Composition for forming a lithium secondary battery anode

Abstract

A composition for forming a lithium secondary battery anode, comprising an anode active material, a conductive material, and a binder. Specifically, the binder contains a triblock copolymer comprising a soft block derived from an aliphatic or alicyclic diene-based monomer and forming a rubbery phase at room temperature, and a first hard block and a second hard block associated with both ends of the soft block, derived from an aromatic ring-containing ethylenically unsaturated monomer, and forming a glassy phase at room temperature, and wherein the binder comprises particles having an average diameter (D 50 ) of 1 µm or more and 50 µm or less.

Description

TECHNICAL FIELD

[0001] The present invention / disclosure relates to a composition for forming a lithium secondary battery anode, and the composition comprises a binder containing a triblock copolymer having a soft block and a hard block. BACKGROUND

[0002] Lithium secondary batteries have been used in the portable electronics market since their introduction in the 1990s and remain the most widely researched energy storage system. Due to the characteristics of lithium secondary batteries, such as high operating voltage, high energy density, low self-discharge, high power, and long cycle stability, lithium secondary batteries meet suitable requirements as a power source for electric vehicles.

[0003] However, the lithium secondary battery used in electric vehicles faces three major problems: safety, operating time, and cost. The problems of safety and operating time can be solved by a solid-state battery, but cost is a factor hindering the widespread application of the lithium secondary battery, prompting much research to reduce the cost of the lithium secondary battery.

[0004] Reducing the energy consumption required for lithium secondary battery production or increasing the electrode thickness is one of the most effective ways to reduce the manufacturing cost of lithium secondary batteries. Conventional electrode manufacturing technology involves pouring a slurry containing an electrode active material, a polymer binder, and a conductive additive in water or an organic solvent onto a current collector, drying, and pressing the slurry. However, since the energy required for preparing the slurry and applying it to the current collector accounts for approximately 50% of the energy consumed in the entire manufacturing process, a process for producing the electrode in a dry, solvent-free manner has been explored to reduce the manufacturing cost of lithium secondary batteries.

[0005] Although the technology for producing the electrode in a dry manner has been extensively researched, there is still a need for research and development regarding the technology for producing an anode in a dry manner with excellent mechanical properties such as formability, electrochemical stability and tensile strength, as well as a composition for forming the anode. EXPLANATION OF THE INVENTION / DISCLOSURE

[0006] In preferred aspects, the present invention / disclosure provides a composition for forming a lithium secondary battery anode. The composition comprises a binder containing a triblock copolymer having a hard block contributing to excellent mechanical properties and a soft block exhibiting flexibility. Such a composition is not only easy to form and stable at a negative potential, but also can firmly bond to an anode active material. Furthermore, it has excellent tensile strength and forms a three-dimensional network that can firmly bond to the anode active material and a conductive material.

[0007] In certain aspects, the lithium secondary battery is a solid-state battery. As used herein, the term "solid-state battery" refers to a rechargeable secondary battery that includes an electrolyte in a solid state, e.g., gel or (cured) polymer, which may include an ionomer and other electrolytic components for transferring ions between the battery's electrodes.

[0008] In one aspect, a composition for forming a lithium secondary battery anode is provided, and the composition comprises: an anode active material (e.g., an anode active material), a conductive material (e.g., an electrically conductive material), and a binder. The binder comprises: (i) a triblock copolymer comprising a soft block derived from an aliphatic or alicyclic diene-based monomer and forming a rubbery (e.g., rubber-like) phase at room temperature, and (ii) a first hard block and a second hard block, each connected to both ends of the soft block (e.g., associated with respective ends of the soft block), which are derived from an ethylenically unsaturated monomer containing an aromatic ring and form a glassy phase at room temperature, and wherein the binder comprises particles having an average diameter (D 50) of about 1 µm or more and 50 µm or less.

[0009] As used herein, a rubbery phase or state is above the T g (glass transition temperature) of the material, ie the material can be in a more rubbery state and be comparatively soft and flexible (e.g. the material can be in a more rubbery state and be comparatively soft and flexible in a rubbery phase or a rubbery state above the T g (glass transition temperature) of the material). Therefore, when it is mentioned here that the material forms a rubbery phase at room temperature (e.g., 25 °C), the material may be above its glass transition temperature at room temperature (25 °C) and be in a comparatively rubbery or more flexible state.

[0010] As used herein, a glassy phase or state lies below the T g(glass transition temperature) of the material, and the material may be in a stiffer or glassy configuration (e.g., the material may be in a stiffer or glassy configuration in a glassy phase or a glassy state below the T g (glass transition temperature) of the material). Therefore, when it is mentioned here that the material forms a glassy phase at room temperature (e.g., 25°C), the material may be below its glass transition temperature at room temperature (25°C) and in a comparatively rigid or hardened state.

[0011] In some embodiments, the binder is spherical and has an average sphericity of about 0.7 or more and about 1.0 or less.

