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 transfer laminate, a method for manufacturing a negative electrode for a lithium secondary battery, a negative electrode for a lithium secondary battery, and a lithium secondary battery.

Description

[Technical Field]

[0001] 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.

[0002] This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0182508, filed with the Korean Intellectual Property Office on December 23, 2022, the entire contents of which are incorporated herein by reference. [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 an energy source 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 / cm 3 ) 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 a 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 methods require a wet process in an electrolyte, which poses risks such as fire and explosion, making it necessary to carefully control an inert environment. Creating this environment requires the use of inert gas in the chamber where the electrochemical method is performed, making it difficult to control conditions such as moisture content. Furthermore, in order to uniformly control the initial irreversible capacity, the rate of prelithiation using the electrochemical method must be as slow as possible, which increases production costs.

[0011] Furthermore, during the pre-lithiation process, there was a problem of heat generation during the process of inserting lithium into the electrode due to the pressure process. In particular, if the temperature of the electrode exceeds 30°C, the lithium may undergo an oxidation reaction, promoting side reactions, and there is also a risk of the electrode catching fire during the lithium transfer process. These risk factors are very important factors that need to be managed when performing the lithium transfer process.

[0012] In order to improve the heat generation phenomenon, appropriate surface treatments are performed on the transfer laminate, but the transfer is easy and there is no measurement method that can quantitatively confirm the degree to which the ignition stability and the suppression of the lithium oxidation reaction are efficiently improved. As a result, problems such as the heat generation phenomenon occurring when the surface treatment is not performed appropriately, the lithium oxidation reaction causing the side reaction not being able to be avoided, and the risk of electrode ignition not being able to be avoided during the lithium transfer process have occurred.

[0013] Therefore, there is a need to research criteria that can quantify surface treatments. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-080971 Summary of the Invention [Problem to be solved by the invention]

[0015] In order to solve the above-mentioned problems, the present inventors have confirmed that the degree of oxidation reaction of surface lithium can be quantified by defining the color difference of the lithium metal surface, and have found that the above-mentioned problems can be solved.

[0016] 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]

[0017] One embodiment of the present specification provides a transfer laminate comprising a substrate layer and a lithium metal layer on one surface of the substrate layer, wherein the lithium metal layer comprises a surface protective film on the surface, the surface protective film comprises lithium carbonate (Li2CO3), and the surface color difference relative to the surface of the lithium metal layer including the surface protective film satisfies the following formula (1): L SCE ≧40-formula (1) In the formula (1), L SCE means the brightness index measured in the SCE (Specular component excluded) mode.

[0018] In 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; and laminating the transfer laminate 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.

[0019] In one embodiment of the present specification, there is provided a negative electrode for a lithium secondary battery manufactured by the method for manufacturing a negative electrode for a lithium secondary battery.

[0020] Finally, one embodiment of the present specification provides a lithium secondary battery comprising: a first electrode; a second electrode; a separator provided between the first electrode and the second electrode; and an electrolyte, wherein any one of the first electrode and the second electrode comprises the negative electrode for the lithium secondary battery. [Effects of the Invention]

[0021] The transfer laminating agent according to one embodiment of the present invention quantifies the degree of surface treatment using color difference, defines characteristics that allow for efficient transfer processes, and makes it easy to grasp the progress of the surface treatment process. By utilizing such indicators of the surface treatment process, quality and stability issues that occur during the transfer process can be effectively reduced. [Brief explanation of the drawings]

[0022] [Figure 1] 1A to 1C are diagrams showing a process for transferring lithium metal to a negative electrode for a lithium secondary battery according to one embodiment of the present specification. [Figure 2] FIG. 1 is a diagram showing a stack structure of a lithium secondary battery according to an embodiment of the present specification. DETAILED DESCRIPTION OF THE INVENTION

[0023] Before describing the present invention, some terms will first be defined. 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.

[0024] In this specification, "p to q" means a range of "not less than p and not more than q."

[0025] In this specification, the "specific surface area" is measured by the BET method, and specifically, is calculated from the nitrogen gas adsorption amount 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 can mean the specific surface area measured by the above-mentioned measurement method.

[0026] In this specification, "Dn" refers to the average particle size, or the particle size at the n% point in the cumulative particle number distribution by particle size. That is, D50 is the 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, the average particle size 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). When the particles pass through a laser beam, the difference in diffraction pattern due to particle size is measured, and the particle size distribution is calculated.

