Silicon-based negative electrode active material, method for producing the silicon-based negative electrode active material, negative electrode containing the silicon-based negative electrode active material, secondary battery containing the negative electrode

Abstract

The present invention relates to a silicon-based negative electrode active material including silicon particles, a core including cetyltrimethylammonium arranged on the surface of the silicon particles, and Mxene arranged on the core and having a hydroxyl group on the surface, a method for producing the silicon-based negative electrode active material, a negative electrode including the silicon-based negative electrode active material, and a secondary battery including the negative electrode.

Description

[Technical Field]

[0001] This application claims priority under Korean Patent Application No. 10-2021-0120515 dated September 9, 2021, and all content disclosed in the said Korean Patent Application is incorporated herein by reference.

[0002] The present invention relates to a silicon-based negative electrode active material comprising a core containing silicon particles and cetyltrimethylammonium disposed on the surface of the silicon particles, and Mxene disposed on the core and having hydroxyl groups on its surface, a method for producing the silicon-based negative electrode active material, a negative electrode containing the silicon-based negative electrode active material, and a secondary battery containing the negative electrode. [Background technology]

[0003] Recently, with the increasing development and demand for mobile device technologies, the demand for batteries as an energy source has risen sharply, and consequently, various research projects are being conducted on batteries that can meet diverse needs. In particular, research is actively being conducted on lithium-ion secondary batteries that have high energy density as well as excellent lifespan and cycle characteristics, making them ideal power sources for such devices.

[0004] A lithium secondary battery refers to a battery in which a non-aqueous electrolyte containing lithium ions is contained in an electrode assembly that includes a positive electrode containing a positive electrode active material capable of inserting and removing lithium ions, a negative electrode containing a negative electrode active material capable of inserting and removing lithium ions, and a microporous separator interposed between the positive and negative electrodes.

[0005] Silicon particles can be used as the negative electrode active material. However, since silicon particles have very low electrical conductivity, a large amount of conductive material is required in the negative electrode, which relatively reduces the content of the negative electrode active material and lowers the energy density of the negative electrode.

[0006] To solve such problems, a technique of forming a carbon coating layer on the surface of the silicon particles is used. Specifically, amorphous carbon can be provided as the carbon coating layer, or graphene can also be used. However, in the process of disposing the graphene on the surface of the silicon particles, defects are easily generated in the graphene, which causes the problem of decreased electrical conductivity. Therefore, in order to improve conductivity more effectively, methods for improving the bonding force between silicon particles and the coating material, either by using other coating materials, have been studied.

[0007] In particular, in order to increase the bonding force between the material to be coated and the silicon particles, techniques including a polymer binder in the coating material are sometimes used, but there is also a problem that conductivity is partially reduced by the polymer binder. Summary of the Invention Problems to be Solved by the Invention

[0008] One object of the present invention is to provide a silicon-based negative electrode active material capable of improving the rate characteristics and cycle life characteristics of a battery.

[0009] Another object of the present invention is to provide a method for producing the silicon-based negative electrode active material.

[0010] Still another object of the present invention is to provide a negative electrode comprising the silicon-based negative electrode active material.

[0011] A still further object of the present invention is to provide a secondary battery comprising the negative electrode. Means for Solving the Problems

[0012] According to one embodiment of the present invention, there is provided a silicon-based negative electrode active material comprising: a core containing silicon particles and cetyltrimethylammonium disposed on the surface of the silicon particles; and Mxene disposed on the core and having hydroxy groups on the surface thereof.

[0013] According to another embodiment of the present invention, there is provided a method for producing a silicon-based negative electrode active material, comprising the steps of: mixing silicon particles and cetyltrimethylammonium bromide, and disposing cetyltrimethylammonium on the silicon particles to form a core; and mixing the core and Mxene having hydroxy groups on the surface, and disposing the Mxene having hydroxy groups on the surface on the core.

[0014] According to still another embodiment of the present invention, there is provided a negative electrode comprising the above silicon-based negative electrode active material.

[0015] According to still another embodiment of the present invention, there is provided a secondary battery comprising the above negative electrode.

Effects of the Invention

[0016] In the silicon-based negative electrode active material according to the present invention, Mxene having hydroxy groups on the surface can be effectively coated on silicon particles via cetyltrimethylammonium. Specifically, the positive charge of the cetyltrimethylammonium allows the silicon-based particles and the surface of the core containing the cetyltrimethylammonium to exhibit positive charge, and the combination of the positive charge and the negative charge of Mxene having hydroxy groups on the surface enables the Mxene to be stably coated on the surface of the core. Thereby, the electrical conductivity of the silicon-based negative electrode active material is improved, and the rate performance and cycle life performance of the battery can be improved. In addition, during operation of the battery, even when the silicon-based negative electrode active material undergoes large volume change, Mxene and the silicon particles can be maintained in a state of strong binding via the cetyltrimethylammonium. Therefore, the cycle life performance of the battery can be further improved. [Modes for carrying out the invention]

[0017] The terms and words used herein and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may define the concepts of terms as appropriate to best describe their invention.

