Lithium secondary battery

Abstract

The present application relates to a lithium secondary battery comprising: a positive electrode; a negative electrode; a separator disposed between the positive electrode and the negative electrode; and an electrolyte, in which the negative electrode includes a negative electrode current collector layer and a negative electrode active material layer including a negative electrode active material layer composition provided on one surface or both surfaces of the negative electrode current collector layer, in which the negative electrode active material layer composition includes a carbon-based active material, the carbon-based active material contains from 1 part by weight to 50 parts by weight (inclusive) of artificial graphite having an initial capacity of 330 mAh / g or more and an NP ratio of 110 or more with respect to 100 parts by weight of the carbon-based active material.

Description

Technical Field

[0001] This application claims the priority and benefit of Korean Patent Application No. 10-2023-0159140, filed with the Korean Intellectual Property Office on November 16, 2023, the entire content of which is incorporated herein by reference.

[0002] This application relates to a lithium secondary battery. Background Art

[0003] Due to the sharp increase in the use of fossil fuels, the demand for using alternative energy or clean energy is increasing, and as part of this trend, the most actively studied field is the field of power generation and power storage using electrochemical reactions.

[0004] Currently, secondary batteries are representative examples of electrochemical devices that use such electrochemical energy, and their specific application scope has a tendency to gradually expand.

[0005] With the development of technology and the increasing demand for mobile devices, the demand for secondary batteries as an energy source has increased sharply. Among such secondary batteries, lithium secondary batteries with high energy density, high voltage, long cycle life, and low self-discharge rate have been commercialized and widely used. In addition, as electrodes for such high-capacity lithium secondary batteries, methods for manufacturing high-density electrodes with higher energy density per unit volume are being actively studied.

[0006] Generally, a secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material for intercalating and deintercalating lithium ions from the positive electrode, and silicon-based particles having a high discharge capacity can be used as the negative electrode active material.

[0007] In particular, in recent years, in order to respond to the demand for high-density energy batteries, as the negative electrode active material, methods for improving the capacity by using silicon-based compounds such as Si / C or SiO having a capacity more than 10 times that of graphite-based materials are being actively studied. x However, although the capacity characteristics of silicon-based compounds themselves as high-capacity materials are excellent compared to graphite used in the related art, they experience rapid volume expansion during the charging process, causing the conduction path to be disconnected, resulting in deterioration of battery characteristics, and correspondingly, the capacity decreases from the initial stage. In addition, for silicon-based negative electrodes, if charge-discharge cycles are repeated, lithium ions are unevenly charged in the depth direction of the negative electrode, and the reaction occurs on the surface, accelerating the surface deterioration, so it is necessary to improve the performance in terms of battery cycling.

[0008] Therefore, in order to solve the problems that occur when using silicon-based compounds as negative electrode active materials, various methods have been discussed, such as methods for adjusting the driving potential, methods for further coating a thin film on the active material layer, methods for controlling the particle size of the silicon-based compounds, etc., which are methods for suppressing self-volume expansion, or developing adhesives that can suppress the volume expansion of the silicon-based compounds to prevent the disconnection of the conduction path. In addition, the following research is underway: By pre-lithiation of the silicon-based active material layer, the proportion of the silicon-based active material used during initial charge and discharge is restricted, and a reservoir function is imparted, thereby supplementing the life characteristics of the silicon-based negative electrode.

[0009] However, the above methods have limitations in their applications because they may instead reduce the performance of the battery, and thus there are still limitations in the commercialization of negative electrode batteries with a high content of silicon compounds.

[0010] Therefore, since recent research has confirmed that when artificial graphite is used as the negative electrode, the capacity is reduced compared to silicon-based negative electrodes, but the battery characteristics are excellent. Therefore, while reducing the use of natural graphite, the use of artificial graphite has increased. However, from a cost perspective, artificial graphite has the disadvantage that its processing cost is higher than that of natural graphite because it requires the firing and graphitization of coke.

[0011] Therefore, the development of lithium secondary batteries that can reduce costs and exhibit the same or better performance as existing batteries is ongoing.

[0012] <Related Technical Literature>

[0013] (Patent Document 1) Japanese Patent Application Laid-Open No. 2009-080971 Summary of the Invention

[0014] [Technical Problem]

[0015] Through research, the present application has discovered a battery that uses a carbon-based active material in the negative electrode, reduces the amount of artificial graphite in terms of cost, and can simultaneously achieve the same or better characteristics as existing batteries even when the amount of artificial graphite is reduced.

[0016] Therefore, the present application aims to provide a lithium secondary battery in which an active material with a specific composition is used for the negative electrode and the NP ratio is adjusted.

[0017] [Technical Solution]

[0018] Exemplary embodiments of the present specification provide a lithium secondary battery, comprising: a positive electrode; a negative electrode; a separator disposed between the positive electrode and the negative electrode; and an electrolyte, wherein the negative electrode includes a negative electrode current collector layer and a negative electrode active material layer containing a negative electrode active material layer composition disposed on one or both surfaces of the negative electrode current collector layer, the negative electrode active material layer composition contains a carbon-based active material, and contains 1 part by weight or more and 50 parts by weight or less of artificial graphite having an initial capacity of 330 mAh / g or more with respect to 100 parts by weight of the carbon-based active material, and the NP ratio is 110 or more.

[0019] [Advantageous Effects]

[0020] In the related art, it has been confirmed that artificial graphite has excellent battery characteristics. Therefore, the amount of artificial graphite has been increased while the amount of natural graphite has been reduced. However, artificial graphite has a high process cost in terms of cost and mass production, so there is a problem of being expensive.

[0021] Therefore, in order to solve the problems of cost and mass production, the present application designs the battery cell by reducing the amount of artificial graphite and simultaneously increasing the amount of natural graphite, and solves the resulting problems by adjusting the NP ratio.

