electrodes, lithium secondary batteries containing them, and battery packs

Abstract

This specification relates to an electrode comprising an electrode current collector layer; an electrode active material layer; and a functional layer interposed between the electrode current collector layer and the electrode active material layer, wherein the functional layer comprises a specific type of flame retardant binder and has a limiting oxygen index of 30% or more, a lithium secondary battery, and a battery pack containing the same. The electrode according to the above embodiment can ensure battery characteristics while preventing thermal runaway.

Description

[Technical Field] 【0001】 This application relates to electrodes, lithium secondary batteries and battery packs including them. 【0002】 This application claims the benefits as of the filing date of Korean Patent Applications No. 10-2023-0192121 and No. 10-2024-0197936, filed with the Korean Intellectual Property Office on December 27, 2023 and December 27, 2024, respectively, and all of the contents thereof are incorporated herein by reference. [Background technology] 【0003】 Rechargeable batteries are batteries that can be reused after discharge through recharging. They can be used as an energy source for small devices such as mobile phones, tablet PCs, and vacuum cleaners, and as an energy source for medium-sized or large devices such as personal mobility devices, automobiles, and ESS (Energy Storage Systems) for smart grids. 【0004】 As a result of the increasing demand for high performance in secondary batteries to enable their use in a wide range of applications, lithium-ion secondary batteries, which possess high energy density, ease of processing, and can be applied to various electronic devices, have gained prominence through numerous research and development efforts. 【0005】 However, lithium secondary batteries are not only vulnerable to external shocks, but also prone to internal degradation and frequent fires. These problems can cause significant damage because they lead to heat transfer between numerous battery cells, resulting in thermal runaway at the assembly level, such as battery modules or battery packs connected in series and / or parallel. 【0006】 Specifically, if the internal temperature of a lithium-ion battery exceeds a certain temperature, the internal pressure of the cell increases due to the vaporization of the electrolyte, which may cause it to be ejected outside the cell or damage the separation membrane. If flammable gaseous substances ignite due to the vaporization of the electrolyte or if the separation membrane is damaged, it can cause an internal short circuit, leading to the heating of adjacent cells and subsequent continuous or chain reaction of inappropriate exothermic reactions, which can lead to ignition. This can cause the fire to spread and eventually throughout the entire battery pack. However, lithium ions are highly reactive with water, so attempting to extinguish the fire with water may only cause it to spread further. 【0007】 To address the aforementioned problems, research is underway on materials that can quickly block or suppress the phenomenon of inappropriate exothermic reactions occurring continuously or in a chain reaction at the electrode level. [Overview of the project] [Problems that the invention aims to solve] 【0008】 The inventors have completed an electrode that, by interposing a functional layer containing a flame-retardant binder with a critical oxygen index of 30% or higher between the current collector and the electrode active material layer, and by limiting the flame-retardant binder to a specific type, maintains the desired battery characteristics while simultaneously blocking inter-cell heat transfer and thermal runaway in advance. 【0009】 Specifically, this specification aims to provide an electrode having the above-mentioned features, a lithium secondary battery and a battery pack containing the same. [Means for solving the problem] 【0010】 One embodiment of the present specification provides an electrode including a current collector layer, an electrode active material layer, and a functional layer interposed between the current collector layer and the electrode active material layer, where the functional layer contains a flame retardant binder having a limiting oxygen index (LOI) of 30% or more measured based on ASTM D2863 method, and the flame retardant binder is one or more selected from phenolic resin, novolak resin, polyimide resin, polybenzoxazole resin, polybenzimidazole resin, polybenzothiazole resin, and halogenated aromatic resin. 【0011】 Another embodiment of the present specification provides a lithium secondary battery including a first electrode, a second electrode, a separator interposed between the first electrode and the second electrode, and an electrolyte, where at least one of the first electrode and the second electrode is the aforementioned electrode. 【0012】 Another embodiment of the present specification provides a battery pack including the aforementioned lithium secondary battery as a unit cell. 【Advantages of the Invention】 【0013】 The electrode according to one embodiment of the present invention maintains characteristics such as long life and low cell resistance, while simultaneously satisfying a high limiting oxygen index, and has a functional layer containing a flame retardant binder within a specific range located between the current collector layer and the electrode active material layer, making it difficult for oxygen to cause self-combustion of the electrode or combustion with other elements of the battery in the future, preventing further runaway, or delaying the time to thermal runaway. Furthermore, compared with a flame retardant electrolyte, the electrode according to the present invention reduces costs, is more easily applicable to processes, and is effective in suppressing side reactions. 【Brief Description of the Drawings】 【0014】 [Figure 1] It is a schematic diagram of the electrode according to the present invention. [Figure 2] It is a schematic diagram of the lithium secondary battery according to the present invention. [Figure 3] It is a schematic diagram of the lithium secondary battery according to the present invention. [Figure 4]This is a schematic diagram of the battery pack according to the present invention. [Figure 5] This is a schematic diagram of a means of transport including a battery pack according to the present invention. [Modes for carrying out the invention] 【0015】 Before describing the present invention, let us first define some terms. 【0016】 In this specification, "p~q" can mean the range "p or greater and q or less". 【0017】 In this specification, when a part is described as "containing" or "having" a component, unless otherwise defined, it may mean that it may include other components rather than excluding them. 【0018】 In this specification, singular expressions include plural expressions unless otherwise defined. 