Anode active material, anode slurry, anode and secondary battery

Abstract

The present invention relates to an anode active material including a silicon carbon composite, a carbon layer provided on at least a portion of the silicon carbon composite, and a coating layer of a catechol derivative or a gallol derivative provided on at least a portion of at least one of the silicon carbon composite and the carbon layer; an anode slurry; an anode including the anode slurry; and a secondary battery including the anode.

Description

[Technical Field]

[0001] The present invention relates to a negative electrode active material, a negative electrode slurry, a negative electrode including the negative electrode slurry, and a secondary battery including the negative electrode.

[0002] This application claims the benefit of the filing date of Korean Patent Application No. 10-2023-0147407, filed with the Korean Intellectual Property Office on October 31, 2023, the entire contents of which are incorporated herein by reference. [Background technology]

[0003] The rapid increase in fossil fuel use has led to an increasing demand for alternative and clean energy, and one of the most actively researched fields in this area is the field of power generation and storage using electrochemical reactions.

[0004] Currently, secondary batteries are a typical example of electrochemical elements that use electrochemical energy, and their range of use is expanding. In recent years, with the increasing technological development and demand for portable devices such as portable computers, mobile phones, and cameras, the demand for secondary batteries as energy sources has rapidly increased. Among these secondary batteries, much research has been conducted on high-energy density, i.e., high-capacity lithium secondary batteries, which have been commercialized and are widely used.

[0005] A secondary battery typically consists of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode contains a negative electrode active material capable of inserting and extracting lithium ions from the positive electrode. Graphite is commonly used as the negative electrode active material in lithium secondary batteries. However, graphite's low capacity per unit mass (372 mAh / g) makes it difficult to increase the capacity of lithium secondary batteries. To address this issue, non-carbon-based negative electrode materials, such as silicon, tin, and their oxides, have been developed to offer higher energy densities than graphite. However, while these non-carbon-based negative electrode materials offer high capacity, they suffer from low initial efficiency, high lithium consumption during the initial charge / discharge process, and significant irreversible capacity loss. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-129017 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention aims to provide an anode active material and an anode slurry that, when applied to a secondary battery, can improve initial efficiency or life characteristics, reduce the viscosity of the slurry, and alleviate the problem of gas generation, as well as an anode and a secondary battery including the same. [Means for solving the problem]

[0008] One embodiment of the present invention provides a negative electrode active material comprising: a silicon carbon composite; a carbon layer disposed on at least a portion of the silicon carbon composite; and a coating layer of a catechol derivative or a gallol derivative disposed on at least a portion of at least one of the silicon carbon composite and the carbon layer.

[0009] One embodiment of the present invention provides a method for manufacturing an anode active material, the method including: forming a carbon layer on at least a portion of a silicon carbon composite; and forming a coating layer of a catechol derivative or a gallol derivative on at least a portion of at least one of the silicon carbon composite and the carbon layer.

[0010] One embodiment of the present invention provides an anode slurry comprising: an anode active material including a silicon carbon composite and a coating layer of a catechol derivative or a gallol derivative provided on at least a portion of the silicon carbon composite; and a catechol derivative or a gallol derivative additive.

[0011] One embodiment of the present invention provides a negative electrode including: a negative electrode current collector; and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, the negative electrode active material layer including the negative electrode slurry or a cured product or polymer thereof.

[0012] One embodiment of the present invention provides a secondary battery including the negative electrode, a separator, and a positive electrode.

[0013] One embodiment of the present invention provides a battery module including the secondary battery, and a battery pack including the battery module.

[0014] One embodiment of the present invention provides a battery pack including the secondary battery. [Effects of the Invention]

[0015] The negative electrode active material according to an embodiment of the present invention can achieve high capacity and high efficiency by using a silicon carbon composite as a core material of the negative electrode active material, and can prevent the problem of gas generation due to contact of silicon with water in an aqueous process by including a carbon layer and a coating layer of a catechol derivative or a gallol derivative.

[0016] Furthermore, the negative electrode slurry according to an embodiment of the present invention can control volumetric expansion by including a negative electrode active material and a catechol derivative or gallol derivative additive. Specifically, the catechol derivative or gallol derivative coating layer in the negative electrode active material and the catechol derivative or gallol derivative additive together form a three-dimensional bond with the binder, thereby increasing the adhesive strength between the negative electrode active material and the binder, thereby suppressing volumetric expansion and improving life characteristics. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will now be described in more detail to aid in understanding the invention.

[0018] The terms and words used in this specification and claims 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 inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0019] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless otherwise clearly indicated in the context.

[0020] It should be understood that in this specification, the terms "comprises," "includes," or "has" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but do not preclude the possible presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0021] In this specification, when a member is said to be located "on" another member, this includes not only when the member is in contact with the other member, but also when another member is present between the two members.

[0022] In this specification, the presence and content of elements in the negative electrode active material can be confirmed by ICP analysis, and the ICP analysis can be performed using an inductively coupled plasma optical emission spectrometer (ICPAES, Perkin-Elmer 7300).