[0022] That is, the lithium secondary battery of the present application contains 1 part by weight or more and 50 parts by weight or less of artificial graphite having an initial capacity of 330 mAh / g or more with respect to 100 parts by weight of the carbon-based active material. And since the NP ratio is adjusted to 110 or more, there can be a large amount of remaining negative electrode, so that the lithium secondary battery has the characteristic that even when using artificial graphite within the above range, the deterioration of the battery cell will not be accelerated. Therefore, the service life characteristic of the battery can be ensured. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a diagram showing the stacked structure of the lithium secondary battery of the exemplary embodiment of the present application.

[0024] [Description of Reference Numerals and Signs]

[0025] 10: Negative electrode current collector layer

[0026] 20: Negative electrode active material layer

[0027] 30: Separator

[0028] 40: Positive electrode active material layer

[0029] 50: Positive electrode current collector layer

[0030] 100: Negative electrode

[0031] 200: Positive electrode DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] Before describing the present invention, some terms are first defined.

[0033] In this specification, when a part "includes" a component, unless otherwise specifically stated, this does not mean excluding other components, but means that other components can be further included.

[0034] In this specification, "p to q" refers to the range of "above p and below q".

[0035] In this specification, the "specific surface area" is measured by the BET method. Specifically, using BELSORP-mino II manufactured by BEL Japan, Inc., it is calculated based on the nitrogen adsorption amount at the liquid nitrogen temperature (77K). That is, in this application, the BET specific surface area can refer to the specific surface area measured by the above measurement method.

[0036] In this specification, "Dn" refers to the particle size distribution and refers to the particle size at the n% point in the cumulative distribution of the number of particles according to the particle size. That is, D50 is the particle size at the 50% point in the cumulative distribution of the number of particles according to the particle size (average particle size, median particle size), D90 is the particle size at the 90% point in the cumulative distribution of the number of particles according to the particle size, and D10 is the particle size at the 10% point in the cumulative distribution of the number of particles according to the particle size. At the same time, the particle size distribution can be measured by the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, the resulting dispersion is introduced into a commercially available laser diffraction particle size measuring device (such as Microtrac S3500). In this device, when a laser beam passes through the particles, the difference in the diffraction pattern corresponding to the particle size is measured, and then the particle size distribution is calculated.

[0037] In this specification, the expression "a polymer contains a monomer as a monomer unit" means that the monomer participates in the polymerization reaction and is thus included in the polymer as a repeating unit. In this specification, when a polymer contains a monomer, this is interpreted as the same as when the polymer contains the monomer as a monomer unit.

[0038] In this specification, the term "polymer" should be understood to be used in a broad sense, which includes copolymers unless otherwise specified as "homopolymers".

[0039] In this specification, the weight-average molecular weight (Mw) and the number-average molecular weight (Mn) are polystyrene-converted molecular weights measured by gel permeation chromatography (GPC) using commercially available monodisperse polystyrene polymers (standard samples) with various degrees of polymerization as standard materials. In this specification, unless otherwise specified, the molecular weight refers to the weight-average molecular weight.

[0040] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art to which the present invention pertains can easily implement the present invention. However, the present invention can be implemented in various different forms and is not limited to the following description.

[0041] Exemplary embodiments of the present specification provide a lithium secondary battery, which includes: a positive electrode; a negative electrode; a separator disposed between the positive electrode and the negative electrode; and an electrolyte, wherein the negative electrode includes a negative electrode current collector layer and a negative electrode active material layer containing a negative electrode active material layer composition disposed on one surface or both surfaces of the negative electrode current collector layer, the negative electrode active material layer composition contains a carbon-based active material, and contains 1 part by weight or more and 50 parts by weight or less of artificial graphite having an initial capacity of 330 mAh / g or more with respect to 100 parts by weight of the carbon-based active material, and the NP ratio is 110 or more.

[0042] With respect to 100 parts by weight of the carbon-based active material, the lithium secondary battery of the present application contains 1 part by weight or more and 50 parts by weight or less of artificial graphite having an initial capacity of 330 mAh / g or more, and by adjusting the NP ratio to 110 or more, a large amount of remaining negative electrode can be obtained, so that the lithium secondary battery has the characteristic that even when using artificial graphite within the above range, the deterioration of the battery cell will not be accelerated, and thus the service life characteristic of the battery can be ensured.

[0043] Figure 1 FIG. is a diagram showing the stacked structure of the lithium secondary battery according to the exemplary embodiment of the present application. Specifically, a negative electrode 100 for a lithium secondary battery can be determined, which includes a negative electrode active material layer 20 disposed on one surface of a negative electrode current collector layer 10; a positive electrode 200 for a lithium secondary battery can be determined, which includes a positive electrode active material layer 40 disposed on one surface of a positive electrode current collector layer 50; and it is shown that the negative electrode 100 for a lithium secondary battery and the positive electrode 200 for a lithium secondary battery form a stacked structure with a separator 30 therebetween.

[0044] Hereinafter, the lithium secondary battery of the present invention will be described in more detail.

[0045] In the present application, the negative electrode includes a negative electrode current collector layer and a negative electrode active material layer, and the negative electrode active material layer contains a negative electrode active material layer composition and is disposed on one surface or both surfaces of the negative electrode current collector layer.

[0046] In the present application, the negative electrode active material layer composition contains a carbon-based active material, and can contain 1 part by weight or more and 50 parts by weight or less of artificial graphite having an initial capacity of 330 mAh / g or more with respect to 100 parts by weight of the carbon-based active material.

[0047] In another embodiment, the negative electrode active material layer composition includes a carbon-based active material, and based on 100 parts by weight of the carbon-based active material, it may include 1 part by weight or more and 50 parts by weight or less, specifically 10 parts by weight or more and 50 parts by weight or less, and more specifically 30 parts by weight or more and 50 parts by weight or less of artificial graphite having an initial capacity of 330 mAh / g or more.

[0048] In an exemplary embodiment of the present application, representative examples of the carbon-based active material include natural graphite, artificial graphite, expandable graphite, carbon fiber, non-graphitized carbon, carbon black, carbon nanotubes, fullerenes, activated carbon, etc., and the carbon-based active material can be used without limitation as long as it is commonly used in carbon materials for lithium secondary batteries. Specifically, it can be processed into spherical or dot-like shapes and used.

