Method for manufacturing positive electrode, positive electrode, and lithium secondary battery comprising positive electrode

Abstract

The present invention provides a method for manufacturing a positive electrode, comprising the steps of: preparing a positive electrode slurry comprising a positive electrode active material comprising lithium iron phosphate particles in the form of secondary particles in which a plurality of primary particles are aggregated; coating the positive electrode slurry onto a positive electrode current collector; and forming a positive electrode active material layer by rolling the coated positive electrode slurry, wherein the particle breaking strength of the lithium iron phosphate particles in the form of secondary particles is 4kgf / mm2 to 20kgf / mm2, and the ratio of the surface roughness Rz1 of the positive electrode current collector before rolling to the surface roughness Rz2 of the positive electrode current collector after rolling is 0.5 or less.

Description

Method for manufacturing a cathode, cathode and lithium secondary battery including the cathode The present invention relates to a method for manufacturing a positive electrode, a positive electrode, and a lithium secondary battery including the positive electrode. As personal IT devices and computer networks have developed due to the development of the information society, and as a result, the overall dependence of society on electric energy has increased, there is a demand for technology development to efficiently store and utilize electric energy. Among the developed technologies, secondary batteries are the most suitable for various applications, and among these secondary batteries, lithium secondary batteries are attracting attention as they can be miniaturized to the point where they can be applied to personal IT devices and have the highest energy density. Typically, lithium secondary batteries are manufactured by injecting or impregnating a non-aqueous electrolyte into an electrode assembly consisting of a cathode, an anode, and a porous separator. Carbon-based active materials and silicon-based active materials are considered as negative active materials for these lithium secondary batteries. Meanwhile, lithium-containing cobalt oxide, LiMnO2 with a layered crystal structure, LiMn2O4 with a spinel crystal structure, lithium-containing nickel oxide (LiNiO2), etc. are being considered as positive active materials. Recently, lithium iron phosphate (e.g., LiFePO4)-based active materials, which have excellent thermal stability and are relatively inexpensive, are being considered as positive active materials. Meanwhile, electrodes such as a positive electrode and a negative electrode include a current collector and an active material layer, and the active material layer includes an active material (positive electrode active material or negative electrode active material). At this time, the current collector acts as a passage to transfer electrons from the outside so that an electrochemical reaction occurs in the active material layer, or to receive electrons from the active material and send them out. At this time, in order to improve the high-rate discharge characteristics of the electrode, it is an important task to increase the contact area between the current collector and the active material and lower the contact resistance. In this respect, methods for roughening the surface of the current collector are being studied, but since the roughening requires the application of a separate inorganic material or an etching process, there are concerns about additional processes and costs. In addition, even if the roughening process is performed on the current collector, if the sizes of the active material and the roughened current collector do not match, a gap is generated between the active material and the roughened current collector, which acts as a detrimental factor to the high-rate discharge characteristics. Meanwhile, in order to increase the contact area between the current collector and the active material, a primer layer having a specific surface roughness is sometimes introduced between the current collector and the active material layer. However, this requires an additional process of introducing the primer layer, which incurs costs, and is disadvantageous in achieving the desired capacity due to unnecessary volume increase. One object of the present invention is to solve the above problems, and to provide a method for manufacturing a positive electrode capable of significantly increasing the contact area between a positive electrode current collector and a positive electrode active material and implementing a positive electrode having excellent high-rate discharge characteristics and capacity characteristics. In addition, another object of the present invention is to provide a cathode having excellent high-rate discharge characteristics and capacity characteristics by reducing the contact resistance between the cathode current collector and the cathode active material. In addition, another object of the present invention is to provide a lithium secondary battery including the aforementioned positive electrode. [1] The present invention comprises a step of preparing a cathode slurry including a cathode active material including lithium iron phosphate particles in the form of secondary particles in which a plurality of primary particles are aggregated; a step of applying the cathode slurry onto a cathode current collector; and a step of forming a cathode active material layer by rolling the applied cathode slurry; wherein the particle breakage strength of the lithium iron phosphate particles in the form of secondary particles is 4 kgf / mm. 2Within 20kgf / mm 2 And, a method for manufacturing a positive electrode is provided, wherein the ratio of the surface roughness Rz1 of the positive electrode collector before rolling to the surface roughness Rz2 of the positive electrode collector after rolling is 0.5 or less. [2] The present invention provides a method for manufacturing a positive electrode in which the positive electrode active material included in the positive electrode slurry applied by the rolling roughens the positive electrode current collector in the above [1]. [3] The present invention relates to a lithium iron phosphate particle in the form of a secondary particle, wherein the average particle diameter (D) of the lithium iron phosphate particle in the form of a secondary particle is at least one of [1] to [2]. 50 ) provides a method for manufacturing a cathode having a diameter of 7 μm to 30 μm. [4] The present invention relates to a method for producing an average particle diameter (D) of the primary particles in at least one of the above [1] to [3]. 50 ) provides a method for manufacturing a positive electrode having a diameter of 0.2 μm to 3 μm. [5] The present invention provides a method for manufacturing a positive electrode, wherein in one or more of the above [1] to [4], the lithium iron phosphate particles in the form of secondary particles are broken into primary particles by rolling the applied positive electrode slurry. [6] The present invention provides a method for manufacturing a positive electrode, wherein the surface roughness Rz2 of the positive electrode current collector after rolling is 3 ㎛ or more, in at least one of [1] to [5]. [7] The present invention provides a method for manufacturing a positive electrode, wherein the surface roughness Rz1 of the positive electrode current collector before rolling is 1.5 ㎛ or less, in at least one of the above [1] to [6]. [8] The present invention provides a method for manufacturing a positive electrode, wherein the rolling ratio of the positive electrode active material layer is 30% or more in at least one of [1] to [7]. [9] The present invention provides a method for manufacturing an anode, wherein in at least one of the above [1] to [8], the rolling is performed through a roll press, and the linear pressure during the roll press is 30 kN / cm to 80 kN / cm.

[0010] The present invention provides a method for manufacturing a positive electrode, wherein the current collector comprises aluminum in at least one of the above [1] to [9].

