Dry binder, electrodes containing the same, and lithium secondary battery containing the same

Abstract

To provide a dry binder that has high adhesive strength, is environmentally friendly, and can be used in dry processes. [Solution] A dry binder is provided which contains a crosslinking reaction product obtained by crosslinking a polyamide polymer with an epoxy crosslinking agent, wherein the epoxy crosslinking agent is a novolac-type epoxy crosslinking agent.

Description

Technical Field

[0001] The present invention relates to a dry binder, an electrode containing the same, and a lithium secondary battery containing the same.

Background Art

[0002] In recent years, with the rapid spread of electronic devices using batteries such as mobile phones, notebook computers, and electric vehicles, the demand for relatively high-capacity secondary batteries that are small and lightweight has been rapidly increasing. In particular, lithium secondary batteries have attracted attention as a driving power source for portable devices because they are lightweight and have a high energy density.

[0003] A lithium secondary battery is a battery including a positive electrode and a negative electrode containing an active material capable of inserting and extracting lithium ions, and an electrolytic solution, and produces electrical energy by oxidation and reduction reactions when lithium ions are inserted and extracted at the positive electrode and the negative electrode.

[0004] As the positive electrode active material of a lithium secondary battery, transition metal compounds such as lithium cobalt-based oxides, lithium nickel-based oxides, and lithium manganese-based oxides are mainly used, and as the negative electrode active material, crystalline carbon materials such as natural graphite and artificial graphite, or amorphous carbon materials are used.

[0005] A binder is used for various components of such a lithium secondary battery. The binder requires high adhesive strength, but a binder having high adhesive strength generally has a disadvantage of increasing resistance.

Summary of the Invention

Problems to be Solved by the Invention

[0006] One embodiment is to provide a dry binder having high adhesive strength, being environmentally friendly, and being applicable to a dry process.

[0007] Other embodiments provide electrodes with excellent tensile strength and adhesive strength by including the dry binder.

[0008] Furthermore, other embodiments provide a lithium secondary battery with excellent lifespan characteristics by including the dry binder. [Means for solving the problem]

[0009] In one embodiment, a dry binder is provided which comprises a crosslinking reaction product obtained by crosslinking a polyamide polymer with an epoxy crosslinking agent, wherein the epoxy crosslinking agent is a novolac-type epoxy crosslinking agent.

[0010] In another embodiment, an electrode for a lithium secondary battery is provided, comprising the dry binder and electrode active material described above.

[0011] In another embodiment, a lithium secondary battery is provided comprising a positive electrode, a negative electrode, and an electrolyte, wherein at least one of the negative electrode and the positive electrode comprises the dry binder described above.

[0012] In another embodiment, the present invention provides a method for producing an electrode, comprising the steps of: dry mixing an electrode active material, a binder, and a conductive material to produce an electrode-forming composition; and applying the electrode-forming composition onto a current collector to form an electrode, wherein the binder comprises a crosslinking reaction product obtained by crosslinking a polyamide polymer with an epoxy crosslinking agent, and the epoxy crosslinking agent is a novolac-based epoxy crosslinking agent. [Effects of the Invention]

[0013] The aforementioned dry binder is environmentally friendly because it does not use fluorine in the dry electrode manufacturing process, and it can improve tensile strength and adhesive strength. By including the binder, an electrode with excellent tensile strength and adhesive strength and a lithium secondary battery with excellent lifespan characteristics are provided. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic diagram showing a lithium secondary battery according to one embodiment. [Figure 2] This is a schematic diagram showing a lithium secondary battery according to one embodiment. [Figure 3] This is a schematic diagram showing a lithium secondary battery according to one embodiment. [Figure 4] This is a schematic diagram showing a lithium secondary battery according to one embodiment. [Modes for carrying out the invention]

[0015] The following describes specific embodiments in detail so that those with ordinary skill in the art can easily implement them. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0016] The terms used herein are for illustrative purposes only and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0017] Here, "these combinations" refers to mixtures of components, laminates, composites, copolymers, alloys, blends, reaction products, etc.

[0018] Here, terms such as “include,” “equip,” or “possess” should be understood as intending to specify the presence of an implemented feature, figure, stage, component, or combination thereof, and not preemptively excluding the possibility of the presence or addition of one or more other features, figures, stages, components, or combinations thereof.

[0019] To clearly represent multiple layers and regions in the drawings, thicknesses are shown enlarged, and similar parts are given the same drawing reference numerals throughout the specification. When a layer, film, region, plate, or other part is said to be "on top of" or "on" another part, this includes not only when it is "directly above" the other part, but also when there is yet another part in between. Conversely, when a part is said to be "directly above" another part, it means that there is no other part in between.

[0020] Furthermore, the term "layer" here includes not only the shapes formed on the entire surface when observed in a plan view, but also the shapes formed on some of the surfaces.