[0049] In the present application, when the NP ratio is adjusted to 110 or more, there can be a large amount of remaining negative electrode, so it has the characteristic that even when using artificial graphite within the above range, the deterioration of the battery cell will not be accelerated, and thus the service life characteristics can be ensured.

[0050] In the present application, the artificial graphite can have an initial capacity of 330 mAh / g or more.

[0051] In another exemplary embodiment, the initial capacity of the artificial graphite can be 330 mAh / g or more, preferably 335 mAh / g or more, can be 450 mAh / g or less, and preferably 400 mAh / g or less.

[0052] The artificial graphite of the present application has an initial capacity within the above range. Different from artificial graphite types such as mesophase carbon, it is a material with a relatively high initial capacity set. In this case, the artificial graphite of the present application has better capacity characteristics than ordinary artificial graphite.

[0053] In an exemplary embodiment of the present application, a lithium secondary battery is provided, wherein the carbon-based active material includes artificial graphite and natural graphite having an initial capacity of 330 mAh / g or more, and based on 100 parts by weight of the carbon-based active material, the weight ratio of the artificial graphite to the natural graphite is 1:99 to 50:50.

[0054] That is, the lithium secondary battery of the present invention is characterized in that a carbon-based active material is used as the negative electrode active material, and artificial graphite and natural graphite satisfying the above specific initial capacity are mixed and used in the above ratio. Specifically, using 100% artificial graphite is excellent in terms of resistance characteristics and service life characteristics, but such artificial graphite is characterized by being unsuitable for mass production because artificial graphite is expensive and requires a very long process time. Therefore, this application uses a blend of natural graphite in the above ratio, and the main object of the present invention is to solve the resulting performance degradation by adjusting the NP ratio.

[0055] In this application, the artificial graphite and natural graphite with an initial capacity of 330 mAh / g or more can be crystalline carbon (graphite).

[0056] The carbon-based active material can be classified into crystalline carbon (graphite) and amorphous carbon, and the amorphous carbon can be further classified into hard carbon and soft carbon. The artificial graphite and natural graphite in this application are mainly characterized by using crystalline carbon (graphite).

[0057] The carbon-based active material of the present invention is a negative electrode material with a higher capacity than soft carbon or hard carbon, excellent initial efficiency, and excellent cycle characteristics.

[0058] In an exemplary embodiment of this application, a lithium secondary battery is provided, in which the negative electrode active material layer composition further includes one or more selected from the group consisting of a silicon-based active material, a tin-based active material, a metal-based active material capable of forming an alloy with lithium, a lithium titanium oxide, and a lithium nitride.

[0059] In particular, the negative electrode active material layer composition of this application includes a carbon-based active material and a silicon-based active material, and can include 50 parts by weight or less of the silicon-based active material relative to 100 parts by weight of the negative electrode active material layer composition.

[0060] The negative electrode active material layer composition of this application includes a carbon-based active material and a silicon-based active material, and can include 30 parts by weight or less, preferably 20 parts by weight or less, 1 part by weight or more, or 10 parts by weight or more of the silicon-based active material relative to 100 parts by weight of the negative electrode active material layer composition.

[0061] In this application, when the content of artificial graphite in the carbon-based active material decreases, problems such as deterioration of resistance characteristics and service life characteristics sometimes occur. Therefore, when the carbon-based active material is mixed with a silicon-based active material or a lithium titanium oxide and used in the negative electrode active material layer composition as described above, the above problems can be solved.

[0062] In an exemplary embodiment of this application, the silicon-based active material can include those selected from SiO x (x = 0), SiO x(0 < x < 2), one or more of SiC and Si alloys.

[0063] In an exemplary embodiment of the present application, the silicon-based active material includes one or more selected from the group consisting of SiO x (0 < x < 2), SiC and Si alloys, and relative to 100 parts by weight of the silicon-based active material, may include 1 part by weight or more of SiO x (0 < x < 2).

[0064] In another exemplary embodiment, the silicon-based active material includes one or more selected from the group consisting of SiO x (0 < x < 2), SiC and Si alloys, and relative to 100 parts by weight of the silicon-based active material, may include 1 part by weight or more or 30 parts by weight or more and 99 parts by weight or less of SiO x (0 < x < 2).

[0065] In another exemplary embodiment, the silicon-based active material may include SiO x (0 < x < 2).

[0066] In another exemplary embodiment, the silicon-based active material may consist of SiO x (0 < x < 2).

[0067] In an exemplary embodiment of the present application, the negative electrode active material layer composition may include a negative electrode conductive material and a negative electrode binder.

[0068] In the related art, generally only graphite-based compounds are used as the negative electrode active material. However, in recent years, with the increasing demand for high-capacity batteries, in order to increase the capacity, attempts to use a silicon-based active material in combination are increasing. However, in the case of a graphite-based active material or a silicon-based active material, the volume expands rapidly during charge and discharge, and thus in some cases, a problem of breaking the conduction path formed in the negative electrode active material layer may occur.

[0069] Therefore, in an exemplary embodiment of the present application, the negative electrode conductive material may include one or more selected from a dot-shaped conductive material, a planar conductive material, and a linear conductive material.

[0070] In an exemplary embodiment of the present application, the punctiform conductive material can be used to improve the conductivity of the negative electrode without causing chemical changes, and refers to a punctiform or spherical conductive material having conductivity. Specifically, the punctiform conductive material can be at least one selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and from the viewpoint of achieving high conductivity and excellent dispersibility, carbon black can be preferably included.

[0071] In an exemplary embodiment of the present application, the BET specific surface area of the punctiform conductive material can be 40 m 2 / g or more and 70 m 2 / g or less, preferably 45 m 2 / g or more and 65 m 2 / g or less, more preferably 50 m 2 / g or more and 60 m 2 / g or less.

[0072] In an exemplary embodiment of the present application, the content of the functional groups (volatile matter) of the punctiform conductive material can satisfy 0.01% or more and 1% or less, preferably 0.01% or more and 0.3% or less, more preferably 0.01% or more and 0.1% or less.

