Transfer laminate, method for manufacturing negative electrode for lithium secondary battery, negative electrode for lithium secondary battery, and lithium secondary battery including negative electrode

Abstract

The present application relates to a negative electrode for a lithium secondary battery, a method for producing a lithium secondary battery, and a lithium secondary battery.

Description

[Technical Field]

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0016609, filed with the Korean Intellectual Property Office on February 9, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present application relates to a transfer laminate, a method for producing a negative electrode for a lithium secondary battery, a negative electrode for a lithium secondary battery, and a lithium secondary battery including the negative electrode. [Background technology]

[0003] The rapid increase in fossil fuel use has led to an increasing demand for alternative and clean energy, and one of the most actively researched fields is power generation and storage using electrochemical reactions.

[0004] Currently, a typical example of an electrochemical element that utilizes such electrochemical energy is a secondary battery, and the range of its use is tending to expand more and more.

[0005] As technological development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and widely used. In addition, active research is being conducted on methods for manufacturing high-density electrodes with higher energy density per unit volume as electrodes for such high-capacity lithium secondary batteries.

[0006] Generally, a 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. The negative electrode active material may be silicon-based particles with a high discharge capacity.

[0007] Generally, carbon materials such as graphite are used for the negative electrode of lithium secondary batteries, and the theoretical capacity density of carbon is 372 mAh / g (833 mAh / cm3 ) Therefore, in order to improve the energy density of the anode, silicon (Si), tin (Sn), and their oxides and alloys, which are alloyed with lithium, are being considered as anode materials. Among these, silicon-based materials have attracted attention due to their low cost and high capacity (4200mAh / g).

[0008] However, the use of silicon-based negative electrode active materials poses the problem of high initial irreversible capacity. Specifically, during the charge-discharge reaction of a lithium secondary battery, lithium is released from the positive electrode and inserted into the negative electrode during charging, and then released from the negative electrode and returned to the positive electrode during discharge. However, with silicon-based negative electrode active materials, volume changes and surface side reactions are so severe that much of the lithium inserted into the negative electrode during initial charging cannot return to the positive electrode, resulting in a high initial irreversible capacity. This high initial irreversible capacity leads to a rapid decrease in battery capacity and cycle life.

[0009] To solve the above problems, a method of prelithiating a silicon negative electrode containing a silicon-based negative electrode active material is known. Known prelithiation methods include a method of preparing an electrode after lithiating the negative electrode by a physical / chemical method such as electroplating, lithium metal transfer, or lithium metal vapor deposition, and a method of electrochemically prelithiating the negative electrode.

[0010] Conventional electrochemical processes require wet processes in an electrolyte, which can pose risks such as fire and explosion, making it necessary to carefully control an inert environment. Creating such an environment requires complex control of conditions, such as controlling moisture content using inert gas in the chamber where the electrochemical process is carried out. Furthermore, uniform control of the initial irreversible capacity requires the electrochemical process to be carried out at the slowest possible rate, which increases production costs.

[0011] Furthermore, during the pre-lithiation process, it is difficult to safely and easily transfer lithium metal in the lithium metal transfer process, and either lithium is not transferred from the transfer laminate, or even if it is transferred, the highly reactive lithium metal immediately begins to react with the electrode active material, causing problems such as particle cracking on the surface of the electrode active material layer.

[0012] Therefore, research is needed into process conditions and materials that can easily transfer lithium metal to the top of the electrode active material layer during the lithium metal transfer process, that are safer and more efficient in prelithiating the electrode, and that can uniformly prelithiate lithium within the electrode active material layer. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-080971 Summary of the Invention [Problem to be solved by the invention]

[0014] In the pre-lithiation process, the lithium metal transfer process includes a process of transferring lithium metal from the transfer laminate to the top of the electrode active material layer. Through research, it was found that the degree of lithium metal transfer can be adjusted depending on the surface characteristics of the substrate layer in the transfer laminate.

[0015] Thus, the present application relates to a transfer laminate, a method for producing a negative electrode for a lithium secondary battery, a negative electrode for a lithium secondary battery, and a lithium secondary battery including the negative electrode. [Means for solving the problem]

[0016] One embodiment of the present specification provides a transfer laminate comprising a substrate layer; a release layer provided on one side of the substrate layer; and a lithium metal layer provided on the opposite side of the release layer from the side that contacts the substrate layer, wherein the thickness of the release layer is 0.1 μm or more and 10 μm or less, and the average surface roughness (Sa) of the substrate layer is 50 nm or more.

[0017] In yet another embodiment, there is provided a method for manufacturing a negative electrode for a lithium secondary battery, the method including: forming a negative electrode current collector layer and a negative electrode active material layer on one or both sides of the negative electrode current collector layer to form a negative electrode for a lithium secondary battery; laminating a transfer laminate according to the present application onto a surface of the negative electrode active material layer opposite to the surface that contacts the negative electrode current collector layer, thereby transferring a lithium metal layer; and prelithiating the negative electrode active material layer.

[0018] In yet another embodiment, there is provided a negative electrode for a lithium secondary battery manufactured according to the method for manufacturing a negative electrode for a lithium secondary battery according to the present application.

[0019] Finally, there is provided a lithium secondary battery including: a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separator disposed between the positive electrode and the negative electrode; and an electrolyte. [Effects of the Invention]

[0020] A transfer laminate according to one embodiment of the present invention is used in a lithium transfer process for prelithiating a negative electrode. In this case, the transfer laminate according to the present application may have a release layer having a thickness within a certain range and an average surface roughness (Sa) of 50 nm or more for the substrate layer. Because the thickness of the release layer satisfies this range, the coating uniformity of the release layer can be improved. Because the average surface roughness of the substrate layer satisfies this range, the use of such a substrate layer is characterized by improved peel strength between the release layer and the substrate layer.

[0021] In other words, the average surface roughness of the substrate layer according to the present application satisfies the above range, thereby reducing the contact area at the interface between the substrate layer and the release layer, thereby reducing wetting and improving the peel strength between the substrate layer and the release layer.

