Binder for a negative electrode of a rechargeable lithium battery, negative electrode for a rechargeable lithium battery comprising a binder, and rechargeable lithium battery comprising a negative electrode

Abstract

Disclosed is a binder for a negative electrode of a rechargeable lithium battery, a negative electrode including the binder, and a rechargeable lithium battery including the negative electrode. The binder for the negative electrode includes a brush-like polymer.

Description

Technical Field

[0001] The example embodiments relate to an adhesive for a negative electrode of a rechargeable lithium battery, a negative electrode for a rechargeable lithium battery including the adhesive, and a rechargeable lithium battery including the negative electrode. Background Technology

[0002] With the increasing prevalence of battery-powered electronic devices (such as mobile phones, laptops, and electric vehicles), the demand for high-energy-density and high-capacity rechargeable lithium-ion batteries is growing. Therefore, improving the performance of rechargeable lithium-ion batteries can be beneficial.

[0003] A rechargeable lithium battery includes a positive electrode and a negative electrode having active materials capable of inserting and deintercalating lithium ions, as well as an electrolyte solution, and generates electrical energy through redox reactions when lithium ions are inserted / deintercalated at the positive and negative electrodes. Summary of the Invention

[0004] One or more example embodiments include an adhesive for the negative electrode of a rechargeable lithium battery that exhibits desired or improved dispersibility and adhesion as well as high elasticity, thereby exhibiting desired or improved durability.

[0005] Another example embodiment includes a negative electrode for a rechargeable lithium battery containing the binder.

[0006] Another example embodiment includes a rechargeable lithium battery containing the negative electrode.

[0007] One or more example embodiments include an adhesive for the negative electrode of a rechargeable lithium battery, said adhesive comprising a brush copolymer represented by the following chemical formula 1.

[0008] Chemical Formula 1:

[0009] In chemical formula 1, R 1 and R 2 The same or different, and including hydrogen or substituted or unsubstituted alkyl groups, either independently. R 3 To R 6 Same or different, and includes, or independently includes, hydrogen, substituted or unsubstituted alkyl groups or R. a COOR b , where R a It is a substituted or unsubstituted alkylene group, R b It is a substituted or unsubstituted alkyl group. R 7 It is hydrogen, substituted or unsubstituted alkyl, or CRd R e COOR f , where R d R e and R f Same or different, and includes hydrogen or alkyl groups, either individually or collectively. n1 is an integer in the range of approximately 1 to approximately 10. n2 is an integer in the range of approximately 2 to approximately 500. n3 is an integer in the range of approximately 1 to approximately 10, and n4 and n5 are each integers in the range of approximately 10 to approximately 100.

[0010] Another example embodiment includes a negative electrode for a rechargeable lithium battery, the negative electrode including a negative electrode active material layer comprising a binder and a negative electrode active material.

[0011] Another example embodiment includes a rechargeable lithium battery comprising: a negative electrode including a negative electrode active material layer, the negative electrode active material layer including a binder and a negative electrode active material; a positive electrode; and a non-aqueous electrolyte.

[0012] The binder for the negative electrode of a rechargeable lithium battery according to one or more example embodiments may have desired or improved dispersibility and adhesion, and exhibit high elasticity, so that the battery including the binder may exhibit desired or improved durability during repeated charging and discharging. Attached Figure Description

[0013] Figures 1 to 4 This is a schematic cross-sectional view of a rechargeable lithium battery according to some example embodiments. Detailed Implementation

[0014] Example embodiments are described in detail below. However, these embodiments are exemplary, and this disclosure is not limited thereto, and is defined by the scope of the claims.

[0015] As used herein, unless otherwise specifically defined, it is understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, the element may be “directly on” the other element, or an intervening element may be present.

[0016] Unless otherwise stated in this specification, a singular expression may also include a plural expression. Furthermore, unless otherwise stated, “A or B” may mean “including A, including B, or including both A and B”.

[0017] As used herein, the term "combination thereof" may include mixtures, laminates, complexes, copolymers, alloys, blends, and reactants of components.

[0018] In this disclosure, unless otherwise defined, particle size can be the average particle size. Particle size represents the average particle size (D50) of a cumulative volume of approximately 50% in a particle size distribution. The average particle size (D50) can be measured by methods known to those skilled in the art, for example, by a particle size analyzer, or by transmission electron microscopy (TEM) images or scanning electron microscopy (SEM) images. In some example embodiments, a dynamic light scattering measurement device is used to perform data analysis and count the number of particles in each particle size range, thereby easily obtaining the average particle size (D50) value by calculation. The average particle size (D50) can be measured by laser diffraction. Laser diffraction can be performed by the following steps: distributing the particles to be measured in a distribution solvent, introducing the particles into a commercially available laser diffraction particle measurement device (e.g., the MT 3000 available from Microtrac Ltd.), irradiating them with ultrasound at a power of approximately 60 W at approximately 28 kHz, and calculating the average particle size (D50) of a 50% volume standard of the particle size distribution in the measurement device.

