Transcription laminate, method for manufacturing a negative electrode for a lithium secondary battery, negative electrode for a lithium secondary battery, and lithium secondary battery including the 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 manufacturing 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] The present 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, and all of its contents are incorporated herein by reference.

Background Art

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

[0004] Currently, a typical example of an electrochemical device that uses such electrochemical energy is a secondary battery, and its usage area is increasingly expanding.

[0005] As the technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among such secondary batteries, lithium secondary batteries having a high energy density, voltage, long cycle life, and low self-discharge rate have been commercialized and widely used. In addition, research on methods for manufacturing high-density electrodes with a higher energy density per unit volume as electrodes for such high-capacity lithium secondary batteries is actively underway.

[0006] Generally, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material that inserts and desorbs lithium ions emitted from the positive electrode, and silicon-based particles having a large discharge capacity can be used as the negative electrode active material.

[0007] Generally, carbon materials such as graphite are used for the negative electrode of lithium secondary batteries. However, the theoretical capacity density of carbon is 372 mAh / g (833 mAh / cm 3 3

[0008] ) Therefore, in order to improve the energy density of the negative electrode, silicon (Si), tin (Sn), their oxides and alloys, which alloy with lithium, are considered as negative electrode materials. Among them, silicon-based materials have attracted attention due to their low price and high capacity (4200 mAh / g).

[0009] However, when using a silicon-based negative electrode active material, there is a problem of a large initial irreversible capacity. That is, in the charge-discharge reaction of a lithium secondary battery, lithium released from the positive electrode during charging is inserted into the negative electrode, and during discharging, it desorbs from the negative electrode and returns to the positive electrode again. In the case of a silicon-based negative electrode active material, volume change and surface side reactions are intense, and a large amount of the lithium inserted into the negative electrode during the initial charging cannot return to the positive electrode again. Therefore, there is a problem that the initial irreversible capacity becomes large. When the initial irreversible capacity becomes large, there is a problem that the battery capacity and cycle rapidly decrease.

[0010] In order to use the conventional electrochemical method, a Wet process must be carried out in an electrolyte, which includes risks such as fire and explosion. Therefore, it is necessary to well control an inert environment. That is, in order to create the above environment, it is difficult to adjust conditions such as moisture control using an inert gas in the room where the electrochemical method proceeds. Also, in order to uniformly control the initial irreversible capacity, it is not possible to implement it unless the rate of pre-lithiation using the electrochemical method is advanced as slowly as possible. Therefore, there is a problem that the production cost increases in the application of the electrochemical method.

[0011] In addition, during the pre-lithiation process, there was a problem of heat generation during the process of lithium being inserted into the electrode by the pressurization process. In particular, when the heat generation temperature of the electrode exceeds 30°C, lithium not only undergoes an oxidation reaction to promote side reactions, but there is also a risk of electrode ignition during the lithium transfer process. Such risk factors are parts that need to be managed as very important factors when performing the lithium transfer process.

[0012] In order to improve the heat generation phenomenon, appropriate surface treatment is performed on the transfer laminate, but there is no measurement method that can quantitatively confirm the degree to which the transfer is easy and the ignition stability and the suppression of the lithium oxidation reaction are efficiently improved. Therefore, problems such as the surface treatment not being properly performed, the heat generation phenomenon appearing, the lithium oxidation reaction occurring and side reactions not being avoidable, or the risk of electrode ignition not being avoidable during the lithium transfer process have occurred.

[0013] Therefore, research on criteria that can quantify the surface treatment is necessary.

Prior Art Documents

Patent Documents

[0014]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

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

[0016] Accordingly, 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 including the negative electrode.

Means for Solving the Problem

[0017] One embodiment of the present specification is a transfer laminate including a base material layer and a lithium metal layer on one surface of the base material layer, wherein the lithium metal layer includes a surface protective film on its surface, the surface protective film includes lithium carbonate (Li2CO3), and the surface color difference of the surface of the lithium metal layer including the surface protective film satisfies the following formula (1). It is intended to provide a transfer laminate. L SCE ≧40 - Formula (1) In the formula (1), L SCE means the lightness index measured in the SCE (Specular component excluded) mode.

[0018] In another embodiment, forming a negative electrode active material layer on one surface or both surfaces of a negative electrode current collector layer to form a negative electrode for a lithium secondary battery; and laminating the transfer laminate on the opposite surface of the surface of the negative electrode active material layer that contacts the negative electrode current collector layer to transfer the lithium metal layer. It is intended to provide a method for manufacturing a negative electrode for a lithium secondary battery including the steps.

[0019] Also, in one embodiment of the present specification, it is intended to provide a negative electrode for a lithium secondary battery manufactured by the method for manufacturing a negative electrode for a lithium secondary battery.

[0020] Finally, in one embodiment of the present specification, it is intended to provide a lithium secondary battery including a first electrode; a second electrode; a separator provided between the first electrode and the second electrode; and an electrolyte, wherein either one of the first electrode and the second electrode includes the negative electrode for a lithium secondary battery.

