Lithium secondary battery with improved life characteristics, method of operating the same, battery module including the same, and battery pack including battery module

Abstract

To provide a lithium secondary battery with improved life characteristics, a method of operating the same, a battery module including the same, and a battery pack including the battery module.SOLUTION: By providing a lithium secondary battery having an operating voltage lower than the plateau voltage of a lithium nickel composite oxide, which serves as a positive electrode active material, it is possible to prevent the lithium nickel composite oxide from transitioning to a spinel structure, with the advantage of being able to improve life characteristics while suppressing capacity deterioration due to increased cycles.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a lithium secondary battery having improved life characteristics, a driving method thereof, a battery module including the same, and a battery pack including the battery module. This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0085971 filed on Jun. 30, 2021, and all contents disclosed in the literature of the Korean patent application are included as part of this specification.

Background Art

[0002] Lithium secondary batteries are used as the main power supply for small devices such as mobile phones and laptop computers, and their application scope is expanding to electric vehicles and energy storage devices with the increasing demand for large devices.

[0003] However, since the current level of energy density is not suitable for application to large devices, research on new cathode materials capable of achieving high capacity is actively underway to improve it.

[0004] To achieve high capacity, lithium secondary batteries containing LiNi a Co b Mn c O2 (0.6 < a ≦ 0.9, a + b + c = 1), a layered lithium nickel composite oxide as a cathode active material, have attracted attention. In particular, when the content of nickel (Ni) in the cathode active material increases, the number of lithium atoms that can enter the lithium layer can reach twice that when other transition metals are used, so the capacity of the lithium secondary battery will increase.

[0005] However, a problem has arisen in that the deterioration of battery characteristics, particularly the deterioration of battery characteristics and the reduction of thermal stability in a high-temperature environment, occur seriously due to the decrease in structural stability accompanying the increase in the nickel content in the lithium nickel composite oxide, which has hindered commercialization.

[0006] Meanwhile, when lithium nickel composite oxide is used as the positive electrode active material, during charging at a high voltage (e.g., 4.2V or more) based on the positive electrode potential, a plateau voltage range is shown in a certain region, and a large amount of gas such as oxygen and carbon dioxide is generated, resulting in a large capacity exceeding 250mAh / g (see Figure 1).

[0007] In this way, when charging at a high voltage (e.g., 4.2 V or higher) based on the positive electrode potential, some of the remaining Li and transition metals due to the excessive desorption of lithium ions and the desorption of oxygen, etc. may migrate, which is thought to cause a phase transition to a spinel-like structure.

[0008] However, if the lithium secondary battery undergoes the transition to the spinel structure as described above when it is charged at or above the plateau voltage range, it is no longer possible to ensure high output characteristics and cycle durability.

[0009] Therefore, in a lithium secondary battery that contains the above-mentioned layered lithium nickel composite oxide as a positive electrode active material, there is a demand for the development of a lithium secondary battery that can improve the life characteristics while suppressing the capacity deterioration that accompanies an increase in cycles. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Korean Patent Publication No. 10-2011-0101332 Summary of the Invention [Problem to be solved by the invention]

[0011] Therefore, an object of the present invention is to provide a lithium secondary battery containing a layered lithium nickel composite oxide as a positive electrode active material, which has improved life characteristics while suppressing capacity deterioration due to increased cycles.

[0012] Another object of the present invention is to provide a method for operating the lithium secondary battery, a battery module including the same, and a battery pack including the battery module. [Means for solving the problem]

[0013] In order to solve the above-mentioned problems, the present invention provides, in one embodiment, A lithium secondary battery comprising an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, The positive electrode contains a lithium nickel composite oxide represented by the following chemical formula 1 as a positive electrode active material, and the lithium nickel composite oxide has a plateau voltage in the range of 4.1 V to 4.5 V in a charge / discharge profile, The lithium secondary battery is characterized in that it has an operating voltage lower than the plateau voltage of the lithium nickel composite oxide.

[0014] [Chemical formula 1] Li x [Ni y Co z Mn w M 1 v ]O u M 1 is one or more doping elements selected from the group consisting of W, Cu, Fe, V, Cr, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; x, y, z, w, v, and u are 1.0≦x≦1.30, 0.6≦y<0.95, and 0.01 <z≦0.5、0.01<w≦0.5、0≦v≦0.2、1.5≦u≦4.5である。

[0015] In a specific example, the lithium nickel composite oxide may have a plateau voltage at an average of 4.2V in the charge / discharge profile, and at this time, the operating voltage may be 3.0V or more and less than 4.2V.

[0016] In one example, the positive electrode active material is Li(Ni 0.6 Co 0.2 Mn 0.2 )O2, Li(Ni 0.7 Co 0.15 Mn 0.15 )O2, Li(Ni 0.8 Co 0.1 Mn 0.1 )O2, Li(Ni 0.9 Co 0.05 Mn 0.05 )O2, Li(Ni 0.6 Co 0.2 Mn 0.1 Zr 0.1 )O2, Li(Ni 0.6 Co 0.2 Mn 0.15Zr0.05 )O2 and Li(Ni 0.7 Co 0.1 Mn 0.1 Zr 0.1 )O2.

