Negative active material, method for preparing the same, negative electrode comprising the same, and secondary battery

Abstract

The present invention relates to a negative active material, a method for preparing the same, a negative electrode comprising the same, and a secondary battery, the negative active material comprising carbon secondary particles assembled from a plurality of carbon primary particles having an average particle diameter (D50) of 5 nm to 200 nm, the carbon secondary particles having an average particle diameter (D50) of 0.5 μm to 20 μm.

Description

Technical Field

[0001] This invention relates to a negative electrode active material, its preparation method, a negative electrode containing the same, and a secondary battery. Specifically, it relates to a negative electrode active material capable of improving the capacity, lifespan, and rate characteristics of a secondary battery, its preparation method, a negative electrode containing the same, and a secondary battery. Background Technology

[0002] Graphite is the primary negative electrode active material in commercial lithium-ion rechargeable batteries. Its layered structure enables reversible electrochemical lithium insertion / extraction, and its low reduction potential allows for high energy density when combined with the positive electrode. However, lithium can only enter and exit through the edge planes of its layered structure. Because graphite is manufactured through a spheroidization process, few edge planes are exposed to the electrolyte, limiting the lithium entry and exit channels. Therefore, during rapid charging, the stagnation of lithium insertion into the graphite active material leads to dendrite formation. This not only reduces the charging speed and lifespan of the rechargeable battery but also causes short circuits at the positive electrode, potentially leading to fires.

[0003] Furthermore, due to the narrow interplanar distance of graphite's substrate (d002 = 0.335 nm), structural deformation occurs during lithium insertion, resulting in a slow initial reaction rate in lithium-ion batteries. Moreover, the Na+ used in next-generation secondary batteries... + K + Mg 2+ Al 3+ The large diameter of cations makes it difficult for them to enter and exit the graphite. Therefore, when graphite is used as the negative electrode active material of a new generation of secondary batteries, it leads to problems such as reduced capacity, lifespan and rate of change of the secondary battery. Summary of the Invention

[0004] The purpose of this invention is to provide a negative electrode active material and a method thereof that can be used in secondary batteries and improve the capacity, lifespan and speed of secondary batteries.

[0005] To achieve the above objectives, the present invention provides a negative electrode active material comprising carbon secondary particles assembled from a plurality of carbon primary particles having an average particle size (D50) of 5 nm to 200 nm, wherein the carbon secondary particles have an average particle size (D50) of 0.5 μm to 20 μm.

[0006] Furthermore, the present invention provides a negative electrode comprising the aforementioned negative electrode active material containing carbon secondary particles.

[0007] Furthermore, the present invention provides a secondary battery comprising the aforementioned negative electrode.

[0008] Meanwhile, the present invention provides a method for preparing a negative electrode active material, comprising: step S100, dissolving a carbonized precursor polymer and a sacrificial polymer in a first solvent as a common solvent to form a first solution; step S200, removing the first solvent from the first solution to form a first aggregate; and step S300, carbonizing the first aggregate, or carbonizing a second aggregate from which the sacrificial polymer has been removed.

[0009] Furthermore, the present invention provides carbon secondary particles assembled from multiple carbon primary particles having an average particle size (D50) of 5 nm to 200 nm, which have a spherical porous structure while having an average particle size (D50) of 0.5 μm to 20 μm.

[0010] The negative electrode active material of the present invention can form a broad interface with the electrolyte, facilitating the entry and exit of cations and exhibiting excellent ion storage capacity. Therefore, it can improve the battery's capacity, lifespan, and speed characteristics. Attached Figure Description

[0011] Figure 1 The image shows a scanning electron microscope (SEM) image of the polyacrylonitrile (PAN) secondary particles prepared in Example 1-1.

[0012] Figure 2 The images are scanning electron microscope (SEM) images of the negative electrode active materials containing carbon secondary particles prepared in Examples 1-2.

[0013] Figure 3 Part (a) is a scanning electron microscope image of the polyacrylonitrile secondary particles prepared in Example 2. Figure 3 Part (b) is a scanning electron microscope image of the polyacrylonitrile secondary particles prepared in Example 1. Figure 3 Part (c) is a scanning electron microscope image of the polyacrylonitrile secondary particles prepared in Example 3.

[0014] Figure 4 A graph showing the average particle size distribution of carbon secondary particles based on the polyacrylonitrile / styrene-co-acrylonitrile (SAN) ratio.

[0015] Figure 5 Part (a) is a focused ion beam microscopy (FIB) image of the cross-section of the carbon secondary particles prepared in Example 4. Figure 5 Part (b) is a transmission electron microscope (TEM) image of the carbon secondary particles prepared in Example 4.

[0016] Figure 6 The initial charge-discharge curves of the lithium-ion battery half-cell prepared in Experimental Example 3 are shown.

[0017] Figure 7 The initial charge-discharge curves of the sodium-ion battery half-cell prepared in Experimental Example 4 are shown. Detailed Implementation

[0018] The present invention will now be described.

[0019] Negative electrode active material and its preparation method

[0020] The negative electrode active material of the present invention comprises carbon secondary particles assembled from multiple primary carbon particles.

