Negative electrode active material, negative electrode, and secondary battery including same

Abstract

Provided, according to exemplary embodiments of the present invention, is a negative electrode active material capable of improving the life characteristics of a secondary battery. The negative electrode active material comprises, in wt%,: 0.01-0.05% of iron (Fe), 0.0025-0.0035% of boron (B), 0.0025-0.0035% of phosphorus (P), and the balance of silicon (Si) and inevitable impurities. Provided, according to other exemplary embodiments of the present invention, are a negative electrode comprising the above-described negative electrode active material, and a secondary battery including same.

Description

Negative active material, negative electrode, and secondary battery including the same

[0001] The present invention relates to a negative electrode active material, a negative electrode, and a secondary battery including the same.

[0002] More specifically, the present invention relates to a lithium secondary battery.

[0003] Recently, the rapid advancement of portable and wireless electronic devices has led to a growing demand for compact, lightweight, and high-energy-density secondary batteries as power sources for these devices. Furthermore, high-output characteristics, long-term durability, and safety are required not only for small consumer applications but also for large-scale secondary batteries used in power storage devices and electric vehicles.

[0004] A secondary battery has a structure in which an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes, and an electrolyte are accommodated in an outer body. The electrode includes an electrode current collector and an electrode active material layer positioned on at least one side of the electrode current collector. Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer positioned on at least one side of the positive electrode current collector. The negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on at least one side of the negative electrode current collector.

[0005] Secondary batteries can be categorized into lead-acid batteries, nickel-cadmium (Cd) batteries, nickel-metal hydride (MH) batteries, and lithium batteries, depending on the type of cathode and anode active materials. Among these, demand for lithium secondary batteries, with their superior energy density, output characteristics, and operating time, is growing.

[0006] The secondary battery reaction of a lithium secondary battery is carried out through a chemical reaction in which lithium ions (Li+) move between the positive electrode active material and the negative electrode active material.

[0007] In the field of secondary batteries, much research is ongoing because the lifespan characteristics of secondary batteries are directly related to the long-term performance of devices that use secondary batteries as power sources.

[0008] (Patent Document 1) Republic of Korea Patent Publication No. 10-1825919.

[0009] The technical idea of ​​the present invention aims to provide a negative electrode active material capable of improving the lifespan characteristics of a secondary battery, and an negative electrode comprising the same. Furthermore, it aims to provide a secondary battery with improved lifespan characteristics.

[0010] The objectives of the present invention are not limited to the above-described content. Those skilled in the art will have no difficulty understanding the additional objectives of the present invention from the overall description of the present invention.

[0011] According to exemplary embodiments of the present invention, a negative electrode active material is provided. The negative electrode active material comprises, in weight %, 0.01 to 0.05% iron (Fe), 0.0025 to 0.0035% boron (B), 0.0025 to 0.0035% phosphorus (P), the remainder silicon (Si), and unavoidable impurities.

[0012] The above negative active material may include, in wt%, 0.001 to 0.005% titanium (Ti), 0.07 to 0.12% aluminum (Al), and 0.005 to 0.02% calcium (Ca).

[0013] The powder conductivity of the above negative active material may be 10-5 S / m or more.

[0014] The above negative active material may have a particle size distribution of D10 of 1 to 5 μm, D50 of 3 to 20 μm, and D90 of 10 to 50 μm or more.

[0015] According to other exemplary embodiments of the present invention, a negative electrode is provided. The negative electrode comprises: a negative electrode current collector; and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, the negative electrode active material layer including, by weight %, 70 to 90% of a negative electrode active material, 10 to 30% of a binder, and 1% or less (including 0%) of a conductive material, wherein the negative electrode active material may include, by weight %, 0.01 to 0.05% of iron (Fe), 0.0025 to 0.0035% of boron (B), 0.0025 to 0.0035% of phosphorus (P), the remainder being silicon (Si), and unavoidable impurities.

[0016] The above negative active material layer may include less than 0.05% (including 0%) of a conductive material.

