Lithium secondary battery and method for manufacturing the same

Abstract

The present invention relates to a lithium secondary battery and a method for manufacturing the lithium secondary battery, the lithium secondary battery including: a positive electrode including a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector; a negative electrode including a negative electrode current collector, a negative electrode active material layer disposed on the negative electrode current collector, and a solid electrolyte film disposed on the negative electrode active material layer; a separator disposed between the positive electrode and the negative electrode; and the electrolyte, wherein the value A according to the following formula 1 can be 10% or more. [Formula 1] A = {(F+C) / (F+C+G+M+E)} x 100 The F and C are the contents of fluoride groups (unit: μg / cm ) confirmed by performing capillary electrophoresis (CE) analysis on the solid electrolyte membrane. 2 ) and carbonate group content (unit: μg / cm 2 ), and G, M, and E are the contents of ethylene glycol groups (unit: μg / cm ) confirmed by subjecting the solid electrolyte membrane to nuclear magnetic resonance (NMR) spectroscopy. 2 ), methyl group content (unit: μg / cm 2 ), and ethyl group content (unit: μg / cm 2 )

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0106403, filed on August 24, 2022, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a lithium secondary battery and a method for manufacturing the lithium secondary battery, and relates to technical features such as the composition of a solid electrolyte film disposed on the surface of a negative electrode, the transfer of a lithium metal layer to a positive electrode, and charging at a specific current rate during an activation process. [Background technology]

[0003] With the rapid increase in the use of fossil fuels, there is an increasing need for alternative and clean energy, and as part of this, the most actively researched field is the field of power generation and storage using electrochemical reactions.

[0004] Currently, secondary batteries are a typical example of electrochemical elements that use such electrochemical energy, and their range of use is gradually expanding. Recently, with the increasing technological development and demand for portable devices such as portable computers, mobile phones, and cameras, the demand for ion secondary batteries as energy sources has rapidly increased. Among such secondary batteries, various studies have been conducted on high-energy density, i.e., high-capacity ion lithium secondary batteries, and they have been commercialized and widely used.

[0005] Generally, a lithium secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode contains a negative electrode active material that inserts and extracts lithium ions from the positive electrode. Silicon-based active material particles with a large discharge capacity can be used as the negative electrode active material. The silicon-based active material particles are made of Si or SiO XIt can correspond to, for example, (0 < X < 2). Silicon-based active material particles have the advantages of a large theoretical capacity and low cost. However, silicon-based active material particles have the drawback 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 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 in advance into the negative electrode containing silicon-based active material particles 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 battery operation, the amount of lithium ions inserted can be suitably reduced to the level required for battery operation, and the volume change of the silicon-based active material particles can be minimized.

[0007] However, during the process of 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. Also, during 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. There is also a possibility of ignition by the silicon-based active material particles subjected to prelithiation.

[0008] Therefore, there is a need for a new technology that can insert lithium ions in advance into the negative electrode before battery operation to improve the battery life and suppress the possibility of excessive heat generation and ignition. Summary of the Invention Problems to be Solved by the Invention

[0009] An object of the present invention is to provide a lithium secondary battery having improved life characteristics and stability, and low resistance.

[0010] Another object of the present invention is to provide a method for manufacturing the lithium secondary battery. [Means for solving the problem]

[0011] According to one embodiment of the present invention, there is provided a lithium secondary battery including: a positive electrode including a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector; a negative electrode including a negative electrode current collector, a negative electrode active material layer disposed on the negative electrode current collector, and a solid electrolyte film disposed on the negative electrode active material layer; a separator disposed between the positive electrode and the negative electrode; and the electrolyte, wherein the value A according to the following formula 1 is 10% or more. [Formula 1] A = {(F+C) / (F+C+G+M+E)} x 100 The F and C are the contents of fluoride groups (unit: μg / cm ) confirmed by performing capillary electrophoresis (CE) analysis on the solid electrolyte membrane. 2 ) and carbonate group content (unit: μg / cm 2 ), and G, M, and E are the contents of ethylene glycol groups (unit: μg / cm ) confirmed by subjecting the solid electrolyte membrane to nuclear magnetic resonance (NMR) spectroscopy. 2 ), methyl group content (unit: μg / cm 2 ), and ethyl group content (unit: μg / cm 2 )

[0012] According to another embodiment of the present invention, a method for manufacturing the positive electrode includes a step B1 of preparing a spare lithium secondary battery including a positive electrode including a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, a negative electrode including a negative electrode including a negative electrode current collector, a negative electrode active material layer disposed on the negative electrode current collector, and a solid electrolyte film disposed on the negative electrode active material layer, a separator disposed between the positive electrode and the negative electrode, and the electrolyte, and a step B2 of activating the spare lithium secondary battery. a step P1 of placing a transfer laminate including a lithium metal layer on a spare positive electrode including a spare positive electrode active material layer to form a positive electrode structure so that the lithium metal layer and the spare positive electrode active material layer are in contact with each other; a step P2 of rolling the positive electrode structure; and a step P3 of removing the substrate film from the transfer laminate after rolling to form a positive electrode, wherein the step B2 includes applying a current to the spare lithium secondary battery at a current rate of 0.1 C to 1.0 C to charge the spare lithium secondary battery. [Effects of the Invention]

[0013] In the positive electrode according to the present invention, a lithium metal layer is disposed 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. A spare lithium secondary battery is manufactured using the positive electrode manufactured by the above method. When the spare lithium 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 a level required for battery operation. This allows the usable capacity of the negative electrode to be reduced while maintaining the battery capacity, and prevents excessive volumetric change of silicon-based active material particles, thereby improving the battery's lifespan.

[0014] In addition, rather than performing pre-lithiation by contacting a lithium metal layer with the negative electrode, a lithium metal layer is transferred and rolled onto the positive electrode, and then the lithium ions inserted into the positive electrode are transferred to the negative electrode during the battery activation process, which avoids the phenomenon of excessive heat generation due to an alloy reaction between lithium and silicon in the negative electrode and significantly reduces the possibility of fire due to a reaction between lithium and moisture. Furthermore, because lithium ions are not inserted into the negative electrode when notching and punching are performed on the negative electrode (because it is not in a pre-lithiation state), the possibility of fire during the notching and punching process can also be significantly reduced.

