is likely to face the active material layer (21a) of the negative electrode (11). For example, in the non-bending portion (22c) of the positive electrode (10) that faces the negative electrode (11) after being folded, the insulating layer (24) may be formed extending to the end of the non-bending portion (22c). However, in the case of the opposite side of the surface facing the negative electrode (11) after being folded, it is preferable that the insulating layer (24) be formed only in a part of the non-bending portion (22c), for example, up to the folding point of the non-bending portion (22c). This is because if the insulating layer (24) is formed in the entire non-bending portion of the opposite side facing the negative electrode (11), electrical contact with the current collection plate is impossible, and thus it cannot function as an electrode tab.

[0181] Meanwhile, the insulating layer (24) can be attached to the anode while ensuring insulating performance, and its material or composition is not particularly limited. For example, the insulating layer may be an insulating coating layer or an insulating tape, and the insulating coating layer may include an organic binder and inorganic particles. In this case, the organic binder may be, for example, styrene-butadiene rubber (SBR), and the inorganic particles may be alumina oxide, but are not limited thereto.

[0182]

[0183] Hereinafter, each component of the electrode assembly of the present invention will be described in more detail. Since the cathode is the same as previously described, a specific description is omitted.

[0184]

[0185] 1) Anode

[0186] The above positive electrode may include a positive electrode current collector; and a positive electrode active material layer; and the positive electrode active material layer may include a positive electrode active material.

[0187]

[0188] Various positive current collectors used in the relevant technical field may be used as the positive current collector. For example, the positive current collector may be stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. The positive current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the positive current collector to increase the adhesion of the positive active material. The positive current collector may be used in various forms, such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0189] The positive active material layer may be located on the positive current collector, and specifically, may be located on one or both sides of the positive current collector. The positive active material layer may be a single layer or a multilayer structure of two or more layers.

[0190] The above-mentioned positive active material may be any positive active material commonly used in the relevant technical field, and its type is not particularly limited. The above-mentioned positive active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, may include a lithium transition metal composite oxide comprising lithium and at least one transition metal composed of nickel, cobalt, manganese, and aluminum, preferably a lithium transition metal composite oxide comprising lithium and a transition metal comprising nickel, cobalt, and manganese.

[0191] Preferably, the positive electrode active material may include a lithium nickel-based oxide. The lithium nickel-based oxide may contain 80 mol% or more of nickel among the total metals excluding lithium. Specifically, the positive electrode active material may contain 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 of nickel among the total metals excluding lithium. When satisfying the above ranges, superior capacity characteristics can be achieved.

[0192] The above lithium nickel-based oxide may include nickel, cobalt, manganese, and aluminum. In this case, it may have excellent capacity and power characteristics, be stable at high potential, and possess excellent structural and thermal stability.

[0193] Specifically, the lithium nickel-based oxide can be represented by the following chemical formula 1.

[0194] [Chemical Formula 1]

[0195] Li 1+a1 [Nix1 Co y1 Mn z1 Al w1 M 1 r1 ]O2

[0196] In the above chemical formula 1, the M 1 may correspond to a doping element that partially substitutes a transition metal element included in lithium nickel-based oxides, and can play a role in improving structural stability by inhibiting the movement of nickel ions, thereby preventing the problem of nickel (Ni) valence changing from 2+ to 4+ and the problem of cation mixing. Specifically, the above M 1 It may be one or more doping elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and preferably one or more doping elements selected from the group consisting of W, Y, Ba, Ca, Ti, Mg, Ta, and Nb.

[0197] The above 1+a1 may represent the molar ratio of lithium (Li) in the lithium nickel-based oxide, and may be 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.

[0198] The above x1 may represent the molar ratio of nickel among all metals excluding lithium in the lithium nickel-based oxide particles, and may be 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, the nickel (Ni) content in the lithium nickel-based oxide is sufficient to contribute to charging and discharging, thereby enabling high capacity.

[0199] The above y1 may represent the molar ratio of cobalt among the total metals excluding lithium in the lithium nickel-based oxide particles, and 0 <y1<0.20, 0<y1≤0.10, 또는 0<y1≤0.08일 수 있다. 상기 범위를 만족하는 경우, Co 함량을 낮춤으로써 비용적인 이점을 가지면서, 양호한 저항 특성 및 출력 특성을 구현할 수 있고, 상대적으로 망간(Mn)의 비율을 높여 양극 활물질의 구조적 안정성을 향상시킬 수 있다.

[0200] The above z1 may refer to the molar ratio of Mn among the total metals excluding lithium in the lithium nickel-based oxide particles, and 0 <z1<0.20, 0<z1≤0.15, 0.001≤z1≤0.10, 또는 0.01≤z1≤0.08일 수 있다. 상기 범위를 만족할 경우, 양극 활물질의 구조적 안정성을 향상시킬 수 있다.

[0201] The above w1 represents the molar ratio of Al among the total metals excluding lithium in the lithium nickel-based oxide, where 0 <w1≤0.2, 0<w1≤0.10, 또는 0.01≤w1≤0.08일 수 있다. 상기 범위를 만족할 경우, 양극 활물질의 구조적 안정성 및 열적 안정성을 더욱 향상시킬 수 있다.

[0202] The above r1 is M among the total metals excluding lithium in the above lithium nickel-based oxide. 1 It represents the molar ratio of the elements, which may be 0≤r1≤0.1, specifically 0≤r1≤0.07, and more specifically 0≤r1≤0.05. When the above range is satisfied, it can play a role in promoting particle growth during the calcination of the positive active material or improving crystal structure stability.

[0203]

[0204] The form of the above lithium nickel-based oxide is not particularly limited and may be in the form of secondary particles in which more than 50 primary particles are aggregated, or in the form of single particles containing 50 or fewer nodules. If necessary, a combination of a positive electrode active material containing a secondary particle-type lithium nickel-based oxide and a positive electrode active material containing a single particle-type lithium nickel-based oxide may be used. In the case of a positive electrode active material containing a secondary particle-type lithium nickel-based oxide, resistance and capacity characteristics are excellent, and in the case of a positive electrode active material containing a single particle-type lithium nickel-based oxide, high temperature / high voltage stability and lifespan characteristics are excellent. Therefore, a lithium nickel-based oxide of an appropriate form can be selected and used considering the performance and specifications of the lithium secondary battery to be manufactured.

[0205] According to one embodiment, the lithium nickel-based oxide may be a single-particle lithium nickel-based oxide containing 50 or fewer nodules.

[0206] In the case of single-particle lithium nickel-based oxides, compared to secondary-particle lithium nickel-based oxides, there is less particle breakage due to rolling during cathode manufacturing and excellent structural stability under high temperature and / or high voltage conditions. Therefore, when single-particle lithium nickel-based oxides are applied, cathode degradation is reduced under high temperature and high voltage conditions, and there is less generation of fine particles after cathode manufacturing, resulting in less gas generation due to side reactions between fine particles and the electrolyte. Thus, when single-particle lithium nickel-based oxides are applied, it is advantageous for manufacturing lithium secondary batteries with long life characteristics.

