Negative electrode for lithium secondary battery, lithium secondary battery comprising same, and method for manufacturing negative electrode for lithium secondary battery

Abstract

The present invention relates to a negative electrode for a lithium secondary battery, comprising: a negative electrode active material layer provided on at least one surface of a negative electrode current collector layer; a surface layer provided on the surface of the negative electrode active material layer; and an inner layer provided between the negative electrode active material layer and the surface layer, wherein the surface layer and the inner layer each include at least one selected from the group consisting of a polyvinyl-based polymer, a polyamide-based polymer, a polysilane-based polymer, a polyfluorene-based polymer, a polyaniline-based polymer, and combinations thereof, and the inner layer and the surface layer include polymers different from each other to suppress a thermal runaway phenomenon.

Description

A negative electrode for a lithium secondary battery, a lithium secondary battery including the same, and a method for manufacturing a negative electrode for a lithium secondary battery

[0001] The present invention claims the benefit of the filing date of Korean Patent Application No. 10-2024-0154421 filed with the Korean Intellectual Property Office on November 4, 2024, the entire contents of which are incorporated herein.

[0002] The present invention relates to a negative electrode for a lithium secondary battery, a lithium secondary battery including the same, and a method for manufacturing a negative electrode for a lithium secondary battery.

[0003] Due to the rapid increase in the use of fossil fuels, there is a growing demand for alternative or clean energy. As part of this effort, the fields of power generation and energy storage utilizing electrochemical reactions are the most actively researched.

[0004] Currently, a representative example of an electrochemical device utilizing such electrochemical energy is the secondary battery, and its scope of application is steadily expanding.

[0005] With the increasing technological development and demand for mobile devices, the demand for secondary batteries as an energy source is rapidly rising. Among these secondary batteries, lithium-ion batteries, which possess high energy density and voltage, long cycle life, and low self-discharge rates, have been commercialized and are widely used. Furthermore, active research is being conducted on methods to manufacture high-density electrodes with higher energy density per unit volume for use in such high-capacity lithium-ion batteries.

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

[0007] Meanwhile, thermal runaway reactions caused by various factors such as defects in lithium secondary batteries, external impact, overcharging, and over-discharging are becoming a problem as they cause positive feedback that generates greater heat, such as swelling of the battery, voltage rise, and electrolyte temperature rise, leading to ignition or explosion accidents. Accordingly, various studies are being conducted to suppress thermal runaway reactions in lithium secondary batteries.

[0008] The present invention aims to provide a negative electrode for a lithium secondary battery capable of suppressing thermal runaway, a lithium secondary battery including the same, and a method for manufacturing the negative electrode for a lithium secondary battery.

[0009] One embodiment of the present specification includes a negative active material layer provided on at least one surface of a negative current collector layer;

[0010] A surface layer provided on the surface of the above-mentioned cathode active material layer; and

[0011] It includes an inner layer provided between the above-mentioned negative electrode active material layer and the above-mentioned surface layer, and

[0012] The above surface layer and the above inner layer comprise one or more selected from the group consisting of polyvinyl-based polymers, polyamide-based polymers, polysilane-based polymers, polyfluorene-based polymers, polyaniline-based polymers, and combinations thereof, and the above inner layer and the above surface layer comprise different polymers, thereby providing a negative electrode for a lithium secondary battery.

[0013] One embodiment of the present specification is a positive electrode for a lithium secondary battery;

[0014] The aforementioned negative electrode for a lithium secondary battery;

[0015] Separator; and

[0016] A lithium secondary battery containing an electrolyte is provided.

[0017] One embodiment of the present specification provides a battery module or battery pack comprising the aforementioned lithium secondary battery.

[0018] Another embodiment of the present specification provides a battery pack comprising the aforementioned battery module.

[0019] Finally, one embodiment of the present specification includes the step of (S1) forming a first negative active material layer by coating a negative active material layer composition on at least one surface of a negative current collector layer;

[0020] (S2) A step of forming an inner layer on the first negative electrode active material layer;

[0021] (S3) A step of forming a second cathode active material layer by coating the cathode active material layer composition on the inner layer; and

[0022] (S4) A step of forming a surface layer on the second negative electrode active material layer, and

[0023] The above S2 to S3 steps provide a method for manufacturing a negative electrode for a lithium secondary battery, which is repeated at least once and no more than five times.

[0024] A negative electrode for a lithium secondary battery according to one embodiment described in this specification includes two or more polymer thin film layers, thereby acting as a barrier against the oxidation reaction of lithium ions and oxygen escaping from the negative electrode active material, which can suppress the thermal runaway reaction caused by the heat of oxidation, and can also improve lifespan performance by suppressing the swelling phenomenon.

[0025] A method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment described in this specification can ensure processability by unifying the coating step for providing a negative electrode active material layer and the deposition step for providing a polymer thin film layer into a roll-to-roll process, thereby facilitating the formation of a protective layer on the surface and inside the negative electrode during manufacturing.

[0026] FIGS. 1 to 3 are drawings showing a stacked structure of a negative electrode for a lithium secondary battery according to one embodiment of the present invention.

[0027] FIG. 4 is a flowchart illustrating a method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present invention.

[0028] FIG. 5 is a diagram showing a stacked structure of a lithium secondary battery according to one embodiment of the present invention.

[0029] Before describing the present invention, we will first define some terms.

[0030] In this specification, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0031] In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0032] In this specification, when a part such as a layer is described as being "on" or "on" another part, this includes not only the case where it is "immediately on" another part, but also the case where there is another part in between. Conversely, when a part is described as being "immediately on" another part, it means that there is no other part in between. Furthermore, being described as being "on" or "on" a reference part means being located above or below the reference part, and does not necessarily mean being located "on" or "on" in a direction opposite to gravity.

