Negative active material and rechargeable lithium battery comprising the same

Abstract

A negative electrode active material for a rechargeable lithium battery and a rechargeable lithium battery are provided. The negative electrode active material comprises a porous silicon-carbon composite, including silicon, carbon, and magnesium silicate (MgSiO3), and has a density of 0.001... MgSiO3(610) / I Si(111) Diffraction peak intensity ratio <0.01 I MgSiO3(610) / I Si(111) The intensity of this diffraction peak is higher than that of I. MgSiO3(610) / I Si(111) The diffraction peak intensity I of MgSiO3 at 2θ = 30° to 32° in X-ray diffraction analysis. MgSiO3(610) The diffraction peak intensity I of Si(111) detected at 2θ = 27.5° to 29.5° is compared with that of Si(111). Si(111) than.​

Description

Technical Field

[0001] The invention relates to a negative electrode active material and a rechargeable lithium battery including the negative electrode active material. Background Technology

[0002] The expansion of the electric vehicle and ESS (energy storage system) markets necessitates high-capacity and high-efficiency batteries, and research has been conducted on using silicon-based materials as the negative electrode active material. Silicon-based negative electrode active materials exhibit advantages such as high capacity and high efficiency, but suffer from drawbacks related to volume expansion during charging and discharging.

[0003] To overcome these drawbacks, attempts have been made to combine the material with a carbon matrix, silicon oxide, or silicon alloy. The information disclosed above in this background section is intended only to enhance understanding of the background of the invention and therefore may contain information that does not constitute prior art known to a person skilled in the art in this country. Summary of the Invention

[0004] One embodiment provides a negative electrode active material for rechargeable lithium batteries that can improve initial efficiency and cycle life characteristics.

[0005] Another embodiment provides a rechargeable lithium battery including a negative electrode active material.

[0006] One embodiment provides a negative electrode active material for a rechargeable lithium battery, the negative electrode active material comprising: a porous silicon-carbon composite comprising silicon, carbon, and magnesium silicate (MgSiO3) and pores, and having a porosity of 0.001 MgSiO3(610) / I Si(111) Diffraction peak intensity ratio <0.01 I MgSiO3(610) / I Si(111) The intensity of this diffraction peak is higher than that of I. MgSiO3(610) / I Si(111) The diffraction peak intensity I of MgSiO3 at 2θ = 30° to 32° in X-ray diffraction analysis. MgSiO3(610) The diffraction peak intensity I of Si(111) detected at 2θ = 27.5° to 29.5° is compared with that of Si(111). Si(111) than.

[0007] Based on the total 100wt% of the negative electrode active material, the amount of magnesium silicate can be from about 0.01wt% to about 1.0wt% or from about 0.01wt% to about 0.6wt%.

[0008] Carbon can be amorphous carbon, and amorphous carbon can be soft carbon, hard carbon, or a combination thereof.

[0009] The amount of carbon can be from about 5 wt% to about 45 wt%, depending on the total weight of the negative electrode active material. ​

[0010] The silicon-carbon composite may include pores, and carbon may coat the outer walls of the pores, silicon, and magnesium silicate.

[0011] The aperture can have an average size of about 50 nm or larger, or about 50 nm to about 500 nm.

[0012] The negative electrode active material can be prepared by the following steps: subjecting magnesium silicide to a primary heat treatment to prepare a heated product; etching the heated product to prepare porous silicon; mixing the porous silicon with an amorphous carbon precursor to prepare a mixture; and subjecting the mixture to a secondary heat treatment.

[0013] A heat treatment can be performed in an air atmosphere. The heat treatment can be performed at approximately 600°C to approximately 700°C for approximately 5 to approximately 30 hours.

[0014] Etching can be performed using acid. Hydrochloric acid can be an example of such acid.

[0015] The mixing ratio of porous silicon and amorphous carbon precursors can be from about 95:5 to about 55:45 by weight.

[0016] Secondary heat treatment can be performed at approximately 800°C to approximately 1200°C.

[0017] Another embodiment provides a rechargeable lithium battery comprising: a negative electrode including a negative electrode active material; a positive electrode including a positive electrode active material; and a non-aqueous electrolyte.

[0018] The negative electrode may also include a first negative electrode active material and crystalline carbon as a second negative electrode active material. The mixing ratio of the first negative electrode active material and the second negative electrode active material may be from about 1:99 to about 40:60 by weight.

