Lithium secondary battery

Abstract

The present application relates to a lithium secondary battery comprising: a positive electrode; a negative electrode; a diaphragm; and an electrolyte, in which a discharge potential of the negative electrode is controlled to 0 V or more and 1.5 V or less (with respect to Li / Li +) without using a full characteristic spectrum of the negative electrode, and an off potential of the negative electrode is controlled to be lower than the discharge potential of the negative electrode according to a type of the negative electrode, thereby leaving a remaining negative electrode capacity and thus improving lifespan characteristics.

Description

Technical Field

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

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

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

[0004] Currently, secondary batteries are a representative example of electrochemical devices using such electrochemical energy, and their specific application range tends to be gradually expanded.

[0005] With technological advancements and the increasing demand for mobile devices, the demand for secondary batteries as energy sources has increased dramatically. Among these secondary batteries, lithium secondary batteries, which offer high energy density and voltage, long cycle life, and low self-discharge rates, have become commercially available and widely used. Furthermore, research is actively underway to develop methods for producing high-density electrodes that achieve even higher energy density per unit volume, serving as electrodes for these high-capacity lithium secondary batteries.

[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 with high discharge capacity can be used as the negative electrode active material.

[0007] In particular, in recent years, in response to the demand for high-density energy batteries, as negative electrode active materials, the combined use of materials such as Si / C or SiO, which have a capacity 10 times or more that of graphite-based materials, has been actively studied. x Methods for increasing capacity by using silicon-based compounds such as silicon-based compounds. However, the capacity characteristics of silicon-based compounds themselves as high-capacity materials are superior to those of commonly used graphite, but they undergo rapid volume expansion during charging, causing the conductive path to be disconnected, resulting in deterioration of battery characteristics and, accordingly, a decrease in capacity from the initial stage. In addition, for silicon-based negative electrodes, if charge and discharge cycles are repeated, lithium ions are unevenly charged in the depth direction of the negative electrode, and the reaction proceeds on the surface, accelerating surface degradation. Therefore, it is necessary to improve the performance of battery cycles.

[0008] Therefore, to address the issues that arise when using silicon-based compounds as negative electrode active materials, various approaches have been explored, including methods for controlling the driving potential, methods for applying an additional thin film to the active material layer, methods for suppressing the volume expansion of the silicon-based compound itself (e.g., methods for controlling the particle size of the silicon-based compound), and the development of binders that can suppress the volume expansion of the silicon-based compound to prevent the disconnection of the conductive path. Furthermore, research is underway to supplement the lifespan characteristics of silicon-based negative electrodes by pre-lithiating the silicon-based active material layer, thereby limiting the proportion of silicon-based active material used during initial charge and discharge and imparting a reservoir function.

[0009] However, the above methods have limitations in their applications as they may instead degrade the performance of the battery, and thus there are still restrictions in the commercialization of anode batteries with high-content silicon compounds.

[0010] In addition, recently, for batteries using NCM positive electrode materials, the NP ratio is designed to be about 100 to 105. This design solves the occurrence of Li plating on the negative electrode and the cost increase associated with excessive use of the negative electrode. Recently, a design that uses the full profile of the negative electrode by ensuring that no residual negative electrode is left is being developed.

[0011] However, using the full spectrum of negative electrode characteristics to ensure no residual negative electrode leads to problems with the negative electrode's lifespan performance. In particular, depending on the type of negative electrode active material, lifetime degradation can occur, leading to further problems. Specifically, using a high-capacity silicon-based active material with a full spectrum of characteristics to ensure capacity characteristics can lead to a reduction in lifetime due to volume expansion.

[0012] Therefore, it is necessary to study how to improve battery performance without using the full characteristic spectrum of the negative electrode.

[0013] <Reference List>

[0014] (Patent Document 1) Japanese Patent Application Laid-Open No. 2009-080971 Summary of the Invention

[0015] [Technical Issues]

[0016] The present application is based on the discovery that when the depth of discharge of a negative electrode is controlled (the cutoff potential is controlled) without using the full characteristic spectrum of the negative electrode, battery characteristics can be improved together with life characteristics.

[0017] Therefore, the present application aims to provide a lithium secondary battery with controlled discharge depth of the negative electrode.

[0018] [Technical solution]

[0019] An exemplary embodiment of the present specification provides a lithium secondary battery comprising: a positive electrode; a negative electrode; a separator provided between the positive electrode and the negative electrode; and an electrolyte, wherein the discharge potential of the negative electrode is controlled to be 0 V or more and 1.5 V or less (relative to Li / Li + ), the remaining negative electrode capacity defined by formula 1 is greater than 2.5%, and the cut-off potential is lower than the discharge potential.

[0020] [Formula 1]

[0021]

[0022] [Beneficial Effects]

[0023] In the lithium secondary battery of the present application, the full characteristic spectrum of the negative electrode is not used, and the discharge potential of the negative electrode is controlled to be greater than 0 V and less than 1.5 V (relative to Li / Li + ), and at the same time, the cutoff potential of the negative electrode is adjusted to be lower than the discharge potential of the negative electrode, so that the residual negative electrode capacity of the negative electrode is expressed as shown in the above formula 1. That is, the main feature is that the life characteristics are improved by not using the full characteristic spectrum of the negative electrode and keeping the residual negative electrode capacity within the range of the above formula 1.

