Composition for coating anode active material, anode active material comprising same, anode composition, anode, and lithium secondary battery

Abstract

The present invention relates to a composition for coating a negative electrode active material, and a negative electrode, a lithium secondary battery, a battery module and a battery pack comprising the same, the composition comprising a polymer having a bonding group-HN-C = O-, in which the polymer having a bonding group-HN-C = O-has a glass transition temperature (Tg) of-30 DEG C to 80 DEG C.

Description

Technical Field

[0001] This specification claims the priority and benefits of Korean Patent Applications Nos. 10-2023-0116103 and 10-2024-0116316, filed with the Korean Intellectual Property Office on September 1, 2023 and August 29, 2024, respectively, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a composition for coating a negative electrode active material, a negative electrode active material containing the same, a negative electrode composition, a negative electrode, and a secondary battery. Background Art

[0003] Recently, with the rapid spread of electronic devices using batteries (such as mobile phones, notebook-sized computers, and electric vehicles), the demand for small and lightweight secondary batteries with a relatively high capacity is increasing rapidly. In particular, lithium secondary batteries are lightweight and have a high energy density, and thus have attracted attention as a driving power source for mobile devices. Therefore, research and development efforts have been actively made to improve the performance of lithium secondary batteries.

[0004] Generally, a lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte, an organic solvent, etc. In addition, for the positive electrode and the negative electrode, an active material layer containing a positive electrode active material and a negative electrode active material, respectively, may be formed on a current collector. Generally, lithium-containing metal oxides such as LiCoO2 and LiMn2O4 have been used as positive electrode active materials for positive electrodes, and lithium-free carbon-based active materials and silicon-based active materials have been used as negative electrode active materials for negative electrodes.

[0005] Among the negative electrode active materials, silicon-based active materials have attracted attention because they have a high capacity and excellent high-speed charging characteristics compared to carbon-based active materials. However, the disadvantage of the silicon-based active materials is that the initial efficiency is low because the degree of volume expansion / contraction caused by charge / discharge is large and the irreversible capacity is large.

[0006] On the other hand, among the silicon-based active materials, compared with other silicon-based active materials (such as silicon (Si)), silicon-based oxides, specifically silicon-based oxides represented by SiO x (0 < x < 2) have the advantage of a low degree of volume expansion / contraction caused by charge / discharge. However, the silicon-based oxides still have the disadvantage that the initial efficiency is reduced depending on the presence of an irreversible capacity.

[0007] In this regard, research has been continuously conducted to reduce the irreversible capacity and improve the initial efficiency by doping or embedding metals such as Li, Al, and Mg into silicon-based oxides. However, in the case of negative electrode slurries containing metal-doped silicon-based oxides as negative electrode active materials, there is a problem that the metal oxide formed by the doped metal reacts with moisture, causing the pH of the negative electrode slurry to increase and the viscosity of the negative electrode slurry to change. As a result, there is a problem that the state of the prepared negative electrode deteriorates and the charge and discharge efficiency of the negative electrode is reduced.

[0008] Therefore, there is a need to develop a negative electrode active material that can improve the phase stability of a negative electrode slurry containing a silicon-based oxide and improve the charge and discharge efficiency of a negative electrode prepared therefrom. Summary of the Invention

[0009] Technical issues

[0010] The present invention relates to a composition for coating a negative electrode active material capable of improving the performance of a lithium secondary battery, a negative electrode active material containing the composition, a negative electrode composition, a negative electrode and a secondary battery.

[0011] Technical Solution

[0012] An exemplary embodiment of the present invention provides a negative electrode active material coating composition including a polymer having a -HN-C=O- bonding group, wherein the polymer having a -HN-C=O- bonding group has a glass transition temperature (Tg) of -30°C to 80°C.

[0013] According to an exemplary embodiment of the present invention, the polymer having a -HN-C=O- bonding group is a polymer of alcohol and isocyanate, and a molar ratio of -NCO groups of the isocyanate to -OH groups of the alcohol is 0.5 to 4.

[0014] An exemplary embodiment of the present invention provides a negative electrode active material including: silicon-based particles; and a coating layer provided on at least a portion of a surface of the silicon-based particles and including the negative electrode active material coating composition according to the exemplary embodiment.

[0015] An exemplary embodiment of the present invention provides a negative electrode composition including the negative electrode active material according to the exemplary embodiment, a binder, and a conductive material.

[0016] An exemplary embodiment of the present invention provides a negative electrode including a negative electrode current collector and the negative electrode composition according to the exemplary embodiment on at least one surface of the negative electrode current collector.

[0017] An exemplary embodiment of the present invention provides a lithium secondary battery including the negative electrode according to the exemplary embodiment, a separator, and a positive electrode.

[0018] An exemplary embodiment of the present invention provides a battery module including the lithium secondary battery according to the exemplary embodiment.

[0019] An exemplary embodiment of the present invention provides a battery pack including the lithium secondary battery according to the exemplary embodiment.

[0020] An exemplary embodiment of the present invention provides a battery pack including the battery module according to the exemplary embodiment.

[0021] Beneficial effects

[0022] According to an exemplary embodiment of the present invention, a coating is formed on at least a portion of the surface of a silicon-based active material using a negative electrode active material coating composition containing a polymer having a -HN-C=O- bonding group, thereby improving the severe volume change and particle breakage of the silicon-based active material during charge and discharge. Specifically, electrodes containing silicon-based active materials have inferior properties compared to graphite-based active materials due to volume change and particle breakage during charge and discharge. However, coating the silicon-based active material with a polymer having a -HN-C=O- bonding group can improve these inferior properties. The polymer having a -HN-C=O- bonding group has impact resistance and excellent shape recovery, wherein even when deformed by the application of force, the polymer attempts to return to its original shape.

[0023] Therefore, a negative electrode active material including the negative electrode active material coating composition according to an exemplary embodiment of the present invention, a negative electrode including the negative electrode active material, and a secondary battery including the negative electrode have the effect of improving the discharge capacity, initial efficiency, resistance performance, or service life characteristics of the battery. DETAILED DESCRIPTION

[0024] Hereinafter, the present invention will be described in more detail to facilitate understanding of the present invention. The present invention can be implemented in a variety of different forms and is not limited to the exemplary embodiments described herein. In this context, the terms or words used in the specification and claims should not be interpreted as being limited to typical or dictionary meanings, but should be interpreted as meanings and concepts consistent with the technical gist of the present invention, based on the principle that the inventor can appropriately define the concept of the term to best describe his / her own invention.

