Anode and lithium secondary battery

Abstract

The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery comprising: a current collector; a first layer provided on the current collector and including a carbon-based active material; a second layer provided on the first layer and including a silicon-based active material; and a third layer provided on the second layer and including aluminum or an aluminum-containing compound, wherein the thickness of the third layer is greater than 0 and not more than 1 / 20 of the sum of the thicknesses of the first layer and the second layer.

Description

[Technical Field]

[0001] This specification claims the benefit of Korean Patent Application No. 10-2023-0118377 filed with the Korean Intellectual Property Office on September 6, 2023, and Korean Patent Application No. 10-2024-0120050 filed with the Korean Intellectual Property Office on September 4, 2024, as of the filing date, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a negative electrode and a lithium secondary battery, a battery module including the same, and a battery pack. [Background technology]

[0003] Recently, with the rapid spread of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles, the demand for small, lightweight, and relatively high-capacity secondary batteries has been rapidly increasing. In particular, lithium secondary batteries, which are lightweight and have high energy density, have attracted attention as a power source for portable devices. Accordingly, active research and development efforts are being 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, and an electrolyte. The positive electrode and the negative electrode may each have an active material layer formed on a current collector, the active material layer including a positive electrode active material and a negative electrode active material. Generally, the positive electrode uses a lithium-containing metal oxide such as LiCoO2 or LiMn2O4 as the positive electrode active material, and the negative electrode uses a lithium-free carbon-based active material or a silicon-based active material as the negative electrode active material.

[0005] Among negative electrode active materials, silicon-based active materials have a higher capacity than carbon-based active materials and are attracting attention as materials for high-capacity secondary batteries. However, silicon-based active materials have drawbacks such as poor life and swelling characteristics due to side reactions with electrolytes. Therefore, it is necessary to develop technology to use silicon-based active materials while minimizing these drawbacks. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention relates to a negative electrode for a lithium secondary battery that uses a silicon-based active material as a negative electrode active material to provide a high-capacity battery while at the same time improving the drawbacks of the silicon-based active material, and a lithium secondary battery including the same. [Means for solving the problem]

[0007] One embodiment of the present invention provides a negative electrode for a lithium secondary battery, comprising: a current collector; a first layer provided on the current collector and including a carbon-based active material; a second layer provided on the first layer and including a silicon-based active material; and a third layer provided on the second layer and including aluminum or an aluminum-containing compound, wherein the thickness of the third layer is greater than 0 and not more than 1 / 20 of the sum of the thicknesses of the first layer and the second layer.

[0008] One embodiment of the present invention provides a lithium secondary battery including the negative electrode for lithium secondary batteries according to the above embodiment; a separator; and a positive electrode, wherein a third layer of the negative electrode is disposed opposite the separator.

[0009] One embodiment of the present invention provides a battery module including the lithium secondary battery according to the aforementioned embodiment.

[0010] One embodiment of the present invention provides a battery pack including the lithium secondary battery according to the aforementioned embodiment.

[0011] One embodiment of the present invention provides a battery pack including a battery module according to the aforementioned embodiment. [Effects of the Invention]

[0012] The negative electrode for a lithium secondary battery according to one embodiment of the present invention includes a silicon-based active material, but the silicon-based active material is included in the upper layer of the two-layer active material structure, and a layer containing aluminum or an aluminum-containing compound is disposed on the surface facing the separator, thereby significantly improving cycle characteristics, lifespan, and swelling characteristics. Specifically, the relatively hard aluminum-containing inorganic layer suppresses changes in volume expansion of the active material layer including the silicon-based active material layer, which has high swelling, thereby improving cycle characteristics, lifespan, and swelling characteristics. DETAILED DESCRIPTION OF THE INVENTION

[0013] This specification will be explained in more detail below.

[0014] In this specification, when a part is said to "comprise" a certain component, this does not mean that it excludes other components, but that it may further include other components, unless otherwise specified.

[0015] In this specification, a member being "located on" another member includes not only a member being in contact with the other member, but also a member being present between the two members.

[0016] The terms and words used in this specification should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to best explain his / her invention.

[0017] As used herein, the singular expression of a term includes the plural expression unless the context clearly indicates otherwise.

[0018] In this specification, the description of only the "negative electrode active material layer" without the expressions "first" and "second" can be applied to either the first layer or the second layer.

[0019] Preferred embodiments of the present invention will be described in detail below. However, the embodiments of the present invention can be modified in various ways, and the scope of the present invention is not limited to the embodiments described below.