[0024] That is, the main feature of the lithium secondary battery of the present application is that the remaining negative electrode capacity is adjusted within the range of Formula 1 by adjusting the cutoff potential rather than the NP ratio, thereby improving the life characteristics of the lithium secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a diagram illustrating a stack structure of a lithium secondary battery according to an exemplary embodiment of the present application.

[0026] Figure 2 It is a graph showing the charge-discharge curve, cutoff potential, and remaining negative electrode capacity (%) of the carbon-based negative electrode.

[0027] Figure 3 It is a graph showing the charge-discharge curve, cutoff potential, and remaining negative electrode capacity (%) of a silicon-based negative electrode.

[0028] Figure 4 It is a graph showing the charge-discharge curves, cutoff potentials, and remaining negative electrode capacity (%) of carbon-based and silicon-based negative electrodes.

[0029] Figures 5 to 9 Graphs showing three-electrode data for confirming information about Examples and Comparative Examples of the present application. DETAILED DESCRIPTION

[0030] Before describing the present invention, some terms are first defined.

[0031] In this specification, when a part “includes,” “contains,” or “has” a component, unless particularly stated otherwise, this does not mean to exclude other components but means that other components may be further included.

[0032] In this specification, “p to q” means a range of “p or more and q or less”.

[0033] In this specification, the "specific surface area" is measured by the BET method, specifically, calculated from the nitrogen adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mino II available from BEL Japan, Inc. That is, in this application, the BET specific surface area may refer to the specific surface area measured by the above-mentioned measurement method.

[0034] 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 (average particle size, center particle size) at the 50% point in the cumulative distribution of the number of particles according to the 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. Note that the particle size distribution can be measured using a 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 which, when the 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.

[0035] In this specification, the expression "a polymer contains a certain monomer as a monomer unit" means that the monomer participates in a polymerization reaction and is contained 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 a monomer as a monomer unit.

[0036] In this specification, the term "polymer" is understood to be used in a broad sense, which includes copolymers, unless otherwise specified as a "homopolymer".

[0037] In this specification, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are polystyrene-equivalent molecular weights measured using gel permeation chromatography (GPC) using commercially available monodisperse polystyrene polymers (standard samples) having various degrees of polymerization for molecular weight measurement as standard materials. In this specification, unless otherwise specified, molecular weight refers to weight average molecular weight.

[0038] Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement the present invention. However, the present invention can be implemented in various forms and is not limited to the following description.

[0039] An exemplary embodiment of the present specification provides a lithium secondary battery comprising: a positive electrode; a negative electrode; a separator provided between the positive electrode and the negative electrode; and an electrolyte, wherein the discharge potential of the negative electrode is controlled to be 0 V or more and 1.5 V or less (relative to Li / Li + ), the remaining negative electrode capacity defined by formula 1 is greater than 2.5%, and the cut-off potential is lower than the discharge potential.

[0040] [Formula 1]

[0041]

[0042] In the lithium secondary battery of the present application, the full characteristic spectrum of the negative electrode is not used, and the discharge potential of the negative electrode is controlled to be greater than 0 V and less than 1.5 V (relative to Li / Li + ), and at the same time, the cutoff potential of the negative electrode is adjusted to be lower than the discharge potential of the negative electrode, so that the residual negative electrode capacity of the negative electrode is expressed as shown in the above formula 1. That is, the main feature is that the life characteristics are improved by not using the full characteristic spectrum of the negative electrode and keeping the residual negative electrode capacity within the range of the above formula 1.

[0043] Figure 1 This figure illustrates the stacked structure of a lithium secondary battery according to an exemplary embodiment of the present application. Specifically, a negative electrode 100 for a lithium secondary battery is shown, comprising a negative electrode active material layer 20 located on one surface of a negative electrode current collector layer 10; and a positive electrode 200 for a lithium secondary battery is shown, comprising a positive electrode active material layer 40 located on one surface of a positive electrode current collector layer 50. The negative electrode 100 and the positive electrode 200 form a stacked structure with a separator 30 interposed 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. The negative electrode active material layer contains a negative electrode active material layer composition and is provided on one surface or both surfaces of the negative electrode current collector layer.

[0046] In the present application, the negative electrode active material layer includes 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.

[0047] In the present application, a lithium secondary battery is provided, wherein the negative electrode active material includes 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 capable of alloying with lithium, a lithium titanium oxide, and a lithium nitride-containing material.

[0048] In an exemplary embodiment of the present application, as a representative example, the carbon-based active materials include natural graphite, artificial graphite, expanded graphite, carbon fiber, non-graphitized carbon, graphitized carbon, carbon black, carbon nanotubes, fullerenes, and activated carbon, which can be used without limitation as long as they are generally used as carbon materials for lithium secondary batteries. Specifically, they can be processed into spherical or dot-like forms for use.

[0049] In an exemplary embodiment of the present application, the silicon-based active material may include one or more selected from SiO x (x = 0), SiO x (0 < x < 2), SiC, and Si alloys.

