Lithium transfer film and method for manufacturing the same, lithium secondary battery electrode on which the lithium transfer film has been transferred, and lithium secondary battery containing the same

Abstract

The present invention relates to a lithium transfer film comprising a base layer; a lithium metal layer; and a passivation layer, wherein the base layer has a Young's modulus of 4.2 GPa or more in the MD (Machine Direction) and TD (Transverse Direction), an elongation of 130% or less in the MD and TD, and a deviation of ±3.5 or less in the elongation of the MD and TD, and can suppress or prevent damage to the passivation layer, a method for manufacturing the same, an electrode for a lithium secondary battery onto which the lithium transfer film has been transferred, and a lithium secondary battery containing the same.

Description

Technical Field

[0001] This invention claims the benefit of the filing dates of Korean Patent Application No. 10-2023-0183303 filed with the Korean Intellectual Property Office on December 15, 2023, and Korean Patent Application No. 10-2024-0182140 filed with the Korean Intellectual Property Office on December 10, 2024, and all of its contents are included herein.

[0002] The present invention relates to a film for lithium transfer, a method for manufacturing the same, an electrode for a lithium secondary battery onto which the film for lithium transfer is transferred, and a lithium secondary battery including the same.

Background Art

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

[0004] Currently, a typical example of an electrochemical device using such electrochemical energy is a secondary battery, and its usage area is showing a tendency to expand more and more.

[0005] On the other hand, as the technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source has been rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density, voltage, long cycle life, and low self-discharge rate have been commercialized and widely used. As the scope of utilization of lithium secondary batteries expands to large-capacity devices such as electric vehicles, research on high-capacity lithium secondary batteries has also been actively conducted. In addition, research on methods for manufacturing high-density electrodes with even higher energy density per unit volume as electrodes for such high-capacity lithium secondary batteries has been actively conducted, and there is a tendency to progress to even higher loadings for energy density improvement.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Korean Registered Patent Publication No. 10-2475886 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The present invention provides a lithium transfer film capable of suppressing or preventing damage to a passivation layer that can suppress lithium loss that may occur during the lithium transfer process, a method for manufacturing the same, an electrode for a lithium secondary battery onto which the lithium transfer film has been transferred, and a lithium secondary battery containing the same. [Means for solving the problem]

[0008] One embodiment of this specification comprises a substrate layer; a lithium metal layer; and a passivation layer. The present invention provides a lithium transfer film in which the substrate layer has a Young's modulus of 4.2 GPa or more in both the MD (Machine Direction) and TD (Transverse Direction), an elongation of 130% or less in both the MD and TD, and a deviation of ±3.5 in the elongation of the MD and TD.

[0009] One embodiment of this specification involves the step of depositing a lithium metal layer on one side of a substrate layer; and The step includes forming a passivation layer on the opposite side of the lithium metal layer from the side on which the substrate layer is located, The present invention provides a method for manufacturing a lithium transfer film, wherein the substrate layer has a Young's Modulus (MD) of 4.2 GPa or higher for both the MD and TD, an elongation of 130% or less for both the MD and TD, and a deviation of ±3.5 for the elongation of the MD and TD.

[0010] One embodiment of this specification is an electrode current collector layer; Electrode active material layer; and The aforementioned lithium transfer films are sequentially laminated, The present invention provides an electrode intermediate in which the passivation layer of the lithium transfer film faces the electrode active material layer.

[0011] One embodiment of this specification is an electrode current collector layer; and The aforementioned lithium transfer films are sequentially laminated, The present invention provides an electrode intermediate in which the passivation layer of the lithium transfer film faces the electrode current collector layer.

[0012] One embodiment of this specification includes an electrode active material layer or an electrode current collector layer, The present invention provides an electrode for a lithium secondary battery, wherein the aforementioned lithium transfer film is transferred to at least one side of the electrode active material layer or electrode current collector layer.

[0013] Another embodiment of this specification is the electrode for the lithium secondary battery described above; Separator; and We provide a lithium secondary battery that includes an electrolyte.

[0014] Another embodiment of this specification provides a battery module or battery pack that includes the lithium secondary battery described above.

[0015] Finally, yet another embodiment of this specification provides a battery pack including the aforementioned battery module. [Effects of the Invention]

[0016] The present invention provides a lithium transfer film and a method for manufacturing the same, characterized in that it can reduce lithium loss and fire risk by suppressing side reactions by lithium oxide or nitride that may occur on the surface of the lithium transfer film during the lithium transfer process via a passivation layer, and that it satisfies certain mechanical properties of the base layer in order to suppress or prevent damage to such a passivation layer by tension application during the roll-to-roll process, as well as an electrode for a lithium secondary battery onto which the lithium transfer film has been transferred, and a lithium secondary battery containing the same. [Brief explanation of the drawing]

[0017] The following drawings attached to this specification are for illustrative purposes of embodiments of the present invention and, together with the detailed description of the invention described later, serve to further illustrate the technical concept of the present invention. Therefore, the present invention should not be construed as being limited solely to the matters depicted in the drawings.

[0018] [Figure 1] This figure shows a laminated structure of a lithium transfer film according to one embodiment of the present invention. [Figure 2] This is a flowchart illustrating a method for manufacturing a lithium transfer film according to one embodiment of the present invention. [Figure 3] This figure shows a stacked structure of a pre-lithiumized negative electrode manufactured according to one embodiment of the present invention. [Figure 4] This figure shows a stacked structure of a lithium secondary battery manufactured according to one embodiment of the present invention. [Modes for carrying out the invention]

[0019] Before describing the present invention, let us first define some terms.

[0020] In this specification, when a part "includes" a component, unless otherwise stated, it means that it may include other components rather than excluding them.

[0021] In this specification, "p~q" means the range "p or greater and q or less".

[0022] In this specification, "specific surface area" refers to the specific surface area measured by the BET (Brunauer, Emmett, Teller) method, for example, calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using a BELSORP-mini II manufactured by BEL Japan. In this specification, BET specific surface area may mean the specific surface area measured by the above measurement method.

[0023] In this specification, "strain" refers to the amount of deformation of a material caused by stress within the material, divided by its original length.

[0024] In this specification, "Young's Modulus" is a mechanical property used to measure the stiffness of a solid material. It is the elastic modulus that defines the relationship between stress (force per unit area) and strain in a linearly elastic material in the uniaxial deformation region, and can be used as a synonym for elastic modulus. This can be expressed by the following equation 1, where a low Young's modulus means high strain, and a high Young's modulus means low strain.

[0025]

number

[0026] In this specification, "elongation" refers to the maximum length that a material stretches to when it breaks under tensile load, expressed as a percentage. It can be used as a synonym for strain, and high elongation means that the material has high ductility.

[0027] In this specification, the Young's modulus and elongation can be measured by cutting or punching a sample of the film to be measured into a 25.4 mm × 250 mm size, and taking a sample, for example, by the ASTM D882 tensile test method at room temperature.

[0028] In this specification, "MD (Machine Direction)" refers to the direction of film movement during film manufacturing, and can be used as a synonym for the longitudinal direction or the machine direction.

[0029] In this specification, "TD (Transverse Direction)" refers to the direction perpendicular to the direction of film movement during film manufacturing, and can be used as a synonym for the transverse direction.

