Anode and lithium secondary battery

Abstract

The present invention provides a negative electrode active material layer comprising a current collector and a negative electrode active material layer provided on at least one surface of the current collector, the negative electrode active material layer including a first region corresponding to 50% of the total thickness of the negative electrode active material layer from a surface facing the current collector, and a second region corresponding to 50% of the total thickness of the negative electrode active material layer from a surface opposite to the surface facing the current collector, the negative electrode active material layer comprising: 50 The negative electrode active material contains two or more different negative electrode active materials, and the formula 1(-3≦|D 50,total -D 50,1st │÷D 50,total ×100≦3) and Equation 2(-3≦│D 50,total -D 50,2nd │÷D 50,total ×100≦3), and a secondary battery including the same.

Description

[Technical Field]

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2023-0099052, filed on July 28, 2023, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery including the same. [Background technology]

[0003] Secondary batteries are widely used not only in portable devices but also in electric vehicles (EVs) and hybrid electric vehicles (HEVs), which are powered by electrical sources.

[0004] Such secondary batteries have the primary advantage of dramatically reducing the use of fossil fuels, as well as the advantage of not producing any by-products associated with energy use, making them environmentally friendly and drawing attention as a new energy source for improving energy efficiency.

[0005] In general, a secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte, etc. Furthermore, the electrodes such as the positive electrode and the negative electrode may have an electrode active material layer provided on a current collector.

[0006] As the use of secondary batteries increases, various battery performances are being demanded, and therefore, attempts are being made to improve the materials and structures of the active material layers in order to improve battery performance. Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a negative electrode for a lithium secondary battery, which can provide a lithium secondary battery with an improved lifespan, and a lithium secondary battery including the same. [Means for solving the problem]

[0008] One embodiment of the present invention comprises: a current collector; and a negative electrode active material layer provided on at least one surface of the current collector, the negative electrode active material layer includes a first region that is from a surface facing the current collector and that accounts for 50% of the total thickness of the negative electrode active material layer, and a second region that is from a surface opposite to the surface facing the current collector and that accounts for 50% of the total thickness of the negative electrode active material layer, The negative electrode active material layer is D 50 two or more negative electrode active materials having different At least one of the first region and the second region is D 50 two or more negative electrode active materials having different Provided is a negative electrode for a lithium secondary battery that satisfies the following formula 1 and formula 2: [Formula 1] -3≦│D 50,total -D 50,1st │÷D 50,total ×100≦3 [Formula 2] -3≦│D 50,total -D 50,2nd │÷D 50,total ×100≦3 In Equation 1 and Equation 2, D 50,total is the D of the negative electrode active material in the entire negative electrode active material layer 50 and D 50,1st is the D of the negative electrode active material in the first region 50 and D 50,2nd is the D of the negative electrode active material in the second region 50 is.

[0009] According to one embodiment of the present invention, the negative electrode active material includes a silicon-based active material, artificial graphite, and natural graphite.

[0010] According to one embodiment of the present invention, the negative electrode active material layer includes a first negative electrode active material layer provided on the current collector; and a second negative electrode active material layer provided on the first negative electrode active material layer.

[0011] Another embodiment of the present invention provides a secondary battery including the negative electrode, positive electrode, and separator for the lithium secondary battery. [Effects of the Invention]

[0012] According to the embodiments described herein, the pore structure within the negative electrode active material layer can be optimized by controlling the particle size of the negative electrode active material. By optimizing the pore structure that serves as a mass transport path within the negative electrode active material layer, not only the movement of lithium ions but also the reactivity between the negative electrode and a lithium-containing electrolyte can be improved, thereby realizing a long battery life. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in more detail below to facilitate understanding of the present invention. The present invention may be embodied in various different forms and is not limited to the embodiments described herein. In this regard, the terms and words used in the specification and claims should not be construed as being limited to their ordinary or dictionary meanings, but should be construed as having meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concepts of terms in order to best describe his or her invention.

[0014] As used herein, terms such as "comprises," "provides," or "having" are intended to specify the presence of stated features, numbers, steps, components, or combinations thereof, but are understood not to preclude the possible presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0015] Furthermore, when a part such as a layer is said to be "on" another part, this does not only mean that it is "directly on top" of that other part, but also includes cases where there is another part between them. Conversely, when a part is said to be "directly above" another part, it means that there is no other part between them. Furthermore, being "on" a reference part means being located above or below the reference part, and does not necessarily mean being "on" in the opposite direction of gravity.

[0016] In this specification, a description referring only to a "negative electrode active material layer" without the terms "first" or "second" can apply to both the first negative electrode active material layer and the second negative electrode active material layer, unless otherwise specified.

