Anode active material, manufacturing method therefor, and anode and secondary battery comprising same

Abstract

The present invention relates to an anode active material comprising a composite, which includes a carbon matrix and silicon particles dispersed in the carbon matrix, wherein the silicon particle includes a film including SiOx(0<x≤2) on the surface thereof, and the peak area ratio of SiOx(0<x≤2) / Si according to X-ray photoelectron spectroscopy is 1.5-3.5.

Description

Negative active material, method for producing same, negative electrode and secondary battery including same

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority from Korean Patent Application No. 10-2024-0072744, filed June 3, 2024, the entire contents of which are incorporated herein by reference.

[0003]

[0004] Technology field

[0005] The present invention relates to a negative electrode active material, a method for producing the same, and a negative electrode and secondary battery including the same.

[0006]

[0007] Recently, as the application areas of lithium secondary batteries have rapidly expanded to include not only power supply for electronic devices such as electric, electronic, communication, and computer devices, but also power storage for large-area devices such as automobiles and power storage devices, the demand for lithium secondary batteries with high capacity, high output, and high stability is increasing.

[0008] In general, a lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte, an organic solvent, etc. In addition, the positive electrode and the negative electrode may have an active material layer including a positive electrode active material or a negative electrode active material formed on a current collector. In general, a lithium-containing metal oxide such as LiCoO2 or LiMn2O4 is used as the positive electrode active material, and accordingly, a carbon-based active material or a silicon-based negative electrode active material that does not contain lithium is used as the negative electrode active material.

[0009] Among the above-mentioned negative electrode active materials, silicon-based negative electrode active materials are notable for their approximately 10-fold higher capacity than carbon-based negative electrode active materials. This high capacity allows for high energy density even with thin electrodes, offering the advantage of achieving high energy density. However, silicon-based negative electrode active materials are not widely used due to problems such as volume expansion during charge and discharge, resulting cracking / damage to active material particles, and reduced lifespan characteristics.

[0010] Meanwhile, silicon / carbon (Si / C) composites, which are being studied as negative electrode active materials for lithium secondary batteries, are attracting attention as high-capacity negative electrode materials because they have a higher theoretical capacity (2,000 to 2,400 mAh / g) than graphite. However, the Si / C negative electrode active material is mainly composed of amorphous nanoparticles of silicon and a carbon support that acts as a matrix buffer, so an aqueous slurry must be prepared as a method for coating it on a copper current collector. However, in the process of preparing such an aqueous slurry, hydrogen gas is generated as a result of the reaction between silicon and water, and this hydrogen gas generation can deteriorate the characteristics of the negative electrode film, and the viscosity also tends to decrease, so the decrease in capacity and lifespan caused by the membrane characteristics are obstacles to the use of silicon-based negative electrodes.

[0011] (Patent Document 1) CN 104091952 A

[0012]

[0013] The problem to be solved by the present invention is to improve the coating stability and processability of silicon / carbon negative electrode active materials by improving the issues of hydrogen gas generation and viscosity reduction.

[0014]

[0015] The present invention provides a negative electrode active material, a method for producing the same, and a negative electrode and secondary battery including the same.

[0016] (1) The present invention comprises a composite comprising a carbon matrix and silicon particles dispersed within the carbon matrix, wherein the silicon particles have SiOx(0) on their surface. <x≤2)를 포함하는 막을 포함하며, X선 광전자 분광법에 의한 SiOx(0<x≤2) / Si의 피크 면적비는 1.5 이상 3.5 이하인 음극 활물질을 제공한다.

[0017] (2) The present invention provides a negative electrode active material in (1) above, wherein the peak area ratio of CC / CO of carbon in the complex by X-ray photoelectron spectroscopy is 0.4 or more and 1.3 or less.

[0018] (3) The present invention provides a negative electrode active material in the above (1) or (2), wherein the average particle diameter (D50) of the silicon particles is 1 nm or more and 50 nm or less.

[0019] (4) The present invention provides a negative electrode active material in any one of the above (1) to (3), wherein the average thickness of the film is 0.1 nm or more and 20 nm or less.

[0020] (5) The present invention provides a negative electrode active material according to any one of the above (1) to (4), wherein the average particle diameter of the negative electrode active material is 1 ㎛ or more and 100 ㎛ or less.

[0021] (6) The present invention provides a negative electrode active material according to any one of the above (1) to (5), wherein the silicon particles include an amorphous phase.

[0022] (7) The present invention provides a negative electrode active material according to any one of the above (1) to (6), wherein the negative electrode active material includes a carbon coating layer located on the surface of the composite.

[0023] (8) The present invention provides a method for manufacturing a negative electrode active material, comprising the steps of: (S1) preparing a mixed solution by immersing a Si / C negative electrode active material in an organic solvent and stirring; (S2) placing the mixed solution in an autoclave reactor, sealing it, and allowing it to stand for 10 to 15 hours at a temperature of 100°C to 200°C; (S3) cooling the mixed solution that has been allowed to stand in (S2) to room temperature while stirring it for a second time; and (S4) washing and drying the powder obtained by filtering the mixed solution.

