Lithium transfer film, method for preparing the same, electrode for lithium secondary battery having the lithium transfer film transferred thereon, and lithium secondary battery including the electrode

Abstract

This invention relates to a lithium transfer film, its preparation method, an electrode for a lithium secondary battery having the lithium transfer film transferred thereon, and a lithium secondary battery including the electrode. The lithium transfer film comprises a substrate layer, a lithium metal layer, and a passivation layer. The Young's modulus of the substrate layer in the longitudinal direction (MD) and transverse direction (TD) is 4.2 GPa or higher, the elongation in the MD and TD is 130% or lower, and the deviation of the elongation in the MD and TD is ±3.5 or lower, thereby suppressing or preventing damage to the passivation layer.

Description

Technical Field

[0001] This invention claims priority and benefit to Korean Patent Application Nos. 10-2023-0183303 and 10-2024-0182140, filed with the Korean Intellectual Property Office on December 15, 2023 and December 10, 2024, respectively, the entire contents of which are incorporated herein by reference.

[0002] This disclosure relates to a lithium transfer film and its preparation method, an electrode for a lithium secondary battery having the lithium transfer film transferred thereon, and a lithium secondary battery including the electrode. Background Technology

[0003] Due to the rapid increase in fossil fuel use, the demand for alternative or clean energy sources is growing. Therefore, research is actively underway in the areas of power generation and energy storage using electrochemical reactions.

[0004] Currently, a representative example of an electrochemical device using this electrochemical energy is a secondary battery, and its application areas are gradually expanding.

[0005] Meanwhile, with the increasing technological development and demand for mobile devices, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium-ion batteries, characterized by high energy density, high voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used. Furthermore, as the application of lithium-ion batteries expands to high-capacity devices such as electric vehicles, research on high-capacity lithium-ion batteries is actively underway. Moreover, methods for manufacturing high-density electrodes with higher energy density per unit volume for use in high-capacity lithium-ion batteries are being actively researched, and the research trend is to gradually increase the load to improve energy density.

[0006] [Related Technical Documents]

[0007] [Patent Literature]

[0008] (Patent Document 1) Korean Patent No. 10-2475886 Summary of the Invention

[0009] [Technical Issues]

[0010] This disclosure provides a lithium transfer film and its preparation method, an electrode for a lithium secondary battery with the lithium transfer film transferred thereon, and a lithium secondary battery including the electrode. The passivation layer can suppress lithium loss that may occur during the lithium transfer process and improve the mechanical properties of the substrate layer, thereby suppressing or preventing damage to the passivation layer during the transfer process.

[0011] [Technical Solution]

[0012] One embodiment of this disclosure provides a lithium transfer film comprising: a substrate layer; a lithium metal layer; and a passivation layer, wherein, in the substrate layer, the Young's modulus in the longitudinal direction (MD) and the transverse direction (TD) is 4.2 GPa or more, the elongation in the MD and TD is 130% or less, and the deviation of the elongation in the MD and TD is ±3.5 or less.

[0013] One embodiment of this disclosure provides a method for manufacturing a lithium transfer film, wherein the method includes: depositing a lithium metal layer on a surface of a substrate layer; and forming a passivation layer on the surface of the lithium metal layer opposite to the surface of the substrate layer, wherein in the substrate layer, the Young's modulus of the MD and TD 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.

[0014] One embodiment of this disclosure provides an electrode intermediate in which an electrode current collector layer, an electrode active material layer, and a lithium transfer film are stacked sequentially, wherein the passivation layer of the lithium transfer film faces the electrode active material layer.

[0015] One embodiment of this disclosure provides an electrode intermediate in which an electrode current collector layer and a lithium transfer film are stacked sequentially, wherein the passivation layer of the lithium transfer film faces the electrode current collector layer.

[0016] One embodiment of this disclosure provides an electrode for a lithium secondary battery, comprising an electrode active material layer or an electrode current collector layer, wherein at least one surface of the electrode active material layer or the electrode current collector layer is coated with the aforementioned lithium transfer film.

[0017] Another embodiment of this disclosure provides a lithium secondary battery, which includes the electrodes, separator, and electrolyte described above for lithium secondary batteries.

[0018] Another embodiment of this disclosure provides a battery module or battery pack that includes the aforementioned lithium secondary battery.

[0019] Finally, another embodiment of this disclosure provides a battery pack that includes the battery module described above.

[0020] [Beneficial Effects]

[0021] This disclosure provides a lithium transfer film and its preparation method, an electrode for a lithium secondary battery having the lithium transfer film transferred thereon, and a lithium secondary battery including the electrode. The lithium transfer film is characterized by a passivation layer that suppresses side reactions caused by lithium oxides or nitrides that may occur on the surface of the lithium transfer film during the lithium transfer process, thereby reducing lithium loss and the risk of fire. Therefore, specific mechanical properties of the substrate layer are satisfied, thereby suppressing or preventing damage to this passivation layer due to the tension applied during the roll-to-roll process. Attached Figure Description

[0022] The accompanying drawings illustrate embodiments of the present disclosure and, together with the detailed description of the present disclosure that follows, are used to aid in a further understanding of the technical concept of the present disclosure. Therefore, the present disclosure should not be construed as limited to the contents shown in the drawings.

[0023] Figure 1 This is a diagram illustrating the stacked structure of a lithium transfer film according to one embodiment of the present disclosure;

[0024] Figure 2 This is a flowchart illustrating a method for manufacturing a lithium transfer film according to one embodiment of the present disclosure;

[0025] Figure 3 This is a diagram illustrating a stacked structure of a pre-lithiated negative electrode manufactured according to one embodiment of the present disclosure; and

[0026] Figure 4 This is a diagram illustrating the stacked structure of a lithium secondary battery manufactured according to one embodiment of the present disclosure. Detailed Implementation

[0027] Before describing this disclosure, some terms will be defined.

[0028] In this disclosure, when a part is referred to as "including" a component, it means that the part may further include other components, rather than excluding other components, unless otherwise expressly stated.

[0029] In this disclosure, "p to q" refers to the range of "p and below q".

[0030] In this disclosure, "specific surface area" is measured by the BET (Brunauer, Emmett, Teller) method and calculated from the amount of nitrogen adsorbed using, for example, the BELSORP-mini II from BEL Japan at a liquid nitrogen temperature (77K). In this disclosure, BET specific surface area can refer to the specific surface area measured by the aforementioned method.

[0031] In this disclosure, "strain" is a quantity obtained by dividing the amount of material deformation caused by stress occurring in the material by the original length.

[0032] In this disclosure, "Young's modulus" is a mechanical property that measures the rigidity of a solid material, and is an elastic coefficient that defines the relationship between stress (force per unit area) and strain in a linear elastic material in a uniaxial deformation region, and can be used as the same concept as elastic modulus. This is expressed by the equation in Equation 1 below. A low Young's modulus indicates high strain, and a high Young's modulus indicates low strain.

[0033] [Equation 1]

[0034]

[0035] In equation 1 above,

[0036] E represents Young's modulus, σ represents stress, and ε represents strain.

[0037] In this disclosure, "elongation" is the maximum length of a material that breaks under tensile load (stress), and is expressed as a percentage (%). This can be used in the same way as strain, and a high elongation indicates that the material has high ductility.

[0038] In this disclosure, after the membrane, which is the target of measurement, is cut or stamped into a sample shape of approximately 25.4 mm x 250 mm, the Young's modulus and elongation of the collected sample can be measured, for example, at room temperature using the tensile testing method of ASTM D882.

[0039] In this disclosure, "longitudinal (MD)" corresponds to the direction of travel of the membrane during membrane manufacturing and can be used in the same sense as the longitudinal direction or mechanical direction.

[0040] In this disclosure, "transverse (TD)" corresponds to the direction perpendicular to the direction of travel of the membrane during membrane manufacturing, and can be used with the same concept as the transverse direction.

