Method for manufacturing an electrode for a lithium secondary battery, an electrode manufactured by the method, and a lithium secondary battery including the electrode

Abstract

The present invention relates to a method for manufacturing an electrode for a lithium secondary battery, the method comprising the steps of: preparing a transfer laminate including a lithium metal layer, a release layer, and a substrate layer; and transferring the lithium metal layer and the release layer to at least one surface of an electrode active material layer so 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 at least one surface of the electrode active material layer has two or more holes, and the shortest distance between adjacent holes satisfies a certain distance, thereby reducing lithium by-products; an electrode manufactured by the method; and a lithium secondary battery including the electrode.

Description

[Technical Field]

[0001] The present invention claims the benefit of the filing date of Korean Patent Application No. 10-2023-0140985 filed with the Korean Intellectual Property Office on October 20, 2023, and Korean Patent Application No. 10-2024-0141418 filed with the Korean Intellectual Property Office on October 16, 2024, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a method for producing an electrode for a lithium secondary battery, an electrode produced thereby, and a lithium secondary battery including the electrode. [Background technology]

[0003] The rapid increase in fossil fuel use has led to an increasing demand for alternative and clean energy, and one of the most actively researched fields in this area is power generation and storage using electrochemical reactions.

[0004] Currently, a typical example of an electrochemical element that utilizes such electrochemical energy is a secondary battery, and the range of its use is tending to expand more and more.

[0005] With technological development and increasing demand for mobile devices, demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and widely used. In addition, research into methods for manufacturing high-density electrodes with higher energy density per unit volume as electrodes for such high-capacity lithium secondary batteries is actively underway, and there is a trend toward increasingly higher loading to improve energy density.

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

[0007] Meanwhile, lithium secondary batteries begin to lose lithium from the first charge after battery manufacture. During subsequent charge-discharge cycles and high-temperature storage, a small amount of lithium continues to be lost, causing the battery to degrade. To compensate for this lithium loss, additional lithium is added to the battery before it is operated, a process known as pre-lithiation. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 7125228 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention relates to a method for manufacturing an electrode for a lithium secondary battery that can reduce by-products on the electrode surface, an electrode manufactured thereby, and a lithium secondary battery including the electrode. [Means for solving the problem]

[0010] One embodiment of the present disclosure provides a method for preparing a transfer laminate comprising the steps of: providing a transfer laminate comprising a lithium metal layer, a release layer, and a substrate layer; and transferring the lithium metal layer and the release layer to at least one surface of the electrode active material layer so that the lithium metal layer is in contact with the electrode active material layer; At least one of the lithium metal layer and the release layer transferred to at least one surface of the electrode active material layer has two or more holes formed therein; The shortest distance between adjacent holes is 0.04 cm or more and 1 cm or less.

[0011] One embodiment of the present specification provides an electrode for a lithium secondary battery produced according to the above-described production method.

[0012] Another embodiment of the present specification is a method for manufacturing an electrode comprising: an electrode current collector layer; an electrode active material layer having a lithium metal layer transferred thereto; and a lithium by-product layer; The lithium by-product layer contains 3% or more of nitrogen (N) and 75% or more of oxygen (O) when analyzed by EDS (Energy-dispersive X-ray Spectroscopy) using a SEM (Scanning Electron Microscope), The area of ​​the lithium by-product layer is 42% or less of the total area of ​​the lithium metal layer transferred to the electrode active material layer.

[0013] Another embodiment of the present specification relates to a lithium secondary battery electrode, A separation membrane; and an electrolyte.

[0014] One embodiment of the present specification provides a battery module or a battery pack including the above-described lithium secondary battery.

[0015] Finally, another embodiment of the present disclosure provides a battery pack including the battery module described above. [Effects of the Invention]

[0016] According to a manufacturing method of one embodiment of the present invention, holes are formed at specific intervals in an electrode active material layer before or after transferring a lithium metal layer, thereby dissipating heat generated during prelithiation and minimizing lithium by-products generated on the electrode surface at high temperatures, thereby manufacturing an electrode for a lithium secondary battery.

[0017] In addition, the electrode for a lithium secondary battery manufactured by the manufacturing method according to an embodiment of the present invention is characterized in that the area of ​​lithium by-products formed on the surface after pre-lithiation is reduced, thereby minimizing the impact on the performance of the electrode and preventing safety issues. [Brief explanation of the drawings]

[0018] [Figure 1]1 is a diagram showing a laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of the present invention. [Figure 2] 1 is a diagram showing a stack structure of a lithium secondary battery according to an embodiment of the present invention. [Figure 3] FIG. 1 is a flowchart illustrating a method for manufacturing an electrode for a lithium secondary battery according to an embodiment of the present specification. [Figure 4] FIG. 10 is a diagram showing the surface of the electrode from which the base layer and release layer have been removed after lithium metal transfer. [Figure 5] 1 is a diagram showing the surfaces of electrodes for lithium secondary batteries according to Example 1, Example 2, and Comparative Examples 1 and 2. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0019] Before describing the present invention, some terms will first be defined.

[0020] In this specification, when a part is said to "comprise" a certain component, this does not mean that it excludes other components, but that it may further include other components, unless otherwise specified.

[0021] In this specification, when a member is said to be located "on" another member, this includes not only when the member is in contact with the other member, but also when there is another member between the two members.

[0022] In this specification, "p to q" means a range of "not less than p and not more than q."

[0023] In this specification, the "specific surface area" is measured by the BET method, and specifically, is calculated from the amount of nitrogen gas adsorption at liquid nitrogen temperature (77 K) using a BELSORP-mini II manufactured by BEL Japan Co., Ltd. That is, in this application, the BET specific surface area can mean the specific surface area measured by the above-mentioned measurement method.

[0024] In this specification, "Dn" refers to particle size distribution, and refers to the particle size at the n% point in the cumulative particle number distribution according to particle size. That is, D50 is the particle size (average particle size) at the 50% point in the cumulative particle number distribution according to particle size, D90 is the particle size at the 90% point in the cumulative particle number distribution according to particle size, and D10 is the particle size at the 10% point in the cumulative particle number distribution according to particle size. Meanwhile, the average particle size can be measured using the laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500). The difference in diffraction patterns due to particle size when the particles pass through a laser beam is measured, and the particle size distribution is calculated.

[0025] The average particle size can be measured using a Microtrac device (manufacturer: Microtrac model name: S3500) with water and Triton-X100 dispersant. Specifically, the average particle size of the positive electrode active material can be measured at a refractive index of 1.5 to 1.7, and the average particle size of the negative electrode active material can be measured at a refractive index of 1.97 or 2.42. For example, the particles can be dispersed in a dispersion medium, introduced into a commercially available laser diffraction particle size analyzer, and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W. A volume cumulative particle size distribution graph can then be obtained, and the particle size corresponding to 50% of the cumulative volume can be determined.

