Positive electrode, method for manufacturing positive electrode, and lithium secondary battery including the positive electrode

Abstract

The present invention relates to a positive electrode, a method for manufacturing the positive electrode, and a lithium secondary battery including the positive electrode. The positive electrode includes a positive electrode active material layer containing a positive electrode active material and can satisfy the following Formula 1. [Formula 1] 1.2 ≤ I [003] / I [200] ≤ 2.0 In Formula 1, the I [003] is the integrated value of the maximum peak that appears in the region where 2θ is 17.0° to 19.0° during XRD measurement with respect to the surface of the positive electrode active material layer, and the I [200] is the integrated value of the maximum peak that appears in the region where 2θ is 43° to 45° during XRD measurement with respect to the surface of the positive electrode active material layer.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0101636 filed on August 12, 2022, and all the contents disclosed in the document of the Korean patent application are incorporated herein by reference in their entirety.

[0002] The present invention relates to an over-lithiated cathode, a method for manufacturing the cathode, and a lithium secondary battery including the cathode.

Background Art

[0003] With the rapid increase in the use of fossil fuels, the need for alternative and clean energy is increasing. As part of this, the fields of power generation and energy storage using electrochemical reactions are the most actively studied.

[0004] Currently, a typical example of an electrochemical device using such electrochemical energy is a secondary battery, and its usage areas are gradually expanding. Recently, as technology development and demand for portable devices such as portable computers, mobile phones, and cameras have increased, the demand for ion secondary batteries as an energy source has increased rapidly. Among such secondary batteries, various studies have been conducted on ion lithium secondary batteries with high energy density, that is, high capacity, and they have also been commercialized and widely used.

[0005] Generally, a lithium-ion secondary battery is composed of a cathode, an anode, an electrolyte, and a separator. The anode contains an anode active material that inserts and desorbs lithium ions emitted from the cathode, and as the anode active material, silicon-based active material particles with a large discharge capacity can be used. The silicon-based active material particles can correspond to Si or SiO X (0 < X < 2), etc. The silicon-based active material particles have the advantages of a large theoretical capacity and a low price. However, the silicon-based active material particles have a drawback that the volume change is excessively large during the operation of the battery, so the battery life rapidly decreases as the battery cycles progress.

[0006] Therefore, in order to minimize the volume change of silicon-based active material particles, there is a method of using only a part of the total capacity of the silicon-based active material particles. For this purpose, a so-called prelithiation process of inserting lithium ions into the negative electrode containing silicon-based active material particles in advance is used. Specifically, when lithium ions are inserted into the negative electrode by a method such as transferring lithium metal to the negative electrode, the lithium ions react with the irreversible sites of the negative electrode, and the total capacity of the negative electrode can be reduced to the level of the reversible capacity. Therefore, during the driving of the battery, the amount of lithium ions inserted can be suitably reduced to the level required for the driving of the battery, and the volume change of the silicon-based active material particles can be minimized.

[0007] However, in the process of performing prelithiation by arranging lithium metal on the surface of the negative electrode, excessive heat is generated by the alloy reaction of lithium and silicon, and the possibility of ignition due to the reaction of lithium and moisture also increases. In addition, in the process of notching and punching the negative electrode, the reaction area of lithium and the silicon-based active material increases, and the possibility of ignition further increases.

[0008] There is also a possibility of ignition due to the prelithiated silicon-based active material particles.

[0009] Therefore, there is a need for a new technology that can insert lithium ions into the negative electrode in advance before the driving of the battery, improve the battery life, and suppress excessive heat generation and the possibility of ignition.

Summary of the Invention

Problems to be Solved by the Invention

[0010] One problem to be solved by the present invention is to provide a positive electrode that can improve the energy density and life characteristics of the battery and improve the safety during the battery manufacturing process.

[0011] Another problem to be solved by the present invention is to provide a method for manufacturing the positive electrode.

[0012] Still another problem to be solved by the present invention is to provide a lithium secondary battery including the positive electrode.

Means for Solving the Problems

[0013] According to an embodiment of the present invention, a positive electrode including a positive electrode active material layer containing a positive electrode active material and satisfying the following formula 1 is provided.

[0014] [Formula 1] 1.2 ≤ I

[0003] / I

[0200] ≤ 2.0 In the above formula 1, the I

[0003] is the integrated value of the maximum peak appearing in the region where 2θ is 17.0° to 19.0° during XRD measurement with respect to the surface of the positive electrode active material layer, and the I

[0200] is the integrated value of the maximum peak appearing in the region where 2θ is 43° to 45° during XRD measurement with respect to the surface of the positive electrode active material layer.

[0015] According to another embodiment of the present invention, a transfer laminate including a base film and a lithium metal layer located on the base film is disposed on a preliminary positive electrode including a preliminary positive electrode active material layer, and a positive electrode structure is formed such that the lithium metal layer is in contact with the preliminary positive electrode active material layer. A P1 step, a P2 step of rolling the positive electrode structure, and a P3 step of removing the base film from the transfer laminate after the rolling are included. During the rolling, the pressure applied to the positive electrode structure is 10 kgf / cm to 90 kgf / cm, and a method for manufacturing a positive electrode is provided.

[0016] According to still another embodiment of the present invention, a lithium secondary battery including a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and the electrolyte is provided. The positive electrode includes a positive electrode active material layer containing a positive electrode active material, and the positive electrode satisfies the following formula 1.

[0017] [Formula 1] 1.2 ≤ I

[0003] / I

[0200] ≤ 2.0 In Formula 1, the I

[0003] is the integrated value of the maximum peak that appears in the region where 2θ is 17.0° to 19.0° during XRD measurement with respect to the surface of the positive electrode active material layer, and the I

[0200] is the integrated value of the maximum peak that appears in the region where 2θ is 43° to 45° during XRD measurement with respect to the surface of the positive electrode active material layer.

[0018] According to still another embodiment of the present invention, there are provided a B1 step of manufacturing a preliminary lithium ion secondary battery including a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, and a B2 step of activating the preliminary lithium ion secondary battery. The method of manufacturing the positive electrode includes a P1 step of disposing a transfer laminate including a base film and a lithium metal layer located on the base film on a preliminary positive electrode including a preliminary positive electrode active material layer to form a positive electrode structure such that the lithium metal layer is in contact with the preliminary positive electrode active material layer, a P2 step of rolling the positive electrode structure, and a P3 step of removing the base film from the transfer laminate after the rolling. The pressure applied to the positive electrode structure during the rolling is 10 kgf / cm to 90 kgf / cm. A method of manufacturing a lithium secondary battery is provided.

Advantages of the Invention

[0019] The positive electrode according to the present invention has a lithium metal layer disposed on the positive electrode by a transfer method, and lithium ions in the lithium metal layer are inserted into the positive electrode active material layer by a rolling process in which an appropriate level of pressure is applied. As a result, the positive electrode satisfies the above formula (1). When a preliminary lithium-ion secondary battery is manufactured using the positive electrode manufactured by the above method and the preliminary lithium-ion secondary battery is activated, the lithium ions inserted into the positive electrode are transferred to the negative electrode, and the irreversible sites of the negative electrode are filled by the reaction of lithium ions. As a result, when the battery is driven, the amount of lithium ions inserted into the negative electrode can be suitably reduced to a level required for driving the battery. Therefore, the capacity of the battery can be maintained, the available area of the negative electrode capacity can be reduced, the excessive volume change of the silicon-based active material particles can be suppressed, and the life characteristics of the battery can be improved.

