Negative electrode and lithium secondary battery

Abstract

The present invention relates to a negative electrode for a secondary battery and a secondary battery comprising same, the negative electrode comprising: a current collector and a negative electrode active material layer provided on at least one surface of the current collector, wherein the negative electrode active material layer includes 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 includes two or more kinds of negative electrode active materials that are different from each other in D50 and satisfies formulas 1 and 2.

Description

Cathode and lithium secondary battery

[0001] This application claims the benefit of Korean Patent Application No. 10-2023-0099052, filed on July 28, 2023, the entire disclosure of which is 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.

[0003] Secondary batteries are widely used in portable devices as well as electric vehicles (EVs) and hybrid electric vehicles (HEVs) that are driven by electrical power sources.

[0004] These secondary batteries are attracting attention as a new energy source for environmental friendliness and energy efficiency because they not only have the primary advantage of being able to drastically reduce the use of fossil fuels, but also have the advantage of producing no byproducts from energy use.

[0005] Typically, a secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte, and the like. In addition, 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 utility of secondary batteries increases, demands for diverse battery performance are increasing. Therefore, efforts are being made to improve the materials and structure of the active material layer to enhance battery performance.

[0007] The present invention aims to provide a negative electrode for a lithium secondary battery capable of providing a lithium secondary battery with an improved lifespan, and a lithium secondary battery including the same.

[0008] One embodiment of the present invention is

[0009] A collector, and a negative electrode active material layer provided on at least one surface of the collector,

[0010] The negative electrode active material layer includes a first region corresponding to 50% of the total thickness of the negative electrode active material layer from the surface facing the current collector, and a second region corresponding to 50% of the total thickness of the negative electrode active material layer from the opposite surface of the surface facing the current collector.

[0011] The above negative active material layer is D 50 Containing two or more different types of negative active materials,

[0012] At least one of the first region and the second region is D 50 It contains two or more different types of negative active materials,

[0013] A negative electrode for a lithium secondary battery is provided that satisfies the following equations 1 and 2:

[0014] [Formula 1]

[0015] -3 ≤ (│D 50,total - D 50,1st │÷ D 50,total X 100 ≤ 3

[0016] [Formula 2]

[0017] -3 ≤ (│D 50,total - D 50,2nd │÷ D 50,total X 100 ≤ 3

[0018] In equations 1 and 2, D 50,total D of the negative electrode active material in the entire negative electrode active material layer 50 And, D 50,1st D of the negative active material in the above first region 50 And, D 50,2nd D of the negative active material in the second region 50 am.

[0019] According to one embodiment of the present invention, the negative electrode active material includes a silicon-based active material, artificial graphite, and natural graphite.

[0020] 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.

[0021] Another embodiment of the present invention provides a secondary battery including the negative electrode, positive electrode, and separator for the lithium secondary battery.

[0022] 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. Accordingly, by optimizing the pore structure that serves as a material transport path within the negative electrode active material layer, not only lithium ion transport but also the reactivity between the negative electrode and the lithium-containing electrolyte can be improved, thereby achieving long-life performance of the battery.

[0023] Hereinafter, the present invention will be described in more detail to facilitate understanding. The present invention may be embodied in various different forms and is not limited to the embodiments described herein. In this regard, terms and words used in this specification and claims should not be construed as limited to their conventional or dictionary meanings. Rather, they should be interpreted in the sense and concept that aligns with the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of a term to best explain his or her invention.

[0024] In this specification, it should be understood that the terms “include,” “comprising,” or “having” are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0025] Furthermore, when we say that a part of a layer or the like is "above" or "on" another part, this includes not only cases where it is "directly above" that part, but also cases where there is another part in between. Conversely, when we say that a part is "directly above" another part, it means that there is no other part in between. Furthermore, when we say that a part is "above" or "on" a reference part, it means that it is located above or below that reference part, and does not necessarily mean that it is located "above" or "on" in the direction opposite to gravity.

[0026] In this specification, the description referred to only as “negative electrode active material layer” without the expressions first and second can be applied to both the first and second negative electrode active material layers, unless otherwise stated.