[0012] In some embodiments, the first and second glass transition temperatures associated with the first hard block and the second hard block are about 50°C or higher and about 120°C or lower, and the third glass transition temperature associated with the soft block is about -120°C or higher and about -50°C or lower.

[0013] In some embodiments, the soft block is derived from an aliphatic diene-based monomer comprising one or more selected from the group consisting of a butadiene-based monomer, a pentadiene-based monomer, and a hexadiene-based monomer.

[0014] In some embodiments, the butadiene-based monomer comprises one or more selected from the group consisting of 1,2-butadiene, 1,3-butadiene, isoprene, and chloroprene.

[0015] In some embodiments, the first hard block and the second hard block are each independently derived from an aromatic ring-containing ethylenically unsaturated monomer containing one or more of a styrene-based monomer and an aromatic (meth)acrylic-based monomer.

[0016] In some embodiments, the styrene-based monomer comprises one or more selected from the group consisting of styrene, α-methylstyrene, p-methylstyrene, p-methoxystyrene, p-ethoxystyrene, t-butoxystyrene, p-acetoxystyrene, p-chlorostyrene, p-bromostyrene, 2,4-dimethylstyrene, 3,5-dimethylstyrene, and 2,4,6-trimethylstyrene.

[0017] In some embodiments, the (meth)acrylic-based aromatic monomer comprises one or more selected from the group consisting of benzyl acrylate, benzyl methacrylate, phenoxyacrylate, phenoxymethacrylate, phenyl acrylate, phenyl methacrylate, phenylethyl acrylate, and phenylethyl methacrylate.

[0018] In some embodiments, the anode active material comprises one or more selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material that may be alloyed with lithium, and a lithium-containing active material.

[0019] In some embodiments, the conductive material comprises one or more selected from the group consisting of graphite, activated carbon, carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, and carbon fibers.

[0020] In some embodiments, the composition comprises the first hard block and the second hard block in a combined amount of about 10 to 60 wt.% based on the total weight of the triblock copolymer.

[0021] In some embodiments, the weight average molecular weight (e.g., average molecular weight) of the first hard block and the second hard block is about 9,000 g / mol or more and about 20,000 g / mol or less, respectively.

[0022] In some embodiments, the composition comprises the binder in an amount of about 3 to 15 wt.% based on the total weight of the composition.

[0023] In one aspect, a lithium secondary battery anode is provided having the composition described herein.

[0024] In one aspect, a lithium secondary battery is provided having the anode described herein.

[0025] In one aspect, a vehicle is provided having the lithium secondary battery described herein.

[0026] The use of the composition for forming a lithium secondary battery anode according to various exemplary embodiments of the present invention / disclosure makes it possible to produce not only a self-standing film for the lithium secondary battery anode that is electrochemically stable even at a negative potential, has excellent tensile strength, and is easy to mold by combining with a strong interaction with an anode active material or a conductive material, but also the lithium secondary battery anode and the lithium secondary battery containing the self-standing film.

[0027] Further aspects of the invention / disclosure are described below. BRIEF DESCRIPTION OF THE DRAWINGS Fig.1 shows an exemplary internal structure of a binder included in a self-standing (e.g., self-supporting) film for a lithium secondary battery anode according to an exemplary embodiment of the present invention / disclosure. Fig. 2 shows an exemplary method of manufacturing an exemplary anode using an exemplary composition for forming the lithium secondary battery anode according to an exemplary embodiment of the present invention / disclosure. Fig. Figure 3A shows an SEM image of SBS particles applied (e.g., coated) to a composition for forming an anode according to Example 1. Fig. Figure 3B shows an SEM image of SBS particles applied (e.g., coated) to a composition for forming an anode according to Comparative Example 1. Fig.Figure 3C is a graph showing the results of particle size analysis for SBS particles applied to a composition for forming an anode according to Example 1. Fig. 4A is a picture showing the result of visual observation of the surface of an electrode prepared using a composition for forming an anode according to Example 4. Fig. 4B is a picture showing the result of visual observation of the surface of an electrode prepared using a composition for forming an anode according to Example 6. DETAILED DESCRIPTION

[0028] Hereinafter, a composition for forming a lithium secondary battery anode will be described in detail so that a person skilled in the art to which the present invention / disclosure belongs can easily apply the present invention / disclosure.