[0020] Further, instead of performing prelithiation such that the lithium metal layer contacts the negative electrode, after transferring and rolling the lithium metal layer onto the positive electrode, the lithium ions inserted into the positive electrode are moved to the negative electrode in the battery activation process, so that the phenomenon of excessive heat generation due to the alloy reaction of lithium and silicon in the negative electrode can be avoided, and the possibility of ignition due to the reaction of lithium and moisture can also be significantly reduced. Furthermore, when notching and punching the negative electrode, since lithium ions are not inserted into the negative electrode (because prelithiation has not been performed), the possibility of ignition in the notching and punching processes can also be significantly reduced.

[0021] In particular, when manufacturing the positive electrode, since lithium ions in the lithium metal layer are inserted into the positive electrode active material layer at an appropriate level of pressure, the degree of cracking of the positive electrode active material can be reduced, the life characteristics of the lithium-ion secondary battery can be improved, and the energy density can be increased. In addition, the lithium side reaction products can be reduced, the lithium loss amount can be reduced, and the long-term life characteristics of the battery can be improved.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0023] Hereinafter, in order to facilitate the understanding of the present invention, the present invention will be described in more detail.

[0024] The terms and words used in this specification and the claims should not be construed as being limited to their ordinary or dictionary meanings. The inventors should interpret them in accordance with the meaning and concept that conform to the technical idea of the present invention, in accordance with the principle that they can appropriately define the concept of the terms in order to explain their invention in the best way.

[0025] The terms used in this specification are merely used to illustrate exemplary embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly has a different meaning.

[0026] In this specification, terms such as "comprising", "including" or "having" are intended to specify the presence of implemented features, numbers, steps, components or combinations thereof, and should be understood not to preclude in advance the presence or addition possibility of one or more different features, numbers, steps, components or combinations thereof.

[0027] In this specification, D 50 can be defined as the particle size corresponding to 50% of the volume cumulative amount in the particle size distribution curve of the particles. The above-mentioned D 50 can be measured, for example, using the laser diffraction method. The laser diffraction method can generally measure particle sizes in the range from the submicron region to about several millimeters, and can obtain highly reproducible and highly resolved results.

[0028] In this specification, the XRD measurement is performed as follows.

[0029] The X-ray wavelength generated by Cu Kα is used, and the wavelength (λ) of the light source is 0.15406 nm.

[0030] 1) Measuring instrument and conditions: Bruker D8 Endeavor (Cu target 40 kV, 40 mA, 1.54 Å), LynxEye position sensitive detector (4.1° slit) 2) Experimental process 2-1) Prep. Cutting / Cross-section: Cut the sample to the size of the Sample holder to produce a test piece.

[0031] 2-2) Prep. Sample Mounting: After firmly attaching the sample (positive electrode) to the glass plate using double-sided tape so that it does not float, mount it using a holder made of PMMA and rubber clay.

[0032] 2-3) Powder XRD (Bruker D8 Endeavor): Adjust the FDS to 0.5° according to the sample size, and measure the region from 2theta 10° to 125° at intervals of 0.0156° for 0.3 seconds each.

[0033] 2-4) XRD Phase Analysis: Identify the phases present in the sample by comparing with the Database (PDF).

[0034] 2-5) Rietveld Analysis: Perform Rietveld refinement using the complete structure model of the phases present in the sample.

[0035] <Positive electrode> The positive electrode according to an embodiment of the present invention includes a positive electrode active material layer containing a positive electrode active material and can satisfy the following formula 1.

[0036] [Formula 1] 1.2 ≤ I

[0003] / I

[0200] ≤ 2.0 In the above formula 1, the I

[0003] is the integrated value of the maximum peak that appears in the region where 2θ is 17.0° to 19.0° during XRD measurement with respect to the surface of the positive electrode active material layer, and the I

[0200] is the integrated value of the maximum peak that appears in the region where 2θ is 43° to 45° during XRD measurement with respect to the surface of the positive electrode active material layer.

[0037] The positive electrode may include a positive electrode active material layer. The positive electrode active material layer can itself constitute the positive electrode, but the positive electrode active material layer can be located on the positive electrode current collector.

[0038] The positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment of the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. can be used. Further, the positive electrode current collector can usually have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesive force of the positive electrode active material. For example, it can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, non-woven fabric bodies, etc.

[0039] The positive electrode active material layer can be located on one or both surfaces of the positive electrode current collector. The positive electrode active material layer can contain a positive electrode active material.

[0040] The positive electrode active material is a particulate material capable of undergoing an electrochemical reaction and can be a lithium transition metal oxide. For example, the positive electrode active material is a layered compound such as lithium cobalt oxide or lithium nickel oxide substituted with one or more transition metals; lithium manganese oxide substituted with one or more transition metals; Li 1+x [Ni a Co b Mn c M 1 (1-a-b-c) O (2-d) A d (where M 1 is at least one selected from the group consisting of Al, Mg, Cr, Ti, Si, and Y, A is at least one selected from the group consisting of F, P, and Cl, -0.5 ≦ x ≦ 0.5, 0.1 ≦ a ≦ 1, 0.05 ≦ b ≦ 0.5, 0.05 ≦ c ≦ 0.5, 0 ≦ d ≦ 0.2, 0 < a + b + c ≦ 1), a lithium nickel cobalt manganese composite oxide represented by; LI[Ni 1-y M 2 y O2(where M 2can be at least one selected from Co, Mn, Al, Cu, Fe, Mg, B, Cr, Zn, and Ga, and is represented by 0.01 ≦ y ≦ 0.7) lithium nickel-based oxide; Li 1+z [M 3 1-q M 4 q PO 4-r X r (where M 3 is at least one selected from the group consisting of Fe, Mn, Co, and Ni, M 4 is at least one selected from the group consisting of Al, Mg, and Ti, X is at least one selected from the group consisting of F, S, and N, -0.5 ≦ z ≦ 0.5, 0 ≦ q ≦ 0.5, 0 ≦ r ≦ 0.1) and can include at least one selected from the group consisting of olivine-type lithium metal phosphates represented by

[0041] Specifically, the positive electrode active material can include a layered lithium nickel-based transition metal composite oxide, and the lithium nickel-based transition metal composite oxide can include a compound of Chemical Formula 1 below, and more specifically, can be a compound of Chemical Formula 1 below.

[0042] [Chemical Formula 1] Li 1+x [Ni a Co b Mn c M 1 (1-a-b-c) O (2-d) A d In Chemical Formula 1 above, M 1 can be at least one selected from the group consisting of Al, Mg, Cr, Ti, Si, and Y, and specifically can be Al.

[0043] A is at least one selected from the group consisting of F, P, and Cl, and specifically can be F.

[0044] The above x can satisfy -0.5 ≤ x ≤ 0.5, specifically -0.3 ≤ x ≤ 0.3.

[0045] The above a can satisfy 0.6 ≤ a < 1, specifically 0.7 ≤ a ≤ 0.9.

[0046] The above b can satisfy 0.03 ≤ b ≤ 0.1, specifically 0.05 ≤ b ≤ 0.1.

[0047] The above c can satisfy 0.03 ≤ c ≤ 0.1, specifically 0.05 ≤ c ≤ 0.1.

[0048] The above d can satisfy 0 ≤ d ≤ 0.1, specifically 0 ≤ d ≤ 0.05.

[0049] The above a, b, and c satisfy 0 < a + b + c ≤ 1, specifically a + b + c = 1.

[0050] The compound of Chemical Formula 1 can be in a particulate form.

