Positive electrode and secondary battary

Abstract

The present invention relates to a secondary battery and a method for manufacturing a secondary battery, comprising a positive electrode for a secondary battery, wherein the positive electrode comprises a current collector; a first positive active material layer provided on the current collector; and a second positive active material layer provided on the first positive active material layer, wherein the first positive active material layer and the second positive active material layer each comprise a single-particle positive active material and a positive active material having a larger particle size than the single-particle positive active material, and wherein the porosity of the first positive active material layer is different from the porosity of the second positive active material layer, or the ratio of the pore area of ​​the second positive active material layer to the ratio of the pore area in a cross-sectional image of the first positive active material layer is 1.05 to 3 times.

Description

Technology Field

[0001] This application claims the benefit of the filing date of Patent Application No. 10-2022-0128886 filed with the Korean Intellectual Property Office on October 7, 2022, the entire contents of which are incorporated herein.

[0002] The present invention relates to a positive electrode for a secondary battery and a secondary battery including the same. Background Technology

[0003] Secondary batteries are widely applied not only to portable devices but also to electric vehicles (EVs) and hybrid electric vehicles (HEVs) powered by electric driving sources.

[0004] These secondary batteries are attracting attention as a new energy source for improving eco-friendliness and energy efficiency, as they not only have the primary advantage of being able to drastically reduce the use of fossil fuels but also the advantage of not generating any by-products from the use of energy.

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

[0006] As the utilization of secondary batteries increases, diverse battery performance characteristics are required. Although attempts are being made to control the composition of active materials or additives in the anode or cathode active layer to improve battery performance, an incorrect combination of materials can actually have an adverse effect on the performance of the final battery. Therefore, research on improving battery performance based on the combination of materials in the anode and cathode is necessary. The problem to be solved

[0007] The present invention aims to provide a positive electrode for a secondary battery capable of improving the energy density, rapid charging performance, and lifespan of the battery, and a secondary battery including the same. means of solving the problem

[0008] One embodiment of the present invention is

[0009] The whole house;

[0010] A first positive active material layer provided on the above current collector; and

[0011] It includes a second positive active material layer provided on the first positive active material layer, and

[0012] The first positive active material layer and the second positive active material layer each comprise a single-particle positive active material and a positive active material having a larger particle size than the single-particle positive active material, and

[0013] A positive electrode for a secondary battery is provided, wherein the porosity of the first positive electrode active material layer is different from the porosity of the second positive electrode active material layer.

[0014] Another embodiment of the present invention is

[0015] The whole house;

[0016] A first positive active material layer provided on the above current collector; and

[0017] It includes a second positive active material layer provided on the first positive active material layer, and

[0018] The first positive active material layer and the second positive active material layer each comprise a single-particle positive active material and a positive active material having a larger particle size than the single-particle positive active material, and

[0019] The present invention provides a positive electrode for a secondary battery in which the ratio of the pore area in the cross-sectional image of the second positive electrode active material layer to the ratio of the pore area in the cross-sectional image of the first positive electrode active material layer is 1.05 to 3 times.

[0020] Another embodiment of the present invention provides a secondary battery comprising a positive electrode, a negative electrode, and a separator for the secondary battery. Effects of the invention

[0021] According to the embodiments described in this specification, the resistance characteristics of the battery can be improved by having a positive active material layer with a two-layer structure and controlling the type of active material and porosity of each layer. Brief explanation of the drawing

[0022] Figure 1 is a graph showing the resistance characteristics according to the state of charge (SOC) of the batteries produced in the examples and comparative examples. Specific details for implementing the invention

[0023] Hereinafter, the present invention will be described in more detail to aid in understanding the invention. The present invention may be embodied in various different forms and is not limited to the embodiments described herein. In this case, terms or words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0024] In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should not be understood as precluding the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0025] Furthermore, when it is said that a part, such as a layer, is "above" or "on" another part, this includes not only the case where it is "directly above" the other part, but also the case where there is another part in between. Conversely, when it is said that a part is "directly above" another part, it means that there is no other part in between. Also, saying that a part is "above" or "on" a reference part means that it is located above or below the reference part, and it does not necessarily mean that it is located "above" or "on" facing the opposite direction of gravity.

[0026] In this specification, a description referred to only as "anode active material layer" without the expressions of the first and second may be applied to both the first and second anode active material layers.