[0019] In some example embodiments, the average particle size can be measured using various techniques, such as a particle size analyzer.

[0020] In some example embodiments, thickness can be measured using cross-sectional SEM or TEM images; however, the measurement technique is not limited to these, and thickness can be measured using any technique, as long as it is applicable to related technologies. The thickness can be the average thickness.

[0021] As used herein, soft carbon refers to a graphitizable carbon material that is readily graphitized by heat treatment at high temperatures (e.g., about 2800°C), and hard carbon refers to a non-graphitizable carbon material that is substantially non-graphitizable or only slightly graphitizable by heat treatment. The terms soft carbon and hard carbon may be well known in the relevant fields.

[0022] In some example embodiments, crystalline carbon and amorphous carbon can be distinguished by XRD measurements. Crystalline carbon includes natural graphite and synthetic graphite. Natural graphite can refer to graphite that is naturally produced by separating graphite from minerals, and whose interplanar spacing (d002) of the (002) facets is in the range of about 3.350 Å to about 3.360 Å when measured by XRD. Synthetic graphite can refer to graphite that is manufactured by graphitization, and whose interplanar spacing (d002) of the (002) facets is in the range of about 3.355 Å to about 3.365 Å when measured by XRD. Meanwhile, amorphous carbon can have an interplanar spacing (d002) of the (002) facets of about 3.34 Å or less when measured by XRD. XRD can be performed using CuKα rays as the target line with an X-ray diffractometer (e.g., product name: X'Pert, manufacturer: Malvern Panalytical) and by removing the monochromator to improve peak intensity resolution. Measurement conditions can be 2θ = 10° to 80°, scanning speed (° / s) from 0.044 to 0.089, and step size (° / step) from 0.013 to 0.039.

[0023] In some example embodiments, the weight-average molecular weight can be measured using gel permeation chromatography (GPC).

[0024] When the terms “about” or “substantially” are used in conjunction with numerical values ​​in this specification, it is intended that the relevant numerical values ​​include a tolerance of ±10% around the stated value. When a range is specified, the range includes all values ​​within that range, such as increments of 0.1%.

[0025] The binder used for the negative electrode of a rechargeable lithium battery comprises a brush copolymer represented by the following chemical formula 1.

[0026] Chemical Formula 1

[0027] In chemical formula 1, R 1 and R 2 The same or different, and includes, or independently includes, hydrogen or substituted or unsubstituted alkyl groups. In one or more example embodiments, R 1 and R 2 They may be the same or different, and may be or independently include unsubstituted alkyl groups. Alkyl groups may be or include C1 to C15 alkyl groups, C1 to C10 alkyl groups, or C1 to C4 alkyl groups. Alkyl groups may be or include straight-chain alkyl groups or branched-chain alkyl groups.

[0028] In chemical formula 1, R 3 To R 6 Same or different, and includes, or independently includes, hydrogen, substituted or unsubstituted alkyl groups or R.a COOR b , where R a It is a substituted or unsubstituted alkylene group, R b It is a substituted or unsubstituted alkyl group. In chemical formula 1, R 7 It is or includes hydrogen, substituted or unsubstituted alkyl groups, or CR. d R e COOR f , where R d R e and R f The same or different, and includes hydrogen or alkyl groups, either individually or separately. Alkylenes may be or include C1 to C15 alkylenes, C1 to C10 alkylenes, or C1 to C4 alkylenes. Alkyl groups may be or include C1 to C15 alkyl groups, C1 to C10 alkyl groups, or C1 to C4 alkyl groups. Alkylenes or alkyl groups may be or include straight-chain alkylenes or alkyl groups or branched alkylenes or alkyl groups.

[0029] According to one or more example embodiments, in the substituted alkyl group or in the substituted alkylene group, the substituent may be or include hydroxyl, methyl, hydrogen or amino groups.

[0030] n1 is an integer in the range of about 1 to about 10, or it can be an integer in the range of about 1 to about 5 or an integer in the range of about 1 to about 3.

[0031] n3 is an integer in the range of about 1 to about 10, or it can be an integer in the range of about 1 to about 5 or an integer in the range of about 1 to about 3.