[0017] According to further exemplary embodiments of the present invention, a secondary battery is provided. The secondary battery may include a positive electrode, the above-described negative electrode, a separator interposed between the positive electrode and the negative electrode, a case housing the positive electrode, the separator, and the negative electrode, and an electrolyte contained within the case.

[0018] The negative active material according to exemplary embodiments of the present invention includes a high content of silicon, and can improve the life characteristics of a secondary battery by controlling the impurity content of the negative active material.

[0019] According to other exemplary embodiments of the present invention, the negative electrode can improve the life characteristics of a secondary battery by minimizing or omitting the content of carbon in the negative electrode.

[0020] A secondary battery according to further exemplary embodiments of the present invention can improve life characteristics even when using a liquid electrolyte because it includes the negative electrode active material or negative electrode described above.

[0021] The various advantageous and beneficial effects of the present invention are not limited to the above-described contents, and will be more easily understood in the course of explaining specific embodiments of the present invention.

[0022] Figure 1 is a graph showing the life characteristics of secondary batteries according to manufacturing examples and comparative manufacturing examples.

[0023] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. Prior to this, it should be noted that the terms and words used in this specification and claims should not be construed as limited to their conventional or dictionary meanings. Based on the principle that the inventor can appropriately define the concepts of terms to best explain his or her invention, they should be interpreted in a way that aligns with the technical spirit of the present invention.

[0024] Hereinafter, when explaining with reference to drawings, identical or corresponding components are given the same drawing reference numerals and redundant descriptions thereof are omitted.

[0025] In the examples below, the terms first, second, etc. are not used in a limiting sense, but are used for the purpose of distinguishing one component from another.

[0026] In the examples below, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0027] In the examples below, terms such as “include” or “have” mean that a feature or component described in the specification is present, and do not preclude the possibility that one or more other features or components may be added.

[0028] For convenience of explanation, the sizes of components in the drawings may be exaggerated or reduced. For example, the sizes and thicknesses of each component shown in the drawings are arbitrarily indicated for convenience of explanation, and thus the present invention is not necessarily limited to what is shown.

[0029] In some embodiments, where implementations are otherwise feasible, specific process sequences may be performed in a different order than described. For example, two processes described in succession may be performed substantially simultaneously, or in a reverse order from the described order.

[0030] In addition, when describing the present invention, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the present invention, the detailed description is omitted.

[0031]

[0032] In the present invention, having a micro-scale size refers to a particle size distribution based on D50. That is, it means a case where D50 is 1.0㎛ or more. Therefore, even if the D10 of a particle is less than 1.0㎛, if the D50 of the particle is 1.0㎛ or more, the particle can be interpreted as having a micro-scale size according to the present invention.

[0033] In the present invention, D50, D10, and D90 can be defined as particle sizes corresponding to 50%, 10%, and 90% of the volume accumulation amount, respectively, in the particle size distribution curve of the particles. The D50, D10, and D90 can be measured using, for example, a laser diffraction method. The laser diffraction method can generally measure particle sizes from the submicron range to several mm, and can obtain results with high reproducibility and high resolution.

[0034]

[0035] Hereinafter, the negative electrode and the negative electrode active material according to exemplary embodiments of the present invention will be specifically described.

[0036]

[0037] [cathode]

[0038] According to exemplary embodiments, the negative electrode may include a negative electrode current collector and a negative electrode active material layer.

[0039]

[0040] The negative electrode current collector is not particularly limited as long as it has high conductivity and does not induce chemical changes in the battery. As non-limiting examples, the negative electrode current collector may include one or more of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and an aluminum-cadmium alloy.

[0041] The thickness of the negative electrode current collector can be 3 to 500 μm.

[0042]

[0043] The negative electrode active material layer may be provided on one or both sides of the negative electrode current collector. The negative electrode active material layer may be obtained by coating and drying a negative electrode slurry containing a binder, a conductive material, and a negative electrode active material on the negative electrode current collector. However, according to exemplary embodiments, the conductive material may be added only in a very small amount or may be omitted within the negative electrode active material layer.

