Lithium secondary battery

Abstract

The present application relates to lithium secondary batteries.

Description

[Technical Field]

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2023-0164404, filed with the Korean Intellectual Property Office on November 23, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present application relates to lithium secondary batteries. [Background technology]

[0003] The rapid increase in fossil fuel use has led to an increasing demand for alternative and clean energy, and one of the most actively researched areas as part of this is the field of power generation and storage using electrochemical reactions.

[0004] Currently, a typical example of an electrochemical element that uses such electrochemical energy is a secondary battery, and the range of its use is tending to expand more and more.

[0005] As technological development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and widely used. In addition, active research is being conducted on methods for manufacturing high-density electrodes with higher energy density per unit volume as electrodes for such high-capacity lithium secondary batteries.

[0006] Generally, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode contains a negative electrode active material that inserts and extracts lithium ions from the positive electrode. Silicon-based particles with a large discharge capacity can be used as the negative electrode active material.

[0007] In particular, with the recent demand for high-density energy batteries, Si / C and SiO, which have capacities 10 times larger than graphite-based materials, are being used as negative electrode active materials. xActive research is being conducted into methods for increasing capacity by using silicon-based compounds such as graphite. However, while silicon-based compounds, which are high-capacity materials, have a higher capacity than conventionally used graphite and offer excellent capacity characteristics, they rapidly expand in volume during charging, disrupting the conductive path and resulting in a decline in battery performance and a decrease in capacity from the start. Furthermore, with silicon-based anodes, lithium ions are not uniformly charged throughout the anode depth during repeated charge and discharge cycles, and reactions occur on the surface, accelerating surface degradation. Therefore, performance improvements are needed from the perspective of battery cycles.

[0008] Therefore, various methods are being discussed to solve the above problems when using silicon-based compounds as negative electrode active materials, such as adjusting the driving potential, coating an additional thin film on the active material layer, suppressing the volume expansion itself by adjusting the particle size of the silicon-based compound, or developing a binder that suppresses the volume expansion of the silicon-based compound to prevent the conductive path from being broken.In addition, research is being conducted to improve the life characteristics of silicon-based negative electrodes by limiting the proportion of silicon-based active material used during initial charge and discharge by pre-lithiating the silicon-based active material layer, thereby providing the layer with the role of a reservoir.

[0009] However, this method has limitations in its application because it may actually reduce the performance of the battery, and there are still limitations in the commercialization of anode battery manufacturing with a high content of silicon-based compounds.

[0010] In addition, in the case of batteries using recent NCM cathode materials, the NP ratio is designed to be around 100-105, but this is due to the occurrence of Li plating on the anode and the increased cost when excessive anodes are used. In recent years, designs are underway to eliminate residual anodes and use a full anode profile.

[0011] However, when a full profile of the negative electrode is used to eliminate residual negative electrode material, problems arise in the lifespan performance of the negative electrode, particularly problems with lifespan degradation depending on the type of negative electrode active material. That is, when a high-capacity silicon-based active material is used in a full profile to ensure capacity characteristics, volume expansion causes a problem of reduced lifespan.

[0012] Therefore, research is needed into methods that can improve cell performance without using a full negative electrode profile. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-080971 Summary of the Invention [Problem to be solved by the invention]

[0014] The present application has found that when the depth of discharge of the negative electrode is controlled (cut-off potential control) without using a full profile of the negative electrode, it is possible to improve the life characteristics as well as the cell characteristics.

[0015] Therefore, an object of the present application is to provide a lithium secondary battery in which the depth of discharge of the negative electrode is controlled. [Means for solving the problem]

[0016] One embodiment of the present specification provides a lithium secondary battery including a positive electrode; a negative electrode; a separator provided between the positive electrode and the negative electrode; and an electrolyte, wherein the negative electrode has a discharge potential controlled to 0 V or more and 1.5 V or less (vs. Li / Li+), the negative electrode has a remaining negative electrode capacity defined by the following formula 1 of 2.5% or more, and the cut-off potential of the negative electrode is lower than the discharge potential of the negative electrode.

[0017]

number

[0018] The lithium secondary battery according to the present application is characterized in that the discharge potential of the negative electrode is controlled to be 0 V or more and 1.5 V or less (vs. Li / Li+) without using a full profile of the negative electrode, and the cut-off potential of the negative electrode is adjusted to be less than the discharge potential of the negative electrode, thereby leaving the remaining negative electrode capacity of the negative electrode represented by Equation 1. In other words, the main feature is that the remaining negative electrode capacity is left within the range of Equation 1 without using a full profile of the negative electrode, thereby improving the life characteristics.

[0019] That is, in the case of the lithium secondary battery according to the present application, the main feature is that the life characteristics of the lithium secondary battery are improved by adjusting the cut-off voltage to leave a residual negative electrode within the range of Equation 1, rather than adjusting the NP ratio to leave a residual negative electrode. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a diagram showing a stack structure of a lithium secondary battery according to an embodiment of the present application. [Figure 2] FIG. 1 is a diagram showing charge and discharge profiles including a carbon-based negative electrode, as well as cut-off potential and remaining negative electrode capacity (%). [Figure 3]FIG. 1 is a diagram showing charge and discharge profiles including a silicon-based negative electrode, as well as cut-off potential and remaining negative electrode capacity (%). [Figure 4] FIG. 1 shows charge and discharge profiles, cut-off potentials, and remaining negative electrode capacities (%) including carbon-based and silicon-based negative electrodes. [Figure 5] FIG. 1 shows three-electrode data for confirming information on examples and comparative examples of the present application. [Figure 6] FIG. 1 shows three-electrode data for confirming information on examples and comparative examples of the present application. [Figure 7] FIG. 1 shows three-electrode data for confirming information on examples and comparative examples of the present application. [Figure 8] FIG. 1 shows three-electrode data for confirming information on examples and comparative examples of the present application. [Figure 9] FIG. 1 shows three-electrode data for confirming information on examples and comparative examples of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0021] Before describing the present invention, some terms will first be defined.