[0017] In this specification, the first region and the second region are defined as the D 50 This is a division for checking particle size distribution, and does not mean that a physical interface exists between the two regions. As will be described later, the two negative electrode active material layers may coincide with the first and second regions, and in some cases, an interface may exist between them. However, even when the two negative electrode active material layers coincide with the first and second regions, the interface between them may not be distinct.

[0018] A negative electrode for a secondary battery according to one embodiment of the present specification includes a current collector and a negative electrode active material layer provided on at least one surface of the current collector, the negative electrode active material layer includes a first region that is from a surface facing the current collector and that accounts for 50% of the total thickness of the negative electrode active material layer, and a second region that is from a surface opposite to the surface facing the current collector and that accounts for 50% of the total thickness of the negative electrode active material layer, The negative electrode active material layer is D 50 two or more negative electrode active materials having different At least one of the first region and the second region is D 50 two or more negative electrode active materials having different The present invention is characterized by satisfying the following formula 1 and formula 2.

[0019] [Formula 1] -3≦│D 50,total -D 50,1st │÷D 50,total ×100≦3 [Formula 2] -3≦│D 50,total -D 50,2nd │÷D 50,total ×100≦3

[0020] In Equation 1 and Equation 2, D 50,total is the D of the negative electrode active material in the entire negative electrode active material layer 50 and D 50,1st is the D of the negative electrode active material in the first region 50 and D 50,2nd is the D of the negative electrode active material in the second region 50 is.

[0021] According to the embodiment, the negative electrode active material layer is D 50 at least one of the first region and the second region comprises three or more different negative electrode active materials, 50 Even though the negative electrode active material layer contains two or more different negative electrode active materials, the pore structure of the negative electrode active material layer can be optimized by satisfying the formulas 1 and 2. This not only makes it possible to optimize the movement of lithium ions in the negative electrode active material layer while maintaining a high energy density, but also ensures a long battery life by uniformly controlling the reaction in the negative electrode active material layer.

[0022] The above formulas 1 and 2 indicate that the difference in particle size distribution between the first region and the second region, respectively, and the particle size distribution throughout the negative electrode active material layer is within 3%. By satisfying this condition, it is possible to design a uniform pore structure throughout the negative electrode active material layer. If the value of formula 1 or 2 is less than -3 or more than 3, it indicates that the particle size distribution and pore structure of each region are different from those of the entire negative electrode active material layer. In this case, not only is lithium ion mobility hindered, but there may also be areas within the negative electrode active material layer that differ in reactivity, which may adversely affect the life of the battery.

[0023] According to one embodiment, the composition of the negative electrode active material in the first region is different from the composition of the negative electrode active material in the second region. The different compositions of the negative electrode active materials means that the types and / or content ratios of the negative electrode active materials are not the same. For example, the different compositions of the negative electrode active materials means that at least one type of the negative electrode active materials is different, or even if the type is the same, the D 50 Use different negative electrode active materials or use the same type and the same D 50 When the first and second regions satisfy the above formulas 1 and 2, they have similar pore structures due to uniform particle size distributions despite their different compositions.

[0024] According to one embodiment, the negative electrode active material layer has a structure of two or more layers, for example, the negative electrode active material layer includes a first negative electrode active material layer provided on the current collector and a second negative electrode active material layer provided on the first negative electrode active material layer.

[0025] In the above embodiment, the boundary between the first negative electrode active material layer and the second negative electrode active material layer may be the same as or different from the boundary between the first region and the second region. The boundary between the first negative electrode active material layer and the second negative electrode active material layer being the same as the boundary between the first region and the second region means that the two layers have the same thickness.

[0026] According to one embodiment, at least one of the first negative electrode active material layer and the second negative electrode active material layer is 50 and the negative electrode active material contains two or more negative electrode active materials having different structures, and the structures satisfy the following formula 3 and the following formula 4: [Formula 3] -3≦│D 50,total -D 50,L1 │÷D 50,total ×100≦3 [Formula 4] -3≦│D 50,total -D 50,L2 │÷D 50,total ×100≦3 In Equation 3 and Equation 4, D 50,totalis the D of the negative electrode active material in the entire negative electrode active material layer 50 and D 50,L1 is the D of the negative electrode active material in the first negative electrode active material layer 50 and D 50,L2 is the D of the negative electrode active material in the second negative electrode active material layer 50 is.

[0027] Similar to the above-described formulas 1 and 2, when formulas 3 and 4 are satisfied, the first and second negative electrode active material layers can have similar pore structures due to uniform particle size distributions even when they contain negative electrode active materials with different compositions.