[0044] More specifically, the negative electrode active material layer may include, in wt%, 70 to 90% of the negative electrode active material, 10 to 30% of the binder, and less than 0.05% (including 0%) of the conductive material, based on the total weight of the negative electrode active material layer. Each material will be described in detail below.

[0045]

[0046] According to exemplary embodiments, the binder may be included in an amount of 10 to 30% by weight.

[0047] A binder is a component that assists in bonding between the negative electrode active material and the current collector. As a non-limiting example, the negative electrode binder may include at least one selected from polyvinyl alcohol, carboxymethyl cellulose / styrene-butadiene rubber, hydroxypropylene cellulose, diacetylene cellulose, polyvinyl chloride, polyvinylpyrrolidone, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, or polypropylene.

[0048]

[0049] According to exemplary embodiments, the conductive agent may be present in an amount of less than 0.05% (including 0%) by weight.

[0050] Conductive agents are components that enhance the conductivity of negative electrode active materials. However, due to their high electrical conductivity and small particle size, their large surface area can cause side reactions with the electrolyte. This can lead to the formation of a thick solid electrolyte interphase (SEI) on the surface of the negative electrode active material layer. This can increase the irreversible capacity of the negative electrode and increase its resistance, thereby reducing the performance of the secondary battery. Furthermore, conductive agents can trigger electrolyte decomposition reactions, generating gas. This can lead to gas accumulation within the secondary battery, causing swelling, which can compromise the safety of the secondary battery.

[0051] From the above, it is desirable to include the conductive agent in a minimal amount. According to exemplary embodiments, the conductive agent may be included in an amount of 1% or less by weight. More specifically, the conductive agent may be included in an amount of less than 0.05% by weight. The conductive agent may be omitted.

[0052] As a non-limiting example, the conductive material may include at least one selected from the group consisting of graphite such as carbon nanotubes, natural graphite, and artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fibers and metal fibers; metal powders such as fluorocarbon, aluminum, and nickel powders; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0053]

[0054] [Cathode active material]

[0055] According to exemplary embodiments, it may include, by weight %, 0.01 to 0.05% iron (Fe), 0.0025 to 0.0035% boron (B), 0.0025 to 0.0035% phosphorus (P), 0.001 to 0.005% titanium (Ti), 0.07 to 0.12% aluminum (Al), and 0.005 to 0.02% calcium (Ca), with the remainder silicon (Si) and unavoidable impurities. More specifically, silicon (Si) may be included in an amount of 99% or more. Silicon (Si) may be included in an amount of 99.5% or more. Silicon (Si) may be included in an amount of 99.9% or more.

[0056] Conventional silicon-based negative electrode active materials were provided in a form existing within a graphene or silicon oxide (SiOx) matrix. However, in these cases, the silicon content within the negative electrode active material was relatively low, at approximately 30-50%.

[0057] However, according to exemplary embodiments, the negative active material includes a high content of silicon. This allows the negative active material to further improve the energy density per weight and volume of the negative electrode.

[0058] In addition, by controlling the contents of iron, boron, and phosphorus within the above-described ranges, the powder conductivity of the negative electrode active material can be increased. This can reduce the energy consumed during the insertion and de-insertion of lithium ions during the charge / discharge process of a secondary battery. Furthermore, a uniform charge / discharge reaction can occur between the area adjacent to the surface of the negative electrode active material layer and the area adjacent to the negative electrode current collector. This can improve the charge / discharge characteristics and lifespan characteristics of the secondary battery. As a non-limiting example, the contents of iron, boron, and phosphorus can be controlled through a de-ironization process after classification and sieving of the silicon raw material.

[0059] According to exemplary embodiments, the powder conductivity of the negative active material may be 10-5 S / m or more. Powder conductivity is a physical quantity indicating the degree to which the negative active material powder can transport electric charges, and means the sheet resistance value measured after making the powder of the material to be measured into pellets and then converting it into conductivity.

[0060] Meanwhile, titanium, aluminum, and calcium may be unavoidable impurities that are added during the manufacturing process of the negative active material or are not removed from the raw material.