[0020] <Negative electrode> A negative electrode for a lithium secondary battery according to one embodiment of the present invention includes a current collector, a first layer provided on the current collector and including a carbon-based active material, and a second layer provided on the first layer and including a silicon-based active material. The negative electrode for a lithium secondary battery further includes a third layer provided on the second layer and including aluminum or an aluminum-containing compound, the third layer having a thickness greater than 0 and not greater than 1 / 20 of the sum of the thicknesses of the first and second layers.

[0021] According to the above embodiment, the laminated structure of the first layer and the second layer has the advantage of being able to suppress the detachment of the active material from the current collector due to the silicon-based active material, which has a large volume change. By further laminating the third layer on the surface of the laminated structure containing the active material, the relatively hard aluminum-containing inorganic layer suppresses the change in volume expansion of the active material layer containing the silicon-based active material, which has a large swelling tendency, thereby improving battery life and swelling characteristics.

[0022] According to one embodiment, the first layer contains a carbon-based active material as an active material, but does not contain a silicon-based active material. According to one embodiment, the carbon-based active material may be graphite, and the graphite may be natural graphite, artificial graphite, or a mixture thereof. The content of the carbon-based active material in the first layer may be 80 parts by weight to 100 parts by weight, for example, 90 parts by weight to 100 parts by weight, or 95 parts by weight to 100 parts by weight, based on 100 parts by weight of the active material in the first layer.

[0023] According to one embodiment, the silicon-based active material of the second layer includes at least one of silicon (Si), silicon oxide, metal-doped silicon oxide, silicon-carbon composite, and silicon-metal alloy. The content of the silicon-based active material of the second layer may be 0.1 to 40 parts by weight, for example, 1 to 20 parts by weight, or 5 to 12 parts by weight, based on 100 parts by weight of the active material in the second layer.

[0024] When the content of the silicon-based active material in the second layer satisfies the above range based on 100 parts by weight of the active material in the second layer, the capacity of the negative electrode can be increased, the electrode can be manufactured thinner, and the battery life and swelling characteristics can be improved. Specifically, when the content of the silicon-based active material in the second layer is 0.1 part by weight or more, it is advantageous for increasing the capacity of the negative electrode. In order to achieve excellent capacity, the negative electrode can be formed relatively thin, and the life and swelling characteristics are improved. Also, when the silicon-based content in the second layer is 40 parts by weight or less, the Si content is not too high, the swelling characteristics of Si are improved within an appropriate range, and the life and swelling characteristics are improved.

[0025] If necessary, the second layer may further include a carbon-based active material. The carbon-based active material in the second layer may be natural graphite, artificial graphite, or a mixture thereof. The content of the carbon-based active material in the second layer may be 60 to 99.9 parts by weight based on 100 parts by weight of the active material in the second layer.

[0026] The silicon-based active material may be an active material including SiO x (0 ≦ x < 2), or may be silicon-based composite particles including SiO x (0 < x < 2) and pores.

[0027] The active material including SiO x (0 ≦ x < 2) may be silicon oxide particles including SiO x (0 < x < 2) and pores.

[0028] The SiOx (0 < x < 2) corresponds to the matrix within the silicon oxide particles. The SiO x (0 < x < 2) may be in a form containing Si and SiO2, and the Si may form a phase. That is, the x corresponds to the number ratio of O to Si contained within the SiO x (0 < x < 2). When the silicon oxide particles contain the SiO x (0 < x < 2), the discharge capacity of the secondary battery can be improved.

[0029] 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 the matrix within the silicon oxide particles.

[0030] The Mg compound and / or the Li compound may be present inside and / or on the surface of the SiO x (0 < x < 2). The initial efficiency of the battery can be improved by the Mg compound and / or the Li compound.

[0031] The Mg compound may include at least one selected from the group consisting of Mg silicate, Mg silicide, and Mg oxide. The Mg silicate may include at least one selected from Mg2SiO4 and MgSiO3. The Mg silicide may include Mg2Si. The Mg oxide may include MgO.

[0032] In one embodiment of the present specification, the Mg element is contained at 0.1 wt% to 20 wt% or may be contained at 0.1 wt% to 15 wt% based on 100 wt% of the total amount of the silicon oxide particles. Specifically, the Mg element may be contained at 0.5 wt% to 10 wt% or 0.8 wt% to 10 wt%. When the above range is satisfied, since the Mg compound is contained in the silicon oxide particles at an appropriate content, the volume change of the silicon oxide particles can be easily suppressed during charging and discharging of the battery, and the discharge capacity and initial efficiency of the battery can be improved.

[0033] The Li compound may contain at least one selected from the group consisting of Li silicate, Li silicide, and Li oxide. The Li silicate may contain at least any one of Li2SiO3, Li4SiO4, and Li2Si2O5. The Li silicide may contain Li7Si2. The Li oxide may contain Li2O.