[0073] In particular, when the content of the functional groups of the punctiform conductive material is within a specified range, functional groups exist on the surface of the punctiform conductive material, so that when water is used as a solvent, the punctiform conductive material can be smoothly dispersed in the solvent. In particular, in the present invention, when a specific silicon-based active material is used, the content of the functional groups of the punctiform conductive material can be reduced, so the present invention has an excellent effect in improving dispersibility.

[0074] In an exemplary embodiment of the present application, the punctiform conductive material having a functional group content within the above range is included together with the silicon-based active material, and the content of the functional groups can be adjusted according to the heat treatment degree of the punctiform conductive material.

[0075] In an exemplary embodiment of the present application, the particle size of the punctiform conductive material can be 10 nm to 100 nm, preferably 20 nm to 90 nm, more preferably 20 nm to 60 nm.

[0076] In an exemplary embodiment of the present application, the conductive material can include a planar conductive material.

[0077] The planar conductive material can improve the conductivity by increasing the surface contact between silicon particles in the negative electrode, and at the same time can be used to suppress the disconnection of the conduction path caused by volume expansion. The planar conductive material can be in the form of a plate-shaped conductive material or a massive conductive material.

[0078] In an exemplary embodiment of the present application, the planar conductive material may include at least one selected from plate-shaped graphite, graphene, graphene oxide, and graphite flakes, and may preferably be plate-shaped graphite.

[0079] In an exemplary embodiment of the present application, the average particle size (D50) of the planar conductive material may be 2 to 7 μm, specifically 3 to 6 μm, and more specifically 3.5 to 5 μm. When the average particle size meets this specified range, the sufficient particle size makes dispersion easy and does not cause an excessive increase in the viscosity of the negative electrode slurry. Therefore, when dispersing particles using the same equipment and time, the dispersion effect is excellent.

[0080] In an exemplary embodiment of the present application, a negative electrode composition is provided, in which the D10 of the planar conductive material is 0.5 μm or more and 2.0 μm or less, the D50 is 2.5 μm or more and 3.5 μm or less, and the D90 is 6.5 μm or more and 15.0 μm or less.

[0081] In an exemplary embodiment of the present application, for the planar conductive material, a high specific surface area planar conductive material with a high BET specific surface area or a low specific surface area planar conductive material can be used.

[0082] In an exemplary embodiment of the present application, a high specific surface area planar conductive material or a low specific surface area planar conductive material can be used for the planar conductive material without limitation. However, specifically, the planar conductive material of the present application may be affected to a certain extent in terms of electrode performance due to the dispersion effect. Therefore, a low specific surface area planar conductive material that does not cause dispersion problems can be particularly preferably used.

[0083] In an exemplary embodiment of the present application, the BET specific surface area of the planar conductive material may be 0.25 m 2 / g or more.

[0084] In another exemplary embodiment, the BET specific surface area of the planar conductive material may be 1 m 2 / g or more and 500 m 2 / g or less, preferably 5 m 2 / g or more and 300 m 2 / g or less, and more preferably 5 m 2 / g or more and 250 m 2 / g or less.

[0085] For the planar conductive material of the present application, a planar conductive material with a high specific surface area or a planar conductive material with a low specific surface area can be used.

[0086] In another exemplary embodiment, the planar conductive material is a planar conductive material with a high specific surface area, and the BET specific surface area can be 50 m 2 / g or more and 500 m 2 / g or less, preferably 80 m 2 / g or more and 300 m 2 / g or less, more preferably 100 m 2 / g or more and 300 m 2 / g or less.

[0087] In another exemplary embodiment, the planar conductive material is a planar conductive material with a low specific surface area, and the BET specific surface area can be 1 m 2 / g or more and 40 m 2 / g or less, preferably 5 m 2 / g or more and 30 m 2 / g or less, and more preferably 5 m 2 / g or more and 25 m 2 / g or less.

[0088] Other conductive materials may include linear conductive materials, such as carbon nanotubes. The carbon nanotubes can be bundled carbon nanotubes. The bundled carbon nanotubes can include a plurality of carbon nanotube units. Specifically, unless otherwise specified, the term "bundled" herein refers to a bundled or cord-like secondary shape in which a plurality of carbon nanotube units are arranged side by side or entangled along an orientation in which the longitudinal axes of the carbon nanotube units are substantially the same. The carbon nanotube unit has a cylindrical graphite sheet with a nanoscale diameter and has an sp 2 bonded structure. In this case, the carbon nanotubes can exhibit the characteristics of a conductive material or a semiconductor material depending on the rolling angle and structure of the graphite sheet. Compared with entangled carbon nanotubes, the bundled carbon nanotubes can be more uniformly dispersed during the manufacture of the negative electrode, and a conductive network can be more smoothly formed in the negative electrode to improve the conductivity of the negative electrode.

[0089] In an exemplary embodiment of the present application, relative to 100 parts by weight of the negative electrode active material layer composition, the content of the negative electrode conductive material can be 0.1 part by weight or more and 40 parts by weight or less.

[0090] In another exemplary embodiment, with respect to 100 parts by weight of the negative electrode active material layer composition, the content of the negative electrode conductive material may be 0.1 part by weight or more and 40 parts by weight or less, preferably 0.2 part by weight or more and 30 parts by weight or less, more preferably 0.4 part by weight or more and 25 parts by weight or less, and most preferably 0.4 part by weight or more and 10 parts by weight or less.

[0091] In an exemplary embodiment of the present application, the negative electrode conductive material may include a planar conductive material or a linear conductive material.

[0092] In an exemplary embodiment of the present application, the negative electrode conductive material may include a planar conductive material and a linear conductive material.

[0093] In an exemplary embodiment of the present application, the negative electrode conductive material may include a dot-shaped conductive material and a linear conductive material.

[0094] In an exemplary embodiment of the present application, the negative electrode conductive material may include a dot-shaped conductive material.

[0095] In an exemplary embodiment of the present application, with respect to 100 parts by weight of the negative electrode conductive material, the negative electrode conductive material may include 80 parts by weight or more and 99.9 parts by weight or less of a planar conductive material and 0.1 part by weight or more and 20 parts by weight or less of a linear conductive material.