【0019】 Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person of ordinary skill in the art to which this invention pertains. Terms that are the same as those defined in commonly used dictionaries should be interpreted as having the meaning consistent with their meaning in the context of the relevant art, and not as ideal or overly formal unless explicitly defined herein. 【0020】 The present invention will be described in detail below with reference to the drawings so that a person with ordinary skill in the art to which the present invention pertains can easily implement it. However, the present invention can be embodied in various different forms and is not limited to the following description. 【0021】 <Electrode> The electrode 10 will be described below with reference to Figure 1. 【0022】 An electrode according to one embodiment of this specification includes a functional layer interposed between an electrode current collector layer and an electrode active material layer, wherein the functional layer contains a flame retardant binder with a limiting oxygen index of 30% or higher as measured according to the ASTM D2863 method, and the flame retardant binder is one or more selected from phenolic resin, novolac resin, polyimide resin, polybenzoxazole resin, polybenzimidazole resin, polybenzothiazole resin, and halogenated aromatic resin. 【0023】 Figure 1 shows an electrode 10 according to an embodiment of the present invention, and it can be seen that a functional layer 2 containing a specific type of flame retardant binder having a limit oxygen index of 30% or more is provided between the electrode current collector layer 1 and the electrode active material layer 3. 【0024】 In this specification, the critical oxygen index is the minimum volume fraction (%) of oxygen required to sustain combustion, and can be calculated using the following formula 1. 【0025】 【number】 【0026】 Furthermore, when measuring LOI based on the ASTM D2863 method, the object of measurement (flame retardant binder) is a Test specimen type IV (70 x 6.5 x 3 mm) 3 Test specimens can be prepared according to the following. 【0027】 The functional layer 2 has a high limiting oxygen index and contains a flame retardant binder within a specific range. Due to the low flammability of the flame retardant binder, it is difficult for the electrodes to self-combust by oxygen or to combust with other elements of the battery in the future, thereby preventing further thermal runaway or delaying the time it takes for thermal runaway to occur. 【0028】 As described above, when the critical oxygen index is 30% or higher and a specific type of flame-retardant binder is used, combustion is less likely to occur due to the flame retardancy of the functional layer when the electrode ignites, and heat transfer to the electrode current collector layer is suppressed. This delays the melting or combustion of the electrode current collector layer and delays the time it takes for thermal runaway to occur. 【0029】 According to one embodiment of this specification, the thickness of the electrode current collector layer may be 3 μm or more and 30 μm or less. 【0030】 Depending on the type of electrode current collector layer, the thickness of the electrode current collector layer can be adjusted. For negative electrode current collector layers using materials such as copper, the thickness is 5 μm or more or 6 μm or more, and it is preferable to change it to 25 μm or less or 20 μm or less. For positive electrode current collector layers using materials such as aluminum, the thickness is 7 μm or more or 8 μm or more, and it is preferable to change it to 25 μm or less or 20 μm or less. 【0031】 According to one embodiment of this specification, the overall thickness of the electrode may be 30 μm or more and 200 μm or less. The overall thickness of the electrode can be adjusted depending on the type of electrode. For example, in the case of a negative electrode, the thickness is 40 μm or more or 50 μm or more, and it is preferable to change it to 170 μm or less or 150 μm or less. In the case of a positive electrode, the thickness is 40 μm or more or 50 μm or more, and it may be preferable to change it to 120 μm or less or 100 μm or less. 【0032】 According to one embodiment of this specification, the thickness of the functional layer may be 0.1 μm or more and 10 μm or less. When the aforementioned thickness range is met, the flame retardancy is maximized while minimizing the increase in electrode thickness due to the functional layer, thereby achieving the desired effect of preventing thermal runaway. 【0033】 Depending on the requirements such as conductivity and heat dissipation characteristics, the upper limit of the thickness of the functional layer can be adjusted, preferably to 5 μm or less, 4 μm or less, or 3 μm or less. 【0034】 According to one embodiment of this specification, the functional layer may further contain a flame retardant. 【0035】 According to one embodiment of this specification, the functional layer may contain a flame-retardant binder in an amount of more than 0 parts by weight and up to 50 parts by weight, based on 100 parts by weight of the entire slurry contained in the functional layer. 【0036】 When the flame-retardant binder meets the aforementioned content range, it is superior in terms of preventing thermal runaway. 【0037】 According to one embodiment of this specification, the functional layer may contain 0.1 to 90 parts by weight of conductive material based on 100 parts by weight of the entire slurry contained in the functional layer. 【0038】 As long as the conductive material meets the above content range, it is excellent in terms of electrical conductivity within the electrode. However, in order to further improve conductivity, in some cases, the conductive material may be included in amounts of 10 parts by weight or more, 20 parts by weight or more, 30 parts by weight or more, 40 parts by weight or more, or 50 parts by weight or more, and 85 parts by weight or less, or 80 parts by weight or less, based on 100 parts by weight of the entire slurry contained in the functional layer. 【0039】 In this specification, the slurry contained in the functional layer may mean a mixture of a flame retardant binder and a solvent for forming the functional layer. 【0040】 In this specification, the solvent for forming the functional layer may be N-methyl-2-pyrrolidone (NMP), water, or the like, but is not limited thereto. 【0041】 According to one embodiment of this specification, the functional layer may contain 1 to 99 parts by weight of a flame-retardant binder based on 100 parts by weight of the entire slurry contained in the functional layer. 【0042】 As long as the flame retardant binder meets the above content range, the thermal runaway problem can be improved. However, in order to further prevent thermal runaway, the flame retardant binder may be included in amounts of 10 parts by weight or more, 15 parts by weight or more, 20 parts by weight or more, or 25 parts by weight or more, and 90 parts by weight or less, 70 parts by weight or less, or 50 parts by weight or less, based on 100 parts by weight of the entire slurry contained in the functional layer. 