[0018] The terms used herein are for illustrative purposes only and are not intended to limit the invention. Singular expressions include plural expressions unless, in context, they have a clearly different meaning.

[0019] In this specification, terms such as “includes,” “equip,” or “have” specify the presence of an implemented feature, figure, step, component, or combination thereof, and should be understood not to preclude the existence or possibility of adding one or more other features, figures, steps, components, or combinations thereof.

[0020] In this specification, "specific surface area" is measured by the BET method, and specifically, it can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using the BELSORP-mini II manufactured by BEL Japan.

[0021] In this specification, the average particle size (D 50 The average particle size (D) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. 50 The particle size can be measured, for example, using the laser diffraction method. This laser diffraction method can generally measure particle sizes from the submicron region to several millimeters in size, and can yield highly reproducible and high-resolution results.

[0022] Hereinafter, the present invention will be specifically described.

[0023] [Silicon-based negative electrode active material] The silicon-based negative electrode active material according to one embodiment of the present invention may comprise a core containing silicon particles and cetyltrimethylammonium disposed on the surface of the silicon particles, and Mxene disposed on the core and containing hydroxy groups on the surface thereof.

[0024] The core may contain silicon particles and cetyltrimethylammonium.

[0025] The silicon particles may be a kind of pure silicon that has not undergone an intentional oxidation process. That is, although the surface may partially contain oxygen atoms or oxygen-containing functional groups due to natural oxidation, the content thereof is different from SiOx (0<x≤2) formed through an intentional oxidation process. The capacity of the negative electrode can be improved by using the silicon particles.

[0026] More specifically, the silicon particles may contain hydroxy groups that are inevitably generated by natural oxidation. The hydroxy groups are disposed on the silicon particles. The content of the hydroxy groups may be 0.1% by weight to 2% by weight relative to the total weight of the silicon particles.

[0027] The average particle diameter of the silicon particles (D 50 ) may be 0.3 μm to 100 μm. When the above range is satisfied, the destruction of silicon particles caused by volume change of the silicon particles during battery operation can be minimized, and side reactions between the electrolyte and the silicon particles are suppressed, whereby the cycle life of the battery can be improved.

[0028] Specifically, the average particle diameter of the silicon particles (D 50The particle size can be 2 μm to 7 μm. When this range is met, the maxine particles, which have hydroxyl groups on a surface with sufficient electrical conductivity, can completely cover the silicon particles and be uniformly distributed. This allows for a stable and significant improvement in the electrical conductivity of the silicon-based negative electrode active material, thereby improving the rate characteristics and life characteristics of the battery.

[0029] The specific surface area of ​​the aforementioned silicon particles is 10 m². 2 / g~200m 2 It can be / g. When the above range is satisfied, side reactions between the negative electrode active material and the electrolyte can be suppressed.

[0030] Specifically, the specific surface area of ​​the silicon particles is 10 m². 2 / g~20m 2 The value can be / g. When the above range is met, a sufficient amount of cetyltrimethylammonium can be strongly adhered to the surface of the silicon particles, which can greatly improve the rate characteristics and life characteristics of the battery.

[0031] The cetyltrimethylammonium can be placed on the silicon particles. The cetyltrimethylammonium corresponds to the following chemical formula 1 and can exhibit a positive charge.

[0032] [ka]

[0033] Generally, silicon particles have a certain amount of hydroxyl groups on their surface due to natural oxidation, and therefore the surface of these silicon particles exhibits a negative charge. When attempting to coat such silicon particles with Maxine, which also exhibits a negative charge, the same negative charge between the silicon particles and Maxine prevents the Maxine from smoothly coating the silicon particles, and even if coating is achieved, the structural stability is very low. As a result, the lifespan characteristics of the manufactured battery are reduced.

[0034] The cetyltrimethylammonium solves these problems. Specifically, when the cetyltrimethylammonium is placed on the surface of the silicon particles, the surface of the core containing the silicon particles exhibits a positive charge, allowing the negatively charged maxine to be smoothly coated onto the core. This improves the structural stability of the silicon-based anode active material and enhances the battery's lifespan. Furthermore, even with large volume changes in the silicon-based anode active material during battery operation, the maxine and silicon particles can be strongly bonded via the cetyltrimethylammonium. Therefore, the battery's lifespan can be further improved.