[0030] In this specification, "elongation deviation" refers to the difference between the average value of the MD elongation measurement and the TD elongation measurement and the MD elongation measurement or the TD elongation measurement. Specifically, it can be calculated using the following [Equation 2]. [Formula 2] Growth deviation = {(MD growth) + (TD growth)} / 2 - (MD or TD growth)

[0031] In this specification, "Dn" refers to the particle size distribution, specifically the particle size at the n% point of the cumulative particle number distribution corresponding to the particle size. That is, D50 is the particle size (average particle size) at the 50% point of the cumulative particle number distribution corresponding to the particle size, D90 is the particle size at the 90% point of the cumulative particle number distribution corresponding to the particle size, and D10 is the particle size at the 10% point of the cumulative particle number distribution corresponding to the 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 analyzer (e.g., MICROTRAC S3500), and the difference in diffraction patterns corresponding to the particle size is measured as the particles pass through the laser beam to calculate the particle size distribution.

[0032] In one embodiment of this specification, particle size may refer to the average diameter or representative diameter of individual particles making up the metal powder.

[0033] The terms and words used herein should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather should be interpreted in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best explain their invention.

[0034] In this specification, singular expressions of terms include plural expressions unless the context clearly indicates otherwise.

[0035] The present invention provides a lithium transfer film and a method for manufacturing the same, which can improve the mechanical properties of the substrate layer and suppress or prevent damage to the passivation layer during the transfer process, an electrode for a lithium secondary battery onto which the lithium transfer film has been transferred, and a lithium secondary battery containing the same.

[0036] Preferred embodiments of the present invention will be described in detail below. However, embodiments of the present invention may be modified in various ways, and the scope of the present invention is not limited to the embodiments described later.

[0037] A lithium transfer film according to one embodiment of this specification comprises sequentially laminated substrate layers; a lithium metal layer; and a passivation layer, wherein the substrate layer has a Young's modulus of 4.2 GPa or more in the MD (Machine Direction) and TD (Transverse Direction), an elongation of 130% or less in the MD and TD, and a deviation of ±3.5 in the elongation of the MD and TD.

[0038] When transferring a lithium transfer film to an electrode, a pre-lithiated electrode can be manufactured. Here, pre-lithiation is a solution to the problem in lithium secondary batteries where lithium is consumed during initial charging to form SEI and various irreversible phases in the negative electrode, resulting in low initial efficiency. Before assembling the cell, the lithium that will be consumed is pre-filled into the electrode to form the irreversible phase (SEI layer, Li2O, Li x SiO y This technology forms a film that significantly increases initial efficiency. Furthermore, when the lithium transfer film is transferred to an electrode current collector such as copper foil, it can form the negative electrode of a lithium metal battery.

[0039] Electrodes onto which lithium has been transferred can be continuously manufactured by applying pressure to one or both sides of the electrode using a roll-to-roll process after bringing a lithium transfer film into contact with an adhesive. In this process, the lithium transfer film and the electrode to be transferred are attached to the roll-to-roll equipment and then pulled with a constant tension. If tension is not applied, wrinkles may form on the electrode during the lithium transfer process, and misalignment may occur between the lithium transfer film and the electrode. However, when the lithium transfer film is pulled by this tension, the low physical properties of the base layer may cause the surface oxide layer, which is intended to prevent lithium oxidation, to crack.

[0040] The aforementioned surface oxide layer is a passivation layer formed on one side of the lithium transfer film, and can suppress or prevent the occurrence of side reactions due to the formation of lithium oxide or nitride on the surface of the lithium transfer film, thereby suppressing or preventing lithium loss. It can also suppress the rapid reaction between the electrode and the lithium metal layer during the lithium transfer process, thereby suppressing the exothermic phenomenon, and can play a role in reducing nitriding or oxidation reactions that may promote additional heat generation.

[0041] Such passivation layers are hard but very thin, and therefore have the problem of easily cracking when tension is applied during the roll-to-roll process. Generally, lithium metal is highly ductile and brittle, and has an elastic modulus (elastic modulus) of several GPa. As the lithium metal layer deforms during the process, the passivation layer of lithium oxide (tens of GPa), which has a relatively very high elastic modulus, easily cracks. Therefore, in order to suppress the deformation of the lithium metal layer during the process, the mechanical properties of the substrate layer on which the lithium metal layer is deposited, such as strain under tensile load (e.g., elastic modulus and elongation), must be small.

[0042] Therefore, the lithium transfer film according to one embodiment of this specification is characterized in that it can suppress or prevent damage to the passivation layer during the roll-to-roll process by using a substrate layer that does not easily stretch when tension is applied, has a small strain below a certain value in all directions of MD (Machine Direction) and TD (Transverse Direction), and has a small deviation of strain below a certain value for each of MD and TD.

[0043] A lithium transfer film according to one embodiment of this specification may be used without limitation as long as it includes a substrate layer, the substrate layer can withstand process conditions such as high temperature during the stage of depositing the lithium metal layer, and can suppress or prevent the problem of reverse peeling, in which the lithium metal layer is transferred onto the substrate layer during the winding process for transferring the deposited lithium metal layer.

[0044] Specifically, in one embodiment of this specification, the substrate layer may be one or more selected from the group consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI), poly(methylmethacrylate) (PMMA), polypropylene, polyethylene, and polycarbonate, and more specifically, polyethylene terephthalate (PET) or polyethylene naphthalate (PEN).

[0045] In one embodiment of this specification, the thickness of the substrate layer may be 1 μm or more and 300 μm or less, more specifically 1 μm or more and 100 μm or less, and more specifically 1 μm or more and 50 μm or less.

[0046] When the thickness of the substrate layer satisfies the aforementioned range, the transfer of lithium metal to the negative electrode active material layer can be efficiently performed, and reverse transfer can be suppressed or prevented.

[0047] In one embodiment of this specification, the Young's moduli of the MD and TD of the substrate layer are each 4.2 GPa or greater, and the elongations of the MD and TD are each 130% or less.

[0048] In one embodiment of this specification, the Young's moduli of the MD and TD of the substrate layer may each be 4.2 GPa or more, specifically 4.5 GPa or more, and more specifically 4.6 GPa or more, and the elongations of the MD and TD may each be 130% or less, specifically 125% or less.

[0049] In one embodiment of this specification, the Young's moduli of the MD and TD of the substrate layer may be 4.2 GPa or more and 8 GPa or less, specifically 4.5 GPa or more and 7 GPa or less, and more specifically 4.6 GPa or more and 6 GPa or less, and the elongation of the MD and TD may be 70% or more and 130% or less, specifically 80% or more and 125% or less.

[0050] When the substrate layer according to one embodiment of this specification satisfies the Young's modulus and elongation range of the MD and TD respectively, it does not easily deform when subjected to tension in the range of approximately 10N to 30N required in the process of transferring the lithium transfer film to the adhesive in a roll-to-roll process, thereby effectively suppressing damage to the passivation layer.

[0051] Furthermore, in one embodiment of this specification, the deviation of the MD and TD elongations of the substrate layer is ±3.5 or less.

[0052] In one embodiment of this specification, the deviation of the elongation of the MD and TD of the substrate layer may be ±3.5 or less, more specifically ±3.3 or less, and more specifically ±3 or less.

[0053] When the substrate layer according to one embodiment of this specification has a deviation range of elongation in the MD and TD directions, it can suppress or prevent damage to the passivation layer by not excessively deforming in only one direction during the roll-to-roll process.

[0054] In particular, even if the elongation of the MD and TD of the substrate layer according to one embodiment of this specification is 130% or less, if the deviation exceeds the aforementioned range, damage to the passivation layer may occur when high tension (30N or more) is applied.

[0055] A lithium transfer film according to one embodiment of this specification includes a lithium metal layer, wherein the lithium metal layer is a layer containing lithium metal for pre-lithifying at least one side of the electrode active material layer or for forming a lithium metal electrode, and may, but is not limited to, a commonly used Li metal foil.

[0056] In one embodiment of this specification, the thickness of the lithium metal layer may be 0.1 μm or more and 15 μm or less, more specifically 0.5 μm or more and 13 μm or less, and more specifically 1 μm or more and 10 μm or less.

