Method for preparing porous silicon composite, porous silicon composite prepared thereby, and lithium secondary battery comprising same

Abstract

Provided are a method for preparing a porous silicon composite, a porous silicon composite prepared by the method, and a lithium secondary battery comprising same, the method comprising the steps of: (a) preparing a composite slurry by adding silicon-based nanoparticles, a first amorphous carbon precursor, amorphous carbon, conductive fibers, and a polymeric pore former into an organic dispersion medium; (b) preparing granular core particles by spray granulation of the composite slurry; (c) preparing a carbonized composite by coating the granular core particles with a second amorphous carbon precursor and performing first heat treatment; and (d) preparing a porous silicon composite by coating the carbonized composite with a third amorphous carbon precursor and performing second heat treatment.

Description

Method for manufacturing a porous silicon composite, a porous silicon composite manufactured thereby, and a lithium secondary battery including the same

[0001] The present invention relates to a method for producing a high-capacity porous silicon composite having excellent conductivity, a porous silicon composite produced thereby, and a lithium secondary battery including the porous silicon composite having excellent life characteristics, output characteristics, and stability.

[0002] The national research and development projects that supported this invention are as follows.

[0003] Assignment ID: 1425171528

[0004] Assignment number 00140827

[0005] Ministry of SMEs and Startups

[0006] Project Management (Professional) Agency Name: Small and Medium Business Technology Information Promotion Agency

[0007] Research Project Name: Demand-Based Technology Transfer

[0008] Research Project Name: Development of a Pitch-Coated Graphite / Silicone Anode Composite for Lithium Secondary Batteries

[0009] Name of the project performing organization: Grabsil Co., Ltd.

[0010] Research period: April 1, 2022 - March 31, 2024

[0011] Demand for high-capacity and high-output lithium secondary batteries is increasing due to the increasing demand for EVs, ESS, etc.

[0012] Most commercially available lithium secondary batteries use carbon-based materials as anode active materials. Graphite, in particular, exhibits highly reversible charge-discharge behavior due to the uniaxial orientation of its graphene layers, demonstrating excellent cycle life. Furthermore, its potential is nearly identical to that of lithium metal, enabling high energy yields when combined with a lithium oxide cathode. Despite these advantages, however, graphite's low theoretical capacity (372 mAh / g) presents a limitation in today's demanding high-capacity batteries.

[0013] There are attempts to use Si, which exhibits relatively high capacity, as a material that can replace carbon-based negative electrode active materials, but Si has problems such as large volume changes during the insertion and de-insertion of lithium, and can cause fine differentiation and loss of conductive paths, which lowers the overall performance of the battery.

[0014] To solve this problem, there have been attempts to mix various carbon materials with Si or to coat the surface of carbon materials with Si, but there are still problems such as deterioration caused by Si volume change during the charge / discharge process of the battery and excessive SEI formation, which limits the ability to increase the silicon addition rate.

[0015] Despite these various attempts, the problem of electrode damage due to Si expansion during the discharge process still remains, and there is a high need for a lithium secondary battery that has high capacity, including a high content of silicon, while also having excellent life and output characteristics and high safety.

[0016] The purpose of the present invention is to solve the problems of the prior art as described above and the technical tasks requested from the past.

[0017] Specifically, the purpose of the present invention is to provide a method for manufacturing a high-capacity porous silicon composite having excellent conductivity.

[0018] Another object of the present invention is to provide a porous silicon composite manufactured by the above method.

[0019] Another object of the present invention is to provide a lithium secondary battery having excellent life characteristics, output characteristics, and stability, which includes the porous silicon composite as a negative electrode active material.

[0020] The present invention,

[0021] (a) A step of preparing a composite slurry by adding silicon-based nanoparticles, a first amorphous carbon precursor, amorphous carbon, conductive fibers, and a polymer pore-forming agent to an organic dispersion medium;

[0022] (I) A step of manufacturing granule core particles by spray granulating the above composite slurry;

[0023] (a) a step of applying a second amorphous carbon precursor to the above granular core particles and performing a first heat treatment to produce a carbon composite; and

[0024] (a) A step of applying a third amorphous carbon precursor to the above carbon composite and performing a second heat treatment to manufacture a porous silicon composite may be included.

[0025] In the above step (a), 40 to 70 parts by weight of silicon-based nanoparticles, 5 to 15 parts by weight of a first amorphous carbon precursor, 10 to 40 parts by weight of amorphous carbon, 0.01 to 1 part by weight of conductive fiber, and 5 to 40 parts by weight of a polymer pore forming agent can be added to 700 to 1500 parts by weight of an organic dispersion medium.

[0026] The above silicon-based nanoparticles may be milled in an organic dispersion medium prior to preparing a composite slurry, and may have an average particle diameter (D50) of 50 to 200 nm.

[0027] The above step (b) can manufacture granular core particles having an average particle size of 1 to 30 ㎛ by spray-drying the composite slurry through a spray nozzle at a temperature of 80 to 150°C and a pressure of 3 to 4 bar, and then recovering the dried powder.

[0028] The weight ratio of the above granular core particles and the second amorphous carbon precursor may be 60:40 to 95:5.