[0050] In an exemplary embodiment of the present application, the silicon-based active material may contain 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, it may contain 1 part by weight or more of SiO x (0 < x < 2). <所

[0051] In another exemplary embodiment, the silicon-based active material may contain 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, it may contain 1 part by weight or more or 10 parts by weight or more and 99 parts by weight or less of SiO x (0 < x < 2).

[0052] In another exemplary embodiment, the silicon-based active material may include SiO x (0 < x < 2).

[0053] In another exemplary embodiment, the silicon-based active material may consist of SiO x (0 < x < 2).

[0054] In an exemplary embodiment of the present application, the negative electrode active material may be composed of a carbon-based active material.

[0055] In an exemplary embodiment of the present application, the negative electrode active material may be composed of a silicon-based active material.

[0056] In an exemplary embodiment of the present application, a lithium secondary battery is provided, wherein a negative electrode active material includes a carbon-based active material and a silicon-based active material, and a content of the silicon-based active material is 30 parts by weight or less relative to 100 parts by weight of the negative electrode active material.

[0057] In particular, the silicon-based active material as described above exhibits a significant change in discharge capacity within the range of 0.2 V to 1.5 V. Therefore, by controlling the depth of discharge of the negative electrode as in the present application, the effect of improving battery characteristics can be maximized.

[0058] In addition, even when the composition and content of the negative electrode active material are changed as described above, life characteristics can be improved by controlling the cutoff potential of the negative electrode to leave residual negative electrode capacity as described below, and the type of negative electrode used is not limited.

[0059] In an exemplary embodiment of the present application, there is provided a lithium secondary battery, wherein the content of the negative electrode active material is 60 parts by weight or more relative to 100 parts by weight of the negative electrode active material layer composition.

[0060] In another exemplary embodiment, the content of the negative electrode active material may be 60 parts by weight or more, 65 parts by weight or more, or 70 parts by weight or more, or 90 parts by weight or less or 85 parts by weight or less, relative to 100 parts by weight of the negative electrode active material layer composition.

[0061] In the 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.

[0062] In related art, only graphite-based compounds have typically been used as negative electrode active materials. However, in recent years, with the increasing demand for high-capacity batteries, attempts to increase capacity by mixing silicon-based active materials have been increasing. However, in the case of silicon-based active materials, even with the aforementioned adjustments to their inherent properties, they can rapidly expand during charge and discharge, leading to problems such as disruption of the conductive paths formed in the negative electrode active material layer.

[0063] Therefore, in the exemplary embodiment of the present application, the negative electrode conductive material may include one or more selected from the group consisting of a point-shaped conductive material, a plane-shaped conductive material, and a line-shaped conductive material.

[0064] In the exemplary embodiments of the present application, the dot-shaped conductive material refers to a conductive dot-shaped or spherical conductive material that can be used to improve the conductivity of the negative electrode without causing chemical changes. Specifically, the dot-shaped 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 black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and a polyphenylene derivative. Carbon black is preferably included due to its high conductivity and excellent dispersibility.

[0065] In an exemplary embodiment of the present application, the BET specific surface area of ​​the dot-shaped conductive material may be 40 m 2 / g or above and 70m 2 / g or less, preferably 45m 2 / g or above and 65m 2 / g or less, more preferably 50m 2 / g or above and 60m 2 / g or less.

[0066] In the exemplary embodiment of the present application, the content of the functional group (volatile matter) of the dot-shaped conductive material may be within a range of 0.01% to 1%, preferably 0.01% to 0.3%, and more preferably 0.01% to 0.1%.

[0067] In particular, when the functional group content of the dot-shaped conductive material is within a specified range, the presence of functional groups on the surface of the dot-shaped conductive material allows the dot-shaped conductive material to be smoothly dispersed in the solvent when water is used as the solvent. In particular, in the present invention, when using a specific silicon-based active material, the functional group content of the dot-shaped conductive material can be reduced, which exhibits an excellent effect in improving dispersibility.

[0068] In the exemplary embodiment of the present application, the dot-shaped conductive material having the functional group content within the above range is included together with the silicon-based active material, and the content of the functional group may be adjusted according to the degree of heat treatment of the dot-shaped conductive material.

[0069] In an exemplary embodiment of the present application, the particle size of the dot-shaped conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

[0070] In the exemplary embodiment of the present application, the conductive material may include a planar conductive material.

[0071] Planar conductive materials improve conductivity by increasing surface contact between silicon-based particles in the negative electrode and can also be used to suppress the disconnection of conductive paths caused by volume expansion. Planar conductive materials can be in the form of plate-like conductive materials or bulk conductive materials.

[0072] In an exemplary embodiment of the present application, the planar conductive material may include at least one selected from plate-like graphite, graphene, graphene oxide, and graphite flakes, preferably plate-like graphite.

[0073] 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 this specified range is met, the sufficient particle size facilitates dispersion without excessively increasing the viscosity of the negative electrode slurry. Therefore, when using the same equipment and time for dispersion, excellent dispersion is achieved.

[0074] In an exemplary embodiment of the present application, a negative electrode composition is provided, wherein the planar conductive material has D10 of 0.5 μm to 2.0 μm, D50 of 2.5 μm to 3.5 μm, and D90 of 6.5 μm to 15.0 μm.

