Binder for negative electrode of rechargeable lithium battery, negative electrode for rechargeable lithium battery comprising same, and rechargeable lithium battery comprising same

Abstract

Disclosed are a binder for a negative electrode of a rechargeable lithium battery, a negative electrode including the binder, and a rechargeable lithium battery including the binder.

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 adhesive. Background Technology

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

[0003] A rechargeable lithium battery includes a positive electrode and a negative electrode as well as an electrolyte. The positive and negative electrodes include active materials capable of inserting and deintercalating lithium ions, and generate electrical energy through oxidation and reduction reactions when lithium ions are deintercalated / intercalated from the positive electrode and intercalated / deintercalated from the negative electrode. Summary of the Invention

[0004] One or more example embodiments include an adhesive for the negative electrode of a rechargeable lithium battery that is capable of reducing or suppressing volume expansion of the negative electrode.

[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, the adhesive being represented by the following chemical formula 1.

[0008] Chemical Formula 1: .

[0009] R 1 and R 2 Same or different, and is hydrogen or substituted or unsubstituted alkyl; R 3 It may include or contain substituted or unsubstituted alkyl groups. n1 is an integer in the range of approximately 50 to approximately 180, and n2 is an integer in the range of approximately 5 to approximately 20.

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

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

[0012] Binders used for the negative electrode of rechargeable lithium batteries can provide batteries that exhibit desired or improved cycle life and improved high-rate characteristics. 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 there may be intervening elements between them.

[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 of components, laminates, complexes, copolymers, alloys, blends, and reaction products.

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

[0019] In some example embodiments, the average particle size can be measured by various techniques, and for example, by a particle size analyzer.

[0020] In some example embodiments, thickness can be measured using cross-sectional SEM or TEM images, but is not limited to these, and thickness can be measured using any technique, as long as that technique is applicable to the related art. 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 ungraphitizable or only slightly graphitized by heat treatment. The terms soft carbon and hard carbon may be 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 can be naturally generated by separating graphite from minerals, and when measured by XRD, the interplanar spacing (d002) of the (002) facet can be in the range of about 3.350 Å to about 3.360 Å. Synthetic graphite can refer to graphite manufactured by graphitization, and if (e.g., when) measured by XRD, the interplanar spacing (d002) of the (002) facet can be in the range of about 3.355 Å to about 3.365 Å. When measured by XRD, the interplanar spacing (d002) of the (002) facet of amorphous carbon can be in the range of about 3.34 Å or less. XRD can be performed using CuKα rays as the target ray, 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] The binder used for the negative electrode of a rechargeable lithium battery is represented by the following chemical formula 1.

[0025] Chemical Formula 1: .

[0026] In chemical formula 1, R 1 and R 2 Same or different, and is: hydrogen; or substituted or unsubstituted alkyl, R 3 It may include or contain substituted or unsubstituted alkyl groups. n1 is an integer in the range of approximately 50 to approximately 180, and n2 is an integer in the range of approximately 5 to approximately 20.

[0027] In one or more example embodiments, R 1 and R 2 They may be the same or different, and may be or include unsubstituted alkyl groups. Alkyl groups may be or include C1 to C15 alkyl groups or C3 to C15 alkyl groups. Alkyl groups may be or include straight-chain alkyl groups or branched-chain alkyl groups.

[0028] R 3 It may be or include unsubstituted alkyl groups. Alkyl groups may be or include C1 to C5 alkyl groups or C3 to C5 alkyl groups. Alkyl groups may be or include branched alkyl groups.

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

[0030] In one or more example embodiments, n1 can be about 60 to about 100.

[0031] In one or more example embodiments, n2 can be at most about 20. When n2 is greater than 20, the binder may become entangled in the slurry used to prepare the negative electrode, resulting in a significant increase in the viscosity of the slurry, and therefore, phase separation may occur. In addition, binders with n2 greater than 20 may exhibit deteriorated adhesion.

[0032] Because hydrogen bonding can occur in the substituted alkyl groups, the binders according to one or more example embodiments exhibit desired or improved adhesion, thus maintaining the adhesion between the active materials or to the current collector as desired, even when the volume of the negative electrode active material expands or contracts during charging and discharging. The binders according to one or more example embodiments can provide desired or improved resilience against volume expansion of the negative electrode active material.