[0029] The above step (d) may include a step of applying crystalline carbon to the granular core particles; and a step of applying a second amorphous carbon precursor to the granular core particles to which the crystalline carbon has been applied and performing a first heat treatment to produce a carbonized composite.

[0030] The weight ratio of the above granular core particles and crystalline carbon may be 99:1 to 99.9:0.1.

[0031] The weight ratio of the granular core particles coated with the above crystalline carbon and the second amorphous carbon precursor may be 60:40 to 95:5.

[0032] The above first heat treatment temperature may be 800 to 1000°C.

[0033] The first to third amorphous carbon precursors are each selected from the group consisting of coal pitch, petroleum pitch, mesophase pitch, tar, low molecular weight heavy oil, glucose, gelatin, sugars, phenol resin, naphthalene resin, furfuryl alcohol resin, polyamide resin, furan resin, polyimide resin, epoxy resin, vinyl chloride resin, gum arabic, citric acid, stearic acid, sucrose, polyvinylidene fluoride, carboxymethylcellulose (CMC), hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, starch, polyacrylic acid, sodium polyacrylate, polyacrylonitrile (PAN), cellulose, styrene, polyvinyl alcohol, and polyvinyl chloride. It could be more than just a species

[0034] The weight ratio of the above carbonized composite and the third amorphous carbon precursor may be 60:40 to 95:5.

[0035] The second heat treatment temperature may be 900 to 1300°C.

[0036] The present invention provides a porous silicon composite manufactured by the above method.

[0037] The present invention provides a lithium secondary battery comprising the porous silicon composite as a negative electrode active material.

[0038] The porous silicon composite manufactured according to the present invention contains a high content of silicon nanoparticles exhibiting high capacity, and due to the porous structure formed inside, even if the silicon particles repeatedly shrink and expand during the charge and discharge process of the battery, the structure of the composite is maintained while securing a passage for the movement of lithium ions, so that the life characteristics and output characteristics of a lithium secondary battery using the composite can be improved.

[0039] The porous silicon composite manufactured according to the present invention can maintain the structure and high conductivity of the composite through conductive fibers dispersed therein, thereby improving the initial efficiency of a secondary battery using the composite.

[0040] The porous silicon composite manufactured according to the present invention can secure high durability with a stable structure in which amorphous carbon is applied to the surface of granular core particles including silicon nanoparticles.

[0041] Figures 1a to 1d are photographs of particles according to Experimental Example 1;

[0042] Figures 2a and 2b are cross-sectional photographs according to Experimental Example 2;

[0043] Fig. 3 is a graph showing the CV curve of the material according to Experimental Example 4.

[0044] FIG. 4 is a graph showing the CV curve of a 500 mAh / g blended electrode plate according to Experimental Example 4; and

[0045] FIG. 5 is a graph showing the CRR of a 500 mAh / g blended electrode plate according to Experimental Example 5.

[0046] The present invention,

[0047] (a) A step of preparing a composite slurry by adding silicon-based nanoparticles, a first amorphous carbon precursor, amorphous carbon, conductive fibers, and a polymer pore-forming agent to an organic dispersion medium;

[0048] (I) A step of manufacturing granule core particles by spray granulating the above composite slurry;

[0049] (a) a step of applying a second amorphous carbon precursor to the above granular core particles and performing a first heat treatment to produce a carbon composite; and

[0050] (A) A method for manufacturing a porous silicon composite is provided, including the step of applying a third amorphous carbon precursor to the carbon composite and performing a second heat treatment to manufacture a porous silicon composite.

[0051] The porous silicon composite manufactured according to the present invention contains a high content of silicon nanoparticles exhibiting high capacity, and due to the porous structure formed inside, even if the silicon particles repeatedly shrink and expand during the charge and discharge process of the battery, the structure of the composite is maintained while securing a passage for the movement of lithium ions, so that the life characteristics and output characteristics of a lithium secondary battery using the composite can be improved.

[0052] The porous silicon composite manufactured according to the present invention can maintain the structure and high conductivity of the composite through conductive fibers dispersed therein, thereby improving the initial efficiency of a lithium secondary battery using the composite.

[0053] The porous silicon composite manufactured according to the present invention can secure high durability with a stable structure in which amorphous carbon is applied to the surface of granular core particles including silicon nanoparticles.

[0054] Specifically, in the above step (a), a composite slurry can be prepared by adding 40 to 70 parts by weight of silicon-based nanoparticles, 5 to 15 parts by weight of a first amorphous carbon precursor, 10 to 40 parts by weight of amorphous carbon, 0.01 to 1 part by weight of conductive fiber, and 5 to 40 parts by weight of a polymer pore-forming agent to 700 to 1500 parts by weight of an organic dispersion medium.

[0055] The above silicon-based nanoparticles may be milled in an organic dispersion medium prior to preparing a composite slurry, and may have an average particle diameter (D50) of 50 to 200 nm.

[0056] If the average particle diameter (D50) of the above silicon nanoparticles is less than 50 nm, the particles may clump together, making it difficult to achieve uniform dispersion in the slurry. If it exceeds 200 nm, the pores in the final porous silicon composite may become excessively large, which may actually deteriorate the lifespan characteristics, which is not desirable.