[0027] In this specification, the first region and the second region are D of the negative electrode active material based on the thickness of the negative electrode active material layer. 50 This distinction is intended to confirm particle size distribution and does not imply the existence of a physical interface between the two regions. As described below, the two negative 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 active material layers coincide with the first and second regions, there are cases where the interface between them is not distinguished.

[0028] 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,

[0029] The negative electrode active material layer includes a first region corresponding to 50% of the total thickness of the negative electrode active material layer from the surface facing the current collector, and a second region corresponding to 50% of the total thickness of the negative electrode active material layer from the opposite surface of the surface facing the current collector.

[0030] The above negative active material layer is D 50Containing two or more different types of negative active materials,

[0031] At least one of the first region and the second region is D 50 It contains two or more different types of negative active materials,

[0032] It is characterized by satisfying the following equations 1 and 2.

[0033] [Formula 1]

[0034] -3 ≤ (│D 50,total - D 50,1st │÷ D 50,total X 100 ≤ 3

[0035] [Formula 2]

[0036] -3 ≤ (│D 50,total - D 50,2nd │÷ D 50,total X 100 ≤ 3

[0037] In equations 1 and 2, D 50,total D of the negative electrode active material in the entire negative electrode active material layer 50 And, D 50,1st D of the negative active material in the above first region 50 And, D 50,2nd D of the negative active material in the second region 50 am.

[0038] According to the above implementation state, the negative active material layer is D 50 It comprises three or more different types of negative active materials, and at least one of the first region and the second region is D 50 Even though it includes two or more different types of negative active materials, the pore structure of the negative active material layer can be optimized by satisfying Equations 1 and 2. Accordingly, not only can the movement of lithium ions within the negative active material layer be optimized while maintaining a high energy density, but also the long-life performance of the battery can be secured by uniformly controlling the reaction within the negative active material layer.

[0039] The above equations 1 and 2 indicate that the difference in particle size distribution in the first region and the second region is within 3% of the difference in particle size distribution in the entire negative electrode active material layer, and by satisfying this, the pore structure in the entire negative electrode active material layer can be designed uniformly. If the value of equation 1 or equation 2 is less than -3 or greater than 3, it indicates that the particle size distribution and pore structure in each region are heterogeneous from the particle size distribution and pore structure of the entire negative electrode active material layer, and in this case, not only does the mobility of lithium ions become inhibited, but also a part with different reactivity exists in the negative electrode active material layer, which may adversely affect the life of the battery.

[0040] According to one embodiment, the composition of the negative electrode active material in the first region and the composition of the negative electrode active material in the second region are different from each other. The different composition of the negative electrode active material means that the types and / or content ratios of the negative electrode active materials are not the same. For example, the different composition of the negative electrode active materials means that at least one type of the negative electrode active materials is different, or is the same type but D 50 Using these different negative active materials, or the same type and same D 50 This includes a case where a negative active material having different contents is used. When the first and second regions satisfy the above-described formulas 1 and 2, they have similar pore structures due to a uniform particle size distribution despite having different compositions.

[0041] 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.

[0042] 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 thicknesses of the two layers are the same.

[0043] According to one embodiment, at least one of the first negative electrode active material layer and the second negative electrode active material layer is D 50 It comprises two or more different types of negative active materials and satisfies the following formula 3 and formula 4:

[0044] [Formula 3]

[0045] -3 ≤ (│D 50,total - D 50,L1 │÷ D 50,total X 100 ≤ 3

[0046] [Formula 4]

[0047] -3 ≤ (│D 50,total - D 50,L2 │÷ D 50,total X 100 ≤ 3

[0048] In equations 3 and 4, D 50,total D of the negative electrode active material in the entire negative electrode active material layer 50 And, D 50,L1 D of the negative electrode active material in the first negative electrode active material layer 50 And, D 50,L2 D of the negative electrode active material in the second negative electrode active material layer 50 lim.