[0019] Other embodiments are included in the following detailed description.

[0020] According to one embodiment, the negative electrode active material for a rechargeable lithium battery can exhibit excellent initial efficiency and cycle life characteristics. Attached Figure Description

[0021] Figure 1 This is a schematic diagram illustrating the structure of a rechargeable lithium battery according to an embodiment. Detailed Implementation

[0022] The embodiments are described in detail below. However, these embodiments are merely examples, and therefore the invention is not limited thereto, but is defined by the scope of the claims.

[0023] The negative electrode active material used in rechargeable lithium batteries includes porous silicon-carbon composites, which include silicon, carbon, and magnesium silicate (MgSiO3).

[0024] The negative electrode active material can have a concentration of 0.001. MgSiO3(610) / I Si(111) Diffraction peak intensity ratio <0.01 I MgSiO3(610) / I Si(111) The intensity of this diffraction peak is higher than that of I. MgSiO3(610) / I Si(111) The diffraction peak intensity I of MgSiO3 at 2θ = 30° to 32° in X-ray diffraction analysis. MgSiO3(610) The diffraction peak intensity I of Si(111) detected at 2θ = 27.5° to 29.5° is compared with that of Si(111). Si(111) The ratio. According to one embodiment, when the diffraction peak intensity of the negative electrode active material is greater than I... MgSiO3(610) / I Si(111) When falling within this range, improved initial efficiency and cycle life characteristics can be observed. If the diffraction peak intensity is higher than I... MgSiO3(610) / I Si(111) If the value is 0.001 or less, or 0.01 or greater, the initial efficiency will deteriorate, and the cycle life characteristics will also deteriorate.

[0025] X-ray diffraction analysis can be performed using CuKα rays as the target ray.

[0026] Based on 100 wt% (i.e., total weight) of the total negative electrode active material, according to one embodiment, the negative electrode active material may include magnesium silicate (MgSiO3) in an amount of about 0.01 wt% to about 1.0 wt% (or according to another embodiment, about 0.01 wt% to about 0.6 wt%). When the amount of magnesium silicate is within this range, charge and discharge efficiency and cycle life characteristics can be improved.

[0027] In the negative electrode active material according to one embodiment, magnesium silicate may exist discontinuously and randomly on the surface of the active material, rather than continuously on the surface of the active material.

[0028] In one embodiment, the carbon may be amorphous carbon. When the carbon included in the silicon-carbon composite is amorphous carbon, it can be uniformly coated on silicon, thus further improving conductivity compared to crystalline carbon, and the power output can be excellent. The amount of amorphous carbon can be from about 5 wt% to about 45 wt% based on the total weight of the negative electrode active material.

[0029] Amorphous carbon can be soft carbon, hard carbon, or a combination thereof.

[0030] ​In the negative electrode active material, the silicon-carbon composite is a porous silicon-carbon composite and may have pores with an average size of about 50 nm or larger, or about 50 nm to about 500 nm. According to one embodiment, the pores may have an average size of about 50 nm to about 100 nm. The silicon-carbon composite includes pores that enable effective suppression of silicon volume expansion during charging and discharging of the negative electrode active material. This is because the included pores absorb the expanded volume, thereby suppressing the overall volume expansion of the negative electrode active material. The effect of suppressing volume expansion due to the pores can be more effectively achieved with an average pore size of about 50 nm or larger.

[0031] In one embodiment, the pore size can be measured by nitrogen adsorption method (BJH method), mercury porosity determination method, etc.

[0032] According to one embodiment, the negative electrode active material may have a structure including internal pores and carbon covering the outer walls of the pores, silicon, and magnesium silicate.

[0033] According to one embodiment, the negative electrode active material can be prepared by the following steps.

[0034] Magnesium silicide (Mg2Si) can be heat-treated once in an air atmosphere. The heat treatment can be performed at approximately 600°C to approximately 700°C. The heat treatment can last from approximately 5 hours to approximately 30 hours.

[0035] A single heat treatment oxidizes magnesium silicide to produce MgO and Si, and partially converts it into magnesium silicate MgSiO3.

[0036] Magnesium silicate can be obtained through a single heat treatment in an air atmosphere, while heat treatment under N2 or CO2 does not produce MgSiO3, which is undesirable.