[0017] At this time, the above M 1 may be Zr.

[0018] For example, the lithium nickel composite oxide may contain a doping element M 1 It may contain 300 ppm to 7,000 ppm.

[0019] Meanwhile, the positive electrode active material may be a lithium nickel composite oxide having a layered structure.

[0020] In addition, the lithium secondary battery according to the present invention may have a capacity retention of 90% or more after 3800 charge / discharge cycles at a temperature of 25°C, and may have a capacity retention of 85% or more after 3400 charge / discharge cycles at a temperature of 45°C.

[0021] Furthermore, the lithium secondary battery according to the present invention may have a DCIR (Direct Current Internal Resistance) increase rate of 10% or less after 3800 charge / discharge cycles at a temperature of 25°C.

[0022] In one embodiment, the present invention provides a method for producing a composition comprising: A method for operating a lithium secondary battery including an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, The positive electrode contains a lithium nickel composite oxide represented by the following chemical formula 1 as a positive electrode active material, and the lithium nickel composite oxide has a plateau voltage in the range of 4.1 V to 4.5 V in a charge / discharge profile, The present invention provides a method for operating a lithium secondary battery, the method including the step of controlling the lithium secondary battery at an operating voltage lower than the plateau voltage of the lithium nickel composite oxide.

[0023] [Chemical formula 1] Li x [Ni y Co z Mn w M 1 v ]O u M 1 is one or more doping elements selected from the group consisting of W, Cu, Fe, V, Cr, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; x, y, z, w, v, and u are 1.0≦x≦1.30, 0.6≦y<0.95, and 0.01 <z≦0.5、0.01<w≦0.5、0≦v≦0.2、1.5≦u≦4.5である。

[0024] In a specific example, the lithium nickel composite oxide has a plateau voltage of an average of 4.2V in the charge / discharge profile, and the operating voltage may be 3.0V or more and less than 4.2V.

[0025] In one embodiment, the present invention provides a battery module including the above-mentioned lithium secondary battery.

[0026] Furthermore, in one embodiment, the present invention provides a battery pack including the above battery module. Effect of the Invention

[0027] The lithium secondary battery with improved life characteristics, the method for operating the same, the battery module including the same, and the battery pack including the battery module according to the present invention provide a lithium secondary battery having an operating voltage lower than the plateau voltage of the lithium nickel composite oxide that is the positive electrode active material, thereby preventing the lithium nickel composite oxide from transitioning to a spinel structure, thereby suppressing capacity degradation due to increased cycles, and improving life characteristics. [Brief description of the drawings]

[0028] [Figure 1a] 1 is a graph showing charge / discharge profiles for different compositions of lithium nickel composite oxides (NCM) when the lithium nickel composite oxides are used as a positive electrode active material of a lithium secondary battery. [Figure 1b] 1b is a graph showing the plateau voltage interval of FIG. 1a; [Diagram 2] 1 is a graph showing evaluation of cycle life performance of lithium secondary batteries according to Examples and Comparative Examples. [Diagram 3] 1 is a graph showing the DC internal resistance characteristics of lithium secondary batteries according to an example and a comparative example. [Figure 4] 1 is a graph showing the cycle life and DC internal resistance characteristics of lithium secondary batteries according to an example and a comparative example under a temperature condition of 25° C. [Diagram 5] 1 is a graph showing the cycle life and DC internal resistance characteristics of lithium secondary batteries according to an example and a comparative example under a temperature condition of 45° C. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Since the present invention can be modified in various ways and can have various embodiments, a specific embodiment will be described in detail.

[0030] However, it should be understood that this is not an attempt to limit the invention to the particular embodiment, but rather to include all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention.

[0031] In the present invention, terms such as "comprise" and "have" are intended to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described herein, but are to be understood as not precluding the presence or additional possibility of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0032] In addition, in the present invention, when a layer, film, region, plate, or other portion is described as being "on" another portion, this includes not only the case where it is "directly on" the other portion, but also the case where there is another portion in between. Conversely, when a layer, film, region, plate, or other portion is described as being "under" the other portion, this includes not only the case where it is "directly under" the other portion, but also the case where there is another portion in between. In addition, in the present application, being "on" can include not only the case where it is located at the top, but also the case where it is located at the bottom.

[0033] In the present invention, the term "state of charge / discharge" refers to the degree of remaining capacity that can be charged or discharged based on the fully charged state of an electrode active material in a secondary battery.

[0034] In addition, in the present invention, the "plateau voltage" refers to a region in the reversible capacity region where the potential of the electrode active material is maintained constant, excluding the initial and / or final stages of charge and discharge on the charge and discharge profile, and refers to a section in the charge and discharge curve where the absolute value of the slope of the charge and discharge profile is close to zero.