[0041] In this disclosure, "elongation deviation" refers to the difference between the average of the MD elongation measurement and the TD elongation measurement and either the MD elongation measurement or the TD elongation measurement. Specifically, this can be calculated using the following [Equation 2].

[0042] [Equation 2]

[0043] Elongation deviation = {(MD elongation) + (TD elongation)} / 2 - (MD or TD elongation)

[0044] In this disclosure, "Dn" refers to the particle size distribution, specifically the particle size at the n% point of the cumulative particle number distribution based on particle size. That is, D50 is the particle size (average particle size) at the 50% point of the cumulative particle number distribution based on particle size, D90 is the particle size at the 90% point of the cumulative particle number distribution based on particle size, and D10 is the particle size at the 10% point of the cumulative particle number distribution based on particle size. The average particle size can be measured using laser diffraction. The target powder is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size measurement device (e.g., MICROTRAC S3500). The particle size distribution is then calculated by measuring the differences in the diffraction pattern based on the particle size as the particles pass through the laser beam.

[0045] In one embodiment of this disclosure, particle size or particle diameter may refer to the average or representative diameter of each fine particle forming the metal powder.

[0046] The terms or words used in this disclosure should not be construed as having their usual or dictionary meanings, but should be interpreted as meanings and concepts consistent with the technical ideas of this disclosure, based on the principle that the inventor can appropriately define the concepts of the terms in order to best interpret his / her own invention.

[0047] Unless the context clearly indicates otherwise, the singular expressions of terms used in this disclosure include the plural expressions.

[0048] Given the inherent manufacturing and material tolerances, terms such as “about,” “approximately,” and “substantially” used in this disclosure are used to refer to a range or approximation of a value or degree.

[0049] This disclosure provides a lithium transfer film with improved mechanical properties of the substrate layer, which can suppress or prevent damage to the passivation layer during the transfer process, a method for manufacturing the same, an electrode for a lithium secondary battery having the lithium transfer film transferred thereon, and a lithium secondary battery including the electrode.

[0050] Embodiments of this disclosure will be described in detail below. However, embodiments of this disclosure may be modified in various ways, and the scope of this disclosure is not limited to the embodiments described below.

[0051] One embodiment of the lithium transfer film disclosed herein includes a substrate layer, a lithium metal layer, and a passivation layer stacked sequentially. In the substrate layer, the Young's modulus on the MD (longitudinal) and TD (transverse) axes is 4.2 GPa or higher, the elongation on the MD and TD axes is 130% or lower, and the elongation deviation between the MD and TD axes is ±3.5 or lower.

[0052] Pre-lithiation electrodes can be fabricated by transferring a lithium transfer film to an electrode. Pre-lithiation typically aims to address the problem that during the initial charging of a lithium-ion secondary battery, lithium is consumed in the negative electrode to form an SEI layer and various irreversible phases, resulting in low initial efficiency. In this technique, lithium corresponding to the amount to be consumed is pre-added to the electrode before assembling the battery cell, thereby forming irreversible phases (SEI layer, Li₂O, and LiₓSiO₂), thus significantly improving initial efficiency. Furthermore, when the lithium transfer film is transferred to an electrode current collector such as copper foil, a negative electrode for a lithium metal battery can be formed.

[0053] After contacting the target of transfer (e.g., an electrode), the lithium transfer film is transferred to one or both sides of the electrode while pressure is applied via a roll-to-roll process. In this way, electrodes with transferred lithium can be continuously manufactured. Here, during the lithium transfer process via roll-to-roll, the lithium transfer film and the electrode, which is the target of transfer, are mounted together in a roll-to-roll process apparatus and then pulled under specific tension. When no tension is applied, wrinkles may occur in the electrode during the lithium transfer process, and misalignment may occur between the lithium transfer film and the electrode. Simultaneously, when the lithium transfer film is pulled under tension, the surface oxide layer used to prevent lithium oxidation may crack due to the low physical properties of the substrate layer.

[0054] A surface oxide layer is a passivation layer formed on one surface of a lithium transfer film. It suppresses or prevents side reactions caused by the formation of lithium oxides or nitrides on the surface of the lithium transfer film, thereby suppressing or preventing lithium loss. The surface oxide layer can suppress sudden reactions between the electrode and the lithium metal layer during the lithium transfer process, thereby suppressing heat generation, and can also be used to reduce nitriding or oxidation reactions that can promote additional heat generation.

[0055] This passivation layer is often very hard, but it is a very thin film. Therefore, there is a problem that the passivation layer may easily break due to the tension applied during roll-to-roll processes. Typically, lithium metal has high ductility and flexibility, and its elastic modulus is several GPa. Therefore, as the lithium metal layer deforms during processing, the passivation layer of the lithium oxide film, with its relatively high elastic modulus (tens of GPa), is prone to breakage. Therefore, in order to suppress the deformation of the lithium metal layer during processing, the mechanical properties of the substrate layer forming the lithium metal layer, such as the strain caused by tensile loads (e.g., elastic modulus and elongation), need to be small.

[0056] One embodiment of the lithium transfer film disclosed herein is characterized by its resistance to stretching under applied tension. For this purpose, a substrate layer with specific mechanical properties is used, resulting in low strain (below a specific value) in all directions of MD (longitudinal) and TD (transverse), and also low strain deviations (below a specific value) in MD and TD, respectively. This suppresses or prevents damage to the passivation layer during roll-to-roll processes.

[0057] One embodiment of the lithium transfer film disclosed herein includes a substrate layer. The substrate layer can be used without limitation, as long as it has the characteristics of withstanding process conditions such as high temperature in the step of depositing the lithium metal layer and suppressing or preventing reverse peeling problems (which are the phenomenon of lithium metal layer transferring onto the substrate layer during the winding process of transferring the deposited lithium metal layer).

[0058] In one embodiment of this disclosure, the substrate layer may be at least one selected from the group consisting of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI), polymethyl methacrylate (PMMA), polypropylene, polyethylene, and polycarbonate. According to one embodiment, the substrate layer may be polyethylene terephthalate (PET) or polyethylene naphthalate (PEN).

[0059] In one embodiment of this disclosure, the thickness of the substrate layer can be from 1 μm to 300 μm, and can be within the range of 1 μm to 100 μm or 1 μm to 50 μm.

[0060] When the thickness of the substrate layer meets the above range, the lithium metal can be efficiently transferred to the negative electrode active material layer side, and reverse transfer can be suppressed or prevented.

[0061] In one embodiment of this disclosure, the Young's modulus on the MD and TD of the substrate layer is 4.2 GPa or more, and the elongation on the MD and TD is 130% or less.

[0062] In one embodiment of this disclosure, the Young's modulus of the substrate layer MD and TD is 4.2 GPa or more, 4.5 GPa or more, or 4.6 GPa or more, respectively, and the elongation of the substrate layer MD and TD is 130% or less or 125% or less, respectively.

[0063] In one embodiment of this disclosure, the Young's modulus on the MD and TD of the substrate layer is 4.2 GPa or more and 8 GPa or less, 4.5 GPa or more and 7 GPa or less, or 4.6 GPa or more and 6 GPa or less, respectively, and the elongation on the MD and TD is 70% or more and 130% or less, or 80% or more and 125% or less, respectively.

[0064] When the Young's modulus and elongation ranges on MD and TD are satisfied respectively, the substrate layer of one embodiment of this disclosure will not be easily deformed by the tension applied in the range of 10N to 30N required during the transfer of the lithium transfer film to the electrode via a roll-to-roll process. Therefore, damage to the passivation layer can be effectively suppressed.

[0065] In one embodiment of this disclosure, the elongation deviation on the MD and TD of the substrate layer is less than ±3.5, less than ±3.3, or less than ±3.

[0066] When the elongation deviation on the MD and TD of the substrate layer in one embodiment of this disclosure is within the above-mentioned range, the substrate layer will not be excessively deformed in one direction during the roll-to-roll process. Therefore, damage to the passivation layer can be suppressed or prevented.