[0023] In this specification, the average particle size (D 50 The average particle size (D) can be defined as the particle size at 50% of the cumulative volume in the particle size distribution curve. 50 ) can be measured, for example, by using a laser diffraction method. The laser diffraction method generally enables measurement of particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0024] The average particle size (D 50 The average particle size (D) of the positive electrode active material particles can be measured using a Microtrac device (manufacturer: Microtrac, model name: S3500) with water and Triton-X100 dispersant. 50 ) can be measured in a refractive index range of 1.5 to 1.7, and the negative electrode active material can be measured under conditions of a refractive index of 1.97 or 2.42. For example, particles can be dispersed in a dispersion medium, introduced into a commercially available laser diffraction particle size analyzer, and irradiated with ultrasonic waves of about 28 kHz at an output of 60 W to obtain a volume cumulative particle size distribution graph, and then the particle size corresponding to 50% of the volume cumulative amount can be measured.

[0025] In this specification, the specific surface area of ​​the negative electrode active material can be measured by the Brunauer-Emmett-Teller (BET) method. For example, it can be measured by the BET 6-point method using a porosimetry analyzer (Belsorp-II mini, Bell Japan Inc.) by nitrogen gas adsorption and flow.

[0026] <Negative electrode active material> According to one embodiment of the present invention, there is provided an anode active material comprising: a silicon carbon composite; a carbon layer disposed on at least a portion of the silicon carbon composite; and a coating layer of a catechol derivative or a gallol derivative disposed on at least a portion of at least one of the silicon carbon composite and the carbon layer.

[0027] The negative electrode active material has a silicon-carbon composite core. The catechol derivative or gallol derivative coating layer is formed after the carbon layer is formed, so it may be formed on the carbon layer or on a surface of the silicon-carbon composite that does not have a carbon layer. The catechol derivative or gallol derivative coating layer may completely surround the carbon layer or may be formed only on a portion of the carbon layer, so that both the carbon layer and the catechol derivative or gallol derivative coating layer can be observed on the surface of the negative electrode active material.

[0028] When the carbon layer and the coating layer of the catechol derivative or gallol derivative are both observed on the surface of the negative electrode active material, the coating layer of the catechol derivative or gallol derivative is located at the outermost layer, whereby the functional groups of the catechol derivative or gallol derivative interact with the functional groups of the binder through hydrogen bonding, thereby improving the life performance.

[0029] Even when exposed silicon is present on the surface of the silicon-carbon composite, the negative electrode active material includes a carbon layer and a coating layer of a catechol derivative or a gallol derivative, thereby blocking contact of the exposed silicon with the outside and improving aqueous processability through a passivation effect.

[0030] The coating layer of the catechol derivative or gallol derivative can preferably form a polymer coating on the surface of at least a portion of the carbon layer on the silicon carbon composite, and the polymer coating has low solubility in water, thereby providing an excellent effect in suppressing gas generation.

[0031] The silicon carbon composite is a composite of Si and C, and contains Si and C (e.g., graphite). For example, peaks of Si and C can be observed by elemental analysis such as XRD or NMR. In this specification, the silicon carbon composite may be expressed as "Si / C." The silicon carbon composite may consist of Si and C that are not bonded to each other, and may contain additional components as needed. For example, the silicon carbon composite may or may not contain silicon carbide, expressed as "SiC." When the silicon carbon composite contains silicon carbide, its content is 3 wt % or less. The silicon carbon composite may exist in a crystalline state, an amorphous state, or a mixture thereof. According to one example, C in the silicon carbon composite may exist in an amorphous state.

[0032] The silicon carbon composite may be a Si / C-based active material.

[0033] The silicon carbon composite may be a composite of silicon and graphite, or may have a structure in which a core of the composite of silicon and graphite is surrounded by graphene or amorphous carbon, etc. The silicon in the silicon carbon composite may be silicon nanoparticles.

[0034] The silicon carbon composite includes porous carbon particles and silicon particles located on the surface or in the internal pores of the porous carbon particles.

[0035] For example, the silicon carbon composite may be manufactured by a method including the steps of: etching carbon-based particles having internal pores to expand the internal pores of the carbon-based particles; and forming silicon particles on the surfaces of the carbon-based particles and in the internal pores of the expanded internal pores.

[0036] The step of expanding the internal pores of the carbon-based particles may be performed in a nitrogen (N2) atmosphere, an oxygen (O2) atmosphere, or an oxygen-containing air atmosphere. Specifically, the flow rate of the oxygen (O2) or oxygen-containing air may be controlled to be 0.1 L / min to 10 L / min.

[0037] 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.

[0038] The pore characteristics of the obtained porous carbon-based particles may vary depending on the conditions for expanding the internal pores of the carbon-based particles.

[0039] The step of forming the silicon particles 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 a silicon coating layer in the form of a film, islands, or a mixture thereof.