[0025] In the present invention, the terms "comprise", "include" or "have" are intended to indicate the existence of the implemented characteristics, numbers, steps, constituent elements or any combination thereof, and should be understood as meaning not excluding the possibility of the existence or addition of one or more other characteristics or numbers, steps, constituent elements or any combination thereof.

[0026] Furthermore, the phrase "above" or "over" a portion, such as a layer, includes not only the phrase "directly above" another portion but also the phrase "directly above" another portion. Conversely, the phrase "directly above" another portion means that there is no portion between them. Furthermore, the phrase "above" or "over" a reference portion means being located above or below the referenced portion, and does not necessarily mean being "above" or "over" in the opposite direction of gravity.

[0027] The terms or words used in the specification should not be construed as being limited to typical or dictionary meanings, but should be construed as meanings and concepts that are consistent with the technical gist of the present invention based on the principle that the inventor can appropriately define the concepts of the terms to describe his / her own invention in the best manner.

[0028] Singular expressions of the terms used in this specification include plural expressions unless they have clearly contrary meanings in the context.

[0029] Hereinafter, preferred exemplary embodiments of the present invention will be described in detail. However, the exemplary embodiments of the present invention may be modified into various other forms, and the scope of the present invention is not limited to the exemplary embodiments to be described below.

[0030] <Negative Electrode Active Material Coating Composition>

[0031] The negative active material coating composition according to an exemplary embodiment of the present invention includes a polymer having a -HN-C=O- bonding group, and the polymer having a -HN-C=O- bonding group has a glass transition temperature (Tg) of -30°C to 80°C.

[0032] Compared to graphite-based active materials, electrodes containing silicon-based active materials used in the prior art have inferior performance due to severe volume changes and particle fragmentation during charge and discharge.

[0033] However, according to exemplary embodiments, the polymer having -HN-C=O- bonding groups exhibits impact resistance and shape recovery, wherein even when deformed by applied force, the polymer returns to its original shape. Thus, the poor characteristics can be improved by including the polymer having -HN-C=O- bonding groups as a coating for the negative electrode active material. This can minimize the breakage of the negative electrode active material and maintain the connectivity of the conductive material, thereby achieving the characteristics of a long-life battery.

[0034] The glass transition temperature of a polymer refers to the temperature at which the Brownian motion of the polymer chain becomes active. Since the glass transition temperature means that a non-crystalline polymer receives and absorbs a certain amount of temperature energy and transfers it to the chain motion of the polymer, the glass transition temperature can be regarded as an indicator of the impact absorption strength and resilience of the molecule.

[0035] The glass transition temperature of the negative electrode active material coating composition was measured by differential scanning calorimetry (DSC). After placing the negative electrode active material coating composition in a differential scanning calorimeter pan, the composition was heated from -100°C to 200°C at a rate of 5°C / min to determine the temperature interval in which the heat flow changes, which is referred to as the glass transition temperature.

[0036] For example, the polymer having a -HN-C=O- bonding group has a glass transition temperature of -30°C to 80°C. Specifically, the glass transition temperature may be -30°C to 70°C, -30°C to 60°C, -30°C to 50°C, -20°C to 40°C, -20°C to 30°C, or -20°C to 20°C. When the glass transition temperature is lower than -30°C, there is a problem in that the polymer having a -HN-C=O- bonding group may dissolve in the slurry without being coated on the surface of the active material. When the glass transition temperature exceeds 80°C, there is a problem in that the recovery of the coating layer during charge and discharge may be reduced due to its high rigidity.

[0037] According to an exemplary embodiment, the polymer having a -HN-C=O- bonding group is a polymer of an alcohol and an isocyanate, and a molar ratio of -NCO groups of the isocyanate to -OH groups of the alcohol is 0.5 to 4.

[0038] When the molar ratio of the -NCO groups of the isocyanate to the -OH groups of the alcohol is 0.5 or greater, the problem of the polymer having the -HN-C=O- bonding group dissolving in the slurry and not being coated on the surface of the active material can be minimized. When the molar ratio of the -NCO groups of the isocyanate to the -OH groups of the alcohol is 4 or less, the hardness of the coating is controlled, thereby appropriately providing a shape recovery effect against the volume change of the active material during charge and discharge. Therefore, by conducting the reaction so that the molar ratio of the -NCO groups of the isocyanate to the -OH groups of the alcohol is 0.5 to 4, the volume change and particle breakage of the negative electrode active material during charge and discharge can be suppressed, thereby effectively improving the service life characteristics of the battery.

[0039] For example, the molar ratio of -NCO groups of the isocyanate to -OH groups of the alcohol may be 0.5 to 4, 0.5 to 3.5, 0.5 to 3, 1 to 3, or 1.2 to 2.6.

[0040] According to one exemplary embodiment, the polymer having a -HN-C=O- bonding group includes a urethane-based polymer.

[0041] According to an exemplary embodiment, the polymer having a -HN-C=O- bonding group has a weight average molecular weight of 5,000 g / mol to 1,000,000 g / mol.

[0042] The weight average molecular weight is a value measured by gel permeation chromatography (GPC) and converted from a standard polystyrene calibration curve.

[0043] According to an exemplary embodiment, the negative electrode active material coating composition may further include a solvent or a catalyst component.

[0044] According to an exemplary embodiment, the solvent may be N-methylpyrrolidone (NMP), dimethylformamide (DMF), toluene, or dimethyl sulfoxide (DMSO).

[0045] According to one exemplary embodiment, the catalyst may be an organometallic catalyst.

[0046] According to one exemplary embodiment, the catalyst may be dibutyltin dilaurate (DBTDL).

[0047] <Negative Electrode Active Material>

[0048] According to an exemplary embodiment of the present invention, a negative electrode active material includes: silicon-based particles; and a coating layer provided on at least a portion of a surface of the silicon-based particles and including the negative electrode active material coating composition.

