Anode active material, anode composition, anode, and lithium secondary battery

Abstract

The present invention relates to a negative electrode active material containing porous silicon-carbon composite particles, a negative electrode composition, a negative electrode, a lithium secondary battery, a battery module, and a battery pack.

Description

[Technical Field]

[0001] The present invention relates to a negative electrode active material, a negative electrode composition, a negative electrode, a lithium secondary battery, a battery module, and a battery pack.

[0002] This application claims the benefit of the filing date of Korean Patent Application No. 10-2023-0103972, filed with the Korean Intellectual Property Office on August 9, 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] Lithium secondary batteries have an organic or polymer electrolyte between a positive electrode and a negative electrode, which are made of active materials that allow lithium ions to be inserted and deintercalated. Electrical energy is produced through oxidation and reduction reactions that occur when lithium ions are inserted into and deintercalated from the positive and negative electrodes.

[0005] Graphite is the main anode active material used in lithium secondary batteries, but its low capacity per unit mass of 372 mAh / g makes it difficult to increase the capacity of lithium secondary batteries. For this reason, non-carbon anode materials such as silicon, tin, and their oxides have been developed to have higher energy densities than graphite. Summary of the Invention [Problem to be solved by the invention]

[0006] While silicon carbon composites have superior initial capacity and energy efficiency compared to graphite or silicon oxide, the higher the degree of silicon exposure in silicon carbon composites, the more hydrogen gas they generate due to reaction with moisture during manufacturing or storage. This can lead to poor coating properties and the risk of explosion during long-term storage. Therefore, embodiments of the present invention provide a negative electrode active material with improved moisture-reactive properties, a negative electrode composition including the same, and a negative electrode. Furthermore, embodiments of the present invention relate to lithium secondary batteries, battery modules, and battery packs including the anodes. [Means for solving the problem]

[0007] One embodiment of the present invention comprises: a porous carbon scaffold; and a porous silicon carbon composite particle comprising silicon disposed at least partially within or on a surface of the porous carbon scaffold; The content of the silicon is 35 to 60 parts by weight based on 100 parts by weight of the silicon carbon composite particles, Specific surface area is 20m 2 / g or less, After forming the planar film, a negative electrode active material is provided that includes porous silicon carbon composite particles having a contact angle with water of 90 degrees or greater measured on the surface of the planar film.

[0008] According to one embodiment, the average diameter of the pores in the porous silicon carbon composite particles is 0.1 nm to 50 nm.

[0009] One embodiment of the present invention provides a negative electrode composition containing the negative electrode active material.

[0010] One embodiment of the present invention provides a negative electrode for a lithium secondary battery, comprising: a current collector; and a negative electrode active material layer provided on at least one surface of the current collector and including the negative electrode composition.

[0011] One embodiment of the present invention provides a lithium secondary battery comprising the above-described negative electrode; a separator; and a positive electrode.

[0012] One embodiment of the present invention provides a battery module including the lithium secondary battery.

[0013] One embodiment of the present invention provides a battery pack including the battery module. [Effects of the Invention]

[0014] According to one embodiment of the present invention, the initial capacity and energy efficiency of a lithium secondary battery are significantly improved by using porous silicon carbon composite particles having a specific structure, silicon content, and specific surface area, and the particles are controlled to have a specific contact angle, thereby minimizing reaction with moisture during the negative electrode manufacturing process or during storage as a negative electrode composition. This prevents hydrogen gas generation, improving coating properties and providing long-term storage stability, and eliminating the risk of process defects and explosions due to hydrogen gas generation. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present specification will be explained in more detail below.

[0016] In this specification, unless otherwise specified, when a part "comprises" a certain component, it does not mean that it may further include other components, but does not exclude other components.

[0017] In this specification, when a member is positioned "on" another member, it does not only mean that the member is in contact with the other member, but also that another member exists between the two members.

[0018] 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.

[0019] As used herein, the singular expression of a term includes the plural expression unless the context clearly indicates otherwise.