[0028] According to one embodiment, the negative electrode active material includes a first negative electrode active material, a second negative electrode active material, and a third negative electrode active material.

[0029] According to one embodiment, the first negative electrode active material, the second negative electrode active material, and the third negative electrode active material may be the same or different, and may each independently be artificial graphite, natural graphite, or a silicon-based active material.

[0030] According to one embodiment, the first negative electrode active material D 50 The thickness may be 15 μm to 25 μm, 18 μm to 25 μm, or 18 μm or more and 22 μm or less.

[0031] According to one embodiment, the second negative electrode active material D 50 The thickness may be 10 μm to 20 μm, 12 μm to 18 μm, or 12 μm or more and 16 μm or less.

[0032] According to one embodiment, the third negative electrode active material D 50 The thickness may be 2 μm to 15 μm, 3 μm to 12 μm, or 6 μm or more and 10 μm or less.

[0033] The particle size of the negative electrode active material may be adjusted depending on the material and pore structure used during the preparation of each negative electrode active material.

[0034] In one embodiment, the silicon-based active material includes at least one of silicon oxide, silicon-metal complex, and silicon-carbon composite. x (0≦x<2), SiM y (M is a metal, 1≦y≦4) and a Si / C composite. The silicon-based active material may be one type only, or two or more types may be included together. When both the first negative electrode active material layer and the second negative electrode active material layer include a silicon-based active material, the first negative electrode active material layer and the second negative electrode active material layer may use the same type of silicon-based active material, or different types or different combinations of silicon-based active materials.

[0035] According to one embodiment, the first negative electrode active material layer includes at least one of artificial graphite and natural graphite and a silicon-based active material, and the second negative electrode active material layer includes at least one of artificial graphite and natural graphite, and the second negative electrode active material layer does not necessarily include a silicon-based active material.

[0036] According to one embodiment, the first negative electrode active material layer includes at least one of artificial graphite and natural graphite, and the second negative electrode active material layer includes at least one of artificial graphite and natural graphite and a silicon-based active material. In this case, the first negative electrode active material layer may not include a silicon-based active material.

[0037] According to one embodiment, the first and second negative electrode active material layers contain a silicon-based active material, and may further contain at least one of artificial graphite and natural graphite.

[0038] When the negative electrode active material layer contains a silicon-based active material, it may contain 1 to 10 parts by weight of the silicon-based active material based on 100 parts by weight of the total negative electrode active material. Further, when at least one of the first negative electrode active material layer and the second negative electrode active material layer contains a silicon-based active material, it may contain 1 to 20 parts by weight of the silicon-based active material based on 100 parts by weight of the total negative electrode active material in each layer.

[0039] In one embodiment of the present specification, the negative electrode active material layer containing the silicon-based active material may further contain a carbon-based active material. At this time, the carbon-based active material may contain at least one of artificial graphite and natural graphite. Based on 100 parts by weight of the total negative electrode active material contained in the negative electrode active material layer, the carbon-based active material may be contained in an amount of 90 parts by weight or more and 99 parts by weight or less.

[0040] As the silicon-based active material, SiO x (0 ≦ x < 2) The active material containing may be silicon-based composite particles containing SiO x (0 < x < 2) and pores.

[0041] The SiO x (0 < x < 2) corresponds to a matrix in the silicon-based composite particles. The SiO x (0 < x < 2) may be in a form containing Si and SiO2, and the Si may form a phase. That is, the x corresponds to the number ratio of O to Si contained in the SiO x (0 < x < 2). When the silicon-based composite particles contain the SiO x (0 < x < 2), the discharge capacity of the secondary battery can be improved.

[0042] The silicon-based composite particles may further contain at least one of a Mg compound and a Li compound. The Mg compound and the Li compound can correspond to a matrix in the silicon-based composite particles.

[0043] The Mg compound and / or Li compound may be present inside and / or on the surface of the SiO x (where 0 < x < 2). The initial efficiency of the battery can be improved by the Mg compound and / or Li compound.

[0044] The Mg compound may include at least one selected from the group consisting of Mg silicate, Mg silicide, and Mg oxide. The Mg silicate may include at least one of Mg2SiO4 and MgSiO3. The Mg silicide may include Mg2Si. The Mg oxide may include MgO.