[0067] In particular, even if the elongation on the MD and TD of the substrate layer in one embodiment of this disclosure is less than 130%, if the elongation deviation exceeds this range, the passivation layer may be damaged due to high tensile force (30 N or more).

[0068] One embodiment of the lithium transfer film disclosed herein includes a lithium metal layer. Here, the lithium metal layer is a layer containing lithium metal for pre-lithiation of at least one surface of the electrode active material layer or for forming a lithium metal electrode, and commonly used Li metal foil can be used, but the present disclosure is not limited thereto.

[0069] In one embodiment of this disclosure, the thickness of the lithium metal layer can be from 0.1 μm to 15 μm, from 0.5 μm to 13 μm, or from 1 μm to 10 μm.

[0070] In one embodiment of this disclosure, when the thickness of the lithium metal layer meets the above-mentioned range, pre-lithiation for compensating for irreversible capacity can be performed. Since the lithium metal layer is difficult to peel off, the possibility of incomplete transfer can be reduced, the heat generated during the transfer process can be reduced, and the formation of lithium by-products that may occur due to excessively long pre-lithiation reaction time can be suppressed, thereby improving the performance of the electrode.

[0071] In one embodiment of this disclosure, the deposition method for depositing a lithium metal layer onto a substrate layer can be selected from physical vapor deposition (PVD) and chemical vapor deposition (CVD). In PVD, thermal evaporation may be primarily used, but is not limited to this, and various deposition methods used in the art can be employed.

[0072] One embodiment of the lithium transfer film disclosed herein includes a passivation layer. The passivation layer may be present on the surface of the lithium metal layer opposite to the surface of the substrate layer. The passivation layer is a hard and thin inorganic film and can suppress lithium loss due to side reactions caused by lithium oxides or nitrides formed on the surface of the lithium transfer film during the transfer process. Furthermore, it can reduce the risk of fire caused by nitriding or oxidation reactions.

[0073] In one embodiment of this disclosure, the passivation layer may be formed on the surface of the lithium metal layer, or it may be formed by treating the surface of the lithium metal layer with carbon dioxide (CO2) gas. According to one embodiment, the passivation layer may include at least one of Li2CO3 and Li2O formed by treating the surface of the lithium metal layer with carbon dioxide (CO2) gas.

[0074] That is, in one embodiment of this specification, the passivation layer may contain at least one of Li2CO3 and Li2O.

[0075] In one embodiment of this disclosure, the Young's modulus of the passivation layer may be more than 5 times, more than 6 times, or more than 10 times higher than the Young's modulus of the substrate layer.

[0076] In one embodiment of this disclosure, the thickness of the passivation layer can be from 1 nm to 200 nm, from 5 nm to 200 nm, or from 5 nm to 100 nm.

[0077] In one embodiment of this disclosure, when the thickness of the passivation layer meets the above-mentioned range, the surface of the lithium metal layer can be sufficiently protected, and the accelerated oxidation and nitriding reactions of the lithium metal layer can be suppressed. Furthermore, side effects such as a decrease in the pre-lithiation reaction rate or an increase in electrode resistance can be suppressed or prevented.

[0078] The lithium transfer film of one embodiment of this disclosure may further include a release layer between the substrate layer and the lithium metal layer.

[0079] In one embodiment of this disclosure, the release layer may be at least one selected from the group consisting of polycarbonate (PC), polydimethylsiloxane (PDMS), polymethylhydrosiloxane (PMHS), polyimide (PI), polymethyl methacrylate (PMMA), and cyclic olefin copolymers (COC). According to one embodiment, the release layer may be polymethyl methacrylate (PMMA).

[0080] In one embodiment of this disclosure, the thickness of the release layer can be from 0.05 μm to 3 μm, or from 0.2 μm to 1 μm.

[0081] In one embodiment of this disclosure, when the thickness of the release layer meets the above-mentioned range, sufficient release force of the lithium metal layer can be ensured. Furthermore, the release layer on the surface after the lithium metal layer is transferred does not prevent heat dissipation, thus not accelerating the formation of byproducts.

[0082] In one embodiment of this disclosure, a release layer can be formed by a coating method. For example, the coating method may be selected from, but is not limited to, methods selected from, dip coating, spray coating, spin coating, die coating, gravure coating, microgravure coating, comma coating, and roll coating. Various coating methods available in the art for forming coatings can be used.

[0083] In one embodiment of this disclosure, the deposition method for depositing a lithium metal layer on a release layer can be applied in the same manner as the deposition method for depositing a lithium metal layer on a substrate layer.

[0084] Figure 1 This diagram illustrates the stacked structure of a lithium transfer film 60 according to one embodiment of the present disclosure. For example, in the lithium transfer film 60, a release layer 62 is provided on one surface of a substrate layer 61, a lithium metal layer 63 is deposited on one surface of the release layer 62, and a passivation layer 64 is formed on one surface of the lithium metal layer 63. Meanwhile, the release layer 62 formed between the substrate layer 61 and the lithium metal layer 63 is optional, and the lithium metal layer 63 can be provided on the substrate layer 61 without the release layer 62.

[0085] Figure 2 This is a flowchart illustrating a method for manufacturing a lithium transfer film 60 according to one embodiment of the present disclosure.

[0086] Assuming a release layer 62 exists between the substrate layer 61 and the lithium metal layer 63, a method for manufacturing a lithium transfer film 60 according to one embodiment of this disclosure includes: step S10 of forming a release layer 62 on one surface of the substrate layer 61; step S20 of forming a lithium metal layer 63 on one surface of the release layer 62; and step S30 of forming a passivation layer 64 on one surface of the lithium metal layer 63. According to one embodiment of this disclosure, in the substrate layer 61, the Young's modulus of MD and TD are both 4.2 GPa or higher, the elongation of MD and TD is both 130% or less, and the deviation between the elongation of MD and TD is ±3.5 or less.

[0087] In one embodiment of the lithium transfer film manufacturing method described in this specification, the substrate layer, lithium metal layer, and passivation layer may be applied in the same manner as described above regarding the substrate layer, lithium metal layer, and passivation layer.

[0088] A method for manufacturing a lithium transfer film 60 according to one embodiment of the present disclosure includes the step of depositing a lithium metal layer 63 on a surface of a substrate layer 61.

[0089] In the deposition step of one embodiment of this disclosure, the deposition method for depositing the lithium metal layer 63 on the substrate layer 61 described above can be applied in the same manner. For example, the lithium metal layer 63 can be deposited on the substrate layer 61 by an evaporation deposition method or a thermal evaporation deposition method.

[0090] In the deposition step of the lithium metal layer 63 in one embodiment of this disclosure, the deposition apparatus can be used in various ways, as long as it is a deposition apparatus used in the art, such as the ULVAC EWK-060.

[0091] In the deposition step of the lithium metal layer 63 in one embodiment of this disclosure, the deposition rate can be 0.5 m / min to 5 m / min, 1 m / min to 3 m / min, or 2 m / min to 2.5 m / min.

[0092] Prior to the deposition step of the lithium metal layer 63 in one embodiment of this disclosure, a step of supplying the lithium metal layer 63 to the substrate layer 61 may be further included.

[0093] In the lithium metal layer 63 supply step of one embodiment of this disclosure, the temperature can be from 10°C to 1,000°C, from 100°C to 800°C, or from 300°C to 600°C.

[0094] In one embodiment of this disclosure, the deposition step of the lithium metal layer 63 may be performed after the step of forming the release layer 62 on one surface of the substrate layer 61.

[0095] A method for manufacturing a lithium transfer film 60 according to one embodiment of the present disclosure may include the steps of forming a release layer 62 on one surface of a substrate layer 61 and depositing a lithium metal layer 63 on the surface of the release layer 62 opposite to the surface of the substrate layer 61.

[0096] In one embodiment of this disclosure, the method for forming release layer 62 described above can be applied in the same manner to the step of forming release layer 62 on one surface of substrate layer 61.