[0022] In this specification, unless otherwise specified, when a part "comprises" a certain component, it does not mean that it may further include other components, but does not exclude other components.

[0023] In this specification, "p to q" means a range of "not less than p and not more than q."

[0024] In this specification, the "specific surface area" is measured by the BET method, and specifically, is calculated from the amount of nitrogen gas adsorption at liquid nitrogen temperature (77 K) using a BELSORP-mini II manufactured by BEL Japan Co., Ltd. That is, in the present application, the BET specific surface area may mean the specific surface area measured by the above-mentioned measurement method.

[0025] In this specification, "Dn" refers to particle size distribution, and refers to the particle size at the n% point in the cumulative particle number distribution according to particle size. That is, D50 is the particle size (average particle size, median particle size) at the 50% point in the cumulative particle number distribution according to particle size, D90 is the particle size at the 90% point in the cumulative particle number distribution according to particle size, and D10 is the particle size at the 10% point in the cumulative particle number distribution according to particle size. Meanwhile, particle size distribution can be measured using the laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500). The particle size distribution is calculated by measuring the difference in diffraction patterns according to particle size when the particles pass through a laser beam.

[0026] In this specification, when a polymer contains a certain monomer as a monomer unit, it means that the monomer participates in a polymerization reaction and is included in the polymer as a repeating unit. In this specification, when a polymer contains a monomer, it is interpreted in the same way as when a polymer contains a monomer as a monomer unit.

[0027] In this specification, the term "polymer" is understood to be used in a broad sense, including copolymers, unless otherwise specified as a "homopolymer."

[0028] In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are polystyrene-equivalent molecular weights measured by gel permeation chromatography (GPC) using commercially available monodisperse polystyrene polymers (standard samples) of various degrees of polymerization as standard substances for molecular weight measurement. In this specification, molecular weight means weight average molecular weight unless otherwise specified.

[0029] The present invention will now be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement the present invention, although the present invention may be embodied in various different forms and is not limited to the following description.

[0030] One embodiment of the present specification provides a lithium secondary battery including a positive electrode; a negative electrode; a separator provided between the positive electrode and the negative electrode; and an electrolyte, wherein the negative electrode has a discharge potential controlled to 0 V or more and 1.5 V or less (vs. Li / Li+), the negative electrode has a remaining negative electrode capacity defined by the following formula 1 of 2.5% or more, and the cut-off potential of the negative electrode is lower than the discharge potential of the negative electrode.

[0031]

number

[0032] The lithium secondary battery according to the present application is characterized in that the discharge potential of the negative electrode is controlled to be between 0 V and 1.5 V (vs. Li / Li+) without using a full profile of the negative electrode, and the cut-off potential of the negative electrode is adjusted to be less than the discharge potential of the negative electrode, thereby leaving the remaining negative electrode capacity of the negative electrode as expressed by Equation 1. In other words, the main feature is that the remaining negative electrode capacity is left within the range of Equation 1 without using a full profile of the negative electrode, thereby improving the life characteristics.

[0033] 1 is a diagram showing a laminated structure of a lithium secondary battery according to one embodiment of the present application. Specifically, a lithium secondary battery anode 100 including an anode active material layer 20 on one side of an anode current collector layer 10 can be seen, and a lithium secondary battery cathode 200 including a cathode active material layer 40 on one side of a cathode current collector layer 50 can be seen, and the lithium secondary battery anode 100 and lithium secondary battery cathode 200 are shown stacked with a separator 30 interposed therebetween.

[0034] The lithium secondary battery of the present invention will be described in more detail below.

[0035] In the present application, 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 or both sides of the negative electrode current collector layer.

[0036] In the present application, the negative electrode active material layer contains a negative electrode active material layer composition, and the negative electrode active material layer composition may include a negative electrode active material, a negative electrode conductive material, and a negative electrode binder.

[0037] In the present application, the negative electrode active material includes one or more selected from the group consisting of a carbon-based active material, a silicon-based active material, a tin-based active material, a metal-based active material capable of alloying with lithium, lithium titanate, and a lithium-containing nitride, to provide a lithium secondary battery.

[0038] In one embodiment of the present application, representative examples of the carbon-based active material include natural graphite, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, graphitizable carbon, carbon black, carbon nanotube, fullerene, or activated carbon, etc. Any material commonly used for carbon materials for lithium secondary batteries can be used without limitation, and specifically, it can be processed into spherical or dot-like shapes for use.

[0039] In one embodiment of the present application, the silicon-based active material is SiO x (x = 0), SiO x (0 < x < 2), SiC, and one or more selected from the group consisting of Si alloys may be included.