[0049] As with the aforementioned equations 1 and 2, when equations 3 and 4 are satisfied, the first and second negative active material layers can have similar pore structures due to a uniform particle size distribution even when they contain negative active materials of different compositions.

[0050] 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.

[0051] According to one embodiment, the first negative electrode active material, the second negative electrode active material, and the third negative electrode active material are the same or different from each other, and may each independently be artificial graphite, natural graphite, or silicon-based active material.

[0052] According to the implementation status, D of the first negative active material 50 The size may be 15 ㎛ to 25 ㎛, 18 ㎛ to 25 ㎛, or 18 ㎛ to 22 ㎛.

[0053] According to the implementation status, D of the second negative active material 50 The size may be 10 ㎛ to 20 ㎛, 12 ㎛ to 18 ㎛, or 12 ㎛ to 16 ㎛.

[0054] According to the implementation status, the D of the third negative active material 50 The size may be 2 ㎛ to 15 ㎛, 3 ㎛ to 12 ㎛, or 6 ㎛ to 10 ㎛.

[0055] The particle size of the above negative active material can be controlled depending on the material or pore structure used in each manufacturing process.

[0056] In one embodiment, the silicon-based active material includes at least one of silicon oxide, silicon metal complex, and silicon carbon composite. Specifically, the silicon-based active material includes at least one of SiOx (0≤x<2), SiMy (M is metal, 1≤y≤4), and Si / C. The silicon-based active material may include only one type, or two or more types may be included together. When both the first and second negative electrode active material layers include silicon-based active materials, the same type of silicon-based active material may be used for the first and second negative electrode active material layers, or different types or different combinations of silicon-based active materials may be used.

[0057] 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. In this case, the second negative electrode active material layer may not include a silicon-based active material.

[0058] 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.

[0059] According to one embodiment, the first and second negative electrode active material layers include a silicon-based active material. In this case, the first and second negative electrode active material layers may further include at least one type of artificial graphite and natural graphite.

[0060] When the negative electrode active material layer includes a silicon-based active material, the silicon-based active material may be included in an amount of 1 to 10 parts by weight based on 100 parts by weight of the total negative electrode active material. In addition, when at least one of the first negative electrode active material layer and the second negative electrode active material layer includes a silicon-based active material, the silicon-based active material may be included in an amount of 1 to 20 parts by weight based on 100 parts by weight of the total negative electrode active material of each layer.

[0061] In one embodiment of the present specification, the negative electrode active material layer including the silicon-based active material may further include a carbon-based active material. In this case, the carbon-based active material may include at least one of artificial graphite and natural graphite. Based on 100 parts by weight of the total negative electrode active material included in the negative electrode active material layer, the carbon-based active material may be included in an amount of 90 parts by weight or more and 99 parts by weight or less.

[0062] The active material containing SiOx (0≤x<2) as the above silicon-based active material is SiO x (0 <x<2) 및 기공을 포함하는 실리콘계 복합 입자일 수 있다.

[0063] The above SiO x (0 <x<2)는 상기 실리콘계 복합 입자 내에서 매트릭스(matrix)에 해당한다. 상기 SiO x (0 <x<2)는 Si 및 SiO2가 포함된 형태일 수 있으며, 상기 Si는 상(phase)을 이루고 있을 수도 있다. 즉, 상기 x는 상기 SiO x (0 <x<2) 내에 포함된 Si에 대한 O의 개수비에 해당한다. 상기 실리콘계 복합 입자가 상기 SiO x (0 <x<2)를 포함하는 경우, 이차 전지의 방전 용량이 개선될 수 있다.

[0064] The above silicon-based composite particles may further include at least one of a Mg compound and a Li compound. The Mg compound and the Li compound may correspond to a matrix within the silicon-based composite particles.

[0065] The above Mg compound and / or Li compound is SiO x (0 <x<2)의 내부 및 / 또는 표면에 존재할 수 있다. 상기 Mg 화합물 및 / 또는 Li 화합물에 의해 전지의 초기 효율이 개선될 수 있다.

[0066] The above 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.