[0035] The present invention will now be described in more detail.

[0036] <Lithium secondary battery> In one embodiment, the present invention comprises: A lithium secondary battery comprising an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, The positive electrode contains a lithium nickel composite oxide represented by the following chemical formula 1 as a positive electrode active material, and the lithium nickel composite oxide has a plateau voltage in the range of 4.1 V to 4.5 V in a charge / discharge profile, The lithium secondary battery is characterized by having an operating voltage lower than the plateau voltage of the lithium nickel composite oxide.

[0037] [Chemical formula 1] Li x [Ni y Co z Mn w M 1 v ]O u M 1 is one or more doping elements selected from the group consisting of W, Cu, Fe, V, Cr, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; x, y, z, w, v, and u are 1.0≦x≦1.30, 0.6≦y<0.95, and 0.01 <z≦0.5、0.01<w≦0.5、0≦v≦0.2、1.5≦u≦4.5である。

[0038] The lithium secondary battery according to the present invention provides a lithium secondary battery having an operating voltage lower than the plateau voltage of the lithium nickel composite oxide, which is a positive electrode active material, and thus has the advantage of being able to prevent the lithium nickel composite oxide from transitioning to a spinel structure, thereby suppressing capacity deterioration due to increased cycles, while improving life characteristics.

[0039] In one example, the positive electrode active material may include a lithium metal composite oxide including nickel (Ni), cobalt (Co) and manganese (Mn), and the lithium metal composite oxide may optionally include other transition metals (M 1For example, the positive electrode active material is a positive electrode active material capable of reversible intercalation and deintercalation, and may include the lithium metal composite oxide represented by Chemical Formula 1 as a main component.

[0040] In a specific example, more specifically, the positive electrode active material is Li(Ni 0.6 Co 0.2 Mn 0.2 )O2, Li(Ni 0.7 Co 0.15 Mn 0.15 )O2, Li(Ni 0.8 Co 0.1 Mn 0.1 )O2, Li(Ni 0.9 Co 0.05 Mn 0.05 )O2, Li(Ni 0.6 Co 0.2 Mn 0.1 Zr 0.1 )O2, Li(Ni 0.6 Co 0.2 Mn 0.15 Zr 0.05 )O2 and Li(Ni 0.7 Co 0.1 Mn 0.1 Zr 0.1 )O2.

[0041] In one example, the positive electrode active material is a lithium metal composite oxide represented by Chemical Formula 1, Li(Ni 0.7 Co 0.15 Mn 0.15 )O2, Li(Ni 0.8 Co 0.1 Mn 0.1 )O2, Li(Ni 0.9 Co 0.05 Mn 0.05 )O2 or Li(Ni 0.6 Co 0.2 Mn 0.1 Zr 0.1 )O2 may be used alone or in combination.

[0042] The lithium nickel composite oxide represented by the above-mentioned positive electrode active material may have a layered structure. In a specific example, the layered lithium oxide has a certain flat level above the oxidation / reduction potential indicated by the change in oxidation number of the components in the positive electrode active material, unlike other existing positive electrode active materials.

[0043] In a specific example, the plateau voltage of the lithium nickel composite oxide used as the positive electrode active material may be in the range of 4.1 V to 4.5 V. Specifically, the plateau voltage of the lithium metal composite oxide may be in the range of 4.2 V to 4.4 V, or in the range of 4.2 V to 4.3 V, or 4.2 V on average.

[0044] Here, the "plateau voltage" refers to a region in the reversible capacity region where the potential of the positive electrode active material is maintained constant, excluding the initial and / or final stages of charging and discharging, and refers to a section in the charge and discharge curve where the absolute value of the slope of the charge and discharge profile is close to zero. Also, the "operating voltage" refers to the voltage during charging of the lithium secondary battery.

[0045] On the other hand, when a lithium nickel composite oxide with a high nickel content is used as a positive electrode active material, a plateau voltage section is shown in a certain region during charging at a high voltage (e.g., 4.2 V or higher) based on the positive electrode potential, and in the plateau voltage section, some of the Li and transition metals remaining due to the excessive desorption of lithium ions and the desorption of oxygen, etc. move, and the layered lithium nickel composite oxide transitions to a spinel structure. However, there has been a problem in that the high output characteristics and cycle life are reduced due to the structural change of the lithium nickel composite oxide.

[0046] Therefore, in the case of a lithium secondary battery including a lithium nickel composite oxide having a layered structure of Chemical Formula 1, the present invention can extend the life of the battery while suppressing capacity degradation with an increase in the number of cycles by appropriately adjusting the material composition and operating voltage. Specifically, the lithium secondary battery can have an operating voltage below the plateau voltage range of the positive electrode active material.

[0047] In one example, in the lithium secondary battery according to the present invention, when the lithium nickel composite oxide has a plateau voltage at an average of 4.2 V in the charge / discharge profile, the operating voltage of the lithium secondary battery may be 3.0 V or more and less than 4.2 V, and may be in the range of 3.0 V to 4.15 V or in the range of 3.0 V to 4.1 V. Since the operating voltage of the lithium secondary battery is in the above range, it is possible to suppress capacity degradation while maintaining energy, thereby improving life characteristics.