[0051] The layered lithium nickel-based transition metal composite oxide can be in the form of secondary particles in which a plurality of primary particles are bonded to each other. Specifically, the compound of Chemical Formula 1 can be in the form of secondary particles in which 10 or more primary particles are bonded to each other. Thereby, there is an effect that lithium can be uniformly inserted and extracted inside the positive electrode active material.

[0052] The lithium nickel-based transition metal composite oxide has D 50 which can be 5 μm to 15 μm, specifically can be 7 μm to 12 μm, and more specifically can be 9 μm to 10 μm. The above D 50 is the D of the secondary particles 50 and can be such. When the above range is satisfied, the dispersion of the positive electrode slurry is easy and a uniform coating of the positive electrode active material layer is possible.

[0053] The positive electrode active material can be contained in the positive electrode active material layer at 90% to 99% by weight, specifically 92% to 98% by weight, and more specifically 95% to 98% by weight.

[0054] The positive electrode active material layer can further contain a positive electrode binder. The positive electrode binder serves to improve the adhesion between positive electrode active material particles and the adhesive force between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene polymer (EPDM), sulfonated - EPDM, styrene - butadiene rubber (SBR), fluororubber, or various copolymers thereof, etc. Among these, one kind alone or a mixture of two or more kinds can be used.

[0055] The positive electrode binder can be contained in the positive electrode active material layer at 0.5% to 5.0% by weight, specifically 1.0% to 2.5% by weight, and more specifically 1.0% to 2.0% by weight.

[0056] The positive electrode active material layer can further contain a positive electrode conductive material. The positive electrode conductive material is used to impart conductivity to the electrode and can be used without particular limitation as long as it has electron conductivity and does not cause a chemical change in the configured battery. Specific examples include graphite such as natural graphite and 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 powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these or a mixture of two or more can be used.

[0057] The positive electrode conductive material can be contained in the positive electrode active material layer at 0.5 wt% to 30.0 wt%, specifically 0.5 wt% to 10.0 wt%, and more specifically 1.0 wt% to 4.0 wt%.

[0058] The positive electrode active material layer can further contain a lithium by-product. The lithium by-product corresponds to a by-product formed by transferring and rolling a lithium metal layer to the positive electrode active material layer during the manufacturing process of the positive electrode. Specifically, the positive electrode active material layer can contain any one selected from the group consisting of Li3N, Li2CO3, and LiOH.

[0059] In addition, when the lithium metal layer is transferred to the positive electrode active material layer, a part of the positive electrode active material in the positive electrode active material layer may cause a change in the crystal structure due to over-lithiation. In particular, in the case of a positive electrode active material having a layered structure represented by LiMO2, there exists a LiMO2-type layered structure corresponding to the space group R-3m, and a Li2MO2-type layered structure corresponding to the space group P-3m1 (T1) is formed due to an excess of lithium, and a rock salt structure corresponding to the space group Fm-3m represented by MO can be formed. Such a crystal structure can be determined according to the amount of the lithium by-product generated due to over-lithiation and the rolling conditions, and as follows, it is necessary to appropriately adjust the production amount of the lithium by-product and the rolling conditions so as to satisfy the following conditions in the graph derived by XRD.

[0060] The positive electrode can satisfy the following formula 1.

[0061] [Formula 1] 1.2 ≦ I

[0003] / I

[0200] ≦ 2.0 In the formula 1, the I

[0003] is the integrated value of the maximum peak appearing in the region where 2θ is 17.0° to 19.0° during XRD measurement with respect to the surface of the positive electrode active material layer. Specifically, the range of 2θ where the maximum peak appears can be 17.5° to 18.5°, and can be 17.5° to 18.2°. The I

[0200] is the integrated value of the maximum peak appearing in the region where 2θ is 43° to 45° during XRD measurement with respect to the surface of the positive electrode active material layer. The range of 2θ where the maximum peak appears can be 43.5° to 44.5°, and can be 43.7° to 44.3°.

[0062] In addition, the I

[0003] / I

[0200] in the formula 1 according to an embodiment of the present invention can preferably be 1.21 or more, 1.22 or more, 1.23 or more, or 1.24 or more, and can preferably be 1.80 or less, 1.70 or less, 1.65 or less, 1.60 or less, or 1.58 or less.

[0063] In the case of the former I

[0003] This is a peak derived from a positive electrode active material corresponding to a layered structure of a hexagonal crystal belonging to the space group R-3m. The intensity of this peak can vary depending on the degree of over-lithiation, the degree of phase transition to the rock salt phase (Fm-3m), and the degree of generation of lithium by-products. I

[0200] is a peak that appears due to the crystal structure transitioned to the rock salt phase, and can be determined according to the degree of cracking of the positive electrode active material by rolling, the degree of cracking of the positive electrode active material by lithium transfer, and the degree of generation of lithium by-products.

[0064] Generally, I

[0003] is large and I

[0200] is small, it can be evaluated as a positive electrode active material having an excellent crystal structure. However, when over-lithiation is performed, the rolling process required during over-lithiation, the damage of the positive electrode active material generated by lithium transfer, and the lithium by-products generated on the surface make it difficult to simply evaluate that those with a large value of I

[0003] and a small value of I

[0200] are excellent, and it may be difficult to improve the value in a desired direction.

[0065] However, according to one embodiment of the present invention, when adjusting the rolling pressure and the degree of over-lithiation during the manufacture of the positive electrode so as to have the above numerical range, considering together the degree of damage of the positive electrode active material particles, the increase or decrease in resistance due to lithium by-products, and the capacity loss of the positive electrode active material due to the generation of the rock salt phase, the most preferable performance can be realized.

[0066] In the process of manufacturing the positive electrode of the present invention, a lithium metal layer is transferred onto the positive electrode active material layer, and then the positive electrode including the lithium metal layer is rolled at a pressure of 10 kgf / cm to 90 kgf / cm, and lithium ions in the lithium metal layer are inserted into the positive electrode active material layer. In this process, lithium by-products are generated by lithium ions. The fact that the positive electrode satisfies the above formula 1 is considered to mean that a lithium metal layer is transferred onto the positive electrode active material layer and rolled at a pressure of 10 kgf / cm to 90 kgf / cm during the manufacture of the positive electrode of the present invention.

[0067] When the pressure during the rolling is less than 10 kgf / cm², during the production of the positive electrode, the lithium metal layer of the transfer laminate cannot be effectively transferred to the positive electrode, and it is difficult to insert lithium into the positive electrode at the target level. For example, when the pressure during the rolling is less than 10 kgf / cm², the I

[0003] / I

[0200] can exceed 2.0. As a result, the amount of lithium transmitted to the negative electrode during the activation process decreases, and lithium remaining on the surface without diffusing into the interior of the active material layer generates a large amount of lithium by-products due to the reaction with air or the electrolyte in the atmosphere. Eventually, there is no improvement in capacity due to an increase in the lithium loss amount, it is difficult to improve the life characteristics of the battery, and the resistance of the electrode can also increase due to the by-products.

[0068] On the other hand, when the pressure during the rolling exceeds 90 kgf / cm², the diffusion rate of lithium is too fast, and excessive cracking of the positive electrode active material can occur. As a result, the capacity of the positive electrode decreases, and the life characteristics of the battery can deteriorate. Also, in this case, there are problems of an increase in damaged positive electrode active materials, and a large amount of lithium by-products are formed by side reactions in which Li₂MO₂ crystals are decomposed into Li₂O and MO, resulting in a decrease in the capacity of the positive electrode. The long-term life characteristics of the battery can deteriorate, and an increase in the rock salt phase can cause problems of capacity reduction, resistance increase, and life reduction. For example, when the pressure during the rolling exceeds 90 kgf / cm², the I

[0003] / I

[0200] can be less than 1.2.