[0061]

[0062] According to exemplary embodiments, the negative active material may have a particle size distribution of D10 of 1 to 5 μm, D50 of 3 to 20 μm, and D90 of 10 to 50 μm or more.

[0063] Reducing the specific surface area of ​​the negative electrode active material is crucial for improving the lifespan of secondary batteries. This is because as the specific surface area of ​​the negative electrode active material increases, the contact area with the electrolyte increases excessively, increasing the likelihood of side reactions. For example, a thick SEI film may form on the surface of the negative electrode active material, reducing the active area of ​​the negative electrode. Furthermore, electrolyte decomposition can trigger excessive gas generation within the secondary battery cell. Furthermore, electrolyte decomposition can consume lithium ions, degrading the performance of the secondary battery. Consequently, as the number of charge / discharge cycles of the secondary battery increases, its charge / discharge capacity may decrease. This can lead to deteriorated lifespan characteristics.

[0064] To reduce the specific surface area of ​​the negative electrode active material, increasing the size of the negative electrode active material particles may be considered. According to exemplary embodiments, the negative electrode active material comprises micro-scale silicon particles. By utilizing these coarse silicon particles, the specific surface area of ​​the negative electrode active material can be reduced. This effectively improves the long-term life characteristics of the secondary battery.

[0065]

[0066] [Secondary battery]

[0067] A lithium secondary battery according to one embodiment of the present invention may more specifically include a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte, and a case accommodating them.

[0068] The above cathode is as described above.

[0069] The above positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and the positive electrode active material layer may include a positive electrode active material.

[0070] The positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesion of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0071] The positive electrode active material may be a compound capable of reversibly intercalating and deintercalating lithium (a lithiated intercalation compound). Specifically, one or more of a composite oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used. A specific example thereof may be a compound represented by one of the following chemical formulas:

[0072] LiaA1-bBbD2 (wherein 0.90 ≤ a ≤ 1.8, and 0 ≤ b ≤ 0.5); LiaE1-bBbO2-cDc (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.05); LiE2-bBbO4-cDc (wherein 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.05); LiaNi1-b-cCobBcDα (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, and 0 < α ≤ 2); LiaNi1-b-cCobBcO2-αTα (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); LiaNi1-b-cCobBcO2-αT2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); LiaNi1-b-cMnbBcDα (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); LiaNi1-b-cMnbBcO2-αTα (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); LiaNi1-b-cMnbBcO2-αT2 (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); LiaNibEcGdO2 (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1); LiaNibCocMndGeO2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); LiaNiGbO2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); LiaCoGbO2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1).); LiaMnGbO2 (wherein 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); LiaMn2GbO4 (wherein 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiIO2; LiNiVO4; Li(3-f)J2(PO4)3 (0 ≤ f ≤ 2); Li(3-f)Fe2(PO4)3 (0 ≤ f ≤ 2); and LiFePO4.

[0073] In the above chemical formula, A is Ni, Co, Mn or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof; D is O, F, S, P or a combination thereof; E is Co, Mn or a combination thereof; T is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof; I is Cr, V, Fe, Sc, Y or a combination thereof; J may be V, Cr, Mn, Co, Ni, Cu or a combination thereof.

[0074] The above-described positive electrode active material layer may further include a binder and / or a conductive material together with the above-described positive electrode active material.

[0075] The above binder serves to improve the adhesion between positive electrode active material particles and the adhesive strength between the positive electrode active material and the positive electrode current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof, but is not limited thereto. The binder may be included in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

[0076] The conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any particular restrictions. 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, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One type alone or a mixture of two or more types may be used among these, but the present invention is not limited thereto. The conductive material may typically be included in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

[0077] The above positive electrode can be manufactured according to a conventional positive electrode manufacturing method. For example, it can be manufactured by coating a positive electrode slurry containing a positive electrode active material, a binder, and a conductive agent on one or both sides of a positive electrode current collector, followed by drying and rolling.