[0048] In a specific example, the lithium secondary battery according to the present invention may have an improved capacity retention rate. For example, the lithium secondary battery may have a capacity retention rate of 90% or more after 3800 charge / discharge cycles at a temperature of 25° C.

[0049] Meanwhile, in the case of a lithium secondary battery in the plateau voltage range of the above positive electrode active material, the maximum capacity retention rate that can be achieved under the same conditions is less than 90%, but the lithium secondary battery according to the present invention can have a capacity retention rate of 90% or more.

[0050] In addition, the lithium secondary battery according to the present invention may have a capacity retention of 85% or more after 3800 charge / discharge cycles at a temperature of 45° C. Meanwhile, in the case of a lithium secondary battery in the plateau voltage range of the positive electrode active material, the maximum capacity retention under the same conditions was less than 85% or less than 75%, but the lithium secondary battery according to the present invention can have a capacity retention of 85% or more. This shows that the lithium secondary battery according to the present invention has excellent high-temperature life characteristics.

[0051] Furthermore, the lithium secondary battery according to the present invention may have an improved DCIR (Direct Current Internal Resistance) increase rate. For example, the lithium secondary battery may have a DCIR increase rate of 10% or less after 3800 charge / discharge cycles at a temperature of 25° C. Meanwhile, in the case of a lithium secondary battery in the plateau voltage range of the positive electrode active material, the DCIR increase rate may exceed 20% under the same conditions.

[0052] That is, the lithium secondary battery according to the present invention has a significantly reduced DCIR increase rate compared to conventional lithium secondary batteries, and can exhibit excellent battery characteristics.

[0053] This fact is supported by the experimental examples described below.

[0054] In addition, the positive electrode active material according to the present invention may include a lithium nickel composite oxide having a layered structure represented by the above-mentioned formula 1, and in this case, the doping element M 1 may be Zr.

[0055] In another example, the lithium nickel composite oxide contains a doping element M 1 In a specific example, the doping element M can be contained in an amount of 300 ppm to 7,000 ppm based on the total weight of the lithium nickel composite oxide. 1 The raw material may be contained at 500 ppm to 7,000 ppm, 1000 ppm to 6,500 ppm, 2,000 ppm to 6,000 ppm, 4,000 ppm to 6,000 ppm, 5,000 ppm to 5,500 ppm, or 5,000 ppm. 1 By including the contained raw material, the surface resistance can be increased and the rate at which lithium ions are released can be slowed down, thereby achieving the effects of improving the structural stability and life span of a battery manufactured using the same.

[0056] As mentioned above, the doping element M 1 may be Zr, and the doping element M 1The source material may be ZrO.

[0057] Meanwhile, the positive electrode includes a positive electrode mixture layer prepared by applying a positive electrode slurry including a positive electrode active material onto a positive electrode current collector, drying, and pressing the positive electrode mixture layer, and the positive electrode mixture layer may further include a conductive material, a binder, an additive, and the like, as necessary.

[0058] The content of the positive electrode active material may be 85 to 95 parts by weight, specifically 88 to 95 parts by weight, 90 to 95 parts by weight, 86 to 90 parts by weight, or 92 to 95 parts by weight, per 100 parts by weight of the positive electrode mixture layer.

[0059] The conductive material is used to improve the electrical performance of the positive electrode, and may be any conductive material commonly used in the art, specifically, one or more selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, denka black, ketjen black, super P, channel black, furnace black, lamp black, thermal black, graphene, and carbon nanotubes.

[0060] As an example, the conductive material may be carbon black or denka black, which may be used alone or in combination.

[0061] The conductive material may be included in an amount of 0.1 to 5 parts by weight, specifically 0.1 to 4 parts by weight, 2 to 4 parts by weight, 1.5 to 5 parts by weight, 1 to 3 parts by weight, 0.1 to 2 parts by weight, or 0.1 to 1 part by weight, relative to 100 parts by weight of the positive electrode mixture layer.

[0062] The binder plays a role of binding the positive electrode active material, the positive electrode additive, and the conductive material to each other, and can be used without any particular limitation as long as it has such a function. Specifically, the binder can include one or more resins selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, and copolymers thereof. As an example, the binder can include polyvinylidene fluoride.

[0063] The binder may be contained in an amount of 1 to 10 parts by weight, specifically 2 to 8 parts by weight, or 1 to 5 parts by weight, based on 100 parts by weight of the total mixture layer.

[0064] The average thickness of the composite layer is not particularly limited, but may be specifically 50 μm to 300 μm, more specifically 100 μm to 200 μm, 80 μm to 150 μm, 120 μm to 170 μm, 150 μm to 300 μm, 200 μm to 300 μm, or 150 μm to 190 μm.