[0040] In one 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 based on 100 parts by weight of the silicon-based active material, SiO x (0 < x < 2) may be included at 1 part by weight or more.

[0041] In another 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 based on 100 parts by weight of the silicon-based active material, SiO x (0 < x < 2) may be included at 1 part by weight or more, 10 parts by weight or more, and may be included at 99 parts by weight or less.

[0042] In another embodiment, the silicon-based active material may contain SiO x (0 < x < 2).

[0043] In still another embodiment, the silicon-based active material may consist of SiO x (0 < x < 2).

[0044] In one embodiment of the present application, the negative electrode active material may consist of a carbon-based active material.

[0045] In one embodiment of the present application, the negative electrode active material may consist of a silicon-based active material.

[0046] In one embodiment of the present application, there is provided a lithium secondary battery, wherein the negative electrode active material includes a carbon-based active material and a silicon-based active material, and contains 30 parts by weight or less of the silicon-based active material based on 100 parts by weight of the negative electrode active material.

[0047] Particularly, the silicon-based active material as described above has a particularly sharp change in discharge capacity from 0.2V to 1.5V. When controlling the discharge depth of the negative electrode as in the present application, the effect of improving cell characteristics can be maximized.

[0048] Also, even if the composition and content of the negative electrode active material are changed as described above, the life characteristics can be improved by adjusting the cut-off potential of the negative electrode described later to leave a residual negative electrode capacity, and the type of negative electrode used can be used without limitation.

[0049] In one embodiment of the present application, there is provided a lithium secondary battery, wherein the negative electrode active material is contained in an amount of 60 parts by weight or more based on 100 parts by weight of the negative electrode active material layer composition.

[0050] In another embodiment, the negative electrode active material may be contained in an amount of 60 parts by weight or more, 65 parts by weight or more, 70 parts by weight or more, and may be contained in an amount of 90 parts by weight or less, 85 parts by weight or less based on 100 parts by weight of the negative electrode active material layer composition.

[0051] In one embodiment of the present application, the negative electrode active material layer composition may include a negative electrode conductive material; and a negative electrode binder.

[0052] While graphite-based compounds have traditionally been used exclusively as negative electrode active materials, attempts to incorporate silicon-based active materials into batteries to increase capacity have been increasing in recent years as demand for high-capacity batteries has grown. However, even if the properties of silicon-based active materials are adjusted as described above, their volume can rapidly expand during charge / discharge processes, potentially damaging the conductive paths formed in the negative electrode active material layer.

[0053] Therefore, in one embodiment of the present application, the negative electrode conductive material may include one or more selected from the group consisting of dot-shaped conductive materials, sheet-shaped conductive materials, and linear conductive materials.

[0054] In one embodiment of the present application, the dot-like conductive material refers to a dot-like or spherical conductive material that can be used to improve the conductivity of a negative electrode, does not cause chemical changes, and has conductivity. Specifically, the dot-like conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably includes carbon black, which achieves high conductivity and excellent dispersibility.

[0055] In one embodiment of the present application, the point-like conductive material has a BET specific surface area of ​​40 m 2 / g or more 70m 2 / g or less, preferably 45m 2 / g or more 65m 2 / g or less, more preferably 50m 2 / g or more 60m 2 / g or less.

[0056] In one embodiment of the present application, the dot-like conductive material may have a volatile matter content of 0.01% or more and 1% or less, preferably 0.01% or more and 0.3% or less, and more preferably 0.01% or more and 0.1% or less.

[0057] In particular, when the content of functional groups in the dot-like conductive material satisfies the above range, the functional groups are present on the surface of the dot-like conductive material, and when water is used as a solvent, the dot-like conductive material can be smoothly dispersed in the solvent. In particular, by using a specific silicon-based active material, the present invention can reduce the content of functional groups in the dot-like conductive material, thereby achieving an excellent effect of improving dispersibility.

[0058] In one embodiment of the present application, the silicon-based active material is characterized by including a dot-like conductive material having a functional group content within the above range, and the content of the functional group can be adjusted depending on the degree of heat treatment of the dot-like conductive material.

[0059] In one embodiment of the present application, the particle size of the dotted conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

[0060] In one embodiment of the present application, the conductive material may include a sheet-shaped conductive material.

[0061] The sheet-like conductive material can improve conductivity by increasing surface contact between silicon particles in the negative electrode and can also prevent the conductive path from being broken due to volume expansion. The sheet-like conductive material can be referred to as a plate-like conductive material or a bulk-like conductive material.

[0062] In one embodiment of the present application, the sheet-like conductive material may include at least one selected from the group consisting of platelet graphite, graphene, graphene oxide, and graphite flakes, and may preferably be platelet graphite.

[0063] In one embodiment of the present application, the average particle size (D50) of the sheet-like conductive material may be 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 3.5 μm to 5 μm. When the average particle size satisfies the above range, the particle size is sufficient to prevent an excessive increase in the viscosity of the negative electrode slurry and facilitate dispersion. Therefore, when dispersion is performed using the same device and for the same time, the dispersion effect is excellent.

[0064] In one embodiment of the present application, the sheet-shaped conductive material provides a negative electrode composition having a D10 of 0.5 μm or more and 2.0 μm or less, a D50 of 2.5 μm or more and 3.5 μm or less, and a D90 of 6.5 μm or more and 15.0 μm or less.