[0057] The above milling process can be performed using a bead mill, a high energy ball mill, a planetary mill, a stirred ball mill, a vibration mill, etc. Specifically, a bead mill or a ball mill can be used, and it can be made of a chemically inert material that does not react with silicon and organic matter, more specifically, a zirconia material.

[0058] If the content of the silicon-based nanoparticles is less than 40 parts by weight, it is difficult to secure the high capacity intended by the present invention, and if it exceeds 70 parts by weight, the phenomenon of micronization may become more severe during the charge / discharge process of the battery, which is not preferable. Specifically, it may be 45 to 60 parts by weight.

[0059] The above first amorphous carbon precursor is not limited to amorphous carbon that is converted into amorphous carbon through heat treatment, for example, coal pitch, petroleum pitch, mesophase pitch, tar, low molecular weight heavy oil, glucose, gelatin, sugars, phenol resin, naphthalene resin, furfuryl alcohol resin, polyamide resin, furan resin, polyimide resin, epoxy resin, vinyl chloride resin, gum arabic, citric acid, stearic acid, sucrose, polyvinylidene fluoride, carboxymethylcellulose (CMC), hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, starch, polyacrylic acid, sodium polyacrylate, polyacrylonitrile (PAN), cellulose, It may be at least one selected from the group consisting of styrene, polyvinyl alcohol, and polyvinyl chloride. It may be at least one selected from the group consisting of coal pitch, petroleum pitch, mesophase pitch, polyvinyl chloride, tar, rayon, polyacrylonitrile (PAN), cellulose, and polyamide fibers.

[0060] The above first amorphous carbon precursor may be used after being milled and pulverized in an organic dispersion medium so that the average particle diameter (D50) is 50 nm to 500 nm.

[0061] If the content of the first amorphous carbon precursor is less than 5 parts by weight, it is difficult to secure sufficient mechanical strength, and if it exceeds 15 parts by weight, agglomeration may occur and the spherical powder shape may collapse and become amorphous, which may deteriorate the overall characteristics of a battery using the same, which is not preferable. The content of the first amorphous carbon precursor may be 8 to 12 parts by weight.

[0062] The above amorphous carbon can maintain the core-shell shape by providing appropriate strength, thereby suppressing expansion of the core. The above amorphous carbon is not limited to any known amorphous carbon in the art, but may be, for example, one or a combination of two or more selected from the group consisting of soft carbon, hard carbon, pitch carbide, mesophase pitch carbide, and calcined coke, and more specifically, pitch carbide.

[0063] If the content of the amorphous carbon is less than 10 parts by weight, it is difficult to secure sufficient mechanical strength, and if it exceeds 40 parts by weight, agglomeration may occur and the spherical powder shape may collapse and become amorphous, which may deteriorate the overall characteristics of the battery using it, which is not preferable. Specifically, the amorphous carbon may be 15 to 30 parts by weight.

[0064] The conductive fiber is not limited as long as it exhibits conductivity, and may be, for example, one or more selected from the group consisting of graphene, carbon fiber, carbon nanotube, conductive polymer fiber, and metal filament. The metal may be, but is not limited to, stainless steel, aluminum, nickel, copper, titanium, platinum, gold, silver, ruthenium, tantalum, niobium, hafnium, zirconium, vanadium, indium, cobalt, tungsten, tin, beryllium, molybdenum, or an alloy or laminate thereof.

[0065] If the content of the conductive fiber is less than 0.01 part by weight, it is difficult to secure sufficient conductivity or structural maintenance effect, and if it exceeds 1 part by weight, the resistance increases due to an increase in the lithium ion path, which may lower the charge / discharge efficiency, which is not preferable. Specifically, it may be less than 0.05 to 0.3 part by weight.

[0066] The diameter and length of the cross-section of the conductive fiber can be determined according to the particle size of the granular core particles or the final porous silicone composite, and for example, the diameter of the cross-section of the conductive fiber can be 10 to 500 nm, and the length can be 0.1 to 100 μm. The conductive fiber can have a diameter that is substantially uniform or variable, and at least a portion of its long axis can be straight, curved, folded, or branched.

[0067] In anode active materials, porosity is a key factor affecting battery performance. A higher porosity leads to more gas within the anode, which in turn affects electrical conductivity and gas diffusion rates within the battery. Therefore, increasing porosity can improve battery electrical performance. However, the material that forms the pores, namely the pore-forming agent, has low electrical conductivity and can degrade battery performance. Therefore, it must be completely removed from the final battery. Removing the pore-forming agent can create gaseous spaces within the anode, increasing porosity.

[0068] In the present invention, the polymer pore-forming agent is a sacrificial material in the form of a polymer used to increase the porosity of the negative electrode active material. It is temporarily used in the manufacturing process of the negative electrode active material, and then is mostly removed in the first carbonization process due to a low carbon conversion rate, and is eventually completely removed in the final product, thereby increasing the porosity and improving the electrical performance and stability of the paper.

[0069] The polymer pore-forming agent may be, for example, PVA (Polyvinyl Alcohol) or PMMA (Polymethyl Methacrylate), but is not limited thereto. Such PVA and PMMA may be added during the active material manufacturing process and then removed using water, other solvents, etc.