[0015] In particular, in the present invention, the current rate applied during charging in the activation process is adjusted to an appropriate level, thereby minimizing cracking of the negative electrode active material particles. Furthermore, because the current rate applied during charging is adjusted to an appropriate level, the ratio of fluoride groups and carbonate groups in the solid electrolyte membrane can be increased. As a result, the structural stability of the negative electrode can be maintained despite a large volume change in the negative electrode active material particles, and the solid electrolyte membrane is not thick, thereby suppressing an increase in battery resistance. This improves the initial capacity and lifespan characteristics of the battery. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 2 is a schematic diagram showing step P1 in the method for producing a positive electrode according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing a P1 step using a transfer laminate including a polymer layer in a method for producing a positive electrode according to one embodiment of the present invention. [Figure 3] FIG. 2 is a schematic diagram showing step P2 in the method for producing a positive electrode according to one embodiment of the present invention. [Figure 4] FIG. 2 is a schematic diagram showing step P3 in a method for producing a positive electrode according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will now be described in more detail to facilitate understanding of the present invention.

[0018] The terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as having meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0019] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise.

[0020] In this specification, the terms "comprises," "includes," "has," and the like are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but are not intended to preclude the possible presence or addition of one or more different features, numbers, steps, components, or combinations thereof.

[0021] Herein, D 50 can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. 50 can be measured using, for example, a laser diffraction method. The laser diffraction method generally enables measurement of particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0022] In this specification, the XRD measurement is carried out as follows.

[0023] The X-ray wavelength used was Cu Kα, and the wavelength (λ) of the light source was 0.15406 nm.

[0024] 1) Measurement equipment and conditions: Bruker D8 Endeavor (Cu target 40 kV, 40 mA, 1.54 Å) LynxEye position sensitive detector (4.1° slit)

[0025] 2) Experimental process 2-1) Prep. Cutting / Cross-section: The sample is cut to the size of the sample holder to prepare a test piece. 2-2) Prep. Sample Mounting: The sample (positive electrode) is firmly attached to a glass plate using double-sided tape so that it does not float, and then mounted using a holder made of PMMA and rubber clay. 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 2θ10° to 125° every 0.0156° for 0.3 seconds. 2-4) XRD Phase Analysis: Identify the phases present in the sample by comparing with a database (PDF). 2-5) Rietveld Analysis: A complete structural model of the phases present in the sample is used to perform Rietveld refinement.

[0026] In this specification, the measurement conditions for laser-induced breakdown spectroscopy (LIBS) analysis are as follows. LIBS was performed using Applied Spectra's J200 (Tandem-LA-LIBS). After that, measurements were performed under the following conditions when the equipment temperature was -20°C.

[0027] -Laser Power: 20% -Spot size: 150μm -Shot number: 15 shots -Spot number: 6×6 -Gate delay: 1μsec -Rep rate: 5Hz -Analytical mode:Mapping & Depth profiling experiment

[0028] In this specification, the content of ethylene glycol groups, the content of ethyl groups, and the content of methyl groups in the solid electrolyte membrane are respectively defined as follows: 1 The peak integral value of the functional group measured by H-NMR analysis was confirmed, taking into account the molecular weights of ethylene glycol, ethanol, and methanol. 1 H-NMR analysis was performed using a 500 MHz spectrometer manufactured by Varian. 1 This is done using H-NMR.

[0029] In this specification, the content of fluoride groups and carbonate groups were confirmed by capillary electrophoresis (CE) analysis. Specifically, the analysis was performed after running an instrument (MDQ Plus manufactured by AB SCIEX). Here, CO2 in the atmosphere was absorbed with MeOD (methanol d4) extraction solution to obtain CO3. 2- Because of the phenomenon of increased fluoride group content, the sample was stored in a glove box (G / B) and then released into the atmosphere before analysis. The fluoride group content and carbonate group content were calculated from the measured CE area.

[0030] The aforementioned 1 The samples used for H-NMR and the CE analysis were prepared as follows. The lithium secondary battery manufactured after activation was fully charged, and then the first discharge was performed by discharging from 4.2 V to 2.5 V. Then, only the negative electrode was separated and washed with dimethyl carbonate (DMC). The solid electrolyte membrane extracted from the negative electrode was dissolved in MeOD (methanol d4) and then 1The sample was used for H-NMR measurement, and then redissolved in deuterium oxide and used for CE analysis.

[0031] <Lithium secondary battery> A lithium secondary battery according to one embodiment of the present invention includes a positive electrode including a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, a negative electrode including a negative electrode current collector, a negative electrode active material layer disposed on the negative electrode current collector, and a solid electrolyte film disposed on the negative electrode active material layer, a separator disposed between the positive electrode and the negative electrode, and the electrolyte, and the value A according to the following formula 1 may be 10% or more.

[0032] [Formula 1] A = {(F+C) / (F+C+G+M+E)} x 100

[0033] The F and C are the contents of fluoride groups (unit: μg / cm ) confirmed by capillary electrophoresis analysis of the solid electrolyte membrane. 2 ) and carbonate group content (unit: μg / cm 2 ), and G, M, and E are the contents of ethylene glycol groups (unit: μg / cm ) confirmed by subjecting the solid electrolyte membrane to nuclear magnetic resonance (NMR) spectroscopy. 2 ), methyl group content (unit: μg / cm 2 ), and ethyl group content (unit: μg / cm 2 )

[0034] (1) Positive electrode The positive electrode may include a positive electrode active material layer. The positive electrode active material layer may constitute a positive electrode by itself, or the positive electrode active material layer may be located on a positive electrode current collector.

[0035] 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 bodies, etc.

[0036] 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.

[0037] The positive electrode active material is a particulate substance 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 2Lithium nickel-based oxides represented by the formula (y) may be at least one selected from Co, Mn, Al, Cu, Fe, Mg, B, Cr, Zn, and Ga, and 0.01≦y≦0.7; 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, and 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, and -0.5≦z≦0.5, 0≦q≦0.5, 0≦r≦0.1.