[0024] (9) The present invention provides a method for manufacturing a negative electrode active material, wherein the Si / C negative electrode active material comprises a composite including a carbon matrix and silicon particles dispersed within the carbon matrix, in the above (8).

[0025] (10) The present invention provides a method for producing a negative electrode active material, wherein in the above (8) or (9), the organic solvent includes dimethyl sulfoxide (DMSO).

[0026] (11) The present invention provides a method for manufacturing a negative electrode active material, wherein the temperature of the step (S2) is 150°C or more and 190°C or less in any one of the above (8) to (10).

[0027] (12) The present invention provides a negative electrode comprising a conductive metal current collector and a negative electrode active material layer provided on at least one surface of the current collector, wherein the negative electrode active material layer comprises a negative electrode active material according to any one of (1) to (6).

[0028] (13) The present invention provides a lithium secondary battery including a negative electrode according to (12); a positive electrode; and a separator and electrolyte interposed between the positive electrode and the negative electrode.

[0029]

[0030] The negative active material of the present invention forms a film on the surface of silicon particles, increases the thickness of the film, and changes the composition, thereby suppressing contact between silicon particles and water and thus suppressing hydrogen gas generation.

[0031] In addition, the negative active material of the present invention is manufactured using an organic solvent, thereby suppressing the generation of hydrogen gas and increasing process stability, and improving the issue of lowering viscosity and increasing coating stability.

[0032] In addition, when the negative electrode active material of the present invention is used as a negative electrode in a secondary battery, it can improve storage stability and suppress the phenomenon of deterioration in initial capacity and efficiency.

[0033]

[0034] Hereinafter, the present invention will be described in more detail to facilitate understanding. The terms and words used in this specification and claims should not be interpreted based on their conventional or dictionary meanings. Based on the principle that the inventor can appropriately define the concepts of terms to best explain his or her invention, they should be interpreted in a way that aligns with the technical spirit of the present invention.

[0035] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0036] In this specification, it should be understood that the terms “include,” “comprising,” or “having” are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0037]

[0038] Negative active material

[0039] The present invention comprises a composite comprising a carbon matrix; and silicon particles dispersed within the carbon matrix, wherein the silicon particles have a surface having SiOx(0 <x≤2)를 포함하는 막을 포함하며, X선 광전자 분광법에 의한 SiOx(0<x≤2) / Si의 피크 면적비는 1.5 이상 3.5 이하인 음극 활물질을 제공한다.

[0040] The negative active material of the present invention can reduce side reactions of the electrolyte by minimizing direct exposure of the silicon to the electrolyte by dispersing the silicon particles within the carbon matrix. In addition, the carbon matrix can serve as a support that can alleviate volume expansion during charge and discharge of the secondary battery by spatially restricting the silicon particles, thereby alleviating problems such as electrical short circuits between silicon particles or from the current collector. In addition, since the negative active material of the present invention is formed in a form in which the silicon particles are dispersed within the carbon matrix rather than simply attached to the carbon particles, it can contain a large amount of silicon, and thus high capacity and lifespan characteristics can be improved.

[0041] Meanwhile, in order to coat the negative electrode active material (Si / C active material) formed by dispersing silicon particles in a carbon matrix on a copper current collector, an aqueous negative electrode slurry must be prepared. However, during the preparation process, silicon and water react to generate hydrogen gas, which may result in a decrease in battery capacity and a shortened lifespan. Therefore, the inventor of the present invention has developed a negative electrode active material that can prevent direct contact between silicon particles and water, suppress the generation of hydrogen gas, and have high capacity, lifespan, and efficiency by stirring and heat-treating the negative electrode active material in an organic solvent to form a type of oxide film on the surface of the silicon particles, and changing the thickness, density, and composition of the oxide film.

[0042] According to one embodiment of the present invention, the weight ratio of carbon and silicon in the negative electrode active material may be 1: 0.5 to 1.5, and for example, the weight ratio may be 1: 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, 0.9 or more, 1.0 or more, 1.5 or less, 1.4 or less, 1.3 or less, 1.2 or less, or 1.1 or less. When the weight ratio is satisfied, the structural stability of the negative electrode active material during charge and discharge can be improved, the phenomenon of the volume expanding and contracting greatly as the particle size becomes excessively large can be suppressed, and the initial efficiency can be maintained at an excellent level.

[0043] The carbon matrix of the present invention may include one or more carbon materials selected from the group consisting of natural graphite, artificial graphite, soft carbon, hard carbon, pitch carbide, calcined coke, graphene, carbon nanotubes, and combinations thereof. The carbon material may be carbonized through a carbonization process to include crystalline carbon, amorphous carbon, or a combination thereof.

[0044] In addition, the silicon particles of the present invention may include Si (silicon), and specifically may be made of Si. Accordingly, the capacity of the secondary battery may increase. In addition, the average particle diameter (D50) of the silicon particles may be 1 nm or more and 50 nm or less, and for example, 1 nm or more, 2 nm or more, 3 nm or more, 5 nm or more, 7 nm or more, 10 nm or more, 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, or 15 nm or less. When the average particle diameter of the silicon particles satisfies the above range, the nano-sized silicon particles are not easily broken during battery charging and discharging, and lithium insertion and de-insertion can be effectively performed. The average particle diameter (D 50) can be defined as the particle size corresponding to 50% of the volume accumulation in the particle size distribution curve. The average particle size (D 50 ) can be measured, for example, using a laser diffraction method. The laser diffraction method can generally measure particle sizes from the submicron range to several millimeters, and can obtain results with high reproducibility and high resolution.