[0096] In another exemplary embodiment, with respect to 100 parts by weight of the negative electrode conductive material, the negative electrode conductive material may contain 80 parts by weight or more and 99.9 parts by weight or less, preferably 85 parts by weight or more and 99.9 parts by weight or less, and more preferably 95 parts by weight or more and 98 parts by weight or less of a planar conductive material.

[0097] In another exemplary embodiment, with respect to 100 parts by weight of the negative electrode conductive material, the negative electrode conductive material may contain 0.1 part by weight or more and 20 parts by weight or less, preferably 0.1 part by weight or more and 15 parts by weight or less, and more preferably 0.2 part by weight or more and 5 parts by weight or less of a linear conductive material.

[0098] In an exemplary embodiment of the present application, with respect to 100 parts by weight of the negative electrode conductive material, the negative electrode conductive material may include 80 parts by weight or more and 99.9 parts by weight or less of a dot-shaped conductive material and 0.1 part by weight or more and 20 parts by weight or less of a linear conductive material.

[0099] In an exemplary embodiment of the present application, since the negative electrode conductive material includes a planar conductive material and a linear conductive material, or a dot-shaped conductive material and a linear conductive material, and the planar conductive material and the linear conductive material, or the dot-shaped conductive material and the linear conductive material each satisfy the above composition and ratio, the negative electrode conductive material has the following characteristics: when including a planar conductive material and a linear conductive material, the service life characteristics of the existing lithium secondary battery are not significantly affected, and particularly the number of points where the battery can be charged and discharged is increased, so that the output characteristics at a high C rate are excellent and the gas generation at high temperature is reduced.

[0100] In an exemplary embodiment of the present application, the negative electrode conductive material may be composed of a linear conductive material.

[0101] In particular, when the linear conductive material is used alone, the electrode tortuosity, which is a problem of carbon-based or silicon-based negative electrodes, can be simplified, so that the electrode structure can be improved. Correspondingly, the negative electrode conductive material has the characteristic of being able to reduce the migration resistance of lithium ions in the electrode.

[0102] In an exemplary embodiment of the present application, when the negative electrode conductive material includes only a linear conductive material, the content of the negative electrode conductive material may be 0.1 part by weight or more and 5 parts by weight or less, preferably 0.2 part by weight or more and 3 parts by weight or less, and more preferably 0.4 part by weight or more and 1 part by weight or less, based on 100 parts by weight of the negative electrode active material layer composition.

[0103] The negative electrode conductive material of the present application has a completely different configuration from the positive electrode conductive material applied to the positive electrode. That is, the negative electrode conductive material of the present application is used to maintain the contact points between silicon-based active materials (whose electrode volume expands very greatly during charge and discharge), while the positive electrode conductive material is used to impart a part of conductivity and play a buffering role during rolling, which is completely different from the negative electrode conductive material of the present invention in terms of configuration and function.

[0104] In an exemplary embodiment of the present application, the planar conductive material used as the above negative electrode conductive material has a different structure and function from the carbon-based active material commonly used as the negative electrode active material. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, which refers to a material processed into a spherical or dot shape and used to promote the storage and release of lithium ions.

[0105] In contrast, the planar conductive material used as the negative electrode conductive material is a material having a planar or plate-like shape, and may be manifested as plate-like graphite. That is, the planar conductive material is a material included to maintain the conduction path in the negative electrode active material layer, which refers to a material used to ensure a planar conduction path inside the negative electrode active material layer, rather than playing the role of storing and releasing lithium.

[0106] That is, in the present application, using plate-shaped graphite as a conductive material means processing the plate-shaped graphite into a planar or plate shape and using it as a material to ensure the conduction path, rather than playing a role in storing or releasing lithium. In this case, the negative electrode active material included together has the high-capacity characteristics of storing and releasing lithium and plays a role in being able to store and release all the lithium ions transferred from the positive electrode.

[0107] In contrast, in the present application, using a carbon-based active material as an active material means processing the carbon-based active material into a dot or spherical shape and using it as a material for storing or releasing lithium.

[0108] That is, in the exemplary embodiments of the present application, artificial graphite or natural graphite as the carbon-based active material has a dot shape, and its BET specific surface area can be 0.1 m 2 / g or more and 4.5 m 2 / g or less. In addition, the plate-shaped graphite as a planar conductive material has a planar shape, and its BET specific surface area can be 5 m 2 / g or more.

[0109] In the exemplary embodiments of the present application, the negative electrode binder may include at least one selected from the group consisting of: polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and the above materials in which hydrogen is replaced by Li, Na, Ca, etc., and may also include various copolymers thereof.

[0110] The negative electrode binder of the exemplary embodiments of the present application is used to support the active material and the conductive material to prevent the distortion and structural deformation of the negative electrode structure during the volume expansion and relaxation of the silicon-based active material. When this function is satisfied, all common binders can be applied. Specifically, a water-based binder can be used, and more specifically, a PAM-based binder can be used.

[0111] In the exemplary embodiments of the present application, with respect to 100 parts by weight of the negative electrode active material layer composition, the content of the negative electrode binder can be 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, can be 5 parts by weight or more, and can be 10 parts by weight or more.

[0112] In an exemplary embodiment of the present application, a lithium secondary battery is provided, wherein the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, and the thickness of the negative electrode active material layer is 5 μm or more and 500 μm or less.

[0113] The thickness of the negative electrode current collector layer is generally 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum cadmium alloy, etc. can be used. In addition, the negative electrode current collector layer can be formed to have fine irregularities on the surface to enhance the adhesion strength with the negative electrode active material, and can be used in various forms such as a film, sheet, foil, net, porous body, foam body, or non-woven fabric body.

[0114] However, the thickness can be variously modified according to the type and use of the negative electrode used, and is not limited thereto.

[0115] In an exemplary embodiment of the present application, the porosity of the negative electrode active material layer can be 10% or more and 60% or less.

[0116] In another exemplary embodiment, the porosity of the negative electrode active material layer can be 10% or more and 60% or less, preferably 20% or more and 50% or less, and more preferably 30% or more and 45% or less.