[0027] DETAILED DESCRIPTION OF THE INVENTION The present invention will now be described in detail with reference to the accompanying drawings so that those skilled in the art can easily understand the present invention. However, the present invention may be embodied in various different forms and is not limited to the following description.

[0028] <Transfer laminate> One embodiment of the present specification provides a transfer laminate including a base layer and a lithium metal layer on one surface of the base layer, wherein the lithium metal layer includes a surface protective film on the surface, the surface protective film includes lithium carbonate (Li2CO3), and the surface color difference relative to the surface of the lithium metal layer including the surface protective film satisfies the following formula (1): L SCE ≧40-formula (1) In the formula (1), L SCE means the brightness index measured in SCE (Specular component excluded) mode.

[0029] In another embodiment of the present specification, in the surface color difference with respect to the surface of the lithium metal layer including the surface protective film, L SCE may have a value of about 40 or greater, preferably about 41 or greater, or more preferably about 42 or greater, or may have a value of about 100 or less, about 95 or less, about 90 or less, preferably 85 or less, or more preferably 83 or less.

[0030] In this specification, the surface color difference can be measured using a device known in the art, and specifically, a CM-2600d manufactured by Konica Minolta may be used.

[0031] According to the above embodiment, the surface color difference is defined as the brightness index measured in the SCE mode, which defines the brightness relative to reflected light (mainly scattered light) excluding specular reflected light, and the surface hardness of the lithium metal layer including the surface protective film can be grasped.

[0032] The transfer laminate according to the above embodiment has a surface color difference within a specific range, and thus can suppress ignition or side reactions due to heat generation.

[0033] In this specification, the measurement conditions for the surface color difference of the lithium metal layer can be in accordance with the conditions of using a D65 standard light source, a 10° field of view, and 100% UV.

[0034] In this specification, the surface treatment can be performed using, but is not limited to, carbon dioxide (CO2). For example, the surface treatment can be performed using a single gas of carbon dioxide (CO2), or a mixture of carbon dioxide and an inert gas (e.g., nitrogen (N2), argon (Ar), etc.).

[0035] In the present specification, a mixture of an inert gas (for example, argon) and carbon dioxide can be used, and the mixture ratio of argon and carbon dioxide can be, but is not limited to, 8:2.

[0036] In this specification, when the surface treatment is performed with a single gas of carbon dioxide (CO2), the surface of the lithium metal layer may contain lithium carbonate (Li2CO3), which is a lithium oxide, as a main component.

[0037] The transfer laminate according to the above embodiment defines the color difference on the surface of the lithium metal layer containing lithium carbonate, which is the lithium oxide, and thus allows for numerical understanding of the surface treatment state that can improve stability in the future lithium transfer process.

[0038] In one embodiment of the present specification, the surface of the lithium metal layer may further contain one or more components selected from LiOH, Li3N, Li2O, Li2O2, and combinations thereof.

[0039] In the present specification, when the lithium metal layer is subjected to the surface treatment by being exposed to oxygen, nitrogen, moisture, etc. in the atmosphere, the surface of the lithium metal layer may further contain an additional component such as lithium oxide (e.g., LiO, LiO), lithium nitride (LiN), lithium hydroxide (LiOH), etc.

[0040] In one embodiment of the present specification, there is provided a transfer laminate in which the surface color difference relative to the surface of the lithium metal layer including the surface protective film satisfies the following formula (2): L SCI ≧90-formula (2) In the formula (2), L SCI means the brightness index measured in SCI (Specular component included) mode.

[0041] In another embodiment of the present specification, in the surface color difference with respect to the surface of the lithium metal layer including the surface protective film, L SCI may have a value of about 80 or greater, preferably about 85 or greater, or more preferably about 90 or greater, or may have a value of about 100 or less, preferably about 98 or less, or more preferably 96 or less.

[0042] The transfer laminate according to the above embodiment can numerically grasp the surface treatment state that can improve stability in future lithium transfer processes by defining the color difference on the surface of the lithium metal layer containing lithium carbonate, which is the lithium oxide.

[0043] In another embodiment of the present specification, the surface color difference relative to the surface of the lithium metal layer including the surface protective film may satisfy both the formula (1) and the formula (2).

[0044] In the transfer laminate according to the above embodiment, by defining the color difference on the surface of the lithium metal layer containing lithium carbonate, which is the lithium oxide, it is possible to numerically grasp the surface treatment state that can improve stability in the subsequent lithium transfer process.