[0034] In one embodiment of the present invention, the Li compound may contain a form of lithium silicate. The lithium silicate is Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and is divided into crystalline lithium silicate and amorphous lithium silicate. The crystalline lithium silicate may exist in the form of at least one lithium silicate selected from the group consisting of Li2SiO3, Li4SiO4, and Li2Si2O5 in the silicon oxide particles, and the amorphous lithium silicate may be Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and is not limited to the above form.

[0035] In one embodiment of the present specification, the Li element may be contained in an amount of 0.1 wt % to 20 wt % or 0.1 wt % to 15 wt % based on 100 wt % of the total amount of the silicon oxide particles. Specifically, the Li element may be contained in an amount of 0.5 wt % to 10 wt %, more specifically, 0.5 wt % to 10 wt %. When this range is satisfied, the Li compound can be contained in the silicon oxide particles at an appropriate content, and volume change of the negative electrode active material during charge and discharge of the battery can be easily suppressed, thereby improving the discharge capacity and initial efficiency of the battery.

[0036] The Mg or Li element content can be confirmed by ICP analysis. For the ICP analysis, a fixed amount (approximately 0.01 g) of the negative electrode active material is accurately separated and transferred to a platinum crucible. Nitric acid, hydrofluoric acid, and sulfuric acid are added and the mixture is completely decomposed on a hot plate. Then, an inductively coupled plasma emission spectrometry (ICPAES, Perkin-Elmer 7300) is used to measure the intensity of a standard solution (5 mg / kg) prepared at the characteristic wavelength of Mg or Li, and a reference calibration curve is created. The pretreated sample solution and the base sample are then introduced into the instrument, and their respective intensities are measured to calculate the actual intensities. The concentration of each component is calculated using the created calibration curve, and the total is converted to a theoretical value. The Mg or Li element content of the resulting silicon oxide particles can then be analyzed.

[0037] In one embodiment of the present invention, the silicon oxide particles may contain additional metal atoms. The metal atoms may exist in the silicon oxide particles in at least one form of metal atoms, metal silicates, metal silicides, and metal oxides. The metal atoms may include at least one selected from the group consisting of Mg, Li, Al, and Ca. This may improve the initial efficiency of the negative electrode active material.

[0038] In one embodiment of the present invention, the silicon oxide particles have a carbon layer formed on at least a portion of their surfaces. In this case, the carbon layer may be formed on at least a portion of the surface, i.e., the particle surface, or may be formed on the entire particle surface. The carbon layer imparts conductivity to the negative electrode active material, thereby improving the initial efficiency, life characteristics, and battery capacity characteristics of the secondary battery.

[0039] In one embodiment of the present invention, the carbon layer contains amorphous carbon. Alternatively, the carbon layer may further contain crystalline carbon.

[0040] The crystalline carbon can further improve the conductivity of the negative electrode active material. The crystalline carbon may include at least one selected from the group consisting of fullerene, carbon nanotube, and graphene.

[0041] The amorphous carbon can appropriately maintain the strength of the carbon layer and suppress the expansion of the silicon-based particles. The amorphous carbon may be a carbon-based material formed by using at least one carbide selected from the group consisting of tar, pitch, and other organic substances, or a hydrocarbon as a source in a chemical vapor deposition process.

[0042] The carbonized organic material may be a carbonized organic material selected from carbonized sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose or kedohexose, and combinations thereof.

[0043] The hydrocarbon may be a substituted or unsubstituted aliphatic or alicyclic hydrocarbon, or a substituted or unsubstituted aromatic hydrocarbon. The aliphatic or alicyclic hydrocarbon of the substituted or unsubstituted aliphatic or alicyclic hydrocarbon may be methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, hexane, or the like. The aromatic hydrocarbon of the substituted or unsubstituted aromatic hydrocarbon may be benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, phenanthrene, or the like.

[0044] In one embodiment of the present invention, the carbon layer may be an amorphous carbon layer.

[0045] In one embodiment of the present invention, the carbon layer may be included in an amount of 0.1 to 50 parts by weight, 0.1 to 30 parts by weight, or 0.1 to 20 parts by weight, based on a total of 100 parts by weight of the silicon-based particles. More specifically, the carbon layer may be included in an amount of 0.5 to 15 parts by weight, 1 to 10 parts by weight, or 1 to 5 parts by weight. When the amount is within the above range, a decrease in the capacity and efficiency of the negative electrode active material can be prevented.

[0046] In one embodiment of the present invention, the thickness of the carbon layer may be 1 nm to 500 nm, specifically 5 nm to 300 nm. When the thickness satisfies the above range, the conductivity of the negative electrode active material is improved, volume change of the negative electrode active material is easily suppressed, and side reactions between the electrolyte and the negative electrode active material are suppressed, resulting in improved initial efficiency and / or lifespan of the battery.