[0020] In this specification, the average particle size D50 can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve (graph curve of a particle size distribution diagram). The average particle size can be measured, for example, using a laser diffraction method. The laser diffraction method generally enables measurement of particle sizes from the submicron range to several mm, and can obtain results with high reproducibility and high resolution. The average particle size can be measured using a Microtrac device (manufacturer: Microtrac, model name: S3500) using water and Triton-X100 dispersant. Specifically, the average particle size of the positive electrode active material can be measured at a refractive index of 1.5 to 1.7, and the average particle size of the negative electrode active material can be measured at a refractive index of 1.97 or 2.42. For example, particles can be dispersed in a dispersion medium, introduced into a commercially available laser diffraction particle size analyzer, and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W. Then, a volume cumulative particle size distribution graph is obtained, and the particle size corresponding to 50% of the volume cumulative amount is determined.

[0021] 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.

[0022] <Negative electrode active material> One embodiment of the present invention relates to an active negative electrode material, comprising porous silicon carbon composite particles.

[0023] The porous silicon carbon composite particles have a structure including a porous carbon scaffold and silicon provided at least partially inside or on the surface of the porous carbon scaffold, and the content of the silicon is 35 to 60 parts by weight, preferably 40 to 60 parts by weight, or 45 to 55 parts by weight, based on 100 parts by weight of the silicon carbon composite particles.

[0024] According to one embodiment, the porous silicon carbon composite particles have a specific surface area of ​​20 m 2 / g or less, and 15m 2 / g or less, and 2 / g or less, and 2 The specific surface area of ​​the porous silicon carbon composite particles may be 0.1 m / g or less. 2 / g or more, and 1m 2 / g or more, and 2 / g or more, and 2 / g or more, and 2 / g or more. The specific surface area refers to the total specific surface area of ​​the substrate measured by the BET method. The BET (Brunauer / Emmett / Teller) method is commonly used in the industry to determine the accessible surface area of ​​a material using an inert gas, such as nitrogen, to measure the amount of gas adsorbed on the material. For example, it can be measured using a BET measuring device (BEL-SORP-MAX, Nippon Bell) by degassing at 200°C for 8 hours and then performing N2 adsorption / desorption at 77K. If the BET specific surface area of ​​the silicon carbon composite particles does not satisfy the above range and is less than 20m 2 If the content exceeds 1 / g, not only may the manufacturing stability be reduced due to changes in physical properties such as viscosity of the negative electrode slurry over time during the manufacturing and storage of the negative electrode composition, but also the coating process may be impaired due to the generation of hydrogen gas due to the promotion of reaction with moisture.

[0025] According to one embodiment, the porous silicon carbon composite particles have an average pore diameter of 0.1 nm to 50 nm. The porous carbon scaffold may include micropores with a diameter of less than 2 nm and mesopores with a diameter of 2 nm to 50 nm.

[0026] Particles with such microporosity can contain a relatively large amount of fine silicon particles, allowing active particles to be electrically connected to each other, thereby reducing the risk of silicon particle cracking or electrical disconnection between active materials during charging and discharging, and thus improving the initial capacity and energy efficiency of batteries. However, if a large amount of small silicon particles are exposed within the pores or on the surface of the particles, this can have a negative impact on gas generation upon contact with moisture. Embodiments of the present invention have a microporous structure and a moderate silicon content, as described above, and a contact angle with water of 90 degrees or more measured on the surface of the planarized layer after formation, thereby minimizing or preventing the reaction between silicon and moisture.

[0027] According to one embodiment of the present invention, the porous structure, pore size, degree of oxidation of the carbon scaffold, silicon content, and contact angle of the porous silicon carbon composite particles can be controlled by various factors such as the processing temperature of the carbon scaffold and the order and amount of raw materials added.

[0028] According to one embodiment of the present invention, the silicon content in the porous silicon carbon composite particles is 35 to 60 parts by weight, for example, 40 to 60 parts by weight, or 40 to 55 parts by weight, based on 100 parts by weight of the porous silicon carbon composite particles. If the silicon content is less than 35 parts by weight, the initial capacity of the active material is not sufficiently high, and if the silicon content is more than 60 parts by weight, it is difficult to form a structure in which hydrogen gas generation is suppressed. If the silicon content is within this range, the capacity and efficiency of the active material are appropriate, and gas generation from the slurry is easily suppressed.