[0032] n2 represents the gap between the brush-like polymers and is an integer in the range of about 2 to about 500, or it can be an integer in the range of about 10 to about 500 or an integer in the range of about 10 to about 100. When n2 is within the above range, the adhesive can exhibit desired or improved elasticity and adhesive strength. When n2 is outside the above range, the thickness change of the rechargeable lithium battery after charging and discharging increases, which is undesirable.

[0033] n4 and n5 are each an integer in the range of about 10 to about 100, or can be an integer in the range of about 10 to about 30. n4 and n5 correspond to side chains bonded to the main chain, and polymers having side chains with lengths corresponding to n4 and n5 can be called “brush-type” polymers. In one or more example embodiments, the lengths corresponding to n4 and n5 as side chains can provide spatial steric hindrance for chain movement and reduce or suppress chain entanglement. When polymer chain entanglement occurs in an adhesive, it can lead to reduced elasticity and plastic deformation when stress or elongation occurs. However, the adhesives according to one or more example embodiments do not cause chain entanglement, resulting in improved elastic properties of the adhesive and no or substantially no plastic deformation.

[0034] In one or more embodiments, the weight-average molecular weight (Mw) of the adhesive can be about 100 kDa to about 5 MDa, about 100 kDa to about 2 MDa, or about 100 kDa to about 1 MDa. When the weight-average molecular weight (Mw) of the adhesive meets this range, desired or improved adhesion and elasticity can be exhibited.

[0035] There are no limitations on the preparation of the binder for the negative electrode according to one or more example embodiments, and the binder can be synthesized by any steps generally known in the relevant art. The binder according to one or more example embodiments can be prepared by the following steps.

[0036] First, the monomer is subjected to an ATRP (atom transfer radical polymerization) reaction to prepare a halogen-containing intermediate, and then the halogen-containing intermediate is subjected to a halogen substitution reaction to prepare a macromolecular monomer as a side chain.

[0037] ATRP reactions can be carried out by using halogenated initiators, ligands, and catalysts in conjunction with monomers. In ATRP reactions, the mixing ratio of monomers, halogenated initiators, and ligands can be in the range of about 1:about 0.01 to about 0.1:about 0.012 to about 0.6 molar ratios or about 1:about 0.01 to about 0.06:about 0.02 to about 0.12 molar ratios. When the mixing ratio of monomers, halogenated initiators, and ligands is included within the above ranges, the advantages associated with low PDI (polydispersity index) of macromonomers can be obtained.

[0038] The catalyst can be used in a suitable amount to initiate the ATRP reaction, and for example, based on 100 wt% of the initiator, the catalyst can be in the range of about 0.01 wt% to about 0.1 wt%, about 0.01 wt% to about 0.05 wt%, or about 0.01 wt% to about 0.02 wt%.

[0039] The monomer may be or include at least one of ethyl acrylate, butyl acrylate, 2-hydroxy acrylate, acrylic acid, 2-ethylhexyl acrylate, isobornyl acrylate, and combinations thereof.

[0040] The halogen-containing initiator may be or include at least one of, for example, ethyl 2-bromo-2-methylpropionate, methyl 2-bromo-2-methylpropionate, 2-hydroxyethyl 2-bromoisobutyrate, 2-bromo-2-methylpropionic acid, and combinations thereof.

[0041] By using an initiator that includes halogens as the initiator, a halogen substitution reaction in which halogens are replaced by acryloyl groups can be initiated, thereby producing a large monomer.

[0042] The ligand may be or include at least one of N,N,N',N'',N''-pentamethyldiethylenetriamine, tris-2-(dimethylamino)ethylamine, tris(2-aminoethyl)amine, tris(3-aminopropyl)amine, and combinations thereof.

[0043] The catalyst may be or include at least one of Cu, Fe and Sn.

[0044] Halogen substitution reactions can be carried out using potassium salts, and the potassium salts can be or include at least one of potassium propionate (potassium propionate), potassium acrylate (potassium acrylate), potassium (meth)acrylate (potassium (meth)acrylate), and combinations thereof. For example, halogen substitution reactions can be carried out by mixing a halogen-containing intermediate and a potassium salt. Here, the mixing ratio of the halogen-containing intermediate and the potassium salt can be in the range of about 1:1 to about 1:5 by weight or about 1:1 to about 1:2 by weight.

[0045] When the preparation of macromonomers is shown as a reaction scheme, for example, using butyl acrylate as a monomer and ethyl 2-bromo-2-methylpropionate as an initiator, the macromonomers are prepared as follows.

[0046] Reaction scheme 1:

[0047] As shown in reaction scheme 1, butyl acrylate is subjected to an ATRP reaction to prepare BA. n -Br, and subject it to halogen substitution reactions, for example, with potassium acrylate, to prepare the macromonomer BA as a side chain. n -AA.

