Anode composition, anode, and lithium secondary battery

Abstract

The present invention relates to a negative electrode composition comprising a silicon-based active material and a carbon-based active material, wherein the content of the silicon-based active material is more than 0 part by weight and not more than 10 parts by weight, based on 100 parts by weight of the total negative electrode active material; the carbon-based active material includes natural graphite and has a total amount of N and O of 200 ppm to 2000 ppm, based on 0.01 g of the natural graphite; and the silicon-based active material includes at least one of a silicon carbon composite and a silicon oxide, and has a total amount of N and O of 0.7% to 3.3% based on 0.01 g of the silicon carbon composite and 30% to 32% based on 0.01 g of the silicon oxide. The present invention also relates to a negative electrode composition, a lithium secondary battery, a battery module, and a battery pack each including the same.

Description

[Technical Field]

[0001] The present application relates to a negative electrode composition, a negative electrode, and a lithium secondary battery.

[0002] This application claims the benefit of the filing date of Korean Patent Application No. 10-2023-0100955, filed with the Korean Intellectual Property Office on August 2, 2023, the entire contents of which are incorporated herein by reference. [Background technology]

[0003] In recent years, with the rapid spread of battery-powered electronic devices, such as mobile phones, laptops, and electric vehicles, as well as power tools and vacuum cleaners, the demand for secondary batteries that are small, lightweight, and have relatively high capacity and / or high output has been rapidly increasing. In particular, lithium secondary batteries, which are lightweight and have high energy density, have attracted attention as power sources for electronic devices. As a result, 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 between the positive electrode and the negative electrode, an electrolyte, an organic solvent, etc. 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] Batteries that use graphite as the negative electrode active material can exhibit a high discharge voltage of 3.6 V, but their capacity is low and there is a limit to how much energy density can be increased.

[0006] In contrast, silicon-based active materials among negative electrode active materials exhibit a higher degree of expansion and contraction during charge and discharge than graphite, and therefore pose a problem of detachment from the negative electrode current collector.

[0007] Therefore, there is a need to develop a negative electrode material that can solve the above problems. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention provides an anode for a lithium secondary battery, which includes graphite and a silicon-based active material including at least one of silicon oxide and silicon carbon composite, and which can improve adhesion between an anode active material layer and an anode current collector, and an anode including the same. Another object of the present invention is to provide a lithium secondary battery including the above anode and having an improved lifespan. [Means for solving the problem]

[0009] One embodiment of the present invention provides a negative electrode composition for a lithium secondary battery, comprising: a negative electrode active material including a silicon-based active material and a carbon-based active material, wherein the content of the silicon-based active material is more than 0 part by weight and not more than 10 parts by weight, based on 100 parts by weight of the total negative electrode active material; the carbon-based active material includes graphite and has a total amount of N and O of 200 ppm to 2000 ppm, based on 0.01 g of the graphite; and the silicon-based active material includes at least one of a silicon carbon composite and a silicon oxide, and has a total amount of N and O of 0.7% to 3.3%, based on 0.01 g of the silicon carbon composite, and a total amount of N and O of 30% to 32%, based on 0.01 g of the silicon oxide.

[0010] According to one embodiment of the present invention, the graphite includes at least one of natural graphite and artificial graphite.

[0011] One embodiment of the present invention provides a negative electrode comprising a negative electrode composition according to the above-described embodiment.

[0012] One embodiment of the present invention provides a lithium secondary battery comprising a negative electrode, a positive electrode, and a separator according to the above-described embodiment.

[0013] One embodiment of the present invention provides a battery module including the lithium secondary battery according to the above-described embodiment.

[0014] One embodiment of the present invention provides a battery pack including the lithium secondary battery according to the above-described embodiment.

[0015] One embodiment of the present invention provides a battery pack including a battery module according to the above-described embodiment. [Effects of the Invention]

[0016] According to an embodiment of the present invention, by using a mixture of a silicon-based active material and a carbon-based active material having N and O contents within a specific range as the negative electrode active material, it is possible to ensure adhesion between the active material and the current collector, as well as effectively prevent the problem of expansion due to a side reaction of the electrolyte, thereby improving cycle performance. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will be described in more detail below to facilitate understanding of the present invention. The present invention may be realized in various different forms and is not limited to the embodiments described herein. In this regard, the terms and words used in the specification and claims should not be interpreted in a limited manner to their ordinary or dictionary meanings, but should be interpreted in a manner 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 describe their invention.