[0022] As a result, the lithium metal layer and release layer on the transfer laminate can be easily peeled off and transferred to the negative electrode active material layer in the lithium transfer process, which has the advantage of being able to solve problems such as reverse transfer to the substrate layer or the generation of by-products during pre-lithiation due to the substrate layer not peeling off.

[0023] That is, the negative electrode for a lithium secondary battery according to the present invention is mainly characterized in that, by including the transfer laminate of the present invention, pre-lithiation can be performed more efficiently during the pre-lithiation process, and pre-lithiation can be performed uniformly throughout the negative electrode active material layer without loss of lithium. [Brief explanation of the drawings]

[0024] [Figure 1] 1A to 1C are diagrams illustrating a process for transferring lithium metal to a negative electrode for a lithium secondary battery according to one embodiment of the present application. [Figure 2] FIG. 1 is a diagram showing a stack structure of a lithium secondary battery according to an embodiment of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0025] Before describing the present invention, some terms will first be defined.

[0026] In this specification, when a part is said to "comprise" a certain component, this means that it may further include other components, rather than excluding other components, unless specifically stated to the contrary.

[0027] In this specification, "p to q" means a range of "not less than p and not more than q."

[0028] In this specification, the "specific surface area" is measured by the BET method, and specifically, is calculated from the amount of nitrogen gas adsorption at liquid nitrogen temperature (77 K) using a BELSORP-mini II manufactured by BEL Japan Co., Ltd. That is, in the present application, the BET specific surface area may mean the specific surface area measured by the above-mentioned measurement method.

[0029] In this specification, "Dn" refers to particle size distribution, and refers to the particle size at the n% point in the cumulative particle number distribution by particle size. That is, D50 is the particle size (average particle size, median particle size) at the 50% point in the cumulative particle number distribution by particle size, D90 is the particle size at the 90% point in the cumulative particle number distribution by particle size, and D10 is the particle size at the 10% point in the cumulative particle number distribution by particle size. Meanwhile, particle size distribution can be measured using the laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500). The particle size distribution is calculated by measuring the difference in diffraction patterns due to particle size when the particles pass through a laser beam.

[0030] In this specification, when a polymer contains a certain monomer as a monomer unit, it means that the monomer is involved in a polymerization reaction and is contained as a repeating unit in the polymer. In this specification, when a polymer contains a monomer, this is interpreted as the same as when a polymer contains a monomer as a monomer unit.

[0031] It is understood that the term "polymer" is used in the broad sense herein to include copolymers unless "homopolymer" is specifically stated.

[0032] In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are polystyrene-equivalent molecular weights measured by gel permeation chromatography (GPC) using commercially available monodisperse polystyrene polymers (standard samples) with various degrees of polymerization that are commercially available for molecular weight measurement as standard substances. In this specification, molecular weight means weight average molecular weight unless otherwise specified.

[0033] The present invention will now be described in detail with reference to the accompanying drawings so that those skilled in the art can easily practice the present invention. However, the present invention may be embodied in various different forms and is not limited to the following description.

[0034] One embodiment of the present specification aims to provide a transfer laminate comprising a substrate layer; a release layer provided on one side of the substrate layer; and a lithium metal layer provided on the opposite side of the release layer from the side that contacts the substrate layer, wherein the thickness of the release layer is 0.1 μm or more and 10 μm or less, and the average surface roughness (Sa) of the substrate layer is 50 nm or more.

[0035] A transfer laminate according to one embodiment of the present invention is used in a lithium transfer process for prelithiating a negative electrode. In this case, the transfer laminate according to the present application may satisfy the average surface roughness (Sa) of the substrate layer of 50 nm or more. When the average surface roughness of the substrate layer satisfies the above range, when such a substrate layer is used, the transfer laminate has the characteristic of improving the peel strength between the release layer and the substrate layer.

[0036] The transfer laminate of the present invention will be specifically described below.

[0037] In one embodiment of the present application, the transfer laminate may include a substrate layer; a release layer formed on one or both sides of the substrate layer; and a lithium metal layer provided on the surface of the release layer opposite the surface that contacts the substrate layer.

[0038] In one embodiment of the present application, the base layer may have an average surface roughness (Sa) of 50 nm or more.

[0039] In another embodiment, the base layer may have an average surface roughness (Sa) of 50 nm or more, 55 nm or more, and may be 0.1 μm or less, preferably 90 nm or less.

[0040] In one embodiment of the present application, the upper limit of the average surface roughness (Sa) of the substrate layer can be used without limitation as long as it is lower than the thickness of the release layer coated together.

[0041] In one embodiment of the present application, there is provided a transfer laminate in which the average surface roughness (Sa) of the base layer is lower than the thickness of the release layer.

[0042] In one embodiment of the present application, the average surface roughness may refer to the surface roughness. The average surface roughness indicates the degree of roughness of the surface, and may represent the degree of unevenness of the surface of the target material.

[0043] As described above, when the substrate layer according to the present application has the above average surface roughness range, the contact area at the interface between the substrate layer and the release layer can be reduced, thereby reducing wetting and improving the peel strength between the substrate layer and the release layer.

[0044] In one embodiment of the present application, the substrate layer can be used without limitation as long as it can withstand process conditions such as high temperatures in the step of depositing lithium metal, and can prevent a reverse peeling problem in which lithium metal is transferred onto the substrate layer during a winding process for transferring the deposited lithium metal, and satisfies the above average surface roughness value.

[0045] The substrate layer according to the present application uses at least one selected from the group consisting of polyethylene terephthalate (PET), polyethylenenaphtalate (PEN), polyimide (PI), poly(methylmethacrylate) (PMMA), polypropylene, polyethylene, and polycarbonate.

[0046] In one embodiment of the present application, the average surface roughness (Sa) value of the substrate layer can satisfy the above-mentioned average surface roughness value of the substrate layer when the type of material added to the substrate layer, the particle size, the particle size and thickness of the material formed during the surface treatment of the substrate layer, or the etching conditions and time during the plasma treatment are appropriately changed.

[0047] That is, the average surface roughness of the substrate layer according to the present application can be set within the above range by adjusting the composition and content of the substrate layer or by performing a surface treatment on the substrate layer.