[0040] According to one embodiment of the present invention, the catechol derivative comprises one or more selected from dopamine, noradrenaline, and catechin, or a salt thereof or a polymer thereof, and the gallol derivative comprises one or more selected from tannic acid, gallocatechin, and gallocatechin gallate, or a salt thereof or a polymer thereof.

[0041] The catechol derivative may be present in the form of a hydrochloride, for example, dopamine hydrochloride or noradrenaline hydrochloride.

[0042] According to one embodiment of the present invention, the content of the catechol derivative or gallol derivative coating layer is 0.5 parts by weight or more and less than 5 parts by weight, based on 100 parts by weight of the total negative active material. Specifically, the content of the catechol derivative or gallol derivative coating layer may be 0.5 parts by weight or more, 0.6 parts by weight or more, 0.7 parts by weight or more, 0.8 parts by weight or more, 0.9 parts by weight or more, or 1 part by weight or more, based on 100 parts by weight of the total negative active material, and may be less than 5 parts by weight, 4.9 parts by weight, 4.8 parts by weight, 4.7 parts by weight, 4.6 parts by weight, or 4.5 parts by weight.

[0043] When the coating layer of the catechol derivative or gallol derivative satisfies the above range, SiO x By including an appropriate amount of silicon carbon composite, which has a higher capacity than the base active material, it is possible to balance the capacity with the positive electrode active material and prevent the problem of gas generation when silicon comes into contact with water in aqueous processes.

[0044] According to one embodiment of the present invention, the content of the carbon layer is 0.1 to 50 parts by weight based on 100 parts by weight of the total negative electrode active material. Specifically, the content of the carbon layer may be 0.1 to 30 parts by weight, 0.1 to 20 parts by weight, 0.5 to 15 parts by weight, or 1 to 10 parts by weight based on 100 parts by weight of the total negative electrode active material.

[0045] When the range is satisfied, the conductivity of the negative electrode active material is improved, and volume change of the negative electrode active material during charging and discharging of the battery is easily suppressed, thereby improving the life characteristics of the battery.

[0046] The carbon layer can be formed by chemical vapor deposition (CVD) using at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene.

[0047] The carbon layer may include at least one of amorphous carbon and crystalline carbon.

[0048] The crystalline carbon may further improve the conductivity of the negative electrode active material. The crystalline carbon may include at least one selected from the group consisting of fluorene, carbon nanotubes, and graphene.

[0049] The amorphous carbon may be a carbon-based material formed by using at least one carbide or hydrocarbon selected from the group consisting of tar, pitch, and other organic materials as a source in a chemical vapor deposition process.

[0050] The carbonized organic material may be a carbonized organic material selected from the group consisting of sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose, and ketohexose, and combinations thereof.

[0051] The hydrocarbon may be a substituted or unsubstituted aliphatic or alicyclic hydrocarbon, or a substituted or unsubstituted aromatic hydrocarbon. Examples of the aliphatic or alicyclic hydrocarbon include methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, and hexane. Examples of the substituted or unsubstituted aromatic hydrocarbon include benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, and phenanthrene.

[0052] According to one embodiment of the present invention, the average particle size (D 50 ) of the negative electrode active material is 0.1 μm to 30 μm. Specifically, it may be 1 μm to 20 μm, 1 μm to 10 μm, or 2 μm to 10 μm. 50When the particle size satisfies the above range, the dispersion of the active material is appropriate when preparing the negative electrode slurry, the structural stability of the active material during charge and discharge is improved, and the coating failure problem caused by large particles is reduced when coating the electrode. In addition, the problem of large volume expansion / contraction caused by excessively large particle size is prevented, and the problem of reduced initial efficiency caused by excessively small particle size is prevented.

[0053] According to one embodiment of the present invention, the BET specific surface area of ​​the negative electrode active material is 20 m 2 / g or less, e.g., 10m 2 For example, the BET specific surface area of ​​the negative electrode active material is preferably 0.1 m / g or less. 2 / g or more 10m 2 / g or less, e.g., 1m 2 / g~8m 2 / g or 4m 2 / g~6m 2 The specific surface area may be 1 / g. The specific surface area can be measured by the Brunauer-Emmett-Teller (BET) method. For example, it may be measured by the BET 6-point method using a porosimetry analyzer (Belsorp-II mini, Bell Japan Inc.) and a nitrogen gas adsorption / flow method.

[0054] <Method of manufacturing negative electrode active material> A method for manufacturing an anode active material according to an embodiment of the present invention may include forming a carbon layer on at least a portion of a silicon carbon composite; and forming a coating layer of a catechol derivative or a gallol derivative on at least a portion of at least one of the silicon carbon composite and the carbon layer.

[0055] Before or after forming the carbon layer, the particle size of the negative active material may be adjusted by a pulverizing method such as mechanical milling, if necessary.