[0045] In this specification, the surface color difference of the lithium metal layer can be measured using a device known in the art, specifically, a CM-2600d manufactured by Konica Minolta.

[0046] In one embodiment of the present specification, the thickness of the substrate layer may be 5 μm to 300 μm, preferably 10 μm to 100 μm. If the substrate thickness is less than 5 μm, process problems such as wrinkles and tears may occur during processing, and if it exceeds 300 μm, it may be difficult to effectively remove heat during lithium deposition, making it difficult to increase the deposition rate, which may result in problems such as increased costs.

[0047] In one embodiment of the present specification, the base layer may be at least one selected from the group consisting of polyethylene terephthalate (PET), polyethylenenaphtalate (PEN), polyimide (PI), poly(methylmethacrylate) (PMMA), polypropylene, polyethylene, and polycarbonate.

[0048] In one embodiment of the present specification, the lithium metal layer may have a thickness of 1 μm or more and 10 μm or less.

[0049] In other embodiments of the present application, the thickness of the lithium metal layer may be about 1 μm or more, about 2 μm or more, or about 3 μm or more, or about 10 μm or less, about 9 μm or less, or about 8 μm or less.

[0050] 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.

[0051] In one embodiment of the present specification, a release layer may be further included between the substrate layer and the lithium metal layer.

[0052] The transfer laminate according to the embodiment includes a substrate layer, a release layer (hereinafter sometimes referred to as a first release layer or a release layer), and a lithium metal layer laminated in this order, where the release layer functions as a release layer for transferring lithium. The release layer can prevent reverse peeling, in which lithium metal is transferred to the substrate layer during a winding process for transferring the deposited lithium metal layer to the negative electrode, and can also easily separate the substrate layer after the lithium metal is transferred to the negative electrode active material layer.

[0053] In another embodiment of the present application, release layers may be formed on both sides of the substrate layer.

[0054] In addition to the first release layer interposed between the substrate layer and the lithium metal layer, the transfer laminate according to the above embodiment may further include a second release layer (also sometimes referred to as an unpeeled layer) on the side opposite to the surface where the substrate layer and the first release layer contact.

[0055] The second release layer is an additional component used to reduce friction with the rolls during the roll-to-roll process.

[0056] In this specification, 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.

[0057] In one embodiment of the present specification, 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, but is not limited thereto, and various coating methods known in the art for forming a coating layer may be used.

[0058] In one embodiment of the present specification, the thickness of the release layer may be 0.1 μm or more and 10 μm or less.

[0059] Preferably, the thickness of the release layer may be about 0.1 μm or more, about 0.2 μm or more, about 0.3 μm or more, about 0.4 μm or more, or about 0.5 μm or more, or may be about 10 μm or less, about 9.9 μm or less, about 9.8 μm or less, about 9.7 μm or less, or about 9.6 μm or less.

[0060] The release layer is transferred onto the negative electrode active material layer together with the lithium metal layer in a lithium metal transfer process described below, and when the thickness of the release layer satisfies the above range, the coating uniformity of the release layer can be improved.Furthermore, when the thickness of the release layer satisfies the above range, the release layer has the characteristic of not causing an increase in battery resistance.

[0061] <Method of manufacturing a negative electrode for a lithium secondary battery> In one embodiment of the present specification, there is provided a method for manufacturing a negative electrode for a lithium secondary battery, including the steps of: preparing a negative electrode for a lithium secondary battery by 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; and laminating the transfer laminate 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.

[0062] In this specification, the step of forming 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.

[0063] In one embodiment of the present specification, the negative electrode slurry may include a negative electrode active material layer composition; and a slurry solvent.

[0064] In one embodiment of the present specification, the solid content of the negative electrode slurry may be 5% or more and 40% or less.

[0065] 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%.

[0066] 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.

[0067] When the solid content of the negative electrode slurry satisfies the above range, the viscosity is appropriate during the formation of the negative electrode active material layer, and the agglomeration of particles of the negative electrode active material layer composition is minimized, thereby enabling the negative electrode active material layer to be efficiently formed.

[0068] In one embodiment of the present specification, the slurry solvent is not limited to any solvent that can dissolve the negative electrode active material layer composition, and specifically, acetone; distilled water; or NMP may be used.

[0069] The negative electrode according to one embodiment of the present specification may be formed by coating the negative electrode slurry on a negative electrode current collector layer and drying it.

[0070] The drying step may allow the slurry solvent in the negative electrode slurry to be dried, and the method may further include rolling the negative electrode.