[0047] Specifically, the carbon layer may be formed by chemical vapor deposition (CVD) using at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene.

[0048] In the present invention, the crystallinity of the carbon layer can be confirmed by calculating the D / G band ratio using Raman spectroscopy. Specifically, measurements can be performed using a Renishaw 2000 Raman microscope system with 532 nm laser excitation and a 100x optical lens at a low laser power density and 30 seconds of exposure time to avoid laser thermal effects. To reduce positional deviations, a total of 25 points are measured over a 5 μm x 5 μm area, and the average values ​​of the D band and G band are calculated after fitting using a Lorentzian function.

[0049] The silicon-based active material may be a silicon carbon composite, which may be a Si / C-based active material.

[0050] In this specification, the silicon carbon composite is a composite of Si and C, and is distinguished from silicon carbide, which is abbreviated as SiC.

[0051] The silicon carbon composite may be a composite of silicon and graphite, or may have a structure in which a core of a composite of silicon and graphite is surrounded by graphene or amorphous carbon, etc. In the silicon carbon composite, the silicon may be nanosilicon.

[0052] According to one embodiment, the silicon carbon composite comprises porous carbon particles and silicon located on the surface or in the internal pores of the porous carbon particles.

[0053] According to one embodiment, the silicon carbon composite has a pore volume of 0.005 cm by the BET method. 3 / g~0.03cm 3The silicon carbon composite may have a pore volume of 0.005 cm3 measured by mercury penetration. 3 / g~0.03cm 3 / g.

[0054] According to one embodiment, the silicon carbon composite may be manufactured by a method including forming silicon on the surface and in the internal pores of porous carbon particles.

[0055] The porous carbon-based particles can be prepared by a method known in the art, for example, by carbonizing organic materials such as petroleum-based materials, polymers, etc., or by chemically treating and then carbonizing natural materials such as palm bark, etc. As another example, the porous carbon-based particles can be prepared by a method including a step of etching carbon-based particles contained in internal pores to expand the internal pores of the carbon-based particles.

[0056] The step of expanding the internal pores of the carbon-based particles may be performed in a nitrogen (N2), oxygen (O2), or air atmosphere. Specifically, the flow rate of the oxygen (O2) or the oxygen-containing air may be controlled to be 0.1 L / min to 10 L / min.

[0057] The step of expanding 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.

[0058] The pore characteristics of the resulting porous carbon-based particles may vary depending on the conditions for expanding the internal pores of the carbon-based particles.

[0059] The silicon forming step may be performed using a chemical vapor deposition method, in which silicon nanoparticles are deposited on the surfaces and / or in the pores of the carbon-based particles with expanded pores, thereby forming silicon in the form of a film, islands, or a mixture thereof.

[0060] The silicon nanoparticles may be crystalline, semi-crystalline, amorphous, or a combination thereof.

[0061] The silicon-based active material may be a silicon metal alloy. For example, the silicon metal alloy (Si-alloy) may be one in which Si is alloyed with one or more metals selected from the group consisting of Zn, Al, Mn, Ti, Fe, and Sn. Examples of the Si-alloy include, but are not limited to, solid solutions, intermetallic compounds, and eutectic alloys.

[0062] In this specification, the average particle size (D50) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve of the particles. The average particle size (D50) can be measured, for example, using a laser diffraction method. The laser diffraction method generally allows measurement of particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0063] The silicon-based active material may have an average particle size (D50) of 1 μm to 10 μm. When the average particle size is within this range, the active material is structurally stable during charge and discharge, preventing the problem of increased volume expansion / contraction caused by an excessively large particle size, and preventing the problem of reduced initial efficiency caused by an excessively small particle size.

[0064] The first layer and the second layer each further contain a binder and a conductive material, and may further contain a thickener and / or a conductive material, as necessary.

[0065] The first and second layers may be formed by applying a negative electrode slurry containing the active material, binder, thickener, and / or conductive material to at least one surface of a current collector, drying, and rolling. The first and second layers may be formed sequentially on the current collector. The first and second layers may have the same thickness, and the ratio of the thickness of the second layer to the thickness of the first layer may be 0.7 to 1.3.

[0066] The negative electrode slurry may further include an additional negative electrode active material.

[0067] The additional negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; and SiO β(0<β<2), metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, lithium titanium oxide, and lithium vanadium oxide; or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites. A mixture of two or more of these may be used. A thin film of metallic lithium may also be used as the negative electrode active material. The carbon material may be either low-crystalline carbon or high-crystalline carbon. Typical low-crystalline carbons include soft carbon and hard carbon, while typical high-crystalline carbons include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-fired carbons such as petroleum or coal tar pitch-derived cokes.