[0048] Specifically, the average surface roughness of the substrate layer can be adjusted during the processing stage of the substrate layer. That is, polyester chips are melted, extruded through a die, and then rapidly cooled to form an amorphous sheet, which is then heated and uniformly stretched in the machine and cross directions. The average surface roughness can be achieved by improving the heat treatment conditions or stretching process after processing. Alternatively, the average surface roughness can be achieved by surface coating using inorganic particles or polymers during the melting or stretching stage.

[0049] Furthermore, the surface treatment of the substrate layer can be carried out by depositing a film of inorganic particles or polymers on the processed substrate layer to meet the average surface roughness of the present application. X Gas (CF XThe surface of the substrate layer can be etched through plasma treatment using a gas, and as a result, the average surface roughness range of the substrate layer according to the present application can be met.

[0050] In one embodiment of the present application, the thickness of the substrate layer may be in the range of 1 μm or more and 300 μm or less, 5 μm or more and 200 μm or less, or 10 μm or more and 100 μm or less.

[0051] When the thickness of the substrate layer is satisfied as described above, transfer from the release layer is facilitated, and the substrate has the characteristic of being able to function as a transfer laminate when the lithium metal layer is transferred.

[0052] In one embodiment of the present application, the substrate layer may have a release layer formed on at least one surface thereof, or may have release layers formed on both surfaces thereof. The release layer can prevent reverse peeling, in which lithium metal is transferred onto the substrate layer during a winding process for transferring the deposited lithium metal layer to the negative electrode, and can also facilitate separation of the substrate layer after the lithium metal is transferred onto the negative electrode active material layer.

[0053] The release layer may contain at least one selected from the group consisting of silicon-modified polyester in which silicon chains are graft-bonded to a polyester main chain, acrylic resin, Si, melamine, and fluorine.

[0054] In one embodiment of the present application, the release layer may be formed by a coating method. For example, the coating method may be a method selected from the group consisting of dip coating, spray coating, spin coating, die coating, gravure coating, micro-gravure coating, comma coating, ink-jet coating, bar coating, wire-bar coating, and roll coating. However, the coating method is not limited thereto, and various coating methods used in the art for forming coating layers may be used.

[0055] In one embodiment of the present application, there is provided a transfer laminate in which the thickness of the release layer is 0.1 μm or more and 10 μm or less, and the average surface roughness (Sa) of the base layer is lower than the thickness of the release layer.

[0056] In another embodiment, the thickness of the release layer may be 0.1 μm or more and 10 μm or less, preferably 0.3 μm or more and 5 μm or less, and more preferably 0.4 μm or more and 1 μm or less.

[0057] The release layer is transferred onto the negative electrode active material layer together with the lithium metal layer in the lithium metal transfer process described below, and when the thickness of the release layer and the average surface roughness of the substrate layer satisfy the above ranges, the coating uniformity of the release layer can be increased. Furthermore, since the release layer is later included on the negative electrode, when the thickness satisfies the above range, it has the characteristic of not causing an increase in battery resistance.

[0058] In one embodiment of the present application, the release layer may include a lithium metal layer provided on the surface opposite to the surface in contact with the base layer.

[0059] The lithium metal layer may be used as a metal for prelithiation of the negative electrode active material layer in the prelithiation step described below.

[0060] In one embodiment of the present application, the deposition method for depositing the lithium metal layer on the substrate layer on which the release layer is formed may be selected from, but is not limited to, vacuum thermal evaporation deposition, chemical vapor deposition (CVD), and physical vapor deposition, and various deposition methods used in the art may be used.

[0061] In one embodiment of the present application, the thickness of the lithium metal layer may be 1 μm or more and 10 μm or less, and preferably 3 μm or more and 10 μm or less.

[0062] When the thickness of the lithium metal layer satisfies the above range, the lithium metal can be efficiently transferred to the negative electrode active material layer, reverse transfer can be prevented, and the negative electrode active material layer can be prelithiated to a desired degree.

[0063] In one embodiment of the present application, there is provided a transfer laminate in which the release force of the surface of the release layer in contact with the base layer is 100 gf / inch or less, and the cross-cut test value of the surface of the release layer in contact with the base layer is 0B to 1B.

[0064] In one embodiment of the present application, the release force of the surface of the release layer in contact with the base layer may be 100 gf / inch or less.

[0065] In another embodiment, the release force of the surface of the release layer in contact with the base layer may be in the range of 100 gf / inch or less, preferably 50 gf / inch or less, and more preferably 30 gf / inch or less, and may be in the range of 5 gf / inch or more, preferably 10 gf / inch or more.

[0066] The release force can be measured by preparing a substrate coated with a release layer, cutting it to a width of 2.54 cm (1 inch), attaching Nitto-31B tape, and performing a 90° peel test at a speed of 300 mm / min using a UTM device (LF-PLUS).

[0067] As described above, by using the base layer according to the present application, the release force satisfies the specific range, and the release force can be reduced compared to the existing case where the release force is 500 gf / inch or more, making it easier to remove only the base layer.Furthermore, by satisfying this range, the problem of reverse transfer to the base layer can be solved.

[0068] In one embodiment of the present application, there is provided a transfer laminate in which the surface of the release layer in contact with the base layer has a crosscut test value of 0B to 1B.

[0069] The cross-cut test can be performed by preparing a transfer laminate in which a substrate layer, a release layer, and a lithium metal layer are sequentially laminated, and performing a cross-cut test according to the method of ASTM 3359. Specifically, the test can be performed under the following conditions: 5B (0% peeling), 4B (less than 5% peeling), 3B (5% to 15% peeling), 2B (15% to 35% peeling), 1B (35% to 65% peeling), and 0B (65% or more peeling).

[0070] By satisfying the cross-cut test results as described above, it can be confirmed that when a substrate layer under specific conditions is used, the release force with the release layer is improved, thereby making it easier to transfer the release layer and lithium metal layer onto the negative electrode active material layer.