[0021] In this case, the average particle size (D50) of the aforementioned primary carbon particles is approximately in the range of 5 nm to 200 nm, specifically, it can be in the range of approximately 5 nm to 100 nm. By assembling multiple such primary carbon particles to aggregate, the average particle size (D50) of the secondary carbon particles of the present invention is approximately in the range of 0.5 μm to 20 μm, specifically, it can be in the range of approximately 1 μm to 10 μm, and more specifically, it can be in the range of approximately 1 μm to 5 μm. The negative electrode active material of the present invention, containing secondary carbon particles having the above-mentioned particle size range, forms a broad interface with the electrolyte, which not only facilitates the formation of lithium ions (Li... + The entry and exit of Na is also easily utilized by the new generation of secondary batteries. + K + Mg 2+ Al 3+ The inflow and outflow of cations are also possible. Furthermore, the negative electrode active material of the present invention can not only increase the electrode density through carbon secondary particles, but also, when carbon secondary particles are mixed with graphite, can increase the charge and discharge speed by compensating for the low starting voltage of graphite, thereby increasing the energy density of the secondary battery.

[0022] Furthermore, in the negative electrode active material of the present invention, the carbon secondary particles have a spherical porous structure. The BET specific surface area of ​​the carbon secondary particles having this spherical porous structure can be 0.5 m². 2 / g to 100m 2 / g range.

[0023] Furthermore, in the negative electrode active material of the present invention, the particle size distribution of the aforementioned carbon secondary particles is uniform and monodisperse. According to one example, the particle size distribution of the aforementioned carbon secondary particles satisfies the following relationship 1.

[0024] Relation 1

[0025] 0.4≤(D90-D10) / D50≤0.7

[0026] In the above formula, D90, D10, and D50 are the particle sizes with a cumulative volume of 90%, 10%, and 50% respectively in the volume-reference particle size distribution determined by laser diffraction particle size distribution method.

[0027] Furthermore, the aforementioned carbon secondary particles may also incorporate microparticles containing one or more metals (M) selected from the group consisting of Group IIIA elements, Group IVA elements, and transition metals. In this case, the negative electrode active material of the present invention can further improve the lithium-ion storage capacity.

[0028] Specifically, examples of the aforementioned metal (M) include tin (Sn), aluminum (Al), silicon (Si), copper (Cu), iron (Fe), cobalt (Co), selenium (Se), nickel (Ni), zinc (Zn), cerium (Ce), and cadmium (Cd), but are not limited thereto. Furthermore, any metal that is electrochemically active within the technical field to which this invention pertains can be used without restriction.

[0029] According to one example, it may also contain one or more metal microparticles selected from the group consisting of tin, aluminum, silicon, and copper. In this case, the negative electrode active material of the present invention can improve the lithium-ion storage capacity.

[0030] In addition to the aforementioned carbon secondary particles, the above-mentioned negative electrode active material may also include graphite. Although the average particle size of the graphite is not particularly limited, considering the average particle size and porosity of the carbon secondary particles, it can be approximately 10 μm to 20 μm, specifically approximately 13 μm to 18 μm.

[0031] In one example, the ratio (D2 / D1) of the graphite particle size (D2) to the particle size (D1) of the aforementioned secondary carbon particles can be 2 to 8. In this case, the ratio of the secondary carbon particles to graphite (mixing ratio) is not particularly limited, and for example, it can be a weight ratio of 5:95 to 90:10. In this case, the energy density and charge / discharge efficiency of the secondary battery can be improved.

[0032] As described above, the carbon secondary particles of the negative electrode active material of the present invention have a spherical porous structure formed by carbon primary particles with an average particle size of less than 200 nm, an average particle size of about 20 μm or less, uniform particle size distribution, and stable structure. Therefore, the negative electrode active material of the present invention can form a broad interface with the electrolyte, facilitating the entry and exit of cations, and exhibits excellent ion storage capacity, thereby improving the battery's capacity, lifespan, and rate characteristics. Such a negative electrode active material of the present invention can be used in all devices that perform electrochemical reactions. For example, all types of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors, with secondary batteries being preferred.

[0033] The aforementioned negative electrode active material of the present invention can be prepared by forming secondary carbon particles through a self-assembly (flocculation) process occurring between different polymer solutions.

[0034] An example of the preparation method of the negative electrode active material of the present invention includes: step S100, dissolving a carbonization precursor polymer and a sacrificial polymer in a first solvent as a common solvent to form a first solution; step S200, removing the first solvent from the first solution to form a first aggregate; and step S300, carbonizing the first aggregate, or carbonizing a second aggregate from which the sacrificial polymer has been removed. However, the method is not limited to the above preparation method; the steps of each process can be modified as needed, or selectively combined.

[0035] The following describes the steps for preparing the negative electrode active material of the present invention.

[0036] Step S100: Step to form the first solution

[0037] First, the carbonized precursor polymer and the sacrificial polymer are dissolved in a first solvent, which serves as a common solvent, to form a first solution.

[0038] Step S100 can be performed by mixing the carbonized precursor polymer and the sacrificial polymer and then adding them to the first solvent, or by adding one of the carbonized precursor polymer and the sacrificial polymer to the first solvent before adding the remaining polymer. No chemical reaction occurs between the carbonized precursor polymer and the sacrificial polymer during the mixing process.

[0039] In this invention, the carbonization precursor polymer is a polymer that can be converted into carbon substances through heat treatment. In the solution phase, the carbonization precursor polymer primary particles (hereinafter referred to as "polymer primary particles") are formed in the form of micro-clusters through self-assembly (flocculation). When the first solvent is removed, such polymer primary particles aggregate with the sacrificial polymer to form a blocky first aggregate.