[0056] The step of forming a carbon layer on the surface of the negative active material may be performed by, for example, injecting a carbon-based source gas, such as methane gas, and performing a heat treatment in a rotary tubular furnace. Specifically, the silicon-based oxide particles are placed in a rotary tubular furnace, and the temperature is increased to 800°C to 1,150°C, 900°C to 1,050°C, or 950°C to 1,000°C at a rate of 3°C / min to 10°C / min, or about 5°C / min. Then, while rotating the rotary tubular furnace, argon gas and a carbon-based source gas are introduced to perform a heat treatment for 30 minutes to 8 hours, thereby forming a carbon layer.

[0057] A coating layer of a catechol derivative or a gallol derivative is then formed on a portion of at least one of the silicon-carbon composite and the carbon layer formed as described above. The coating layer of the catechol derivative or the gallol derivative may be formed by oxidative self-polymerization, in which a polymer is formed by adding the catechol derivative or the gallol derivative to a weakly basic solution. The weakly basic solution may be a solution such as tris-HCl buffer or bicine buffer, and the pH of the weakly basic solution may be 7.5 to 9. Specifically, the lower pH limit of the weakly basic solution may be 7.5, 7.6, 7.7, 7.8, 7.9, or 8.0, and the upper pH limit of the weakly basic solution may be 9.0, 8.9, 8.8, 8.7, 8.6, or 8.5.

[0058] In order for the oxidative self-polymerization reaction to occur smoothly, the content of solids including the catechol derivative or gallol derivative and silicon carbon complex is preferably 0.1% to 5%.

[0059] <Negative electrode slurry> According to one embodiment of the present invention, an anode slurry includes an anode active material including a silicon carbon composite and a coating layer of a catechol derivative or a gallol derivative provided on at least a portion of the silicon carbon composite; and a catechol derivative or a gallol derivative additive.

[0060] According to one embodiment of the present invention, an anode slurry includes an anode active material including a silicon carbon composite, a carbon layer provided on at least a portion of the silicon carbon composite, and a coating layer of a catechol derivative or a gallol derivative provided on at least a portion of at least one of the silicon carbon composite and the carbon layer; and a catechol derivative or a gallol derivative additive.

[0061] The catechol derivative or gallol derivative contained in the coating layer provided on at least a portion of the silicon carbon composite may be the same as or different from the catechol derivative or gallol derivative of the additive.

[0062] The catechol derivative or gallol derivative is used as an additive and as a coating layer provided on at least a portion of the silicon carbon composite, thereby improving the stability of the slurry by preventing a decrease in viscosity due to an interaction between the coating layer and the additive.

[0063] According to one embodiment of the present invention, the content of the catechol derivative or gallol derivative coating layer in the negative electrode active material included in the negative electrode slurry is 0.5 parts by weight or more and less than 5 parts by weight, based on 100 parts by weight of the total negative electrode active material. Specifically, the content of the catechol derivative or gallol derivative coating layer may be 0.5 parts by weight or more, 0.6 parts by weight or more, 0.7 parts by weight or more, 0.8 parts by weight or more, 0.9 parts by weight or more, or 1.0 parts by weight or more, based on 100 parts by weight of the total negative electrode active material, or may be less than 5 parts by weight, 4.9 parts by weight, 4.8 parts by weight, 4.7 parts by weight, 4.6 parts by weight, or 4.5 parts by weight.

[0064] When the coating layer of the catechol derivative or gallol derivative satisfies the above range, SiO x By including an appropriate amount of silicon carbon composite, which has a higher capacity than the base active material, it is possible to balance the capacity with the positive electrode active material and prevent the problem of gas generation when silicon comes into contact with water in aqueous processes.

[0065] According to one embodiment of the present invention, the content of the catechol derivative or gallol derivative additive in the negative electrode slurry is 0.01 to 0.5 parts by weight, based on 100 parts by weight of the total solid content of the negative electrode slurry. Specifically, based on 100 parts by weight of the total solid content of the negative electrode slurry, the content may be 0.02 parts by weight or more, 0.03 parts by weight or more, 0.04 parts by weight or more, or 0.05 parts by weight or more, and may be 0.49 parts by weight or less, 0.48 parts by weight or less, 0.47 parts by weight or less, 0.46 parts by weight or less, or 0.45 parts by weight or less.

[0066] When the content of the catechol derivative or gallol derivative additive satisfies the above range, the volume expansion can be controlled by three-dimensional bonding with the binder, and although the catechol derivative or gallol derivative itself is an insulator, it can also function as a conductive material by changing into a material capable of electrical conduction during the initial charge / discharge process.

[0067] According to one embodiment of the present invention, the negative electrode active material included in the negative electrode slurry comprises the carbon layer between the silicon carbon composite and a coating layer of a catechol derivative or a gallol derivative provided on at least a portion of the silicon carbon composite.