[0067] In one embodiment of the present specification, the Mg element may be included 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 included in an amount of 0.5 wt% to 8 wt% or 0.8 wt% to 4 wt%. When the above range is satisfied, the Mg compound can be included in an appropriate amount in the silicon-based active material, so that volume change of the silicon-based 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.

[0068] 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.

[0069] In one embodiment of the present invention, the Li compound may include a lithium silicate form. The lithium silicate may include Li a Si b O c (2≤a≤4, 0 <b≤2, 2≤c≤5)로 표시되며, 결정질 리튬 실리케이트와 비정질 리튬 실리케이트로 구분될 수 있다. 상기 결정질 리튬 실리케이트는 상기 실리콘계 복합 입자 내에서 Li2SiO3, Li4SiO4및 Li2Si2O5로 이루어진 군에서 선택된 적어도 1종의 리튬 실리케이트의 형태로 존재할 수 있으며, 비정질 리튬 실리케이트는 Li a Si b O c (2≤a≤4, 0 <b≤2, 2≤c≤5)의 형태일 수 있고, 상기 형태에 한정되지는 않는다.

[0070] In one embodiment of the present specification, the Li element may be included 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. In another embodiment, the Li element may be included in an amount of 0.5 wt% to 8 wt%, and in another embodiment, may be included in an amount of 0.5 wt% to 4 wt%. When the above range is satisfied, the Li compound may be included in an appropriate amount in the silicon-based active material, so that a change in the volume of the negative electrode active material during charging and discharging of the battery can be easily suppressed, and the discharge capacity and initial efficiency of the battery can be improved.

[0071] The content of the above Mg element or Li element can be confirmed through ICP analysis. For the ICP analysis, a certain amount (approximately 0.01 g) of the negative active material is precisely aliquoted, transferred to a platinum crucible, and completely decomposed on a hot plate by adding nitric acid, hydrofluoric acid, and sulfuric acid. Thereafter, an inductively coupled plasma electroluminescence spectrometer (ICPAES, Perkin-Elmer 7300) is used to measure the intensity of a standard solution prepared using a standard solution (5 mg / kg) at the wavelength unique to the Mg element or Li element, thereby creating a reference calibration curve. Thereafter, the pretreated sample solution and blank sample are introduced into the device, and the respective intensities are measured to calculate the actual intensity, and the concentration of each component is calculated against the created calibration curve, and then the content of the Mg element or Li element of the manufactured silicon-based active material can be analyzed by converting so that the sum of the entire values ​​becomes the theoretical value.

[0072] 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. By the carbon layer, conductivity is provided to the silicon-based composite particles, and the initial efficiency, life characteristics, and battery capacity characteristics of a secondary battery including a negative active material including the silicon-based composite particles may be improved. The total weight of the carbon layer may be comprised in an amount of 5 wt% to 40 wt% based on a total of 100 wt% of the silicon-based composite particles.

[0073] In one embodiment of the present specification, the carbon layer may include at least one of amorphous carbon and crystalline carbon.

[0074] The average particle diameter (D) of the above silicon-based composite particles 50 ) may be 2 ㎛ to 15 ㎛, specifically 3 ㎛ to 12 ㎛, and more specifically 6 ㎛ to 10 ㎛. When the above range is satisfied, the side reaction between the silicon-based composite particles and the electrolyte is controlled, and the discharge capacity and initial efficiency of the battery can be effectively implemented.

[0075] In this specification, the average particle diameter (D 50 ) can be defined as the particle size corresponding to 50% of the volume accumulation in the particle size distribution curve. The average particle size (D 50 ) can be measured, for example, using a laser diffraction method. The laser diffraction method can generally measure particle diameters from the submicron range to several mm, and can obtain results with high reproducibility and high resolution.

[0076] The above silicon-based active material, which includes Si / C, is a composite of Si and C and is distinct from silicon carbide, which is denoted as SiC. The silicon-carbon composite may be a composite of silicon and graphite, and may form a structure in which a core composed of silicon and graphite is surrounded by graphene or amorphous carbon. In the silicon-carbon composite, the silicon may be nano silicon. The average particle diameter (D) of the active material including the Si / C 50 ) may be 2 ㎛ to 15 ㎛, specifically 3 ㎛ to 12 ㎛, and more specifically 6 ㎛ to 10 ㎛. A carbon layer may be provided on the surface of the active material including the Si / C.