[0057] In one embodiment of this specification, if the thickness of the lithium metal layer satisfies the range, pre-lithification to compensate for irreversible capacity can be performed, reducing the possibility that the lithium metal layer is difficult to peel off and not completely transferred, reducing the heat generated during the transfer process, suppressing the formation of lithium byproducts that may occur due to an excessively long pre-lithification reaction time, and improving electrode performance.

[0058] In one embodiment of this specification, the deposition method for depositing the lithium metal layer onto the substrate layer may be selected from physical vapor deposition (PDV) and chemical vapor deposition (CVD), and among the physical vapor deposition methods, thermal deposition may be mainly used, but is not limited thereto, and various deposition methods used in the industry may be used.

[0059] A lithium transfer film according to one embodiment of this specification includes a passivation layer, which may be located on the side opposite to the surface where the substrate layer exists, centered on the lithium metal layer. The passivation layer is a hard and thin inorganic film that can suppress lithium loss due to side reactions by lithium oxide or nitride formed on the surface of the lithium transfer film during the transfer process, and can also reduce the risk of ignition due to nitriding or oxidation reactions.

[0060] In one embodiment of this specification, the passivation layer may be formed on the surface of the lithium metal layer, more specifically by treating the surface of the lithium metal layer with carbon dioxide (CO2) gas, and more specifically, it may contain at least one of Li2CO3 and Li2O formed by treating the surface of the lithium metal layer with carbon dioxide (CO2) gas.

[0061] In other words, in one embodiment of this specification, the passivation layer may contain at least one of Li2CO3 and Li2O.

[0062] In one embodiment of this specification, the Young's modulus of the passivation layer may be about 5 times or more greater than the Young's modulus of the substrate layer, more specifically about 6 times or more, and more specifically about 10 times or more.

[0063] In one embodiment of this specification, the thickness of the passivation layer may be 1 nm or more and 200 nm or less, more specifically 5 nm or more and 200 nm or less, and more specifically 5 nm or more and 100 nm or less.

[0064] In one embodiment of this specification, when the thickness of the passivation layer satisfies the range, the surface of the lithium metal layer can be adequately protected, thereby suppressing the acceleration of oxidation and nitridation reactions of the lithium metal layer, and suppressing or preventing side effects such as a decrease in the pre-lithification reaction rate and an increase in electrode resistance.

[0065] A lithium transfer film according to one embodiment of this specification may further include a release layer between the substrate layer and the lithium metal layer.

[0066] In one embodiment of this specification, the release layer may be one or more selected from the group consisting of polycarbonate (PC), polydimethylsiloxane (PDMS), polymethylhydrosiloxane (PMHS), polyimide (PI), polymethylmethacrylate (PMMA), and cycloolefin copolymer (COC), and specifically, it may be polymethylmethacrylate (PMMA).

[0067] In one embodiment of this specification, the thickness of the release layer may be 0.05 μm or more and 3 μm or less, and more specifically, 0.2 μm or more and 1 μm or less.

[0068] In one embodiment of this specification, when the thickness of the release layer satisfies the range, sufficient release force of the lithium metal layer can be ensured, and the release layer located on the surface of the lithium metal layer after transfer does not hinder heat dissipation, thus not accelerating the formation of by-products.

[0069] In one embodiment of this specification, the release layer may be formed by a coating method, for example, a method selected from the group consisting of dip coating, spray coating, spin coating, die coating, gravure coating, micro-gravure coating, comma coating, and roll coating, but not limited thereto, and a variety of coating methods available in the industry for forming a coating layer may be used.

[0070] In one embodiment of this specification, the deposition method for depositing the lithium metal layer onto the release layer can be similarly applied to the deposition method for depositing the lithium metal layer onto the substrate layer.

[0071] Figure 1 shows a laminated structure of a lithium transfer film 60 according to one embodiment of this specification. Specifically, referring to Figure 1, the lithium transfer film 60 may have a release layer 62 provided on one side of a base layer 61, a lithium metal layer 63 deposited on one side of the release layer 62, and a passivation layer 64 formed on one side of the lithium metal layer 63. On the other hand, the release layer 62 formed between the base layer 61 and the lithium metal layer 63 is selective, and the lithium metal layer 63 may be provided on the base layer 61 without a release layer 62, but is not limited to this.

[0072] Figure 2 is a flowchart illustrating a method for manufacturing a lithium transfer film 60 according to one embodiment of this specification.

[0073] A method for manufacturing a lithium transfer film 60 according to one embodiment of this specification, when a release layer 62 is provided between a base layer 61 and a lithium metal layer 63, includes the steps of: forming a release layer 62 on one side of the base layer 61 (S10); forming a lithium metal layer 63 on one side of the release layer 62 (S20); and forming a passivation layer 64 on one side of the lithium metal layer 63 (S30). According to one embodiment of the present invention, the base layer 61 has a Young's modulus of MD and TD of 4.2 GPa or more, an elongation of MD and TD of 130% or less, and a deviation of elongation of MD and TD of ±3.5 or less.

[0074] In a method for manufacturing a lithium transfer film according to one embodiment of this specification, the substrate layer, lithium metal layer, and passivation layer can be similarly adapted to the provisions relating to the substrate layer, lithium metal layer, and passivation layer described above.

[0075] A method for manufacturing a lithium transfer film 60 according to one embodiment of this specification includes the step of depositing a lithium metal layer 63 onto one side of a substrate layer 61.

[0076] The deposition method in the deposition step according to one embodiment of this specification can be similarly applied to the deposition method for depositing the lithium metal layer 63 onto the substrate layer 61 as described above. Specifically, the lithium metal layer 63 may be deposited onto the substrate layer 61 by vacuum deposition, or more specifically, by thermal evaporation deposition.

[0077] In the step of depositing the lithium metal layer 63 according to one embodiment of this specification, the deposition equipment can be any deposition equipment used in the industry, for example, the EWK-060 manufactured by ULVAC can be used.

[0078] In the step of depositing the lithium metal layer 63 according to one embodiment of this specification, the deposition rate may be 0.5 m / min or more and 5 m / min or less, more specifically 1 m / min or more and 3 m / min or less, and more specifically 2 m / min or more and 2.5 m / min or less.

[0079] The step of supplying the lithium metal layer 63 to the substrate layer 61 may be further included before the step of depositing the lithium metal layer 63 according to one embodiment of this specification.

[0080] The temperature at the stage in which the lithium metal layer 63 is supplied according to one embodiment of this specification may be 10°C or more and 1,000°C or less, more specifically 100°C or more and 800°C or less, and more specifically 300°C or more and 600°C or less.

[0081] In one embodiment of this specification, the step of depositing the lithium metal layer 63 may be performed after the step of forming a release layer 62 on one side of the substrate layer 61.

[0082] Specifically, a method for manufacturing a lithium transfer film 60 according to one embodiment of this specification may include the steps of forming a release layer 62 on one side of a base layer 61, and depositing a lithium metal layer 63 on the opposite side of the release layer 62 from the side on which the base layer 61 is located.

[0083] In one embodiment of this specification, the step of forming a release layer 62 on one side of the base material layer 61 can be similarly applied to the method for forming the release layer 62 described above.

[0084] A method for manufacturing a lithium transfer film 60 according to one embodiment of this specification includes the step of forming a passivation layer 64 on the opposite side of the lithium metal layer 63 from the side on which the substrate layer 61 is located.

[0085] Specifically, the steps of forming the passivation layer 64 may include: positioning the substrate layer 61 on which the lithium metal layer 63 is deposited in a vacuum chamber; injecting Ar gas and CO2 gas into the vacuum chamber; and forming the passivation layer 64 on the opposite side of the surface of the lithium metal layer 63 that is in contact with the substrate layer 61.