[0033] In this specification, when it is stated that a certain member is provided on both sides of another member, it means that a certain member is provided on one side of another member, and a certain member is provided on another side corresponding to said one side. Furthermore, this includes not only cases where another member is in direct contact with one side of a certain member and its corresponding side, but also cases where another member exists between the two members.

[0034] In this specification, 'p to q' means a range of 'p or more and q or less'.

[0035] In this specification, terms such as “…part,” “device,” etc. refer to a unit that processes at least one function or operation.

[0036] In this specification, "Dn" refers to the particle size distribution and represents the particle size (average particle size) at the n% point of the cumulative distribution of particle numbers according to particle size. That is, D 50 is the particle size at the 50% point of the cumulative distribution of particle numbers according to particle size, and D 90 D is the particle size at the 90% point of the cumulative distribution of particle numbers according to particle size. 10 is the particle size at the 10% point of the cumulative distribution of the number of particles according to particle size. Meanwhile, the average particle size can be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) and the difference in diffraction patterns according to particle size is measured as the particles pass through the laser beam to calculate the particle size distribution.

[0037] In one embodiment of the present specification, particle size or particle diameter may refer to the average diameter or representative diameter of each individual grain constituting the metal powder or inorganic particle.

[0038] The singular expressions of terms used in this specification include the plural expressions unless the context clearly indicates otherwise.

[0039] Terms or words used in this specification should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0040] Preferred embodiments of the present invention are described in detail below. However, embodiments of the present invention may be modified in various forms, and the scope of the present invention is not limited to the embodiments described below.

[0041] A negative electrode for a lithium secondary battery according to one embodiment of the present specification comprises: a negative electrode active material layer provided on at least one surface of a negative electrode current collector layer; a surface layer provided on the surface of the negative electrode active material layer; and an inner layer provided between the negative electrode active material layer and the surface layer, wherein the surface layer and the inner layer comprise one or more selected from the group consisting of polyvinyl-based polymers, polyamide-based polymers, polysilane-based polymers, polyfluorene-based polymers, polyaniline-based polymers, and combinations thereof, and the inner layer and the surface layer comprise polymers that are different from each other.

[0042] The primary cause of the thermal runaway reaction of the cathode is the heat of oxidation generated when lithium ions released from the cathode active material undergo an oxidation reaction with oxygen. Therefore, to improve the thermal safety of the cathode, the researchers of the present invention propose this invention to prevent direct contact between the cathode active material and oxygen at the cathode surface and to suppress the diffusion of lithium ions from within the cathode to the surface to a degree that prevents contact between lithium ions and oxygen during thermal runaway.

[0043] To solve the above problem, the present invention is characterized by being able to suppress an initial thermal runaway reaction by preventing lithium ions escaping from the cathode active material through a surface layer provided on the surface of the cathode active material layer from causing an oxidation reaction with oxygen surrounding the cathode, and by having one or more inner layers provided inside the cathode active material layer to prevent thermal runaway to the inside of the cathode when the temperature continuously rises due to thermal runaway occurring despite the surface layer. That is, the present invention can suppress the thermal runaway phenomenon by including a total of two or more thin film layers.

[0044] In addition, since the surface layer and the inner layer include polymers, there is an advantage that it is easy to optimize the thermal runaway prevention performance by controlling the thickness of each layer compared to cases where they are made of inorganic layers such as metal or ceramic.

[0045] In a negative electrode for a lithium secondary battery according to one embodiment of the present specification, the presence of the surface layer and the inner layer can be confirmed through cross-sectional image analysis, and the type of polymer formed in each thin film layer can be confirmed through FRIR (Fourier-Transform Infrared Spectroscopy) and NMR (Nuclear Magnetic Resonance) analysis.

[0046] In one embodiment of the present specification, the surface layer is provided on the surface of the negative electrode active material layer, and the surface layer and the surface of the negative electrode active material layer may be in direct contact or may not be in direct contact. Specifically, the negative electrode for a lithium secondary battery according to one embodiment of the present specification may have the surface layer, the negative electrode active material layer, and the negative electrode current collector layer stacked in sequence.

[0047] In addition, in one embodiment of the present specification, the surface layer may cover at least a portion of the surface opposite to the negative electrode current collector layer with respect to the negative electrode active material layer, and specifically, may cover the entire surface.

[0048] In one embodiment of the present specification, the surface layer can act as a barrier that prevents the oxidation reaction of lithium ions released from the cathode active material by chemically reacting with oxygen present on the surface of the cathode and absorbing oxygen. As a result, the initial thermal runaway reaction of the cathode and the lithium secondary battery containing it can be prevented or delayed.

[0049] In one embodiment of the present specification, the inner layer is provided between the negative electrode active material layer and the surface layer, and may be provided in contact with the surface layer or may be provided spaced apart from the surface layer by a certain distance.

[0050] Specifically, in the case where the inner layer according to one embodiment of the present specification is provided at a certain distance from the surface layer, the inner layer may be provided between the negative active material layer adjacent to the negative current collector layer and the negative active material layer adjacent to the surface layer.

[0051] For example, when the inner layer is provided in contact with the surface layer, the negative electrode for a lithium secondary battery according to one embodiment of the present specification may have the surface layer, the inner layer, the negative electrode active material layer, and the negative electrode current collector layer stacked in order.

[0052] For example, if the inner layer is provided at a certain distance from the surface layer, the negative active material layer may be provided between the inner layer and the surface layer. Specifically, a negative electrode for a lithium secondary battery according to one embodiment of the present specification may be formed by stacking the surface layer, the negative active material layer, the inner layer, and the negative current collector layer in that order, and more specifically, the surface layer, the negative active material layer, the inner layer, the negative active material layer, and the negative current collector layer in that order.

[0053] In a negative electrode for a lithium secondary battery according to one embodiment of the present specification, the negative electrode active material layer comprises two or more negative electrode active material layers, and the inner layer may be provided between at least one pair of adjacent negative electrode active material layers.