[0040] Non-limiting examples of such carbonization precursor polymers include polyacrylonitrile (PAN), polyvinyl pyrrolidone (PVP), polyimide, polyvinyl alcohol (PVA), polyvinyl chloride (PVC), pitch, lignin, and cellulose. These can be used alone or in combination of two or more. For example, the carbonization precursor polymer can be polyacrylonitrile.

[0041] The aforementioned sacrificial polymer not only does not chemically react with the carbonized precursor polymer, but is also an immiscible polymer that undergoes phase separation when mixed with the carbonized precursor polymer. In the solution phase, it can assist the carbonized precursor polymer in forming micro-clusters through a network, and can also be easily removed by organic solvents.

[0042] According to one example, when the carbonization precursor polymer contains at least one repeating unit, the sacrificial polymer can be a copolymer containing the aforementioned repeating unit. Examples of sacrificial polymers include, but are not limited to, styrene-co-acrylonitrile (SAN), polylactic acid (PLA), poly(lactic-co-glycolic acid) (PLGA), polymethyl methacrylate (PMMA), and poly(vinylidene fluoride) (PVDF). For example, the sacrificial polymer can be styrene-co-acrylonitrile.

[0043] The aforementioned ratio (mixing ratio) of the carbonization precursor polymer to the sacrificial polymer is not particularly limited, and can be, for example, a weight ratio of 1:2 to 9. When the ratio of the carbonization precursor polymer to the sacrificial polymer is within the aforementioned range, carbon secondary particles with a uniform particle size distribution and an average particle size of less than 20 μm can be obtained without reducing the yield. According to one example, the ratio (mixing ratio) of the carbonization precursor polymer to the sacrificial polymer can be 1:3 to 5 by weight. In this case, carbon secondary particles with an average particle size of approximately 2 μm to 6 μm can be easily prepared.

[0044] As an example, the mixing ratio of the carbonization precursor polymer to the sacrificial polymer can be a weight ratio of 1:2 to 9 (e.g., 1:4). In this case, spherical porous carbon secondary particles with a particle size of about 0.5 μm to 20 μm can be prepared in high yield.

[0045] The first solvent mentioned above is a common solvent for the carbonization precursor polymer and the sacrificial polymer; it is not particularly limited as long as it can dissolve them.

[0046] Examples of the first solvent mentioned above include dimethylformamide, diethyl ether, ethanol, methanol, n-propanol, isopropanol, acetone, n-pentane, dichloroethane, methyl acetate, ethyl acetate, acetonitrile, tetrahydrofuran (THF), n-hexane, chlorohexane, chloropentane, carbon tetrachloride, 1,2-dichloroethane, 1,2-dichloroethylene, trichloroethylene, methyl ethyl ketone, or 1,2-dimethoxyethane (DME), but are not limited to these.

[0047] If the first solvent can fully dissolve the carbonized precursor polymer and the sacrificial polymer, their content is not particularly limited.

[0048] The aforementioned method of mixing carbonization precursors and sacrificial polymers is not particularly limited; for example, it can be done using a mixer, a high-speed rotary / rotation mixer, or a ball mill.

[0049] Selectively, in addition to the aforementioned carbonization precursor polymers and sacrificial polymers, a metal precursor comprising one or more metals (M) selected from the group consisting of Group IIIA elements, Group IVA elements, and transition metals may be added to the first solvent of the present invention. Specifically, examples of the aforementioned metals (M) include tin (Sn), aluminum (Al), silicon (Si), copper (Cu), iron (Fe), cobalt (Co), selenium (Se), nickel (Ni), zinc (Zn), cerium (Ce), and cadmium (Cd), but are not limited thereto. Furthermore, any metal precursor comprising a metal that is electrochemically active within the technical field to which this invention pertains can be used without limitation. Such a metal precursor, during carbonization, leaves behind the metal component while other components are removed, thus allowing pores to form in the secondary carbon particles. Furthermore, the remaining metal component is contained within the secondary carbon particles in the form of metal microparticles, thereby increasing the lithium-ion storage capacity.

[0050] For example, one or more metal precursors selected from the group consisting of tin precursors, aluminum precursors, silicon precursors and copper precursors may be added to the first solvent.

[0051] Examples of tin precursors include tin acetate, tin chloride (SnCl2), and tin sulfate (SnSO4). Examples of aluminum precursors include aluminum chloride, aluminum bromide, aluminum sulfate, aluminum nitrate, and aluminum acetate. Examples of silicon precursors include silane (SiH4), dichlorosilane (SiH2Cl2), chlorosilane (SiH3Cl), silicon chloride (SiCl4), hexachlorosilane (Si2Cl6), and tetraethyl orthosilicate (TEOS). Examples of copper precursors include copper chloride (CuCl2), copper nitrate (Cu(NO3)2), copper sulfate (CuSO4), copper acetate ((CH3COO)2Cu), and copper acetoacetate (Cu(acac)2), but are not limited to these.