[0045] In one embodiment of the present specification, the Mg element may be contained in an amount of 0.1 wt% to 20 wt%, or 0.1 wt% to 10 wt%, based on 100 wt% of the total silicon-based active material. Specifically, the Mg element may be contained in an amount of 0.5 wt% to 8 wt% or 0.8 wt% to 4 wt%. When the above range is satisfied, the volume change of the silicon-based active material during charging and discharging of the battery can be easily suppressed by the appropriate content of the Mg compound in the silicon-based active material, and the discharge capacity and initial efficiency of the battery can be improved.

[0046] The Li compound may include at least one selected from the group consisting of Li silicate, Li silicide, and Li oxide. The Li silicate may include at least one of Li2SiO3, Li4SiO4, and Li2Si2O5. The Li silicide may include Li7Si2. The Li oxide may include Li2O.

[0047] In one embodiment of the present invention, the Li compound may include a lithium silicate form. The lithium silicate is Li a Si b O cIt is represented by (2 ≦ a ≦ 4, 0 < b ≦ 2, 2 ≦ c ≦ 5) and can be divided into crystalline lithium silicate and amorphous lithium silicate. The crystalline lithium silicate can exist in the form of at least one lithium silicate selected from the group consisting of Li2SiO3, Li4SiO4, and Li2Si2O5 within the silicon-based composite particles, and the amorphous lithium silicate is Li a Si b O c It may be in the form of (2 ≦ a ≦ 4, 0 < b ≦ 2, 2 ≦ c ≦ 5) and is not limited to the above form.

[0048] In one embodiment of the present specification, the Li element may be contained at 0.1% to 20% by weight or 0.1% to 10% by weight based on 100% by weight of the total silicon-based active material. In another embodiment, the Li element may be contained at 0.5% to 8% by weight, and in another embodiment, it may be contained at 0.5% to 4% by weight. When the above range is satisfied, the Li compound can be contained in an appropriate content in the silicon-based active material, the volume change of the negative electrode active material can be easily suppressed during charging and discharging of the battery, and the discharge capacity and initial efficiency of the battery can be improved.

[0049] The content of the Mg element or Li element can be confirmed by ICP (Inductively Coupled Plasma) analysis. After accurately sampling a certain amount (about 0.01 g) of the negative electrode active material for the ICP analysis, it is transferred to a platinum crucible, nitric acid, hydrofluoric acid, and sulfuric acid are added, and it is completely decomposed on a hot plate. Then, using an Inductively Coupled Plasma Atomic Emission Spectrometer (ICPAES, Perkin-Elmer 7300), the intensity of the standard solution (5 mg / kg) prepared with a standard solution at the specific wavelength of the Mg element or Li element is measured to create a calibration curve. Then, the pretreated sample solution and the background sample are introduced into the instrument, the intensities of each are measured to calculate the actual intensity, the concentration of each component is calculated with respect to the created calibration curve, and after conversion so that the sum of the whole becomes the theoretical value, the content of the Mg element or Li element in the manufactured silicon-based active material can be analyzed.

[0050] In one embodiment of the present specification, a carbon layer may be provided on the surface and / or inside the pores of the silicon-based composite particles. The carbon layer imparts electrical conductivity to the silicon-based composite particles, thereby improving the initial efficiency, life characteristics, and battery capacity characteristics of a secondary battery including a negative electrode active material containing the silicon-based composite particles. The carbon layer may be included in an amount of 5 wt % to 40 wt % based on 100 wt % of the silicon-based composite particles.

[0051] In one embodiment of the present specification, the carbon layer may contain at least one of amorphous carbon and crystalline carbon.

[0052] The average particle size (D 50 ) may be 2 μm to 15 μm, specifically 3 μm to 12 μm, and more specifically 6 μm to 10 μm. When the above range is satisfied, side reactions between the silicon-based composite particles and the electrolyte are controlled, and the discharge capacity and initial efficiency of the battery can be effectively achieved.

[0053] In this specification, the average particle size (D 50 The average particle size (D) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. 50 ) can be measured using, for example, a laser diffraction method. The laser diffraction method generally enables measurement of particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0054] The active material containing Si / C as the silicon-based active material is a composite of Si and C and is distinguished from silicon carbide, which is abbreviated as SiC. The silicon carbon composite may be a composite of silicon and graphite, or may have a structure in which a core of silicon and graphite is surrounded by graphene or amorphous carbon. In the silicon carbon composite, the silicon may be nanosilicon. The average particle size (D 50 ) may be 2 μm to 15 μm, specifically 3 μm to 12 μm, and more specifically 6 μm to 10 μm. A carbon layer may be provided on the surface of the active material containing Si / C.