[0065] In one embodiment of the present application, the sheet-shaped conductive material may be a sheet-shaped conductive material having a high BET specific surface area; or a sheet-shaped conductive material having a low specific surface area.

[0066] In one embodiment of the present application, the sheet-like conductive material can be a sheet-like conductive material with a high specific surface area or a sheet-like conductive material with a low specific surface area, without any restrictions. However, since dispersion can have some effect on electrode performance, it is particularly preferable to use a sheet-like conductive material with a low specific surface area in which dispersion does not cause problems.

[0067] In one embodiment of the present application, the sheet-shaped conductive material has a BET specific surface area of ​​0.25 m 2 / g or more.

[0068] In another embodiment, the sheet-shaped conductive material has a BET specific surface area of ​​1 m 2 / g or more 500m 2 / g or less, preferably 5m 2 / g or more 300m 2 / g or less, more preferably 5m 2 / g or more 250m 2 / g or less.

[0069] The sheet-shaped conductive material according to the present application may be a sheet-shaped conductive material with a high specific surface area or a sheet-shaped conductive material with a low specific surface area.

[0070] In another embodiment, the sheet-shaped conductive material is a sheet-shaped conductive material having a high specific surface area, and a BET specific surface area of ​​50 m 2 / g or more 500m 2 / g or less, preferably 80m 2 / g or more 300m 2 / g or less, more preferably 100m 2 / g or more 300m 2 / g or less.

[0071] In another embodiment, the sheet-shaped conductive material is a sheet-shaped conductive material having a low specific surface area, and a BET specific surface area of ​​1 m 2 / g or more 40m 2 / g or less, preferably 5m 2 / g or more 30m 2 / g or less, more preferably 5m 2 / g or more 25m 2 / g or less.

[0072] Other conductive materials include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundled carbon nanotubes. The bundled carbon nanotubes may include multiple carbon nanotube units. Specifically, unless otherwise specified, the term "bundle type" refers to a secondary shape in which multiple carbon nanotube units are arranged side by side or entangled with each other, in a bundle or rope-like configuration. The carbon nanotube units have graphite sheets with nanosized diameters and a cylindrical sp2 bond structure. Depending on the curved angle and structure of the graphite sheets, they can exhibit conductive or semiconductive properties. Compared to entangled carbon nanotubes, the bundled carbon nanotubes can be more uniformly dispersed during negative electrode fabrication, smoothly forming a conductive network within the negative electrode and improving the conductivity of the negative electrode.

[0073] In one embodiment of the present application, the negative electrode conductive material may be included in an amount of 0.1 parts by weight to 40 parts by weight based on 100 parts by weight of the negative electrode active material layer composition.

[0074] In another embodiment, the negative electrode conductive material may be included in an amount of 0.1 parts by weight to 40 parts by weight, preferably 0.2 parts by weight to 30 parts by weight, more preferably 0.4 parts by weight to 25 parts by weight, and most preferably 0.4 parts by weight to 10 parts by weight, based on 100 parts by weight of the negative electrode active material layer composition.

[0075] In one embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode conductive material includes a sheet-shaped conductive material or a linear conductive material.

[0076] In one embodiment of the present application, the negative electrode conductive material may include a sheet-shaped conductive material; and a linear conductive material.

[0077] In one embodiment of the present application, the negative electrode conductive material may include 80 parts by weight or more and 99.9 parts by weight or less of the sheet-like conductive material and 0.1 parts by weight or more and 20 parts by weight or less of the linear conductive material, based on 100 parts by weight of the negative electrode conductive material.

[0078] In another embodiment, 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 the sheet-like conductive material, based on 100 parts by weight of the negative electrode conductive material.

[0079] In another embodiment, the negative electrode conductive material may contain 0.1 parts by weight or more and 20 parts by weight or less, preferably 0.1 parts by weight or more and 15 parts by weight or less, and more preferably 0.2 parts by weight or more and 5 parts by weight or less of the linear conductive material, based on 100 parts by weight of the negative electrode conductive material.

[0080] In one embodiment of the present application, the negative electrode conductive material includes a sheet-like conductive material and a linear conductive material, and by satisfying the above-mentioned composition and proportions, the battery does not have a significant effect on the life characteristics of conventional lithium secondary batteries. In particular, when the negative electrode conductive material includes a sheet-like conductive material and a linear conductive material, the battery has the following characteristics: there are more points at which charging and discharging are possible, output characteristics are excellent at a high C-rate, and the amount of high-temperature gas generated is reduced.

[0081] In one embodiment of the present application, the negative electrode conductive material may be made of a linear conductive material.

[0082] In particular, when linear conductive materials are used alone, the tortuosity of the electrode, which is a problem with silicon-based negative electrodes, can be simplified, improving the electrode structure and thereby reducing the resistance to lithium ion migration within the electrode.

[0083] In one embodiment of the present application, when the negative electrode conductive material includes only a linear conductive material, the negative electrode conductive material may be included in an amount of 0.1 parts by weight to 5 parts by weight, preferably 0.2 parts by weight to 3 parts by weight, and more preferably 0.4 parts by weight to 1 part by weight, based on 100 parts by weight of the negative electrode active material layer composition.