[0070] If the content of the polymer pore forming agent is less than 5 parts by weight, it is difficult to achieve a sufficient adhesive effect, and if it exceeds 40 parts by weight, the manufacturing process may be degraded and it is difficult to sufficiently remove it during the manufacturing process, which is not preferable. Specifically, it may be 8 to 20 parts by weight.

[0071] There is no limitation on the organic dispersion medium as long as it is commonly used, and for example, at least one selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran can be used.

[0072] If the organic dispersion medium content is less than 700 parts by weight or 1500 parts by weight, the subsequent granulation process may be difficult, which may lower the manufacturing processability, and thus is not preferable. Specifically, it may be 800 parts by weight to 1200 parts by weight.

[0073] In step (b), the above composite slurry can be spray granulated to produce granular core particles.

[0074] The above spray granulation can be performed by a general drying method including rotary spraying, nozzle spraying, ultrasonic spraying, or a combination thereof, and the flow rate of the solution, spraying pressure, spraying speed, and performing temperature during spraying can be appropriately adjusted according to the average particle diameter of the granule core particles to be manufactured.

[0075] As an example, in the present invention, the composite slurry may be spray-dried through a spray nozzle at a temperature range of 80 to 150°C at an inlet temperature or outlet temperature of 3 to 4 bar, and then the dry powder may be recovered. If the temperature and pressure conditions deviate from the above, the particle size of the granular core particles may become excessively small or large, which may affect the manufacturing process, such as the drying time, and is therefore undesirable.

[0076] The above spray nozzle may be, for example, an atomized nozzle, a two-fluid nozzle, a rotary nozzle, a flat jet nozzle, a concentric nozzle, a porous nozzle, an ultrasonic spray nozzle, etc. These nozzles may be appropriately selected depending on the desired particle size distribution, purpose, environment, productivity, etc.

[0077] For example, atomized nozzles utilize the high-speed rotation of a disk to spray, allowing them to be used even at relatively high viscosities. Two-fluid nozzles, which break down droplets into spray particles by high-pressure fluid (gas) at the nozzle tip, are difficult to use at high viscosities, but they offer the advantage of utilizing high spray pressure to create smaller, more uniform particle sizes.

[0078] The average particle size of the above granular core particles may be 1 to 30 μm. If the average particle size of the granular core particles is 1 μm, the agglomeration of particles becomes severe, making it difficult to properly perform the subsequent coating process. If it exceeds 30 μm, the spray drying process may not be smoothly performed, which may deteriorate the manufacturing process, which is not preferable. Specifically, the average particle size may be 5 to 20 μm.

[0079] In step (d), a second amorphous carbon precursor can be applied to the granular core particles and a first heat treatment can be performed to manufacture a carbon composite.

[0080] The second amorphous carbon precursor may be at least one selected from the group consisting of coal-based pitch, petroleum-based pitch, mesophase pitch, polyvinyl chloride, and tar.

[0081] The weight ratio of the granular core particles and the second amorphous carbon precursor may be 60:40 to 95:5. If the content of the granular core particles is too large or the content of the second amorphous carbon precursor is too small beyond the above range, it is difficult to provide sufficient strength, and if the content of the granular core particles is too small or the content of the second amorphous carbon precursor is too large, agglomeration occurs, which lengthens the pulverization process and causes the spherical powder shape to collapse and become amorphous, which may deteriorate the overall characteristics of a battery using the same, which is undesirable.

[0082] The above first heat treatment temperature may be 800 to 1000°C. Within the above temperature range, a high-density second amorphous carbon layer is formed, which can minimize structural changes in the active material due to volume expansion of silicon during the charge / discharge process of the battery and can block contact with the electrolyte, thereby improving overall performance of the battery. Specifically, the temperature may be 850 to 950°C.

[0083] In some cases, the step (d) may include: a step of applying crystalline carbon to the granular core particles; and a step of applying a second amorphous carbon precursor to the granular core particles to which the crystalline carbon has been applied and performing a first heat treatment to produce a carbon composite.

[0084] By applying the above crystalline carbon, the effects of improving conductivity, suppressing volume expansion, blocking electrolyte contact with the interior of particles, and preventing absorption of solution during polymer coating during the process can be obtained.

[0085] The weight ratio of the granular core particles and the crystalline carbon may be 99:1 to 99.9:0.1. If the content of the granular core particles is too large or the content of the crystalline carbon is too small beyond the above range, it is difficult to provide sufficient conductivity, and if the content of the granular core particles is too small or the content of the crystalline carbon is too large, agglomeration occurs, which prolongs the pulverization process and the spherical powder shape may collapse and become amorphous, which may deteriorate the overall characteristics of the battery using the same, which is not preferable.

[0086] The above-mentioned crystalline carbon can further improve electrical conductivity by forming a conductive path. The conductive carbon is not limited to any known material in the art, but may be, for example, one or a combination of two or more materials selected from the group consisting of natural graphite, artificial graphite, expanded graphite, graphene, carbon black, and fullerene soot, but is not limited thereto. Specifically, it may be graphene, which is a single layer of graphite.