[0029] According to one embodiment of the present invention, the average pore diameter of the porous silicon carbon composite particles may be 0.1 nm to 50 nm. When the average pore diameter is within this range, there is no significant problem with silicon growth due to silane gas, and problems such as reduced life performance and volume expansion during charge and discharge can be minimized. The average pore diameter can be measured using a mercury porosimeter.

[0030] According to one embodiment of the present invention, the porous silicon carbon composite particles may have a contact angle with water of 90 degrees or more, e.g., 95 degrees or more, 100 degrees or more, 105 degrees or more, or 120 degrees or more, measured on the surface of the planarized film after forming the planarized film. This contact angle range is advantageous for preventing reaction with water. The contact angle can be measured on the surface of the planarized film after coating and planarizing the particles using a contact angle measuring device, such as one manufactured by Phoenix MT. Rolling can be performed during the planarization.

[0031] In this specification, the water contact angle is a characteristic (value) that indicates the reactivity (affinity) of a silicon carbon composite particle with water. In the process of producing the silicon carbon composite particle, the water affinity of the silicon carbon composite particle can be changed by adjusting the flow rate of silane gas, the heat treatment temperature, whether or not the particle is coated with carbon or other materials, and the thickness of the coating, thereby controlling the water contact angle within the above range.

[0032] A water contact angle within this range means that the silicon carbon composite particles have low reactivity with water, and an anode composition having a water contact angle within this range suppresses hydrogen gas generation during the manufacturing process, thereby improving / maintaining the electrode coating processability and stability. Furthermore, the anode composition can be provided with storage stability because changes over time in physical properties such as the viscosity of the anode slurry are suppressed.

[0033] According to one embodiment of the present invention, the porous silicon carbon composite particles may generate a gas amount of 4,000 μL / g or less when left at 60° C. for 24 hours in a state where they are dispersed in water at a concentration of 30 wt %. According to another embodiment, a negative electrode composition for a lithium secondary battery containing the porous silicon carbon composite particles may generate a gas amount of 4,000 μL / g or less when left at 60° C. for 24 hours. The amount of gas generated varies depending on the component ratio of Si to C in the active material particles, the degree of Si exposure, and the pH of the slurry, and is specifically affected by the composition, structure, and size of the components in the active material particles, and the composition of the slurry.

[0034] Specifically, it is preferable to collect and measure the amount of hydrogen (H2) gas generated after dispersing an active material in water and leaving it at 60°C for one day using GC / MS, and limit the amount to a certain level. For example, it is preferable that the amount of hydrogen gas generated from a 30 wt% aqueous dispersion of active material be 4,000 μL / g or less, 2,000 μL / g or less, or 1,000 μL / g or less. Furthermore, by limiting the amount of hydrogen (H2) gas generated from an electrode-producing slurry to 4,000 μL / g or less, 2,000 μL / g or less, or 1,000 μL / g or less after leaving it at 60°C for one day, coating defects such as pinholes, a decrease in the initial capacity of the active material, and the risk of explosion during electrode production can be minimized. By controlling the porous structure, silicon content, scaffold structure, and contact angle of the particles within specific ranges, the performance of the active material can be maintained, and the gas generation amount measured by the above method can be 4000 μL / g or less, 2000 μL / g or less, 1000 μL / g or less, 500 μL / g or less, 300 μL / g or less, or 150 μL / g or less.

[0035] According to one embodiment of the present invention, the total amount of carbon and silicon is 90 to 100 parts by weight based on 100 parts by weight of the porous silicon-carbon composite particles.

[0036] According to one embodiment of the present invention, the average particle size D50 of the porous silicon-carbon composite particles is 1 μm to 20 μm, and may be, for example, 1.5 μm to 15 μm, or 3 μm to 10 μm. When the particle size is within the above range, the dispersibility of the active material is suitable during slurry production, and there are few problems with coating defects caused by large particles during electrode coating.

