Transfer laminate, method for prelithiation of electrodes for lithium secondary batteries, and lithium secondary batteries including the electrodes

Abstract

The present application relates to a transfer laminate, a method for prelithiation of an electrode for a lithium secondary battery, and a lithium secondary battery including the electrode.

Description

[Technical Field]

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0010583, filed with the Korean Intellectual Property Office on January 25, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present application relates to a transfer laminate, a method for prelithiation of an electrode for a lithium secondary battery, 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 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] As technological development and demand for mobile devices increase, the demand for secondary batteries as energy sources 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.

[0006] Generally, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode contains a negative electrode active material that inserts and extracts lithium ions from the positive electrode. The negative electrode active material may be silicon-based particles with a high discharge capacity.

[0007] Generally, carbon materials such as graphite are used for the negative electrode of lithium secondary batteries, and the theoretical capacity density of carbon is 372 mAh / g (833 mAh / cm3 ) Therefore, in order to improve the energy density of the anode, silicon (Si), tin (Sn), and their oxides and alloys, which are alloyed with lithium, are being considered as anode materials. Among these, silicon-based materials have attracted attention due to their low cost and high capacity (4200mAh / g).

[0008] However, the use of silicon-based negative electrode active materials poses the problem of high initial irreversible capacity. During 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 then released from the negative electrode and returned to the positive electrode during discharge. However, with silicon-based negative electrode active materials, volume changes and surface side reactions are so severe that much of the lithium inserted into the negative electrode during initial charging cannot return to the positive electrode, resulting in a high initial irreversible capacity. This high initial irreversible capacity leads to a rapid decrease in battery capacity and cycle life.

[0009] To solve the above problems, a method of prelithiating a silicon negative electrode containing a silicon-based negative electrode active material is known. Known prelithiation methods include a method of preparing an electrode after lithiating the negative electrode by a physical / chemical method such as electroplating, lithium metal transfer, or lithium metal vapor deposition, and a method of electrochemically prelithiating the negative electrode.

[0010] Conventional electrochemical processes require a wet process in an electrolyte, which poses risks such as fire and explosion, making it necessary to carefully control an inert environment. Creating this environment requires difficult control of conditions, such as moisture control using inert gas in the chamber where the electrochemical process is performed. Furthermore, uniform control of the initial irreversible capacity requires the electrochemical process to be performed at the slowest possible rate, which increases production costs.

[0011] In the lithium metal transfer process, which is another method, it is difficult to transfer lithium metal safely and easily, and lithium is not transferred from the transfer laminate, or even if it is transferred, the highly reactive lithium metal immediately begins to react with the negative electrode active material, causing problems such as particle cracking on the surface of the negative electrode active material layer.

[0012] In addition, to control the reactivity of lithium metal, a release layer is transferred at the same time as the lithium metal is transferred, but the adhesive strength of the release layer increases due to the temperature rise after pre-lithiation, making it difficult to remove, which can lead to an increase in the resistance of the battery.

[0013] Therefore, research is needed into transfer laminates that are safer and more efficient for prelithiation and that allow lithium to be prelithiated uniformly within the electrode active material layer. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-080971 Summary of the Invention [Problem to be solved by the invention]

[0015] The lithium metal transfer process includes a process of transferring lithium metal from a transfer laminate to the top of an electrode active material layer during a pre-lithiation process. Through research, it was confirmed that adjusting the temperature when depositing lithium metal on the top of the transfer laminate can adjust the adhesive strength conditions of the transfer laminate, thereby facilitating the transfer of lithium metal.

[0016] The present application relates to a transfer laminate, a method for prelithiation of an electrode for a lithium secondary battery, and a lithium secondary battery including the electrode. [Means for solving the problem]

[0017] One embodiment of the present specification provides a transfer laminate comprising a substrate layer; and a release layer formed in direct contact with one surface of the substrate layer; wherein the release layer contains lithium metal formed on the surface opposite to the surface in contact with the substrate layer, the release layer has a thickness of 1 nm or more and 1 μm or less, the transfer laminate has a thickness of 5 μm or more and 120 μm or less, and the release layer is made of a non-metallic material.

[0018] In yet another embodiment, there is provided a method for pre-lithiation of an electrode for a lithium secondary battery, comprising the steps of: forming an electrode current collector layer and an electrode active material layer on one or both sides of the electrode current collector layer; and transferring lithium metal onto the electrode active material layer, wherein the step of transferring the lithium metal comprises the steps of: preparing a transfer laminate according to the present application; laminating the transfer laminate on the electrode active material layer so that a surface of the lithium metal opposite to a surface that contacts the release layer is in contact with a surface of the electrode active material layer opposite to a surface that contacts the electrode current collector layer; and removing the base layer.

[0019] Finally, in one embodiment of the present application, there is provided a lithium secondary battery comprising: a positive electrode for a lithium secondary battery; a negative electrode for a lithium secondary battery; a separator provided between the positive electrode and the negative electrode; and an electrolyte, wherein at least one of the positive electrode for the lithium secondary battery and the negative electrode for the lithium secondary battery is a lithium secondary battery electrode that has been prelithiated by the method of the present application. [Effects of the Invention]

[0020] A transfer laminate according to one embodiment of the present invention is characterized in that the thickness of the release layer is 1 nm or more and 1 μm or less, and the thickness of the transfer laminate is 5 μm or more and 120 μm or less. When the release layer and the transfer laminate including the same have the above thicknesses, heat generated when lithium metal is laminated on the transfer laminate is easily released, the change in adhesive strength of the release layer is small, and the removal of the base layer during the transfer of lithium metal is easy.

[0021] In addition, the manufacturing method of the transfer laminate includes a step of adjusting a deposition temperature during the step of depositing lithium metal, and the step of adjusting the deposition temperature adjusts the temperature of the surface opposite to the surface on which lithium metal is deposited to between -30°C and 10°C, and adjusts the temperature of the transfer laminate to 80°C or less, thereby removing heat generated during the lithium metal deposition process through cooling and minimizing changes in adhesive strength of the release layer.

[0022] That is, the present invention is for easily transferring lithium metal onto an electrode active material layer, and is characterized by including a thickness adjustment and cooling step of the transfer laminate, which facilitates dissipation of heat generated during deposition of lithium metal and maintains low adhesive strength of the release layer.