[0087] The weight ratio of the granular core particles coated with the above crystalline carbon and the second amorphous carbon precursor may be 60:40 to 95:5. If the content of the granular core particles is too large or the content of the second amorphous carbon precursor is too small beyond the above range, it is difficult to provide sufficient strength, and if the content of the granular core particles is too small or the content of the second amorphous carbon precursor is too large, agglomeration may occur, which lengthens the pulverization process and may cause the spherical powder shape to collapse and become amorphous, which may deteriorate the overall characteristics of a battery using the same, which is undesirable.

[0088] The above first heat treatment temperature may be 800 to 1000°C. Within the above temperature range, a high-density second amorphous carbon layer is formed, which can minimize structural changes in the active material due to volume expansion of silicon during the charge / discharge process of the battery and can block contact with the electrolyte, thereby improving overall performance of the battery. Specifically, the temperature may be 850 to 950°C.

[0089] In step (a), a third amorphous carbon precursor can be applied to the carbonized composite and a second heat treatment can be performed.

[0090] The third amorphous carbon precursor is, for example, one selected from the group consisting of coal pitch, petroleum pitch, mesophase pitch, tar, low molecular weight heavy oil, glucose, gelatin, sugars, phenol resins, naphthalene resins, furfuryl alcohol resins, polyamide resins, furan resins, polyimide resins, epoxy resins, vinyl chloride resins, gum arabic, citric acid, stearic acid, sucrose, polyvinylidene fluoride, carboxymethylcellulose (CMC), hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, starch, polyacrylic acid, sodium polyacrylate, polyacrylonitrile (PAN), cellulose, styrene, polyvinyl alcohol, and polyvinyl chloride. It could be more than just a species.

[0091] The weight ratio of the above carbon composite and the third amorphous carbon precursor may be 60:40 to 95:5. If the content of the granular core particles is too large or the content of the third amorphous carbon precursor is too small beyond the above range, it is difficult to provide sufficient strength, and if the content of the granular core particles is too small or the content of the third amorphous carbon precursor is too large, agglomeration occurs, which prolongs the pulverization process and the spherical powder shape may collapse and become amorphous, which may deteriorate the overall characteristics of a battery using the same, which is undesirable.

[0092] The second heat treatment temperature may be 900 to 1300°C. Within this temperature range, a high-density carbon layer is formed, which minimizes structural changes in the active material due to volume expansion of silicon during the charge / discharge process of the battery and blocks contact with the electrolyte, thereby improving overall battery performance. Specifically, the temperature may be 960 to 1100°C.

[0093] The present invention provides a porous silicon composite manufactured by the above method.

[0094] The porous silicon composite according to the present invention contains a high content of silicon nanoparticles exhibiting high capacity, and due to the porous structure formed inside, even if the silicon particles repeatedly shrink and expand during the charge and discharge process of the battery, the structure of the composite is maintained while securing a passage for the movement of lithium ions, so that the life characteristics and output characteristics of a lithium secondary battery using the composite can be improved.

[0095] The porous silicon composite manufactured according to the present invention can maintain the structure and high conductivity of the composite through conductive fibers dispersed therein, thereby improving the initial efficiency of a secondary battery using the composite.

[0096] The porous silicon composite manufactured according to the present invention can secure high durability with a stable structure in which amorphous carbon is applied to the surface of granular core particles including silicon nanoparticles.

[0097] In addition, the present invention provides a lithium secondary battery including the porous silicon composite as a negative electrode active material.

[0098] The above lithium secondary battery includes a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and an electrolyte.

[0099] The above positive electrode is formed by applying a positive electrode mixture containing a positive electrode active material to a current collector, and the positive electrode mixture may further include a binder and a conductive material as needed.

[0100] The above positive electrode active material is, for example, LiNi 0.8-x Co 0.2 AlxO2, LiCo x Mn y O2, LiNi x Co y O2, LiNi x Mn y O2, LiNi x Co y Mn z O2, LiCoO2, LiNiO2, LiMnO2, LiFePO4, LiCoPO4, LiMnPO4, and Li4Ti5O 12 Lithium metal oxide (0) <x<1, 0<y<1); Cu2Mo6S8, FeS, CoS 및 MiS 등의 칼코겐화물, 스칸듐, 루테늄, 티타늄, 바나듐, 몰리브덴, 크롬, 망간, 철, 코발트, 니켈, 구리, 아연 등의 산화물, 황화물 또는 할로겐화물이 사용될 수 있으며, 보다 구체적으로는, LiNi 0.8 Co 0.1 Mn 0.1 O2, TiS2, ZrS2, RuO2, Co3O4, Mo6S8, V2O5, etc. can be used, but are not limited thereto.

[0101] The shape of the positive electrode active material is not particularly limited, and may be in the form of particles, such as spheres, ellipses, and rectangular parallelepipeds. The average particle diameter of the positive electrode active material may be in the range of 1 to 50 μm, but is not limited thereto. The average particle diameter of the positive electrode active material can be obtained, for example, by measuring the particle diameter of the active material observed by a scanning electron microscope and calculating the average value thereof.

[0102] The above binder is not particularly limited, and fluorine-containing binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) may be used, but are not limited thereto.