[0026] In this specification, whether or not lithium by-products are formed can be confirmed by analyzing the element content of the surface. Specifically, the element content in each surface region can be analyzed by EDS (Energy-dispersive X-ray Spectroscopy) analysis (JSM-7610F) of a SEM (Scanning Electron Microscope).

[0027] In this specification, the particle size or particle size may refer to the average diameter or representative diameter of each particle constituting the metal powder.

[0028] In this specification, when a polymer contains a certain monomer as a monomer unit, it means that the monomer participates in a polymerization reaction and is contained as a repeating unit in the polymer. In the present invention, when a polymer contains a monomer, this is interpreted as meaning the same as saying that the polymer contains the monomer as a monomer unit.

[0029] In this specification, the term "polymer" is understood to be used in a broad sense, including copolymers, unless specifically referred to as a "homopolymer."

[0030] The terms and words used in this specification should not be construed as being limited to their ordinary or dictionary meanings, but should be construed in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to best explain his / her invention.

[0031] As used herein, the singular expression of a term includes the plural expression unless the context clearly indicates otherwise.

[0032] Preferred embodiments of the present invention will be described in detail below. However, the embodiments of the present invention can be modified in various ways, and the scope of the present invention is not limited to the embodiments described below.

[0033] A method for manufacturing an electrode for a lithium secondary battery according to one embodiment of the present specification includes the steps of preparing a transfer laminate including a lithium metal layer, a release layer, and a substrate layer, and transferring the lithium metal layer and the release layer to at least one surface of an electrode active material layer so 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 at least one surface of the electrode active material layer has two or more holes, and the shortest distance between adjacent holes is 0.04 cm or more and 1 cm or less.

[0034] The method for manufacturing an electrode for a lithium secondary battery according to the present specification involves transferring lithium to at least one surface of an electrode active material layer to promote prelithiation in order to solve the irreversibility problem of silicon-based electrodes and improve Coulomb efficiency. This allows for a faster process speed and greater scale (scale-up) than prelithiation methods using stabilized lithium metal powder (SLMP®) or electrochemical methods, making it a technology suitable for mass production.

[0035] However, when prelithiation is performed using the transfer method, the reaction rate between the electrode active material and lithium metal is so fast that the maximum temperature of the electrode surface prelithiated with lithium metal may rise to about 40°C or more, resulting in the formation of by-products on the electrode surface and a loss of electrode capacity.To solve this problem, the present invention is characterized by forming two or more holes with an appropriate shortest distance in at least one of the lithium metal layer and the release layer, thereby dissipating heat generated during prelithiation and reducing the formation of by-products on the electrode surface.

[0036] In this specification, the shortest distance between adjacent holes means the shortest distance between the outermost periphery of any one hole and the outermost periphery of an adjacent hole.

[0037] A method for manufacturing an electrode for a lithium secondary battery according to one embodiment of the present specification includes a step of transferring a lithium metal layer and a release layer to at least one surface of an electrode active material layer so that the lithium metal layer is in contact with the electrode active material layer, and at least one of the lithium metal layer and the release layer transferred to at least one surface of the electrode active material layer has two or more holes.

[0038] In this specification, the two or more holes provided 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 may be formed on the transfer laminate at the stage of preparing the transfer laminate, may be formed on the transfer laminate at the stage of contacting the transfer laminate with at least one surface of the electrode active material layer, or may be formed on the electrode after transfer is completed.

[0039] In one 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 may include the steps of laminating the transfer laminate to the electrode active material layer so that the lithium metal layer contacts at least one surface of the electrode active material layer, separating the base layer from the release layer, and forming two or more holes in at least one of the lithium metal layer and the release layer.

[0040] In another embodiment of the present specification, the step of preparing the transfer laminate may further include forming two or more holes in at least one of the lithium metal layer, the release layer, and the substrate layer.

[0041] For example, the step of forming the holes may include forming holes in the lithium metal layer, the release layer, or both the lithium metal layer and the release layer, and laminating the lithium metal layer and the release layer on one side of the substrate layer.

[0042] For example, the step of forming the holes may include the steps of: laminating the lithium metal layer and the release layer on one surface of the substrate layer to form a transfer laminate; and forming the two or more holes in at least one of the lithium metal layer, the release layer, and the substrate layer.

[0043] In one embodiment of the present specification, the method for forming the holes can be any known method without any limitations.

[0044] In this specification, the holes can be formed in at least one of the lithium metal layer, the release layer, and the substrate layer, but there is no limitation thereto.

[0045] In this specification, the depth of the hole may be within 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 specifically, may be within the thickness of the release layer or the total thickness of the release layer and the lithium metal layer.

[0046] In one embodiment of the present specification, the shortest distance between adjacent holes may be 0.04 cm or more and 1 cm or less.

[0047] In one embodiment of the present specification, the shortest distance between adjacent holes may be 0.04 cm or more and 1 cm or less, specifically 0.1 cm or more and 0.9 cm or less, and more specifically 0.2 cm or more and 0.9 cm or less.

[0048] In this specification, the adjacent holes refer to two holes with the shortest distance between them, with no other holes present between them.

[0049] When the shortest distance between adjacent pores according to one embodiment of the present specification satisfies the above range, the heat generated by prelithiation can be most effectively released, thereby suppressing the formation of lithium oxide or nitride on the electrode surface.

[0050] However, the shorter the shortest distance between adjacent holes, the greater the area of ​​at least one of the lithium metal layer and the release layer. 2 Since the total area occupied by the two or more holes per one electrode increases, there is a risk of loss of the lithium metal layer to be used for prelithiation. Therefore, it is preferable to satisfy the above range in order to most effectively release the heat generated by prelithiation while minimizing the amount of wasted lithium metal layer.

[0051] In one embodiment of the present specification, the longest diameter of the two or more pores may be 5 μm to 50 μm, specifically 7 μm to 40 μm, and more specifically 10 μm to 20 μm.

[0052] In this regard, in one embodiment of the present specification, the shape of the hole is not limited, and the longest diameter refers to the distance between the two points with the greatest distance within the hole. For example, if the shape of the hole is square, the longest diameter may be the length of the diagonal. Alternatively, for example, if the shape of the hole is circular, the longest diameter may be the diameter.

[0053] When the longest diameter of the pores according to one embodiment of the present specification satisfies the above range, the amount of lithium wasted due to the formation of the pores is small, and the generation of lithium by-products on the electrode surface is suppressed due to the effect of heat release during the prelithiation process. As a result, the amount of lithium that is not prelithiated inside the electrode and is wasted is small, and sufficient prelithiation can be performed.

[0054] In this specification, the longest diameter of the pores can be observed under a microscope in a dry room.

[0055] In another embodiment of the present specification, in the method for producing an electrode for a lithium secondary battery, at least one of the lithium metal layer and the release layer transferred to at least one surface of the electrode active material layer is provided with two or more holes, and at least one of the lithium metal layer and the release layer has an area of ​​1 cm 2 In contrast, the area ratio occupied by the two or more pores as a whole may be 1.2% or less.