【0043】 According to one embodiment of this specification, the functional layer may include 0.1 parts by weight to 90 parts by weight of a conductive material and 1 part by weight to 99 parts by weight of a flame-retardant binder. 【0044】 According to one embodiment of this specification, the flame retardant may include an inorganic flame retardant, an organic flame retardant, or a combination thereof. 【0045】 In this specification, inorganic flame retardants can be selected from silicon-based flame retardants, aluminum-based flame retardants, molybdenum-based flame retardants, and the like, but those known in the industry may be used as long as they do not deviate from the scope of the present invention. 【0046】 In this specification, organic flame retardants can be selected from carbon-based flame retardants, halogen-based flame retardants, phosphorus-based flame retardants, nitrogen-based flame retardants, and the like, but those known in the industry may be used as long as they do not deviate from the scope of the present invention. 【0047】 According to one embodiment of this specification, the conductive material may be at least one of a planar conductive material, a linear conductive material, and a point conductive material. 【0048】 In this specification, the planar conductive material plays a role in improving conductivity by increasing surface contact with other elements within the functional layer, and can be described as a plate-like or bulk conductive material. Examples of planar conductive materials on the side surface of the functional layer can be selected from graphene, graphene oxide, etc., but graphene is preferred. 【0049】 In this specification, the linear conductive material may be a carbon nanotube. The carbon nanotube may be a bundle-type carbon nanotube. The bundle-type carbon nanotube may contain a plurality of carbon nanotube units. Specifically, unless otherwise specified, "bundle type" here refers to a bundle or rope-like secondary shape in which a plurality of carbon nanotube monomers are arranged in parallel or intertwined with substantially the same orientation along the longitudinal direction of the carbon nanotube monomers. The carbon nanotube unit has a graphite sheet that is cylindrical in shape with a nanoscale diameter, and sp 2 It has a bonded structure. Depending on the angle and structure in which the graphite surface is wound, it can exhibit conductive or semiconductor properties. Compared to entangled type carbon nanotubes, the bundled carbon nanotubes can be dispersed more uniformly, smoothly forming a conductive network within the functional layer and further improving conductivity. 【0050】 In this specification, the dot-shaped conductive material can be selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, conductive fibers, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, polyphenylene derivatives, etc., but any material known to the industry may be used as long as it does not deviate from the scope of the present invention. 【0051】 According to one embodiment of this specification, the flame retardant binder may include polymers and halogen-substituted polymers containing aromatic hydrocarbon rings, heterocycles, etc. Alternatively, the flame retardant binder may be one or more selected from the group consisting of phenolic resins, novolac resins, polyimide resins, polybenzoxazole (PBO) resins, polybenzimidazole resins, polybenzothiazole (PBT) resins, halogenated resins, etc. 【0052】 The functional layer containing the aforementioned flame-retardant binder can further prevent thermal runaway. 【0053】 According to one embodiment of this specification, the vertical resistance of the functional layer may be 0.5 Ω or less. When the vertical resistance of the functional layer satisfies the upper limit, problems with conductive connectivity due to the introduction of the functional layer can be prevented, and the electrical conductivity is excellent. The lower limit of the vertical resistance of the functional layer is not particularly limited as long as it is 0 Ω, but it is preferable that it be at least 0.1 Ω or more in order for the functional layer to maintain the desired conductivity between the electrode current collector layer and the electrode active material layer. 【0054】 In this specification, vertical resistance means measuring the resistance value Ω in the vertical direction when conductive loads (for example, circular metal blocks plated with Au on a Cu metal surface) are placed below and above the target material. The effect of the thickness on the functional layer is not significant, but preferably a thickness of 0.1 μm or more and 10 μm or less can exhibit a similar level of vertical resistance. 【0055】 According to one embodiment of this specification, the functional layer may further include a heat-dissipating filler. 【0056】 In this specification, the heat-dissipating filler may be selected from graphene, expandable graphite, and the like, but any material known in the industry may be used as long as it does not deviate from the scope of the present invention. 【0057】 According to one embodiment of this specification, the functional layer may further contain graphene. 【0058】 In this specification, graphene is included as a flame retardant, a conductive material, and / or a heat-dissipating filler. 【0059】 According to one embodiment of this specification, the functional layer may further include SWCNTs (in addition to graphene). 【0060】 In this specification, the SWCNT is included as a conductive material. 【0061】 <Lithium-ion secondary battery> The lithium secondary batteries shown in Figures 2 and 3 will be described below. 【0062】 According to one embodiment of this specification, a lithium secondary battery comprising a first electrode; a second electrode; a separation membrane interposed between them; and an electrolyte, characterized in that either the first electrode or the second electrode is the aforementioned electrode. 【0063】 The lithium secondary battery of the above embodiment includes the aforementioned electrodes, thereby enabling the pre-emptive isolation of the lithium secondary battery components and factors that could cause thermal runaway. 【0064】 Referring to Figure 2, a separation membrane 11 is interposed between the first electrode 10-1 and the second electrode 10-2, and at least one of the first electrode 10-1 and the second electrode 10-2 may be the aforementioned electrode. Specifically, referring to Figure 3, one surface of the separation membrane 11 is in contact with one surface of the electrode active material layer 3, one surface of the functional layer 2 is in contact with the surface of the electrode active material layer 3 opposite to the surface in contact with the separation membrane 11, and the electrode current collector layer 1 may be provided on the surface of the functional layer 2 opposite to the surface in contact with the electrode active material layer 3. 