[0021] The average particle size can be measured by methods widely known to those skilled in the art, for example, by a particle size analyzer, or by transmission electron microscope images or scanning electron microscope images. Alternatively, it can be measured using dynamic light scattering and data analysis to count the number of particles for each particle size range, from which the average particle size value can be calculated. Unless otherwise defined, the average particle size is the diameter (D) of the particle whose cumulative volume in the particle size distribution is 50% by volume. 50 ) can mean. Also, unless otherwise defined, the average particle size is obtained by measuring the size (diameter or length of the long axis) of more than 20 random particles in a scanning electron microscope image to obtain a particle size distribution, and the diameter (D) of the particle whose cumulative volume is 50% in the said particle size distribution. 50 ) may be taken using the average particle size.

[0022] Here, "or" is not interpreted as having an exclusive meaning; for example, "A or B" is interpreted as including A, B, A+B, etc.

[0023] Here, "dry binder" refers to a binder that allows electrodes to be manufactured in a dry manner without the use of solvents. For example, it refers to a binder used in dry electrodes where an active material, a dry binder, and a conductive material are mixed without solvent to produce an active material layer composition, and this composition is then used to manufacture electrodes.

[0024] Dry binder In one embodiment, a dry binder is provided that contains a crosslinking reaction product obtained by crosslinking a polyamide polymer with an epoxy crosslinking agent. The epoxy crosslinking agent is a novolac-based epoxy crosslinking agent.

[0025] The aforementioned dry binder plays a role in ensuring that electrode active material particles adhere well to each other and that the active material adheres well to the current collector. In recent years, much development has been carried out on dry electrode manufacturing processes that are environmentally friendly and improve manufacturing efficiency. As a dry binder, fluorine-based binders such as polytetrafluoroethylene (PTFE) are mainly used. However, due to recent environmental concerns, attempts are being made to replace fluorine-based binders such as PTFE with even more environmentally friendly materials.

[0026] As part of the need for such environmentally friendly research, research is underway on binders that do not contain fluorine atoms. However, most binders that do not contain fluorine atoms have insufficient adhesion and do not reach the level of PTFE.

[0027] Therefore, there is a need to develop a dry binder that offers excellent adhesion and can improve battery performance, serving as an alternative to fluorine-based binders such as PTFE.

[0028] Therefore, in one embodiment, we aim to provide a dry binder that can improve the performance of a battery by introducing a binder into the electrodes that does not contain fluorine atoms and has improved adhesion, electrolyte stability, and current density.

[0029] In one embodiment, the polyamide polymer may include structural units represented by chemical formula 1-1, structural units represented by chemical formula 1-2, or combinations thereof.

[0030] [ka]

[0031] [Chemical formula]

[0032] In the above chemical formulas 1-1 and 1-2, R 1 , R 2 , and R 3 are each independently a linking group which is a substituted or unsubstituted C2-C20 alkylene group, a substituted or unsubstituted C3-C20 cycloalkylene group, or a combination thereof, and * indicates the linking site with the main chain.

[0033] The substituted or unsubstituted C2-C20 alkylene group may contain a structural unit of -(CH2) n -(where n is an integer from 2 to 14).

[0034] At least one non-adjacent methylene group (-(CH2)-) among the above linking groups can be replaced by -NH-, -C(=O)-, or a combination thereof.

[0035] In one embodiment, R 1 , R 2 , and R 3 can each contain any one of the moieties of the following Group 1.

[0036] [Chemical formula]

[0037] In the above Group 1, * indicates the linking site with the main chain.

[0038] In one embodiment, the polyamide polymer is included in an amount of 60 to 95 parts by weight per 100 parts by weight of the dry binder, for example, 70 to 90 parts by weight. When the amount is within this range, the electrode manufacturing process using the dry binder is simplified, and the adhesive strength of the electrodes can be improved.

[0039] The weight-average molecular weight (Mw) of the polyamide polymer may be between 600 g / mol and 800,000 g / mol. Within this range, the electrode manufacturing process using a dry binder is easy, and the adhesive strength of the electrode can be improved.

[0040] In one embodiment, the polyamide polymer may include nylon 6, nylon 66, a copolymer of nylon 6 and nylon 66, nylon 12, nylon 610, and polymetaxylenediamine adipamide (MXD6). In this case, the polyamide polymer may use only one type of polyamide, or two or more types of polyamide may be used in combination.

[0041] Novolac epoxy crosslinking agents may contain structural units of chemical formula 2.

[0042] [ka]

[0043] In the aforementioned chemical formula 2, R 4 , R 5 and R 6 These elements are either identical or different from each other, and each is independently a hydrogen atom (H) or a substituted or unsubstituted C1-C6 alkyl group, such as a substituted or unsubstituted methyl group, n is between 1 and 30, a and c are independently integers between 0 and 4, and b is an integer between 0 and 3.

[0044] The novolac-based epoxy crosslinking agent exists as a solid at room temperature, and does not cause aggregation when mixed with polyamide polymers that exist in the solid phase, allowing the novolac-based epoxy crosslinking agent to be uniformly dispersed in the polyamide polymer.