[0035] Furthermore, the length of the alkyl chain of cetyltrimethylammonium can be at an appropriate level, and the distance between the silicon particles and the maxine can not be too large, making it possible for the core surface to easily exhibit a positive charge. In addition, it is possible to effectively prevent the anode active material from aggregating with each other during the manufacturing process of the anode active material.

[0036] In particular, while maxine contains atoms such as Ti in addition to carbon, it is preferable that these atoms do not oxidize in order to improve the electrical conductivity of the negative electrode active material. However, there is a problem that the atoms of maxine are easily oxidized in environments with high pH. Therefore, it is preferable that the pH of the solution containing the maxine-coated core be adjusted to a low level during the process of coating the core with maxine. When the core contains cetyltrimethylammonium, the pH of the solution can be at a low level, so that the oxidation of the atoms of maxine can be minimized, and the improvement of the electrical conductivity of the negative electrode active material can be made much easier.

[0037] Furthermore, unlike other surfactants (e.g., methylammonium hydroxide), cetyltrimethylammonium has low toxicity, making it a desirable substance in terms of safety and environmental protection.

[0038] Within the core, the weight ratio of the silicon particles to the cetyltrimethylammonium can be 10:1 to 10,000:1, more specifically 80:1 to 1,000:1, and more specifically 100:1 to 500:1. When this range is satisfied, the silicon particles and the maxine can be effectively bonded, and the electrical conductivity of the manufactured silicon-based anode active material can be effectively improved.

[0039] A maxine containing a hydroxyl group on its surface can be placed on the core. The maxine (also referred to as mexene) means a compound having a two-dimensional planar structure bonded to a transition metal and at least one of carbon and nitrogen.

[0040] The maxine may include at least one selected from the group consisting of M3X2, M4X3, M2X, and M4X4. Of these, M3X2 is most preferred in terms of the stability of the structure and performance maintenance of the silicon-based anode active material. The M may be a transition metal, specifically at least one selected from the group consisting of Ti, V, Nb, Mo, and Zr. The X may be at least one of carbon and nitrogen.

[0041] The maxine can be at least one selected from the group consisting of Ti3C2, Ti4C3, Ti2C, Ti4N3, Ti3CN, V2C, V4C3, Nb2C, Nb4C3, Mo2C, (Mo,V)4C3, and Zr3C2. Specifically, the maxine can be at least one selected from the group consisting of Ti3C2, Ti4C3, Ti2C, Ti4N3, and Ti3CN, in which case the electrical conductivity of the silicon-based anode active material can be further improved. More specifically, the maxine can be Ti3C2, in which case the stability of the structure and performance maintenance of the silicon-based anode active material can be further improved.

[0042] Specifically, the MAXIN is a two-dimensional material obtained from MAX, which has a three-dimensional crystalline structure consisting of an M layer, an A layer, and an X layer, where M is the transition metal, A is a group 13 or group 14 element, and X can be at least one of carbon and nitrogen. The MAXIN is obtained by exfoliating MAX with a strong acid or the like, and during such exfoliation, hydroxyl groups can be incorporated into the surface of the MAXIN. Thus, the MAXIN mentioned above can also contain hydroxyl groups on its surface, and in this specification, this is referred to as "MAXIN containing hydroxyl groups on its surface."

[0043] Since the maxine containing hydroxyl groups on its surface has high electrical conductivity, it can improve the electrical conductivity of the silicon-based negative electrode active material and improve the lifespan characteristics of the negative electrode.

[0044] The hydroxyl group can be present in the maxine containing the hydroxyl group on its surface in an amount of 1% to 10% by weight, specifically 1% to 2% by weight. When this range is met, the degree of oxidation of the maxine is reduced, and the electrical conductivity of the silicon-based negative electrode active material can be further improved by the maxine.

[0045] The average size of the maxines containing hydroxyl groups on their surface can be 0.1 μm to 50 μm, more specifically 0.5 μm to 20 μm, and more specifically 1 μm to 10 μm. When this range is met, the maxines containing hydroxyl groups on their surface can effectively encase the surface of the core, thereby further improving the electrical conductivity of the silicon-based anode active material. The size of the maxine refers to the maximum length that any two points selected within the maxine can have, and the average size refers to the average size of the top 10 largest maxines and the bottom 10 largest maxines (selected from a total of 50 maxines) contained in the silicon-based anode active material. The maximum length can be measured by atomic force microscopy (AFM) after dropping a solution containing maxines onto a silicon wafer and drying it.

[0046] The maxine containing hydroxyl groups on its surface can be present in the silicon-based anode active material in an amount of 0.5% to 50% by weight, more specifically 1% to 30% by weight, and more specifically 3% to 6% by weight. Meeting this range minimizes the reduction in the initial discharge capacity of the silicon-based anode active material and improves the cycle characteristics of the anode.