[0054] Specifically, the negative active material layer comprises two or more separated negative active material layers, and the inner layer may be provided between at least one pair of adjacent negative active material layers. In this case, the two or more negative active material layers are all the same negative active material layer, and the inner layer and the two or more negative active material layers may be arranged in an overlapping manner in the thickness direction.

[0055] In a negative electrode for a lithium secondary battery according to one embodiment of the present specification, one surface of one of the two or more negative electrode active material layers may be in contact with the inner layer, and the other surface may be in contact with the inner layer or the surface layer.

[0056] In another embodiment of the present specification, a negative electrode for a lithium secondary battery is provided with n layers, and the negative active material layer is provided with n+1 layers, and the inner layer and the negative active material layer are alternately stacked, and n may be an integer greater than or equal to 1, specifically, n may be an integer from 2 to 5. In this case, the negative active material layer provided with n+1 layers is all the same negative active material layer.

[0057] As described above, when an inner layer is provided between the cathode active material layers, it can act as a barrier that allows the active material layers to react stepwise rather than all at once during thermal runaway, thereby having the effect of delaying thermal runaway.

[0058] In one embodiment of the present specification, the inner layer may be provided with 1 to 5 layers, and specifically, with 2 to 5 layers. According to the method for manufacturing a negative electrode for a lithium secondary battery described below, the inner layer may be provided with 1 to 5 layers between the negative electrode active material layer and the surface layer, and in this case, the thermal stability of the negative electrode can be optimized.

[0059] In one embodiment of the present specification, the inner layer can serve to prevent thermal runaway to the inside of the cathode when the temperature continuously rises due to thermal runaway occurring despite the surface layer.

[0060] In one embodiment of the present specification, the surface layer and the inner layer comprise one or more selected from the group consisting of polyvinyl-based polymers, polyamide-based polymers, polysilane-based polymers, polyfluorene-based polymers, polyaniline-based polymers and combinations thereof, and the inner layer and the surface layer comprise polymers different from each other.

[0061] Specifically, in one embodiment of the present specification, the surface layer may comprise one or more selected from the group consisting of polyvinyl-based polymers, polyamide-based polymers, polyaniline-based polymers, and combinations thereof.

[0062] Specifically, in one embodiment of the present specification, the surface layer may comprise one or more selected from the group consisting of polyvinyl alcohol, polyvinyl chloride, polyvinyl acetate, polyvinyl pyrrolidone, polyamide 6, polyamide 6,6, polyamide 12, polyamide 46, polyaniline, and combinations thereof.

[0063] In one embodiment of the present specification, the polymer included in the surface layer may be a material capable of absorbing oxygen through a chemical reaction with oxygen.

[0064] Specifically, in one embodiment of the present specification, the weight change (%) when heated to 600°C according to thermogravimetric analysis (TGA) of the polymer included in the surface layer may be 0.01% or more and 20% or less, specifically 0.05% or more and 15% or less, and more specifically 0.1% or more and 10% or less.

[0065] The weight change (%) by thermal mass spectrometry of the polymer included in the surface layer is the weight change that increases as the polymer chemically reacts with oxygen. If the above range is satisfied, the material can effectively absorb oxygen, thereby suppressing direct contact between the cathode active material and lithium ions and oxygen. Consequently, it can prevent or delay the initial thermal runaway reaction of the cathode and the lithium secondary battery containing it.

[0066] In one embodiment of the present specification, the inner layer may comprise one or more selected from the group consisting of polysilane-based polymers, polyfluorene-based polymers, and combinations thereof.

[0067] Specifically, in one embodiment of the present specification, the inner layer may comprise one or more selected from the group consisting of polyV4D4 (poly-2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane), polyvinylidene fluoride, and combinations thereof.

[0068] In one embodiment of the present specification, the polymer included in the inner layer may be a material having low oxygen permeability and high heat resistance.

[0069] Specifically, in one embodiment of this specification, the oxygen permeability of the polymer included in the inner layer is 10cc / (m 2 ·day·atm) or more 2000cc / (m 2 It may be less than 20cc / (m² / day / atm²), specifically 20cc / (m² / day / atm²). 2 ·day·atm) or more 1500cc / (m 2 ·day·atm) or less, more specifically 50cc / (m 2 ·day·atm) or more 1000cc / (m 2 It may be less than ·day·atm)

[0070] In one embodiment of the present specification, the temperature at which the viscosity of the polymer included in the inner layer changes rapidly according to the Thermomechanical Analyzer (TMA) may be 50°C or higher and 1000°C or lower, specifically 60°C or higher and 800°C or lower, and more specifically 100°C or higher and 500°C or lower.

[0071] If the oxygen permeability or heat resistance of the polymer included in the inner layer satisfies the above range, thermal runaway to the interior of the cathode can be suppressed even if thermal runaway continues and the temperature of the cathode continuously rises.

[0072] In one embodiment of the present specification, the total thickness of the surface layer and the inner layer may be 2 μm or less.

[0073] In one embodiment of the present specification, the total thickness of the surface layer and the inner layer may be 2 nm or more and 2 μm or less, specifically 10 nm or more and 1.5 μm or less, and more specifically 25 nm or more and 1 μm or less.

[0074] When the total thickness of the surface layer and the one or more inner layers satisfies the above range, the thickness is not excessively thick, so the resistance increase rate is not high, and active diffusion of lithium ions is maintained, thereby securing excellent rate capability characteristics of the lithium secondary battery.

[0075] In one embodiment of the present specification, the thickness of the surface layer and the inner layer may each be 1 nm or more and 400 nm or less.

[0076] In one embodiment of the present specification, the thickness of the surface layer and the inner layer may each be 1 nm or more and 400 nm or less, specifically 2 nm or more and 300 nm or less, and more specifically 5 nm or more and 200 nm or less.