[0027] In this specification, the particle size refers to the average particle size indicated by D50. D50 can be defined as the particle size at the 50% reference of the particle size distribution and can be measured using a laser diffraction method. For example, a method for measuring the average particle size (D50) of the cathode active material can be performed by dispersing the particles of the cathode active material in a dispersion medium, introducing them into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiating them with ultrasound of approximately 28 kHz at an output of 60 W, and then calculating the average particle size (D50) corresponding to 50% of the volume accumulated in the measuring device.

[0028] In this specification, 'primary particle' refers to a particle that does not appear to have grain boundaries when observed at a field of view of 5,000 to 20,000 times using a scanning electron microscope.

[0029] In this specification, 'secondary particle' refers to a particle formed by the aggregation of the primary particle.

[0030] In this specification, the term "single particle" is used to distinguish it from the cathode active material particles in the form of secondary particles formed by the aggregation of tens to hundreds of primary particles that were conventionally used, and is a concept that includes a single particle consisting of one primary particle and an aggregate particle of 10 or fewer primary particles.

[0031] In this specification, when the term 'particle' is used, it may mean that any one or all of a single particle, a secondary particle, or a primary particle are included.

[0032] A positive electrode for a secondary battery according to one embodiment of the present specification comprises a current collector; a first positive active material layer provided on the current collector; and a second positive active material layer provided on the first positive active material layer, wherein the first positive active material layer and the second positive active material layer each comprise a single-particle positive active material and a positive active material having a particle size larger than that of the single-particle positive active material, and wherein the porosity of the first positive active material layer is different from the porosity of the second positive active material layer.

[0033] A cathode for a secondary battery according to another embodiment is The apparatus comprises a current collector; a first positive active material layer provided on the current collector; and a second positive active material layer provided on the first positive active material layer, wherein the first positive active material layer and the second positive active material layer each comprise a single-particle positive active material and a positive active material having a larger particle size than the single-particle positive active material, and wherein the ratio of the pore area in the cross-sectional image of the second positive active material layer to the ratio of the pore area in the cross-sectional image of the first positive active material layer is 1.05 to 3 times.

[0034] In the above embodiment, the anode has a structure in which the anode active material layer is two layers, and each layer includes a single-particle anode active material and also includes two types of anode active materials with different particle sizes. In addition, the porosity of the first anode active material layer is different from the porosity of the second anode active material layer. Preferably, the porosity of the first anode active material layer is smaller than the porosity of the second anode active material layer.

[0035] In this way, the resistance characteristics of the anode can be improved by making the porosity of the first anode active material layer, which is positioned closest to the current collector among the two-layer anode active material layers containing the aforementioned anode active material, smaller. Since the pore area ratio in the cross-sectional image of the anode active material layer increases or decreases as the porosity of the anode active material layer increases or decreases, the effect of improving the resistance characteristics of the anode as described above can be similarly obtained by making the pore area ratio in the cross-sectional image of the first anode active material layer smaller than the pore area ratio in the cross-sectional image of the second anode active material layer. Such porosity or pore area ratio in the cross-sectional image can be achieved according to the materials of each layer described above and the manufacturing method described below.

[0036] According to one embodiment of the present specification, the first and second positive active material layers comprise a single-particle positive active material and a positive active material having a larger particle size than the single-particle positive active material. Here, the positive active material having a larger particle size than the single-particle positive active material exists in a secondary particle state, meaning that the particle size of the secondary particle is larger than the particle size of the single-particle positive active material. In the present specification, the positive active material having a larger particle size than the single-particle positive active material is referred to as a large-particle positive active material for convenience.

[0037] According to one embodiment, the large particle cathode active material may have a particle size 2 to 15 μm larger than the single particle cathode active material, for example, 3 to 10 μm larger.

[0038] According to one embodiment, the particle size of the large particle cathode active material may be 5 to 15 μm, and the particle size of the single particle cathode active material may be 2 to 7 μm.

[0039] According to one embodiment, the content ratio of the single-particle cathode active material and the cathode active material having a larger particle size than the single-particle cathode active material in the second cathode active material layer may be 1:9 to 9:1.

[0040] According to one embodiment, the porosity of the first positive active material layer may be 0.5% to 25%, for example 0.5% to 20%, specifically 1% to 10% smaller than the porosity of the second positive active material layer.

[0041] For example, the porosity of the first and second positive active material layers may be 15% to 40%.

[0042] Here, the porosity can be calculated by measuring the weight per electrode area using an electronic balance and measuring the cross-sectional thickness of each layer using a scanning electron microscope, thereby determining the porosity of the first and second positive active material layers.

