Positive electrode, method for manufacturing a 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 documents 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 has been increasing. As part of this, the fields of power generation and power 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 been rapidly increasing. 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 in that the volume change is excessively large during battery operation, so the battery life rapidly decreases as the battery cycles progress.

[0006] Therefore, in order to minimize the change in volume of silicon-based active material particles, there is a method that uses only a portion of the total volume of silicon-based active material particles. For this purpose, a so-called pre-lithification process is used, in which lithium ions are pre-inserted into the negative electrode containing silicon-based active material particles. Specifically, by inserting lithium ions into the negative electrode by methods such as transferring lithium metal to the negative electrode, the lithium ions react with irreversible sites in the negative electrode, and the total volume of the negative electrode can be reduced to a reversible capacity level. Therefore, when the battery is operated, the amount of lithium ions inserted can be suitably reduced to the level necessary for battery operation, and the change in volume of silicon-based active material particles can be minimized.

[0007] However, during the pre-lithification process, which involves placing lithium metal on the surface of the negative electrode, excessive heat is generated by the alloy reaction between lithium and silicon, increasing the possibility of ignition due to the reaction between lithium and water. Furthermore, during the notching and punching processes of the negative electrode, the reaction area between lithium and silicon-based active material increases, further increasing the possibility of ignition.

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

[0009] Therefore, there is a need for a new technology that can improve battery life and suppress excessive heat generation and the possibility of fire by pre-inserting lithium ions into the negative electrode before the battery is activated. [Overview of the project] [Problems that the invention aims to solve]

[0010] One problem that this invention aims to solve is to provide a positive electrode that can improve the energy density and lifespan characteristics of a battery, and improve safety during the battery manufacturing process.

[0011] Another problem that the present invention aims to solve is to provide a method for manufacturing the positive electrode.

[0012] Another problem that the present invention aims to solve is to provide a lithium secondary battery including the positive electrode. [Means for solving the problem]

[0013] According to one embodiment of the present invention, a positive electrode is provided which includes a positive electrode active material layer containing a positive electrode active material and satisfies the following formula 1.

[0014] [Formula 1] 1.2 ≤ I

[0003] / I

[0200] ≤2.0 In formula 1, the I

[0003] This is the integral value of the maximum peak that appears in the region where 2θ is 17.0° to 19.0° when XRD measurement is performed on the surface of the positive electrode active material layer, and the I

[0200] This is the integral value of the maximum peak that appears in the region where 2θ is 43° to 45° when XRD measurement is performed on the surface of the positive electrode active material layer.

[0015] According to another embodiment of the present invention, a method for manufacturing a positive electrode is provided, comprising the steps of: P1, arranging a transfer laminate including a base film and a lithium metal layer located on the base film on a pre-positive electrode including a pre-positive electrode active material layer to form a positive electrode structure such that the lithium metal layer and the pre-positive electrode active material layer are in contact; P2, rolling the positive electrode structure; and P3, removing the base film from the transfer laminate after rolling, wherein the pressure applied to the positive electrode structure during rolling is 10 kgf / cm to 90 kgf / cm.

[0016] According to yet another embodiment of the present invention, a lithium secondary battery is provided 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 comprises 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 and the preliminary positive electrode active material layer are in contact with each other, 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.

Advantages of the Invention

[0019] In the positive electrode according to the present invention, a lithium metal layer is placed on the positive electrode by a transfer method, and lithium ions from 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 spare lithium-ion secondary battery is manufactured using the positive electrode manufactured by the above method and the spare lithium-ion secondary battery is activated, the lithium ions inserted into the positive electrode are transferred to the negative electrode, and the lithium ions react and fill the irreversible sites of the negative electrode. As a result, the amount of lithium ions inserted into the negative electrode during battery operation can be suitably reduced to the level necessary for battery operation. Therefore, the battery capacity can be maintained, the usable region of the negative electrode capacity can be reduced, excessive volume changes of silicon-based active material particles can be suppressed, and the battery life characteristics can be improved.

[0020] Furthermore, instead of pre-lithifying the negative electrode by having the lithium metal layer in contact with it, the lithium metal layer is transferred and rolled onto the positive electrode, and then the lithium ions inserted into the positive electrode are moved to the negative electrode during the battery activation process. This avoids the phenomenon of excessive heat generation due to the alloy reaction between lithium and silicon at the negative electrode, and significantly reduces the possibility of ignition due to the reaction between lithium and water. In addition, when notching and punching are performed on the negative electrode, lithium ions are not inserted into the negative electrode (because it is not in a pre-lithified state), so the possibility of ignition during the notching and punching processes is also significantly reduced.