[0018] It should be understood that in this specification, terms such as "comprises," "provides," or "has" specify the presence of embodied features, numbers, steps, components, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0019] Furthermore, when a part such as a layer exists "on" or "above" another part, it does not only mean that it is "directly above" that part, but also includes the case where there is another part between them. In contrast, when a part exists "directly above" another part, it means that there is no other part between them. Furthermore, when a part exists "on" or "above" a reference part, it does not necessarily mean that it is located above or below the reference part, and is not necessarily located "above" or "above" the direction opposite to gravity.

[0020] The terms and words used in this specification should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that are 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.

[0021] As used herein, the singular expression of a term includes the plural expression unless the context clearly indicates otherwise.

[0022] Preferred embodiments of the present invention will be described in detail below. However, the embodiments of the present invention may be modified in various ways, and the scope of the present invention is not limited to the embodiments described below.

[0023] According to one embodiment of the present invention, the negative electrode composition includes a negative electrode active material containing a silicon-based active material and a carbon-based active material, wherein the silicon-based active material is present in an amount of 10 parts by weight or less based on 100 parts by weight of the total negative electrode active material. The carbon-based active material includes graphite and has a total N and O content of 200 ppm to 2000 ppm based on 0.01 g of the graphite. The silicon-based active material includes at least one of a silicon carbon composite and a silicon oxide, and has a total N and O content of 0.7% to 3.3% based on 0.01 g of the silicon carbon composite and a total N and O content of 30% to 32% based on 0.01 g of the silicon oxide.

[0024] As described above, negative electrodes containing silicon-based active materials, including at least one of silicon oxide and silicon-carbon composite, tend to exhibit poorer swelling and adhesion to the current collector than negative electrodes using carbon-based active materials such as graphite as the 100% negative electrode active material due to the material properties of the silicon-based active material. However, the present invention improves dispersibility in the slurry and adhesion between the negative electrode active material layer and the negative electrode current collector by including 10 parts by weight or less of the silicon-based active material per 100 parts by weight of the total negative electrode active material and adjusting the total amount of N and O in the silicon-based active material and carbon-based active material within the above range. In particular, if the oxygen (O) content of the silicon-based active material is too low, the domain size of silicon (Si) increases, which is advantageous in terms of capacity, but the relatively large volume expansion can lead to detachment from the current collector or reduced lifespan. Furthermore, if the nitrogen (N) content of the silicon-based active material is excessively high, it can lead to reduced dispersibility of the slurry in the same amount of aqueous binder and conductive material, reduced conductivity, and therefore reduced adhesion to the current collector and lifespan. However, in embodiments of the present invention, by designing the total amount of N and O in the silicon-based active material and graphite to fall within the above ranges, it is possible to improve dispersibility in the slurry, adhesion to the current collector, and lifespan characteristics. Herein, the N and O content of each material can be analyzed in powder form using an ONH analyzer, for example, an ONH Analyzer (Bruker, G8 Galileo).

[0025] According to one embodiment, the total amount of N and O in the silicon oxide is 160 to 1,500 times, for example, 160 to 1,000 times, or 160 to 875 times the total amount of N and O in the graphite. A content within this range is advantageous for improving dispersibility in a slurry and adhesion to a current collector, thereby improving the life characteristics of a battery.

[0026] According to one embodiment, the total amount of N and O in the silicon carbon composite is 16.5 to 35 times, for example, 16.5 to 25 times, or 16.5 to 21 times the total amount of N and O in the graphite. A content within this range is advantageous for improving dispersibility in a slurry and adhesion to a current collector, thereby improving the life characteristics of a battery.