[0097] A method for manufacturing a lithium transfer film 60 according to one embodiment of the present disclosure includes the step of forming a passivation layer 64 on the surface of a lithium metal layer 63 opposite to the surface of a substrate layer 61.

[0098] The step of forming the passivation layer 64 may include: placing a substrate layer 61 on which a 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 surface of the lithium metal layer 63 to the surface in contact with the substrate layer 61.

[0099] In one embodiment of this disclosure, the pressure in the vacuum chamber during the step of forming the passivation layer 64 can be 10. -3 torr to 10 -1 torr, or 10 -2 torr to 10 -1 torr.

[0100] In one embodiment of this disclosure, in the step of injecting Ar gas and CO2 gas into a vacuum chamber to form a passivation layer 64, the Ar gas and CO2 gas can be injected at a ratio of 1:10 to 10:1, or at a ratio of, for example, 8:2 to 2:8, or 8:2 to 1:1.

[0101] In one embodiment of this disclosure, the step of forming the passivation layer 64, after the step of injecting Ar gas and CO2 gas into the vacuum chamber, further includes a step of purging gas until the vacuum chamber reaches atmospheric pressure, and then performing a treatment for 1 min to 20 min, or 5 min to 10 min.

[0102] In one embodiment of this disclosure, the step of forming the passivation layer 64 can be performed at a temperature above 0°C and below 40°C, specifically above 10°C and below 30°C, more specifically above 20°C and below 28°C.

[0103] In one embodiment of this disclosure, the step of forming the passivation layer 64 can be performed at room temperature.

[0104] In one embodiment of this disclosure, an electrode current collector layer, an electrode active material layer, and the aforementioned lithium transfer film 60 are sequentially stacked in the electrode intermediate of a lithium secondary battery, and the passivation layer 64 of the lithium transfer film 60 may face the electrode active material layer of the electrode intermediate.

[0105] The electrode intermediate is the electrode intermediate used to manufacture the pre-lithiation electrode, and refers to the state in which the lithium transfer film 60 of this disclosure is stacked on one surface of the electrode active material layer for pre-lithiation before or during the transfer of the lithium metal layer 63 to one surface of the electrode active material layer. Here, the pre-lithiation reaction may begin simultaneously with the transfer of the lithium metal layer 63 to one surface of the electrode active material layer, or the pre-lithiation reaction may begin within a few seconds after the transfer begins.

[0106] In one embodiment of this disclosure, an electrode current collector layer is sequentially stacked in an electrode intermediate; 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.

[0107] The electrode intermediate is an electrode intermediate used to manufacture the negative electrode of the Li metal electrode, and represents the state in which the lithium transfer film 60 is stacked on one surface of the electrode current collector layer in order to transfer the lithium metal layer to one surface of the electrode current collector layer.

[0108] In one embodiment of this disclosure, the electrode for a lithium secondary battery includes an electrode active material layer or an electrode current collector layer, wherein the lithium transfer film can be transferred to at least one surface of the electrode active material layer or the electrode current collector layer.

[0109] When the lithium transfer film 60 of one embodiment of the present disclosure is transferred to at least one surface of the electrode active material layer, a pre-lithiated electrode can be formed, and when the lithium transfer film 60 is transferred to at least one surface of the electrode current collector layer, a negative electrode of a lithium metal battery can be formed.

[0110] In another embodiment of this disclosure, the electrode for a lithium secondary battery may be a pre-lithiated electrode or the negative electrode of a lithium metal battery.

[0111] In another embodiment of this disclosure, the pre-lithiated electrode may be a pre-lithiated negative electrode, and the pre-lithiated negative electrode may include a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer may contain a negative electrode active material. Furthermore, the negative electrode active material layer may also contain a thickener.

[0112] Figure 3 This is a diagram illustrating the stacked structure of a pre-lithiated negative electrode according to one embodiment of the present disclosure. For example, a negative electrode 100 for a lithium secondary battery can be seen, wherein a negative electrode active material layer 20 is included on one surface of the negative electrode current collector layer 10. Although Figure 3 It is shown that the negative electrode active material layer 20 is formed on one surface of the negative electrode current collector layer 10, but the negative electrode active material layer 20 can be formed on both surfaces of the negative electrode current collector layer 10.

[0113] In one embodiment of this disclosure, the thickness of the negative electrode current collector layer is typically from 1 μm to 100 μm. There are no particular limitations on the negative electrode current collector layer, as long as it has high conductivity and does not cause chemical changes in the corresponding battery. For example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. Furthermore, the bonding strength of the negative electrode active material can be enhanced by forming fine irregularities on the surface, and it can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0114] In one embodiment of the present disclosure, the thickness of the negative electrode current collector layer is from 1 μm to 100 μm, and the thickness of the negative electrode current collector layer may be from 20 μm to 50 μm. However, the thickness can be variously modified according to the type and use of the negative electrode to be used, but is not limited thereto.

[0115] The negative electrode active material layer 20 can be formed by coating a negative electrode slurry containing a negative electrode active material, a negative electrode binder, a negative electrode conductive material, and / or a thickener on at least one surface of the negative electrode current collector layer 10. This means that the negative electrode active material layer 20 can be formed by coating the negative electrode slurry on at least one surface of the negative electrode current collector layer 10, and drying and rolling.

[0116] In one embodiment of the present disclosure, the negative electrode slurry may include: a negative electrode active material layer composition containing a negative electrode active material, a negative electrode binder, a negative electrode conductive material, and / or a thickener; and a slurry solvent.

[0117] In one embodiment of the present disclosure, the solid content of the negative electrode slurry may satisfy the range of 5% to 40%.

[0118] In another embodiment, the solid content of the negative electrode slurry may satisfy the range of 5% to 40%, 7% to 35%, or 10% to 30%.

[0119] The solid content of the negative electrode slurry may refer to the amount of the composition of the negative electrode active material layer 20 contained in the negative electrode slurry, and may refer to the content of the composition of the negative electrode active material layer relative to 100 parts by weight of the negative electrode slurry.

[0120] When the solid content of the negative electrode slurry satisfies the above range, the viscosity is appropriate when forming the negative electrode active material layer. Therefore, the particle aggregation phenomenon of the composition of the negative electrode active material layer 20 can be minimized, and thus the negative electrode active material layer can be efficiently formed.

[0121] In one embodiment of the present disclosure, 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).

[0122] The negative electrode of one embodiment of the present disclosure can be formed by coating the negative electrode slurry on one surface or both surfaces of the negative electrode current collector layer 10 and drying, and the slurry solvent in the negative electrode slurry can be dried by a drying step.

[0123] In one embodiment of the present disclosure, the negative electrode active material layer 20 includes a negative electrode active material, a negative electrode conductive material, and a negative electrode binder, and the negative electrode active material includes a silicon-based active material. The silicon-based active material may include at least one selected from the group consisting of Si, SiOx (0 < x < 2), Si / C, and Si alloys.

[0124] In one embodiment of the present disclosure, the silicon-based active material may include at least one selected from the group consisting of Si and SiOx (0 < x < 2).

[0125] In one embodiment of the present disclosure, for the negative electrode active material, pure silicon (Si) may be used as the silicon-based active material. Using pure silicon (Si) as the negative electrode active material may mean that, based on a total of 100 parts by weight of the above negative electrode active material, the content of pure Si particles not combined with other particles or elements relative to 100 parts by weight of the silicon-based active material may be 60 parts by weight or more, 65 parts by weight or more, or 70 parts by weight or more, or may be in the range of 95 parts by weight or less, 90 parts by weight or less, or 85 parts by weight or less.

[0126] In one embodiment of the present disclosure, the negative electrode active material may use SiOx (0 < x < 2) as the silicon-based active material, and SiOx (0 < x < 2) corresponds to an amorphous matrix in the silicon-based active material. SiOx (0 < x < 2) may have a form partially containing Si and SiO2, and Si may form a phase. That is, x corresponds to the number ratio of O to Si contained in SiOx (0 < x < 2).