[0065] In addition, the positive electrode can be a positive electrode current collector having high conductivity without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, baked carbon, etc. can be used, and in the case of aluminum or stainless steel, it is also possible to use a surface-treated one with carbon, nickel, titanium, silver, etc. In addition, the positive electrode current collector can be formed with fine irregularities on the surface to increase the adhesive force of the positive electrode active material, and can be in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc. In addition, the average thickness of the current collector can be suitably applied to be 3 to 500 μm in consideration of the conductivity and total thickness of the positive electrode to be manufactured.

[0066] In addition, the negative electrode of the lithium secondary battery according to the present invention is manufactured by applying a negative electrode active material onto a negative electrode current collector, drying and pressing the negative electrode active material, and may further selectively include a conductive material, an organic binder polymer, an additive, etc., similar to those of the positive electrode, as necessary.

[0067] In addition, the negative electrode active material may include, for example, a carbon material and a silicon material. The carbon material means a carbon material mainly composed of carbon atoms, and examples of such carbon materials include graphite having a completely layered crystal structure such as natural graphite, soft carbon having a low crystalline layered crystal structure (graphene structure, a structure in which planes of a hexagonal honeycomb pattern of carbon are arranged in layers), and hard carbon in which such a structure is mixed with an amorphous part, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, acetylene black, ketjen black, fullerene, activated carbon, graphene, carbon nanotubes, etc., and preferably includes at least one selected from the group consisting of natural graphite, artificial graphite, graphene, and carbon nanotubes. More preferably, the carbon material includes natural graphite and / or artificial graphite, and may include at least one of graphene and carbon nanotubes together with the natural graphite and / or artificial graphite. In this case, the carbon material may contain 0.1 to 10 parts by weight of graphene and / or carbon nanotubes relative to 100 parts by weight of the total carbon material, and more specifically, may contain 0.1 to 5 parts by weight, or 0.1 to 2 parts by weight of graphene and / or carbon nanotubes relative to 100 parts by weight of the total carbon material.

[0068] The silicon material is a particle containing silicon (Si) as a metal component as a main component, and is composed of silicon (Si) particles and silicon oxide (SiO x , 1≦x≦2) particles. As an example, the silicon material may include silicon (Si) particles, silicon monoxide (SiO) particles, silicon dioxide (SiO2) particles, or a mixture of these particles.

[0069] In addition, the silicon material may have a mixed form of crystalline particles and amorphous particles, and the ratio of the amorphous particles may be 50 to 100 parts by weight, specifically 50 to 90 parts by weight, 60 to 80 parts by weight, or 85 to 100 parts by weight, based on 100 parts by weight of the total silicon material. By controlling the ratio of the amorphous particles contained in the silicon material within the above range, the present invention can improve thermal stability and flexibility without deteriorating the electrical properties of the electrode.

[0070] The silicon material may include a carbon material and a silicon material, and may be contained in an amount of 1 to 20 parts by weight relative to 100 parts by weight of the negative electrode composite layer. Specifically, the silicon material may be contained in an amount of 5 to 20 parts by weight, 3 to 10 parts by weight, 8 to 15 parts by weight, 13 to 18 parts by weight, or 2 to 7 parts by weight relative to 100 parts by weight of the negative electrode composite layer.

[0071] By adjusting the contents of the carbon material and silicon material contained in the negative electrode active material within the above ranges, the present invention can reduce the lithium consumption and irreversible capacity loss during the initial charge and discharge of the battery, while improving the charge capacity per unit mass.

[0072] For example, the negative electrode active material may include 95±2 parts by weight of graphite and 5±2 parts by weight of a mixture of silicon monoxide (SiO) particles and silicon dioxide (SiO2) particles uniformly mixed, relative to 100 parts by weight of the negative electrode composite layer. By adjusting the contents of the carbon material and silicon material contained in the negative electrode active material within the above ranges, the present invention can reduce the amount of lithium consumption and irreversible capacity loss during initial charging and discharging of the battery, while improving the charging capacity per unit mass.

[0073] The negative electrode mixture layer may have an average thickness of 100 μm to 200 μm, specifically, 100 μm to 180 μm, 100 μm to 150 μm, 120 μm to 200 μm, 140 μm to 200 μm, or 140 μm to 160 μm.

[0074] The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, nickel, titanium, baked carbon, etc. can be used, and in the case of copper or stainless steel, those surface-treated with carbon, nickel, titanium, silver, etc. can also be used. In addition, the negative electrode current collector can be formed with fine irregularities on the surface to strengthen the binding force with the negative electrode active material, as with the positive electrode current collector, and can be in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc. In addition, the average thickness of the negative electrode current collector can be suitably applied to be 3 to 500 μm in consideration of the conductivity and total thickness of the negative electrode to be manufactured.