[0071] In one embodiment of the present invention, there is provided a method for manufacturing a negative electrode for a lithium secondary battery, the method including: forming a negative electrode current collector layer and a negative electrode active material layer on one or both sides of the negative electrode current collector layer to form a negative electrode for a lithium secondary battery; laminating a transfer laminate according to the present application onto a surface of the negative electrode active material layer opposite to the surface that contacts the negative electrode current collector layer, thereby transferring a lithium metal layer; and prelithiating the negative electrode active material layer.

[0072] The method for producing a negative electrode for a lithium secondary battery will be described in more detail below.

[0073] A method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present application includes forming a negative electrode current collector layer and a negative electrode active material layer on one or both sides of the negative electrode current collector layer to form a negative electrode for a lithium secondary battery.

[0074] The step is a step of forming a negative electrode for a lithium secondary battery, and the step of forming a negative electrode current collector layer and a negative electrode active material layer on one or both surfaces of the negative electrode current collector layer may include coating one or both surfaces of the negative electrode current collector layer with a negative electrode slurry including a negative electrode active material layer composition, and the negative electrode active material layer composition may include at least one selected from the group consisting of a silicon-based active material; a negative electrode conductive material; and a negative electrode binder.

[0075] In one embodiment of the present application, the negative electrode slurry may include a negative electrode active material layer composition; and a slurry solvent.

[0076] In one embodiment of the present application, the solid content of the negative electrode slurry may be 5% or more and 40% or less.

[0077] In another embodiment, the solid content of the negative electrode slurry may be in the range of 5% to 40%, preferably 7% to 35%, and more preferably 10% to 30%.

[0078] The solid content of the negative electrode slurry may refer to the content of the negative electrode active material layer composition contained in the negative electrode slurry, and may refer to the content of the negative electrode active material composition based on 100 parts by weight of the negative electrode slurry.

[0079] When the solid content of the negative electrode slurry satisfies the above range, the viscosity during the formation of the negative electrode active material layer is appropriate, and the particle aggregation phenomenon of the negative electrode active material layer composition is minimized, thereby enabling the negative electrode active material layer to be efficiently formed.

[0080] In one embodiment of the present application, the slurry solvent is not limited as long as it can dissolve the negative electrode active material layer composition, and specifically, acetone; distilled water; or NMP can be used.

[0081] The negative electrode according to one embodiment of the present application can be formed by coating the negative electrode slurry on a negative electrode current collector layer and drying it.

[0082] The drying step may be performed to remove the slurry solvent from the negative electrode slurry, and the method may further include rolling the negative electrode.

[0083] In one embodiment of the present application, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, aluminum-cadmium alloy, etc., can be used. Furthermore, the bonding strength of the negative electrode active material can be strengthened by forming fine irregularities on the surface, and the negative electrode current collector layer can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0084] In one embodiment of the present application, the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, and the thickness of the negative electrode active material layer may be 20 μm or more and 500 μm or less.

[0085] However, the thickness can be variously deformed according to the type and use of the negative electrode used, and is not limited thereto.

[0086] In one embodiment of the present application, a negative electrode active material layer including a negative electrode active material composition formed on one or both surfaces of the negative electrode current collector layer is included.

[0087] In one embodiment of the present application, the negative electrode active material composition may include a silicon-based active material; a negative electrode conductive material; and a negative electrode binder.

[0088] In one embodiment of the present application, the silicon-based active material may include at least one selected from the group consisting of Si particles, SiOx (0 < x < 2), SiC, metal impurities, and Si alloys.

[0089] In one embodiment of the present application, the silicon-based active material includes one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and may include 70 parts by weight or more of the SiOx (x = 0) based on 100 parts by weight of the silicon-based active material.

[0090] In another embodiment, the silicon-based active material may include 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, and may include 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less of the SiOx (x = 0) based on 100 parts by weight of the silicon-based active material.

[0091] In one embodiment of the present application, the silicon-based active material may be, in particular, pure silicon (Si). Using pure silicon (Si) as the silicon-based active material may mean that the silicon-based active material contains pure Si particles (SiOx (x=0)) that are not bonded to other particles or elements in the above range, based on 100 parts by weight of the total silicon-based active material.

[0092] Silicon-based active materials have significantly higher capacities than conventional graphite-based active materials, and attempts to use them have been increasing, but because of their high volume expansion during charge and discharge, they have only been used in small amounts by mixing with graphite-based active materials. Despite these advantages, however, they suffer from high initial irreversible capacity, resulting in reduced lifespan. To address this issue, a pre-lithiation process is being developed to pre-lithiate the anode.

[0093] Therefore, a primary object of the present invention is to provide a transfer laminate that can more smoothly transfer a lithium metal layer onto the top of a negative electrode active material layer to solve the above-mentioned problems while using only a high-content silicon-based active material as a negative electrode active material to improve capacity performance.

[0094] The average particle size (D50) of the silicon-based active material of the present invention may be 5 μm to 10 μm, specifically 5.5 μm to 8 μm, and more specifically 6 μm to 7 μm. When the average particle size is within this range, the specific surface area of ​​the particles is within an appropriate range, and the viscosity of the negative electrode slurry is formed within an appropriate range. This allows for smooth dispersion of the particles constituting the negative electrode slurry. Furthermore, when the size of the silicon-based active material is equal to or greater than the lower limit of the range, the composite of the conductive material and the binder in the negative electrode slurry has an excellent contact area between the silicon particles and the conductive material, increasing the likelihood of maintaining a conductive network, and thereby increasing the capacity retention rate. When the average particle size is within this range, excessively large silicon particles are excluded, resulting in a smooth negative electrode surface, thereby preventing non-uniform current density during charge and discharge.

[0095] In one embodiment of the present application, the silicon-based active material generally has a characteristic BET specific surface area. The BET specific surface area of ​​the silicon-based active material is preferably 0.01 m 2 / g~150.0m 2 / g, more preferably 0.1m 2 / g~100.0m 2 / g, particularly preferably 0.2m 2 / g~80.0m 2 / g, most preferably 0.2m 2 / g~18.0m 2 / g. The BET specific surface area is determined in accordance with DIN 66131 (using nitrogen).

[0096] In one embodiment of the present application, the silicon-based active material can be, for example, in crystalline or amorphous form, and is preferably not porous.The silicon particles are preferably spherical or shard particles.Alternatively, but less preferably, the silicon particles can also have a fibrous structure or be in the form of a silicon-containing film or coating.