[0068] According to one embodiment of the present invention, the negative electrode slurry may have a pH of 7 to 11 at 25°C. When the pH of the negative electrode slurry satisfies this range, the rheological properties of the slurry are stabilized. On the other hand, if the pH of the negative electrode slurry is less than 7 or exceeds 11, decomposition of carboxymethyl cellulose (CMC) used as a thickener occurs, causing a decrease in the viscosity of the slurry and a decrease in the degree of dispersion of the active material contained in the slurry.

[0069] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, the current collector can be made of copper, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like. Specifically, a transition metal that easily adsorbs carbon, such as copper or nickel, can be used as the current collector. The thickness of the current collector can be 6 μm to 20 μm, but is not limited to this.

[0070] The binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which hydrogen is substituted with Li, Na, Ca, or the like, or may include various copolymers thereof.

[0071] The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive. For example, graphite such as natural graphite and 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 and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used.

[0072] The thickener may be carboxymethyl cellulose (CMC), but is not limited thereto, and any thickener used in the technical field may be appropriately adopted.

[0073] In one embodiment of the present invention, the total amount of negative electrode active materials contained in the negative electrode slurry may be 60 parts by weight to 99 parts by weight, specifically 70 parts by weight to 98 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0074] In one embodiment of the present invention, the binder may be included in an amount of 0.5 to 30 parts by weight, specifically 1 to 20 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0075] In one embodiment of the present invention, the conductive material may be included in an amount of 0.01 to 25 parts by weight, specifically 0.05 to 20 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0076] In one embodiment of the present invention, the thickener may be included in an amount of 0.5 parts by weight to 25 parts by weight, specifically 0.5 parts by weight to 20 parts by weight, more specifically 1 part by weight to 20 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry.

[0077] The negative electrode slurry according to an embodiment of the present invention may further include a solvent for forming the negative electrode slurry. Specifically, the solvent for forming the negative electrode slurry may include at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically distilled water, in order to facilitate dispersion of the components.

[0078] In one embodiment of the present invention, the solid content weight of the negative electrode slurry may be 20 parts by weight to 75 parts by weight, specifically 30 parts by weight to 70 parts by weight, based on 100 parts by weight of the total negative electrode slurry.

[0079] In the present invention, the third layer contains aluminum or an aluminum-containing compound, and its thickness is greater than 0 and not greater than 1 / 20 of the sum of the thicknesses of the first and second layers. The thickness of the third layer refers to the thickness of the third layer at the portion where the third layer is present. That is, the third layer may cover the entire surface of the second layer, or may cover only a portion of the surface of the second layer. In this case, the thickness of the third layer refers to the thickness of the region where the third layer covers the second layer. The thickness and thickness ratio of each layer can be obtained by measuring the thickness using a cross-sectional SEM of the electrode. The thickness measurement may be performed before impregnation with the electrolyte, after impregnation, or after the battery has been cycled. The effects of the present invention can be achieved when the thickness ratio calculated from the thicknesses measured at any time falls within the range of the present invention. In this material, the relatively hard aluminum-containing third layer has the advantage of suppressing volumetric expansion changes in active material layers, including silicon-based active material layers that exhibit high swelling, thereby improving cycle characteristics, lifespan, and swelling. Meeting the above thickness range has the advantage of suppressing volumetric expansion without reducing the conductivity of the negative electrode.

[0080] According to one embodiment, the third layer is configured to cover only a portion of the second layer or to cover the entire second layer. When the third layer covers only a portion of the second layer, it may cover 30% or more, 50% or more, 70% or more, or 90% or more of the second layer.

[0081] According to one embodiment, the third layer may further contain a binder in addition to aluminum or an aluminum-containing compound, in which the binder may be contained in an amount of 1 to 20 parts by weight, for example, 5 to 15 parts by weight, based on 100 parts by weight of the third layer.

[0082] According to one embodiment, the third layer may be produced by the following method. First, a dispersion is prepared by mixing and dispersing at least one of aluminum and an aluminum-containing compound with a solvent and a polymer binder. The dispersion is then applied to the second layer of the laminate structure of the first and second layers. Here, the laminate structure of the first and second layers may be in a state where rolling has been completed. A drying step may be further performed as necessary. The dispersion of aluminum or an aluminum-containing compound according to one embodiment of the present invention may further contain a dispersion-forming solvent. Specifically, the dispersion-forming solvent may contain at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically distilled water, in order to facilitate dispersion of the components.

[0083] The polymer binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which hydrogen is substituted with Li, Na, Ca, or the like, or may include various copolymers thereof.