[0049] In an exemplary embodiment of the present specification, the negative electrode active material is a negative electrode active material in which the amount of the coating layer is greater than or equal to 0.1% by weight and less than or equal to 5% by weight based on 100% by weight of the total negative electrode active material. For example, the amount of the coating layer may be greater than or equal to 0.1% by weight and less than or equal to 4% by weight, greater than or equal to 0.1% by weight and less than or equal to 3% by weight, greater than or equal to 0.2% by weight and less than or equal to 3% by weight, or greater than or equal to 0.3% by weight and less than or equal to 3% by weight based on 100% by weight of the total negative electrode active material. When the amount of the coating layer exceeds 5% by weight, the capacity is reduced due to the increase in the weight of the coating layer relative to the total weight of the active material, and the charge and discharge of lithium is not conducive due to the polyurethane characteristics with low lithium ion conductivity. When the amount of the coating layer is less than 0.1% by weight, the recovery due to the volume change of the active material is small, so that there is a risk that the coating layer will detach during slurry mixing.

[0050] In an exemplary embodiment of the present specification, the coating layer has a thickness of 1 nm to 1 μm.

[0051] The thickness of the surface coating can be measured by X-ray photoelectron spectroscopy (XPS) depth profile.

[0052] The thickness of the surface coating layer may be determined based on whether nitrogen (N) disappears while etching the surface of the negative active material including the coating layer to be detected.

[0053] For example, the coating layer has a thickness of 1 nm to 1 μm. Specifically, the coating layer may have a thickness of 1 nm to 800 nm, 5 nm to 500 nm, 5 nm to 300 nm, 5 nm to 100 nm, or 5 nm to 50 nm. When the coating layer is thicker than 1 μm, the surface resistance is too high to charge and discharge lithium, resulting in low capacity. When the coating layer is thinner than 1 nm, the negative electrode active material has a weak recovery due to volume changes during charge and discharge, and there is a risk of the coating layer detaching during slurry mixing.

[0054] According to an exemplary embodiment of the present invention, the silicon-based particles are silicon-carbon composite particles or silicon oxide particles.

[0055] According to an exemplary embodiment, the silicon-based particles may include a silicon-carbon composite, silicon oxide, or both.

[0056] According to an exemplary embodiment, the silicon-carbon composite may be a Si / C-based active material.

[0057] In this specification, the silicon carbon composite is a composite of Si and C and is distinguished from the silicon carbide phase denoted as SiC. Since silicon carbide does not electrochemically react with lithium, all performance parameters (such as service life) can be measured as zero.

[0058] The silicon-carbon composite may include at least one of the following: a silicon-carbon composite formed by depositing silicon on a porous carbon structure; and a silicon-carbon composite in which carbon is composited on a porous silicon structure. The silicon-carbon composite may be a composite in which silicon, graphite, or the like are composited. In the silicon-carbon composite, the silicon may be nanosilicon.

[0059] According to an exemplary embodiment, the silicon-carbon composite includes porous carbon-based particles and a silicon coating layer located on a surface or in internal pores of the porous carbon-based particles.

[0060] According to an exemplary embodiment, the silicon carbon composite may have a thickness of 0.5 m 2 / g to 10 m 2 / g of specific surface area by BET method, 0.005 cm 3 / g to 0.03 cm 3 The silicon-carbon composite may have a pore volume of 0.005 cm 3 / g to 0.03 cm 3 / g of pore volume as measured by mercury penetration.

[0061] According to an exemplary embodiment, the silicon-carbon composite may have a D90 particle size of 11 μm to 20 μm, a D50 particle size of 3 μm to 10 μm, and a D10 particle size of 0.1 μm to 3 μm.

[0062] According to an exemplary embodiment, the silicon-carbon composite may be prepared by a method comprising: etching carbon-based particles containing internal pores to expand the internal pores of the carbon-based particles; and forming a silicon coating on the surface of the carbon-based particles containing the expanded internal pores or in the internal pores.

[0063] The expansion of the internal pores of the carbon-based particles can be performed in a nitrogen (N2) atmosphere, an oxygen (O2) atmosphere, or an air atmosphere. Specifically, the flow rate of the oxygen (O2) or oxygen-containing air can be controlled to be 0.1 to 10 L / min.

[0064] The expansion of the internal pores of the carbon-based particles may be performed at a temperature ranging from 400° C. to 1200° C. for 30 minutes to 4 hours.

[0065] Depending on the conditions for expanding the internal pores of the carbon-based particles, the pore characteristics of the resulting porous carbon-based particles may vary.

[0066] The formation of the silicon coating can be carried out using chemical vapor deposition. In this case, silicon nanoparticles can be deposited on the surface and / or in the internal pores of the carbon-based particles having expanded internal pores, thereby forming a silicon coating in the form of a film, islands or a mixture thereof.

[0067] The silicon nanoparticles can be crystalline, quasi-crystalline, amorphous or a combination thereof.

[0068] According to an exemplary embodiment, the silicon oxide may contain SiO x (0 ≤ x < 2).

[0069] The active material containing SiO x (0 ≤ x < 2) can be silicon oxide particles containing SiO x (0 < x < 2) and pores.

[0070] The SiO x (0 < x < 2) corresponds to the matrix in the silicon oxide particles. The SiO x (0 < x < 2) can be in the form of containing Si and SiO2, and the Si can also form a phase. That is, x corresponds to the number ratio of O to Si contained in SiO x (0 < x < 2). When the silicon oxide particles contain SiO x (0 < x < 2), the discharge capacity of the secondary battery can be improved.

[0071] The silicon oxide particles may further contain at least one of a Mg compound and a Li compound. The Mg compound and the Li compound can correspond to dopants in the silicon oxide particles.

[0072] The Mg compound and / or the Li compound may be present inside and / or on the surface of SiO <^ x (0 < x < 2). The initial efficiency of the battery can be improved by the Mg compound and / or the Li compound.

[0073] The Mg compound may contain at least any one selected from the group consisting of Mg silicate, Mg silicide and Mg oxide. The Mg silicate may contain at least any one of Mg2SiO4 and MgSiO3. The Mg silicide may contain Mg2Si. The Mg oxide may contain MgO.