[0011] The present invention provides a method for manufacturing an anode, wherein the method further comprises a step of drying the applied anode slurry between the application of the anode slurry and the rolling of the applied anode slurry in at least one of the above [1] to

[0010] .

[0012] The present invention relates to a positive electrode comprising a positive electrode current collector; and a positive electrode active material layer disposed on the positive electrode current collector, wherein the surface roughness Rz2 of the positive electrode current collector is 3 ㎛ or more, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes lithium iron phosphate particles, and the MP resistance measured using a multi-probe resistivity measuring device with a sample formed into a sheet shape of 5 cm in width and 5 cm in length is 0.1 Ω cm. 2 The following bipolar electrodes are provided.

[0013] The present invention provides a positive electrode having a porosity of the positive electrode active material layer of 25% to 45% in the above

[0012] .

[0014] The present invention provides a positive electrode, wherein in one or more of the above

[0012] to

[0013] , the lithium iron phosphate particles exist in the form of primary particles or a mixture of primary particles and secondary particles.

[0015] The present invention provides a positive electrode, wherein, in one or more of the above

[0012] to

[0014] , when the lithium iron phosphate particles are a mixture of primary particles and secondary particles, the content of the primary particles is 90 wt% or more and less than 100 wt% of the lithium iron phosphate particles.

[0016] The present invention provides a positive electrode having a thickness of the positive electrode active material layer of 50 ㎛ to 500 ㎛ in at least one of the above

[0012] to

[0015] .

[0017] The present invention provides a positive electrode in which the positive electrode current collector and the positive electrode active material layer are in direct contact with each other in at least one of the above

[0012] to

[0016] .

[0018] The present invention provides a lithium secondary battery including a positive electrode according to at least one of the above