[0037] According to one embodiment of the present invention, the pore volume of the porous carbon scaffold contained in the porous silicon-carbon composite particles is more than 0.1 cm 3 / g, for example, more than 0.2 cm 3 / g, for example, more than 0.5 cm 3 / g, for example, more than 0.7 cm 3 / g, for example, more than 1.0 cm 3 / g, for example, more than 1.5 cm 3 / g, for example, more than 2.0 cm 3 / g or more. The pore volume distribution of the porous carbon scaffold may vary. For example, the pores may include micropores, mesopores, and macropores, and the micropores may be 0% to 90%, the mesopores may be 5% to 90%, and the macropores may be 0% to 50%.

[0038] The porous silicon-carbon composite particles do not necessarily need to be manufactured by a specific manufacturing method, and may be manufactured by methods well-known in the art. For example, the production of the porous silicon-carbon composite may include the step of producing a porous carbon scaffold (the step of thermally decomposing a polymer to produce a porous carbon body), and flowing silane gas through the porous carbon scaffold and thermally decomposing it at a high temperature to grow silicon inside the porous carbon scaffold. It may be carried out by a method including this step, and a step of modifying the surface layer with carbon or other components may be further carried out according to the purpose. Also, as another example, after simultaneously depositing Si and SiO2 to produce a Si-containing SiO x oxide (0 < x < 2), the oxide can be chemically etched to produce porous Si, and porous Si / C can be produced through the process of heat-treating porous Si with carbon gas.

[0039] <Negative electrode composition and negative electrode> A negative electrode composition according to one embodiment of the present invention includes the negative electrode active material.

[0040] Also, a negative electrode for a lithium secondary battery according to one embodiment of the present invention includes a current collector; and a negative electrode active material layer provided on at least one surface of the current collector and including the negative electrode composition.

[0041] The negative electrode composition may further include a binder and a conductive material, and may further include a thickener as needed.

[0042] The negative electrode active material layer may be formed by applying a negative electrode composition containing a negative electrode active material, a binder, a thickener, and / or a conductive material to at least one surface of a current collector, followed by drying and rolling.

[0043] The negative electrode composition may further include an additional negative electrode active material.

[0044] The additional negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; and SiO. β (0<β<2), metal oxides that can be doped and dedoped with lithium, such as SnO2, vanadium oxide, lithium titanium oxide, and lithium vanadium oxide; or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used.

[0045] The carbon material may be either low-crystalline carbon or high-crystalline carbon. Typical low-crystalline carbons include soft carbon and hard carbon, while typical high-crystalline carbons include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-fired carbons such as petroleum or coal tar pitch-derived cokes.

[0046] The additional negative electrode active material may be a carbon-based negative electrode active material, for example, graphite.

[0047] In one embodiment of the present invention, the weight ratio of the negative electrode active material to the additional negative electrode active material contained in the negative electrode composition may be 1:99 to 99:1, specifically 10:90 to 90:10, for example, 5:95 to 50:50, or 10:90 to 30:70.

[0048] 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.

[0049] 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, such as copolymers containing acrylamide or acrylonitrile.

[0050] 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.

[0051] The thickener may be carboxymethyl cellulose (CMC), but is not limited thereto, and any thickener used in the technical field may be appropriately adopted.

[0052] In one embodiment of the present invention, the total amount of the negative electrode active material contained in the negative electrode composition may be 60 parts by weight to 99 parts by weight, specifically 70 parts by weight to 98 parts by weight, based on 100 parts by weight of the solid content of the negative electrode composition.

[0053] In one embodiment of the present invention, the binder may be included in an amount of 0.5 to 30 parts by weight, specifically 1 to 20 parts by weight, based on 100 parts by weight of the solid content of the negative electrode composition.

[0054] In one embodiment of the present invention, the conductive material may be included in an amount of 0.5 to 25 parts by weight, specifically 1 to 20 parts by weight, based on 100 parts by weight of the solid content of the negative electrode composition.