[0055] In one embodiment of the present specification, the negative electrode active material may be included in an amount of 80 parts by weight to 99.9 parts by weight, 90 parts by weight to 99.9 parts by weight, 95 parts by weight to 99.9 parts by weight, or 98 parts by weight to 99.9 parts by weight in 100 parts by weight of the negative electrode active material layer.

[0056] According to an additional embodiment of the present specification, the negative electrode active material layer may further include a negative electrode binder in addition to the negative electrode active material.

[0057] The negative electrode binder may improve adhesion between negative electrode active material particles and between the negative electrode active material particles and the negative electrode current collector. The negative electrode binder may be any binder known in the art, and non-limiting examples thereof may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which hydrogen is substituted with Li, Na, Ca, or the like, or various copolymers thereof.

[0058] The negative electrode binder may be included in an amount of 0.1 to 20 parts by weight, for example, 0.3 to 20 parts by weight, or 0.5 to 10 parts by weight, based on 100 parts by weight of the negative electrode active material layer.

[0059] The negative electrode active material layer may not contain a conductive material, but may further contain a conductive material if necessary. The conductive material contained in the negative electrode active material layer is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. Examples of the conductive material include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. The content of the conductive material in the negative electrode active material layer may be 0.01 to 20 parts by weight, or 0.03 to 18 parts by weight, per 100 parts by weight of the negative electrode active material layer.

[0060] In one embodiment of the present specification, the first and second negative electrode active material layers may each have a thickness of 30 μm or more and 100 μm or less, for example, 45 μm or more and 75 μm or less, and the sum of the thicknesses of the first and second negative electrode active material layers may be 90 μm or more and 150 μm or less.

[0061] In one embodiment of the present specification, the negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like. Specifically, transition metals that adsorb carbon well, such as copper and nickel, can be used as the current collector. The thickness of the current collector may be 1 μm to 500 μm, but the thickness of the current collector is not limited thereto.

[0062] Additional embodiments herein provide secondary batteries comprising a negative electrode, a positive electrode, and a separator according to the previous embodiments.

[0063] In one embodiment of the present specification, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing the positive electrode active material. The positive electrode active material layer may have a thickness of 20 μm to 500 μm.

[0064] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. The positive electrode current collector typically has a thickness of 1 to 500 μm, and fine irregularities can be formed on the collector surface to enhance adhesion of the positive electrode active material. It can be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0065] In one embodiment of the present specification, the positive electrode may include a lithium composite transition metal compound containing nickel (Ni) and cobalt (Co) as an active material. The lithium composite transition metal compound may further include at least one of manganese and aluminum. The lithium composite transition metal compound may include nickel in an amount of 60 mol % or more, 80 mol % or more, for example, 80 mol % or more but less than 100 mol %, among metals other than lithium.

[0066] In one embodiment, the positive electrode active material may be contained in an amount of 80 parts by weight to 99.9 parts by weight, 90 parts by weight to 99.9 parts by weight, 95 parts by weight to 99.9 parts by weight, or 98 parts by weight to 99.9 parts by weight in 100 parts by weight of the positive electrode active material layer.

[0067] According to additional embodiments herein, the positive electrode active material layer according to the foregoing embodiments may further include a positive electrode binder and a conductive material.

[0068] The positive electrode binder may serve to improve adhesion between positive electrode active material particles and between the positive electrode active material particles and the positive electrode current collector. The positive electrode binder may be any binder known in the art, and non-limiting examples thereof include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These binders may be used alone or in combination.

[0069] The positive electrode binder may be included in an amount of 0.1 to 50 parts by weight, 0.3 to 35 parts by weight, or 0.5 to 20 parts by weight, based on 100 parts by weight of the positive electrode active material layer.

[0070] The conductive material contained in the positive electrode active material layer is used to impart conductivity to the electrode. Any conductive material can be used without particular limitations as long as it has electronic conductivity and does not cause chemical changes within the battery. Specific examples include graphite, such as natural graphite or artificial graphite; carbon-based materials, such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotubes; metal powders or fibers, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials may be used alone or in combination. Specifically, in one embodiment, the conductive material may include one or more of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs).

[0071] The conductive material may be included in an amount of 0.1 parts by weight to 10 parts by weight, 0.1 parts by weight to 7 parts by weight, or 0.1 parts by weight to 5 parts by weight, based on 100 parts by weight of the composition for a positive electrode active material layer.

[0072] According to one embodiment, the sum of the weights of the first and second negative electrode active material layers of the negative electrode is 170 to 280 mg / 25 cm 2 Here, the weight is based on the weight (solid content) after drying excluding the solvent. This range is advantageous for high energy density and rapid charging characteristics.