【0065】 In this specification, the first electrode may be a negative electrode and the second electrode a positive electrode, or the first electrode may be a positive electrode and the second electrode a negative electrode. 【0066】 Consequently, when the aforementioned electrode is the negative electrode, the aforementioned electrode current collector layer is sometimes referred to as the negative electrode current collector layer, and the aforementioned electrode active material layer is sometimes referred to as the negative electrode active material layer. The specific details are as follows. 【0067】 In this specification, the negative electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and is conductive. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treatments with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. 【0068】 In this specification, the negative electrode current collector generally can have a thickness of 1 μm to 100 μm, and fine irregularities can also be formed on the surface of the current collector to enhance the adhesive force of the negative electrode active material. Further, the negative electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric body, etc. 【0069】 In one embodiment of this specification, the negative electrode active material layer may contain at least one of a silicon-based active material and a carbon-based active material. 【0070】 In one embodiment of this specification, the negative electrode active material layer may contain a carbon-based active material. 【0071】 The carbon-based active material can prevent expansion due to repeated charge and discharge on the side of the negative electrode of the present invention or the lithium secondary battery, and contribute to the improvement of excellent cycle characteristics or battery life performance. 【0072】 In one embodiment of this specification, the negative electrode active material layer may contain a silicon-based active material. 【0073】 Generally, it is known that a silicon-based active material has a capacity 10 times or more higher than that of a carbon-based active material. Thereby, when applying a silicon-based active material to the negative electrode, an electrode having a high level of energy density can be realized even with a thin thickness. 【0074】 In one embodiment of this specification, the silicon-based active material may contain one or more selected from the group consisting of SiOx (x = 0), SiOx (0 <x <2), Si / C composite, and Si alloy. 【0075】 On the other hand, in the case of SiO2, since it does not react with lithium ions and cannot store lithium, x is preferably within the above range. The silicon-based active material may be a Si / C composite composed of a composite of Si and C or Si. 【0076】 If necessary, the silicon-based active material can mean a single substance or a mixed substance composed of two or more substances combined. 【0077】 In one embodiment of the present specification, the silicon-based active material includes one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 <x <2), and based on 100 parts by weight of the silicon-based active material, there is provided a negative electrode composition containing 70 parts by weight or more of the SiOx (x = 0). 【0078】 In one embodiment of the present specification, the silicon-based active material may contain 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more of the SiOx (x = 0), based on 100 parts by weight of the silicon-based active material, and may contain 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less. 【0079】 The silicon-based active material according to the present specification contains 70 parts by weight or more of the SiOx (x = 0) based on 100 parts by weight of the silicon-based active material. Compared with a silicon-based active material using a SiOx (0 <x <2) system as the main substance, the theoretical capacity can be much higher than that of the silicon-based active material of the present specification. 【0080】 In one embodiment of the present specification, pure silicon (Si) can be used as the silicon-based active material. Using pure silicon (Si) as the silicon-based active material means, as described above, that the silicon-based active material contains pure Si particles (SiOx (x = 0)) not bonded to other particles or elements within the above range when based on 100 parts by weight in total. 【0081】 In one embodiment of the present specification, the negative electrode active material layer may further include a negative electrode conductive material and a negative electrode binder. 【0082】 The aforementioned negative electrode conductive material is used to impart conductivity to the electrode and can be used without particular limitations as long as it does not cause chemical changes on the side of the battery and possesses electronic conductivity. However, the negative electrode conductive material is applied to the negative electrode and has a completely different structure from the positive electrode conductive material applied to the positive electrode. In other words, the negative electrode conductive material plays the role of capturing the contact points between silicon-based active materials, where the volume expansion of the electrodes is very large due to charging and discharging, while the positive electrode conductive material plays the role of a buffer when rolled, while also imparting some conductivity. Therefore, the negative electrode conductive material and the positive electrode conductive material have different structures and roles. 【0083】 Specific examples of the negative electrode conductive material may include one or more selected from the group consisting of point-shaped conductive materials, planar conductive materials, and linear conductive materials. 【0084】 Specifically, the point-like conductive material is 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 fibers, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives. Preferably, it may contain carbon black and / or artificial graphite in that it exhibits high conductivity and excellent dispersibility. 【0085】 The planar conductive material can improve conductivity by increasing surface contact between silicon particles within the negative electrode, and at the same time suppress the disruption of the conductive path due to volume expansion. The planar conductive material can be described as a plate-type conductive material or a bulk-type conductive material. An example of the planar conductive material may include at least one selected from the group consisting of plate graphite, graphene, graphene oxide, and graphite flakes, and is preferably plate graphite. 