[0068] According to one embodiment of the present invention, the content of the carbon layer is 0.1 to 50 parts by weight based on 100 parts by weight of the total negative electrode active material. Specifically, the content of the carbon layer may be 0.1 to 30 parts by weight, 0.1 to 20 parts by weight, 0.5 to 15 parts by weight, or 1 to 10 parts by weight based on 100 parts by weight of the total negative electrode active material.

[0069] The negative electrode slurry may further include an additional negative electrode active material.

[0070] The additional negative electrode active material may be a compound capable of reversibly inserting and extracting 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 Examples of the negative electrode active material include metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, lithium titanium oxide, and lithium vanadium oxide (0<β<2); 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. Both low-crystalline carbon and high-crystalline carbon may be used as the carbon material. 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.

[0071] The additional negative electrode active material may be a carbon-based negative electrode active material.

[0072] The weight ratio of the negative electrode active material and the additional negative electrode active material contained in the negative electrode slurry may be 10:90 to 90:10, specifically, 10:90 to 50:50.

[0073] The negative electrode slurry may include a solvent for forming a negative electrode slurry. Specifically, the solvent for forming a negative electrode slurry may include at least one solvent selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically distilled water, in order to facilitate dispersion of components.

[0074] The negative electrode slurry according to one embodiment of the present invention further includes a binder and a conductive material.

[0075] The binder may improve the bonding between negative electrode active materials and the adhesive strength between the negative electrode active material and the negative electrode current collector. The binder may be any binder known in the art, and non-limiting examples thereof 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, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and materials in which hydrogen is substituted with Li, Na, Ca, or the like, or various copolymers thereof.

[0076] The 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 10 parts by weight, based on 100 parts by weight of the negative electrode active material layer.

[0077] The conductive material is not particularly limited as long as it does not induce chemical changes in the battery and is conductive, and examples thereof include 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; fluorocarbons; metal powders such as 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.

[0078] <Negative electrode> According to an embodiment of the present invention, a negative electrode may include a negative electrode current collector and a negative electrode active material layer including the negative electrode slurry or a cured or polymerized negative electrode slurry provided on at least one surface of the negative electrode current collector. The negative electrode active material layer may include the negative electrode active material, and the negative electrode active material may include the negative electrode active material described above. The negative electrode active material layer may further include a binder and / or a conductive material.

[0079] The negative electrode current collector is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like. Specifically, a transition metal that easily adsorbs carbon, such as copper or nickel, may be used as the current collector. The thickness of the current collector may be 1 μm to 500 μm, but is not limited thereto.

[0080] <Secondary battery> A secondary battery according to an embodiment of the present invention may include the above-described negative electrode. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

[0081] The positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, or the positive electrode active material layer may include the positive electrode active material.

[0082] The positive electrode current collector is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may typically have a thickness of 3 to 500 μm, and the surface of the current collector may be formed with fine irregularities to enhance adhesion of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0083] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; a lithium iron oxide such as LiFe3O4; 1+c1 Mn 2-c1 O4 (0≦c1≦0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented by the chemical formula LiMnO2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and 0.01≦c2≦0.3 is satisfied); 2-c3 M c3Examples of the lithium manganese composite oxide include, but are not limited to, lithium manganese composite oxides represented by Li2Mn3MO8 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≦c3≦0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); and LiMn2O4, in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion. The positive electrode may be lithium metal (Li-metal).

[0084] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the above-described positive electrode active material.

[0085] 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 has electronic conductivity without causing chemical changes in the battery that is constructed. Specific examples include graphite such as natural graphite and artificial graphite; carbon-containing 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, and the like, and one or more of these may be used alone or in combination.

[0086] The positive electrode binder functions to improve the bonding between positive electrode active material particles and the adhesive strength 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, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof, and one or more of these may be used alone or in combination.

[0087] The positive and negative electrodes may be fabricated by a conventional method for fabricating positive and negative electrodes, except for using the above-described positive and negative electrode active materials. Specifically, they may be fabricated by coating a composition for forming an active material layer, including the active material and, optionally, a binder and a conductive material, on a current collector, followed by drying and rolling. The types and contents of the positive and negative electrode active materials, binder, and conductive material are as described above. The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination. The solvent volume is sufficient to dissolve or disperse the active material, conductive material, and binder, and to provide excellent thickness uniformity when applied to fabricate positive and negative electrodes, taking into account the coating thickness and manufacturing yield of the slurry. Alternatively, the positive electrode and the negative electrode may be manufactured by casting the active material layer-forming composition on a separate support, peeling the active material layer from the support, and laminating the resulting film on a current collector.

[0088] The separator separates the negative electrode and the positive electrode and provides a path for lithium ion migration. Any separator typically used in secondary batteries can be used without particular limitations. In particular, a separator with low resistance to electrolyte ion migration and excellent electrolyte humidification is preferred. Specifically, a porous polymer film, such as a porous polymer film made from a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material can be used, and it can be selectively used in a single-layer or multi-layer structure.

[0089] The electrolyte may be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten inorganic electrolyte that can be used in manufacturing a lithium secondary battery, but is not limited thereto.