[0097] In one embodiment of the present application, the silicon-based active material may be present in an amount of 60 parts by weight or more based on 100 parts by weight of the negative electrode active material layer composition.

[0098] In yet another embodiment, the silicon-based active material may be included in an amount of 60 parts by weight or more, preferably 65 parts by weight or more, and more preferably 70 parts by weight or more, based on 100 parts by weight of the negative electrode active material layer composition, and may be included in an amount of 95 parts by weight or less, preferably 90 parts by weight or less, and more preferably 80 parts by weight or less.

[0099] The negative electrode active material layer composition according to the present application uses a conductive material and a binder that can suppress the volume expansion rate during charge and discharge, even when a silicon-based active material with a significantly high capacity is used within the above range, and therefore, even when the silicon-based active material is contained within the above range, the negative electrode performance is not deteriorated and the composition has the characteristic of excellent output characteristics during charge and discharge.

[0100] In one embodiment of the present application, the silicon-based active material may have a non-spherical morphology, and the sphericity thereof is, for example, 0.9 or less, for example, 0.7 to 0.9, for example, 0.8 to 0.9, for example, 0.85 to 0.9.

[0101] In this application, the circularity is determined by the following formula 1, where A is the area and P is the perimeter. [Formula 1] 4πA / P 2

[0102] While graphite-based compounds have traditionally been used exclusively as anode active materials, attempts to incorporate silicon-based compounds into batteries to increase capacity have been increasing in recent years as demand for high-capacity batteries has grown. However, silicon-based compounds have limitations, such as their rapid volume expansion during charge / discharge processes, damaging the conductive pathways formed within the anode active material layer and reducing battery performance.

[0103] Accordingly, in one embodiment of the present application, the negative electrode conductive material may include at least one selected from the group consisting of a dot-like conductive material, a linear conductive material, and a planar conductive material.

[0104] In one embodiment of the present application, the dot-like conductive material refers to a conductive material that can be used to improve the conductivity of a negative electrode and has conductivity without inducing a chemical change. Specifically, the dot-like conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably includes carbon black, which realizes high conductivity and has excellent dispersibility.

[0105] In one embodiment of the present application, the point-like conductive material has a BET specific surface area of ​​40 m2 / g or more 70m 2 / g or less, preferably 45m 2 / g or more 65m 2 / g or less, more preferably 50m 2 / g or more 60m 2 / g or less.

[0106] In one embodiment of the present application, the particle size of the dotted conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

[0107] In one embodiment of the present application, the conductive material may include a planar conductive material.

[0108] The planar conductive material increases the surface contact between silicon particles in the negative electrode to improve conductivity, and at the same time, prevents the conductive path from being broken due to volume expansion. The planar conductive material can be referred to as a plate-type conductive material or a bulk-type conductive material.

[0109] In one embodiment of the present application, the sheet conductive material may include at least one selected from the group consisting of platelet graphite, graphene, graphene oxide, and graphite flakes, and may be preferably platelet graphite.

[0110] In one embodiment of the present application, the average particle size (D50) of the sheet conductive material may be 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When the average particle size satisfies this range, the sufficient particle size facilitates dispersion without excessively increasing the viscosity of the negative electrode slurry. Therefore, when dispersing using the same device and time, the dispersion effect is excellent.

[0111] In one embodiment of the present application, the sheet conductive material provides a negative electrode composition having a D10 of 0.5 μm or more and 1.5 μm or less, a D50 of 2.5 μm or more and 3.5 μm or less, and a D90 of 7.0 μm or more and 15.0 μm or less.

[0112] In one embodiment of the present application, the sheet conductive material may be a sheet conductive material having a high BET specific surface area; or a sheet conductive material having a low specific surface area.

[0113] In one embodiment of the present application, the planar conductive material may be a high-specific surface area planar conductive material or a low-specific surface area planar conductive material without any restrictions. However, the planar conductive material of the present application may be affected to some extent by dispersion in terms of electrode performance, and it may be particularly preferable to use a low-specific surface area planar conductive material that does not cause dispersion problems.

[0114] In one embodiment of the present application, the sheet conductive material has a BET specific surface area of ​​5 m 2 / g or more.

[0115] In another embodiment, the sheet conductive material has a BET specific surface area of ​​5 m 2 / g or more 500m 2 / g or less, preferably 5m 2 / g or more 300m 2 / g or less, more preferably 5m 2 / g or more 250m 2 / g or less.

[0116] In another embodiment, the sheet conductive material is a high specific surface area sheet conductive material having a BET specific surface area of ​​50 m 2 / g or more 500m 2 / g or less, preferably 80m 2 / g or more 300m 2 / g or less, more preferably 100m 2 / g or more 300m 2 / g or less.

[0117] In another embodiment, the sheet conductive material is a sheet conductive material with a low specific surface area, and has a BET specific surface area of ​​5 m 2 / g or more 40m 2 / g or less, preferably 5m 2 / g or more 30m 2 / g or less, more preferably 5m 2 / g or more 25m2 / g or less.

[0118] Other conductive materials include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundled carbon nanotubes. The bundled carbon nanotubes may include multiple carbon nanotube units. Specifically, unless otherwise specified, the term "bundle type" refers to a secondary shape in which multiple carbon nanotube units are arranged side by side or entangled with the longitudinal axes of the carbon nanotube units in substantially the same orientation, forming a bundle or rope-like shape. The carbon nanotube units have graphite sheets with nanosized diameters and a cylindrical sp2 bonding structure. Depending on the winding angle and structure of the graphite sheets, the carbon nanotubes may exhibit conductive or semiconductive properties. Compared to entangled carbon nanotubes, the bundled carbon nanotubes can be more uniformly dispersed during negative electrode fabrication, smoothly forming a conductive network within the negative electrode, and improving the conductivity of the negative electrode.

[0119] In one embodiment of the present application, the negative electrode conductive material may be 10 parts by weight or more and 40 parts by weight or less based on 100 parts by weight of the negative electrode active material layer composition.