[0043] According to one embodiment, the ratio of the pore area of ​​the second positive active material layer to the ratio of the pore area in the cross-sectional image of the first positive active material layer may be 1.1 to 2.8 times, 1.3 to 2.8 times, and 1.5 to 2.5 times.

[0044] Here, the pore area ratio in the cross-sectional images of the first and second positive active material layers was calculated by preparing a cross-sectional sample perpendicular to the plane direction from the electrode sample through the following method, measuring the cut surface using a scanning electron microscope with an acceleration voltage of 5 kV and a magnification of 1.00 k to 2.00 kV, and then calculating the image obtained.

[0045] At this time, when preparing the cross-sectional sample, PDMS resin was used and dried at room temperature for 48 hours under reduced pressure conditions, and then Ar+ ion milling was performed using Hitachi IM5000 with an acceleration voltage of 6 kV to prepare the cross-sectional sample.

[0046] When the above porosity range is satisfied, the porosity of the first positive electrode active material layer is kept low, which improves contact between the current collector and the positive electrode active material and thus allows for the expectation of a reduction in interfacial resistance. Additionally, since the porosity of the second positive electrode active material layer can be kept relatively high, there is an advantage in that it facilitates the impregnation of the electrolyte and is favorable for electrode lifespan.

[0047] In addition, when the pore area ratio in the cross-sectional image above is satisfied, the pore area ratio in the cross-sectional image of the second positive active material layer has a larger value than the pore area ratio in the cross-sectional image of the first positive active material layer, and as described above, as the porosity of the positive active material layer increases or decreases, the pore area ratio in the cross-sectional image of the positive active material layer also increases or decreases, so the advantages of satisfying the above porosity range can be obtained.

[0048] According to one embodiment, the content of the single-particle cathode active material in the first cathode active material layer may be greater than the content of the single-particle cathode active material in the second cathode active material layer. Accordingly, the porosity of the first cathode active material layer can be controlled to be lower than that of the second cathode active material layer.

[0049] Specifically, the content ratio of the single-particle cathode active material and the cathode active material having a larger particle size than the single-particle cathode active material in the first cathode active material layer may be 5:5 to 9:1, for example 6:4 to 9:1, or 7:3 to 9:1, and the content ratio of the single-particle cathode active material and the cathode active material having a larger particle size than the single-particle cathode active material in the second cathode active material layer may be 1:9 to 5:5, for example 1:9 to 4:6, or 1:9 to 3:7.

[0050] When the above range is satisfied, the first positive electrode active material layer is applied with a high content ratio of single particles that are advantageous for forming a low porosity, and the second positive electrode active material layer is applied with a high content ratio of large particles that can be applied without breakage due to high porosity, thereby having the advantage of obtaining the effect of lowering diffusion resistance.

[0051] According to one embodiment, the single-particle or large-particle cathode active material may comprise a lithium composite transition metal compound comprising nickel (Ni) and cobalt (Co). The lithium composite transition metal compound may further comprise at least one of manganese and aluminum. The lithium composite transition metal compound may comprise 80 mol% or more, for example, 80 mol% or more and less than 100 mol%, of nickel among metals excluding lithium. For example, the lithium composite transition metal compound is Li a Ni (1-x-y) Co x M1 y M2 w The cathode active material may be represented by O2 (1.0≤a≤1.5, 0≤x≤0.2, 0≤y≤0.2, 0≤w≤0.1, 0≤x+y≤0.2, M1 is at least one metal among Mn and Al, and M2 is one or more metal elements selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb and Mo).

[0052] The thickness of the first and second positive active material layers may each be 10 μm or more and 500 μm or less.

[0053] The positive active material in the 100 parts by weight of the above positive active material layer may be included in an amount of 80 parts by weight or more and 99.9 parts by weight or less, preferably 80 parts by weight or more and 99 parts by weight or less.

[0054] According to additional embodiments of the present specification, the positive active material layer according to the above embodiments may further include a positive binder and a conductive material.

[0055] The anode binder described above can serve to improve adhesion between anode active material particles and adhesion between anode active material particles and anode current collector. The anode binder may be one known in the art, and non-limiting examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0056] The anode binder may be included in an amount of 0.1 parts by weight or more and 50 parts by weight or less based on 100 parts by weight of the anode active material layer, for example, preferably 0.3 parts by weight or more and 35 parts by weight or less, more preferably 0.5 parts by weight or more and 20 parts by weight or less.