[0045] In one embodiment, the novolac epoxy crosslinking agent is included in an amount of 5 to 40 parts by weight, for example, 10 to 30 parts by weight, per 100 parts by weight of the dry binder. Within this range, the novolac epoxy crosslinking agent can form crosslink bonds with the polyamide polymer to exhibit an adhesive strength improvement effect.

[0046] The weight-average molecular weight (Mw) of the novolac epoxy crosslinking agent may be between 500 g / mol and 10,000 g / mol. Within this range, the novolac epoxy crosslinking agent can form crosslink bonds with polyamide polymers to exhibit an adhesive strength improvement effect.

[0047] In one embodiment, the novolac epoxy crosslinking agent includes cresol novolac, phenol novolac, and phenol-modified novolac epoxy crosslinking agents.

[0048] The aforementioned dry binder has the effect of improving tensile strength and adhesive strength, and can be usefully used as a binder contained in the positive and negative electrodes of lithium secondary batteries.

[0049] electrode Another embodiment provides an electrode for a lithium secondary battery, comprising a dry binder and electrode active material according to the above-described embodiment.

[0050] The electrode can be manufactured by providing an electrode composition for a lithium secondary battery containing the dry binder and electrode active material of the above-described embodiment, and applying this electrode composition to a current collector and rolling it. In one embodiment, 0.5 to 20 parts by weight of the dry binder is used per 100 parts by weight of the electrode active material.

[0051] The electrode may be either a negative electrode or a positive electrode. The binder has high adhesive strength and low resistance even when used as a negative electrode, which undergoes large volume changes due to charging and discharging of the lithium secondary battery, and can therefore contribute to improving the performance of the lithium secondary battery.

[0052] The following describes a positive electrode and a negative electrode for a lithium secondary battery according to one embodiment.

[0053] negative electrode The negative electrode includes a current collector and a negative electrode active material layer located on the current collector. The negative electrode active material layer includes a negative electrode active material and may further include a binder and / or a conductive material. The binder may be a dry binder according to the embodiment described above.

[0054] For example, the negative electrode active material layer may contain 90% to 99.5% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0% to 5% by weight of the conductive material.

[0055] The negative electrode active material includes a substance capable of reversibly inserting / de-inserting lithium ions, lithium metal, an alloy of lithium metal, a lithium-doped and de-doped substance, or a transition metal oxide.

[0056] The material capable of reversibly inserting / deinserting lithium ions is a carbon-based anode active material, which may include, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, while examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, and calcined coke.

[0057] As the lithium metal alloy, an alloy of lithium and a metal selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0058] As the material that can be doped and dedoped with lithium, a Si-based anode active material or a Sn-based anode active material can be used. The Si-based anode active material is silicon, silicon-carbon composite, SiO x(0 < x ≤ 2), an Si-Q alloy (where Q is selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements (excluding Si), Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof), or a combination of these may also be used. The Sn-based negative electrode active material may be Sn, SnO2, an Sn-based alloy, or a combination of these.

[0059] The silicon-carbon composite may be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite may be in a form in which silicon particles are coated with amorphous carbon on the surface of the silicon particles. For example, it may include secondary particles (cores) formed by granulating primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. The amorphous carbon is also located between the primary silicon particles. For example, the primary silicon particles are coated with amorphous carbon. The secondary particles can be dispersed and present in an amorphous carbon matrix.

[0060] The silicon-carbon composite may further contain crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the surface of the core.

[0061] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by mixing with a carbon-based negative electrode active material.

[0062] The binder plays a role in ensuring that the negative electrode active material particles adhere well to each other and that the negative electrode active material adheres well to the current collector. In addition to the dry binder according to one embodiment, the binder may include additional binders. Typical examples of the additional binders include, but are not limited to, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylic styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0063] The conductive material is used to impart conductivity to the electrodes, and any electronically conductive material that does not undergo chemical changes in the battery can be used. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials containing copper, nickel, aluminum, silver, etc., in the form of metal powders or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0064] As the negative electrode current collector, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof can be selected.

[0065] positive electrode The positive electrode may include a current collector and a positive electrode active material layer formed on the current collector. The positive electrode active material layer may include a positive electrode active material and further include a binder and / or a conductive material. The binder may be a dry binder according to one embodiment described above.

[0066] The content of the positive electrode active material may be 90% to 99% by weight relative to 100% by weight of the positive electrode active material layer, and the content of the binder and conductive material may be 0.5% to 5% by weight, respectively, relative to 100% by weight of the positive electrode active material layer.

[0067] As the positive electrode active material, a compound that allows for reversible insertion and removal of lithium (a lithium-inserted compound) can be used. Specifically, one or more composite oxides of lithium with metals selected from cobalt, manganese, nickel, and combinations thereof can be used.

[0068] The aforementioned composite oxide may be a lithium transition metal composite oxide, and specific examples include lithium nickel oxide, lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate compound, cobalt-free lithium nickel-manganese oxide, or a combination thereof.