[0069] That is, when the positive electrode satisfies the formula 1, sufficient lithium is supplied to the positive electrode, and prelithiation of the negative electrode can be smoothly performed during battery activation, which has the advantage of improving the capacity of the positive electrode and the life characteristics of the battery.

[0070] The positive electrode can further include a lithium metal layer located on the positive electrode active material layer. The lithium metal layer serves to supply lithium ions to the positive electrode active material layer. Specifically, the positive electrode active material layer can be located between the positive electrode current collector and the lithium metal layer. The lithium metal layer can be in contact with the positive electrode active material layer. The lithium metal layer contains solid-phase lithium metal. Specifically, the lithium metal layer can be composed of solid-phase lithium metal.

[0071] The positive electrode can further include a polymer layer located on the positive electrode active material layer. The polymer layer can play a role in effectively peeling the lithium metal layer from the transfer laminate and facilitating the transfer of the lithium metal layer to the positive electrode active material layer during the manufacture of the positive electrode. That is, the polymer layer can be located on the positive electrode active material layer away from the transfer laminate together with the lithium metal layer. The polymer layer can be in contact with the positive electrode active material layer. Different from this, a lithium metal layer can also exist between the polymer layer and the positive electrode active material layer.

[0072] The polymer layer can be at least any one selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), poly(methylmethacrylate) (PMMA), polypropylene, polyethylene, and polycarbonate. Thereby, in the secondary battery including the positive electrode, the polymer layer can be dissolved in the electrolyte contained in the secondary battery, and an increase in the resistance of the battery can be prevented. In particular, the polymer layer can contain PMMA, and in that case, the above-mentioned effect can be further improved.

[0073] In the positive electrode, the porosity of the positive electrode active material layer can be 10% to 40%, specifically 15% to 35%, and more specifically 25% to 30%. In this case, no further change in thickness can occur during rolling.

[0074] <Method for manufacturing positive electrode> The method for manufacturing a positive electrode according to another embodiment of the present invention includes a P1 step of arranging a transfer laminate including a base film and a lithium metal layer located on the base film on a preliminary positive electrode including a preliminary positive electrode active material layer to form a positive electrode structure such that the lithium metal layer is in contact with the preliminary positive electrode active material layer, a P2 step of rolling the positive electrode structure, and a P3 step of removing the base film from the transfer laminate after the rolling to manufacture a positive electrode. The pressure applied to the positive electrode structure during the rolling can be 10 kgf / cm to 90 kgf / cm.

[0075] (1) P1 step Referring to FIG. 1, the transfer laminate 300 can include a base film 310 and a lithium metal layer 320 located on the base film 310. The base film 310 can be used without limitation as long as it is a material that can withstand the high temperature conditions generated during the process of depositing the lithium metal layer 320 on the base film 310. Specifically, the base film can include one or more selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), poly(methylmethacrylate) (PMMA), polypropylene, polyethylene, and polycarbonate.

[0076] The lithium metal layer can be located on the substrate film. The lithium metal layer can serve to supply lithium ions to the preliminary cathode active material layer. The lithium metal layer contains solid-phase lithium metal. Specifically, the lithium metal layer can be composed of solid-phase lithium metal.

[0077] In the transfer laminate, the thickness of the lithium metal layer can be 1.0 μm to 10.0 μm, specifically 3.0 μm to 9.0 μm, and more specifically 4.0 μm to 6.5 μm. When the above range is satisfied, the degree of cracking of the cathode active material particles on the surface of the cathode can be reduced, and the decrease in the initial capacity of the battery can be suppressed.

[0078] The loading amount (unit: mAh / cm 2 ) of the lithium metal layer can be 4% to 40% of the loading amount (unit: mAh / cm 2 ) of the preliminary cathode active material layer. Specifically, it can be 12% to 35%, and more specifically 20% to 30%. When the above range is satisfied, the generation of by-products is small, lithium can be easily inserted into the cathode active material, and the target lithium insertion capacity can be easily achieved.

[0079] In the P1 step, referring to FIG. 1, the preliminary cathode active material layer 120' is located on the cathode current collector 110, the transfer laminate 300 is disposed on the preliminary cathode active material layer 120', and the cathode structure 400 can be formed such that the lithium metal layer 320 and the preliminary cathode active material layer are in contact with each other.

[0080] Here, the cathode current collector 110 is the same as the cathode current collector described in the above-described embodiment regarding the cathode.

[0081] On the one hand, referring to FIG. 2, the transfer laminate 300 can further include a polymer layer 330. The polymer layer 330 can be located between the base film 310 and the lithium metal layer 320. The polymer layer can play a role in effectively peeling the lithium metal layer from the transfer laminate during the manufacture of the positive electrode, so that the lithium metal layer can be easily transferred to the positive electrode active material layer. That is, the polymer layer can be separated from the transfer laminate together with the lithium metal layer and located on the positive electrode active material layer. The polymer layer can be in contact with the positive electrode active material layer, and differently, a lithium metal layer can also be present between the polymer layer and the positive electrode active material layer.

[0082] The polymer layer can be at least any one selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), poly(methylmethacrylate) (PMMA), polypropylene, polyethylene, and polycarbonate. Thereby, in the secondary battery including the positive electrode, the polymer layer can be dissolved in the electrolyte contained in the secondary battery, and an increase in the resistance of the battery can be prevented. In particular, the polymer layer can include PMMA, and in that case, the above-described effect can be further improved.

[0083] The thickness of the polymer layer can be 0.1 μm to 10.0 μm, specifically 0.5 μm to 5.0 μm, and more specifically 1.0 μm to 2.5 μm. When the above range is satisfied, the lithium metal layer can be easily transferred to the positive electrode active material layer, and the reverse transfer phenomenon in which the positive electrode active material layer is transferred to the transfer laminate can be prevented.

[0084] (2) P2 step Referring to FIG. 3, in the P2 step, the manufactured positive electrode structure 400 can be rolled. The rolling can be performed by a roll press method. Specifically, pressure can be applied in the vertical direction to the positive electrode structure 400 passing through the space via two rolls R spaced apart with a predetermined space in the vertical direction, and the pressure can be a linear pressure. By the rolling process, at least a part of the lithium ions in the lithium metal layer contained in the transfer laminate can be inserted into the inside of the preliminary positive electrode active material layer. In this process, the preliminary positive electrode active material layer can become a positive electrode active material layer. FIGS. 3 and 4 illustrate the case where the lithium metal layer is included in the positive electrode, but in the rolling process, when the entire lithium metal layer is inserted into the inside of the preliminary positive electrode active material layer, the lithium metal layer may not exist as a separate layer.

[0085] The pressure applied to the positive electrode structure during the rolling can be 10 kgf / cm to 90 kgf / cm, specifically 15 kgf / cm to 80 kgf / cm, more specifically 20 kgf / cm to 60 kgf / cm, and more preferably 20 kgf / cm to 50 kgf / cm.

[0086] When the pressure during the rolling is less than 10 kgf / cm, during the manufacture of the positive electrode, the lithium metal layer of the transfer laminate cannot be effectively transferred to the positive electrode, and it is difficult to insert lithium into the positive electrode to the target level. For example, when the pressure during the rolling is less than 10 kgf / cm, the I

[0003] / I

[0200] can be more than 2.0. As a result, the amount of lithium transmitted to the negative electrode during the activation process decreases, and a large amount of lithium by-products are generated by the lithium remaining on the surface without diffusing into the inside of the active material layer, making it difficult to improve the life characteristics of the battery, and the resistance of the electrode may increase.