[0075] The separator is interposed between the positive and negative electrodes, and is an insulating thin film having high ion permeability and mechanical strength. The separator is not particularly limited as long as it is one commonly used in the industry. Specifically, a sheet or nonwoven fabric made of chemically resistant and hydrophobic polypropylene, glass fiber, or polyethylene may be used, and in some cases, a composite separator in which inorganic particles / organic particles are coated with an organic binder polymer on a porous polymer substrate such as the sheet or nonwoven fabric may be used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as the separator. The pore diameter of the separator may be an average of 0.01 to 10 μm, and the thickness may be an average of 5 to 300 μm.

[0076] Meanwhile, the positive electrode and the negative electrode may be wound in a jelly roll shape and housed in a cylindrical battery, a prismatic battery, or a pouch-type battery, or may be housed in a folded or stacked and folded form in a pouch-type battery, but is not limited thereto.

[0077] The lithium salt-containing electrolyte according to the present invention may include an electrolyte and a lithium salt, and the electrolyte may be a non-aqueous organic solvent, an organic solid electrolyte, or an inorganic solid electrolyte.

[0078] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, ethylene carbonate, propylene 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, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0079] As the organic solid electrolyte, for example, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate polymers, polyagitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, polymers containing ionic dissociation groups, and the like can be used.

[0080] Examples of the inorganic solid electrolyte that can be used include nitrides, halides, and sulfates of Li, such as Li3N, LiI, Li5NI2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, and Li3PO4-Li2S-SiS2.

[0081] The lithium salt is a substance that is easily dissolved in a non-aqueous electrolyte, and examples of the lithium salt include LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylates, lithium tetraphenylboronate, imides, and the like may be used.

[0082] In addition, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., the electrolyte may contain, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. In some cases, in order to impart non-flammability, a halogen-containing solvent such as carbon tetrachloride or trifluoroethylene may be further contained, and carbon dioxide gas may be further contained to improve high-temperature storage characteristics, and FEC (Fluoro-Ethylene Carbonate), PRS (Propene Sultone), etc. may be further contained.

[0083] In addition, the positive electrode and the negative electrode may be wound in a jelly roll shape and housed in a cylindrical battery, a prismatic battery, or a pouch-type battery, or may be folded or stacked and folded and housed in a pouch-type battery. For example, the lithium secondary battery according to the present invention may be a pouch-type battery.

[0084] As described above, the lithium secondary battery including the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, and is therefore useful in portable devices such as mobile phones, notebook computers, and digital cameras, and in the field of electric vehicles such as hybrid electric vehicles (HEVs), etc.

[0085] <Method of driving lithium secondary batteries> In one embodiment, the present invention comprises: A method for operating a lithium secondary battery, the method comprising: an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, The positive electrode includes a lithium nickel composite oxide represented by the following chemical formula 1 as a positive electrode active material, and the lithium nickel composite oxide has a plateau voltage in the range of 4.2 V to 4.5 V in a charge-discharge profile, The method includes controlling the lithium secondary battery at an operating voltage lower than the plateau voltage of the lithium nickel composite oxide.

[0086] [Chemical formula 1] Li x [Ni y Co z Mn w M 1 v ]O u M 1 is one or more doping elements selected from the group consisting of W, Cu, Fe, V, Cr, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; x, y, z, w, v, and u are 1.0≦x≦1.30, 0.6≦y<0.95, and 0.01 <z≦0.5、0.01<w≦0.5、0≦v≦0.2、1.5≦u≦4.5である。

[0087] The method for operating a lithium secondary battery according to the present invention includes a step of controlling the operating voltage at a voltage lower than the plateau voltage of the lithium nickel composite oxide during charging and discharging, thereby preventing the lithium nickel composite oxide from transitioning to a spinel structure, thereby suppressing capacity deterioration due to increased cycles and improving life characteristics.

[0088] In a specific example, the plateau voltage of the lithium nickel composite oxide used as the positive electrode active material may be in the range of 4.2 V to 4.5 V. Specifically, the plateau voltage of the lithium metal composite oxide may be in the range of 4.2 V to 4.4 V, in the range of 4.2 V to 4.3 V, or on average 4.2 V.

[0089] In one example, the operating voltage of the lithium secondary battery according to the present invention may be 3.0 V or more and less than 4.2 V, and may be in the range of 3.0 V to 4.15 V or in the range of 3.0 V to 4.1 V. Since the operating voltage of the lithium secondary battery is in the above range, it is possible to suppress capacity degradation while maintaining energy, thereby improving life characteristics.

[0090] <Battery modules and battery packs> In one embodiment, the present invention provides a battery module including the above-mentioned lithium secondary battery.

[0091] In one embodiment, the present invention provides a battery pack including the above-mentioned battery module.

[0092] In a specific example, the lithium secondary battery according to the present invention may be used in a high-output, large-capacity battery that requires a particularly long life and excellent durability, or in a battery module or battery pack including a plurality of such batteries as unit batteries.