[0021] In particular, during the manufacturing of the positive electrode, lithium ions from the lithium metal layer are inserted into the positive electrode active material layer at an appropriate pressure level. This reduces the degree of cracking in the positive electrode active material, improving the lifespan characteristics of the lithium-ion secondary battery and increasing its energy density. Furthermore, lithium by-reaction products can be reduced, lithium loss can be decreased, and the long-term lifespan characteristics of the battery can be improved. [Brief explanation of the drawing]

[0022] [Figure 1] This is a schematic diagram showing step P1 in a method for manufacturing a positive electrode according to one embodiment of the present invention. [Figure 2] This is a schematic diagram showing step P1 in a method for manufacturing a cathode according to one embodiment of the present invention, in which a transfer laminate containing a polymer layer is used. [Figure 3] This is a schematic diagram showing step P2 in a method for manufacturing a positive electrode according to one embodiment of the present invention. [Figure 4] This is a schematic diagram showing step P3 in a method for manufacturing a positive electrode according to one embodiment of the present invention. [Figure 5] This graph shows the XRD measurement results for the positive electrode of Example 1-1 of the present invention. [Figure 6] This graph shows the XRD measurement results for the positive electrode of Example 1-2 of the present invention. [Figure 7] This graph shows the XRD measurement results for the positive electrode of Comparative Examples 1-2 of the present invention. [Modes for carrying out the invention]

[0023] The present invention will be described in more detail below to facilitate understanding of it.

[0024] The terms and words used herein and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may define the concepts of terms as appropriate to best describe their invention.

[0025] The terms used herein are for illustrative purposes only and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0026] In this specification, terms such as “includes,” “equip,” or “have” indicate the presence of implemented features, figures, steps, components, or combinations thereof, but should be understood not to preclude the existence or possibility of adding one or more different features, figures, steps, components, or combinations thereof.

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

[0028] In this specification, XRD measurements are 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) Measurement equipment and conditions: Bruker D8 Endeavor (Cu target 40kV, 40mA, 1.54Å), LynxEye position sensitive detector (4.1° slit) 2) Experimental process 2-1) Prep. Cutting / Cross-section: Prepare test specimens by cutting the sample to the size of the sample holder.

[0031] 2-2) Prep. Sample Mounting: After firmly attaching the sample (positive electrode) to the glass plate using double-sided tape to prevent it from floating, 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 size of the sample, and measure the region from 2theta 10° to 125° for 0.0156° intervals for 0.3 seconds each.

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

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

[0035] <Positive electrode> A positive electrode according to one 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 formula 1, the I

[0003] This is the integral value of the maximum peak that appears in the region where 2θ is 17.0° to 19.0° when XRD measurement is performed on the surface of the positive electrode active material layer, and the I

[0200] This is the integral value of the maximum peak that appears in the region where 2θ is 43° to 45° when XRD measurement is performed on 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 may constitute the positive electrode itself, or it may be located on a 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. Also, 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 sides 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 can be 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 2Li is a lithium nickel oxide (where y is at least one selected from Co, Mn, Al, Cu, Fe, Mg, B, Cr, Zn, and Ga, and y is 0.01 ≤ ≤ 0.7); Li 1+z [M 3 1-q M 4 q ]PO 4-r X r (Here, M 3 is at least one selected from the group consisting of Fe, Mn, Co, and Ni, and M 4 X is at least one selected from the group consisting of Al, Mg, and Ti, and X is at least one selected from the group consisting of F, S, and N, and can include at least one selected from the group consisting of olivine-based lithium metal phosphates (where -0.5 ≤ z ≤ 0.5, 0 ≤ q ≤ 0.5, and 0 ≤ r ≤ 0.1).

[0041] Specifically, the positive electrode active material may include a layered lithium nickel-based transition metal composite oxide, and the lithium nickel-based transition metal composite oxide may include the compound of the following chemical formula 1, or more specifically, the compound of the following chemical formula 1.

[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 the above chemical formula 1, M 1 This 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 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 into and desorbed from the inside of 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 in an amount of 90% to 99% by weight, more specifically 92% to 98% by weight, and more specifically 95% to 98% by weight.

[0054] The positive electrode active material layer may further contain a positive electrode binder. The positive electrode binder plays a role in improving adhesion between positive electrode active material particles and adhesion 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, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, of which one alone or a mixture of two or more can be used.

[0055] The positive electrode binder can be contained in the positive electrode active material layer in an amount of 0.5% to 5.0% by weight, more 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 may 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 limitations as long as it does not cause a chemical change and has electronic conductivity in the battery in which it is constructed. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal 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, and one of these alone 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 in an amount of 0.5% to 30.0% by weight, more specifically 0.5% to 10.0% by weight, and more specifically 1.0% to 4.0% by weight.

[0058] The positive electrode active material layer may further contain lithium by-products. These lithium by-products are formed when the lithium metal layer is transferred to and rolled onto the positive electrode active material layer during the manufacturing process of the positive electrode. Specifically, the positive electrode active material layer may contain any one selected from the group consisting of Li3N, Li2CO3, and LiOH.

[0059] Furthermore, when the lithium metal layer is transferred to the positive electrode active material layer, a portion of the positive electrode active material within the positive electrode active material layer may undergo a change in its crystal structure due to overlithiation. In particular, in the case of a positive electrode active material with a layered structure represented by LiMO2, a LiMO2-type layered structure corresponding to space group R-3m exists, and due to an excess of lithium, a Li2MO2-type layered structure corresponding to space group P-3m1(T1) is formed, and a rock salt structure corresponding to space group Fm-3m represented by MO can be formed. Such a crystal structure can be determined according to the amount of lithium byproducts generated by overlithiation and the rolling conditions, and it is necessary to appropriately adjust the amount of lithium byproducts generated and the rolling conditions so that the following conditions are satisfied in the graph derived by XRD, as shown below.