[0048] A binder according to one or more example embodiments is prepared by copolymerizing macromonomers and monomers having double bonds via a free radical reaction. Here, the control of n1, n2, n3 in Formula 1 depends on the mixing ratio of the macromonomers and monomers having double bonds.

[0049] In one or more example embodiments, the mixing ratio of the macromonomer and the monomer having double bonds can be in the range of about 1:2 molar ratio to about 1:500 molar ratio or about 1:2 molar ratio to about 1:100 molar ratio. When the mixing ratio of the macromonomer and the monomer having double bonds is within the above range, the desired brush copolymer represented by Formula 1 can be prepared as needed. For example, when the mixing ratio of the macromonomer and the monomer having double bonds is about 1:2 molar ratio, a copolymer in Formula 1 with n1 being 1, n2 being 2, and n3 being 1 can be prepared.

[0050] In one or more example embodiments, since free radical reactions are utilized, a variety of monomers (e.g., monomers with double bonds) can be used, and therefore, free radical reactions can be economical.

[0051] Monomers having double bonds may be or include at least one of ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, acrylic acid, and combinations thereof.

[0052] The mixing ratio of macromonomers and monomers with double bonds can be in the range of about 1:2 to about 1:500 molar ratio or about 1:2 to about 1:100 molar ratio. When the mixing ratio of macromonomers and monomers with double bonds is within the above range, flexibility and adhesion can be improved.

[0053] Negative electrode for rechargeable lithium batteries: The negative electrode according to one or more example embodiments includes a layer of negative electrode active material comprising a binder and a negative electrode active material. The binder may be or may include the binder according to one or more example embodiments.

[0054] In one or more example embodiments, the amount of binder may range from about 1 wt% to about 5 wt%, about 1 wt% to about 3 wt%, or about 1 wt% to about 2 wt%, based on the total weight of the negative electrode active material layer. When the amount of binder is within the above range, the negative electrode active materials can adhere sufficiently to each other, the negative electrode active material layer can adhere sufficiently to the current collector, and the desired or improved resilience against volume expansion of the negative electrode active materials can be provided.

[0055] The negative electrode active material may be or include a Si-based negative electrode active material. The Si-based negative electrode active material has a relatively high capacity, but has disadvantages including severe volume expansion and contraction during charging and discharging. By using the Si-based negative electrode active material together with a binder according to one or more exemplary embodiments, these disadvantages can be effectively eliminated. Accordingly, the negative electrode according to one or more exemplary embodiments can satisfy the high capacity obtained by using the Si-based negative electrode active material and the desired or improved cycle life characteristics obtained by the binder according to one or more exemplary embodiments.

[0056] The Si-based negative electrode active material may be or include silicon, a Si-C composite, SiO x (0 < x ≤ 2), a Si-Q alloy (where Q is an element such as or including at least one of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element (excluding Si), a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof), and combinations thereof.

[0057] The Si-based negative electrode active material may be or include silicon or a silicon-carbon composite.

[0058] The silicon-carbon composite may be or include a composite of silicon and amorphous carbon. According to one or more exemplary embodiments, the silicon-carbon composite may include silicon particles and an amorphous carbon coating on the surface of the silicon particles. For example, the silicon-carbon composite may include secondary particles (cores) in which silicon primary particles are aggregated and an amorphous carbon coating layer (shell) on the secondary particles. Amorphous carbon is also present between the silicon primary particles, for example, to coat the silicon primary particles. For example, the secondary particles may be distributed in an amorphous carbon matrix.

[0059] In addition, the silicon-carbon composite may include silicon particles and an amorphous carbon coating on the surface of the silicon particles.

[0060] The secondary particles are located at the center of the Si-C composite, and thus the secondary particles may be referred to as nuclei or central portions. The amorphous carbon coating layer may be referred to as the exterior or shell.

[0061] The silicon particles may be or include nano-silicon particles. The nano-silicon particles may have an average particle size in the range of about 10 nm to about 1000 nm, and according to one or more exemplary embodiments, the average particle size of the nano-silicon particles may be in the range of about 20 nm to about 900 nm, about 20 nm to about 500 nm, about 20 nm to about 300 nm, or about 20 nm to about 150 nm. When the average particle size of the silicon particles is in the above range, significant volume expansion during charging and discharging can be reduced or suppressed, and interruption of the conduction path due to particle breakage during charging and discharging can be reduced or prevented.

[0062] The mixing ratio of nano-silicon particles and amorphous carbon can be in the range of approximately 20:80 to approximately 70:30 by weight.