[0069] As an example, a compound represented by any of the following chemical formulas can be used: Li a A 1-b X b O 2-c D c (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05);Li a Mn 2-b X b O 4-c D c (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05);Li a Ni 1-b-c Co b X c O 2-α D α (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.5, 0<α<2);Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.5, 0<α<2);Li a Ni b Coc L 1 d GeO2(0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, 0≦e≦0.1);Li a NiG b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a CoG b O2(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn 1-b G b O2(0.90≦a≦1.8, 0.001b≦0.1);Li a Mn2G b O4(0.90≦a≦1.8, 0.001≦b≦0.1);Li a Mn 1-g G g PO4(0.90≦a≦1.8, 0≦g≦0.5);Li (3-f) Fe2(PO4)3(0≦f≦2);Li a FePO4 (0.90 ≤ a ≤ 1.8).

[0070] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; L 1 These are Mn, Al, or a combination of these.

[0071] The positive electrode active material may include, for example, a lithium nickel oxide represented by chemical formula 11 below, a lithium cobalt oxide represented by chemical formula 12 below, a lithium iron phosphate compound represented by chemical formula 13 below, a cobalt-free lithium nickel-manganese oxide represented by chemical formula 14, or a combination thereof.

[0072] [Chemical formula 11] Li a1 Ni x1 M 1 y1 M2 z1 O 2-b1 X b1 In the aforementioned chemical formula 11, 0.9≦a1≦1.8, 0.3≦x1≦1, 0≦y1≦0.7, 0≦z1≦0.7, 0.9≦x1+y1+z1≦1.1, and 0≦b1≦0.1, M 1 and M 2 Each of the elements is independently selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from F, P, and S.

[0073] In the chemical formula 11, 0.6 ≤ x1 ≤ 1, 0 ≤ y1 ≤ 0.4, and 0 ≤ z1 ≤ 0.4, or 0.8 ≤ x1 ≤ 1, 0 ≤ y1 ≤ 0.2, and 0 ≤ z1 ≤ 0.2.

[0074] [Chemical formula 12] Li a2 Co x2 M 3 y2 O 2-b2 X b2 In the aforementioned chemical formula 12, 0.9≦a2≦1.8, 0.7≦x2≦1, 0≦y2≦0.3, 0.9≦x2+y2≦1.1, and 0≦b2≦0.1, M 3 X is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from F, P, and S.

[0075] [Chemical formula 13] Li a3 Fe x3 M 4 y3 PO 4-b3 X b3 In the aforementioned chemical formula 13, 0.9 ≤ a³ ≤ 1.8, 0.6 ≤ x³ ≤ 1, 0 ≤ y³ ≤ 0.4, and 0 ≤ b³ ≤ 0.1, M 4X is one or more elements selected from Al, B, Ba, Ca, Ce, Co, Cr, Cu, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements selected from F, P, and S.

[0076] [Chemical formula 14] Li a4 Ni x4 Mn y4 M 5 z4 O 2-b4 X b4 In the above chemical formula 14, 0.9 ≤ a4 ≤ 1.8, 0.8 ≤ x4 < 1, 0 <y4≦0.2、0≦z4≦0.2、0.9≦x4+y4+z4≦1.1、および0≦b4≦0.1であり、M 5 X is one or more elements selected from Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements selected from F, P, and S.

[0077] As an example, the positive electrode active material may be a high-nickel positive electrode active material in which the nickel content relative to 100 mol% of the metal obtained by removing lithium from the lithium transition metal composite oxide is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more and 99 mol% or less. High-nickel positive electrode active materials can achieve high capacity and are applied to high-capacity, high-density lithium secondary batteries.

[0078] The aforementioned dry binder can be used as the binder included in the positive electrode, and other additional binders may also be included. The positive electrode binder plays a role in ensuring that the positive electrode active material particles adhere well to each other and that the positive electrode active material adheres well to the current collector. Such additional binders can be any binder commonly used in the art without limitation. Typical examples of such additional binders include, but are not limited to, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylic styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0079] The conductive material is used to impart conductivity to the electrodes, and any electronically conductive material that does not undergo chemical changes in the battery can be used. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials containing copper, nickel, aluminum, silver, etc., in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0080] Al can be used as the current collector, but is not limited to it.

[0081] electrolyte An electrolyte for a lithium secondary battery is, for example, a electrolyte solution, which may contain a non-aqueous organic solvent and a lithium salt.

[0082] Non-aqueous organic solvents act as a medium through which ions involved in the electrochemical reactions of the battery can move. Non-aqueous organic solvents may be carbonate-based, ester-based, ketone-based, or alcohol-based solvents, aprotic solvents, or combinations thereof.

[0083] As carbonate-based solvents, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC) can be used. As ester-based solvents, methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone can be used. As ester-based solvents, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran can be used. Furthermore, ketone solvents such as cyclohexanone can be used. As alcoholic solvents, ethyl alcohol and isopropyl alcohol can be used, and as aprotic solvents, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and can include double bonds, aromatic rings, or ether groups); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes can be used.