[0207] Meanwhile, the above-mentioned single-particle lithium nickel-based oxide may preferably contain 50 or fewer nodules, preferably 30 or fewer, more preferably 1 to 25, and even more preferably 1 to 15 nodules. This is because if the above-mentioned single-particle lithium nickel-based oxide contains an excessive number of nodules, particle breakage increases during electrode manufacturing, and the occurrence of internal cracks due to volume expansion / contraction of nodules during charging and discharging increases, which may result in inferior high-temperature life characteristics and high-temperature storage characteristics.

[0208] The above positive active material may be included in an amount of 80% to 99% by weight, preferably 92% to 98.5% by weight, based on the total weight of the positive active material layer, taking into consideration the sufficient capacity exertion of the positive active material.

[0209] Meanwhile, the above positive active material layer may optionally further include at least one of a positive conductive material and a positive binder.

[0210] The above-mentioned positive electrode conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it may be used without special limitations as long as it possesses electronic conductivity without causing chemical changes. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, carbon nanotube; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used. The above-mentioned positive electrode conductive material may typically be included in an amount of 1 to 30 weight%, preferably 1 to 20 weight%, and more preferably 1 to 10 weight% based on the total weight of the positive electrode active material layer.

[0211] The above-mentioned anode binder serves to improve adhesion between anode material particles and adhesion between the anode material and the anode current collector. Specific examples include fluoropolymer-based binders comprising polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber-based binders comprising styrene butadiene rubber (SBR), acrylonitrile-butadiene rubber, or styrene-isoprene rubber; cellulose-based binders comprising carboxyl methyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; polyalcohol-based binders comprising polyvinyl alcohol; polyolefin-based binders comprising polyethylene or polypropylene; polyimide-based binders; and polyester-based binders. Examples include silane-based binders, and one of these alone or a mixture of two or more may be used. The anode binder may be included in an amount of 1 to 30 weight%, preferably 1 to 20 weight%, and more preferably 1 to 10 weight% based on the total weight of the anode active material layer.

[0212]

[0213] The above anode can be manufactured by applying an anode slurry to one or both sides of a sheet-shaped anode current collector, removing the solvent of the anode slurry through a drying process, and then rolling. Meanwhile, an anode including an uncoated portion can be manufactured by not applying the anode slurry to a portion of the anode current collector, for example, one end of the anode current collector, when applying the anode slurry.

[0214] In addition, the anode slurry can be prepared by dispersing the anode material according to the present invention in a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water.

[0215]

[0216] 2) Separator

[0217] The above separator is interposed between the anode and the cathode.

[0218] The above separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions; any separator typically used as a separator in a lithium secondary battery can be used without any special restrictions. Specifically, the above separator may be a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength.

[0219]

[0220] (2) Electrolyte

[0221] The electrolyte according to the present invention may include a lithium salt and an organic solvent.

[0222] The above lithium salt can be used without special limitations as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably used within the range of 0.1 to 5.0 M, more preferably 0.1 to 3.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and allow lithium ions to move effectively.

[0223]

[0224] The above organic solvent may include at least one of a cyclic carbonate-based organic solvent, a linear carbonate-based organic solvent, a linear ester-based organic solvent, and a cyclic ester-based organic solvent.

[0225] The above-mentioned cyclic carbonate-based organic solvent is a high-viscosity organic solvent and may include at least one organic solvent selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate.

[0226] In addition, the above-mentioned linear carbonate-based organic solvent is an organic solvent having low viscosity and low dielectric constant, and as a representative example, at least one organic solvent selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate may be used, and specifically, it may include ethylmethyl carbonate (EMC).

[0227] Specific examples of the above linear ester-based organic solvent may include 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.

[0228] The above-mentioned cyclic ester-based organic solvent may include at least one organic solvent selected from the group consisting of butyrolactone, valerolactone, and caprolactone.

[0229] Preferably, the electrolyte according to the present invention may include ethylene carbonate and dimethyl carbonate as organic solvents.

[0230]

[0231] Meanwhile, in addition to the electrolyte components, the above electrolyte may additionally include other additives for the purpose of improving the lifespan characteristics of the battery, suppressing the reduction of battery capacity, and improving the discharge capacity of the battery.

[0232] These other additives may include at least one other additive selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sulfone compounds, sulfate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds different from the lithium salt contained in the electrolyte, as representative examples.

[0233] Specifically, the above other additives are vinylene carbonate (VC), vinylethylene carbonate, fluoroethylene carbonate (FEC), 1,3-propane sulfone (PS), 1,4-butane sulfone, ethene sulfone, 1,3-propene sulfone (PRS), 1,4-butene sulfone, 1-methyl-1,3-propene sulfone, ethylene sulfate (ESA), trimethylene sulfate (TMS), methyl trimethylene sulfate (MTMS), tetraphenyl borate, lithium oxalyl difluoroborate, succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, Examples include one or more compounds selected from the group consisting of 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(trifluoromethane sulfonyl)imide, LiTFSI), LiPO2F2, LiODFB, LiBOB (lithium bis-oxalate toborate (LiB(C2O4)2)) and LiBF4.

[0234] The above other additives may be included in an amount of 0.01 to 20 weight% based on the total weight of the electrolyte, and preferably in an amount of 0.05 to 5.0 weight%. If the content of the above other additives is less than 0.01 weight%, the effect of improving low-temperature output, high-temperature storage characteristics, and high-temperature life characteristics of the battery is negligible, and if the content of the above other additives exceeds 20 weight%, there is a possibility that excessive side reactions may occur within the electrolyte during charging and discharging of the battery. In particular, when the above SEI film-forming additives are added in excess, they may not decompose sufficiently at high temperatures and may remain as unreacted substances or precipitated within the electrolyte at room temperature. Accordingly, side reactions that degrade the lifespan or resistance characteristics of the secondary battery may occur.

[0235]

[0236] (3) Battery case

[0237] The above battery case may be a can-type battery case, a pouch-type battery case, etc. used in the relevant technical field.

[0238] Specifically, the battery case may be a can-type battery case. The can-type battery case may be either a prismatic battery case or a cylindrical battery case. More specifically, the battery case may be a cylindrical battery case. However, it is not limited thereto, and the lithium secondary battery according to the present invention may use various battery cases depending on the situation.

[0239] Specifically, the lithium secondary battery according to the present invention may be 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, 0.4 to 0.8, or 0.5 to 0.8. When the above range is satisfied, high capacity characteristics can be realized. Hereinafter, the ratio of the diameter (R) of the lithium secondary battery to the height (h) of the lithium secondary battery is referred to as the form factor.