[0029] The above objects, as well as other objects, features, and advantages of the present invention / disclosure will be readily understood from the following preferred embodiments taken in conjunction with the accompanying drawings. However, the present invention / disclosure is not limited to the embodiments described herein and may be embodied in other forms. The embodiments described herein are provided so that the invention / disclosure will be thorough and complete, and so that the present invention / disclosure may be fully conveyed to those skilled in the art. Throughout the drawings, like or similar elements are designated by like or similar reference numerals. In the accompanying drawings, the dimensions of the structures are larger than actual sizes to clarify the present invention / disclosure. The terms "first," "second," etc., as used in the description, indicate the following:may be used to describe various components, but the components are not to be construed as limited to these terms. These terms are used only to distinguish one component from another. For example, without departing from the scope of the present invention / disclosure, a first component may be referred to as a second component, and a second component may also be referred to as a first component. As used herein, the singular forms "a," "the," "the," and "the" also include the plural forms unless the context clearly indicates otherwise.It is further understood that the terms "comprise," "include," or "have," when used in this specification, specify the presence of certain features, ranges, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, ranges, integers, steps, operations, elements, components, and / or combinations thereof. It is also understood that when an element, such as a layer, film, area, or sheet, is referred to as being "on" another element, it may be directly on top of the other element, or intervening elements may be present.Likewise, when an element, such as a layer, film, area, or sheet, is referred to as being "beneath" another element, it may be directly beneath the other element, or there may be intervening elements. Unless otherwise noted, all numbers, values, and / or representations expressing the amounts of components, reaction conditions, polymer compositions, and blends used herein are to be understood as approximate, including various measurement uncertainties that, among other things, occur in the determination of these values, and should therefore be understood in all cases as modified by the term "about." Unless expressly stated or evident from the context, the term "about" as used herein is within a normal range of tolerance, e.g., within two standard deviations of the mean."Approximately" can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless the context otherwise indicates, all numerical values ​​stated herein are modified by the term "approximately."

[0030] Whenever a range of numbers is specified in this description, it is continuous and includes all values ​​from the minimum value of the range to its maximum value, unless otherwise specified. Furthermore, when such a range refers to integer values, all integers including the minimum value up to the maximum value are included, unless otherwise specified. For example, the range "5 to 10" includes all subranges such as 6 to 10, 7 to 10, 6 to 9, 7 to 9, and the like, as well as individual values ​​5, 6, 7, 8, 9, and 10, and is also understood to include all values ​​between the valid integers within the specified range, such as 5.5, 6.5, 7.5, 5.5 to 8.5, 6.5 to 9, and the like. The range “10% to 30%” is understood, subranges such as 10% to 15%, 12% to 18%, 20% to 30%, etc., as well as all integers with values ​​of 10%, 11%, 12%, 13%, etc.up to 30% and also includes any value between valid integers within the specified range, such as 10.5%, 15.5%, 25.5%, and the like.

[0031] It is to be understood that the term "vehicle" or "vehicular" or a similar term, as used herein, includes motor vehicles in general, such as passenger cars including sport utility vehicles (SUVs), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and also hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles, and other alternative fuel vehicles (e.g., fuels derived from resources other than petroleum). A hybrid vehicle, as used herein, is a vehicle that has two or more sources of power, e.g., both gasoline-powered and electric-powered vehicles.In certain preferred aspects, a vehicle may be electrically powered, including hybrid vehicles, plug-in hybrids, or vehicles where electrical energy is the primary or sole source of propulsion.

[0032] According to one embodiment of the present invention / disclosure, a composition for forming a lithium secondary battery anode comprises: an anode active material (e.g., an anode active material), a conductive material, and a binder. The binder comprises (i) a triblock copolymer having a soft block derived from an aliphatic or alicyclic diene-based monomer and forming a rubbery phase at room temperature, and (ii) a first hard block and a second hard block, each bonded to both ends of the soft block (e.g.,the first hard block is connected to one end of the soft block and the second hard block is connected to the other end of the soft block), which are derived from an ethylenically unsaturated monomer containing an aromatic ring and form a glassy phase at room temperature, and wherein the binder comprises particles with an average diameter (D. 50 ) of 1 µm or more and 50 µm or less.

[0033] The average diameter (D 50 ) of the binder refers to a diameter corresponding to 50% of the cumulative volume distribution measured with a laser diffraction / scattering particle size distribution meter.

[0034] The soft block may contain a repeating unit derived from an aliphatic diene-based monomer and / or an alicyclic diene-based monomer and exhibit a rubbery phase at room temperature. Specifically, the soft block may be derived from an aliphatic diene-based monomer comprising one or more selected from the group consisting of a butadiene-based monomer, a pentadiene-based monomer, and a hexadiene-based monomer.

[0035] The butadiene-based monomer may comprise one or more selected from the group consisting of 1,2-butadiene, 1,3-butadiene, isoprene and chloroprene.

[0036] The pentadiene-based monomer may comprise one or more selected from the group consisting of 1,2-pentadiene, 1,3-pentadiene, 1,4-pentadiene, 2,3-pentadiene, 2-methyl-1,3-pentadiene, 2-methyl-1,4-pentadiene, 2-methyl-2,3-pentadiene, 2-methyl-2,4-pentadiene, 3-methyl-1,3-pentadiene, 3-methyl-1,4-pentadiene, 4-methyl-1,3-pentadiene, 2-ethyl-1,3-pentadiene, 2-ethyl-1,4-pentadiene, 2-ethyl-2,4-pentadiene, 3-ethyl-1,3-pentadiene, 3-ethyl-1,4-pentadiene, 4-ethyl-1,3-pentadiene, 1-chloro-1,3-pentadiene, 1-chloro-2,4-pentadiene, 2-chloro-1,3-pentadiene, 3-chloro-1,3-pentadiene, 3-chloro-1,4-pentadiene and 5-chloro-1,3-pentadiene.

