Method for manufacturing electrode for lithium secondary battery, electrode manufactured thereby, and lithium secondary battery comprising same

Abstract

The present invention relates to a method for manufacturing an electrode for a lithium secondary battery, an electrode manufactured by the method, and a lithium secondary battery comprising the electrode, the method comprising the steps of: preparing a transfer laminate comprising a lithium metal layer, a release layer, and a base material layer; transferring the lithium metal layer and the release layer to at least one surface of the electrode active material layer such that the lithium metal layer is in contact with the electrode active material layer, in which at least one of the lithium metal layer and the release layer transferred to the at least one surface of the electrode active material layer includes two or more pores, and the shortest distance between adjacent pores satisfies a predetermined range, so that lithium by-products can be reduced.

Description

TECHNICAL FIELD

[0001] This application claims priority to and the benefit of Korean Patent Application No. 10-2023-0140985, filed on October 20, 2023, and Korean Patent Application No. 10-2024-0141418, filed on October 16, 2024, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a manufacturing method of an electrode for a lithium secondary battery, an electrode manufactured by the method, and a lithium secondary battery including the electrode. BACKGROUND

[0003] Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative or clean energy is growing, and as part of this, the field of power generation and power storage using electrochemical reactions is the most active field of research.

[0004] Currently, a secondary battery is a representative example of an electrochemical device that utilizes such electrochemical energy, and the specific range of its use tends to gradually expand.

[0005] As technology develops and the demand for mobile devices increases, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life, and low self-discharge rate have been commercialized and widely used. In addition, methods of manufacturing high-density electrodes having higher energy density per unit volume as electrodes of such high-capacity lithium secondary batteries are being actively researched, and the trend is turning to higher load to improve energy density.

[0006] In general, a secondary battery includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, an electrolyte, and the like. In addition, an electrode such as a positive electrode and a negative electrode can have an electrode active material layer disposed on a current collector.

[0007] Note that lithium loss occurs in a lithium secondary battery from the first charge after the battery is manufactured. During subsequent charge and discharge cycles and high-temperature storage, trace but continuous lithium loss continues to occur, resulting in degradation of the battery. To compensate for such loss of lithium, lithium is additionally intercalated into the battery before the battery is operated, which is called pre-lithiation.

[0008] [LIST OF CITATIONS]

[0009] [PATENT LITERATURE]

[0010] Japanese Patent No. 7125228 B SUMMARY

[0011] TECHNICAL PROBLEM

[0012] The present invention relates to a manufacturing method of an electrode for a lithium secondary battery capable of reducing by-products on the surface of the electrode, an electrode manufactured by the method, and a lithium secondary battery including the electrode.

[0013] Technical Solution

[0014] One exemplary embodiment of the present specification provides a manufacturing method of an electrode for a lithium secondary battery, the method including: preparing a transfer stack including a lithium metal layer, a release layer, and a base material layer; and transferring the lithium metal layer and the release layer to at least one surface of an electrode active material layer such that the lithium metal layer is in contact with the electrode active material layer, wherein at least one of the lithium metal layer and the release layer transferred to the at least one surface of the electrode active material layer contains two or more holes, and a shortest distance between adjacent holes is 0.04 cm or more and 1 cm or less.

[0015] One exemplary embodiment of the present specification provides an electrode for a lithium secondary battery manufactured according to the above manufacturing method.

[0016] Another exemplary embodiment of the present specification provides an electrode for a lithium secondary battery, the electrode including: an electrode current collector layer; an electrode active material layer on which a lithium metal layer is transferred; and a lithium by-product layer, wherein the lithium by-product layer exhibits 3% or more of nitrogen (N) and 75% or more of oxygen (O) when analyzed by energy dispersive X-ray spectroscopy (EDS) using a scanning electron microscope (SEM), and an area of the lithium by-product layer is 42% or less with respect to a total area of the lithium metal layer transferred to the electrode active material layer.

[0017] Another exemplary embodiment of the present specification provides a lithium secondary battery including: the above-described electrode for a lithium secondary battery; a separator; and an electrolyte.

[0018] One exemplary embodiment of the present specification provides a battery pack or a battery module including the above-described lithium secondary battery.

[0019] In addition, another exemplary embodiment of the present specification provides a battery module including the above-described battery pack.

[0020] Advantageous Effects

[0021] The manufacturing method of one exemplary embodiment of the present invention can manufacture an electrode for a lithium secondary battery in which, before or after the lithium metal layer is transferred to the electrode active material layer, holes are formed at a specific interval to release heat generated in a pre-lithiation process, thereby minimizing lithium by-products generated on the surface of the electrode at high temperature.

[0022] Further, the electrode for a lithium secondary battery manufactured according to the manufacturing method of one exemplary embodiment of the present application has a feature of reducing the area of lithium by-products formed on the surface after pre-lithiation is completed, thereby minimizing the influence on the performance of the electrode, and also avoiding a safety problem. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 FIG. 1 is a view showing a stack structure of a negative electrode for a lithium secondary battery according to one exemplary embodiment of the present application.

[0024] Figure 2 FIG. 2 is a view showing a stack structure of a lithium secondary battery according to one exemplary embodiment of the present application.

[0025] Figure 3 FIG. 3 is a flowchart showing a manufacturing method of an electrode for a lithium secondary battery according to one exemplary embodiment of the present application.

[0026] Figure 4 FIG. 4 is a view showing the surface of an electrode after a base material layer and a release layer are removed after transferring lithium metal.

[0027] Figure 5 FIG. 5 is a view showing the surface of an electrode for a lithium secondary battery of Example 1, Example 2, and Comparative Examples 1 and 2. DETAILED DESCRIPTION

[0028] Before describing the present application, first, some terms are defined.

[0029] In the present specification, when a part "includes", "comprises" or "has" a constituent element, unless otherwise specifically described, this does not mean that another constituent element is excluded, but means that another constituent element can be further included.

[0030] In the present specification, when a member is positioned "on" another member, the member can be in direct contact with the other member, or another intermediate member can be further present.

[0031] In the present specification, "p to q" means a range of "p or more and q or less".

[0032] In the present specification, "specific surface area" is measured by a BET method, specifically, calculated from the amount of nitrogen adsorption at a liquid nitrogen temperature (77 K) using a BELS0RP-mini II of BEL Japan Co. In the present application, the BET specific surface area can mean a specific surface area measured by the above measurement method.

[0033] In the present specification, "Dn" means a particle size distribution, and means a particle size at an n% point in a cumulative distribution of the number of particles according to particle size. That is, D50 is a particle size at a 50% point in a cumulative distribution of the number of particles according to particle size (average particle size), D90 is a particle size at a 90% point in a cumulative distribution of the number of particles according to particle size, and D10 is a particle size at a 10% point in a cumulative distribution of the number of particles according to particle size. Note that the average particle size can be measured using a laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, the resulting dispersion is introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac S3500), in which, when a laser beam passes through a particle, the difference in the diffraction pattern corresponding to the particle size is measured, and then the particle size distribution is calculated.

[0034] The measurement of the average particle size can be confirmed using a Microtrac device (manufacturer: Microtrac, model: S3500) using water and Triton-X100 dispersant. Specifically, the average particle size of the positive electrode active material can be measured under the condition that the refractive index is 1.5 to 1.7, and the average particle size of the negative electrode active material can be measured under the condition that the refractive index is 1.97 or 2.42. For example, after dispersing the particles in a dispersion medium, the resulting dispersion is introduced into a commercially available laser diffraction particle size measuring device, and is irradiated with ultrasonic waves of about 28 kHz with an output of 60 W. Then, a cumulative volume particle size distribution chart is obtained, and then the average particle size can be determined by acquiring the particle size corresponding to 50% of the cumulative volume.

[0035] In the present specification, it can be confirmed whether or not lithium by-products are formed by analyzing the surface elemental content, and specifically, the elemental content of each surface region can be analyzed by energy dispersive X-ray spectroscopy (EDS) analysis using a scanning electron microscope (SEM) (JSM-7610F).