[0075] In the exemplary embodiment of the present application, as for the planar conductive material, a high specific surface area planar conductive material having a high BET specific surface area or a low specific surface area planar conductive material may be used.

[0076] In the exemplary embodiments of the present application, for the planar conductive material, a high specific surface area planar conductive material or a low specific surface area planar conductive material can be used without restriction. However, specifically, the planar conductive material involved in the present application may be affected to a certain extent in terms of electrode performance due to a dispersion effect, and therefore it is particularly preferred to use a low specific surface area planar conductive material that does not cause dispersion problems.

[0077] 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 above.

[0078] In another exemplary embodiment, the BET specific surface area of ​​the planar conductive material may be 1 m 2 / g and above and 500m 2 / g or less, preferably 5m 2 / g and above and 300m 2 / g or less, and more preferably 5m 2 / g and above and 250m 2 / g or less.

[0079] As 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.

[0080] In another exemplary embodiment, the planar conductive material is a high specific surface area planar conductive material, and the BET specific surface area may be 50 m 2 / g and above and 500m 2 / g or less, preferably 80m 2 / g and above and 300m 2 / g or less, more preferably 100m 2 / g and above and 300m 2 / g or less.

[0081] In another exemplary embodiment, the planar conductive material is a low specific surface area planar conductive material, and the BET specific surface area may be 1 m 2 / g or above and 40m 2 / g or less, preferably 5m 2 / g or more and 30m 2 / g or less, and more preferably 5m 2 / g or above and 25m 2 / g or less.

[0082] Other conductive materials may include linear conductive materials, such as carbon nanotubes. The carbon nanotubes may be bundle-type carbon nanotubes. The bundle-type carbon nanotubes may include a plurality of carbon nanotube units. Specifically, unless otherwise specified, the term "bundle-type" herein refers to a bundle-like or rope-like secondary shape in which a plurality of carbon nanotube units are arranged side by side or entangled along an orientation that makes the longitudinal axes of the carbon nanotube units substantially the same. The carbon nanotube units have cylindrical graphene sheets with nanometer-scale diameters and have sp 2 Bonded structure. In this case, the graphene sheet can exhibit properties of either a conductive material or a semiconductor material depending on the roll angle and structure. Compared to tangled carbon nanotubes, bundled carbon nanotubes can be more evenly dispersed during negative electrode manufacturing and can more smoothly form a conductive network in the negative electrode, improving its conductivity.

[0083] In the exemplary embodiment of the present application, the content of the negative electrode conductive material may be 0.1 parts by weight or more and 40 parts by weight or less relative to 100 parts by weight of the negative electrode active material layer composition.

[0084] In another exemplary embodiment, the content of the negative electrode conductive material may be 0.1 parts by weight or more and 40 parts by weight or less, preferably 0.2 parts by weight or more and 30 parts by weight or less, more preferably 0.4 parts by weight or more and 25 parts by weight or less, and most preferably 0.4 parts by weight or more and 10 parts by weight or less, relative to 100 parts by weight of the negative electrode active material layer composition.

[0085] In an exemplary embodiment of the present application, a negative electrode composition is provided, wherein the negative electrode conductive material includes a planar conductive material or a linear conductive material.

[0086] In the exemplary embodiment of the present application, the negative electrode conductive material may include a planar conductive material and a linear conductive material.

[0087] In an exemplary 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 a planar conductive material and 0.1 parts by weight or more and 20 parts by weight or less of a linear conductive material relative to 100 parts by weight of the negative electrode conductive material.

[0088] In another exemplary embodiment, the negative electrode conductive material may include 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 planar conductive material, relative to 100 parts by weight of the negative electrode conductive material.

[0089] In another exemplary embodiment, the negative electrode conductive material may include 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 relative to 100 parts by weight of the negative electrode conductive material.

[0090] In an exemplary embodiment of the present application, the negative electrode conductive material includes both a planar conductive material and a linear conductive material, each of which satisfies the above-mentioned composition and proportion, so the service life characteristics of a conventional lithium secondary battery are not significantly affected. In particular, including both a planar conductive material and a linear conductive material increases the number of points that can be charged and discharged, resulting in excellent output characteristics at high C rates and reduced gas generation at high temperatures.

[0091] In the exemplary embodiment of the present application, the negative electrode conductive material may be composed of a linear conductive material.

[0092] In particular, when a linear conductive material is used alone, electrode tortuosity, which is a problem of silicon-based negative electrodes, can be simplified, so that the electrode structure can be improved, and accordingly, the migration resistance of lithium ions in the electrode can be reduced.

[0093] In an exemplary embodiment of the present application, when the negative electrode conductive material includes only linear conductive material, the content of the negative electrode conductive material may be 0.1 parts by weight or more and 5 parts by weight or less, preferably 0.2 parts by weight or more and 3 parts by weight or less, and more preferably 0.4 parts by weight or more and 1 part by weight or less, relative to 100 parts by weight of the negative electrode active material layer composition.