[0087] On the other hand, when the pressure exceeds 90 kgf / cm during the rolling, the diffusion rate of lithium is too fast, and excessive cracking of the positive electrode active material may occur. As a result, the capacity of the positive electrode decreases, and the life characteristics of the battery may deteriorate. Also, in this case, there are problems of an increase in damaged positive electrode active material, and a large amount of lithium by-products are formed due to the side reaction in which Li2MO2 crystals are decomposed into Li2O and MO, resulting in a decrease in the capacity of the positive electrode, and the long-term life characteristics of the battery may deteriorate. The rock salt phase may also increase, leading to problems of capacity reduction, resistance increase, and life reduction. For example, when the pressure exceeds 90 kgf / cm during the rolling, the I

[0003] / I

[0200] can be less than 1.2.

[0088] (3) P3 step Referring to FIG. 4, in the P3 step, after the rolling performed in the P2 step, the base film 310 can be removed from the transfer laminate to manufacture the positive electrode 100. When the polymer layer 330 is located between the base film 310 and the lithium metal layer 320, the polymer layer 330 can more easily remove the base film 310.

[0089] Further, the method for manufacturing the positive electrode may further include a P4 step of leaving (letting stand) the preliminary positive electrode for 1 minute to 600 minutes, specifically 1 minute to 30 minutes. The P4 step can be performed after the P2 step. Specifically, the P4 step can be performed in at least one of the steps "between the P2 step and the P3 step" and "immediately after the P3 step". By the P4 step, the reaction heat generated by the reaction between the lithium metal layer and the preliminary positive electrode active material layer in the P2 step can be effectively released, and lithium can be uniformly inserted into the positive electrode, resulting in a reduction in the generation of by-products.

[0090] Since the manufactured positive electrode is the same as the positive electrode of the above-described embodiment, a detailed description thereof is omitted.

[0091] The method for manufacturing the positive electrode of the present embodiment is such that, by a transfer method, a lithium metal layer is disposed on the positive electrode, and rolling is performed under a pressure of 10 kgf / cm to 90 kgf / cm, so that lithium ions in the lithium metal layer are inserted into the preliminary positive electrode active material layer. As a result, by-products containing lithium such as Li3N are generated in the positive electrode, and the positive electrode satisfies 1.2 ≦ I

[0003] / I

[0200] ≦ 2.0. Using the positive electrode manufactured by the above method, a preliminary secondary battery is manufactured, and when the preliminary secondary battery is activated, the lithium ions inserted into the positive electrode are transmitted to the negative electrode, and the irreversible sites of the negative electrode are filled by the reaction of lithium ions. Thereby, the amount of lithium ions inserted into the negative electrode during the driving of the battery can be appropriately reduced to the level required for the driving of the battery. Therefore, the capacity of the battery can be maintained, the available area of the capacity of the negative electrode can be reduced, the excessive volume change of the silicon-based active material particles can be suppressed, and the life characteristics of the battery can be improved. One of the features of the present invention is that, usually, instead of performing prelithiation by contacting the negative electrode with a lithium metal layer, after transferring and rolling the lithium metal layer on the positive electrode, the lithium ions inserted into the positive electrode are moved to the negative electrode in the battery activation step. That is, without the negative electrode contacting the lithium metal layer, lithium ions are not directly inserted into the negative electrode from the lithium metal layer. Therefore, it is possible to avoid the phenomenon of excessive heat generation due to the alloy reaction of lithium and silicon in the negative electrode, and the possibility of ignition due to the reaction of lithium and moisture can also be significantly reduced. Furthermore, when notching and punching the negative electrode, since lithium ions are not inserted into the negative electrode (because prelithiation has not been performed), the possibility of ignition in the notching and punching processes can also be significantly reduced.

[0092] Above all, during the production of the positive electrode, since lithium ions in the lithium metal layer are inserted into the positive electrode active material layer at an appropriate pressure (10 kgf / cm to 90 kgf / cm), the degree of cracking of the positive electrode active material can be reduced, and the life characteristics and energy density of the lithium ion secondary battery can be improved. In addition, excessive generation of lithium by-products can be suppressed, the amount of lithium loss can be reduced, and the long-term life characteristics of the battery can be improved.

[0093] <Lithium-ion secondary battery> A lithium ion secondary battery according to an embodiment of the present invention includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and the electrolyte. The positive electrode includes a positive electrode active material layer containing a positive electrode active material, and the positive electrode can satisfy the following formula 1.

[0094] [Formula 1] 1.2 ≦ I

[0003] / I

[0200] ≦ 2.0 In the formula 1, the I

[0003] is the integrated value of the maximum peak that appears in the region where 2θ is 17.0° to 19.0° during XRD measurement with respect to the surface of the positive electrode active material layer, and the I

[0200] is the integrated value of the maximum peak that appears in the region where 2θ is 43° to 45° during XRD measurement with respect to the surface of the positive electrode active material layer.

[0095] Since the positive electrode is the same as the positive electrode in the above-described embodiment, the description is omitted.

[0096] The negative electrode includes a negative electrode active material layer, and the negative electrode active material layer can contain a negative electrode active material.

[0097] The negative electrode active material can include a silicon-based negative electrode active material. The silicon-based negative electrode active material can include at least one of Si and SiO x (0 < X < 2).

[0098] The Si is silicon particles and can be silicon particles (particles composed of silicon) so-called Pure Silicon. The silicon particles can effectively improve the capacity of the negative electrode. The SiO x (0 < X < 2) can be in a form containing Si and SiO2, and the Si can also form a phase. That is, the X corresponds to the ratio of the number of O to Si contained in the SiO x (0 < X < 2). When the silicon-based composite particles contain the SiO x (0 < X < 2), the discharge capacity of the secondary battery can be improved.

[0099] The positive electrode included in the lithium-ion secondary battery of this embodiment can satisfy the above formula 1, which means that it is manufactured by the method for manufacturing the positive electrode of the above-described embodiment, and in particular, lithium is transferred to the positive electrode at an appropriate level of pressure. Furthermore, the fact that the positive electrode satisfies the above formula 1 has a greater meaning when the negative electrode contains a silicon-based negative electrode active material. After including the positive electrode manufactured by the above-described method for manufacturing the positive electrode in the secondary battery and passing through the activation process, a predetermined amount of lithium ions are transferred from the positive electrode to the silicon-based negative electrode active material of the negative electrode, and excessive volume change of the silicon-based active material during battery driving can be suppressed, and the life characteristics of the battery can be improved. Furthermore, since another lithium metal layer is not transferred to the negative electrode, lithium ions are not directly inserted into the negative electrode from the lithium metal layer without the negative electrode contacting the lithium metal layer. Therefore, it is possible to avoid the phenomenon of excessive heat generation due to the alloy reaction of lithium and silicon in the negative electrode, and the possibility of ignition due to the reaction of lithium and moisture can also be significantly reduced. Furthermore, when notching and punching are performed on the negative electrode, since lithium ions are not inserted into the negative electrode (because prelithiation is not performed), the possibility of ignition in the notching and punching processes can also be significantly reduced.

[0100] The negative electrode active material can further include a carbon-based negative electrode active material. The carbon-based negative electrode active material can include at least any one selected from the group consisting of artificial graphite, natural graphite, and graphitized mesocarbon microbeads.