[0052] The content of the aforementioned metal precursors is not particularly limited. For example, the aforementioned metal precursors can be added such that the C:M elemental ratio based on the carbon (C) of the carbide precursor polymer is 10 to 1:1 (specifically 8 to 3:1). When the content of the metal precursor is within the aforementioned range, the lithium-ion storage capacity can be increased without reducing lifetime characteristics. For example, tin precursors can be added such that the C:M elemental ratio based on the carbon (C) of the carbide precursor polymer is 8 to 3:1.

[0053] Step S200: The step of forming the first aggregate

[0054] The first aggregate can be formed by removing the first solvent from the first solution obtained in step S100 above.

[0055] For example, if the first solution is dried, the first aggregate can be obtained by evaporating and removing the first solvent from the first solution.

[0056] The aforementioned first aggregate consists of block-shaped particles containing primary carbonized precursor polymer particles and sacrificial polymers. Specifically, the first aggregate is formed by the assembly of multiple primary carbonized precursor polymer ions, with sacrificial polymers present among these primary polymer particles.

[0057] Step S300: The step of carbonizing the first aggregate or the second aggregate

[0058] The first aggregate obtained in step S200 above, or the second aggregate from which the sacrificial polymer is removed, is carbonized.

[0059] In step S300, the carbonization precursor polymer particles can be converted into carbon particles by removing the sacrificial polymer, thereby preparing a negative electrode active material containing carbon secondary particles assembled and condensed from primary carbon particles.

[0060] Specifically, in step S300, the first or second aggregate can be carbonized by heating to approximately 600°C to 1600°C (specifically, approximately 800°C to 1200°C) at a heating rate of approximately 3°C / min to 7°C / min under an inert gas atmosphere for approximately 1.5 hours to 2.5 hours (specifically, approximately 1.8 hours to 2.2 hours). In particular, when the first aggregate is carbonized, the carbonization precursor polymer particles within the first aggregate are converted into carbon particles, while the sacrificial polymer within the first aggregate is thermally decomposed and removed, thereby preparing aggregated secondary carbon particles by assembling primary carbon particles. In this case, the secondary carbon particles can be spherical porous structures.

[0061] Prior to the aforementioned carbonization process, the first or second aggregate can be stabilized. Specifically, after heating to approximately 200°C to 300°C (specifically, approximately 250°C to 300°C) at a heating rate of approximately 5°C / min to 15°C / min, the first or second aggregate is heat-treated in an oxygen-containing atmosphere for 0.5 hours to 1.5 hours (specifically, approximately 0.8 hours to 1.2 hours) to stabilize it, and then the stabilized first or second aggregate is carbonized.

[0062] The second aggregate is a particle that is the carbonized precursor polymer remaining after removing the sacrificial polymer from the first aggregate obtained in step S200. It can be obtained by the following steps: step (a), dissolving the sacrificial polymer in the first aggregate using a second solvent that dissolves the sacrificial polymer to form a second solution containing the second aggregate; and step (b), separating the second aggregate from the second solution.

[0063] Step (a) above is a step of removing sacrificial polymers from the first aggregate obtained in step S200. When the first aggregate is placed in the second solvent, the sacrificial polymers in the first aggregate dissolve in the second solvent, resulting in the removal of sacrificial polymers from the first aggregate. The second solution obtained through this process contains a blocky second aggregate formed by the second solvent, the sacrificial polymer component dissolved in the second solvent, and the primary particles of the carbonized precursor polymer.

[0064] The second solvent that can be used in this invention is not particularly limited as long as it is a solvent that can dissolve only the sacrificial polymer in the first aggregate.

[0065] Non-limiting examples of the second solvent mentioned above can be solvents such as ketone solvents (e.g., acetone).

[0066] The content of the second solvent can be adjusted according to the content of the sacrificial polymer or the content of the first aggregate. According to one example, the ratio (W2 / W1) of the second solvent content (W2) to the sacrificial polymer content (W1) can be in the range of approximately 18 to 22. According to another example, the usage ratio (mixing ratio) of the first aggregate to the second solvent can be a weight ratio of 1:14 to 18.

[0067] Step (b) above is the step of separating the second aggregate from the second solution, which can be carried out by a solid-liquid separation process or a drying process of the organic solvent, but is not limited to these.

[0068] The above-described solid-liquid separation process can be carried out using solid-liquid-liquid separation methods commonly known in the technical field to which this invention pertains, such as filter presses, centrifuges, and vacuum filters, but is not limited to these. Such a solid-liquid separation process can be repeated multiple times, for example, approximately 1 to 5 times.

[0069] According to one example, (b) above can be obtained by separating the second aggregate from the second solvent in the second solution using a centrifuge. In the centrifugal separation using the centrifuge described above, the primary particles of the carbonized precursor polymer are easily aggregated due to centrifugal force, thereby making it easier to obtain the second aggregate formed by the secondary particles of the carbonized precursor polymer.

[0070] Selectively, after the above solid-liquid separation process, the second solvent remaining in the second aggregate can be removed by drying the separated second aggregate.

[0071] The drying process of the aforementioned organic solvent removes the second solvent by drying the second solution, thereby separating the second aggregate. During the removal of the second solvent, the sacrificial polymer component dissolved in the second solvent is also removed.

[0072] The drying temperature is not particularly limited, but it is preferable to carry out the drying at a temperature lower than the carbonization temperature of the carbonization precursor polymer to prevent carbonization. According to one example, step (b) can be performed by drying the second solution at a temperature of 90°C to 110°C for 22 to 26 hours. However, the drying time and temperature can be varied depending on the environment.