[0103] The content of the above binder is not particularly limited as long as it can fix the positive electrode active material, and may be within the range of 0 to 10 wt% with respect to the entire positive electrode.

[0104] The above conductive material is not particularly limited as long as it can improve the conductivity of the anode, and examples thereof include nickel powder, cobalt oxide, titanium oxide, carbon, etc. Specifically, the carbon may be any one selected from the group consisting of Ketjen black, acetylene black, furnace black, graphite, carbon fiber, and fullerene, or one or more thereof.

[0105] The content of the above-mentioned conductive material may be selected in consideration of the type of conductive material and other battery conditions, and may be, for example, within the range of 1 to 10 wt% with respect to the entire positive electrode.

[0106] The thickness of the positive electrode mixture layer, which is formed by applying the positive electrode mixture including the positive electrode active material, binder, and conductive agent to a current collector, may be, for example, 0.1 micrometer to 1000 micrometers.

[0107] The above positive electrode mixture may, in some cases, contain the solid electrolyte according to the present invention in an amount of 0.1 wt% to 60 wt%, specifically 10 wt% to 50 wt%, based on the total weight of the positive electrode mixture.

[0108] The thickness of the above-mentioned positive electrode composite layer may be, for example, 0.1 micrometer to 1000 micrometers.

[0109] The above-mentioned positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, various forms such as films, sheets, foils, nets, porous bodies, foams, and non-woven bodies having fine irregularities formed on the surface may be used.

[0110] The negative electrode may be formed by coating a negative electrode mixture containing a negative electrode active material on a negative electrode current collector. The negative electrode active material may be the negative electrode active material according to the present invention, but in some cases, a metal oxide, a metal, a lithium composite oxide, a crystalline carbon, an amorphous carbon, etc. may be used together. The negative electrode mixture may further include a binder and a conductive material having the composition described above, if necessary.

[0111] At this time, the negative electrode current collector is not particularly limited as long as it is conductive and does not cause chemical changes in the lithium secondary battery, and examples thereof include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, aluminum-cadmium alloy, etc. In addition, the negative electrode current collector, like the positive electrode current collector, may be in various forms such as a film, sheet, foil, net, porous body, foam, non-woven body, etc. having fine irregularities formed on the surface.

[0112] The electrolyte consists of an organic solvent and an electrolyte.

[0113] The organic solvent is not limited as long as it is a commonly used one, and for example, at least one selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran can be used.

[0114] There is no limitation on the lithium salt that can be included in the above electrolyte, as long as it is commonly used, and for example, the anion of the above lithium salt is F - , Cl - , I - , NO 3- , N(CN) 2- , BF 4- , ClO 4- , PF 6- , (CF3)2PF 4- , (CF3)3PF 3- , (CF3)4PF 2- , (CF3)5PF - , (CF3)6P - , CF3SO 3- , CF3CF2SO 3- , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO 3- , CF3CO 2- , CH3CO 2- , SCN - and (CF3CF2SO2)2N - One type selected from the group consisting of can be used.

[0115] A secondary battery is completed by placing a separator between the positive and negative electrodes to form a battery structure, winding or folding the battery structure and placing it in a cylindrical or square battery case, and then injecting an electrolyte. Alternatively, a lithium secondary battery is completed by stacking the battery structures in a bi-cell structure, impregnating them with an electrolyte, and placing the resulting product in a pouch and sealing it.

[0116]

[0117] The following examples are provided to illustrate the present invention, but the scope of the present invention is not limited to these examples.

[0118]

[0119] <Example 1>

[0120] Milling silicon in IPA to D 50 These 100 nm silicon nanoparticles were prepared. The pitch was milled in IPA to form a particle size of 200 nm.

[0121] A composite slurry was prepared by adding 55 parts by weight of the above-mentioned milled silicon nanoparticles, 10 parts by weight of the above-mentioned milled pitch, 25 parts by weight of graphite, 10 parts by weight of PVA, and 0.1 parts by weight of CNT to IPA. At this time, the solid concentration was 10 wt%.

[0122] The above composite slurry was spray granulated at 100°C with a fluid pressure of 3.4 bar using a two-fluid nozzle to produce granule core particles having an average particle size (D50) of 10 to 13 micrometers.

[0123] A carbon composite was manufactured by applying 20 wt% of pitch to 80 wt% of the above granular core particles and performing a first heat treatment at 900°C.

[0124] A porous silicon composite was manufactured by applying 20 wt% of pitch to 80 wt% of the above carbon composite and performing a second heat treatment at 1000°C.

[0125]

[0126] <Example 2>

[0127] Granular core particles were manufactured using the same method as in Example 1.

[0128] Afterwards, 0.3 wt% of graphene was applied to 99.7 wt% of the granular core particles to manufacture a graphene composite, and then 20 wt% of pitch was applied to 80 wt% of the graphene composite and a first heat treatment was performed at 900°C to manufacture a carbonized composite.

[0129] A porous silicon composite was manufactured by applying 20 wt% of PAN to 80 wt% of the above carbon composite and performing a second heat treatment at 1000°C.