[0036] In the present specification, the particle size or particle diameter can mean the average diameter or representative diameter of each fine particle constituting the metal powder.

[0037] In the present specification, the description that "a polymer contains a certain monomer as a monomer unit" means that the monomer participates in the polymerization reaction and is contained in the polymer as a repeating unit. In the present application, when a polymer contains a monomer, it is understood to be the same as the polymer containing the monomer as a monomer unit.

[0038] In the present specification, it is understood that the term "polymer" is used in a broad sense to include copolymers, unless otherwise specified as "homopolymer".

[0039] It should be understood that the terms or words used throughout the specification should not be interpreted as limited to the ordinary meanings or dictionary meanings, but should be interpreted based on the concepts of the inventors appropriately defining the terms or words in order to best explain the principles of the present application, and can be interpreted as having meanings and concepts consistent with the technical idea of the present application.

[0040] As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0041] Hereinafter, preferred exemplary embodiments of the present application will be described in detail. However, it should be understood that the scope of the present application is not limited to the exemplary embodiments described below, and the embodiments of the present application can be modified in various ways.

[0042] The manufacturing method of an electrode for a lithium secondary battery of one exemplary embodiment of the present specification includes the steps of: preparing a transfer laminate containing a lithium metal layer, a release layer, and a base material layer; and transferring the lithium metal layer and the release layer to at least one surface of an electrode active material layer such that the lithium metal layer is in contact with the electrode active material layer, wherein at least one of the lithium metal layer and the release layer transferred to the at least one surface of the electrode active material layer contains two or more holes, and the shortest distance between adjacent holes is 0.04 cm or more and 1 cm or less.

[0043] The manufacturing method of an electrode for a lithium secondary battery of the present specification performs prelithiation by transferring lithium to at least one surface of an electrode active material layer, thereby improving coulombic efficiency by solving the problem of irreversibility of a silicon-based electrode, compared to SLMP or electrochemical prelithiation, and is a technology suitable for mass production processes since it can improve process speed and enable mass production.

[0044] However, when prelithiation is performed by a transfer method, the reaction speed of the electrode active material with lithium metal is fast, which can cause the maximum temperature of the electrode surface prelithiated with lithium metal to rise to about 40°C or more, which can cause the formation of byproducts on the electrode surface and a problem of loss of electrode capacity. Therefore, in order to solve the above problem, the present application is characterized in that by forming two or more holes having an appropriate shortest distance on at least one of the lithium metal layer and the release layer, heat generated at the time of prelithiation is released, thereby reducing the formation of byproducts on the electrode surface.

[0045] In the present specification, the shortest distance between adjacent holes refers to the shortest distance among the distances between the outermost edges of one hole and the outermost edges of adjacent holes.

[0046] The manufacturing method of an electrode for a lithium secondary battery of one example embodiment of the present specification includes the steps of transferring a lithium metal layer and a release layer to at least one surface of an electrode active material layer such that the lithium metal layer is in contact with the electrode active material layer, in which case at least one of the lithium metal layer and the release layer transferred to at least one surface of the electrode active material layer contains two or more holes.

[0047] In the present specification, the two or more holes in at least one of the lithium metal layer and the release layer transferred to at least one surface of the electrode active material layer can be formed on the transfer stack in the step of preparing the transfer stack, can be formed on the transfer stack in the step of bringing the transfer stack into contact with at least one surface of the electrode active material layer, or can be formed on the electrode after the transfer is completed.

[0048] In one example embodiment of the present specification, the step of transferring the lithium metal layer and the release layer to at least one surface of the electrode active material layer can include the steps of stacking the transfer stack and the electrode active material layer such that the lithium metal layer is in contact with at least one surface of the electrode active material layer; separating the substrate layer from the release layer; and forming two or more holes in at least one of the lithium metal layer and the release layer.

[0049] In another example embodiment of the present specification, the step of preparing the transfer stack can further include the step of forming two or more holes in at least one of the lithium metal layer, the release layer, and the substrate layer.

[0050] For example, the step of forming holes can include the steps of forming holes in the lithium metal layer, the release layer, or the lithium metal layer and the release layer; and stacking the lithium metal layer and the release layer on one surface of the substrate layer.

[0051] For example, the step of forming holes can include the steps of stacking the lithium metal layer and the release layer on one surface of the substrate layer to form a transfer stack; and forming two or more holes in at least one of the lithium metal layer, the release layer, and the substrate layer.

[0052] In one example embodiment of the present specification, any publicly known method of forming holes can be used without limitation.

[0053] In the present specification, holes can be formed in at least one of the lithium metal layer, the release layer, and the substrate layer, but are not limited thereto.

[0054] In the present specification, the depth of the holes can be the thickness of the lithium metal layer and the substrate layer, or at least one of the lithium metal layer, the release layer, and the substrate layer, and in particular, the thickness of the release layer, or the total thickness of the release layer and the lithium metal layer.

[0055] In one exemplary embodiment of the present specification, the shortest distance between adjacent pores can be 0.04 cm or more and 1 cm or less.

[0056] In one exemplary embodiment of the present specification, the shortest distance between adjacent pores can be 0.04 cm or more and 1 cm or less, specifically 0.1 cm or more and 0.9 cm or less, more specifically 0.2 cm or more and 0.9 cm or less.

[0057] In the present specification, adjacent pores refer to two pores having the shortest distance between the pores without other pores in between.

[0058] When the shortest distance between adjacent pores of one exemplary embodiment of the present specification satisfies the prescribed range, heat generated by pre-lithiation can be most effectively released, thereby suppressing the formation of lithium oxides or nitrides on the surface of the electrode.

[0059] However, as the shortest distance between adjacent pores decreases, the amount of lithium metal layer per 1 cm 2 The total area occupied by two or more pores per 1 cm increases, which can result in the loss of the lithium metal layer intended for pre-lithiation. Therefore, in order to most effectively release the heat generated during the pre-lithiation process while minimizing the amount of lithium metal layer discarded, it is preferable to satisfy a specific range.

[0060] In one exemplary embodiment of the present specification, the longest diameter of two or more pores can be 5 μm to 50 μm, specifically 7 μm to 40 μm, more specifically 10 μm to 20 μm.

[0061] In this case, in one exemplary embodiment of the present specification, the shape of the pores is not limited, and the longest diameter refers to the distance between two points within the pore that are farthest apart. For example, when the shape of the pore is rectangular, the longest diameter can correspond to the length of the diagonal. Alternatively, for example, when the shape of the pore is circular, the longest diameter can correspond to the diameter.

[0062] When the longest diameter of the pores of one exemplary embodiment of the present specification falls within this prescribed range, the amount of lithium discarded due to the formation of pores is small, and the formation of lithium by-products on the surface of the electrode is suppressed due to the effect of heat released during the pre-lithiation process, thereby reducing the amount of lithium discarded without being pre-lithiated into the electrode, and enabling sufficient pre-lithiation.

[0063] In the present specification, the longest diameter of the pores can be observed with a microscope in a dry room.

[0064] In the manufacturing method of the electrode for a lithium secondary battery of another exemplary embodiment of the present specification, at least one of the lithium metal layer and the release layer transferred to at least one surface of the electrode active material layer includes two or more holes, and the total area ratio of the two or more holes can be 1.2% or less with respect to 1 cm 2 of the square area of at least one of the lithium metal layer and the release layer.

[0065] In one exemplary embodiment of the present specification, the total area ratio of the two or more holes can be 1.2% or less, specifically 0.8% or less, and more specifically 0.1% or less with respect to 1 cm 2 of the square area of at least one of the lithium metal layer and the release layer.

[0066] In this case, the total area ratio (area ratio) of the two or more holes is calculated according to Equation A below, and the number of holes within 1 cm 2 of the square area is calculated by the shortest distance between adjacent holes.