[0033] Therefore, when the binder according to one or more example embodiments is used in a negative electrode comprising a Si-based active material (which exhibits a significantly higher capacity of about 4,200 mAh / g, but shows degraded cycle life during repeated charging and discharging due to volume expansion in the range of about 300% to about 400%), the degradation of cycle life characteristics due to volume expansion of the Si-based active material can be effectively reduced or suppressed.

[0034] In one or more example embodiments, the binder may have a weight-average molecular weight (Mw) in the range of about 100,000 Daltons to about 1,000,000 Daltons, about 100,000 Daltons to about 800,000 Daltons, about 100,000 Daltons to about 600,000 Daltons, or about 100,000 Daltons to about 400,000 Daltons. In another embodiment, the binder may have a weight-average molecular weight (Mw) in the range of about 60,000 Daltons to about 90,000 Daltons or about 6,000 Daltons to 10,000 Daltons. When the weight-average molecular weight (Mw) of the binder meets the above ranges, the phase stability and processability of the negative electrode active material layer slurry can be ensured, and the solid content of the slurry (e.g., about 40 wt% to about 55 wt%) can be adjusted to improve adhesion. Furthermore, when the weight-average molecular weight (Mw) of the binder is within the above range, the degree of surface contact between the active material and the binder increases, thereby ensuring the desired or improved adhesion and phase stability.

[0035] In one or more example embodiments, the adhesive may have a glass transition temperature (Tg) in the range of about 70°C to about 140°C, about 80°C to about 140°C, or about 85°C to about 140°C. When the glass transition temperature (Tg) of the adhesive is included in the above range, desired or improved cycle life characteristics can be achieved.

[0036] The negative electrode active material layer slurry including a binder, according to one or more example embodiments, can have a suitable or desired viscosity in the range of about 1400 cps (centipoise) to about 3000 cps at room temperature (about 20°C to about 25°C).

[0037] The binder for the negative electrode according to one or more example embodiments can be synthesized by polymerizing a first monomer represented by chemical formula 2 and a second monomer represented by chemical formula 3.

[0038] Chemical formula 2:

[0039] In chemical formula 2, R 1 and R 2 Same or different, and is hydrogen or substituted or unsubstituted alkyl, R 3 It is or includes substituted or unsubstituted alkyl groups, and m is an integer in the range of about 1 to about 100.

[0040] Chemical formula 3:

[0041] In chemical formula 3, p is an integer in the range of about 1 to about 100.

[0042] Polymerization can be carried out by mixing the first monomer of Formula 2 and the second monomer of Formula 3. During the mixing process, the NH2 group in Formula 3 attacks the oxygen in the first monomer of Formula 2 to initiate a ring-opening reaction, thereby causing the polymerization reaction.

[0043] The mixing ratio of the first monomer of Formula 2 to the second monomer of Formula 3 can be a molar ratio in the range of about 1:10 to about 1:100, about 1:20 to about 1:100, about 1:40 to about 1:100, about 1:60 to about 1:100, or about 1:80 to about 1:100. When the mixing ratio of the first monomer of Formula 2 to the second monomer of Formula 3 meets the above ranges, there are advantages such as ensuring solubility as an aqueous negative electrode binder and being able to control the glass transition temperature, which ensures the physical properties of the electrode.

[0044] In one or more embodiments, the first monomer of Formula 2 can be synthesized by a conventional process. For example, the first monomer can be synthesized by polymerizing isobutylene and maleic anhydride in a solvent. The solvent can be dimethylaldehyde, but is not limited thereto. Furthermore, the polymerization can be carried out at about 60°C for about 12 hours, but is not limited thereto, as it is well known that polymerization can be carried out at temperatures and times sufficient for polymerization to occur.

[0045] Negative electrode for rechargeable lithium batteries: The negative electrode according to one or more example embodiments includes a negative electrode active material layer, which includes an adhesive and a negative electrode active material. The adhesive may be or include the adhesive according to one or more example embodiments.