[0073] negative electrode

[0074] The present invention provides a negative electrode comprising the aforementioned negative electrode active material.

[0075] As an example, the negative electrode of the present invention comprises: a current collector; and a layer of the aforementioned negative electrode active material, located on at least one side of the current collector.

[0076] The aforementioned current collectors are metals with high conductivity that can be easily adhered to by the slurry of the negative electrode active material. Any metal can be used as long as it is non-reactive within the battery's voltage range. Examples include aluminum (Al), copper (Cu), gold (Au), nickel (Ni), titanium (Ti), sintered carbon, stainless steel, aluminum alloys (e.g., aluminum-cadmium alloys), or copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., or meshes or foils prepared from combinations thereof. The thickness of these current collectors is not particularly limited and can range from approximately 3 μm to 500 μm, which is commonly used.

[0077] The aforementioned negative electrode active material layer can be prepared by coating a negative electrode slurry containing the aforementioned negative electrode active material, binder, and solvent, and optionally a conductive material, onto at least one side of the current collector, drying it, and then calendering it.

[0078] The description of the aforementioned negative electrode active material is the same as the previous content, therefore its description will be omitted.

[0079] Based on the total amount of the negative electrode slurry, the content of the above-mentioned negative electrode active material can be approximately 80% to 99% by weight.

[0080] The aforementioned adhesive binds the negative electrode active material particles together while simultaneously attaching the negative electrode active material to the current collector. It is not particularly limited to any adhesive commonly used within the technical field to which this invention pertains. Examples include polyvinylidene fluoride-co-hexafluoropropylene (PVDF-co-HEP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, styrene-butadiene rubber (SBR), lithium-substituted polyacrylate (Li-PAA), etc., which can be used alone or in combination of two or more.

[0081] The content of the aforementioned binder is not particularly limited; for example, based on the total amount of the negative electrode slurry, it can be from approximately 0.1% to 20% by weight.

[0082] The aforementioned conductive materials are used to impart conductivity to the electrodes and are not particularly limited as long as they do not cause chemical changes in the constructed battery and possess conductivity. Examples include natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, conductive fibers (e.g., carbon fibers or metal fibers), metal powders (e.g., fluorocarbons, copper, aluminum, nickel, silver powders), conductive whiskers (e.g., zinc oxide, potassium titanate), conductive metal oxides (e.g., titanium oxide), conductive polymers (e.g., polyphenylene derivatives), or mixtures thereof. Based on the total amount of the negative electrode slurry composition, the content of the aforementioned conductive materials can be approximately 0.1% to 20% by weight.

[0083] Non-limiting examples of the solvents mentioned above include dimethyl sulfoxide (DMSO), N-methyl pyrrolidone (NMP), and dimethylformamide (DMF). The content of these solvents is not particularly limited, and they can be used in amounts that give the negative electrode slurry a preferred viscosity.

[0084] The method for applying the negative electrode slurry described above is not particularly limited as long as it is a method commonly used in the technical field to which this invention pertains. For example, there are slot extrusion coating, gravure coating, dip coating, and spray coating methods.

[0085] Secondary batteries

[0086] On the other hand, the present invention provides a secondary battery comprising the aforementioned electrodes.

[0087] The secondary battery of the present invention comprises the aforementioned negative electrode, positive electrode, electrolyte, and separator. Such a secondary battery can be used in all devices that undergo continuous chemical reactions through charging and discharging, for example, it can be a lithium (Li) secondary battery, a sodium (Na) secondary battery, etc. According to one example, the secondary battery of the present invention can be a lithium-ion secondary battery or a sodium-ion secondary battery.

[0088] The aforementioned positive electrode can be prepared by mixing positive electrode active material, conductive material, adhesive and solvent to prepare a positive electrode slurry and then directly coating it onto the current collector, or by casting it onto a separate support and then laminating the positive electrode active material film peeled off from the support onto the current collector.

[0089] The positive electrode active material used in this invention is not particularly limited as long as it is a positive electrode active material used in secondary batteries (such as lithium-ion secondary batteries, sodium-ion secondary batteries, etc.) within the technical field to which this invention pertains. Non-limiting examples of positive electrode active materials include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, and Li(Ni) a Co b Mn c)O2 (0 < a < 1, 0 < b < 1, a + b + c = 1), LiNi 1-Y Co Y O2, LiCo 1-Y Mn Y O2, LiNi 1-Y Mn Y O2 (where 0 ≤ Y < 1), Li(Ni a Co b Mn c )O4 (0 < a < 2, 0 < b < 2, a + b + c = 2), LiMn 2-Z Ni Z O4, LiMn 2-Z Co Z O4 (where 0 < Z < 2), lithium transition metal oxides such as LiCoPO4, LiFePO4, and their mixtures; Na x CoO2 (where 0 < x ≤ 1), Na x Co 2 / 3 Mn 1 / 3 O2 (where 0 < x ≤ 1), Na x Fe 1 / 2 Mn 1 / 2O2 (where 0 < x ≤ 1), NaCrO2, NaLi 0.2 Ni 0.25 Mn 0.75 O 2.35 、Na 0.44 MnO2, NaMnO2, Na 0.7 VO2, Na 0.33 V2O5, Na3V2(PO4)3, NaFePO4, NaMn 0.5 Fe 0.5 PO4, Na3V2(PO4)3, Na2FePO4F, Na3V2(PO4)3, NaFeSO4F, and their mixtures, etc., such as sodium transition metal oxides.