Effect of the Invention

[0021] According to one embodiment of the present invention, the transfer laminating agent can define the property of numerically expressing the degree of surface treatment by color difference, enabling efficient performance of the transfer process, and can easily grasp the progress of the surface treatment process. By utilizing such an index of the surface treatment process, quality problems and stability problems occurring during the transfer process can be effectively reduced.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0023] Before describing the present invention, first, several terms are defined. In this specification, when a certain part "includes" a certain component, this means that, unless otherwise stated to the contrary, it does not exclude other components, but may further include other components.

[0024] In this specification, "p to q" means the range of "p or more and q or less".

[0025] In this specification, the "specific surface area" is measured by the BET method, specifically calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mini II of BEL Japan. That is, in this application, the BET specific surface area can mean the specific surface area measured by the above measurement method.

[0026] In this specification, "Dn" means the average particle size and refers to the particle size at the n% point of the cumulative particle number distribution by particle size. That is, D50 is the particle size at the 50% point of the cumulative particle number distribution by particle size, D90 is the particle size at the 90% point of the cumulative particle number distribution by particle size, and D10 is the particle size at the 10% point of the cumulative particle number distribution by particle size. On the other hand, the average particle size can be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac S3500). When the particles pass through the laser beam, the diffraction pattern difference due to the particle size is measured to calculate the particle size distribution.

[0027] Hereinafter, a detailed description will be given with reference to the drawings so that those having ordinary knowledge in the technical field to which the present invention pertains can easily implement the present invention. However, the present invention can be embodied in various different forms and is not limited to the following description.

[0028] <Transfer laminate> One embodiment of this specification is a transfer laminate including a base material layer and a lithium metal layer on one surface of the base material 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 of the lithium metal layer including the surface protective film with respect to the surface satisfies the following formula (1). L SCE ≧40 - Formula (1) In the formula (1), L SCE means the lightness index measured in the SCE (Specular component excluded, excluding specular light) mode.

[0029] In another embodiment of this specification, in the surface color difference of the lithium metal layer including the surface protective film with respect to the surface, L SCE has a value of about 40 or more, preferably about 41 or more, or more preferably about 42 or more, 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 by an apparatus known in the art, and specifically, CM-2600d of Konica Minolta may be used.

[0031] According to the embodiment, the surface color difference is defined by the lightness index measured in the SCE mode that defines the brightness with respect to the reflected light (mainly scattered light) excluding the specularly reflected light, and the hardness of the surface of the lithium metal layer including the surface protective film can be grasped.

[0032] The transfer laminate according to the embodiment can suppress the ignition phenomenon or side reaction due to heat generation by having a surface color difference within a specific range.

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

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

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

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

[0037] By defining the color difference with respect to the surface of the lithium metal layer containing lithium carbonate which is the lithium oxide, the transfer laminate according to the embodiment can numerically grasp the surface treatment state that can improve the stability in the subsequent 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, in the surface treatment process, when the lithium metal layer is exposed to oxygen, nitrogen, moisture, etc. in the air and surface-treated, lithium oxide (for example, Li2O, Li2O2), lithium nitride (Li3N), lithium hydroxide (LiOH), etc. may be further included as additional components on the surface of the lithium metal layer.

[0040] In one embodiment of the present specification, a transfer laminate is provided in which the surface color difference with respect 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 lightness index measured in the 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 more, preferably about 85 or more, or more preferably about 90 or more, or may have a value of about 100 or less, preferably about 98 or less, or more preferably 96 or less.

[0042] By defining the color difference with respect to the surface of the lithium metal layer containing lithium carbonate, which is the lithium oxide, the transfer laminate according to the above embodiment can numerically grasp the surface treatment state that can improve the stability in the subsequent lithium transfer process.

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

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

[0045] In the present specification, the surface color difference of the lithium metal layer can be measured by an apparatus known in the art. Specifically, CM-2600d manufactured by Konica Minolta may be used.

[0046] In one embodiment of the present specification, the thickness of the base material layer is 5 μm or more and 300 μm or less, and preferably may be 10 μm or more and 100 μm or less. When the thickness of the base material is less than 5 μm, process problems such as wrinkles and breaks during the process may occur. When it exceeds 300 μm, it is difficult to effectively remove heat during lithium evaporation, so it is difficult to increase the evaporation rate, which may cause problems such as cost increase.

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

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

[0049] In another embodiment of the present application, the thickness of the lithium metal layer may be about 1 μm or more, about 2 μm or more, or 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 transfer of the lithium metal to the negative electrode active material layer side can occur efficiently, reverse transfer can be prevented, and the negative electrode active material layer can be pre-lithiated to a desired degree.

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

[0052] The transfer laminate according to the above embodiment is laminated in the order of a base material layer, a release layer (hereinafter sometimes referred to as a first release layer or a peeling layer), and a lithium metal layer, where the release layer functions as a peeling layer for transferring lithium. During the winding process for transferring the lithium metal layer vapor-deposited on the release layer to the negative electrode, the problem of reverse peeling in which the lithium metal is transferred onto the base material layer can be prevented, and further, after transferring the lithium metal onto the negative electrode active material layer, the base material layer can be easily separated.