[0127] The silicon-based active material may be formed by heating and evaporating a mixed powder of Si powder and SiO2 powder and then depositing the evaporated mixed gas, and the mixed powder of Si powder and SiO2 powder may be heat-treated under vacuum at 1400 °C to 1800 °C or at 1400 °C to 1600 °C.

[0128] In one embodiment of the present disclosure, relative to a total of 100 parts by weight of the negative electrode active material layer 20, the content of SiOx (0 < x < 2) may be 40 parts by weight or more, 50 parts by weight or more, or 60 parts by weight or more, or its content may be 100 parts by weight or less, 90 parts by weight or less, or 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.

[0129] In one embodiment of the present disclosure, the negative electrode active material may include metal impurities.

[0130] The metal impurities are impurities that may be contained in silicon, and relative to 100 parts by weight of the negative electrode active material layer, its content may satisfy the range of 0.1 part by weight or less.

[0131] Meanwhile, the average particle size (D50) of the silicon-based active material of the present disclosure may be 5 µm to 10 µm, 5.5 µm to 8 µm, or 6 µm to 7 µm.

[0132] When the average particle size falls within the aforementioned range, the specific surface area of ​​the particles falls within an appropriate range, and a negative electrode slurry with a viscosity within an appropriate range is formed. Therefore, the particles constituting the negative electrode slurry are smoothly dispersed. Furthermore, since the size of the silicon-based active material has a value equal to or greater than the aforementioned lower limit, the contact area between the silicon particles and the conductive material is excellent due to the composite of the conductive material and binder in the negative electrode slurry. This increases the likelihood of a sustained conductive network, thereby improving capacity retention. Simultaneously, when the average particle size meets the aforementioned range, excessively large silicon particles are excluded, forming a smooth surface for the negative electrode. This can suppress or prevent uneven current density during charging / discharging.

[0133] In one embodiment of this disclosure, the silicon-based active material typically has a characteristic BET specific surface area. The BET specific surface area of ​​the silicon-based active material is 0.01 m². 2 / g to 150.0 m 2 / g, 0.1 m 2 / g to 100.0 m 2 / g, 0.2 m 2 / g to 80.0m 2 / g, or 0.2 m 2 / g to 18.0 m 2 / g. BET specific surface area is measured according to DIN (Deutsches Institut für Normung, German Association for Standardization) 66131 (using nitrogen).

[0134] In one embodiment of this disclosure, the silicon-based active material may exist, for example, in a crystalline or amorphous form and may not be porous. The Si may be spherical or fragmented particles. The silicon particles may also have a fibrous structure or may exist in the form of a silicon-containing film or coating.

[0135] In one embodiment of this disclosure, the silicon-based active material may be 40 parts by weight or more relative to a total of 100 parts by weight of the negative electrode active material layer 20.

[0136] In one embodiment of this disclosure, the content of silicon-based active material may be 40 parts by weight or more, 50 parts by weight or more, or 60 parts by weight or more, relative to a total of 100 parts by weight of negative electrode active material layer 20, and its content may be 95 parts by weight or less, 90 parts by weight or less, or 80 parts by weight or less.

[0137] In the charge / discharge reaction of lithium-ion batteries, lithium released from the positive electrode inserts into the negative electrode during charging and deintercalates from the negative electrode during discharging, returning to the positive electrode. In the case of silicon-based negative electrode active materials, significant volume changes and surface side reactions occur, resulting in a large amount of lithium inserted into the negative electrode during the initial charging phase failing to return to the positive electrode, leading to an increase in initial irreversible capacity. This increase in initial irreversible capacity results in reduced battery capacity and cycle life.

[0138] In view of this, in the lithium transfer process of the pre-lithiation process, a pretreatment process of the negative electrode is provided before the pre-lithiation process, so that lithium metal can be easily transferred from the transfer stack, and the pre-lithiation of lithium can be carried out uniformly within the negative electrode active material layer 20.

[0139] Traditionally, graphite-based compounds have been used exclusively as anode active materials. However, with the increasing demand for high-capacity batteries, there have been more attempts to combine silicon-based compounds to improve capacity. However, silicon-based compounds suffer from the following limitation: rapid volume expansion during charging / discharging can damage the conductive pathways formed in the anode active material layer, thereby reducing battery performance. Therefore, the type of anode conductive material used in conjunction with silicon-based active materials is crucial.

[0140] Therefore, in one embodiment of this disclosure, the negative electrode conductive material may include at least one selected from the group consisting of planar conductive materials, linear conductive materials and dot conductive materials, and may include at least one selected from the group consisting of, for example, planar conductive materials and linear conductive materials.

[0141] In one embodiment of this disclosure, the negative electrode conductive material may be 1 to 40 parts by weight relative to a total of 100 parts by weight of negative electrode active material layer.

[0142] In one embodiment, the content of the negative electrode conductive material may be from 1 part to 40 parts by weight, 5 parts to 30 parts by weight, or 10 parts to 25 parts by weight relative to a total of 100 parts by weight of the negative electrode active material layer.

[0143] When the content of the negative electrode conductive material meets the above range, it has the effect of not damaging the conductive path formed in the negative electrode active material layer.

[0144] In one embodiment of this disclosure, the planar conductive material used as the negative electrode conductive material has a structure and function different from that of carbon-based active materials typically used as negative electrode active materials. For example, the carbon-based active material used as the negative electrode active material can be artificial graphite or natural graphite, and refers to a material processed and used in a spherical or dot-like form to promote the storage and release of lithium ions.

[0145] Meanwhile, the planar conductive material used as the negative electrode conductive material is a material with a planar or plate shape, and can be represented as plate-shaped graphite. The planar conductive material is a material included to maintain the conductive path within the negative electrode active material layer 20, and refers to a material that does not play a role in storing and releasing lithium, but is used to ensure the conductive path within the negative electrode active material layer 20 in a planar shape.

[0146] In one embodiment of this disclosure, the use of plate-shaped graphite as the conductive material means that the graphite is processed into a planar or plate shape and does not serve to store or release lithium, but rather as a material to ensure a conductive path. Here, the negative electrode active material included with the plate-shaped graphite has high capacity characteristics in storing and releasing lithium, and serves to store and release all lithium ions transferred from the positive electrode.

[0147] In one embodiment of this disclosure, using carbon-based active materials as active materials means that the carbon-based active materials are processed into dots or spheres and used as materials that store or release lithium.

[0148] In one embodiment of this disclosure, the negative electrode conductive material may include a planar conductive material.

[0149] In one embodiment of this disclosure, a planar conductive material refers to a conductive material having a two-dimensional (2D) structure, wherein atoms have a thickness of a single atomic layer or multiple atomic layers (two or more layers) and form a crystal structure on a plane. A planar conductive material is a material that ensures a conductive path with a planar shape within the negative electrode active material layer, while also suppressing the interruption of the conductive path due to volume expansion, and can be represented as a plate-shaped conductive material or a block-shaped conductive material.

[0150] In one embodiment of this disclosure, the planar conductive material may include at least one selected from the group consisting of plate graphite, graphene, graphene oxide and flake graphite, and in one embodiment it may be plate graphite.

[0151] In one embodiment of this disclosure, the average particle size (D50) of the planar conductive material can be 2 μm to 7 μm, 3 μm to 6 μm, or 4 μm to 5 μm. When these ranges are met, the sufficient particle size makes it easy to disperse without causing an excessive increase in the viscosity of the negative electrode slurry. Therefore, excellent dispersion results are achieved when the same equipment and time are used for dispersion.

[0152] In one embodiment of this disclosure, the planar conductive material may have a D10 of 0.5 μm to 1.7 μm, a D50 of 2.5 μm to 3.5 μm, and a D90 of 6.8 μm to 15.0 μm.

[0153] In one embodiment of this disclosure, for planar conductive materials, a high specific surface area planar conductive material with a high BET specific surface area or a low specific surface area planar conductive material can be used.