[0090] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0091] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methylpyrrolidone, 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, 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.

[0092] In particular, among the carbonate organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, can be preferably used as high-viscosity organic solvents, because they have a high dielectric constant and dissociate lithium salts well. When such cyclic carbonates are mixed in an appropriate ratio with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, an electrolyte having high conductivity can be prepared, and therefore these cyclic carbonates can be used even more preferably.

[0093] 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:

[0094] In addition to the constituent 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, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, 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.

[0095] According to one embodiment of the present invention, there is provided a battery module including the secondary battery as a unit cell, and a battery pack including the same. Also provided is a battery pack including the secondary battery. The battery module and battery pack include the secondary battery having high capacity, high rate characteristics, and high cycle characteristics. The secondary battery can be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0096] Below, preferred examples are presented to help understand the present invention. However, the above examples are merely illustrative of the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present description. It goes without saying that such changes and modifications fall within the scope of the appended claims.

[0097] <Production of negative electrode active material> [Example 1-1: Production of negative electrode active material] A 0.5M sucrose solution was placed in an autoclave and reacted at 180°C for 24 hours to synthesize spherical particles. The resulting carbon-based particles were washed two to three times with ethanol. The carbon-based particles were dried at 100°C for over 12 hours and mixed with KOH in a 1:3 ratio. The mixture was then heated at 800°C for two hours in a nitrogen atmosphere to expand the pores. The mixture was then washed with distilled water and dried at 100°C for over 12 hours. The carbon-based particles were then placed in the hot zone of a CVD reactor and subjected to a flow of SiH4 / H2 = 5 / 95 gas at a flow rate of 50 ml / min at 600°C for two hours to produce a silicon / carbon composite. The silicon / carbon composite was then placed in the hot zone of a CVD reactor and reacted for one hour with methane at 700°C using Ar as a carrier gas, forming a carbon layer on the surface. Then, tannic acid and the silicon / carbon composite were mixed in a weakly basic aqueous solution at a weight ratio of 5:95 and stirred at room temperature for 2 hours to produce a negative electrode active material including a carbon layer and a tannic acid coating layer on the surface of the silicon / carbon composite.

[0098] [Example 1-2: Production of negative electrode active material] A negative active material was prepared in the same manner as in Example 1-1, except that the weight ratio of tannic acid to silicon / carbon composite was 10:90.

[0099] [Example 1-3: Production of negative electrode active material] The negative electrode active material was prepared in the same manner as in Example 1-1, except that the carbon layer was formed at 700° C. for 2 hours.

[0100] [Example 1-4: Production of negative electrode active material] A negative active material was prepared in the same manner as in Example 1-1, except that tannic acid was replaced with dopamine hydrochloride.

[0101] Comparative Example 1-1: Production of negative electrode active material A negative electrode active material was prepared in the same manner as in Example 1-1, except that a coating layer of a catechol derivative or a gallol derivative was not formed during the preparation of the negative electrode active material.

[0102] Comparative Example 1-2: Production of negative electrode active material A negative active material was prepared in the same manner as in Example 1-1, except that the weight ratio of tannic acid to silicon / carbon composite was 30:70.

[0103] [Comparative Example 1-3: Production of negative electrode active material] A negative electrode active material was prepared in the same manner as in Example 1-1, except that a carbon layer was formed on the coating layer of the catechol derivative or gallol derivative.

[0104] [Table 1]

[0105] <Production of negative electrode slurry> [Example 2-1: Preparation of negative electrode slurry] The negative electrode active material prepared in Example 1-1 and artificial graphite were mixed in a weight ratio of 2:8 to prepare a mixed negative electrode active material, carbon black as a conductive material, carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR) as binders, and an additive (tannic acid). These were mixed together with water as a solvent in a weight ratio of mixed negative electrode active material:conductive material:binder (CMC):binder (SBR):additive (tannic acid) = 96.4:1:1:1.5:0.1 to prepare a negative electrode slurry of Example 2-1.

[0106] [Example 2-2: Preparation of negative electrode slurry] A negative electrode slurry of Example 2-2 was prepared in the same manner as in Example 2-1, except that the negative electrode active material of Example 1-2 was used.

[0107] [Example 2-3: Production of negative electrode slurry] A negative electrode slurry of Example 2-3 was prepared in the same manner as in Example 2-1, except that the negative electrode active material of Example 1-3 was used.

[0108] Comparative Example 2-1: Preparation of negative electrode slurry A negative electrode slurry of Comparative Example 2-1 was prepared in the same manner as in Example 2-1, except that the negative electrode active material of Comparative Example 1-1 was used.

[0109] [Comparative Example 2-2: Production of negative electrode slurry] A negative electrode slurry of Comparative Example 2-2 was prepared in the same manner as in Example 2-1, except that the negative electrode active material of Comparative Example 1-2 was used.