[0084] The non-aqueous organic solvent can be used alone or in combination of two or more kinds. When used in combination of two or more kinds, the mixing ratio can be appropriately adjusted according to the target battery performance, which is widely understood by those skilled in the art.

[0085] When using a carbonate solvent, a cyclic carbonate and a chain carbonate can be mixed and used, and the cyclic carbonate and the chain carbonate are mixed at a volume ratio of 1:1 to 1:9.

[0086] The non-aqueous organic solvent can further contain an aromatic hydrocarbon-based organic solvent. For example, the carbonate solvent and the aromatic hydrocarbon-based organic solvent can be mixed and used at a volume ratio of 1:1 to 30:1.

[0087] The electrolyte can further contain vinyl ethyl carbonate, vinylene carbonate or an ethylene carbonate-based compound in order to improve the battery life.

[0088] Typical examples of the ethylene carbonate-based compounds include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate and the like.

[0089] The lithium salt dissolves in the organic solvent and acts as a source of lithium ions in the battery, enabling the operation of a basic lithium secondary battery and promoting the movement of lithium ions between the positive electrode and the negative electrode. Typical examples of the lithium salt include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide; LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1It may contain one or more selected from SO2) (where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFBOP), and lithium bis(oxalate) borate (LiBOB).

[0090] The lithium salt concentration is preferably used within the range of 0.1 M to 2.0 M. When the lithium salt concentration falls within this range, the electrolyte has appropriate ionic conductivity and viscosity, resulting in excellent performance and effective lithium ion movement.

[0091] Separator Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators can be made of polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers of these materials. Mixed multilayer films such as polyethylene / polypropylene two-layer separators, polyethylene / polypropylene / polyethylene three-layer separators, and polypropylene / polyethylene / polypropylene three-layer separators can also be used.

[0092] The separator may include a porous substrate and a coating layer comprising organic, inorganic, or a combination thereof located on one or both sides of the porous substrate.

[0093] The porous substrate may be a polymer film formed from any polymer selected from polyethylene, polyolefins such as polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyetherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, and polytetrafluoroethylene (PTFE; Teflon®), or from a copolymer or mixture of two or more of these polymers.

[0094] The porous substrate can have a thickness of approximately 1 μm to 40 μm, for example, 1 μm to 30 μm, 1 μm to 20 μm, 5 μm to 15 μm, or 10 μm to 15 μm.

[0095] The organic material may include a (meth)acrylic copolymer comprising a first structural unit derived from (meth)acrylamide, and a second structural unit comprising at least one of a first structural unit derived from (meth)acrylic acid or (meth)acrylate, and a second structural unit derived from (meth)acrylamide sulfonic acid or a salt thereof.

[0096] The inorganic material may include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof. The average particle size (D) of the inorganic particles is 50 The wavelength range is 1 nm to 2000 nm, and may also be, for example, 100 nm to 1000 nm or 100 nm to 700 nm.

[0097] The organic and inorganic materials can exist mixed together in a single coating layer, or in a form where a coating layer containing organic materials and a coating layer containing inorganic materials are stacked on top of each other.

[0098] The thickness of the coating layer is 0.5 μm to 20 μm, and may be, for example, 1 μm to 10 μm, or 1 μm to 5 μm.

[0099] Lithium-ion battery Lithium-ion batteries can be classified into cylindrical, prismatic, pouch-type, coin-type, and other types depending on their form. Figures 1 to 4 are schematic diagrams showing a lithium-ion battery according to one embodiment, where Figure 1 is cylindrical, Figure 2 is prismatic, and Figures 3 and 4 are pouch-type batteries.

[0100] Referring to Figures 1-4, the lithium secondary battery 100 may include an electrode assembly 40 with a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is housed. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). The lithium secondary battery 100 may include a sealing member 60 that seals the case 50, as shown in Figure 1.

[0101] Furthermore, in Figure 2, the lithium secondary battery 100 may include a positive lead tap 11 and a positive terminal 12, and a negative lead tap 21 and a negative terminal 22. As shown in Figures 3 and 4, the lithium secondary battery 100 may also include electrode taps 70, namely a positive tap 71 and a negative tap 72, which serve as electrical pathways for guiding the current formed in the electrode assembly 40 to the outside.

[0102] The following describes examples and comparative examples of the present invention. The following examples are merely illustrative of the present invention and are not limited to the following examples.

[0103] Example 1 Example 1-1: Manufacturing of dry binder Nylon 6 (Goodfellow's AM300) as a polyamide polymer and cresol novolac epoxy (DIC's EPICLON N-660) as a crosslinking agent were mixed in a weight ratio of 7:3 using a thinky mixer at 2000 rpm for 3 minutes.