[0037] Furthermore, when heat treatment is performed at temperatures outside this range, Mg₂Si remains and side reactions occur. However, when heat treatment can be performed under these conditions, a negative electrode active material comprising the desired amount of magnesium silicate can be appropriately prepared.

[0038] Subsequently, the heat-treated product can be etched using acid. This step can be performed by immersing the heat-treated product in acid. After etching, it can be filtered to obtain the etched product. During the etching step, the MgO produced dissolves in the acid, thus the etched product can be formed in the form of porous silicon.

[0039] The acid can be hydrochloric acid.

[0040] The resulting porous silicon can then be mixed with an amorphous carbon precursor.

[0041] Amorphous carbon precursors can be petroleum coke, coal coke, petroleum pitch, coal pitch, raw coke, or combinations thereof.

[0042] The mixing ratio of porous silicon and amorphous carbon precursors can be from about 95:5 to about 55:45 by weight.

[0043] Therefore, the step of mixing porous silicon and amorphous carbon precursors can control the resulting pores to a desired size. Specifically, when the mixing ratio of porous silicon and amorphous carbon precursors meets this range, the obtained pore size can be controlled to about 50 nm or larger (according to one embodiment, about 50 nm or larger and about 500 nm or smaller).

[0044] The mixture can be subjected to a secondary heat treatment to prepare the negative electrode active material. The secondary heat treatment can be carried out at approximately 800°C to approximately 1200°C.

[0045] According to the secondary heat treatment, the amorphous carbon precursor can be converted into amorphous carbon that can be included in the final product as amorphous carbon.

[0046] Another embodiment provides a rechargeable lithium battery including a negative electrode, a positive electrode, and an electrolyte.

[0047] The negative electrode may include a current collector and a negative electrode active material layer including a negative electrode active material according to one embodiment.

[0048] The negative electrode active material layer may also include crystalline carbon negative electrode active material. The crystalline carbon negative electrode active material may be amorphous, plate-like, sheet-like, spherical, or fibrous natural or artificial graphite.

[0049] When the negative electrode active material layer includes a negative electrode active material according to one embodiment as a first negative electrode active material and a crystalline carbon negative electrode active material as a second negative electrode active material, the first negative electrode active material is positioned between the particles of the second negative electrode active material to achieve good contact with the second negative electrode active material, thereby more effectively suppressing the expansion of the negative electrode. Here, the mixing ratio of the first negative electrode active material to the second negative electrode active material can be from about 1:99 to about 40:60 by weight. When the first and second negative electrode active materials are mixed and used within this range, the current density of the negative electrode can be further improved, and a thin film electrode can be fabricated. Furthermore, the first negative electrode active material including silicon in the negative electrode can be more uniformly present, thus more effectively suppressing the expansion of the negative electrode.

[0050] In the negative electrode active material layer, the amount of negative electrode active material can be from about 95 wt% to about 99 wt%, based on the total weight of the negative electrode active material layer.

[0051] The negative electrode active material layer may include a binder and may also include a conductive material. In the negative electrode active material layer, the amount of binder may be from about 1 wt% to about 5 wt% based on the total weight of the negative electrode active material layer. Furthermore, when a conductive material is also included, about 90 wt% to about 98 wt% of the negative electrode active material, about 1 wt% to about 5 wt% of the binder, and about 1 wt% to about 5 wt% of the conductive material may be used.

[0052] Binders improve the adhesion between negative electrode active material particles and between negative electrode active material particles and current collector. Binders can be non-aqueous binders, aqueous binders, or combinations thereof.

[0053] Non-aqueous adhesives may be ethylene-propylene copolymers, polyacrylonitrile, polystyrene, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0054] Waterborne adhesives may be styrene-butadiene rubber, acrylated styrene-butadiene rubber (ABR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyepoxychloropropane, polyphosphazene, ethylene-propylene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, or combinations thereof.

[0055] When an aqueous binder is used as a negative electrode binder, cellulosic compounds can also be used as thickeners to provide viscosity. Cellulosic compounds include one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and their alkali metal salts. The alkali metal can be Na, K, or Li. Based on 100 parts by weight of the negative electrode active material, the thickener may be included in an amount from about 0.1 parts by weight to about 3 parts by weight.

[0056] Conductive materials are included to provide electrode conductivity; any electrically conductive material can be used as a conductive material unless it causes a chemical change. Examples of conductive materials can be: carbon-based materials, such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.; metal-based materials such as metal powders or metal fibers, including copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0057] The current collector may include, but is not limited to, one selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and combinations thereof.