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

[0061] [Formula 1] 1.2 ≤ I

[0003] / I

[0200] ≤2.0 In formula 1, the I

[0003] This is the integral value of the maximum peak that appears in the region where 2θ is 17.0° to 19.0° when XRD measurement is performed on the surface of the positive electrode active material layer. Specifically, the range of 2θ in which the maximum peak appears can be 17.5° to 18.5°, or 17.5° to 18.2°.

[0200] This is the integral value of the maximum peak that appears in the region where 2θ is 43° to 45° when XRD measurement is performed on the surface of the positive electrode active material layer, and the range of 2θ in which the maximum peak appears can be 43.5° to 44.5° or 43.7° to 44.3°.

[0062] Furthermore, according to one embodiment of the present invention, I of formula 1

[0003] / I

[0200] Preferably, it can be 1.21 or higher, 1.22 or higher, 1.23 or higher, or 1.24 or higher, and preferably 1.80 or lower, 1.70 or lower, 1.65 or lower, 1.60 or lower, or 1.58 or lower.

[0063] The above I

[0003] In this case, the peak is derived from the positive electrode active material, which corresponds to the layered structure of a hexagonal crystal in space group R-3m, and the intensity of this peak may vary depending on the degree of hyperlithiation, the degree of phase transition to the rock salt phase (Fm-3m), and the degree of lithium byproduct formation.

[0200] This peak appears due to the transition to the rock salt phase of the crystal structure and can be determined according to the degree to which the positive electrode active material fractures due to rolling, the degree to which the positive electrode active material fractures due to lithium transfer, and the degree to which lithium by-products are formed.

[0064] Generally, I

[0003] Large I

[0200] If the value is small, it can be evaluated as a positive electrode active material with an excellent crystal structure, but when overlithiation is performed, the rolling process required during overlithiation, the damage to the positive electrode active material caused by lithium transfer, and the lithium by-products generated on the surface mean that, simply put, I

[0003] It has a large value, I

[0200] It is difficult to evaluate items with small values ​​as superior, and it may be difficult to improve those values ​​in the desired direction.

[0065] However, according to one embodiment of the present invention, when the rolling pressure and the degree of overlithiation are adjusted during the manufacturing of the positive electrode to have the numerical range described above, the most desirable performance can be achieved by taking into account the degree of damage to 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 formation of the rock salt phase.

[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. Subsequently, the positive electrode containing the lithium metal layer is rolled at a pressure of 10 kgf / cm to 90 kgf / cm, and lithium ions from the lithium metal layer are inserted into the interior of the positive electrode active material layer. During this process, lithium by-products are generated by the lithium ions. The fact that the positive electrode satisfies formula 1 means that, during the manufacturing of the positive electrode of the present invention, the lithium metal layer was transferred onto the positive electrode active material layer and rolled at a pressure of 10 kgf / cm to 90 kgf / cm.

[0067] If the pressure during rolling is less than 10 kgf / cm, the lithium metal layer of the transfer laminate cannot be effectively transferred to the positive electrode during manufacturing, making it difficult to insert lithium into the positive electrode at the desired level. For example, if the pressure during rolling is less than 10 kgf / cm,

[0003] / I

[0200] This can be greater than 2.0. As a result, the amount of lithium transferred to the negative electrode during the activation process decreases, and the lithium that remains on the surface without diffusing into the active material layer generates a large amount of lithium by-products through reaction with air in the atmosphere or the electrolyte. Consequently, the increase in lithium loss prevents improvement in capacity, making it difficult to improve the battery's lifespan characteristics, and the by-products may also increase the resistance of the electrodes.

[0068] On the other hand, if the pressure during rolling exceeds 90 kgf / cm, the rate of lithium diffusion is too fast, which can cause excessive cracking of the positive electrode active material, thereby reducing the capacity of the positive electrode and potentially degrading the battery's lifespan. In this case as well, problems can arise such as an increase in damaged positive electrode active material, and the formation of a large amount of lithium byproducts due to a side reaction in which the Li2MO2 crystal decomposes into Li2O and MO, which reduces the capacity of the positive electrode and potentially degrades the battery's long-term lifespan. Furthermore, an increase in the rock salt phase can lead to problems of reduced capacity, increased resistance, and reduced lifespan. For example, if the pressure during rolling exceeds 90 kgf / cm, the I

[0003] / I

[0200] It may be less than 1.2.

[0069] In other words, when the positive electrode satisfies formula 1, sufficient lithium is supplied to the positive electrode, pre-lithification of the negative electrode can be performed smoothly during battery activation, and there is an advantage in that the capacity of the positive electrode and the life characteristics of the battery are improved.

[0070] The positive electrode may 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 may be located between the positive electrode current collector and the lithium metal layer. The lithium metal layer may be in contact with the positive electrode active material layer. The lithium metal layer contains solid-phase lithium metal, and specifically, the lithium metal layer may consist of solid-phase lithium metal.

[0071] The positive electrode may further include a polymer layer located on the positive electrode active material layer. The polymer layer can play a role in ensuring that the lithium metal layer is effectively detached from the transfer laminate and easily transferred to the positive electrode active material layer during the manufacturing of the positive electrode. That is, the polymer layer may be located on the positive electrode active material layer, separate from the transfer laminate, together with the lithium metal layer. The polymer layer may be in contact with the positive electrode active material layer, or, conversely, a lithium metal layer may be present between the polymer layer and the positive electrode active material layer.