[0012] to

[0017] ; a negative electrode opposing the positive electrode; a separator interposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte. According to the method for manufacturing a positive electrode according to the present invention, a positive electrode active material including lithium iron phosphate particles in the form of secondary particles having a specific particle breakage strength is added to a positive electrode slurry, and then the positive electrode slurry is rolled on a positive electrode collector to form a positive electrode active material layer, and the ratio of the surface roughness of the current collector before and after rolling satisfies a specific range by the rolling process. The lithium iron phosphate particles in the form of secondary particles are first particles after roughening the positive electrode collector through the rolling process, thereby increasing the contact area between the positive electrode active material and the positive electrode collector and minimizing the occurrence of gaps between the positive electrode active material and the positive electrode collector. Therefore, a positive electrode realized from the method for manufacturing a positive electrode according to the present invention can have excellent high-rate discharge characteristics and high capacity. In addition, according to the positive electrode according to the present invention, the surface roughness of the positive electrode current collector satisfies a specific range, and the MP resistance of the positive electrode measured under specific conditions satisfies a specific range. Satisfaction of the MP resistance range may mean that the contact area between the positive electrode active material including lithium iron phosphate particles and the positive electrode current collector is large and the contact resistance is low. The positive electrode according to the present invention and the lithium secondary battery including the same may have excellent high-rate discharge characteristics and high capacity. Figure 1 is a SEM photograph of the cross-section of the anode of Example 1. Figure 2 is an SEM photograph of the anode cross-section of Comparative Example 1. Figure 3 is an SEM photograph of the anode cross-section of Comparative Example 2. Figure 4 is an SEM photograph of the anode cross-section of Comparative Example 3. Figure 5 shows the results of a three-dimensional microscopic observation of a positive electrode collector according to Example 1. Figure 6 shows the results of a three-dimensional microscopic observation of a positive electrode collector according to Comparative Example 1. First, before describing the present invention, it should be noted that the terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, and should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concept of the term in order to explain his or her own invention in the best manner. Meanwhile, the terms used in this specification are only used to describe exemplary embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, it should be understood that the terms “comprise,” “include,” or “have,” etc., are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof. In this specification, “%” means weight percent unless otherwise explicitly indicated. 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. In this specification, 'primary particle' means a single particle, i.e., one particle, and 'secondary particle' means an aggregate in which multiple primary particles are aggregated through an intentional assembly or bonding process. Hereinafter, the present invention will be described in more detail. Method for manufacturing anode The present invention provides a method for manufacturing a positive electrode. Specifically, the method for manufacturing the positive electrode may be a method for manufacturing a positive electrode for a lithium secondary battery. Specifically, the method for manufacturing a cathode according to the present invention comprises the steps of: preparing a cathode slurry including a cathode active material including lithium iron phosphate particles in the form of secondary particles in which a plurality of primary particles are aggregated; applying the cathode slurry onto a cathode current collector; and forming a cathode active material layer by rolling the applied cathode slurry; wherein the particle breakage strength of the lithium iron phosphate particles in the form of secondary particles is 4 kgf / mm. 2 Within 20kgf / mm 2 And, it is characterized in that the ratio of the surface roughness Rz1 of the positive electrode collector before rolling to the surface roughness Rz2 of the positive electrode collector after rolling is 0.5 or less. According to the method for manufacturing a positive electrode according to the present invention, a positive electrode active material including lithium iron phosphate particles in the form of secondary particles having a specific particle breakage strength is added to a positive electrode slurry, and then the positive electrode slurry is rolled on a positive electrode collector to form a positive electrode active material layer, and the ratio of the surface roughness of the current collector before and after rolling satisfies a specific range by the rolling process. The lithium iron phosphate particles in the form of secondary particles are first particles after roughening the positive electrode collector through the rolling process, thereby increasing the contact area between the positive electrode active material and the positive electrode collector and minimizing the occurrence of gaps between the positive electrode active material and the positive electrode collector. Therefore, a positive electrode realized from the method for manufacturing a positive electrode according to the present invention can have excellent high-rate discharge characteristics and high capacity. According to the method for manufacturing an anode according to the present invention, first, an anode slurry is prepared. The above cathode slurry contains a cathode active material. The above cathode active material contains lithium iron phosphate particles in the form of secondary particles in which a plurality of primary particles are aggregated. The above lithium iron phosphate particles may include a compound represented by the following chemical formula A. [Chemical Formula A] Li 1+a Fe 1-s M s (PO 4-b )X b In the chemical formula A, M is one or more elements selected from Co, Ni, Mn, Al, Mg, Ti, and V, X is F, S, or N, and 0≤s≤0.5; -0.5≤a≤+0.5; 0≤b≤0.1. The above chemical formula A can be specifically represented as LiFePO4 (a = 0, s = 0, and b = 0). The above positive electrode active material includes lithium iron phosphate particles in the form of secondary particles in which a plurality of primary particles are aggregated. The positive electrode active material at this time may mean the positive electrode active material before the application of the positive electrode slurry or before the rolling of the applied positive electrode slurry. The particle breaking strength (or compressive fracture strength) of the lithium iron phosphate particles in the form of the above secondary particles is 4 kgf / mm. 2 Within 20kgf / mm 2 According to the satisfaction of the above range, when the applied positive electrode slurry is rolled as described below, the lithium iron phosphate particles in the form of secondary particles can be broken into primary particles after roughening the positive electrode current collector, and the contact area of ​​the roughened positive electrode current collector can be maximized, so that the high-rate discharge characteristics of the positive electrode can be significantly improved. Preferably, the particle breakage strength of the lithium iron phosphate particles in the form of secondary particles is 5 kgf / mm. 2- Within 15kgf / mm 2- , specifically 8kgf / mm 2- Within 12kgf / mm 2- It could be. If the particle breaking strength of the lithium iron phosphate particles in the form of the above secondary particles is 4 kgf / mm 2 If the particle breaking strength of the lithium iron phosphate particles in the secondary particle form is less than 20 kgf / mm, the phenomenon of breaking occurs before roughening of the cathode current collector through the lithium iron phosphate particles, and the desired effect of roughening of the cathode current collector or increasing the contact area between the cathode active material and the current collector cannot occur. In addition, if the particle breaking strength of the lithium iron phosphate particles in the secondary particle form is less than 20 kgf / mm 2 If it exceeds this, the particles are not broken even by rolling, so instead, the contact area between the positive active material and the positive current collector decreases, and problems such as a gap occurring between the positive active material and the positive current collector occur. The particle breaking strength (St) of the present invention was measured using a micro compression tester MCT-W of Shimadzu Corporation, and can be a value obtained through the Hiramatsu formula (Literature [Journal of the Japan Mining and Mining Association, Vol. 81, No. 932, December 1965, pp. 1024-1030]) expressed by the following mathematical formula 1. [Mathematical Formula 1] St=0.28P / πd 2 (P: load applied to the particle [kgf], d: particle diameter (mm)) The specific measurement conditions are as follows. 