[0073] The positive and negative electrodes may be fabricated according to conventional methods for fabricating positive and negative electrodes, except for using the positive and negative electrode active materials. Specifically, they may be fabricated by coating a composition for forming an active material layer containing the active material and, optionally, a binder and a conductive material, on a current collector, followed by drying and rolling. The types and contents of the positive and negative electrode active materials, binder, and conductive material are as described above. The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination. The amount of solvent used should be sufficient to dissolve or disperse the active material, conductive material, and binder, and to provide a viscosity that allows excellent thickness uniformity during subsequent coating for fabricating positive and negative electrodes, taking into account the coating thickness and manufacturing yield of the slurry. Alternatively, the positive electrode and the negative electrode may be produced by casting the active material layer-forming composition on a separate support, peeling the composition from the support, and laminating the resulting film on a current collector.

[0074] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without limitation. In particular, a separator that exhibits low resistance to electrolyte ion movement and excellent electrolyte humidification is preferred. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material may be used, and may be used in a single-layer or multi-layer structure.

[0075] Examples of the electrolyte include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing lithium secondary batteries, but are not limited to these.

[0076] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0077] Examples of the non-aqueous organic solvent that may be used include non-proton organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0078] In particular, among the carbonate-based organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate can be used because they are high-viscosity organic solvents with high dielectric constants that allow them to dissociate lithium salts well. When such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte with high electrical conductivity can be prepared, and therefore can be used.

[0079] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, the anion of the lithium salt may be F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 -, (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more selected from the group consisting of:

[0080] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving the discharge capacity of the battery.

[0081] A secondary battery according to one embodiment of the present invention includes an assembly including a positive electrode, a negative electrode, a separator, and an electrolyte, and may be a lithium secondary battery.

[0082]

[0013] An additional embodiment of the present invention provides a battery module including the aforementioned secondary battery as a unit cell, and a battery pack including the same. The battery module and battery pack include the secondary battery having high capacity, excellent rate-limiting characteristics, and excellent cycle characteristics, and can be used as a power source for medium- to large-sized devices selected from the group consisting of, but not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0083] The secondary battery according to the embodiment of the present invention stably exhibits excellent discharge capacity, output characteristics, and cycle performance, and therefore can be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems, as well as portable devices such as mobile phones, laptops, and digital cameras. For example, the battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0084] Examples are presented below to aid in understanding the present invention. However, the above examples are merely illustrative of the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present description. Naturally, such changes and modifications fall within the scope of the appended claims.

[0085] Examples 1 and 2 and Comparative Examples 1 and 2 <Cel production> Example 1 Positive electrode production A lithium composite transition metal compound containing nickel (Ni), cobalt (Co), and manganese (Mn) in an atomic ratio of 84:8:8 as the positive electrode active material and doped with aluminum (Al), a conductive material (CNT), and a binder (PVDF) were added to a methylpyrrolidone (NMP) solvent in a weight ratio of 97:1:2 to prepare a positive electrode slurry (the solid content of the positive electrode slurry was 70 parts by weight of the total positive electrode slurry).

[0086] The prepared positive electrode slurry was coated on an Al current collector, dried, and then rolled at room temperature to prepare a positive electrode.

[0087] Negative electrode production For the first negative electrode active material layer, a carbon-based active material (artificial graphite and natural graphite in a weight ratio of 4:6), a conductive material (carbon black), a binder (SBR), and a thickener (Li-CMC) were added to a distilled water solvent in a weight ratio of 96:1:2:1 to prepare a negative electrode slurry (the solid content of the negative electrode slurry was 50 parts by weight of the total negative electrode slurry).

[0088] For the second negative electrode active material layer, negative electrode active materials including Mg-doped SiO active material and carbon-based active material (containing only natural graphite) (the Mg-doped SiO active material was included in an amount of 5 parts by weight based on 100 parts by weight of the total negative electrode active materials, and 10 parts by weight based on 100 parts by weight of the negative electrode active materials of the second negative electrode active material layer), a conductive material (carbon black), a binder (SBR), and a thickener (Li-CMC) were added to a distilled water solvent in a weight ratio of 96:1:2:1 to prepare a negative electrode slurry (the solid content of the negative electrode slurry was 50 parts by weight of the total negative electrode slurry).

[0089] The natural graphite D 50 is 18 μm, and the D of the artificial graphite 50 is 16 μm, and the D of the Mg-doped SiO active material 50 is 6 μm.

[0090] The first negative electrode active material layer slurry prepared above was coated on a Cu current collector, and then the second negative electrode active material layer slurry was sequentially coated on the first negative electrode active material layer, dried, and rolled at room temperature to fabricate a negative electrode.