[0071] In one embodiment of the present specification, 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, fired carbon, a surface-treated material with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, an aluminum-cadmium alloy, etc. may be used. Further, fine irregularities can be formed on the surface to strengthen the binding force of the negative electrode active material, and it may be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric body, etc.

[0072] In one embodiment of the present specification, a negative electrode active material layer containing a negative electrode active material layer composition formed on one or both surfaces of the negative electrode current collector layer is included.

[0073] In one embodiment of the present specification, the negative electrode active material layer composition may include a silicon-based active material; a negative electrode conductive material; and a negative electrode binder.

[0074] In one embodiment of the present specification, the silicon-based active material may include at least one selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), SiC, metal impurities, and Si alloys.

[0075] In one embodiment of the present specification, the silicon-based active material includes at least one selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) may be included in an amount of 70 parts by weight or more.

[0076] In another embodiment, based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) may be included in an amount of 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, and may be included in an amount of 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less.

[0077] In one embodiment of the present specification, 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, based on 100 parts by weight of the total silicon-based active material, pure Si particles (SiOx (x=0)) not bonded to other particles or elements are contained within the above range.

[0078] 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, their high initial irreversible capacity results in reduced lifespan. To address this issue, a pre-lithiation process in which the anode is pre-lithiated is being developed.

[0079] 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.

[0080] 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. On the other hand, when the average particle size is within this range, excessively large silicon particles are excluded, resulting in a smooth negative electrode surface, which prevents current density variations during charge and discharge.

[0081] In one embodiment of the present specification, 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).

[0082] In one embodiment of the present specification, the silicon-based active material may be, for example, in a crystalline or amorphous form, and is preferably not porous.The silicon particles are preferably spherical or shard-like particles.Alternatively, but less preferably, the silicon particles may also have a fibrous structure or be in the form of a silicon-containing film or coating.

[0083] In one embodiment of the present specification, the silicon-based active material may be 60 parts by weight or more based on 100 parts by weight of the negative electrode active material layer composition.

[0084] In another embodiment, the silicon-based active material may comprise 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 comprise 95 parts by weight or less, preferably 90 parts by weight or less, and more preferably 80 parts by weight or less.

[0085] The negative electrode active material layer composition according to the present application uses a silicon-based active material having an extremely high capacity within the above range, and also uses a conductive material and a binder that can suppress the volume expansion rate during charge and discharge, so that the negative electrode performance is not reduced even when the above range is included, and the composition has the characteristic of excellent output characteristics during charge and discharge.

[0086] 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.

[0087] Thus, in one embodiment of the present specification, 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 sheet-like conductive material.

[0088] In one embodiment of the present specification, the dot-like conductive material may be used to improve the conductivity of the negative electrode and refers to a conductive material that 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, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably includes carbon black because it achieves high conductivity and has excellent dispersibility.

[0089] In one embodiment of the present specification, the point-like conductive material has a BET specific surface area of ​​40 m 2 / 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.

[0090] In one embodiment of the present specification, the particle diameter 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.

[0091] In one embodiment of the present specification, the conductive material may include a planar conductive material.

[0092] 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 may be referred to as a plate-shaped conductive material or a bulk-type conductive material.

[0093] In one embodiment of the present specification, the planar 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.

[0094] In one embodiment of the present specification, 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 causing an excessive increase in the viscosity of the negative electrode slurry. Therefore, when dispersion is performed using the same equipment and time, the dispersion effect is excellent.

[0095] In one embodiment of the present specification, the planar 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.

[0096] In one embodiment of the present specification, 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.

[0097] In one embodiment of the present specification, 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, since the planar conductive material of the present application may be affected to some extent by dispersion in terms of electrode performance, it may be particularly preferable to use a low-specific surface area planar conductive material that does not cause dispersion problems.

[0098] In one embodiment of the present specification, the planar conductive material has a BET specific surface area of ​​5 m 2 / g or more.

[0099] 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.

[0100] In another embodiment, the sheet conductive material is a high specific surface area sheet conductive material, and has 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.

[0101] In another embodiment, the sheet conductive material is a low specific surface area sheet conductive material, and the BET specific surface area is 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 25m 2 / g or less.