[0027] According to one embodiment, the natural graphite may have a tap density of 0.9 g / cc or more, specifically, a tap density of 0.9 to 1.2 g / cc. The higher the tap density within the range, the higher the sphericity of the natural graphite, and in this case, the content of N and O impurities may be increased. In this specification, the tap density can be measured using a conventional tap density measuring device, specifically, a TAP-2S manufactured by LOGAN. For example, the tap density may be calculated by placing 40 g of a sample in a container and tapping it 1,000 times.

[0028] In addition, the N and O contents of natural graphite can be controlled by a process such as mining the raw material, acid treatment to remove impurities, and carbonization with pitch after the spheroidization process.

[0029] According to one embodiment, the N and O contents of the silicon-based active material can be controlled by selecting the materials used in the manufacturing process or by controlling the process conditions. For example, the N and O contents can be controlled by maintaining an inert atmosphere during all heat treatment processes included in the manufacturing process, and by whether or not an artificial oxidation process is performed before or after forming a carbon coating layer on the surface of the active material. According to one example, the silicon-based active material can be prepared by mixing Si / SiO2 in a 1:1 ratio in one chamber and evaporating it in a gas state at 1400°C, and evaporating Mg in a gas state at 750°C in another chamber. These materials are then reacted in a gas phase, cooled, and deposited in a bulk state on a plate. The deposited bulk material is then pulverized into small particles by a milling process to form D. 50After grinding to the 5μm level, a carbon coating layer can be formed by performing a CVD process using a carbon coating raw material (methane) under an inert gas atmosphere. At this time, the oxygen can be controlled according to the ratio of SiO2 in the vacuum state raw material of the evaporation and deposition sections.

[0030] According to one embodiment, the silicon-based active material may be contained in an amount of more than 0 parts by weight and not more than 10 parts by weight, for example, 1 part by weight to 10 parts by weight, based on 100 parts by weight of the total negative electrode active material contained in the negative electrode composition.

[0031] According to one embodiment, the carbon-based active material may be present in an amount of 90 parts by weight or more but less than 100 parts by weight, for example, 90 to 99 parts by weight, based on 100 parts by weight of the total negative electrode active material contained in the negative electrode composition. The carbon-based active material may include at least one of natural graphite and artificial graphite. When the carbon-based active material includes both natural graphite and artificial graphite, the weight ratio of the artificial graphite to the natural graphite may be 1:9 to 9:1, for example, 3:7 to 7:3. For example, based on 100 parts by weight of the carbon-based active material, the natural graphite may be present in an amount of 10 to 70 parts by weight; and the artificial graphite may be present in an amount of 30 to 90 parts by weight.

[0032] According to one embodiment, the silicon-based active material may include a silicon carbon composite, a silicon oxide, or both.

[0033] According to one embodiment, the silicon carbon composite may be a Si / C based active material.

[0034] In this specification, the silicon carbon composite is a composite of Si and C and is distinguished from silicon carbide, which is represented as SiC. Silicon carbide does not electrochemically react with lithium, and all performance characteristics, including lifespan, can be measured as zero.

[0035] 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 nanosilicon.

[0036] According to one embodiment, the silicon carbon composite includes porous carbon-based particles and a silicon coating layer located on the surface or in the internal pores of the porous carbon-based particles. The silicon coating layer may be formed by depositing silicon on the porous carbon-based particles using silane gas. If necessary, a carbon layer may be further formed on the surface of the silicon carbon composite. The carbon layer may be formed in accordance with the method for forming a carbon layer on silicon oxide described below.

[0037] According to one embodiment, the silicon carbon composite is produced by the BET method to a surface area of ​​0.5 m 2 / g~10m 2 / g, with a pore volume of 0.005 cm 3 / g~0.03cm 3 The silicon carbon composite may have a pore volume of 0.005 cm3 measured by mercury penetration method, and the pore size measured by BET method may be 10 nm to 20 nm. 3 / g~0.03cm 3 / g.

[0038] According to one embodiment, the silicon carbon composite is 90 The particle size may be 5 μm to 15 μm, and D 50 The particle size may be 1 μm to 10 μm, Dmin may be 1 μm to 3 μm, and Dmax may be 17 μm to 23 μm.