[0046] In one or more example embodiments, the amount of binder may range from about 1 wt% to about 5 wt% or from about 1 wt% to about 3 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 can provide the desired or improved resilience against volume expansion of the negative electrode active materials.

[0047] 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 high capacity, but there are challenges of severe volume expansion and contraction during charging and discharging, and 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 reduced or eliminated. Accordingly, the negative electrode according to one or more exemplary embodiments can satisfy both the high capacity due to the use of the Si-based negative electrode active material and the desired or improved cycle life characteristics due to the binder according to one or more exemplary embodiments.

[0048] 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.

[0049] The Si-based negative electrode active material may be or include a silicon-carbon composite.

[0050] 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. The amorphous carbon may also be located between the silicon primary particles, for example, to coat the silicon primary particles. The secondary particles may be distributed in an amorphous carbon matrix.

[0051] In addition, the silicon-carbon composite may include silicon particles and an amorphous carbon coating layer on the surface of the silicon particles.

[0052] The secondary particles are located at the center of the Si-C composite, so the secondary particles may be referred to as the core or the central part. The amorphous carbon coating layer may be referred to as the exterior or the shell.

[0053] The silicon particles may be or include nanosilicon particles. The nanosilicon 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 may be in the range of about 20 nm to about 900 nm, about 20 nm to about 800 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 within the above range, the large volume expansion that usually occurs during charging and discharging can be reduced or suppressed, and the breakage of the conduction path due to the fragmentation of the particles during charging and discharging can be reduced or prevented.

[0054] The mixing ratio of nano-silicon to amorphous carbon can be in the range of about 20:80 to about 70:30 by weight.

[0055] In one or more example embodiments, the silicon-carbon composite may further comprise crystalline carbon. In some example embodiments, the silicon-carbon composite may comprise a core comprising crystalline carbon and silicon particles and an amorphous carbon coating layer located on the surface of the core.

[0056] When the silicon-carbon composite comprises silicon particles, crystalline carbon, and amorphous carbon, the amount of amorphous carbon, based on 100 wt% of the total silicon-carbon composite, can range from about 10 wt% to about 70 wt%, and the amount of crystalline carbon, based on 100 wt% of the total silicon-carbon composite, can range from about 10 wt% to about 70 wt%. The amount of silicon particles, based on 100 wt% of the total silicon-carbon composite, can range from about 20 wt% to about 69 wt%, and, according to one or more example embodiments, can range from about 30 wt% to about 60 wt%.

[0057] The particle size of silicon-carbon composites can be adjusted as needed, and is not limited to this.

[0058] When amorphous carbon surrounds the surface of secondary particles, the thickness of the amorphous carbon can be adjusted as needed, but it can exist, for example, in the range of about 5 nm to about 100 nm.

[0059] The negative electrode active material layer according to one or more example embodiments may also include an aqueous binder.

[0060] Waterborne adhesives may include at least one of the following: 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, and combinations thereof.

[0061] Aqueous binders may be or include cellulose compounds, or may be or include cellulose compounds together with the aforementioned aqueous binders. Since cellulose compounds can impart viscosity, they may be referred to as thickeners, or they may be configured as binders and therefore referred to as binders. Cellulose compounds may be included in suitable or desired amounts within the quantity of the aqueous binder, and are not limited thereto. Cellulose compounds include one or more of carboxymethyl cellulose, hydroxypropyl methylcellulose, methylcellulose, and their alkali metal salts. Alkali metals may be or include at least one of Na, K, and Li.

[0062] When the negative electrode active material layer further includes an aqueous binder, the mixing ratio of the binder to the aqueous binder according to one or more example embodiments may be a weight ratio in the range of about 1:1.6 to about 1:2.75, a weight ratio in the range of about 1:1.8 to about 1:2.5, a weight ratio in the range of about 1:1.88 to about 1:2.5, or a weight ratio in the range of about 1:2 to about 1:2.5.

[0063] Even when the negative electrode active material layer includes both an adhesive and an aqueous adhesive according to one or more example embodiments, the total amount of adhesive may be in the range of about 1 wt% to about 5 wt% based on the total weight of the negative electrode active material layer.