[0045] According to one embodiment of the present invention, the silicon particles may include an amorphous phase. By including an amorphous phase, the silicon particles may exhibit excellent life performance and initial efficiency.

[0046] The present invention can include a carbon coating layer on the surface of the composite, and can prevent direct contact between the composite surface and water during the preparation of an aqueous slurry, and can more effectively suppress hydrogen gas. The carbon coating layer can be an amorphous carbon coating layer. For example, the carbon coating layer can be formed by carbonizing a carbon precursor by heat treatment on the surface of the composite, and can be formed using either a dry or wet mixing method. Specifically, the carbon coating layer may be formed by chemical vapor deposition (CVD) using one or more hydrocarbon gases selected from the group consisting of gases obtained by vaporizing a carbon precursor that is liquid at room temperature, such as methane, ethane, propane, ethylene, acetylene, and toluene, or may be formed using amorphous carbon precursors, such as resins such as phenol resin, naphthalene resin, polyvinyl alcohol resin, urethane resin, polyimide resin, furan resin, cellulose resin, epoxy resin, and polystyrene resin, coal pitch, petroleum pitch, tar, or low molecular weight heavy oils. The carbon coating layer may be included in the negative electrode active material in an amount of 0.1 wt% to 10 wt%, for example, 0.1 wt% or more, 0.5 wt% or more, 1 wt% or more, 2 wt% or more, 3 wt% or more, 4 wt% or more, 5 wt% or more, 10 wt% or less, 9 wt% or less, 8 wt% or less, or 7 wt% or less. In addition, the thickness of the carbon coating layer may be 1 nm or more and 1 ㎛ or less, for example, 1 nm or more, 10 nm or more, 50 nm or more, 100 nm or more, 200 nm or more, 300 nm or more, 400 nm or more, 1000 nm or less, 900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less, or 500 nm or less. When the content and thickness of the carbon coating layer are within the above range, the carbon coating layer is preferable in that it can control the volume expansion of silicon-based oxide particles at an excellent level while preventing side reactions with the electrolyte.

[0047] The negative active material of the present invention is SiOx(0) on the surface of the silicon particles. <x≤2)를 포함하는 막을 포함할 수 있다. 상기 막은 상기 복합체와 유기 용매에 교반 및 열처리하여 형성될 수 있다. 상기 막은 상기 실리콘 입자의 표면 상에 배치되며, 실리콘 입자의 표면 전부 또는 적어도 어느 일부에 피복되어 형성될 수 있다.

[0048] The above film may be formed by natural oxidation of silicon particles, but in the case of the present invention, the thickness, density, and composition of the film can be controlled by stirring and heat-treating the complex in an organic solvent to form an optimal film. Specifically, the density and thickness of the film can form a trade-off relationship between the outgassing of hydrogen gas and the capacity and efficiency of the battery, and the film formed on the surface of the silicon particles can be SiOx(0 <x≤2)을 포함하며, 본 발명은 상기 복합체를 유기 용매에 혼합하여 상기 막의 밀도 및 두께를 제어함으로써, 수소 가스의 발생량과 방전용량 및 초기 효율 간의 최적의 음극 활물질을 제공할 수 있다.

[0049] According to one embodiment of the present invention, the average thickness of the film may be 0.1 nm or more and 20 nm or less. For example, the average thickness of the film may be 0.1 nm or more, 0.3 nm or more, 0.5 nm or more, 1 nm or more, 2 nm or more, 3 nm or more, 4 nm or more, 5 nm or more, 6 nm or more, 7 nm or more, 8 nm or more, 9 nm or more, 10 nm or more, 20 nm or less, 19 nm or less, 18 nm or less, 17 nm or less, 16 nm or less, 15 nm or less, 14 nm or less, 13 nm or less, 12 nm or less, or 11 nm or less. When the average thickness of the film satisfies the above range, the amount of hydrogen gas generated per unit mass of active material can be effectively reduced, while excessive volume change of silicon particles can be suppressed, and further, the discharge capacity and initial efficiency of the battery can be maintained at excellent levels.