[0057] The conductive material included in the above-mentioned positive electrode active material layer is used to impart conductivity to the electrode, and can be used without special restrictions as long as it has electronic conductivity without causing 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, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxide such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more of these may be used.

[0058] Specifically, in one embodiment, the conductive material may include one or more of single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT). The conductive material may be included in an amount of 0.1 parts by weight or more and 5 parts by weight or less based on 100 parts by weight of the composition for the cathode active material layer, for example, preferably 0.3 parts by weight or more and 3 parts by weight or less, more preferably 0.5 parts by weight or more and 2 parts by weight or less.

[0059] The above positive current collector is not particularly limited as long as it is conductive without causing chemical changes 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 above positive current collector may typically have a thickness of 1 to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0060] Further embodiments of the present specification provide a secondary battery comprising a positive electrode, a negative electrode, and a separator according to the embodiments described above.

[0061] The above cathode may include a current collector and a cathode active material layer provided on the current collector.

[0062] According to one embodiment, the cathode comprises a silicon-based active material.

[0063] According to one embodiment, the silicon-based active material is SiO x (0≤x<2), SiM y (M is a metal, 1≤y≤4) and includes at least one of Si / C. The silicon-based active material may include only one type, or two or more types together.

[0064] As the above silicon-based active material, SiOx The active material containing (0≤x<2) is SiO x (0 <x<2) 및 기공을 포함하는 실리콘계 복합 입자일 수 있다.

[0065] 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.

[0066] The silicon-based composite particles may further contain at least one of an Mg compound and a Li compound. The Mg compound and the Li compound may correspond to a matrix within the silicon-based composite particles.

[0067] The above Mg compound and / or Li compound is the above 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.

[0068] 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.

[0069] In one embodiment of the present specification, the Mg element may be included in an amount of 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. Specifically, the Mg element may be included in an amount of 0.5% to 8% by weight or 0.8% to 4% by weight. When the above range is satisfied, the Mg compound may be included in the silicon-based active material in an appropriate amount, so that volume changes of the silicon-based active material during charging and discharging of the battery are easily suppressed, and the discharge capacity and initial efficiency of the battery can be improved.

[0070] The above 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.

[0071] 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 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.

[0072] In one embodiment of the present specification, the Li element may be included in an amount of 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. Specifically, the Li element may be included in an amount of 0.5% to 8% by weight, and more specifically, in an amount of 0.5% to 4% by weight. When the above range is satisfied, the Li compound may be included in the silicon-based active material in an appropriate amount, so that the volume change of the negative electrode active material during charging and discharging of the battery is easily suppressed, and the discharge capacity and initial efficiency of the battery can be improved.

[0073] The content of the Mg or Li elements can be confirmed through ICP analysis. For the ICP analysis, a specific amount (approx. 0.01 g) of the cathode active material is accurately aliquoted, transferred to a platinum crucible, and completely decomposed on a hot plate by adding nitric acid, hydrofluoric acid, and sulfuric acid. Subsequently, a reference calibration curve is constructed by measuring the intensity of a standard solution (5 mg / kg) prepared using an inductively

[0074] 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 imparted to the silicon-based composite particles, and the initial efficiency, lifespan characteristics, and battery capacity characteristics of a secondary battery including a negative electrode active material comprising the silicon-based composite particles may be improved. The total weight of the carbon layer may be included in an amount of 5% to 40% by weight based on 100% by weight of the total silicon-based composite particles.

[0075] In one embodiment of the present specification, the carbon layer may include at least one of amorphous carbon and crystalline carbon.

[0076] The average particle size (D50) of the silicon-based active material may be 2 μm to 15 μm, specifically 3 μm to 12 μm, and more specifically 4 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 realized.

[0077] In this specification, the average particle size (D50) can be defined as the particle size corresponding to 50% of the volume accumulation in the particle size distribution curve. The average particle size (D50) can be measured, for example, using a laser diffraction method. The laser diffraction method generally enables the measurement of particle sizes ranging from the submicron region to several millimeters, and can obtain results with high reproducibility and high resolution.

[0078] In one embodiment of the present specification, the negative electrode active material layer comprising the silicon-based active material may further comprise a carbon-based active material. In this case, based on a total of 100 parts by weight of active material included in the negative electrode active material layer comprising the silicon-based active material, the silicon-based active material may be included in an amount of 1 to 40 parts by weight, for example, 1 to 20 parts by weight.