[0056] In one embodiment of the present specification, at least one of the lithium metal layer and the release layer has an area of ​​1 cm 2 In contrast, the proportion of the area occupied by the two or more pores as a whole may be 1.2% or less, specifically 0.8% or less, and more specifically 0.1% or less.

[0057] In this case, the area ratio of the two or more holes to the total area of ​​1 cm is calculated using the following formula A. 2 The number of holes in a square was calculated based on the shortest distance between adjacent holes.

[0058] [Formula A] Area ratio (%) = (area of ​​one hole (cm 2 ))×(1cm 2 (number of holes in a square) / (area of ​​a square 1cm 2 ) x 100

[0059] At least one of the lithium metal layer and the release layer has an area of ​​1 cm 2 On the other hand, when the area ratio occupied by the two or more pores as a whole satisfies the above range, the heat generated during the pre-lithiation process can be sufficiently released, and the amount of lithium metal layer wasted due to the formation of pores can be minimized.

[0060] In this specification, at least one of the lithium metal layer and the release layer has an area of ​​1 cm 2 The number of holes per layer may 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 that satisfies the shortest distance and longest diameter between the holes is provided within the above range, the heat release effect due to prelithiation can be maximized, and the amount of lithium metal layer that is wasted due to the formation of holes can be minimized.

[0061] A method for producing an electrode for a lithium secondary battery according to one embodiment of the present specification includes the step of providing a transfer laminate including a lithium metal layer, a release layer, and a substrate layer.

[0062] In the method for manufacturing an electrode for a lithium secondary battery according to one embodiment of the present specification, the transfer laminate includes a lithium metal layer, a release layer, and a substrate layer, and specifically, the lithium metal layer, the release layer, and the substrate layer may be sequentially laminated.

[0063] In one 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 may be, but is not limited to, a commonly used Li metal foil.

[0064] In one embodiment of the present specification, the thickness of the lithium metal layer may be 0.1 μm or more and 10 μm or less, specifically 1 μm or more and 8 μm or less, and more specifically 1 μm or more and 6.2 μm or less.

[0065] In one embodiment of the present specification, when the thickness of the lithium metal layer satisfies the above range, prelithiation can proceed to a degree that solves the irreversibility problem of the electrode and improves the Coulomb efficiency, and the amount of heat generated during prelithiation is low, heat is efficiently released, and lithium loss and safety issues due to the generation of lithium by-products can be prevented.

[0066] In addition, in one embodiment of the present specification, the substrate layer may be any layer that can withstand process conditions such as high temperatures in the step of depositing the lithium metal layer and can prevent a problem of reverse peeling, in which the deposited lithium metal layer is transferred onto the substrate layer during a winding process for transferring the deposited lithium metal layer, without any limitations.

[0067] Specifically, in one embodiment of the present specification, the base layer may be one or more selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), poly(methylmethacrylate) (PMMA), polypropylene, polyethylene, and polycarbonate.

[0068] In one embodiment of the present specification, the thickness of the base layer may be 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.

[0069] When the thicknesses of the substrate layer and the lithium metal layer satisfy the above ranges, the lithium metal is efficiently transferred to the electrode active material layer side, and reverse transfer can be prevented.

[0070] In one embodiment of the present specification, a deposition method for depositing the lithium metal layer on the substrate layer may be selected from physical vapor deposition (PDV) and chemical vapor deposition (CVD). Among the physical vapor deposition methods, thermal evaporation may be mainly used, but is not limited thereto, and various deposition methods used in the art may be used.

[0071] In one embodiment of the present specification, the release layer is one or more selected from the group consisting of polycarbonate (PC), polydimethylsiloxane (PDMS), polymethylhydrosiloxane (PMHS), polyimide (PI), and polymethylmethacrylate (PMMA).

[0072] In one embodiment of the present specification, the thickness of the release layer may be 0.2 μm or more and 3 μm or less, specifically 0.5 μm or more and 1 μm or less.

[0073] In one embodiment of the present specification, when the thickness of the release layer satisfies the above range, a sufficient release force can be ensured.

[0074] In one embodiment of the present specification, the release layer may be formed by a coating method. For example, the coating method may be a method selected from the group consisting of dip coating, spray coating, spin coating, die coating, gravure coating, micro-gravure coating, comma coating, and roll coating, but is not limited thereto. Various coating methods known in the art for forming a coating layer may be used.

[0075] In one 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 may include a step of laminating the transfer laminate to the electrode active material layer so that the lithium metal layer contacts at least one surface of the electrode active material layer, and a step of separating the base layer from the release layer.

[0076] In one embodiment of the present specification, the laminating step includes a step of contacting the transfer laminate with at least one surface of the electrode active material layer so that the lithium metal layer is in contact with the electrode active material layer, which is a preparatory step for transferring the electrode active material layer to the lithium metal.

[0077] In one embodiment of the present specification, the laminating step may further include a pressurizing step, which may allow pre-lithiation by transfer to the electrode active material layer to proceed more actively, thereby enabling the electrode to be formed thinly despite having a high energy density.

[0078] In one embodiment of the present specification, the step of applying pressure is 50 kgf / cm 2 More than 2000kgf / cm 2It may be a step of pressurizing at the following pressure, specifically, 100 kgf / cm 2 or more and 1000 kgf / cm 2 or less. It may also be a step of pressurizing at the following pressure.

[0079] When the pressure in the pressurizing step satisfies the above range, prelithiation can proceed at an appropriate rate, and the heat generated during prelithiation can be reduced. As a result, the formation of surface by-products can be decreased, and the energy density of the electrode can be improved.

[0080] The method for manufacturing an electrode for a lithium secondary battery according to an embodiment of the present specification may include a step of separating the base material layer from the release layer.

[0081] In an embodiment of the present specification, the electrode active material layer may be a negative electrode active material layer or a positive electrode active material layer.

[0082] In an embodiment of the present specification, the electrode active material layer may be a negative electrode active material layer. The negative electrode active material layer includes a negative electrode active material, a negative electrode conductive material, and a negative electrode binder. The negative electrode active material may 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.

[0083] In an embodiment of the present specification, the negative electrode active material may 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).

[0084] In an embodiment of the present specification, the negative electrode active material may 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). The silicon-based negative electrode active material may be included in an amount of 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.

[0085] The negative electrode composition according to one embodiment of the present specification uses a specific conductive material and binder that can suppress the volume expansion rate during charge and discharge even when a silicon-based active material with extremely high capacity is used within the above range, and therefore the negative electrode performance is not reduced even when the range is included, and the negative electrode composition has excellent output characteristics during charge and discharge.

[0086] In one embodiment of the present specification, the silicon-based negative electrode active material may be, in particular, pure silicon (Si). The use of pure silicon (Si) as the negative electrode active material may mean that the negative electrode active material contains pure Si particles not bonded to other particles or elements in the above range, based on 100 parts by weight of the total.