[0050]

[0051] In addition, the negative active material of the present invention is SiOx(0) by X-ray photoelectron spectroscopy (XPS). <x≤2) / Si의 피크 면적비는 1.5 이상 3.5 이하일 수 있다. 예시적으로, 본 발명의 음극 활물질의 상기 SiOx(0<x≤2) / Si의 피크 면적비는 1.50 이상, 1.70 이상, 1.75 이상, 1.78 이상, 1.80 이상, 1.85 이상, 1.90 이상, 1.95 이상, 2.00 이상, 2.05 이상, 2.10 이상, 2.15 이상, 2.20 이상, 2.25 이상, 2.30 이상, 2.35 이상, 2.38 이상, 3.50 이하, 3.45 이하, 3.40 이하, 3.35 이하, 3.30 이하, 3.25 이하, 3.20 이하, 3.15 이하, 3.10 이하, 3.05 이하, 3.00 이하, 2.95 이하, 2.90 이하, 2.85 이하, 2.80 이하일 수 있다. 한편, 상기 XPS에 의한 피크 면적비를 통해 각 원소 물질의 함량을 도출할 수 있다. 통상의 Si / C 음극 활물질의 경우, SiOx(0<x≤2) / Si의 피크 면적비는 1.5 미만일 수 있고, 이는 실리콘 입자가 대기 중 자연적으로 산화되어 생성된 SiOx(0<x≤2)를 포함하는 산화막에 의한 것이라 예측될 수 있다. 다만, 상기 통상의 SiOx(0<x≤2) / Si의 피크 면적비 범위에 해당되는 경우, 즉, 상기 SiOx(0<x≤2) / Si의 피크 면적비가 본 발명의 상기 수치 범위를 벗어나는 경우, 상기 산화막이 실리콘 입자와 물과의 접촉을 억제하기에 부족하며, 이에, 이차 전지의 수명 특성이 저하되는 문제점을 가질 수 있다.

[0052] That is, the present invention relates to a negative electrode active material that changes the composition, thickness, and density of an oxide film on the surface of a silicon particle by stirring and heat-treating a Si / C negative electrode active material in an organic solvent and controls this, thereby effectively preventing contact between silicon particles and water and suppressing the generation of hydrogen gas, while at the same time exhibiting excellent initial efficiency, discharge capacity, and lifespan characteristics.

[0053] According to one embodiment of the present invention, the peak area ratio of CC / CO by X-ray photoelectron spectroscopy of carbon in the complex may be 0.4 or more and 1.3 or less. Here, CC refers to a carbon-carbon bonded functional group, and CO refers to a carbon-oxygen bonded functional group. CO refers to all functional groups bonded to carbon and oxygen, such as CO, C=O, OC=O, (OC=O)-O, etc. As described above, the negative electrode active material of the present invention can increase the bonding between carbon and oxygen in the complex by stirring and heat-treating the negative electrode active material in an organic solvent. Accordingly, before treating the negative active material with an organic solvent, the peak area ratio of CC / CO may be greater than 1.3, but the peak area ratio of CC / CO of the negative active material of the present invention may be 1.3 or less, and for example, 0.40 or more, 0.45 or more, 0.5 or more, 0.55 or more, 0.6 or more, 0.65 or more, 0.7 or more, 1.30 or less, 1.27 or less, 1.25 or less, 1.23 or less, 1.20 or less, 1.19 or less, 1.17 or less, 1.15 or less, 1.13 or less, 1.10 or less, 1.08 or less, 1.05 or less, 1.03 or less, 1.00 or less, 0.97 or less, 0.95 or less, 0.93 or less, 0.90 or less, 0.87 or less, 0.85 or less, It can be less than 0.82, less than 0.80.

[0054] According to one embodiment of the present invention, the average particle diameter of the negative electrode active material may be 1 ㎛ or more and 100 ㎛ or less. For example, the average particle diameter of the negative electrode active material may be 1 ㎛ or more, 2 ㎛ or more, 3 ㎛ or more, 5 ㎛ or more, 7 ㎛ or more, 10 ㎛ or more, 15 ㎛ or more, 20 ㎛ or more, 25 ㎛ or more, 30 ㎛ or more, 35 ㎛ or more, 100 ㎛ or less, 90 ㎛ or less, 85 ㎛ or less, 80 ㎛ or less, 70 ㎛ or less, 60 ㎛ or less, 50 ㎛ or less, or 40 ㎛ or less. When the average particle diameter of the negative electrode active material satisfies the above range, the structural stability of the active material during charge and discharge can be improved, the phenomenon of the volume expanding and contracting greatly as the particle diameter becomes excessively large can be suppressed, and the initial efficiency can be maintained at an excellent level.

[0055] Meanwhile, the average particle diameter of the negative active material can be measured using a laser diffraction method.

[0056]

[0057] Method for manufacturing negative electrode active material

[0058] The present invention provides a method for producing a negative electrode active material, comprising the steps of (S1) preparing a mixed solution by immersing a Si / C negative electrode active material in an organic solvent and stirring it, (S2) placing the mixed solution in an autoclave reactor, sealing it, and allowing it to stand for 10 to 15 hours at a temperature of 100°C to 200°C, (S3) cooling the mixed solution that has been allowed to stand in (S2) to room temperature while stirring it a second time, and (S4) washing and drying the powder obtained by filtering the mixed solution.

[0059] According to one embodiment of the present invention, the Si / C negative electrode active material may include a composite including a carbon matrix and silicon particles dispersed within the carbon matrix. The contents of the composite and the Si / C negative electrode active material have been described above.