[0094] The negative electrode conductive material of this application has a completely different configuration from the positive electrode conductive material used in the positive electrode. Specifically, the negative electrode conductive material of this application is used to maintain contact with the silicon-based active material (the volume of the electrode expands significantly due to charge and discharge), while the positive electrode conductive material is used to impart a certain degree of conductivity and also acts as a buffer during rolling. Their configuration and function are completely different from those of the negative electrode conductive material of this application.

[0095] Furthermore, the negative electrode conductive material of the present invention, when used with a silicon-based active material, has a completely different configuration than the conductive material used with a graphite-based active material. Specifically, the conductive material used in an electrode with a graphite-based active material simply has particles smaller than the active material. This conductive material has the properties of improving output characteristics and imparting a certain degree of conductivity. Furthermore, its configuration and function are completely different from the negative electrode conductive material used with a silicon-based active material, as in the present invention.

[0096] In the exemplary embodiment of the present application, the planar conductive material used as the negative electrode conductive material has a structure and function different from that of 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, and refers to a material processed into a spherical or dot-like shape and used to promote the storage and release of lithium ions.

[0097] On the other hand, the planar conductive material used as the negative electrode conductive material is a material having a flat or plate-like shape, and can be in the form of plate-like graphite. Specifically, the planar conductive material is included to maintain the conductive path within the negative electrode active material layer, and is used to ensure a planar conductive path within the negative electrode active material layer, rather than to store and release lithium.

[0098] That is, in this application, the use of plate-like graphite as a conductive material means processing graphite into a flat or plate-like shape and using it as a material to ensure a conductive path, rather than playing a role in storing or releasing lithium. In this case, the negative electrode active material included together has a high capacity characteristic for storing and releasing lithium, and is used to store and release all lithium ions transferred from the positive electrode.

[0099] On the other hand, in the present application, using a carbon-based active material as an active material means that the carbon-based active material is processed into a dot shape or a spherical shape and used as a material for storing or releasing lithium.

[0100] That is, in the exemplary embodiment of the present application, artificial graphite or natural graphite as the carbon-based active material has a dot-like shape, and its BET specific surface area may be 0.1 m 2 / g or above and 4.5m 2 / g or less. In addition, plate-like graphite as a planar conductive material has a planar shape and its BET specific surface area can be 5m2 / g or above.

[0101] In an exemplary 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, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, 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.

[0102] The negative electrode binder of the exemplary embodiment of the present application is used to retain the active material and the conductive material to prevent distortion and structural deformation of the negative electrode structure during volume expansion and relaxation of the silicon-based active material. When this function is satisfied, all common binders can be used, specifically aqueous binders, and more specifically PAM-based binders can be used.

[0103] In an exemplary embodiment of the present application, the content 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, and may be 5 parts by weight or more, or may be 10 parts by weight or more, relative to 100 parts by weight of the negative electrode active material layer composition.

[0104] In an exemplary embodiment of the present application, there is provided a lithium secondary battery in which 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.

[0105] 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., as well as aluminum-cadmium alloys, 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 bonding strength with the negative electrode active material, and can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, or non-woven fabrics.

[0106] However, the thickness may be variously modified according to the type and purpose of the negative electrode used, and is not limited thereto.

[0107] In the exemplary embodiment of the present application, the porosity of the negative electrode active material layer may be 10% or more and 60% or less.

[0108] In another exemplary embodiment, the porosity of the negative electrode active material layer may 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.

[0109] 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 conductivity and resistance within appropriate ranges.

[0110] 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, wherein the positive electrode active material layer includes a positive electrode active material layer composition and is provided on one or both surfaces of the positive electrode current collector layer, wherein the positive electrode active material layer composition includes a positive electrode active material.

[0111] 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., etc. can be used. In addition, the positive electrode current collector layer can generally have a thickness of 3 μm to 500 μm, and fine irregularities can 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 can be used in various forms such as a film, a sheet, a foil, a mesh, a porous body, a foam, a non-woven fabric, etc.

[0112] 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) and lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; lithium manganese oxide such as Li 1+c1 Mn 2-c1 O4 (0≤c1≤0.33), LiMnO3, LiMn2O3 and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5 and Cu2V2O7; 1-c2 M c2 Ni-type lithium nickel oxide represented by O2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B and Ga, and satisfies 0.01≤c2≤0.3); 2-c3 M c3Lithium manganese composite oxide represented by LiMn2O4 (wherein 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 (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu and Zn); LiMn2O4, wherein a portion of Li in the chemical formula is substituted by alkaline earth metal ions; and the like, but not limited thereto. The positive electrode may be Li metal.

[0113] In the present application, a lithium secondary battery is provided, wherein the positive electrode active material comprises a material 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 One or more selected from the group consisting of PO4 (M: transition metal, x+y=1).

[0114] 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 constructed battery. 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 powders or metal fibers, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and the like, and any one of these or a mixture of two or more thereof can be used.

[0115] In addition, the positive electrode binder is used to improve the bonding 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 may include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber or its various copolymers, and any one of them or a mixture of two or more thereof can be used.

[0116] The present application provides 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 discharge potential of the negative electrode is controlled to be greater than 0V and less than 1.5V (relative to Li / Li + ).