[0047] Since the maxine containing hydroxyl groups on its surface exhibits a negative charge, and the cetyltrimethylammonium exhibits a positive charge, the maxine containing hydroxyl groups on its surface can bond to the cetyltrimethylammonium by electrostatic attraction. This can also be considered as the core coated with cetyltrimethylammonium and exhibiting a positive charge being bonded to the maxine containing hydroxyl groups on its surface by electrostatic attraction.

[0048] In the silicon-based anode active material, when confirmed by elemental content analysis (SEM EDS), the nitrogen atom content on the surface of the silicon-based anode active material can be 0.001 atom% to 1 atom%, specifically 0.005 atom% to 0.01 atom%. When this range is satisfied, an appropriate amount of cetyltrimethylammonium exists between the silicon particles and the maxine containing hydroxyl groups on its surface, thereby improving the bonding force between the silicon particles and the maxine containing hydroxyl groups on its surface, and minimizing the decrease in electrical conductivity on the surface of the silicon particles. During the analysis of the elemental content, the atom% can be confirmed by detecting nitrogen-specific X-rays. The instrument used here was a Hitachi S-4800, and a region with a magnification of ×3,000 was measured for 1.5 minutes using an accelerating voltage of 20 kV.

[0049] When the maxine is selected from the group consisting of Ti3C2, Ti4C3, Ti2C, Ti4N3, and Ti3CN, elemental content analysis (SEM EDS) of the silicon-based anode active material revealed that the Ti atom content on the surface of the silicon-based anode active material was 5 atom% or more, specifically 5 atom% to 30 atom%, and more specifically 10 atom% to 15 atom%. Meeting this range indicates that the maxine is effectively coated on the core, thereby more effectively improving the electrical conductivity of the silicon-based anode active material. During the elemental content analysis, the atom% can be confirmed by detecting the Ti characteristic X-ray. The instrument used was a Hitachi S-4800, and a 20kV acceleration voltage was used to measure a region at ×3,000 magnification for 1.5 minutes.

[0050] [Method for producing silicon-based negative electrode active material] A method for producing a silicon-based negative electrode active material according to another embodiment of the present invention may include the steps of: mixing silicon particles with cetyltrimethylammonium bromide and arranging the cetyltrimethylammonium on the silicon particles to form a core; and mixing the core with maxine having a hydroxyl group on its surface and arranging the maxine having a hydroxyl group on its surface on the core. Here, the silicon particles, the cetyltrimethylammonium, and the maxine having a hydroxyl group on its surface are the same as the silicon particles, cetyltrimethylammonium, and maxine having a hydroxyl group on its surface described above, so their description is omitted.

[0051] In the step of forming the core, the silicon particles and the cetyltrimethylammonium bromide can be added to a solvent and stirred. The solvent can be water (distilled water). Specifically, solid cetyltrimethylammonium bromide can be dispersed in distilled water, then silicon particle powder can be further dispersed in the distilled water, and then stirred to mix the silicon particles and the cetyltrimethylammonium bromide. The stirring can also be performed using a magnetic stirrer. The stirring can be performed at room temperature for 20 minutes to 1 hour, after which the solvent other than the solid mixture (solids) is removed. Next, the mixture is washed with distilled water via a centrifuge to remove unreacted cetyltrimethylammonium bromide and any remaining bromine ions.

[0052] In the step of arranging the maxine containing hydroxyl groups on the surface, the process may include dispersing the core in distilled water to form an aqueous solution of the core, then adding the aqueous solution containing the maxine containing hydroxyl groups on the surface to the aqueous solution of the core and stirring to form a mixed solution in which the core and the maxine containing hydroxyl groups on the surface are mixed. Specifically, the stirring can be carried out at room temperature for 40 to 80 minutes.

[0053] Next, the mixed solution can be washed with distilled water using a centrifuge to remove maxine containing hydroxyl groups from the unreacted surface. Then, the solvent other than the solid mixture (solid content) can be removed, and the mixture can be dried in an oven at 40°C to 80°C (1.5 hours to 4.5 hours). This allows the silicon-based negative electrode active material of the above embodiment to be obtained.

[0054] [Negative electrode] A negative electrode according to yet another embodiment of the present invention may include the silicon-based negative electrode active material of the above-described embodiment. Specifically, the negative electrode may include a negative electrode active material layer, and the negative electrode active material layer may include the silicon-based negative electrode active material of the above-described embodiment.

[0055] The negative electrode can be a self-supporting negative electrode, in which case the negative electrode active material layer itself constitutes the negative electrode. Alternatively, the negative electrode may include a negative electrode current collector that supports the negative electrode active material layer.