[0039] According to one embodiment, the silicon oxide is SiO x (0≦x<2) may be included.

[0040] The SiO xThe active material containing (0≦x<2) is SiO x It may be silicon oxide particles containing (0<x<2) and pores.

[0041] The aforesaid SiO x (0<x<2) corresponds to a matrix within the aforesaid silicon oxide particles. The aforesaid SiO x (0<x<2) may be in a form containing Si and SiO2, and the aforesaid Si may form a phase. That is, the aforesaid x corresponds to the number ratio of O to Si contained in the aforesaid SiO x (0<x<2). When the aforesaid silicon oxide particles contain the aforesaid SiO x (0<x<2), the discharge capacity of the secondary battery can be improved.

[0042] The aforesaid silicon oxide particles may further contain at least one of a Mg compound and a Li compound. The aforesaid Mg compound and the aforesaid Li compound may correspond to a matrix within the aforesaid silicon oxide particles.

[0043] The aforesaid Mg compound and / or the aforesaid Li compound may be present inside and / or on the surface of the aforesaid SiO x (0<x<2). The initial efficiency of the battery can be improved by the aforesaid Mg compound and / or the aforesaid Li compound.

[0044] The aforesaid Mg compound may contain at least any one selected from the group consisting of Mg silicate, Mg silicide, and Mg oxide. The aforesaid Mg silicate may contain at least any one of Mg2SiO4 and MgSiO3. The aforesaid Mg silicide may contain Mg2Si. The aforesaid Mg oxide may contain MgO.

[0045] In one embodiment of the present specification, the Mg element may be contained in an amount of 0.1% to 9% by weight based on 100% by weight of the total amount of the silicon oxide particles. When the above range is satisfied, the Mg compound can be contained in an appropriate content in the silicon oxide particles, so that it affects the irreversible capacity of the silicon oxide, and the volume change of the silicon oxide particles during charging and discharging of the battery can be easily suppressed, and the discharge capacity and initial efficiency of the battery can be improved.

[0046] 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 one of Li2SiO3, Li4SiO4, and Li2Si2O5. The Li silicide may contain Li7Si2. The Li oxide may contain Li2O.

[0047] 7>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 can be classified 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 in the form of Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and is not limited to the above form.

[0048] In one embodiment of the present specification, the lithium element may be contained in an amount of 0.1 wt % to 20 wt %, or 0.1 wt % to 10 wt %, based on the total amount (100 wt %) of the silicon oxide particles. Specifically, the lithium element may be contained in an amount of 0.5 wt % to 8 wt %, or more specifically, 0.5 wt % to 4 wt %. When the above range is satisfied, the lithium compound can be contained in the silicon oxide particles in an appropriate amount, which can easily suppress volumetric changes of the negative electrode active material during charging and discharging of the battery, thereby improving the discharge capacity and initial efficiency of the battery.

[0049] The Mg or Li element content can be confirmed by ICP analysis. For the ICP analysis, a certain 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 optical emission spectrometer (ICPAES, Perkin-Elmer 7300) is used to measure the intensity of a standard solution (5 mg / kg) prepared at a wavelength specific to Mg or Li, creating a reference calibration curve. The pretreated sample solution and a blank sample are then introduced into the instrument, and their respective intensities are measured to calculate the actual intensities. The concentrations of each component are 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.

[0050] In one embodiment of the present specification, a carbon layer may be provided on the surface and / or inside the pores of the silicon oxide particles. The carbon layer imparts electrical conductivity to the silicon oxide particles, thereby improving the initial efficiency, life characteristics, and capacity characteristics of a secondary battery including a negative electrode active material containing the silicon oxide particles. The total weight of the carbon layer may be 5 wt % to 40 wt % based on 100 wt % of the total amount of the silicon oxide particles.

[0051] In one embodiment of the present specification, the carbon layer may include at least one of amorphous carbon and crystalline carbon.