[0074] In an exemplary embodiment of the present specification, based on a total of 100% by weight of the silicon oxide particles, the content of the Mg element may be 0.1% to 20% by weight or 0.1% to 10% by weight. Specifically, the content of the Mg element may be 0.5% to 8% by weight or 0.8% to 4% by weight. When the above ranges are satisfied, the Mg compound can be included in the silicon oxide particles in an appropriate content, so that the volume change of the silicon oxide particles during battery charge and discharge can be easily suppressed, and the discharge capacity and initial efficiency of the battery can be improved.

[0075] The Li compound may include at least any one selected from the group consisting of Li silicate, Li silicide, and Li oxide. The Li silicate may include at least any one of Li2SiO3, Li4SiO4, and Li2Si2O5. The Li silicide may include Li7Si2. The Li oxide may include Li2O.

[0076] In an exemplary embodiment of the present invention, the Li compound may exist in the form of lithium silicate. The lithium silicate is represented by Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and can be classified into crystalline lithium silicate and amorphous lithium silicate. The crystalline lithium silicate may exist in the silicon oxide particles in the form of at least one lithium silicate selected from the group consisting of Li2SiO3, Li4SiO4, and Li2Si2O5, and the amorphous lithium silicate may exist in the silicon oxide particles in the form of Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and is not limited to this form.

[0077] In an exemplary embodiment of the present specification, based on a total of 100% by weight of the silicon oxide particles, the content of the Li element may be 0.1% to 20% by weight or 0.1% to 10% by weight. Specifically, the content of the Li element may be 0.5% to 8% by weight, and more specifically 0.5% to 4% by weight. When the above ranges are satisfied, the Li compound can be included in the silicon oxide particles in an appropriate content, so that the volume change of the negative electrode active material during battery charge and discharge can be easily suppressed, and the discharge capacity and initial efficiency of the battery can be improved.

[0078] The content of the Mg element or the Li element can be confirmed by ICP analysis. For the ICP analysis, after a predetermined amount (about 0.01 g) of the negative electrode active material is accurately fractionated, the fractionated sample is transferred to a platinum crucible and nitric acid, hydrofluoric acid or sulfuric acid is added thereto so that the negative electrode active material is completely decomposed on a hot plate. Thereafter, a reference calibration curve is prepared by measuring the intensity of a standard liquid prepared using a standard solution (5 mg / kg) at the inherent wavelength of the Mg element or the Li element using an inductively coupled plasma atomic emission spectrometer (ICPAES, Perkin-Elmer 7300). Thereafter, the pretreated sample solution and the blank sample are each introduced into the device, the actual intensity is calculated by measuring the intensity of each, the concentration of each component is calculated relative to the prepared calibration curve, and then the content of the Mg element or the Li element of the prepared silicon oxide particles can be analyzed by converting the sum to a theoretical value.

[0079] In one exemplary embodiment of the present specification, a carbon layer may be provided on the surface and / or in the internal pores of the silicon oxide particles. The carbon layer imparts conductivity to the silicon oxide particles, and can improve the initial efficiency, service life, and battery capacity characteristics of a secondary battery containing the negative electrode active material containing the silicon oxide particles. The total weight of the carbon layer may be 5% to 40% by weight based on 100% by weight of the silicon oxide particles.

[0080] In an exemplary embodiment of the present specification, the carbon layer may include at least any one of amorphous carbon and crystalline carbon.

[0081] The negative electrode active material may have an average particle size (D50) of 0.1 μm to 30 μm, specifically 1 μm to 20 μm, more specifically 1 μm to 10 μm. When the above range is met, the active material is structurally stable during charge and discharge, and the problem of increasing volume expansion / contraction with excessive increase in particle size can be prevented, as well as the problem of reduced initial efficiency due to excessively small particle size can be prevented.

[0082] In this specification, the average particle size (D50) may be defined as the particle size corresponding to 50% of the volume cumulative amount in the particle size distribution curve of the particles. The average particle size (D50) may be measured using, for example, a laser diffraction method. The laser diffraction method is generally capable of measuring particle sizes from the submicron region to about several millimeters, and can obtain results with high reproducibility and high resolution. The silicon-based active material may have a particle size of 2 m 2 / g to 10 m 2 In this specification, the specific surface area is measured by the BET method.

[0083] <Method for preparing negative electrode active material>

[0084] According to an exemplary embodiment of the present invention, the method of preparing a negative electrode active material includes: preparing silicon-based particles; and forming a coating layer on the silicon-based particles.

[0085] [Preparation of Silicon-Based Particles]

[0086] In an exemplary embodiment of the present invention, the silicon-based particles may be silicon-carbon composite particles or silicon oxide particles.

[0087] In an exemplary embodiment of the present invention, the silicon-based particles may be silicon oxide particles formed by heat-treating powder in which Si powder and SiO 2 powder are mixed.

[0088] For example, the silicon oxide particles may be prepared by evaporating a mixed powder of Si powder and SiO 2 powder by heat treatment at 1000° C. to 1800° C. or 1200° C. to 1500° C.

[0089] The silicon oxide particles may further include one or more of Mg and Li elements, and the Mg or Li elements may be distributed on the surface and / or inside of the silicon oxide particles in a state of being doped into the silicon oxide particles.

[0090] The silicon oxide particles may further include a carbon layer.

[0091] In an exemplary embodiment of the present invention, the silicon-based particles may be a silicon-carbon composite prepared by flowing SiH 4 / He gas through a porous carbon structure formed by heat-treating cellulose powder.

[0092] The silicon-carbon composite may further include a carbon layer.

[0093] [Forming a coating on silicon-based particles]

[0094] In an exemplary embodiment of the present invention, the negative electrode active material coating composition coated on the silicon-based particles may include a polymer having a -HN-C=O- bonding group.

[0095] The above description of the polymer having a —HN—C═O— bonding group can be applied to the polymer having a —HN—C═O— bonding group.

[0096] According to an exemplary embodiment of the present invention, the negative electrode active material having the coating layer formed thereon may be prepared by stirring the silicon-based particles and the negative electrode active material coating composition including the polymer having the -HN-C=O- bonding group.

[0097] For example, the negative electrode active material having the coating layer formed thereon may be prepared by stirring the prepared silicon-based particles and the negative electrode active material coating composition including the polymer having the -HN-C=O- bonding group at a speed of 200 rpm to 5000 rpm.