[0091] Cell production A separator was interposed between the prepared positive and negative electrodes, and the resulting assembly was assembled. An electrolyte was then injected and activated as follows to prepare a cell.

[0092] - Electrolyte composition: 1M LiPF6, ethylene carbonate (EC) / ethyl methyl carbonate (EMC) (volume ratio 3 / 7), vinylene carbonate (VC) / propane sultone (PS, propane sultone) (contained in the electrolyte at 3 parts by weight and 1.5 parts by weight, respectively) - Activation: 0.1C, 3 hours. After charging, high temperature / normal temperature aging, degassing

[0093] Example 2. An electrode and a cell were fabricated in the same manner as in Example 1, except that the first negative electrode active material layer contained artificial graphite, natural graphite, and Mg-doped SiO in a weight ratio of 40:55:5, and the second negative electrode active material layer contained natural graphite and Mg-doped SiO in a weight ratio of 95:5.

[0094] Comparative Example 1 The first negative electrode active material layer contains artificial graphite and Mg-doped SiO in a weight ratio of 40:60, and the second negative electrode active material layer contains D 50 Electrodes and cells were fabricated similarly to Example 1, except that the electrode contained natural graphite with a particle size of 9 μm and Mg-doped SiO in a weight ratio of 90:10.

[0095] Comparative Example 2 An electrode and a cell were fabricated in the same manner as in Example 1, except that the first negative electrode active material layer contained artificial graphite and Mg-doped SiO in a weight ratio of 40:60, and the second negative electrode active material layer contained natural graphite and Mg-doped SiO in a weight ratio of 90:10.

[0096] The values ​​of Equations 1 and 2 for the negative electrodes prepared in Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 1 below.

[0097] [Table 1]

[0098] Experimental example 1: Room temperature (25°C) cycle performance The fabricated cells were subjected to charge-discharge cycling at room temperature (25°C) by constant current / constant voltage (CC / CV) charging at 0.33 C to 4.2 V (0.05 C cutoff), followed by 0.33 C constant current (CC) discharge (2.8 V cutoff). After 200 cycles, the discharge capacity was measured. After charging as described above, the cells were set to 50% SOC at 0.33 C discharge and pulse-discharged at 2.5 C for 10 seconds, and the resistance was measured. The capacity retention (capacity after 200 cycles / initial capacity x 100%) was measured. The results are shown in Table 2 below.

[0099] Experimental example 2: High temperature cycle performance The fabricated cells were subjected to charge-discharge cycling at high temperature (45°C) by constant current / constant voltage (CC / CV) charging at 0.33 C up to 4.2 V (0.05 C cutoff), followed by 0.33 C constant current (CC) discharge (2.5 V cutoff). After 200 cycles, the capacity was measured in the same manner as in Experimental Example 1, and the capacity retention (capacity after 200 cycles / initial capacity x 100%) was measured. The results are shown in Table 2 below.

[0100] [Table 2]

[0101] As shown in Table 1, in Examples 1 and 2, the difference in particle size distribution between the first and second regions of the negative electrode active material is within 3% in the particle size distribution of the entire negative electrode active material layer.

[0102] As can be seen from the results of Examples 1 and 2 in Table 2, the batteries having negative electrodes satisfying Formulas 1 and 2 exhibited excellent capacity retention in both room temperature cycle life performance and high temperature cycle life performance.

[0103] In contrast, batteries that do not satisfy the ranges of Formula 1 and Formula 2, such as those in Comparative Examples 1 and 2, exhibited a capacity retention rate of within the mid-90% range when measuring cycle life performance at room temperature, and a capacity retention rate of just under 90% when measuring cycle life performance at high temperature. This is because when the average particle size of each region of the negative electrode active material layer is non-uniform, it inhibits the mobility of lithium ions, causing non-uniform reactions between the active materials in the negative electrode and adversely affecting the battery life.

Claims

1. a current collector; and a negative electrode active material layer provided on at least one surface of the current collector, the negative electrode active material layer includes a first region that is from a surface facing the current collector and that accounts for 50% of the total thickness of the negative electrode active material layer, and a second region that is from a surface opposite to the surface facing the current collector and that accounts for 50% of the total thickness of the negative electrode active material layer, The negative electrode active material layer is D ５０ and the negative electrode active material contains two or more negative electrode active materials having different structures, and the negative electrode active materials satisfy the following formulas 1 and 2: [Formula 1] -3≦│D ５０，ｔｏｔａｌ -D ５０，１ｓｔ │÷D ５０，ｔｏｔａｌ ×100≦3 [Formula 2] -3≦│D ５０，ｔｏｔａｌ -D ５０，２ｎｄ │÷D ５０，ｔｏｔａｌ ×100≦3 In the formula 1 and the formula 2, D ５０，ｔｏｔａｌ is the D of the negative electrode active material in the entire negative electrode active material layer ５０ and D ５０，１ｓｔ is the D of the negative electrode active material in the first region ５０ and D ５０，２ｎｄ is the D of the negative electrode active material in the second region ５０ A negative electrode for a lithium secondary battery.

2. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the composition of the negative electrode active material in the first region is different from the composition of the negative electrode active material in the second region.

3. The negative electrode active material layer is D ５０ The negative electrode for a lithium secondary battery according to claim 1 , comprising three or more negative electrode active materials having different structures.

4. At least one of the first region and the second region is D ５０ The negative electrode for a lithium secondary battery according to claim 1 , comprising two or more negative electrode active materials having different structures.

5. The first region and the second region are D ５０ The negative electrode for a lithium secondary battery according to claim 1 , comprising two or more negative electrode active materials having different structures.

6. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the negative electrode active material layer has a structure of two or more layers.

7. The negative electrode active material layer is a first negative electrode active material layer provided on the current collector; a second negative electrode active material layer provided on the first negative electrode active material layer,

8. At least one of the first negative electrode active material layer and the second negative electrode active material layer is D ５０ and the negative electrode active material contains two or more negative electrode active materials having different structures, and the negative electrode active materials satisfy the following formulas 3 and 4: [Formula 3] -3≦│D ５０，ｔｏｔａｌ -D ５０，Ｌ１ │÷D ５０，ｔｏｔａｌ ×100≦3 [Formula 4] -3≦│D ５０，ｔｏｔａｌ -D ５０，Ｌ２ │÷D ５０，ｔｏｔａｌ ×100≦3 In the formula 3 and the formula 4, D ５０，ｔｏｔａｌ is the D of the negative electrode active material in the entire negative electrode active material layer ５０ and D ５０，Ｌ１ is the D of the negative electrode active material in the first negative electrode active material layer ５０ and D ５０，Ｌ２ is the D of the negative electrode active material in the second negative electrode active material layer ５０ 8. The negative electrode for a lithium secondary battery according to claim 7, wherein

9. 8. The negative electrode for a lithium secondary battery according to claim 7, wherein a boundary between the first negative electrode active material layer and the second negative electrode active material layer is different from a boundary between the first region and the second region.

10. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the negative electrode active material comprises a silicon-based active material, artificial graphite, and natural graphite.

11. 11. The negative electrode for a lithium secondary battery according to claim 10, wherein the silicon-based active material includes at least one of a silicon oxide, a silicon metal complex, and a silicon carbon composite.

12. 8. The negative electrode for a lithium secondary battery according to claim 7, wherein the first negative electrode active material layer contains at least one of artificial graphite and natural graphite and a silicon-based active material, and the second negative electrode active material layer contains at least one of artificial graphite and natural graphite and a silicon-based active material.

13. 8. The negative electrode for a lithium secondary battery according to claim 7, wherein the first negative electrode active material layer contains at least one of artificial graphite and natural graphite, and the second negative electrode active material layer contains at least one of artificial graphite and natural graphite and a silicon-based active material.

14. 8. The negative electrode for a lithium secondary battery according to claim 7, wherein the first negative electrode active material layer contains artificial graphite and natural graphite, and the second negative electrode active material layer contains natural graphite and a silicon-based active material.

15. The negative electrode for a lithium secondary battery according to claim 14 , wherein the first negative electrode active material layer further comprises a silicon-based active material.

16. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the negative electrode active material layer contains 1 to 10 parts by weight of a silicon-based active material based on 100 parts by weight of a total of negative electrode active materials.

17. 8. The negative electrode for a lithium secondary battery according to claim 7, wherein at least one of the first negative electrode active material layer and the second negative electrode active material layer contains 1 part by weight to 20 parts by weight of a silicon-based active material, based on a total of 100 parts by weight of the negative electrode active materials of each layer.

18. A lithium secondary battery comprising the negative electrode for a lithium secondary battery according to any one of claims 1 to 17, a positive electrode, and a separator.

19. 19. The lithium secondary battery according to claim 18, wherein the positive electrode contains a lithium composite transition metal compound containing nickel (Ni) and cobalt (Co) as an active material.

20. The lithium secondary battery according to claim 19 , wherein the lithium composite transition metal compound further contains at least one of manganese and aluminum.

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