[0093] The battery pack can be used as a power source for medium- to large-sized devices that require high temperature stability, long cycle characteristics, high rate characteristics, etc., and specific examples of such medium- to large-sized devices include power tools powered by electric motors, electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs) and plug-in hybrid electric vehicles (PHEVs), electric bicycles (E-bikes), electric two-wheeled vehicles including electric scooters (E-scooters), electric golf carts, electric trucks, electric commercial vehicles, and power storage systems.

[0094] Since the structure and manufacturing method of such a medium- or large-sized battery module or battery pack are well known in the art, detailed description thereof will be omitted.

[0095] The present invention will now be described in detail with reference to examples and experimental examples.

[0096] However, the following examples and experimental examples are only for illustrating the present invention, and the contents of the present invention are not limited to the following examples and experimental examples.

[0097] <Production example: Manufacturing of lithium secondary batteries> LiNi as the positive electrode active material 0.8 Co 0.1 Mn 0.1 96 parts by weight of O2, 2 parts by weight of PVDF as a binder, and 2 parts by weight of carbon black as a conductive material were weighed and mixed in N-methylpyrrolidone (NMP) solvent to produce a slurry for a positive electrode composite layer. The slurry for the composite layer was applied to an aluminum foil, dried, and then rolled to form a positive electrode having a positive electrode composite layer (average thickness: 130 μm). Meanwhile, the plateau voltage of the positive electrode active material was 4.2 V.

[0098] Separately, 87 parts by weight of natural graphite as a carbon-based active material, 7 parts by weight of SiO (silicon oxide) as a silicon-based active material, 3 parts by weight of carbon black as a conductive material, and 3 parts by weight of styrene-butadiene rubber (SBR) as a binder were mixed in an N-methylpyrrolidone solvent to prepare a slurry for the negative electrode composite layer, which was then applied to a copper foil to prepare a negative electrode having a negative electrode composite layer (average thickness: 180 μm).

[0099] The electrode assemblies were prepared by laminating the prepared positive and negative electrodes with a separator (thickness: about 16 μm) made of a porous polyethylene (PE) film between them. The electrode assemblies were placed inside a battery case, and an electrolyte was injected into the case. The case was then left at room temperature for 3 days to allow the electrolyte to be fully impregnated, producing a lithium secondary battery. The electrolyte was prepared by dissolving 1.0M lithium hexafluorophosphate (LiPF6) in an organic solvent made of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (EC / DMC / EMC mixed in a volume ratio of 3 / 4 / 3).

[0100] <Examples 1 to 2, Comparative Example 1> The lithium secondary batteries prepared as above were charged and then discharged under the following conditions to be activated (C rate=0.1C).

[0101] The operating voltage range of each lithium secondary battery was set as shown in Table 1 below, and cycles were performed.

[0102] [Table 1]

[0103] <Experimental Example> In order to evaluate the performance of the lithium secondary battery according to the present invention, the following experiment was carried out.

[0104] a) Evaluation of cycle life performance The lithium secondary batteries of the examples and comparative examples were each subjected to 3800 cycles within a set operating voltage range after discharge at 0.1 C, and the capacity of each battery was measured. The measurement results are shown in Figure 2, and the charge / discharge capacity retention rate was calculated after 3800 charge / discharge cycles.

[0105] The capacity retention rate is defined by the following formula 1, and the results are shown in Table 2.

[0106] [Formula 1] Capacity retention rate (%) = (discharge capacity after n charge / discharge cycles / discharge capacity after 1 charge / discharge cycle) x 100

[0107] b) Evaluation of DC internal resistance (DCIR) characteristics An experiment for evaluating the DC internal resistance of the lithium secondary batteries of the Examples and Comparative Examples was carried out as follows.

[0108] Each lithium secondary battery was subjected to 3800 cycles, and DCIR evaluation was performed every 100 cycles. At this time, DCIR can be measured by the slope of the voltage change amount against the applied current amount, for example, by discharging at 0.2C for 10 seconds and then refilling the same capacity, discharging at 0.5C for 10 seconds and then refilling the same capacity, and discharging at 1C for 10 seconds and then refilling the same capacity at SOC50%. DCIR can be measured during discharge as described above, and can also be measured during charging, and Figure 3 shows the DCIR during discharge. SOC50% means a state in which the battery is charged to 50% of its charge capacity when the entire battery is taken as 100%.

[0109] The results are shown in FIG. 3, and the DCIR increase rates are shown in Table 2.

[0110] [Table 2]

[0111] 2 and Table 2, the lithium secondary batteries of the Examples had significantly higher capacity retention rates with cycling compared to the lithium secondary batteries of the Comparative Examples, and the DCIR increase rate with cycling was significantly reduced to 10% or less.

[0112] C) Evaluation of high-temperature cycle life and DC internal resistance characteristics For the lithium secondary batteries of the Examples and Comparative Examples, experiments were carried out as follows to evaluate the cycle life and the DC internal resistance at high temperature (45° C.).

[0113] The evaluation conditions are shown in Table 3 below, and the evaluation methods are omitted since they have been described above. The results are shown in Figs. 4 and 5 and Table 3.