[0055] In one embodiment of the present invention, the thickener may be contained in an amount of 0.5 parts by weight to 25 parts by weight, specifically 0.5 parts by weight to 20 parts by weight, more specifically 1 part by weight to 20 parts by weight, based on 100 parts by weight of the solid content of the negative electrode composition.

[0056] The negative electrode composition according to an embodiment of the present invention may further include a solvent for forming the negative electrode composition. Specifically, the solvent for forming the negative electrode composition may include at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically distilled water, in order to facilitate dispersion of the components.

[0057] In one embodiment of the present invention, the solid content weight of the negative electrode composition may be 20 parts by weight to 75 parts by weight, specifically 30 parts by weight to 70 parts by weight, based on 100 parts by weight of the negative electrode composition.

[0058] <Secondary battery> A secondary battery according to an embodiment of the present invention may include the anode according to the embodiment described above. Specifically, the secondary battery includes an anode, a cathode, and a separator interposed between the cathode and the anode, and may further include an electrolyte. The anode has been described above, so a detailed description thereof will be omitted.

[0059] 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.

[0060] 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.

[0061] 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≦0.5 is satisfied); 2-c3 M c3Examples of the lithium manganese composite oxide include, but are not limited to, lithium manganese composite oxides represented by Li2Mn3MO8 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≦c3≦0.1), Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); or LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion. The positive electrode may be lithium metal.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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 has low resistance to ion migration in the electrolyte and excellent electrolyte humidification capacity. 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.

[0066] Examples of the electrolytic solution 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 manufacturing lithium secondary batteries.

[0067] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0068] 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.

[0069] 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 solution having high electrical conductivity can be prepared, and therefore these cyclic carbonates can be used even more preferably.

[0070] 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:

[0071] In addition to the components of the electrolyte, the electrolyte may further include one or more additives, such as a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid 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.

[0072] 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. The battery module and the battery pack include the secondary battery having high capacity, high rate characteristics, and high cycle characteristics, and can be used as a power source for medium to large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0073] Below, preferred examples are presented to help understand the present invention. However, the following examples are merely for the purpose of illustrating the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present description, and it is natural that such changes and modifications fall within the scope of the appended claims. [Example]

[0074] <Examples and Comparative Examples> Example 1 Specific surface area 1500m 2 / g~1800m 2 / g, pore volume 0.7 cm 3 / g~0.85cm 3 0.5 g of amorphous porous carbon scaffold with a SiO2 / g was placed in a ceramic crucible and placed in the center of a horizontal tube furnace. The furnace was sealed and purged with nitrogen gas. The furnace temperature was then increased to 400-500°C at 10°C / min, followed by 10-30 minutes of silane and hydrogen gas at varying flow rates. The furnace temperature was then increased to 780-830°C at 10°C / min, followed by 10-30 minutes of silane and hydrogen gas at varying flow rates. Porous silicon-carbon composites with the properties shown in Table 1 were produced.

[0075] Example 2 The same procedure as in Example 1 was carried out, except that the silane flow rate was increased so that the silicon content in the porous silicon carbon composite was 52 parts by weight.

[0076] Comparative Example 1 The same procedure as in Example 1 was carried out, except that the final heating temperature was lowered and the contact angle was adjusted to 78 degrees.

[0077] Comparative Example 2 The same procedure as in Example 1 was carried out, except that the flow rate of silane was reduced so that the silicon content in the porous silicon carbon composite was 33 parts by weight.

[0078] Comparative Example 3 The same procedure as in Example 1 was carried out, except that the primary heating temperature was increased so that the silicon content in the porous silicon carbon composite was 62 parts by weight, and the residence time was increased while the silane flow rate was decreased.

[0079] Comparative Example 4 The flow rate of silane was adjusted so that the silicon content in the porous silicon carbon composite was 44 parts by weight, and the particles were crushed to a specific surface area of ​​25 m 2 The same procedure as in Example 1 was carried out except that the concentration was adjusted to / g.