[0084] The negative electrode conductive material according to the present application has a structure that is completely different from the positive electrode conductive material used in the positive electrode. That is, the negative electrode conductive material according to the present application serves to form a contact between silicon-based active materials, which undergo a very large volume expansion in the electrode upon charge and discharge, while the positive electrode conductive material serves to act as a buffer during rolling and to impart some conductivity, and therefore has a structure and role that are completely different from the negative electrode conductive material of the present invention.

[0085] Furthermore, the negative electrode conductive material according to the present application is applied to a silicon-based active material and has a completely different structure from conductive materials applied to graphite-based active materials. That is, conductive materials used in electrodes having graphite-based active materials simply have smaller particles than the active material, and therefore have the properties of improving output characteristics and imparting some conductivity, and are completely different in structure and role from negative electrode conductive materials applied together with silicon-based active materials as in the present invention.

[0086] In one embodiment of the present application, the sheet-like conductive material used as the negative electrode conductive material has a structure and function different from that of a carbon-based active material generally used as a negative electrode active material. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, and refers to a material that is processed into a spherical or dotted shape to facilitate the storage and release of lithium ions.

[0087] In contrast, the sheet-like conductive material used as the negative electrode conductive material is a material having a sheet or plate shape and can be expressed as plate-like graphite. That is, it is a material contained in the negative electrode active material layer to maintain a conductive path, and does not play a role in storing and releasing lithium, but refers to a material in sheet form to ensure a conductive path inside the negative electrode active material layer.

[0088] That is, in this application, the use of plate-like graphite as a conductive material means that it is processed into a sheet or plate shape and used as a material to ensure a conductive path rather than to store or release lithium. In this case, the negative electrode active material contained therein has high capacity characteristics for storing and releasing lithium, and plays a role in storing and releasing all lithium ions transferred from the positive electrode.

[0089] In contrast, in the present application, the term "carbon-based active material is used as an active material" means that the carbon-based active material is processed into a dotted or spherical shape and used as a material that plays a role in storing or releasing lithium.

[0090] That is, in one embodiment of the present application, the carbon-based active material, artificial graphite or natural graphite, is dot-shaped and has a BET specific surface area of ​​0.1 m 2 / g or more 4.5m 2 The sheet-shaped conductive material, plate-shaped graphite, may be in the form of a sheet and have a BET specific surface area of ​​5 m 2 / g or more.

[0091] In one embodiment 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, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which hydrogen is substituted with Li, Na, Ca, or the like, or may include various copolymers thereof.

[0092] The negative electrode binder according to one embodiment of the present application plays a role in holding the active material and the conductive material together to prevent distortion and structural deformation of the negative electrode structure when the volume of the silicon-based active material expands and relaxes. Any common binder that fulfills the above role can be used; specifically, a water-based binder may be used, and more specifically, a PAM-based binder may be used.

[0093] In one embodiment of the present application, the amount of the negative electrode binder may be 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, or may be 5 parts by weight or more, or 10 parts by weight or more, based on 100 parts by weight of the negative electrode active material layer composition.

[0094] In one embodiment of the present application, there is provided a lithium secondary battery, 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.

[0095] The negative electrode current collector layer generally has a thickness of 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, and examples thereof include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys. Furthermore, the surface may be provided with fine irregularities to strengthen the bonding strength of the negative electrode active material, and the negative electrode current collector layer may be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0096] However, the thickness may vary depending on the type and application of the negative electrode used, and is not limited to the above.

[0097] In one embodiment of the present application, the porosity of the negative electrode active material layer may be in the range of 10% or more and 60% or less.

[0098] In another embodiment, the porosity of the negative electrode active material layer may satisfy the range of 10% to 60%, preferably 20% to 50%, more preferably 30% to 45%.

[0099] 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, and is characterized by having an appropriate range for the electrical conductivity and resistance of the electrode.

[0100] In one embodiment of the present application, the positive electrode includes a positive electrode current collector layer; and a positive electrode active material layer including a positive electrode active material layer composition provided on one or both surfaces of the positive electrode current collector layer, and the positive electrode active material layer composition includes a positive electrode active material.

[0101] In the positive electrode, the positive electrode current collector layer is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like may be used. The positive electrode current collector layer may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. It may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0102] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; a lithium iron oxide such as LiFe3O4; 1+c1 Mn 2-c1 O4 (0≦c1≦0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented by the chemical formula LiMnO2 (wherein 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 is satisfied); 2-c3 M c3 Examples of the lithium manganese composite oxide include, but are not limited to, lithium manganese composite oxides represented by Li2Mn3MO8 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 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); or LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion. The positive electrode may be Li metal.

[0103] In the present application, the positive electrode active material is 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 Provided is a lithium secondary battery containing one or more selected from the group consisting of PO4 (M: transition metal, x+y=1).

[0104] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be any material that has electronic conductivity without causing chemical changes in the battery that is constructed. Specific examples 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 black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These may be used alone or in combination of two or more.

[0105] The positive electrode binder serves to improve adhesion between particles of the positive electrode active material and between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination.

[0106] The present application relates to a lithium secondary battery including a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, wherein the discharge potential of the negative electrode is controlled to be between 0 V and 1.5 V (vs. Li / Li+).