[0114] [Table 3]

[0115] 4, 5 and Table 3, the lithium secondary batteries of the Examples have higher capacity retention rates at high temperatures and significantly lower DCIR increase rates with cycling than the lithium secondary batteries of the Comparative Examples.

[0116] These results show that the lithium secondary batteries of the examples have an operating voltage lower than the plateau voltage of the lithium nickel composite oxide and can prevent the lithium nickel composite oxide from transitioning to a spinel structure, thereby making it possible to improve the life characteristics while suppressing capacity deterioration due to increased cycles.

[0117] Although the present invention has been described above with reference to preferred embodiments thereof, it will be understood that a person skilled in the art or having ordinary knowledge in the art can make various modifications and changes to the present invention without departing from the spirit and technical scope of the present invention as described in the claims below.

[0118] Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the claims.

Claims

1. A lithium secondary battery comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, The positive electrode includes a lithium nickel composite oxide represented by the following Chemical Formula 1 as a positive electrode active material, and the lithium nickel composite oxide has a plateau voltage in the range of 4.1 V to 4.5 V in a charge / discharge profile, The lithium secondary battery has an operating voltage below a plateau voltage, [Chemical formula 1] Li ｘ [Ni ｙ Co ｚ Mn ｗ M １ ｖ ]O ｕ M １ is one or more doping elements selected from the group consisting of W, Cu, Fe, V, Cr, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; A lithium secondary battery, wherein x, y, z, w, v, and u are 1.0≦x≦1.30, 0.6≦y<0.95, 0.01<z≦0.5, 0.01<w≦0.5, 0≦v≦0.2, and 1.5≦u≦4.5, respectively.

2. The lithium nickel composite oxide has a plateau voltage at an average of 4.2 V in the charge / discharge profile, 2. The lithium secondary battery according to claim 1, wherein the operating voltage is 3.0 V or more and less than 4.2 V.

3. The positive electrode active material is Li(Ni ０．６ Co ０．２ Mn ０．２ ) O ２ , Li(Ni ０．７ Co ０．１５ Mn ０．１５ ) O ２ , Li(Ni ０．８ Co ０．１ Mn ０．１ ) O ２ , Li(Ni ０．９ Co ０．０５ Mn ０．０５ ) O ２ , Li(Ni ０．６ Co ０．２ Mn ０．１ Zr ０．１ ) O ２ , Li(Ni ０．６ Co ０．２ Mn ０．１５Ｚｒ０．０５ ) O ２ and Li(Ni ０．７ Co ０．１ Mn ０．１ Zr ０．１ ) O ２ 2. The lithium secondary battery according to claim 1, wherein the lithium secondary battery comprises one or more selected from the group consisting of:

4. Said M １ The lithium secondary battery according to claim 1 , wherein is Zr.

5. The lithium nickel composite oxide contains a doping element M １ The lithium secondary battery according to claim 4, containing 300 ppm to 7,000 ppm of

6. The lithium secondary battery according to claim 1 , wherein the positive electrode active material has a layered structure.

7. 2. The lithium secondary battery according to claim 1, wherein the capacity retention rate of the lithium secondary battery after 3,800 charge / discharge cycles at a temperature of 25° C. is 90% or more.

8. 2. The lithium secondary battery according to claim 1, wherein the capacity retention rate of the lithium secondary battery after 3,400 charge / discharge cycles at a temperature of 45° C. is 85% or more.

9. 2. The lithium secondary battery according to claim 1, wherein the lithium secondary battery has a DCIR increase rate of 10% or less after 3800 charge / discharge cycles at a temperature of 25°C.

10. A method for operating a lithium secondary battery including an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, The positive electrode includes a lithium nickel composite oxide represented by the following Chemical Formula 1 as a positive electrode active material, and the lithium nickel composite oxide has a plateau voltage in the range of 4.1 V to 4.5 V in a charge / discharge profile, Controlling the lithium secondary battery at an operating voltage lower than a plateau voltage of a lithium nickel composite oxide; [Chemical formula 1] Li ｘ [Ni ｙ Co ｚ Mn ｗ M １ ｖ ]O ｕ M １ is one or more doping elements selected from the group consisting of W, Cu, Fe, V, Cr, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; A method for driving a lithium secondary battery, wherein x, y, z, w, v, and u are 1.0≦x≦1.30, 0.6≦y<0.95, 0.01<z≦0.5, 0.01<w≦0.5, 0≦v≦0.2, and 1.5≦u≦4.5, respectively.

11. The lithium nickel composite oxide has a plateau voltage at an average of 4.2 V in the charge / discharge profile, The method for driving a lithium secondary battery according to claim 10, wherein the operating voltage is 3.0 V or more and less than 4.2 V.

12. A battery module comprising the lithium secondary battery according to claim 1.

13. A battery pack comprising the battery module according to claim 12.

14. The battery pack according to claim 13 , wherein the battery pack is used as a power source for a medium to large device.

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