[0038] 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 a compound represented by the following Chemical Formula 1, more specifically, a compound represented by the following Chemical Formula 1:

[0039] [Chemical formula 1] Li 1+x [Ni a Co b Mn c M 1 (1-a-b-c) ]O (2-d) A d

[0040] In the above Chemical Formula 1, 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.

[0041] A is at least one selected from the group consisting of F, P, and Cl, and specifically can be F.

[0042] The said x can satisfy -0.5 ≦ x ≦ 0.5, specifically -0.3 ≦ x ≦ 0.3.

[0043] The said a can satisfy 0.6 ≦ a < 1, specifically 0.7 ≦ a ≦ 0.9.

[0044] The said b can satisfy 0.03 ≦ b ≦ 0.1, specifically 0.05 ≦ b ≦ 0.1.

[0045] The said c can satisfy 0.03 ≦ c ≦ 0.1, specifically 0.05 ≦ c ≦ 0.1.

[0046] The said d can satisfy 0 ≦ d ≦ 0.1, specifically 0 ≦ d ≦ 0.05.

[0047] The said a, b, c satisfy 0 < a + b + c ≦ 1, specifically a + b + c = 1.

[0048] The said layered lithium nickel-based transition metal composite oxide can be in particle form.

[0049] The said 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.

[0050] The D of the said layered lithium nickel-based transition metal composite oxide 50 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. When the above range is satisfied, the positive electrode slurry dispersion is easy and a uniform coating of the positive electrode active material layer is possible.

[0051] The positive electrode active material may be contained in the positive electrode active material layer in an amount of 90% by weight to 99% by weight, specifically 92% by weight to 99% by weight, and more specifically 95% by weight to 98.5% by weight.

[0052] The positive electrode active material layer may further include a positive electrode binder. The positive electrode binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples of the positive electrode binder 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, and various copolymers thereof. These binders may be used alone or in combination.

[0053] The positive electrode binder may be included in the positive electrode active material layer in an amount of 0.5 wt % to 5.0 wt %, specifically 1.0 wt % to 2.5 wt %, and more specifically 1.0 wt % to 2.0 wt %.

[0054] The positive electrode active material layer may further include a positive electrode conductive material. The positive electrode conductive material is used to impart conductivity to the electrode. Any material may be used without particular limitation as long as it does not cause chemical changes in the resulting battery and has electronic conductivity. 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 powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These materials may be used alone or in combination.

[0055] The positive electrode conductive material may be included in the positive electrode active material layer in an amount of 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 %.

[0056] The positive electrode active material layer may further include a lithium by-product, which corresponds to a by-product formed when a lithium metal layer is transferred 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 include any one selected from the group consisting of LiN, LiCO, and LiOH.

[0057] The positive electrode can satisfy the following formula 3.

[0058] [Formula 3] 1.2≦I

[0003] / I

[0200] ≦2.0

[0059] In the formula 1,

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

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

[0060] Specifically, the range of 2θ in which the maximum peak appears may be 17.5° to 18.5°, or 17.5° to 18.2°.

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

[0061] In addition, I of Formula 1 according to one embodiment of the present invention

[0003] / I

[0200] is preferably 1.21 or more, 1.22 or more, 1.23 or more, or 1.24 or more, and is preferably 1.80 or less, 1.70 or less, 1.65 or less, 1.60 or less, or 1.58 or less.

[0062] When the above range is satisfied, a sufficient amount of lithium can be supplied to the negative electrode during the activation process, improving the battery life characteristics, and the amount of lithium by-products in the positive electrode is small, resulting in good positive electrode capacity and long-term battery life characteristics.

[0063] The positive electrode may further include a lithium metal layer positioned 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 positioned 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 may include solid-phase lithium metal, specifically, the lithium metal layer may be made of solid-phase lithium metal.

[0064] The positive electrode may further include a polymer layer positioned on the positive electrode active material layer. The polymer layer may facilitate effective peeling of the lithium metal layer from a transfer laminate during fabrication of the positive electrode, allowing the lithium metal layer to be easily transferred to the positive electrode active material layer. That is, the polymer layer may be positioned on the positive electrode active material layer, separate from the transfer laminate along with the lithium metal layer. The polymer layer may be in contact with the positive electrode active material layer, or alternatively, a lithium metal layer may be present between the polymer layer and the positive electrode active material layer.

[0065] The polymer layer may be at least one selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), poly(methylmethacrylate) (PMMA), polypropylene, polyethylene, and polycarbonate. As a result, in a secondary battery including the positive electrode, the polymer layer can be dissolved in an electrolyte solution contained in the secondary battery, preventing an increase in the resistance of the battery. In particular, the polymer layer may include PMMA, in which case the above-mentioned effects can be further improved.

[0066] In the positive electrode, the porosity of the positive electrode active material layer may be 10% to 40%, specifically 15% to 35%, and more specifically 25% to 30%. In this case, it is possible that no further change in thickness occurs during rolling. The porosity can be confirmed by measuring the apparent density and true density of the positive electrode active material layer.

[0067] The loading amount of the positive electrode active material layer is 3 mAh / cm 2 ~5.5mAh / cm 2 Specifically, 4 mAh / cm 2 ~5mAh / cm 2 It can be.

[0068] (2) Negative electrode The negative electrode can include a negative electrode current collector, a negative electrode active material layer disposed on the negative electrode current collector, and a solid electrolyte membrane (SEI) disposed on the negative electrode active material layer.

[0069] The negative electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those surface-treated with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. can be used. Also, the negative electrode current collector can usually have a thickness of 3 μm to 500 μm, and similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the binding force of the negative electrode active material. For example, it can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, non-woven fabrics, etc.

[0070] The negative electrode active material layer can be disposed on one or both sides of the negative electrode current collector. The negative electrode active material layer can contain negative electrode active material particles.

[0071] The negative electrode active material particles can include silicon-based negative electrode active material particles. The silicon-based negative electrode active material particles can include at least one of Si and SiO x (0 < X < 2).