[0086] In one embodiment of this specification, the pressure in the vacuum chamber during the step of forming the passivation layer 64 is 10 -3 Torr or above 10 -1 It may be less than or equal to torr, specifically 10 -2 Torr or above 10 -1 It can also be anything below torr.

[0087] In the step of injecting Ar gas and CO2 gas into the vacuum chamber to form a passivation layer 64 according to one embodiment of this specification, the Ar gas and CO2 gas may be injected in a volume ratio of 1:10 to 10:1, more specifically in a volume ratio of 8:2 to 2:8, and more specifically in a volume ratio of 8:2 to 1:1.

[0088] In one embodiment of this specification, the step of forming the passivation layer 64 further includes, after injecting Ar gas and CO2 gas into the vacuum chamber, purging the gases from the vacuum chamber until it reaches atmospheric pressure and processing for 1 to 20 minutes or 5 to 10 minutes.

[0089] In one embodiment of this specification, the step of forming the passivation layer 64 may be carried out at any temperature between 0°C and 40°C, more specifically at any temperature between 10°C and 30°C, and more specifically at any temperature between 20°C and 28°C.

[0090] In one embodiment of this specification, the step of forming the passivation layer 64 may be carried out at room temperature.

[0091] In one embodiment of this specification, the electrode intermediate of a lithium secondary battery is formed by sequentially laminating an electrode current collector layer; an electrode active material layer; and the aforementioned lithium transfer film 60, wherein the passivation layer 64 of the lithium transfer film 60 may face the electrode active material layer of the electrode intermediate.

[0092] The electrode intermediate is an electrode intermediate for manufacturing a pre-lithified electrode, and shows a state in which the lithium transfer film 60 of the present invention is laminated on one side of the pre-lithified electrode active material layer before the transfer of the lithium metal layer 63 of the present invention is started on one side of the electrode active material layer or while the transfer is progressing. In this case, the pre-lithification reaction may start at the same time as the transfer of the lithium metal layer 63 to one side of the electrode active material layer is started, or the pre-lithification reaction may start within a few seconds from the start of the transfer.

[0093] In one embodiment of this specification, the electrode intermediate is formed by sequentially laminating an electrode current collector layer; and a lithium transfer film 60 including a substrate layer 61, a lithium metal layer 63, and a passivation layer 64, wherein the passivation layer 64 of the lithium transfer film 60 may face the electrode current collector layer.

[0094] The electrode intermediate is an electrode intermediate for manufacturing the negative electrode of a Li-metal electrode, and shows a state in which a lithium transfer film 60 is laminated on one side of the electrode current collector layer in order to transfer a lithium metal layer to one side of the electrode current collector layer.

[0095] In one embodiment of this specification, the electrode for the lithium secondary battery includes an electrode active material layer or an electrode current collector layer, and the lithium transfer film described above may be transferred to at least one side of the electrode active material layer or electrode current collector layer.

[0096] When the lithium transfer film 60 according to one embodiment of this specification described above is transferred to at least one side of the electrode active material layer, a pre-lithified electrode can be formed, and when it is transferred to at least one side of the electrode current collector layer, a negative electrode of a lithium metal battery can be formed.

[0097] In other words, in one embodiment of this specification, the electrode for the lithium secondary battery may be either a pre-lithium electrode or the negative electrode of a lithium metal battery.

[0098] In another embodiment of this specification, the pre-lithiumized electrode may be a pre-lithiumized negative electrode, which may include a negative electrode active material layer disposed on at least one side of a negative electrode current collector. The negative electrode active material layer may include the negative electrode active material. Furthermore, the negative electrode active material layer may further include a thickening agent.

[0099] Figure 3 shows a stacked structure of a pre-lithiumized negative electrode according to one embodiment of this specification. Specifically, a negative electrode 100 for a lithium secondary battery can be seen, which includes a negative electrode active material layer 20 on one side of a negative electrode current collector layer 10. In Figure 3, the negative electrode active material layer 20 is shown as being formed on one side of the negative electrode current collector layer 10, but the negative electrode active material layer 20 may be formed on both sides of the negative electrode current collector layer 10.

[0100] In one embodiment of this specification, the negative electrode current collector layer may generally have a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. Furthermore, fine irregularities may be formed on the surface to strengthen the bonding force of the negative electrode active material, and it may be used in various forms such as film, sheet, foil, mesh, porous body, foam, and nonwoven fabric.

[0101] In one embodiment of this specification, the thickness of the negative electrode current collector layer is 1 μm to 100 μm, and may be 20 μm or more and 50 μm or less. However, the thickness can be varied in various ways depending on the type and application of the negative electrode used, and is not limited thereto.

[0102] The negative electrode active material layer 20 may be formed by coating at least one side of the negative electrode current collector layer 10 with a negative electrode slurry containing a negative electrode active material, a negative electrode binder, a negative electrode conductive material, and / or a thickener, meaning that it can be formed by applying the negative electrode slurry to at least one side of the negative electrode current collector layer 10, drying and rolling it.

[0103] In one embodiment of this specification, the negative electrode slurry may include a negative electrode active material layer composition comprising the negative electrode active material, a negative electrode binder, a negative electrode conductive material, and / or a thickener; and a slurry solvent.

[0104] In one embodiment of this specification, the solid content of the negative electrode slurry may be 5% or more and 40% or less.

[0105] In another embodiment, the solid content of the negative electrode slurry may be in the range of 5% to 40%, specifically 7% to 35%, and more specifically 10% to 30%.

[0106] The solid content of the negative electrode slurry refers 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 layer composition based on 100 parts by weight of the negative electrode slurry.

[0107] When the solid content of the negative electrode slurry satisfies the aforementioned range, the viscosity during the formation of the negative electrode active material layer is suitable, minimizing particle aggregation in the negative electrode active material layer composition and enabling efficient formation of the negative electrode active material layer.

[0108] In one embodiment of the present specification, the solvent may include those known in the art. For example, the solvent may be water (e.g., distilled water) or NMP (N-methyl-2-pyrrolidone).

[0109] The negative electrode according to one embodiment of the present specification may be formed by coating and drying the negative electrode slurry on one or both sides of the negative electrode current collector layer 10, and the slurry solvent in the negative electrode slurry may be dried in the drying step.

[0110] In one embodiment of the present specification, the negative electrode active material layer 20 includes a negative electrode active material, a negative electrode conductive material, and a negative electrode binder. The negative electrode active material includes a silicon-based active material, and the silicon-based active material may include one or more selected from the group consisting of Si, SiOx (0 < x < 2), Si / C, and Si alloys.

[0111] In one embodiment of the present specification, the silicon-based active material may include one or more selected from the group consisting of Si and SiOx (0 < x < 2).

[0112] In one embodiment of the present specification, the negative electrode active material may use pure silicon (Si) as the silicon-based active material. Using pure silicon (Si) as the negative electrode active material means that, based on 100 parts by weight of the negative electrode active material as described above, pure Si particles not bonded to other particles or elements are included in an amount of 60 parts by weight or more, specifically 65 parts by weight or more, more specifically 70 parts by weight or more, based on 100 parts by weight of the silicon-based active material, and may be included in a range of 95 parts by weight or less, specifically 90 parts by weight or less, more specifically 85 parts by weight or less.

[0113] In one embodiment of this specification, the negative electrode active material may use SiOx (0 < x < 2) as the silicon-based active material, and the SiOx (0 < x < 2) corresponds to an amorphous phase matrix in the silicon-based active material. The SiOx (0 < x < 2) may be in a form that partially contains Si and SiO2, and the Si may form a phase. That is, the x corresponds to the number ratio of O to Si contained in the SiOx (0 < x < 2).