[0077] In one embodiment of the present specification, the negative electrode active material in 100 parts by weight of the negative electrode active material layer may be included in an amount of 80 parts by weight or more and 99.9 parts by weight or less, 90 parts by weight or more and 99.9 parts by weight or less, 95 parts by weight or more and 99.9 parts by weight or less, or 98 parts by weight or more and 99.9 parts by weight or less.

[0078] 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.

[0079] The above negative electrode binder can play a role in improving the adhesion between negative electrode active material particles and the adhesive strength between the negative electrode active material particles and the negative electrode current collector. The above-mentioned negative electrode binder may be one known in the art, and non-limiting examples thereof include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluoroelastomer, polyacrylic acid, and a material in which hydrogens of these are substituted with Li, Na, Ca, etc., and may also include various copolymers thereof.

[0080] The above negative electrode binder may be included in an amount of 0.1 to 20 parts by weight based on 100 parts by weight of the negative electrode active material layer, for example, 0.3 to 20 parts by weight, or 0.5 to 10 parts by weight.

[0081] The above-described negative electrode active material layer may not include a conductive material, but may further include a conductive material as needed. The conductive material included in the negative electrode active material layer is not particularly limited as long as it has conductivity and does not cause a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black; conductive fibers such as carbon fiber or 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 may be used. 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, based on 100 parts by weight of the negative electrode active material layer.

[0082] In one embodiment of the present specification, the thickness of the first and second negative electrode active material layers may be 30 µm or more and 100 µm or less, for example, 45 µm or more and 75 µm or less. 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.

[0083] In one embodiment of the present specification, the negative electrode current collector may be any conductive material that does not cause a chemical change in the battery, and is not particularly limited thereto. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like. Specifically, a transition metal that adsorbs carbon well, such as copper or nickel, may 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.

[0084] An additional embodiment of the present disclosure provides a secondary battery including a negative electrode, a positive electrode, and a separator according to the above-described embodiments.

[0085] 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 including the positive electrode active material. The thickness of the positive electrode active material layer may be 20 μm or more and 500 μm or less.

[0086] The positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 1 to 500 ㎛, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesive strength of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0087] In one embodiment of the present specification, the positive electrode may include a lithium composite transition metal compound including 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 and less than 100 mol%, of a metal other than lithium.

[0088] In one embodiment, the positive electrode active material may be included in 100 parts by weight of the positive electrode active material layer in an amount of 80 parts by weight or more and 99.9 parts by weight or less, 90 parts by weight or more and 99.9 parts by weight or less, 95 parts by weight or more and 99.9 parts by weight or less, or 98 parts by weight or more and 99.9 parts by weight or less.

[0089] According to an additional embodiment of the present specification, the positive electrode active material layer according to the above-described embodiment may further include a positive electrode binder and a conductive material.

[0090] The above-described positive electrode binder can serve to improve adhesion between positive electrode active material particles and adhesion between the positive electrode active material particles and the positive electrode current collector. Those known in the art can be used as the positive electrode binder, and non-limiting examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof.

[0091] The above positive electrode binder may be included in an amount of 0.1 to 50 parts by weight based on 100 parts by weight of the positive electrode active material layer, 0.3 to 35 parts by weight, or 0.5 to 20 parts by weight.

[0092] The conductive material included in the positive electrode active material layer is used to provide conductivity to the electrode, and can be used without special restrictions as long as it does not cause chemical changes within the battery and has electronic conductivity. 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, summer black, carbon fiber, and carbon nanotube; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used. Specifically, in one embodiment, the conductive material may include at least one of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs).

[0093] The above-mentioned conductive material may be included in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the composition for the positive electrode active material layer, or may be included in an amount of 0.1 to 7 parts by weight, or 0.1 to 5 parts by weight.