[0117] Typically, the negative electrode undergoes charge and discharge in the range of 0.005V to 1.5V, depending on the composition and content of the active material used. However, for materials such as Si or Sn, charge and discharge are carried out in the range of 0.005V to 3V, and a characteristic spectrum with a 3V cutoff can also be used. However, in this case, the characteristic spectrum meets the discharge potential of the characteristic spectrum of the positive electrode as the counter electrode of the full battery, so that the voltage is close to 0V, thereby falling outside the actual operating voltage range of the lithium secondary battery. In this regard, the negative electrode for the lithium secondary battery of the present application has the following characteristics: the discharge potential is controlled to be above 0V and below 1.5V (relative to Li / Li + ), regardless of the composition and content of the active material used.

[0118] In this case, the negative electrode of the present application may have the residual negative electrode capacity represented by the above formula 1.

[0119] The residual negative electrode capacity represented by Formula 1 may mean that the negative electrode has a capacity greater than 0 V and less than 1.5 V (relative to Li / Li + ) range is different from the negative electrode discharge capacity up to the cutoff potential. Specifically, if the value of Formula 1 is 2.5% or more, the negative electrode can be applied without restriction.

[0120] In the present application, a lithium secondary battery is provided, wherein the residual negative electrode capacity of the negative electrode represented by the above formula 1 is 2.5% or more and 50% or less.

[0121] In the present application, the residual negative electrode capacity represented by the above 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.

[0122] In this application, the “(0V or more and 1.5V or less (relative to Li / Li)” in Formula 1 + ) range of negative electrode discharge capacity – above 0V and below cutoff potential (relative to Li / Li + The value of the negative electrode discharge capacity within the range of ) can be 1μAh / cm 2 As described above, the cut-off potential of the negative electrode can be 0 V or more and 1.4 V or less.

[0123] In this application, the “(0V or more and 1.5V or less (relative to Li / Li)” in Formula 1 +) range of negative electrode discharge capacity – above 0V and below cutoff potential (relative to Li / Li + The value of the negative electrode discharge capacity within the range of ) can be 1μAh / cm 2 Above and 20mAh / cm 2 Specifically, 10 μAh / cm 2 Above and 15mAh / cm 2 More specifically, 100 μAh / cm 2 Above and 10mAh / cm 2 the following.

[0124] By leaving the remaining negative electrode capacity within a specified range, the life characteristics can be improved compared to when the full characteristic spectrum of the negative electrode is used.

[0125] In the exemplary embodiment of the present application, the cut-off potential of the negative electrode may be lower than the discharge potential of the negative electrode.

[0126] In this case, the off potential of the negative electrode may be 0 V or higher and 1.4 V or lower.

[0127] In the present application, the degree of the remaining negative electrode capacity represented by the above formula 1 can be determined according to the cut-off potential of the negative electrode.

[0128] In an exemplary embodiment of the present application, there is provided a lithium secondary battery, wherein a negative electrode active material includes a carbon-based active material, and a cutoff potential of the negative electrode is 0.1 V or more and 0.9 V or less.

[0129] Specifically, Figure 2 An anode having 100% carbon-based active material is shown, wherein the anode may have a residual anode capacity of Formula 1 when a cutoff potential below 0.5 V is set.

[0130] In an exemplary embodiment of the present application, there is provided a lithium secondary battery, wherein a negative electrode active material includes a silicon-based active material, and a cutoff potential of the negative electrode is 0.1 V or more and 1.4 V or less.

[0131] Specifically, Figure 3 An anode having 100% silicon-based active material is shown, wherein the anode can have a residual anode capacity of Formula 1 when a cutoff potential below 1.3 V is set.

[0132] In an exemplary embodiment of the present application, there is provided a lithium secondary battery in which a negative electrode active material includes a silicon-based active material and a carbon-based active material, and a cutoff potential of the negative electrode is 0.2 V or more and 1.3 V or less.

[0133] Specifically, Figure 4A negative electrode having a mixture of a silicon-based active material and a carbon-based active material is shown, wherein the negative electrode may have a residual negative electrode capacity of Formula 1 when a cutoff potential lower than 0.7 V is set.

[0134] Right now, Figures 2 to 4 It is a diagram showing the charge and discharge characteristic spectrum of the negative electrode corresponding to the type of negative electrode. Specifically, the capacity value of the x-axis varies according to the type of negative electrode, and the remaining negative electrode capacity can be compared according to the cutoff potential of the negative electrode. Specifically, for the carbon-based negative electrode, there is almost no capacity difference between 1.5V and 1.4V to 1.45V, so there is no remaining capacity. Therefore, for the carbon-based negative electrode, the cutoff potential can be adjusted to above 0.1V and below 0.9V, leaving the remaining negative electrode capacity within the range of Formula 1. In addition, for the silicon-based negative electrode, the capacity change occurs near 1.5V, and the capacity difference appears near 1.3V. Therefore, for the silicon-based negative electrode, the cutoff potential can be adjusted to above 0.1V and below 1.4V, leaving the remaining negative electrode capacity within the range of Formula 1.