[0114] The silicon-based active material may be formed by heating and vaporizing a mixed powder of Si powder and SiO2 powder, and then depositing the vaporized mixed gas. Specifically, the mixed powder of Si powder and SiO2 powder may be heat-treated at 1400 °C to 1800 °C, or 1400 °C to 1600 °C under vacuum.

[0115] In one embodiment of this specification, based on 100 total parts by weight of the negative electrode active material layer, the SiOx (0 < x < 2) may be included in an amount of 40 parts by weight or more, specifically 50 parts by weight or more, and more specifically 60 parts by weight or more, and may be included in an amount of 100 parts by weight or less, specifically 90 parts by weight or less, and more specifically 80 parts by weight or less. When the silicon-based active material contains SiOx (0 < x < 2) within the above range, the discharge capacity of the lithium secondary battery can be improved.

[0116] In one embodiment of this specification, the negative electrode active material may contain metal impurities.

[0117] The metal impurities may be impurities that may be contained in silicon, and the content thereof may satisfy the range of 0.1 part by weight or less based on 100 parts by weight of the negative electrode active material layer.

[0118] On the other hand, the average particle size (D50) of the silicon-based active material in this specification may be 5 μm to 10 μm, specifically 5.5 μm to 8 μm, and more specifically 6 μm to 7 μm.

[0119] When the average particle size is within the above range, the specific surface area of the particles is within a suitable range, so that the viscosity of the negative electrode slurry is formed within a suitable range. As a result, 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, the contact area between the silicon particles and the conductive material in the negative electrode slurry becomes good due to the composite composed of the conductive material and the binder, and the possibility of the conductive network continuing is increased, and the capacity retention rate increases. On the other hand, when the average particle size satisfies the above range, excessively large silicon particles are excluded, and the surface of the negative electrode is formed smoothly, thereby suppressing or preventing the non-uniformity phenomenon of the current density during charge and discharge.

[0120] In one embodiment of the present specification, the silicon-based active material has a generally 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 (German institute for standardization) 66131 (using nitrogen).

[0121] In one embodiment of the present specification, the silicon-based active material may exist, for example, in a crystalline or amorphous form and is non-porous. The Si may be spherical or flaky particles. Further, the silicon particles may have a fibrous structure or may exist in the form of a silicon-containing film or coating.

[0122] In one embodiment of the present specification, the silicon-based active material may be 40 parts by weight or more based on 100 parts by weight of the entire negative electrode active material layer 20.

[0123] In one embodiment of this specification, the silicon-based active material may be 40 parts by weight or more, specifically 50 parts by weight or more, more specifically 60 parts by weight or more, based on 100 parts by weight of the entire negative electrode active material layer 20, or 95 parts by weight or less, specifically 90 parts by weight or less, more specifically 80 parts by weight or less.

[0124] In the charge-discharge reaction of lithium secondary batteries, lithium released from the positive electrode is inserted into the negative electrode during charging, and desorbed from the negative electrode and returns to the positive electrode during discharging. However, in the case of silicon-based negative electrode active materials, due to the large volume change and surface side reactions, much of the lithium inserted into the negative electrode during initial charging cannot return to the positive electrode, resulting in a problem of a large initial irreversible capacity. A large initial irreversible capacity leads to a rapid decrease in battery capacity and cycle life.

[0125] Considering these factors, the present invention solves the problem of initial irreversible capacity by pre-lithifying the negative electrode of a lithium secondary battery. In the pre-lithification process, the present invention provides a step of pre-treating the negative electrode before the pre-lithification process so that lithium metal is easily transferred from the transfer laminate during the lithium transfer process, and the lithium in the negative electrode active material layer 20 is uniformly pre-lithified.

[0126] Traditionally, graphite-based compounds were the only type of negative electrode active material used. However, in recent years, with the increasing demand for high-capacity batteries, there has been a growing trend to mix in silicon-based compounds to increase capacity. However, silicon-based compounds have limitations: their volume expands rapidly during the charge / discharge process, damaging the conductive paths formed in the negative electrode active material layer and actually degrading battery performance. Therefore, the type of negative electrode conductive material used in combination with the silicon-based active material is crucial.

[0127] Accordingly, in one embodiment of this specification, the negative electrode conductive material may include one or more selected from the group consisting of sheet-like conductive materials, linear conductive materials, and point-like conductive materials, and more specifically, it may include one or more selected from the group consisting of sheet-like conductive materials and linear conductive materials.

[0128] In one embodiment of this specification, the negative electrode conductive material may be 1 part by weight or more and 40 parts by weight or less, based on 100 parts by weight of the entire negative electrode active material layer.

[0129] Specifically, in the above embodiment, the negative electrode conductive material may be 1 part by weight or more and 40 parts by weight or less, more specifically 5 parts by weight or more and 30 parts by weight or less, or more specifically 10 parts by weight or more and 25 parts by weight or less, based on 100 parts by weight of the entire negative electrode active material layer.

[0130] When the content of the negative electrode conductive material satisfies the aforementioned range, it has the effect of not impairing the conductive paths formed in the negative electrode active material layer.

[0131] In one embodiment of this specification, the sheet-like conductive material used as the negative electrode conductive material described above has a different structure and role from the 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 shape to facilitate the storage and release of lithium ions.

[0132] In contrast, the sheet-like conductive material used as the negative electrode conductive material is a substance having a sheet-like or plate-like shape, and can be described as plate-like graphite. That is, it is a substance included in the negative electrode active material layer 20 to maintain conductive pathways, and does not play a role in lithium storage and release, but rather refers to a substance that secures conductive pathways in a sheet-like form within the negative electrode active material layer 20.

[0133] In other words, in one embodiment of this specification, when plate graphite is used as a conductive material, it means that it is processed into a sheet or plate shape and used as a material to secure a conductive path, rather than to play a role in the storage or release of lithium. In this case, the negative electrode active material contained together has high capacity characteristics for the storage and release of lithium and plays a role in storing and releasing all lithium ions transmitted from the positive electrode.

[0134] In contrast, in one embodiment of this specification, the use of a carbon-based active material as an active material means that it is processed into a point-like or spherical shape and used as a substance that stores or releases lithium.

[0135] In one embodiment of this specification, the negative electrode conductive material may include a sheet-like conductive material.

[0136] In one embodiment of this specification, the sheet-like conductive material refers to a conductive material having a two-dimensional (2D) structure in which atoms have the thickness of a single atomic layer or two or more atomic layers and form a crystalline structure in a plane. The sheet-like conductive material refers to a material that secures conductive paths in a sheet-like manner inside the negative electrode active material layer, and at the same time can play a role in suppressing the disruption of conductive paths due to volume expansion, and can be expressed as a plate-like conductive material or a bulk conductive material.

[0137] In one embodiment of this specification, the sheet-like conductive material may include at least one selected from the group consisting of plate graphite, graphene, graphene oxide, and graphite flakes, and preferably plate graphite.

[0138] In one embodiment of this specification, the average particle size (D50) of the sheet-like conductive material may be 2 μm to 7 μm, more specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When this range is satisfied, the particle size is sufficient to prevent an excessive increase in the viscosity of the negative electrode slurry, and dispersion is easy, resulting in excellent dispersion effect when dispersed using the same apparatus and time.

[0139] In one embodiment of this specification, the sheet-like conductive material may have a D10 of 0.5 μm or more and 1.7 μm or less, a D50 of 2.5 μm or more and 3.5 μm or less, and a D90 of 6.8 μm or more and 15.0 μm or less.