[0072] The polymer layer can be at least one selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), poly(methylmethacrylate) (PMMA), polypropylene, polyethylene, and polycarbonate. This allows the polymer layer to dissolve in the electrolyte contained in the secondary battery, thereby preventing an increase in the battery's resistance. In particular, the polymer layer may contain PMMA, in which case the above-mentioned effects can be further improved.

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

[0074] <Manufacturing method for positive electrode> A 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 pre-positive electrode including a pre-positive electrode active material layer to form a positive electrode structure such that the lithium metal layer and the pre-positive electrode active material layer are in contact; a P2 step of rolling the positive electrode structure; and a P3 step of manufacturing a positive electrode by removing the base film from the transfer laminate after rolling, wherein the pressure applied to the positive electrode structure during rolling can be 10 kgf / cm to 90 kgf / cm.

[0075] (1) P1 step Referring to Figure 1, the transfer laminate 300 may 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 made of a material that can withstand the high temperature conditions that occur during the process of depositing the lithium metal layer 320 onto the base film 310. Specifically, the base film may include one or more materials selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), poly(methylmethacrylate) (PMMA), polypropylene, polyethylene, and polycarbonate.

[0076] The lithium metal layer may be located on the substrate film. The lithium metal layer may serve to supply lithium ions to the pre-positive electrode active material layer. The lithium metal layer comprises solid-phase lithium metal, and specifically, the lithium metal layer may consist 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, more specifically 3.0 μm to 9.0 μm, and more specifically 4.0 μm to 6.5 μm. When this range is met, the degree of cracking of the positive electrode active material particles on the surface of the positive electrode can be reduced, and the decrease in the initial capacity of the battery can be suppressed.

[0078] The loading amount of the lithium metal layer (unit: mAh / cm²) 2 ) is the loading amount of the pre-positive electrode active material layer (unit: mAh / cm²). 2 This can be 4% to 40%, specifically 12% to 35%, and more specifically 20% to 30%. When this range is satisfied, the generation of by-products is small, lithium can be easily inserted into the positive electrode active material, and the target lithium insertion capacity can be easily achieved.

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

[0080] Here, the positive electrode current collector 110 is the same as the positive electrode current collector described in the above-described embodiment relating to the positive electrode.

[0081] On the other hand, referring to Figure 2, the transfer laminate 300 may further include a polymer layer 330. The polymer layer 330 may be located between the base film 310 and the lithium metal layer 320. The polymer layer can play a role in ensuring that the lithium metal layer is effectively peeled from the transfer laminate and easily transferred to the positive electrode active material layer during the manufacturing of the positive electrode. That is, the polymer layer may be located on the positive electrode active material layer, separate from the transfer laminate together with the lithium metal layer. The polymer layer may be in contact with the positive electrode active material layer, or, conversely, the lithium metal layer may be present between the polymer layer and the positive electrode active material layer.

[0082] The polymer layer can be at least one selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), poly(methylmethacrylate) (PMMA), polypropylene, polyethylene, and polycarbonate. This allows the polymer layer to dissolve in the electrolyte contained in the secondary battery, thereby preventing an increase in the battery's resistance. In particular, the polymer layer may contain PMMA, in which case the above-mentioned effect can be further improved.

[0083] The thickness of the polymer layer can be 0.1 μm to 10.0 μm, more specifically 0.5 μm to 5.0 μm, and more specifically 1.0 μm to 2.5 μm. When this range is met, 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 Figure 3, in step P2, the manufactured positive electrode structure 400 can be rolled. The rolling can be performed using a roll press. Specifically, pressure can be applied vertically to the positive electrode structure 400 passing through two rolls R spaced apart with a predetermined space between them in the vertical direction, and this pressure can be linear pressure. Through this rolling process, at least some of the lithium ions from the lithium metal layer contained in the transfer laminate can be inserted into the interior of the pre-positive electrode active material layer. In this process, the pre-positive electrode active material layer can become the positive electrode active material layer. Although Figures 3 and 4 illustrate the lithium metal layer being included in the positive electrode, if the entire lithium metal layer is inserted into the pre-positive electrode active material layer during the rolling process, the lithium metal layer may not exist as a separate layer.

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

[0086] If the pressure during rolling is less than 10 kgf / cm, the lithium metal layer of the transfer laminate cannot be effectively transferred to the positive electrode during manufacturing, making it difficult to insert lithium into the positive electrode to the desired level. For example, if the pressure during rolling is less than 10 kgf / cm,

[0003] / I

[0200] This can be greater than 2.0. As a result, the amount of lithium transferred to the negative electrode during the activation process decreases, and lithium that does not diffuse into the active material layer but remains on the surface generates a large amount of lithium by-products, making it difficult to improve the battery's lifespan characteristics and potentially increasing the electrode resistance.