[0079] In one embodiment of the present specification, the carbon-based active material may be graphite, and the graphite may be natural graphite, graphite graphite, or a mixture thereof. The carbon-based active material may be included in an amount of 60 parts by weight or more and 99 parts by weight or less based on 100 parts by weight of the total negative electrode active material included in the negative electrode active material layer.

[0080] 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, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less, and even more preferably 98 parts by weight or more and 99.9 parts by weight or less.

[0081] According to further embodiments of the present specification, the negative electrode active material layer may additionally include a negative electrode binder in addition to the active material.

[0082] The above-mentioned cathode binder can serve to improve adhesion between cathode active material particles and adhesion between the cathode active material particles and the cathode current collector. The above-mentioned cathode binder may be any known in the art, and non-limiting examples may include at least one selected from the group consisting of polyvinylidenefluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and materials in which hydrogens thereof are substituted with Li, Na, or Ca, etc., and may also include various copolymers thereof.

[0083] The above-mentioned cathode binder may be included in an amount of 0.1 parts by weight or more and 20 parts by weight or less based on 100 parts by weight of the cathode active material layer, for example, preferably 0.3 parts by weight or more and 20 parts by weight or less, more preferably 0.5 parts by weight or more and 10 parts by weight or less.

[0084] The above-mentioned negative electrode active material layer may not include a conductive material, but may additionally include a conductive material if necessary. The conductive material included in the above-mentioned negative electrode active material layer is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, Farnes black, lamp black, thermal black; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used. The content of the conductive material in the above-mentioned negative electrode active material layer may be 0.01 to 20 parts by weight, preferably 0.03 to 18 parts by weight, relative to 100 parts by weight of the negative electrode active material layer.

[0085] In one embodiment of the present specification, the thickness of the negative electrode active material layer may be 5 μm or more and 500 μm or less.

[0086] In one embodiment of the present specification, the negative current collector may be conductive without causing chemical changes in the battery, and is not particularly limited. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used as the current collector. Specifically, transition metals that adsorb carbon well, such as copper and 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.

[0087] The above-described anode and cathode may be manufactured according to conventional methods for manufacturing anodes and cathodes, except for using the above-described anode and cathode active materials. Specifically, they may be manufactured by applying a composition for forming an active material layer, comprising the above-described active material and optionally a binder and a conductive material, onto a current collector, followed by drying and rolling. At this time, the types and contents of the above-described anode and cathode active materials, binder, and conductive material are as described above. The above-described solvent may be a solvent generally used in the relevant technical field, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above-described solvent used is sufficient to dissolve or disperse the above-described active material, conductive material, and binder, considering the coating thickness of the slurry and the manufacturing yield, and to have a viscosity that allows for excellent thickness uniformity during subsequent coating for the manufacture of anodes and cathodes. Alternatively, the anode and cathode may be manufactured by casting the composition for forming the active material layer onto a separate support and then laminating the film obtained by peeling off from the support onto a current collector.

[0088] Further embodiments of this specification provide a method for manufacturing a positive electrode for a secondary battery according to the aforementioned embodiments. The manufacturing method is

[0089] A step of forming a first positive active material layer by coating a first composition comprising a single-particle positive active material and a positive active material having a larger particle size than the single-particle positive active material onto a current collector and rolling it;

[0090] The method includes the step of coating a second composition comprising a single-particle positive active material and a positive active material having a larger particle size than the single-particle positive active material on the first positive active material layer, and rolling, thereby forming a second positive active material layer having a porosity different from the porosity of the first positive active material layer.

[0091] The composition for forming the first and second positive active material layers may further include the aforementioned binder, conductive material, etc., in addition to the aforementioned positive active material. If necessary, the aforementioned solvent may further include.

[0092] The above manufacturing method performs rolling after coating at each stage when forming the first and second positive active material layers. The porosity of each positive active material layer can be controlled by adjusting the rolling conditions at each stage. For example, a condition can be applied in which the linear pressure during rolling in the step of forming the second positive active material layer is greater than the linear pressure during rolling in the step of forming the first positive active material layer. Specifically, the first positive active material layer can be rolled at a low linear pressure, e.g., 1 to 1.5 ton / cm, and the second positive active material layer can be additionally rolled at a high linear pressure, e.g., 1.5 ton / cm.

[0093] By performing separate rolling when forming each positive active material layer according to the above manufacturing method, along with the type of active material of each positive active material layer described above, the porosity of the first positive active material layer can be configured to be different from, specifically smaller than, the second positive active material layer.