[0087] Specifically, in one embodiment of the present specification, the negative electrode active material may contain Si, and the Si may be contained in an amount of 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, relative to 100 parts by weight of the negative electrode active material layer composition.

[0088] In the charge-discharge reaction of a lithium secondary battery, lithium is released from the positive electrode and inserted into the negative electrode during charging, and is released from the negative electrode and returned to the positive electrode during discharge. However, in the case of silicon-based negative electrode active materials, volume changes and surface side reactions are severe, so much of the lithium inserted into the negative electrode during initial charging cannot return to the positive electrode, resulting in a problem of large initial irreversible capacity. This large initial irreversible capacity leads to a rapid decrease in battery capacity and cycle life.

[0089] In order to solve the above-mentioned problems, the present invention relates to a process of pre-treating a negative electrode of a lithium secondary battery by pre-lithiating the negative electrode to solve the problem of initial irreversible capacity. Specifically, the pre-lithiating process relates to a process of pre-treating a negative electrode before the pre-lithiating process so that lithium metal is easily transferred from a transfer laminate during the lithium transfer process and lithium in the negative electrode active material layer is uniformly pre-lithiated.

[0090] In addition, in the present invention, a silicon-based negative electrode active material is used as the negative electrode active material to improve capacity performance, but a conductive material and binder meeting specific conditions are used to solve the problems of maintaining a conductive path due to volume expansion and maintaining the bond between the conductive material, binder, and active material.

[0091] Meanwhile, the average particle size (D50) of the silicon-based negative electrode active material in this specification may be 3 μm to 10 μm, specifically 3.5 μm to 8 μm. When the average particle size is within this range, the specific surface area of ​​the particles is within an appropriate range, and the viscosity of the electrode slurry is formed within an appropriate range. This allows for smooth dispersion of the particles constituting the electrode slurry. Furthermore, when the size of the silicon-based active material is equal to or greater than the lower limit of the range, the contact area between the silicon-based negative electrode active material and the negative electrode conductive material is improved by the composite of the conductive material and the binder in the electrode slurry, increasing the likelihood of maintaining the conductive network and improving the capacity retention rate. On the other hand, when the average particle size satisfies the above range, excessively large silicon-based negative electrode active material is excluded, resulting in a smooth electrode surface, thereby preventing non-uniform current density during charge and discharge.

[0092] In one 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~150.0m 2 / g, specifically, 0.1m 2 / g~100.0m 2 / g, more specifically, 0.2m 2 / g~80.0m 2 / g, particularly 0.2m 2 / g~18.0m 2 / g. The BET specific surface area is determined in accordance with DIN 66131 (using nitrogen).

[0093] In one embodiment of the present specification, the silicon-based negative electrode active material may have a non-spherical shape, and the sphericity 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.

[0094] In this specification, the circularity is determined by the following formula A-1, where A is the area and P is the boundary line.

[0095] [Formula A-1] 4πA / P 2

[0096] While graphite-based compounds have traditionally been used exclusively as anode active materials, recent attempts to incorporate silicon-based compounds to boost capacity have been increasing in response to growing demand for high-capacity batteries. However, silicon-based compounds have limitations, such as their rapid volume expansion during charge / discharge processes, damaging the conductive pathways formed within the anode active material layer and reducing battery performance. Therefore, the type of anode conductive material used together with the silicon-based active material is important.

[0097] Thus, in one embodiment of the present specification, the negative electrode conductive material may include one or more selected from the group consisting of dot-like conductive materials, linear conductive materials, and planar conductive materials.

[0098] In one embodiment of the present specification, the dot-like conductive material refers to a conductive material with a zero-dimensional (0D) structure in which a crystalline mass structure consisting of one to several hundred atoms or less is formed into a round ball shape and has volume. The dot-like conductive material can be used to improve the conductivity of a negative electrode and has conductivity without causing a chemical change. Specifically, the dot-like conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives. Preferably, the dot-like conductive material may include carbon black, which realizes high conductivity and has excellent dispersibility.

[0099] In one embodiment of the present specification, the point-like conductive material has a BET specific surface area of ​​40 m 2 / g or more 70m 2 / g or less, specifically 45m 2 / g or more 65m 2 / g or less, more specifically 50m 2 / g or more 60m 2 / g or less.

[0100] In one embodiment of the present specification, the particle size of the dotted conductive material may be 10 nm to 100 nm, specifically 20 nm to 90 nm, and more specifically 20 nm to 60 nm.

[0101] In one embodiment of the present specification, the negative electrode conductive material may include a sheet conductive material.

[0102] In one embodiment of the present specification, the planar conductive material refers to a conductive material with a two-dimensional (2D) structure in which atoms have a thickness of a single atomic layer or two or more atomic layers and form a crystalline structure when viewed from above. The planar conductive material refers to a material that ensures a planar conductive path within the negative electrode active material layer and simultaneously plays a role in suppressing the disconnection of the conductive path due to volume expansion, and can be expressed as a plate-like conductive material or a bulk conductive material. Specifically, the planar conductive material may include at least one selected from the group consisting of plate-like graphite, graphene, graphene oxide, and graphite flakes, and may be preferably plate-like graphite.

[0103] In one embodiment of the present specification, the average particle size (D50) of the sheet conductive material may be 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When the average particle size satisfies the above range, the sufficient particle size facilitates dispersion without causing an excessive increase in the viscosity of the negative electrode slurry. Therefore, when dispersion is performed using the same equipment and time, the dispersion effect is excellent.

[0104] In one embodiment of the present specification, the sheet conductive material may have a D10 of 0.5 μm or more and 1.5 μm or less, a D50 of 2.5 μm or more and 3.5 μm or less, and a D90 of 7.0 μm or more and 15.0 μm or less.

[0105] In one embodiment of the present specification, the sheet conductive material may be a sheet conductive material having a high BET specific surface area; or a sheet conductive material having a low specific surface area.

[0106] In one embodiment of the present specification, the planar conductive material may be a high-specific surface area planar conductive material or a low-specific surface area planar conductive material without any restrictions. However, since the planar conductive material according to the present specification may be affected to some extent by dispersion in terms of electrode performance, it may be particularly preferable to use a planar conductive material with a low specific surface area that does not cause problems in dispersion.

[0107] In one embodiment of the present specification, the planar conductive material has a BET specific surface area of ​​5 m 2 / g or more.

[0108] In another embodiment, the sheet conductive material has a BET specific surface area of ​​5 m 2 / g or more 500m 2 / g or less, specifically 5m 2 / g or more 300m 2 / g or less, more specifically 5m 2 / g or more 250m 2 / g or less.

[0109] In another embodiment, the sheet conductive material is a high specific surface area sheet conductive material having a BET specific surface area of ​​50 m 2 / g or more 500m 2 / g or less, specifically 80m 2 / g or more 300m 2 / g or less, more specifically 100m 2 / g or more 300m 2 / g or less.