[0060] In addition, according to one embodiment of the present invention, the organic solvent may include dimethyl sulfoxide (DMSO). Conventionally, an oxide film is formed on the surface of silicon particles by natural oxidation in the air, or in order to intentionally form an oxide film on the surface of silicon particles, a simple heat treatment in oxygen or air or a milling process is used. However, in the case of natural oxidation or the conventional method of forming an oxide film, since an organic solvent is not mixed, it is impossible to control the composition, thickness, and density contained in the oxide film, and it is impossible to manufacture an anode active material having optimal performance between outgassing of hydrogen gas and discharge capacity and efficiency of the battery.

[0061] Accordingly, in the case of the method for manufacturing a negative electrode active material of the present invention, by performing an oxidation treatment on the negative electrode active material using an organic solvent, for example, dimethyl sulfoxide, the thickness, density, and composition of the film on the surface of the silicon particles can be controlled, so that it is possible to manufacture a negative electrode active material having optimal performance between outgassing of hydrogen gas and discharge capacity and efficiency of the battery. Here, the autoclave reactor is a high-pressure sterilization reactor, and the negative electrode active material can be immersed in a solvent and stirred in the autoclave reactor, sealed, and heat-treated for a long period of time.

[0062] According to one embodiment of the present invention, the temperature of the step (S2) may be 100°C or more and 200°C or less. For example, the temperature may be 100°C or more, 105°C or more, 110°C or more, 115°C or more, 120°C or more, 125°C or more, 130°C or more, 135°C or more, 140°C or more, 145°C or more, 150°C or more, 200°C or less, 190°C or less, 185°C or less, 180°C or less, 175°C or less, 170°C or less, and specifically, 150°C or more and 190°C or less. In addition, the political, i.e., heat treatment process in the above (S2) step can be performed for 10 hours or more and 15 hours or less, and for example, can be performed for 10 hours or more, 11 hours or more, 12 hours or more, 15 hours or less, 14 hours or less, and 13 hours or less. If the above temperature range and time range are not satisfied, it is difficult to form a film having an optimal thickness and density on the surface of the silicon particles, it is difficult to effectively reduce the amount of hydrogen gas generated per unit mass of the negative electrode active material, and at the same time, it is difficult to maintain an excellent level of discharge capacity and initial efficiency.

[0063] Additionally, the mixed solution that has been purified in the above (S2) can be stirred a second time while cooling to room temperature. By the second stirring, the particles can be uniformly distributed without agglomeration.

[0064] Additionally, the washing in step (S4) can be performed twice or more with ethanol on the obtained powder, and then dried in a vacuum oven at a temperature of 80° C. for 12 hours.

[0065]

[0066] cathode

[0067] The present invention provides a negative electrode comprising a conductive metal current collector and a negative electrode active material layer provided on at least one surface of the current collector, wherein the negative electrode active material layer includes a negative electrode active material according to the present invention.

[0068] The above negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, the negative electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., or an aluminum-cadmium alloy.

[0069] The above negative electrode current collector may typically have a thickness of 3 to 500 μm.

[0070] The above-described negative electrode current collector may have fine irregularities formed on its surface to enhance the bonding strength of the negative electrode active material. For example, the above-described negative electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0071] The above negative electrode active material layer is formed on the negative electrode current collector, and the negative electrode active material layer may include a negative electrode material including the above-described negative electrode active material. The negative electrode active material may be included in the negative electrode to exhibit excellent capacity characteristics and lifespan characteristics. The description of the above-described negative electrode active material has been described above.

[0072] The above-mentioned negative electrode material may further include a carbon-based active material in addition to the aforementioned negative electrode active material, and thus the degree of volume expansion of the entire negative electrode material can be reduced by the carbon-based active material having a low degree of volume expansion due to charge and discharge.

[0073] The above carbon-based active material may include at least one selected from the group consisting of graphite, artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, acetylene black, Ketjen black, Super P, graphene, and fibrous carbon, and preferably may include at least one selected from the group consisting of artificial graphite and natural graphite.

[0074] The average particle diameter (D) of the above carbon-based active material 50) may be 5 ㎛ to 35 ㎛, preferably 10 ㎛ to 20 ㎛, in order to ensure structural stability during charging and discharging and reduce side reactions with the electrolyte.

[0075] Specifically, the negative electrode material preferably uses both the negative electrode active material and the carbon-based active material in terms of simultaneously improving capacity characteristics and cycle characteristics, and specifically, the negative electrode material preferably includes the negative electrode active material and the carbon-based active material in a weight ratio of 1:99 to 50:50, preferably 3:97 to 20:80. The negative electrode material may be included in the negative electrode active material layer in an amount of 80 wt% to 99 wt%, preferably 90 wt% to 98.5 wt%.

[0076] The above negative active material layer includes a binder.

[0077] The binder may include at least one selected from the group consisting of styrene butadiene rubber (SBR), acrylonitrile butadiene rubber, acrylic rubber, butyl rubber, fluoro rubber, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyethylene glycol (PEG), polyacrylonitrile (PAN), and polyacryl amide (PAM), in that it can further improve electrode adhesion and provide sufficient resistance to volume expansion / contraction of the active material. Preferably, the binder includes styrene-butadiene rubber in that it has high strength, excellent resistance to volume expansion / contraction of the silicon-based negative electrode active material, and excellent flexibility can be imparted to the binder to prevent distortion, bending, etc. of the electrode.