【0086】 The linear conductive material may be a carbon nanotube. The carbon nanotube may be a bundle-type carbon nanotube. The bundle-type carbon nanotube may contain multiple carbon nanotube units. Specifically, "bundle type" here refers to a bundle or rope-like secondary shape in which multiple carbon nanotube monomers are arranged in parallel or intertwined with substantially the same orientation of their longitudinal axes. The carbon nanotube unit has a graphite sheet that is cylindrical in shape with a nanoscale diameter, and sp 2 It has a bonded structure. Depending on the angle and structure in which the graphite surface is wound, it can exhibit conductive or semiconductor properties. Compared to entangled type carbon nanotubes, the bundled carbon nanotubes can be dispersed more uniformly during anode manufacturing, smoothly forming a conductive network within the anode and improving the conductivity of the anode. 【0087】 In one embodiment of this specification, the negative electrode conductive material is provided in an amount of 0.1 parts by weight or more and 40 parts by weight or less, based on 100 parts by weight of the negative electrode composition. 【0088】 In another embodiment, the negative electrode conductive material may contain 0.1 parts by weight or more and 40 parts by weight or less, preferably 0.2 parts by weight or more and 30 parts by weight or less, more preferably 0.4 parts by weight or more and 25 parts by weight or less, and most preferably 0.4 parts by weight or more and 10 parts by weight or less, based on 100 parts by weight of the negative electrode composition. 【0089】 The anode binder plays a role in improving adhesion between anode active material particles and adhesion between the anode active material and the anode current collector. Depending on whether it dissolves well in an aqueous solvent such as water, it can be classified into aqueous binders and non-aqueous binders (organic binders). Specific examples of the anode binder include carboxymethylcellulose (CMC) binders, styrene-butadiene rubber (SBR) binders, polyacrylic acid (PAA) binders, polyacrylamide (PAM) binders, polyacrylonitrile (PAN) binders, polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyethylene glycol (PEG), etc., or various copolymers derived from these may be used, or a mixture of two or more selected from these may be used. 【0090】 In one embodiment of this specification, a negative electrode composition is provided in which the weight-average molecular weight of the negative electrode binder is 100,000 g / mol or more and 1,000,000 g / mol or less. 【0091】 In this specification, 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 of various degrees of polymerization (standard samples) as standard substances. In this specification, molecular weight refers to weight-average molecular weight unless otherwise specified. 【0092】 By satisfying the aforementioned weight-average molecular weight range, the material will exhibit excellent mechanical strength, high intermolecular interaction, and superior electrode bonding strength. Furthermore, satisfying this range allows the binder viscosity to be set to an appropriate range, and when this is used to manufacture the negative electrode, it will exhibit excellent electrode coating properties. 【0093】 In one embodiment of this specification, the negative electrode binder is provided in an amount of 1 to 20 parts by weight, based on 100 parts by weight of the negative electrode composition. 【0094】 In one embodiment of this specification, the negative electrode binder may contain 20 parts by weight or less, preferably 15 parts by weight or less, based on 100 parts by weight of the negative electrode composition, and may also contain 1 part by weight or more, 5 parts by weight or more, or 10 parts by weight or more. 【0095】 As described above, when it includes a negative electrode active material, a negative electrode conductive material, and a negative electrode binder, it can be referred to as a negative electrode composition. 【0096】 In some cases, a solvent may be added to the negative electrode composition, which may be referred to as a negative electrode slurry. The solvent used here may be referred to as a solvent for forming the negative electrode slurry. 【0097】 The solvent for forming the negative electrode slurry may be, but is not limited to, N-methyl-2-pyrrolidone (NMP) or water. 【0098】 In this specification, the negative electrode means that the negative electrode has undergone a series of electrode processes, including a coating step of applying a negative electrode slurry to at least one surface of the negative electrode current collector, a pressing step of pressing it to a certain thickness with a roll press, and a slitting step of cutting it out according to the specifications of the electrode. 【0099】 In one embodiment of this specification, the negative electrode may be formed by coating one or both sides of a current collector with a negative electrode slurry containing the negative electrode composition. 【0100】 In one embodiment of this specification, the solid content of the negative electrode slurry may be 5% or more and 40% or less. 【0101】 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%. 【0102】 The solid content of the negative electrode slurry can mean the content of the negative electrode composition contained in the negative electrode slurry, and can mean the content of the negative electrode composition based on 100 parts by weight of the negative electrode slurry. 【0103】 When the solid content of the negative electrode slurry satisfies the aforementioned range, the viscosity is appropriate during the formation of the negative electrode active material layer, minimizing the clumping phenomenon of the negative electrode composition particles and enabling efficient formation of the negative electrode active material layer. 【0104】 Further details regarding the aforementioned negative electrode are subject to the standards known in this industry. 【0105】 Therefore, when the aforementioned electrode is the positive electrode, the aforementioned electrode current collector layer can be called the positive electrode current collector layer, and the aforementioned electrode active material layer can be called the positive electrode active material layer. The specific details are as follows. 【0106】 The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc., can be used. The positive electrode current collector can usually have a thickness of 1 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to increase the adhesion strength of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as film, sheet, foil, net, porous material, foam, or nonwoven fabric. 【0107】 In one embodiment of the present specification, the thickness of the positive electrode current collector layer is 1 μm or more and 100 μm or less, and the thickness of the positive electrode active material layer may be 20 μm or more and 500 μm or less. However, the thickness can be variously deformed depending on the type and use of the positive electrode used, and is not limited thereto. 