[0072] The Si is silicon particles, and can be silicon particles (particles made of silicon) called so-called pure silicon (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 are the SiOx When including (0 < X < 2), the discharge capacity of the secondary battery can be improved.

[0073] When passing through the activation process in the process of manufacturing the lithium secondary battery of the present invention, a predetermined lithium ion is transmitted 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 particles during the driving of the battery 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, the 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, 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 notch and punching are performed on the negative electrode, since lithium ions are not inserted into the negative electrode (because pre-lithiation is not performed), the possibility of ignition in the notch and punching processes can also be significantly reduced. That is, in the present invention, it is more significant when the negative electrode active material particles include silicon-based active material particles.

[0074] 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.

[0075] The negative electrode active material can be contained in the negative electrode active material layer at 70% to 98% by weight, specifically 80% to 90% by weight.

[0076] The negative electrode active material layer may further include a negative electrode binder. The negative electrode binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, 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 hydrogen is substituted with Li, Na, Ca, or the like, or may include various copolymers thereof.

[0077] The negative electrode binder may be included in the negative electrode active material layer in an amount of 5% by weight to 30% by weight, specifically 10% by weight to 20% by weight.

[0078] The negative electrode active material layer may 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, and examples thereof include 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; and conductive materials such as polyphenylene derivatives.

[0079] The negative electrode conductive material may be contained in the negative electrode active material layer in an amount of 1% by weight to 15% by weight, specifically 5% by weight to 10% by weight.

[0080] The porosity of the negative electrode active material layer may be 30% to 50%, specifically 35% to 48%. In this case, despite a large volume change of the negative electrode active material, the structure of the negative electrode can be maintained, and lithium transferred from the positive electrode can be effectively inserted. The porosity can be confirmed by measuring the apparent density and true density of the negative electrode active material layer.

[0081] The loading amount of the negative electrode active material layer is 7 mAh / cm 2 ~14mAh / cm 2 Specifically, it can be 7.5 mAh / cm 2 ~11.9mAh / cm 2 It can be.

[0082] The solid electrolyte membrane may be disposed on the negative electrode active material layer. Specifically, the negative electrode active material layer may be disposed between the solid electrolyte membrane and the negative electrode current collector. The solid electrolyte membrane suppresses excessive decomposition reaction of the electrolyte and allows lithium ions to pass through but not electrons, thereby ensuring smooth battery operation.

[0083] The solid electrolyte membrane can include organic and inorganic components.

[0084] The organic component may include a compound of Formula 1 below.

[0085] [ka]

[0086] In the above Chemical Formula 1, R may be at least one selected from an alkyl group having 1 to 4 carbon atoms and an alkylene glycol group having 1 to 4 carbon atoms. Specifically, R may be at least one selected from the group consisting of a methyl group, an ethyl group, and an ethylene glycol group.

[0087] The inorganic component may include at least one selected from the group consisting of LiF and Li2CO3.

[0088] (3) Separator The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without particular limitations. In particular, a separator that exhibits low resistance to electrolyte ion movement and excellent electrolyte humidification capability is preferred. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material can also be used, and can be used in a single-layer or multi-layer structure.

[0089] (4) Electrolyte 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 manufacturing lithium secondary batteries.

[0090] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0091] Examples of the non-aqueous organic solvent that can be used 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, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0092] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are preferred because they are high-viscosity organic solvents with high dielectric constants and can dissociate lithium salts well. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte having high electrical conductivity can be produced, and thus such a mixture is more preferred.

[0093] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, the anion of the lithium salt may be 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:

[0094] 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, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing a decrease in the capacity of the battery, and improving the discharge capacity of the battery.

[0095] In the lithium secondary battery, the value A according to the following formula 1 can be 10% or more, specifically 10% to 20%, more specifically 11% to 15%, for example, 13.5% to 15%.

[0096] [Formula 1] A = {(F+C) / (F+C+G+M+E)} x 100

[0097] The F and C are the contents of fluoride groups (unit: μg / cm ) confirmed by capillary electrophoresis analysis of the solid electrolyte membrane. 2) and carbonate group content (unit: μg / cm 2 ) and The G, M, and E are the contents of ethylene glycol groups (unit: μg / cm ) confirmed by subjecting the solid electrolyte membrane to nuclear magnetic resonance (NMR) spectroscopy. 2 ), methyl group content (unit: μg / cm 2 ), and ethyl group content (unit: μg / cm 2 )

[0098] If the A value is less than 10%, the solid electrolyte membrane cannot effectively suppress excessive volume expansion of the negative electrode active material particles, which may result in further lithium side reactions and a decrease in the initial capacity of the battery.

[0099] In the process of manufacturing the lithium secondary battery of the present invention, when the current rate of the current applied during charging is adjusted to 0.1 C to 1.0 C, the phenomenon of cracking of negative electrode active material particles due to lithium ions transferred from the positive electrode to the negative electrode active material layer can be minimized. As a result, the solid electrolyte film formed on the negative electrode active material layer may contain more inorganic components such as LiF and Li2CO3 than organic components such as the compound of Formula 1, and the A value in Formula 1 may be 10% or more. As a result, the solid electrolyte film may be formed firmly, damage to the negative electrode active material layer may be effectively prevented, and further side reactions of the electrolyte may be effectively suppressed.

[0100] The lithium secondary battery may have an L value according to the following formula 2 of 45% or more, specifically 45% to 80%, more specifically 55% to 70%, for example, 63% to 68%.

[0101] [Formula 2] L=L2 / L1

[0102] L1 and L2 are integrals of the lithium peak in a graph obtained by laser-induced breakdown spectroscopy (LIBS), The L1 is measured at the interface between the negative electrode active material layer and the negative electrode current collector, The L2 is measured at a point 20% of the thickness of the negative electrode active material layer from the interface between the negative electrode active material layer and the solid electrolyte membrane in the thickness direction of the negative electrode active material layer.