[0078] The above binder may be included in the negative electrode active material layer at 0.5 wt% to 10 wt%, and is preferable in that the volume expansion of the active material can be more effectively controlled when it is within the above range.

[0079] The above negative electrode active material layer may further include a conductive material. The conductive material may be used to improve the conductivity of the negative electrode, and it is preferable that the conductive material have conductivity without causing chemical changes. Specifically, the conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black, conductive fiber, carbon nanotube (CNT), fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably, may include carbon black in order to realize high conductivity.

[0080] The above-mentioned conductive material may be included in the negative electrode active material layer at 0.5 wt% to 10 wt%.

[0081] The above negative electrode active material layer may have a thickness of 30 ㎛ to 100 ㎛, preferably 40 ㎛ to 80 ㎛, in order to increase electrical contact with the components of the negative electrode material.

[0082] The above negative electrode can be manufactured by dispersing a negative electrode material, a binder, and a conductive material in a solvent for forming a negative electrode slurry on the negative electrode current collector to prepare a negative electrode slurry, coating the negative electrode slurry on the negative electrode current collector, and then drying and rolling.

[0083] The solvent for forming the above cathode slurry may include at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, preferably distilled water, in order to facilitate dispersion of the components.

[0084]

[0085] secondary batteries

[0086] The present invention provides a secondary battery, specifically a lithium secondary battery, comprising the aforementioned negative electrode. Specifically, the secondary battery according to the present invention comprises the aforementioned negative electrode, the positive electrode facing the negative electrode, and a separator and electrolyte interposed between the negative electrode and the positive electrode.

[0087] The above positive electrode may include a positive electrode current collector; and a positive electrode active material layer formed on the positive electrode current collector.

[0088] The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, the negative electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., or an aluminum-cadmium alloy.

[0089] The above positive electrode current collector may typically have a thickness of 3 μm to 500 μm.

[0090] The above-described positive electrode current collector may also form fine irregularities on its surface to strengthen the bonding strength of the negative electrode active material. For example, the above-described negative electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0091] The above positive electrode active material layer may include a positive electrode active material.

[0092] The above positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, may include a lithium transition metal composite oxide containing lithium and at least one transition metal composed of nickel, cobalt, manganese, and aluminum, preferably a lithium transition metal composite oxide containing lithium and a transition metal including nickel, cobalt, and manganese.

[0093] More specifically, the lithium transition metal composite oxides include lithium-manganese oxides (e.g., LiMnO2, LiMn2O4, etc.), lithium-cobalt oxides (e.g., LiCoO2, etc.), lithium-nickel oxides (e.g., LiNiO2, etc.), lithium-nickel-manganese oxides (e.g., LiNi 1-Y Mn Y O2 (here, 0 <Y<1), LiMn 2-z Ni z O4 (where 0<Z<2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y1 Co Y1 O2 (here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2 (here, 0 <Y2<1), LiMn 2-z1 Co z1 O4 (wherein, 0<Z1<2) etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p Co q Mn r1 )O2(wherein, 0<p<1, 0<q<1, 0<r1<1, p+q+r1=1) or Li(Ni p1 Co q1 Mn r2 )O4 (wherein, 0<p1<2, 0<q1<2, 0<r2<2, p1+q1+r2=2) etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r3 M S2)O2(wherein, M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r3 and s2 are atomic fractions of independent elements, 0<p2<1, 0<q2<1, 0<r3<1, 0<s2<1, p2+q2+r3+s2=1), etc.), and any one or more compounds thereof may be included. Among these, the lithium transition metal composite oxide is LiCoO2, LiMnO2, LiNiO2, lithium nickel-manganese-cobalt oxide (e.g., Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2 or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc.), or lithium nickel cobalt aluminum oxide (e.g., Li(Ni 0.8 Co 0.15 Al 0.05 )O2, etc.), and considering the remarkable improvement effect according to the control of the type and content ratio of the constituent elements forming the lithium transition metal composite oxide, the lithium transition metal composite oxide may be Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2, Li(Ni 0.7 Mn 0.15 Co 0.15 )O2 or Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, etc., and any one of these or a mixture of two or more of them may be used.

[0094] The above-mentioned positive electrode active material may be included in the positive electrode active material layer at 80 wt% to 99 wt%, preferably 92 wt% to 98.5 wt%, taking into account sufficient capacity of the positive electrode active material.

[0095] The above-described positive electrode active material layer may further include a binder and / or a conductive material together with the above-described positive electrode active material.

[0096] The above binder is a component that assists in the binding of the active material and the conductive material and the binding to the current collector, and specifically, may include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, preferably polyvinylidene fluoride.

[0097] The above binder may be included in the positive electrode active material layer at 1 wt% to 20 wt%, preferably 1.2 wt% to 10 wt%, in order to sufficiently secure binding force between components such as the positive electrode active material.