[0107] Generally, a negative electrode is charged and discharged between 0.005 V and 1.5 V depending on the composition and content of the active material used. However, in the case of Si or Sn, a 3 V cut-off profile may be used, where the charge and discharge is performed between 0.005 V and 3 V. In this case, the voltage approaches 0 V when it meets the discharge potential of the positive electrode profile, which is the opposite electrode of the full cell, and thus falls outside the actual operating voltage range of the lithium secondary battery. However, the negative electrode for a lithium secondary battery according to the present application is characterized in that the discharge potential is controlled to between 0 V and 1.5 V (vs. Li / Li+) regardless of the composition and content of the active material used.

[0108] In this case, the negative electrode according to the present application may have a remaining negative electrode capacity represented by the above-mentioned formula 1.

[0109] Having a residual negative electrode capacity represented by formula 1 means that the discharge capacity of the negative electrode between 0 V and 1.5 V (vs. Li / Li+) is not the same as the discharge capacity of the negative electrode up to the cut-off potential. Specifically, formula 1 can be applied without limitation as long as it has a value of 2.5% or more.

[0110] In the present application, there is provided a lithium secondary battery in which the remaining negative electrode capacity of the negative electrode, represented by the formula 1, is 2.5% or more and 50% or less.

[0111] In the present application, the remaining negative electrode capacity represented by the formula 1 may be 2.5% or more, specifically 5% or more, more specifically 10% or more, and may be 80% or less, specifically 60% or less, more specifically 50% or less.

[0112] In the present application, in the above formula 1, the value of the negative electrode discharge capacity (vs. Li / Li+) from 0 V to 1.5 V or less - the negative electrode discharge capacity (vs. Li / Li+) from 0 V to the cut-off potential is 1 μAh / cm 2 The cut-off potential of the negative electrode may be 0V or more and 1.4V or less.

[0113] In the present application, in the above formula 1, the value of the negative electrode discharge capacity (vs. Li / Li+) from 0 V to 1.5 V or less - the negative electrode discharge capacity (vs. Li / Li+) from 0 V to the cut-off potential is 1 μAh / cm 2 More than 20mAh / cm 2 Specifically, 10 μAh / cm 2 More than 15mAh / cm 2 More specifically, 100 μAh / cm 2 More than 10mAh / cm 2 The following ranges may be satisfied:

[0114] By leaving the remaining negative electrode capacity in the above range, the negative electrode can be left and the life characteristics can be improved compared to using a full profile of the negative electrode.

[0115] In one embodiment of the present application, the cut-off potential of the negative electrode may be less than the discharge potential of the negative electrode.

[0116] In this case, the cut-off potential of the negative electrode may be 0V or more and 1.4V or less.

[0117] In the present application, the level of the remaining negative electrode capacity represented by the formula 1 can be determined according to the cut-off potential of the negative electrode.

[0118] In one embodiment of the present application, there is provided a lithium secondary battery, wherein the negative electrode active material includes a carbon-based active material, and the cut-off potential of the negative electrode is 0.1 V or more and 0.9 V or less.

[0119] Specifically, FIG. 2 shows an example of a negative electrode containing 100% carbon-based active material, and when the cut-off potential is set to less than 0.5 V, the remaining negative electrode capacity can be expressed as in Equation 1.

[0120] In one embodiment of the present application, there is provided a lithium secondary battery, wherein the negative electrode active material includes a silicon-based active material, and the cut-off potential of the negative electrode is 0.1 V or more and 1.4 V or less.

[0121] Specifically, FIG. 3 shows an example of a negative electrode containing 100% silicon-based active material, and when the cut-off potential is set to less than 1.3 V, the negative electrode can have a remaining negative electrode capacity as shown in Equation 1.

[0122] In one embodiment of the present application, there is provided a lithium secondary battery, wherein the negative electrode active material includes a silicon-based active material and a carbon-based active material, and the cut-off potential of the negative electrode is 0.2 V or more and 1.3 V or less.

[0123] Specifically, FIG. 4 shows an example of a negative electrode having a mixture of a silicon-based active material and a carbon-based active material. When a cutoff potential of less than 0.7 V is set, the negative electrode can have a remaining negative electrode capacity as shown in Equation 1.

[0124] 2 to 4 show charge and discharge profiles of anodes depending on the type of anode. Specifically, the capacity value on the x-axis varies depending on the type of anode, allowing comparison of the remaining anode capacity depending on the cut-off potential of the anode. Specifically, for carbon-based anodes, there is almost no difference in capacity between 1.5 V and 1.4 to 1.45 V, meaning no remaining capacity remains. Therefore, for carbon-based anodes, adjusting the cut-off potential to 0.1 V or more and 0.9 V or less allows the remaining anode capacity to remain within the range of Equation 1. Furthermore, for silicon-based anodes, a capacity change occurs around 1.5 V, and a capacity difference appears around 1.3 V. For silicon-based anodes, adjusting the cut-off potential to 0.1 V or more and 1.4 V or less allows the remaining anode capacity to remain within the range of Equation 1.

[0125] For reference, the method for measuring the profile curves of the negative and positive electrodes in Figures 2 to 4 can be achieved by using the negative or positive electrode to be measured as the working electrode, lithium metal as the counter electrode, and filling the inside of the coin cell with a PE separator and electrolyte to create a coin cell, and then charging and discharging it.

[0126] That is, as described above, the cut-off potential can be adjusted depending on the type of negative electrode used, and by adjusting the remaining negative electrode capacity to fall within the range of Equation 1, it is possible to improve the capacity characteristics as well as the life characteristics, which is a main feature of the present invention.