[0154] In one embodiment of this disclosure, a high specific surface area planar conductive material or a low specific surface area planar conductive material can be used as the planar conductive material. However, the planar conductive material of this disclosure may be affected to some extent by the dispersion effect on the electrode performance, therefore a low specific surface area planar conductive material that does not cause dispersion problems can be used.

[0155] In one embodiment of this disclosure, the BET specific surface area of ​​the planar conductive material can be 5 m². 2 / g to 500m 2 / g、5 m 2 / g to 300 m 2 / g, or 5 m 2 / g to 250 m 2 / g.

[0156] In another embodiment, the planar conductive material is a planar conductive material with a high specific surface area, and its BET specific surface area can meet the requirement of 50 m². 2 / g to 500 m 2 / g、80 m 2 / g to 300 m 2 / g, or 100 m 2 / g to 300 m 2 The range of / g.

[0157] In another embodiment, the planar conductive material is a planar conductive material with a low specific surface area, and its BET specific surface area can meet the requirement of 5 m². 2 / g to 40 m 2 / g、5 m 2 / g to 30 m 2 / g, or 5 m 2 / g to 25 m 2 The range of / g.

[0158] In one embodiment of this disclosure, the negative electrode conductive material may include a linear conductive material. A linear conductive material refers to a conductive material with a one-dimensional (1D) structure having a nanometer-scale diameter and a high aspect ratio, or a conductive material with a fibrous structure such as a cylinder or tube. Examples of linear conductive materials may include carbon nanotubes, etc.

[0159] Carbon nanotubes can be bundled carbon nanotubes. Bundled carbon nanotubes can contain multiple carbon nanotube units. Here, unless otherwise specified, "bundled" refers to a secondary shape in the form of a bundle or rope, in which carbon nanotube units are arranged side by side or entangled, with the longitudinal axes of the carbon nanotube units being substantially in the same orientation. The carbon nanotube units have a cylindrical graphite surface (graphite sheet) with a nanometer-scale diameter and an sp2 bond structure. Here, depending on the angle and structure of the graphite surface winding, conductive or semiconductor properties can be exhibited. Compared to wound carbon nanotubes, bundled carbon nanotubes can be uniformly dispersed in the fabrication of the negative electrode, and then a conductive network can be smoothly formed in the negative electrode, thereby improving the conductivity of the negative electrode.

[0160] In one embodiment of this disclosure, the negative electrode conductive material may include at least one selected from the group consisting of plate-like graphite, single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs), but is not limited thereto.

[0161] In one embodiment of this disclosure, the BET specific surface area of ​​the linear conductive material can be 100 m². 2 / g to 10,000 m 2 / g、500 m 2 / g to 5,000 m 2 / g, or 1,000 m 2 / g to 1,500 m 2 / g.

[0162] Furthermore, in one embodiment of this disclosure, the aspect ratio of the linear conductive material can be 500 or more, 1,000 or more, or 10,000 or more, and can be 1,000,000 or less, or 100,000 or less.

[0163] In one embodiment of this disclosure, when the linear conductive material meets the range of BET specific surface area and aspect ratio, it has the effect of suppressing electrical short circuits between negative electrode active materials.

[0164] In one embodiment of this disclosure, the negative electrode conductive material may further include a dot-shaped conductive material.

[0165] In one embodiment of this disclosure, a dot-like conductive material refers to a conductive material having a zero-dimensional (OD) structure, wherein the crystal cluster structure consisting of one to several hundred atoms is spherical and has volume. A dot-like conductive material is a conductive material that can be used to improve the conductivity of the negative electrode and has conductivity without causing chemical changes. The dot-like conductive material may be selected from at least one of the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermally cracked carbon black, conductive fibers, fluorocarbons, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium dioxide, and polyphenylene derivatives, and may include carbon black for achieving high conductivity and excellent dispersibility.

[0166] In one embodiment of this disclosure, the BET specific surface area of ​​the dot-shaped conductive material can be 40 m². 2 / g to 70m 2 / g、45 m 2 / g to 65 m 2 / g, or 50 m 2 / g to 60 m 2 / g.

[0167] In one embodiment of this disclosure, the particle size of the dot-shaped conductive material can be 10 nm to 100 nm, 20 nm to 90 nm, or 20 nm to 60 nm.

[0168] The negative electrode conductive material disclosed herein has a structure substantially different from that of the conductive material used in the positive electrode. The negative electrode conductive material of this disclosure functions to form contact points between silicon-based active materials that cause significant volume expansion of the electrode during charging and discharging. The negative electrode conductive material has a structure and function substantially different from that of the positive electrode conductive material, which acts as a buffer during rolling and provides partial conductivity.

[0169] Furthermore, the negative electrode conductive material of this disclosure is applied to silicon-based negative electrode active materials and has a structure substantially different from that of conductive materials applied to graphite-based active materials. The conductive material used for electrodes with graphite-based active materials simply has small particles relative to the active material and possesses properties that improve output characteristics and provide partial conductivity; therefore, it has a different structure and function than the negative electrode conductive material used in this disclosure together with silicon-based negative electrode active materials.

[0170] In one embodiment of this disclosure, the negative electrode adhesive may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyacrylamide, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and alternatives obtained by replacing hydrogen with Li, Na, or Ca, and may include various copolymers of these.

[0171] In one embodiment of this disclosure, the negative electrode adhesive serves to support the active and conductive materials, thereby suppressing or preventing distortion and structural deformation of the negative electrode structure during the volume expansion and relaxation of the silicon-based active material. General adhesives that satisfy the above-described functions can be applied, and may include at least one adhesive selected from the group consisting of polyacrylamide (PAM) and styrene-butadiene rubber.

[0172] In one embodiment of this disclosure, the content of the negative electrode binder may be less than 30 parts by weight, less than 20 parts by weight, or less than 10 parts by weight relative to a total of 100 parts by weight of the negative electrode active material layer 20, and may be more than 1 part by weight or more than 3 parts by weight.

[0173] In one embodiment of this disclosure, the weight-average molecular weight of the adhesive can be from 100,000 g / mol to 1,500,000 g / mol.

[0174] When the weight-average molecular weight of the adhesive meets the above-mentioned range, it is characterized by excellent mechanical strength and high intermolecular interaction, resulting in excellent electrode bonding strength. Furthermore, when the above range is met, the viscosity of the adhesive can be selected within an appropriate range. Therefore, when using this adhesive to manufacture a negative electrode, the coating performance of the electrode can be further improved.

[0175] In another embodiment of the manufacturing method of the pre-lithiated negative electrode, the pre-lithiated negative electrode can be formed by transferring a lithium transfer film to at least one surface of the above-mentioned negative electrode active material layer 20.

[0176] The method for manufacturing a pre-lithiated anode disclosed herein is characterized in that, in order to improve coulombic efficiency, pre-lithiation is performed on at least one surface of the anode active material layer. Since the process speed is faster than that using the stabilized lithium metal powder (SLMP) method or electrochemical methods for pre-lithiation, a lithium transfer method with high yield is used for pre-lithiation.

[0177] In one embodiment of this disclosure, the step of transferring the lithium transfer film to at least one surface of the negative electrode active material layer 20 and forming a pre-lithiated negative electrode includes: contacting the lithium transfer film with the negative electrode active material layer 20 such that the lithium metal layer faces at least one surface of the negative electrode active material layer; and applying pressure.

[0178] In one embodiment of this disclosure, the step of contacting the lithium transfer film with the negative electrode active material layer 20 such that the lithium metal layer 63 faces at least one surface of the negative electrode active material layer 20 is the step of transferring lithium metal to the negative electrode active material layer 20.

[0179] In one embodiment of this disclosure, during the pressure application step, the pre-lithiation caused by the transfer to the negative electrode active material layer 20 can proceed more aggressively, and despite having a high energy density, it has the effect of forming a thinner negative electrode.