[0110] In another embodiment, the sheet conductive material is a sheet conductive material having a low specific surface area, and a BET specific surface area of ​​5 m 2 / g or more 40m 2 / g or less, specifically 5m 2 / g or more 30m 2 / g or less, more specifically 5m 2 / g or more 25m 2 / g or less.

[0111] In one embodiment of the present specification, the linear conductive material refers to a conductive material having a one-dimensional (1D) structure with a nanometer-level diameter and a high aspect ratio, or a conductive material having a fibrous structure such as a cylindrical or tubular structure. An example of the linear conductive material is a carbon nanotube, which may be a bundle-type carbon nanotube. The bundle-type carbon nanotube may 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 monomers are arranged side by side or intertwined with the longitudinal axes of the carbon nanotube monomers in substantially the same orientation. The carbon nanotube units have a cylindrical shape with a nanometer-sized diameter graphite sheet and sp 2 The bundled carbon nanotubes have a bonding structure. Depending on the angle and structure of the graphite plane wrapping, they can exhibit conductive or semiconductive properties. Compared to entangled carbon nanotubes, the bundled carbon nanotubes can be more uniformly dispersed during negative electrode fabrication, smoothly forming a conductive network within the negative electrode and improving the conductivity of the negative electrode.

[0112] In one embodiment of the present specification, the linear conductive material may include any one selected from the group consisting of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs), and specifically, may include single-walled carbon nanotubes (SWCNTs).

[0113] In one embodiment of the present specification, the linear conductive material has a BET specific surface area of ​​100 m 2 / g or more 100,000m 2 / g or less, specifically 500m 2 / g or more 10,000m 2 / g or less, more specifically 1,000m 2 / g or more 5,000m 2 / g or less.

[0114] In addition, in one embodiment of the present specification, the aspect ratio of the linear conductive material may be 500 or more and 1,000,000 or less, specifically 1,000 or more and 100,000 or less, and more specifically 10,000 or more and 100,000 or less.

[0115] In one embodiment of the present specification, the negative electrode conductive material may preferably include, but is not limited to, one or more selected from the group consisting of platelet graphite, single-walled carbon nanotubes (SWCNTs), and multi-walled carbon nanotubes (MWCNTs).

[0116] In one embodiment of the present specification, the conductive material may preferably include any one selected from the group consisting of platelet graphite, single-walled carbon nanotubes (SWCNTs), and multi-walled carbon nanotubes (MWCNTs) as a first conductive material, and may include any other one selected from the group consisting of platelet graphite, single-walled carbon nanotubes (SWCNTs), and multi-walled carbon nanotubes (MWCNTs) as a second conductive material, but is not limited thereto.

[0117] In one embodiment of the present specification, the negative electrode conductive material may be 10 parts by weight or more and 40 parts by weight or less based on 100 parts by weight of the negative electrode active material layer composition.

[0118] In another embodiment, the negative electrode conductive material may be included in an amount of 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.

[0119] The negative electrode conductive material according to the present specification has a completely different structure from the conductive material applied to the positive electrode. That is, the negative electrode conductive material according to the present specification plays a role in capturing the contact points between the silicon-based active materials, which undergo a very large volume expansion of the electrode upon charge and discharge, and has a completely different structure and role from the positive electrode conductive material, which plays a buffer role during rolling and imparts partial conductivity.

[0120] Furthermore, the negative electrode conductive material according to the present specification is applied to a silicon-based negative electrode active material and has a completely different structure from a conductive material applied to a graphite-based active material. That is, a conductive material used in an electrode having a graphite-based active material simply has smaller particles than the active material, and therefore has the properties of improving output characteristics and imparting some conductivity, and its structure and role are completely different from those of a negative electrode conductive material applied together with a silicon-based negative electrode active material as in the present invention.

[0121] In one embodiment of the present specification, the dot-like conductive material used as the negative electrode active material has a structure and function different from that of a carbon-based active material generally used as a negative electrode active material. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, and refers to a material that is processed into a spherical or dot-like shape to facilitate the storage and release of lithium ions.

[0122] Meanwhile, the planar conductive material used as the negative electrode conductive material is a material having a planar or plate-like shape and can be expressed as plate-like graphite. That is, it is a material contained in the negative electrode active material layer to maintain a conductive path, and does not play a role in storing and releasing lithium, but rather a material that ensures a planar conductive path within the negative electrode active material layer.

[0123] That is, in one embodiment of the present specification, the use of plate-like graphite as a conductive material means that the graphite is processed into a planar or plate-like shape and is used as a material for securing a conductive path, rather than for storing or releasing lithium. In this case, the negative electrode active material included therein has high capacity characteristics for storing and releasing lithium, and therefore plays a role in storing and releasing all lithium ions conducted from the positive electrode.

[0124] In one embodiment of the present specification, the negative electrode binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylamide, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which hydrogen in these substances is substituted with Li, Na, Ca, or the like, or may include various copolymers thereof.

[0125] The negative electrode binder according to one embodiment of the present specification plays a role of capturing the active material and the conductive material to prevent distortion and deformation of the negative electrode structure when the silicon-based active material expands and relaxes in volume. Any common binder can be used as long as it fulfills this role. Specifically, a water-based binder may be used, and more specifically, a polyacrylamide (PAM)-based binder may be used.

[0126] In one embodiment of the present specification, the negative electrode binder may be included in an amount of 1 part by weight to 30 parts by weight, specifically 3 parts by weight to 25 parts by weight, more specifically 3 parts by weight to 20 parts by weight, relative to 100 parts by weight of the negative electrode active material layer composition.

[0127] When the content of the negative electrode binder satisfies the above range, the electrode has excellent mechanical strength and strong intermolecular interaction, resulting in excellent electrode binding strength. Furthermore, when the content of the negative electrode binder satisfies the above range, the viscosity of the negative electrode binder can be selected within an appropriate range, and when an electrode is manufactured using the binder, the coating properties of the electrode can be further improved.

[0128] A negative electrode according to one embodiment of the present specification may include the above-described negative electrode active material; a negative electrode conductive material; and a negative electrode binder.

[0129] Specifically, the negative electrode may 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 may include the negative electrode active material. Furthermore, the negative electrode active material layer may further include a thickener.

[0130] In one embodiment of the present specification, the negative electrode current collector layer may generally have a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, aluminum-cadmium alloy, etc. can be used. In addition, the surface can be formed with fine irregularities to strengthen the binding force of the negative electrode active material, and the negative electrode current collector layer may be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0131] In one embodiment of the present specification, the thickness of the negative electrode current collector layer may be 1 μm or more and 100 μm or less, and the thickness of the negative electrode may be 20 μm or more and 500 μm or less, but the thickness may vary depending on the types and applications of the negative electrode active material, negative electrode conductive material, and negative electrode binder used, and is not limited thereto.

[0132] The negative electrode active material layer may be formed by applying a negative electrode slurry containing a negative electrode active material, a binder, a thickener, and / or a conductive material to at least one surface of the negative electrode current collector, followed by drying and rolling.