[0087] On the other hand, if the pressure during rolling exceeds 90 kgf / cm, the rate of lithium diffusion is too fast, which can cause excessive cracking of the positive electrode active material, thereby reducing the capacity of the positive electrode and potentially degrading the battery's lifespan. In this case as well, problems can arise such as an increase in damaged positive electrode active material, and the formation of a large amount of lithium byproducts due to a side reaction in which the Li2MO2 crystal decomposes into Li2O and MO, which reduces the capacity of the positive electrode and potentially degrades the battery's long-term lifespan. Furthermore, an increase in the rock salt phase can lead to problems of reduced capacity, increased resistance, and reduced lifespan. For example, if the pressure during rolling exceeds 90 kgf / cm,

[0003] / I

[0200] It can be less than 1.2.

[0088] (3) P3 step Referring to Figure 4, in step P3, after the rolling performed in step P2, the base film 310 can be removed from the transfer laminate to produce 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 makes it easier to remove the base film 310.

[0089] Furthermore, the method for manufacturing the positive electrode may further include a P4 step in which the pre-positive electrode is left to rest (stand) for 1 to 600 minutes, specifically 1 to 30 minutes. The P4 step may be performed after the P2 step. Specifically, the P4 step may be performed in at least one of the following steps: "between the P2 step and the P3 step" and "immediately after the P3 step". The P4 step effectively releases the reaction heat generated by the reaction between the lithium metal layer and the pre-positive electrode active material layer in the P2 step, resulting in uniform insertion of lithium into the positive electrode and a reduction in the generation of by-products.

[0090] Since the manufactured positive electrode is identical to the positive electrode in the embodiment described above, a detailed explanation is omitted.

[0091] In this embodiment, the positive electrode is manufactured by a transfer method, in which a lithium metal layer is placed on the positive electrode, and rolling is performed at a pressure of 10 kgf / cm to 90 kgf / cm, thereby inserting lithium ions from the lithium metal layer into the preliminary positive electrode active material layer. As a result, lithium-containing by-products such as Li3N are produced in the positive electrode, and the positive electrode becomes 1.2 ≤ I

[0003] / I

[0200] The condition ≤2.0 is satisfied. When a backup secondary battery is manufactured using a positive electrode manufactured by the above method and the backup secondary battery is activated, the lithium ions inserted in the positive electrode are transferred to the negative electrode, and the lithium ions react and fill the irreversible sites of the negative electrode. As a result, the amount of lithium ions inserted into the negative electrode when the battery is running can be appropriately reduced to the level necessary for battery operation. Therefore, the battery capacity can be maintained and the usable region of the negative electrode capacity can be reduced, excessive volume changes of silicon-based active material particles can be suppressed, and the battery life characteristics can be improved. One of the features of the present invention is that, instead of prelithiation being performed by bringing the lithium metal layer into contact with the negative electrode as is usually done, the lithium metal layer is transferred and rolled onto the positive electrode, and then the lithium ions inserted into the positive electrode are moved to the negative electrode during the battery activation process. That is, the negative electrode and the lithium metal layer do not come into contact, and lithium ions are not directly inserted into the negative electrode from the lithium metal layer. Therefore, the phenomenon of excessive heat generation due to the alloy reaction between lithium and silicon at the negative electrode can be avoided, and the possibility of ignition due to the reaction between lithium and water can be significantly reduced. Furthermore, when notching and punching are performed on the negative electrode, lithium ions are not inserted into the negative electrode (because it is not in a pre-lithiumized state), so the possibility of ignition during the notching and punching process can be significantly reduced.

[0092] Above all, 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 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. Further, excessive generation of lithium by-products is suppressed and the amount of lithium loss can be reduced, and the long-term life characteristics of the battery can be improved.

[0093] <Lithium-ion rechargeable 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 formula (1), 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 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 of the above-described embodiment, the description thereof 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 contain 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 contained in the lithium-ion secondary battery of this embodiment can satisfy the above formula 1, which is manufactured by the manufacturing method of the positive electrode of the above-described embodiment, and in particular, it means that lithium has been transferred to the positive electrode at an appropriate pressure level. Further, 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 manufacturing method of the positive electrode in the secondary battery and passing through the activation process, a predetermined lithium ion is transferred from the positive electrode to the silicon-based negative electrode active material of the negative electrode, and the 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. Further, 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. Further, when notchting and punching the negative electrode, since lithium ions are not inserted into the negative electrode (because pre-lithiation has not been performed), the possibility of ignition in the notchting and punching processes can also be significantly reduced.

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

[0101] The negative electrode active material layer may further contain a negative electrode binder. The negative electrode binder may contain at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which the hydrogen atoms of these are substituted with Li, Na, or Ca, and may also contain various copolymers thereof.

[0102] The negative electrode active material layer may further contain 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 is conductive, and for example, graphite such as natural graphite or 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; and conductive materials such as polyphenylene derivatives can be used.

[0103] As the separator, any material commonly used as a separator in secondary batteries to separate the negative and positive electrodes and provide a pathway for lithium ions can be used without particular limitations, and those with low resistance to ion movement of the electrolyte while having excellent electrolyte moisture absorption capacity are particularly preferred. Specifically, porous polymer films, such as porous polymer films made from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof can be used. Ordinary porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, coated separators containing ceramic components or polymeric substances can be used to ensure heat resistance or mechanical strength, and can be selectively used in single-layer or multi-layer structures.

[0104] Examples of the aforementioned electrolytes 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 may include a non-aqueous organic solvent and a metal salt.