[0023] When the above conditions are met, the substrate layer can be smoothly removed in the pre-lithiation process including the transfer laminate.

[0024] That is, the transfer laminate according to the present application has an adjusted adhesive strength at the interface between the base layer and the release layer, which improves lithium transferability during the pre-lithiation step, thereby suppressing the generation of by-products during the pre-lithiation step. [Brief explanation of the drawings]

[0025] [Figure 1] 1A to 1C are diagrams illustrating a process for transferring lithium metal to a negative electrode for a lithium secondary battery according to one embodiment of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0026] Prior to describing the present invention, some terms will first be defined. In this specification, when a part is said to "comprise" a certain component, this means that it may further include other components, rather than excluding other components, unless specifically stated to the contrary.

[0027] In this specification, "p to q" means a range of "not less than p and not more than q." 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 the present application, the BET specific surface area may mean the specific surface area measured by the above-mentioned measurement method.

[0028] 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 by particle size. That is, D50 is the particle size at the 50% point in the cumulative particle number distribution by particle size, D90 is the particle size at the 90% point in the cumulative particle number distribution by particle size, and D10 is the particle size at the 10% point in the cumulative particle number distribution by particle size. Meanwhile, particle size distribution 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 particle size distribution is calculated by measuring the difference in diffraction patterns due to particle size when the particles pass through a laser beam.

[0029] In this specification, when a polymer contains a certain monomer as a monomer unit, it means that the monomer is involved in a polymerization reaction and is contained as a repeating unit in the polymer. In this specification, when a polymer contains a monomer, this is interpreted as the same as when a polymer contains a monomer as a monomer unit.

[0030] It is understood that the term "polymer" is used in the broad sense herein to include copolymers unless "homopolymer" is specifically stated.

[0031] In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are polystyrene-equivalent molecular weights measured by gel permeation chromatography (GPC) using commercially available monodisperse polystyrene polymers (standard samples) with various degrees of polymerization that are commercially available for molecular weight measurement as standard substances. In this specification, molecular weight means weight average molecular weight unless otherwise specified.

[0032] The present invention will now be described in detail with reference to the accompanying drawings so that those skilled in the art can easily practice the present invention. However, the present invention may be embodied in various different forms and is not limited to the following description.

[0033] One embodiment of the present specification provides a transfer laminate comprising a substrate layer; and a release layer formed in direct contact with one surface of the substrate layer; wherein the release layer contains lithium metal formed on the surface opposite to the surface in contact with the substrate layer, the release layer has a thickness of 1 nm or more and 1 μm or less, the transfer laminate has a thickness of 5 μm or more and 120 μm or less, and the release layer is made of a non-metallic material.

[0034] A transfer laminate according to one embodiment of the present invention is characterized in that the thickness of the release layer is 1 nm or more and 1 μm or less, and the thickness of the transfer laminate is 5 μm or more and 120 μm or less. When the release layer and the transfer laminate including the same have the above thicknesses, heat generated when lithium metal is laminated on the transfer laminate is easily released, the change in adhesive strength of the release layer is small, and the removal of the base layer during the transfer of lithium metal is easy.

[0035] In one embodiment of the present application, a transfer laminate is provided in which, after the transfer laminate is left at 80°C for 2 hours, the first adhesive strength of the surface where the base layer and the release layer contact is 10 gf / inch or more and 150 gf / inch or less.

[0036] In another embodiment, the first adhesive strength may be in the range of 10 gf / inch or more and 150 gf / inch or less, preferably 30 gf / inch or more and 130 gf / inch or less, and more preferably 50 gf / inch or more and 110 gf / inch or less.

[0037] The first adhesive strength can be measured using a Nitto 31B tape as a peel strength tester at a 90° angle and a peel rate of 300 mm / min.

[0038] When the first adhesive strength of the contact surface between the base layer and the release layer of the transfer laminate satisfies the above range, the release layer and the base layer can be easily separated during the subsequent pre-lithiation process, resulting in excellent transferability of lithium metal and the release layer onto the negative electrode active material layer. In particular, the first adhesive strength range can be satisfied, which simultaneously satisfies the thickness range of the release layer and the thickness range of the transfer laminate described below, thereby providing excellent lithium metal transferability.

[0039] The first adhesive strength may be measured under an external pressure condition of 5 kgf / cm to 150 kgf / cm. This may refer to the pressure conditions when laminating the transfer laminate onto the electrode active material layer. That is, the lamination conditions may refer to the conditions after laminating the transfer laminate on the electrode active material layer, and then carrying out the process at a running speed of 1 mpm to 50 mpm with an external pressure of 5 kgf / cm to 150 kgf / cm applied between two rolls. In particular, the unit kgf / cm is defined as the load between the two rolls divided by the unit length of the sample. The first adhesive strength satisfies the above range, and the substrate layer can be easily peeled off even under the lamination conditions.

[0040] In one embodiment of the present application, a transfer laminate is provided in which a first adhesive strength at the surface where the base layer and the release layer contact is lower than the adhesive strength at the surface where the release layer contacts the lithium metal.

[0041] The first adhesive strength at the interface between the substrate layer and the release layer satisfies a range lower than the adhesive strength at the interface between the release layer and the lithium metal, thereby preventing reverse transfer problems during the pre-lithiation process. Furthermore, since the adhesive strength range is satisfied, not only is lithium metal transferred alone, but both the release layer and lithium metal are transferred onto the electrode active material layer, and the release layer also serves as a protective layer that prevents highly reactive lithium metal from reacting in air.

[0042] Furthermore, the release layer may cause a problem of increased resistance when later included in a battery, and it is a primary object of the present invention that the release layer be easily removed after prelithiation.

[0043] In one embodiment of the present application, the substrate layer may be any layer that can withstand process conditions such as high temperatures in the step of depositing lithium metal and that can prevent a reverse peeling problem in which lithium metal is transferred onto the substrate layer during a winding process for transferring the deposited lithium metal.

[0044] In particular, the thickness of the substrate layer according to the present application may be in the range of 1 μm to 50 μm, specifically 10 μm to 40 μm, and more specifically 15 μm to 30 μm. When the substrate layer satisfies this thickness range, heat dissipation through the substrate layer during lithium deposition is facilitated, and changes in adhesive strength of the release layer can be minimized.