[0052] D of the silicon-based active material 90 The particle size may be 5 μm to 15 μm, and D 50 The particle size may be 1 μm to 10 μm, Dmin may be 1 μm to 3 μm, and Dmax may be 17 μm to 23 μm. 2 / g~10m 2 / g, and specifically, the specific surface area of ​​silicon oxide is 6 m 2 / g~7m 2 / g, silicon carbon composite is 3m 2 / g~8m 2 / g. In this specification, the specific surface area is measured by the BET method.

[0053] When the above range is satisfied, the active material can be structurally stable during charge and discharge, the problem of an excessively large particle size resulting in an increased level of volume expansion / contraction can be prevented, and the problem of a decrease in initial efficiency due to an excessively small particle size can be prevented.

[0054] In this specification, the average particle size (D 50 The average particle size (D) can be defined as the particle size corresponding to 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 is generally capable of measuring particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0055] According to one embodiment, the graphite may include one or more of natural graphite and artificial graphite.

[0056] The natural graphite refers to graphite that is naturally occurring, and examples thereof include flake graphite, scaly graphite, and soil graphite. Natural graphite has the advantages of being abundant, inexpensive, having a high theoretical capacity and a high compressed density, and being able to achieve high output.

[0057] According to one example, the natural graphite may have a sphericity of 0.9 or more. According to one example, the natural graphite may be spheroidized natural graphite and may have a tap density of 0.9 g / cc or more.

[0058] In this specification, sphericity may be the value obtained by dividing the circumference of a circle having the same area as the projected image by the perimeter of the projected image when a particle is projected. The sphericity can be determined from an SEM image or measured using a particle shape analyzer such as the Sysmex FPIA3000 manufactured by Malvern. Crystal size can also be confirmed by XRD analysis.

[0059] According to one embodiment of the present invention, the negative electrode composition further comprises a water-based binder and a conductive material.

[0060] 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.

[0061] 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.

[0062] According to one embodiment, the aqueous binder may be contained in an amount of 1 wt % to 5 wt %, for example, about 3 wt % to 4 wt %, based on the solid content of the negative electrode composition, and the conductive material may be contained in an amount of 0.1 wt % to 2 wt %, for example, about 1 wt %, based on the solid content of the negative electrode composition.

[0063] One embodiment of the present invention provides a negative electrode comprising a negative electrode composition according to the above-described embodiment.

[0064] Specifically, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the negative electrode active material layer including the negative electrode composition according to the above-described embodiment.

[0065] The negative electrode active material layer may be formed by applying a negative electrode slurry containing the above-described negative electrode composition to at least one surface of a negative electrode current collector, followed by drying and rolling.

[0066] 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 may 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, may be used as the current collector. The thickness of the current collector may be 6 μm to 20 μm, but is not limited to this.

[0067] In particular, when the negative electrode current collector contains Cu, the adhesive strength between the active material and the current collector can be further improved by using an active material having a specific N and O content in the negative electrode active material layer.

[0068] 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.

[0069] One embodiment of the present invention provides a lithium secondary battery comprising a negative electrode, a positive electrode, and a separator according to the above-described embodiment.

[0070] 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.

[0071] 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. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0072] 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 c3 Examples of the lithium manganese composite oxides 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 satisfying 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 Li metal.

[0073] 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.

[0074] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be any material that 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-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.

[0075] The positive electrode binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples of the positive electrode binder 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 binders may be used singly or in combination.

[0076] The separator separates the negative electrode and positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without particular limitation. It is particularly preferable that the separator exhibits low resistance to ion migration and has excellent electrolyte humidifying ability. Specifically, porous polymer films, such as those made from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymeric material may be used, and it may be selectively used as a single-layer or multi-layer structure.

[0077] The lithium secondary battery may further include an electrolyte, which may be used in manufacturing a lithium secondary battery, such as, but not limited to, 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.

[0078] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0079] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, 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.

[0080] 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 with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte having high electrical conductivity can be prepared, and therefore such cyclic carbonates can be more preferably used.

[0081] 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:

[0082] 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, hexamethylphosphoric triamide, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, in order to improve the life characteristics of the battery, suppress a decrease in battery capacity, and improve the discharge capacity of the battery.

[0083] According to another 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. According to yet another embodiment of the present invention, there is provided 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, and therefore 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.