[0084] According to one embodiment, the aluminum-containing compound of the third layer includes at least one of aluminum oxide and Al(OH)3.

[0085] According to one embodiment, the content of the aluminum or aluminum-containing compound is 90 to 100 parts by weight, for example, 90 to 95 parts by weight, based on 100 parts by weight of the composition of the third layer.

[0086] When the content of aluminum or an aluminum compound in the third layer is within the above range, the content of the polymer binder in the third layer composition does not exceed 10 parts by weight, which prevents the polymer binder from acting as a resistance layer and reducing electrical conductivity, thereby improving the battery life and swelling characteristics.

[0087] <Secondary battery> One embodiment of the present invention provides a lithium secondary battery comprising the anode according to the above embodiment, a separator, and a cathode, wherein the inorganic layer of the anode is disposed facing the separator. In this case, a third layer of the anode is disposed facing the separator. When the third layer contacts the separator, the adhesive strength between the third layer and the separator is increased, which is advantageous for battery fabrication.

[0088] According to one embodiment of the present application, 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 the positive electrode active material.

[0089] The positive electrode current collector in the positive electrode is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like may be used. The positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. It may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0090] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the above-mentioned positive electrode active material.

[0091] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without any particular limitation as long as it does not cause chemical changes in the constructed battery and has electronic conductivity. Specific examples include graphite such as natural graphite and 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 powder or metal fiber 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. These may be used alone or in combination of two or more.

[0092] The positive electrode binder serves to improve adhesion between particles of the positive electrode active material and between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination.

[0093] The positive electrode binder may be included in an amount of 0.1 parts by weight to 50 parts by weight, for example, preferably 0.3 parts by weight to 35 parts by weight, more preferably 0.5 parts by weight to 20 parts by weight, based on 100 parts by weight of the positive electrode active material layer.

[0094] The conductive material contained in the positive electrode active material layer is used to impart conductivity to the electrode, and can be any material that does not undergo chemical changes in the battery and has electronic conductivity. Specific examples include graphite such as natural graphite and 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 powder or metal fiber 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. These materials can be used alone or in combination.

[0095] Specifically, in one embodiment, the conductive material may include one or more of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). The conductive material may be included in an amount of 0.1 to 2 parts by weight, preferably 0.3 to 1.5 parts by weight, more preferably 0.5 to 1.2 parts by weight, based on 100 parts by weight of the composition for a positive electrode active material layer.

[0096] A secondary battery according to an embodiment of the present invention includes the above-described negative electrode, positive electrode, and separator interposed between the positive electrode and the negative electrode, and may further include an electrolyte.

[0097] The separator separates the negative electrode and positive electrode and provides a path for lithium ions to move. Any separator commonly used in secondary batteries can be used without particular limitations. In particular, a separator that exhibits low resistance to ion migration in the electrolyte and excellent electrolyte humidification is preferred. Specifically, porous polymer films, such as those made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminate structures of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymeric material may be used, and may be used in a single-layer or multi-layer structure.

[0098] According to one embodiment of the present invention, the separation membrane may be a safety reinforced separator (SRS) separation membrane.

[0099] Examples of the electrolytic solution include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing lithium secondary batteries, but are not limited to these.

[0100] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0101] Examples of the non-aqueous organic solvent that may be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0102] In particular, among the carbonate-based organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate are preferred because they are high-viscosity organic solvents with high dielectric constants that allow them to dissociate lithium salts well. Mixing such cyclic carbonates with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio can produce an electrolyte with high electrical conductivity, making them more preferred.

[0103] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, the anion of the lithium salt may be 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 selected from the group consisting of:

[0104] In addition to the components of the electrolyte, the electrolyte may further include one or more additives, such as a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, a cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, a nitrobenzene derivative, sulfur, a quinoneimine dye, an N-substituted oxazolidinone, an N,N-substituted imidazolidine, an ethylene glycol dialkyl ether, an ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving the discharge capacity of the battery.

[0105] According to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same.

[0106] According to another embodiment of the present invention, there is provided a battery pack including the lithium secondary battery.

[0107] According to another embodiment of the present invention, there is provided a battery pack including the battery module.

[0108] The battery module and battery pack include the secondary battery having high capacity and excellent rate-limiting and cycle characteristics, and therefore can be used as a power source for a medium- to large-sized device selected from the group consisting of an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system. [Example]

[0109] <Examples and Comparative Examples> Example 1 A composition for forming the first layer was prepared containing 96.3 parts by weight of graphite, 2.55 parts by weight of SBR (styrene butadiene rubber) and 1 part by weight of CMC (carboxymethyl cellulose) as binders, 0.1 parts by weight of dispersant, and a CNT pre-dispersion containing 0.05 parts by weight of single-walled CNTs, based on 100 parts by weight of the first layer. The graphite was prepared using an airflow milling method to a size of D50 = 17 μm. The composition for forming the first layer was coated onto a 15 μm-thick copper foil to form a first layer with a dry thickness of 50 μm.