[0090] The descriptions of the above conductive materials, adhesives, and solvents are the same as those described in the previous negative electrode part, and the descriptions thereof will be omitted.

[0091] The separation membrane described above is not particularly limited as long as it is used as a separation membrane within the technical field to which this invention pertains. Porous separation membranes are preferred, and in particular, porous polymer films prepared from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers can be used; as well as porous nonwoven fabrics prepared from high-melting-point glass fibers, polyethylene terephthalate fibers, etc., can be used alone or in layers of two or more. In addition, insulating films with ion permeability and mechanical strength can also be used.

[0092] The electrolyte may contain non-aqueous solvents and electrolyte salts, and may also selectively contain additives such as overcharge inhibitors.

[0093] There are no particular restrictions on non-aqueous solvents, as long as they are commonly used as non-aqueous electrolytes. Cyclic carbonates, linear carbonates, lactones, ethers, esters, or ketones can be used.

[0094] Examples of the aforementioned cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butenyl carbonate (BE), and fluoroethylene carbonate (FEC). Examples of the aforementioned linear carbonates include diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl ethyl carbonate (EMC), and methyl propyl carbonate (MPC). Examples of the aforementioned lactones include γ-butyrolactone (GBL). Examples of the aforementioned ethers include dibutyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and 1,2-dimethoxyethane. Furthermore, examples of the aforementioned esters include methyl n-acetate, methyl propionate, and methyl pivalate, and examples of the aforementioned ketones include polymethyl vinyl ketone. These non-aqueous solvents can be used alone or in mixtures of two or more.

[0095] Electrolyte salts are not particularly restricted as long as they are commonly used as non-aqueous electrolytes. Examples of non-restricted electrolyte salts include those with A... + B - Salts with structures like A + For including Li + Na + K + B is an ion composed of metal ions or combinations thereof. - Includes PF6 - BF4 - Cl - ,Br - I - ClO4 - AsF6 - CH3CO2 - CF3SO3 - N(CF3SO2)2- C(CF2SO2)2 - These are anions or combinations thereof that form ions. These electrolyte salts can be used alone or in mixtures of two or more. For example, the electrolyte salt can be a lithium salt or a sodium salt.

[0096] The aforementioned secondary battery can be prepared by forming an electrode assembly by configuring a separation membrane between the positive and negative electrodes, then placing the electrode assembly in a bag, cylindrical battery case, or square battery, and finally injecting electrolyte. Alternatively, the electrode assemblies can be stacked, immersed in electrolyte, and the resulting product placed in a battery case and sealed.

[0097] Such secondary batteries can be used not only as batteries in small devices, but also as unit cells in large and medium-sized battery modules containing multiple batteries. Examples of such large and medium-sized devices include electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems. They are particularly useful in hybrid electric vehicles requiring high output power and in new renewable energy storage batteries.

[0098] The present invention will now be described in more detail through examples and comparative examples. However, the following examples are merely illustrative of the invention, and the scope of the invention is not limited to these examples.

[0099] Example 1

[0100] 1-1. Preparation of secondary polymer particles

[0101] Polyacrylonitrile was used as a carbonization precursor polymer, and styrene-co-acrylonitrile (styrene repeating units : acrylonitrile repeating units = 7 : 3) was used as a sacrificial polymer. The mixture was prepared at a weight ratio of 1:4 (polyacrylonitrile : styrene-co-acrylonitrile) and dissolved in N,N-dimethylformamide (DMF) as a co-solvent to obtain a first solution. Then, the N,N-dimethylformamide was evaporated from the first solution to obtain a bullion aggregate. Next, 1 g of the aggregate was added to 20 g of acetone, a solvent that can only dissolve styrene-co-acrylonitrile, to dissolve the styrene-co-acrylonitrile within the aggregate, thus obtaining a second solution. The obtained second solution was a solution containing polyacrylonitrile secondary particles after removing styrene-co-acrylonitrile from the aggregate. Then, after separating the polyacrylonitrile secondary particles from the second solution by five centrifugations, the separated polyacrylonitrile particles were dried at 100°C for 24 hours to remove acetone from the polyacrylonitrile secondary particles.

[0102] Figure 1The image shows a scanning electron microscope (SEM) image of the polyacrylonitrile secondary particles prepared above. The particle size of the polyacrylonitrile secondary particles is approximately 3 μm to 5.1 μm (refer to...). Figure 1 (a) of the particles are spherical (see reference). Figure 1 Part (b) is composed of primary particles of approximately 46 nm to 53 nm, and can be particles with a porous structure (see reference). Figure 1 (c) score).

[0103] 1-2. Preparation of negative electrode active material

[0104] After heating to 280°C at a heating rate of 10°C / min, the polyacrylonitrile secondary particles obtained in Example 1-1 were stabilized in an air atmosphere for 1 hour, and then carbonized in an N2 atmosphere at a heating rate of 5°C / min to about 1000°C to prepare a negative electrode active material containing carbon secondary particles.

[0105] Figure 2 The scanning electron microscope images of the aforementioned secondary carbon particles confirm that they are spherical (see reference). Figure 2 Parts (a) and (b) are composed of multiple primary carbon particles assembled together, forming porous particles (see reference). Figure 2 (part (c)).