[0135] For reference, Figures 2 to 4 The method for measuring the characteristic spectrum curves of the negative electrode and the positive electrode can be carried out as follows: a coin battery is made, wherein the negative electrode or positive electrode to be measured is used as the working electrode, lithium metal is used as the counter electrode, a separator is placed between them, and the interior of the coin battery is filled with an electrolyte solution, and charged and discharged.

[0136] That is, as described above, the cutoff potential can be adjusted according to the type of negative electrode used, thereby adjusting the remaining negative electrode capacity to within the range of Formula 1, thereby improving the life characteristics along with the capacity characteristics, which is a main feature of the present invention.

[0137] Separator is used to separate negative electrode and positive electrode and provide a migration path for lithium ions, wherein any separator can be used as a separator without particular limitation, as long as it is commonly used for secondary batteries, and in particular, it is preferred to use a separator having high moisture retention capacity and low resistance to the migration of electrolyte solution ions. Specifically, a porous polymer film can be used, for example, a porous polymer film made of a polyolefin polymer (such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer), or a stacked structure with more than two layers thereof. In addition, conventional porous non-woven fabrics can be used, for example, a non-woven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc. In addition, a coated separator comprising a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and a separator with a single layer or multilayer structure can be selectively used.

[0138] Examples of the electrolyte may include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a melt-type inorganic electrolyte that can be used to manufacture a lithium secondary battery, but are not limited thereto.

[0139] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0140] As the non-aqueous organic solvent, for example, an aprotic organic solvent 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, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate or ethyl propionate can be used.

[0141] In particular, among carbonate organic solvents, ethylene carbonate and propylene carbonate as cyclic carbonates are high-viscosity organic solvents and can be preferably used because they have a high dielectric constant to dissociate lithium salts well. When cyclic carbonates are mixed with low-viscosity and low-dielectric-constant linear carbonates (such as dimethyl carbonate and diethyl carbonate) in a suitable ratio, an electrolyte with high conductivity can be prepared, and therefore can be more preferably used.

[0142] Lithium salt can be used as the metal salt. Lithium salt is a material that is easily soluble in a non-aqueous electrolyte. As the anion of the lithium salt, for example, a material selected from the group consisting of 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 of the groups.

[0143] In order to improve the service life characteristics of the battery, inhibit the reduction of the battery capacity, improve the discharge capacity of the battery, etc., in addition to the above-mentioned electrolyte components, the electrolyte may also include one or more additives, such as halogenated alkylene carbonate compounds (such as difluoroethylene carbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glycol diether, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol or aluminum chloride.

[0144] An exemplary embodiment of the present invention provides 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 secondary batteries with 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 equipment selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0145] Hereinafter, preferred embodiments will be provided to better understand the present invention. It will be apparent to those skilled in the art that the embodiments are provided only to illustrate the present invention, and various modifications and changes may 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.

[0146] Example

[0147] <Preparation Example>

[0148] <Example 1>

[0149] <Preparation of Secondary Battery>

[0150] 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 in a weight ratio of 95.7:1:2.3:1 to prepare a negative electrode slurry (solid concentration 50 wt%).

[0151] As a mixing method, carbon black, a binder, and distilled water were dispersed at 2500 rpm for 30 minutes using a homomixer, the active material was added to the dispersion, and the resulting mixture was dispersed at 2500 rpm for 30 minutes to prepare a negative electrode slurry.

[0152] The negative electrode slurry was applied on both sides of a copper current collector (thickness 15 μm) as a negative electrode current collector, and then dried in a vacuum oven at 130° C. for 1 hour and roll-pressed to form a negative electrode active material layer (porosity 35%).

[0153] LiNi as the positive electrode active material 0.6 Co 0.2 Mn 0.2 O2 (average particle size (D50): 15 μm), carbon black (trade name: Super C65, manufacturer: Timcal) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent for forming a positive electrode slurry in a weight ratio of 95:2.5:2.5 to prepare a positive electrode slurry (solid concentration: 63 wt %).

[0154] The positive electrode slurry was applied on both surfaces 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%).

[0155] A polyethylene separator was provided between the positive electrode and the negative electrode and an electrolyte was injected, thereby preparing a lithium secondary battery.

[0156] The electrolyte is obtained by adding vinylene carbonate in an amount of 3 wt % relative to the total weight of the electrolyte to an organic solvent in which fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) are mixed in a volume ratio of 30:70, and adding LiPF6 as a lithium salt to a concentration of 1 M.

[0157] <Example 2>

[0158] <Preparation of Secondary Battery>

[0159] A lithium secondary battery was prepared in the same manner as in Example 1, except that the carbon-based active materials (artificial graphite (D50: 18 μm): natural graphite (D50: 18 μm): SiO x A negative electrode slurry was prepared by adding carbon black, SBR as a binder, and CMC as a thickener at a weight ratio of 95.7:1:2.3:1 to distilled water as a solvent for forming a negative electrode slurry.

[0160] <Example 3>

[0161] <Preparation of Secondary Battery>

[0162] A lithium secondary battery was prepared in the same manner as in Example 1, except that the carbon-based active materials (artificial graphite (D50: 18 μm): natural graphite (D50: 18 μm): SiO x A negative electrode slurry was prepared by adding carbon black, SBR as a binder, and CMC as a thickener at a weight ratio of 95.7:1:2.3:1 to distilled water as a solvent for forming a negative electrode slurry.