[0094] 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 This can be done. The weight here is based on the weight after drying (solids content) excluding the solvent. This range is advantageous for high energy density and rapid charging characteristics.

[0095] The positive electrode and the negative electrode can be manufactured according to a conventional method for manufacturing positive and negative electrodes, except that the positive and negative electrode active materials described above are used. Specifically, the composition for forming an active material layer, which includes the active material described above and optionally a binder and a conductive material, is applied to a current collector, followed by drying and rolling. At this time, 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 generally used in the relevant technical field, and examples thereof include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, and water. One type alone or a mixture of two or more types thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the active material, conductive material, and binder in consideration of the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity during subsequent coating for manufacturing the positive and negative electrodes. Alternatively, the positive and negative electrodes may be manufactured by casting the composition for forming the active material layer on a separate support, then peeling the film from the support and laminating the resulting film on a current collector.

[0096] The separator is used to separate the negative electrode and the positive electrode and to provide a passage for lithium ions. Any separator commonly used in secondary batteries can be used without any particular restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, 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, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0097] Examples of the above electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0098] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0099] As the above non-aqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolan, formamide, dimethylformamide, dioxolan, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxy methane, dioxolan derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyrropionate, ethyl propionate, etc. can be used.

[0100] In particular, among the above carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants and thus can be used because they easily dissociate lithium salts. By mixing and using low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate in an appropriate ratio with these cyclic carbonates, an electrolyte with high electrical conductivity can be produced and used.

[0101] The metal salt may be a lithium salt, and the lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte, for example, as an anion of the lithium salt, at least one selected from the group consisting of F-, Cl-, I-, NO3-, N(CN)2-, BF4-, ClO4-, PF6-, (CF3)2PF4-, (CF3)3PF3-, (CF3)4PF2-, (CF3)5PF-, (CF3)6P-, CF3SO3-, CF3CF2SO3-, (CF3SO2)2N-, (FSO2)2N-, CF3CF2(CF3)2CO-, (CF3SO2)2CH-, (SF5)3C-, (CF3SO2)3C-, CF3(CF2)7SO3-, CF3CO2-, CH3CO2-, SCN-, and (CF3CF2SO2)2N- may be used. Can be.

[0102] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as, for example, a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, a cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery.

[0103] 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.

[0104]

[0105] A further 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, high rate characteristics, and cycle characteristics, and thus 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, but are not limited thereto.

[0106] The secondary battery according to the embodiments of the present invention stably exhibits excellent discharge capacity, output characteristics, and cycle performance, and therefore can be used as a power source for portable devices such as mobile phones, laptop computers, and digital cameras, as well as 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. For example, the battery module or battery pack can be used as a power source for any one or more medium- to large-sized devices selected from the group consisting of power tools; electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0107]

[0108] Hereinafter, examples are presented to help understand the present invention, but the examples are only illustrative of the present disclosure, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present disclosure, and it is natural that such changes and modifications fall within the scope of the appended patent claims.

[0109] Examples 1 and 2 and Comparative Examples 1 and 2

[0110] Cell Production

[0111] Example 1.

[0112] Bipolar production

[0113] A cathode slurry was prepared by adding a lithium composite transition metal compound doped with aluminum (Al), a conductive agent (CNT), and a binder (PVDF) in a weight ratio of 97:1:2 to a methylpyrrolidone (NMP) solvent, containing nickel (Ni), cobalt (Co), and manganese (Mn) as cathode active materials in an atomic ratio of 84:8:8 (the solid content of the cathode slurry was included as 70 parts by weight of the total cathode slurry).

[0114] The positive electrode slurry manufactured above was applied onto an Al current collector, dried, and then rolled at room temperature to manufacture a positive electrode.

[0115]

[0116] Cathode production

[0117] The first negative electrode active material layer was prepared by adding a carbon-based active material (including artificial graphite and natural graphite in a weight ratio of 4:6), a conductive agent (carbon black), a binder (SBR), and a thickener (Li-CMC) to a distilled water solvent in a weight ratio of 96:1:2:1 to prepare a negative electrode slurry (the negative electrode slurry solid content was included as 50 parts by weight of the total negative electrode slurry).