[0058] According to one embodiment, the negative electrode can be prepared by the following steps: mixing a negative electrode active material, a binder, and optionally a conductive material in a solvent to prepare an active material composition; and coating the active material composition onto a current collector. The solvent may be water.

[0059] Since this method for forming an active material layer is well known in the art, its detailed description will be omitted here.

[0060] The positive electrode may include a current collector and a layer of positive electrode active material formed on the current collector.

[0061] The positive electrode active material may include a lithiation compound that reversibly inserts and deintercalates lithium ions. Specifically, it may use a composite oxide of lithium with one or more metals selected from cobalt, manganese, nickel, and combinations thereof. More specifically, it may use a compound represented by one of the following chemical formulas: Li a A 1-b X b D 1 2(0.90≤a≤1.8, 0≤b≤0.5); Li a A 1-b X b O 2-c1 D 1 c1 (0.90≤a≤1.8, 0≤b≤0.5, 0≤c1≤0.05); Li a E 1-b X b O 2-c1 D 1 c1 (0.90≤a≤1.8, 0≤b≤0.5, 0≤c1≤0.05); Li a E 2-b X b O 4-c1 D 1 c1 (0.90≤a≤1.8, 0≤b≤0.5, 0≤c1≤0.05); Li a Ni 1-b-c Co b X c D 1 a (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0 <a=2);Li a Ni 1-b- c Co b X c O 2-a T a(0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0 <a<2);Li a Ni 1-b-c Co b X c O 2-a T2(0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0 <a<2);Li a Ni 1-b-c Mr b X c D 1 a (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0 <a≤2);Li a Ni 1-b-c Mr b X c O 2-a T a (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0 <a<2);Li a Ni 1-b-c Mr b X c O 2-a T2(0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0 <a<2);Li a Ni b HAVE BEEN c G d O2(0.90≤a≤1.8,0≤b≤0.9,0≤c≤0.5,0.001≤d≤0.1);Li a Ni b Co c Mr d G e O2(0.90≤a≤1.8,0≤b≤0.9,0≤c≤0.5,0≤d≤0.5,0.001≤e≤0.1);Li a NiG b O2(0.90≤a≤1.8,0.001≤b≤0.1);Li a CoG b O2(0.90≤a≤1.8,0.001≤b≤0.1);Li a Mr 1-b G b O2(0.90≤a≤1.8,0.001≤b≤0.1);Li a Mn2G b O4(0.90≤a≤1.8,0.001≤b≤0.1);Li a Mr 1-g Gg PO4(0.90≤a≤1.8, 0≤g≤0.5); QO2; QS2; LiQS2; V2O5; LiV2O5; LiZO2; LiNiVO4; Li (3-f) J2(PO4)3 (0≤f≤=2); Li (3-f) Fe2(PO4)3 (0≤f≤2); Li a FePO4 (0.90≤a≤1.8).

[0062] In the above chemical formulas, A is selected from Ni, Co, Mn, and combinations thereof; X is selected from Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, and combinations thereof; D 1 The elements are selected from O, F, S, P and combinations thereof; E is selected from Co, Mn and combinations thereof; T is selected from F, S, P and combinations thereof; G is selected from Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V and combinations thereof; Q is selected from Ti, Mo, Mn and combinations thereof; Z is selected from Cr, V, Fe, Sc, Y and combinations thereof; and J is selected from V, Cr, Mn, Co, Ni, Cu and combinations thereof.

[0063] Furthermore, the compound may have a coating layer on the surface, or may be mixed with another compound having a coating layer. The coating layer may include at least one coating element compound selected from the group consisting of oxides of the coating element, hydroxides of the coating element, hydroxyoxides of the coating element, oxycarbonates of the coating element, and hydroxycarbonates of the coating element. The compound used for the coating layer may be amorphous or crystalline. The coating element included in the coating layer may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The coating layer can be formed by using these elements in the compound in a manner that does not adversely affect the properties of the positive electrode active material. For example, the method may include any coating method (such as spraying, dipping, etc.), but since it is well known in the art, it is not described in more detail here.

[0064] In the positive electrode, the content of the positive electrode active material can be from about 90 wt% to about 98 wt%, based on the total weight of the positive electrode active material layer.