[0101] The negative electrode active material layer can further include a negative electrode binder. The negative electrode binder can include at least any one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, 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, poly acrylic acid, and substances in which hydrogen thereof is substituted with Li, Na, Ca, etc., and can also include various copolymers thereof.

[0102] The negative electrode active material layer can further include a negative electrode conductive material. The negative electrode conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. can be used.

[0103] As the separator, any material can be used without particular limitation as long as it separates the negative electrode and the positive electrode and provides a migration path for lithium ions, and is usually used as a separator in a secondary battery. In particular, a material with low resistance to ion migration of the electrolyte and excellent electrolyte moisture retention ability is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as a polyethylene homopolymer, a polypropylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof can be used. Also, a normal porous nonwoven fabric, for example, a nonwoven fabric made of high-melting glass fibers, polyethylene terephthalate fibers, etc. can also be used. Further, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer substance can also be used, and optionally, it can be used in a single-layer or multi-layer structure.

[0104] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0105] Specifically, the electrolyte can contain a non-aqueous organic solvent and a metal salt.

[0106] Examples of the non-aqueous organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl pyruvate, ethyl propionate, etc. can be used.

[0107] In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, have a high dielectric constant as high-viscosity organic solvents and can preferably be used because they can well dissociate lithium salts. When such cyclic carbonates are mixed and used with low-viscosity and low-dielectric-constant linear carbonates such as dimethyl carbonate and diethyl carbonate at an appropriate ratio, an electrolyte having a high electric conductivity can be produced and can be more preferably used.

[0108] As the metal salt, a lithium salt can be used. The lithium salt is a substance that is easily dissolved 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 selected from the group consisting of can be used.

[0109] In addition to the constituent components of the electrolyte, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n - glyme, hexamethyltriamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N - substituted oxazolidinone, N,N - substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2 - methoxyethanol or aluminum trichloride for the purpose of improving the life characteristics of the battery, suppressing the capacity reduction of the battery, improving the discharge capacity of the battery, etc.

[0110] <Method for manufacturing lithium-ion secondary battery> The manufacturing method of a lithium-ion secondary battery according to an embodiment of the present invention includes a B1 step of manufacturing a preliminary lithium-ion secondary battery including a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, and a B2 step of activating the preliminary lithium-ion secondary battery. The method of manufacturing the positive electrode includes a P1 step of disposing a transfer laminate including a base film and a lithium metal layer located on the base film on a preliminary positive electrode including a preliminary positive electrode active material layer to form a positive electrode structure such that the lithium metal layer is in contact with the preliminary positive electrode active material layer, a P2 step of rolling the positive electrode structure, and a P3 step of removing the base film from the transfer laminate after the rolling. During the rolling, the pressure applied to the positive electrode structure can be 10 kgf / cm to 90 kgf / cm.

[0111] Here, the secondary battery can be the same as the secondary battery of the above-described embodiment.

[0112] The positive electrode is the same as the positive electrode of the above-described embodiment, and the method of manufacturing the positive electrode is the same as the method of manufacturing the positive electrode described above, so the description is omitted.

[0113] Since the negative electrode is the same as the negative electrode of the above-described embodiment, the description is omitted.

[0114] In the B1 step, the preliminary lithium-ion secondary battery can include a positive electrode and a negative electrode. Specifically, the preliminary lithium-ion secondary battery can include a positive electrode, a negative electrode, a separator, and an electrolyte. Specifically, the positive electrode and the negative electrode are laminated separately with the separator interposed therebetween and can be impregnated with the electrolyte. The negative electrode before undergoing the activation process can be a preliminary negative electrode, which means a state where lithium ions have not been inserted yet. The preliminary lithium-ion secondary battery means a battery before undergoing the activation process.

[0115] The method for manufacturing the positive electrode may further include a P4 step of allowing the preliminary positive electrode to rest (be left alone) for 1 minute to 600 minutes, specifically 1 minute to 30 minutes, after the P2 step. The P4 step can be performed after the P2 step. Specifically, the P4 step can be performed in at least one of the steps "between the P2 step and the P3 step" and "immediately after the P3 step". By the P4 step, the heat generated by the reaction between the lithium metal layer and the preliminary positive electrode active material layer in the P2 step can be effectively released, and lithium can be uniformly inserted into the positive electrode, resulting in a reduction in the generation of by-products.

[0116] The B2 step may include applying a current to the preliminary lithium-ion secondary battery. The preliminary lithium-ion secondary battery can be activated by the current, and lithium ions can be inserted into the negative electrode to perform prelithiation of the negative electrode.

[0117] According to still another embodiment of the present invention, there are provided a battery module including the lithium-ion secondary battery as a unit cell and a battery pack including the same. Since the battery module and the battery pack include the lithium-ion secondary battery having high capacity, high rate characteristics, and cycle characteristics, they can be used as a power source for medium and large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0118] Hereinafter, preferred examples are presented to facilitate understanding of the present invention. However, it is obvious to those skilled in the art that the examples are only illustrative of the description, and various changes and modifications are possible within the scope of the description and the scope of the technical idea. Needless to say, such variations and modifications belong to the scope of the appended claims.

[0119] [Examples and Comparative Examples] Example 1-1: Manufacturing of positive electrode A PET film (substrate film), a polymer layer made of PMMA (thickness of 2.5 μm) disposed on the PET film, and a lithium metal layer made of solid lithium metal (thickness of 6 μm, loading amount of 1.24 mAh / cm 2 were prepared to form a transfer laminate.

[0120] On the other hand, as the positive electrode active material, Li[Ni 0.86 Co 0.05 Mn 0.08 Al 0.01 O2 was used. The positive electrode active material is in the form of secondary particles where a plurality (10 or more) of primary particles of Li[Ni 0.86 Co 0.05 Mn 0.08 Al 0.01 O2 are bonded to each other, and the average particle diameter D 50 of the secondary particles was 9 μm. A preliminary positive electrode active material layer containing the positive electrode active material, PVdF as the positive electrode binder, and carbon nanotubes as the positive electrode conductive material in a weight ratio of 98:1:1 was prepared on an aluminum foil (thickness: 12 μm) which is the positive electrode current collector. The loading amount of the preliminary positive electrode active material layer was 4.5 mAh / cm 2 and the thickness was 140 μm.

[0121] The transfer laminate was placed on the preliminary positive electrode active material layer such that the lithium metal layer was in contact with the preliminary positive electrode active material layer.

[0122] Thereafter, the positive electrode on which the transfer laminate was placed was rolled by a roll press method and then left for 24 hours. The pressure during rolling was 20 kgf / cm. As a result, lithium ions in the lithium metal layer were inserted into the preliminary positive electrode active material layer to form a positive electrode active material layer. Next, the substrate film was removed and left for 10 minutes to fabricate a positive electrode including a positive electrode current collector, a positive electrode active material layer, and a polymer layer.

[0123] Example 1-2: Manufacturing of positive electrode The positive electrode was manufactured in the same manner as in Example 1-1, except that the pressure during rolling was applied at 50 kgf / cm instead of 20 kgf / cm.

[0124] Example 1-3: Manufacturing of positive electrode The positive electrode was manufactured in the same manner as in Example 1-1, except that the pressure during rolling was applied at 30 kgf / cm instead of 20 kgf / cm.

[0125] Example 1-4: Manufacturing of positive electrode The positive electrode was manufactured in the same manner as in Example 1-1, except that the pressure during rolling was applied at 10 kgf / cm instead of 20 kgf / cm.

[0126] Example 1-5: Manufacturing of positive electrode The positive electrode was manufactured in the same manner as in Example 1-1, except that the pressure during rolling was applied at 90 kgf / cm instead of 20 kgf / cm.