[0117] The porosity varies depending on the composition and content of the active material, conductive material, and binder contained in the negative electrode active material layer, so that the electrode has appropriate conductivity and resistance within a certain range.

[0118] In an exemplary embodiment of the present application, the positive electrode includes a positive electrode current collector layer and a positive electrode active material layer. The positive electrode active material layer contains a positive electrode active material layer composition and is provided on one or both surfaces of the positive electrode current collector layer. The positive electrode active material layer composition contains a positive electrode active material.

[0119] In the positive electrode, the positive electrode current collector layer is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used, and so on. In addition, the positive electrode current collector layer generally can have a thickness of 3 μm to 500 μm, and fine irregularities can also be formed on the surface of the positive electrode current collector layer to increase the adhesion of the positive electrode active material. For example, the positive electrode current collector layer can be used in various forms such as a film, sheet, foil, net, porous body, foam body, non-woven fabric body.

[0120] The positive electrode active material can be a commonly used positive electrode active material. Specifically, the positive electrode active material includes: layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or compounds substituted by one or more transition metals; lithium iron oxide such as LiFe3O4; lithium manganese oxide such as the chemical formula Li 1+c1 Mn 2-c1 O4(0≤c1≤0.33), LiMnO3, LiMn2O3 and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxide such as LiV3O8, V2O5 and Cu2V2O7; represented by the chemical formula LiNi 1-c2 M c2 O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B and Ga, and 0.01≤c2≤0.3) nickel-site type lithium nickel oxide; represented by the chemical formula LiMn 2-c3 M c3 O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn and Ta, and 0.01≤c3≤0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu and Zn) lithium manganese composite oxide; LiMn2O4, in which a part of Li in the chemical formula is substituted by alkaline earth metal ions; and so on, but not limited thereto. The positive electrode can be Li metal.

[0121] The present application provides a lithium secondary battery, wherein the positive electrode active material includes at least one selected from the group consisting of LiNi x Co y Mn z O2(x + y + z = 1), LiNi a Co b Mn c Al d O2(a + b + c + d = 1), LiMn2O4, LiNi 0.5 Mn 1.5 O2 and LiM x Fe y PO4 (M: transition metal, x + y = 1).

[0122] In the present application, a lithium secondary battery is provided, wherein the positive electrode active material layer composition contains LiNi x Co y Mn z O2(x + y + z = 1) or LiNi a Co b Mn c Al dO2 (a + b + c + d = 1), z is 0.5 or more, and c is 0.4 or more.

[0123] That is, the lithium secondary battery of the present application is characterized by using a Mn-rich positive electrode active material.

[0124] In addition to the above positive electrode active material, the positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder.

[0125] In this case, the positive electrode conductive material is used to impart conductivity to the electrode and can be used without particular limitation as long as it has electronic conductivity and does not cause chemical changes in the formed battery. Specific examples may include: graphite, such as natural graphite and artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, and carbon fiber; 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, etc., and any one of them or a mixture of two or more of them can be used.

[0126] Furthermore, the positive electrode binder is used to improve the binding between the particles of the positive electrode active material and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples thereof may include polyvinylidene fluoride (PVDF), vinylidene fluoride - hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene monomer (EPDM), sulfonated - EPDM, styrene - butadiene rubber (SBR), fluororubber, or various copolymers thereof, etc., and any one of them or a mixture of two or more of them can be used.

[0127] In the present application, the lithium secondary battery may have an NP ratio of 110 or more.

[0128] In another exemplary embodiment, the NP ratio may be 110 or more and 200 or less, 113 or more and 150 or less, or 115 or more and 140 or less.

[0129] By adjusting the NP within the above range, even if the amount of artificial graphite is reduced and the amount of natural graphite is increased, battery characteristics equivalent to or better than those of existing batteries can be exhibited. That is, when the NP is designed and adjusted within the above range, a large amount of remaining negative electrode can be obtained. Therefore, even if the amount of artificial graphite is reduced and the amount of natural graphite is increased, the lithium secondary battery has the characteristic of preventing accelerated deterioration of the battery cell.

[0130] Generally, the NP ratio may satisfy the following equation A.

[0131] [Equation A]

[0132] N / P ratio = Discharge capacitance per unit area of the negative electrode / Discharge capacitance per unit area of the positive electrode × 100

[0133] As used herein, "discharge capacity per unit area" refers to the discharge capacity per unit area in the first cycle of the negative electrode or the positive electrode.

[0134] The discharge capacitance per unit area of the negative electrode can be obtained by the following method. Specifically, a half-cell is fabricated using a negative electrode sample containing a negative electrode active material and a counter electrode (e.g., a lithium metal electrode) opposed to the negative electrode sample. The "discharge capacity of the negative electrode active material per unit weight of the negative electrode sample" is obtained by dividing the discharge capacity measured by charging and discharging the half-cell by the weight of the negative electrode active material. A secondary battery is fabricated using a negative electrode containing the same negative electrode active material as that used in the half-cell and a positive electrode containing a positive electrode active material. The discharge capacitance per unit area of the negative electrode can be obtained by multiplying the "discharge capacity of the negative electrode active material per unit weight of the negative electrode sample" by the weight of the negative electrode active material contained in the secondary battery and dividing by the area of the negative electrode contained in the secondary battery.

[0135] The discharge capacitance per unit area of the positive electrode can be obtained by the following method. Specifically, a half-cell is fabricated using a positive electrode sample containing a positive electrode active material and a counter electrode (e.g., a lithium metal electrode) opposed to the positive electrode sample. The "discharge capacity of the positive electrode active material per unit weight of the positive electrode sample" is obtained by dividing the discharge capacity measured by charging and discharging the half-cell by the weight of the positive electrode active material. A secondary battery is fabricated using a positive electrode containing the same positive electrode active material as that used in the half-cell and a negative electrode containing a negative electrode active material. The discharge capacitance per unit area of the positive electrode can be obtained by multiplying the "discharge capacity of the positive electrode active material per unit weight of the positive electrode sample" by the weight of the positive electrode active material contained in the secondary battery and dividing by the area of the positive electrode contained in the secondary battery.