[0056] The negative electrode current collector is not particularly limited, as long as it does not cause a chemical change in the battery and is conductive. For example, the negative electrode current collector can be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. Specifically, transition metals that readily adsorb carbon, such as copper and nickel, can be used as the negative electrode current collector.

[0057] The negative electrode active material layer can be arranged on one or both sides of the negative electrode current collector. In the case of the self-supporting negative electrode, it goes without saying that the negative electrode active material layer can become a negative electrode itself without the negative electrode current collector.

[0058] The negative electrode active material layer may contain a silicon-based negative electrode active material, and the silicon-based negative electrode active material may be the silicon-based negative electrode active material of the above-described embodiment.

[0059] The anode active material layer may further contain a carbon-based anode active material. The carbon-based anode active material may be at least one selected from the group consisting of artificial graphite, natural graphite, and graphitized mesocarbon microbeads.

[0060] The negative electrode active material layer may further contain a binder. The binder is for ensuring adhesion between silicon-based negative electrode active materials or between silicon-based negative electrode active materials and the current collector, and any binder commonly used in the art may be used, and the type is not particularly limited. Examples of the binder include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one or more of these may be used. In particular, when using an aqueous dispersion process, the binder is preferably an aqueous binder such as SBR or CMC.

[0061] The negative electrode active material layer may further contain a conductive material. The conductive material may be at least one selected from the group consisting of fullerene, carbon black, carbon nanotubes, graphene, plate-like graphite, and the like.

[0062] [Secondary battery] Next, a secondary battery according to yet another embodiment of the present invention will be described.

[0063] A secondary battery according to yet another embodiment of the present invention may include the negative electrode of the above-described embodiment. The secondary battery may be a lithium-ion secondary battery.

[0064] Specifically, the secondary battery may include the negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the negative electrode is the same as the negative electrode in the above-described embodiment. Since the negative electrode has been described above, a specific description thereof is omitted.

[0065] The positive electrode may include a positive electrode current collector and a positive electrode active material layer that is formed on the positive electrode current collector and contains the positive electrode active material.

[0066] In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has conductivity. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or materials obtained by surface-treating the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, or the like can be used. In addition, the positive electrode current collector can generally have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. For example, it can be used in various forms such as films, sheets, foils, meshes, porous bodies, foamed bodies, and non-woven fabrics.

[0067] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO₂) or lithium nickel oxide (LiNiO₂), or a compound substituted with one or more transition metals; a lithium iron oxide such as LiFe₃O₄; a compound of formula Li 1+c1 Mn 2-c1 O₄ (0≦c1≦0.33), lithium manganese oxides such as LiMnO₃, LiMn₂O₃, and LiMnO₂; lithium copper oxide (Li₂CuO₂); vanadium oxides such as LiV₃O₈, V₂O₅, and Cu₂V₂O₇; a compound of formula LiNi 1-c2Ni-site type lithium nickel oxide represented as Mc2O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, satisfying 0.01 ≤ c2 ≤ 0.3); chemical formula LiMn 2-c3 M c3 Lithium manganese composite oxides represented as O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, satisfying 0.01 ≤ c3 ≤ 0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion, etc., are examples, but are not limited to these. The positive electrode may be Li metal (Li-metal).

[0068] The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder, along with the positive electrode active material described above.

[0069] Here, the positive electrode conductive material is used to impart conductivity to the electrode and can be used without particular limitations as long as it does not cause chemical changes in the battery and has electronic conductivity. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more can be used.

[0070] Furthermore, the positive electrode binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one or more of these can be used.

[0071] As a separator, any material commonly used as a separator in secondary batteries to separate the negative and positive electrodes and provide a pathway for lithium ions can be used without particular limitations. Particularly preferred are those with low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity. Specifically, porous polymer films, such as porous polymer films made from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof can be used. Ordinary porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, coated separators containing ceramic components or polymeric substances can be used to ensure heat resistance or mechanical strength, and can be selectively used as single-layer or multi-layer structures.

[0072] Examples of the aforementioned electrolytes include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0073] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0074] Examples of non-aqueous organic solvents that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0075] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, can be preferably used because they are high-viscosity organic solvents with high dielectric constants, thus effectively dissociating lithium salts. Furthermore, when such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in appropriate proportions, electrolytes with high electrical conductivity can be produced, and these can be used even more preferably.

[0076] The metal salt can be a lithium salt, which is a substance that dissolves easily in the non-aqueous electrolyte, for example, the anion of the lithium salt is F - Cl - , I - NO3 - , N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 -(CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - (CF3SO2)2N - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - (SF5)3C - , (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - One type selected from the group consisting of can be used.