[0104] Examples 1-2: Manufacturing of the negative electrode After crushing the manufactured dry binder, a mixture of 3% by weight of the dry binder, 95% by weight of artificial graphite as the negative electrode active material, and 2% by weight of carbon black (Super P) as a conductive material was used to produce a sheet-like negative electrode active material layer in a calendering process at 1 rpm at 180°C. The negative electrode active material layer was then rolled onto a copper current collector at 180°C to produce a negative electrode having a negative electrode active material layer with a thickness of approximately 250 μm.

[0105] Examples 1-3: Battery Manufacturing A half-cell was manufactured using the aforementioned negative electrode, lithium metal counter electrode, and electrolyte. As the electrolyte, a mixed solvent of ethylene carbonate and diethyl carbonate in which 1M LiPF6 was dissolved (50:50 volume ratio) was used.

[0106] Example 2 A dry binder was manufactured by crosslinking nylon 610 (Alfa) as a polyamide polymer and cresol novolac epoxy (DIC's EPICLON N-660) as a crosslinking agent in an 8:2 weight ratio. The dry binder, negative electrode, and battery were manufactured in the same manner as in Example 1, except that the thickness of the negative electrode active material layer was changed to 220 μm.

[0107] Example 3 A dry binder was prepared by crosslinking nylon 12 (Aldrich) as a polyamide polymer and cresol novolac epoxy (DIC's EPICLON N-660) as a crosslinking agent in a weight ratio of 9:1. The dry binder, negative electrode, and battery were manufactured in the same manner as in Example 1, except that the thickness of the negative electrode active material layer was changed to 200 μm.

[0108] Example 4 A dry binder was prepared by crosslinking nylon 610 (Alfa) as a polyamide polymer and cresol novolac epoxy (DIC's EPICLON N-655-EXP-S) as a crosslinking agent in an 8:2 weight ratio, and a dry binder, a negative electrode, and battery were manufactured in the same manner as in Example 1, except that the thickness of the negative electrode active material layer was changed to 250 μm.

[0109] Example 5 A dry binder was prepared by crosslinking nylon 12 as a polyamide polymer and a phenol novolac epoxy (DIC's EPICLON N-770) as a crosslinking agent in a weight ratio of 9:1, and the negative electrode active material layer thickness was changed to 210 μm, except that it was manufactured in the same manner as in Example 1.

[0110] Example 6 A dry binder for the process was manufactured in the same manner as in Example 1, except that nylon 6 (Goodfellow's AM300) was used as the polyamide polymer and cresol novolac epoxy (DIC's EPICLON N-655-EXP-S) was used as the crosslinking agent, and the thickness of the negative electrode active material layer was changed to 250 μm.

[0111] Example 7 A dry binder was prepared by crosslinking nylon 6 (Goodfellow's AM300) as a polyamide polymer and phenol novolac epoxy (DIC's EPICLON N-770) as a crosslinking agent in an 8:2 weight ratio, and the dry binder, negative electrode, and battery were manufactured in the same manner as in Example 1, except that the thickness of the negative electrode active material layer was changed to 240 μm.

[0112] Comparative Example 1 A binder containing only nylon 6 (Goodfellow's AM300) as the polyamide polymer was manufactured, and the negative electrode and battery were manufactured in the same manner as in Example 1, except that the thickness of the negative electrode active material layer was changed to 150 μm.

[0113] Comparative Example 2 The negative electrode and battery were manufactured in the same manner as in Example 1, except that a binder containing only a cresol novolac epoxy (DIC's EPICLON N-660) was used.

[0114] Comparative Example 3 A binder was prepared by mixing nylon 610 as a polyamide polymer and bis(4-glycidyloxyphenyl)propane (Alfa) as a crosslinking agent in a weight ratio of 7:3 to create a crosslinked binder, and a dry binder, anode, and battery were manufactured in the same manner as in Example 1, except that the thickness of the negative electrode active material layer was changed to 220 μm.

[0115] Comparative Example 4 A binder was manufactured by crosslinking nylon 610 as a polyamide polymer and ethylene glycol diglycidyl ether (TCI) as a crosslinking agent in a weight ratio of 7:3. A dry binder, negative electrode, and battery were manufactured in the same manner as in Example 1, except that the thickness of the negative electrode active material layer was changed to 200 μm.

[0116] Comparative Example 5-1 The negative electrode and battery were manufactured in the same manner as in Example 1, except that they contained a PTFE binder (Syensqo DF681F).

[0117] Comparative Example 5-2 The negative electrode and battery were manufactured in the same manner as in Comparative Example 5-1, except that the copper current collector was rolled to form a current collector to which an adhesive primer layer containing a PVDF binder and a conductive material of carbon black (Super-P) was added.

[0118] Evaluation Example 1: Tensile Strength and Adhesion Test The tensile strength of the negative electrode active material layer in sheet form according to Examples 1 to 7 and Comparative Examples 1 to 5-1 was measured using a UTM tensile strength tester, and the results are shown in Table 1 below.