[0037] The hexadiene-based monomer may comprise one or more selected from the group consisting of 1,2-hexadiene, 1,3-hexadiene, 1,4-hexadiene, 1,5-hexadiene, 2,3-hexadiene, 2,4-hexadiene, 2,5-hexadiene, 3,5-hexadiene, 2-methyl-1,3-hexadiene, 2-methyl-1,4-hexadiene, 2-methyl-1,5-hexadiene, 2-methyl-2,3-hexadiene, 2-methyl-2,4-hexadiene, 3-methyl-1,2-hexadiene, 3-methyl-1,3-hexadiene, 3-methyl-1,4-hexadiene, 3-methyl-1,5-hexadiene, 3-methyl-2,4-hexadiene, 3-methyl-2,5-hexadiene, 4-methyl-1,3-hexadiene, 4-methyl-1,4-hexadiene, 4-methyl-2,3-hexadiene, 5-methyl-1,3-hexadiene, 5-methyl-1,4-hexadiene, 2-ethyl-1,3-hexadiene, 2-ethyl-1,4-hexadiene, 3-ethyl-1,2-hexadiene, 3-ethyl-1,3-hexadiene, 3-ethyl-1,4-hexadiene and 3-ethyl-1,5-hexadiene.

[0038] The triblock copolymer containing the soft block is characterized by the properties of excellent flexibility, extrusion formability and wear resistance.

[0039] The first hard block and the second hard block may contain a repeating unit derived from an ethylenically unsaturated monomer having an aromatic ring and exhibit a glassy phase at room temperature. In particular, the aromatic ring contained in the ethylenically unsaturated monomer may be a substituted or unsubstituted benzene ring or a substituted or unsubstituted naphthalene ring.

[0040] In addition, the aromatic ring may be connected to the main chain or the side chain of the repeating unit of the first hard block and the second hard block, and may preferably be connected to the side chain of the repeating unit of the first hard block and the second hard block.

[0041] The first hard block and the second hard block may each be independently derived from an ethylenically unsaturated monomer containing an aromatic ring comprising at least one of a styrene-based monomer and a (meth)acrylic-based aromatic monomer.

[0042] The styrene-based monomer may comprise one or more selected from the group consisting of styrene, α-methylstyrene, p-methylstyrene, p-methoxystyrene, p-ethoxystyrene, t-butoxystyrene, p-acetoxystyrene, p-chlorostyrene, p-bromostyrene, 2,4-dimethylstyrene, 3,5-dimethylstyrene and 2,4,6-trimethylstyrene.

[0043] The (meth)acrylic-based aromatic monomer may comprise one or more selected from the group consisting of benzyl acrylate, benzyl methacrylate, phenoxyacrylate, phenoxymethacrylate, phenyl acrylate, phenyl methacrylate, phenylethyl acrylate and phenylethyl methacrylate.

[0044] Due to the aromatic ring structure contained in the repeating unit, the first hard block and the second hard block can be tightly bonded to an anode active material or a conductive material through pi-pi interactions. Furthermore, the first hard block and the second hard block form a cross-linked physical bond with a relatively low binding energy, allowing, for example, the shape and size of the blocks to be maintained below their glass transition temperature, while allowing the blocks to be easily deformed above their glass transition temperature.

[0045] In addition, the first hard block and the second hard block can impart high strength property to the triblock copolymer containing them.

[0046] A combined amount of the first hard block and the second hard block may be about 10 to 60 wt%, preferably about 15 to 55 wt%, more preferably about 20 to 50 wt%, based on the total amount (e.g., the total weight) of the triblock copolymer. When the amount of the first hard block and the second hard block satisfies the above numerical range, the bonding strength can be further improved due to strong interaction with the anode active material or the conductive material, so that the triblock copolymer can exhibit more excellent formability due to adequate flexibility.

[0047] A weight-average molecular weight (e.g., an average molecular weight) of the first hard block and the second hard block may be about 9,000 g / mol or more and about 20,000 g / mol or less, preferably about 9,500 g / mol or more and about 20,000 g / mol or less, more preferably about 10,000 g / mol or more and about 20,000 g / mol or less. When the weight-average molecular weight of both the first hard block and the second hard block satisfies the above numerical range, a physical cross-linking force between the binder and the anode active material or the conductive material can be improved to form a more stable three-dimensional network.