[0140] In one embodiment of this specification, the sheet-like conductive material may be a high-specific-surface-area sheet-like conductive material with a high BET specific-surface-area; or a low-specific-surface-area sheet-like conductive material.

[0141] In one embodiment of this specification, the sheet-like conductive material can be any sheet-like conductive material with a high specific surface area or a sheet-like conductive material with a low specific surface area without limitation. However, since dispersion can affect electrode performance to some extent in the sheet-like conductive material according to this specification, a sheet-like conductive material with a low specific surface area that does not cause dispersion problems may also be used.

[0142] In one embodiment of this specification, the sheet-like conductive material has a BET specific surface area of ​​5 m². 2 / g or more 500m 2 It may be less than / g, specifically 5m 2 / g or more 300m 2 Less than / g, more specifically 5m 2 / g or more 250m 2 It may be less than / g.

[0143] In another embodiment, the sheet-like conductive material is a sheet-like conductive material with a high specific surface area, and has a BET specific surface area of ​​50 m². 2 / g or more 500m 2 Less than / g, specifically 80mg 2 / g or more 300m 2 Less than / g, more specifically 100m 2 / g or more 300m 2 The range of / g or less may also be satisfied.

[0144] In another embodiment, the sheet-like conductive material is a sheet-like conductive material with a low specific surface area, and the BET specific surface area is 5m². 2 / g or more 40m 2 Less than / g, specifically 5m 2 / g or more 30m 2 Less than / g, more specifically 5m 2 / g or more 25m 2 The range of / g or less may also be satisfied.

[0145] In one embodiment of this specification, the negative electrode conductive material may include a linear conductive material. The linear conductive material refers to a conductive material having a one-dimensional structure with a diameter on the nanometer level and a high aspect ratio, or a conductive material having a fibrous structure such as a cylindrical or tubular shape. An example of the linear conductive material is a carbon nanotube, and the carbon nanotube may be a bundled carbon nanotube. The bundled carbon nanotube may include a plurality of carbon nanotube units. Here, "bundle type" refers to a secondary shape in which a plurality of carbon nanotube units are arranged side by side or intertwined with substantially the same orientation along the longitudinal direction of the carbon nanotube units. The carbon nanotube unit has a graphite sheet that is cylindrical with a nanoscale diameter and sp 2 It has a bonded structure. In this case, the graphite sheet can exhibit conductive or semiconductor properties depending on the angle and structure at which it is rolled. The bundled carbon nanotubes can be dispersed more uniformly during anode manufacturing compared to entangled type carbon nanotubes, smoothly forming a conductive network within the anode and improving the conductivity of the anode.

[0146] In one embodiment of this specification, the negative electrode conductive material preferably includes, but is not limited to, one or more selected from the group consisting of plate-like graphite, single-walled carbon nanotubes (SWCNTs), and multi-walled carbon nanotubes (MWCNTs).

[0147] In one embodiment of this specification, the linear conductive material has a BET specific surface area of ​​100 m². 2 / g or more 10,000m 2 It may be less than / g, specifically 500m 2 / g or more 5,000m 2 Less than / g, more specifically 1,000m 2 / g or more 1,500m 2 It may be less than / g.

[0148] Furthermore, in one embodiment of this specification, the aspect ratio of the linear conductive material may be 500 or more, more specifically 1,000 or more, more specifically 10,000 or more, or 1,000,000 or less, more specifically 100,000 or less.

[0149] In one embodiment of this specification, when the linear conductive material satisfies the BET specific surface area and aspect ratio range, it has the effect of suppressing electrical short circuits between the negative electrode active materials.

[0150] In one embodiment of this specification, the negative electrode conductive material may further include a point conductive material.

[0151] In one embodiment of this specification, the dot-shaped conductive material refers to a conductive material having a zero-dimensional (0D) structure in which the structure of a crystalline mass consisting of 1 to several hundred atoms forms a round ball shape and has volume. The dot-shaped conductive material is a conductive material that can be used to improve conductivity in the negative electrode, does not cause chemical changes, and is conductive. 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, conductive fibers, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably contains carbon black in that it achieves high conductivity and has excellent dispersibility.

[0152] In one embodiment of this specification, the point-shaped conductive material has a BET specific surface area of ​​40 m². 2 / g or more 70m 2 It may be less than / g, specifically 45m 2 / g or more 65m 2 / g or less, more specifically 50m2 / g or more 60m 2 It may be less than / g.

[0153] In one embodiment of this specification, the particle size of the dot-like conductive material may be 10 nm to 100 nm, more specifically 20 nm to 90 nm, and more specifically 20 nm to 60 nm.

[0154] The negative electrode conductive material according to this specification has a completely different structure from the conductive material applied to the positive electrode. The negative electrode conductive material according to this specification serves to create contact between silicon-based active materials, which undergo very large volume expansion during charging and discharging. Its structure and role are completely different from that of the positive electrode conductive material, which acts as a buffer during rolling and imparts some conductivity.

[0155] Furthermore, the negative electrode conductive material according to this specification is applied to silicon-based negative electrode active materials and has a completely different structure from the conductive material applied to graphite-based active materials. The conductive material used in electrodes with graphite-based active materials simply has particles that are smaller than the active material, and therefore has the properties of improving output characteristics and imparting some conductivity, and its structure and role are different from the negative electrode conductive material applied together with silicon-based negative electrode active materials as in the present invention.

[0156] In one embodiment of this specification, the negative electrode binder may contain at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyacrylamide, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which the hydrogen atoms of these substances are substituted with Li, Na, or Ca, and may also contain various copolymers thereof.

[0157] The negative electrode binder according to one embodiment of this specification plays a role in holding the active material and conductive material in order to suppress or prevent strain and structural deformation of the negative electrode structure during the volume expansion and relaxation of the silicon-based active material. A general binder that satisfies the above role can be applied, and specifically, it may include one or more binders selected from the group consisting of polyacrylamide (PAM) and styrene-butadiene rubber.

[0158] In one embodiment of this specification, the negative electrode binder may be 30 parts by weight or less, specifically 20 parts by weight or less, more specifically 10 parts by weight or less, based on 100 parts by weight of the entire negative electrode active material layer 20, or it may be 1 part by weight or more, or 3 parts by weight or more.

[0159] In one embodiment of the present invention, the weight-average molecular weight of the binder may be 100,000 g / mol or more and 1,500,000 g / mol or less.

[0160] When the weight-average molecular weight of the binder satisfies the aforementioned range, it will have excellent mechanical strength, high intermolecular interaction, and superior electrode bonding strength. Furthermore, when the aforementioned range is met, the viscosity of the binder can be selected within a suitable range, and when using it to manufacture a negative electrode, the coating properties of the electrode can be further improved.

[0161] In another embodiment of this specification, the method for manufacturing the pre-lithified negative electrode may be formed by transferring the lithium transfer film to at least one side of the negative electrode active material layer 20 described above.

[0162] The method for manufacturing a pre-lithiumized negative electrode according to this specification involves pre-lithiumizing at least one side of the negative electrode active material layer in order to solve the irreversibility problem of silicon-based electrodes and improve Coulomb efficiency. It is characterized by using a lithium transfer method for pre-lithiumization, which has a faster process speed than methods using SLMP (Stabilized Lithium Metal Powder) or electrochemical pre-lithiumization, thus offering high mass productivity.

[0163] In one embodiment of this specification, the step of transferring the lithium transfer film described above to at least one side of the negative electrode active material layer 20 to form a pre-lithified negative electrode includes the steps of bringing the lithium transfer film into contact with at least one side of the negative electrode active material layer such that the lithium metal layer faces it, and applying pressure.