1. Test pressure: FLAT50 2. Measurement mode: Compression test 3. Load applied to the particle: 20.00[mN] 4. Load speed: 0.892405[mN] / sec] The average particle diameter (D) of the lithium iron phosphate particles in the form of the above secondary particles 50 ) may be 7 ㎛ to 30 ㎛, specifically 10 ㎛ to 20 ㎛, and more specifically 12 ㎛ to 18 ㎛. In addition, the average particle diameter (D of the primary particles 50 ) may be 0.2 ㎛ to 3.0 ㎛, specifically 0.2 ㎛ to 2.0 ㎛, more specifically 0.3 ㎛ to 1.5 ㎛, and even more specifically 0.3 ㎛ to 1 ㎛. The above positive electrode active material may further include a carbon coating layer positioned on the surface of the lithium iron phosphate particles. The carbon coating layer may be introduced for the purpose of protecting the lithium iron phosphate particles, improving electrical conductivity, etc. The above-mentioned positive electrode active material may be included in the positive electrode slurry at 80 wt% to 99 wt% based on the solid content weight of the positive electrode slurry. The above positive electrode slurry may further include a binder, a conductive agent and / or a solvent together with the positive electrode active material. The above binder is a component that assists in the binding of the active material and the conductive material and the binding to the current collector, and specifically, may include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, preferably polyvinylidene fluoride. In order to sufficiently secure binding force between components such as the positive electrode active material, the binder may be included in the positive electrode slurry in an amount of 1 wt% to 20 wt%, preferably 1.2 wt% to 10 wt%, based on the solid content weight of the positive electrode slurry. The conductive material may be used to assist and improve conductivity in a secondary battery, and is not particularly limited as long as it has conductivity without causing a chemical change. Specifically, the conductive material may include at least one selected from the group consisting of graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, KETJENBLACK®, channel black, paneth black, lamp black, thermal black, etc.; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives. In order to sufficiently secure electrical conductivity, the above-mentioned conductive material may be included in the positive electrode slurry in an amount of 1 wt% to 20 wt%, preferably 1.2 wt% to 10 wt%, based on the solid content weight of the positive electrode slurry. The above solvent may include an organic solvent such as NMP (N-methyl-2-pyrrolidone). The solid content of the above cathode slurry may be 40 wt% to 90 wt%, specifically 50 wt% to 80 wt%. Next, the above positive electrode slurry is applied onto the positive electrode current collector. The above positive electrode slurry can be applied to at least one surface of the positive electrode current collector, specifically, one surface or both surfaces of the positive electrode current collector. The thickness of the above positive electrode collector may typically be 3 to 500 μm, more specifically 5 to 30 μm, and more specifically 10 to 25 μm. The above positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, the positive electrode current collector may be made of aluminum, stainless steel, copper, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, an aluminum-cadmium alloy, or the like. More specifically, the positive electrode current collector may include aluminum. The above-mentioned positive electrode slurry can be applied without limitation using any method known in the art, such as spray coating, spin coating, or doctor blade method. Next, the applied positive electrode slurry is rolled to form a positive electrode active material layer. By the above rolling, the positive electrode active material (lithium iron phosphate particles in the form of secondary particles) included in the applied positive electrode slurry can roughen the positive electrode collector. By the rolling process, the lithium iron phosphate particles in the form of secondary particles can press the positive electrode collector to roughen it or form an uneven structure. In addition, by the rolling process, the lithium iron phosphate particles in the form of secondary particles can be formed into primary particles after roughening the positive electrode collector. In particular, since the lithium iron phosphate particles in the form of secondary particles have the particle breaking strength at the level described above, when they sufficiently roughen the positive electrode collector and then break, the gap between the positive electrode active material and the current collector can be minimized, and the contact area between the positive electrode active material and the current collector is significantly increased. In the present invention, a step of drying the applied positive electrode slurry may be further included between the application of the positive electrode slurry and the rolling of the applied positive electrode slurry. The above drying can be performed at, but is not limited to, 80°C to 150°C. During the above rolling, the rolling ratio of the positive electrode active material layer may be 30% or more, specifically 30% to 50%, and more specifically 35% to 48%. When within the above range, roughening of the positive electrode active material by pressing the positive electrode current collector occurs sufficiently, and primary particle formation of lithium iron phosphate particles occurs sufficiently, so that the gap between the active material and the current collector can be minimized. The above rolling ratio can be calculated by the following mathematical formula 2. [Mathematical formula 2] Rolling ratio (%) = {(thickness of positive electrode active material layer before rolling - thickness of positive electrode active material layer after rolling) / thickness of positive electrode active material layer before rolling} × 100 In the above mathematical expression 2, the thickness of the positive electrode active material layer before rolling may mean the thickness of the applied positive electrode slurry or the thickness of the dried positive electrode slurry. The above rolling can be performed through a roll press. Specifically, the roll press process can be performed by passing the anode between two rolls, and the rolling rate can be controlled by adjusting the gap between the two rolls. The linear pressure during the above roll press may be 30 kN / cm to 80 kN / cm, specifically 40 kN / cm to 60 kN / cm. In the present invention, the ratio of the surface roughness Rz1 of the positive electrode collector before rolling to the surface roughness Rz2 of the positive electrode collector after rolling is 0.5 or less. If the ratio of the surface roughness Rz1 of the positive electrode collector before rolling to the surface roughness Rz2 of the positive electrode collector after rolling exceeds 0.5, the roughening of the positive electrode collector due to the pressing of the positive electrode collector by the lithium iron phosphate particles in the form of secondary particles does not occur sufficiently, and it is difficult to improve the contact area between the desired positive electrode active material and the positive electrode collector and the high-rate discharge performance. In particular, the change in surface roughness in the above-described ratio range is difficult to implement by a method such as etching of the positive electrode collector, and can be implemented by pressing of the positive electrode collector by the lithium iron phosphate particles in the form of secondary particles having the specific particle breaking strength described above, particle breaking, etc. The ratio of the surface roughness Rz1 of the positive electrode collector before rolling to the surface roughness Rz2 of the positive electrode collector after the rolling may be specifically 0.4 or less, more specifically 0.35 or less, and even more specifically 0.38 or less. Meanwhile, when lithium iron phosphate particles in the form of secondary particles having excessively high particle breakage strength are used, although the surface roughness change at the above-described level may be achieved to some extent, the contact area between the positive electrode active material and the positive electrode collector may be reduced, and a gap may be generated between the positive electrode active material and the positive electrode collector, which may cause problems such as an increase in resistance. In this specification, surface roughness (Rz) can be measured using an Optical profiler from Nanosystem Inc. Specifically, surface roughness is measured through a topo image obtained by selecting five measurement areas for each sample at a measurement magnification (e.g., 500x) using an Optical Profiler. Meanwhile, the surface roughness Rz2 of the positive electrode current collector after the rolling can be measured after the manufactured positive electrode is immersed in a solvent (e.g., NMP) and heated at 80°C to 150°C (specifically 100°C) for 1 hour to 10 hours (specifically 2 hours) to peel off and remove the positive electrode active material layer, thereby obtaining the positive electrode current collector. The surface roughness Rz2 of the positive electrode collector after the rolling may be 3 ㎛ or more, specifically 4 ㎛ to 1,000 ㎛, more specifically 4 ㎛ to 500 ㎛, and even more specifically 4 ㎛ to 20 ㎛. The surface roughness Rz1 of the positive electrode collector before the rolling may be 1.5 ㎛ or less, more specifically 0.5 ㎛ to 1.5 ㎛, and even more specifically 1 ㎛ to 1.5 ㎛. The thickness of the above positive electrode active material layer may be 50 ㎛ to 500 ㎛, specifically 100 ㎛ to 300 ㎛, and more specifically 100 ㎛ to 200 ㎛. anode In addition, the present invention provides a positive electrode, specifically a positive electrode for a lithium secondary battery. Specifically, the