[0180] Here, a lithium transfer film 60 is placed such that the lithium metal layer 63 of the lithium transfer film 60 contacts one or both surfaces of the negative electrode active material layer 20, and then a load of 10 kgf to 500 kgf is applied, and the transfer process can be performed by rolling. Next, a process for removing the substrate layer or release layer and the substrate layer may be included.

[0181] In one embodiment of this disclosure, after the lithium metal layer 63 and the negative electrode active material layer 20 are brought into contact with each other and transferred by applying pressure, the step of removing the substrate layer 61 or release layer 62 and substrate layer 61 of the lithium transfer film 60 can be performed.

[0182] In a method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present disclosure, pre-lithiation can be performed at the moment when the lithium metal layer 63 of the lithium transfer film 60 comes into contact with the negative electrode active material layer 20, or it can be performed in a step of applying pressure, or it can be performed in a step of removing the substrate layer or release layer and the substrate layer.

[0183] In another embodiment of this disclosure, the negative electrode of a lithium metal battery may include a negative electrode current collector on at least one surface of which the lithium transfer film 60 described above has been transferred.

[0184] Here, the above content can be applied to the transfer method of the negative electrode current collector and the lithium transfer film 60.

[0185] One embodiment of the lithium secondary battery disclosed herein may include the electrode for a lithium secondary battery described in one embodiment. The secondary battery may include a lithium secondary battery electrode, a separator, and an electrolyte, and the lithium secondary battery electrode may be a negative electrode or a positive electrode.

[0186] Figure 4This diagram illustrates a stacked structure of a lithium-ion secondary battery using a pre-lithiated electrode according to an embodiment of the present disclosure. The stacked structure of the lithium-ion secondary battery includes: a negative electrode 100 for a lithium-ion secondary battery having a negative electrode active material layer 20 on one surface of a negative electrode current collector layer 10; and a positive electrode 200 for a lithium-ion secondary battery having a positive electrode active material layer 40 on one surface of a positive electrode current collector layer 50. This shows that the negative electrode 100 and the positive electrode 200 for a lithium-ion secondary battery are formed in a stacked structure, with a separator 30 inserted therebetween.

[0187] The positive electrode may include: a positive electrode current collector layer; and a positive electrode active material layer formed on at least one surface of the positive electrode current collector layer and comprising a positive electrode active material.

[0188] In the positive electrode, there are no particular limitations on the positive electrode current collector layer, as long as it is conductive and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel with surface treatments such as carbon, nickel, titanium, or silver can be used. Moreover, the thickness of the positive electrode current collector layer can typically range from 3 μm to 500 μm, and the adhesion of the positive electrode active material can be improved by forming fine irregularities on the surface of the positive electrode current collector layer. For example, it can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0189] The positive electrode active material of one embodiment of this disclosure may include at least one lithium composite oxide selected from the group consisting of lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, lithium aluminum oxide, or combinations thereof.

[0190] Examples of positive electrode active materials may include: layered compounds, such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2) or compounds substituted with one or more transition metals; lithium iron oxides, such as LiFe3O4; and lithium manganese oxides, such as those with the chemical formula Li 1+c1 Mn 2-c1 O4 (0≤c1≤0.33), LiMnO3, LiMn2O3 and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides, such as LiV3O8, V2O5 and Cu2V2O7; and 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 ≤ 0.5) represents a Ni-site type lithium nickel oxide; LiMn 2-c3Lithium-manganese composite oxides represented by Mc3O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01 ≤ c3 ≤ 0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); and LiMn2O4 in which a portion of the Li in the chemical formula is replaced by an alkaline earth metal ion, but not limited to these. The cathode may also be Li metal.

[0191] The positive electrode active material layer may include a positive electrode conductive material, a positive electrode binder, and the aforementioned positive electrode active material.

[0192] Here, the positive electrode conductive material is used to provide electrode conductivity, and can be used as long as it has electronic conductivity and does not cause chemical changes in the battery. Examples may include: graphite, such as natural or artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, and carbon fibers; metal powders or 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, and among these, one or a mixture of two or more may be used alone.

[0193] Furthermore, the positive electrode binder enhances the adhesion between positive electrode active material particles and the adhesion strength between the positive electrode active material and the positive electrode current collector. Examples include polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one or more of these can be used alone or in mixtures thereof.

[0194] The solvent used for the positive electrode composition slurry can be a solvent commonly used in the relevant art. Examples include dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, and water, and one or more of these can be used alone or in mixtures. The amount of solvent to be used can be set considering the coating thickness and manufacturing yield of the slurry. As a result, when the active material, conductive material, and binder are dissolved or dispersed and then coated to manufacture the positive and negative electrodes, a viscosity exhibiting excellent thickness uniformity can be obtained. Moreover, in another method of manufacturing the positive and negative electrodes, the active material layer forming composition can be cast onto a separate support, and then the film layer obtained by peeling off from the support can be pressed onto the current collector.

[0195] The separator separates the negative and positive electrodes and provides a pathway for lithium ion movement. It can be used without particular limitations, as long as it is typically used as a separator in a secondary battery. The separator can exhibit low resistance to ion movement of the electrolyte and excellent electrolyte retention. Porous polymer membranes can be used, such as those made from polyolefin polymers (e.g., ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers), or stacked structures of these two or more layers. Conventional porous nonwoven fabrics, such as those made from high-melting-point glass fibers, polyethylene terephthalate fibers, etc., can also be used. Furthermore, coated separators containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and can optionally be used in single-layer or multi-layer structures.

[0196] Examples of electrolytes may include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used to manufacture lithium secondary batteries.

[0197] Electrolytes can include non-aqueous organic solvents and metal salts.

[0198] For non-aqueous organic solvents, aprotic organic solvents such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butyl 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, triphosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate can be used.

[0199] Among the aforementioned carbonate organic solvents, ethylene carbonate and propylene carbonate, as cyclic carbonates, can be used because they are high-viscosity organic solvents and can readily dissociate lithium salts due to their high dielectric constant. Then, when these cyclic carbonates are mixed with straight-chain carbonates (e.g., dimethyl carbonate and diethyl carbonate) having low viscosity and low dielectric constant in appropriate ratios, electrolytes with high conductivity can be prepared.

[0200] For metal salts, lithium salts can be used, and lithium salts are materials that are readily soluble in non-aqueous electrolytes. For example, as an anion of lithium salts, materials selected from those including 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 - At least one of the groups.

[0201] In addition to the electrolyte component, the electrolyte may further include one or more additives, such as alkyl halogenated carbonates (e.g., ethylene difluorocarbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol diether, hexamethylphosphotriamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidinanes, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum trichloride.

[0202] One embodiment of this specification provides a battery module comprising the above-described lithium secondary battery as a unit cell, and a battery pack comprising the battery module.

[0203] In addition, another embodiment of this specification provides a battery pack including the lithium secondary battery.

[0204] The lithium secondary batteries of the present disclosure stably exhibit excellent discharge capacity, output characteristics, and cycle performance, and therefore can be used as power sources not only for portable devices such as mobile phones, laptops, and digital cameras, but also for medium to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems. For example, the battery module or battery pack can be used as a power source for one or more medium to large-sized devices including: power tools; electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); and energy storage systems.

[0205] [Example]

[0206] In the following description, embodiments will be given to aid in understanding this disclosure, but these embodiments are merely illustrative of this specification. It will be apparent to those skilled in the art that various modifications and alterations can be made within the scope of this specification and the technical concept, and it is obvious that such modifications and alterations fall within the scope of the appended claims.

[0207] <Preparation Example 1>

[0208] Example 1

[0209] <Preparation of Lithium Transfer Film>

[0210] A transfer film was prepared by coating a 1 μm layer of acrylic resin (release layer) onto a PET A substrate layer. Here, polyethylene terephthalate (PETA) that meets the mechanical properties specified in Table 1 below was used as PET A.

[0211] Lithium was deposited onto the acrylic resin coating of the transfer film using a thermal evaporation deposition method to form a lithium layer with a thickness of 6 μm. Here, the deposition apparatus was a ULVAC EWK-060, and the deposition process was performed by setting the speed to 2.5 m / min, the lithium supply temperature to 500˚C, and the main roll temperature to -25°C.