[0080] The silicon content, contact angle, and gas generation rate of the porous silicon carbon composites prepared in the examples and comparative examples were measured by the following methods. The results are shown in Table 1.

[0081] Silicon content: The silicon content of the composite was measured by pyrolyzing the carbon using a TGA thermal analyzer and measuring the weight.

[0082] Contact angle: Double-sided tape was attached to a flat substrate, and the porous silicon carbon composite particle powder was coated on the substrate. The coated substrate was then flattened with a 1 kgf / mm rolling roll to form a flat film. The contact angle with water was then measured using a contact angle measuring device manufactured by Phoenix MT.

[0083] -Gas generation amount: 5g of active material or slurry was placed in a 9cm x 9cm pouch, sealed, and then stored in a constant temperature chamber at high temperature (60℃) for 24 hours. The gas inside the pouch was then collected and the amount of gas generated was measured using GC / MS.

[0084] [Table 1]

[0085] Experimental Example 1 (Binder synthesis) In a reactor equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube, (meth)acrylamide (50% aqueous solution) and AA (80% aqueous solution) were mixed in a molar ratio of 6:4, and 0.1 parts by weight of a polymerization initiator (ammonium persulfate) was added per 100 parts by weight of the monomers ((meth)acrylamide and AA). The mixture was reacted at 80°C for 6 hours to produce a polymer in an aqueous solution state.

[0086] Next, the mixture was neutralized with an aqueous NaOH solution to produce a (meth)acrylic binder.

[0087] (Production of negative electrode slurry) The porous silicon-carbon composite particles prepared in Example 1 were used as the negative electrode active material, and two types of conductive materials, a particulate conductive material (SFG6L) and SWCNTs (product name: Tuball OCSiAl), were used as the conductive materials. Using the aqueous binder prepared above, the negative electrode active material:particulate conductive material:SWCNTs:aqueous binder=80:9.6:0.8:9.6 (weight ratio) were mixed to prepare a negative electrode composition.

[0088] A negative electrode slurry was prepared by adding water as a solvent, and the water content was adjusted in consideration of coating properties, viscosity, and solid content, so that the viscosity of the resulting negative electrode slurry was 8000 cps.

[0089] Experimental Example 2 The same procedure as in Experimental Example 1 was carried out, except that the porous silicon carbon composite particles prepared in Example 2 were used instead of those in Example 1.

[0090] Comparative Experiment Example 1 The same procedure as in Experimental Example 1 was carried out, except that the porous silicon carbon composite particles prepared in Comparative Example 1 were used instead of those in Example 1.

[0091] Comparative Experiment Example 2 The same procedure as in Experimental Example 1 was carried out, except that the porous silicon carbon composite particles prepared in Comparative Example 2 were used instead of Example 1.

[0092] Comparative Experiment Example 3 The same procedure as in Experimental Example 1 was carried out, except that the porous silicon carbon composite particles prepared in Comparative Example 3 were used instead of Example 1.

[0093] Comparative Experiment Example 4 The same procedure as in Experimental Example 1 was carried out, except that the porous silicon carbon composite particles prepared in Comparative Example 4 were used instead of those in Example 1.

[0094] <Experimental Example 1: Measurement of H2 gas generation amount from negative electrode slurry> Five grams of the negative electrode slurries from Examples 1 and 2 and Comparative Examples 1 to 4 were placed in 9 cm x 9 cm pouches, sealed, and then left in a thermostatic chamber at 60°C for 24 hours. The gas generated in the pouches was then collected, and the amount of H gas generated was quantitatively analyzed using GC / MS. The results are shown in Table 2 below.

[0095] <Experimental Example 2: Coating properties of negative electrode slurry> After the electrodes were manufactured, the presence or absence of surface contamination was measured. If no pinholes were found within the electrode (30cm x 30cm), an O was displayed, and if pinholes were found, an X was displayed.

[0096] <Experimental Example 3: Viscosity Change> Using a rheometer manufactured by TA Corporation, the shear viscosity was set at a shear rate of 2.5, and the viscosity of the negative electrode slurry immediately after production and after standing for 24 hours was measured, and the viscosity reduction rate relative to the initial viscosity was measured.