[0077] When the thicknesses of the surface layer and the inner layer each satisfy the above range, the thermal stability of the negative electrode can be optimized, while at the same time, excellent rate capability characteristics of the lithium secondary battery can be secured.

[0078] At this time, the thickness of the surface layer and the inner layer can be measured through SEM (Scanning Electron Microscope) analysis of the cross-section of the negative electrode before fabrication of the lithium secondary battery.

[0079] FIGS. 1 to 3 are drawings showing a stacked structure of a negative electrode (100) for a lithium secondary battery according to one embodiment of the present specification. Specifically, a negative electrode (100) for a lithium secondary battery having a stacked structure in which a negative active material layer (20) provided on one side of a negative current collector layer (10), a surface layer (400) provided on the surface of the negative active material layer (20), and an inner layer (300) provided between the negative active material layer (20) and the surface layer (400) can be seen.

[0080] Specifically, FIG. 1 shows a stacked structure of a negative electrode (100) for a lithium secondary battery in which the inner layer (300) and the surface layer (400) are in contact, but a negative active material layer (20) may be further provided between the inner layer (300) and the surface layer (400), and a stacked structure of a negative electrode (100) for a lithium secondary battery in which a negative active material layer (20) is further provided between the inner layer (300) and the surface layer (400) is shown in FIG. 2.

[0081] At this time, FIGS. 1 and FIGS. 2 are shown as having one inner layer (300), but the inner layer (300) may be further provided in 2 to 5 layers or less, and FIGS. 3 shows an example in which the inner layer (300) is provided in 3 layers, but there are no limitations thereon.

[0082] Additionally, the thickness of the negative active material layer (20) located between the negative current collector layer (10) and the inner layer (300), and the thickness of the negative active material layer (20) located between the inner layer (300) and the surface layer (400) may be the same or different, and there are no limitations on this.

[0083] Additionally, the thickness of the inner layer (300) and the surface layer (400) may be the same or different, and there are no restrictions on this.

[0084] In one embodiment of the present specification, the surface layer and the inner layer may be deposited on one surface of the cathode active material layer. Specifically, the surface layer and the inner layer may be deposited on one surface of the cathode active material layer by a deposition method selected from Physical Vapor Deposition (PDV), Chemical Vapor Deposition (CVD), and Atomic Layer Deposition (ALD). More specifically, they may be deposited by Physical Vapor Deposition (PDV) or Chemical Vapor Deposition (CVD), but are not limited thereto, and various deposition methods used in the art may be used.

[0085] Specifically, the method for manufacturing the negative electrode for the lithium secondary battery according to one embodiment of the present specification is as follows.

[0086] A method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present specification comprises: (S1) forming a first negative electrode active material layer by coating a negative electrode active material layer composition on at least one surface of a negative electrode current collector layer; (S2) forming an inner layer on the first negative electrode active material layer; (S3) forming a second negative electrode active material layer by coating the negative electrode active material layer composition on the inner layer; and (S4) forming a surface layer on the second negative electrode active material layer, wherein steps S2 to S3 may be repeated at least once and no more than five times.

[0087] In a method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present specification, steps S1 to S4 may be performed by a roll-to-roll processing. Here, "roll-to-roll processing" refers to a method of applying a specific material while winding a thin material, such as a film or copper foil, onto a rotating roll to provide a new function. The present invention is characterized by the ability to improve processability by introducing a step of depositing an inner layer or a surface layer through a roll-to-roll processing during the process of roll-to-roll coating a negative electrode active material layer on at least one surface of a negative electrode current collector layer.

[0088] That is, in one embodiment of the present specification, steps S2 and S4 may be performed by a deposition method using a roll-to-roll process. The same content regarding the method for depositing the surface layer and the inner layer described above may be applied to the deposition method.

[0089] In one embodiment of the present specification, the method for manufacturing a negative electrode for a lithium secondary battery comprises the step of (S1) forming a first negative active material layer by coating a negative active material layer composition on at least one surface of a negative current collector layer, and specifically, the step S1 may include (S1-1) forming a negative active material layer composition by mixing a negative active material, a negative conductive material, and a negative binder; (S1-2) applying the negative active material layer composition to at least one surface of a negative current collector layer; and (S1-3) drying the negative current collector layer on which the negative active material layer composition is applied to at least one surface, and the steps S1-1 to S1-3 may be performed by a roll-to-roll process.

[0090] In one embodiment of the present specification, the method for manufacturing a negative electrode for a lithium secondary battery comprises (S2) a step of forming an inner layer on the first negative electrode active material layer, specifically, the step S2 may be a step of depositing the inner layer on the first negative electrode active material layer by a roll-to-roll process, and more specifically, the step S2 may be a step of forming the inner layer by depositing it on the first negative electrode active material layer by a CVD method during a roll-to-roll process.

[0091] For example, if the above S2 step is deposited by a CVD method, the inner layer is formed by depositing it between the cathode active material layers during a roll-to-roll process, allowing for uniform deposition on a curved surface and thus providing good step coverage, but any known deposition method can be used without limitation.

[0092] In one embodiment of the present specification, the method for manufacturing a negative electrode for a lithium secondary battery comprises the step (S3) of forming a second negative electrode active material layer by coating the negative electrode active material layer composition on the inner layer, and specifically, may comprise the step (S3) of forming a second negative electrode active material layer by roll-to-roll coating the negative electrode active material layer composition on the inner layer.

[0093] At this time, the cathode active material layer composition in step S3 is identical to the cathode active material layer composition in step S1, and the first cathode active material layer is identical to the second cathode active material layer. That is, step S3 is a step of forming a cathode active material layer identical to the cathode active material layer in step S1, and steps S1-1 to S1-3 may be applied identically, but the cathode active material layer composition of step S1-2 may be a step of applying it onto the inner layer (step S1-2').