[0133] In one embodiment of the present specification, the negative electrode slurry may include a negative electrode active material layer composition; and a slurry solvent.

[0134] In one embodiment of the present specification, the solid content of the negative electrode slurry may be 5% or more and 40% or less.

[0135] In another embodiment, the solid content of the negative electrode slurry may be in the range of 5% to 40%, preferably 7% to 35%, and more preferably 10% to 30%.

[0136] The solid content of the negative electrode slurry may refer to the content of the negative electrode active material layer composition contained in the negative electrode slurry, and may refer to the content of the negative electrode active material layer composition based on 100 parts by weight of the negative electrode slurry.

[0137] When the solid content of the negative electrode slurry satisfies the above range, the viscosity during the formation of the negative electrode active material layer is appropriate, and the agglomeration of particles of the negative electrode active material layer composition is minimized, thereby enabling the negative electrode active material layer to be efficiently formed.

[0138] In other embodiments herein, the solvent may include those known to those skilled in the art, for example, the solvent may be water (e.g., distilled water) or N-methylpyrrolidone (NMP).

[0139] The negative electrode according to one embodiment of the present specification may be formed by coating one or both surfaces of a negative electrode current collector layer with the negative electrode slurry and drying the coating. The drying step may evaporate a slurry solvent from the negative electrode slurry.

[0140] In an embodiment of the present disclosure, the method for manufacturing an electrode for a lithium secondary battery may further include, before the step of transferring the lithium metal layer and the release layer to at least one surface of the electrode active material layer, a step of coating at least one surface of an electrode current collector layer with an electrode composition slurry to form an electrode active material layer.

[0141] In the method for manufacturing an electrode for a lithium secondary battery according to an embodiment of the present specification, the step of coating one or both surfaces of the electrode current collector layer with the electrode slurry may further include a drying step, and a slurry solvent in the electrode slurry may be dried through the drying step.

[0142] In this regard, the electrode in the method for manufacturing an electrode for a lithium secondary battery according to an embodiment of the present specification may refer to an anode or a cathode, and the step of forming the electrode active material layer may be applied to the method for forming the anode active material layer described above, and may also be applied to the cathode active material layer described below.

[0143] The electrode for a lithium secondary battery according to another embodiment of the present specification may be manufactured according to the manufacturing method according to the embodiment of the present specification described above.

[0144] In another embodiment of the electrode for a lithium secondary battery according to the present specification, the area of ​​the lithium by-product formed on the surface of the electrode may be 42% or less of the area of ​​the transfer laminate in contact with at least one surface of the electrode active material layer. Specifically, the area of ​​the lithium by-product layer may be 42% or less of the total area of ​​the lithium metal layer transferred to the electrode active material layer.

[0145] When the electrode active material layer is prelithiated using the conventional transfer method, lithium by-products are formed on the electrode surface, and the area of ​​the by-products is approximately 44% or more of the area of ​​the electrode active material layer that is transferred to the lithium metal layer.

[0146] However, in an electrode for a lithium secondary battery according to one embodiment of the present specification, the area of ​​lithium by-products formed on the surface of the electrode is 42% or less, specifically, 40% or less, of the area of ​​the transferred laminate in contact with at least one surface of the electrode active material layer. In other words, it is possible to reduce the loss of lithium due to the generation of by-products such as lithium oxides or nitrides from the transferred lithium.

[0147] In addition, the lithium by-products can be confirmed through EDS (Energy-dispersive X-ray Spectroscopy) analysis using a SEM (Scanning Electron Microscope). Specifically, when EDS (Energy-dispersive X-ray Spectroscopy) analysis is performed using a SEM (Scanning Electron Microscope), nitrogen (N) is 3% or more and oxygen (O) is 75% or more.

[0148] That is, according to another embodiment of the present specification, an electrode for a lithium secondary battery includes an electrode current collector layer, an electrode active material layer having a lithium metal layer transferred thereto, and a lithium by-product layer, wherein the lithium by-product layer has nitrogen (N) of 3% or more and oxygen (O) of 75% or more when analyzed by EDS (Energy-dispersive X-ray Spectroscopy) using a SEM (Scanning Electron Microscope), and the area of ​​the lithium by-product layer with respect to the total area of ​​the lithium metal layer transferred to the electrode active material layer may be 42% or less.

[0149] In another embodiment of the present specification, the pre-lithiation capacity per unit area of ​​the electrode for a lithium secondary battery produced by the above-mentioned production method may be 20% or less, specifically 15% or less, of the capacity per unit area of ​​the electrode.

[0150] The pre-lithiation capacity per unit area is the capacity of lithium added to the electrode by pre-lithiation, and when the pre-lithiation capacity satisfies the above range, it is possible to compensate for the irreversible capacity of the electrode while balancing with the capacity of the negative electrode or positive electrode.

[0151] In addition, a lithium secondary battery according to an embodiment of the present specification includes the above-described lithium secondary battery electrode, a separator, and an electrolyte, wherein the lithium secondary battery electrode is at least one of the positive electrode and the negative electrode. Since the negative electrode has been described above, detailed description thereof will be omitted.

[0152] 1 is a diagram showing a laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of the present specification. Specifically, a negative electrode for a lithium secondary battery 100 including a negative electrode active material layer 20 on one surface of a negative electrode current collector layer 10 can be seen. While FIG. 1 shows the negative electrode active material layer formed on one surface of the negative electrode current collector layer, it may also be formed on both surfaces of the negative electrode current collector layer.

[0153] 2 is a diagram showing a laminated structure of a lithium secondary battery according to an embodiment of the present disclosure. Specifically, a lithium secondary battery anode 100 including an anode active material layer 20 on one side of an anode current collector layer 10 can be seen, and a lithium secondary battery cathode 200 including a cathode active material layer 40 on one side of a cathode current collector layer 50 can be seen, and the lithium secondary battery anode 100 and the lithium secondary battery cathode 200 are stacked with a separator 30 sandwiched between them. In this case, at least one of the lithium secondary battery anode and cathode may be manufactured according to a manufacturing method according to an embodiment of the present disclosure.

[0154] Fig. 3 is a flowchart showing a method for manufacturing an electrode for a lithium secondary battery according to one embodiment of the present specification. Specifically, (a) of Fig. 3 shows the method for manufacturing an electrode for a lithium secondary battery, including 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 the electrode active material layer so that the lithium metal layer is in contact with the electrode active material layer.

[0155] FIG. 3(b) shows a method for manufacturing an electrode for a lithium secondary battery, the method including the steps of: preparing a transfer laminate (S1) including a lithium metal layer, a release layer, and a substrate layer; laminating the transfer laminate onto the electrode active material layer (S21) so 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 (S22); and, after separating the substrate layer, forming two or more holes in at least one of the lithium metal layer and the release layer (S23).

[0156] FIG. 3(c) shows a method for manufacturing an electrode for a lithium secondary battery, the method including: 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 the electrode active material layer so that the lithium metal layer is in contact with the electrode active material layer.