[0106] Example 2

[0107] Except for mixing polyacrylonitrile and styrene-CO-acrylonitrile in a weight ratio of 1:9 (polyacrylonitrile: styrene-CO-acrylonitrile), polyacrylonitrile secondary particles and negative electrode active materials were prepared in the same manner as in Example 1.

[0108] Example 3

[0109] Except for mixing polyacrylonitrile and styrene-CO-acrylonitrile in a weight ratio of 3:7 (polyacrylonitrile: styrene-CO-acrylonitrile), polyacrylonitrile secondary particles and negative electrode active materials were prepared in the same manner as in Example 1.

[0110] Experimental Example 1

[0111] In the process of preparing the negative electrode active material of the present invention, in order to confirm the change in the morphology and size of the secondary particles of the carbonized precursor polymer with the mixing ratio of the carbonized precursor polymer and the sacrificial polymer, scanning electron microscopy was used to confirm the polyacrylonitrile secondary particles prepared in Examples 2, 1, and 3, respectively. The results are as follows: Figure 3 Parts (a) to (c) are shown.

[0112] like Figure 3 As shown, the smaller the ratio of styrene-CO-acrylonitrile content to polyacrylonitrile content (…), the better. Figure 3 Part (a) (Example 2) → Figure 3 (b) (Example 1) → Figure 3 In part (c) (Example 3), the particle size of the polyacrylonitrile secondary particles is larger, but the porosity is reduced. Conversely, the smaller the ratio of styrene-CO-acrylonitrile content to polyacrylonitrile content, the better. Figure 3 Part (c) (Example 3) → Figure 3 (b) (Example 1) → Figure 3 In part (a) (Example 2), the smaller the particle size of the polyacrylonitrile secondary particles, the lower the yield.

[0113] Experiment Example 2

[0114] In the process of preparing the negative electrode active material of the present invention, in order to confirm the change in the average particle size of the carbon secondary particles with the mixing ratio of the carbonization precursor polymer and the sacrificial polymer, the particle size of the carbon secondary particles prepared in Examples 1 to 3 was measured respectively, and the results are as follows: Figure 4 As shown.

[0115] like Figure 4 As shown, the average particle size of the carbon secondary particles ranges from approximately 2 μm to 8 μm depending on the weight ratio of polyacrylonitrile to styrene-CO-acrylonitrile (polyacrylonitrile:styrene-CO-acrylonitrile). In particular, when the content of polyacrylonitrile is reduced to less than 20% by weight, carbon secondary particles with an average particle size of approximately 2 μm to 5 μm can be easily prepared.

[0116] Example 4

[0117] Except for obtaining a first solution by dissolving tin acetate (II) in N,N-dimethylformamide while simultaneously dissolving polyacrylonitrile and styrene-CO-acrylonitrile to obtain a first solution, secondary polyacrylonitrile particles and secondary carbon particles were prepared by the same method as in Example 1. In this case, tin acetate (II) was added such that the elemental ratio of C:Sn to carbon (C) of polyacrylonitrile was 5:1.

[0118] Figure 5 Part (a) is a focused ion beam microscopy photograph of the cross-section of the aforementioned secondary carbon particles. Figure 5 Part (b) is a transmission electron microscope image of the aforementioned carbon secondary particles.

[0119] Experimental Example 3

[0120] A negative electrode was prepared by mixing the negative electrode active material prepared in Example 1, super P as the conductive material, and polyvinylidene fluoride as the binder in a weight ratio of 80:10:10 (carbon secondary particles: conductive material: binder). Then, a lithium-ion battery half-cell was prepared using the negative electrode prepared above, and the initial charge-discharge capacity was measured at a rate of 20 mA / g between 0.005V and 2V. The measurement results are as follows: Figure 6 As shown. In this case, the electrolyte composition is a 1.2M LiPF6 ethylene carbonate / methyl ethyl carbonate solution (1.2M LiPF6 in EC / EMC).

[0121] The measurement results show that the initial discharge capacity of the aforementioned lithium-ion battery half-cell is approximately 687 mAh / g, the initial charge capacity is approximately 454 mAh / g, and the initial efficiency is 66%. This is about 22% higher in reversible capacity compared to the graphite anode material with a theoretical capacity of approximately 372 mAh / g.

[0122] Experiment Example 4

[0123] A negative electrode was prepared by mixing the negative electrode active material prepared in Example 1, super P as the conductive material, and polyvinylidene fluoride as the binder in a weight ratio of 80:10:10 (carbon secondary particles: conductive material: binder). Then, a sodium-ion battery half-cell was prepared using the negative electrode prepared above, and the initial charge-discharge capacity was measured at a rate of 20 mA / g between 0.005V and 2V. The measurement results are as follows: Figure 7 As shown. In this case, the electrolyte composition is 1.0M NaPF6 propylene carbonate solution + 2% FMC (1M NaPF6 in PC + 2% FMC).

[0124] like Figure 7 As shown, the initial discharge capacity of the sodium-ion battery half-cell is approximately 283 mAh / g, the initial charge capacity is approximately 160 mAh / g, and the initial efficiency is approximately 56%.