[0103] During the activation process, a current is applied at an appropriate current rate, and lithium ions are uniformly distributed within the negative electrode active material layer, so that the value A in Equation 1 is satisfied and the value L is 45% or greater. This allows a solid electrolyte film to be uniformly formed on the negative electrode active material layer, reducing the formation of lithium by-products within the negative electrode and improving the initial capacity and lifespan characteristics of the battery.

[0104] <Method of manufacturing lithium secondary batteries> A method for manufacturing a lithium secondary battery according to another embodiment of the present invention includes a step B1 of preparing a spare lithium secondary battery including a positive electrode including a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, a negative electrode including a negative electrode including a negative electrode current collector, a negative electrode active material layer disposed on the negative electrode current collector, and a solid electrolyte film disposed on the negative electrode active material layer, a separator disposed between the positive electrode and the negative electrode, and the electrolyte; and a step B2 of activating the spare lithium secondary battery, wherein the method for manufacturing the positive electrode includes a step B2 of activating the spare lithium secondary battery, wherein the method for manufacturing the lithium secondary battery includes a step B3 of activating the spare lithium secondary battery, and a step B4 of activating the spare lithium secondary battery. The method includes a step P1 of placing a transfer laminate including a lithium metal layer positioned on a film on a spare cathode including a spare cathode active material layer to form a cathode structure such that the lithium metal layer and the spare cathode active material layer are in contact with each other, a step P2 of rolling the cathode structure, and a step P3 of removing the substrate film from the transfer laminate after the rolling to manufacture a cathode, and the step B2 may include applying a current to the spare lithium secondary battery at a current rate of 0.1 C to 1.0 C to charge the spare lithium secondary battery.

[0105] The positive electrode, the negative electrode, the separator, and the electrolyte are the same as those in the above-described embodiment, and therefore description thereof will be omitted.

[0106] (1) B1 Step In step B1, the spare lithium secondary battery may include a positive electrode and a negative electrode. Specifically, the spare lithium 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 with a separator therebetween and may be impregnated with the electrolyte. The negative electrode before the activation process may be a spare negative electrode, meaning that lithium ions have not yet been inserted. The spare lithium secondary battery refers to a battery before the activation process.

[0107] 1) P1 step 1, the transfer laminate 300 may include a substrate film 310 and a lithium metal layer 320 disposed on the substrate film 310. The substrate film 310 may be made of any material that can withstand the high temperature conditions that occur during the deposition of the lithium metal layer 320 on the substrate film 310. Specifically, the substrate film may include at least one material selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), poly(methylmethacrylate) (PMMA), polypropylene, polyethylene, and polycarbonate.

[0108] The lithium metal layer may be located on the substrate film. The lithium metal layer may serve to supply lithium ions to the spare positive electrode active material layer. The lithium metal layer may include solid-phase lithium metal, and more specifically, the lithium metal layer may be composed of solid-phase lithium metal.

[0109] In the transfer laminate, the lithium metal layer may have a thickness of 1 μm to 10 μm, specifically 3 μm to 9 μm, and more specifically 4 μm to 6.5 μm. When the thickness is within this range, the degree of cracking of the positive electrode active material particles on the surface of the positive electrode can be reduced, and a decrease in the initial capacity of the battery can be suppressed.

[0110] The loading amount of the lithium metal layer (unit: mAh / cm 2 ) is the loading amount (unit: mAh / cm 2 ) can be 4% to 40%, specifically 12% to 35%, 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.

[0111] In step P1, referring to FIG. 1 , the preliminary positive electrode active material layer 120′ is positioned on the preliminary positive electrode current collector 110, and the transfer laminate 300 is disposed on the preliminary positive electrode active material layer 120′, so that the lithium metal layer 320 and the preliminary positive electrode active material layer are in contact with each other to form a positive electrode structure 400.

[0112] Here, the positive electrode current collector 110 is the same as the positive electrode current collector described in the above embodiment relating to the positive electrode.

[0113] Meanwhile, referring to FIG. 2 , the transfer laminate 300 may further include a polymer layer 330. The polymer layer 330 may be located between the substrate film 310 and the lithium metal layer 320. The polymer layer may facilitate the lithium metal layer being effectively peeled from the transfer laminate and easily transferred to the positive electrode active material layer during the manufacture of the positive electrode. That is, the polymer layer may be located on the positive electrode active material layer, separate from the transfer laminate along with the lithium metal layer. The polymer layer may be in contact with the positive electrode active material layer, or alternatively, a lithium metal layer may be located between the polymer layer and the positive electrode active material layer.

[0114] The polymer layer may be at least one selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), poly(methylmethacrylate) (PMMA), polypropylene, polyethylene, and polycarbonate. As a result, in a secondary battery including the positive electrode, the polymer layer can be dissolved in an electrolyte solution contained in the secondary battery, preventing an increase in the resistance of the battery. In particular, the polymer layer may include PMMA, in which case the above-mentioned effects can be further improved.

[0115] The thickness of the polymer layer may be 0.1 μm to 10 μm, specifically 0.5 μm to 5 μm, and more specifically 1 μm to 2.5 μm. When the thickness is within this range, the lithium metal layer can be easily transferred to the positive electrode active material layer, and reverse transfer, in which the positive electrode active material layer is transferred to the transfer laminate, can be prevented.

[0116] 2) P2 step Referring to FIG. 3, in step P2, the fabricated cathode structure 400 may be rolled. The rolling may be performed using a roll press. Specifically, pressure may be applied vertically to the cathode structure 400 passing through the space between two rolls R spaced apart by a predetermined vertical distance, and the pressure may be linear pressure. The rolling process may cause at least some of the lithium ions in the lithium metal layer contained in the transfer laminate to be inserted into the preliminary cathode active material layer. During this process, the preliminary cathode active material layer may become a cathode active material layer. Although FIGS. 3 and 4 illustrate the lithium metal layer as being included in the cathode, if the lithium metal layer is entirely inserted into the preliminary cathode active material layer during the rolling process, the lithium metal layer may not exist as a separate layer.