[0053] In other embodiments of the present application, release layers may be formed on both sides of the base material layer.

[0054] In addition to the first release layer interposed between the base material layer and the lithium metal layer, the transfer laminate according to the above embodiment may further include a second release layer (which may sometimes be referred to as an unpeeled layer) on the opposite surface of the surface where the base material layer and the first release layer are in contact.

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

[0056] In this specification, the release layer may include one or more selected from the group consisting of a silicon-modified polyester in which a silicon chain is graft-bonded to a polyester main chain, an acrylic resin, Si, melamine, and fluorine.

[0057] In one embodiment of this 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 that can be used to form a coating layer in the art can be used.

[0058] In one embodiment of this 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, together with the lithium metal layer, is transferred onto the upper part of the negative electrode active material layer in the lithium metal transfer process described later. When the thickness of the release layer satisfies the above range, the coating uniformity of the release layer can be increased. Also, when the release layer satisfies the above thickness range, it will have the characteristic of not causing the problem of increased battery resistance.

[0061] <Method for manufacturing negative electrode for lithium secondary battery> In one embodiment of the present specification, a step 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 a step of laminating the above-described transfer laminate on the opposite surface of the negative electrode active material layer that contacts the negative electrode current collector layer to transfer the lithium metal layer are included.

[0062] In the present specification, the step of forming a negative electrode active material layer on one or both surfaces of the negative electrode current collector layer includes a step of coating a negative electrode slurry containing a negative electrode active material layer composition on one or both surfaces of the negative electrode current collector layer, 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 satisfy 5% or more and 40% or less.

[0065] In another embodiment, the solid content of the negative electrode slurry may satisfy the range of 5% or more and 40% or less, preferably 7% or more and 35% or less, and more preferably 10% or more and 30% or less.

[0066] The solid content of the negative electrode slurry can mean the content of the negative electrode active material layer composition contained in the negative electrode slurry, and can mean 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 it has the characteristic that the lumping phenomenon of the particles of the negative electrode active material layer composition can be minimized and the negative electrode active material layer can be efficiently formed.

[0068] In one embodiment of the present specification, the slurry solvent is not limited as long as it can dissolve the negative electrode active material layer composition. 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 and drying the negative electrode slurry on a negative electrode current collector layer.

[0070] By the drying step, the slurry solvent in the negative electrode slurry can be dried, and then, an electrode rolling step may be further included.

[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. Also, 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 including 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, as the silicon-based active material, pure silicon (Si) may be particularly used. Using pure silicon (Si) as the silicon-based active material means, as described above, that when based on 100 parts by weight of the total silicon-based active material, it can be meant to contain pure Si particles (SiOx (x = 0)) not bonded to other particles or elements within the above range.

[0078] In the case of a silicon-based active material, when compared with the conventionally used graphite-based active material, the capacity is significantly higher, and attempts to apply it have been increasing. However, the volume expansion rate during charge and discharge is high, and it has remained at the level of, for example, using it by mixing a small amount with a graphite-based active material. Further, despite the above advantages, since the initial irreversible capacity is large, a decrease in life has occurred. To solve this, a prelithiation process of prelithiating the negative electrode in advance has been advanced.

[0079] Therefore, in the case of the present invention, while only using a high-content silicon-based active material as the negative electrode active material to improve the capacity performance, in order to solve the above problems, a main object of the present invention is to provide a transfer laminate that can more smoothly transfer a lithium metal layer to the upper part of the negative electrode active material layer.

[0080] On the other hand, the average particle size (D50) of the silicon-based active material of the present invention is 5 μm to 10 μm, specifically 5.5 μm to 8 μm, and more specifically may be 6 μm to 7 μm. When the average particle size is included in the above range, the specific surface area of the particles is included in an appropriate range, and the viscosity of the negative electrode slurry is formed in an appropriate range. Thereby, the dispersion of the particles constituting the negative electrode slurry becomes smooth. Further, since the size of the silicon-based active material has a value equal to or greater than the lower limit value of the above range, the contact area between the silicon particles and the conductive material by the composite composed of the conductive material and the binder in the negative electrode slurry is excellent, and the possibility of the conductive network continuing is high, and the capacity retention rate increases. On the other hand, when the average particle size satisfies the above range, silicon particles that are too large are excluded, and the surface of the negative electrode is formed smoothly, thereby preventing the current density variation phenomenon 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 to 150.0 m 2 / g, more preferably 0.1 m 2 / g to 100.0 m 2 / g, particularly preferably 0.2 m 2 / g to 80.0 m 2 / g, most preferably 0.2 m 2 / g to 18.0 m 2 / g. The BET specific surface area is measured in accordance with DIN 66131 (using nitrogen).