[0118] The second negative electrode active material layer includes a negative electrode active material including a Mg-doped SiO active material and a carbon-based active material (including only natural graphite) (the Mg-doped SiO active material is 5 parts by weight based on 100 parts by weight of the total negative electrode active material (10 parts by weight based on 100 parts by weight of the negative electrode active material in the second negative electrode active material layer)), a conductive agent (carbon black), a binder (SBR), and a thickener (Li-CMC) in a weight ratio of 96: 1: 2: 1 in distilled water to prepare a negative electrode slurry (the negative electrode slurry solid content is included as 50 parts by weight of the total negative electrode slurry).

[0119] D of the above natural graphite 50 is 18㎛, and the D of the artificial graphite 50 is 16㎛, and the D of the Mg-doped SiO active material 50 is 6㎛.

[0120] After the first negative electrode active material layer slurry manufactured above was applied onto a Cu current collector, the second negative electrode active material layer slurry was sequentially applied onto the first negative electrode active material layer, dried, and then rolled at room temperature to manufacture a negative electrode.

[0121]

[0122] Cell production

[0123] A separator was inserted between the positive and negative electrodes manufactured above, assembled, and an electrolyte was injected and then activated to manufacture a cell.

[0124] - Electrolyte composition: 1M LiPF6, ethylene carbonate (EC) / ethyl methyl carbonate (EMC) (volume ratio 3 / 7), vinylene carbonate (VC) / propane sultone (PS, propane sultone) (included in the electrolyte at 3 parts by weight and 1.5 parts by weight, respectively)

[0125] - Activation: 0.1C, 3hrs. Degas after high temperature / room temperature aging after charging.

[0126]

[0127] Example 2.

[0128] An electrode and a cell were manufactured 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.

[0129]

[0130] Comparative Example 1.

[0131] The first negative electrode active material layer includes artificial graphite and Mg-doped SiO in a weight ratio of 40:60, and the second negative electrode active material layer includes D 50 An electrode and a cell were manufactured in the same manner as in Example 1, except that the 9 μm natural graphite and Mg-doped SiO were included in a weight ratio of 90:10.

[0132]

[0133] Comparative Example 2.

[0134] An electrode and a cell were manufactured 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.

[0135]

[0136] The values ​​of Equations 1 and 2 in the cathodes manufactured in Examples 1 and 2 and Comparative Examples 1 and 2 are listed in Table 1 below.

[0137] Equation 1 Equation 2 Example 1 - 2.44 + 2.44 Example 2 - 2.38 + 2.38 Comparative Example 1 + 5.08 - 5.08 Comparative Example 2 - 6.19 + 6.19

[0138]

[0139] Experimental Example 1. Cycle performance at room temperature (25℃)

[0140] The fabricated cell was cycled by constant current / constant voltage (CC / CV) charging (0.05C-cut) to 4.2 V at 0.33 C at room temperature (25℃) and constant current (CC) discharging (2.8V-cut) at 0.33 C. The discharge capacity was measured after 200 repetitions. After charging as above, the SOC was set to 50% with a 0.33 C discharge, and the resistance was measured by performing a 2.5 C 10-second pulse discharge to measure the capacity retention rate (capacity after 200 cycles / initial capacity x 100%). The results are shown in Table 2 below.

[0141]

[0142] Experimental Example 2. High-temperature cycle performance

[0143] The fabricated cell was cycled by constant current / constant voltage (CC / CV) charging (0.05C-cut) and constant current (CC) discharging (2.5V-cut) at 0.33C at high temperature (45℃) to 4.2V. After 200 cycles, the capacity was measured using the same method as in Experimental Example 1 to determine the capacity retention rate (capacity after 200 cycles / initial capacity x 100%). The results are shown in Table 2 below.