[0045] Specifically, in one embodiment of the present application, the base layer may be at least one selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), poly(methylmethacrylate) (PMMA), polypropylene, polyethylene, and polycarbonate.

[0046] In one embodiment of the present application, the thickness of the lithium metal may be 1 μm or more and 10 μm or less, and preferably 3 μm or more and 10 μm or less.

[0047] When the thickness of the lithium metal satisfies the above range, the lithium metal can be efficiently transferred to the electrode active material layer side, and reverse transfer can be prevented.

[0048] In one embodiment of the present application, a release layer is included on the surface of the transfer laminate that comes into contact with the substrate layer and the lithium metal in order to improve the peelability of the lithium metal, ensure transferability to the electrode active material layer, and serve as a protective layer after the lithium metal is transferred.

[0049] That is, the substrate layer may have a release layer formed on at least one surface thereof, or may have release layers formed on both surfaces thereof. The release layer can prevent the problem of reverse peeling, in which lithium metal is transferred onto the substrate layer during a winding process for transferring the deposited lithium metal to the electrode, and can also facilitate separation of the substrate layer after the lithium metal is transferred onto the electrode active material layer.

[0050] In one embodiment of the present application, the thickness of the release layer may be 1 nm or more and 1 μm or less.

[0051] In another embodiment, the thickness of the release layer may be in the range of 1 nm or more and 1 μm or less, preferably 100 nm or more and 1 μm or less, and more preferably 500 nm or more and 1 μm or less.

[0052] In one embodiment of the present application, the thickness of the transfer laminate may be in the range of 5 μm or more and 120 μm or less, specifically 6 μm or more and 50 μm or less, and more specifically 15 μm or more and 40 μm or less.

[0053] The release layer and transfer laminate satisfy the above-described thickness range and a specific first adhesive strength range. In other words, while heat generated during lithium metal deposition can increase the adhesive strength of the release layer, physically adjusting the thickness as described above facilitates heat release and prevents the increase in adhesive strength of the release layer. This facilitates removal of the substrate layer after lithium metal transfer and prevents problems such as the formation of by-products during prelithiation. Furthermore, the release layer has the above-described thickness range, which allows the adhesive strength range with the top of the prelithiated electrode to be adjusted to the lower limit of a certain range after prelithiation, preventing side reactions between the release layer and the electrode active material layer.

[0054] In one embodiment of the present application, there is provided a transfer laminate in which the release layer is made of a non-metallic material.

[0055] That is, in the case of a release layer containing a metal material, even if the thickness is adjusted as described above, the adhesive strength of the release layer will change due to heat conduction. However, as described above, when the release layer is made of a non-metallic material, the heat conduction to the release layer can be reduced, and an increase in the adhesive strength of the release layer can be prevented.

[0056] The release layer may contain at least one selected from the group consisting of silicon-modified polyester in which silicon chains are graft-bonded to a polyester main chain, acrylic resin, Si, melamine, and fluorine.

[0057] In one embodiment of the present application, the release layer may comprise polymethyl methacrylate (PMMA).

[0058] One embodiment of the present application provides a pre-lithiation method for an electrode for a lithium secondary battery, comprising the steps of: forming an electrode current collector layer and an electrode active material layer on one or both sides of the electrode current collector layer; and transferring lithium metal onto the electrode active material layer, wherein the step of transferring the lithium metal comprises the steps of: preparing a transfer laminate according to the present application; laminating the transfer laminate on the electrode active material layer so that a surface of the lithium metal opposite to a surface that contacts the release layer is in contact with a surface of the electrode active material layer opposite to a surface that contacts the current collector layer; and removing the base layer.

[0059] 1 is a diagram showing a process for transferring lithium metal to a negative electrode for a lithium secondary battery according to one embodiment of the present application. Specifically, the process shows a step of laminating a transfer laminate 100, which is formed by sequentially laminating a substrate layer 10, a release layer 35, and lithium metal 20, on a lithium secondary battery electrode 200 formed from an electrode current collector layer 40 and an electrode active material layer 30, and then removing the substrate layer 10 from the transfer laminate 100.

[0060] The specific details of the pre-lithiation method for a lithium secondary battery electrode of the present invention will be described below.

[0061] In one embodiment of the present application, there is provided a method for pre-lithiation of an electrode for a lithium secondary battery, wherein the step of preparing a transfer laminate includes the steps of: preparing a substrate layer provided with a release layer; and depositing lithium metal on the substrate layer provided with the release layer; and the step of depositing lithium metal includes the step of adjusting a deposition temperature, in which the step of adjusting the deposition temperature includes adjusting the temperature of a surface opposite to the surface on which the lithium metal is deposited to between −30° C. and 10° C., and forming the temperature of the transfer laminate to 80° C. or less.

[0062] During lithium metal deposition, the temperature of the surface on which the substrate layer is held is controlled for a transfer laminate having a substrate layer and a release layer stacked thereon. This surface can be defined as the opposite surface of the surface on which lithium metal is deposited, or as the opposite surface of the substrate layer that contacts the release layer. That is, the temperature of the surface on which the substrate layer is attached (held) during lithium metal deposition can be specifically controlled within a range of −30°C to 10°C, with the temperature of the surface on which lithium metal is deposited varying depending on the thickness of the transfer laminate. Consequently, maintaining the temperature of the transfer laminate at 80°C or below is equivalent to maintaining the temperature of the surface on which lithium metal is deposited at 80°C or below. The objective of the present application is to maintain the surface temperature on which lithium metal is deposited low while minimizing changes in the adhesive strength of the release layer and ensuring the transferability of lithium metal, while satisfying the above-mentioned thickness range.

[0063] In the past, it was impossible to control the heat generated when depositing lithium metal on a transfer laminate, which resulted in an increase in the adhesive strength of the release layer when depositing lithium metal on the transfer laminate. To solve this problem, the pre-lithiation method according to the present application includes a step of adjusting the temperature during lithium metal deposition, and the specific conditions are adjusted as described above. In this way, by lowering the temperature during the deposition process and adjusting the thicknesses of the transfer laminate and the release layer as described above, heat release can be made easier, and as a result, the adhesive strength of the release layer does not change, which is a major feature.