[0048] A first glass transition temperature and a second glass transition temperature associated with the first hard block and the second hard block may be about 50°C or higher and about 120°C or lower, and a third glass transition temperature associated with the soft block may be about -120°C or higher and -50°C or lower. Preferably, the first glass transition temperature and the second glass transition temperature are about 80°C or higher and 120°C or lower, and the third glass transition temperature is about -120°C or higher and about -80°C or lower. More preferably, the first glass transition temperature and the second glass transition temperature are about 80°C or higher and about 110°C or lower, and the third glass transition temperature is about -110°C or higher and about -80°C or lower.When the first hard block, the second hard block, and the soft block contained in the triblock copolymer have glass transition temperatures within the above-mentioned numerical ranges, it is possible to perform more reversible molding of a composition for forming a lithium secondary battery anode having a binder containing the triblock copolymer. Furthermore, the durability and flexibility of the electrode made from the composition are further improved, allowing its shape to be better (e.g., more effectively) maintained.

[0049] The soft block, the first hard block, and the second hard block contained in the triblock copolymer can each realize independent properties without affecting each other. In other words, the soft block can provide flexibility, and the first hard block and the second hard block can provide strong bonding force with the anode active material for the self-standing film (e.g., the self-supporting film) for the anode of the finally formed lithium secondary battery. Furthermore, since the soft block and the hard block (e.g., the first hard block and / or the second hard block) have different glass transition temperatures, the formability of the triblock copolymer becomes easier when the self-standing film for the anode is formed at a temperature higher than the glass transition temperature of the hard block (e.g., by calendering, rolling, etc.).When the self-standing film is exposed to corresponding temperatures below the glass transition temperature of the hard block and above the glass transition temperature of the soft block immediately after the film is formed, the triblock copolymer has the flexibility and maintains the high strength (e.g., maintains the high strength), so that the self-standing film for the lithium secondary battery anode made from it cannot be easily broken by an external stimulus.

[0050] The triblock copolymer is stable at a negative potential to suppress the occurrence of side reactions. Therefore, when used as a binder for the lithium secondary battery anode, the electrode life can be extended.

[0051] The binder has a substantially spherical (e.g., spherical) shape and may be spherical or nearly spherical. In particular, the binder may have an average sphericity of about 0.7 or more and about 1.0 or less, preferably about 0.8 or more and about 1.0 or less, more preferably about 0.9 or more and about 1.0 or less. That is, before forming the self-standing film for the anode, the particles of the binder in the composition for forming the lithium secondary battery anode may be dispersed in the composition for forming the anode while maintaining a substantially spherical shape.

[0052] The sphericity of the binder is determined by measuring the long and short diameters of ten randomly selected particles using an image of the binder particles taken with a scanning electron microscope (SEM), and calculating the ratio of the long and short diameters of each particle. The sphericity is an average value resulting from the ratio of the long and short diameters of the ten particles, and the closer the sphericity is to 1, the more likely it is to be considered spherical.

[0053] The anode active material may comprise (or be) one or more materials selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of being alloyed with lithium, and a lithium-containing active material.

[0054] The carbon-based active material can be, for example, graphite, hard carbon, soft carbon, or graphene. The graphite can be artificial graphite, natural graphite, a mixture of artificial and natural graphite, natural graphite coated with artificial graphite, or a combination thereof.

[0055] The active silicon-based material can be, for example: Si, SiO m, a Si-C composite, a Si-Q alloy or a combination thereof, wherein 0 <m≤2 ist und Q ein Alkalimetall, ein Erdalkalimetall, ein Element der Gruppen 13 bis 16 des Periodensystems, ein Übergangsmetall, ein Seltenerdelement oder eine Kombination davon ist, mit der Ausnahme, dass Q Si ausschließt.

[0056] The metal-based active material suitable for being alloyed with the lithium may comprise, for example, B, Al, Ga, In, Ge, Sn, Pb, P, As, Sb, Bi, Mg, Ca, Zn, Cd, Pd, Ag, Au, Pt or an alloy thereof or an oxide thereof.

[0057] The lithium-containing active material can be, for example, a lithium-containing titanium complex oxide (LTO).

[0058] The conductive material may comprise (or be) one or more materials selected from the group consisting of graphite, activated carbon, carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, and carbon fibers.

[0059] The binder may be contained in an amount of about 3 to 15 wt%, preferably in an amount of about 6 to 14 wt%, and more preferably in an amount of about 10 to 14 wt%, based on the total weight of the composition for forming the lithium secondary battery anode. When an amount of the binder satisfies the above numerical range, the composition for forming the lithium secondary battery anode containing the binder can form a self-standing film for the anode, which has excellent tensile strength and is electrochemically stable even at a negative potential, due to strong interaction with the anode active material.

[0060] A film-forming process can be performed to form a self-supporting film for the anode using the composition for forming the lithium secondary battery anode. The film-forming process can be performed in a dry manner. In other words, the composition for forming the lithium secondary battery anode used in the film-forming process can be substantially free of a solvent. When the film-forming process is performed in a wet manner, the charge amount of the electrode can only be increased to a limited extent due to a liquid slurry, and there are cases where a network structure cannot be formed between the binder and the active material / conductive material.However, since the film forming process according to the present invention / disclosure is carried out in a dry manner, it is possible to manufacture a lithium secondary battery in which a high charge amount of the electrode realizing a high energy density is possible and the network structure between the binder and the active material is formed more effectively.