[0157] In this regard, the method for manufacturing an electrode for a lithium secondary battery according to an embodiment of the present specification may further include a step (not shown) of providing an electrode active material layer on at least one surface of the electrode current collector layer, which may be performed before S1, simultaneously with S1, between S1 and S2, or between S1 and S21, but there is no limitation thereon.

[0158] 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 containing the positive electrode active material.

[0159] The positive electrode current collector layer in the positive electrode is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector layer typically has a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the positive electrode current collector layer to enhance adhesion of the positive electrode active material. For example, the positive electrode current collector layer may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0160] The positive electrode active material according to one embodiment of the present specification may include one or more selected from the group consisting of lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, lithium aluminum oxide, and lithium composite oxides that are a combination thereof.

[0161] Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2) or a compound substituted with one or more transition metals; a lithium iron oxide such as LiFe3O4; 1+c1 Mn 2-c1 O4 (0≦c1≦0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented by the chemical formula LiMnO2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and 0.01≦c2≦0.5 is satisfied); 2-c3 M c3Examples of the lithium manganese composite oxide include, but are not limited to, lithium manganese composite oxides represented by Li2Mn3MO8 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≦c3≦0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); or LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion. The positive electrode may be lithium metal (Li-Metal).

[0162] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the above-mentioned positive electrode active material.

[0163] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without any particular limitation as long as it does not cause chemical changes in the constructed battery and has electronic conductivity. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These may be used alone or in combination of two or more.

[0164] The positive electrode binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination.

[0165] The solvent used in the positive electrode composition slurry may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. These may be used alone or in combination. The amount of solvent used is sufficient to dissolve or disperse the active material, conductive material, and binder, and to provide a viscosity that allows excellent thickness uniformity when applied to produce positive and negative electrodes, taking into consideration the coating thickness and production yield of the slurry. Alternatively, the positive and negative electrodes may be fabricated by casting the active material layer-forming composition on a separate support, peeling it off from the support, and laminating the resulting film on a current collector layer.

[0166] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without particular limitations. In particular, a separator that exhibits low resistance to ion migration in the electrolyte and excellent electrolyte humidification is preferred. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material may be used, and may be used in a single-layer or multi-layer structure.

[0167] Examples of the electrolyte include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing lithium secondary batteries, but are not limited to these.

[0168] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0169] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methylpyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0170] In particular, among the carbonate-based organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate are preferably used because they are high-viscosity organic solvents with high dielectric constants and can effectively dissociate lithium salts. When such cyclic carbonates are mixed with linear carbonates such as dimethyl carbonate and diethyl carbonate, which have low viscosity and low dielectric constants, in an appropriate ratio, an electrolyte solution having high electrical conductivity can be prepared, and these cyclic carbonates are more preferably used.

[0171] The metal salt can be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, the anion of the lithium salt can be F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3- , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more selected from the group consisting of:

[0172] In addition to the components of the electrolytic solution, the electrolyte may further contain one or more additives, such as a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the battery's life characteristics, suppressing a decrease in battery capacity, and improving the battery's discharge capacity.

[0173] A battery module or a battery pack according to an embodiment of the present specification may include the above-described lithium secondary battery.

[0174] A battery pack according to another embodiment of the present specification may include a battery module including the above-described lithium secondary battery.

[0175] The lithium secondary batteries according to the embodiments of the present specification stably exhibit excellent discharge capacity, output characteristics, and cycle performance, and therefore can be used as power sources for portable devices such as mobile phones, laptops, and digital cameras, as well as medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. For example, the battery modules or battery packs can be used as power sources 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); or power storage systems. [Example]

[0176] Below, preferred examples are shown to help understand the present invention, but the following examples are merely illustrative of the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present description, and it is natural that such changes and modifications fall within the scope of the appended claims.

[0177] <Production example> [Example 1] A negative electrode active material layer composition was prepared by mixing a silicon-based active material (average particle size (D50): 4 μm), SWCNTs, and a polyacrylamide binder in a weight ratio of 80:10:10. The negative electrode slurry was prepared by adding the resulting mixture to distilled water as a solvent for forming the negative electrode slurry (solid concentration: 30 wt%).

[0178] The mixing method was as follows: the conductive material, binder, and water were dispersed using a homomixer at 2500 rpm for 30 minutes, and then the active material was added and dispersed at 2500 rpm for 30 minutes to prepare the negative electrode slurry.

[0179] The negative electrode slurry was applied to both sides of a copper current collector (thickness: 8 μm) as a negative electrode current collector at 8 mAh / cm.2 The coated layer was rolled and dried in a vacuum oven at 130° C. for 10 hours to form a negative electrode active material layer (thickness: 30 μm).

[0180] A solution containing polymethylmethacrylate (PMMA) was coated on a PET substrate layer (thickness: 25 μm) to form a release layer (thickness: 0.5 μm), and a lithium metal layer (thickness: 6.2 μm) was deposited on top of the release layer using physical vapor deposition (PVD) to prepare a transfer laminate (thickness: 32.2 μm). The lithium metal layer was then brought into contact with the negative electrode active material layer so that it faced the negative electrode active material layer, and the transfer laminate (1.27 mAh / cm) was obtained. 2 After removing the PET substrate layer (i.e., after transfer), two or more holes with a minimum distance between holes of 0.9 cm were formed on the surface to a depth equivalent to the thickness of the release layer.

[0181] [Example 2] A prelithiated electrode of Example 2 was prepared in the same manner as in Example 1, except that the shortest distance between holes in the negative electrode of Example 1 was 0.2 cm.

[0182] [Comparative Example 1] A prelithiated electrode of Comparative Example 1 was prepared in the same manner as in Example 1, except that no holes were formed in the negative electrode of Example 1.

[0183] Comparative Example 2 A prelithiated electrode of Comparative Example 2 was prepared in the same manner as in Example 1, except that the shortest distance between holes in the negative electrode of Example 1 was 1.5 cm.

[0184] [Example 3] A prelithiated electrode of Example 3 was prepared in the same manner as in Example 1, except that the shortest distance between holes in the negative electrode of Example 1 was 0.1 cm.

[0185] [Example 4] A prelithiated electrode of Example 4 was prepared in the same manner as in Example 1, except that the shortest distance between holes in the negative electrode of Example 1 was 0.05 cm.

[0186] [Example 5] A prelithiated electrode of Example 5 was prepared in the same manner as in Example 1, except that the shortest distance between holes in the negative electrode of Example 1 was 0.04 cm.

[0187] Comparative Example 3 A prelithiated electrode of Comparative Example 3 was prepared in the same manner as in Example 1, except that the shortest distance between holes in the negative electrode of Example 1 was 0.02 cm.

[0188] Comparative Example 4 A prelithiated electrode of Comparative Example 4 was prepared in the same manner as in Example 1, except that the shortest distance between holes in the negative electrode of Example 1 was 0.01 cm.