[0098] The conductive material may be used to assist and improve conductivity in a secondary battery, and is not particularly limited as long as it has conductivity without causing chemical changes. Specifically, the conductive material may include at least one selected from the group consisting of graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powders; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives, and preferably, the conductive material may include carbon black in terms of improving conductivity.

[0099] The above-mentioned conductive material may be included in the positive electrode active material layer at 1 wt% to 20 wt%, preferably 1.2 wt% to 10 wt%, in order to sufficiently secure electrical conductivity.

[0100] The thickness of the positive electrode active material layer may be 30 ㎛ to 400 ㎛, preferably 50 ㎛ to 110 ㎛.

[0101] The above positive electrode can be manufactured by coating a positive electrode slurry containing a positive electrode active material and optionally a binder, a conductive material, and a solvent for forming a positive electrode slurry on the positive electrode current collector, and then drying and rolling.

[0102] The solvent for forming the positive electrode slurry may include an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount that provides a desirable viscosity when including the positive electrode active material, and optionally a binder and a conductive material. For example, the solvent for forming the positive electrode slurry may be included in the positive electrode slurry such that the concentration of the solid content including the positive electrode active material, and optionally a binder and a conductive material, is 50 wt% to 95 wt%, preferably 70 wt% to 90 wt%.

[0103] The above separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without any particular restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0104] In addition, examples of the electrolyte used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of secondary batteries.

[0105] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0106] As the organic solvent, any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move may be used without particular limitation. Specifically, the organic solvent includes ester solvents such as methyl acetate, ethyl acetate, gamma-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, which may include a double-bonded aromatic ring or an ether bond); Amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, carbonate solvents are preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferable. In this case, the performance of the electrolyte can be excellent when the cyclic carbonate and the linear carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9.

[0107] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. It is preferable that the concentration of the lithium salt be used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0108] The above secondary battery can be manufactured by inserting a separator between the above-described negative electrode and positive electrode and then injecting an electrolyte according to a conventional secondary battery manufacturing method.

[0109] The secondary battery according to the present invention is useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in electric vehicles such as hybrid electric vehicles (HEVs), and can be particularly preferably used as a component battery of a medium- to large-sized battery module. Accordingly, the present invention also provides a medium- to large-sized battery module comprising the secondary battery described above as a unit battery.

[0110] These medium- to large-sized battery modules can be preferably applied to power sources that require high output and large capacity, such as electric vehicles, hybrid electric vehicles, and power storage devices.

[0111]

[0112] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0113]

[0114] Example 1

[0115] 1.5 g of Si / C active material was added to 15 mL of dimethyl sulfoxide (DMSO) and stirred for 10 minutes. Here, the Si / C active material was prepared by placing 2 g of porous activated carbon (PCT (Power Carbon Technology) Co., Ltd., model number BA21E) in a tube furnace, heating it to 475°C under an Ar atmosphere, and then flowing 1.25 vol% SiH4 / Ar at a flow rate of 300 cc / min for 5 hours to deposit Si on the activated carbon. The stirred solution was placed in a 100 mL autoclave, sealed, and then heat-treated in an oven at 160°C for 12 hours. Thereafter, the heat-treated solution was cooled to room temperature and stirred a second time for an additional hour. Afterwards, the cooled solution was filtered to obtain powders, which were washed twice with ethanol and dried in a vacuum oven at 80°C for 12 hours to prepare a negative electrode active material. At this time, the SiOx(0) of the prepared negative electrode active material <x≤2) / Si의 XPS에 의해 측정된 피크 면적비는 1.78 이고, C-C / C-O의 피크 면적비는 1.17이다.

[0116] [XPS Analysis Conditions]

[0117] * X-ray source: monochromatic Al K alpha (1486.6 Ev)

[0118] * Operation mode: CAE (constant analyzer energy) mode

[0119] * Software: Avantage software (ver. 5.9925)

[0120] * X-ray spot size: 400 ㎛

[0121] Survey (Narrow scan)

[0122] * Scan range: 0~1360 ev (~20 ev)

[0123] * Step size: 1 ev (0.1 ev)

[0124] * Per point dwell time: 20 ms (50 ms)

[0125] * Number of scans: 10 (4~10)

[0126] * Psaa energy: 200 ev (50 ev)

[0127]

[0128] Example 2

[0129] The negative electrode active material was manufactured by the same method as in Example 1, except that the heat treatment was performed at a temperature of 170°C. At this time, the SiOx(0) of the manufactured negative electrode active material <x≤2) / Si의 XPS에 의해 측정된 피크 면적비는 1.95 이고, C-C / C-O의 피크 면적비는 1.08 이다.

[0130]

[0131] Example 3

[0132] The negative electrode active material was manufactured by the same method as in Example 1, except that the heat treatment was performed at a temperature of 190°C. At this time, the SiOx(0) of the manufactured negative electrode active material <x≤2) / Si의 XPS에 의해 측정된 피크 면적비는 2.38 이고, C-C / C-O의 피크 면적비는 0.82 이다.

[0133]

[0134] Comparative Example 1

[0135] 1.5 g of the same Si / C active material as the Si / C active material used in Example 1 was used as is without any separate process. At this time, the SiOx(0) of the manufactured negative active material <x≤2) / Si의 XPS에 의해 측정된 피크 면적비는 1.41 이고, C-C / C-O의 피크 면적비는 1.38 이다.