[0082] In one embodiment of the present specification, the silicon-based active material may be present, for example, in crystalline or amorphous form and is preferably not porous. The silicon particles are preferably spherical or flaky particles. As an alternative, although less preferred, the silicon particles may also have a fibrous structure or be present 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 contain 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more, and may contain 95 parts by weight or less, preferably 90 parts by weight or less, more preferably 80 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer composition.

[0085] Even if the negative electrode active material layer composition according to the present application uses a silicon-based active material with a significantly high capacity within the above range, by using a conductive material and a binder capable of suppressing the volume expansion rate during the charge and discharge process, the performance of the negative electrode will not be deteriorated even if it includes the above range, and it will have excellent characteristics in output characteristics during charging and discharging.

[0086] Conventionally, it has been common to use only graphite-based compounds as the negative electrode active material. However, in recent years, as the demand for high-capacity batteries has increased, there has been an increasing number of attempts to mix and use silicon-based compounds to increase the capacity. However, in the case of silicon-based compounds, there is a limit in that the volume rapidly expands during the charge / discharge process, damaging the conductive path formed in the negative electrode active material layer and rather deteriorating the battery performance.

[0087] Accordingly, 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-shaped conductive material, a linear conductive material, and a planar conductive material.

[0088] In one embodiment of the present specification, the dot-shaped conductive material may be used to improve the conductivity of the negative electrode, and means a conductive material having conductivity without inducing a chemical change. Specifically, the dot-shaped 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 may include carbon black in terms of embodying high conductivity and excellent dispersibility.

[0089] In one embodiment of the present specification, the dot-shaped conductive material has a BET specific surface area of 40 m 2 / g or more and 70 m 2 / g or less, preferably 45 m 2 / g or more and 65 m 2 / g or less, more preferably 50 m 2 / g or more and 60 m 2 / g or less.

[0090] In one embodiment of the present specification, the particle size of the dot-shaped conductive material is 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 can play a role in increasing the surface contact between silicon particles in the negative electrode to improve conductivity, and at the same time suppressing the interruption of the conductive path due to volume expansion, and can be expressed 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 any one selected from the group consisting of plate-shaped graphite, graphene, graphene oxide, and graphite flakes, and preferably may be plate-shaped graphite.

[0094] In one embodiment of the present specification, the average particle size (D50) of the planar conductive material is 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically may be 4 μm to 5 μm. When the above range is satisfied, due to the sufficient particle size, dispersion is easy without causing an excessive increase in the viscosity of the negative electrode slurry. Therefore, when dispersing 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 in which D10 is 0.5 μm or more and 1.5 μm or less, D50 is 2.5 μm or more and 3.5 μm or less, and D90 is 7.0 μm or more and 15.0 μm or less.

[0096] In one embodiment of the present specification, as the planar conductive material, a high specific surface area planar conductive material with a high BET specific surface area; or a low specific surface area planar conductive material may be used.

[0097] In one embodiment of the present specification, the high specific surface area planar conductive material; or the low specific surface area planar conductive material can be used without limitation as the planar conductive material. However, particularly for the planar conductive material according to the present application, since the electrode performance may be affected by dispersion to some extent, it is particularly preferable to use a low specific surface area planar conductive material that does not cause problems in dispersion in some cases.

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

[0099] In another embodiment, the planar conductive material has a BET specific surface area of 5 m 2 / g or more and 500 m 2 / g or less, preferably 5 m 2 / g or more and 300 m 2 / g or less, more preferably 5 m 2 / g or more and 250 m 2 / g or less.

[0100] In another embodiment, the planar conductive material is a high specific surface area planar conductive material, and the BET specific surface area is 50 m 2 / g or more and 500 m 2 / g or less, preferably 80 m 2 / g or more and 300 m 2 / g or less, more preferably 100 m 2 / g or more and 300 m 2 / g or less.

[0101] In another embodiment, the planar conductive material is a low specific surface area planar conductive material, and the BET specific surface area is 5 m 2 / g or more and 40 m 2 / g or less, preferably 5 m 2 / g or more and 30 m 2 / g or less, more preferably 5 m 2 / g or more and 25 m 2 / g or less.

[0102] As other conductive materials, there may be linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundle-type carbon nanotubes. The bundle-type carbon nanotubes may include a plurality of carbon nanotube unit bodies. Specifically, here, the "bundle type" refers to a bundle or rope-like secondary shape in which a plurality of carbon nanotube unit bodies are arranged side by side with the axes in the longitudinal direction of the carbon nanotube unit bodies being substantially in the same orientation or intertwined, unless otherwise specified. The carbon nanotube unit body has a graphite sheet having a nanosize diameter in a cylindrical shape and has a sp 2 bonding structure. At this time, depending on the angle and structure around which the graphite sheet is wound, the characteristics of a conductor or a semiconductor can be exhibited. The bundle-type carbon nanotubes can be uniformly dispersed during the production of the negative electrode as compared with entangled-type carbon nanotubes, and can smoothly form a conductive network in the negative electrode, and the conductivity of the negative electrode can be improved.