[0130]

[0131] <Comparative Example 1>

[0132] Milling silicon in IPA to D 50 These 100 nm silicon nanoparticles were prepared. The pitch was milled in IPA to form a particle size of 200 nm.

[0133] A composite slurry was prepared by adding 55 parts by weight of the above-mentioned milled silicon nanoparticles, 20 parts by weight of the above-mentioned milled pitch, and 25 parts by weight of graphite to IPA. At this time, the solid concentration was 20 to 30 wt%.

[0134] The above composite slurry was spray-dried at 100°C using an atomizing nozzle to produce granular core particles.

[0135] A carbon composite was manufactured by applying 20 wt% of pitch to 80 wt% of the above granular core particles and performing a first heat treatment at 900°C.

[0136] A silicon composite was manufactured by applying 20 wt% of pitch to 80 wt% of the above carbon composite and performing a second heat treatment at 1000°C.

[0137]

[0138] Comparative Example 2

[0139] A silicon composite was prepared in the same manner as in Example 1, except that CNTs were not used in preparing the composite slurry in Example 1.

[0140]

[0141] Experimental Example 1

[0142] The composite particles manufactured in Examples 1 and 2 and Comparative Examples 1 and 2 were observed using SEM and are shown in Figures 1a to 1d, respectively.

[0143] According to FIGS. 1a to 1d, it can be confirmed that the composite particles according to Examples 1 and 2 have a more densely formed coating surface compared to the composite particles according to Comparative Examples 1 and 2.

[0144]

[0145] Experimental Example 2

[0146] The cross-sections of the composite particles manufactured in Examples 1, 2 and Comparative Example 1 were observed using SEM and are shown in Figs. 2(a) to 2(c), respectively.

[0147]

[0148] According to FIGS. 2(a) to 2(c), it can be confirmed that the composite particles according to Example 1 have more pores formed compared to Comparative Example 1.

[0149]

[0150] Experimental Example 3

[0151] The specific surface areas of the composite particles manufactured in Examples 1 and 2 and Comparative Examples 1 and 2 were observed using the BET measurement method and are shown in Table 1.

[0152] Specific surface area (m 2 / g) Example 128.017 Example 224.841 Comparative Example 16.993 Comparative Example 222.065

[0153] <Experimental Example 4> CV curves of the composite particle materials manufactured in Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Fig. 3, and CV curves of 500 mAh / g blended electrode plates are shown in Fig. 4. The CV curves of the materials were measured by adding a small amount of conductive agent without mixing graphite in order to measure the capacity of the material itself, and were mixed in the ratios in Table 2. CV of the blended electrode plates were measured with a half-cell for the designed negative electrode plates by adding graphite, and were mixed in the ratios in Table 3.

[0154]

[0155] In addition, the composite particles manufactured in Examples 1 and 2 and Comparative Examples 1 and 2 were used as negative active materials to manufacture half cells under the following conditions, and the charge capacity, discharge capacity, and one-time efficiency were measured, which are shown in Table 4. Specifically, the negative electrode plates manufactured using the composite particles manufactured in Examples 1 and 2 and Comparative Examples 1 and 2 as negative active materials, respectively, were measured at 1.4875 cm 2 Cut it into a circle and use it as a cathode, and 1.4875 cm 2 A lithium (Li) metal thin film cut into a circle was used as the anode. In the design of the negative electrode plate, the rolling density was 1.55 g / cc, and the current density was 2.95 mA / cm 2 , the plate capacity was 500 mAh / g. A porous polyethylene separator was interposed between the positive and negative electrodes, and vinylene carbonate dissolved at 0.5 wt% in a mixed solution of methyl ethyl carbonate (EMC) and ethylene carbonate (EC) having a volume ratio of 7:3 was dissolved, and an electrolyte solution containing 1 M LiPF6 was injected to manufacture a lithium coin half-cell.

[0156] The charge capacity, discharge capacity, and initial efficiency of the lithium coin half cell are shown in Table 2 below.

[0157]

[0158] - Charging conditions: CC / CV, 0.1C, 0.01V & 0.01C cut off

[0159] - Discharge conditions: CC, 0.1C, 1.5V Cut off

[0160] Based on the results of a single charge / discharge cycle, the discharge capacity (mAh / g) and initial efficiency (%) were derived. Specifically, the initial efficiency (%) was derived using the following calculation.

[0161] - Initial efficiency (%) = (1-time discharge post-discharge capacity / 1-time charge capacity) Х 100

[0162] Composite Particles (%) Conductive Material (%) CNT (%) Binder (%) CMCSBR91.95.000.101.501.50

[0163] Composite Particles (%) Graphite (%) Conductive Material (%) CNT (%) Binder (%) CMCSBR18.2077.501.000.101.701.50

[0164] Charge capacity (mAh / g)Discharge capacity (mAh / g)1st efficiency (%)Example 11,5571,33385.6Example 21,5621,35586.7Comparative example 11,5551,31084.3Comparative example 21,5481,31584.9

[0165] According to Table 4, it can be confirmed that the half-cell using the composite particles according to Examples 1 and 2 as the negative electrode active material exhibits high charging / discharging capacity and initial efficiency.