[0084] Hereinafter, the present specification will be described in detail with reference to examples. However, the examples according to the present specification may be modified into various other forms, and the scope of the present application should not be interpreted as being limited to the examples described below. The examples of the present application are provided to more completely explain the present specification to those skilled in the art. [Example]

[0085] Example 1 (1) Manufacturing method of magnesium-containing silicon oxide Si and SiO2 were mixed in a 1:1 molar ratio in crucible 1, and then heated to a sublimation temperature of 1400°C. Metallic magnesium was separately heated and evaporated in crucible 2 between 600°C and 1000°C. Both crucibles were decompressed to a 0.1 torr level. The vapor mixture containing Mg obtained from crucibles 1 and 2 was reacted for 6 hours, and then solidified into a solid phase in a vacuum state at 800°C. The silicon-based active material produced by the above method was pulverized using a ball mill for about 3 to 4 hours, and then D 50 After that, under an inert gas atmosphere of Ar, a CVD device was used to produce particles of 6 μm level. -1 The magnesium-containing silicon oxide was produced by reacting the silicon oxide at 1 L / min for about 5 hours at torr to form a carbon layer on the surface of the silicon active material. The Mg content in the powder was determined to be 8 wt% by ICP-MS analysis.

[0086] (2) Manufacturing of the negative electrode A negative electrode slurry was prepared by mixing the above-prepared magnesium-doped silicon oxide and artificial graphite in a weight ratio of 10:90 as a negative electrode active material, the conductive material including carbon black and SWCNT, and the binder including carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) in a weight ratio of 95.3:1:3.6 with an appropriate amount of distilled water added to make the total solid content about 46 wt%.

[0087] The negative electrode slurry was applied to a Cu metal thin film with a thickness of 20 μm, and then dried in circulating air at 60° C. After rolling, it was dried in a vacuum oven at 130° C. for 1 day, and then cut into 1.4875 cm 2 The negative electrode was then manufactured by punching out a circular piece.

[0088] The total amount of N and O in the artificial graphite and magnesium-containing silicon oxide contained in Example 1 was analyzed using an ONH Analyzer (Bruker, G8 Galileo). The N content of the artificial graphite was measured to be 76 ppm, the O content was measured to be 267 ppm, and the total amount of N and O was measured to be 343 ppm. The N content of the magnesium-containing silicon oxide was measured to be 910 ppm, the O content was measured to be 29.96%, and the total amount of N and O was measured to be 30 wt%.

[0089] (3) Secondary battery manufacturing 1.7671cm 2 A Li metal thin film punched into the shape of a square was used as the positive electrode. A porous polyethylene separator was placed between the positive and negative electrodes, and an electrolyte solution of 1M LiPF6 dissolved in a 7:3 mixture of EMC (ethyl methyl carbonate) and EC (ethylene carbonate) was poured into the separator to fabricate a Li coin half cell.

[0090] <Example 2> Silicon oxide was prepared in the same manner as in Example 1, except that 75 wt% of the metallic magnesium used in Example 1 was used. The Mg content of the product prepared by the method of Example 2 was measured to be 6 wt%. The total amount of N and O in the magnesium-containing silicon oxide prepared in this manner was measured to be 32 wt%, which was 2 wt% more than in Example 1.

[0091] In Example 2, artificial graphite containing 1986 ppm of N and O in total, which is 1643 ppm more than the artificial graphite contained in Example 1, was used.

[0092] In Example 2, a negative electrode and a secondary battery were manufactured in the same manner as in Example 1, except for the negative electrode active material.

[0093] Example 3 (1) Production of porous carbon particles A 0.5M sucrose solution was placed in an autoclave and reacted at 180°C for 24 hours to synthesize spherical particles. After the reaction, the resulting carbon-based particles were washed 3 to 5 times with ethanol. The carbon-based particles, which had been dried at 100°C for 24 hours or more, were mixed with KOH in a 1:3 weight ratio and heated at 800°C for 3 hours in a nitrogen atmosphere to expand the pores. The particles were then washed with distilled water and dried at 80°C for 12 hours or more to produce porous carbon particles.