[0117] The pressure applied to the positive electrode structure during the rolling process may be 10 kgf / cm to 90 kgf / cm, specifically 15 kgf / cm to 80 kgf / cm, and more specifically 20 kgf / cm to 40 kgf / cm. When this range is satisfied, the amount of lithium transferred to the negative electrode during the activation process may be sufficient, and cracking of the positive electrode active material particles and the formation of lithium by-products may be suppressed, thereby improving the capacity of the positive electrode and the life characteristics of the battery.

[0118] 3) P3 step 4, in step P3, after the rolling performed in step P2, the substrate film 310 is removed from the transfer laminate to manufacture the cathode 100. When the polymer layer 330 is positioned between the substrate film 310 and the lithium metal layer 320, the polymer layer 330 may make it easier to remove the substrate film 310.

[0119] The method for manufacturing a positive electrode may further include a step P4 in which the preliminary positive electrode is left to rest (stand) for 1 minute to 600 minutes, specifically 1 minute to 30 minutes. The step P4 may be performed after the step P2. Specifically, the step P4 may be performed between the steps P2 and P3 or immediately after the step P3. The step P4 effectively releases reaction heat generated by the reaction between the lithium metal layer and the preliminary positive electrode active material layer in the step P2, and uniformly inserts lithium into the positive electrode, thereby reducing the generation of by-products.

[0120] The method for manufacturing the positive electrode may further include a step P4 after the step P2, in which the preliminary positive electrode is rested (left to stand) for 1 minute to 600 minutes, specifically 1 minute to 30 minutes. The step P4 may be performed after the step P2. Specifically, the step P4 may be performed between the steps P2 and P3 or immediately after the step P3. The step P4 effectively releases reaction heat generated by the reaction between the lithium metal layer and the preliminary positive electrode active material layer in the step P2, and uniformly inserts lithium into the positive electrode, thereby reducing the generation of by-products.

[0121] The manufactured positive electrode is the same as the positive electrode of the above-described embodiment, and therefore a detailed description thereof will be omitted.

[0122] (2) B2 Step The step B2 may include charging the spare lithium secondary battery by applying a current to the spare lithium secondary battery at a current rate of 0.1C to 1C.

[0123] Specifically, step B2 corresponds to a so-called “activation step.” In step B2, the spare lithium secondary battery is charged and discharged, whereby excess lithium ions present in the positive electrode active material layer formed by the lithium metal layer migrate to the negative electrode active material layer, thereby prelithiating the negative electrode.

[0124] When charging the spare lithium secondary battery in step B2, a current may be applied to the spare lithium secondary battery at a current rate of 0.1 C to 1 C, specifically, 0.1 C to 0.7 C, more specifically, 0.1 C to 0.3 C. If the current rate is less than 0.1 C, the amount of lithium ions migrating from the positive electrode active material layer to the negative electrode active material layer is insufficient, making it difficult to improve the battery's lifespan. If the current rate exceeds 1 C, excessive cracking of the negative electrode active material particles may occur, increasing the formation of lithium by-products in the negative electrode, and reducing the initial capacity and lifespan of the battery.

[0125] Step B2 may be performed at a temperature of 15° C. to 85° C., specifically 20° C. to 60° C., more specifically 20° C. to 40° C. When the temperature is within this range, the ionic conductivity of the electrolyte is improved, the proportion of inorganic components in the solid electrolyte membrane is increased, and the initial resistance of the battery can be reduced.

[0126] According to yet another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same. The battery module and the battery pack include the lithium secondary battery having high capacity, excellent rate-limiting characteristics, and excellent cycle characteristics, and can be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0127] Below, preferred embodiments are presented to facilitate understanding of the present invention. However, the above embodiments are merely illustrative of the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of the scope and technical ideas of the present description. It goes without saying that such changes and modifications fall within the scope of the appended claims.

[0128] Examples and Comparative Examples Example 1: Manufacture of a lithium secondary battery (1) Manufacturing of the positive electrode A PET film (base film), a polymer layer (thickness 2.5 μm) made of PMMA disposed on the PET film, and a lithium metal layer (thickness 6 μm, 1.24 mAh / cm) made of solid-phase lithium metal disposed on the polymer layer. 2 A transfer laminate containing the same (loading amount: 1000 μm) was prepared.

[0129] 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 ]O2 A plurality of primary particles (10 or more) are bonded to form secondary particles, and the average particle diameter of the secondary particles is D 50 The loading capacity of the preliminary positive electrode active material layer was 4.5 mAh / cm. ... 2 and the thickness was 140 μm.

[0130] The transfer laminate was placed on the preliminary positive electrode active material layer so that the lithium metal layer and the preliminary positive electrode active material layer were in contact with each other.

[0131] The positive electrode with the transfer laminate disposed thereon was then rolled using a roll press and left 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 a positive electrode active material layer. Next, the substrate film was removed, and the resulting mixture was left for 10 minutes to produce a positive electrode comprising a positive electrode current collector, a positive electrode active material layer, and a polymer layer.

[0132] (2) Manufacture of spare lithium secondary batteries As the negative electrode active material, the average particle size D50 Silicon particles with a particle size of 5 μm were used. A negative electrode was prepared including a preliminary negative electrode active material layer containing the above 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 capacity of the preliminary negative electrode active material layer was 10 mAh / cm. 2 and the thickness was 75 μm.

[0133] The positive electrode prepared in (1), the negative electrode, and a porous polyethylene separator 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 mol) was injected into the assembled battery, and the battery was left for 48 hours to prepare a spare lithium secondary battery.

[0134] (3) Manufacture of lithium secondary batteries The spare lithium secondary battery was charged to 4.2 V at 25° C. with a current of 0.1 C, and then discharged to 2.5 V at 0.5 C to perform an activation process.

[0135] Examples 2 to 5 and Comparative Examples 1 and 2: Production of Lithium Secondary Batteries The lithium secondary batteries of Examples 2 to 5 and Comparative Examples 1 and 2 were manufactured in the same manner as in Example 1, except that the current rate of the applied current during charging of the spare lithium secondary battery (charging in the activation process) was modified as shown in Table 1.