[0120] In another embodiment, the negative electrode conductive material may be contained in an amount of 10 parts by weight or more and 40 parts by weight or less, preferably 10 parts by weight or more and 30 parts by weight or less, and more preferably 10 parts by weight or more and 20 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer composition.

[0121] The negative electrode conductive material according to the present application has a completely different structure from the conductive material used in the positive electrode. That is, the negative electrode conductive material according to the present application serves to secure the contact point between the silicon-based active materials, which undergo a large volume expansion during charging and discharging, while the positive electrode conductive material serves to provide partial conductivity while acting as a buffer with a shock-absorbing function during rolling, and is completely different in structure and role from the negative electrode conductive material of the present invention.

[0122] Furthermore, the negative electrode conductive material according to the present application is applied to a silicon-based active material and has a completely different structure from conductive materials applied to graphite-based active materials. That is, conductive materials used in electrodes having graphite-based active materials simply have smaller particles than the active material, and therefore have the properties of improving output characteristics and imparting some conductivity, and are completely different in structure and role from negative electrode conductive materials applied together with silicon-based active materials as in the present invention.

[0123] In one embodiment of the present application, the planar conductive material used as the negative electrode conductive material has a structure and function different from that of a carbon-based active material generally used as a negative electrode active material. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, and refers to a material that is processed into a spherical or dot-like shape to facilitate the storage and release of lithium ions.

[0124] Meanwhile, the planar conductive material used as the negative electrode conductive material is a material having a planar or plate-like shape and can be expressed as plate-like graphite. That is, it is a material contained in the negative electrode active material layer to maintain a conductive path, and does not play a role in storing and releasing lithium, but rather a material that ensures a planar conductive path within the negative electrode active material layer.

[0125] That is, in this application, the use of plate-shaped graphite as a conductive material means that it is processed into a planar or plate-like shape and used as a material to ensure a conductive path, rather than to store or release lithium. In this case, the negative electrode active material included therein has high capacity characteristics for storing and releasing lithium, and plays a role in storing and releasing all lithium ions transferred from the positive electrode.

[0126] Meanwhile, in the present application, the use of a carbon-based active material as an active material means that the carbon-based active material is processed into a dotted or spherical shape and is used as a material that stores or releases lithium.

[0127] That is, in one embodiment of the present application, the carbon-based active material, artificial graphite or natural graphite, has a BET specific surface area of ​​0.1 m 2 / g or more 4.5m 2 The plate-shaped graphite, which is a planar conductive material, may have a planar BET specific surface area of ​​5 m 2 / g or more.

[0128] In one embodiment of the present application, 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, tetrafluoroethylene, 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.

[0129] The negative electrode binder according to one embodiment of the present application plays a role in holding down the active material and conductive material to prevent twisting and structural deformation of the negative electrode structure when the volume expansion and relaxation of the silicon-based active material occurs. As long as the binder fulfills this role, any of the general negative electrode binders can be applied, specifically, a water-based binder can be used, and more specifically, a PAM-based binder can be used.

[0130] In one embodiment of the present application, there is provided a step of laminating a transfer laminate according to the present application on a surface of the negative electrode active material layer that contacts the negative electrode current collector layer to transfer a lithium metal layer.

[0131] The details regarding the transfer laminate are the same as those described above.

[0132] In one embodiment of the present invention, there is provided a method for manufacturing a negative electrode for a lithium secondary battery, comprising: laminating the transfer laminate onto a surface of the negative electrode active material layer opposite to a surface that contacts the negative electrode current collector layer to transfer a lithium metal layer; laminating the transfer laminate so that a surface of the lithium metal layer opposite to a surface that contacts the release layer contacts a surface of the negative electrode active material layer opposite to a surface that contacts the negative electrode current collector layer; and removing the base layer.

[0133] 1 is a diagram showing a method for producing a negative electrode for a lithium secondary battery according to one embodiment of the present application. Specifically, the process shows the steps of preparing a transfer laminate 200 including a base layer 40, a release layer 30, and a lithium metal layer 35, laminating a negative electrode 100 for a lithium secondary battery, in which a negative electrode active material layer 20 is formed on a negative electrode current collector layer 10, so that the negative electrode active material layer 20 and the lithium metal layer 35 are in contact with each other, and then removing the base layer 40 and transferring only the lithium metal layer 35 onto the negative electrode active material layer 20.

[0134] In particular, as described above, the method includes a step of transferring the lithium metal layer through a transfer laminate including the specific substrate layer according to the present application, which allows the lithium metal layer to be transferred more easily.

[0135] In one embodiment of the present application, there is provided a method for manufacturing a negative electrode for a lithium secondary battery, wherein the laminating step is performed at a temperature of 20°C to 80°C and under a pressure of 20 kgf / cm to 60 kgf / cm.

[0136] The lamination can be performed as a transfer process using a roll press. A subsequent process of removing the substrate layer is included. The inclusion of the release layer according to the present application during removal can prevent direct contact between the lithium metal layer and air, thereby protecting the lithium metal layer. Furthermore, the presence of the release layer allows for easy removal of the substrate layer with only a weak linear pressure, making it easy to control the prelithiation rate, and facilitating the release of heat generated during prelithiation by removing the substrate layer, thereby suppressing the generation of by-products.

[0137] In one embodiment of the present application, a step of prelithiating the negative electrode active material layer is provided.

[0138] The prelithiation of the negative electrode active material layer may be performed simultaneously with transferring a lithium metal layer onto the negative electrode active material layer, and completion of the prelithiation may be confirmed when the lithium metal layer is completely removed with the naked eye.

[0139] In one embodiment of the present application, there is provided a method for manufacturing a negative electrode for a lithium secondary battery, wherein the step of pre-lithiating the negative electrode active material layer is performed within 30 minutes to 48 hours after transferring lithium metal.

[0140] As described above, the substrate layer can be removed immediately after the lithium metal layer is transferred, and the removal of the substrate layer proceeds easily. Furthermore, heat is easily released during prelithiation, in which the lithium metal layer reacts with the negative electrode active material layer, and by-products are generated less. As a result, the negative electrode active material layer can be uniformly prelithiated.