[0102] Other conductive materials may include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundled carbon nanotubes. The bundled carbon nanotubes may include a plurality of carbon nanotube units. Specifically, unless otherwise specified, the term "bundle type" refers to a secondary shape in which a plurality of carbon nanotube units are arranged side by side with the longitudinal axes of the carbon nanotube units substantially aligned in the same direction or are intertwined, forming a bundle or rope. The carbon nanotube units have a cylindrical graphite sheet with a nano-sized diameter, and sp 2 The bundled carbon nanotubes have a bonding structure. Depending on the angle and structure of the graphite plane wrapping, they can exhibit conductive or semiconductive properties. Compared to entangled carbon nanotubes, the bundled carbon nanotubes can be dispersed more uniformly during negative electrode fabrication, smoothly forming a conductive network within the negative electrode and improving the conductivity of the negative electrode.

[0103] In one embodiment of the present specification, 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.

[0104] In another embodiment, the negative electrode conductive material may contain 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.

[0105] 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 very large volume expansion of the electrode upon charge and discharge, while the positive electrode conductive material serves to provide a buffer during rolling and also to impart some conductivity, and therefore has a completely different structure and role from the negative electrode conductive material of the present invention.

[0106] 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.

[0107] In one embodiment of the present specification, 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.

[0108] 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 means a material for ensuring a planar conductive path within the negative electrode active material layer.

[0109] That is, in this application, the use of plate-like graphite as a conductive material means that it is used as a material that ensures a conductive path, rather than being processed into a planar or plate-like shape 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.

[0110] 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.

[0111] That is, in one embodiment of the present specification, 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 be planar and have a BET specific surface area of ​​5 m 2 / g or more.

[0112] In one embodiment of the present specification, 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.

[0113] The negative electrode binder according to one embodiment of the present specification plays a role in holding down the active material and the conductive material to prevent twisting and structural deformation of the negative electrode structure during volume expansion and relaxation of the silicon-based active material. Any common binder can be used as long as it fulfills this role. Specifically, an aqueous binder can be used, and more specifically, a PAM-based binder may be used.

[0114] In one embodiment of the present specification, there is provided a method for manufacturing a negative electrode for a lithium secondary battery, wherein the step of 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 the lithium metal layer includes the steps of: laminating the transfer laminate so that a surface of the lithium metal layer opposite to a surface that contacts the substrate 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.

[0115] 1 is a diagram showing a method for producing a negative electrode for a lithium secondary battery according to one embodiment of the present specification. Specifically, the process shows the steps of preparing a transfer laminate 100 including a substrate layer 10 and a lithium metal layer 20, laminating a negative electrode 200 for a lithium secondary battery having a negative electrode active material layer 30 formed on a negative electrode current collector layer 40 so that the negative electrode active material layer 30 and the lithium metal layer 20 are in contact with each other, removing the substrate layer 10, and transferring only the lithium metal layer 20 onto the negative electrode active material layer 30.

[0116] 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.

[0117] In one embodiment of the present specification, there is provided a method for manufacturing a negative electrode for a lithium secondary battery, wherein the laminating step is performed under a load of 200 kgf.

[0118] The lamination can be performed by 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 the substrate layer to be easily removed with only a weak linear pressure, making it easy to control the prelithiation rate, and by removing the substrate layer, it can easily release heat generated during prelithiation, thereby suppressing the generation of by-products.

[0119] In this specification, the method may further include a step of prelithiating the negative electrode active material layer after the step of transferring the lithium metal layer. This step may be performed simultaneously with transferring the lithium metal layer onto the negative electrode active material layer, and completion of the prelithiation can be confirmed when the lithium metal layer is completely removed by visual inspection.

[0120] In one embodiment of the present specification, there is provided a method for manufacturing a negative electrode for a lithium secondary battery, further comprising the step of prelithiating the negative electrode active material layer after the step of transferring the lithium metal layer, wherein the step of prelithiating the negative electrode active material layer is performed within 30 minutes to 48 hours after transferring the lithium metal.

[0121] 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 less likely to be produced. As a result, the negative electrode active material layer can be uniformly prelithiated.

[0122] 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.

[0123] <Anode for lithium secondary batteries> In one embodiment of the present specification, 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. The above-described features may be applied to the negative electrode according to this embodiment.

[0124] <Lithium secondary battery> In one embodiment of the present specification, there is provided a lithium secondary battery comprising: a first electrode; a second electrode; a separator membrane provided between the first electrode and the second electrode; and an electrolyte, wherein either the first electrode or the second electrode comprises the negative electrode for a lithium secondary battery.

[0125] In this specification, the first electrode may be a positive electrode and the second electrode may be a negative electrode, or the first electrode may be a negative electrode and the second electrode may be a positive electrode.

[0126] In this specification, 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.