【0108】 The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; chemical formula Li 1+c1 Mn 2-c1 O4 (0 ≦ c1 ≦ 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 O2 (where M is at least any one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01 ≦ c2 ≦ 0.3), Ni-site type lithium nickel oxide represented by; chemical formula LiMn 2-c3 M c3 O2 (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 lithium manganese composite oxide represented by Li2Mn3MO8 (where M is at least any one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); examples include LiMn2O4 in which a part of Li in the chemical formula is substituted with an alkaline earth metal ion, but are not limited thereto. The positive electrode may be Li-Metal. 【0109】 The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the aforementioned positive electrode active material. When including the positive electrode active material, the positive electrode conductive material, and the positive electrode binder, it is referred to as a positive electrode composition, and when further including a solvent for forming a positive electrode slurry in the positive electrode composition, it can be referred to as a positive electrode slurry. 【0110】 The positive electrode conductive material is used to impart conductivity to the electrode and can be used without particular limitations in the battery it is configured in, as long as it does not cause chemical changes and has electronic conductivity. Specific examples include graphite such as natural graphite or 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 powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these may be used alone or in mixtures of two or more. 【0111】 The positive electrode binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples of the positive electrode binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, etc., or various copolymers derived from these, or mixtures of two or more selected from these can be used. 【0112】 When the aforementioned solvent refers to a solvent for forming a positive electrode slurry, it may, but is not limited to, N-methyl-2-pyrrolidone (NMP), water, etc. 【0113】 In this specification, the positive electrode means one that has undergone a series of electrode processes, including a coating step of applying a positive electrode composition to at least one surface of a positive electrode current collector, a pressing step of pressing it to a certain thickness with a roll press, and a slitting step of cutting it out according to the specifications of the electrode. 【0114】 Further details regarding the aforementioned positive electrode are subject to the standards known in the industry. 【0115】 In this specification, the term "electrolyte" refers to a substance that can be used in the manufacture of a lithium secondary battery, and includes, but is not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes. 【0116】 Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt. 【0117】 Specific examples of the aforementioned non-aqueous organic solvents include non-protonate 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, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate. 【0118】 In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are preferred because they have high dielectric constants as high-viscosity organic solvents and effectively dissociate lithium salts. Furthermore, when such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in appropriate proportions, an electrolyte with high electrical conductivity can be created, and this mixture is more preferably used. 【0119】 The metal salt may be a lithium salt, and the lithium salt is a substance that is easily soluble in the non-aqueous electrolyte, for example, the anion of the lithium salt is 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 - You may use one or more selected from the group consisting of the following: 【0120】 In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for the purpose of improving the battery's lifespan, suppressing the decrease in battery capacity, and improving the battery's discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. 【0121】 In this specification, the separation membrane separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any membrane commonly used as a separation membrane in lithium secondary batteries is generally acceptable. In particular, the separation membrane is preferably one that exhibits low resistance to ion movement in the electrolyte while having excellent electrolyte moisture absorption capacity. Specifically, porous polymer films, such as those made from polyolefin polymers like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof, may be used. Alternatively, ordinary porous nonwoven fabrics, such as those made from high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, coated separation membranes containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and may be selectively used in single-layer or multi-layer structures. 【0122】 In this specification, a lithium secondary battery may be a concept that includes an electrode assembly comprising a positive electrode, a negative electrode, and a separator membrane, and a battery case containing an electrolyte. 【0123】 <Battery Pack> The battery pack described herein is shown in Figure 4. 【0124】 One embodiment of this specification provides a battery module and / or battery pack 300 that includes the lithium secondary battery 200 as a unit cell. 【0125】 Since the battery module and / or battery pack includes the lithium secondary battery 200, the above-mentioned provisions regarding lithium secondary batteries can be applied as is. 【0126】 In this specification, the battery pack 300 may have a structure in which a lithium secondary battery 200 is included in the pack housing 201. However, the lithium secondary battery 200 may be replaced with a coin-shaped, pouch-shaped, rectangular, or the like, as needed, in addition to the cylindrical shape shown. 【0127】 In some cases, the battery packs described herein may include one or more battery module units. 【0128】 As shown in Figure 5, the battery pack 300 can be used as a power source for medium- and large-sized devices selected as needed from a group consisting of means of transport 400 such as electric vehicles, hybrid electric vehicles, and plug-in hybrid electric vehicles, and energy storage systems (EES). [Examples] 【0129】 The following are preferred embodiments to aid in understanding the present invention. However, these embodiments are for illustrative purposes only, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of this description and the technical concept, and such variations and modifications will naturally fall within the scope of the appended claims. 