[0119] [Evaluation Criteria] Tensile strength exceeding 1.5N was evaluated as ◎, tensile strength between 1.0N and 1.5N was evaluated as ○, and tensile strength below 1.0N was evaluated as ×.

[0120] In the following examples, the adhesive strength between the current collector and the negative electrode active material layer was measured using a UTM tensile strength tester in the negative electrodes manufactured according to Examples 1 to 7 and Comparative Examples 1 to 5-1. A sample was prepared by attaching a slide glass to one side of a double-sided adhesive tape and attaching the negative electrode to the other side of the double-sided adhesive tape. The sample was placed in a UTM tensile strength tester, and the adhesive strength was measured when the negative electrode was peeled from the slide glass at a peeling angle of 180°. The results are shown in Table 1 below.

[0121] [Evaluation Criteria] Adhesion strength was evaluated as follows: 0.8 gf / mm or less was rated as ×, between 0.8 gf / mm and 1.0 gf / mm was rated as ○, and above 1.0 gf / mm was rated as ◎.

[0122] [Table 1]

[0123] Referring to Table 1, it can be seen that Comparative Example 1, which did not use a novolac epoxy crosslinking agent and used a binder containing only a polyamide polymer, has low tensile strength. When the volac epoxy crosslinking agent in Comparative Example 2 was used alone as a binder, the flexibility of the electrode plate decreased, cracks occurred, making electrode formation difficult, and tensile strength and adhesive strength could not be measured. Comparative Example 3 used bis(4-glycidyloxyphenyl)propane, a bisphenol A epoxy compound, as the crosslinking agent, and Comparative Example 4 used glycol diglycidyl ether, an aliphatic epoxy compound. These crosslinking agents exist as liquid substances, and when mixed with the polyamide polymer in a dry powder state, aggregation occurs, preventing the crosslinking agent from being evenly dispersed, resulting in decreased tensile properties and adhesive strength compared to Examples 1 to 5. In the case of Comparative Example 5-1, it can be seen that the adhesive strength is very poor when a PTFE binder is used.

[0124] In contrast, Examples 1-7 are binders obtained by mixing a polyamide polymer with a novolac epoxy crosslinking agent. The novolac epoxy crosslinking agent has a higher melting point than the crosslinking agents of Comparative Examples 3 and 4, exists in a solid state at room temperature, and the crosslinking agent can be uniformly dispersed. As a result, the tensile strength and adhesive strength were improved compared to Comparative Examples 1-5-1.

[0125] Evaluation Example 2: Electrolyte Stability The electrolyte stability was assessed by immersing the negative electrodes produced in Examples 1-7 and Comparative Examples 1, 3, 4, and 5-2 in the electrolyte and observing the desorption phenomenon after 3 days at 60°C. The results are shown in Table 2 below.

[0126] [Evaluation Criteria] Electrolyte stability was evaluated based on the desorption phenomenon, with a rating of × if desorption was observed. If no desorption was observed, but the solution was pressed by hand after the evaluation, it was rated ○. If neither desorption nor pressure was observed, it was rated ◎.

[0127] [Table 2]

[0128] Referring to Table 2, when the polyamide polymer of Comparative Example 1 is used alone as a binder, the polyamide polymer readily absorbs moisture, causing the electrolyte to deteriorate and reducing its stability. In Comparative Examples 3 and 4, aggregation occurred during the powder mixing process, resulting in uneven dispersion. This is thought to have prevented the uniform formation of the crosslinked structure and reduced the stability of the electrolyte. Comparative Example 5-1 lacked sufficient adhesive strength, making an electrolyte stability test impossible. In Comparative Example 5-2, which was manufactured by rolling a current collector with an adhesive primer layer, it can be seen that the electrolyte stability was reduced.

[0129] In contrast, Examples 1-7 demonstrated excellent electrolyte stability. Such electrolyte stability indicates excellent anode durability, and it is predicted that excellent electrolyte stability leads to a better battery life retention rate.

[0130] Evaluation Example 3: Current Density and Initial Charge / Discharge Efficiency Current density was measured by constantly charging the half-cells of Examples 1-7 and Comparative Examples 1-5-2 with a 0.5C rate current until the voltage reached 4.25V, then cutting off the voltage with a 0.02C rate current while maintaining 4.25V in constant voltage mode. Subsequently, the batteries were discharged with a constant current of 0.5C rate until the voltage reached 2.8V.

[0131] [Evaluation Criteria] The current density is 4 mA / cm². 2 The following are marked with ×, 4mA / cm 2 Super 5mA / cm 2 The following are marked with ○, 5mA / cm 2 I gave it an excellent rating (◎).

[0132] After performing one charge-discharge cycle on the half-cells of Examples 1-7 and Comparative Examples 1, 3, 4, and 5-2, the ratio of discharge capacity to charge capacity (single discharge capacity / single charge capacity) was calculated, and the results are shown in Table 3 as the initial charge-discharge efficiency.

[0133] [Evaluation Criteria] Initial charge / discharge efficiency is indicated as ◎ if it is 90% or higher, ○ if it is 87% or higher but less than 90%, △ if it is 84% ​​or higher but less than 87%, and × if it is less than 84%.