[0127] 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, baked carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. The positive electrode current collector layer may typically have 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. For example, the positive electrode current collector layer may be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0128] 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-c1 O4 (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 Ni-site type lithium nickel oxide represented by the chemical formula LiMnO2 (wherein 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 c3Examples of the lithium manganese composite oxide 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 metallic lithium (Li-metal).

[0129] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the above-described positive electrode active material.

[0130] 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 may be used alone or in combination.

[0131] The positive electrode binder serves to improve adhesion between particles of the positive electrode active material and between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination.

[0132] The separator separates the negative electrode and 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 migration and excellent electrolyte humidification capacity is preferred. Specifically, a porous polymer film, such as a porous polymer film made from 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, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymeric material may also be used, and may be used in a single-layer or multi-layer structure.

[0133] 2 is a diagram showing a laminated structure of a lithium secondary battery according to one embodiment of the present disclosure. Specifically, a lithium secondary battery anode 200 including an anode active material layer 30 on one side of an anode current collector layer 40 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 100 and lithium secondary battery cathode 300 are stacked with a separator 55 sandwiched between them.

[0134] In this case, the release layer transferred during pre-lithiation may be partially removed by the electrolyte used, resulting in a small amount being present on the top of the negative electrode. Although the release layer is not shown in Figure 2, it may be present between the substrate layer 10 and the lithium metal layer 20.

[0135] In one embodiment of the present specification, 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 producing lithium secondary batteries.

[0136] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0137] 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.

[0138] 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 with low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte with high electrical conductivity can be produced, and therefore, these cyclic carbonates are more preferably used.

[0139] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte. 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:

[0140] 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 battery capacity, and improving the discharge capacity of the battery.

[0141] One embodiment of the present invention provides a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same. The battery module and 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. [Example]

[0142] Preferred examples are presented below to aid in understanding the present invention. However, the following 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. It is to be understood that such changes and modifications fall within the scope of the appended claims.

[0143] Manufacturing example: Manufacturing of transfer laminate Manufacturing Example 1 A polyethylene terephthalate substrate was prepared as a base layer, and a film (manufacturer: I-One Film) coated with a 1 μm acrylic resin was prepared as a release layer on the base layer. A lithium metal layer was deposited on the release layer using thermal evaporation to form a lithium metal layer with the thickness listed in Table 1 below, producing a transfer laminate. The deposition equipment used was an ULVAC EWK-060, and the deposition process was carried out at a speed of 2.5 m / min, with the lithium supply temperature set to 500°C and the main roll temperature set to -25°C.

[0144] Example: Surface treatment of transfer laminate Example 1 Each of the previously prepared transfer laminates (Li Film, Li thickness 3 μm) was placed in the chamber, and 10 -3 After creating a vacuum of less than torr, the vacuum valve was closed, the gas purge valve was opened, and argon (gas) and carbon dioxide (gas) were injected into the chamber at a ratio of 8:2 at room temperature.

[0145] Each gas was purged until the vacuum in the chamber reached atmospheric pressure, and after 30 minutes of treatment, the surface color difference of the lithium metal layer (film) was analyzed using a CM-2600d.

[0146] The surface-treated transfer laminate (Li Film) was attached to both sides of a silicon negative electrode, and then lithium was transferred to the electrode portion using a rolling machine with a load of approximately 200 kgf.

[0147] Example 2 The same procedure as in Example 1 was carried out, except that the Li thickness (lithium metal layer thickness) of the transfer laminate used was 4 μm.

[0148] Example 3 The same procedure as in Example 1 was followed, except that the Li thickness of the transfer stack used was 5 μm.

[0149] Example 4 The same procedure as in Example 1 was followed, except that the Li thickness of the transfer stack used was 6 μm.

[0150] Example 5 Each of the previously prepared transfer laminates (Li Film, Li thickness 6 μm) was placed in the chamber, and 10 -3 After creating a vacuum of less than torr, the vacuum valve was closed, the gas purge valve was opened, and argon (gas) and carbon dioxide (gas) were injected into the chamber at a ratio of 8:2 at room temperature.

[0151] Each gas was purged until the vacuum in the chamber reached atmospheric pressure, and the temperature of the chamber was maintained at 60° C. After 5 hours of gas treatment, the surface color difference of the lithium metal layer was analyzed using a CM-2600d.

[0152] The surface-treated transfer laminate (Li Film) was attached to both sides of a silicon negative electrode, and then lithium was transferred to the electrode portion using a rolling machine with a load of approximately 200 kgf.