[0094] In one embodiment of the present specification, the method for manufacturing a negative electrode for a lithium secondary battery comprises (S4) a step of forming a surface layer on the second negative electrode active material layer, specifically, the step S4 may be a step of depositing the surface layer on the second negative electrode active material layer by a roll-to-roll process, and more specifically, the step S4 may be a step of depositing the surface layer on the second negative electrode active material layer by a PVD method during a roll-to-roll process.

[0095] For example, if the above S4 step is performed by deposition using a PVD method, it is suitable for forming a surface layer on the outermost surface of the cathode as it causes less contamination than a CVD deposition method; however, any known deposition method may be used without limitation, and it may be the same method as the deposition method in the above S2 step or a different method.

[0096] In a method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present specification, steps S2 to S3 may be repeated at least once and no more than five times.

[0097] For example, when the above steps S2 to S3 are performed once, the negative electrode for the manufactured lithium secondary battery may have a structure in which the negative electrode current collector layer (10) / first negative electrode active material layer (20) / inner layer (300) / second negative electrode active material layer (20) / surface layer (400) are stacked in that order.

[0098] For example, if steps S2 to S3 above are performed twice, the negative electrode for the manufactured lithium secondary battery may have a stacked structure in the order of negative electrode current collector layer (10) / first negative electrode active material layer (20) / inner layer (300) / second negative electrode active material layer (20) / inner layer (300) / second negative electrode active material layer (20) / surface layer (400).

[0099] For example, when the above steps S2 to S3 are performed 5 times, the inner layer (300) within the negative electrode active material layer (20) may be a negative electrode for a lithium secondary battery formed with 5 layers.

[0100] FIG. 4 is a flowchart illustrating a method for manufacturing a negative electrode for a lithium secondary battery according to one embodiment of the present specification. Specifically, FIG. 4 illustrates a method for manufacturing a negative electrode for a lithium secondary battery comprising the steps of: forming a first negative electrode active material layer by coating a negative electrode active material layer composition on one surface of a negative electrode current collector layer (S1); forming an inner layer on the first negative electrode active material layer (S2); forming a second negative electrode active material layer by coating a negative electrode active material layer composition on the inner layer (S3); and forming a surface layer on the second negative electrode active material layer (S4), wherein steps S2 and S3 may be repeated one or more times.

[0101] A negative electrode for a lithium secondary battery according to one embodiment of the present specification comprises a negative electrode active material layer provided on at least one surface of a negative electrode current collector layer, and the negative electrode active material layer may comprise a negative electrode active material layer composition comprising a negative electrode active material; a negative electrode conductive material; and a negative electrode binder.

[0102] In one embodiment of the present specification, the cathode active material layer composition may include one or more selected from the group consisting of a cathode active material described below; a cathode conductive material; and a cathode binder. Specifically, when the cathode active material layer composition includes a cathode active material, the cathode active material may include a carbon-based active material or a silicon-based active material.

[0103] In other words, the negative electrode for the lithium secondary battery according to one embodiment of the present specification may include a carbon-based active material or a silicon-based active material as the negative electrode active material.

[0104] According to one embodiment of the present specification, the negative electrode for a lithium secondary battery may include a carbon-based active material or a silicon-based active material as a negative electrode active material, and the silicon-based active material may include one or more selected from the group consisting of Si, silicon oxide, Si / C, and Si alloy.

[0105] Specifically, in one embodiment of the present specification, the silicon-based active material may comprise one or more selected from the group consisting of Si and silicon oxide, and more specifically, the silicon-based active material may comprise Si.

[0106] In one embodiment of the present specification, the carbon-based active material may comprise one or more selected from the group consisting of graphite such as natural graphite or artificial graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotubes, fullerene, and activated carbon, and specifically, may comprise one or more selected from the group consisting of natural graphite and artificial graphite.

[0107] When the above-described carbon-based active material is used as a negative electrode active material according to one embodiment of the present specification, reversible intercalation and extraction of lithium ions are possible, and structural and electrical properties can be maintained. Among these, the graphite-based active material can guarantee the lifespan characteristics of a lithium secondary battery due to its excellent reversibility. Since the discharge voltage of the graphite-based active material is low at -0.2V compared to lithium, a battery using the graphite-based active material can exhibit a high discharge voltage of 3.6V, thereby providing many advantages in terms of energy density of the lithium secondary battery.

[0108] In one embodiment of the present specification, when artificial graphite is used as the carbon-based active material, the degree of orientation during electrode rolling is relatively low, so the lithium ion inflow / outflow characteristics are good, resulting in excellent rapid charging performance of the battery, and the degree of expansion due to charging and discharging is low, so the lifespan characteristics can be excellent.

[0109] The above natural graphite may generally exist as plate-shaped aggregates prior to processing, and the plate-shaped particles may be manufactured into a spherical shape with a smooth surface through post-processing such as particle grinding and reassembly processes in order to be used as an active material for manufacturing electrodes.

[0110] In one embodiment of the present specification, when natural graphite is used as a carbon-based active material, the output and capacity of the lithium secondary battery are improved, and since the adhesive strength is excellent, the amount of binder used can be reduced and a high-capacity, high-density negative electrode can be realized.

[0111] In one embodiment of the present specification, the negative electrode for the lithium secondary battery comprises a carbon-based active material and a silicon-based active material as negative electrode active materials, wherein the carbon-based active material comprises one or more selected from the group consisting of natural graphite and artificial graphite, and the silicon-based active material may comprise Si.

[0112] In one embodiment of the present specification, the negative electrode active material may include the carbon-based active material and the silicon-based active material in a weight ratio of 95:5 to 40:60, specifically 90:10 to 50:50, and more specifically 85:15 to 60:40.

[0113] In one embodiment of the present specification, the negative electrode active material may be included in an amount of 60 parts by weight or more and 99 parts by weight or less based on 100 parts by weight of the negative electrode active material layer composition, specifically 70 parts by weight or more and 98 parts by weight or less, and more specifically 80 parts by weight or more and 96 parts by weight or less.