positive electrode may be a positive electrode manufactured by the method for manufacturing a positive electrode described above. Specifically, the positive electrode is a positive electrode including a positive electrode current collector; and a positive electrode active material layer disposed on the positive electrode current collector, wherein the surface roughness Rz2 of the positive electrode current collector is 3 ㎛ or more, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes lithium iron phosphate particles, and the MP resistance measured using a multi-probe resistivity measuring device with a sample formed into a sheet shape of 5 cm in width and 5 cm in length is 0.1 Ω cm.2 It is characterized by the following. According to the present invention, a positive electrode has a surface roughness Rz2 of a positive electrode current collector of 3㎛ or more and an MP resistance satisfying a specific range. A positive electrode having these characteristics may mean that the contact area between the positive electrode active material and the positive electrode current collector is wide and the gap formed between them is minimized. Through this, it is possible to implement a positive electrode and a lithium secondary battery having excellent high-rate discharge characteristics. The surface roughness Rz2 of the positive electrode current collector is 3 ㎛ or more, and may be specifically 4 ㎛ to 1,000 ㎛, more specifically 4 ㎛ to 500 ㎛, and even more specifically 4 ㎛ to 20 ㎛. If the surface roughness Rz2 of the positive electrode current collector is less than 3 ㎛, the positive electrode current collector is not sufficiently roughened, and it is difficult to improve the contact area between the intended positive electrode active material and the positive electrode current collector and the high-rate discharge performance. The description of the above positive electrode collector is as described above. The above-described positive electrode active material layer is disposed on the positive electrode current collector. The above-described positive electrode active material layer may be specifically disposed on at least one side of the positive electrode current collector, more specifically on one side or both sides of the positive electrode current collector. Specifically, the positive electrode current collector and the positive electrode active material layer can be in direct contact with each other. More specifically, the positive electrode current collector and the positive electrode active material layer can be in direct contact with each other without the interposition of another substrate such as a primer layer therebetween. The above positive electrode active material includes lithium iron phosphate particles. The lithium iron phosphate particles may exist in the form of primary particles or as a mixture of primary particles and secondary particles. If the lithium iron phosphate particles are a mixture of primary particles and secondary particles, the content of the primary particles may be 90 wt% or more and less than 100 wt%, more specifically 95 wt% or more and less than 100 wt%, of the lithium iron phosphate particles. In the above lithium iron phosphate particles, the average particle diameter (D) of the secondary particles 50 ) may be 7 ㎛ to 30 ㎛, specifically 10 ㎛ to 20 ㎛, and more specifically 12 ㎛ to 18 ㎛. In addition, the average particle diameter (D of the primary particles 50 ) may be 0.2 ㎛ to 3.0 ㎛, specifically 0.2 ㎛ to 2.0 ㎛, more specifically 0.3 ㎛ to 1.5 ㎛, and even more specifically 0.3 ㎛ to 1 ㎛. The description of other positive electrode active materials is as described above. The above positive electrode active material layer may further include a binder and / or a conductive material together with the positive electrode active material. The above binder is a component that assists in the binding of the active material and the conductive material and the binding to the current collector, and specifically, may include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, preferably polyvinylidene fluoride. In order to sufficiently secure binding force between components such as the positive electrode active material, the binder may be included in an amount of 1 to 20 wt%, preferably 1.2 to 10 wt%, based on the weight of the positive electrode active material layer. The conductive material may be used to assist and improve conductivity in a secondary battery, and is not particularly limited as long as it has conductivity without causing a chemical change. Specifically, the conductive material may include at least one selected from the group consisting of graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, KETJENBLACK®, channel black, paneth black, lamp black, thermal black, etc.; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; fluorocarbons; metal powders such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives. In order to sufficiently secure electrical conductivity, the above-mentioned conductive agent may be included in an amount of 1 wt% to 20 wt%, preferably 1.2 wt% to 10 wt%, based on the weight of the positive electrode active material layer. The description of the other positive electrode active material layers is as described above. The MP resistance measured using a multi-probe resistivity measuring device for a sample of the above anode in the form of a sheet of 5 cm in width and 5 cm in length was 0.1Ω cm. 2 Below. If the MP resistance is 0.1Ω·cm 2 If it exceeds , it can be evaluated that the contact area between the positive electrode collector and the positive electrode active material is not sufficiently secured, and thus it is difficult to improve the desired high-rate discharge performance. The above MP resistance is 0.1Ω·cm 2 Below, specifically 0.01 Ω cm 2 Within 0.1Ω·cm 2 , more specifically 0.01 Ω cm 2 Within 0.07 Ω cm 2 It could be. The method of implementing the above MP resistance range is not particularly limited, and for example, the surface roughness of the positive electrode current collector may be adjusted to the level described above, or the average particle diameter (D) of the lithium iron phosphate particles used may be adjusted. 50 ) can be implemented by various methods, such as controlling the MP resistance range. Specifically, the implementation of the MP resistance range can be implemented by the above-described method for manufacturing the anode. The porosity of the above positive electrode may be 25% to 45%, specifically 30% to 40%. When within the above range, it is possible to sufficiently secure a movement path of lithium ions within the positive electrode active material, while improving the contact area between the positive electrode active materials or between the positive electrode active material and the positive electrode current collector, which may be advantageous in improving high-rate discharge performance. The porosity of the above anode can be calculated by the following mathematical formula 3. [Mathematical Formula 3] Porosity (%) = {1-(electrode density of positive electrode / true density of positive electrode)} × 100 In the above mathematical expression 3, the true density of the positive electrode is the density of the positive electrode active material layer measured when the positive electrode is cut into a certain size and pressed with a press machine until the thickness of the positive electrode does not change, and the electrode density of the positive electrode is the density of the positive electrode active material layer measured when the positive electrode is cut into a certain size. Lithium secondary battery In addition, the present invention provides a lithium secondary battery. Specifically, the lithium secondary battery may include the positive electrode described above. More specifically, the lithium secondary battery includes a positive electrode; a negative electrode opposite to the positive electrode; a separator interposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte. The lithium secondary battery can be manufactured by a method including a step of manufacturing an electrode assembly including a positive electrode, a negative electrode, and a separator; a step of housing the electrode assembly in a battery case; a step of manufacturing a non-aqueous electrolyte including a lithium salt, an organic solvent, and an additive; and a step of injecting or impregnating the non-aqueous electrolyte into the battery case. The above-mentioned anodes have been described above, and other components are described below. (1) Cathode The above cathode can be opposed to the above anode. The above negative electrode includes a negative electrode active material. The above negative electrode may include a negative electrode current collector; and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. In this case, the negative electrode active material may be included in the negative electrode active material layer. The above negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, the negative electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., an aluminum-cadmium alloy, etc. The above negative electrode collector may typically have a thickness of 3 to 500 μm. The above negative electrode current collector may form fine irregularities on the surface to strengthen the bonding strength of the negative electrode active material. For example, the above negative electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc. The negative electrode active material layer is disposed on at least one surface of the negative electrode current collector. Specifically, the negative electrode active material layer may be disposed on one surface or both surfaces of the negative electrode current collector. The above negative