[0064] In one or more example embodiments, the negative electrode active material layer may also include a conductive material.

[0065] 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 other example embodiments, the negative electrode active material layer may comprise a negative electrode active material ranging from about 91.5 wt% to about 98.5 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 an aqueous binder and the binder according to one or more example embodiments.

[0066] The conductive material is included to provide electrode conductivity, and may include any electrically conductive material as the conductive material unless the electrically conductive material causes a chemical change in the battery. Examples of conductive materials may be 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 such as metal powders or metal fibers, including at least one of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0067] 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.

[0068] Rechargeable lithium batteries: Other example embodiments include rechargeable lithium batteries comprising a negative electrode, a positive electrode, and a non-aqueous electrolyte.

[0069] In rechargeable lithium batteries, the negative electrode can be observed at approximately 1605 cm⁻¹ when measured by FT-IR. -1Approximately 1713cm -1 The peak appears at wavelengths within the range of [specific wavelength range]. In one embodiment, when measured by FT-IR, the negative electrode can be displayed at approximately 1605 cm⁻¹. -1 Approximately 1713cm -1 Two peaks, one related to carbonyl groups and the other to amide groups, appear at wavelengths within the range of [specific wavelength range]. The presence of these peaks in the FT-IR measurements indicates that the binder according to one or more example embodiments (e.g., a binder in which the first monomer of Formula 2 and the second monomer of Formula 3 are polymerized) may be included in the negative electrode. No peak appears at this wavelength when the first monomer of Formula 2 and the second monomer of Formula 3 are not polymerized and exist as a mixture (e.g., they exist individually) in the negative electrode. No peak is displayed at approximately 1605 cm⁻¹ when the first monomer of Formula 2 and the second monomer of Formula 3 are present in the negative electrode as a mixture. -1 Approximately 1713cm -1 The peak appears at wavelengths within the range of .

[0070] 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 further include a binder and / or a conductive material.

[0071] For example, the positive electrode may further include additives that can be configured as a sacrificial positive electrode.

[0072] 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 99wt%, 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.

[0073] The positive electrode active material may include compounds capable of reversibly inserting and deintercalating lithium (lithium-intercalating 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.

[0074] 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.

[0075] 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).

[0076] In the above chemical formulas, 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.

[0077] 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 a lithium transition metal complex oxide, wherein the nickel content of the high-nickel positive electrode active material is 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.

[0078] The binder improves 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 include, 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.

[0079] The conductive material is included to provide electrode conductivity, and any suitable electrically conductive material may be included as the conductive material unless the electrically conductive material causes an adverse chemical change in the battery. Examples of conductive materials may 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 such as metal powders or metal fibers, including at least one of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0080] The current collector may include, but is not limited to, Al.

[0081] Electrolyte: Electrolytes used in rechargeable lithium batteries include non-aqueous organic solvents and lithium salts.

[0082] Non-aqueous organic solvents are constructed as media for transporting ions that participate in the electrochemical reactions of the battery.

[0083] 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.

[0084] 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 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.

[0085] Organic solvents may be included alone or as a mixture of two or more solvents.

[0086] When carbonate solvents are included, cyclic carbonates and linear carbonates may be included together, and cyclic carbonates and linear carbonates may be mixed in a volume ratio ranging from about 1:1 to about 1:9.

[0087] The electrolyte may also include at least one of ethylene ethyl carbonate, vinylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, fluoroethylene carbonate, and combinations thereof as additives.

[0088] Lithium salts dissolved in organic solvents are configured to supply lithium ions to the battery to enable the operation of rechargeable lithium batteries and to improve lithium ion transport between the positive and negative electrodes. Examples of lithium salts include or contain 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 F2x+1 SO2)(C y F 2y+1 The supporting electrolyte salts are: (SO2) (where x and y are integers in the range of about 1 to about 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFOP), and lithium bis(oxalate)borate (LiBOB).