[0164] In one embodiment of this specification, the step of bringing the lithium transfer film into contact with at least one side of the negative electrode active material layer 20 such that the lithium metal layer 63 faces it is a step for transferring lithium metal to the negative electrode active material layer 20.

[0165] In one embodiment of this specification, the pressurizing step allows for more active pre-lithiation by transfer to the negative electrode active material layer 20, which has the effect of allowing for the formation of a thinner negative electrode despite a high energy density.

[0166] In this case, the lithium transfer film 60 may be positioned so that the lithium metal layer 63 of the lithium transfer film 60 is in contact with one or both sides of the negative electrode active material layer 20, and then the transfer process may be performed by roll pressing while applying a load of 10 kgf to 500 kgf. After that, the process may include a step of removing the base material layer or the release layer and base material layer.

[0167] In one embodiment of this specification, the step of removing the base layer 61 of the lithium transfer film 60 or the release layer 62 and the base layer 61 may be performed after bringing the lithium metal layer 63 into contact with the negative electrode active material layer 20 and transferring it under pressure.

[0168] In a method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of this specification, prelithiation may be performed from the moment the lithium metal layer 63 of the lithium transfer film 60 comes into contact with the negative electrode active material layer 20, from the pressurization stage, or from the stage of removing the base material layer or the release layer and base material layer.

[0169] In another embodiment of this specification, the negative electrode of the lithium metal battery may include a negative electrode current collector on which the lithium transfer film 60 described above is transferred to at least one side.

[0170] In this case, the method for transferring the negative electrode current collector and the lithium transfer film 60 can be the one described above.

[0171] A lithium secondary battery according to one embodiment of this specification may include an electrode for a lithium secondary battery according to the above-described embodiment. Specifically, the secondary battery may include an electrode for a lithium secondary battery, a separator, and an electrolyte, and the electrode for the lithium secondary battery may be a negative electrode or a positive electrode.

[0172] Figure 4 shows a stacked structure of a lithium secondary battery using pre-lithium-treated electrodes according to one embodiment of this specification. Specifically, the stacked structure of the lithium secondary battery includes a negative electrode 100 for the lithium secondary battery, which includes a negative electrode active material layer 20 on one side of a negative electrode current collector layer 10, and a positive electrode 200 for the lithium secondary battery, which includes a positive electrode active material layer 40 on one side of a positive electrode current collector layer 50, and the negative electrode 100 and the positive electrode 200 for the lithium secondary battery are stacked with a separator 30 in between.

[0173] The positive electrode may include a positive electrode current collector layer and a positive electrode active material layer formed on at least one side of the positive electrode current collector layer, which contains the positive electrode active material.

[0174] In the positive electrode, the positive electrode current collector layer is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector layer may also typically 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 adhesion of the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0175] The positive electrode active material according to one embodiment of this specification may include one or more selected from the group consisting of lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, lithium aluminum oxide, or lithium composite oxides combining these.

[0176] Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; or a compound with the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4 (0 ≤ c1 ≤ 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented as O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, satisfying 0.01 ≤ c2 ≤ 0.5); chemical formula LiMn 2-c3 M c3 Lithium manganese composite oxides represented as O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, satisfying 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); or LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion, etc., are examples, but are not limited thereto. The positive electrode may be Li metal.

[0177] The positive electrode active material layer may also include a positive electrode conductive material and a positive electrode binder, along with the positive electrode active material described above.

[0178] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without particular limitation as long as it has electronic conductivity without causing a chemical change in the battery that is constructed. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more may be used.

[0179] Furthermore, the positive electrode binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer (PVdF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0180] The solvent used in the positive electrode composition slurry may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of solvent used should be sufficient to dissolve or disperse the active material, conductive material, and binder, and to have a viscosity that allows for excellent thickness uniformity when applied for the manufacture of the positive and negative electrodes, taking into consideration the coating thickness and manufacturing yield of the slurry. Alternatively, the positive and negative electrodes may also be manufactured by casting the active material layer forming composition onto another support, peeling it off the support, and then laminating the resulting film onto a current collector.

[0181] The separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. It can be used without particular limitations as long as it is the type of separator normally used in secondary batteries, and may be particularly suitable if it has low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity. Specifically, porous polymer films, such as porous polymer films made from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof may be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, to ensure heat resistance or mechanical strength, coated separators containing ceramic components or polymeric substances may be used, and may be selectively used as single-layer or multi-layer structures.

[0182] Examples of the aforementioned electrolytes include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0183] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0184] As the non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate may be used.

[0185] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, can be preferably used as high-viscosity organic solvents because they have high dielectric constants and dissociate lithium salts well. Furthermore, when such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in appropriate proportions, an electrolyte with high electrical conductivity can be produced, making them even more preferable.

[0186] As the metal salt, a lithium salt may be used, and the lithium salt is a substance that is easily soluble 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 - You may use one or more selected from the group consisting of the following:

[0187] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for purposes such as improving the battery's lifespan, suppressing the decrease in battery capacity, and improving the battery's discharge capacity.

[0188] One embodiment of this specification provides a battery module and a battery pack including the lithium secondary battery as a unit cell.

[0189] Another embodiment of this specification provides a battery pack including the lithium secondary battery.

[0190] The lithium secondary batteries according to the embodiments of this specification exhibit excellent discharge capacity, output characteristics, and cycle performance, and can therefore be used as power sources for portable devices such as mobile phones, laptops, and digital cameras, as well as 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. For example, the battery module or battery pack can be used as a power source for one or more medium- and large-sized devices, including power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems. [Examples]

[0191] The following are preferred embodiments to aid in understanding the present invention. However, these embodiments are merely illustrative examples, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of this description and the technical concept, and such variations and modifications will naturally fall within the scope of the appended claims.

[0192] <Manufacturing example> [Example 1] <Manufacturing of lithium transfer film> A transfer film was prepared by coating a PET A substrate layer with a 1 μm thick acrylic resin (release layer). In this case, polyethylene terephthalate satisfying the mechanical properties shown in Table 1 below was used as the PET A.

[0193] A lithium layer with a thickness of 6 μm was formed by depositing lithium onto the acrylic resin coating layer of the transfer film using a vacuum thermal evaporation deposition method. The deposition equipment used was an EWK-060 manufactured by ULVAC, 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 to -25°C.

[0194] The manufactured transfer film is placed inside the chamber, and the vacuum level of the chamber is set to 10 -1 After reducing the pressure to below torr, the vacuum valve was closed, the gas purge valve was opened, and argon (Ar) gas and carbon dioxide (CO2) gas were injected into the chamber at room temperature in an 8:2 volume ratio. The chamber was then purged with each gas until the vacuum pressure reached atmospheric pressure, and the process was carried out for approximately 10 minutes. This process resulted in the production of a lithium transfer film in which a passivation layer containing Li2CO3 was formed on the surface of the deposited lithium thin film.

[0195] [Example 2] A lithium transfer film was manufactured in the same manner as in Example 1, except that PEN (polyethylene naphthalate) having the mechanical properties shown in Table 1 below was used as the base layer.

[0196] [Comparative Example 1] A lithium transfer film was manufactured in the same manner as in Example 1, except that PET B having the mechanical properties shown in Table 1 below was used as the base layer.

[0197] [Comparative Example 2] A lithium transfer film was manufactured in the same manner as in Example 1, except that PET C having the mechanical properties shown in Table 1 below was used as the base layer.

[0198] [Comparative Example 3] A lithium transfer film was manufactured in the same manner as in Example 1, except that PET D having the mechanical properties shown in Table 1 below was used as the base layer.

[0199] [Comparative Example 4] A lithium transfer film was manufactured in the same manner as in Example 1, except that PET E having the mechanical properties shown in Table 1 below was used as the base layer.