active material layer may include a negative active material. The above negative active material is a material capable of reversibly inserting / deleting lithium ions, and may include at least one selected from the group consisting of a carbon-based active material, a (semi)metal-based active material, and lithium metal, and specifically may include at least one selected from a carbon-based active material and a (semi)metal-based active material. The above carbon-based active material may include at least one selected from the group consisting of graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon, and preferably may include graphite. The graphite may include at least one selected from the group consisting of artificial graphite and natural graphite. The average particle diameter (D) of the above carbon-based active material 50 ) may be 5 ㎛ to 30 ㎛, preferably 7 ㎛ to 15 ㎛, in order to ensure structural stability during charging and discharging and reduce side reactions with the electrolyte. Specifically, the (semi)metal-based active material may include at least one (semi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; an alloy of lithium and at least one (semi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; an oxide of at least one (semi)metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, V, Ti, and Sn; lithium titanium oxide (LTO); lithium vanadium oxide; and the like. More specifically, the (semi)metal-based active material may include a silicon-based active material. The above silicon-based active material is SiO xIt may include a compound represented by (0≤x<2). In the case of SiO2, since it does not react with lithium ions and thus cannot store lithium, it is preferable that x is within the above range, and more preferably, the silicon-based active material may be SiO. The average particle diameter (D) of the above silicon-based active material 50 ) may be 1 ㎛ to 30 ㎛, preferably 2 ㎛ to 15 ㎛, in order to reduce side reactions with the electrolyte while ensuring structural stability during charging and discharging. The above negative active material may be included in the negative active material layer in an amount of 60 to 99 wt%, preferably 75 to 95 wt%. The above negative electrode active material layer may further include a binder, a conductive agent, and / or a thickener together with the negative electrode active material. The above binder is used to improve the performance of the battery by improving the adhesion between the negative electrode active material layer and the negative electrode current collector, and may include, for example, at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, and materials in which hydrogens of these are substituted with Li, Na or Ca, etc., and also may include various copolymers thereof. may include: The above binder may be included in the negative electrode active material layer in an amount of 0.5 wt% to 10 wt%, preferably 1 wt% to 5 wt%. The conductive material is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, KETJENBLACK®, channel black, paneth black, lamp black, thermal black, etc.; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; fluorocarbon; metal powder such as 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, etc. can be used. The above-mentioned conductive agent may be included in the negative electrode active material layer in an amount of 0.5 wt% to 10 wt%, preferably 1 wt% to 5 wt%. The thickness of the above negative active material layer may be 50 ㎛ to 300 ㎛, preferably 100 ㎛ to 200 ㎛. The above negative electrode can be manufactured by coating a negative electrode slurry including a negative electrode active material, a binder, a conductive material and / or a solvent for forming a negative electrode slurry on at least one surface of a negative electrode current collector, and then drying and rolling. The solvent for forming the negative electrode slurry may include at least one selected from the group consisting of distilled water, NMP (N-methyl-2-pyrrolidone), ethanol, methanol, and isopropyl alcohol, preferably distilled water, in order to facilitate dispersion of the negative electrode active material, binder, and / or conductive agent, for example. The solid content of the negative electrode slurry may be 30 wt% to 80 wt%, specifically 40 wt% to 70 wt%. (2) Membrane The above separator may be interposed between the anode and the cathode. As the above-mentioned separator, a conventional porous polymer film used as a conventional separator, 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, can be used alone or in a laminated manner, or a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc., can be used, but is not limited thereto. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength can be used, and can optionally be used in a single-layer or multi-layer structure. (3) Non-aqueous electrolyte In addition, the electrolyte used in the present invention may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc. that can be used in the manufacture of a lithium secondary battery. Specifically, the electrolyte may include an organic solvent and a lithium salt. The lithium salt above can be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. It is preferable to use the concentration of the lithium salt within the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively. The organic solvent may include at least one selected from linear carbonates, cyclic carbonates, linear esters, cyclic esters, ethers, glymes, and nitriles. The above linear carbonate may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate. The above cyclic carbonate may include at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, and 2,3-pentylene carbonate. Specific examples of the linear esters include, but are not limited to, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate. Specific examples of the above cyclic esters include, but are not limited to, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone. Specific examples of the above ethers include, but are not limited to, dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, 1,3-dioxolane (DOL), and 2,2-bis(trifluoromethyl)-1,3-dioxolane (TFDOL). Specific examples of the above glymes include, but are not limited to, dimethoxyethane (glyme, DME), diethoxyethane, diglyme, triglyme, and tetra-glyme (TEGDME). Specific examples of the above nitriles include, but are not limited to, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile. The above electrolyte may further include an additive along with a lithium salt and an organic solvent. The above additive may include at least one selected from the group consisting of vinylethylene carbonate, propane sultone, lithium tetrafluoro borate (LiBF4), lithium difluoro(oxalato) borate (LiODFB), 1,3,6-HTCN (Hexane Tri-Cyanide), and sodium superoxide (NaO2), specifically, fluoroethylene carbonate, difluoroethylene carbonate, vinylethylene carbonate, propane sultone, lithium tetrafluoro borate (LiBF4), lithium difluoro(oxalato) borate (LiODFB), 1,3,6-HTCN (Hexane Tri-Cyanide), succinonitrile, 1,4-dicyano-2-butyne, adipionitrile, lithium difluorophosphate (LiPO2F2), and sodium superoxide (NaO2). The lithium secondary battery according to the present invention as described above can be usefully used in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs). Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided. The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, including power tools; electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems. There is no particular limitation on the external shape of the lithium secondary battery of the present invention, but it may be in the shape of a cylinder, a square, a pouch, or a coin using a can. The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but can also be preferably used as a unit battery in a medium- to large-sized battery module including a plurality of battery cells. Hereinafter, the present invention will be specifically described through examples. At this time, the embodiments according to the present invention can be modified into various different forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to a person having average knowledge in the art. Hereinafter, the present invention will be specifically described through specific examples. Example Example 1 (manufacturing of positive electrode) Lithium iron phosphate (LiFePO4) particles as a cathode active material, carbon nanotubes as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent at a weight ratio of 96.5:1.0:2.5 to prepare a cathode slurry. At this time, the lithium iron phosphate particles were in the form of secondary particles, and the average particle diameter (D) of the secondary particles was 50 ) was 16㎛, and the average particle diameter of the primary particles (D 50) was 0.4㎛. In addition, the particle breaking strength of the lithium iron phosphate particles in the form of secondary particles was 10kgf / mm. 2 It was. The above cathode slurry was applied to a cathode current collector (Al thin film) having a thickness of 20 μm and a surface roughness Rz1 of 1.5 μm at a concentration of 330 mg / 25 cm. 2 It was applied and dried with a loading amount of . Afterwards, a roll press was performed with a pressure of 50 kN / cm to manufacture a positive electrode (thickness of positive electrode active material: 120 μm). At this time, the rolling ratio of the positive electrode was 46%, and the porosity was 33%. Comparative Example 1 A positive electrode was manufactured in the same manner as in Example 1, except that lithium iron phosphate (LiFePO4) particles in the form of primary particles were used as the positive electrode active material. The average particle diameter (D) of