[0063] In one or more example embodiments, the silicon-carbon composite may further include crystalline carbon. In some example embodiments, the silicon-carbon composite may include a core comprising crystalline carbon and silicon particles, and an amorphous carbon coating layer on the surface of the core.

[0064] When the silicon-carbon composite comprises silicon particles, crystalline carbon, and amorphous carbon, the amount of amorphous carbon can range from about 10 wt% to about 70 wt% based on a total of 100 wt% of the silicon-carbon composite, and the amount of crystalline carbon can range from about 10 wt% to about 70 wt% based on a total of 100 wt% of the silicon-carbon composite. The amount of silicon particles can range from about 20 wt% to about 69 wt% based on a total of 100 wt% of the silicon-carbon composite, and according to one or more example embodiments, the amount of silicon particles can range from about 30 wt% to about 60 wt%.

[0065] The particle size of the silicon-carbon composite can be adjusted as needed, and the particle size is not particularly limited thereto.

[0066] When amorphous carbon is present around the surface of secondary particles, the thickness of the amorphous carbon can be adjusted as needed, but it can be present, for example, in the range of about 5 nm to about 100 nm.

[0067] In one or more example embodiments, the negative electrode active material layer may also include a conductive material.

[0068] For example, the negative electrode active material layer may comprise a negative electrode active material ranging from about 95 wt% to about 99 wt% and a binder ranging from about 1 wt% to about 5 wt%. In another example embodiment, the negative electrode active material layer may comprise a negative electrode active material ranging from about 91.5 wt% to about 99 wt%, a binder ranging from about 1 wt% to about 5 wt%, and a conductive material ranging from about 0.5 wt% to about 5 wt%. The binder may be or include the binder according to one or more example embodiments or a mixture of the binder according to one or more example embodiments and an aqueous binder.

[0069] Waterborne adhesives may include styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepoxychloropropane, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, or combinations thereof.

[0070] Conductive materials are included to provide electrode conductivity, and any electrically conductive material can be used as the conductive material unless it causes an adverse chemical change in the battery. Examples of conductive materials may include or include: carbon-based materials, such as at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.; metallic materials including at least one of metal powder or metal fiber of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0071] The negative electrode current collector may include at least one of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and combinations thereof.

[0072] Rechargeable lithium batteries: Other example embodiments include a rechargeable lithium battery that includes a negative electrode, a positive electrode, and a non-aqueous electrolyte.

[0073] Positive electrode: The positive electrode may include a current collector and a layer of positive electrode active material on the current collector. The layer of positive electrode active material includes a positive electrode active material and may also include a binder and / or a conductive material.

[0074] For example, the positive electrode may also include additives that can be configured as a sacrificial positive electrode.

[0075] Based on a 100wt% positive electrode active material layer, the amount of positive electrode active material can be in the range of about 90wt% to about 99.5wt%, and based on a 100wt% positive electrode active material layer, the amounts of binder and conductive material can be in the range of 0.5wt% to 5wt%, respectively.

[0076] The positive electrode active material may include compounds capable of intercalating and deintercalating lithium (lithiation intercalation compounds). In some example embodiments, it may include at least one of a composite oxide of lithium and a metal (such as or including at least one of cobalt, manganese, nickel, and combinations thereof).

[0077] The composite oxide can be or includes lithium transition metal composite oxides, and examples of such composite oxides can include at least one of lithium nickel oxides, lithium cobalt oxides, lithium manganese oxides, lithium iron phosphate compounds, cobalt-free lithium nickel manganese oxides, and combinations thereof.

[0078] For example, it may include the following compounds represented by any of the following chemical formulas: 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 About 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 About 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 About 2-α D α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0<α<2);Li a Ni b Co c L 1 d G e O2(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≤1.8,0.001≤b≤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).

[0079] In the above chemical formula, A is or includes at least one of Ni, Co, Mn, and combinations thereof; X is or includes at least one of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, and combinations thereof; D is or includes at least one of O, F, S, P, and combinations thereof; G is or includes at least one of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and combinations thereof; and L 1 It is or includes at least one of Mn, Al and combinations thereof.

[0080] For example, the positive electrode active material can be or includes a high-nickel positive electrode active material. Based on 100 mol% of metals other than lithium in the lithium transition metal complex oxide, the high-nickel positive electrode active material has a nickel content of greater than or equal to about 80 mol%, greater than or equal to about 85 mol%, greater than or equal to about 90 mol%, greater than or equal to about 91 mol%, or greater than or equal to about 94 mol% and less than or equal to about 99 mol%. High-nickel positive electrode active materials can achieve high capacity and can be applied to high-capacity, high-density rechargeable lithium batteries.