[0065] In this embodiment, the positive electrode active material layer may further include a binder and a conductive material. Here, based on the total amount of the positive electrode active material layer, the binder and conductive material may be included in amounts from about 1 wt% to about 5 wt%, respectively.

[0066] Binders improve the adhesion between positive electrode active material particles and between the positive electrode active material particles and the current collector. Examples of binders include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc., but are not limited to these.

[0067] Conductive materials are included to provide electrode conductivity; any electrically conductive material can be used as a conductive material unless it causes a chemical change. Examples of conductive materials include: carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.; metal-based materials such as metal powders or metal fibers, including copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0068] The current collector can be made of aluminum foil, nickel foil, or a combination thereof, but is not limited to these.

[0069] The positive and negative active material layers can be prepared by the following steps: mixing active materials, a binder, and optionally a conductive material in a solvent to prepare an active material composition; and coating the active material composition onto a current collector. This preparation of the active material layer is well known in the art, and a detailed description is omitted in the specification. The solvent can be N-methylpyrrolidone, but is not limited thereto. Furthermore, if an aqueous binder is used in the negative active material layer, the solvent can be water, which is used as the solvent in the preparation of the negative active material composition.

[0070] Electrolytes include non-aqueous organic solvents and lithium salts.

[0071] Non-aqueous organic solvents are used as media for transporting ions that participate in the electrochemical reactions of the battery.

[0072] Non-aqueous organic solvents can include carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, or aprotic solvents.

[0073] Carbonate solvents can include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate (BC), etc. Ester solvents can include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, propyl propionate, decanolactone, mevalonolactone, caprolactone, etc. Ether solvents can include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. Additionally, ketone solvents can include cyclohexanone, etc. Alcohol solvents may include ethanol, isopropanol, etc. Examples of aprotic solvents include: nitriles, such as R-CN (where R is a C2 to C20 straight-chain, branched or cyclic hydrocarbon, and may include double bonds, aromatic rings or ether bonds); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane; sulfolane, etc.

[0074] Organic solvents can be used alone or in mixtures. When organic solvents are used in mixtures, the mixing ratio can be controlled according to the desired battery performance, and this is well known to those skilled in the art.

[0075] Furthermore, carbonate solvents may preferably include mixtures of cyclic carbonates and linear carbonates. When cyclic carbonates and linear carbonates are mixed together in a volume ratio of about 1:1 to about 1:9, the mixture can exhibit enhanced performance when used as an electrolyte.

[0076] When mixing and using non-aqueous organic solvents, mixed solvents of cyclic carbonates and linear carbonates, mixed solvents of cyclic carbonates and propionate solvents, or mixed solvents of cyclic carbonates, linear carbonates, and propionate solvents may be used. Propionate solvents may include methyl propionate, ethyl propionate, propyl propionate, or combinations thereof.

[0077] Here, when using a mixture of cyclic carbonates and linear carbonates, or a mixture of cyclic carbonates and propionate solvents, it is desirable to use it at a volume ratio of about 1:1 to about 1:9, considering performance. Furthermore, cyclic carbonates, linear carbonates, and propionate solvents can be mixed and used at volume ratios of 1:1:1 to 3:3:4. The mixing ratio of the solvents can be appropriately adjusted according to the desired properties.

[0078] Organic solvents may also include aromatic hydrocarbon solvents and carbonate solvents. Carbonate solvents and aromatic hydrocarbon solvents can be mixed together in a volume ratio of about 1:1 to about 30:1.

[0079] Aromatic hydrocarbon organic solvents can be aromatic hydrocarbon compounds represented by chemical formula 1.

[0080] [Chemical Formula 1]

[0081]

[0082] In Formula 1, R1 to R6 may be the same or different, and may all be selected from hydrogen, halogens, C1 to C10 alkyl groups, haloalkyl groups and combinations thereof.

[0083] Specific examples of aromatic hydrocarbon organic solvents may be selected from benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, and fluoromethylbenzene. Benzene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene, and combinations thereof.

[0084] Electrolytes may also include vinylene carbonate, or ethylene carbonate compounds represented by chemical formula 2, as additives to improve cycle life.

[0085] [Chemical Formula 2]

[0086]

[0087] In Formula 2, R7 and R8 may be the same or different, and may each be independently hydrogen, halogen, cyano (CN), nitro (NO2) or fluorinated C1 to C5 alkyl, provided that at least one of R7 and R8 is halogen, cyano (CN), nitro (NO2) or fluorinated C1 to C5 alkyl, and R7 and R8 are not both hydrogen.