[0078]

[0079] The above separator separates the positive and negative electrodes and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without any particular restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0080]

[0081] According to exemplary embodiments, the electrolyte may include a liquid electrolyte usable in the manufacture of a lithium secondary battery. More specifically, it may be at least one of an organic liquid electrolyte and an inorganic liquid electrolyte. In this way, the secondary battery according to exemplary embodiments can minimize volume expansion of the negative electrode and side reactions with the electrolyte even when a liquid electrolyte is used because it uses the above-described negative electrode active material and negative electrode. As a result, swelling of the secondary battery can be prevented and life characteristics can be improved.

[0082] The above organic liquid electrolyte may include an organic solvent and a lithium salt.

[0083] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.In this case, the performance of the electrolyte may be improved when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9.

[0084] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. It is preferable that the concentration of the lithium salt be used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0085] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexamethylphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be contained in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

[0086]

[0087] The case is not particularly limited as long as it can appropriately accommodate the components constituting the secondary battery described above. The shape of the case may be one or more selected from the group consisting of a cylindrical shape using a can, a square shape, a pouch shape, and a coin shape. However, the shape of the battery case is not limited thereto, and may have various shapes used in the relevant industry.

[0088] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0089]

[0090] (Example)

[0091] A negative electrode active material having a particle size distribution and component composition as shown in Table 1 below was prepared.

[0092] Particle size distribution component composition powder conductivity (S / m) D10 (㎛) D50 (㎛) D90 (㎛) Si (wt%) Fe (wt%) B (wt%) P (wt%) 1.26 3.39 45 6.17 69 9.8 0.04 0.00 30 0.00 25 1.9*10 -5

[0093] A negative electrode was manufactured using the negative electrode active material according to Table 1 above. Polyacrylic acid (PAA) was used as the binder required for the negative electrode manufacture. Super C65 (Timcal) was used as the conductive material. At this time, the ratio of negative electrode active material:binder:conductive material was as shown in Table 2 below. A secondary battery (2032 Coin Half Cell) was manufactured by impregnating the manufactured negative electrode into an electrolyte. An organic liquid electrolyte was used as the electrolyte, and the organic liquid electrolyte was an organic liquid electrolyte in which 1.0 M LiPF6 was mixed in an organic solvent of ethyl methyl carbonate: ethylene carbonate in a ratio of 7:3. At this time, lithium metal was used as the counter electrode.

[0094] Cathode active material content (wt%)Binder content (wt%)Conductor content (wt%)Manufacturing example 180200Manufacturing example 290100Comparative manufacturing example 1603010Comparative manufacturing example 2909.950.05

[0095] The life characteristics and relative volume expansion rate of the negative electrode of the secondary batteries according to the manufacturing examples and comparative manufacturing examples shown in Table 2 were measured.

[0096] The life characteristics of secondary batteries were repeatedly charged and discharged under predetermined conditions for each of the secondary batteries according to the manufacturing examples and comparative manufacturing examples shown in Table 2. The charge and discharge capacities of the secondary batteries were measured for each cycle (charge-discharge) to confirm the charge and discharge efficiency.

[0097] Charging of secondary batteries was performed under controlled conditions of 0.5C, 0.5mV CC-CV, and a cut-off current of 0.005C. CC-CV stands for constant current-constant voltage charging.

[0098] The discharge of secondary batteries was controlled at 0.5C and a cutoff voltage of 1.0 V.

[0099] In this experimental example, the 1C rate was defined as 2,500 mAh / gSi, and after calculating the current, charging and discharging was performed at 0.5C according to the weight (g) of Si (active material) of the electrode.

[0100]

[0101] Figure 1 is a graph showing the life characteristics of secondary batteries according to manufacturing examples and comparative manufacturing examples.

[0102] Referring to Fig. 1, it was confirmed that the secondary batteries according to Comparative Manufacturing Examples 1 and 2, in which the content of the conductive agent was outside the range suggested by the present invention, did not maintain their capacity from the beginning of the charge / discharge cycle. In contrast, the secondary batteries according to Manufacturing Examples 1 and 2, in which no conductive agent was added, were confirmed to maintain their capacity during the charge / discharge cycle. In particular, it was confirmed that the charge / discharge efficiency was the highest in the case of Manufacturing Examples 1 and 2, in which no conductive agent was added.