[0127] Comparative Example 1-1: Manufacturing of positive electrode The positive electrode was manufactured in the same manner as in Example 1-1, except that the pressure during rolling was applied at 5 kgf / cm instead of 20 kgf / cm.

[0128] Comparative Example 1-2: Manufacturing of positive electrode The positive electrode was manufactured in the same manner as in Example 1-1, except that the pressure during rolling was applied at 120 kgf / cm instead of 20 kgf / cm.

[0129] Comparative Example 1-3: Manufacturing of positive electrode The positive electrode was manufactured in the same manner as in Example 1-1, except that the pressure during rolling was applied at 100 kgf / cm instead of 20 kgf / cm.

[0130] Comparative Example 1-4: Manufacturing of negative electrode A PET film (substrate film), a polymer layer (1 μm thick) made of PMMA disposed on the PET film, and a lithium metal layer (3 μm thick, 0.6 mAh / cm) made of solid lithium metal disposed on the polymer layer 2A transfer laminate including (loading amount) was prepared.

[0131] On the other hand, as the negative electrode active material, silicon particles with an average particle diameter D 50 of 5 μm were used. A negative electrode including a preliminary negative electrode active material layer containing the negative electrode active material, carboxymethyl cellulose (CMC) as the negative electrode binder, and carbon nanotubes as the negative electrode conductive material in a weight ratio of 80:10:10 was prepared. The loading amount of the preliminary negative electrode active material layer was 10 mAh / cm 2 and the thickness was 75 μm.

[0132] The transfer laminate was placed on the preliminary negative electrode active material layer so that the lithium metal layer was in contact with the preliminary negative electrode active material layer.

[0133] Thereafter, after rolling the negative electrode on which the transfer laminate was placed in a roll-to-roll manner, the negative electrode was left for 24 hours. As a result, lithium ions in the lithium metal layer were inserted into the preliminary negative electrode active material layer to form a negative electrode active material layer. The pressure during rolling was 50 kgf / cm.

[0134] Next, the base film was removed to produce a negative electrode including a negative electrode current collector, a negative electrode active material layer, and a polymer layer.

[0135] Experimental Example 1: Measurement of I

[0003] / I

[0200] of For Examples 1-1 to 1-5 and Comparative Examples 1-1 to 1-4, XRD was measured by the following method, and I

[0003] / I

[0200] was confirmed and shown in Table 1. Figures 5, 6, and 7 are graphs showing the XRD results of Examples 1-1, 1-2, and Comparative Example 1-2 among them.

[0136] Using the X-ray wavelength generated by Cu Kα, the wavelength (λ) of the light source is 0.15406 nm.

[0137] 1) Measuring instrument and conditions: Bruker D8 Endeavor (Cu target, 40 kV, 40 mA, 1.54 Å), LynxEye position sensitive detector (4.1° slit) 2) Experimental procedure 2-1) Prep. Cutting / Cross-section: Cut the sample to the size of the Sample holder to produce a test piece.

[0138] 2-2) Prep. Sample Mounting: After attaching the sample (positive electrode) firmly to the glass plate using double-sided tape so that it does not float, mount it using a holder made of PMMA and rubber clay.

[0139] 2-3) Powder XRD (Bruker D8 Endeavor): Adjust the FDS to 0.5° according to the size of the sample, and measure the region from 2theta 10° to 125° at intervals of 0.0156° for 0.3 seconds each.

[0140] 2-4) XRD Phase Analysis: Identify the phases present in the sample by comparing with the Database (PDF).

[0141] 2-5) Rietveld Analysis: Perform Rietveld refinement using the complete structure model of the phases present in the sample.

[0142] Example 2-1: Manufacturing of secondary battery As the negative electrode active material, silicon particles with an average particle size D 50 of 5 μm were used. A negative electrode including a preliminary negative electrode active material layer containing the negative electrode active material, CMC as the negative electrode binder, and carbon nanotubes as the negative electrode conductive material in a weight ratio of 80:10:10 was prepared. The loading amount of the preliminary negative electrode active material layer was 10 mAh / cm 2 and the thickness was 75 μm.

[0143] The positive electrode of Example 1-1, the negative electrode, and the porous polyethylene separator were assembled using the winding method, and an electrolyte (ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 3 / 7 (volume ratio), 1 mol of lithium hexafluorophosphate (LiPF6)) was injected into the assembled battery to manufacture a preliminary lithium-ion secondary battery.

[0144] After charging the preliminary lithium-ion secondary battery at 4.2 V at a 0.1C C-rate, it was discharged to 2.5 V to perform an activation process.

[0145] Example 2-2: Manufacturing of secondary battery A lithium-ion secondary battery was manufactured in the same manner as in Example 2-1, except that the positive electrode of Example 1-2 was used instead of the positive electrode of Example 1-1.

[0146] Example 2-3: Manufacturing of secondary battery A lithium-ion secondary battery was manufactured in the same manner as in Example 2-1, except that the positive electrode of Example 1-3 was used instead of the positive electrode of Example 1-1.

[0147] Example 2-4: Manufacturing of secondary battery A lithium-ion secondary battery was manufactured in the same manner as in Example 2-1, except that the positive electrode of Example 1-4 was used instead of the positive electrode of Example 1-1.

[0148] Example 2-5: Manufacturing of secondary battery A lithium-ion secondary battery was manufactured in the same manner as in Example 2-1, except that the positive electrode of Example 1-5 was used instead of the positive electrode of Example 1-1.

[0149] Comparative Example 2-1: Manufacturing of secondary battery A lithium-ion secondary battery was manufactured in the same manner as in Example 2-1, except that the positive electrode of Comparative Example 1-1 was used instead of the positive electrode of Example 1-1.

[0150] Comparative Example 2-2: Manufacturing of secondary battery A lithium-ion secondary battery was manufactured in the same manner as in Example 2-1, except that the positive electrode of Comparative Example 1-2 was used instead of the positive electrode of Example 1-1.

[0151] Comparative Example 2-3: Manufacturing of secondary battery A lithium-ion secondary battery was manufactured in the same manner as in Example 2-1, except that the positive electrode of Comparative Example 1-3 was used instead of the positive electrode of Example 1-1.

[0152] Comparative Example 2-4: Manufacturing of secondary battery As the positive electrode active material, Li[Ni 0.86 Co 0.05 Mn 0.08 Al 0.01 O2 was used. The positive electrode active material was in the form of secondary particles in which a plurality (10 or more) of primary particles of Li[Ni 0.86 Co 0.05 Mn 0.08 Al 0.01 O2 were combined with each other, and the average particle diameter D 50 of the secondary particles was 9 μm. A positive electrode was prepared in which a preliminary positive electrode active material layer containing the positive electrode active material, PVdF as the positive electrode binder, and carbon nanotubes as the positive electrode conductive material in a weight ratio of 98:1:1 was disposed on an aluminum foil (thickness: 12 μm). The loading amount of the preliminary positive electrode active material layer was 4.5 mAh / cm 2 and the thickness was 140 μm.

[0153] The negative electrode of Comparative Example 1-4, the positive electrode, and the porous polyethylene separator were assembled using the winding method, and an electrolyte (ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 1 / 2 (volume ratio), lithium hexafluorophosphate (LiPF6 1 mol)) was injected into the assembled battery to manufacture a lithium-ion secondary battery.

[0154] Experimental Example 2: Measurement of lithium loss amount The lithium loss amounts of the lithium-ion secondary batteries of Examples 2-1 to 2-5 and Comparative Examples 2-1 to 2-4 were measured and shown in Table 1.