[0110] [Comparative Example 2-3: Production of negative electrode slurry] A negative electrode slurry of Comparative Example 2-3 was prepared in the same manner as in Example 2-1, except that the negative electrode active material of Comparative Example 1-3 was used.

[0111] [Reference Example 2-1: Production of negative electrode slurry] A negative electrode slurry of Reference Example 2-1 was prepared in the same manner as in Example 2-1, except that the tannic acid additive was not used during the preparation of the negative electrode slurry.

[0112] [Reference Example 2-2: Production of negative electrode slurry] A negative electrode slurry of Reference Example 2-2 was prepared in the same manner as in Example 2-1, except that 5 parts by weight of tannic acid additive was used in preparing the negative electrode slurry.

[0113] <Evaluation of viscosity and gas generation amount of negative electrode slurry> The prepared negative electrode slurry was stored at room temperature for 2 days, and then its viscosity was measured at 23°C using a rheometer (TA, HR20). Specifically, the relative viscosity (%) of the negative electrode slurry after storing it at room temperature for 2 days, based on the viscosity immediately after preparation, is shown in Table 2 below.

[0114] Viscosity (%) = {Viscosity of negative electrode slurry after 2 days of storage / Viscosity of negative electrode slurry immediately after production} × 100

[0115] Gas generation can be confirmed by placing 20 g of the above-mentioned negative electrode slurry in a pouch, sealing it, storing it in a chamber at 40°C for 7 days, and then measuring the volume of the pouch. The amount of gas generated can be confirmed by placing the sealed pouch in water and measuring the volume of water that has changed. The amount of gas generated is shown in Table 2 below.

[0116] [Table 2]

[0117] <Production of anodes and lithium secondary batteries> [Example 3-1: Production of negative electrode and lithium secondary battery] The negative electrode slurry prepared in Example 2-1 was coated on one side of a copper current collector and dried in a circulating air atmosphere at 60° C. The coated copper current collector was then rolled and punched to a predetermined size to prepare a negative electrode.

[0118] A Li metal was used as a counter electrode, and a polyolefin separator was interposed between the negative electrode and the Li metal. An electrolyte prepared by dissolving 1M LiPF in a solvent prepared by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 30:70 was then injected to prepare the negative electrode and lithium secondary battery of Example 3-1.

[0119] [Example 3-2: Production of negative electrode and lithium secondary battery] The negative electrode and lithium secondary battery of Example 3-2 were manufactured in the same manner as in Example 3-1, except that the negative electrode slurry of Example 2-2 was used.

[0120] [Example 3-3: Production of negative electrode and lithium secondary battery] An anode and a lithium secondary battery of Example 3-3 were fabricated in the same manner as in Example 3-1, except that the anode slurry of Example 2-3 was used.

[0121] Comparative Example 3-1: Production of negative electrode and lithium secondary battery The negative electrode and lithium secondary battery of Comparative Example 3-1 were manufactured in the same manner as in Example 3-1, except that the negative electrode slurry of Comparative Example 2-1 was used.

[0122] Comparative Example 3-2: Production of negative electrode and lithium secondary battery The negative electrode and lithium secondary battery of Comparative Example 3-2 were manufactured in the same manner as in Example 3-1, except that the negative electrode slurry of Comparative Example 2-2 was used.

[0123] [Comparative Example 3-3: Production of negative electrode and lithium secondary battery] An anode and a lithium secondary battery of Comparative Example 3-3 were manufactured in the same manner as in Example 3-1, except that the anode slurry of Comparative Example 2-3 was used.

[0124] Reference Example 3-1: Production of negative electrode and lithium secondary battery The negative electrode and lithium secondary battery of Reference Example 3-1 were manufactured in the same manner as in Example 3-1, except that the negative electrode slurry of Reference Example 2-1 was used.

[0125] Reference Example 3-2: Production of negative electrode and lithium secondary battery The negative electrode and lithium secondary battery of Reference Example 3-2 were manufactured in the same manner as in Example 3-1, except that the negative electrode slurry of Reference Example 2-2 was used.

[0126] <Evaluation of discharge capacity, initial efficiency, and cycle characteristics of secondary batteries> The secondary batteries of Examples 3-1 to 3-3, Comparative Examples 3-1 to 3-3, and Reference Examples 3-1 and 3-2 were charged and discharged, and the discharge capacity, initial efficiency, and cycle characteristics were evaluated. The results are shown in Table 3 below.

[0127] The batteries produced in Examples 3-1 to 3-3, Comparative Examples 3-1 to 3-3, and Reference Examples 3-1 and 3-2 were charged at 25° C. at a constant current (CC) of 0.1 C until the voltage reached 5 mV, and then charged at a constant voltage (CV) until the charge current reached 0.005 C (cut-off current), for the first charge. After leaving the batteries for 20 minutes, they were discharged at a constant current (CC) of 0.1 C until the voltage reached 1.5 V, and the initial efficiency was confirmed.

[0128] Thereafter, the charge / discharge cycle was repeated at 0.5 C up to 40 times, and the capacity retention rate was measured to evaluate the cycle characteristics.