[0136] Comparative Example 3: Manufacture of a lithium secondary battery A PET film (base film), a polymer layer (2.5 μm thick) made of PMMA disposed on the PET film, and a lithium metal layer (6 μm thick, 1.24 mAh / cm) made of solid-phase lithium metal disposed on the polymer layer. 2 A transfer laminate containing the same (loading amount: 1000 μm) was prepared.

[0137] On the other hand, as the negative electrode active material, the average particle size D 50Silicon particles with a particle size of 5 μm were used. A negative electrode was prepared including a preliminary negative electrode active material layer containing the above negative electrode active material, carboxymethyl cellulose (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 capacity of the preliminary negative electrode active material layer was 10 mAh / cm. 2 and the thickness was 75 μm.

[0138] The transfer laminate was placed on the preliminary negative electrode active material layer so that the lithium metal layer and the preliminary negative electrode active material layer were in contact with each other.

[0139] The negative electrode with the transfer laminate disposed thereon was then rolled using a roll-to-roll method, and the negative electrode was then left for 24 hours. As a result, lithium ions from the lithium metal layer were inserted into the preliminary negative electrode active material layer, forming a negative electrode active material layer. The pressure during the rolling was 50 kgf / cm.

[0140] Next, the substrate film was removed to prepare a negative electrode including a negative electrode current collector, a negative electrode active material layer, and a polymer layer.

[0141] (2) Manufacture of spare lithium 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 ]O2 A plurality of primary particles (10 or more) are bonded to form secondary particles, and the average particle diameter of the secondary particles is D 50 The loading capacity of the preliminary positive electrode active material layer was 4.5 mAh / cm. ... 2 and the thickness was 140 μm.

[0142] The negative electrode prepared in (1), the positive electrode, and a porous polyethylene separator 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) were injected into the assembled battery to prepare a spare lithium secondary battery.

[0143] (3) Manufacture of lithium secondary batteries The spare lithium secondary battery was charged to 4.2 V at 25° C. at a current rate of 1.0 C, and then discharged to 2.5 V at a current rate of 0.5 C to perform an activation process.

[0144] Comparative Example 4: Manufacture of a lithium secondary battery (1) Manufacturing of the positive electrode 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 ]O2 A plurality of primary particles (10 or more) are bonded to form secondary particles, and the average particle diameter of the secondary particles is D 50 The loading capacity of the preliminary positive electrode active material layer was 4.5 mAh / cm. ... 2 and the thickness was 140 μm.

[0145] The positive electrode and a lithium metal counter electrode facing the positive electrode were prepared, and a polyethylene separator was interposed between the positive electrode and the lithium metal counter electrode. An electrolyte (ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 3 / 7 (volume ratio), lithium hexafluorophosphate (LiPF 61 mol)) was injected to prepare a prelithiation cell.

[0146] An electrochemical charger / discharger was connected to the prelithiation cell, and the prelithiation cell was electrochemically charged at 0.1 C to 120% of the charge capacity of the positive electrode to overlithiate the positive electrode.

[0147] (2) Manufacture of spare lithium secondary batteries As the negative electrode active material, the average particle size D 50 Silicon particles with a particle size of 5 μm were used. A negative electrode was prepared including a preliminary negative electrode active material layer containing the above 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 capacity of the preliminary negative electrode active material layer was 10 mAh / cm. 2 and the thickness was 75 μm.

[0148] The positive electrode prepared in (1), the negative electrode, and a porous polyethylene separator were assembled using a winding method, and an electrolyte (ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 3 / 7 (volume ratio), lithium hexafluorophosphate (LiPF 61 mol)) was injected into the assembled battery, and the battery was left for 48 hours to prepare a spare lithium secondary battery.

[0149] (3) Manufacture of lithium secondary batteries The spare lithium secondary battery was charged to 4.2 V at 25° C. at a current rate of 1.0 C, and then discharged to 2.5 V at a current rate of 0.5 C to perform an activation process.

[0150] [Experimental Example 1: Confirmation of A value] The A values ​​of the lithium secondary batteries of the Examples and Comparative Examples were confirmed by the following method.

[0151] [Formula 1] A = {(F+C) / (F+C+G+M+E)} x 100

[0152] The F and C are the contents of fluoride groups (unit: μg / cm ) confirmed by performing capillary electrophoresis (CE) analysis on the solid electrolyte membrane. 2) and carbonate group content (unit: μg / cm 2 ), and G, M, and E are the contents of ethylene glycol groups (unit: μg / cm ) confirmed by subjecting the solid electrolyte membrane to nuclear magnetic resonance (NMR) spectroscopy. 2 ), methyl group content (unit: μg / cm 2 ), and ethyl group content (unit: μg / cm 2 )

[0153] [Experimental Example 2: Confirmation of L value] The L values ​​of the lithium secondary batteries of the Examples and Comparative Examples were confirmed by the following method.

[0154] L=L2 / L1

[0155] L1 and L2 are integrated intensity values ​​of lithium peaks in a graph obtained from laser-induced breakdown spectroscopy (LIBS) analysis; The L1 is measured at the interface between the negative electrode active material layer and the negative electrode current collector, The L2 is measured at a point 20% of the thickness of the negative electrode active material layer from the interface between the negative electrode active material layer and the solid electrolyte membrane in the thickness direction of the negative electrode active material layer.

[0156] [Experimental Example 3: Confirmation of initial capacity] The initial capacities of the lithium secondary batteries of the Examples and Comparative Examples were confirmed by the following method.

[0157] Specifically, the lithium secondary battery was charged to 4.2 V at a current density of 1 C, and discharged to 2.5 V at a current rate of 0.5 C, and the capacity during discharge was confirmed.

[0158] [Experimental Example 4: Confirmation of initial resistance] The initial resistance of the lithium secondary batteries of the Examples and Comparative Examples was confirmed by the following method.

[0159] The lithium secondary battery was charged and discharged, fully charged again, and then discharged to 50% SOC. A 2.5C pulse current was then applied for 30 seconds, and the resistance was calculated by dividing the difference between the voltage before and 10 seconds after the current was applied by the current value.

[0160] [Experimental Example 5: Confirmation of capacity maintenance rate] The lithium secondary batteries of the examples and comparative examples were charged and discharged by the following method, and the capacity retention rates were confirmed.