[0077] In addition to the components of the electrolyte, the electrolyte may also contain one or more additives, such as haloalkylene carbonate compounds including difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for purposes such as improving the battery's lifespan, suppressing the decrease in battery capacity, and improving the battery's discharge capacity.

[0078] According to yet another embodiment of the present invention, a battery module and a battery pack including the secondary battery as a unit cell are provided. Since the battery module and battery pack include the secondary battery having high capacity, high rate-limiting characteristics and cycle characteristics, they can be used as a power source for medium to large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems.

[0079] The present invention will be described in more detail below with reference to specific examples.

[0080] [Examples and Comparative Examples] [Example 1: Manufacturing of silicon-based negative electrode active material and negative electrode] (1) Manufacturing of silicon-based negative electrode active material Average particle size (D 50 The surface area is 5 μm and the specific surface area is 10 m². 2 A solution containing 20 g of silicon particles (at a concentration of / g) and 5% by weight of cetyltrimethylammonium bromide (solvent: distilled water) was prepared and then stirred using a magnetic stirrer at room temperature (25°C) for 30 minutes at 200 rpm. Next, the solution was washed with distilled water using a centrifuge to remove the cetyltrimethylammonium bromide that could not bind to the silicon particles and was present on the surface of the silicon particles.

[0081] On the other hand, a maxine aqueous solution was prepared by dispersing maxine (Ti3C2) with an average size of 7 μm and containing hydroxyl groups on its surface (the hydroxyl group content was 1% by weight relative to the total maxine containing hydroxyl groups on its surface) in distilled water. After mixing 20.2 g of the core and 60 g of a 5 wt% maxine aqueous solution containing 3 g of the maxine containing hydroxyl groups on its surface, the mixture was stirred using a magnetic stirrer at room temperature (25°C) for 60 minutes at 200 rpm. The pH of the solution measured after stirring was 8.1. Next, the mixture was washed with distilled water using a centrifuge to remove "maxine that could not bind to the silicon particles" from the surface of the silicon particles, and then a drying process was performed. This produced a silicon-based negative electrode active material.

[0082] The weight ratio of silicon particles to cetyltrimethylammonium in the core was 100:1. Maxine, which has a hydroxyl group on its surface, was present in the silicon-based anode active material at a concentration of 4% by weight.

[0083] (2) Manufacturing of the negative electrode A mixture was prepared by mixing the aforementioned silicon-based negative electrode active material, the conductive material carbon black, the binder carboxymethylcellulose (CMC), and styrene-butadiene rubber (SBR) in a weight ratio of 95.8:1:1.7:1.5. Next, 7.8g of distilled water was added to 5g of the mixture and stirred to produce a negative electrode slurry. The negative electrode slurry was applied to a copper (Cu) metal thin film, which was a negative electrode current collector with a thickness of 20μm, and dried. The temperature of the circulating air was 60°C. Subsequently, the film was rolled (rolled in a roll press) and dried in a vacuum oven at 130°C for 12 hours to produce a negative electrode.

[0084] [Example 2: Manufacturing of silicon-based negative electrode active material and negative electrode] The silicon-based anode active material and anode were manufactured in the same manner as in Example 1, except that the conditions were changed so that the weight ratio of silicon particles to cetyltrimethylammonium in the core was 10:1 and the amount of maxine containing hydroxyl groups on its surface was 5.5% by weight in the silicon-based anode active material.

[0085] [Example 3: Manufacturing of silicon-based negative electrode active material and negative electrode] A silicon-based anode active material and anode were manufactured in the same manner as in Example 1, except that Ti4C3 was used instead of Ti3C2 in maxine containing hydroxyl groups on its surface. The weight ratio of silicon particles to cetyltrimethylammonium in the core was 100:1. The maxine containing hydroxyl groups on its surface was present in the silicon-based anode active material at a concentration of 4.5% by weight.

[0086] [Comparative Example 1: Manufacturing of silicon-based negative electrode active material and negative electrode] (1) Manufacturing of silicon-based negative electrode active material Maxine (Ti3C2), which has an average size of 7 μm and contains hydroxyl groups on its surface (the hydroxyl group content is 1% by weight relative to the total amount of maxine containing hydroxyl groups on its surface), was dispersed in distilled water to prepare an aqueous solution of maxine (a 5 wt% aqueous solution of maxine containing 3 g of the aforementioned maxine containing hydroxyl groups on its surface). Average particle size (D 50 The surface area is 5 μm and the specific surface area is 10 m².2 20 g of silicon particles (at a concentration of / g) and 60 g of an aqueous solution of Maxine containing hydroxyl groups on its surface were mixed and then stirred using a magnetic stirrer at room temperature (25°C) for 60 minutes at 200 rpm. Next, the mixture was washed with distilled water using a centrifuge to remove "Maxine that could not bond with the silicon particles" from the surface of the silicon particles, and then dried. This produced a silicon-based anode active material.