[0114] In one embodiment of the present specification, the cathode conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, Farnes black, lamp black, thermal black; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. may be used, and may further include an additional dispersant.

[0115] In one embodiment of the present invention, the content of the cathode conductive material in the cathode active material layer may be 0.01 to 30 parts by weight, specifically 0.03 to 25 parts by weight, and more specifically 0.1 to 20 parts by weight, based on 100 parts by weight of the cathode active material layer composition.

[0116] In one embodiment of the present specification, the cathode binder may serve to improve adhesion between cathode active material particles and adhesion between the cathode active material particles and the cathode current collector. The above-mentioned cathode binder may include those known in the art, and non-limiting examples may include at least one selected from the group consisting of polyvinylidenefluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, polyhydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and materials in which the hydrogens thereof are substituted with Li, Na, or Ca, etc., and may also include various copolymers thereof.

[0117] In particular, the cathode binder according to one embodiment of the present specification serves to hold the cathode active material and the cathode conductive material in order to prevent distortion or structural deformation of the cathode structure during volume expansion and relaxation of the silicon-based active material. Any general cathode binder satisfying the above role may be applied, specifically, an aqueous binder may be used, and more specifically, SBR and CMC may be used.

[0118] In one embodiment of the present invention, the content of the negative binder in the negative active material layer may be 0.5 to 30 parts by weight, specifically 1 to 25 parts by weight, and more specifically 2 to 25 parts by weight, based on 100 parts by weight of the negative active material layer composition.

[0119] In one embodiment of the present specification, the negative current collector layer may generally have a thickness of 1 μm to 100 μm. Such a negative current collector layer is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy may be used. In addition, fine irregularities may be formed on the surface to strengthen the bonding strength of the negative active material, and it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven body, etc.

[0120] A lithium secondary battery according to another embodiment of the present specification comprises a positive electrode for a lithium secondary battery; a negative electrode for the lithium secondary battery described above; a separator; and an electrolyte.

[0121] FIG. 5 is a diagram showing a stacked structure of a lithium secondary battery according to one embodiment of the present specification. Specifically, a negative electrode (100) for a lithium secondary battery including a negative active material layer (20) on one surface of a negative current collector layer (10) can be seen, and a positive electrode (200) for a lithium secondary battery including a positive active material layer (40) on one surface of a positive current collector layer (50) can be seen, and the structure is formed such that the negative electrode (100) for a lithium secondary battery and the positive electrode (200) for a lithium secondary battery are stacked with a separator (30) in between. At this time, the surface layer (not shown) and the internal layer (not shown) included in the negative electrode (100) for a lithium secondary battery are omitted from the illustration.

[0122] In one embodiment of the present specification, the anode may comprise a lithium complex transition metal compound as an anode active material, comprising nickel (Ni) and cobalt (Co) and further comprising one or more elements selected from the group consisting of Na, K, Mg, Ca, Sr, Ni, Co, Ti, Al, Si, Sn, Mn, Cr, Fe, V, and Zr.

[0123] In one embodiment of the present specification, the anode may include a lithium complex transition metal compound comprising nickel (Ni), cobalt (Co), and manganese (Mn) as the anode active material.

[0124] In one embodiment of the present specification, the positive active material may be included in an amount of 60 parts by weight or more and 99 parts by weight or less based on 100 parts by weight of the positive active material layer composition, specifically 70 parts by weight or more and 98 parts by weight or less, and more specifically 80 parts by weight or more and 97 parts by weight or less.

[0125] In one embodiment of the present specification, the anode slurry comprises an anode conductive material and an anode binder, and may further comprise a thickener and a slurry solvent.

[0126] In one embodiment of the present specification, additional components such as the anode current collector layer, anode conductive material, anode binder, thickener and slurry solvent, and the method for manufacturing the anode may be used without limitation as long as they are known in the art within the scope to which the above description applies.

[0127] In one embodiment of the present specification, the separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. It may be used without special limitations as long as it is typically used as a separator in a secondary battery, and it is particularly desirable that it has low resistance to the movement of ions in the electrolyte and excellent electrolyte wettability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, a coated separator containing a ceramic component or a polymer material may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure.

[0128] One embodiment of the present specification may provide a battery module or battery pack comprising the aforementioned lithium secondary battery.

[0129] Another embodiment of the present specification may provide a battery pack comprising the aforementioned battery module.

[0130] According to another embodiment of the present specification, a battery module comprising the lithium secondary battery as a unit cell, a battery pack comprising the same, and a battery pack comprising the lithium secondary battery may be provided. Since the battery module and the battery pack include the lithium secondary battery having high capacity, high rate capability and cycle capability, they may be used as a power source for medium-to-large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0131] Hereinafter, preferred embodiments are presented to aid in understanding the present invention; however, the above embodiments are merely illustrative of the description, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of the description, and that such variations and modifications fall within the scope of the appended claims.

[0132] Preparation Example

[0133] Example 1

[0134] Manufacturing of the cathode

[0135] A cathode slurry was prepared by including 130g (95.27 parts by weight) of graphite and Si in a ratio of 85:15 as cathode active materials, 3.5g (2.57 parts by weight) of SBR (styrene-butadiene rubber) and 1.5g (1.1 parts by weight) of CMC (carboxymethyl cellulose) as binders, and additionally 0.09g (0.07 parts by weight) of a dispersant and 1.3g (0.95 parts by weight) of Super-C and 0.06g (0.04 parts by weight) of single-walled CNT as conductive materials.

[0136] The above cathode slurry is placed on a copper foil (thickness 15 μm) with a capacity of 2 mAh / cm² per unit area 2 A first cathode active material layer was formed by coating and drying using a roll-to-roll method (Step S1).