[0134] [Table 3]

[0135] Referring to Table 3, in the case of the half-cells of Examples 1 to 7, the negative electrode had a relatively high dielectric constant and exhibited high current density and initial charge / discharge efficiency.

[0136] In contrast, the half-cell of Comparative Example 1 showed a low current density, and in the case of the half-cells of Comparative Examples 3 and 4, the liquid crosslinking agent underwent aggregation and was not evenly dispersed, resulting in resistance and low current density and initial charge / discharge efficiency. The half-cell of Comparative Example 5-2 was found to have a negative electrode with low reduction stability, and its initial charge / discharge efficiency was confirmed to be low.

[0137] Although preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art that utilize the basic concepts defined in the claims also fall within the scope of the present invention. [Explanation of Symbols]

[0138] 100: Lithium-ion rechargeable battery 10: Positive electrode 11: Positive lead tap 12: Positive terminal 20: Negative electrode 21: Negative lead tap 22: Negative terminal 30: Separator 40: Electrode Assembly 50: Case 60: Sealing member 70: Electrode Tap 71: Positive Tap 72: Negative electrode tap

Claims

1. It contains a crosslinking reaction product in which a polyamide polymer is crosslinked with an epoxy crosslinking agent. A dry binder wherein the epoxy crosslinking agent is a novolac-based epoxy crosslinking agent.

2. The dry binder according to claim 1, wherein the polyamide polymer is contained in an amount of 60 to 95 parts by weight per 100 parts by weight of the dry binder.

3. The dry binder according to claim 1, wherein the novolac-based epoxy crosslinking agent is contained in an amount of 5 to 40 parts by weight per 100 parts by weight of the dry binder.

4. The dry binder according to claim 1, wherein the polyamide polymer comprises a structural unit represented by either chemical formula 1-1 or chemical formula 1-2. 【Chemistry 1】 【Chemistry 2】 (In the above chemical formulas 1-1 and 1-2, R 1 , R 2 , and R 3 Each of these is independently a substituted or unsubstituted C2-C20 alkylene group, a substituted or unsubstituted C3-C20 cycloalkylene group, or a linking group which is a combination thereof, and * indicates the linking site to the main chain.

5. The substituted or unsubstituted C2-C20 alkylene group is -(CH 2 ) n The dry binder according to claim 4, comprising structural units of - (where n is an integer from 2 to 14).

6. At least one non-adjacent methylene group (-(CH) among the linking groups (-(CH) 2 The dry binder according to claim 4, wherein )-) can be replaced with -NH-, -C(=O)-, or a combination thereof.

7. The novolac-based epoxy crosslinking agent is a dry binder according to claim 1, comprising the structure of chemical formula 2. 【Transformation 3】 (In the above chemical formula 2, R 4 , R 5 and R 6 are the same as or different from each other, and each independently is hydrogen (H), or a substituted or unsubstituted C1-C6 alkyl group, n is an integer of 1 or more and 30 or less, a and c are each independently an integer of 0 or more and 4 or less, and b is an integer of 0 to 3.)

8. The dry binder according to claim 1, wherein the weight-average molecular weight (Mw) of the polyamide polymer is 600 g / mol to 800,000 g / mol.

9. The dry binder according to claim 1, wherein the weight-average molecular weight (Mw) of the epoxy crosslinking agent is 500 g / mol to 10,000 g / mol.

10. A dry binder according to any one of claims 1 to 8, and electrode active material Electrodes for lithium secondary batteries, including those mentioned above.

11. The electrode for a lithium secondary battery according to claim 10, wherein the dry binder is used in an amount of 0.5 to 20 parts by weight per 100 parts by weight of the electrode active material.

12. The electrode for a lithium secondary battery according to claim 10, wherein the electrode is a negative electrode.

13. The electrode for a lithium secondary battery according to claim 12, wherein the negative electrode comprises a negative electrode active material including a carbon-based negative electrode active material, a silicon-based negative electrode active material, a Sn-based negative electrode active material, or a combination thereof.

14. The electrode for a lithium secondary battery according to claim 10, wherein the electrode is a positive electrode.

15. It includes a positive electrode, a negative electrode, and an electrolyte, A lithium secondary battery comprising at least one of the negative electrode and positive electrode, which is a dry binder according to any one of claims 1 to 8.

16. A method for manufacturing electrodes, An electrode-forming composition is manufactured by dry-mixing an electrode active material, a binder, and a conductive material. The step includes applying the electrode-forming composition onto a current collector to form an electrode, The binder comprises a crosslinking reaction product obtained by crosslinking a polyamide polymer with an epoxy crosslinking agent. A method for manufacturing an electrode, wherein the epoxy crosslinking agent is a novolac-based epoxy crosslinking agent.

17. The method for manufacturing an electrode according to claim 16, wherein the step of forming the electrode is carried out in a calendering step.

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