[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 include 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] In the case of the negative electrode conductive material according to the present application, it has a completely different configuration from the conductive material applied to the positive electrode. That is, in the case of the negative electrode conductive material according to the present application, it serves to capture the contacts between silicon-based active materials having a very large volume expansion of the electrode during charging and discharging, and the positive electrode conductive material serves to impart partial conductivity while serving as a buffer having a buffering role when rolled, and the configuration and role of the negative electrode conductive material of the present invention are completely different.

[0106] Furthermore, the negative electrode conductive material according to the present application is applicable to a silicon-based active material and has a completely different configuration from the conductive material applicable to a graphite-based active material. That is, the conductive material used for an electrode having a graphite-based active material has particles that are simply smaller than the active material, and thus has the characteristics of improving output characteristics and imparting some conductivity. The configuration and role of the negative electrode conductive material applied together with the silicon-based active material as in the present invention are completely different.

[0107] In one embodiment of the present specification, the planar conductive material used as the aforementioned negative electrode conductive material generally has a different structure and role from the carbon-based active material used as the 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 means a material processed into a spherical or dot-like form in order to facilitate the storage and release of lithium ions.

[0108] On the other hand, the planar conductive material used as the negative electrode conductive material is a material having a planar or plate-like form and can be expressed as plate-like graphite. That is, it is a material included in order to maintain a conductive path within the negative electrode active material layer, and means a material for ensuring a planar conductive path inside the negative electrode active material layer, rather than playing a role in the storage and release of lithium.

[0109] That is, in the present application, the fact that plate-like graphite is used as the conductive material means that it is used as a material for ensuring a conductive path, rather than being processed into a planar or plate-like form to store or release lithium. At this time, the negative electrode active material included together has a high capacity characteristic for lithium storage and release and will play a role of storing and releasing all lithium ions transmitted from the positive electrode.

[0110] On the other hand, in the present application, the fact that the carbon-based active material is used as the active material means that it is used as a material processed into a dot-like or spherical form to play a role of storing or releasing lithium.

[0111] That is, in one embodiment of the present specification, artificial graphite or natural graphite, which is a carbon-based active material, may satisfy the range of a BET specific surface area of 0.1 m 2 / g or more and 4.5 m 2 / g or less. Further, the plate-shaped graphite, which is a planar conductive material, is planar and may 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 is polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid and at least one selected from the group consisting of substances in which hydrogen thereof is substituted with Li, Na, Ca, etc., and various copolymers thereof may also be included.

[0113] The negative electrode binder according to one embodiment of the present specification plays a role of suppressing the active material and the conductive material in order to prevent twisting and structural deformation of the negative electrode structure in the volume expansion and relaxation of the silicon-based active material. Any general binder can be applied as long as the role is satisfied. 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, the step of laminating the transfer laminate on the surface of the negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer to transfer the lithium metal layer includes laminating the transfer laminate so that the surface of the lithium metal layer opposite to the surface in contact with the base material layer contacts the surface of the negative electrode active material layer opposite to the surface in contact with the negative electrode current collector layer; and removing the base material layer, and provides a method for manufacturing a negative electrode for a lithium secondary battery.

[0115] FIG. 1 is a diagram showing a method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present specification. Specifically, a transfer laminate 100 including a base material layer 10 and a lithium metal layer 20 is prepared, and the negative electrode active material layer 30 and the lithium metal layer 20 of the negative electrode 200 for a lithium secondary battery in which the negative electrode active material layer 30 is formed on the negative electrode current collector layer 40 are laminated so as to be in contact with each other. Then, the base material layer 10 is removed, and only the lithium metal layer 20 is transferred onto the negative electrode active material layer 30.

[0116] In particular, as described above, it includes the step of transferring the lithium metal layer through a transfer laminate including a specific base material layer according to the present application, and has the characteristic that the lithium metal layer can be transferred more easily.

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

[0118] The lamination can proceed with the transfer process through roll pressing. Then, a step of removing the base material layer is included. By including the release layer according to the present application during the removal, direct contact between the lithium metal layer and the air can be prevented, and the lithium metal layer can be protected. Further, due to the presence of the release layer, the base material layer can be easily removed even with a weak line pressure, the prelithiation rate can be easily adjusted, the release of heat generated during prelithiation by removing the base material layer can be facilitated, and the generation of by-products can be suppressed.

[0119] In this specification, after the step of transferring the lithium metal layer, a step of pre-lithiating the negative electrode active material layer may further be included. At this time, it may proceed simultaneously with transferring the lithium metal layer onto the negative electrode active material layer. When all of the lithium metal layer is visually removed, it can be confirmed that the pre-lithiation is completed.

[0120] In one embodiment of this specification, the method for manufacturing a negative electrode for a lithium secondary battery further includes a step of pre-lithiating the negative electrode active material layer after the step of transferring the lithium metal layer. The step of pre-lithiating the negative electrode active material layer provides a method for manufacturing a negative electrode for a lithium secondary battery, which is pre-lithiated within 30 minutes to 48 hours after transferring lithium metal.