[0141] The pre-lithiation completion time can be calculated by measuring the time from the time of lithium metal transfer until the transferred lithium metal is no longer observed on the surface of the negative electrode active material layer.

[0142] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery manufactured according to the method for manufacturing a negative electrode for a lithium secondary battery.

[0143] In one embodiment of the present application, there is provided a lithium secondary battery including: a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separator disposed between the positive electrode and the negative electrode; and an electrolyte.

[0144] The positive electrode may include a positive electrode current collector layer and a positive electrode active material layer formed on the positive electrode current collector layer and containing the positive electrode active material.

[0145] The positive electrode current collector layer in the positive electrode is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. The positive electrode current collector layer typically has a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the positive electrode current collector layer to enhance the adhesive strength of the positive electrode active material. It may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0146] The positive electrode active material may be a commonly used positive electrode active material, such as a layered compound or a compound substituted with one or more transition metals, such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2); a lithium iron oxide such as LiFe3O4; 1+c1 Mn 2-c1O4 (0≦c1≦0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; chemical formula LiNi 1-c2 M c2 O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and 0.01≦c2≦0.3 is satisfied); 2-c3 M c3 Examples of suitable lithium manganese composite oxides include, but are not limited to, lithium manganese composite oxides represented by Li2Mn3MO8 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≦c3≦0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); and LiMn2O4, in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion. The positive electrode may be Li metal.

[0147] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the above-mentioned positive electrode active material.

[0148] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without any particular limitation as long as it has electronic conductivity without undergoing chemical changes in the battery that is constructed. 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, and the like, and one or more of these can be used alone or in combination.

[0149] 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, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These binders may be used singly or in combination.

[0150] The separator separates the negative electrode and positive electrode and provides a path for lithium ions to move. Any separator commonly used in secondary batteries can be used without particular limitations. It is particularly preferable for the separator to have low resistance to electrolyte ion movement and excellent electrolyte humidification capacity. Specifically, porous polymer films, such as those made from polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminate structures of two or more layers thereof, can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from 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 it can be used in a single-layer or multi-layer structure.

[0151] 2 is a diagram showing a laminated structure of a lithium secondary battery according to one embodiment of the present application. Specifically, a lithium secondary battery anode 100 including an anode active material layer 20 on one side of an anode current collector layer 10 can be seen, and a lithium secondary battery cathode 300 including a cathode active material layer 70 on one side of a cathode current collector layer 60 can be seen, and the lithium secondary battery anode 200 and lithium secondary battery cathode 100 are stacked with a separator 50 sandwiched between them.

[0152] At this time, the release layer transferred during the pre-lithiation may be partially removed depending on the electrolyte solution used, resulting in a small amount being contained on the top of the negative electrode. The release layer is not shown in Figure 2.

[0153] In one embodiment of the present application, the electrolytic solution may be an organic liquid electrolytic solution, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolytic solution, a solid inorganic electrolytic solution, or a molten inorganic electrolytic solution that can be used in manufacturing a lithium secondary battery, but is not limited to these.

[0154] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0155] Examples of the non-aqueous organic solvent that may 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, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0156] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are preferably used 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 prepared, and therefore, these cyclic carbonates are more preferably used.

[0157] 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:

[0158] In addition to the components of the electrolyte solution, the electrolyte solution 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 battery capacity, and improving the discharge capacity of the battery.

[0159] According to one 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 a secondary battery having high capacity, high rate characteristics, and high 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. [Example]

[0160] Below, preferred examples are presented to help understand the present invention, but these examples are for the purpose of illustrating 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, and it is natural that such changes and modifications fall within the scope of the appended claims.

[0161] <Example> <Production of Transfer Laminate> A film was prepared with a polyethylene terephthalate substrate layer coated with an acrylic resin release layer. A lithium metal layer was deposited on the acrylic resin release layer of the film using thermal evaporation to form a 6μm-thick lithium metal layer, producing a transfer laminate. The deposition equipment used was ULVAC's EWK-050, and the deposition process was carried out at a speed of 2.5m / min, with the lithium supply temperature set to 500°C and the main roll temperature set to -25°C.

[0162] In producing the transfer laminate, each transfer laminate was produced that satisfied the thickness of the base layer, the average surface roughness of the base layer, the type of the release layer, and the thickness of the release layer in Table 1 below.

[0163] [Table 1]

[0164] <Production of negative electrodes> A negative electrode slurry was prepared by adding Si (average particle size (D50): 3.5 μm) as a silicon-based active material, Denka Black as a conductive material, SBR as a binder, and CMC as a thickener in a weight ratio of 80:15.8:3:1.2 to distilled water as a solvent for forming a negative electrode slurry (solid concentration: 25 wt%).

[0165] The mixing method was as follows: the conductive material, binder, thickener and water were dispersed using a homomixer at 2500 rpm for 30 minutes, and then the active material was added, followed by dispersion at 2500 rpm for 30 minutes to prepare a slurry.

[0166] The negative electrode current collector was a copper current collector (thickness: 8 μm) and the negative electrode slurry was applied to both sides of the copper current collector at a rate of 85 mg / 25 cm. 2 The coated layer was rolled and dried in a vacuum oven at 130°C for 10 hours to form a negative electrode active material layer (thickness: 33 μm), which was used as a negative electrode (negative electrode thickness: 41 μm, negative electrode porosity: 40.0%).

[0167] The results of the release force and cross-cut test for the transfer laminates of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 2 below. [Table 2]

[0168] In Table 2 above, the tests were carried out under the following conditions.

[0169] -Release force The transfer laminate was prepared and cut to a width of 2.54 cm (1 inch). Ichiban Nitto-31B tape was then attached to the electrode, and a 90° peel test was performed at a speed of 300 mm / min using a UTM device (LF-PLUS), and the results were recorded.

[0170] -Cross-cut test The cross-cut test was performed by preparing the transfer laminate in which a substrate layer, a release layer, and a lithium metal layer were sequentially laminated, and then conducting a cross-cut test according to the method of ASTM 3359. Specifically, the test was performed under the following conditions: 5B (0% peeling), 4B (less than 5% peeling), 3B (5% to 15% peeling), 2B (15% to 35% peeling), 1B (35% to 65% peeling), and 0B (65% or more peeling).