[0189] <Experimental Example 1> After pre-lithiation is complete, the areas where white by-products have formed on the electrode surface have a different color and shade from the background, as can be seen in Figure 4. Specifically, Figure 4 is a photograph showing the pre-lithiated electrode surface after the transfer laminate has been transferred and the base layer and release layer have been removed using tape. To confirm that the white color on the electrode surface is a by-product in the form of lithium oxide, an EDS analysis of elements (particularly nitrogen and oxygen) in each area was performed using an SEM (JSM-7610F) and the results are shown in Table 1 below.

[0190] [Table 1]

[0191] From Table 1, it can be seen that the nitrogen (N) and oxygen (O) contents are high in region A in FIG. 4, and this indicates that this region has turned white due to the formation of lithium nitride and oxide.

[0192] On the other hand, areas B and C, which are black like the background, show low nitrogen (N) and oxygen (O) contents. The purple area is the same as the black area, and the purple area is the color of the release layer that was transferred along with the lithium on the surface, while the black area is the color of the state where the release layer was removed using tape.

[0193] The area of ​​the by-product region on the electrode surface can be calculated using the difference in shading. Photographs of the electrode surfaces of Examples 1 and 2 and Comparative Examples 1 and 2 prepared according to the above preparation examples are shown in Figure 5. The amount of by-product formed on the surface of each electrode was calculated using the above method and is listed in Table 2 below.

[0194] [Table 2]

[0195] As can be seen from FIG. 5, the formation of by-products was significantly reduced around the pores formed on the electrode surfaces of Examples 1 and 2, while white by-products in the form of lithium oxides were widely formed on the electrode surfaces of Comparative Example 1, where no pores were formed, and Comparative Example 2, where the shortest distance between pores was 1.5 cm.

[0196] Specifically, as can be seen from Table 2, the area of ​​the by-products formed on the electrode surface in Examples 1 and 2 was only 41% or less of the area transferred to the lithium metal layer, and it was confirmed that the area of ​​the by-products was significantly reduced compared to Comparative Example 1 in which no holes were formed on the electrode surface and Comparative Example 2 in which the shortest distance between holes was 1.5 cm.

[0197] <Experimental Example 2> In the following, in order to confirm that the loss of lithium metal to be used for prelithiation increases as the shortest distance between pores becomes narrower, the prelithiation electrodes of Examples 2 to 5 and Comparative Examples 3 and 4 were measured at 1 cm 2The area ratio of pores with the shortest distance between pores and the longest diameter of 50 μm in each square was calculated and shown in Table 3 below.

[0198] In this case, 1 cm 2 The longest diameter of all holes in the square is 50 μm, and the longest diameter of all holes in the square is 1 cm 2 The number of holes in the square was calculated based on the shortest distance between adjacent holes, and the area ratio occupied by the holes was calculated using the following formula A.

[0199] [Formula A] Area ratio (%) = (area of ​​one hole (cm 2 ))×(1cm 2 (number of holes in a square) / (area of ​​a square 1cm 2 ) x 100

[0200] [Table 3]

[0201] According to Table 3, in the electrodes of Examples 2 to 5, in which the shortest distance between adjacent pores is 0.04 cm or more, the shortest distance between adjacent pores becomes narrower and the area ratio occupied by pores increases, resulting in less lithium metal loss and easier dissipation of heat generated during pre-lithiation. However, in the case of Comparative Examples 3 and 4, the shortest distance between adjacent pores is significantly narrower at less than 0.04 cm, resulting in a four-fold increase in the area ratio occupied by pores compared to Examples 2 to 5. As a result, the amount of lithium metal lost without being used in pre-lithiation is significantly increased.

[0202] In conclusion, the electrode manufacturing method according to the present specification can minimize the loss of lithium metal to be used during prelithiation by forming two or more holes with a shortest distance between the holes of 0.04 cm or more and 1 cm or less, and can suppress the formation of lithium by-products on the electrode surface by releasing heat caused by prelithiation. [Explanation of symbols]

[0203] 10 Negative electrode current collector layer 20...Negative electrode active material layer 30...Separation membrane 40...Cathode active material layer 50 Positive electrode current collector layer 100 ···Negative electrode for lithium secondary battery 200 ···Positive electrode for lithium secondary battery

Claims

1. providing a transfer laminate comprising 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 the electrode active material layer so that the lithium metal layer is in contact with the electrode active material layer; Including, At least one of the lithium metal layer and the release layer transferred to at least one surface of the electrode active material layer has two or more holes formed therein; In the method for manufacturing an electrode for a lithium secondary battery, the shortest distance between adjacent holes is 0.04 cm or more and 1 cm or less.

2. The method for producing an electrode for a lithium secondary battery according to claim 1 , wherein the longest diameter of the two or more pores is 5 μm or more and 50 μm or less.

3. 2. The method for producing an electrode for a lithium secondary battery according to claim 1, wherein the shortest distance between the adjacent holes is 0.2 cm or more and 0.9 cm or less.

4. The step of transferring the lithium metal layer and the release layer to at least one surface of the electrode active material layer includes: laminating the transfer laminate onto the electrode active material layer so that the lithium metal layer contacts at least one surface of the electrode active material layer; separating the substrate layer from the release layer; forming the two or more holes in at least one of the lithium metal layer and the release layer after separating the substrate layer; The method for producing an electrode for a lithium secondary battery according to claim 1, comprising:

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

6. 2. The method for producing an electrode for a lithium secondary battery according to claim 1, wherein the lithium metal layer has a thickness of 1 μm or more and 8 μm or less.

7. Before transferring the lithium metal layer and the release layer to at least one surface of the electrode active material layer, The method of claim 1 , further comprising the step of coating at least one surface of an electrode current collector layer with an electrode composition slurry to form the electrode active material layer.

8. 2. The method for producing an electrode for a lithium secondary battery according to claim 1, wherein the electrode active material layer comprises 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 produced by the method according to any one of claims 1 to 8.

10. 10. The electrode for a lithium secondary battery according to claim 9, wherein an area of ​​lithium by-products formed on the surface of the electrode for a lithium secondary battery is 42% or less of an area of ​​the transfer laminate in contact with at least one surface of the electrode active material layer.

11. an electrode current collector layer; an electrode active material layer to which the lithium metal layer has been transferred; a lithium by-product layer; Including, The lithium by-product layer contains 3% or more of nitrogen (N) and 75% or more of oxygen (O) when analyzed by EDS (Energy-dispersive X-ray Spectroscopy) using a SEM (Scanning Electron Microscope), An electrode for a lithium secondary battery, wherein the area of ​​the lithium by-product layer is 42% or less of the total area of ​​the lithium metal layer transferred to the electrode active material layer.

12. The electrode for a lithium secondary battery according to claim 9 ; A separation membrane; Electrolytes, A lithium secondary battery comprising:

13. A battery module comprising the lithium secondary battery according to claim 12.

14. A battery pack comprising the lithium secondary battery according to claim 12.

15. A battery pack comprising the battery module according to claim 13.

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