[0136] The separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions. It can be used without particular limitation as long as it is commonly used as a separator in secondary batteries. In particular, a separator having a high moisture retention ability for the electrolyte and a low resistance to ion migration in the electrolyte can be preferably used. Specifically, a porous polymer membrane can be used, such as a porous polymer membrane made of polyolefin polymers (such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers), or a stacked structure having two or more layers thereof. In addition, commonly used porous non-woven fabrics can be used, such as non-woven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers, etc. Further, a coated separator containing a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and a separator having a single-layer or multi-layer structure can be selectively used.

[0137] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, or molten-type inorganic electrolytes that can be used to manufacture lithium secondary batteries.

[0138] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0139] As the non-aqueous organic solvent, for example, an aprotic organic solvent can be used, such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, or ethyl propionate.

[0140] In particular, among carbonate organic solvents, ethylene carbonate and propylene carbonate as cyclic carbonates can be preferably used because cyclic carbonates have a high dielectric constant as high-viscosity organic solvents to dissociate lithium salts well. When cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constant (such as dimethyl carbonate and diethyl carbonate) in a suitable ratio, an electrolyte having high conductivity can be prepared, and thus can be more preferably used.

[0141] As the metal salt, a lithium salt can be used, which is a material easily soluble in the non-aqueous electrolyte. Among them, as the anion of the lithium salt, for example, those selected from F - , Cl - , I - , NO3- , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more selected from the group consisting of

[0142] In order to improve the service life characteristics of the battery, suppress the reduction of the battery capacity, improve the discharge capacity of the battery, etc., in addition to the above electrolyte components, the electrolyte may further include one or more additives, such as haloalkyl carbonate compounds (such as ethylene difluorocarbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol diether, hexaphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol or aluminum trichloride.

[0143] Exemplary embodiments of the present invention provide a battery module including the lithium secondary battery as a unit cell and a battery pack including the battery module. Since the battery module and the battery include a secondary battery having high capacity, high rate capability and high cycle characteristics, the battery module and the battery pack can be used as a power source for medium and large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems.

[0144] In the following, preferred embodiments will be provided to better understand the present invention. It is obvious to those skilled in the art that providing the embodiments is only for illustrating the present invention, and various modifications and changes can be made within the scope and technical spirit of the present invention. Such modifications and changes naturally fall within the scope of the claims included herein.

[0145] Example

[0146] <Preparation Example>

[0147] <Manufacture of Secondary Battery>

[0148] <Example>

[0149] A carbon-based active material (artificial graphite (D50 = 18 μm): natural graphite (D50 = 18 μm) = 50:50), carbon black, SBR as a binder, and CMC as a thickener were added to distilled water as a solvent for forming a negative electrode slurry at a weight ratio of 95.7:1:2.3:1 to prepare a negative electrode slurry (solid concentration 50 wt%).

[0150] As a mixing method, a homogenizer was used to disperse carbon black, the binder, and water at 2500 rpm for 30 minutes, then the active materials (artificial graphite, natural graphite) were added, and then dispersed at 2500 rpm for 30 minutes to prepare the slurry.

[0151] The negative electrode slurry was coated on both sides of a copper current collector (thickness: 15 μm) as a negative electrode current collector at a loading amount of 5.48 mAh / cm 2 and dried in a vacuum oven at 130 °C for 1 hour and then roll-pressed to form a negative electrode active material layer (negative electrode porosity 35%).

[0152] LiNi 0.6 Co 0.2 Mn 0.2 O2 (average particle size (D50): 15 μm), carbon black as a conductive material (trade name: Super C65, manufacturer: Timcal), and polyvinylidene fluoride (PVdF) as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent for forming a positive electrode slurry at a weight ratio of 95:2.5:2.5 to prepare a positive electrode slurry (solid concentration 63 wt%).

[0153] The positive electrode slurry was coated on both sides of an aluminum current collector (thickness: 15 μm) as a positive electrode current collector at a loading amount of 4.0 mAh / cm 2 and the aluminum current collector was dried in a vacuum oven at 130 °C for 1 hour and then roll-pressed to form a positive electrode active material layer, thereby manufacturing a positive electrode (positive electrode porosity: 25%).

[0154] A lithium secondary battery was fabricated by disposing a polyethylene separator between the positive electrode and the negative electrode of the example and injecting an electrolyte therein (based on 4.2 V to 2 V, NP ratio of 137).

[0155] <Comparative Example>

[0156] A carbon-based active material (artificial graphite (D50 = 18 μm): natural graphite (D50 = 18 μm) = 80:20), carbon black, SBR as a binder, and CMC as a thickener were added to distilled water as a solvent for forming a negative electrode slurry at a weight ratio of 95.7:1:2.3:1 to prepare a negative electrode slurry (solid concentration: 50 wt%).

[0157] As a mixing method, a homogenizer was used to disperse carbon black, the binder, and water at 2500 rpm for 30 minutes, and then the active materials (artificial graphite and natural graphite) were added, followed by dispersion at 2500 rpm for 30 minutes to prepare the slurry.

[0158] The negative electrode slurry was coated on both sides of a copper current collector (thickness: 15 μm) as a negative electrode current collector at a loading amount of 5.48 mAh / cm 2 and dried in a vacuum oven at 130 °C for 1 hour, followed by roll pressing to form a negative electrode active material layer (negative electrode porosity: 35%).

[0159] LiNi 0.6 Co 0.2 Mn 0.2 O2 (average particle size (D50): 15 μm), carbon black as a conductive material (trade name: Super C65, manufacturer: Timcal), and polyvinylidene fluoride (PVdF) as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent for forming a positive electrode slurry at a weight ratio of 95:2.5:2.5 to prepare a positive electrode slurry (solid concentration: 63 wt%).

[0160] The positive electrode slurry was coated on both sides of an aluminum current collector (thickness: 15 μm) as a positive electrode current collector at a loading amount of 4.0 mAh / cm 2 and the aluminum current collector was dried in a vacuum oven at 130 °C for 1 hour, followed by roll pressing to form a positive electrode active material layer, thereby fabricating a positive electrode (positive electrode porosity: 25%).