[0064] In one embodiment of the present application, the deposition method for depositing the lithium metal on the substrate layer on which the release layer is formed may be selected from among, but not limited to, vacuum deposition, chemical vapor deposition (CVD), and physical vapor deposition, and various deposition methods used in the art may be used.

[0065] At this time, the lamination process can be carried out by applying a load of 5 kgf / cm to 500 kgf / cm to the lithium secondary battery electrode on which the transfer laminate is laminated, and then performing a roll pressing process. A subsequent process of removing the substrate layer is included, and by satisfying the range of adhesive strength according to the present application during removal, problems such as reverse transfer of lithium metal do not occur.

[0066] In one embodiment of the present application, 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, and various coating methods used in the art to form coating layers may be used.

[0067] In one embodiment of the present application, the electrode may be a negative electrode or a positive electrode. A method for prelithiating an electrode for a lithium secondary battery according to an embodiment of the present application may include forming an electrode current collector layer and an electrode active material layer on one or both sides of the electrode current collector layer.

[0068] In one embodiment of the present application, the step of forming the electrode current collector layer and an electrode active material layer on one or both surfaces of the electrode current collector layer comprises coating one or both surfaces of the electrode current collector layer with an electrode slurry containing an electrode active material layer composition, and the electrode active material layer composition includes at least one selected from the group consisting of an electrode active material; an electrode conductive material; and an electrode binder.

[0069] At this time, the electrode active material contains a silicon-based active material, and the silicon-based active material includes one or more selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), SiC, and Si alloys. A pre-lithiation method for an electrode for a lithium secondary battery is provided.

[0070] In one embodiment of the present application, the electrode may be a negative electrode, and the following describes an explanation regarding a pre-lithiation method for a negative electrode for a lithium secondary battery.

[0071] A pre-lithiation method for a negative electrode for a lithium secondary battery according to one embodiment of the present application may include a step of forming a negative electrode current collector layer and a negative electrode active material layer on one or both surfaces of the negative electrode current collector layer.

[0072] In one embodiment of the present application, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it has high conductivity without inducing a chemical change in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those surface-treated with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. can be used. Also, fine irregularities can be formed on the surface to strengthen the binding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc.

[0073] In one embodiment of the present application, the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, and the thickness of the negative electrode active material layer may be 20 μm or more and 500 μm or less.

[0074] However, the thickness can be variously deformed according to the type and use of the negative electrode used, and is not limited thereto.

[0075] In one embodiment of the present application, there is provided a method for pre-lithiation of an electrode for a lithium secondary battery, wherein the step of forming a negative electrode current collector layer and a negative electrode active material layer on one or both surfaces of the negative electrode current collector layer includes coating one or both surfaces of the negative electrode current collector layer with a negative electrode slurry including a negative electrode active material layer composition, and the negative electrode active material layer composition includes at least one selected from the group consisting of a silicon-based active material; a negative electrode conductive material; and a negative electrode binder.

[0076] In one embodiment of the present application, the negative electrode slurry may include a negative electrode active material layer composition; and a slurry solvent.

[0077] In one embodiment of the present application, the solid content of the negative electrode slurry may be 5% or more and 40% or less.

[0078] 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%.

[0079] 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 composition based on 100 parts by weight of the negative electrode slurry.

[0080] 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 particle aggregation phenomenon of the negative electrode active material layer composition is minimized, thereby enabling the negative electrode active material layer to be efficiently formed.

[0081] In one embodiment of the present application, the slurry solvent is not limited as long as it can dissolve the negative electrode active material layer composition, and specifically, distilled water can be used.

[0082] The negative electrode according to one embodiment of the present application can be formed by coating the negative electrode slurry on a negative electrode current collector layer and drying it.

[0083] Through the drying stage, the slurry solvent in the negative electrode slurry can be dried.

[0084] In one embodiment of the present application, the negative electrode active material layer composition may include at least one selected from the group consisting of a negative electrode active material, a negative electrode conductive material, and a negative electrode binder.

[0085] In one embodiment of the present application, a silicon-based active material can be used as the negative electrode active material, or a negative electrode containing a silicon-based active material and a carbon-based active material together can be used. In this case, a lithium secondary battery with improved performance such as cycle life characteristics can be manufactured.

[0086] In one embodiment of the present application, the silicon-based active material may include at least one selected from the group consisting of Si particles, SiOx (0 < x < 2), SiC, and Si alloys.

[0087] In one embodiment of the present application, the silicon-based active material includes one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x ≤ 2), and may include 70 parts by weight or more of the SiOx (x = 0) based on 100 parts by weight of the silicon-based active material.

[0088] In another embodiment, based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) may be included in an amount of 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, and may be included in an amount of 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less.

[0089] In one embodiment of the present application, particularly, pure silicon (Si) can be used as the silicon-based active material. Using pure silicon (Si) as the silicon-based active material may mean including pure Si particles (SiOx (x = 0)) not combined with other particles or elements within the above range when based on 100 parts by weight of the total silicon-based active material as described above.

[0090] 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 then 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 large initial irreversible capacity. This large initial irreversible capacity leads to a rapid decrease in battery capacity and cycle life.

[0091] In order to solve the above-mentioned problems, the present invention relates to a method for prelithiating the negative electrode of a lithium secondary battery to solve the initial irreversible capacity problem. Specifically, the prelithiation process involves a process for suppressing the generation of by-products so that lithium metal can be easily transferred from the transfer laminate during the lithium transfer process and lithium in the negative electrode active material layer can be uniformly prelithiated.

[0092] Meanwhile, the average particle size (D50) of the silicon-based active material of the present invention may be 5 μm to 10 μm, specifically 5.5 μm to 8 μm, and more specifically 6 μm to 7 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 negative electrode slurry is formed within an appropriate range. This allows for smooth dispersion of the particles constituting the negative electrode slurry. Furthermore, when the size of the silicon-based active material is equal to or greater than the lower limit of this range, the composite of the conductive material and the binder in the negative electrode slurry has an excellent contact area between the silicon particles and the conductive material, increasing the likelihood of maintaining a conductive network, and thereby increasing the capacity retention rate. On the other hand, when the average particle size is within this range, excessively large silicon particles are excluded, resulting in a smooth negative electrode surface, thereby preventing non-uniform current density during charge and discharge.