[0067] [Equation A]

[0068] Area ratio (%) = {(area of a single hole (cm 2 )) x (number of holes within 1 cm 2 of the square area)} / (square area of 1 cm 2 ) x 100

[0069] When the total area ratio of the two or more holes satisfies the above range with respect to 1 cm 2 of the square area of at least one of the lithium metal layer and the release layer, it is possible to minimize the amount of lithium metal layer discarded due to the formation of holes while sufficiently releasing the heat generated in the pre-lithiation process.

[0070] In the present specification, the number of holes within 1 cm 2 of the square area of at least one of the lithium metal layer and the release layer can be 2 or more and 1000 or less, specifically 10 or more and 800 or less, and more specifically 15 or more and 80 or less. When the number of holes in which the shortest distance between holes and the longest diameter falls within a prescribed range is satisfied, it is possible to minimize the amount of lithium metal layer discarded due to the formation of holes while maximizing the release of heat generated in the pre-lithiation process.

[0071] The manufacturing method of the electrode for a lithium secondary battery of one exemplary embodiment of the present specification includes a step of preparing a transfer laminate including a lithium metal layer, a release layer, and a substrate layer.

[0072] The manufacturing method of the electrode for a lithium secondary battery of one exemplary embodiment of the present specification, the transfer laminate can include a lithium metal layer, a release layer, and a substrate layer, and specifically, the lithium metal layer, the release layer, and the substrate layer can be sequentially stacked.

[0073] In one exemplary embodiment of the present specification, the lithium metal layer is a layer containing lithium metal for prelithiating at least one surface of the electrode active material layer, and Li metal foil can be generally used, but is not limited thereto.

[0074] In one exemplary embodiment of the present specification, the thickness of the lithium metal layer can be 0.1 μm or more and 10 μm or less, specifically 1 μm or more and 8 μm or less, more specifically 1 μm or more and 6.2 μm or less.

[0075] In one exemplary embodiment of the present specification, when the thickness of the lithium metal layer falls within this prescribed range, prelithiation can be performed to the extent of solving the electrode irreversible problem, thereby improving the coulombic efficiency. In addition, heat generated during prelithiation is little, and heat dissipation is good, and thus lithium loss and safety problems due to formation of lithium byproducts can not occur.

[0076] In addition, in one exemplary embodiment of the present specification, the use of the substrate layer is not limited as long as it has a feature capable of withstanding process conditions such as high temperature in the step of depositing the lithium metal layer and preventing a reverse peeling problem in which the lithium metal layer is transferred to the substrate layer during winding of the deposited lithium metal layer.

[0077] Specifically, in one exemplary embodiment of the present specification, the substrate layer can be one or more selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), polymethyl methacrylate (PMMA), polypropylene, polyethylene, and polycarbonate.

[0078] In one exemplary embodiment of the present specification, the thickness of the substrate layer can range from 1 μm or more and 300 μm or less, specifically 5 μm or more and 200 μm or less, more specifically 10 μm or more and 100 μm or less.

[0079] When the thicknesses of the substrate layer and the lithium metal layer satisfy the prescribed range, lithium metal can be efficiently transferred to the electrode active material layer, and reverse transfer can be prevented.

[0080] In one exemplary embodiment of the present specification, the deposition method for depositing the lithium metal layer on the substrate layer can be selected from physical vapor deposition (PVD) and chemical vapor deposition (CVD), and in the physical vapor deposition method, thermal evaporation can be mainly used. However, such a limitation is not intended to be set, and various deposition methods used in the art can be used.

[0081] In one exemplary embodiment of the present specification, the release layer can be one or more selected from the group consisting of polycarbonate (PC), polydimethylsiloxane (PDMS), polymethylhydrosiloxane (PMHS), polyimide (PI), and polymethyl methacrylate (PMMA).

[0082] In one exemplary embodiment of the present specification, the thickness of the release layer can be 0.2 μm or more and 3 μm or less, specifically, 0.5 μm or more and 1 μm or less.

[0083] In one exemplary embodiment of the present specification, when the thickness of the release layer satisfies the prescribed range, sufficient release force can be ensured.

[0084] In one exemplary embodiment of the present specification, the release layer can be formed by a coating method. For example, the coating method can be one method selected from the group consisting of dip coating, spray coating, spin coating, die coating, gravure coating, microgravure coating, comma coating, and roll coating, but is not limited thereto, and various coating methods available in the art for forming a coating layer can be used.

[0085] In one exemplary embodiment of the present specification, the step of transferring the lithium metal layer and the release layer to at least one surface of the electrode active material layer can include the steps of: laminating the transfer laminate and the electrode active material such that the lithium metal layer is in contact with at least one surface of the electrode active material layer; and separating the substrate layer from the release layer.

[0086] In one exemplary embodiment of the present specification, the lamination step includes the step of bringing the transfer laminate into contact such that the lithium metal layer is in contact with at least one surface of the electrode active material layer, which is a preparation step of transferring lithium metal to the electrode active material layer.

[0087] In one exemplary embodiment of the present specification, the lamination step can further include a pressurization step, which makes prelithiation caused by the transfer to the electrode active material layer more actively proceed, thereby enabling a thinner electrode even with higher energy density.

[0088] In one exemplary embodiment of the present specification, the pressurization step can include applying a pressure of 50 kgf / cm 2 or more and 2000 kgf / cm 2 or less, specifically, 100 kgf / cm 2 or more and 1000 kgf / cm 2 or less.

[0089] When the pressure of the pressurization step satisfies the prescribed range, prelithiation can proceed at an appropriate speed, thereby reducing heat generated upon prelithiation, further reducing the formation of surface byproducts, and improving the energy density of the electrode.

[0090] The method for manufacturing an electrode for a lithium secondary battery of one example embodiment of the present specification can include a step of separating the base material layer from the release layer.

[0091] In one example embodiment of the present specification, the electrode active material layer can be a negative electrode active material layer or a positive electrode active material layer.

[0092] In one example embodiment of the present specification, the electrode active material layer can be a negative electrode active material layer, the negative electrode active material layer can include a negative electrode active material, a negative electrode conductive material, and a negative electrode binder, and the negative electrode active material can be a silicon-based negative electrode active material including one or more selected from the group consisting of Si, SiO x (0 < x < 2), Si / C, and Si alloys.

[0093] In one example embodiment of the present specification, the negative electrode active material can be a silicon-based negative electrode active material including one or more selected from the group consisting of Si and SiO x (0 < x < 2).

[0094] In one example embodiment of the present specification, the negative electrode active material can be a silicon-based negative electrode active material including one or more selected from the group consisting of Si and SiO x (0 < x < 2), and the content of the silicon-based negative electrode active material can be 10 parts by weight or more and 99 parts by weight or less, specifically 20 parts by weight or more and 90 parts by weight or less, and more specifically 30 parts by weight or more and 80 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer composition.

[0095] According to one example embodiment of the present specification, the negative electrode composition uses a specific conductive material and a binder, and even when a silicon-based active material having a relatively high capacity within a prescribed range is used, it can control the volume expansion rate during charging and discharging. Therefore, even within the prescribed range, the performance of the negative electrode does not deteriorate, and excellent output characteristics can be achieved at the time of charging and discharging.

[0096] In one example embodiment of the present specification, the silicon-based negative electrode active material can employ, in particular, pure silicon (Si) as the silicon-based active material. Using pure silicon (Si) as the active material can mean that the content of the pure Si particles not combined with other particles or elements is within the above range, based on 100 parts by weight of the total amount of the above negative electrode active material.

[0097] Specifically, in one example embodiment of the present specification, the negative electrode active material can include Si, and the content of Si can be 10 parts by weight or more and 99 parts by weight or less, specifically 20 parts by weight or more and 90 parts by weight or less, more specifically 30 parts by weight or more and 80 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer composition.