[0161] Charging conditions: Charging to 4.2V at a current density of 1C Discharge conditions: Discharge to 3.0V at a current rate of 0.5C

[0162] The capacity retention rates were calculated as follows:

[0163] Capacity retention rate (%) = (100th discharge capacity / 1st discharge capacity) x 100

[0164] [Table 1]

[0165] Referring to Table 1, it can be seen that Examples 1 to 5, in which the A value is 10% or more, have higher initial capacity, higher capacity retention, and lower battery resistance than Comparative Examples 1 and 2, in which the A value is less than 10%. Furthermore, in Comparative Example 3, in which the anode was prelithiated, the A value was less than 10% due to severe cracking of the active material particles on the surface of the anode and an increase in the organic component in the solid electrolyte film. This resulted in a thin, non-uniform initial solid electrolyte film with high resistance, which in turn led to problems with reduced capacity and shorter lifespan.

[0166] In addition, in the case of Comparative Example 4, in which lithium was injected into the positive electrode by an electrochemical method using the prelithiation method, unlike the transfer method according to the present invention, the content of inorganic components in the solid electrolyte membrane was low, making it difficult to form a thin and strong solid electrolyte membrane, and therefore, it was confirmed that poor effects were observed in the capacity and life characteristics. [Explanation of symbols]

[0167] 300 Transfer laminate 310 Base film 320 Lithium metal layer 330 Polymer layer 100 positive electrode 110 Positive electrode current collector 120' Spare positive electrode active material layer 400 Positive electrode structure R Roll

Claims

1. a positive electrode including a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector; a negative electrode including a negative electrode current collector, a negative electrode active material layer disposed on the negative electrode current collector, and a solid electrolyte membrane disposed on the negative electrode active material layer; a separator disposed between the positive electrode and the negative electrode; the electrolyte, A lithium secondary battery having an A value of 10% or more according to the following formula 1: [Formula 1] A={(F+C) / (F+C+G+M+E)}×100 The F and C are the fluoride group contents (unit: μg / cm) determined by performing capillary electrophoresis analysis on the solid electrolyte membrane. ２ ) and carbonate group content (unit: μg / cm ２ ) and The G, M, and E are the contents of ethylene glycol groups (unit: μg / cm ) confirmed by subjecting the solid electrolyte membrane to nuclear magnetic resonance (NMR) spectroscopy. ２ ), methyl group content (unit: μg / cm ２ ), and the content of ethyl groups (unit: μg / cm ２ )

2. 2. The lithium secondary battery according to claim 1, wherein the L value according to the following formula 2 is 45% or more: [Formula 2] L = L2 / L1 L1 and L2 are integrated intensity values ​​of lithium peaks in a graph obtained from laser-induced breakdown spectroscopy (LIBS), The L1 is measured at the interface between the negative electrode active material layer and the negative electrode current collector, The L2 is measured at a point 20% of the thickness of the negative electrode active material layer from the interface between the negative electrode active material layer and the solid electrolyte membrane in the thickness direction of the negative electrode active material layer.

3. the negative electrode active material layer contains negative electrode active material particles, The lithium secondary battery according to claim 1 , wherein the negative electrode active material particles include silicon-based negative electrode active material particles.

4. The lithium secondary battery according to claim 1, which satisfies the following formula 3: [Formula 3] 1.2≦I ［００３］ / I ［２００］ ≦2.0 In the formula 3, I ［００３］ is the integral value of the maximum peak appearing in the region where 2θ is 17.0° to 19.0° when XRD is measured on the surface of the positive electrode active material layer, I ［２００］ is the integral value of the maximum peak appearing in the region where 2θ is 43° to 45° when XRD is measured on the surface of the positive electrode active material layer.

5. The positive electrode active material layer is ３ N., Li. ２ CO ３ 2. The lithium secondary battery according to claim 1, comprising at least one selected from the group consisting of:

6. The lithium secondary battery of claim 1 , wherein the positive electrode further comprises a lithium metal layer located on the positive electrode active material layer.

7. a step B1 of preparing a spare lithium secondary battery including: a positive electrode including a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector; a negative electrode including a negative electrode current collector, a negative electrode active material layer disposed on the negative electrode current collector, and a solid electrolyte film disposed on the negative electrode active material layer; a separator disposed between the positive electrode and the negative electrode; and the electrolyte; and B2 step of activating the spare lithium secondary battery; The method for producing the positive electrode comprises: a step P1 of placing a transfer laminate including a substrate film and a lithium metal layer disposed on the substrate 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 step P2 of rolling the positive electrode structure; and a step P3 of removing the substrate film from the transfer laminate after the rolling to produce a positive electrode, The method for manufacturing a lithium secondary battery includes applying a current to the spare lithium secondary battery at a current rate of 0.1 C to 1.0 C to charge the spare lithium secondary battery.

8. 8. The method of claim 7, wherein in step B2, the current rate applied to the spare lithium secondary battery is 0.1C to 0.7C.

9. The method for manufacturing a lithium secondary battery according to claim 7, wherein the step B2 is carried out at a temperature of 15°C to 85°C.

10. The method for manufacturing a lithium secondary battery according to claim 7, further comprising a step P4 of leaving the preliminary positive electrode for 1 minute to 600 minutes after the step P2.

11. In the P2 step, The method for producing a lithium secondary battery according to claim 7 , wherein the rolling is performed by a rolling method.

12. 8. The method for producing a lithium secondary battery according to claim 7, wherein the lithium metal layer has a thickness of 1 μm to 10 μm.

13. 8. The method of claim 7, wherein the loading amount of the lithium metal layer is 4% to 40% of the loading amount of the preliminary positive electrode active material layer.

14. the transfer laminate further comprises a polymeric layer; The method for producing a lithium secondary battery according to claim 7 , wherein the polymer layer is located between the substrate film and the lithium metal layer.

15. 8. The method for producing a lithium secondary battery according to claim 7, wherein the pressure applied to the positive electrode structure during the rolling is 10 kgf / cm to 90 kgf / cm.

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