[0081] The binder is configured to improve the adhesion properties between the positive electrode active material particles and between the positive electrode active material particles and the current collector. Examples of binders may be, but are not limited to, at least one of the following: polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylate resin, polyester resin, nylon, etc.

[0082] The conductive material is included to provide electrode conductivity, and any suitable electrically conductive material may be included as the conductive material unless it causes an adverse chemical change in the battery. Examples of conductive materials may include: carbon-based materials, such as or including at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.; metallic materials including at least one of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0083] The current collector may include, but is not limited to, Al.

[0084] Electrolyte: Electrolytes used in rechargeable lithium batteries may include non-aqueous organic solvents and lithium salts.

[0085] Non-aqueous organic solvents are constructed as media for transporting ions that participate in the electrochemical reactions of the battery.

[0086] Non-aqueous organic solvents may include at least one of carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, aprotic solvents, and combinations thereof.

[0087] Carbonate solvents may include at least one of 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 butyl carbonate (BC). Esters may include at least one of methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolactone, γ-butyrolactone, mevalonolactone, valproic acid lactone, and caprolactone. Ether solvents may include at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. Ketone solvents may include cyclohexanone. Alcohol solvents may include at least one of ethanol and isopropanol. Aprotic solvents may include at least one of the following: nitriles, such as R-CN (wherein R is or includes a C2 to C20 straight-chain, branched or cyclic hydrocarbon group, and may include double bonds, aromatic rings or ether bonds, etc.); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane, 1,4-dioxolane, etc.; sulfolane, etc.

[0088] Organic solvents may be included alone or as a mixture of two or more solvents.

[0089] When carbonate solvents are included, cyclic carbonates and chain carbonates may be included together, and cyclic carbonates and chain carbonates may be mixed in a volume ratio ranging from about 1:1 to about 1:9.

[0090] The electrolyte may also include at least one of the following as an additive: vinyl ethyl carbonate, vinylene carbonate, difluoroethylene carbonate, ethylene chloride carbonate, dichloroethylene carbonate, ethylene bromide carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, fluoroethylene carbonate, and combinations thereof.

[0091] Lithium salts dissolved in organic solvents are configured to supply lithium ions to the battery, enabling the operation of rechargeable lithium batteries and improving lithium ion transport between the positive and negative electrodes. Examples of lithium salts include one or more electrolyte-supporting salts, such as or including 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+1 At least one of the following: (SO2) (where x and y are integers in the range of 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFBOP), and lithium bis(oxalate)borate (LiBOB).

[0092] Diaphragm: Depending on the type of rechargeable lithium battery, a separator may be present between the positive and negative electrodes. The separator may include at least one of polyethylene, polypropylene, polyvinylidene fluoride, and multilayers having two or more layers, and may be or include multilayers mixed together, such as polyethylene / polypropylene bilayer separators, polyethylene / polypropylene / polyethylene trilayer separators, polypropylene / polyethylene / polypropylene trilayer separators, etc.

[0093] The membrane may include a porous substrate and a coating layer comprising an organic material, an inorganic material, or a combination thereof on one or both surfaces of the porous substrate (e.g., on one or two opposing surfaces).

[0094] The porous substrate may be or include a membrane formed of a copolymer or mixture of any one or two or more of the following, or a membrane comprising a copolymer or mixture of any one or two or more of the following: polyolefins (such as polyethylene and polypropylene), polyesters (such as polyethylene terephthalate and polybutylene terephthalate), polyacetal, polyamide, polyimide, polycarbonate, polyetherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene ether, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fiber, and polytetrafluoroethylene (e.g., Teflon).

[0095] Organic materials may include polyvinylidene fluoride polymers or (meth)acrylamide polymers.

[0096] Inorganic materials may be or include inorganic particles, such as or include at least one of Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite and combinations thereof, but are not limited thereto.

[0097] Organic and inorganic materials can be mixed in a coating layer, or a coating layer containing organic materials and a coating layer containing inorganic materials can be stacked together.