[0088] Examples of ethylene carbonate compounds may be difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or fluoroethylene carbonate. The amount of additive used to improve cycle life characteristics may be used within appropriate limits.

[0089] Electrolytes may also include ethylene carbonate, propanesulfonate lactone, succinate, or combinations thereof, and the amount used may be appropriately controlled.

[0090] Lithium salts dissolved in organic solvents supply lithium ions to the battery, enabling basic operation of rechargeable lithium batteries and improving lithium ion transport between the positive and negative electrodes. Examples of lithium salts include those selected from LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, and LiN(C x F 2x+1 SO2)(C y F 2y+1 At least one or two supporting salts of SO2 (where x and y are positive integers, for example, integers from 1 to 20), LiCl, LiI, and LiB(C2O4)2 (lithium bis(oxalate)borate: LiBOB). The concentration of the lithium salt can range from about 0.1 M to about 2.0 M. When lithium salts are included in the above concentration range, the electrolyte can exhibit excellent performance and lithium-ion mobility due to optimal electrolyte conductivity and viscosity.

[0091] Depending on the type of rechargeable lithium battery, a separator can be disposed between the positive and negative electrodes. The separator can be made of polyethylene, polypropylene, polyvinylidene fluoride, or multilayers of these materials with two or more layers, and can be a hybrid multilayer (such as polyethylene / polypropylene double-layer separators, polyethylene / polypropylene / polyethylene triple-layer separators, polypropylene / polyethylene / polypropylene triple-layer separators, etc.).

[0092] Figure 1 This is an exploded perspective view of a rechargeable lithium battery according to an embodiment. The rechargeable lithium battery according to the embodiment is shown as a prismatic battery, but is not limited thereto, and may include batteries of various shapes such as cylindrical batteries, pouch batteries, etc.

[0093] Reference Figure 1 The rechargeable lithium battery 100 according to an embodiment may include an electrode assembly 40 manufactured by winding a separator 30 disposed between a positive electrode 10 and a negative electrode 20, and a housing 50 for housing the electrode assembly 40. An electrolyte (not shown) may be immersed in the positive electrode 10, the negative electrode 20, and the separator 30.

[0094] Examples and comparative examples of the invention are described below. However, these examples are not to be construed in any way as limiting the scope of the invention.

[0095] (Example 1)

[0096] Magnesium silicide (Mg2Si) was subjected to a single heat treatment at 610°C for 20 hours in air atmosphere.

[0097] The heat-treated product is then added to hydrochloric acid for etching, and then filtered to obtain the etched product (i.e., porous silicon).

[0098] The obtained porous silicon was mixed with petroleum pitch, which served as an amorphous carbon precursor, in a certain proportion to achieve the amount of amorphous carbon in the final negative electrode active material shown in Table 3.

[0099] The resulting mixture was subjected to a secondary heat treatment at 1000°C to prepare the negative electrode active material. The produced negative electrode active material has pores with an average size of 50 nm and includes silicon, magnesium silicate, and soft carbon coated on the pores, silicon, and magnesium silicate.

[0100] A negative electrode active material is used as the first negative electrode active material, and natural graphite is used as the second negative electrode active material. The first negative electrode active material, the second negative electrode active material, a styrene-butadiene rubber binder, and carboxymethyl cellulose as a thickener are mixed in an aqueous solvent at a weight ratio of 12:85.5:1.5:1.0 to prepare a negative electrode active material slurry. Here, the mixing ratio of the styrene-butadiene rubber binder and the carboxymethyl cellulose thickener is 60:40 by weight.

[0101] A negative electrode comprising a current collector and a layer of negative active material formed on the current collector is prepared by coating a negative active material slurry onto a Cu foil current collector and drying it through a general procedure.

[0102] A rechargeable lithium battery was fabricated using a negative electrode, a LiCoO2 positive electrode, and an electrolyte. As the electrolyte, 1.5 M LiPF6 was dissolved in a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (20:10:70 volume ratio).

[0103] (Example 2)

[0104] Except for a single heat treatment at 600°C, the negative electrode active material is prepared using the same steps as in Example 1. Using the negative electrode active material, a negative electrode and a rechargeable lithium battery are manufactured using the same steps as in Example 1.