the lithium iron phosphate (LiFePO4) particles in the form of primary particles used in Comparative Example 1 50 ) was 0.9㎛, and the particle breaking strength was 50kgf / mm. 2 At this time, the rolling ratio of the anode was 50% and the porosity was 33%. Comparative Example 2 Lithium iron phosphate particles in the form of secondary particles, with an average particle diameter (D) of the secondary particles 50 ) is 16㎛, and the average particle diameter of the primary particles (D 50 ) is 0.4㎛, and the particle breaking strength of lithium iron phosphate particles in the form of secondary particles is 1.5kgf / mm. 2 A positive electrode was manufactured in the same manner as in Example 1, except that the positive electrode active material was used. At this time, the rolling ratio of the positive electrode was 46%, and the porosity was 33%. Comparative Example 3 Lithium iron phosphate particles in the form of secondary particles, with an average particle diameter (D) of the secondary particles 50 ) is 13㎛, and the average particle diameter of the primary particles (D 50) is 0.2㎛, and the particle breaking strength of lithium iron phosphate particles in the form of secondary particles is 25kgf / mm. 2 A positive electrode was manufactured in the same manner as in Example 1, except that the positive electrode active material was used. At this time, the rolling ratio of the positive electrode was 46%, and the porosity was 33%. Experimental example Experimental Example 1: Measurement of surface roughness Rz2 of the positive electrode collector after rolling The positive electrodes of Example 1 and Comparative Examples 1 to 3 were immersed in NMP solvent, and then heated at 100°C for 2 hours to peel and remove the positive electrode active material layer. The surface roughness Rz2 was measured through the topo images obtained by selecting 5 measurement areas for each sample at a measurement magnification (e.g., 500x) using an Optical profiler from Nanosystems Co., Ltd. The results are shown in Table 1 below. Rz1Rz2Rz1 / Rz2Example 11.55.00.30Comparative Example 11.51.80.83Comparative Example 21.51.90.79Comparative Example 31.55.00.30 Referring to Table 1 above, in the case of Example 1, where lithium iron phosphate particles in the form of secondary particles are used as the positive electrode active material and the particle breakage strength satisfies a specific range, it can be seen that, unlike the comparative examples, the surface roughness Rz2 and Rz1 / Rz2 of the positive electrode collector after rolling satisfies the range of the present invention, through which it can be confirmed that the positive electrode collector is roughened to an excellent level through rolling using lithium iron phosphate particles in the form of secondary particles. In addition, it can be expected that excellent high-rate discharge characteristics will be exhibited since the contact area between the positive electrode active material and the positive electrode collector is improved through this. Experimental Example 2: SEM Photo Observation The cross sections of the anodes of Example 1, Comparative Example 1, and Comparative Example 3 were observed using a scanning electron microscope (SEM). An SEM image of a cross-section of the anode of Example 1 is shown in Fig. 1, an SEM image of a cross-section of the anode of Comparative Example 1 is shown in Fig. 2, an SEM image of a cross-section of the anode of Comparative Example 2 is shown in Fig. 3, and an SEM image of a cross-section of the anode of Comparative Example 3 is shown in Fig. 4. Referring to FIGS. 1 to 4, in the positive electrode of Example 1, all lithium iron phosphate particles in the form of secondary particles were broken and converted into primary particles, and it was confirmed that the primary particles were in contact with the current collector. The positive electrode of Comparative Example 1 uses lithium iron phosphate particles in the form of primary particles, and since these particles press the current collector at a uniform level during rolling, the current collector is not roughened well. In the case of the positive electrode of Comparative Example 2, since the current collector is broken before being roughened during rolling for the manufacture of the positive electrode, the current collector is not roughened well. In the positive electrode of Comparative Example 3, a certain level of roughening of the positive electrode current collector is observed, but since the lithium iron phosphate particles in the form of secondary particles are not broken, a gap is observed between the positive electrode active material and the positive electrode current collector. In cases where the surface roughening of the current collector is not achieved well, as in Comparative Examples 1 and 2, or where a gap occurs between the positive electrode active material and the current collector, as in Comparative Example 3, the contact area between the positive electrode active material and the current collector is not sufficiently secured, so that the performance of the battery, such as the resistance characteristics, may deteriorate. Experimental Example 3: 3D Microscopic Observation The positive electrodes of Example 1 and Comparative Example 1 were immersed in an NMP solvent, and then heated at 100°C for 2 hours to peel off and remove the positive electrode active material layer, thereby obtaining a positive electrode current collector. Afterwards, the surface of the positive electrode collector after rolling was observed using a 3D microscope. Figure 5 shows the results of observing the surface of the positive electrode collector after rolling in Example 1, and Figure 6 shows the results of observing the surface of the positive electrode collector in Comparative Example 1. Referring to FIGS. 5 and 6, it can be observed that the surface of the positive electrode collector according to Example 1 is roughened, but it can be confirmed that the surface of the positive electrode collector according to Comparative Example 1 is hardly roughened. Experimental Example 4: Measurement of MP resistance The MP resistance was measured using a multi-probe resistivity measuring device using samples made by stamping the anodes manufactured in Example 1 and Comparative Examples 1 to 3 into sheets measuring 5 cm in width and 5 cm in length. MP resistance (Ω cm) 2 ) Example 10.05 Comparative Example 10.17 Comparative Example 20.25 Comparative Example 30.22 Referring to Table 2 above, in the case of Example 1, where lithium iron phosphate particles in the form of secondary particles are used as the positive electrode active material and the particle breakage strength satisfies a specific range, it can be confirmed that the MP resistance is significantly reduced, unlike the comparative examples. Through this, it can be confirmed that the positive electrode current collector is excellently roughened through rolling using lithium iron phosphate particles in the form of secondary particles. In addition, it can be expected that excellent high-rate discharge characteristics will be exhibited since the contact area between the positive electrode active material and the positive electrode current collector is improved through this. Experimental Example 5: Resistance Evaluation (Manufacturing of secondary batteries) A negative electrode slurry having a solid content of 50% was prepared by dispersing a negative electrode active material (graphite), a conductive agent (carbon black), a binder (SBR), and a thickener (CMC) in water at a weight ratio of 93.5:2.0:1.0:3.5. The negative electrode slurry was applied to a copper foil having a thickness of 8 ㎛ at a concentration of 160 mg / cm 2 A cathode having a thickness of 145 μm was manufactured by coating it to have a loading amount of . An electrode assembly was manufactured by sequentially stacking the positive electrode, separator, and negative electrode manufactured in Example 1, and then the assembly was placed in a pouch-type battery case and an electrolyte was injected to manufacture a pouch-type cell of Example 1 having a capacity of 5 Ah. Pouch-type cells of Comparative Examples 1 to 3 were manufactured in the same manner as Example 1, except that the respective positive electrodes of Comparative Examples 1 to 3 were used. (0.1 second discharge resistance measurement) Activation was performed on the manufactured pouch-type cell, the activated secondary battery was charged to 100% SOC, discharged by applying a discharge pulse of 2.5C, and the voltage change was measured after 0.1 second to determine the 0.1 second discharge resistance (R 0.1s ) was measured. 0.1 second discharge resistance (R 0.1s ) can be used to check the resistance between the entire collector and the positive electrode active material layer. The results are shown in Table 3 below. (Ohmic resistance measurement) After setting the SOC to 50%, the ohmic resistance value (relative ohmic resistance) of the pouch-type cells manufactured in Example 1 to Comparative Examples 1 to 3 was measured using the EIS (Electrochemical Impedance Spectroscopy) method. The results are shown in Table 3 below. R 0.1s (mΩ)Ohmic Resistance (mΩ)Example 10.650.55Comparative Example 12.201.20Comparative Example 22.701.55Comparative Example 32.601.65 Referring to Table 3 above, it can be seen that the positive electrode of Example 1 has significantly lower 0.1 second discharge resistance and Ohmic resistance compared to the comparative examples. Through this, it can be confirmed that the positive electrode of Example 1 can exhibit high-temperature discharge characteristics at a high level due to the reduced resistance between the positive electrode current collector and the positive electrode active material layer.