[0098] Based on their shape, rechargeable lithium batteries can be classified into cylindrical batteries, prismatic batteries, pouch batteries, or coin-shaped batteries, etc. Figures 1 to 4 This is a schematic diagram illustrating a rechargeable lithium battery according to an example embodiment. Figure 1 A cylindrical battery is shown. Figure 2 A prismatic battery is shown, and Figure 3 and Figure 4 A pouch-type battery is shown. (See reference) Figures 1 to 4 The rechargeable lithium battery 100 may include an electrode assembly 40 and a housing 50. The electrode assembly 40 includes a separator 30 between a positive electrode 10 and a negative electrode 20, and the electrode assembly 40 is housed within the housing 50. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). Figure 1 As shown, the rechargeable lithium battery 100 may include a sealing member 60 of the sealed housing 50. Figure 2 In this context, the rechargeable lithium battery 100 may include a positive electrode lead connector 11 and a positive electrode terminal 12 connected to the positive electrode lead connector 11, a negative electrode lead connector 21 and a negative electrode terminal 22 connected to the negative electrode lead connector 21. For example... Figure 4 As shown, the rechargeable lithium battery 100 may include electrode terminals 70, which may form an electrical path for guiding current formed in the electrode assembly 40 to the outside of the rechargeable lithium battery 100, or as... Figure 3 As shown, the rechargeable lithium battery 100 may include a positive electrode terminal 71 and a negative electrode terminal 72.

[0099] As a non-limiting example, the rechargeable lithium battery according to the example embodiment can be applied to, for example, vehicles, mobile phones and / or various suitable types of electronic devices.

[0100] The following examples and comparative examples are provided to highlight the features of one or more example embodiments; however, it is understood that the examples and comparative examples are not to be construed as limiting the scope of the example embodiments, nor are the comparative examples to be construed as being outside the scope of the example embodiments. Furthermore, it is understood that the example embodiments are not limited to the specific details described in the examples and comparative examples.

[0101] Example 1: 1) Preparation of adhesive The macromolecular monomer is prepared as shown in reaction scheme 1 below.

[0102] Reaction scheme 1:

[0103] BA was prepared by ATRP reaction of butyl acrylate, ethyl 2-bromo-2-methylpropionate initiator, and tris(dimethylamino)ethylamine ligand in a molar ratio of 1:0.05:0.06 in the presence of Cu catalyst. n -Br. Based on 100wt% initiator, the amount of Cu catalyst is 0.1wt%. BA at a weight ratio of 1:2. n -Br and potassium propionate undergo a halogen substitution reaction to prepare the macromonomer BA as a side chain. n -AA.

[0104] A brush-like adhesive with a polymer structure having the following chemical formula 1 was prepared by copolymerizing a macromonomer and a butyl acrylate monomer in a molar ratio of 1:2 via a free radical reaction (weight average molecular weight (Mw): 1MDa).

[0105] Chemical Formula 1:

[0106] In chemical formula 1, R 1 and R 2 Similarly, it is butyl. R 3 To R 6 Similarly, it is CH2CH2COOCH2CH3. R 7 It is C(CH3)2COOCH2CH3. n1 is an integer 1. n2 is an integer 10. n3 is an integer 1. n4 and n5 are independent integers of 20.

[0107] Silicon negative electrode active material (98 wt% of the negative electrode active material layer slurry) and binder (2 wt% of the negative electrode active material layer slurry) are mixed in an aqueous solvent to prepare a negative electrode active material layer slurry with a solid content of 55 wt%.

[0108] The negative electrode is prepared by coating a slurry of the active material layer of the negative electrode onto a copper current collector, drying it, and then pressing it.

[0109] LiNi 0.8 Co 0.1 Mn 0.1 O2 positive electrode active material (96 wt% constituting the positive electrode active material layer slurry), Ketjen black (2 wt% constituting the positive electrode active material layer slurry), and polyvinylidene fluoride (2 wt% constituting the positive electrode active material layer slurry) are mixed in N-methylpyrrolidone solvent to prepare the positive electrode active material layer slurry. The positive electrode active material layer slurry is coated onto an Al foil current collector and dried, and then pressed to prepare the positive electrode.

[0110] A full cell is constructed using a negative electrode, a positive electrode, and an electrolyte. As the electrolyte, 1.15 M LiPF6 is dissolved in ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (volume ratio 3:5:2).

[0111] Example 2: The binder (weight average molecular weight: 1 MDa) in which n2, serving as the gap between the brush polymers in Formula 1, is equal to 50 is prepared using the same steps as in Example 1, except that the mixing ratio of the macromonomer and the butyl acrylate monomer is changed to a 1:50 molar ratio.

[0112] The full cell was prepared using the same steps as in Example 1 using this binder.

[0113] Example 3: The binder (weight average molecular weight: 1 MDa) in which n2, serving as the gap between the brush polymers in Formula 1, is equal to 100 is prepared using the same steps as in Example 1, except that the mixing ratio of the macromonomer and the butyl acrylate monomer is changed to a 1:100 molar ratio.

[0114] The full cell was prepared using the same steps as in Example 1 using this binder.

[0115] Example 4: The binder (weight average molecular weight: 1 MDa) in which n2, serving as the gap between the brush polymers in Formula 1, is equal to 500 is prepared by the same steps as in Example 1, except that the mixing ratio of the macromonomer and the butyl acrylate monomer is changed to a 1:500 molar ratio.