[0240] The lithium secondary battery according to the present invention may be, for example, a 46110 cell (diameter 46 mm, height 110 mm, form factor ratio 0.418), a 4875 cell (diameter 48 mm, height 75 mm, form factor ratio 0.640), a 48110 cell (diameter 48 mm, height 110 mm, form factor ratio 0.436), a 4880 cell (diameter 48 mm, height 80 mm, form factor ratio 0.600), or a 4680 cell (diameter 46 mm, height 80 mm, form factor ratio 0.575). In the numerical value representing the form factor, the first two digits represent the diameter of the lithium secondary battery, and the next two or three digits represent the height of the lithium secondary battery.

[0241]

[0242] Next, an embodiment of a lithium secondary battery according to the present invention will be described.

[0243] Embodiments of a lithium secondary battery according to the present invention are disclosed in FIGS. 4 and FIGS. 5. Hereinafter, a lithium secondary battery according to the present invention will be described with reference to FIGS. 4 and FIGS. 5. However, FIGS. 4 and FIGS. 5 are merely examples of embodiments of the present invention, and the structure of the battery of the present invention is not limited to the range disclosed in FIGS. 4 and FIGS. 5.

[0244]

[0245] FIG. 4 shows a cross-sectional view of a lithium secondary battery according to one embodiment of the present invention.

[0246] Referring to FIG. 4, a lithium secondary battery (140) according to the present invention may include an electrode assembly (141), a battery can (142) in which the electrode assembly (141) and an electrolyte (not shown) are housed, and a sealing body (143) that seals the open end of the battery can (142).

[0247] In this case, the electrode assembly is formed by sequentially stacking an anode, a separator, and a cathode and winding them in one direction. Additionally, the anode and cathode of the electrode assembly each include a blank portion where an active material layer is not formed, and the anode blank portion and cathode blank portion may be stacked and wound such that they are located at the top and bottom of the electrode assembly, respectively. Since the electrode assembly has been described above, only the remaining components excluding the electrode assembly will be described below.

[0248] Meanwhile, the battery can (142) is a can-shaped container with an open end formed at the top and is made of a conductive metal material such as aluminum or steel. The battery can accommodates an electrode assembly (141) in the inner space through the upper open end and also accommodates an electrolyte (not shown).

[0249] Meanwhile, it is preferable that the lithium secondary battery (140) of the present invention does not include a current interruption device (CID).

[0250] Meanwhile, as shown in FIG. 4, the battery can (142) is electrically connected to the non-negative portion (146b) of the negative electrode and can function as a negative terminal that contacts an external power source to transmit current applied from the external power source to the negative electrode.

[0251] If necessary, a beading portion (147) and a crimping portion (148) may be provided on the top of the battery can (142). The beading portion (147) may be formed by pressing the outer circumference of the battery can (142) to a distance of D1. The beading portion (147) prevents the electrode assembly (141) housed inside the battery can (142) from escaping through the top opening of the battery can (142) and may function as a support portion on which the seal (143) is seated.

[0252] The above-mentioned crimping portion (148) may be formed on the upper part of the above-mentioned beading portion (147) and has an extended and bent shape to wrap around the outer surface of the cap plate (143a) placed on the beading portion (147) and a part of the upper surface of the cap plate (143a).

[0253]

[0254] Next, the seal (143) is intended to seal the open end of the battery can (142) and includes a cap plate (143a), a first gasket (143b) that provides airtightness and insulation between the cap plate (143a) and the battery can (142), and, if necessary, may further include a connecting plate (143c) electrically and mechanically coupled to the cap plate (143a). The cap plate (143a) is pressed onto a beading portion (147) formed on the battery can (142) and may be secured by a crimping portion (148).

[0255] The cap plate (143a) is a component made of a conductive metal material and covers the upper opening of the battery can (142). The cap plate (143a) is electrically connected to the positive electrode of the electrode assembly (141) and is electrically insulated from the battery can (142) through the first gasket (143b). Thus, the cap plate (143a) can function as a positive terminal of a lithium secondary battery. The cap plate (143a) may have a formed protrusion (143d) protruding upward from its center C, and the protrusion (143d) may come into contact with an external power source to allow current to be applied from the external power source.

[0256] A first gasket (143b) may be interposed between the cap plate (143a) and the crimping portion (148) to ensure airtightness of the battery can (142) and to provide electrical insulation between the battery can (142) and the cap plate (143a).

[0257] Meanwhile, the lithium secondary battery (140) according to the present invention may further include a current collection plate (144, 145) as needed. The current collection plate is coupled to a positive electrode uncoated portion (146a) and a negative electrode uncoated portion (146b) and is connected to electrode terminals (i.e., positive terminal and negative terminal).

[0258] Specifically, the lithium secondary battery (140) according to the present invention may include a first current collection plate (144) coupled to the upper part of an electrode assembly (141) and a second current collection plate (145) coupled to the lower part of the electrode assembly (141).

[0259] It may further include a first current collector plate (144) and / or a second current collector plate (145).

[0260] The first current collector plate (144) is coupled to the upper part of the electrode assembly (141). The first current collector plate (144) is made of a conductive metal material such as aluminum, copper, nickel, etc., and is electrically connected to the non-conductive portion (146a) of the anode. A lead (149) may be connected to the first current collector plate (144). The lead (149) may extend upward from the electrode assembly (141) and be coupled to the connecting plate (143c) or directly coupled to the lower surface of the cap plate (143a). The coupling of the lead (149) and other parts may be achieved through welding. Preferably, the first current collector plate (144) may be formed integrally with the lead (149). In this case, the lead (149) may have a plate shape extending outward from the center of the first current collector plate (144).

[0261] Meanwhile, the first current collector plate (144) is coupled to the end of the non-positive portion (146a) of the anode, and the coupling can be achieved by methods such as, for example, laser welding, resistance welding, ultrasonic welding, soldering, etc.

[0262] The second current collector plate (145) is coupled to the lower part of the electrode assembly (141). The second current collector plate (145) is made of a conductive metal material such as aluminum, copper, nickel, etc., and is electrically connected to the non-conductive portion (146b) of the negative electrode. One side of the second current collector plate (145) can be coupled to the non-conductive portion (146b) of the negative electrode, and the opposite side can be coupled to the inner bottom surface of the battery can (142). At this time, the coupling can be achieved by methods such as laser welding, resistance welding, ultrasonic welding, or soldering.

[0263] Meanwhile, the lithium secondary battery (140) according to the present invention may further include an insulator (146) as needed. The insulator (146) may be positioned to cover the upper surface of the first current collector plate (144). By the insulator (146) covering the first current collector plate (144), direct contact between the first current collector plate (144) and the inner surface of the battery can (142) can be prevented.