[0121] As described above, after transferring the lithium metal layer, the substrate layer can be removed immediately, the removal of the substrate layer proceeds easily, heat release is easy during pre-lithiation when the lithium metal layer reacts with the negative electrode active material layer, the generation of by-products is small, and thereby it has the characteristic that the negative electrode active material layer can be uniformly pre-lithiated.

[0122] The pre-lithiation completion time can be calculated by measuring the time when the transferred lithium metal is not observed on the surface of the negative electrode active material layer from the time of lithium metal transfer.

[0123] <Negative electrode for lithium secondary battery> In one embodiment of this specification, a negative electrode for a lithium secondary battery manufactured according to the method for manufacturing a negative electrode for a lithium secondary battery is provided. The negative electrode according to this embodiment can apply the foregoing content.

[0124] <Lithium secondary battery> In one embodiment of this specification, a lithium secondary battery is provided, which includes a first electrode; a second electrode; a separator provided between the first electrode and the second electrode; and an electrolyte, and either the first electrode or the second electrode includes the negative electrode for a lithium secondary battery.

[0125] In this specification, the first electrode may be the positive electrode and the second electrode may be the negative electrode, or the first electrode may be the negative electrode and the second electrode may be the 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] In the positive electrode, the positive electrode current collector layer is not particularly limited as long as it has conductivity without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. can be used. Further, the positive electrode current collector layer may usually have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the positive electrode current collector layer to enhance the adhesive force of the positive electrode active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven bodies, etc.

[0128] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; the chemical formula Li 1+c1 Mn 2-c1 O4 (0 ≦ c1 ≦ 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; the 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 satisfies 0.01 ≦ c2 ≦ 0.3) represented by Ni-site type lithium nickel oxide; the chemical formula LiMn 2-c3 M c3O2 (where M is at least any 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 any one selected from the group consisting of Fe, Co, Ni, Cu, and Zn).); Examples include, but are not limited to, LiMn2O4 in which a part of 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 together with the positive electrode active material described above.

[0130] At this time, the positive electrode conductive material is used to impart conductivity to the electrode, and in the battery to be configured, it can be used without particular limitation as long as it has electron conductivity without undergoing a chemical change. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these or a mixture of two or more thereof can be used.

[0131] In addition, the positive electrode binder plays a role in improving the adhesion between the positive electrode active material particles and the adhesive force between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, etc. Among these, one kind alone or a mixture of two or more kinds may be used.

[0132] As the separator, it separates the negative electrode and the positive electrode and provides a migration path for lithium ions. Usually, it can be used without particular limitation as long as it is used as a separator in a secondary battery. In particular, those with low resistance to the ion migration of the electrolyte and excellent electrolyte moisture retention ability are preferred. Specifically, a porous polymer film, for example, a porous polymer film made from polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof may be used. Also, a normal porous non-woven fabric, for example, a non-woven fabric made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc. may be used. In addition, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer substance can also be used, and it may be selectively used in a single-layer or multi-layer structure.

[0133] FIG. 2 is a diagram showing a laminated structure of a lithium secondary battery according to an embodiment of the present specification. Specifically, a negative electrode 200 for a lithium secondary battery including a negative electrode active material layer 30 can be confirmed on one surface of a negative electrode current collector layer 40, and a positive electrode 300 for a lithium secondary battery including a positive electrode active material layer 70 can be confirmed on one surface of a positive electrode current collector layer 60, indicating that the negative electrode 100 for a lithium secondary battery and the positive electrode 300 for a lithium secondary battery are formed in a structure laminated with a separator 55 interposed therebetween.

[0134] At this time, the release layer transferred together during prelithiation may be partially removed by the electrolyte used, and thus a small amount will be contained on the upper part of the negative electrode. Although the release layer is not shown in FIG. 2, it can be interposed between the base material layer 10 and the lithium metal layer 20.

[0135] In an 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 the manufacture of lithium secondary batteries.

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

[0137] Examples of the non-aqueous organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate ester, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, and ethyl propionate.

[0138] In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, are organic solvents with high viscosity and high dielectric constant, which can dissociate lithium salts well, and are preferably used. When such cyclic carbonates are mixed and used with linear carbonates with low viscosity and low dielectric constant such as dimethyl carbonate and diethyl carbonate at an appropriate ratio, an electrolyte having high electrical conductivity can be produced and can be more preferably used.

[0139] As the metal salt, a lithium salt can be used. The lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte. For example, as the anion of the lithium salt, F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more selected from the group consisting of can be used.

[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 ether, ethylenediamine, n-glyme, triamide hexaline, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride for the purpose of improving the life characteristics of the battery, suppressing the reduction of the battery capacity, 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. Since the battery module and the battery pack include the lithium secondary battery having a high capacity, high rate characteristics, and cycle characteristics, they can be used as a power source for medium and large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

Examples

[0142] Hereinafter, preferred examples are presented to assist in the understanding of the present invention. However, it is obvious to those skilled in the art that the following examples are for illustrative purposes only, and various changes and modifications are possible within the scope of the present description and the scope of the technical idea. It is natural that such modifications and amendments belong to the scope of the appended claims.