[0093] In one embodiment of the present application, the silicon-based active material generally has a characteristic BET specific surface area. The BET specific surface area of ​​the silicon-based active material is preferably 0.01 m 2 / g~150.0m 2 / g, more preferably 0.1m 2 / g~100.0m 2 / g, particularly preferably 0.2m 2 / g~80.0m 2 / g, most preferably 0.2m 2 / g~18.0m 2 / g. The BET specific surface area is determined in accordance with DIN 66131 (using nitrogen).

[0094] In one embodiment of the present application, the silicon-based active material can be, for example, in crystalline or amorphous form, and is preferably not porous. The silicon particles are preferably spherical or shard-like particles. Alternatively, but less preferably, the silicon particles may also have a fibrous structure or be in the form of a silicon-containing film or coating.

[0095] In one embodiment of the present application, the silicon-based active material may be present in an amount of 60 parts by weight or more based on 100 parts by weight of the negative electrode active material layer composition.

[0096] In yet another embodiment, the silicon-based active material may be included in an amount of 60 parts by weight or more, preferably 65 parts by weight or more, and more preferably 70 parts by weight or more, based on 100 parts by weight of the negative electrode active material layer composition, and may be included in an amount of 95 parts by weight or less, preferably 90 parts by weight or less, and more preferably 80 parts by weight or less.

[0097] The negative electrode active material layer composition according to the present application contains a conductive material and a 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 thus does not deteriorate the performance of the negative electrode even when the range is included, and has the characteristic of excellent output characteristics during charge and discharge.

[0098] In one embodiment of the present application, the silicon-based active material may have a non-spherical morphology, 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.

[0099] In this application, the circularity is determined by the following formula 1, where A is the area and P is the perimeter. [Formula 1] 4πA / P 2

[0100] While graphite-based compounds were typically used exclusively as anode active materials in recent years, attempts to incorporate silicon-based compounds to increase capacity have been increasing in response to the growing demand for high-capacity batteries. However, silicon-based compounds have limitations, such as their rapid volume expansion during the charge / discharge process 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.

[0101] In one embodiment of the present application, the negative electrode conductive material may include at least one selected from the group consisting of a dot-like conductive material, a sheet-like conductive material, and a linear conductive material.

[0102] In one embodiment of the present application, the dot-like conductive material can be used to improve the conductivity of the negative electrode and has conductivity without inducing chemical changes. 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, and preferably includes carbon black, which realizes high conductivity and has excellent dispersibility.

[0103] In one embodiment of the present application, the point-like conductive material has a BET specific surface area of ​​40 m 2 / g or more 70m 2 / g or less, preferably 45m 2 / g or more 65m 2 / g or less, more preferably 50m 2 / g or more 60m 2 / g or less.

[0104] In one embodiment of the present application, the particle size of the dotted conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 40 nm to 60 nm.

[0105] In one embodiment of the present application, the negative electrode conductive material may include a sheet conductive material.

[0106] The planar conductive material can improve conductivity by increasing surface contact between silicon particles in the negative electrode, and at the same time, can prevent the conductive path from being broken due to volume expansion, and is used as a concept including bulk conductive materials and plate-shaped conductive materials.

[0107] In one embodiment of the present application, the sheet conductive material may include at least one selected from the group consisting of platelet graphite, graphene, graphene oxide, and graphite flakes, and may be preferably platelet graphite.

[0108] In one embodiment of the present application, 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 this range, the sufficient particle size facilitates dispersion without excessively increasing the viscosity of the negative electrode slurry. Therefore, when dispersion is performed using the same equipment and time, the dispersion effect is excellent.

[0109] In one embodiment of the present application, the sheet conductive material provides a negative electrode active material layer composition having 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.

[0110] In one embodiment of the present application, 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.

[0111] In one embodiment of the present application, 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, the planar conductive material of the present application may be affected to some extent by dispersion in terms of electrode performance, and it may be particularly preferable to use a low-specific surface area planar conductive material that does not cause dispersion problems.

[0112] In one embodiment of the present application, the sheet conductive material has a BET specific surface area of ​​5 m 2 / g or more.

[0113] 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, preferably 5m 2 / g or more 300m 2 / g or less, more preferably 5m 2 / g or more 300m 2 / g or less.

[0114] 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, preferably 80m 2 / g or more 300m 2 / g or less, more preferably 100m 2 / g or more 300m 2 / g or less.

[0115] In another embodiment, the sheet conductive material is a sheet conductive material with a low specific surface area, and has a BET specific surface area of ​​5 m 2 / g or more 40m 2 / g or less, preferably 5m 2 / g or more 30m 2 / g or less, more preferably 5m 2 / g or more 25m 2 / g or less.

[0116] Other examples of anode conductive materials include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundled carbon nanotubes. The bundled carbon nanotubes may include multiple carbon nanotube units. Specifically, unless otherwise specified, the term "bundle type" refers to a secondary shape in which multiple carbon nanotube units are arranged side by side or entangled with their longitudinal axes aligned in substantially the same direction, forming a bundle or rope-like shape. The carbon nanotube units each have a cylindrical graphite sheet with a nanometer-sized diameter and an sp2 bonding structure. Depending on the angle and structure of the graphite sheet, the unit can exhibit conductive or semiconductive properties. Compared to entangled carbon nanotubes, the bundled carbon nanotubes can be more uniformly dispersed during anode fabrication, smoothly forming a conductive network within the anode, and improving the conductivity of the anode.

[0117] In one embodiment of the present application, 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 contained in an amount of 10 parts by weight or more and 40 parts by weight or less, preferably 10 parts by weight or more and 30 parts by weight or less, and more preferably 15 parts by weight or more and 25 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 application has a completely different structure from the conductive material used in the positive electrode. That is, the negative electrode conductive material according to the present application serves to secure the contact point between the silicon-based active materials, which undergo a large volume expansion of the electrode upon charging and discharging, while the positive electrode conductive material serves to provide a buffer during rolling while also imparting partial conductivity, and therefore has a completely different structure and role from the negative electrode conductive material of the present invention.