[0264] The insulator (146) is provided with a lead hole (151) so that a lead (149) extending upward from the first current collection plate (144) can be drawn out. The lead (149) is drawn out upward through the lead hole (151) and coupled to the lower surface of the connecting plate (143c) or the lower surface of the cap plate (143a).

[0265] The insulator (146) may be made of an insulating polymer resin, such as polyethylene, polypropylene, polyimide, or polybutylene terephthalate.

[0266] Meanwhile, the lithium secondary battery (140) according to the present invention may further include a venting portion (152) formed on the lower surface of the battery can (142) as needed. The venting portion (152) corresponds to an area on the lower surface of the battery can (142) that has a thinner thickness compared to the surrounding area. Because the venting portion (152) has a thin thickness, it is structurally weaker compared to the surrounding area. Therefore, when the pressure inside the lithium secondary battery (140) increases above a certain level, the venting portion (152) ruptures, allowing the gas inside the battery can (152) to be discharged to the outside, thereby preventing the battery from exploding.

[0267]

[0268] FIG. 5 shows a cross-sectional view of a lithium secondary battery according to another embodiment of the present invention.

[0269] Referring to FIG. 5, a lithium secondary battery (170) according to another embodiment of the present invention has a different structure of the battery can and seal compared to the lithium secondary battery (140) shown in FIG. 4, and the composition of the electrode assembly and electrolyte is substantially the same.

[0270] Specifically, a lithium secondary battery (170) according to another embodiment of the present invention comprises a battery can (171) through which a rivet terminal (172) is installed. The rivet terminal (172) is installed on a partially closed closed surface (upper surface of the drawing) at one end of the battery can (171). The rivet terminal (172) is riveted into a through hole (first opening at the first end) of the battery can (171) with an insulating second gasket (173) interposed therein. The rivet terminal (172) is exposed to the outside in a direction opposite to the direction of gravity.

[0271] 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 in the center of the partially closed surface of the battery can (171). The maximum diameter of the terminal exposure portion (172a) may be formed to be larger than the maximum diameter of the through hole formed in the battery can (171). The terminal insertion portion (172b) may penetrate approximately in the center of the closed surface of the battery can (171) and be electrically connected to the non-positive portion (146a) of the positive electrode. The terminal insertion portion (172b) may be rivet-joined onto the inner surface of the battery can (171). That is, the end of the terminal insertion portion (172b) may have a curved shape toward the inner surface of the battery can (171). The maximum diameter of the end of the terminal insertion part (172b) may be larger than the maximum diameter of the through hole of the battery can (171).

[0272] The lower surface of the terminal insertion portion (172b) can be welded to the first current collector plate (144) connected to the non-positive portion (146a) of the positive electrode. An insulating cap (174) made of an insulating material can be interposed between the first current collector plate (144) and the inner surface of the battery can (171). The insulating cap (174) covers the upper portion of the first current collector plate (144) and the upper edge portion of the electrode assembly (141). This prevents the outer non-positive portion (B3) of the electrode assembly (141) from coming into contact with the inner surface of the battery can (171) having a different polarity and causing a short circuit. The terminal insertion portion (172b) of the rivet terminal (172) can be welded to the first current collector plate (144) by penetrating the insulating cap (174).

[0273] The second gasket (173) is interposed between the battery can (171) and the rivet terminal (172) to prevent the battery can (171) and the rivet terminal (172), which have opposite polarities, from coming into electrical contact. As a result, the upper surface of the battery can (171), which has a roughly flat shape, can function as the positive terminal of the lithium secondary battery (170).

[0274] The second gasket (173) includes a gasket exposure portion (173a) and a gasket insertion portion (173b). The gasket exposure portion (173a) is interposed between the terminal exposure portion (172a) of the rivet terminal (172) and the battery can (171). The gasket insertion portion (173b) is interposed between the terminal insertion portion (172b) of the rivet terminal (172) and the battery can (171). The gasket insertion portion (173b) can be deformed together with the terminal insertion portion (172b) during riveting and adhere to the inner surface of the battery can (171). The second gasket (173) may be made of, for example, an insulating polymer resin.

[0275] The gasket exposure portion (173a) of the second gasket (173) may have an extended shape to cover the outer surface of the terminal exposure portion (172a) of the rivet terminal (172). When the second gasket (173) covers the outer surface of the rivet terminal (172), it is possible to prevent a short circuit from occurring during the process of connecting electrical connection components, such as a busbar, to the upper surface of the battery can (171) and / or the rivet terminal (172). Although not shown in the drawing, the gasket exposure portion (173a) may have an extended shape to cover not only the outer surface of the terminal exposure portion (172a) but also a part of the upper surface.

[0276] In the case where the second gasket (173) is made of a polymer resin, the second gasket (173) can be joined to the battery can (171) and the rivet terminal (172) by heat fusion. In this case, the airtightness at the joint interface between the second gasket (173) and the rivet terminal (172) and the joint interface between the second gasket (173) and the battery can (171) can be enhanced. Meanwhile, in the case where the gasket exposure portion (173a) of the second gasket (173) has a shape that extends to the upper surface of the terminal exposure portion (172a), the rivet terminal (172) can be joined integrally with the second gasket (173) by insert injection.

[0277] The remaining area (175) of the upper surface of the battery can (171), excluding the area occupied by the rivet terminal (172) and the second gasket (173), corresponds to a negative terminal having opposite polarity to the rivet terminal (172).

[0278] The second current collector plate (176) is coupled to the lower part of the electrode assembly (141). The second current collector plate (176) is made of a conductive metal material such as aluminum, steel, copper, or nickel, and is electrically connected to the non-conductive portion (146b) of the negative electrode.

[0279] Preferably, the second current collector plate (176) is electrically connected to the battery can (171). To this end, at least a portion of the edge portion of the second current collector plate (176) may be interposed and fixed between the inner surface of the battery can (171) and the first gasket (178b). In one example, at least a portion of the edge portion of the second current collector plate (176) may be fixed to the beading portion (180) by welding while being supported on the bottom surface of the beading portion (180) formed at the bottom of the battery can (171). In a variation, at least a portion of the edge portion of the second current collector plate (176) may be directly welded to the inner wall surface of the battery can (171).

[0280] The second current collector plate (176) may have a plurality of irregularities (not shown) formed radially on a surface facing the non-contact portion (146b). When irregularities are formed, the second current collector plate (176) can be pressed to press the irregularities into the non-contact portion (146b).

[0281] Preferably, the ends of the second current collector plate (176) and the non-current portion (146b) can be joined by welding, for example, laser welding.

[0282] A sealing body (178) that seals the lower open end of a battery can (171) includes a cap plate (178a) and a first gasket (178b). The first gasket (178b) electrically separates the cap plate (178a) from the battery can (171). A crimping portion (181) secures the edge of the cap plate (178a) and the first gasket (178b) together. The cap plate (178a) is provided with a vent portion (179). The configuration of the vent portion (179) is substantially the same as that of the above-described embodiment.