[0089] Diaphragm: Depending on the type (or variety) of rechargeable lithium-ion battery, the separator may be located 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 a mixture of multiple layers, such as a polyethylene / polypropylene bilayer separator, a polyethylene / polypropylene / polypropylene trilayer separator, a polypropylene / polypropylene / polypropylene trilayer separator, etc.

[0090] The membrane may include a porous substrate and a coating layer on one or both surfaces of the porous substrate (e.g., one or two opposing surfaces) comprising an organic material, an inorganic material, or a combination thereof.

[0091] The porous substrate may be or include a membrane formed of or containing any one polymer or a copolymer or mixture thereof, such polymer as or including at least one of polyolefins (such as polyethylene, polypropylene, etc.), polyesters (such as polyethylene terephthalate, polybutylene terephthalate, etc.), 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).

[0092] Organic materials may include polymers such as polyvinylidene fluoride or (meth)acrylic acid polymers.

[0093] 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.

[0094] 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.

[0095] Rechargeable lithium batteries can be classified according to their shape, such as cylindrical batteries, prismatic batteries, pouch batteries, or coin-shaped batteries. 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. 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 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 4 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, 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 battery 100. Alternatively, the rechargeable lithium battery 100 may include a positive electrode terminal 71 and a negative electrode terminal 72, as shown. Figure 3 As shown in the image.

[0096] As a non-limiting example, the rechargeable lithium battery according to the example embodiment can be used in, for example, automobiles, mobile phones and / or various suitable types (or kinds) of electronic devices.

[0097] 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.

[0098] Example 1: The first monomer of chemical formula 2a and the second monomer of chemical formula 3 were mixed in a molar ratio of 1:10 to prepare a polymer binder of chemical formula 1a (weight average molecular weight: 120 kDalton, glass transition temperature: 134 °C).

[0099] Chemical formula 2a:

[0100] Where n equals 50; Chemical formula 3:

[0101] Where p equals 10; Chemical formula 1a:

[0102] Where n1 equals 50 and n2 equals 10.

[0103] A slurry of negative electrode active material (solid content: 48wt%, viscosity (at 25°C): 1500cps) was prepared by mixing 94wt% silicon-carbon composite negative electrode active material, 3wt% binder, and 3wt% carbon black conductive material in an aqueous solvent.

[0104] The negative electrode is prepared by coating a slurry of the active material layer of the negative electrode onto a copper current collector and drying it, followed by pressure application.

[0105] 96wt% LiNi 0.8 Co 0.1 Mn 0.1 O2 positive electrode active material, 2 wt% Ketjen black, and 2 wt% polyvinylidene fluoride were mixed in N-methylpyrrolidone solvent to prepare a positive electrode active material layer slurry. The positive electrode active material layer slurry was coated onto an Al foil current collector and dried, and then pressurized to prepare the positive electrode.

[0106] 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).

[0107] Example 2: The polymer binder (weight average molecular weight: 150 kDaltons, glass transition temperature: 128 °C) in which n1 equals 80 and n2 equals 10 in formula 1a is prepared by the same steps as in Example 1, except that the first monomer of formula 2a and the second monomer of formula 3 are mixed in a molar ratio of 1:40.

[0108] Using this binder, a negative electrode active material layer slurry (solid content: 48 wt%, viscosity (at 25°C): 1480 cps) and a full cell are manufactured by following the same steps as in Example 1.

[0109] Example 3: The polymer binder (weight average molecular weight: 200 kDaltons, glass transition temperature: 110 °C) in which n1 equals 160 and n2 equals 10 in formula 1a is prepared by the same steps as in Example 1, except that the first monomer of formula 2a and the second monomer of formula 3 are mixed in a molar ratio of 1:80.

[0110] Using this binder, a negative electrode active material layer slurry (solid content: 48wt%, viscosity (at 25°C): 1450cps) and a full cell are manufactured by following the same steps as in Example 1.

[0111] Example 4: The polymer binder (weight-average molecular weight: 220 kDaltons, glass transition temperature: 88°C) in which n1 equals 180 and n2 equals 10 in formula 1a is prepared by the same steps as in Example 1, except that the first monomer of formula 2a and the second monomer of formula 3 are mixed in a molar ratio of 1:100.