【0130】 Examples: Manufacturing of lithium secondary batteries Example 1 (1) Manufacturing of negative electrodes with functional layers Functional layers (thickness: 3 μm) were positioned on both sides of a negative electrode current collector (thin copper (Cu) film, thickness: 8 μm). Here, the functional layer was prepared by dispersing SWCNT and SFG6L as conductive materials and polybenzimidazole as a flame retardant binder in a weight ratio of 2:70:28 in a solvent (N-methyl-2-pyrrolidone, NMP (solvent for forming functional layers)) to make a slurry, which was then applied to the negative electrode current collector and dried to provide a functional layer on one side of the negative electrode current collector. 【0131】 Next, a negative electrode slurry is applied to the opposite side of the negative electrode current collector from the surface in contact with the functional layer and to the opposite side of the functional layer from the surface in contact with the negative electrode current collector at a rate of 3.75 mAh / cm³. 2 The negative electrode was manufactured by coating it with the specified loading amount, drying it in a vacuum oven at 130°C for 10 hours, and then rolling it (roll press). 【0132】 Specifically, the negative electrode slurry was manufactured as follows: Graphite and Si / C (average particle size (D)) were used as the negative electrode active material. 50 A negative electrode slurry was prepared by adding a first conductive material and a second conductive material as conductive materials, and polyacrylamide and SBB (styrene-butadiene rubber) as binders in a weight ratio of 8:13:1.6:0.4:2.5:2.5 to a solvent (distilled water) (solid content concentration 35% by weight). Here, the first conductive material was a plate-shaped graphite (specific surface area 17 m²). 2 / g, average particle size (D 50 The first conductive material was 3.5 μm thick, and the second conductive material was a single-walled carbon nanotube (SWCNT). As a mixing method, the first conductive material, the second conductive material, the binder, and water were dispersed in a HOMO MIXER (PRIMIX) at 2,500 rpm for 30 minutes, and then the negative electrode active material was added and dispersed at 2,500 rpm for 30 minutes to produce a negative electrode slurry. 【0133】 (2) Manufacturing of the positive electrode Cathode active material (LiN 6.1 Co 0.8 Mn 3.1A cathode slurry was prepared by adding O2, a cathode conductive material (multiwalled carbon nanotube, MWCNT), and a binder (PVdF, KF9700) to a solvent (N-methyl-2-pyrrolidone, NMP) in a weight ratio of 97.4:1.1:1.5 (solid content concentration 67 wt%). The cathode slurry was tested at 3.6 mAh / cm³. 2 After coating and drying the positive electrode current collector (aluminum (Al) thin film, thickness: 12 μm) with the loading amount (same as the negative electrode manufacturing method), the positive electrode was manufactured by rolling it in a roll press to form a positive electrode active material layer on the positive electrode current collector. 【0134】 (3) Manufacturing of lithium secondary batteries An electrode assembly was manufactured by placing a compression-resistant thin film separation membrane (PE15μm) with a ceramic coating of 4μm / 4μm between the negative electrode and the positive electrode. After positioning the electrode assembly inside the battery case, an electrolyte (a mixed solution of ethyl carbonate (EC):methyl ethyl carbonate (EMC) = 50:50 (volume ratio) in which 1M LiPF6 was dissolved) was injected into the case to manufacture a lithium secondary battery. 【0135】 Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the functional layer, which was previously provided on the negative electrode current collector, was instead provided on the positive electrode current collector. 【0136】 Example 3 A lithium secondary battery was manufactured in the same manner as in Example 1, except that 15 parts by weight of fluorophosphazene was further used as a flame retardant, and the content of other components (i.e., conductive materials) in the slurry was proportionally reduced. 【0137】 Example 4 The lithium secondary battery was manufactured in the same manner as in Example 1, except that the functional layer used SWCNTs and graphene as conductive materials, and polybenzimidazole was prepared as a flame retardant binder in a weight ratio of 2:75:23 to produce the slurry. 【0138】 Comparative Example 1 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the functional layer provided on the negative electrode current collector was removed. 【0139】 Comparative Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the functional layer provided on the negative electrode current collector contained PAA (poly(meth)acrylic acid) instead of polybenzimidazole as a flame retardant binder. Comparative Example 3 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the functional layer provided on the negative electrode current collector contained polyvinyl alcohol as a flame retardant binder, and a conductive material consisting of SWCNTs, graphene, and polyvinyl alcohol dispersed in water in a weight ratio of 2:70:28 was used. 【0140】 Comparative Example 4 A lithium secondary battery was manufactured in the same manner as in Example 1, except that a functional layer provided on the negative electrode current collector was manufactured using a binder containing PTFE (polytetrafluoroethylene) instead of polybenzimidazole as a flame retardant. 【0141】 Reference example 1 A lithium secondary battery was manufactured in the same manner as in Example 1, except that the functional layer provided on the negative electrode current collector did not contain SWCNTs as a conductive material. 【0142】 Experimental example Experimental Example 1: Measurement of Limiting Oxygen Index (LOI) The critical oxygen index was measured for the flame retardant binder contained in each of the functional layers of Examples 1 and 3 and Comparative Examples 2 to 4. The critical oxygen index was measured using an oxygen index meter (LOI-404 (Korean Industrial Laboratory Equipment)) based on the ASTM D2863 method, and the evaluation results of the critical oxygen index are shown in Table 1 below. 【0143】 [Table 1] 【0144】 According to Table 1, Examples 1 and 3 and Comparative Example 4 had a functional layer containing polybenzimidazole or PTFE as a flame retardant binder, and their LOIs were 42%, 51%, and 95%, respectively, exceeding 30%. In contrast, Comparative Examples 2 and 3, even though they had a functional layer containing PAA and PVA as flame retardant binders, respectively, had LOIs below 17%, 24%, and 30%, respectively. 【0145】 Experiment Example 2: Measurement of Vertical Resistance A 2.6 cm diameter gold-plated Cu circular metal plate was placed in contact with the electrodes (negative or positive) of Examples 1-4, Comparative Examples 1-4, and Reference Example 1, both above and below them. The electrode resistance in the vertical direction was measured three times, and the average value was defined as the vertical resistance. The evaluation results for the vertical resistance are shown in Table 2 below. 