[0171] By satisfying the cross-cut test results as described above, it can be confirmed that when a substrate layer under specific conditions is used, the release force with the release layer is improved, thereby making it easier to transfer the release layer and lithium metal layer onto the negative electrode active material layer.

[0172] <Pre-lithiation process progress> A pre-lithiation process was carried out using the prepared negative electrode as follows: To transfer the transfer laminate to the negative electrode active material layer, the lithium metal layer of the transfer laminate was positioned on top of the negative electrode active material layer, and then roll pressing was carried out at room temperature with a load of 40 kgf / cm applied.

[0173] <Calculation experiment of lithium loss after pre-lithiation> To confirm the loss of lithium transferred after the pre-lithiation process, a half-bicell battery was fabricated using a negative electrode (pre-lithiation process) prepared using the transfer laminate in Table 1 and a lithium metal foil as the counter electrode. The electrolyte used in this battery was a fluoroethylene carbonate (FEC) / ethyl methyl carbonate (EMC) solution of 1M LiPF6 at a volume ratio of 3 / 7.

[0174] To measure lithium loss, the amount of pre-lithiated lithium was determined as the difference in the initial charge capacity between a non-pre-lithiated electrode and a pre-lithiated electrode, and the lithium loss was calculated as the ratio of the pre-lithiated lithium capacity to the theoretical lithium capacity. This was expressed as Equation A below, and the results are shown in Table 3 below.

[0175] [Formula A] Lithium loss (%) = 1 - {("non-lithiated electrode charge capacity" - "lithiated electrode charge capacity) / theoretical capacity of lithium used during pre-lithiation}

[0176] [Table 3]

[0177] When the transfer laminates of Examples 1 and 2 were used to transfer onto a negative electrode, the polyethylene terephthalate substrate layer could be readily removed after roll pressing, and the lithium metal layer and release layer were effectively transferred onto the negative electrode active material layer, as confirmed from Tables 2 and 3. That is, the substrate layer was effectively removed after transfer due to the low release force, which facilitated the dissipation of heat generated during prelithiation, suppressed the generation of by-products, and reduced the amount of lithium loss.

[0178] Meanwhile, Comparative Example 1 shows a case where the average surface roughness of the substrate layer is below the range of the present application, and Comparative Example 2 shows a case where the thickness of the release layer coated on the substrate layer is below the lower limit of the range of the present application. As can be seen from the results in Tables 2 and 3, in Comparative Examples 1 and 2, the release force from the release layer was high, so the polyethylene terephthalate substrate layer was not immediately removed after roll pressing. When the polyethylene terephthalate substrate layer was forcibly removed, the anode detached, making it impossible to remove the polyethylene terephthalate substrate layer after pressing. Ultimately, the substrate layer could be removed approximately 4 hours later, at which point the lithiation reaction was complete before the lithium metal layer was inserted into the anode.

[0179] As a result, in the case of the negative electrodes of Comparative Examples 1 and 2, the substrate layer was not effectively removed, making it difficult to dissipate heat during prelithiation, and problems such as the generation of by-products led to uneven prelithiation on the surface, resulting in increased lithium loss. It was also confirmed that the capacity of the prelithiated lithium was inferior to that of Examples 1 and 2. [Explanation of symbols]

[0180] 10 Negative electrode current collector layer 20...Negative electrode active material layer 35 Lithium metal layer 30...Release layer 40...Base material layer 50...Separation membrane 60 Positive electrode current collector layer 70...Cathode active material layer 100 ···Negative electrode for lithium secondary battery 200 Transfer laminate 300 ···Positive electrode for lithium secondary battery

Claims

1. Base material layer; a release layer provided on one surface of the substrate layer; and a lithium metal layer provided on the surface of the release layer opposite to the surface that contacts the base layer; A transfer laminate comprising: the thickness of the release layer is 0.1 μm or more and 10 μm or less, A transfer laminate, wherein the base layer has an average surface roughness (Sa) of 50 nm or more.

2. The transfer laminate according to claim 1 , wherein the average surface roughness (Sa) of the base layer is lower than the thickness of the release layer.

3. the release force of the surface of the release layer in contact with the base layer is 100 gf / inch or less; 2. The transfer laminate according to claim 1, wherein a crosscut test value of the surface of the release layer in contact with the base layer is 0B to 1B.

4. The transfer laminate according to claim 1 , wherein the lithium metal layer has a thickness of 1 μm or more and 10 μm or less.

5. The transfer laminate according to claim 1 , wherein the thickness of the base layer is 1 μm or more and 300 μm or less.

6. 2. The transfer laminate according to claim 1, wherein the substrate layer is at least one selected from the group consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI), poly(methylmethacrylate) (PMMA), polypropylene, polyethylene, and polycarbonate.

7. forming a negative electrode current collector layer and a negative electrode active material layer on one or both sides of the negative electrode current collector layer to form a negative electrode for a lithium secondary battery; a step of laminating the transfer laminate according to any one of claims 1 to 6 onto a surface of the negative electrode active material layer opposite to a surface in contact with the negative electrode current collector layer, thereby transferring a lithium metal layer; and prelithiating the negative electrode active material layer; A method for producing a negative electrode for a lithium secondary battery, comprising:

8. The step of laminating the transfer laminate onto a surface of the negative electrode active material layer opposite to a surface in contact with the negative electrode current collector layer to transfer the lithium metal layer includes: laminating the transfer laminate so that a surface of the lithium metal layer opposite to a surface that contacts the release layer contacts a surface of the negative electrode active material layer opposite to a surface that contacts the negative electrode current collector layer; and removing the substrate layer; The method for producing a negative electrode for a lithium secondary battery according to claim 7, comprising:

9. 8. The method for producing a negative electrode for a lithium secondary battery according to claim 7, wherein the lamination is performed at a temperature of 20° C. to 80° C. and under a pressure of 20 kgf / cm to 60 kgf / cm.

10. 8. The method of claim 7, wherein the prelithiation of the negative electrode active material layer is performed within 30 minutes to 48 hours after transferring the lithium metal.

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