[0127] The separator separates the negative electrode and positive electrode and provides a path for lithium ion migration. Any separator typically used in secondary batteries can be used without particular limitation. It is particularly preferable that the separator exhibits low resistance to electrolyte ion migration and has excellent electrolyte humidification capacity. Specifically, porous polymer films, such as those made from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymeric material may be used, and it may be selectively used as a single-layer or multi-layer structure.

[0128] 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, and molten inorganic electrolytes that can be used in manufacturing lithium secondary batteries.

[0129] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0130] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, 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, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0131] In particular, among the carbonate organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, can be preferably used as high-viscosity organic solvents, because they have a high dielectric constant and dissociate lithium salts well. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte having high electrical conductivity can be prepared, and therefore such cyclic carbonates can be more preferably used.

[0132] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte. For example, the anion of the lithium salt may be 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:

[0133] In addition to the constituent components of the electrolyte, the electrolyte may further include one or more additives, such as a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, in order to improve the life characteristics of the battery, suppress a decrease in battery capacity, and improve the discharge capacity of the battery.

[0134] According to one embodiment of the present invention, there is provided a battery module including the secondary battery as a unit cell, and a battery pack including the same. The battery module and the battery pack include the secondary battery having high capacity, high rate characteristics, and high cycle characteristics, and therefore can be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0135] Below, preferred examples are presented to help understand the present invention. However, the following examples are merely for the purpose of illustrating the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present description, and it is natural that such changes and modifications fall within the scope of the appended claims. [Example]

[0136] <Production example> Example 1 <Secondary battery manufacturing> A carbon-based active material (artificial graphite (D50:18μm):natural graphite (D50:18μm) = 50:50), carbon black, SBR as a binder, and CMC as a thickener were added in a weight ratio of 95.7:1:2.3:1 to distilled water as a solvent for forming a negative electrode slurry to prepare a negative electrode slurry (solid concentration 50 wt%).

[0137] The carbon black, binder, and distilled water were dispersed using a homomixer at 2500 rpm for 30 minutes, and then the active material was added, followed by dispersion at 2500 rpm for 30 minutes to prepare a slurry.

[0138] The negative electrode slurry was coated on both sides of a copper current collector (thickness: 15 μm) as a negative electrode current collector, dried in a vacuum oven at 130° C. for 1 hour, and roll pressed to form a negative electrode active material layer (porosity: 35%).

[0139] LiNi as the positive electrode active material 0.6 Co 0.2 Mn 0.2 O2 (average particle size (D50): 15 μm), carbon black (product name: Super C65, manufacturer: Timcal) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were added in a weight ratio of 95:2.5:2.5 to N-methyl-2-pyrrolidone (NMP) as a solvent for forming a positive electrode slurry to prepare a positive electrode slurry (solid concentration: 63 wt%).

[0140] The positive electrode slurry was coated on both sides of an aluminum current collector (thickness: 12 μm) as a positive electrode current collector, dried in a vacuum oven at 130° C. for 1 hour, and roll pressed to prepare a positive electrode active material layer (porosity: 30%).

[0141] A polyethylene separator was interposed between the positive electrode and the negative electrode, and an electrolyte was injected into the separator to prepare a lithium secondary battery.

[0142] The electrolyte was an organic solvent made by mixing fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) in a volume ratio of 30:70, to which 3 wt % vinylene carbonate was added based on the total weight of the electrolyte, and LiPF6 was added as a lithium salt at a concentration of 1 M.

[0143] <Example 2> <Secondary battery manufacturing> Carbon-based active material (artificial graphite (D50: 18 μm): natural graphite (D50: 18 μm): SiO x The negative electrode slurry was prepared in the same manner as in Example 1, except that the negative electrode slurry was prepared by adding carbon black, SBR as a binder, and CMC as a thickener in a weight ratio of 95.7:1:2.3:1 (D50:7 μm) to distilled water as a solvent for forming the negative electrode slurry.

[0144] Example 3 <Secondary battery manufacturing> Carbon-based active material (artificial graphite (D50: 18 μm): natural graphite (D50: 18 μm): SiO x The negative electrode slurry was prepared in the same manner as in Example 1, except that the negative electrode slurry was prepared by adding carbon black, SBR as a binder, and CMC as a thickener in a weight ratio of 95.7:1:2.3:1 (D50:7 μm) of 48.75:48.75:2.5 to distilled water as a solvent for forming the negative electrode slurry.

[0145] Example 4 <Secondary battery manufacturing> Carbon-based active material (artificial graphite (D50: 18 μm): natural graphite (D50: 18 μm): SiO x The negative electrode slurry was prepared in the same manner as in Example 1, except that the negative electrode slurry was prepared by adding carbon black, SBR as a binder, and CMC as a thickener in a weight ratio of 95.7:1:2.3:1 to distilled water as a solvent for forming the negative electrode slurry.

[0146] <Comparative Example 1> <Secondary battery manufacturing> Carbon-based active material (artificial graphite (D50: 18 μm): natural graphite (D50: 18 μm): SiO x The negative electrode slurry was prepared in the same manner as in Example 1, except that the negative electrode slurry was prepared by adding carbon black, SBR as a binder, and CMC as a thickener in a weight ratio of 95.7:1:2.3:1 (D50:7 μm) of 47.25:47.25:5.5 to distilled water as a solvent for forming the negative electrode slurry.