[0283] Preferably, the cap plate (178a) is made of a conductive metal material. However, since a first gasket (178b) is interposed between the cap plate (178a) and the battery can (171), the cap plate (178a) does not have electrical polarity. The seal (178) seals the open end of the lower part of the battery can (171) and functions to release gas when the internal pressure of the battery cell (170) increases above a critical value.

[0284] Preferably, the rivet terminal (172), which is electrically connected to the non-positive portion (146a) of the positive electrode, is used as the positive electrode terminal. Additionally, the portion (175) of the upper surface of the battery can (171), which is electrically connected to the non-negative portion (146b) of the negative electrode through the second current collector plate (176), excluding the rivet terminal (172), is used as the negative electrode terminal. In this way, when two electrode terminals are located on the upper part of the lithium secondary battery, it is possible to place electrical connection components, such as busbars, on only one side of the lithium secondary battery (170). This can lead to simplification of the battery pack structure and improvement of energy density. Furthermore, since the portion (175) used as the negative electrode terminal has a roughly flat shape, a sufficient bonding area can be secured for bonding electrical connection components, such as busbars. Accordingly, the lithium secondary battery (170) can reduce the resistance at the bonding site of the electrical connection components to a desirable level.

[0285] When a lithium secondary battery is formed with a tabless structure as described above, the current concentration is less than that of a conventional battery equipped with electrode tabs, so the heat generated inside the battery can be effectively reduced, and accordingly, the thermal safety of the battery can be improved.

[0286]

[0287] Next, a battery pack comprising a lithium secondary battery as a unit cell according to the present invention will be described.

[0288] The lithium secondary battery of the present invention as described above can be used as a unit cell to manufacture a battery pack. Fig. 6 schematically illustrates the configuration of a battery pack according to an embodiment of the present invention. Referring to Fig. 6, the battery pack (3) according to an embodiment of the present invention includes an assembly in which lithium secondary batteries (1) are electrically connected and a pack housing (2) that accommodates the same. The lithium secondary battery (1) is a lithium secondary battery according to the embodiment described above. In the drawings, for convenience of drawing, components such as a busbar, a cooling unit, and an external terminal for electrically connecting the lithium secondary batteries (1) are omitted.

[0289] The above battery pack (3) can be mounted in a vehicle. The vehicle may be, for example, an electric vehicle, a hybrid vehicle, or a plug-in hybrid vehicle. The vehicle includes a four-wheeled vehicle or a two-wheeled vehicle.

[0290]

[0291] The present invention will be explained more specifically through the following specific embodiments.

[0292]

[0293] Examples and Comparative Examples

[0294] Example 1

[0295] A first cathode active material layer slurry was prepared by mixing a first cathode active material, a cathode conductive material, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water in a weight ratio of 98.15:0.05:0.9:0.9. At this time, a Si / C composite and natural graphite were mixed in a weight ratio of 15:85 and used as the first cathode active material, and single-walled carbon nanotubes were used as the cathode conductive material.

[0296] Next, a second cathode active material layer slurry was prepared by mixing the second cathode active material, the cathode conductive material, styrene-butadiene rubber (SBR), and carboxymethyl cellulose in water in a weight ratio of 98.1:0.1:0.9:0.9. At this time, a Si / C composite and artificial graphite were mixed in a weight ratio of 5:95 and used as the second cathode active material, and single-walled carbon nanotubes were used as the cathode conductive material.

[0297] A first cathode active material layer slurry prepared above was applied onto a copper current collector and dried at 80°C to form a first cathode active material layer, and then a second cathode active material layer slurry prepared above was applied onto the applied first cathode active material layer, dried at 80°C, and rolled to produce a cathode. In the cathode, the first cathode active material layer had a thickness of 60 μm and a porosity of 22%, and the second cathode active material layer had a thickness of 70 μm and a porosity of 28%. At this time, the pore volume contained in the first cathode active material layer and the pore volume contained in the second cathode active material layer were measured to have a ratio of 30:70.

[0298]

[0299] Example 2

[0300] A first cathode active material layer slurry was prepared by mixing a first cathode active material, a cathode conductive material, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water in a weight ratio of 98.15:0.05:0.9:0.9. At this time, a Si / C composite and natural graphite were mixed in a weight ratio of 15:85 and used as the first cathode active material, and single-walled carbon nanotubes were used as the cathode conductive material.

[0301] Next, a second cathode active material layer slurry was prepared by mixing the second cathode active material, the cathode conductive material, styrene-butadiene rubber (SBR), and carboxymethyl cellulose in water in a weight ratio of 98.1:0.1:0.9:0.9. At this time, a Si / C composite and artificial graphite were mixed in a weight ratio of 5:95 and used as the second cathode active material, and single-walled carbon nanotubes were used as the cathode conductive material.

[0302] A first cathode active material layer slurry prepared above was applied onto a copper current collector, and a second cathode active material layer slurry prepared above was applied onto the first cathode active material layer slurry. After drying at 80°C, the cathode was rolled. In the cathode, the first cathode active material layer had a thickness of 64 μm and a porosity of 26%, and the second cathode active material layer had a thickness of 66 μm and a porosity of 24%. At this time, the pore volume contained in the first cathode active material layer and the pore volume contained in the second cathode active material layer were measured to have a ratio of 24:76.

[0303]

[0304] Comparative Example 1

[0305] A first cathode active material layer slurry was prepared by mixing a first cathode active material, a cathode conductive material, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water in a weight ratio of 98.125:0.075:0.9:0.9. At this time, a Si / C composite and natural graphite were mixed in a weight ratio of 10:90 and used as the first cathode active material, and single-walled carbon nanotubes were used as the cathode conductive material.

[0306] Next, a second cathode active material layer slurry was prepared by mixing the second cathode active material, the cathode conductive material, styrene-butadiene rubber (SBR), and carboxymethyl cellulose in water in a weight ratio of 98.125:0.075:0.9:0.9. At this time, a Si / C composite and artificial graphite were mixed in a weight ratio of 10:90 and used as the second cathode active material, and single-walled carbon nanotubes were used as the cathode conductive material.

[0307] A first active material layer slurry prepared above was applied onto a copper current collector, and a second negative active material layer slurry prepared above was applied onto the first negative active material layer slurry. After drying at 80°C, the negative was rolled to produce a negative. In the negative, the first negative active material layer had a thickness of 65 μm and a porosity of 25%, and the second negative active material layer had a thickness of 65 μm and a porosity of 25%. At this time, the pore volume contained in the first negative active material layer and the pore volume contained in the second negative active material layer were measured to have a ratio of 50:50.

[0308]

[0309] Comparative Example 2

[0310] A first cathode active material layer slurry was prepared by mixing a first cathode active material, a cathode conductive material, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water in a weight ratio of 98.1:0.1:0.9:0.9. At this time, a Si / C composite and natural graphite were mixed in a weight ratio of 5:95 and used as the first cathode active material, and single-walled carbon nanotubes were used as the cathode conductive material.