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

[0121] In one embodiment of the present application, the planar conductive material used as the negative electrode conductive 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 this application, the use of plate-like graphite as a conductive material means that it is processed into a planar or plate-like shape and used as a material to ensure a conductive path rather than to store or release lithium. In this case, the negative electrode active material contained therein has high capacity characteristics for storing and releasing lithium, and plays a role in storing and releasing all lithium ions transferred from the positive electrode.

[0124] Meanwhile, in the present application, the use of a carbon-based active material as an active material means that the carbon-based active material is processed into a dotted or spherical shape and is used as a material that plays a role in storing or releasing lithium.

[0125] That is, in one embodiment of the present application, the carbon-based active material, artificial graphite or natural graphite, has a BET specific surface area of ​​0.1 m 2 / g or more 4.5m 2 / g or less. The plate-shaped graphite, which is a planar conductive material, may have a planar BET specific surface area of ​​5 m 2 / g or more.

[0126] In one embodiment of the present application, 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, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which hydrogen is substituted with Li, Na, Ca, or the like, or may include various copolymers thereof.

[0127] The binder according to one embodiment of the present application plays a role in holding down the negative electrode active material and the negative electrode conductive material to prevent twisting and structural deformation of the negative electrode structure when the volume expansion and relaxation of the silicon-based active material occurs. As long as the binder fulfills this role, any of the general negative electrode binders can be applied, and specifically, an aqueous binder can be used, and more specifically, a PAM-based binder can also be used.

[0128] In one embodiment of the present application, the negative electrode binder may be contained in an amount of 30 parts by weight or less, preferably 25 parts by weight or less, and more preferably 20 parts by weight or less, or may be contained in an amount of 5 parts by weight or more, or 10 parts by weight or more, based on 100 parts by weight of the negative electrode active material layer composition.

[0129] In one embodiment of the present application, the electrode may be a positive electrode, and the following describes a method for pre-lithiation of a positive electrode for a lithium secondary battery, which is similar to the method for pre-lithiation of a negative electrode for a lithium secondary battery described above, except for the positive electrode.

[0130] A method for prelithiating an electrode for a lithium secondary battery according to an embodiment of the present application may include forming a positive electrode current collector layer and a positive electrode active material layer on one or both surfaces of the positive electrode current collector layer.

[0131] In one embodiment of the present application, the positive electrode current collector layer is not particularly limited as long as it does not induce 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, or the like can be used. The positive electrode current collector layer typically has a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the positive electrode current collector layer to enhance the adhesive strength of the positive electrode active material. 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.

[0132] The thickness of the positive electrode current collector layer may vary depending on the type and application of the negative electrode used, but is not limited thereto.

[0133] In one embodiment of the present application, there is provided a method for pre-lithiation of an electrode for a lithium secondary battery, wherein the step of forming a positive electrode current collector layer and a positive electrode active material layer on one or both surfaces of the positive electrode current collector layer includes coating one or both surfaces of the positive electrode current collector layer with a positive electrode slurry containing a positive electrode active material layer composition, and the positive electrode active material layer composition includes at least one selected from the group consisting of a positive electrode active material; a positive electrode conductive material; and a positive electrode binder.

[0134] In one embodiment of the present application, the content regarding the positive electrode slurry can be applied in the same manner as the content regarding the negative electrode slurry, except that it is a positive electrode.

[0135] In one embodiment of the present application, the positive electrode active material layer composition may include at least one selected from the group consisting of a positive electrode active material; a positive electrode conductive material; and a positive electrode binder.

[0136] The positive electrode active material may be a commonly used positive electrode active material, such as a layered compound or a compound substituted with one or more transition metals, such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2); 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 O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and 0.01≦c2≦0.3 is satisfied); 2-c3 M c3 Examples of suitable lithium manganese composite oxides 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); and LiMn2O4, in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion. The positive electrode may be Li metal.

[0137] 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 has electronic conductivity without undergoing chemical changes in the battery that is constructed. 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, and the like, and one or more of these may be used alone or in combination.

[0138] The positive electrode binder serves to improve adhesion between particles of the positive electrode active material 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, tetrafluoroethylene, 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.

[0139] In addition, the contents of the positive electrode active material, the positive electrode conductive material, and the positive electrode binder contained in the positive electrode active material layer composition may be the same as those applied to the negative electrode active material layer composition described above.

[0140] In one embodiment of the present application, the present invention may include a method for pre-lithiation of an electrode for a lithium secondary battery, the method comprising the step of transferring lithium metal onto the electrode active material layer.

[0141] Generally, the prelithiation process is a chemical or physical process of prelithiating lithium metal onto an electrode, and specifically, it can be carried out by a lithium metal transfer process, a lithium metal powder deposition process, an electrochemical process, or a lithium metal deposition process. The prelithiation process according to the present application may include a lithium metal transfer process.

[0142] The lithium metal transfer process has the advantage that highly reactive lithium metal can be transferred more stably to the upper part of the electrode active material layer. In this case, a process is required that can easily transfer lithium metal from the transfer laminate to the upper part of the electrode active material layer.

[0143] In one embodiment of the present application, the method may include the steps of: preparing the above-mentioned transfer laminate; laminating the transfer laminate onto the electrode active material layer so that the surface of the lithium metal opposite to the surface that contacts the release layer contacts the surface of the electrode active material layer opposite to the surface that contacts the electrode current collector layer; and removing the substrate layer.

[0144] In one embodiment of the present application, there is provided a step of laminating the transfer laminate onto the electrode active material layer such that a surface of the lithium metal opposite to a surface that contacts the release layer contacts a surface of the electrode active material layer opposite to a surface that contacts the current collector layer.

[0145] At this time, the lamination step may be performed under temperature conditions of 20° C. to 90° C. and pressure conditions of 5 kgf / cm to 500 kgf / cm.

[0146] After the lamination step, prelithiation of the electrode active material layer with highly reactive lithium metal can proceed.

[0147] In one embodiment of the present application, there is provided a method for prelithiating an electrode for a lithium secondary battery, comprising: prelithiating the electrode active material layer after the step of removing the base layer; wherein the step of prelithiating the electrode active material layer is performed within 30 minutes to 24 hours after transferring lithium metal.