[0166] Experimental Example 5

[0167] The composite particles manufactured in Examples 1 and 2 and Comparative Examples 1 and 2 were used as negative electrode active materials to manufacture negative electrode materials under the conditions of Table 3. Full cells were manufactured under the conditions of NCM622 as the positive electrode material and 1M LiPF6 EC: DEC = 1:1 + FEC 5 wt% as the electrolyte, and the capacity, single-cycle efficiency, and capacity retention rate were measured, which are shown in Table 5. The capacity retention rate (CRR) of the 500 mAh / g blended electrode plate is shown in Fig. 5.

[0168] -Charging conditions: CC / CV, 0.5C, 4.20V & 0.05C cut off

[0169] -Discharge conditions: CC, 1.0C, 2.7V Cut off

[0170] Based on the results of a single charge / discharge cycle, the discharge capacity (mAh / g) and initial efficiency (%) were derived. Specifically, the initial efficiency (%) was derived using the following calculation.

[0171] - Initial efficiency (%) = (1-time discharge post-discharge capacity / 1-time charge capacity) Х 100

[0172] Capacity (mAh / g)1 st Efficiency(%)Retention(%, 300cycle)Example 150689.786.7Example 251390.988.8Comparative Example 149688.378.4Comparative Example 249688.683.3

[0173] According to Table 5, it can be confirmed that the full cell using the composite particles according to Examples 1 and 2 as the negative active material exhibits high capacity, initial efficiency, and capacity retention rate.

Claims

1. (a) A step of preparing a composite slurry by adding silicon-based nanoparticles, a first amorphous carbon precursor, amorphous carbon, conductive fibers, and a polymer pore-forming agent to an organic dispersion medium; (I) A step of manufacturing granule core particles by spray granulating the above composite slurry; (a) a step of applying a second amorphous carbon precursor to the above granular core particles and performing a first heat treatment to produce a carbon composite; and (a) A step of applying a third amorphous carbon precursor to the above carbon composite and performing a second heat treatment to manufacture a porous silicon composite; A method for manufacturing a porous silicon composite, comprising:

2. In paragraph 1, the step (a) is A step of preparing a composite slurry by adding 40 to 70 parts by weight of silicon-based nanoparticles, 5 to 15 parts by weight of a first amorphous carbon precursor, 10 to 40 parts by weight of amorphous carbon, 0.01 to 1 part by weight of conductive fiber, and 5 to 40 parts by weight of a polymer pore-forming agent to 700 to 1500 parts by weight of an organic dispersion medium; A method for manufacturing a porous silicon composite comprising:

3. In paragraph 1, A method for producing a porous silicon composite, wherein the silicon-based nanoparticles are milled in an organic dispersion medium before producing a composite slurry, and have an average particle diameter (D50) of 50 to 200 nm.

4. In paragraph 1, the step (b) is A method for producing a porous silicon composite, comprising spray drying the above composite slurry through a spray nozzle at a temperature of 80 to 150°C and a pressure of 3 to 4 bar, and then recovering the dry powder to produce granular core particles having an average particle size of 1 to 30 μm.

5. In paragraph 1, A method for manufacturing a porous silicon composite, wherein the weight ratio of the above granular core particles and the second amorphous carbon precursor is 60:40 to 95:

5.

6. In the first paragraph, the step (d) is A step of applying crystalline carbon to the above granular core particles; and A step of applying a second amorphous carbon precursor to the granular core particles coated with the above crystalline carbon and performing a first heat treatment to produce a carbon composite; A method for manufacturing a porous silicon composite, comprising:

7. In paragraph 6, A method for manufacturing a porous silicon composite, wherein the weight ratio of the granular core particles and the crystalline carbon is 99:1 to 99.9:0.

1.

8. In paragraph 6, A method for manufacturing a porous silicon composite, wherein the weight ratio of the granular core particles coated with the above crystalline carbon and the second amorphous carbon precursor is 60:40 to 95:

5.

9. In paragraph 1, A method for manufacturing a porous silicon composite, wherein the first heat treatment temperature is 800 to 1000°C.

10. In paragraph 1 or paragraph 6, The first to third amorphous carbon precursors are each one selected from the group consisting of coal pitch, petroleum pitch, mesophase pitch, tar, low molecular weight heavy oil, glucose, gelatin, saccharides, phenol resins, naphthalene resins, furfuryl alcohol resins, polyamide resins, furan resins, polyimide resins, epoxy resins, vinyl chloride resins, gum arabic, citric acid, stearic acid, sucrose, polyvinylidene fluoride, carboxymethylcellulose (CMC), hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, starch, polyacrylic acid, sodium polyacrylate, polyacrylonitrile, cellulose, styrene, polyvinyl alcohol, and polyvinyl chloride. A method for manufacturing a porous silicon composite.

11. In paragraph 1, A method for manufacturing a porous silicon composite, wherein the weight ratio of the above carbon composite and the third amorphous carbon precursor is 60:40 to 95:

5.

12. In paragraph 1, A method for manufacturing a porous silicon composite, wherein the second heat treatment temperature is 900 to 1300°C.

13. A porous silicon composite manufactured by the method according to paragraph 1.

14. A lithium secondary battery comprising a porous silicon composite according to Article 13 as a negative electrode active material.

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