[0098] In the charge-discharge reaction of the lithium secondary battery, lithium is inserted into the negative electrode from the positive electrode at the time of charging, and is de-inserted from the negative electrode and returned to the positive electrode at the time of discharging. In the case of the silicon-based negative electrode active material, the volume change and the surface side reaction are severe, and thus a large amount of lithium inserted into the negative electrode during initial charging does not return to the positive electrode again, and thus the initial irreversible capacity increases. When the initial irreversible capacity increases, a problem of rapid reduction in the battery capacity and the cycle occurs.

[0099] In the present application, in order to solve the above problem, the negative electrode of the lithium secondary battery is pre-lithiated to solve the initial irreversible capacity problem. Specifically, the negative electrode is pre-treated before the pre-lithiation process, and thus, in the pre-lithiation process, lithium metal can be easily transferred from the transfer stack at the time of lithium transfer, and lithium in the negative electrode active material layer can be uniformly pre-lithiated.

[0100] In addition, the present application uses a silicon-based negative electrode active material as the negative electrode active material to improve the capacity performance, and simultaneously uses an adhesive and a conductive material under specific conditions to solve the problems related to the maintenance of the conductive path and the combination of the conductive material, the adhesive, and the active material, which are associated with the volume expansion.

[0101] Note that the average particle diameter (D50) of the silicon-based negative electrode active material of the present specification can be 3 μm to 10 μm, specifically 3.5 μm to 8 μm. When the average particle diameter is within the prescribed range, the specific surface area of the particles is within a suitable range, and thus the negative electrode slurry viscosity falls within a suitable range. Therefore, the particles constituting the electrode slurry are smoothly dispersed. In addition, when the size of the silicon-based active material is equal to or greater than the lower limit value of the range, the contact area of the silicon-based negative electrode active material and the negative electrode conductive material is excellent due to the complex of the conductive material and the adhesive in the electrode slurry, and thus the possibility of the continuous conductive network is increased, thereby improving the capacity retention rate. Note that when the average particle diameter is within the prescribed range, excessively large silicon-based negative electrode active materials are excluded, and thus a smooth electrode surface is formed. Therefore, it is possible to prevent the phenomenon of non-uniformity of the current density during charging and discharging.

[0102] In one example embodiment of the present specification, the silicon-based negative electrode active material generally has a characteristic BET specific surface area. The BET specific surface area of the silicon-based negative electrode active material is 0.01 m 2 / g to 150.0 m 2 / g, more specifically 0.1 m 2 / g to 100.0 m 2 / g, more specifically 0.2 m 2 / g to 80.0 m 2 / g, more specifically 0.2 m 2 / g to 18.0 m 2 / g. The BET specific surface area is measured according to DIN 66131 (using nitrogen).

[0103] In one exemplary embodiment of the present specification, the silicon-based negative electrode active material can have a non-spherical shape, and a sphericity (circularity) thereof is, for example, 0.9 or less, for example, 0.7 to 0.9, for example, 0.8 to 0.9, for example, 0.85 to 0.9.

[0104] In the present specification, the circularity is determined by the following formula A-1, in which A is an area and P is a boundary line.

[0105] [Formula A-1]

[0106] 4πA / P 2

[0107] In the related art, generally only graphite-based compounds are used as negative electrode active materials. However, in recent years, as the demand for high-capacity batteries has been increasing, attempts to mix and use silicon-based compounds in order to increase capacity have been increasing. However, silicon-based compounds have limitations in that the volume rapidly expands during charge and discharge, causing the conductive path formed in the negative electrode active material layer to be damaged, thereby deteriorating the performance of the battery. Therefore, the type of negative electrode conductive material used with the silicon-based active material is important.

[0108] Therefore, in one exemplary embodiment of the present specification, the negative electrode conductive material can include one or more selected from the group consisting of a point-shaped conductive material, a line-shaped conductive material, and a planar conductive material.

[0109] In one exemplary embodiment of the present specification, the point-shaped conductive material refers to a conductive material having a zero-dimensional (0D) structure of a crystal cluster structure consisting of one to several hundred atoms in the shape of a circular sphere and having a volume. The point-shaped conductive material can be used to improve the conductivity of the negative electrode and has conductivity without causing chemical changes. Specifically, the point-shaped conductive material can 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 cracking carbon black, conductive fibers, carbon fluoride, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and in terms of high conductivity and excellent dispersibility, it is preferable that carbon black can be included.

[0110] In one exemplary embodiment of the present specification, the BET specific surface area of the point-shaped conductive material can be 40 m 2 / g or more and 70 m 2 / g or less, specifically 45 m 2 / g or more and 65 m 2 / g or less, more specifically 50 m 2 / g or more and 60 m 2 / g or less.

[0111] In one exemplary embodiment of the present specification, the particle diameter of the point-shaped conductive material can be 10 nm to 100 nm, specifically 20 nm to 90 nm, more specifically 20 nm to 60 nm.

[0112] In one exemplary embodiment of the present specification, the negative electrode conductive material can include a planar conductive material.

[0113] In one exemplary embodiment of the present specification, the planar conductive material refers to a conductive material in which atoms form a two-dimensional (2D) structure of a crystal structure having a thickness of a single atomic layer or a plurality of atomic layers of two or more layers in a plane. The planar conductive material refers to a material that secures a conductive path in a planar form inside the negative electrode active material layer, and at the same time, can play a role in inhibiting the disconnection of the conductive path due to volume expansion, and can be referred to as a sheet-shaped conductive material or a block-shaped conductive material. Specifically, the planar conductive material can include at least one selected from the group consisting of plate-shaped graphite, graphene, graphene oxide, and graphite sheet, and preferably can be plate-shaped graphite.

[0114] In one exemplary embodiment of the present specification, the average particle diameter (D50) of the planar conductive material can be 2 μm to 7 μm, specifically 3 μm to 6 μm, more specifically 4 μm to 5 μm. When the prescribed range is satisfied, the sufficient particle diameter makes it easy to disperse, and does not cause excessive increase in the viscosity of the negative electrode slurry. Therefore, when dispersion is performed using the same equipment and time, the dispersion effect is excellent.

[0115] In one exemplary embodiment of the present specification, the D10 of the planar conductive material can be 0.5 μm or more and 1.5 μm or less, the D50 can be 2.5 μm or more and 3.5 μm or less, and the D90 can be 7.0 μm or more and 15.0 μm or less.

[0116] In one exemplary embodiment of the present specification, for the planar conductive material, a high specific surface area planar conductive material having a high BET specific surface area or a low specific surface area planar conductive material can be used.

[0117] In one exemplary embodiment of the present specification, for the planar conductive material, a planar conductive material with a high specific surface area or a planar conductive material with a low specific surface area can be used without limitation. However, particularly, the planar conductive material of the present specification can affect the electrode performance to some extent due to a dispersion effect, and thus, it is particularly preferable to use a planar conductive material with a low specific surface area which does not cause a dispersion problem.

[0118] In one exemplary embodiment of the present specification, the BET specific surface area of the planar conductive material can be 5 m 2 / g or more.

[0119] In another exemplary embodiment, the BET specific surface area of the planar conductive material can be 5 m 2 / g or more and 500 m 2 / g or less, specifically 5 m 2 / g or more and 300 m 2 / g or less, more specifically 5 m 2 / g or more and 250 m 2 / g or less.

[0120] In another exemplary embodiment, the planar conductive material is a planar conductive material with a high specific surface area, and the BET specific surface area can satisfy the following range: 50 m 2 / g or more and 500 m 2 / g or less, specifically 80 m 2 / g or more and 300 m 2 / g or less, more specifically 100 m 2 / g or more and 300 m 2 / g or less.

[0121] In another exemplary embodiment, the planar conductive material is a planar conductive material with a low specific surface area, and the BET specific surface area can satisfy the following range: 5 m 2 / g or more and 40 m 2 / g or less, specifically 5 m 2 / g or more and 30 m 2 / g or less, more specifically 5 m 2 / g or more and 25 m 2 / g or less.