[0148] In the conventional lithium metal transfer process, there is a problem that the substrate layer is difficult to peel off during the prelithiation process after lamination of the transfer laminate. As a result, prelithiation proceeds without the substrate layer being removed, and the heat generated during prelithiation is blocked by the substrate layer and not released, resulting in the formation of by-products on the surface during prelithiation of the lithium metal. The prelithiation method for a lithium secondary battery electrode according to the present application has the characteristics of being able to easily peel off the substrate layer immediately after lamination of the transfer laminate and suppressing the formation of by-products during prelithiation by adjusting the adhesive strength range as described above.

[0149] The step of prelithiating the electrode active material layer is carried out at 25° C. and 1 atm for 30 minutes to 24 hours.

[0150] The pre-lithiation step is a step of setting conditions for diffusing lithium metal into the electrode active material layer, and whether the pre-lithiation step is complete can be determined by whether lithium is completely removed from the upper part of the electrode active material layer.

[0151] In one embodiment of the present application, the activation reaction time may be 30 minutes to 48 hours, preferably 1 hour to 2 hours.

[0152] In one embodiment of the present application, there is provided a lithium secondary battery comprising: a positive electrode for a lithium secondary battery; a negative electrode for a lithium secondary battery; a separator provided between the positive electrode and the negative electrode; and an electrolyte, wherein at least one of the positive electrode for the lithium secondary battery and the negative electrode for the lithium secondary battery is a lithium secondary battery electrode that has been prelithiated according to the present application.

[0153] At this time, the release layer 35 used in the pre-lithiation may be removed as described above, so that it does not remain on the electrode and can prevent an unnecessary increase in resistance. That is, the release layer can improve transfer force and also serve to protect the lithium metal before pre-lithiation, and can be removed before electrolyte injection.

[0154] In one embodiment of the present application, 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. Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0155] Examples of the non-aqueous organic solvent that may be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0156] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are preferably used because they are high-viscosity organic solvents with high dielectric constants and can dissociate lithium salts well. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte having high electrical conductivity can be produced, and therefore, these cyclic carbonates are more preferably used.

[0157] The metal salt may 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 may 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:

[0158] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purposes of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving the discharge capacity of the battery.

[0159] According to one embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same. The battery module and the battery pack include a secondary battery having high capacity, high rate characteristics, and high cycle characteristics, and can be used as a power source for 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. [Example]

[0160] Below, preferred examples are presented to help understand the present invention, but these examples are for the purpose of illustrating the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of the scope and technical ideas of the present description, and it is natural that such changes and modifications fall within the scope of the appended claims.

[0161] <Example> <Production of Transfer Laminate> A release layer meeting the conditions in Table 1 below, which can improve transferability, was coated on the PET layer. Lithium metal was then deposited on the PET substrate to a thickness of 6 μm using the PVD method to prepare a transfer laminate.

[0162] <Production of negative electrodes> A negative electrode slurry was prepared by adding Si (average particle size (D50): 3.5 μm) as a silicon-based active material, Denka Black as a conductive material, SBR as a binder, and CMC as a thickener in a weight ratio of 80:15.8:3:1.2 to distilled water as a solvent for forming a negative electrode slurry (solid content concentration: 25 wt%).

[0163] The mixing method was as follows: the conductive material, binder, thickener 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 a slurry.

[0164] The negative electrode current collector was a copper current collector (thickness: 8 μm) and the negative electrode slurry was applied to both sides of the copper current collector at a rate of 85 mg / 25 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: 33 μm), which was used as a negative electrode (negative electrode thickness: 41 μm, negative electrode porosity: 40.0%).

[0165] Then, to transfer the transfer laminate to the negative electrode active material layer, the lithium metal of the transfer laminate was positioned on top of the negative electrode active material layer, and then external pressure was applied and roll pressing was performed to bond the lithium metal and the negative electrode active material layer. Immediately after lamination, the PET layer of the transfer laminate was removed, and the negative electrode was prelithiated.

[0166] After the negative electrode was prelithiated, the release layer remaining on the surface of the negative electrode active material layer was removed using scotch tape. The adhesive strength and the evaluation results after pre-lithiation are shown in Table 1 below.

[0167] [Table 1]

[0168] In Table 1, the temperature of the surface on which the substrate layer is attached can be defined as the surface opposite to the surface on which lithium metal is deposited, and also refers to the temperature of the surface of the substrate layer in contact with the release layer.

[0169] In Table 1, the pre-lithiation rate was measured as the time from immediately after removing the PET layer of the transfer laminate until all lithium metal was removed from the top of the negative electrode material layer. The transferability was represented as follows: ◯ if the PET layer was peeled from the transfer laminate without detachment of lithium metal and the surface of the negative electrode active material layer; × if detachment of lithium metal and the surface of the negative electrode active material layer occurred; and △ if partial detachment occurred but no by-products were generated in the pre-lithiation process.

[0170] As can be seen from Table 1, it was confirmed that the lithium transferability during the pre-lithiation process could be improved when the transfer laminates of Examples 1 to 3 were used. The pre-lithiation method according to the present application includes a step of adjusting the deposition temperature during lithium metal deposition, and the temperature of the side opposite to the side on which lithium metal is deposited can be adjusted to between -30°C and 10°C, so that the surface temperature of the transfer laminate on which lithium metal is deposited can be set to 80°C or less.

[0171] That is, as described above, it was confirmed that heat dissipation could be made easier by adjusting the thickness of the transfer laminate and the release layer, and thus the adhesive strength of the release layer did not change, ensuring lithium transferability.

[0172] Furthermore, in Examples 1 to 3, it was confirmed that the release layer was easily removed from the top of the pre-lithiated negative electrode active material layer, which suppressed the generation of by-products and reduced the resistance value on the negative electrode surface, thereby suppressing the subsequent increase in resistance of the lithium secondary battery.

[0173] In Comparative Example 1, the thickness of the release layer was outside the range of the present application, resulting in an increase in the overall thickness of the transfer laminate. It was confirmed that the first adhesive strength was exceeded, the first adhesive strength was not satisfied, and the transferability of lithium metal was poor, resulting in rapid pre-lithiation. Furthermore, after pre-lithiation, the release layer was not smoothly removed from the top of the negative electrode and instead adhered. In this case, it was confirmed that the surface resistance of the negative electrode increased, causing problems with the operation of the lithium secondary battery.