[0137] PolyV4D4 (poly-2,4,6,8-Tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane) was deposited on the first cathode active material layer using a roll-to-roll CVD deposition method to form an inner layer with a thickness of 50 nm (Step S2).

[0138] The aforementioned cathode slurry on the inner layer has a capacity of 2 mAh / cm² per unit area. 2A second negative electrode active material layer was formed by coating and drying using a roll-to-roll method (Step S3), and then polyaniline was deposited on the surface using a roll-to-roll PVD deposition method to form a surface layer with a thickness of 100 nm (Step S4) to manufacture a negative electrode for a lithium secondary battery (refer to the stacked structure in Fig. 2).

[0139] Manufacturing of lithium secondary batteries

[0140] A cathode slurry was prepared comprising 97g (97 parts by weight) of NCM-based cathode active material, 1.5g (1.5 parts by weight) of PVDF as a binder, and 1.5g (1.5 parts by weight) of Super C65 as a conductive material.

[0141] The above anode slurry is coated onto aluminum foil (thickness: 12 μm) to a dry thickness of 65 μm, and then dried to obtain a capacity of 3.7 mAh / cm² per unit area. 2 A positive electrode for a lithium secondary battery was manufactured.

[0142] A lithium secondary battery (Full-cell) of Example 1 was produced by interposing a polyethylene separator between the positive electrode for a lithium secondary battery and the negative electrode for a lithium secondary battery prepared above, and injecting an electrolyte.

[0143] The above electrolyte is prepared by adding 10 wt% of FEC (fluoroethylene carbonate) to an organic solvent of EC (ethylene carbonate) / EMC (ethyl methyl carbonate) / DEC (diethyl carbonate) = 20 / 70 / 10 (Vol%) relative to 100 wt% of the total electrolyte, and adding LiPF6 as a lithium salt at a concentration of 1.0 M.

[0144] Example 2

[0145] The cathode slurry of Example 1 was placed on a copper foil (thickness 15 μm) with a capacity of 2 mAh / cm² per unit area. 2 A first cathode active material layer was formed by coating and drying using a roll-to-roll method (Step S1).

[0146] After forming an inner layer with a thickness of 50 nm by depositing polyV4D4 (poly-2,4,6,8-Tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane) on the first cathode active material layer using a roll-to-roll CVD deposition method (Step S2), the aforementioned cathode slurry is deposited on the inner layer with a capacity of 1 mAh / cm² per unit area. 2 A second cathode active material layer was formed by coating and drying using a roll-to-roll method (Step S3).

[0147] After repeating steps S2 and S3 under the same conditions as above once each on the inner layer, polyaniline was deposited on the surface using a roll-to-roll PVD deposition method to form a surface layer with a thickness of 100 nm (step S4) to produce a negative electrode for a lithium secondary battery (refer to the stacked structure in Fig. 3) and a lithium secondary battery (Full-cell) of Example 2 containing the same.

[0148] Comparative Example 1

[0149] The electrode for a lithium secondary battery of Comparative Example 1 was manufactured using the same method as Example 1, except that step S2 of the manufacturing method of Example 1 was not performed (inner layer not provided).

[0150] Comparative Example 2

[0151] The electrode for a lithium secondary battery of Comparative Example 1 was manufactured using the same method as Example 1, except that step S4 of the manufacturing method of Example 1 was not performed (surface layer not provided).

[0152] Comparative Example 3

[0153] The electrode for a lithium secondary battery of Comparative Example 1 was prepared using the same method as Example 1, except that the same polymer polyaniline was used in steps S2 and S4 of the manufacturing method of Example 1.

[0154] Experimental Example 1: Evaluation of Thermal Runaway Duration and Maximum Temperature

[0155] The thermal runaway duration and maximum temperature of the lithium secondary batteries of Example 1 and Comparative Examples 1 to 3 were evaluated and are shown in Table 1 below. Specifically, after activating each lithium secondary battery and charging it to an SOC of 100, the battery was heated using a heat pad at a rate of 20°C / min. The thermal runaway duration was defined as the time from the point at which the secondary battery ignited as the temperature rose until the ignition continued and then naturally extinguished. The maximum temperature of the lithium secondary battery observed during this process was measured by attaching a thermocouple to the surface of the battery.

[0156] Type of Inner Layer Type Type of Surface Layer Total Number of Polymer Thin Film Layers Total Thickness of Polymer Thin Film Layers (nm) Duration of Thermal Runaway (sec) Maximum Temperature (°C) Example 1 PolyV4D4 Polyaniline 2150 3.4650 Example 2 PolyV4D4 Polyaniline 3200 3.0620 Comparative Example 1 Polyaniline 1100 8.4920 Comparative Example 2 PolyV4D4 Poly150 6.6850 Comparative Example 3 Polyaniline Polyaniline 2150 6.0800

[0157] Referring to Table 1 above, in the lithium secondary battery of Comparative Example 1, which had only a surface layer without an inner layer, the initial thermal runaway reaction was delayed by the surface layer, but as a result of continuous heating, thermal runaway eventually occurred at the surface of the battery, and as the thermal runaway continued to progress, the temperature continuously rose until thermal runaway occurred inside the battery and it took 8.4 seconds to naturally extinguish, and it was confirmed that the maximum temperature of the battery reached 920℃.

[0158] In Comparative Example 2, the lithium secondary battery equipped with only an inner layer without a surface layer exhibited thermal runaway from the beginning of heating due to the absence of a surface layer. Although the inner layer temporarily delayed the thermal runaway to the inside of the battery, it eventually occurred to the inside, resulting in a thermal runaway duration of 6.6 seconds and a maximum battery temperature of 850°C.