[0122] In one exemplary embodiment of the present specification, the linear conductive material refers to a conductive material having a one-dimensional (1D) structure with a nanoscale diameter and a high aspect ratio or a conductive material having a fibrous structure such as a cylindrical or tubular shape. Examples of the linear conductive material include carbon nanotubes, which can be bundle-type carbon nanotubes. The bundle-type carbon nanotubes can include a plurality of carbon nanotube units. Specifically, unless otherwise specified, the term "bundle-type" refers to a bundle or rope-like secondary shape in which a plurality of carbon nanotube units are arranged side by side or entangled in substantially the same direction of the longitudinal axis of the carbon nanotube units. The carbon nanotube unit has a cylindrical graphite sheet with a nanoscale diameter, and has an sp 2 bond structure. In this case, the properties of a conductive material or a semiconductor material can be exhibited depending on the curling angle and structure of the graphite sheet. Compared to the entangled carbon nanotubes, the bundle-type carbon nanotubes can be more uniformly dispersed during the manufacturing of the negative electrode, and can form a more smooth conductive network in the negative electrode, thereby improving the conductivity of the negative electrode.

[0123] In one exemplary embodiment of the present specification, the linear conductive material can include any one selected from the group consisting of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs), and specifically can include single-walled carbon nanotubes (SWCNTs).

[0124] In one exemplary embodiment of the present specification, the BET specific surface area of the linear conductive material can be 100 m 2 / g or more and 100,000 m 2 / g or less, specifically 500 m 2 / g or more and 10,000 m 2 / g or less, more specifically 1,000 m 2 / g or more and 5,000 m 2 / g or less.

[0125] Further, in one exemplary embodiment of the present specification, the aspect ratio of the linear conductive material can be 500 or more and 1,000,000 or less, specifically 1,000 or more and 100,000 or less, more specifically 10,000 or more and 100,000 or less.

[0126] In one exemplary embodiment of the present specification, the negative electrode conductive material can include one or more selected from the group consisting of flaky graphite, single-walled carbon nanotubes (SWCNTs), and multi-walled carbon nanotubes (MWCNTs), but is not limited thereto.

[0127] In one exemplary embodiment of the present specification, the conductive material can preferably include one selected from the group consisting of flaky graphite, single-walled carbon nanotube (SWCNT), and multi-walled carbon nanotube (MWCNT) as a first conductive material, and can include another as a second conductive material, but is not limited thereto.

[0128] In one exemplary embodiment of the present specification, the content of the negative electrode conductive material can be 10 parts by weight or more and 40 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer composition.

[0129] In another exemplary embodiment, the content of the negative electrode conductive material can be 10 parts by weight or more and 40 parts by weight or less, specifically 10 parts by weight or more and 30 parts by weight or less, more specifically 10 parts by weight or more and 20 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer composition.

[0130] The negative electrode conductive material of the present specification is completely different in composition from the conductive material applied to the positive electrode. That is, the negative electrode conductive material of the present specification is used to support the connection points of the silicon-based active material that undergoes a large volume change during charging and discharging, and is completely different in composition and role from the positive electrode conductive material that plays a buffering role during rolling and imparts partial conductivity.

[0131] In addition, the negative electrode conductive material of the present specification is applied to the silicon-based active material, and has a completely different composition from the conductive material applied to the graphite-based active material. That is, the conductive material used in the electrode having the graphite-based active material has only a small particle relative to the active material, and thus has a characteristic of improving output characteristics and imparting partial conductivity, and is completely different in composition and role from the negative electrode conductive material applied with the silicon-based active material in the present specification.

[0132] In one exemplary embodiment of the present specification, the point-shaped conductive material used as the negative electrode conductive material has a different structure and role from the carbon-based active material generally used as the negative electrode active material. Specifically, 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 into a spherical or point shape and used to facilitate storage and release of lithium ions.

[0133] On the other hand, the planar conductive material used as the negative electrode conductive material is a material having a planar or plate shape, and can be expressed as plate-shaped graphite. That is, the planar conductive material is a material contained to maintain the conductive path in the negative electrode active material layer, and refers to a material for securing a planar conductive path inside the negative electrode active material layer rather than playing a role of storing and releasing lithium.

[0134] That is, in one exemplary embodiment of the present specification, using a plate-shaped graphite as a conductive material means processing it into a flat surface or a plate shape and using it as a material that ensures a conductive path rather than playing a role of storing or releasing lithium. In this case, the negative active material included together has a high capacity characteristic with respect to storing and releasing lithium, and is used to store and release all lithium ions transferred from the positive electrode.

[0135] In one exemplary embodiment of the present specification, the negative electrode binder can include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylamide, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluoro rubber, polyacrylic acid, and a material in which hydrogen is replaced with Li, Na, Ca, or the like, and can further include various copolymers thereof.

[0136] According to one exemplary embodiment of the present specification, the negative electrode binder is used to support the active material and the conductive material, thereby preventing distortion and structural deformation of the negative electrode structure in the process of volume expansion and relaxation of the silicon-based active material. All commonly used binders can be applied as long as the above-described roles are satisfied, and specifically, an aqueous binder can be used, and more specifically, a polyacrylamide (PAM)-based binder can be used.

[0137] In one exemplary embodiment of the present specification, the content of the negative electrode binder can be 1 part by weight or more and 30 parts by weight or less, specifically 3 parts by weight or more and 25 parts by weight or less, and more specifically 3 parts by weight or more and 20 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer composition.

[0138] When the content of the negative electrode binder satisfies the above-described range, the mechanical strength is excellent, the intermolecular interaction is strong, thereby making the inter-electrode adhesion excellent. In addition, when the above-described range is satisfied, the viscosity of the negative electrode binder can be set in an appropriate range, thereby further improving the coatability of the electrode when an electrode is manufactured using the same.

[0139] The negative electrode of one exemplary embodiment of the present specification can include the above-described negative electrode active material, negative electrode conductive material, and negative electrode binder.

[0140] Specifically, the negative electrode can include a negative electrode current collector layer and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector layer. The negative electrode active material layer can include the above-described negative electrode active material. In addition, the negative electrode active material layer can further include a thickening agent.

[0141] In one exemplary embodiment of the present specification, the thickness of the negative electrode current collector layer can be typically 1 μm to 100 μm. The negative electrode current collector layer is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or copper or stainless steel treated with carbon, nickel, titanium, silver, or the like on the surface, aluminum cadmium alloy, or the like can be used. In addition, the negative electrode current collector layer can have micro-irregularities formed on the surface to enhance the adhesion of the negative electrode active material, and can be used in various forms such as a film, a sheet, a foil, a mesh, a porous body, a foam, or a nonwoven fabric body.

[0142] In one exemplary embodiment of the present specification, the thickness of the negative electrode current collector layer can be 1 μm or more and 100 μm or less, and the thickness of the negative electrode can be 20 μm or more and 500 μm or less. However, the thickness can vary depending on the type and use of the negative electrode active material, the negative electrode conductive material, and the negative electrode binder, and is not limited thereto.

[0143] The negative electrode active material layer can be formed by coating at least one surface of the negative electrode current collector with a negative electrode slurry containing a negative electrode active material layer composition and a slurry solvent, and then drying and roll-pressing.

[0144] In one exemplary embodiment of the present specification, the negative electrode slurry can include a negative electrode active material layer composition and a slurry solvent.

[0145] In one exemplary embodiment of the present specification, the solid content of the negative electrode slurry can be in the range of 5% or more and 40% or less.

[0146] In another exemplary embodiment, the solid content of the negative electrode slurry can satisfy the range of 5% or more and 40% or less, preferably 7% or more and 35% or less, and more preferably 10% or more and 30% or less.

[0147] The solid content of the negative electrode slurry can refer to the content of the negative electrode active material layer composition contained in the negative electrode slurry, and can refer to the content of the negative electrode active material composition based on 100 parts by weight of the negative electrode slurry.