[0174] In Comparative Example 2, which does not use a release layer according to the present application, the temperature on the surface where lithium metal is deposited is maintained low, but because a release layer is not included, lithium transfer is poor, and the prelithiation reaction occurs too quickly or by-products are generated to the extent that the prelithiation reaction does not occur, resulting in the prelithiation concentrating on the electrode surface and causing cracking of the active material. Furthermore, in Comparative Example 2, the transfer itself does not occur smoothly, and prelithiation proceeds with the substrate layer still attached, trapping heat and causing the prelithiation rate to proceed very quickly, resulting in non-uniform prelithiation.

[0175] In Comparative Example 3, the thickness of the release layer was satisfactory, but the thickness of the transfer laminate exceeded the range of the present application. In this case, even if the temperature of the side opposite to the side on which lithium metal is deposited was adjusted to between -30°C and 10°C, the thickness of the transfer laminate itself was thick, making it difficult to dissipate the heat generated during the lithium metal deposition process, and it was confirmed that the first adhesive strength increased. As a result, it was confirmed that it was difficult to remove the substrate layer during the transfer process, causing problems in the pre-lithiation process. [Explanation of symbols]

[0176] 10...Base material layer 20 Lithium metal 30...electrode active material layer 35...Release layer 40 Electrode current collector layer 100 Transfer laminate 200 Electrodes for lithium secondary batteries

Claims

1. a substrate layer including at least one selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), poly(methylmethacrylate) (PMMA), polypropylene, polyethylene, and polycarbonate; and a release layer formed in direct contact with one surface of the base material layer; A transfer laminate for transferring lithium metal onto an upper portion of an electrode active material layer, comprising: lithium metal formed on a surface of the release layer opposite to a surface that contacts the base layer, the thickness of the release layer is 1 nm or more and 1 μm or less; The thickness of the transfer laminate is 5 μm or more and 40 μm or less, The release layer is made of a non-metallic substance and includes at least one selected from the group consisting of silicon-modified polyester in which silicon chains are grafted to a polyester main chain, Si, melamine, and fluorine.

2. A substrate layer comprising at least one selected from the group consisting of polyethylene terephthalate (PET), polyimide (PI), poly(methylmethacrylate) (PMMA), polypropylene, polyethylene, and polycarbonate; and a release layer formed in direct contact with one surface of the base material layer; A transfer laminate for transferring lithium metal onto an upper portion of an electrode active material layer, comprising: lithium metal formed on a surface of the release layer opposite to a surface that contacts the base layer, the thickness of the release layer is 1 nm or more and 1 μm or less; The thickness of the transfer laminate is 5 μm or more and 120 μm or less, The release layer is made of a non-metallic substance and includes at least one selected from the group consisting of a silicon-modified polyester in which a silicon chain is graft-bonded to a polyester main chain, an acrylic resin, Si, melamine, and fluorine, A transfer laminate, wherein the first adhesive strength of the surface where the base layer and the release layer contact after leaving the transfer laminate at 80°C for 2 hours is 10 gf / inch or more and 150 gf / inch or less.

3. The transfer laminate according to claim 1 , wherein a first adhesive strength at a surface where the base layer and the release layer contact each other is lower than an adhesive strength at a surface where the release layer and the lithium metal contact each other.

4. The transfer laminate according to claim 1 , wherein the lithium metal has a thickness of 1 μm or more and 10 μm or less.

5. forming an electrode current collector layer and an electrode active material layer on one or both sides of the electrode current collector layer; transferring lithium metal onto the electrode active material layer; A method for prelithiating an electrode for a lithium secondary battery, comprising:

5. A method for pre-lithiation of an electrode for a lithium secondary battery, wherein the step of transferring the lithium metal includes the steps of: preparing a transfer laminate according to any one of claims 1 to 4; laminating the transfer laminate on the electrode active material layer so that a surface of the lithium metal opposite to a surface that contacts the release layer contacts a surface of the electrode active material layer opposite to a surface that contacts the transfer laminate; and removing the base layer.

6. The step of preparing the transfer laminate includes the steps of: preparing a substrate layer having a release layer; and depositing lithium metal on the substrate layer having the release layer; The step of depositing lithium metal includes controlling a deposition temperature; 6. The method of claim 5, wherein the adjusting the deposition temperature comprises adjusting the temperature of the surface opposite to the surface onto which the lithium metal is deposited to between −30° C. and 10° C., and setting the temperature of the transfer laminate to 80° C. or less.

7. 6. The method of pre-lithiation of a lithium secondary battery electrode according to claim 5, wherein the laminating step is performed at a temperature of 20° C. to 90° C. and under a pressure of 5 kgf / cm to 500 kgf / cm.

8. After removing the substrate layer, prelithiating the electrode active material layer, 6. The method of claim 5, wherein the step of prelithiating the electrode active material layer is performed within 30 minutes to 24 hours after transferring the lithium metal.

9. The step of forming the electrode current collector layer and the electrode active material layer on one or both surfaces of the electrode current collector layer includes coating one or both surfaces of the electrode current collector layer with an electrode slurry including an electrode active material layer composition, 6. The method for pre-lithiation of an electrode for a lithium secondary battery according to claim 5, wherein the electrode active material layer composition includes at least one selected from the group consisting of an electrode active material, an electrode conductive material, and an electrode binder.

10. the electrode active material includes a silicon-based active material, 10. The method for pre-lithiation of an electrode for a lithium secondary battery according to claim 9, wherein the silicon-based active material comprises at least one selected from the group consisting of SiOx (x=0), SiOx (0<x<2), SiC, and a Si alloy.

11. Positive electrodes for lithium secondary batteries, Negative electrodes for lithium secondary batteries, a separator provided between the positive electrode and the negative electrode; and electrolyte A method for producing a lithium secondary battery, comprising:

6. A method for producing a lithium secondary battery, comprising forming at least one of the positive electrode for the lithium secondary battery and the negative electrode for the lithium secondary battery by prelithiation according to the method of claim 5.

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