[0087] The maxine containing hydroxyl groups on its surface was present in the silicon-based negative electrode active material at a concentration of 0.01% by weight.

[0088] (2) Manufacturing of the negative electrode A mixture was prepared by mixing the aforementioned silicon-based negative electrode active material, the conductive material carbon black, and the binders carboxymethylcellulose (CMC) and styrene-butadiene rubber (SBR) in a weight ratio of 95.8:1:1.7:1.5. Next, 7.8g of distilled water was added to 5g of the mixture and stirred to produce a negative electrode slurry. The negative electrode slurry was applied to a copper (Cu) metal thin film, which was a negative electrode current collector with a thickness of 20μm, and dried. The temperature of the circulating air was 60°C. Subsequently, the film was rolled (rolled in a roll press) and dried in a vacuum oven at 130°C for 12 hours to produce a negative electrode.

[0089] [Comparative Example 2: Manufacturing of silicon-based negative electrode active material and negative electrode] A silicon-based anode active material and anode were prepared in the same manner as in Example 1, except that sodium dodecyl sulfate (SDS) was used instead of cetyltrimethylammonium bromide. Maxine, which has a hydroxyl group on its surface, was present in the silicon-based anode active material at a concentration of 0.02% by weight.

[0090] [Comparative Example 3: Manufacturing of silicon-based negative electrode active material and negative electrode] A silicon-based negative electrode active material and a negative electrode were manufactured in the same manner as in Example 1, except that graphene oxide was used instead of maxine, which contains hydroxyl groups on its surface. The average size of the graphene oxide was 5 μm. The graphene was present in the silicon-based negative electrode active material at a concentration of 5% by weight.

[0091] [Comparative Example 4: Manufacturing of silicon-based negative electrode active material and negative electrode] A silicon-based anode active material and anode were prepared in the same manner as in Example 1, except that lauryl methyl gluceth-10 hydroxypropyldimonium chloride was used instead of cetyltrimethylammonium bromide. Maxine, which has a hydroxyl group on its surface, was present in the silicon-based anode active material at a concentration of 0.3% by weight.

[0092] [Comparative Example 5: Manufacturing of silicon-based negative electrode active material and negative electrode] A silicon-based anode active material and anode were prepared in the same manner as in Example 1, except that methyl ammonium hydroxide was used instead of cetyltrimethylammonium bromide. Maxine, which has a hydroxyl group on its surface, was present in the silicon-based anode active material at a concentration of 1% by weight.

[0093] [Comparative Example 6: Manufacturing of silicon-based negative electrode active material and negative electrode] A silicon-based anode active material and anode were prepared in the same manner as in Example 1, except that polydiallyldimethylammonium chloride was used instead of cetyltrimethylammonium bromide. Maxine, which has a hydroxyl group on its surface, was present in the silicon-based anode active material at a concentration of 0.5% by weight.

[0094] [Example of experiment] [Experimental Example 1: Evaluation of Coating Properties] The content of Ti on the surface of the silicon-based anode active materials used in the examples and comparative examples was evaluated using EDS (energy-dispersive spectroscopy) and is shown in Table 1. The instrument used was a Hitachi S-4800, and a region at ×3,000 magnification was measured for 1.5 minutes using an accelerating voltage of 20kV. The atom percentage of Ti among the elements measured overall was confirmed by EDS analysis, and the coating properties were indirectly evaluated.

[0095] [Experimental Example 2: Evaluation of C-rate] Using the negative electrodes of the examples and comparative examples, batteries were manufactured as follows.

[0096] As the positive electrode active material, Li[Ni 0.6 Mn 0.2 Co 0.2 O2 was used. The positive electrode active material, the conductive material carbon black, and the binder polyvinylidene fluoride (PVdF) were mixed in the solvent N-methyl-2-pyrrolidone in a weight ratio of 94:4:2 to produce a positive electrode slurry.

[0097] The manufactured positive electrode slurry was applied to and dried on a 15 μm thick aluminum metal thin film, which served as the positive electrode current collector. The circulating air temperature was 110°C. The slurry was then rolled and dried in a vacuum oven at 130°C for 2 hours to form the positive electrode active material layer.

[0098] The negative electrodes of the examples and comparative examples, the manufactured positive electrode, and the porous polyethylene separator were assembled using a stacking method. An electrolyte (ethylene carbonate (EC) / ethyl methyl carbonate (EMC) = 1 / 2 (volume ratio) and lithium hexafluorophosphate (LiPF 61 mol)) was injected into the assembled battery to produce a lithium-ion secondary battery.