[0148] When the solid content of the negative electrode slurry falls within the prescribed range, appropriate viscosity can be ensured when the negative electrode active material layer is formed, thereby minimizing the aggregation of particles of the negative electrode active material layer composition, and the negative electrode active material layer can be effectively formed.

[0149] In another exemplary embodiment of the present specification, the solvent can include a solvent known in the art. For example, the solvent can be water (e.g., distilled water) or NMP.

[0150] According to an exemplary embodiment of this specification, a negative electrode can be formed by coating a negative electrode slurry onto one or both surfaces of the negative electrode current collector layer and drying it, and the slurry solvent in the negative electrode slurry can be dried by a drying step.

[0151] A method for manufacturing an electrode for a lithium secondary battery according to an exemplary embodiment of this specification may further include the step of forming an electrode active material layer by coating an electrode composition slurry on at least one surface of an electrode current collector layer before transferring a stacked lithium metal layer and a release layer to at least one surface of the electrode active material layer.

[0152] In a method for manufacturing an electrode for a lithium secondary battery according to an exemplary embodiment of this specification, the step of coating an electrode slurry on one or both surfaces of the electrode current collector layer may further include a drying step, through which the slurry solvent in the electrode slurry can be dried.

[0153] In this case, the electrode in the method for manufacturing an electrode for a lithium secondary battery according to an exemplary embodiment of this specification can refer to a negative electrode or a positive electrode. The description of the method for forming the negative electrode active material layer can be applied to the steps of the method for forming the negative electrode active material layer, and can also be applied to the following positive electrode active material layer.

[0154] The electrode for a lithium secondary battery according to another exemplary embodiment of this specification can be manufactured using the manufacturing method of the exemplary embodiments described above.

[0155] In another exemplary embodiment of the lithium secondary battery electrode described in this specification, the area of ​​lithium byproducts formed on the surface of the electrode can be 42% or less relative to the area of ​​the transfer laminate that contacts at least one surface of the electrode active material layer. Specifically, the area of ​​the lithium byproduct layer can be 42% or less relative to the total area of ​​the lithium metal layer transferred to the electrode active material layer.

[0156] When the electrode active material layer is pre-lithiated using conventional transfer methods, lithium byproducts are formed on the electrode surface. The area of ​​these byproducts is approximately 44% or more of the area of ​​the transferred lithium metal layer in the electrode active material layer.

[0157] However, in an exemplary embodiment of the lithium secondary battery electrode described in this specification, the area of ​​the lithium byproduct region formed on the electrode surface can be 42% or less, specifically 40% or less, relative to the area of ​​the transfer laminate that contacts at least one surface of the electrode active material layer. That is, lithium loss caused by the formation of byproducts such as lithium oxides or lithium nitrides formed by the transferred lithium can be reduced.

[0158] Further, in the present specification, lithium by-products can be confirmed by energy dispersive X-ray spectroscopy (EDS) analysis using a scanning electron microscope (SEM). Specifically, when analyzed by EDS using a SEM, nitrogen (N) was found to be 3% or more and oxygen (O) was found to be 75% or more.

[0159] That is, the electrode for a lithium secondary battery of another exemplary embodiment of the present specification includes: an electrode current collector layer; an electrode active material layer having a lithium metal layer transferred thereon; and a lithium by-product layer, wherein the lithium by-product layer exhibits 3% or more of nitrogen (N) and 75% or more of oxygen (O) when analyzed by energy dispersive X-ray spectroscopy (EDS) using a scanning electron microscope (SEM), and the area of the lithium by-product layer is 42% or less with respect to the total area of the lithium metal layer transferred to the electrode active material layer.

[0160] In another exemplary embodiment of the present specification, the unit area pre-lithiation capacity of the electrode for a lithium secondary battery manufactured by the above-described manufacturing method can be 20% or less, specifically 15% or less, of the unit area capacity of the electrode.

[0161] The unit area pre-lithiation capacity is the capacity of lithium added to the electrode by pre-lithiation, and when the above-described prescribed range is satisfied, capacity balance with the negative electrode or the positive electrode can be maintained while compensating for the irreversible capacity of the electrode.

[0162] Further, the lithium secondary battery of one exemplary embodiment of the present specification includes the above-described electrode for a lithium secondary battery, a separator, and an electrolyte, wherein the electrode for a lithium secondary battery can be at least one of a positive electrode and a negative electrode. Since the negative electrode has been described above, a detailed description thereof will be omitted.

[0163] Figure 1 FIG. 1 is a view showing the stacked structure of a negative electrode for a lithium secondary battery of one exemplary embodiment of the present specification. Specifically, it can be seen that the negative electrode for a lithium secondary battery 100 having a negative electrode active material layer 20 on one surface of a negative electrode current collector layer 10. Figure 1 The negative electrode active material layer is shown as being formed on one surface of the negative electrode current collector layer, but the negative electrode active material layer can also be formed on both surfaces of the negative electrode current collector layer.

[0164] Figure 2is a diagram showing a stacked structure of a lithium secondary battery according to one example embodiment of the present specification. Specifically, a negative electrode 100 for a lithium secondary battery including a negative electrode active material layer 20 on one surface of a negative electrode current collector layer 10 can be seen, a positive electrode 200 for a lithium secondary battery including a positive electrode active material layer 40 on one surface of a positive electrode current collector layer 50 can be seen, and it is shown that the negative electrode 100 for a lithium secondary battery and the positive electrode 200 for a lithium secondary battery are formed in a structure in which a separator 30 is interposed therebetween. In this case, at least one of the negative electrode and the positive electrode for a lithium secondary battery can be manufactured according to the manufacturing method of the electrode according to one example embodiment of the present specification.

[0165] Figure 3 is a flowchart showing a manufacturing method of an electrode for a lithium secondary battery according to one example embodiment of the present specification. Specifically, Figure 3 (a) shows a manufacturing method of an electrode for a lithium secondary battery, which includes: a step S1 of preparing a transfer laminate including a lithium metal layer, a release layer, and a substrate layer; and a step S2 of transferring the lithium metal layer and the release layer to at least one surface of an electrode active material layer such that the lithium metal layer is in contact with the electrode active material layer.

[0166] Figure 3 (b) shows a manufacturing method of an electrode for a lithium secondary battery, which includes: a step S1 of preparing a transfer laminate including a lithium metal layer, a release layer, and a substrate layer; a step S21 of laminating the transfer laminate and an electrode active material layer such that the lithium metal layer is in contact with at least one surface of the electrode active material layer; a step S22 of separating the substrate layer from the release layer; and a step S23 of forming two or more holes in at least one of the lithium metal layer and the release layer after the separation of the substrate layer.

[0167] Figure 3 (c) shows a manufacturing method of an electrode for a lithium secondary battery, which includes: a step S1 of preparing a transfer laminate including a lithium metal layer, a release layer, and a substrate layer; a step S1-1 of forming two or more holes in at least one of the lithium metal layer, the release layer, and the substrate layer; and a step S2 of transferring the lithium metal layer and the release layer to at least one surface of an electrode active material layer such that the lithium metal layer is in contact with the electrode active material layer.

[0168] In this case, the manufacturing method of the electrode for a lithium secondary battery according to one example embodiment of the present specification can further include a step (not shown) of providing an electrode active material layer on at least one surface of an electrode current collector layer, which can be performed before the step S1, or can be performed simultaneously with the step S1, or can be performed between the steps S1 and S2, or can be performed between the steps S1 and S21, but is not limited thereto.

[0169] The positive electrode can 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 including a positive electrode active material.

[0170] In the positive electrode, the positive electrode current collector layer is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, and, for example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel treated with carbon, nickel, titanium, silver, or the like on the surface can be used. Further, the thickness of the positive electrode current collector layer can generally be 3 μm to 500 μm, and fine irregularities can be formed on the surface of the positive electrode current collector to improve the adhesion strength of the positive electrode active material. For example, the positive electrode current collector layer can be used in various forms such as a film, a sheet, a foil, a mesh, a porous body, a foam body, a nonwoven fabric body, and the like.