[0311] Next, a second cathode active material layer slurry was prepared by mixing the second cathode active material, the cathode conductive material, styrene-butadiene rubber (SBR), and carboxymethyl cellulose in water in a weight ratio of 98.15:0.05:0.9:0.9. At this time, a Si / C composite and artificial graphite were mixed in a weight ratio of 15:85 and used as the second cathode active material, and single-walled carbon nanotubes were used as the cathode conductive material.

[0312] A first active material layer slurry prepared above was applied onto a copper current collector, and a second negative active material layer slurry prepared above was applied onto the first negative active material layer slurry. After drying at 98°C, the negative was rolled to produce a negative. In the negative, the first negative active material layer had a thickness of 70 μm and a porosity of 28%, and the second negative active material layer had a thickness of 60 μm and a porosity of 22%. At this time, the pore volume contained in the first negative active material layer and the pore volume contained in the second negative active material layer were measured to have a ratio of 70:30.

[0313]

[0314] Comparative Example 3

[0315] A first cathode active material layer slurry was prepared by mixing a first cathode active material, a cathode conductive material, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water in a weight ratio of 98.15:0.05:0.9:0.9. At this time, a Si / C composite and natural graphite were mixed in a weight ratio of 15:85 and used as the first cathode active material, and single-walled carbon nanotubes were used as the cathode conductive material.

[0316] Next, a second cathode active material layer slurry was prepared by mixing the second cathode active material, the cathode conductive material, styrene-butadiene rubber (SBR), and carboxymethyl cellulose in water in a weight ratio of 98.1:0.1:0.9:0.9. At this time, a Si / C composite and artificial graphite were mixed in a weight ratio of 5:95 and used as the second cathode active material, and single-walled carbon nanotubes were used as the cathode conductive material.

[0317] A first active material layer slurry prepared above was applied onto a copper current collector, and a second negative active material layer slurry prepared above was applied onto the first negative active material layer slurry. After drying at 80°C, the negative was rolled to produce a negative. In the negative, the first negative active material layer had a thickness of 60 μm and a porosity of 28%, and the second negative active material layer had a thickness of 70 μm and a porosity of 22%. At this time, the pore volume contained in the first negative active material layer and the pore volume contained in the second negative active material layer were measured to have a ratio of 70:30.

[0318]

[0319] Comparative Example 4

[0320] A first cathode active material layer slurry was prepared by mixing a first cathode active material, a cathode conductive material, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water in a weight ratio of 98.15:0.05:0.9:0.9. At this time, a Si / C composite and natural graphite were mixed in a weight ratio of 15:85 and used as the first cathode active material, and single-walled carbon nanotubes were used as the cathode conductive material.

[0321] Next, a second cathode active material layer slurry was prepared by mixing the second cathode active material, the cathode conductive material, styrene-butadiene rubber (SBR), and carboxymethyl cellulose in water in a weight ratio of 98.1:0.1:0.9:0.9. At this time, a Si / C composite and artificial graphite were mixed in a weight ratio of 5:95 and used as the second cathode active material, and single-walled carbon nanotubes were used as the cathode conductive material.

[0322] A first active material layer slurry prepared above was applied onto a copper current collector, and a second negative active material layer slurry prepared above was applied onto the first negative active material layer slurry. After drying at 80°C, the negative was rolled to produce a negative. In the negative, the first negative active material layer had a thickness of 55 μm and a porosity of 20%, and the second negative active material layer had a thickness of 75 μm and a porosity of 30%. At this time, the pore volume contained in the first negative active material layer and the pore volume contained in the second negative active material layer were measured to have a ratio of 10:90.

[0323]

[0324] Comparative Example 5

[0325] A first cathode active material layer slurry was prepared by mixing a first cathode active material, a cathode conductive material, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water in a weight ratio of 98.15:0.05:0.9:0.9. At this time, a Si / C composite and natural graphite were mixed in a weight ratio of 5:95 and used as the first cathode active material, and single-walled carbon nanotubes were used as the cathode conductive material.

[0326] Next, a second cathode active material layer slurry was prepared by mixing the second cathode active material, the cathode conductive material, styrene-butadiene rubber (SBR), and carboxymethyl cellulose in water in a weight ratio of 98.1:0.1:0.9:0.9. At this time, a Si / C composite and artificial graphite were mixed in a weight ratio of 15:85 and used as the second cathode active material, and single-walled carbon nanotubes were used as the cathode conductive material.

[0327] A first active material layer slurry prepared above was applied onto a copper current collector, and a second negative active material layer slurry prepared above was applied onto the first negative active material layer slurry. After drying at 80°C, the negative was rolled to produce a negative. In the negative, the first negative active material layer had a thickness of 60 μm and a porosity of 22%, and the second negative active material layer had a thickness of 70 μm and a porosity of 28%. At this time, the pore volume contained in the first negative active material layer and the pore volume contained in the second negative active material layer were measured to have a ratio of 30:70.

[0328]

[0329] Comparative Example 6: Satisfies Main Compositions 2 and 3 + includes artificial graphite in the first layer and natural graphite in the second layer

[0330] A first cathode active material layer slurry was prepared by mixing a first cathode active material, a cathode conductive material, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water in a weight ratio of 98.15:0.05:0.9:0.9. At this time, a Si / C composite and artificial graphite were mixed in a weight ratio of 15:85 and used as the first cathode active material, and single-walled carbon nanotubes were used as the cathode conductive material.

[0331] Next, a second cathode active material layer slurry was prepared by mixing the second cathode active material, the cathode conductive material, styrene-butadiene rubber (SBR), and carboxymethyl cellulose in water in a weight ratio of 98.1:0.1:0.9:0.9. At this time, a Si / C composite and natural graphite were mixed in a weight ratio of 5:95 and used as the second cathode active material, and single-walled carbon nanotubes were used as the cathode conductive material.

[0332] A first cathode active material layer slurry prepared above was applied onto a copper current collector, and a second cathode active material layer slurry prepared above was applied onto the first cathode active material layer slurry. After drying at 80°C, the cathode was rolled. In the cathode, the first cathode active material layer had a thickness of 60 μm and a porosity of 22%, and the second cathode active material layer had a thickness of 70 μm and a porosity of 28%. At this time, the pore volume contained in the first cathode active material layer and the pore volume contained in the second cathode active material layer were measured to have a ratio of 28:72.

[0333]

[0334] The characteristics of the cathodes prepared in the above examples and comparative examples are shown in Table 1 below. At this time, the volume of pores in the first cathode active material layer and the volume of pores and porosity in the second cathode active material layer of the cathodes prepared in the above examples and comparative examples were measured by the following method.