【0146】 [Table 2] 【0147】 According to Table 2, while the vertical resistance of the functional layer in Examples 1-4 and Comparative Examples 1-4 was 0.5Ω or less, in Reference Example 1, which does not contain conductive material such as SWCNTs in the functional layer, the vertical resistance was 0.95Ω, exceeding 0.5Ω. This confirms that it is not suitable as a functional layer located between the electrode active material layer and the electrode current collector. Here, Examples 1-4 showed a vertical resistance of 0.1Ω or less, while Comparative Examples 2-4 showed a vertical resistance of 0.1Ω or more, indicating a difference. 【0148】 Experiment Example 3: Stability Experiment A heat pad was applied to one side of the lithium secondary battery cells of Examples 1-4, Comparative Examples 1-4, and Reference Example 1, and the temperature of the heat pad was raised until the cell exploded. The explosion pressure was measured using an Autoclave device. 【0149】 The reaction time is a value obtained from the test results of the autoclave equipment, and the definition of the reaction time is the point at which the pressure rises during thermal runaway (TR), as shown in Equation 2 below. initial ) from the point where the maximum pressure is reached (TR max This refers to the time until ). 【0150】 【number】 【0151】 Furthermore, the TR rate is a value obtained by normalizing the explosion rate of the cell during thermal runaway by the cell capacity, using the reaction time value derived from Equation 2 above. This value was also calculated from the test results of the Autoclave device, and its unit is mbar / (sec*mAh). The evaluation results are shown in Table 3 below. 【0152】 [Table 3] 【0153】 According to Table 3, the TR rate of Examples 1-4 and Comparative Example 4 was a maximum of 4.3 mbar / (sec*mAh), which was lower than the TR rate values ​​of Comparative Examples 1-3 and Reference Example 1. This result suggests that even with lithium secondary batteries of the same capacity, the lithium secondary batteries of Examples 1-4 and Comparative Example 4 have improved stability because their cell explosion rates are lower than those of Comparative Examples 1-3 and Reference Example 1. 【0154】 Experimental Example 4: Capacity Retention Rate and Lifetime Characteristics For the lithium secondary batteries of Examples 1-4, Comparative Examples 1-4, and Reference Example 1, life evaluations were performed using an electrochemical charger / discharger, and the capacity retention rate was evaluated. 【0155】 In-situ cycle testing was performed on lithium secondary batteries at 4.2-3.0V 1C / 0.5C. During the test, the batteries were charged / discharged at 0.33C / 0.33C (4.2-3.0V) every 50 cycles, and the life retention rate was calculated using Equation 3 below (where N is 100). The evaluation results are shown in Table 4 below. 【0156】 【number】 【0157】 [Table 4] 【0158】 According to Table 4, Examples 1-4 and Comparative Example 1 showed a lifetime retention rate of 80% or more, suggesting that lithium secondary batteries with a functional layer (Examples 1-4) are no different from lithium secondary batteries without a functional layer (Comparative Example 1) in terms of lifetime retention rate. However, the lithium secondary batteries of Comparative Examples 2 and 3, which had a functional layer but an LOI of less than 30%, had low lifetime retention rates of 75% and 71%, respectively, suggesting that the complex interrelationship between the functional layer and the electrode current collector layer or electrode active material layer affects the reduction in lifetime retention rate. In the case of Comparative Example 4, although the LOI was high at 95%, it was confirmed that the dispersion and coating properties were poor, the cell resistance was poor (exceeding 0.1Ω), and the lifetime retention rate was also poor. 【0159】 Furthermore, even with a functional layer, the lithium secondary battery in Reference Example 1, which lacked conductive materials such as SWCNTs, had the lowest life retention rate at 32%. This suggests that, given the introduction of the functional layer between the electrode active material layer and the electrode current collector layer, it is necessary to ensure conductivity in the functional layer. [Explanation of Symbols] 【0160】 1 ···Electrode current collector layer 2 ··· Functional Layer 3...electrode active material layer 10...electrode 10-1...1st electrode 10-2...Second electrode 11...Separation membrane 20 ···Lithium secondary battery (cross-section) 100 ···Lithium rechargeable batteries 201 ···Housing 300... Battery pack 400 ··Means of transportation

Claims

[Claim 1] It includes an electrode current collector layer, an electrode active material layer, and a functional layer interposed between the electrode current collector layer and the electrode active material layer, The functional layer contains a flame-retardant binder with a Limiting Oxygen Index of 30% or higher, as measured according to the ASTM D2863 method. The flame-retardant binder is one or more selected from phenolic resin, novolac resin, polyimide resin, polybenzoxazole resin, polybenzimidazole resin, polybenzothiazole resin, and halogenated aromatic resin, in the electrode. [Claim 2] The electrode according to claim 1, wherein the thickness of the functional layer is 0.1 μm or more and 10 μm or less. [Claim 3] The electrode according to claim 1, wherein the functional layer further comprises a flame retardant. [Claim 4] The electrode according to claim 1, wherein the functional layer further comprises a conductive material. [Claim 5] The electrode according to claim 1, wherein the functional layer comprises 0.1 parts by weight or more and 90 parts by weight or less of a conductive material and 1 part by weight or more and 99 parts by weight or less of a flame-retardant binder. [Claim 6] The electrode according to claim 3, wherein the flame retardant comprises at least one inorganic flame retardant and an organic flame retardant. [Claim 7] The electrode according to claim 4, wherein the conductive material is at least one of a planar conductive material, a linear conductive material, and a point conductive material. [Claim 8] The electrode according to claim 1, wherein the functional layer further comprises a heat-dissipating filler. [Claim 9] The electrode according to claim 1, wherein the functional layer further comprises graphene. [Claim 10] The electrode according to claim 9, wherein the functional layer further comprises single-walled carbon nanotubes (SWCNTs). [Claim 11] The electrode according to claim 1, wherein the vertical resistance of the functional layer is 0.5 Ω or less. [Claim 12] first electrode; second electrode; A separation membrane interposed between the first electrode and the second electrode; and electrolyte Includes, A lithium secondary battery in which at least one of the first electrode and the second electrode is the electrode described in any one of claims 1 to 11. [Claim 13] A battery pack comprising a lithium secondary battery as described in claim 12 as a unit cell.

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