Claims

1. A negative electrode active material, characterized in that, Carbon secondary particles comprising a plurality of carbon primary particles assembled together, the carbon primary particles having an average particle diameter D 50 of 5 nm to 200 nm, The above-mentioned carbon secondary particles have an average particle diameter D of 0.5 μm to 20 μm 50 , a specific surface area of 0.5 m 2 / g to 100 m 2 / g, and The particle size distribution of the aforementioned secondary carbon particles satisfies the following relationship 1: Relationship 1 : 0.4 ≤ (D 90 D 10 ) / D 50 ≤ 0.7 In the above formula, D 90 D 10 and D 50 These represent the particle sizes with a cumulative volume percentage of 90%, 10%, and 50% respectively in the volume-reference particle size distribution determined by laser diffraction particle size distribution method.

2. The negative electrode active material according to claim 1, characterized by The aforementioned carbon secondary particles have a spherical porous structure.

3. The negative electrode active material according to claim 1, characterized by It also contains graphite.

4. The negative electrode active material according to claim 3, characterized by The ratio of the graphite particle size D2 to the aforementioned carbon secondary particle size D1, D2 / D1, is between 2 and 8. The weight ratio of the aforementioned secondary carbon particles to graphite is 5:95 to 90:

10.

5. A negative electrode characterized by comprising: It comprises the negative electrode active material according to any one of claims 1 to 4.

6. A secondary battery characterized by comprising: It includes the negative electrode as described in claim 5.

7. A method for producing a negative electrode active material, characterized by, The negative electrode active material contains materials with a spherical structure and an average particle size D. 50 The carbon secondary particles are 0.5 μm to 20 μm in size, and the carbon secondary particles have an average particle size D of 5 nm to 200 nm. 50 It is assembled from multiple primary carbon particles. The method includes: Step S100: The carbonized precursor polymer and the sacrificial polymer are dissolved in a first solvent as a common solvent to form a first solution, wherein the carbonized precursor polymer and the sacrificial polymer undergo phase separation and self-assemble to form carbonized precursor polymer primary particles in the form of micro-clusters. Step S200: Remove the first solvent from the first solution to form a blocky first aggregate, wherein after removing the first solvent, the first aggregate comprises the following structure: a plurality of carbonized precursor polymer primary particles aggregated with sacrificial polymers, and the sacrificial polymers are present between the primary particles; and Step S300: Carbonize the first aggregate or carbonize the second aggregate from which the sacrificial polymer is removed; The weight ratio of the carbonized precursor polymer to the sacrificial polymer is in the range of 1:2 to 9.

8. The method of producing a negative electrode active material according to claim 7, characterized by, The aforementioned second aggregate is formed through the following steps: The step of using a second solvent to dissolve the sacrificial polymer in the first aggregate to form a second solution containing the second aggregate; and The step of separating the second aggregate from the second solution described above.

9. The method of producing a negative electrode active material according to claim 7, characterized by, The aforementioned carbonized precursor polymer comprises one or more of the following groups: polyacrylonitrile, polyvinylpyrrolidone, polyimide, polyvinyl alcohol, polyvinyl chloride, asphalt, lignin, and cellulose.

10. The method of producing a negative electrode active material according to claim 7, characterized by, The aforementioned sacrificial polymer comprises one or more of the group consisting of styrene-co-acrylonitrile, polylactic acid, polylactic acid-glycolic acid copolymer, polymethyl methacrylate, and polyvinylidene fluoride.

11. The method of producing a negative electrode active material according to claim 7, characterized by, The first solvent further comprises a metal precursor, which comprises one or more metals M selected from the group consisting of group IIIA elements, group IVA elements and transition metals.

12. The method of producing a negative electrode active material according to claim 11, characterized by, The above-mentioned metal precursor is added so that the elemental ratio of C to M based on the carbon C of the above-mentioned carbonized precursor polymer is 10 to 1:

1.

13. The method of producing a negative electrode active material according to claim 8, characterized by, The ratio of the content of the second solvent W2 to the content of the sacrificial polymer W1, W2 / W1, is in the range of 18 to 22.

14. The method of producing a negative electrode active material according to claim 8, characterized by, The weight ratio of the first aggregate to the second solvent is 1:14 to 18.

15. The method of producing a negative electrode active material according to claim 7, characterized by, In the above carbonization step, the first aggregate or the second aggregate is heat-treated after being heated to 600℃~1600℃ in an inert gas atmosphere.

16. The method of producing a negative electrode active material according to claim 15, characterized by, After heating to 200℃~300℃, the first or second aggregate is stabilized by heat treatment in an oxygen-containing atmosphere, and then carbonization is carried out as described above.

17. A carbon secondary particle, characterized by, The average particle size D is from 5 nm to 200 nm. 50 It is assembled from multiple primary carbon particles, with an average particle size D of 0.5 μm to 20 μm. 50 and 0.5m 2 / g to 100m 2 While possessing a specific surface area of ​​ / g, it also exhibits a spherical porous structure, and The particle size distribution of the aforementioned secondary carbon particles satisfies the following relationship 1: Relationship 1: 0.4 ≤ (D 90 D 10 ) / D 50 ≤ 0.7 In the above formula, D 90 , D 10 , and D 50 are the particle diameters at 90 vol%, 10 vol%, and 50 vol%, respectively, of the cumulative volume in the volume-based particle size distribution by laser diffraction particle size distribution measurement.

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