[0161] A lithium secondary battery was fabricated by disposing a polyethylene separator between the positive electrode and the negative electrode of the comparative example and injecting an electrolyte therein (based on 4.2 V to 2 V, NP ratio of 137).

[0162] [Table 1]

[0163]

[0164] Experimental Example 1: Evaluation of service life characteristics

[0165] Using an electrochemical charge / discharge device, the service life evaluations of three cells each were conducted on secondary batteries containing the negative electrodes fabricated in the examples and comparative examples, and the capacity retention rate was evaluated. The secondary batteries were subjected to an in-situ cycling test at 4.2 to 2.0 V at 1C / 0.5C, and during the test, the secondary batteries were charged / discharged at 0.33C / 0.33C (4.2 to 2.0 V) every 50 cycles to measure the capacity retention rate. Table 2 below shows the in-situ capacity retention rate instead of the RPT capacity retention rate.

[0166] Capacity retention rate (%) = {(discharge capacity at the nth cycle) / (discharge capacity at the first cycle)} × 100

[0167] Experimental Example 2: Measurement and evaluation of the resistance increase rate

[0168] During the test in Experimental Example 1, after measuring the capacity retention rate by charging / discharging the secondary battery at 0.33C / 0.33C (4.2 to 2.0 V) every 50 cycles, the resistance was measured by discharging the secondary battery with a 2.5C pulse at SOC50, and thus the resistance increase rate was compared and analyzed.

[0169] In addition, for the service life characteristic evaluation and the resistance increase rate measurement evaluation, data at 100 cycles, 200 cycles, and 400 cycles were calculated respectively, and the results are shown in Table 2 below.

[0170] In Table 2 below, for the three secondary batteries of the examples, denoted as Examples 1 to 3, the service life evaluations were conducted respectively, and for the three secondary batteries of the comparative examples, denoted as Comparative Examples 1 to 3, the service life evaluations were conducted respectively. The average values and standard deviation values of Examples 1 to 3 and the average values and standard deviation values of Comparative Examples 1 to 3 were recorded respectively.

[0171] [Table 2]

[0172]

[0173] It can be confirmed from Table 1 and Table 2 above that the lithium secondary battery of the example of the present application contains 1 part by weight or more and 50 parts by weight or less of artificial graphite having an initial capacity of 330 mAh / g or more with respect to 100 parts by weight of the carbon-based active material, and since the NP ratio is adjusted to 110 or more, a large amount of remaining negative electrode can be obtained. Therefore, even when artificial graphite is used within the above range, the deterioration of the battery cell is not accelerated, and thus the service life characteristics and resistance characteristics are maintained or improved.

[0174] In addition, it can be confirmed that, in the case of a comparative example where the usage amount of artificial graphite exceeds the scope of the present application, it is difficult to manufacture an electrode due to the difficulty in processing artificial graphite. As a result, the standard deviation of the electrochemical performance value is larger than that of the examples. That is, it can be seen that the batteries of the comparative examples are not suitable for mass production and do not have good processability. Therefore, it can be seen that when the NP ratio is 110 or more, it is necessary to include natural graphite that is easy to process and use a specific weight of artificial graphite of the present application at the same time.

Claims

1. A lithium secondary battery, comprising: a positive electrode; a negative electrode; a separator disposed between the positive electrode and the negative electrode; and an electrolyte, wherein the negative electrode includes a negative electrode current collector layer and a negative electrode active material layer containing a negative electrode active material layer composition disposed on one or both surfaces of the negative electrode current collector layer, the negative electrode active material layer composition contains a carbon-based active material, and contains 1 part by weight or more and 50 parts by weight or less of artificial graphite having an initial capacity of 330 mAh / g or more with respect to 100 parts by weight of the carbon-based active material, and the NP ratio is 110 or more.

2. The lithium secondary battery according to claim 1, wherein, The carbon-based active material contains natural graphite and artificial graphite having an initial capacity of 330 mAh / g or more, and the weight ratio of the artificial graphite to the natural graphite is 1:99 to 50:50 with respect to 100 parts by weight of the carbon-based active material.

3. The lithium secondary battery according to claim 1, wherein The negative electrode active material layer composition further contains one or more selected from the group consisting of a silicon-based active material, a tin-based active material, a metal-based active material capable of forming an alloy with lithium, lithium titanium oxide, and lithium nitride.

4. The lithium secondary battery according to claim 1, wherein, The NP ratio is 110 or more and 200 or less.

5. The lithium secondary battery according to claim 3, wherein, The negative electrode active material layer composition contains a carbon-based active material and a silicon-based active material, and the content of the silicon-based active material is 50 parts by weight or less with respect to 100 parts by weight of the negative electrode active material layer composition.

6. The lithium secondary battery according to claim 2, wherein, The artificial graphite having an initial capacity of 330 mAh / g or more and the natural graphite are crystalline carbon.

7. The lithium secondary battery according to claim 1, wherein The positive electrode includes a positive electrode current collector layer and a positive electrode active material layer, the positive electrode active material layer contains a positive electrode active material layer composition and is disposed on one or both surfaces of the positive electrode current collector layer, and the positive electrode active material layer composition contains one or more positive electrode active materials selected from the group consisting of: LiNi x Co y Mn z O2, where x + y + z = 1; LiNi a Co b Mn c Al d O2, where a + b + c + d = 1; LiMn2O4; LiNi 0.5 Mn 1.5 O₂; and LiM x Fe y PO4, where M is a transition metal and x + y = 1.

8. The lithium secondary battery according to claim 7, wherein, The positive electrode active material layer composition contains: LiNi x Co y Mn z O2, where x + y + z = 1; or LiNi a Co b Mn c Al d O2, where a + b + c + d = 1, z is 0.5 or more, and c is 0.4 or more.

9. The lithium secondary battery according to claim 1, wherein, The thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, and the thickness of the negative electrode active material layer is 5 μm or more and 500 μm or less.

10. The lithium secondary battery according to claim 7, wherein The thickness of the positive electrode current collector layer is 1 μm or more and 100 μm or less, and the thickness of the positive electrode active material layer is 5 μm or more and 500 μm or less.

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