[0061] The film-forming process may include calendering (rolling). In other words, the anode active material layer may be formed by passing the lithium secondary battery anode-forming composition, which contains the anode active material, the conductive material, and the binder, between a pair of rollers and pressing and rolling the composition. By applying external forces such as shearing and tensile forces through such calendering, the self-supporting film for the lithium secondary battery anode can ultimately be produced.

[0062] Furthermore, the triblock copolymer can form a three-dimensional network under pressure at a temperature at which the film-forming process is performed. As described above, a region (e.g., a domain, a region) of the active material or a region (e.g., a domain, a region) of the conductive material and the binder are bonded together to form the three-dimensional network, thereby making it possible to manufacture the lithium secondary battery anode with excellent tensile strength. EXAMPLES

[0063] The present invention / disclosure is described in more detail below using examples. However, these examples are intended only to facilitate understanding of the present invention / disclosure and do not limit the scope of the present invention / disclosure in any way to these examples. <Beispiel 1>Preparing 1 a composition for forming an anode

[0064] Graphite as an anode active material, carbon black as a conductive material and an SBS triblock copolymer (glass transition temperature of the polystyrene block: 100 °C, glass transition temperature of the polybutadiene block: -100 °C) as a binder in powder form were mixed in a mass ratio of 96:1:3 without solvent.

[0065] The polystyrene block content was 40.5 wt%, based on the total weight of the SBS triblock copolymer. The molecular weight of the SBS triblock copolymer was 57,000 g / mol, of which the polystyrene block had a molecular weight of 11,500 g / mol and the polybutadiene block a molecular weight of 34,000 g / mol. <Beispiel 2> Preparing 2 a composition for forming an anode

[0066] A composition for forming an anode was prepared by the same method as in Example 1, except that a mass ratio of the graphite, the conductive material, and the binder was 95:1:4. <Beispiel 3> Preparing 3 a composition for forming an anode

[0067] A composition for forming an anode was prepared by the same method as in Example 1, except that the mass ratio of the graphite, the conductive material, and the binder was 94:1:5. <Beispiel 4> Preparing 4 a composition for forming an anode

[0068] A composition for forming an anode was prepared by the same method as in Example 1, except that the mass ratio of the graphite, the conductive material, and the binder was 93:1:6. <Beispiel 5> Preparing 5 a composition for forming an anode

[0069] A composition for forming an anode was prepared by the same method as in Example 1, except that the mass ratio of the graphite, the conductive material, and the binder was 87:1:12. <Beispiel 6> Preparing 6 a composition for forming an anode

[0070] Graphite as an anode active material, carbon black as a conductive material and an SBS triblock copolymer (glass transition temperature of the polystyrene block: 100°C, glass transition temperature of the polybutadiene block: -100°C) as a binder in a powder form were mixed in a mass ratio of 93:1 without a solvent.

[0071] The polystyrene block content was 31 wt%, based on the total weight of the SBS triblock copolymer. The molecular weight of the SBS triblock copolymer was 73,000 g / mol, of which the polystyrene block had a molecular weight of 11,200 g / mol and the polybutadiene block a molecular weight of 51,000 g / mol. <Vergleichsbeispiel 1> Preparing 7 a composition for forming an anode

[0072] A composition for forming an anode was prepared by the same procedure as in Example 1, except that SBS was used in a pellet form (average diameter (D 50 ): 5 mm) was used as a binder instead of the SBS in powder form. <Experimentelles Beispiel 1> Observation of SBS particles

[0073] In order to observe a shape of the SBS particles, the SBS particles applied (e.g., coated) to the composition for forming the anode according to Example 1 and Comparative Example 1 were subjected to SEM micrographs. These are shown in the Fig. 3A and 3B respectively. Fig. Figure 3A shows an SEM image of the SBS powder particles after they were pulverized (converted into powder form), and Fig. Figure 3B shows an SEM image of the SBS pellets before they were pulverized (converted into powder form).

[0074] As in Fig. As shown in Figure 3A, the SBS binder has a spherical particle shape even after being pulverized.