[0099] The manufactured lithium-ion secondary batteries were charged at a 0.5C rate (constant current charging at 0.5C, constant voltage charging at 0.05V, and 0.05C cutoff), and discharged at specific C rates (0.5C, 1C, 2C, 5C) (constant current discharge at the respective C rate, 1.5V cutoff). The discharge capacity under each rate-limiting condition was measured. The discharge capacity was calculated based on the weight of the negative electrode active material, and the capacity development rate was calculated using the following formula.

[0100] Capacity development rate (%) = {Discharge capacity at the given C-rate / Discharge capacity at 0.5C} × 100

[0101] The results are shown in Table 1 below.

[0102] [Experimental Example 3: Evaluation of Volume Retention Rate] The lithium-ion secondary battery manufactured in Experimental Example 1 was subjected to charging and discharging under the following conditions.

[0103] Charging conditions: Constant current charging at 0.5C until 4.25V, then charging at 4.2V until a current rate of 0.1C flows. Discharge conditions: Discharge at a current rate of 0.5C until the voltage reaches 2.8V.

[0104] The above charging and discharging process was considered one cycle, and 100 cycles were performed at 25°C. Next, the discharge capacity after the 100th cycle (capacity retention rate) was evaluated using the discharge capacity after the 1st cycle as the baseline (100%), and is shown in Table 1.

[0105] On the other hand, when the charge capacity of the first cycle was set to 100%, the percentage of the discharge capacity of the first cycle was measured as the initial efficiency (%).

[0106] [Table 1]

[0107] In Table 1, "solution" refers to an aqueous solution containing a core (or silicon particles) coated with Maxine, specifically an aqueous solution containing the manufactured silicon-based anode active material. Referring to Table 1, in the example, the pH of the solution is low during the manufacturing process of the silicon-based anode active material, which suppresses the oxidation of Ti atoms in Maxine. Furthermore, in the case of a silicon-based anode active material containing cetyltrimethylammonium and Maxine, the effective coating of Maxine was confirmed by the Ti atom percentage. As a result, oxidation of the silicon-based anode active material is suppressed, improving electrical conductivity, and it can be seen that the discharge capacity, C-rate, and capacity retention rate in the example are at excellent levels.

Claims

1. A core comprising silicon particles and cetyltrimethylammonium disposed on the surface of the silicon particles, The core is disposed on the said core and contains a maxine (Mxene) having a hydroxyl group on its surface, The average particle size (D) of the silicon particles ５０ The surface area is 2 μm to 7 μm, and the specific surface area is 10 m² / g to 20 m² / g. The hydroxyl group is contained in a silicon-based negative electrode active material in an amount of 1% to 10% by weight within the maxine containing the hydroxyl group on its surface.

2. The silicon-based negative electrode active material according to claim 1, wherein the weight ratio of the silicon particles to the cetyltrimethylammonium in the core is 10:1 to 10,000:

1.

3. The aforementioned maxine is M ３ X ２ M ４ X ３ M ２ X, and M ４ X ４ The silicon-based negative electrode active material according to claim 1, wherein M is selected from the group consisting of the following, and X is at least one of carbon and nitrogen.

4. Said MAX phase is Ti ３ C ２ , Ti ４ C ３ , Ti ２ C, Ti ４ N ３ , and Ti ３ CN, wherein the silicon-based negative electrode active material according to claim 3 is at least one selected from the group consisting of the above.

5. The aforementioned maxine is Ti ３ C ２ The silicon-based negative electrode active material according to claim 4.

6. The silicon-based negative electrode active material according to claim 1, wherein the average size of the maxine containing hydroxyl groups on the surface is 0.1 μm to 50 μm.

7. The silicon-based anode active material according to claim 1, wherein the maxine having a hydroxyl group on its surface is contained in the silicon-based anode active material in an amount of 0.5% to 50% by weight.

8. The silicon-based anode active material according to claim 4, wherein, during SEM EDS analysis of the silicon-based anode active material, the Ti atom content on the surface of the silicon-based anode active material is 5 atom% or more.

9. The process involves mixing silicon particles with cetyltrimethylammonium bromide and arranging the cetyltrimethylammonium on the silicon particles to form a core, The steps include mixing the core with a maxine having a hydroxyl group on its surface, and placing the maxine on the core. The average particle size (D) of the silicon particles ５０ The surface area is 2 μm to 7 μm, and the specific surface area is 10 m² / g to 20 m² / g. A method for producing a silicon-based negative electrode active material, wherein the hydroxyl group is contained in a maxine containing a hydroxyl group on its surface in an amount of 1% to 10% by weight.

10. A negative electrode comprising a silicon-based negative electrode active material according to any one of claims 1 to 8.

11. A secondary battery comprising the negative electrode described in claim 10.

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