[0335] - Pore volume: The cathodes prepared in the above examples and comparative examples are cross-sectionally cut using an ion milling device utilizing an Ar+ ion beam (Manufacturer: Hitachi, Product name: Ar blade5000, Acceleration voltage: 6 kV, Ion beam current: 350 μA). The first cathode active material layer and the second cathode active material layer are distinguished by comprehensively considering the brightness difference according to the content of silicon-based active material in the scanning electron microscope (SEM) image of the cross-section of the cathode and the thickness of the first cathode active material layer and the second cathode active material layer. Subsequently, the volume is calculated for each of the first cathode active material layer and the second cathode active material layer from the nitrogen adsorption isotherm under a 77 K liquid nitrogen atmosphere obtained using BELSORP-MAX (MicrotracBEL corp.). At this time, the calculation was performed using a BJH (Barrett-Joyner-Halenda) plot for pores with a diameter of 2 nm to 185 nm.

[0336] - Porosity: The first cathode active material layer and the second cathode active material layer are separated by the same method as when measuring the volume of the pores, and the volume of each layer is calculated from the cross-sectional area of ​​the first cathode active material layer and the second cathode active material layer. Afterwards, the percentage of the volume of the pores relative to the total volume is calculated for each of the first cathode active material layer and the second cathode active material layer.

[0337] First cathode active material layer Second cathode active material layer Volume of pores included in the first cathode active material layer / Total volume of pores included in the entire first cathode active material layer and the second cathode active material layer (%) Si / C composite content in the first cathode active material (weight%) Porosity (%) Si / C composite content in the second cathode active material (weight%) Porosity (%) Example 1 152252830 Example 2 152652430 Comparative Example 1 1025102550 Comparative Example 2 528152270 Comparative Example 3 152852270 Comparative Example 4 152053010 Comparative Example 5 522152830 Comparative Example 6 152252828

[0338] Experimental Example 1: Cathode Performance Evaluation

[0339] (1) Curvature measurement

[0340] After preparing two cathodes of Examples 1 to 2 and Comparative Examples 1 to 6 prepared above, an electrode assembly was manufactured by interposing a separator between the two cathodes. The electrode assembly was placed in a battery case, an electrolyte not containing lithium salt (ethylene carbonate:ethyl methyl carbonate = 3:7 volume ratio) was injected, and the cell was aged for 24 hours to produce a symmetric coin cell. Subsequently, a current of 0.1 to 1,000,000 Hz and 10 mV was applied to the symmetric coin cell, and the curvature was measured according to Equation A below using a graph measured by Electrochemical Impedance Spectroscopy (EIS). The results are shown in Table 2 below.

[0341] - Equation A: Curvature (τ) = R / R th

[0342] In the above Equation A, R is the x-intercept value calculated by extrapolating the straight-line segment of the graph measured through EIS measurement, and R th is a value defined by the following equation B.

[0343] - Equation B: R th = (Thickness of 1st cathode active material layer + Thickness of 2nd cathode active material layer) (㎛) / (Electrolyte ion conductivity (S / cm) × Cathode area (cm²) 2 ) × Cathode porosity (%)

[0344]

[0345] (2) MP resistance measurement

[0346] The total sheet resistance of the cathodes prepared in Examples 1 to 2 and Comparative Examples 1 to 6, and the interface resistance between the first cathode active material layer and the current collector were measured using an MP resistor (Product name: RM2610, Manufacturer: HIOKI). The results are shown in Table 2 below.

[0347]

[0348] (3) Evaluation of electrolyte impregnation

[0349] An impregnation evaluation was performed on the cathodes prepared in Examples 1 to 2 and Comparative Examples 1 to 6 above. Specifically, the cathode was punched out to a size of 5 cm × 5 cm, then attached to a glass plate with tape so that the cathode adhered flatly, and a 10 µl syringe was filled with electrolyte without any air bubbles. Afterward, 1 µl of electrolyte was dropped onto the cathode attached to the glass plate, and the time until the surface of the cathode dried was measured to evaluate the electrolyte impregnation of each cathode.

[0350] At this time, the electrolyte used was prepared by adding 0.5 M LiPF6 and 0.5 M LiFSI to an organic solvent mixed with ethylene carbonate:ethylmethyl carbonate:dimethyl carbonate in a volume ratio of 20:5:75, and adding 3 wt% vinylene carbonate, 1 wt% propane sulfone, 0.2 wt% succinonitrile, 0.2 wt% methyl prop-2-yn-1-yl carbonate, and 0.2 wt% propargyl 1H-imidazole-1-carboxylate as additives. The results are shown in Table 2 below.

[0351]

[0352] Tortuosity Total surface resistance [mΩ·cm] Interface resistance [mΩ·cm] 2 ]Electrolyte impregnation [sec] Example 1 2.05244.406.9556 Example 22.05448.657.1365 Comparative Example 12.17294.1814.15184 Comparative Example 22.07480.1811.53175 Comparative Example 32.21595.6315.21254 Comparative Example 42.05649.127.9971 Comparative Example 52.05478.9810.3167 Comparative Example 62.19689.6613.24178

[0353] Referring to Table 2 above, it can be seen that the cathodes prepared in Examples 1 and 2 have significantly better flexibility, total sheet resistance, interfacial resistance, and electrolyte impregnation than the cathodes prepared in Comparative Examples 1 to 6.

[0354] Experimental Example 2: Evaluation of Initial Discharge Capacity

[0355] An electrode assembly was manufactured by interposing a separator between the negative electrode and the positive electrode prepared in Examples 1 to 2 and Comparative Examples 1 to 6 above, and then the assembly was placed inside a battery case, and then an electrolyte was injected into the battery case to manufacture a lithium secondary battery (coin pool cell).

[0356] The above-mentioned anode was manufactured by preparing an anode slurry by mixing lithium nickel-based oxide as the anode active material, single-walled carbon nanotubes as the conductive material, and polyvinylidene fluoride (PVDF) as the binder in a weight ratio of 97.6:0.6:1.8 in an N-methylpyrrolidone solvent, applying the anode slurry onto an aluminum current collector, drying it, and then rolling it. At this time, the lithium nickel-based oxide contains 93 mol% of nickel among the total metals excluding lithium, contains nickel, cobalt, manganese, and aluminum, and is a single-particle type particle.

[0357] The above electrolyte was prepared by adding 0.5 M LiPF6 and 0.5 M LiFSI to an organic solvent mixed in a volume ratio of 20:5:75 of ethylene carbonate:ethylmethyl carbonate:dimethyl carbonate, and added 3 wt% vinylene carbonate, 1 wt% propane sulfone, 0.2 wt% succinonitrile, 0.2 wt% methyl prop-2-yn-1-yl carbonate, and 0.2 wt% propargyl 1H-imidazole-1-carboxylate as additives.