[0112] Using this binder, a negative electrode active material layer slurry (solid content: 48wt%, viscosity (at 25°C): 1530cps) and a full cell are manufactured by following the same steps as in Example 1.

[0113] Comparison Example 1: The polymer binder (weight-average molecular weight: 160 kDaltons, glass transition temperature: 150 °C) in which n1 equals 150 and n2 equals 0 in Formula 1a is prepared by the same steps as in Example 1, except that the first monomer of Formula 2a and the second monomer of Formula 3 are mixed in a molar ratio of 1:0.

[0114] Using this binder, a negative electrode active material layer slurry (solid content: 48wt%, viscosity (at 25°C): 1500cps) and a full cell are manufactured by following the same steps as in Example 1.

[0115] Experimental Example 1) Evaluating Adhesion The adhesion of the negative electrode according to Examples 1 to 4 and Comparative Example 1 was measured using the following techniques.

[0116] Adhesive tape was attached to a glass slide and then to the negative electrode active material layer. The tape was then peeled off the negative electrode active material layer using a 180° UTM tensile strength tester to measure adhesion. The peeling speed was set to 10 mm / min, and three measurements were performed to obtain the average force required to peel 40 mm after the start of peeling. The results are shown in Table 1 below.

[0117] Experimental Example 2) Evaluating the separation rate of the negative electrode during full charging. The batteries according to Examples 1 to 4 and Comparative Example 1 were fully charged at 0.7C, and then the negative electrode was separated. The separation rate of the negative electrode was measured by calculating the area of ​​the fully charged electrode active material relative to the area of ​​the initial negative electrode. The results are shown in Table 1 below.

[0118] Experiment Example 3) Evaluating DC Internal Resistance (DC-IR: DC Internal Resistance) The full cells according to Examples 1 to 4 and Comparative Example 1 were charged and discharged at 0.2C at 25°C in one cycle. The voltage drop (V) was measured while the current flowed at 1C for 1 second at SOC50 (based on 100% of the total battery charge capacity, charged to 50% of the charge capacity, and then discharged at 50% in the discharge state). Based on the voltage drop measurement results, the DC internal resistance (DC-IR) was calculated. The results are shown in Table 1 below.

[0119] Experimental Example 4) Evaluating Capacity Retention The full cells from Examples 1 to 4 and Comparative Example 1 were charged and discharged 100 times at 0.3C. The ratio of the capacity at the 100th discharge cycle to the capacity at the 1st discharge cycle was measured. The results, as capacity retention, are shown in Table 1 below.

[0120] Table 1:

[0121] As shown in Table 1 above, the batteries using the binders of Examples 1 to 4 exhibited the desired or improved negative electrode adhesion, and even when fully charged, the separation rate of the negative electrode was quite low, or there was no separation. Furthermore, the batteries of Examples 1 to 4 exhibited low resistance and high capacity retention.

[0122] However, the battery in Comparative Example 1 exhibits low negative electrode adhesion, high negative electrode separation rate, high resistance, and low capacity retention.

[0123] Example 5: The polymer binder (weight-average molecular weight: 300 kDaltons, glass transition temperature: 100 °C) in which n1 equals 50 and n2 equals 8 in chemical formula 1a is prepared by the same steps as in Example 1, except that a second monomer of chemical formula 3 in which p equals 8 is used.

[0124] Using this binder, a negative electrode active material layer slurry (solid content: 48.3 wt%, viscosity (at 25°C): 2432 cps) and a full cell were manufactured by following the same steps as in Example 1.

[0125] Example 6: The polymer binder (weight-average molecular weight: 340 kDaltons, glass transition temperature: 120 °C) in which n1 equals 50 and n2 equals 12 in chemical formula 1a is prepared by the same steps as in Example 1, except that a second monomer of chemical formula 3 in which p equals 12 is used.

[0126] Using this binder, a negative electrode active material layer slurry (solid content: 48.1 wt%, viscosity (at 25°C): 2579 cps) and a full cell were manufactured by following the same steps as in Example 1.