[0097] <Experimental Example 4: Battery production and evaluation of battery characteristics> The negative electrode slurry was coated onto 18 μm-thick copper foil and dried. A 50 μm-thick electrode active material layer was formed on one side of the copper foil, and the foil was punched into a circle with a diameter of 14 mm to produce a test electrode (negative electrode). A 0.3 mm-thick lithium metal foil was used as the positive electrode. A 0.1 mm-thick porous polyethylene sheet was used as the separator. The electrolyte used was a 1:1 volumetric mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in which LiPF6 was dissolved as a lithium salt at a concentration of approximately 1 mol / L.

[0098] The negative electrode, positive electrode, separator, and electrolyte were sealed in a stainless steel container to produce a coin cell for evaluation, 2 mm thick and 32 mm in diameter. The coin cell was charged at a constant current of 0.05 C until the voltage reached 0.01 V, and then discharged at a constant current of 0.05 C until the voltage reached 1.5 V, and the discharge capacity and initial efficiency were determined. The results are shown in Table 2 below.

[0099] [Table 2]

[0100] As shown in Table 2, Examples 1 and 2 contained porous silicon carbon composite particles within the scope of the present invention, and thus exhibited significantly less gas generation from the slurry than the Comparative Example. Furthermore, Examples 1 and 2 exhibited superior initial efficiency and higher initial discharge capacity than the Comparative Example. The relatively low gas generation rate in Comparative Example 2 was due to the high contact angle and low silicon content, resulting in poor battery performance, including initial efficiency and initial discharge capacity. Despite its high silicon content, Comparative Example 3 exhibited a lower initial capacity than Examples with lower silicon contents. The slurries of the Examples did not cause electrode defects, such as pinhole contamination, during electrode coating, and did not experience a decrease in viscosity during storage, allowing for the production of good electrodes.

Claims

1. A porous silicon carbon composite particle comprising: a porous carbon scaffold; and silicon disposed at least partially within or on a surface of the porous carbon scaffold, The silicon content is 35 to 60 parts by weight based on 100 parts by weight of the silicon carbon composite particles, Specific surface area is 20m ２ / g or less, 1. A negative electrode active material comprising porous silicon carbon composite particles, the contact angle of which with water measured on the surface of a planar film after the planar film is formed is 90 degrees or more.

2. 2. The negative electrode active material of claim 1, wherein the porous silicon carbon composite particles have an average particle size D50 of 1 μm to 20 μm.

3. 2. The negative electrode active material of claim 1, wherein the porous silicon carbon composite particles have pores with an average diameter of 0.1 nm to 50 nm.

4. 2. The negative electrode active material of claim 1, wherein the porous silicon-carbon composite particles generate a gas amount of 4,000 μL / g or less when left at 60° C. for 24 hours in a state where the porous silicon-carbon composite particles are dispersed in water at a concentration of 30 wt %.

5. 2. The negative electrode active material of claim 1, wherein the total amount of carbon and silicon is 90 to 100 parts by weight based on 100 parts by weight of the porous silicon-carbon composite particles.

6. A negative electrode composition for a lithium secondary battery, comprising the negative electrode active material according to any one of claims 1 to 5.

7. The negative electrode composition for a lithium secondary battery according to claim 6 , further comprising a binder and a conductive material.

8. 7. The negative electrode composition for a lithium secondary battery according to claim 6, wherein the amount of gas generated when left at 60°C for 24 hours is 4,000 μL / g or less.

9. A negative electrode for a lithium secondary battery, comprising: a current collector; and a negative electrode active material layer provided on at least one surface of the current collector, the negative electrode active material layer comprising the negative electrode composition according to claim 6.

10. A lithium secondary battery comprising the negative electrode for lithium secondary batteries according to claim 9; a separator; and a positive electrode.

11. A battery module comprising the lithium secondary battery according to claim 10.

12. A battery pack comprising the battery module according to claim 11.

13. A battery pack comprising the lithium secondary battery according to claim 10.

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