[0110] A second layer-forming composition was prepared using 100 parts by weight of negative electrode active material. The composition included 97.7 parts by weight of graphite (90 parts by weight based on 100 parts by weight of negative electrode active material), 97.7 parts by weight of methane-CVD carbon-coated silicon oxide active material (10 parts by weight based on 100 parts by weight of negative electrode active material), 1.15 parts by weight of SBR (styrene butadiene rubber) and 1 part by weight of CMC (carboxymethyl cellulose) as binders, 0.1 parts by weight of dispersant, and a CNT pre-dispersion containing 0.05 parts by weight of single-walled CNTs. The carbon-coated silicon oxide active material was milled to a size of D50 = 6 μm, and the graphite was milled to a size of D50 = 17 μm, using an airflow milling method. The second layer-forming composition was then coated onto the first layer to a dry thickness of 100 μm.

[0111] The negative electrode coated with the first and second layers was rolled to a thickness of 60 μm. Next, alumina (Al2O3) as an inorganic material and SBR and CMC as binders were mixed in a ratio of 90:6:4 and dissolved in water. The inorganic particles were then crushed and dispersed using a ball mill for at least 12 hours to produce an aluminum compound dispersion. This dispersion was then applied to the second layer of the negative electrode coated with the first and second layers, producing a negative electrode with a combined thickness of 62 μm for the first, second, and third layers in a dry state.

[0112] Example 2 A negative electrode was prepared in the same manner as in Example 1, except that a Mg-doped carbon-coated silicon oxide active material was used instead of the carbon-coated silicon oxide active material.

[0113] Example 3 A negative electrode was prepared in the same manner as in Example 1, except that a Li-doped carbon-coated silicon oxide active material was used instead of the carbon-coated silicon oxide active material.

[0114] Example 4 A negative electrode was prepared in the same manner as in Example 1, except that a silicon carbon composite (Si / C) was used instead of the carbon-coated silicon oxide active material.

[0115] Example 5 A negative electrode was prepared in the same manner as in Example 1, except that a Si metal alloy (Si6Cu3Sn1) was used instead of the carbon-coated silicon oxide active material.

[0116] Example 6 A negative electrode was produced in the same manner as in Example 1, except that the sum of the thicknesses of the first to third layers after the third layer was applied was 61 μm.

[0117] Example 7 A negative electrode was fabricated in the same manner as in Example 1, except that the second layer contained graphite (50 parts by weight based on 100 parts by weight of the negative electrode active material) and a silicon oxide active material carbon-coated by methane CVD (50 parts by weight based on 100 parts by weight of the negative electrode active material).

[0118] Example 8 A negative electrode was prepared in the same manner as in Example 1, except that the ratio of alumina (Al2O3) as an inorganic material, SBR as a binder, and CMC was 50:30:20 based on 100 parts by weight of the composition of the third layer.

[0119] Comparative Example 1 A negative electrode was prepared in the same manner as in Example 1, except that the third layer was not applied.

[0120] Comparative Example 2 A negative electrode was prepared in the same manner as in Example 2, except that the third layer was not applied.

[0121] Comparative Example 3 A negative electrode was prepared in the same manner as in Example 3, except that the third layer was not applied.

[0122] Comparative Example 4 A negative electrode was prepared in the same manner as in Example 4, except that the third layer was not applied.

[0123] Comparative Example 5 A negative electrode was prepared in the same manner as in Example 5, except that the third layer was not applied.

[0124] Comparative Example 6 A negative electrode was produced in the same manner as in Example 1, except that the sum of the thicknesses of the first to third layers after the third layer was applied was 65 μm.

[0125] Comparative Example 7 A negative electrode was produced in the same manner as in Example 2, except that the sum of the thicknesses of the first to third layers after the third layer was applied was 65 μm.

[0126] Comparative Example 8 A negative electrode was produced in the same manner as in Example 3, except that the sum of the thicknesses of the first to third layers after the third layer was applied was 65 μm.

[0127] Comparative Example 9 A negative electrode was produced in the same manner as in Example 4, except that the sum of the thicknesses of the first to third layers after the third layer was applied was 65 μm.

[0128] Comparative Example 10 A negative electrode was produced in the same manner as in Example 5, except that the sum of the thicknesses of the first to third layers after the third layer was applied was 65 μm.

[0129] 〕 Comparative Example 11 A negative electrode was produced in the same manner as in Example 1, except that the sum of the thicknesses of the first to third layers after the third layer was applied was 64.6 μm.