[0094] The above separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. Any separator typically used as a separator in a secondary battery can be used without special limitations, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte wettability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure.

[0095] Examples of the above electrolytes include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which can be used in the manufacture of lithium secondary batteries, but are not limited to these.

[0096] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0097] As the above-mentioned non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyl lactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolone, formamide, dimethylformamide, dioxolone, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolone derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate, etc. may be used.

[0098] 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 that effectively dissociate lithium salts, so they can be used preferably. Furthermore, if low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate are mixed with these cyclic carbonates in appropriate proportions, an electrolyte with high electrical conductivity can be produced, making it even more preferable to use.

[0099] The metal salt mentioned above may be a lithium salt, and the lithium salt is a substance that dissolves well in the non-aqueous electrolyte; for example, as the anion of the lithium salt, 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 types selected from the group consisting of can be used.

[0100] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0101] A secondary battery according to one embodiment of the present invention comprises an assembly including a positive electrode, a negative electrode, a separator, and an electrolyte, and may be a lithium secondary battery.

[0102] Further embodiments of the present invention provide a battery module comprising the aforementioned secondary battery as a unit cell and a battery pack comprising the same. Since the battery module and the battery pack include the secondary battery having high capacity, high rate capability and cycle capability, they can be used as a power source for medium-to-large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems.

[0103] Since the secondary battery according to the embodiments of the present invention stably exhibits excellent discharge capacity, output characteristics, and cycle performance, it can be used as a power source for portable devices such as mobile phones, laptop computers, and digital cameras, as well as for medium-to-large 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 one or more medium-to-large devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0105] Hereinafter, preferred embodiments are presented to aid in understanding the present invention; however, the above embodiments are merely illustrative of the description, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of the description, and that such variations and modifications fall within the scope of the appended claims.

[0107] Example 1

[0108] Slurries for forming a first positive active material layer and a second positive active material layer on a positive current collector were prepared, respectively, and the following coatings were performed. After coating the first positive active material layer, it was dried in a drying oven at a speed of 30 m / min. Subsequently, hot rolling was performed at a temperature of 90°C while adjusting the linear pressure. Then, the second positive active material layer was coated using the same method, and hot rolling was performed at a temperature of 90°C while adjusting the linear pressure, thereby producing an electrode having a porosity of 20% for the first positive active material layer and a porosity of 24% for the second positive active material layer.

[0109] As a composition for manufacturing a first positive active material layer and a second positive active material layer, a positive slurry was used in which a Ni-based positive active material, a conductive material (CNT), and a binder (PVDF) were added to a methylpyrrolidone (NMP) solvent in a weight ratio of 97.0:1:2. The Ni-based positive active material of the first positive active material layer composition contained a single-particle positive active material and a large-particle positive active material in a weight ratio of 8:2, and the Ni-based positive active material of the second positive active material layer composition contained a single-particle positive active material and a large-particle positive active material in a weight ratio of 2:8.

[0110] The above single-particle cathode active material is Li 1.0 Ni 0.86 Co 0.08 Mn 0.06 The cathode active material having the composition of O2 is a Ni-based cathode active material having a particle size of 4㎛, and the large particle cathode active material is Li 1.0 Ni 0.87 Co 0.04 Mn 0.07 Al 0.02 A Ni-based cathode active material having a particle size of 9 μm was used as the cathode active material having the composition of O2.

[0111] The porosity of the anode manufactured above is shown in Table 1 below.

[0112] A negative electrode active material comprising SiO and a carbon-based active material (including artificial graphite and natural graphite) in a negative electrode current collector (the SiO-based active material is included at 5 parts by weight based on 100 parts by weight of the total negative electrode active material), a conductive material (carbon black), a binder (SBR), and a thickener (CMC) in a ratio of 96:1:2:1 A cathode was manufactured by coating a composition containing a cathode slurry added to a distilled water solvent in a weight ratio, followed by drying and rolling.

[0113] A battery was fabricated by stacking the above anode and cathode with a separator in between and injecting an electrolyte having the composition of 1M LiPF6, ethylene carbonate (EC) / ethylmethyl carbonate (EMC) (volume ratio 3 / 7), and vinylene carbonate (VC) / propane sulfone (PS) (containing 3 parts by weight and 1.5 parts by weight, respectively, based on 100 parts by weight of the total electrolyte).

[0115] Example 2

[0116] The procedure was carried out in the same manner as Example 1, except that the porosity of the first positive electrode active material layer was 30% lower than the porosity of the second positive electrode active material layer.