[0105] (Example 3)

[0106] Except for a heat treatment at 620°C, the negative electrode active material is prepared using the same steps as in Example 1. Using the negative electrode active material, a negative electrode and a rechargeable lithium battery are manufactured using the same steps as in Example 1.

[0107] (Example 4)

[0108] Except for a 10-hour heat treatment, the negative electrode active material is prepared using the same steps as in Example 1. Using the negative electrode active material, a negative electrode and a rechargeable lithium battery are manufactured using the same steps as in Example 1.

[0109] (Example 5)

[0110] Except for a 15-hour heat treatment, the negative electrode active material is prepared using the same steps as in Example 1. Using the negative electrode active material, a negative electrode and a rechargeable lithium battery are manufactured using the same steps as in Example 1.

[0111] (Example 6)

[0112] Except for a 30-hour heat treatment, the negative electrode active material is prepared using the same steps as in Example 1. Using the negative electrode active material, a negative electrode and a rechargeable lithium battery are manufactured using the same steps as in Example 1.

[0113] (Example 7)

[0114] Except for a single 25-hour heat treatment, the negative electrode active material is prepared using the same steps as in Example 1. Using the negative electrode active material, a negative electrode and a rechargeable lithium battery are manufactured using the same steps as in Example 1.

[0115] (Example 8)

[0116] Except for a single heat treatment at 615°C, the negative electrode active material is prepared using the same steps as in Example 1. Using the negative electrode active material, a negative electrode and a rechargeable lithium battery are manufactured using the same steps as in Example 1.

[0117] (Example 9)

[0118] Except for a 5-hour heat treatment, the negative electrode active material is prepared using the same steps as in Example 1. Using the negative electrode active material, a negative electrode and a rechargeable lithium battery are manufactured using the same steps as in Example 1.

[0119] (Compare with Example 1)

[0120] Except for a single heat treatment at 550°C, the negative electrode active material is prepared using the same steps as in Example 1. Using the negative electrode active material, a negative electrode and a rechargeable lithium battery are manufactured using the same steps as in Example 1.

[0121] (Compare with Example 2)

[0122] Except for a single heat treatment at 560°C, the negative electrode active material is prepared using the same steps as in Example 1. Using the negative electrode active material, a negative electrode and a rechargeable lithium battery are manufactured using the same steps as in Example 1.

[0123] (Compare with Example 3)

[0124] Except for a single heat treatment at 570°C, the negative electrode active material is prepared using the same steps as in Example 1. Using the negative electrode active material, a negative electrode and a rechargeable lithium battery are manufactured using the same steps as in Example 1.

[0125] (Compare with Example 4)

[0126] Except for a one-hour heat treatment, the negative electrode active material is prepared using the same steps as in Example 1. Using the negative electrode active material, a negative electrode and a rechargeable lithium battery are manufactured using the same steps as in Example 1.

[0127] (Compare with Example 5)

[0128] Except for a single heat treatment at 710°C, the negative electrode active material is prepared using the same steps as in Example 1. Using the negative electrode active material, a negative electrode and a rechargeable lithium battery are manufactured using the same steps as in Example 1.

[0129] (Compare with Example 6)

[0130] Except for a single heat treatment of magnesium silicide (Mg2Si) at 610°C for 20 hours under a nitrogen atmosphere, the negative electrode active material is prepared using the same steps as in Example 1. Using the negative electrode active material, a negative electrode and a rechargeable lithium battery are manufactured using the same steps as in Example 1.

[0131] (Compare with Example 7)

[0132] Except for a single heat treatment of magnesium silicide (Mg2Si) at 610°C for 20 hours under a CO2 atmosphere, the negative electrode active material is prepared using the same steps as in Example 1. Using the negative electrode active material, a negative electrode and a rechargeable lithium battery are manufactured using the same steps as in Example 1.

[0133] The heat treatment conditions for magnesium silicide in Examples 1 to 9 and Comparative Examples 1 to 7 are summarized in Table 1.

[0134] Table 1

[0135]

[0136]

[0137] Experimental Example 1) Evaluation of Physical Properties

[0138] The X-ray diffraction peak intensities of the negative electrode active materials of Examples 1 to 9 and Comparative Examples 1 to 7 were measured using CuKα rays. The results are shown in Table 2. From the results, I... MgSiO3(610) / I Si(111) The results are shown in Table 2.