[0116] The full cell was prepared using the same steps as in Example 1 using this binder.

[0117] Comparison Example 1: The binder (weight average molecular weight: 1 MDa) in which n2, serving as the gap between the brush polymers in Formula 1, is equal to 1 is prepared using the same steps as in Example 1, except that the mixing ratio of the macromonomer and the butyl acrylate monomer is changed to a 1:1 molar ratio.

[0118] The full cell was prepared using the same steps as in Example 1 using this binder.

[0119] Experimental Example 1) Evaluation of Modulus After the adhesive was coated to a thickness of 300 μm on a flat plate with a diameter of 8 φ, the shear modulus of the adhesives according to Examples 1 to 4 and Comparative Example 1 was measured at frequencies from 0.01 Hz to 100 Hz under 0.1% strain conditions. Among these results, the modulus results obtained at 10 Hz are shown in Table 1 below.

[0120] Table 1:

[0121] As shown in Table 1, the binders of Examples 1 to 4, where n² is equal to 10 to 500, exhibit suitable moduli of 25 kPa to 100 kPa at 10 Hz. This suitable modulus indicates improved adhesion strength to the active material, conductive material, and current collector, thus effectively reducing or preventing volume expansion and separation of the active material from the current collector during charging and discharging. Therefore, it is anticipated that batteries exhibiting desired or improved cycle life characteristics can be provided.

[0122] However, Comparative Example 1 exhibits a significantly low modulus of 15 kPa at 10 Hz, which results in low adhesive strength, causing the active material to separate from the current collector during charging and discharging, and causing volume expansion.

[0123] While this disclosure has been described in conjunction with exemplary embodiments which are now considered to be practical, it will be understood that the disclosure is not limited to the disclosed embodiments, but rather is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. An adhesive for a negative electrode of a rechargeable lithium battery, the adhesive comprising: Brush-like copolymer represented by chemical formula 1; Chemical Formula 1: Among them, R 1 and R 2 Independently includes hydrogen or substituted or unsubstituted alkyl groups, R 3 To R 6 Independently includes hydrogen, substituted or unsubstituted alkyl groups, or R. a COOR b , where R a It is a substituted or unsubstituted alkylene group, R b It is a substituted or unsubstituted alkyl group; R 7 It is hydrogen, substituted or unsubstituted alkyl, or CR d R e COOR f , where R d R e and R f Independently includes hydrogen or alkyl groups; n1 is an integer in the range of 1 to 10. n2 is an integer in the range of 2 to 500. n3 is an integer in the range of 1 to 10, and n4 and n5 are each integers in the range of 10 to 100.

2. The binder for the negative electrode of a rechargeable lithium battery according to claim 1, wherein, R 1 and R 2 It independently includes unsubstituted alkyl groups.

3. The binder for the negative electrode of a rechargeable lithium battery according to claim 1, wherein: Alkyl groups include C1 to C15 alkyl groups; and Alkylenes include C1 to C15 alkylenes.

4. The binder for the negative electrode of a rechargeable lithium battery according to claim 1, wherein: Alkyl groups include one of straight-chain alkyl groups and branched-chain alkyl groups; and Alkylenes include one of straight-chain alkylenes and branched alkylenes.

5. The binder for the negative electrode of a rechargeable lithium battery according to claim 1, wherein, The binder has a weight-average molecular weight in the range of 100 kDa to 5 MDa.

6. The binder for the negative electrode of a rechargeable lithium battery according to claim 1, wherein, n2 is in the range of 10 to 500.

7. The binder for the negative electrode of a rechargeable lithium battery according to claim 1, wherein, n4 and n5 are independently in the range of 10 to 30.

8. A negative electrode for a rechargeable lithium battery, the negative electrode comprising: The negative electrode active material layer comprises: a binder according to any one of claims 1 to 7; and a negative electrode active material.

9. The negative electrode for a rechargeable lithium battery according to claim 8, wherein, The amount of binder is in the range of 1 wt% to 5 wt% based on the total weight of the negative electrode active material layer.

10. The negative electrode for a rechargeable lithium battery according to claim 8, wherein, The negative electrode active material includes Si-based negative electrode active materials.

11. The negative electrode for a rechargeable lithium battery according to claim 10, wherein, The active material of the Si-type negative electrode includes one of silicon and silicon-carbon composites.

12. A rechargeable lithium battery, said rechargeable lithium battery comprising: The negative electrode comprises the binder and negative electrode active material according to any one of claims 1 to 7; Positive electrode; as well as Non-aqueous electrolyte.

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