[0136]

[0137] Experimental Example 1 - Measurement of slurry gas generation

[0138] Using the negative electrode active materials of the above examples and comparative examples, negative electrode slurry was prepared, and the amount of hydrogen gas generated was measured, which is shown in Table 1 below. Specifically, the negative electrode slurry was prepared by mixing the graphite negative electrode active material, the negative electrode active materials of the above examples and comparative examples, the conductive agent super C, and the SBR / CMC binder in an aqueous system at a weight ratio of 77: 19.3: 1.0: 1.1: 1.6. 5 g of the above negative electrode slurry was placed in a pouch, sealed, and stored in an oven at 60°C for 7 days, and the volume change of the pouch was measured using a specific gravity balance. Specifically, the amount of gas generated per mass of negative electrode active material was calculated based on the volume change.

[0139]

[0140] Experimental Example 2 - Measurement of Discharge Capacity and Initial Efficiency

[0141] Half cells were manufactured using the negative active materials of the examples and comparative examples, and the battery characteristics were measured, and the results are shown in Table 1 below.

[0142] Each negative electrode active material was mixed with Super-C as a conductive agent and Li-PAA as a binder in a weight ratio of 80:10:10 to prepare a negative electrode slurry, which was then applied to copper foil and dried, rolled, and punched to produce a negative electrode.

[0143] Lithium metal was used as a counter electrode, and a porous polyethylene separator was placed between the negative electrode and the lithium metal, and a coin half-cell was manufactured by injecting an electrolyte solution in which 1 M LiPF6, 1.5 wt% VC, and 0.5 wt% PS were dissolved in a solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 30:70.

[0144] After leaving the above coin half-cell for 24 hours, 0.005-1.5 V vs. Li / Li + In the section, the battery was charged to 0.005 V with a constant current (CC) of 0.1 C, then charged with a constant voltage (CV) until the charging current became 0.02 C, and discharged with a constant current (CC) of 0.1 C until the voltage became 1.5 V, and the discharge capacity and initial efficiency were measured.

[0145]

[0146] Processing temperatureGas generation per unit mass of negative active material (mL / g) @60 ℃Coin cell measurementDay 1Day 2Day 3Day 4Day 5Day 6Day 7Discharge capacity (mAh)Initial efficiency (%)Example 1160 ℃1247--12186090.5Example 2170 ℃--2-567188087.4Example 3190 ℃-123--6192085.6Comparative example 1-37---2023204090.7

[0147] Referring to Table 1, Examples 1 to 3 are SiOx(0) of the present invention.

Claims

1. A composite comprising a carbon matrix and silicon particles dispersed within the carbon matrix, The above silicon particles have SiOx(0) on their surface. <x≤2)를 포함하는 막을 포함하며, SiOx(0) by X-ray photoelectron spectroscopy <x≤2) / Si의 피크 면적비는 1.5 이상 3.5 이하인 음극 활물질.

2. In claim 1, A negative active material having a peak area ratio of CC / CO by X-ray photoelectron spectroscopy of carbon in the above complex of 0.4 or more and 1.3 or less.

3. In claim 1, A negative electrode active material wherein the average particle diameter (D50) of the above silicon particles is 1 nm or more and 50 nm or less.

4. In claim 1, A negative active material having an average thickness of the above film of 0.1 nm or more and 20 nm or less.

5. In claim 1, A negative electrode active material having an average particle diameter of 1 ㎛ or more and 100 ㎛ or less.

6. In claim 1, The above silicon particles are a negative active material comprising an amorphous phase.

7. In claim 1, The negative electrode active material is a negative electrode active material comprising a carbon coating layer located on the surface of the composite.

8. Step (S1) of preparing a mixed solution by immersing the Si / C negative electrode active material in an organic solvent and stirring; Step (S2) of placing the above mixed solution into an autoclave reactor, sealing it, and then allowing it to stand for 10 to 15 hours at a temperature of 100°C to 200°C; Step (S3) of secondary stirring while cooling the mixed solution that has been regulated in the above (S2) to room temperature; and A method for manufacturing a negative active material, comprising a step (S4) of washing and drying a powder obtained by filtering the above mixed solution.

9. In claim 8, A method for manufacturing a negative electrode active material, wherein the Si / C negative electrode active material comprises a composite including a carbon matrix and silicon particles dispersed within the carbon matrix.

10. In claim 8, A method for producing a negative active material, wherein the organic solvent comprises dimethyl sulfoxide (DMSO).

11. In claim 8, A method for manufacturing a negative active material, wherein the temperature of the above step (S2) is 150°C or more and 190°C or less.

12. Conductive metal current collector; and The above-mentioned collector comprises a negative active material layer provided on at least one surface thereof, A negative electrode, wherein the negative electrode active material layer comprises the negative electrode active material according to claim 1.

13. A lithium secondary battery comprising a negative electrode according to claim 12; a positive electrode; and a separator and electrolyte interposed between the positive electrode and the negative electrode.