[0103]

[0104] During the charge / discharge test of the above negative electrode, the volume change of the negative electrode was measured and the volume expansion rate of the negative electrode was compared.

[0105] More specifically, the volume expansion rate of the cathode was calculated using the following relationship.

[0106] [Relationship 1]

[0107] Volume expansion ratio = [(post-thickness)-(initial thickness)] / initial thickness

[0108]

[0109] The initial thickness was measured as the thickness of the negative electrode active material layer (the thickness of the negative electrode excluding the thickness of the negative electrode current collector) before assembling the secondary battery. This is because the part that actually changes volume during the charge / discharge process of the secondary battery is the negative electrode active material layer containing the active material. The post-charge thickness was measured by disassembling the secondary battery at the 51st charge state after 50 charge / discharge cycles and measuring the thickness of the negative electrode. Similarly, the thickness of the negative electrode active material layer was measured as the post-charge thickness.

[0110] Thereafter, the volume expansion rate of other manufacturing examples was evaluated based on the volume expansion rate of the secondary battery according to Comparative Manufacturing Example 1.

[0111] Relative volume expansion rate (%) Manufacturing example 10.46 Manufacturing example 20.539 Comparative manufacturing example 11 Comparative manufacturing example 20.619

[0112] Referring to Table 3, it was confirmed that the volume expansion rate of the cathode was the highest in Comparative Manufacturing Example 1, which had an excessively high content of conductive agent. Furthermore, the volume expansion rate was measured to be relatively high even in Comparative Manufacturing Example 2, which had a very low content of conductive agent. In contrast, when no conductive agent was added, the volume expansion rate was confirmed to be relatively low.

[0113] From the above, it was confirmed that the negative active material according to exemplary embodiments and the negative electrode including the same can improve the life characteristics of a secondary battery and prevent the swelling phenomenon of the secondary battery due to volume expansion of the negative electrode.

[0114] The present invention has been described in more detail through drawings and examples. However, the configurations described in the drawings or examples described in this specification are merely embodiments of the present invention and do not represent all of the technical ideas of the present invention. Therefore, it should be understood that various equivalents and modified examples may exist as of the time of this application.

Claims

1. A negative active material containing, by weight %, 0.01 to 0.05% iron (Fe), 0.0025 to 0.0035% boron (B), 0.0025 to 0.0035% phosphorus (P), the remainder silicon (Si), and unavoidable impurities.

2. In paragraph 1, The above negative active material is a negative active material containing, in weight %, 0.001 to 0.005% titanium (Ti), 0.07 to 0.12% aluminum (Al), and 0.005 to 0.02% calcium (Ca).

3. In paragraph 1, The above negative active material has a powder conductivity of 10-5 S / m or more.

4. In paragraph 1, The above negative active material is a negative active material having a particle size distribution of D10 of 1 to 5 μm, D50 of 3 to 20 μm, and D90 of 10 to 50 μm or more.

5. Negative current collector; and A negative electrode active material layer provided on at least one side of the negative electrode current collector, comprising, in weight %, 70 to 90% of a negative electrode active material, 10 to 30% of a binder, and 1% or less (including 0%) of a conductive material, The above negative electrode active material is a negative electrode containing, in weight %, 0.01 to 0.05% iron (Fe), 0.0025 to 0.0035% boron (B), 0.0025 to 0.0035% phosphorus (P), the remainder silicon (Si), and unavoidable impurities.

6. In paragraph 5, The above negative electrode active material layer is a negative electrode containing less than 0.05% (including 0%) of a conductive material.

7. In paragraph 5, The above negative electrode active material is a negative electrode having a particle size distribution of D10 of 1 to 5 μm, D50 of 3 to 20 μm, and D90 of 10 to 50 μm or more.

8. In paragraph 5, A cathode having a powder conductivity of the above cathode active material of 10-5 S / m or more.

9. Bipolar; A cathode according to any one of claims 5 to 8; A separator interposed between the positive and negative electrodes; A case accommodating the anode, separator, and cathode; and A secondary battery containing an electrolyte accommodated within the case.

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