[0143] Production Example. Production of Transfer Laminate Production Example 1 A polyethylene terephthalate was prepared as the base material layer, and a film (manufacturer: Iwan Film) coated with an acrylic resin at 1 μm as the release layer was prepared on the base material layer. A lithium metal layer was deposited on the release layer by thermal evaporation to form a lithium metal layer with the thickness shown in Table 1 below, thereby manufacturing a transfer laminate. At this time, the vapor deposition equipment was EWK-060 of ULVAC, the speed was 2.5 m / min, the temperature of the lithium supply part was set at 500 °C, and the temperature of the main roll was set at -25 °C to proceed with the vapor deposition process.

[0144] Example. Surface treatment of the transfer laminate Example 1 Each of the previously manufactured transfer laminates (Li Film, Li thickness 3 μm) was placed in the chamber, and after evacuating to a vacuum of 10 -3 torr or less, 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 degree of vacuum in the chamber returned to normal pressure, and after treatment for 30 minutes, the surface color difference of the lithium metal layer (film) was analyzed using CM-2600d.

[0146] After the surface-treated transfer laminate (Li Film) was attached to both sides of the silicon negative electrode, lithium was transferred to the electrode part with a load of about 200 kgf using a rolling device.

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

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

[0149] Example 4 It proceeded in the same manner as in Example 1, except that the thickness of Li in the transfer laminate used was made 6 μm.

[0150] Example 5 Each of the previously manufactured transfer laminates (Li Film, Li thickness 6 μm) was placed in the chamber, and after evacuating to a vacuum of 10 -3 torr or less, 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] After purging each gas until the degree of vacuum in the chamber reached normal pressure, 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 CM-2600d.

[0152] After attaching the surface-treated transfer laminate (Li Film) to both sides of the silicon negative electrode, lithium was transferred to the electrode part at a load of about 200 kgf using a rolling device.

[0153] Example 6 It proceeded in the same manner as in Example 5, except that the gas treatment was performed for about 24 hours.

[0154] Example 7 It proceeded in the same manner as in Example 5, except that the gas treatment was performed for about 12 hours.

[0155] Example 8 It proceeded in the same manner as in Example 1, except that the thickness of Li in the transfer laminate used was made 9 μm.

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

[0157] After pasting the surface-treated transfer laminate (Li Film - lithium metal layer) on both sides of the silicon negative electrode, lithium was transferred to the Si electrode part prepared in Production Example 2 with a load of about 200 kgf using a rolling device. At this time, an electrode with a size of 5 cm × 5 cm was used for the transfer.

[0158] Comparative Example 2 Each of the previously produced transfer laminates (Li Film, 6 μm thick Li) was placed in the chamber, and after evacuating to a vacuum of 10 -3 torr or less, the vacuum valve was closed, the Gas purge valve was opened, and at 25 °C, CDA (Cleaned Dry Air, dew point -40 °C) was purged until the vacuum degree of the chamber returned to normal pressure. After that, 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.

[0159] After pasting the surface-treated transfer laminate (Li Film - lithium metal layer) on both sides of the silicon negative electrode, lithium was transferred to the Si electrode part prepared in Production Example 2 with a load of about 200 kgf using a rolling device. At this time, an electrode with a size of 5 cm × 5 cm was used for the transfer.

[0160] Comparative Example 3 Each of the previously produced transfer laminates (Li Film, 6 μm thick Li) was placed in the chamber, and after evacuating to a vacuum of 10 -3 torr or less, 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 degree of the chamber returned to normal 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] After pasting the surface-treated transfer laminate (Li Film) on both sides of the silicon negative electrode, lithium was transferred to the Si electrode part prepared in Production Example 2 with a load of about 200 kgf using a rolling device. At this time, an electrode with a size of 5 cm × 5 cm was used for the transfer.

[0163] Comparative Example 4 Each previously produced transfer laminate (Li Film, Li thickness 6 μm) was placed in the chamber, and after making it into a vacuum state at 10 -3 torr or less, 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 degree of vacuum in the chamber reached normal 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] After pasting the surface-treated transfer laminate (Li Film) on both sides of the silicon negative electrode, lithium was transferred to the Si electrode part prepared in Production Example 2 with a load of about 200 kgf using a rolling device. At this time, an electrode with a size of 5 cm × 5 cm was used for the transfer.

[0166] Comparative Example 5 Each previously produced transfer laminate (Li Film, Li thickness 6 μm) was placed in the chamber, and after making it into a vacuum state at 10 -3 torr or less, 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 degree of vacuum in the chamber reached normal 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] After pasting the surface-treated transfer laminate (Li Film) on both sides of the silicon negative electrode, lithium was transferred to the Si electrode part prepared in Production Example 2 with a load of about 200 kgf using a rolling device. At this time, an electrode with a size of 5 cm × 5 cm was used for the transfer.