[0171] According to one example embodiment of the present specification, the positive electrode active material can 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 a lithium composite oxide containing a combination thereof.

[0172] Specifically, the positive electrode active material can be a layered compound, for example, lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2); or a compound substituted with one or more transition metals; lithium iron oxide, for example, LiFe3O4; lithium manganese oxide, for example, LiMnO4 (0≤c1≤0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxide, for example, LiV3O8, V2O5, and Cu2V2O7; Ni-site type lithium nickel oxide represented by the chemical formula LiNi 1+c1 Mn 2-c1 O4 (0≤c1≤0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxide, for example, LiV3O8, V2O5, and Cu2V2O7; Ni-site type lithium nickel oxide represented by the chemical formula LiNi 1-c2 M c2 O2 (wherein 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); lithium manganese composite oxide represented by the chemical formula LiMn 2-c3 M c3 O2 (wherein 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); lithium manganese composite oxide represented by the chemical formula LiMn

[0173] In addition to the above-described positive electrode active material, the positive electrode active material layer can further include a positive electrode conductive material and a positive electrode binder.

[0174] 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 and does not cause chemical changes in the configured battery. Specific examples can include graphite, such as natural graphite and artificial graphite; carbon-based materials, such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal crack carbon black, and carbon fiber; metal powder or metal fiber, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, etc., and any one of these or a mixture of two or more of these can be used.

[0175] In addition, the positive electrode binder is used to improve the binding between the positive electrode active material particles, and the adhesion of the positive electrode active material to the positive electrode current collector. Specific examples can 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, etc., and any one of these or a mixture of two or more of these can be used.

[0176] The solvent used in the positive electrode composition slurry can be a solvent commonly used in the relevant art, and can include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methyl pyrrolidone (NMP), acetone, or water, and can be used alone or as a mixture of two or more of these. The amount of solvent used is sufficient in consideration of the coating thickness of the slurry and the manufacturing yield, if the solvent can dissolve or disperse the active material, the conductive material, and the binder, and has a viscosity that can exhibit excellent thickness uniformity when subsequently used to manufacture the positive and negative electrodes. Alternatively, the positive and negative electrodes can also be manufactured by casting the composition used to form the active material layer on a separate carrier, and then laminating the film obtained by peeling the carrier from the carrier onto the current collector.

[0177] The separator is used to separate the negative electrode and the positive electrode and to provide a movement path of lithium ions, and any separator can be used as the separator without particular limitation as long as it is generally used for secondary batteries, and particularly, a separator having a high moisture retention capacity with respect to electrolyte and a low resistance to electrolyte ion migration is preferably used. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or having a stacked structure of two or more layers thereof, can be used. In addition, a non-woven fabric made of a commonly used porous non-woven fabric such as a glass fiber having a high melting point, a polyethylene terephthalate fiber, or the like can also be used. In addition, a coated separator including a ceramic component or a polymeric material can be used to secure heat resistance or mechanical strength, and a separator having a single layer or a multi-layer structure can be selectively used.

[0178] Examples of the electrolyte can include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten-type inorganic electrolyte, etc. that can be used to manufacture a lithium secondary battery, but are not limited thereto.

[0179] Specifically, the electrolyte can include a non-aqueous organic solvent and a metal salt.

[0180] As the non-aqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, or ethyl propionate can be used.

[0181] Specifically, among carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents, and can be preferably used because they have a high dielectric constant to well dissociate lithium salts. When cyclic carbonates are mixed with linear carbonates (for example, dimethyl carbonate or diethyl carbonate) having low viscosity and low dielectric constant at a suitable ratio and used, an electrolyte having high electrical conductivity can be prepared, and thus can be more preferably used.

[0182] The lithium salt can be used as the metal salt, and the lithium salt is a material that is easily soluble in a non-aqueous electrolyte, in which, for example, one or more selected from the group consisting of 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 - .

[0183] For the purpose of improving the service life characteristics of the battery, suppressing the capacity reduction of the battery, improving the service discharge capacity of the battery, and the like, one or more additives, for example, halogenated alkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glycol diether, hexamethylphosphoramide, nitrobenzene derivatives, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, can be further contained in the electrolyte in addition to the above-described electrolyte components.

[0184] The battery pack or the battery module of one example embodiment of the present specification can include the above-described lithium secondary battery.

[0185] The battery module of another example embodiment of the present specification can include a battery pack including the above-described lithium secondary battery.

[0186] Since the lithium secondary battery of the example embodiments of the present specification stably exhibits excellent discharge capacity, output characteristics, and cycle performance, it can be used as a power source for portable devices such as mobile phones, notebook computers, digital cameras, and the like, and large- or medium-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. For example, a battery pack or a battery pack can be used as a power source for one or more of the following medium- or large-sized devices: electric power tools; electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); and power storage systems, for example.

[0187] Embodiments

[0188] Hereinafter, preferred embodiments will be provided to better understand the present application. It will be apparent to those skilled in the art that the embodiments are provided only for the purpose of illustration of the present application, and various modifications and changes can be made within the scope and technical spirit of the present application. Such modifications and changes naturally fall within the scope of the claims included herein.

[0189] <Preparation Example>

[0190] Example 1

[0191] A negative electrode active material layer composition was prepared using a silicon-based active material (average particle diameter (D50): 4 μm) as a negative electrode active material, SWCNT, and polyacrylamide binder at a weight ratio of 80:10:10. A negative electrode slurry was manufactured by adding the composition to distilled water as a solvent for negative electrode slurry formation (solid concentration: 30% by weight).

[0192] The mixing method was to prepare a negative electrode slurry by dispersing the conductive material, the binder, and water at 2500 rpm for 30 minutes using a homogenizer, adding the active material to the dispersion, and then dispersing the resulting mixture at 2500 rpm for 30 minutes.

[0193] The negative electrode slurry was coated at a capacity of 8 mAh / cm 2 on both surfaces of a copper current collector (thickness: 8 μm) as a negative electrode current collector, then roll-pressed, dried in a vacuum oven at 130°C for 10 hours to form a negative electrode active material layer (thickness: 30 μm).

[0194] A transfer laminate (thickness: 32.2 pm) was prepared by coating a PET substrate layer (thickness: 25 pm) with a solution containing polymethyl methacrylate (PMMA) to form a release layer (thickness: 0.5 pm), depositing a lithium metal layer (thickness: 6.2 pm) on top of the release layer by a physical vapor deposition (PVD) method, and then subjecting the transfer laminate to contact so that the lithium metal layer faces the negative active material layer and is laminated, the lamination thus prelithiating with a capacity of 1.27 mAh / cm 2 After the removal of the PET substrate layer (i.e., after the transfer), two or more holes with a depth equivalent to the thickness of the release layer and an inter-hole shortest distance of 0.9 cm were formed on the surface.

[0195] Example 2

[0196] A prelithiation electrode of Example 2 was prepared in the same manner as Example 1, except that the inter-hole shortest distance of the negative electrode of Example 1 was 0.2 cm.

[0197] Comparative Example 1

[0198] A prelithiation electrode of Comparative Example 1 was prepared in the same manner as Example 1, except that no holes were formed on the negative electrode of Example 1.

[0199] Comparative Example 2

[0200] A prelithiation electrode of Comparative Example 2 was prepared in the same manner as Example 1, except that the inter-hole shortest distance of the negative electrode of Example 1 was 1.5 cm.

[0201] Example 3

[0202] A prelithiation electrode of Example 3 was prepared in the same manner as Example 1, except that the inter-hole shortest distance of the negative electrode of Example 1 was 0.1 cm.

[0203] Example 4

[0204] A prelithiation electrode of Example 4 was prepared in the same manner as Example 1, except that the inter-hole shortest distance of the negative electrode of Example 1 was 0.05 cm.

[0205] Example 5

[0206] A prelithiation electrode of Example 5 was prepared in the same manner as Example 1, except that the inter-hole shortest distance of the negative electrode of Example 1 was 0.04 cm.