[0106] As the non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidone, 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 pyropionate, 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 electrical 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 reduction of the battery capacity, improving the discharge capacity of the battery, etc.

[0110] <Manufacturing method for lithium-ion secondary batteries> A method for manufacturing a lithium-ion secondary battery according to one embodiment of the present invention includes a B1 step of manufacturing a preliminary lithium-ion secondary battery comprising 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, wherein the method for manufacturing the positive electrode includes a P1 step of arranging a transfer laminate comprising a base film and a lithium metal layer located on the base film on a preliminary positive electrode comprising a preliminary positive electrode active material layer to form a positive electrode structure such that the lithium metal layer and the preliminary positive electrode active material layer are in contact, a P2 step of rolling the positive electrode structure, and a P3 step of removing the base film from the transfer laminate after rolling, wherein the pressure applied to the positive electrode structure during rolling can be 10 kgf / cm to 90 kgf / cm.

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

[0112] The positive electrode is identical to the positive electrode in the above-described embodiment, and the method for manufacturing the positive electrode is the same as the method for manufacturing the positive electrode described above, so a description is omitted.

[0113] Since the aforementioned negative electrode is the same as the negative electrode in the embodiment described above, its explanation will be omitted.

[0114] In step B1, the reserve lithium-ion secondary battery may include a positive electrode and a negative electrode. Specifically, the reserve lithium-ion secondary battery may include a positive electrode, a negative electrode, a separator, and an electrolyte. Specifically, the positive electrode and the negative electrode may be stacked separated by a separator and impregnated with the electrolyte. The negative electrode before the activation process may be a reserve negative electrode, meaning that lithium ions have not yet been inserted. The reserve lithium-ion secondary battery means the battery before the activation process.

[0115] The method for manufacturing the positive electrode may further include a P4 step after the P2 step, in which the pre-positive electrode is left to rest (set to stand) for 1 to 600 minutes, specifically 1 to 30 minutes. The P4 step may be performed after the P2 step. Specifically, the P4 step may be performed in at least one of the following steps: "between the P2 step and the P3 step" and "immediately after the P3 step". The P4 step effectively releases the reaction heat generated by the reaction between the lithium metal layer and the pre-positive electrode active material layer in the P2 step, resulting in uniform insertion of lithium into the positive electrode and a reduction in by-product formation.

[0116] Step B2 may include applying current to the reserve lithium-ion secondary battery. The current can activate the reserve lithium-ion secondary battery, causing lithium ions to be inserted into the negative electrode and pre-lithiumizing the negative electrode.

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

[0118] Hereinafter, preferred embodiments are presented to facilitate understanding of the present invention. However, these embodiments are merely illustrative examples, and it will be obvious to those skilled in the art that various changes and modifications are possible within the scope of the present description and the technical concept. It goes without saying that such variations and modifications fall within the scope of the appended claims.

[0119] [Examples and Comparative Examples] Example 1-1: Manufacturing of a positive electrode A PET film (base film), a polymer layer made of PMMA (2.5 μm thick) disposed on the PET film, and a lithium metal layer made of solid-phase lithium metal (6 μm thick, 1.24 mAh / cm²) disposed on the polymer layer. 2 A transfer layer containing the loading amount was prepared.

[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 was Li[Ni 0.86 Co 0.05 Mn 0.08 Al 0.01 Multiple (10 or more) primary O2 particles combine with each other to form secondary particles, and the average particle size D of the secondary particles 50 The thickness was 9 μm. A positive electrode was prepared that included a preliminary positive electrode active material layer containing the positive electrode active material, PVdF as a positive electrode binder, and carbon nanotubes as a positive electrode conductive material in a weight ratio of 98:1:1, and aluminum foil (thickness: 12 μm) as the positive electrode current collector. The loading amount of the preliminary positive electrode active material layer was 4.5 mAh / cm². 2 The thickness was 140 μm.

[0121] The transfer laminate is placed in the pre-positive electrode active material layer so that the lithium metal layer and the pre-positive electrode active material layer are in contact.

[0122] Subsequently, the positive electrode on which the transfer laminate was placed was rolled using a roll press method, and then the positive electrode was left to stand for 24 hours. The pressure during the rolling was 20 kgf / cm. As a result, lithium ions from the lithium metal layer were inserted into the preliminary positive electrode active material layer, forming the positive electrode active material layer. Next, the base film was removed and left for 10 minutes to produce a positive electrode containing the positive electrode current collector, positive electrode active material layer, and polymer layer.

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

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

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

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

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

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

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

[0130] Comparative Example 1-4: Manufacturing of the negative electrode A PET film (base film), a polymer layer made of PMMA (1 μm thick) disposed on the PET film, and a lithium metal layer made of solid-phase lithium metal (3 μm thick, 0.6 mAh / cm²) disposed on the polymer layer. 2A transfer laminate containing the loading amount was prepared.

[0131] On the other hand, as the negative electrode active material, the average particle size D 50 Silicon particles with a diameter of 5 μm were used. A negative electrode was prepared containing a preliminary negative electrode active material layer containing the aforementioned negative electrode active material, carboxymethylcellulose (CMC) as a negative electrode binder, and carbon nanotubes as a negative electrode conductive material in a weight ratio of 80:10:10. The loading amount of the preliminary negative electrode active material layer was 10 mAh / cm². 2 The thickness was 75 μm.