[0358] The lithium secondary battery manufactured above was charged to 4.2V at a 0.2C C-rate and then discharged to 2.5V to perform an activation process. Afterward, the lithium secondary battery was charged to 4.2V at a 0.2C C-rate in CCCV mode (cut-off 0.005C) and discharged at 2.5V at 0.2C, and the capacity at the first discharge was measured as the initial capacity. The results are shown in Table 3 below.

[0359]

[0360] Experimental Example 3: Evaluation of Initial Resistance

[0361] A lithium secondary battery containing the negative electrodes of Examples 1 to 2 and Comparative Examples 1 to 6 prepared in Experimental Example 2 above was charged to 4.2V at 25°C under 0.2C conditions and then discharged to 2.5V to perform an activation process. Next, the battery was charged to 4.2V under CC-CV conditions (0.005C cut off) at 25°C under 0.5C (reference capacity 1C = 6.3mAh / g) to reach 100% SOC. Subsequently, the coin half cell discharged to 50% SOC was discharged at 25°C with a constant current of 0.5C for 10 seconds, the resulting voltage drop was measured, and the initial resistance (DCIR) was calculated using Ohm's law based on the measured value. The results are shown in Table 3 below.

[0362] Experimental Example 4: Evaluation of Rapid Charging Characteristics

[0363] A lithium secondary battery containing the negative electrodes of Examples 1 to 2 and Comparative Examples 1 to 6 prepared in Experimental Example 2 above was charged at 25°C under CC-CV conditions until it reached 4.2V (0.005C cut off), and discharged at a constant current of 1.0C until it reached 2.5V, thereby performing 124 charge-discharge cycles. The discharge capacity after 1 cycle and the discharge capacity after 124 cycles were measured. Then, the capacity retention rate was measured according to the following formula C. The results are shown in Table 3 below.

[0364] - Equation C: Capacity retention rate (%) = {Discharge capacity after 124 cycles / Discharge capacity after 1 cycle} x 100

[0365] Initial Capacity [mAh] Initial Resistance (DCIR) [mΩ] Capacity Retention Rate [%, @124 cycles] Example 16.13 9.71 88.71 Example 26.12 9.89 88.13 Comparative Example 15.86 10.8 85.24 Comparative Example 26.11 9.9 86.13 Comparative Example 35.78 10.9 86.43 Comparative Example 46.07 10.19 87.12 Comparative Example 56.08 10.67 86.91 Comparative Example 66.04 10.18 6.65

[0366] Referring to Table 3 above, it can be seen that the lithium secondary battery manufactured using the cathode manufactured in Examples 1 to 2 above has a higher initial capacity, lower initial resistance, and a higher capacity retention rate during rapid charging compared to the lithium secondary battery manufactured using the cathode manufactured in Comparative Examples 1 to 6 above.

[0367]

[0368] (Explanation of symbols)

[0369] 1: Lithium secondary battery

[0370] 2: Pack Housing

[0371] 3: Battery pack

[0372] 10: Anode

[0373] 11: Cathode

[0374] 12: Separator

[0375] 20: Whole house

[0376] 21: Active material layer

[0377] 21a: Cathode active material layer

[0378] 22: Mujibu

[0379] 22a: Undisturbed portion of the cathode

[0380] 22c: The indeterminate part of the pole

[0381] 24: Insulating layer

[0382] C: Winding center

[0383] 140: Lithium secondary battery

[0384] 141: Electrode assembly

[0385] 142: Battery Can

[0386] 143: Seal

[0387] 143a: Cap plate

[0388] 143b: First gasket

[0389] 143c: Connecting plate

[0390] 143d: Protrusion

[0391] 144: First collector plate

[0392] 145: Second collection plate

[0393] 146: Insulator

[0394] 146a: Positive indeterminate region

[0395] 146b: Cathode-free region

[0396] 147: Bidding Department

[0397] 148: Creaming Department

[0398] 149: Lead

[0399] 151: Reed Hall

[0400] 152: Venting Department

[0401] 170: Lithium secondary battery

[0402] 171: Battery Can

[0403] 172: Rivet terminal

[0404] 172a: Terminal exposure

[0405] 172b: Terminal insertion part

[0406] 173: Second gasket

[0407] 173a: Gasket exposure

[0408] 173b: Gasket insert

[0409] 174: Insulating cap

[0410] 176: Second collector plate

[0411] 178: Seal

[0412] 178a: Cap plate

[0413] 178b: First gasket

[0414] 179: Vent

[0415] 180: Bidding Department

[0416] 181: Creaming Department

Claims

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

2. In Paragraph 1, A cathode in which the ratio (X1 / X2) of the content (X1) of the first silicon-based cathode active material included in the first cathode active material layer and the content (X2) of the second silicon-based cathode active material included in the second cathode active material layer is greater than 1 and less than or equal to 10.

3. In Paragraph 1, The cathode, wherein the first silicon-based negative electrode active material is included in an amount of 5 to 30 weight percent based on the total weight of the first negative electrode active material.

4. In Paragraph 1, The cathode, wherein the second silicon-based negative electrode active material is included in an amount of 1 to 20 weight percent based on the total weight of the second negative electrode active material.

5. In Paragraph 1, The first cathode active material layer has a porosity of 15% to 30%, forming a cathode.

6. In Paragraph 1, The second cathode active material layer is a cathode having a porosity of 20% to 35%.

7. In Paragraph 1, A cathode, wherein the thickness of the first cathode active material layer is 35% to 50% of the total thickness of the first cathode active material layer and the second cathode active material layer.

8. In Paragraph 1, The first silicon-based negative electrode active material and the second silicon-based negative electrode active material each comprise a Si / C composite, forming a negative electrode.

9. An electrode assembly comprising a cathode, an anode, and a separator interposed between the cathode and the anode according to any one of claims 1 to 8; an electrolyte; and a battery case housing the electrode assembly and the electrolyte; comprising a lithium secondary battery.

10. In Paragraph 9, A lithium secondary battery, wherein the ratio of the diameter (R) of the lithium secondary battery to the height (h) of the lithium secondary battery is 0.4 or greater.

11. In Paragraph 9, The above lithium secondary battery is a lithium secondary battery that is a 46110 cell, a 48110 cell, a 4880 cell, or a 4680 cell.

12. In Paragraph 9, The above anode and cathode each include an unactive portion in which an active material layer is not formed, and A lithium secondary battery in which at least a portion of the unused portion of the positive electrode and the unused portion of the negative electrode defines an electrode tab.

13. In Paragraph 12, A lithium secondary battery in which a current collecting plate is coupled to each of the non-positive portion of the positive electrode and the non-negative portion of the negative electrode, and the current collecting plate is connected to an electrode terminal.

14. In Paragraph 12, The above-mentioned unbought portions of the anode and cathode can be folded independently but are processed into multiple segmented pieces, and A lithium secondary battery in which at least some of the plurality of segments are bent toward the winding center of the electrode assembly.

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