[0163] <Example 4>

[0164] <Preparation of Secondary Battery>

[0165] A lithium secondary battery was prepared in the same manner as in Example 1, except that the carbon-based active materials (artificial graphite (D50: 18 μm): natural graphite (D50: 18 μm): SiO x A negative electrode slurry was prepared by adding carbon black, SBR as a binder, and CMC as a thickener at a weight ratio of 95.7:1:2.3:1 to distilled water as a solvent for forming a negative electrode slurry.

[0166] <Comparative Example 1>

[0167] <Preparation of Secondary Battery>

[0168] A lithium secondary battery was prepared in the same manner as in Example 1, except that the carbon-based active materials (artificial graphite (D50: 18 μm): natural graphite (D50: 18 μm): SiO x A negative electrode slurry was prepared by adding carbon black, SBR as a binder, and CMC as a thickener at a weight ratio of 95.7:1:2.3:1 to distilled water as a solvent for forming a negative electrode slurry.

[0169] In Examples and Comparative Examples, the negative electrode and the positive electrode were controlled based on the information shown in Table 1 below.

[0170] [Table 1]

[0171]

[0172] Specifically, if Figures 5 to 9 As shown, a double-cell three-electrode evaluation was performed to confirm the cutoff potential in Table 1, and the results shown in Table 1 were obtained.

[0173] Experimental example

[0174] For the examples and comparative examples, the results shown in Table 2 were obtained.

[0175] In this case, in Table 2, the 0.33C capacity retention rate was evaluated using an electrochemical charge-discharge device at a high temperature of 45°C. Based on the battery driving voltage listed in Table 1, the secondary battery was subjected to an in-situ cycle test at 1C / 0.5C, and the capacity retention rate was calculated as follows based on 300 cycles.

[0176] Capacity retention (%) = {(discharge capacity at the nth cycle) / (discharge capacity at the first cycle)} × 100

[0177] [Table 2]

[0178]

[0179] As can be seen from Table 2 above, for all batteries in Examples 1 to 4 of the present invention, when the negative electrode cutoff potential is controlled to leave the residual negative electrode capacity within the range of Formula 1, it is confirmed that the life characteristics are also improved. That is, the life characteristics are improved by controlling the cutoff potential and are not significantly affected by the negative electrode type, and it is confirmed that it is important to design the battery to include the residual negative electrode capacity defined in Formula 1. Specifically, Example 1 corresponds to a carbon-based negative electrode, and Examples 2 to 4 correspond to a carbon-based and silicon-based hybrid negative electrode.

[0180] In Comparative Example 1, the cutoff potential was controlled, but the remaining negative electrode capacity was maintained at 2.4%. In this case, it was confirmed that the initial capacity also decreased to a certain extent, and the capacity retention rate did not remain above 80%, that is, the life characteristics were degraded.

Claims

1. A lithium secondary battery comprising: positive electrode; negative electrode; a separator disposed between the positive electrode and the negative electrode; and electrolytes, including The discharge potential of the negative electrode is controlled to be relative to Li / Li + 0V or more and 1.5V or less, The residual negative electrode capacity of the negative electrode defined by Formula 1 is 2.5% or more, and The cut-off potential of the negative electrode is lower than the discharge potential; [Formula 1] 2. The lithium secondary battery according to claim 1, wherein The negative electrode has a residual negative electrode capacity represented by Formula 1 of 2.5% or more and 50% or less.

3. The lithium secondary battery according to claim 1, wherein In formula 1, "(relative to Li / Li + Negative electrode discharge capacity in the range of 0V to 1.5V – relative to Li / Li + The negative electrode discharge capacity in the range above 0V and below the cutoff potential is 1μAh / cm 2 above, and The negative electrode has a cutoff potential of 0 V or higher and 1.4 V or lower.

4. The lithium secondary battery according to claim 1, wherein The negative electrode includes a negative electrode current collector layer and a negative electrode active material layer disposed on one or both surfaces of the negative electrode current collector layer. The negative electrode active material layer comprises a negative electrode active material layer composition, The negative electrode active material layer composition comprises a negative electrode active material, a negative electrode conductive material and a negative electrode binder, and The negative electrode active material includes one or more selected from the group consisting of carbon-based active materials, silicon-based active materials, tin-based active materials, metal-based active materials capable of alloying with lithium, lithium titanium oxide, and lithium-containing nitride.

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

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

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

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

9. The lithium secondary battery according to claim 4, wherein The content of the negative electrode active material is 60 parts by weight or more relative to 100 parts by weight of the negative electrode active material layer composition.

10. 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 containing a positive electrode active material layer composition and disposed on one or both surfaces of the positive electrode current collector layer. The positive electrode active material layer comprises a positive electrode active material, a positive electrode conductive material and a positive electrode binder, and The positive electrode active material comprises one or more 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.

11. The lithium secondary battery according to claim 4, wherein The thickness of the negative electrode current collector layer is not less than 1 μm and not more than 100 μm. The thickness of the negative electrode active material layer is 5 μm or more and 500 μm or less.

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

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