[0153] Example 6 The procedure was the same as in Example 5, except that the gassing was carried out for approximately 24 hours.

[0154] Example 7 The procedure was the same as in Example 5, except that the gassing was carried out for approximately 12 hours.

[0155] Example 8 The same procedure as in Example 1 was followed, except that the Li thickness of the transfer stack used was 9 μm.

[0156] Comparative Example 1 The Li 6 μm thick transfer laminate produced in Production Example 1 was analyzed for surface color difference of the lithium metal layer using a CM-2600d without additional gas purging.

[0157] The surface-treated transfer laminate (Li Film-lithium metal layer) was attached to both sides of a silicon negative electrode, and then a rolling machine was used to transfer the lithium to the Si electrode part prepared in Production Example 2 under a load of approximately 200 kgf. The electrode used for the transfer was 5 cm x 5 cm in size.

[0158] Comparative Example 2 Each of the previously prepared transfer laminates (Li Film, Li thickness 6 μm) was placed in the chamber, and 10 -3 After creating a vacuum of less than 100 torr, the vacuum valve was closed, the gas purge valve was opened, and cleaned dry air (CDA, dew point -40°C) was purged at 25°C until the vacuum in the chamber reached atmospheric pressure, and the chamber temperature was maintained at 25°C. After 30 minutes of gas treatment, the surface color difference of the lithium metal layer was analyzed using a CM-2600d.

[0159] The surface-treated transfer laminate (Li Film-lithium metal layer) was attached to both sides of a silicon negative electrode, and then a rolling machine was used to transfer the lithium to the Si electrode part prepared in Production Example 2 under a load of approximately 200 kgf. The electrode used for the transfer was 5 cm x 5 cm in size.

[0160] Comparative Example 3 Each of the previously prepared transfer laminates (Li Film, Li thickness 6 μm) was placed in the chamber, and 10 -3 After creating a vacuum of less than torr, the vacuum valve was closed, the gas purge valve was opened, and argon (gas) and carbon dioxide (gas) were injected into the chamber at a ratio of 99:1 at 25°C.

[0161] After purging each gas until the vacuum level in the chamber reached atmospheric pressure, the temperature of the chamber was maintained at 25° C. After 30 minutes of gas treatment, the surface color difference of the lithium metal layer was analyzed using a CM-2600d.

[0162] The surface-treated transfer laminate (Li Film) was attached to both sides of the silicon negative electrode, and then a rolling machine was used to transfer the lithium to the Si electrode part prepared in Production Example 2 under a load of approximately 200 kgf. At this time, the electrode used for transfer was 5 cm x 5 cm in size.

[0163] Comparative Example 4 Each of the previously prepared transfer laminates (Li Film, Li thickness 6 μm) was placed in the chamber, and 10 -3 After creating a vacuum of less than torr, the vacuum valve was closed, the gas purge valve was opened, and argon (gas) and carbon dioxide (gas) were injected into the chamber at a ratio of 8:2 at 25°C.

[0164] After purging each gas until the vacuum in the chamber reached atmospheric pressure, the temperature of the chamber was maintained at 10° C. After 30 minutes of gas treatment, the surface color difference of the lithium metal layer was analyzed using a CM-2600d.

[0165] The surface-treated transfer laminate (Li Film) was attached to both sides of the silicon negative electrode, and then a rolling machine was used to transfer the lithium to the Si electrode part prepared in Production Example 2 under a load of approximately 200 kgf. At this time, the electrode used for transfer was 5 cm x 5 cm in size.

[0166] Comparative Example 5 Each of the previously prepared transfer laminates (Li Film, Li thickness 6 μm) was placed in the chamber, and 10 -3 After creating a vacuum of less than torr, the vacuum valve was closed, the gas purge valve was opened, and argon (gas) and carbon dioxide (gas) were injected into the chamber at a ratio of 8:2 at 25°C.

[0167] After purging each gas until the vacuum in the chamber reached atmospheric pressure, the temperature of the chamber was maintained at 25° C. After 3 minutes of gas treatment, the surface color difference of the lithium metal layer was analyzed using a CM-2600d.

[0168] The surface-treated transfer laminate (Li Film) was attached to both sides of a silicon negative electrode, and then a rolling machine was used to transfer lithium under a load of approximately 200 kgf onto the Si electrode part prepared in Production Example 2. The electrode used for the transfer was 5 cm x 5 cm in size.