[0144] Room temperature cycle life performance (%, @200 cycles) High temperature cycle life performance (%, @200 cycles) Example 19796 Example 29794 Comparative example 19390 Comparative example 29591

[0145]

[0146] As shown in Table 1 above, in Examples 1 and 2, the particle size distribution in the first and second regions of the negative electrode active material corresponds to a difference of less than 3% in the particle size distribution in the entire negative electrode active material layer.

[0147] As can be seen from the results of Examples 1 and 2 in Table 2 above, a battery having a negative electrode satisfying Equations 1 and 2 exhibited excellent capacity retention in room temperature cycle life performance and high temperature cycle life performance.

[0148] In contrast, batteries that do not satisfy the ranges of Equations 1 and 2, such as Comparative Examples 1 and 2, exhibited a capacity retention rate in the mid-90s when measuring room temperature cycle life performance, and a capacity retention rate in the early 90s when measuring high temperature cycle life performance. 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 a non-uniform reaction between the active materials in the negative electrode, thereby adversely affecting the life of the battery.

Claims

1. Including a current collector and a negative active material layer provided on at least one surface of the current collector, The negative electrode active material layer includes a first region corresponding to 50% of the total thickness of the negative electrode active material layer from the surface facing the current collector, and a second region corresponding to 50% of the total thickness of the negative electrode active material layer from the opposite surface of the surface facing the current collector. The above negative active material layer is D 50 A negative electrode for a lithium secondary battery comprising two or more different types of negative active materials and satisfying the following formula 1 and formula 2: [Formula 1] -3 ≤ (│D 50,total - D 50,1st │÷ D 50,total X 100 ≤ 3 [Formula 2] -3 ≤ (│D 50,total - D 50,2nd │÷ D 50,total X 100 ≤ 3 In equations 1 and 2, D 50,total D of the negative electrode active material in the entire negative electrode active material layer 50 And, D 50,1st D of the negative active material in the above first region 50 And, D 50,2nd D of the negative active material in the second region 50 lim.

2. A negative electrode for a lithium secondary battery according to claim 1, wherein the composition of the negative electrode active material in the first region and the composition of the negative electrode active material in the second region are different from each other.

3. In claim 1, the negative electrode active material layer is D 50 A negative electrode for a lithium secondary battery comprising three or more different types of negative active materials.

4. In claim 1, at least one of the first region and the second region is D 50 A negative electrode for a lithium secondary battery comprising two or more different types of negative active materials.

5. In claim 1, the first region and the second region are D 50 A negative electrode for a lithium secondary battery comprising two or more different types of negative active materials.

6. A 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. In claim 1, the negative electrode active material layer A first negative electrode active material layer provided on the above-mentioned collector; and A second negative electrode active material layer provided on the first negative electrode active material layer A negative electrode for a lithium secondary battery comprising:

8. In claim 7, at least one of the first negative electrode active material layer and the second negative electrode active material layer is D 50 A negative electrode for a lithium secondary battery comprising two or more different types of negative active materials and satisfying the following formulas 3 and 4: [Formula 3] -3 ≤ (│D 50,total - D 50,L1 │÷ D 50,total X 100 ≤ 3 [Formula 4] -3 ≤ (│D 50,total - D 50,L2 │÷ D 50,total X 100 ≤ 3 In equations 3 and 4, D 50,total D of the negative electrode active material in the entire negative electrode active material layer 50 And, D 50,L1 D of the negative electrode active material in the first negative electrode active material layer 50 And, D 50,L2 D of the negative electrode active material in the second negative electrode active material layer 50 lim.

9. A negative electrode for a lithium secondary battery according to claim 7, wherein the boundaries of the first negative electrode active material layer and the second negative electrode active material layer and the boundaries of the first region and the second region are different.

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

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

12. A negative electrode for a lithium secondary battery according to claim 7, wherein 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 a silicon-based active material.

13. A negative electrode for a lithium secondary battery according to claim 7, wherein 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.

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

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

16. A 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 the total negative electrode active material.

17. A 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 to 20 parts by weight of a silicon-based active material based on 100 parts by weight of the total negative electrode active material of each layer.

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

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

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