[0132] The transfer laminate is placed in the pre-negative active material layer so that the lithium metal layer and the pre-negative active material layer are in contact.

[0133] Subsequently, the negative electrode on which the transfer laminate was placed was rolled using a roll-to-roll method, and then the negative electrode was left to stand for 24 hours. As a result, lithium ions from the lithium metal layer were inserted into the preliminary negative electrode active material layer, forming the negative electrode active material layer. The pressure during the rolling process was 50 kgf / cm.

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

[0135] Experimental Example 1:I

[0003] / I

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

[0003] / I

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

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

[0137] 1) Measurement equipment and conditions: Bruker D8 Endeavor (Cu target 40kV, 40mA, 1.54Å), LynxEye position sensitive detector (4.1° slit) 2) Experimental process 2-1) Prep. Cutting / Cross-section: Prepare test specimens by cutting the sample to the size of the sample holder.

[0138] 2-2) Prep. Sample Mounting: After firmly attaching the sample (positive electrode) to the glass plate using double-sided tape to prevent it from floating, 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 sample size, and measure the region from 2theta 10° to 125° for 0.0156° intervals for 0.3 seconds each.

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

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

[0142] Example 2-1: Manufacturing of a secondary battery As the negative electrode active material, the average particle size D 50 Silicon particles with a diameter of 5 μm were used. A negative electrode was prepared containing a preliminary negative electrode active material layer containing the aforementioned negative electrode active material, CMC as a negative electrode binder, and carbon nanotubes as a negative electrode conductive material in a weight ratio of 80:10:10. The loading amount of the preliminary negative electrode active material layer was 10 mAh / cm². 2 The thickness was 75 μm.

[0143] The positive electrode, negative electrode, and porous polyethylene separator of Example 1-1 were assembled using a winding method, and an electrolyte (ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 3 / 7 (volume ratio) and lithium hexafluorophosphate (LiPF 61 moles)) was injected into the assembled battery to produce a preliminary lithium-ion secondary battery.

[0144] The aforementioned spare lithium-ion secondary battery was charged at 4.2V with a C-rate of 0.1C, and then discharged to 2.5V to perform an activation process.

[0145] Example 2-2: Manufacturing of a 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 a 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 a 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] Examples 2-5: Manufacturing of a 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 a 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 a 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 Batteries 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 Batteries 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 Li[Ni 0.86 Co 0.05 Mn 0.08 Al 0.01 Multiple (10 or more) primary O2 particles are bonded together to form secondary particles, and the average particle size of the secondary particles is D 50 The thickness was 9 μm. A cathode was prepared in which a preliminary cathode active material layer containing the cathode active material, PVdF as a cathode binder, and carbon nanotubes as a cathode conductive material in a weight ratio of 98:1:1 was placed on aluminum foil (thickness: 12 μm). The loading amount of the preliminary cathode active material layer was 4.5 mAh / cm². 2 The thickness was 140 μm.

[0153] The negative electrode, positive electrode, and porous polyethylene separator of Comparative Examples 1-4 were assembled using a winding method, and an electrolyte (ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 1 / 2 (volume ratio) and lithium hexafluorophosphate (LiPF 61 mol)) was injected into the assembled battery to produce a lithium-ion secondary battery.

[0154] Experimental Example 2: Measurement of Lithium Loss The amount of lithium loss was measured for the lithium-ion secondary batteries of Examples 2-1 to 2-5 and Comparative Examples 2-1 to 2-4, and is shown in Table 1.

[0155] First, as a control group, the initial charge capacity of a cathode without lithium ions transferred and inserted (the spare cathode used in Example 1-1) and the initial charge capacity of the cathode in Example 2-1 were measured under the following conditions.

[0156] After CC / CV charging up to 0.1C and 4.2V, the voltage cuts off at 0.05C. CC discharge up to 0.1C and 2.3V The theoretical capacity of the lithium metal layer used in the experiment was 1 mAh / cm². 2 That was the case.

[0157] The amount of lithium loss was calculated using the following formula.

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

[0159] This method was carried out in exactly the same way for the remaining examples and comparative examples 2-1 to 2-3.

[0160] For Comparative Examples 2-4, the amount of lithium loss was measured for the negative electrode using the method described above.

[0161] Experimental Example 3: Evaluation of Lifetime Characteristics (Capacity Retention Rate) The lithium-ion secondary batteries of Examples 2-1 to 2-5 and Comparative Examples 2-1 to 2-4 were subjected to charging and discharging, and their life characteristics (capacity retention rate) were evaluated.

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

[0163] Capacity retention rate (%) = (Discharge capacity for 100 cycles / Discharge capacity for 1 cycle) × 100

[0164] [Table 1]

[0165] Referring to Table 1 above, in the example where rolling was performed at a pressure that satisfies the range of 10 kgf / cm to 90 kgf / cm, I

[0003] / I

[0200] It was found that the range of 1.2 to 2.0 was satisfied, resulting in low lithium loss and high capacity retention. This indicates that stability and process advantages are ensured, and superior effects can be expected compared to Comparative Example 2-4, in which pre-lithification was directly applied to the negative electrode. On the other hand, in Comparative Example 2-1, where a rolling pressure of 5 kgf / cm was applied, it was found that relatively less rock salt phase was formed compared to the example. However, it was confirmed that the amount of lithium loss doubled due to the generation of a large amount of lithium by-products, and as a result, the lifetime characteristics also deteriorated. Furthermore, in Comparative Examples 2-2 and 2-3, where a rolling pressure exceeding 90 kgf / cm was applied, a large amount of lithium loss was shown. This is due to the cracking phenomenon of the positive electrode active material particles and the decomposition of the Li2MO2 phase due to overlithiation.