[0129] From the results of one charge / discharge, the initial efficiency (%) was calculated using the following formula.

[0130] Initial efficiency (%) = {discharge capacity of negative electrode active material (mAh / g) / charge capacity of negative electrode active material (mAh / g)} × 100

[0131] The capacity retention rate was calculated using the following formula:

[0132] Capacity retention rate (%)=(40 discharge capacity / 1 discharge capacity)×100

[0133] [Table 3]

[0134] From the results in Tables 2 and 3, it was confirmed that in the case of Comparative Example 3-1, the negative electrode slurry (Comparative Example 2-1) was prepared using a negative electrode active material (Comparative Example 1-1) that did not form a catechol derivative or gallol derivative coating layer, and therefore the gas generation suppression effect of the coating layer was low, resulting in a lower capacity retention rate compared to Examples 3-1 to 3-3.

[0135] In Comparative Example 3-2, the amount of gas generation was small because a coating layer containing 5 parts by weight or more of a catechol derivative or a gallol derivative was added based on 100 parts by weight of the total negative active material, resulting in a very thick coating layer (Comparative Example 1-2). However, since the coating layer was not a material that contributed to the initial efficiency and capacity retention, it was confirmed that the discharge capacity, initial efficiency, and capacity retention were lower than those of Examples 3-1 to 3-3.

[0136] In Comparative Example 3-3, the negative electrode slurry (Comparative Example 2-3) was prepared using a negative electrode active material (Comparative Example 1-3) in which a carbon layer was formed on a coating layer of a catechol derivative or gallol derivative. As a result, the coating layer of the catechol derivative or gallol derivative was unable to properly prevent contact with water, and the gas generation suppression effect of the coating layer was low. As a result, processability was deteriorated, and the capacity retention rate was slightly lower than in Examples 3-1 to 3-3.

Claims

1. a silicon carbon composite; a carbon layer provided on at least a portion of the silicon carbon composite; a coating layer of a catechol derivative or a gallol derivative disposed on at least a portion of at least one of the silicon carbon composite and the carbon layer; A negative electrode active material comprising:

2. the catechol derivative includes one or more selected from dopamine, noradrenaline, and catechin, or a salt thereof or a polymer thereof; The negative electrode active material according to claim 1 , wherein the gallol derivative comprises one or more selected from the group consisting of tannic acid, gallocatechin, and gallocatechin gallate, or a salt or polymer thereof.

3. The negative electrode active material of claim 1 , wherein the coating layer of the catechol derivative or the gallol derivative has an amount of 0.5 parts by weight or more and less than 5 parts by weight, based on 100 parts by weight of the total negative electrode active material.

4. The negative electrode active material of claim 1 , wherein the carbon layer has an amount of 0.1 parts by weight or more and 50 parts by weight or less, based on 100 parts by weight of the total negative electrode active material.

5. The average particle size (D ５０ 5. The negative electrode active material according to claim 1, wherein the thickness of the first electrode is 0.1 μm or more and 30 μm or less.

6. forming a carbon layer on at least a portion of the silicon carbon composite; forming a coating layer of a catechol derivative or a gallol derivative on at least a portion of the silicon carbon composite and at least one of the carbon layers; A method for producing a negative electrode active material, comprising:

7. a negative electrode active material including a silicon carbon composite and a coating layer of a catechol derivative or a gallol derivative provided on at least a portion of the silicon carbon composite; a catechol derivative or gallol derivative additive; a negative electrode slurry comprising:

8. The negative electrode slurry of claim 7 , wherein the content of the catechol derivative or gallol derivative coating layer is 0.5 parts by weight or more and less than 5 parts by weight, based on 100 parts by weight of the total negative electrode active material.

9. The negative electrode slurry of claim 7 , wherein the content of the catechol derivative or gallol derivative additive is 0.01 parts by weight or more and 0.5 parts by weight or less, based on 100 parts by weight of a total solid content of the negative electrode slurry.

10. 8. The negative electrode slurry of claim 7, wherein the negative electrode active material comprises a carbon layer between the silicon carbon composite and a coating layer of a catechol derivative or a gallol derivative provided on at least a portion of the silicon carbon composite.

11. The negative electrode slurry of claim 10 , wherein the carbon layer has an amount of 0.1 parts by weight to 50 parts by weight based on 100 parts by weight of the total negative electrode active material.

12. Binder and A conductive material; The negative electrode slurry of claim 7 further comprising:

13. a negative electrode current collector; a negative electrode active material layer comprising the negative electrode slurry according to any one of claims 7 to 12 or a cured product or polymer thereof, the negative electrode active material layer being provided on at least one surface of the negative electrode current collector; a negative electrode.

14. The negative electrode according to claim 13; A separation membrane; A positive electrode and A secondary battery comprising:

15. A battery module comprising the secondary battery according to claim 14.

16. A battery pack comprising the secondary battery according to claim 14.

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

Images