[0098] According to an exemplary embodiment of the present invention, the method may further include a drying step of removing all solvents by leaving the negative electrode active material having the coating layer formed thereon at 20° C. to 100° C. under a vacuum state.

[0099] <Negative Electrode Composition>

[0100] According to an exemplary embodiment of the present invention, a negative electrode composition may include the above-mentioned negative electrode active material particles.

[0101] According to an exemplary embodiment of the present invention, the negative electrode composition may further include a binder.

[0102] According to an exemplary embodiment of the present invention, the negative electrode composition may further include a conductive material.

[0103] According to an exemplary embodiment of the present invention, the negative electrode composition may further include a binder and a conductive material.

[0104] According to an exemplary embodiment of the present invention, the negative electrode composition may include a negative electrode active material, a binder, and a conductive material.

[0105] According to an exemplary embodiment of the present invention, the binder may include carboxymethyl cellulose.

[0106] The adhesive may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid and materials whose hydrogen is replaced by Li, Na, Ca, etc., and may also include various copolymers thereof.

[0107] According to an exemplary embodiment of the present invention, the conductive material may include one or more of carbon black and single-walled carbon nanotubes.

[0108] The above-mentioned conductive material is not particularly limited as long as the conductive material has conductivity and does not cause chemical changes to the battery. For example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black and thermal black; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; fluorocarbon powder; metal powder such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. can be used.

[0109] According to an exemplary embodiment of the present invention, the conductive material may be carbon black, conductive fibers, carbon nanotubes, or metal powder. Specifically, in an exemplary embodiment of the present invention, the conductive material may be graphite, such as natural graphite or artificial graphite; or carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black. In an exemplary embodiment of the present invention, the conductive material may be conductive fibers, such as carbon fibers or metal fibers. In an exemplary embodiment of the present invention, the conductive material may be conductive tubes, such as carbon nanotubes. The conductive material may be fluorocarbon powder, metal powder, such as aluminum powder and nickel powder.

[0110] According to an exemplary embodiment of the present invention, the conductive material may be present in an amount of 0.01 parts by weight or more and 20 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer composition. Specifically, in an exemplary embodiment of the present invention, the conductive material may be present in an amount of 0.01 parts by weight or more and 10 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer composition. In an exemplary embodiment of the present invention, the conductive material may be present in an amount of 0.01 parts by weight or more and 7 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer composition. The conductive material may be present in an amount of 0.1 parts by weight or more and 3 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer composition.

[0111] <Negative electrode>

[0112] An exemplary embodiment of the present invention provides a negative electrode including the negative electrode composition according to the exemplary embodiment.

[0113] Specifically, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector.

[0114] The negative electrode active material layer includes the negative electrode composition according to the above exemplary embodiment.

[0115] The negative electrode active material layer may be formed by applying a negative electrode slurry including the negative electrode composition to at least one surface of a negative electrode current collector, and drying and rolling the negative electrode current collector.

[0116] The negative electrode slurry may include a solvent for forming the negative electrode slurry. Specifically, the solvent may include at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol. In terms of promoting dispersion of components, distilled water is particularly preferred.

[0117] As long as the negative electrode current collector has conductivity and does not cause chemical changes to the battery, the negative electrode current collector is sufficient and is not particularly limited. For example, as the current collector, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, etc. can be used. Specifically, a transition metal such as copper or nickel that adsorbs carbon well can be used as a current collector. Although the current collector can have a thickness of 6 μm to 20 μm, the thickness of the current collector is not limited thereto.

[0118] <Lithium Secondary Battery>

[0119] An exemplary embodiment of the present invention provides a lithium secondary battery including the negative electrode according to the above exemplary embodiment, a separator, and a positive electrode.

[0120] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including a positive electrode active material.

[0121] In the positive electrode, the positive electrode current collector is not particularly limited as long as the positive electrode current collector has conductivity and does not cause chemical changes to the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, etc. can be used. In addition, the positive electrode current collector can generally have a thickness of 3 to 500 μm, and the adhesion of the positive electrode active material can also be enhanced by forming fine concave and convex on the surface of the current collector. For example, the positive electrode current collector can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and non-woven fabrics.

[0122] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material includes: a layered compound such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or a compound substituted by one or more transition metals; a lithium iron oxide such as LiFe3O4; a lithium manganese oxide such as Li 1+c1 Mn 2-c1O4 (0≤c1≤0.33), LiMnO3, LiMn2O3 and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5 and Cu2V2O7; Ni-site lithium nickel oxide, represented by the chemical formula LiNi 1-c2 M c2 O2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and c2 satisfies 0.01≤c2≤0.3); lithium manganese composite oxide, represented by the chemical formula LiMn 2-c3 M c3 O2 (wherein M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and c3 satisfies 0.01≤c3≤0.1) or Li2Mn3MO8 (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4 in which the Li in the chemical formula is partially replaced by an alkaline earth metal ion, etc., but is not limited thereto. The positive electrode may be Li metal.

[0123] In addition to the positive electrode active material, the positive electrode active material layer may further include a positive electrode conductive material and a positive electrode binder.

[0124] In this case, the positive electrode conductive material is used to impart conductivity to the electrode and can be used without particular limitation, as long as the positive electrode conductive material has electronic conductivity and does not cause chemical changes to the battery. Specific examples include graphite, such as natural graphite or artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. Any one of these or a mixture of two or more thereof may be used.

[0125] Alternatively, the positive electrode binder is used to improve the bonding between the positive electrode active materials and the adhesion between the positive electrode active materials and the positive electrode current collector. Specific examples thereof may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber or various copolymers thereof, and any one thereof or a mixture of two or more thereof may be used.

[0126] The diaphragm separates the negative electrode from the positive electrode and provides a channel for the movement of lithium ions, and can be used without particular limitation, as long as the diaphragm is commonly used as a diaphragm in a secondary battery, in particular, a diaphragm having excellent ability to retain electrolyte moisture and low resistance to ion movement in the electrolyte is preferred. Specifically, a porous polymer film can be used, for example, a porous polymer film formed by a polyolefin polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer and an ethylene / methacrylate copolymer, or a laminated structure of more than two layers thereof. In addition, a typical porous non-woven fabric can also be used, for example, a non-woven fabric made of glass fiber with a high melting point, polyethylene terephthalate fiber, etc. In addition, a coated diaphragm comprising a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and can be selectively used as a single layer or multilayer structure.