Claims

1. A step of preparing a cathode slurry including a cathode active material including lithium iron phosphate particles in the form of secondary particles in which a plurality of primary particles are aggregated; A step of applying the above positive electrode slurry onto the positive electrode current collector; and A step of forming a positive electrode active material layer by rolling the above-described applied positive electrode slurry; The particle breaking strength of the lithium iron phosphate particles in the form of the above secondary particles is 4 kgf / mm. 2 Within 20kgf / mm 2 And, A method for manufacturing a positive electrode, wherein the ratio of the surface roughness Rz1 of the positive electrode collector before rolling to the surface roughness Rz2 of the positive electrode collector after rolling is 0.5 or less.

2. In claim 1, A method for manufacturing a positive electrode, wherein the positive electrode active material contained in the positive electrode slurry applied by the above rolling roughens the positive electrode current collector.

3. In claim 1, The average particle diameter (D) of the lithium iron phosphate particles in the form of the above secondary particles 50 ) is a method for manufacturing a positive electrode having a diameter of 7㎛ to 30㎛.

4. In claim 1, The average particle diameter of the above primary particles (D 50 ) is a method for manufacturing a positive electrode having a diameter of 0.2㎛ to 3㎛.

5. In claim 1, A method for manufacturing a positive electrode, wherein the lithium iron phosphate particles in the form of secondary particles are broken into primary particles by rolling the applied positive electrode slurry.

6. In claim 1, A method for manufacturing a positive electrode having a surface roughness Rz2 of 3㎛ or more after the above rolling.

7. In claim 1, A method for manufacturing a positive electrode having a surface roughness Rz1 of 1.5 ㎛ or less before the above rolling.

8. In claim 1, A method for manufacturing a positive electrode having a rolling ratio of the positive electrode active material layer of 30% or more.

9. In claim 1, The above rolling is performed through a roll press, A method for manufacturing an anode wherein the pressure applied during the above roll press is 30 kN / cm to 80 kN / cm.

10. In claim 1, The above-mentioned whole body is a method for manufacturing an anode including aluminum.

11. In claim 1, A method for manufacturing an anode, further comprising the step of drying the applied anode slurry between the application of the anode slurry and the rolling of the applied anode slurry.

12. A positive electrode including a positive electrode current collector; and a positive electrode active material layer disposed on the positive electrode current collector, The surface roughness Rz2 of the above positive electrode collector is 3㎛ or more, The above positive electrode active material layer includes a positive electrode active material, The above positive electrode active material comprises lithium iron phosphate particles, The MP resistance measured using a multi-probe resistivity measuring device for a sample of the above anode in the form of a sheet of 5 cm in width and 5 cm in length was 0.1Ω cm. 2 Below are the polarities.

13. In claim 12, A positive electrode having a porosity of the positive electrode active material layer of 25% to 45%.

14. In claim 12, A cathode wherein the lithium iron phosphate particles exist in the form of primary particles or as a mixture of primary particles and secondary particles.

15. In claim 12, A positive electrode wherein, when the lithium iron phosphate particles are a mixture of primary particles and secondary particles, the content of the primary particles is 90 wt% or more and less than 100 wt% of the lithium iron phosphate particles.

16. In claim 12, A positive electrode having a thickness of the positive electrode active material layer of 50 ㎛ to 500 ㎛.

17. In claim 12, A cathode in which the cathode current collector and the cathode active material layer are in direct contact.

18. Anode according to claim 12; A cathode opposite to the above anode; A separator interposed between the positive electrode and the negative electrode; and A lithium secondary battery comprising a non-aqueous electrolyte.

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