[0155] First, the initial charge capacity of the positive electrode without lithium ion transfer and insertion (the preliminary positive electrode used in Example 1-1) as the control group and the initial charge capacity of the positive electrode of Example 2-1 were measured under the following conditions.

[0156] 0.1C, after CC / CV charging to 4.2V, 0.05C cut-off 0.1C, CC discharge to 2.3V The theoretical capacity of the lithium metal layer used in the experiment was 1 mAh / cm 2 was.

[0157] The lithium loss was calculated as follows.

[0158] Lithium loss (%) = [1 - {(Initial charge capacity of the positive electrode of Example 2-1 - Initial charge capacity of the positive electrode of the control group) / Theoretical capacity of the lithium metal layer}] × 100

[0159] Such a method was also carried out in exactly the same way for the remaining examples and Comparative Examples 2-1 to 2-3.

[0160] For Comparative Example 2-4, the lithium loss was measured for the negative electrode by the above method.

[0161] Experimental Example 3: Evaluation of life characteristics (capacity retention rate) Charge and discharge were performed on each of the lithium ion secondary batteries of Examples 2-1 to 2-5 and Comparative Examples 2-1 to 2-4, and the life characteristics (capacity retention rate) were evaluated.

[0162] Charging conditions: Charge to 4.2V at a current density of 1C Discharging conditions: Discharge to 2.5V at a current rate of 0.5C The capacity retention rate was derived by the following calculations respectively.

[0163] Capacity retention rate (%) = (Discharge capacity after 100 cycles / Discharge capacity in the first cycle) × 100

[0164]

Table 1

[0165] Referring to Table 1 above, in the case of the examples where rolling was performed at a pressure satisfying the range of 10 kgf / cm to 90 kgf / cm during rolling, I

[0003] / I

[0200] satisfies the range of 1.2 to 2.0, the lithium loss amount is low, and the capacity retention rate is high. It can be seen that compared with Comparative Examples 2-4 where direct prelithiation was performed on the negative electrode, stability and process advantages can be ensured, and excellent effects can also be expected. On the other hand, in the case of Comparative Example 2-1 where a rolling pressure of 5 kgf / cm was applied, it can be seen that relatively less rock salt phase was formed compared to the examples, but the lithium loss amount increased by a factor of 2 due to the generation of a large amount of lithium by-products, and it can be confirmed that the life characteristics also decreased accordingly. Also, in Comparative Examples 2-2 and 2-3 where a rolling pressure exceeding 90 kgf / cm was applied, a large lithium loss amount is shown. This is due to the cracking phenomenon of the positive electrode active material particles and the decomposition of the Li2MO2 phase due to over-lithiation. I

[0003] / I

[0200] has a value smaller than 1.2, and it can be seen that the life characteristics also decreased accordingly.

Explanation of Reference Signs

[0166] 110 Positive electrode current collector 120, 120’ Preliminary positive electrode active material layer 300 Transfer laminate 310 Substrate film 320 Lithium metal layer 330 Polymer layer 400 Positive electrode structure R Roll

Claims

1. A positive electrode comprising a positive electrode active material layer containing a positive electrode active material, The positive electrode satisfying the following formula 1. [Formula 1] 1.2 ≤ I ［００３］ / I ［２００］ ≤ 2.0 In the formula 1, the I ［００３］ is the integrated value of the maximum peak that appears in the region where 2θ is 17.0° to 19.0° during XRD measurement with respect to the surface of the positive electrode active material layer, Said I ［２００］ is the integrated value of the maximum peak that appears in the region where 2θ is 43° to 45° during XRD measurement with respect to the surface of the positive electrode active material layer.

2. The positive electrode active material layer contains Li ３ N, Li ２ CO ３ and at least one selected from the group consisting of LiOH, the positive electrode according to claim 1.

3. The positive electrode according to claim 1, wherein the positive electrode active material contains a layered lithium nickel-based transition metal composite oxide, and the lithium nickel-based transition metal composite oxide contains a compound represented by the following chemical formula 1. [Chemical formula 1] Li １＋ｘ [Ni ａ Co ｂ Mn ｃ M １ （１－ａ－ｂ－ｃ） O （２－ｄ） A ｄ In the above chemical formula 1, M １ is at least any one selected from the group consisting of Al, Mg, Cr, Ti, Si, and Y, A is at least one selected from the group consisting of F, P, and Cl, -0.5 ≦ x ≦ 0.5, 0.6 ≦ a < 1, 0.03 ≦ b ≦ 0.1, 0.03 ≦ c ≦ 0.1, 0 ≦ d ≦ 0.1, 0 < a + b + c ≦ 1 are satisfied.

4. The positive electrode active material contains a layered lithium nickel-based transition metal composite oxide, and the D of the lithium nickel-based transition metal composite oxide ５０ is 5 μm or more and 15 μm or less. The positive electrode according to claim 1.

5. The positive electrode according to claim 1, wherein the positive electrode active material contains a layered lithium nickel-based transition metal composite oxide, and the lithium nickel-based transition metal composite oxide is in the form of secondary particles in which a plurality of primary particles are bonded to each other.

6. The positive electrode according to any one of claims 1 to 5, further comprising at least one layer of a lithium metal layer and a polymer layer located on the positive electrode active material layer.

7. A P1 step of forming a positive electrode structure by disposing a transfer laminate including a base film and a lithium metal layer located on the base film on a preliminary positive electrode including a preliminary positive electrode active material layer so that the lithium metal layer is in contact with the preliminary positive electrode active material layer; A P2 step of rolling the positive electrode structure; After the rolling, a P3 step of removing the base film from the transfer laminate is included, The method for manufacturing a positive electrode, wherein the pressure applied to the positive electrode structure during the rolling is 10 kgf / cm or more and 90 kgf / cm or less.

8. In the P2 step, The rolling is performed by a roll press method, and the method for manufacturing a positive electrode according to claim 7.

9. The method for manufacturing a positive electrode according to claim 7, wherein the thickness of the lithium metal layer is 1 μm or more and 10 μm or less.

10. The method for manufacturing a positive electrode according to claim 7, wherein the loading amount of the lithium metal layer is 4% or more and 40% or less of the loading amount of the preliminary positive electrode active material layer.

11. The transfer laminate further includes a polymer layer, The method for manufacturing a positive electrode according to any one of claims 7 to 10, wherein the polymer layer is located between the base film and the lithium metal layer.

12. The manufacturing method of the positive electrode according to claim 11, wherein the polymer layer contains at least any one selected from the group consisting of polyethylene terephthalate, polyimide, polymethyl methacrylic acid, polypropylene, polyethylene, and polycarbonate.

13. A lithium secondary battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode includes a positive electrode active material layer containing a positive electrode active material, and satisfies the following formula 1. [Formula 1] 2 ≤ I ［００３］ / I ［２００］ ≤ 2.0 In the formula 1, the I ［００３］ is the integrated value of the maximum peak that appears in the region where 2θ is 17.0° to 19.0° during XRD measurement with respect to the surface of the positive electrode active material layer, Said I ［２００］ is the integrated value of the maximum peak that appears in the region where 2θ is 43° to 45° during XRD measurement with respect to the surface of the positive electrode active material layer.

14. wherein the negative electrode includes a negative electrode active material layer, and the negative electrode active material layer contains a silicon-based negative electrode active material, the lithium secondary battery according to claim 13.

15. The lithium secondary battery according to claim 13, wherein the silicon-based negative electrode active material is pure silicon (Pure Si).

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