[0127] The lithium secondary battery may further include an electrolyte. Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used to prepare lithium secondary batteries.

[0128] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0129] As the non-aqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate or ethyl propionate can be used.

[0130] In particular, among the carbonate-based organic solvents, cyclic carbonates ethylene carbonate and propylene carbonate can be preferably used because the cyclic carbonates have a high dielectric constant as high-viscosity organic solvents and thus dissociate lithium salts well; when the cyclic carbonates are mixed in an appropriate proportion with low-viscosity and low-dielectric-constant linear carbonates such as dimethyl carbonate and diethyl carbonate, an electrolyte with high conductivity can be prepared, so such a combined use is more preferred.

[0131] As the metal salt, a lithium salt which is a material easily dissolved in the non-aqueous electrolyte can be used, and as the anion of the lithium salt, for example, a metal salt selected from the group consisting of F- 、Cl - , I - 、NO3 - 、N(CN)2 - 、BF4 - 、ClO4 - PF6 - 、(CF3)2PF4 - 、(CF3)3PF3 - 、(CF3)4PF2 - 、(CF3)5PF - 、(CF3)6P - CF3SO3 - CF3CF2SO3 - 、(CF3SO2)2N - 、(FSO2)2N - CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、(SF5)3C - 、(CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - 、CH3CO2 - 、SCN - and (CF3CF2SO2)2N - One or more of the group consisting of.

[0132] In the electrolyte, in order to improve the service life characteristics of the battery, inhibit the reduction of the battery capacity and improve the discharge capacity of the battery, in addition to containing the above electrolyte components, one or more additives may be included, such as halogenated alkylene carbonate compounds (such as difluoroethylene carbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme dimethyl ether, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol or aluminum chloride.

[0133] According to another exemplary embodiment of the present invention, there are provided a battery module including the lithium secondary battery as a unit cell and a battery pack including the battery module.

[0134] According to yet another exemplary embodiment of the present invention, there is provided a battery pack including the lithium secondary battery.

[0135] According to yet another exemplary embodiment of the present invention, there is provided a battery pack including the battery module.

[0136] The battery module and battery pack include secondary batteries having high capacity, high rate characteristics, and cycle characteristics, and thus can be used as power sources for medium and large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0137] Modes for Carrying Out the Invention

[0138] Hereinafter, this specification will be described in detail with reference to the embodiments used to specifically describe this specification. However, the embodiments according to this specification can be modified in various forms and should not be interpreted as limiting the scope of this application to the embodiments described in detail below. The embodiments of this specification are provided to more fully explain this specification to those of ordinary skill in the art.

[0139] <Examples and Comparative Examples>

[0140] Example 1

[0141] [Preparation of Negative Electrode Active Material and Negative Electrode Active Material Coating Composition]

[0142] [Preparation of Silicon-Based Particles]

[0143] [Preparation of Silicon Oxide Particles]

[0144] SiO2, in which Si and SiO2 are mixed in a molar ratio of 1:1, is placed in a crucible 1 and evaporated by heating to a sublimation temperature of 1400°C. Metal magnesium is evaporated alone by heating at 800°C. After the crucible is completely evacuated to a pressure of 0.1 torr, the raw material is evaporated. The vapor mixture containing Mg is reacted for 6 hours and then condensed into a solid state in a vacuum zone at 800°C. The silicon-based active material prepared by the method is pulverized for 3 to 4 hours using a ball mill device. Thereafter, methane (CH4) is reacted for about 5 hours using a CVD device at 0.1 torr at 1 L / min in an inert gas Ar atmosphere to form a carbon layer on the surface of the silicon-based active material, thereby preparing a magnesium silicon oxide active material coated with a carbon layer. The final active material has a D50 controlled at a level of 6 μm.

[0145] [Preparation of Silicon-Carbon Composite]

[0146] Cellulose powder was placed in a tube furnace, heated to 400°C at a rate of 4°C / min, and then heated in a nitrogen atmosphere for 2 hours. The tube furnace was then heated to 900°C at a rate of 4°C / min and then heated in a nitrogen atmosphere for 2 hours. After sulfuric acid and nitric acid were mixed with the powder in a 3:1 volume ratio, the resulting mixture was stirred at 60°C for 2 hours and then centrifuged to obtain a precipitate. The resulting powder was washed five times with a solvent containing ethanol and distilled water in a 1:3 volume ratio and then dried at 120°C for 12 hours. The carbon-based particles were placed in a KOH solvent and heated at 800°C for 2 hours under a nitrogen atmosphere to form a porous carbon structure. The porous carbon structure was washed three times with distilled water and then dried at 120°C for at least 12 hours. The porous carbon structure was placed in a horizontal furnace and flowed with SiH4 / He = 5 / 95 gas at a flow rate of 50 ml / min at 700°C for 1 hour to produce a silicon-carbon composite. Thereafter, the silicon-carbon composite was put into an electric furnace, and methane was flowed and reacted at 700° C. for 2 hours to prepare a silicon-carbon composite negative active material having a carbon layer on the surface.

[0147] [Forming a coating on silicon-based particles]

[0148] A negative electrode active material coating composition containing a polymer having a -HN-C=O- bonding group was prepared by adding polyethylene glycol (PEG) with a molecular weight of 600 g / mol and isophorone diisocyanate (IPDI) at an NCO / OH molar ratio of 1.8 in a dimethylformamide (DMF) solvent, and adding dibutyltin dilaurate (DBTDL) as a reaction catalyst at a weight ratio of 0.03 relative to the total weight of the negative electrode active material coating composition. Thereafter, the mixture was stirred in a nitrogen atmosphere in an oil bath at 60°C for 3 hours to prepare the negative electrode active material coating composition.

[0149] The polymer having a -HN-C=O- bonding group contained in the prepared negative electrode active material coating composition is mixed with the negative electrode active material in a weight ratio of 1.0:99.0. After stirring the corresponding mixture at a speed of 2000 rpm per minute using a disperser for 10 minutes, the solvent and the polymer-coated silicon-carbon composite are separated by a vacuum filtration device to obtain a polymer-coated carbon-silicon composite. The obtained polymer-coated silicon-carbon composite is placed in a vacuum oven at 80°C for 12 hours to remove any residual solvent. The amount of the polymer coating is confirmed to be 0.9% by weight based on a total of 100% by weight of the negative electrode active material by the weight of polyethylene glycol (PEG) and isophorone diisocyanate (IPDI) added during polymer synthesis and the reduced weight of the dried polymer-coated silicon-carbon composite relative to the total weight of the added silicon-carbon composite.