[0094] (2) Silicon deposition and carbon composite Silane gas was injected into a chemical vapor deposition (CVD) reactor at a flow rate of 40 mL / min to 110 mL / min, and the reactor was heated at a rate of 10°C / min to 15°C / min at a temperature below 800°C for approximately 3 hours to produce a negative electrode active material in which silicon was deposited on porous carbon particles. The silicon-deposited porous carbon particles were then treated using a CVD apparatus under an inert Ar atmosphere by injecting ethylene (C2H4) gas for 10 minutes. -1 Silicon carbon composites were prepared by reacting the silicon-based active material at 700°C and torr for approximately 5 hours at a rate of 1 L / min to form a carbon layer on the surface of the silicon-based active material. The silicon carbon composites prepared in this manner were analyzed to contain 0.2 wt% N and 0.5 wt% O.

[0095] An anode and a secondary battery were manufactured in the same manner as in Example 1, except that the silicon carbon composite prepared in Example 3 was used instead of silicon oxide.

[0096] Example 4 An anode active material was prepared in the same manner as in Example 3, except that it was artificially oxidized after silicon deposition and carbon composite formation. The oxidation was carried out by creating an atmosphere of 90% or more Ar with a balance gas of less than 10% O2 and reacting at 1,000°C for 3 hours. The degree of oxidation was determined by N / O analysis to be 1.8 wt% oxygen in the entire silicon carbon composite. Using the method of Example 4, the silicon carbon composite was analyzed to contain 1.5 wt% N and 1.8 wt% O.

[0097] In Example 4, the artificial graphite used in Example 2 was used as the artificial graphite.

[0098] In Example 4, a negative electrode and a secondary battery were manufactured in the same manner as in Example 1, except for the negative electrode active material.

[0099] <Comparative Example 1> A negative electrode active material, a negative electrode, and a secondary battery were produced in the same manner as in Example 1, except that Mg was not included.

[0100] The total N / O content of the graphite and silicon oxide contained in Comparative Example 1 was analyzed in the same manner as in Example 1. The total amount of N and O in the graphite contained in Comparative Example 1 was the same as in Example 1, and the total amount of N and O in the magnesium-free silicon oxide was measured to be 35 wt%, 5% more than in Example 1.

[0101] <Comparative Example 2> A negative electrode active material, a negative electrode, and a secondary battery were manufactured in the same manner as in Example 3, except that the temperature for forming the carbon layer on the surface was 800°C.

[0102] It was confirmed by XRD analysis that silicon carbide was formed in the negative electrode active material prepared by this method.

[0103] The total amount of N and O in the silicon carbon composite produced by the method of Comparative Example 2 was analyzed to be 0.4 wt%. The graphite contained in Comparative Example 2 was the same as that in Example 1.

[0104] <Comparative Example 3> In Comparative Example 2, a negative electrode active material, a negative electrode, and a secondary battery were manufactured in the same manner as in Comparative Example 2, except that an additional oxidation process was performed after forming a carbon coating layer on the surface.

[0105] XRD analysis of the negative electrode composition prepared by this method confirmed that silicon carbide was formed.

[0106] The silicon carbon composite produced by the method of Comparative Example 3 was analyzed to contain 2 wt% N and 3 wt% O. The graphite contained in Comparative Example 3 was the same as the graphite in Example 1.

[0107] <Comparative Example 4> A negative electrode and a secondary battery were manufactured in the same manner as in Example 1, except that in the negative electrode manufacturing process, silicon oxide or silicon carbon composite was not used as the negative electrode active material, and artificial graphite was used 100%.

[0108] [Table 1]

[0109] The negative electrode active materials and lithium secondary batteries used in the examples and comparative examples were evaluated as follows, and the results are shown in Table 2 below.

[0110] <Particle size analysis> The particle size of the negative electrode active material was analyzed by laser diffraction particle size analysis using a Malvern device.