[0118] Example 3

[0119] The procedure was carried out in the same manner as Example 1, except that the weight ratio of the single-particle cathode active material to the large-particle cathode active material in the first cathode active material layer was 2:8 and the weight ratio of the single-particle cathode active material to the large-particle cathode active material in the second cathode active material layer was 8:2.

[0121] Comparative Example 1

[0122] Coating of the first cathode active material layer was carried out using a slurry containing the above single-particle cathode active material and large-particle cathode active material in a weight ratio of 8:2, and the procedure was carried out in the same manner as Example 1 except for this.

[0124] Comparative Example 2

[0125] Two layers of positive active material having the same porosity were manufactured under the following process conditions.

[0126] A slurry of a first positive active material layer and a second positive active material layer was prepared on a positive current collector, and the following coating was performed. After coating each layer of the first positive active material layer and the second positive active material layer, they were dried in a drying oven at a speed of 30 m / min. Subsequently, hot rolling was performed at a temperature of 90°C while adjusting the linear pressure to produce an electrode having a porosity of 24%.

[0127] The procedure was carried out in the same manner as Example 1, except that the weight ratio of the single-particle cathode active material to the large-particle cathode active material of the first cathode active material layer was 2:8, with a higher proportion of the single-particle cathode active material, and the weight ratio of the single-particle cathode active material to the large-particle cathode active material of the second cathode active material layer was 8:2 to prepare the slurry.

[0129] Comparative Example 3

[0130] Two layers of positive active material having the same porosity were manufactured using the following process.

[0131] A slurry of a first positive active material layer and a second positive active material layer was prepared on a positive current collector, and the following coating was performed. After simultaneously coating each layer of the first positive active material layer and the second positive active material layer, the materials were dried in a drying oven at a speed of 30 m / min. Subsequently, hot rolling was performed at a temperature of 90°C while adjusting the linear pressure to produce an electrode having a porosity of 24%.

[0132] The above-mentioned Ni-based cathode active material layer of the first cathode active material layer composition comprises a small particle cathode active material and a large particle cathode active material in a weight ratio of 8:2, and the above-mentioned Ni-based cathode active material of the second cathode active material layer composition is prepared as a 2:8 slurry of a single particle cathode active material and a large particle cathode active material, except that it was carried out in the same manner as Example 1.

[0134] Comparative Example 4

[0135] Two layers of positive active material having the same porosity were manufactured using the following process.

[0136] A slurry of a first positive active material layer and a second positive active material layer was prepared on a positive current collector, and the following coating was performed. After simultaneously coating each layer of the first positive active material layer and the second positive active material layer, the materials were dried in a drying oven at a speed of 30 m / min. Subsequently, hot rolling was performed at a temperature of 90°C while adjusting the linear pressure to produce an electrode having a porosity of 24%.

[0137] The above-mentioned Ni-based cathode active material of the first cathode active material layer composition comprises a single-particle cathode active material, and the above-mentioned Ni-based cathode active material of the second cathode active material layer composition is prepared as a slurry of a single-particle cathode active material and a large-particle cathode active material in a ratio of 2:8, except that it was carried out in the same manner as Example 1.

[0139] Comparative Example 5

[0140] Two layers of positive active material having the same porosity were manufactured using the following process.

[0141] A slurry of the first and second positive active material layers was prepared on a positive current collector, and coating was performed as follows. After simultaneously coating each layer of the first and second positive active material layers, the materials were dried in a drying oven at a speed of 30 m / min. Subsequently, hot rolling was performed at a temperature of 90°C while adjusting the linear pressure to produce an electrode having a porosity of 24%.

[0142] The above-mentioned Ni-based cathode active material of the first cathode active material layer composition comprises a single-particle cathode active material and a large-particle cathode active material in a weight ratio of 8:2, and the above-mentioned Ni-based cathode active material of the second cathode active material layer composition is prepared as a slurry of the single-particle cathode active material, except that it was carried out in the same manner as Example 1.