[0150] [Preparation of negative electrode composition]

[0151] The negative electrode active material, single-walled carbon nanotubes (SWCNTs) as a conductive material, and carboxymethyl cellulose (CMC) as a binder were mixed in a weight ratio of 95.3:1:3.7 to prepare a negative electrode slurry.

[0152] [Manufacturing of negative electrode]

[0153] The negative electrode slurry was applied to a Cu metal film having a thickness level of 20 μm and then dried at a circulating air temperature of 60° C. Subsequently, after calendering, the calendered film was dried in a vacuum oven at 130° C. for about one day and then punched into 1.4875 cm 2 to make the negative electrode.

[0154] [Manufacturing of Secondary Batteries]

[0155] Used to be punched into 1.7671 cm 2 A lithium metal thin film was used as the positive electrode. A porous polyethylene separator was inserted between the positive and negative electrodes, and an electrolyte was injected to produce a lithium coin half-cell. The electrolyte contained a mixed solvent of EC (ethylene carbonate) and EMC (ethyl methyl carbonate) with a mixing ratio of 3:7 and 1 M LiPF6 dissolved therein.

[0156] Example 2

[0157] A negative electrode active material was prepared in the same manner as in Example 1, except that the negative electrode active material coating composition was prepared with a molar ratio of NCO / OH of the polymer reactant of 1.3.

[0158] Example 3

[0159] A negative electrode active material was prepared in the same manner as in Example 1, except that the negative electrode active material coating composition was prepared with a molar ratio of NCO / OH of the polymer reactant of 2.5.

[0160] Example 4

[0161] A negative electrode active material was prepared in the same manner as in Example 1, except that the polymer contained in the negative electrode active material coating composition was mixed with the negative electrode active material at a weight ratio of 0.5:99.5 to prepare a coating on the surface of the active material. The amount of the polymer coating was 0.45 wt % based on 100 wt % of the negative electrode active material, as determined by the weight of polyethylene glycol (PEG) and isophorone diisocyanate (IPDI) added during polymer synthesis and the reduced weight of the dried polymer-coated silicon-carbon composite relative to the total weight of the added silicon-carbon composite.

[0162] Example 5

[0163] A negative electrode active material was prepared in the same manner as in Example 1, except that the polymer contained in the negative electrode active material coating composition was mixed with the negative electrode active material at a weight ratio of 3.0:97.0 to prepare a coating on the surface of the active material. The amount of the polymer coating was 2.8 wt % based on 100 wt % of the negative electrode active material, as determined by the weight of polyethylene glycol (PEG) and isophorone diisocyanate (IPDI) added during polymer synthesis and the reduced weight of the dried polymer-coated silicon-carbon composite relative to the total weight of the added silicon-carbon composite.

[0164] Example 6

[0165] A negative active material was prepared in the same manner as in Example 1, except that the reactants for preparing the negative active material coating composition were prepared by mixing polyethylene glycol (PEG) having a molecular weight of 400 with hexamethylene diisocyanate (HMDI).

[0166] Comparative Example 1

[0167] The negative electrode active material was prepared in the same manner as in Example 1, except that the negative electrode active material coating composition was prepared by mixing the polymer reactants at a molar ratio of NCO / OH of 0.3, and the coating was prepared on the surface of the active material by mixing the polymer contained in the negative electrode active material coating composition with the negative electrode active material at a weight ratio of 0.05:99.95. The weight of polyethylene glycol (PEG) and isophorone diisocyanate (IPDI) added during polymer synthesis and the reduced weight of the dried polymer-coated silicon-carbon composite relative to the total weight of the added silicon-carbon composite confirmed that the amount of the polymer coating was 0.03% by weight based on a total of 100% by weight of the negative electrode active material.

[0168] Comparative Example 2

[0169] The negative electrode active material was prepared in the same manner as in Example 1, except that the negative electrode active material coating composition was prepared by mixing the polymer reactants at a molar ratio of NCO / OH of 0.2, and the coating was prepared on the surface of the active material by mixing the polymer contained in the negative electrode active material coating composition with the negative electrode active material at a weight ratio of 10.0:90.0. The weight of polyethylene glycol (PEG) and isophorone diisocyanate (IPDI) added during polymer synthesis and the reduced weight of the dried polymer-coated silicon-carbon composite relative to the total weight of the added silicon-carbon composite confirmed that the amount of the polymer coating was 6.8% by weight based on 100% by weight of the negative electrode active material.

[0170] Comparative Example 3

[0171] The negative electrode active material was prepared in the same manner as in Example 1, except that the negative electrode active material coating composition was prepared by mixing the polymer reactants at a molar ratio of NCO / OH of 8.0, and the coating was prepared on the surface of the active material by mixing the polymer contained in the negative electrode active material coating composition with the negative electrode active material at a weight ratio of 0.05:99.95. The weight of polyethylene glycol (PEG) and isophorone diisocyanate (IPDI) added during polymer synthesis and the reduced weight of the dried polymer-coated silicon-carbon composite relative to the total weight of the added silicon-carbon composite confirmed that the amount of the polymer coating was 0.05% by weight based on a total of 100% by weight of the negative electrode active material.

[0172] Comparative Example 4

[0173] The negative electrode active material was prepared in the same manner as in Example 1, except that the negative electrode active material coating composition was prepared by mixing the polymer reactants at a molar ratio of NCO / OH of 12.0, and the coating was prepared on the surface of the active material by mixing the polymer contained in the negative electrode active material coating composition with the negative electrode active material at a weight ratio of 10.0:90.0. The weight of polyethylene glycol (PEG) and isophorone diisocyanate (IPDI) added during polymer synthesis and the reduced weight of the dried polymer-coated silicon-carbon composite relative to the total weight of the added silicon-carbon composite confirmed that the amount of the polymer coating was 9.9% by weight based on a total of 100% by weight of the negative electrode active material.