[0207] Comparative Example 3

[0208] A pre-lithiated electrode of Comparative Example 3 was prepared in the same manner as Example 1, except that the interstitial shortest distance of the negative electrode of Example 1 was 0.02 cm.

[0209] Comparative Example 4

[0210] A pre-lithiated electrode of Comparative Example 4 was prepared in the same manner as Example 1, except that the interstitial shortest distance of the negative electrode of Example 1 was 0.01 cm.

[0211] [Experimental Example 1]

[0212] As Figure 4 shown, it was confirmed that the portion where the white by-product was formed on the electrode surface after the pre-lithiation was completed exhibited a different color tone compared to the background color. Specifically, Figure 4 A photograph of the surface of the pre-lithiated electrode after the transfer of the transfer laminate and the removal of the substrate layer and the release layer using a tape was taken. In this case, in order to confirm that the white color of the electrode surface was a by-product in the form of lithium oxide, the content of elements (particularly nitrogen and oxygen) in each region was analyzed by EDS analysis using an SEM (JSM-7610F), and the results are shown in Table 1 below.

[0213] [Table 1]

[0214] Element (%) Zone A Zone B Zone C Carbon (C) 9.10 24.70 39.37 Nitrogen (N) 6.31 1.37 1.33 Oxygen (O) 84.58 73.83 59.18

[0215] As can be confirmed from Table 1, Figure 4 the content of nitrogen (N) and oxygen (O) in Area A was high, which indicates that the white appearance of this region was due to the formation of lithium nitride and lithium oxide.

[0216] On the other hand, it was confirmed that the content of nitrogen (N) and oxygen (O) in Areas B and C was low, and these two regions were black regions that were the same color as the background color. In this case, the purple region was the same region as the black region. The purple region was the color caused by the release layer that was transferred to the surface along with lithium, and the black region was the color after the release layer was removed using a tape.

[0217] Using the above-described difference in shading, the area of the by-product region on the electrode surface can be calculated. The photographs of the electrode surfaces of Example 1, 2, and Comparative Examples 1, 2 prepared according to the above-described preparation examples are shown in Figure 5 The amount of by-product formed on each electrode surface was calculated by the above-described method, and the results are shown in Table 2 below.

[0218] [Table 2]

[0219]

[0220] From Figure 5As can be seen, the formation of by-products around the pores formed on the electrode surface of Examples 1 and 2 was confirmed to be significantly reduced, and white by-products in the form of lithium oxide were generated in a large area on the electrode surface of Comparative Example 1 in which no pores were formed and Comparative Example 2 in which the shortest distance between pores was 1.5 cm.

[0221] Specifically, as can be seen from Table 2 above, the area of by-products formed on the electrode surface of Examples 1 and 2 was only 41% or less of the area to which the lithium metal layer was transferred, and the area of by-products was significantly reduced compared to Comparative Example 1 in which no pores were formed on the electrode surface and Comparative Example 2 in which the shortest distance between pores was 1.5 cm.

[0222] <Experimental Example 2>

[0223] In order to confirm that the loss of lithium metal for prelithiation increases as the shortest distance between pores decreases, for the prelithiation electrodes of Examples 2 to 5 and Comparative Examples 3 and 4, the change in the area ratio of pores within a 1 cm 2 square to the shortest distance between pores of pores each having a longest diameter of 50 µm was calculated. The results are shown in Table 3 below.

[0224] At this time, the longest diameter of the pores within a 1 cm 2 square was 50 µm, the number of pores within a 1 cm 2 square was calculated based on the shortest distance between adjacent pores, and the area ratio of pores was calculated by Equation A below.

[0225] [Equation A]

[0226] Area ratio (%) = {(area of a single pore (cm 2 )) × (number of pores within a 1 cm 2 square)} / (area of a 1 cm 2 square) × 100

[0227] [Table 3]

[0228]

[0229] According to Table 3 above, it can be seen that in the electrodes of Examples 2 to 5 in which the shortest distance between adjacent pores was 0.04 cm or more, as the shortest distance between adjacent pores became narrower and the area ratio of pores increased, the amount of loss of lithium metal became smaller, and the heat generated by prelithiation was easily released; and in Comparative Examples 3 and 4 in which the shortest distance between adjacent pores was less than 0.04 cm, the area ratio of pores increased by more than 4 times compared to Examples 2 to 5, and thus the amount of lithium metal lost for prelithiation significantly increased.

[0230] In the electrode manufacturing method of the present specification, two or more holes having a shortest distance between holes of 0.04 cm or more and 1 cm or less are formed. Therefore, the amount of lithium metal used for prelithiation can be minimized, heat generated during prelithiation can be released, and the formation of electrode surface by-products can be suppressed.

[0231] <Legend>

[0232] 10: negative current collector layer

[0233] 20: negative active material layer

[0234] 30: separator

[0235] 40: positive active material layer

[0236] 50: positive current collector layer

[0237] 100: negative electrode for lithium secondary battery

[0238] 200: positive electrode for lithium secondary battery

Claims

1. A method of manufacturing an electrode for a lithium secondary battery, the method comprising: preparing a transfer stack including a lithium metal layer, a release layer, and a substrate layer; transferring the lithium metal layer and the release layer to at least one surface of an electrode active material layer such that the lithium metal layer is in contact with the electrode active material layer, wherein at least one of the lithium metal layer and the release layer transferred to the at least one surface of the electrode active material layer includes two or more holes, and wherein a shortest distance between adjacent holes is 0.04 cm or more and 1 cm or less.

2. The method of claim 1, wherein, a longest diameter of the two or more holes is 5 μm to 50 μm.

3. The method of claim 1, wherein, the shortest distance between adjacent holes is 0.2 cm or more and 0.9 cm or less.

4. The method of claim 1, wherein, the process of transferring the lithium metal layer and the release layer to the at least one surface of the electrode active material layer includes: stacking the transfer stack with the electrode active material layer such that the lithium metal layer is in contact with the at least one surface of the electrode active material layer; separating the substrate layer from the release layer; and forming two or more holes in at least one of the lithium metal layer and the release layer after separating the substrate layer.

5. The method of claim 1, wherein, the process of preparing the transfer stack further includes forming two or more holes in at least one of the lithium metal layer, the release layer, and the substrate layer.

6. The method of claim 1, wherein, a thickness of the lithium metal layer is 1 μm or more and 8 μm or less.

7. The method of claim 1, further comprising: the electrode active material layer is formed by coating an electrode composition paste on at least one surface of an electrode current collector layer before transferring the lithium metal layer and the release layer to the at least one surface of the electrode active material layer.

8. The method of claim 1, wherein, the electrode active material layer includes a silicon-based negative electrode active material, a negative electrode conductive material, and a negative electrode binder. 9.An electrode for a lithium secondary battery manufactured by the method of any one of claims 1 to 8.

10. The electrode for a lithium secondary battery according to claim 9, wherein an area of a lithium by-product formed on a surface of the electrode is 42% or less with respect to an area of the transfer stack in contact with the at least one surface of the electrode active material layer. 11.An electrode for a lithium secondary battery, comprising: an electrode current collector layer; an electrode active material layer having a lithium metal layer transferred thereon; and a lithium by-product layer, wherein, the lithium by-product layer exhibits 3% or more of nitrogen (N) and 75% or more of oxygen (O) when analyzed by energy dispersive X-ray spectroscopy (EDS) using a scanning electron microscope (SEM), and wherein an area of the lithium by-product layer is 42% or less with respect to a total area of the lithium metal layer transferred to the electrode active material layer. 12.A lithium secondary battery, comprising: the electrode for a lithium secondary battery of claim 9; a separator; and an electrolyte. 13.A battery pack, comprising the lithium secondary battery of claim 12. 14.A battery pack, comprising the lithium secondary battery of claim 12. 15.A battery pack, comprising the battery pack of claim 13.

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