[0212] The prepared transfer membrane was placed in the chamber, and the chamber vacuum was set to 10. -1The pressure is reduced below torr, then the vacuum valve is closed. The gas purging valve is opened, and argon (Ar) and carbon dioxide (CO2) gases are injected into the chamber at a ratio of 8:2 at room temperature. Each gas is purged until the vacuum level in the chamber becomes atmospheric pressure. After processing for about 10 minutes, a lithium transfer film containing a passivation layer of Li2CO3 is prepared on the surface of the deposited lithium film.

[0213] Example 2

[0214] The lithium transfer film was prepared in the same manner as in Example 1, except that PEN (polyethylene naphthalate) with the mechanical properties shown in Table 1 below was used as the substrate layer.

[0215] Comparative Example 1

[0216] The lithium transfer film was prepared in the same manner as in Example 1, except that PET B, which has the mechanical properties shown in Table 1 below, was used as the substrate layer.

[0217] Comparative Example 2

[0218] The lithium transfer film was prepared in the same manner as in Example 1, except that PET C with the mechanical properties shown in Table 1 below was used as the substrate layer.

[0219] Comparative Example 3

[0220] The lithium transfer film was prepared in the same manner as in Example 1, except that PET D with the mechanical properties shown in Table 1 below was used as the substrate layer.

[0221] Comparative Example 4

[0222] The lithium transfer film was prepared in the same manner as in Example 1, except that PET E with the mechanical properties shown in Table 1 below was used as the substrate layer.

[0223] Comparative Example 5

[0224] The lithium transfer film was prepared in the same manner as in Example 1, except that PET F, which has the mechanical properties shown in Table 1 below, was used as the substrate layer.

[0225] The mechanical properties of the substrate layers used in Examples 1 and 2 and Comparative Examples 1 to 5 were determined at room temperature according to the tensile testing method of ASTM D882, and the results are summarized in Table 1 below.

[0226] <Experimental Example>

[0227] If no passivation layer is formed on the surface of the lithium transfer film, it exhibits the characteristic of undergoing a nitriding reaction in a nitrogen atmosphere (a controlled environment with oxygen and moisture <10 ppm) and the surface being rapidly nitrided. Therefore, this phenomenon is used to check whether the passivation layer on the surface of the lithium transfer film is damaged.

[0228] Two shafts are arranged in the chamber, and tension can be applied to the shafts to enable unwinding / rewinding of the film roll. The lithium transfer films of Examples 1, 2, and Comparative Examples 1 to 5 prepared according to the above preparation examples are placed on the shafts inside the chamber, and the chamber is then purged with nitrogen for 30 minutes. Afterward, the chamber is circulated using a purifier for 30 minutes. When the oxygen and moisture concentrations reach below 10 ppm, tensions of 10 N and 30 N are applied to each lithium transfer film. After 10 minutes, the surface of the lithium metal layer is observed for nitriding and recorded in Table 1 below. “X” indicates no nitriding reaction, and “O” indicates nitriding reaction. When nitriding occurs, the surface of the lithium metal layer turns black, so the occurrence of the nitriding reaction can be observed with the naked eye.

[0229] [Table 1]

[0230]

[0231] As can be seen from Table 1 above, the lithium transfer film of Comparative Example 1 does not meet the characteristic mechanical properties of this disclosure because the elongation at MD and TD of the substrate layer is more than 130%. Therefore, it can be found that during the roll-to-roll process, under high tension of 30N, the passivation layer is damaged and a nitriding reaction occurs on the lithium surface.

[0232] Similarly, the lithium transfer film of Comparative Example 2 does not possess the characteristic mechanical properties of this disclosure because the TD elongation of the substrate layer is over 130%, and the elongation deviation between MD and TD is greater than ±3.5. Therefore, it can be observed that a nitriding reaction occurs on the lithium surface under high tensile conditions of 30 N.

[0233] In Comparative Example 3, since the elongation and Young's modulus of MD and TD did not meet the requirements of this application, nitriding was observed even under relatively low tension conditions of 10 N. Comparative Example 4 was similar to Comparative Example 2, but the elongation deviation increased significantly. Then, even under low tension conditions of 10 N, the passivation layer was damaged, and nitriding was observed.

[0234] In Comparative Example 5, the range of elongation and Young's modulus was met, but due to the small Young's modulus of TD and the undesirable deviation, a nitriding reaction was observed under a tension of 30 N.

[0235] However, the substrate layers used in Examples 1 and 2 of this application meet all the conditions: the Young's modulus on MD and TD is 4.2 GPa or higher, the elongation on MD and TD is 130% or lower, and the elongation deviation between MD and TD is ±3.5 or lower. Therefore, the lithium transfer film is not easily stretched by applied tension, regardless of the tension magnitude. Moreover, since the strain along either the MD axis or the TD axis is small, damage to the passivation layer can be suppressed or prevented during the roll-to-roll lithium transfer process, and nitriding or oxidation of the lithium surface can be prevented.

[0236] In the foregoing description, since those skilled in the art can make various substitutions, modifications, and alterations to this disclosure without departing from the technical concept of this disclosure, this disclosure is not limited to the foregoing embodiments and the accompanying drawings, but can selectively combine all or part of the embodiments to achieve various modifications. Therefore, the technical scope of this disclosure is not limited to the description herein, but should be defined by the claims.

[0237] [Explanation of reference numerals in the attached figures]

[0238] 10: Negative electrode current collector layer

[0239] 20: Negative electrode active material layer

[0240] 30: Diaphragm

[0241] 40: Positive electrode active material layer

[0242] 50: Positive current collector layer

[0243] 60: Lithium transfer membrane

[0244] 61: Substrate layer

[0245] 62: Release layer

[0246] 63: Lithium metal layer

[0247] 64: Passivation layer

[0248] 100: Negative electrode for lithium secondary batteries

[0249] 200: Positive electrode for lithium secondary batteries

Claims

1. A lithium transfer film, comprising: A substrate layer; A lithium metal layer; And A passivation layer, wherein, in the substrate layer, the Young's modulus in the machine direction (MD) and the transverse direction (TD) is respectively 4.2 GPa or more, the elongation rate in MD and TD is respectively 130% or less, and the elongation rate deviation in MD and TD is ±3.5 or less.

2. The lithium transfer film according to claim 1, wherein, The passivation layer contains at least one of Li2CO3 and Li2O.

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

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

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 method for manufacturing a lithium transfer film, the method comprising: Depositing a lithium metal layer on one surface of a substrate layer; And Forming a passivation layer on the surface of the lithium metal layer opposite to the surface where the substrate layer is located, wherein, in the substrate layer, the Young's modulus in MD and TD is respectively 4.2 GPa or more, the elongation rate in MD and TD is respectively 130% or less, and the elongation rate deviation in MD and TD is ±3.5 or less.

7. The method according to claim 6, wherein, The step of forming the passivation layer includes: Placing the substrate layer deposited with the lithium metal layer in a vacuum chamber; Injecting Ar gas and CO2 gas into the vacuum chamber; and Forming a passivation layer on the surface of the lithium metal layer opposite to the surface in contact with the substrate layer.

8. The method according to claim 6, wherein, The deposition of the lithium metal layer is carried out after forming a release layer on one surface of the substrate layer.

9. An electrode intermediate, wherein, There are sequentially stacked: An electrode current collector layer; An electrode active material layer; And The lithium transfer film according to any one of claims 1 to 5, wherein the passivation layer of the lithium transfer film faces the electrode active material layer.

10. An electrode intermediate, wherein, There are sequentially stacked: An electrode current collector layer; ​ ​ ​ ​ ​ ​ 12. The electrode according to claim 11, wherein, ​ 13. The electrode according to claim 11, wherein, ​ ​ ​ ​ ​ ​ ​ ​ ​

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