[0144] Porosity of the second positive electrode active material layer (%) Porosity of the first positive electrode active material layer (%) Ratio of pore area in the cross-sectional image of the second positive active material / Ratio of pore area in the cross-sectional image of the first positive active material layer Example 1 24 20 1.5 Example 2 50 20 2.5 Example 3 24 20 1.5 Comparative Example 1 24 - Comparative Example 2 24 24 1.0 Comparative Example 3 24 24 1.0 Comparative Example 4 24 24 1.0 Comparative Example 5 24 24 1.0

[0145] Figure 1 shows the resistance values ​​according to the state of charge (SOC) of the batteries prepared in Examples 1 to 3 and Comparative Examples 1 to 5. It can be confirmed that Examples 1 to 3 exhibit superior resistance characteristics at the total state of charge (SOC) compared to Comparative Examples 1 to 5. In this case, the resistance was measured by performing three cycles of constant current / constant voltage (CC / CV) charging (0.05C-cut) to 4.2V at 0.33C and constant current (CC) discharging (2.5V-cut) at 0.33C. After charging, the cells were discharged at 0.33C, and the resistance was measured by performing a 10-second pulse discharge at 2.5C with the respective SOC (%) settings.

Claims

Claim 1 A positive electrode for a secondary battery comprising: a current collector; a first positive active material layer provided on the current collector; and a second positive active material layer provided on the first positive active material layer, wherein the first positive active material layer and the second positive active material layer each comprise a single-particle positive active material and a positive active material having a particle size larger than that of the single-particle positive active material, and wherein the porosity of the first positive active material layer is different from the porosity of the second positive active material layer, and the porosity of the first positive active material layer is 0.5% to 25% lower than the porosity of the second positive active material layer. Claim 2 A positive electrode for a secondary battery comprising: a current collector; a first positive active material layer provided on the current collector; and a second positive active material layer provided on the first positive active material layer, wherein the first positive active material layer and the second positive active material layer each comprise a single-particle positive active material and a positive active material having a larger particle size than the single-particle positive active material, and wherein the ratio of the pore area in the cross-sectional image of the second positive active material layer to the ratio of the pore area in the cross-sectional image of the first positive active material layer is 1.05 to 3 times. Claim 3 delete Claim 4 delete Claim 5 A cathode for a secondary battery according to claim 1, wherein the porosity of the first cathode active material layer and the second cathode active material is each 15% to 40%. Claim 6 A cathode for a secondary battery according to claim 1, wherein the cathode active material having a larger particle size than the single-particle cathode active material among the first and second cathode active material layers has a particle size 2 to 15 μm larger than that of the single-particle cathode active material. Claim 7 A cathode for a secondary battery according to claim 1, wherein the content ratio of the single-particle cathode active material and the cathode active material having a larger particle size than the single-particle cathode active material in the first and second cathode active material layers is 1:9 to 9:

1. Claim 8 A positive electrode for a secondary battery according to claim 1, wherein the content of the single-particle positive electrode active material in the first positive electrode active material layer is greater than the content of the single-particle positive electrode active material in the second positive electrode active material layer. Claim 9 A cathode for a secondary battery according to claim 1, wherein the content ratio of the single-particle cathode active material and the cathode active material having a larger particle size than the single-particle cathode active material in the first cathode active material layer is 5:5 to 9:1, and the content ratio of the single-particle cathode active material and the cathode active material having a larger particle size than the single-particle cathode active material in the second cathode active material layer is 1:9 to 5:

5. Claim 10 A cathode for a secondary battery according to claim 1, wherein the first and second cathode active material layers comprise a lithium composite transition metal compound comprising nickel (Ni) and cobalt (Co). Claim 11 A positive electrode for a secondary battery according to claim 10, wherein the lithium composite transition metal compound further comprises at least one of manganese and aluminum. Claim 12 A secondary battery comprising a positive electrode, a negative electrode, and a separator according to any one of claims 1, 2, and 5 to 11. Claim 13 A secondary battery according to claim 12, wherein the negative electrode comprises a silicon-based active material. Claim 14 A secondary battery according to claim 13, wherein the negative electrode further comprises a carbon-based active material. Claim 15 A method for manufacturing a positive electrode for a secondary battery according to any one of claims 1 and 5 to 11, comprising: a step of forming a first positive electrode active material layer by coating a first composition comprising a single-particle positive electrode active material and a positive electrode active material having a larger particle size than the single-particle positive electrode active material on a current collector and rolling; and a step of forming a second positive electrode active material layer having a porosity different from the porosity of the first positive electrode active material layer by coating a second composition comprising a single-particle positive electrode active material and a positive electrode active material having a larger particle size than the single-particle positive electrode active material on the first positive electrode active material layer and rolling. Claim 16 A method for manufacturing a positive electrode for a secondary battery according to claim 15, wherein the linear pressure during rolling in the step of forming the second positive electrode active material layer is greater than the linear pressure during rolling in the step of forming the first positive electrode active material layer.

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