[0174] [Reference example]

[0175] A battery was manufactured in the same manner as in Example 1, except that a binder composition including a polyurethane polymer having a glass transition temperature of 75° C. was used instead of carboxymethyl cellulose (CMC) as the binder material in Example 1, and no coating layer was formed on the silicon-based particles.

[0176] The silicon-based negative electrode active materials prepared in Examples and Comparative Examples are shown in Table 1 below.

[0177]

[0178] <Experimental Example: Evaluation of Discharge Capacity, Initial Efficiency, and Lifespan (Capacity Retention) Characteristics>

[0179] The discharge capacity, initial efficiency, and capacity retention ratio were evaluated by charging and discharging the fabricated batteries and are shown in Table 2 below.

[0180] For the 1st and 2nd cycles, the battery was charged and discharged at 0.1 C, and from the 3rd to the 299th cycles, the battery was charged and discharged at 0.5 C. The 300th cycle was completed in the charged state (in which lithium was contained in the negative electrode).

[0181] Charging conditions: CC (constant current) / CV (constant voltage) (5 mV / 0.005 C current cutoff)

[0182] Discharge condition: CC (constant current) condition 1.5 V

[0183] The discharge capacity (mAh / g) and initial efficiency (%) were calculated from the results of the first charge and discharge period. Specifically, the initial efficiency (%) was calculated using the following calculation.

[0184] Initial efficiency (%) = (first discharge capacity / first charge capacity) × 100%

[0185] The capacity retention ratio was each obtained by the following calculation.

[0186] Capacity retention rate (%) = (49th discharge capacity / 1st discharge capacity) × 100%

[0187]

[0188] In Comparative Examples 1 and 2, a polymer having a -HN-C=O- bonding group and a glass transition temperature lower than -30°C was used as the negative electrode active material coating composition, and since the coating was dissolved in the slurry and not coated on the surface of the active material, a low capacity retention rate was exhibited.

[0189] In Comparative Examples 3 and 4, a polymer having a -HN-C=O- bonding group with a glass transition temperature exceeding 80°C was used as the negative electrode active material coating composition, and low capacity retention was shown because the shape recovery of the coating during charge and discharge was reduced due to the high rigidity of the coating.

[0190] In contrast, Examples 1 to 6 showed higher capacity retention than Comparative Examples 1 to 4 by using a polymer having a -HN-C=O- bonding group having a glass transition temperature of -30°C to 80°C as the negative electrode active material coating composition.

[0191] In addition, in Comparative Examples 1 and 2, a polymer having a -HN-C=O- bonding group synthesized from reactants of an alcohol having an NCO / OH molar ratio of less than 0.5 and an isocyanate was used as a negative electrode active material coating composition, and since the coating was dissolved in the slurry and not coated on the surface of the active material, a low capacity retention rate was exhibited.

[0192] In Comparative Examples 3 and 4, a polymer having a -HN-C=O- bonding group synthesized from a reactant of an alcohol having an NCO / OH molar ratio exceeding 4 and an isocyanate was used as a negative electrode active material coating composition, and a low capacity retention rate was exhibited due to the formation of a hard coating layer (which reduced the shape recovery of the active material to volume changes during charge and discharge).

[0193] In contrast, by using the polymer having a -HN-C=O- bonding group synthesized from reactants of an alcohol and an isocyanate having an NCO / OH molar ratio of 0.5 to 4 as the negative electrode active material coating composition, Examples 1 to 6 showed higher capacity retention than Comparative Examples 1 to 4.

[0194] Furthermore, as a reference example, a battery using a binder composition including a polyurethane polymer having a glass transition temperature of 75° C. and a negative electrode active material in which no coating layer was formed on silicon-based particles showed lower capacity retention than Examples 1 to 6 of the present application.

[0195] That is, it was possible to confirm that by forming a coating layer on at least a portion of the surface of the negative electrode active material using the negative electrode active material coating composition according to an exemplary embodiment of the present invention (including a polymer having a -HN-C=O- bonding group), there is an effect of improving severe volume change and particle breakage of the negative electrode active material during charge and discharge, and a battery including the negative electrode active material having the coating layer formed thereon has improved service life characteristics.

Claims

1. A negative electrode active material coating composition comprising a polymer having a -HN-C=O- bonding group, The polymer having a -HN-C=O- bonding group has a glass transition temperature (Tg) of -30°C to 80°C.

2. The composition according to claim 1, wherein the polymer having a -HN-C=O- bonding group is a polymer of an alcohol and an isocyanate, and The molar ratio of the -NCO groups of the isocyanate to the -OH groups of the alcohol is 0.5 to 4.

3. A negative electrode active material comprising: Silicon-based particles; and A coating layer provided on at least a portion of the surface of the silicon-based particles and comprising the negative electrode active material coating composition according to claim 1 or 2. 4 . The negative electrode active material according to claim 3 , wherein an amount of the coating layer is 0.1 wt % or more and 5 wt % or less based on 100 wt % of the entire negative electrode active material. 5 . The negative electrode active material according to claim 3 , wherein the coating layer has a thickness of 1 nm to 1 μm. The negative electrode active material according to claim 3 , wherein the silicon-based particles are silicon-carbon composite particles or silicon oxide particles. 7 . A negative electrode composition comprising the negative electrode active material according to claim 3 , a binder and a conductive material. 8 . The negative electrode composition according to claim 7 , wherein the conductive material comprises one or more of carbon black and single-walled carbon nanotubes. 9 . The negative electrode composition according to claim 7 , wherein a content of the conductive material is 0.01 parts by weight or more and 20 parts by weight or less based on 100 parts by weight of the negative electrode composition. 10 . The negative electrode composition according to claim 7 , wherein the binder comprises carboxymethyl cellulose.

11. A negative electrode comprising: a negative electrode current collector; and A negative electrode active material layer is provided on at least one surface of the negative electrode current collector and comprises the negative electrode composition of claim 7 . 12 . A lithium secondary battery comprising the negative electrode according to claim 11 , a separator and a positive electrode. 13 . A battery module comprising the lithium secondary battery according to claim 12 . 14 . A battery pack comprising the lithium secondary battery according to claim 12 .

15. A battery pack comprising the battery module according to claim 13.

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