[0003] / I

[0200] This can be seen from the fact that the value is smaller than 1.2, which indicates that the lifetime characteristics have also decreased. [Explanation of Symbols]

[0166] 110 Positive electrode current collector 120, 120' Pre-existing positive electrode active material layer 300 Transfer Layers 310 Base film 320 Lithium metal layer 330 Polymer layer 400 Positive Electrode Structure R Roll

Claims

1. It includes a positive electrode active material layer containing positive electrode active material, The following equation 1 is satisfied, The positive electrode active material layer is Li ３ N, Li ２ CO ３ A positive electrode comprising at least one selected from the group consisting of , and LiOH. [Formula 1] 1.2≦I ［００３］ / I ［２００］ ≦2.0 In formula 1, the I ［００３］ This is the integral value of the maximum peak that appears in the region where 2θ is 17.0° to 19.0° when XRD measurement is performed on the surface of the positive electrode active material layer. The above I ［２００］ This is the integral value of the maximum peak that appears in the region where 2θ is 43° to 45° when XRD measurement is performed on the surface of the positive electrode active material layer.

2. The positive electrode according to claim 1, wherein the positive electrode active material comprises a layered lithium nickel-based transition metal composite oxide, and the lithium nickel-based transition metal composite oxide comprises a compound of 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 aforementioned chemical formula 1, 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, 0.6 ≤ a < 1, 0.03 ≤ b ≤ 0.1, 0.03 ≤ c ≤ 0.1, 0 ≤ d ≤ 0.1, and 0 < a + b + c ≤ 1 are satisfied.

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

4. The positive electrode according to claim 1, wherein the positive electrode active material comprises 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.

5. The positive electrode according to any one of claims 1 to 4, wherein the positive electrode further comprises at least one layer among a lithium metal layer and a polymer layer located on the positive electrode active material layer.

6. Step P1 involves arranging a transfer laminate, which includes a base film and a lithium metal layer located on the base film, on a pre-positive electrode including a pre-positive electrode active material layer, to form a positive electrode structure such that the lithium metal layer and the pre-positive electrode active material layer are in contact. Step P2 involves rolling the positive electrode structure, The process includes step P3 of removing the base film from the transfer laminate after the rolling, A method for manufacturing a positive electrode, wherein the pressure applied to the positive electrode structure during rolling is 10 kgf / cm or more and 90 kgf / cm or less, The positive electrode is, It includes a positive electrode active material layer containing positive electrode active material, The following equation 1 is satisfied, The positive electrode active material layer is Li ３ N, Li ２ CO ３ A method for manufacturing a positive electrode, comprising at least one selected from the group consisting of , and LiOH. [Formula 1] 1.2≦I ［００３］ / I ［２００］ ≦2.0 In formula 1, the I ［００３］ This is the integral value of the maximum peak that appears in the region where 2θ is 17.0° to 19.0° when XRD measurement is performed on the surface of the positive electrode active material layer. The above I ［２００］ This is the integral value of the maximum peak that appears in the region where 2θ is 43° to 45° when XRD measurement is performed on the surface of the positive electrode active material layer.

7. In step P2, The method for manufacturing a positive electrode according to claim 6, wherein the rolling is performed by a roll-press method.

8. The method for manufacturing a positive electrode according to claim 6, wherein the thickness of the lithium metal layer is 1 μm or more and 10 μm or less.

9. The method for manufacturing a positive electrode according to claim 6, 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.

10. The transfer laminate further comprises a polymer layer, The method for manufacturing a positive electrode according to any one of claims 6 to 9, wherein the polymer layer is located between the base film and the lithium metal layer.

11. The method for producing a positive electrode according to claim 10, wherein the polymer layer comprises at least one selected from the group consisting of polyethylene terephthalate, polyimide, polymethyl methacrylic acid, polypropylene, polyethylene, and polycarbonate.

12. It includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte. The positive electrode includes a positive electrode active material layer containing a positive electrode active material, The following equation 1 is satisfied, The positive electrode active material layer is Li ３ N, Li ２ CO ３ A lithium secondary battery comprising at least one selected from the group consisting of , and LiOH. [Formula 1] 1.2≦I ［００３］ / I ［２００］ ≦2.0 In formula 1, the I ［００３］ This is the integral value of the maximum peak that appears in the region where 2θ is 17.0° to 19.0° when XRD measurement is performed on the surface of the positive electrode active material layer. The above I ［２００］ This is the integral value of the maximum peak that appears in the region where 2θ is 43° to 45° when XRD measurement is performed on the surface of the positive electrode active material layer.

13. The aforementioned negative electrode includes a negative electrode active material layer, The lithium secondary battery according to claim 12, wherein the negative electrode active material layer includes a silicon-based negative electrode active material.

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

Images