[0127] Example 7: The polymer binder (weight-average molecular weight: 330 kDaltons, glass transition temperature: 110 °C) in which n1 equals 50 and n2 equals 20 in chemical formula 1a is prepared by the same steps as in Example 1, except that a second monomer of chemical formula 3 in which p equals 20 is used.

[0128] Using this binder, a negative electrode active material layer slurry (solid content: 48.3 wt%, viscosity (at 25°C): 2531 cps) and a full cell were manufactured by following the same steps as in Example 1.

[0129] Compare with Example 2: The polymer binder (weight-average molecular weight: 600 kDaltons, glass transition temperature: 150 °C) in which n1 equals 125 and n2 equals 10 in Formula 10 is prepared by the same steps as in Example 1, except that the first monomer of Formula 2a is used instead of the first monomer of Formula 5 (where R is methyl and n is 125).

[0130] Chemical formula 5:

[0131] Chemical Formula 10:

[0132] Using this binder, a negative electrode active material layer slurry (solid content: 48.3 wt%, viscosity (at 25°C): 2432 cps) and a full cell were manufactured by following the same steps as in Example 1.

[0133] Experimental Example 6) Viscosity Change Rate The negative electrode active material layer slurries of Examples 5 to 7 and Comparative Example 2 were left to stand at room temperature (25°C) for one day, and then the viscosity change rate was measured. The results are shown in Table 2 below.

[0134] After standing for 1 day, phase separation was observed. The results are shown in Table 2 below.

[0135] Table 2

[0136] As shown in Table 2, the adhesives of Examples 5 to 7 showed almost no viscosity change rate and no phase separation, while the adhesive of Comparative Example 2 showed a large viscosity change rate and phase separation.

[0137] While this disclosure has been described in conjunction with what are now considered to be exemplary embodiments, 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. A binder for the negative electrode of a rechargeable lithium battery, said binder being represented by chemical formula 1: Chemical Formula 1: ； in, R 1 and R 2 Same or different, and is hydrogen or substituted or unsubstituted alkyl, R 3 Including substituted or unsubstituted alkyl groups, n1 is an integer in the range of 50 to 180. n2 is an integer in the range of 5 to 20.

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

3. The binder for the negative electrode of a rechargeable lithium battery according to claim 2, wherein, The alkyl group includes C1 to C15 alkyl groups.

4. The binder for the negative electrode of a rechargeable lithium battery according to claim 1, wherein, R 3 Includes substituted or unsubstituted C1 to C5 alkyl groups.

5. The binder for the negative electrode of a rechargeable lithium battery according to claim 1, wherein, The adhesive has a weight-average molecular weight in the range of 100,000 Daltons to 1,000,000 Daltons.

6. The binder for the negative electrode of a rechargeable lithium battery according to claim 1, wherein, The adhesive has a glass transition temperature in the range of 70°C to 140°C.

7. A negative electrode for a rechargeable lithium battery, the negative electrode comprising: The negative electrode active material layer comprises the binder and the negative electrode active material according to any one of claims 1 to 6.

8. The negative electrode for a rechargeable lithium battery according to claim 7, 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.

9. The negative electrode for a rechargeable lithium battery according to claim 7, wherein, The negative electrode active material includes Si-based negative electrode active materials.

10. The negative electrode for a rechargeable lithium battery according to claim 9, wherein, The active material of the Si-type negative electrode includes a silicon-carbon composite.

11. The negative electrode for a rechargeable lithium battery according to claim 7, wherein, The negative electrode active material layer also includes an aqueous binder.

12. The negative electrode for a rechargeable lithium battery according to claim 11, wherein, The mixing weight ratio of the adhesive and the water-based adhesive is in the range of 1:1.6 to 1:2.

75.

13. A rechargeable lithium battery, said rechargeable lithium battery comprising: The negative electrode comprises the binder and the negative electrode active material according to any one of claims 1 to 6; Positive electrode; as well as Non-aqueous electrolyte.

14. The rechargeable lithium battery according to claim 13, wherein, When measured by FT-IR, the negative electrode has a value of 1605 cm⁻¹. -1 Up to 1713cm -1 Peaks related to carbonyl groups and amide groups appear at wavelengths within the range.

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