[0169] [Measurement of Exothermic Temperature] The exothermic temperatures of the electrodes of Examples 1 to 8 and Comparative Examples 1 to 5 were measured in the following manner. Immediately after transferring Li to the electrode part, the PET was removed, and a TC (Thermocouple) was attached to the center of the surface of the electrode to which Li was transferred, and the maximum value of the surface temperature of the exothermic electrode 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 being the same as the components of normal atmosphere.

[0173] According to Table 1 above, in the case of Comparative Examples 1 to 5, even when the brightness (L) measured in the SCI mode is 90 or more, the brightness (L) measured in the SCE mode is less than 40, and thereby, it can be confirmed that the exothermic temperature immediately after transfer is 38°C or more.

[0174] On the other hand, in the case of Examples 1 to 8, the brightness (L) measured in the SCI mode is 90 or more, and the brightness (L) measured in the SCE mode is 40 or more, and thereby, it can be confirmed that the exothermic temperature immediately after transfer is as low as 30°C or less.

[0175] In particular, as in the cases of Comparative Examples 2 and 3, by changing the carbon dioxide content in the surface treatment gas (either trace amounts of carbon dioxide are present in CDA or the ratio is Ar:CO2 = 99:1), or as in the case of Comparative Example 4, by changing the temperature of the chamber after purging the surface treatment gas to as low as 10°C, or as in the case of Comparative Example 5, by setting the surface treatment time as short as 3 minutes, in all cases, the brightness measured in the SCE mode was less than 40. According to this result, compared with the comparative example group, in the example group, even by slightly changing the surface treatment conditions, it is possible to easily predict whether lithium carbonate (Li2CO3) is formed within a short time. Therefore, the degree of surface treatment can be precisely grasped, and thereby, the degree of the exothermic temperature immediately after transfer can be easily predicted, and the risk of ignition during pre-lithiation can be greatly reduced.

Explanation of Reference Numerals

[0176] 10 ··· Substrate layer 20 ··· Lithium metal layer 30 ··· Anode active material layer 40 ··· Anode current collector layer 55 ··· Separator 60 ··· Cathode current collector layer 70 ··· Cathode active material layer 100 ··· Transfer laminate 200 ··· Anode for lithium secondary battery 300 ··· Cathode for lithium secondary battery

Claims

1. A transfer laminate including a base material layer and a lithium metal layer on one surface of the base material layer, wherein the lithium metal layer includes a surface protective film on its surface, The surface protective film contains lithium carbonate (Li ２ CO ３ ), and and the surface color difference of the surface of the lithium metal layer including the surface protective film satisfies the following formula (1): A transfer laminate: L ＳＣＥ ≥ 40 - formula (1) In the formula (1), L ＳＣＥ means the lightness index measured in the SCE (Specular component excluded) mode.

2. The transfer laminate according to Claim 1, wherein the surface color difference of 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 lightness index measured in the SCI (Specular component included) mode.

3. On the surface of the lithium metal layer, one or more components selected from LiOH, Li ３ N, Li ２ O, Li ２ O ２ , and combinations thereof are further included. The transfer laminate according to claim 1.

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

5. The transfer laminate according to Claim 1, wherein the base material layer is one or more selected from the group consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI), polymethyl methacrylate (PMMA), polypropylene, polyethylene, and polycarbonate.

6. The transfer laminate according to Claim 1, wherein the thickness of the lithium metal layer is 1 μm or more and 10 μm or less.

7. The transfer laminate according to Claim 1, further including a release layer between the base material layer and the lithium metal layer.

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

9. Preparing a negative electrode for a lithium secondary battery by forming a negative electrode active material layer on one surface or both surfaces of a negative electrode current collector layer; and Laminating the transfer laminate according to any one of Claims 1 to 8 on the opposite surface of the surface of the negative electrode active material layer that contacts the negative electrode current collector layer to transfer the lithium metal layer; A method for manufacturing a negative electrode for a lithium secondary battery, including.

10. The step of laminating the transfer laminate to transfer the lithium metal layer on the opposite surface of the surface of the negative electrode active material layer that contacts the negative electrode current collector layer includes laminating the transfer laminate such that the opposite surface of the surface of the lithium metal layer that contacts the base material layer contacts the opposite surface of the surface of the negative electrode active material layer that contacts the negative electrode current collector layer; and Removing the base material layer; The method for manufacturing a negative electrode for a lithium secondary battery according to Claim 9, including.

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

12. After the step of transferring the lithium metal layer, the method further includes a step of prelithiation of the negative electrode active material layer. In the step of prelithiation of the negative electrode active material layer, after transferring the lithium metal layer, the negative electrode active material layer is prelithiated within 30 minutes to 48 hours. The method for manufacturing a negative electrode for a lithium secondary battery according to claim 9.

13. A negative electrode for a lithium secondary battery manufactured by the method for manufacturing a negative electrode for a lithium secondary battery according to claim 9.

14. A first electrode; A second electrode; A separator provided between the first electrode and the second electrode; and An electrolyte; comprising Either the first electrode or the second electrode includes the negative electrode for a lithium secondary battery according to claim 13. A lithium secondary battery.

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