[0200] [Comparative Example 5] A lithium transfer film was manufactured in the same manner as in Example 1, except that PET F having the mechanical properties shown in Table 1 below was used as the base layer.

[0201] The mechanical properties of the substrate layers used in Examples 1 and 2 and Comparative Examples 1 to 5 were measured at room temperature using the ASTM D882 tensile test method and are shown in Table 1 below.

[0202] <Example of experiment> If a passivation layer is not formed on the surface of the lithium transfer film, a nitridation reaction occurs in a nitrogenous environment (an environment controlled to oxygen and moisture <10 ppm), and the surface is rapidly nitrided. Therefore, this phenomenon was used to check for damage to the passivation layer on the surface of the lithium transfer film.

[0203] In a chamber configured with two shafts capable of applying tension to enable unwinding and rewinding of a film roll, the lithium transfer films of Examples 1 and 2 and Comparative Examples 1 to 5, manufactured according to the above manufacturing example, were mounted on the internal shafts of the chamber, and the inside of the chamber was purged with nitrogen for 30 minutes. Afterward, the inside of the chamber was circulated with a purifier for 30 minutes until the oxygen and moisture concentrations were below 10 ppm. Then, tensions of 10N and 30N were applied to each lithium transfer film, and after 10 minutes, the presence or absence of nitriding on the surface of the lithium metal layer was observed, as shown in Table 1 below. "×" indicates that the nitriding reaction did not occur, and "O" indicates that the nitriding reaction occurred. When the nitriding reaction occurs, the surface of the lithium metal layer changes to black, allowing the presence or absence of nitriding to be observed with the naked eye.

[0204] [Table 1]

[0205] As can be seen from Table 1 above, the lithium transfer film of Comparative Example 1 had an elongation of 130% or more in both the MD and TD of the substrate layer, and did not satisfy the characteristic mechanical properties of this specification. It was confirmed that the passivation layer was damaged under the high tension condition of 30 N during the roll-to-roll process, and that a nitriding reaction occurred on the lithium surface.

[0206] Similarly, the lithium transfer film of Comparative Example 2 had a substrate layer elongation of TD of 130% or more, and the deviation of MD and TD elongation exceeded ±3.5, failing to satisfy the characteristic mechanical properties of this specification. It was confirmed that a nitriding reaction occurred on the lithium surface under high tension conditions of 30 N.

[0207] Comparative Example 3 did not meet the elongation and Young's modulus requirements for MD and TD of the present application, and therefore a nitriding reaction was observed even under relatively low tension conditions of 10 N. Comparative Example 4 was similar to Comparative Example 2, but the deviation in elongation increased significantly, and the passivation layer was damaged and a nitriding reaction was observed even under low tension conditions of 10 N.

[0208] Comparative Example 5 met the ranges for elongation and Young's modulus, but its Young's modulus of TD was small and did not meet the deviation, and nitridation was observed under a tension of 30 N.

[0209] However, in Examples 1 and 2 of the present application, by using a substrate layer that satisfies all the conditions that the Young's modulus of MD and TD is 4.2 GPa or more, the elongation of MD and TD is 130% or less, and the deviation of the elongation of MD and TD is ±3.5 or less, regardless of the magnitude of the tension, it is difficult to stretch easily when tension is applied, and there is little strain in either the uniaxial direction of MD or TD, so damage to the passivation layer can be prevented during the roll-to-roll lithium transfer process, and nitriding or oxidation of the lithium surface can be suppressed or prevented.

[0210] As described above with reference to the embodiments of this disclosure, any person skilled in the art or with ordinary knowledge in the art can understand that the various embodiments of this disclosure can be modified and altered in various ways, without departing from the technical scope of the various embodiments of this disclosure as described in the claims below. Therefore, the technical scope of the various embodiments of this disclosure is not limited to what is described in the detailed description of the specification, but must be determined by the claims. [Explanation of Symbols]

[0211] 10 ···Negative electrode current collector layer 20...Negative electrode active material layer 30 ···Separator 40...Cathode active material layer 50 ···Positive electrode current collector layer 60 ···Lithium transfer film 61...Base material layer 62...Release layer 63 ···Lithium metal layer 64 ··· Passivation layer 100 ···Negative electrode for lithium secondary batteries 200 ···Positive electrode for lithium secondary batteries

Claims

1. It comprises a substrate layer; a lithium metal layer; and a passivation layer. The substrate layer is a lithium transfer film in which the Young's modulus of the MD (Machine Direction) and TD (Transverse Direction) is 4.2 GPa or more, the elongation of the MD and TD is 130% or less, and the deviation of the elongation of the MD and TD is ±3.5 or less.

2. The passivation layer is Li ２ CO ３ and Li ２ A lithium transfer film according to claim 1, comprising at least one of O.

3. The lithium transfer film according to claim 1, wherein the thickness of the lithium metal layer is 1 μm or more and 10 μm or less.

4. The lithium transfer film according to claim 1, wherein the thickness of the passivation layer is 5 nm or more and 200 nm or less.

5. The lithium transfer film according to claim 1, further comprising a release layer between the substrate layer and the lithium metal layer.

6. A step of depositing a lithium metal layer onto one side of a substrate layer; and The step of forming a passivation layer on the opposite side of the lithium metal layer from the side where the substrate layer is located. Includes, A method for manufacturing a lithium transfer film, wherein the substrate layer has a Young's Modulus of 4.2 GPa or more for both the medium-density (MD) and the TD, an elongation of 130% or less for both the MD and the TD, and a deviation of ±3.5 for the elongation of the MD and the TD.

7. The step of forming the passivation layer is: A step of positioning the substrate layer on which the lithium metal layer has been deposited in a vacuum chamber; Ar gas and CO2 are placed in the vacuum chamber. ２ The stage of injecting gas; and The step of forming a passivation layer on the opposite side of the surface of the lithium metal layer that is in contact with the substrate layer. A method for producing a lithium transfer film according to claim 6, including the method described in claim 6.

8. The step of depositing the lithium metal layer is as follows: A method for manufacturing a lithium transfer film according to claim 6, which is carried out after the step of forming a release layer on one side of the base material layer.

9. Electrode current collector layer; Electrode active material layer; and A lithium transfer film according to any one of claims 1 to 5 is sequentially laminated, An electrode intermediate wherein the passivation layer of the lithium transfer film faces the electrode active material layer.

10. Electrode current collector layer; and A lithium transfer film according to any one of claims 1 to 5 is sequentially laminated, An electrode intermediate wherein the passivation layer of the lithium transfer film faces the electrode current collector layer.

11. It includes an electrode active material layer or an electrode current collector layer, An electrode for a lithium secondary battery, wherein the lithium transfer film according to any one of claims 1 to 5 is transferred to at least one side of the electrode active material layer or the electrode current collector layer.

12. The electrode for a lithium secondary battery according to claim 11, wherein the electrode active material layer comprises a silicon-based active material, and the silicon-based active material comprises one or more selected from the group consisting of Si, SiOx (0 < x < 2), Si / C, and Si alloy.

13. The electrode for a lithium secondary battery according to claim 11, wherein the electrode active material layer includes a negative electrode conductive material, and the negative electrode conductive material includes one or more selected from the group consisting of plate graphite, single-walled carbon nanotubes (SWCNTs), and multi-walled carbon nanotubes (MWCNTs).

14. Electrode for lithium secondary battery according to claim 11; separator; and electrolyte Lithium-ion batteries, including lithium-ion batteries.

15. A battery module comprising the lithium secondary battery described in claim 14.

16. A battery pack comprising the lithium secondary battery described in claim 14.

17. A battery pack comprising the battery module described in claim 15.

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