[0147] In the examples and comparative examples, the negative and positive electrodes were controlled according to the information in Table 1 below.

[0148] [Table 1]

[0149] Specifically, as shown in FIGS. 5 to 9, a bicell 3-electrode evaluation was carried out to confirm the cut-off potentials in Table 1, and the results were derived as shown in Table 1.

[0150] Experimental example The results of the examples and comparative examples are shown in Table 2 below.

[0151] In this regard, the 0.33C capacity retention rate in Table 2 was evaluated at a high temperature of 45°C using an electrochemical charger / discharger. The secondary battery was subjected to an in-situ cycle test at 1C / 0.5C in accordance with the cell driving voltage listed in Table 1, and the following calculation was made based on 300 cycles.

[0152] Capacity retention rate (%) = {(discharge capacity at Nth cycle) / (discharge capacity at first cycle)} × 100

[0153] [Table 2]

[0154] As can be seen from Table 2, in all cases of Examples 1 to 4 of the present invention, it was confirmed that when the cut-off potential of the negative electrode was controlled to leave the remaining negative electrode capacity within the range of Equation 1, the life characteristics were improved. In other words, it was confirmed that the life characteristics were improved by controlling the cut-off potential without being significantly affected by the type of negative electrode, and that it is important to design the battery to include the remaining negative electrode according to Equation 1. Specifically, Example 1 corresponds to a carbon-based negative electrode, and Examples 2 to 4 correspond to a carbon-based and silicon-based mixed negative electrode.

[0155] In Comparative Example 1, the cut-off potential was controlled, but the remaining negative electrode capacity remained at 2.4%. In this case, the initial capacity was partially reduced and the capacity retention rate was not maintained at 80% or more. In other words, it was confirmed that the life characteristics were reduced.

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, The negative electrode has a discharge potential controlled to 0 V or more and 1.5 V or less (vs. Li / Li+), The remaining negative electrode capacity defined by the following formula 1 is 2.5% or more, A lithium secondary battery, wherein a cut-off potential of the negative electrode is lower than a discharge potential of the negative electrode. [Equation 1]

2. 2. The lithium secondary battery according to claim 1, wherein the remaining negative electrode capacity of the negative electrode represented by formula 1 is 2.5% or more and 50% or less.

3. In the above formula 1, the value of the negative electrode discharge capacity (vs. Li / Li+) from 0 V to 1.5 V or less - the negative electrode discharge capacity (vs. Li / Li+) from 0 V to the cut-off potential is 1 μAh / cm ２ That's all, 2. The lithium secondary battery according to claim 1, wherein the cut-off potential of the negative electrode is 0 V or more and 1.4 V or less.

4. the negative electrode includes a negative electrode current collector layer; and a negative electrode active material layer provided on one or both surfaces of the negative electrode current collector layer, the negative electrode active material layer includes a negative electrode active material layer composition, the negative electrode active material layer composition includes a negative electrode active material; a negative electrode conductive material; and a negative electrode binder, 4. The lithium secondary battery according to claim 1, wherein the negative electrode active material comprises at least one selected from the group consisting of a carbon-based active material, a silicon-based active material, a tin-based active material, a metal-based active material that can be alloyed with lithium, a lithium-titanium oxide, and a lithium-containing nitride.

5. the negative electrode active material includes a carbon-based active material, 5. The lithium secondary battery according to claim 4, wherein the cut-off potential of the negative electrode is 0.1 V or more and 0.9 V or less.

6. the negative electrode active material includes a silicon-based active material, 5. The lithium secondary battery according to claim 4, wherein the cut-off potential of the negative electrode is 0.1 V or more and 1.4 V or less.

7. the negative electrode active material includes a silicon-based active material and a carbon-based active material, 5. The lithium secondary battery according to claim 4, wherein the cut-off potential of the negative electrode is 0.2 V or more and 1.3 V or less.

8. the negative electrode active material includes a carbon-based active material; and a silicon-based active material, The lithium secondary battery according to claim 4 , comprising 30 parts by weight or less of the silicon-based active material based on 100 parts by weight of the negative electrode active material.

9. The lithium secondary battery of claim 4 , wherein the negative electrode active material is contained in an amount of 60 parts by weight or more based on 100 parts by weight of the negative electrode active material layer composition.

10. the positive electrode includes a positive electrode current collector layer; and a positive electrode active material layer provided on one or both surfaces of the positive electrode current collector layer and including a positive electrode active material layer composition, the positive electrode active material layer includes a positive electrode active material; a positive electrode conductive material; and a positive electrode binder, The positive electrode active material is LiNi ｘ Co ｙ Mn ｚ O ２ (x+y+z=1);LiNi ａ Co ｂ Mn ｃ Al ｄ O ２ (a+b+c+d=1);LiMn ２ O ４ ;LiNi ０．５ Mn １．５ O ２ and LiM ｘ Fe ｙ P.O. ４ 2. The lithium secondary battery according to claim 1, comprising one or more selected from the group consisting of (M: transition metal, x+y=1).

11. the negative electrode current collector layer has a thickness of 1 μm or more and 100 μm or less, 5. The lithium secondary battery according to claim 4, wherein the thickness of the negative electrode active material layer is 5 μm or more and 500 μm or less.

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

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