[0159] In the lithium secondary battery of Comparative Example 3, which used the same polymer for both the surface and inner layers, the initial thermal runaway reaction was delayed by the surface layer, similar to Comparative Example 1; however, as a result of continuous heating, thermal runaway eventually occurred at the surface of the battery. Furthermore, since the inner layer also used a polymer capable of absorbing oxygen well, the oxidation reaction of lithium occurred even in the inner layer, and the thermal runaway could not be suppressed. Consequently, it was confirmed that the duration of the thermal runaway was 6.0 seconds and the maximum temperature of the battery reached 800℃.

[0160] However, the thermal runaway duration of the lithium secondary battery in Example 1, which is provided with a surface layer on the surface of the negative electrode active material layer using a polymer capable of absorbing oxygen well and an inner layer between the negative electrode active material layer and the surface layer using a polymer with low oxygen permeability and strong heat resistance, was only 3.4 seconds, confirming that the ignition of the battery was naturally extinguished more quickly compared to Comparative Examples 1 to 3. In addition, the maximum temperature reached during the thermal runaway process was 650°C, which was a decrease of 18.75% compared to Comparative Example 3, which had the lowest maximum temperature among the comparative examples. As the temperature rose less, the degree of swelling of the battery was also reduced, improving the battery's lifespan.

[0161] In particular, the thermal runaway duration of the lithium secondary battery of Example 2, which includes two inner layers, was the shortest at 3.0 seconds, and the maximum temperature reached during the thermal runaway process was 620°C, which is a decrease of 22.5% compared to Comparative Example 3. Similar to the lithium secondary battery of Example 1, the degree of swelling of the battery was the least as the temperature rose less, and thus the battery life was improved.

[0162] That is, the negative electrode for a lithium secondary battery according to one embodiment described in this specification includes a surface layer and an inner layer, which are polymer thin film layers, thereby acting as a barrier against the oxidation reaction of lithium ions and oxygen escaping from the negative electrode active material, which can suppress thermal runaway reactions caused by oxidation heat and suppress swelling phenomena, thereby improving lifespan performance. In particular, by unifying the coating step for providing the negative electrode active material layer and the deposition step for providing the polymer thin film layer into a roll-to-roll process, it is possible to facilitate the formation of a protective layer on the surface and inside the negative electrode during manufacturing, thus ensuring processability.

[0163]

[0164] [Explanation of the symbol]

[0165] 10: Cathode current collector layer

[0166] 20: Cathode active material layer (first or second cathode active material layer)

[0167] 30: Separator

[0168] 40: Positive active material layer

[0169] 50: Positive current collector layer

[0170] 100: Negative electrode for lithium secondary battery

[0171] 200: Cathode for lithium secondary batteries

[0172] 300: Inner layer

[0173] 400: Surface layer

Claims

1. A negative active material layer provided on at least one surface of a negative current collector layer; A surface layer provided on the surface of the above-mentioned cathode active material layer; and It includes an inner layer provided between the above-mentioned negative electrode active material layer and the above-mentioned surface layer, and A negative electrode for a lithium secondary battery, wherein the surface layer and the inner layer comprise one or more selected from the group consisting of polyvinyl-based polymers, polyamide-based polymers, polysilane-based polymers, polyfluorene-based polymers, polyaniline-based polymers, and combinations thereof, and the inner layer and the surface layer comprise different polymers.

2. In Claim 1, A negative electrode for a lithium secondary battery, wherein the above surface layer comprises one or more selected from the group consisting of polyvinyl-based polymers, polyamide-based polymers, polyaniline-based polymers, and combinations thereof.

3. In Claim 1, A negative electrode for a lithium secondary battery, wherein the inner layer comprises one or more selected from the group consisting of polysilane-based polymers, polyfluorene-based polymers, and combinations thereof.

4. In Claim 1, The above negative electrode active material layer comprises two or more negative electrode active material layers, and A negative electrode for a lithium secondary battery, wherein the inner layer is provided between at least one pair of adjacent negative active material layers.

5. In Claim 1, The above inner layer is provided with n layers, and The above negative electrode active material layer is provided with n+1 layers, and A negative electrode for a lithium secondary battery, wherein the inner layer and the negative active material layer are alternately stacked, and n is an integer greater than or equal to 1.

6. In Claim 1, A negative electrode for a lithium secondary battery, wherein the total thickness of the surface layer and the inner layer is 2 μm or less.

7. In Claim 1, A negative electrode for a lithium secondary battery, wherein the thickness of the surface layer and the inner layer are each 1 nm or more and 400 nm or less.

8. In Claim 1, A negative electrode for a lithium secondary battery, wherein the above inner layer is provided in 1 to 5 layers.

9. In Claim 1, A negative electrode for a lithium secondary battery, wherein the above surface layer and the above inner layer are deposited on one surface of the above negative electrode active material layer.

10. Cathode for lithium secondary battery; A negative electrode for a lithium secondary battery according to any one of claims 1 to 9; Separator; and A lithium secondary battery containing an electrolyte.

11. A battery module comprising a lithium secondary battery according to claim 10.

12. A battery pack comprising a lithium secondary battery according to claim 10.

13. A battery pack comprising a battery module according to claim 11.

14. (S1) A step of forming a first negative active material layer by coating a negative active material layer composition on at least one surface of a negative current collector layer; (S2) A step of forming an inner layer on the first negative electrode active material layer; (S3) A step of forming a second cathode active material layer by coating the cathode active material layer composition on the inner layer; and (S4) A step of forming a surface layer on the second negative electrode active material layer, and A method for manufacturing a negative electrode for a lithium secondary battery, wherein the above steps S2 to S3 are repeated at least once and no more than five times.

15. In Claim 14, A method for manufacturing a negative electrode for a lithium secondary battery, wherein steps S1 to S4 are performed by a roll-to-roll process.

16. In Claim 14, A method for manufacturing a negative electrode for a lithium secondary battery, wherein the above S2 step and the above S4 step are performed by a deposition method using a roll-to-roll process.

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