[0169] [Measurement of fever temperature] The heat generation temperatures of the electrodes of Examples 1 to 8 and Comparative Examples 1 to 5 were measured as follows: Immediately after Li was transferred to the electrode part, the PET was removed, a thermocouple (TC) was attached to the center of the surface of the electrode to which Li was transferred, and the maximum surface temperature of the electrode that generated heat was measured.

[0170] The results of Examples 1 to 8 and Comparative Examples 1 to 5 are shown in Table 1 below.

[0171] [Table 1]

[0172] However, in Table 1 above, CDA means that the components are the same as those of general air.

[0173] According to Table 1, in the case of Comparative Examples 1 to 5, even though the brightness (L) measured in SCI mode was 90 or more, the brightness (L) measured in SCE mode was less than 40, which confirms that the heat generation temperature immediately after transfer was 38°C or higher.

[0174] In contrast, in Examples 1 to 8, the brightness (L) measured in SCI mode was 90 or more, and the brightness (L) measured in SCE mode was 40 or more, which confirms that the heat generation temperature immediately after transfer was low, at 30°C or less.

[0175] In particular, when the carbon dioxide content in the surface treatment gas (a trace amount of carbon dioxide present in CDA or a ratio of Ar:CO2 = 99:1) was changed as in Comparative Examples 2 and 3, the chamber temperature after purging the surface treatment gas was lowered to 10°C as in Comparative Example 4, or the surface treatment time was shortened to 3 minutes as in Comparative Example 5, the lightness measured in SCE mode was less than 40. These results show that, compared to the Comparative Examples, even slight changes in the surface treatment conditions in the Examples can easily predict whether lithium carbonate (Li2CO3) will be formed within a short period of time, allowing the degree of surface treatment to be accurately determined. This allows the degree of heat generation immediately after transfer to be easily predicted, significantly reducing the risk of fire during pre-lithiation. [Explanation of symbols]

[0176] 10...Base material layer 20 Lithium metal layer 30...Negative electrode active material layer 40 Negative electrode current collector layer 55...Separation membrane 60 Positive electrode current collector layer 70...Cathode active material layer 100 Transfer laminate 200 ···Anode for lithium secondary battery 300 ···Positive electrode for lithium secondary battery

Claims

1. A transfer laminate including a substrate layer and a lithium metal layer on one surface of the substrate layer, the lithium metal layer includes a surface protective film on the surface; The surface protection film is made of lithium carbonate (Li ２ CO ３ ), The surface color difference relative to the surface of the lithium metal layer including the surface protective film satisfies the following formula (1): Transfer laminate used in pre-lithium processing of battery anodes: L ＳＣＥ ≧40-Formula (1) In the formula (1), L ＳＣＥ means the brightness index measured in SCE (Specular component excluded) mode.

2. The transfer laminate according to claim 1, wherein the surface color difference relative to the surface of the lithium metal layer including the surface protective film satisfies the following formula (2): L ＳＣＩ ≧90-Formula (2) In the formula (2), L ＳＣＩ means the brightness index measured in SCI (Specular component included) mode.

3. On the surface of the lithium metal layer, LiOH, Li ３ N., Li. ２ O, Li ２ O ２ 10. The transfer laminate of claim 1, further comprising one or more components selected from:

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

5. 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.

6. 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.

7. The transfer laminate of claim 1 , further comprising a release layer between the substrate layer and the lithium metal layer.

8. The transfer laminate according to claim 7 , wherein the release layer has a thickness of 0.1 μm or more and 10 μm or less.

9. 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 prepare a negative electrode for a lithium secondary battery; and a step of laminating the transfer laminate according to any one of claims 1 to 8 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; A method for producing a negative electrode for a lithium secondary battery, comprising:

10. The step of transferring the lithium metal layer by laminating the transfer laminate onto the surface of the negative electrode active material layer opposite to the surface that contacts the negative electrode current collector layer includes laminating the transfer laminate so that the surface of the lithium metal layer opposite to the surface that contacts the substrate layer contacts the surface of the negative electrode active material layer opposite to the 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 9 , comprising:

11. The method for producing a negative electrode for a lithium secondary battery according to claim 9 , wherein the lamination is performed under a load of 200 kgf.

12. The method further includes prelithiating the negative electrode active material layer after transferring the lithium metal layer, 10. The method of claim 9, wherein in the prelithiation of the negative electrode active material layer, the negative electrode active material layer is prelithiated within 30 minutes to 48 hours after transferring the lithium metal layer.

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