[0075] Further, as a result of analyzing a particle size of the SBS particles applied (e.g., coated) to the composition for forming the anode according to Example 5 using a particle size analyzer (model name: SALD-2300, manufacturer: SHIMADZU), it was found that an average diameter (D 50 ) of the particles was about 20 µm (see Fig. 3C). Furthermore, in the case of the SBS particles coated on the composition for forming the anode according to Comparative Example 1, an average diameter (D 50 ) of the particles of about 0.5 cm. Accordingly, it was confirmed that the SBS particles according to Example 1, after being pulverized, can form a smaller size of the SBS particles. <Vergleichsbeispiel 2> Preparation 8 of a composition for forming an anode

[0076] A composition for forming an anode was prepared by the same procedure as in Example 1, except that PTTF (polytetrafluoroethylene) was used as a binder instead of SBS. <Versuchsbeispiel 2> Observation of whether a self-supporting film for an anode is formed according to a film formation temperature

[0077] In order to observe the effect of a film-forming temperature on the formation of a self-standing film for an anode, the composition for forming the anode according to Example 4 was formed into a film by rolling the composition using a two-roll press heated to a temperature of 120 °C, while the composition for forming the anode according to Example 4 was formed into a film by rolling the composition using a two-roll press heated to a temperature of 80 °C.

[0078] As a result, film formation was clearly observed at 120 °C, while no film formation was observed at 80 °C. This means that film formation can occur at a temperature of 100 °C or higher, which corresponds to the glass transition temperature of the polystyrene contained in the triblock copolymer. <Versuchsbeispiel 3> Observation of the surface condition of a self-supporting film for an anode as a function of the polystyrene content

[0079] In order to observe the effect of the polystyrene content contained in an SBS triblock copolymer on the surface state of a self-supporting film for an anode, the film forming process was carried out by rolling the compositions for forming the anode according to Examples 4 and 6 with a two-roll press heated to a temperature of 120 °C.

[0080] As a result, film formation was observed for both the anode-forming compositions of Examples 4 and 6. However, in the case of Example 6, which had a relatively low polystyrene block content, the surface condition of the self-supporting film was inferior to that of the self-supporting film formed by the anode-forming composition of Example 4. <Versuchsbeispiel 4> Measurement of the tensile strength of a self-supporting film for an anode

[0081] First, the self-supporting films for the anode were prepared by rolling the compositions for forming the anode according to Example 1 (the content of SBS binder: 3 wt%), Example 4 (the content of SBS binder: 6 wt%, the content of SBS-based polystyrene block: 40.5 wt%), Example 6 (the content of SBS binder: 6 wt%, the content of SBS-based polystyrene block: 31 wt%), and Comparative Example 1 (the content of PTFE binder: 3 wt%) using a two-roll press under the following temperature conditions.

[0082] Each of the prepared self-supporting films for the anode was punched to a width of 2 cm and a length of 6 cm to prepare self-supporting film samples, and the tensile strength was measured at a speed of 5 mm / min using a universal testing machine (UTM). The tensile strength measurement results are shown in Table 1 below. Table 1 composition Content of the binder Film formation temperature Tensile strength Example 1 SBS 3 wt.% 120°C 0.728 mPa Example 1 SBS 3 wt.% 140°C 0.556 mPa Example 4 SBS 6 wt% 120°C 1.281 mPa Example 6 SBS 6 wt% 120°C 0.874 mPa Comparison example 1 PTFE 3 wt.% 120°C 0.253 mPa

[0083] As shown in Table 1, the tensile strength decreases when the film-forming process is carried out at a higher temperature, relative to the content of the same binders. This is believed to be due to the fact that the higher the temperature at which the film-forming process is carried out, the more the binder is stretched. When the temperature is lowered to room temperature after the film-forming process, the shrinkage rate of the binder becomes relatively large, resulting in the disruption of some of the three-dimensional network bonds within the binder.

[0084] On the other hand, when the film forming process is carried out at the same temperature, the tensile strength is even more excellent when the binder content is 6 wt% than when it is 3 wt%, and the tensile strength is even more excellent when using SBS than when using PTFE as the binder (Comparative Example 1).

[0085] The above results may be due to the SBS binder forming a three-dimensional network connecting between the active materials, between the conductive materials or between the active material and the conductive material to bind them tightly.

[0086] Even when the film formation process was carried out at the same temperature using the anode-forming composition containing the same SBS binder content, the tensile strength of the produced self-supporting anode film was excellent when the polystyrene block content in the SBS was higher. In other words, the higher the proportion of the polystyrene block in the SBS binder, the better the mechanical properties of the self-supporting anode film produced from the binder-containing composition. <Experimentelles Beispiel 5> Observation of whether an anode is produced

[0087] The self-supporting films were prepared by rolling the anode-forming compositions according to Examples 1 to 6 through a two-roll press under the temperature conditions shown in Table 2 below. The self-supporting films were placed on one side of a corresponding copper foil (a current collector) coated with a primer layer and laminated by a laminating roll maintained at 120 °C to prepare anodes for a lithium secondary battery.