[0111] <Discharge capacity, initial efficiency, capacity retention rate> 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

[0112] The discharge capacity (mAh / g) and initial efficiency (%) were calculated from the results of one charge / discharge. Specifically, the initial efficiency (%) was calculated as follows: Initial efficiency (%) = (single discharge capacity / single charge capacity) x 100%

[0113] The capacity retention rate was calculated as follows. Capacity retention rate (%) = (49 discharge capacity / 1 discharge capacity) × 100%

[0114] <Evaluation of slurry dispersibility> The negative electrode active material and distilled water were mixed in a weight ratio of 20:80, ultrasonicated for 5 minutes, and then left for 10 minutes. max The mixture was passed through a mesh having a diameter corresponding to the size of 1. The active material remaining on the mesh was dried in an oven at 80° C. for more than half a day, and then its weight was measured.

[0115] Dispersibility was calculated as follows:

number

[0116] W t means the total weight of the negative electrode active material contained in the mixture, W r means the weight of the negative electrode active material that did not pass through the mesh when the mixture was passed through the mesh.

[0117] <Evaluation of adhesive strength> The adhesive strength test was performed using a 90-degree peel tester from IMADA, INC. The electrode was attached to a glass slide using double-sided tape. The entire electrode length was 11 cm. The portion of the current collector without active material was approximately 1 cm long, and this portion was fixed to a load cell. The force applied to the load cell was measured until the electrode detached, and the average value was calculated when the force applied to the load cell stabilized.

[0118] [Table 2]

[0119] As shown in Table 2, the electrodes (Examples 1 to 4) in which silicon oxide or silicon carbon composite satisfying the total amount of N and O of the present invention is mixed with graphite exhibit superior adhesion to the current collector, aqueous dispersibility, and life characteristics compared to the electrode containing only graphite (Comparative Example 4) or the electrodes containing silicon oxide or silicon carbon composite with a total amount of N and O outside the range (Comparative Examples 1 to 3). As a result, the discharge capacity, initial efficiency, and capacity retention rate of the lithium secondary batteries manufactured in Examples 1 to 4 are superior to those of Comparative Examples 1 to 4.

Claims

1. a negative electrode active material including a silicon-based active material and a carbon-based active material; The content of the silicon-based active material is more than 0 parts by weight and 10 parts by weight or less based on 100 parts by weight of the total negative electrode active material, The carbon-based active material contains graphite and has a total amount of N and O of 200 ppm or more and 2000 ppm or less based on 0.01 g of the graphite, the silicon-based active material comprises at least one of a silicon carbon composite and a silicon oxide, and the silicon carbon composite has a total amount of N and O of 0.7% to 3.3% based on 0.01 g of the silicon carbon composite, and the silicon oxide has a total amount of N and O of 30% to 32% based on 0.01 g of the silicon oxide.

2. The negative electrode composition according to claim 1 , wherein the graphite comprises at least one of natural graphite and artificial graphite.

3. 3. The negative electrode composition according to claim 2, wherein the total amount of N and O in the silicon oxide is 160 to 1,500 times the total amount of N and O in the graphite.

4. 3. The negative electrode composition according to claim 2, wherein the total amount of N and O in the silicon carbon composite is 16.5 to 35 times the total amount of N and O in the graphite.

5. The silicon oxide is SiO ｘ The negative electrode composition of claim 1 , wherein (0<x<2) and Mg is included.

6. The negative electrode composition of claim 5 , wherein the Mg content is more than 0 wt % and not more than 9 wt % based on 100 parts by weight of the silicon oxide.

7. The negative electrode composition according to claim 1 , further comprising a water-based binder and a conductive material.

8. 8. The negative electrode composition according to claim 7, wherein the aqueous binder is contained in an amount of 1 wt % to 5 wt % based on the solid content of the negative electrode composition, and the conductive material is contained in an amount of 0.1 wt % to 2 wt % based on the solid content of the negative electrode composition.

9. An anode comprising the anode composition of claim 1 .

10. 10. The negative electrode according to claim 9, wherein the negative electrode comprises: a negative electrode current collector; and a negative electrode active material layer provided on at least one surface of the negative electrode current collector and including the negative electrode composition, wherein the negative electrode current collector contains Cu.

11. A lithium secondary battery comprising the negative electrode according to claim 9, a positive electrode, and a separator.

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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