[0130] [Experimental Example 1] The negative electrode was dried in a vacuum oven at 130° C. for 12 hours.

[0131] The manufactured negative electrode and 1.7671 cm 2 A lithium (Li) metal thin film cut into a circular shape was used as the positive electrode. A porous polyethylene separator was placed between the positive electrode and the negative electrode, and an electrolyte solution of 1M LiPF6 dissolved in a 7:3 volumetric mixture of methyl ethyl carbonate (EMC) and ethylene carbonate (EC) with 0.5 parts by weight of vinylene carbonate was dissolved was injected to fabricate a lithium coin half-cell.

[0132] The produced batteries were charged and discharged, and the capacity retention rate and electrode expansion rate were evaluated. The results are shown in Table 1 below.

[0133] The first and second cycles were charged and discharged at 0.1 C, and the third to 49th cycles were charged and discharged at 0.5 C. The 50th cycle was completed in a charged state (with lithium in the anode). Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off) Discharge condition: CC (constant current) condition 1.5V

[0134] The capacity retention rate was calculated as follows from the results of one charge / discharge cycle: Capacity retention rate (%) = (49 discharge capacity / 1 discharge capacity) x 100

[0135] The electrode expansion rate was calculated as follows. Electrode expansion rate (%) = (electrode thickness after 50 cycles / initial electrode thickness) x 100

[0136] [Table 1]

[0137] As shown in Table 1, the batteries manufactured in Examples 1 to 6, in which the thickness of the third layer was greater than 0 and less than 1 / 20 of the sum of the thicknesses of the first and second layers, exhibited significantly higher capacity retention and significantly reduced electrode expansion rates compared to Comparative Examples 1 to 5, in which no third layer was formed. Furthermore, in Comparative Examples 6 to 11, in which the third layer was formed thicker than in the Examples, the electrode expansion rate was reduced to some extent, but compared to the thicker third layer, the electrode expansion rate was still relatively higher than in the Examples in which the third layer was formed thinner. Furthermore, Comparative Examples 6 to 11 were found to have poor capacity retention rates due to the thick third layer.

[0138] The battery manufactured in Example 7, in which the silicon-based active material in the second layer was 50 parts by weight based on 100 parts by weight of the active material in the second layer, had a higher capacity retention rate than Comparative Example 1, but a lower capacity retention rate than Example 1, in which the silicon-based active material in the second layer was 0.4 parts by weight to 40 parts by weight based on 100 parts by weight of the active material in the second layer.

[0139] In addition, the battery manufactured in Example 8, in which the content of the aluminum-containing compound was 50 parts by weight based on 100 parts by weight of the composition of the third layer, exhibited a higher capacity retention rate than that of Comparative Example 1, but a lower capacity retention rate than that of Example 1, in which the content of the aluminum compound was 90 parts by weight based on 100 parts by weight of the composition of the third layer.

Claims

1. current collector; a first layer provided on the current collector and including a carbon-based active material; a second layer disposed on the first layer and including a silicon-based active material; and a third layer provided on the second layer and containing aluminum or an aluminum-containing compound; Including, a thickness of the third layer that is greater than 0 and not greater than 1 / 20 of the sum of the thicknesses of the first layer and the second layer;

2. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the carbon-based active material of the first layer is graphite.

3. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the carbon-based active material of the first layer is 80 parts by weight to 100 parts by weight based on 100 parts by weight of the active material in the first layer.

4. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the silicon-based active material of the second layer includes at least one of silicon (Si), silicon oxide, metal-doped silicon oxide, silicon-carbon composite, and silicon-metal alloy.

5. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the silicon-based active material of the second layer is 0.1 to 40 parts by weight based on 100 parts by weight of the active material in the second layer.

6. The aluminum-containing compound of the third layer is aluminum oxide and Al(OH). ３ The negative electrode for a lithium secondary battery according to claim 1 , comprising at least one of:

7. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the content of aluminum or an aluminum compound in the third layer is 90 parts by weight to 100 parts by weight based on 100 parts by weight of the composition of the third layer.

8. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the third layer is provided so as to cover only a part of or the entire second layer.

9. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the first layer and the second layer each further comprise a binder and a conductive material.

10. A lithium secondary battery comprising: the negative electrode according to any one of claims 1 to 9; a separator; and a positive electrode, wherein the third layer of the negative electrode is disposed so as to face the separator.

11. The lithium secondary battery according to claim 10, wherein the separator is a safety reinforced separator (SRS).

12. A battery module comprising the lithium secondary battery according to claim 11.

13. A battery pack comprising the lithium secondary battery according to claim 11.

14. A battery pack comprising the battery module according to claim 12.

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