[0088] Table 2 shows the results of lamination under each condition, where ◯ (or ◯ or ⊚) indicates a strong bond between the binder and the current collector without deformation of the self-supporting film for the anode, △ indicates that the self-standing film is broken or separated from the current collector when strong pressure is applied, and X indicates a case where the lamination itself is impossible. Table 2 composition Content of the binder Film formation temperature lamination Example 1 SBS 3 wt.% 120°C △ Example 2 SBS 4 wt.% 120°C ◯ Example 3 SBS 5 wt.% 120°C ◯ Example 4 SBS 6 wt% 120°C ◯ Example 5 SBS 12 wt.% 120°C ⊚ Example 6 SBS 6 wt% 120°C △

[0089] When lamination is performed on the self-supporting anode films formed at 120°C using the anode-forming compositions of Examples 1 to 5, the binder and the current collector can be bonded more firmly as the binder content contained in the compositions increases. Specifically, when the binder content is only 3 wt%, the physical properties of the produced self-supporting film are poor, which also leads to the poor physical properties of the anode produced after the lamination process. Whereas when the binder content is 12 wt%, a strong anode can be formed by firmly bonding the self-supporting anode film to the copper foil.The above results may be due to the fact that the higher the content of the SBS binder, the more three-dimensional networks can be formed to connect between the anode active materials, between the conductive materials, or between the active material and the conductive material.

[0090] Meanwhile, in order to observe whether the anode is produced according to the content of the polystyrene block contained in the SBS binder, the film forming process was carried out at a temperature of 120 °C using the compositions for forming the anode according to Example 4 and Example 6, and the anode after lamination is in Fig.4A and 4B, respectively. As a result, the anode prepared using the anode-forming composition of Example 6 had a lower (inferior) bond between the binder and the current collector compared to the anode prepared using the anode-forming composition of Example 4.

Claims

[1] A composition for forming a lithium secondary battery anode, comprising: an anode active material, a conductive material and a binding agent, wherein the binder comprises: a triblock copolymer having a soft block derived from an aliphatic or alicyclic diene-based monomer and forming a rubbery phase at room temperature, and a first hard block and a second hard block associated with both ends of the soft block, which are derived from an ethylenically unsaturated monomer containing an aromatic ring and form a glassy phase at room temperature, and wherein the binder comprises particles with an average diameter (D 50 ) of about 1 µm or more and 50 µm or less. [2] The composition of claim 1, wherein the binder has a spherical shape and an average sphericity of about 0.7 or more and about 1.0 or less. [3] The composition according to claim 1 or 2, wherein the first and second glass transition temperatures associated with the first hard block and the second hard block are about 50°C or higher and about 120°C or lower, and the third glass transition temperature associated with the soft block is about -120°C or higher and about -50°C or lower. [4] The composition according to any one of claims 1 to 3, wherein the soft block is derived from an aliphatic diene-based monomer containing one or more monomers selected from the group consisting of a butadiene-based monomer, a pentadiene-based monomer, and a hexadiene-based monomer. [5] The composition according to claim 4, wherein the butadiene-based monomer comprises one or more selected from the group consisting of 1,2-butadiene, 1,3-butadiene, isoprene and chloroprene. [6] A composition according to any one of claims 1 to 5, wherein the first hard block and the second hard block are each independently derived from an aromatic ring-containing ethylenically unsaturated monomer containing a styrene-based monomer and / or an aromatic (meth)acrylic-based monomer. [7] The composition according to claim 6, wherein the styrene-based monomer comprises one or more selected from the group consisting of styrene, α-methylstyrene, p-methylstyrene, p-methoxystyrene, p-ethoxystyrene, t-butoxystyrene, p-acetoxystyrene, p-chlorostyrene, p-bromostyrene, 2,4-dimethylstyrene, 3,5-dimethylstyrene and 2,4,6-trimethylstyrene. [8] The composition according to claim 6 or 7, wherein the (meth)acrylic-based aromatic monomer comprises one or more selected from the group consisting of benzyl acrylate, benzyl methacrylate, phenoxyacrylate, phenoxymethacrylate, phenyl acrylate, phenyl methacrylate, phenylethyl acrylate and phenylethyl methacrylate. [9] The composition according to any one of claims 1 to 8, wherein the anode active material comprises one or more selected from the group consisting of a carbon-based active material, a silicon-based active material, a metal-based active material capable of being alloyed with lithium, and a lithium-containing active material. [10] The composition according to any one of claims 1 to 9, wherein the conductive material comprises one or more selected from the group consisting of graphite, activated carbon, carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, and carbon fibers. [11] The composition of any one of claims 1 to 10, wherein the composition comprises the first hard block and the second hard block in a combined amount of about 10 to 60 wt.% based on the total weight of the triblock copolymer. [12] The composition according to any one of claims 1 to 11, wherein a weight average molecular weight of the first and second hard blocks is about 9,000 g / mol or more and about 20,000 g / mol or less, respectively. [13] A composition according to any one of claims 1 to 12, wherein the composition comprises the binder in an amount of about 3 to 15% by weight based on the total weight of the composition. [14] A lithium secondary battery anode comprising a composition according to any one of claims 1 to 13. [15] A lithium secondary battery comprising an anode according to claim 14. [16] A vehicle comprising a lithium secondary battery according to claim 15.

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