[0139] For Si included in the prepared negative electrode active material, the full width at half maximum (FWHM) of the diffraction peaks in the (111) plane was measured using CuKα X-ray diffraction. Detailed measurement conditions are as follows:

[0140] Device: Malvern Panalytical (Xpert pro)

[0141] wavelength:

[0142] Scan rate: ~1.5 degrees / minute

[0143] 2θ window: 20°-80°

[0144] The results are shown in Table 2.

[0145] In addition, the crystal size of the negative electrode active material was measured. The results are shown in Table 2.

[0146] The pore sizes of the negative electrode active materials according to Examples 1 to 9 and Comparative Examples 1 to 7 were measured by nitrogen adsorption methods (BET, BJH method). The results are shown in Table 2.

[0147] Table 2

[0148]

[0149]

[0150] As shown in Table 2, the negative electrode active materials according to Examples 1 to 9 have a content falling below 0.001 MgSiO3(610) / I Si(111) The ratio (I) in the range <0.01 MgSiO3(610) / I Si(111) However, Comparative Examples 1 to 5 have ratios outside that range.

[0151] The fact that the negative electrode active materials of Comparative Examples 6 and 7 do not have peaks related to MgSiO3 indicates that MgSiO3 is not generated.

[0152] Experimental Example 2) Battery Characteristic Evaluation

[0153] ​The batteries according to Examples 1 to 9 and Comparative Examples 1 to 7 were subjected to one formation charge and discharge cycle at 0.1C, and the formation charge and discharge capacities were measured. The discharge capacity results are shown in Table 3. The initial efficiency was measured using the formation charge and discharge capacities. The results are shown in Table 3.

[0154] The capacity of amorphous carbon is considered to be 250 mAh / g. The silicon capacity is obtained by subtracting the value corresponding to the amount of amorphous carbon included in the negative electrode active material from the formation discharge capacity, and then dividing that value by the amount of silicon. The results are shown in Table 3.

[0155] The batteries from Examples 1 to 7 and Comparative Examples 1 to 3 were charged and discharged at 1C for 50 cycles, and the capacity ratio of the 50th discharge capacity to the 1st discharge capacity was measured. The results are shown in Table 3 as cycle life retention.

[0156] Experimental Example 3) Amount of MgSiO3

[0157] The amount of MgSiO3 in the negative electrode active materials according to Examples 1 to 9 and Comparative Examples 1 to 7 was measured by ICP analysis. The results are shown in Table 3.

[0158] Table 3

[0159]

[0160]

[0161] As shown in Table 3, batteries comprising the negative electrode active materials according to Examples 1 to 9 exhibit excellent initial efficiency and capacity retention, but batteries comprising the negative electrode active materials according to Comparative Examples 1 to 7 exhibit degraded initial efficiency and cycle life retention. The negative electrode active materials according to Examples 1 to 9 have a capacity retention of 0.001. MgSiO3(610) / I Si(111) The ratio <0.01 (I) MgSiO3(610) / I Si(111) According to Comparative Examples 1 to 7, the negative electrode active material has a content of 0.001. MgSiO3(610) / I Si(111) Ratios other than 0.01 (I) MgSiO3(610) / I Si(111) ).

[0162] While the invention has been described in conjunction with what are now considered practical exemplary embodiments, it will be understood that the invention is not limited to the disclosed embodiments, but rather, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Therefore, the above embodiments should be understood as illustrative and not as limiting the invention in any way.​​

Claims

1. A negative electrode active material for a rechargeable lithium battery, said negative electrode active material comprising: Porous silicon-carbon composites, comprising silicon, carbon, and magnesium silicate, have a density of 0.001... 硅酸镁(610) / I 硅(111) Diffraction peak intensity ratio <0.01 I 硅酸镁(610) / I 硅(111) The diffraction peak intensity is higher than I 硅酸镁(610) / I 硅(111) The diffraction peak intensity I of magnesium silicate at 2θ = 30° to 32° in X-ray diffraction analysis. 硅酸镁(610) The diffraction peak intensity I of silicon (111) detected at 2θ = 27.5° to 29.5° is compared with that of silicon (111). 硅(111) than.​ 2. The negative electrode active material for a rechargeable lithium battery according to claim 1, wherein, Based on the total 100wt% of the negative electrode active material, the amount of magnesium silicate is 0.01wt% to 1.0wt%.

3. The negative electrode active material for a rechargeable lithium battery according to claim 1, wherein, Based on the total 100wt% of the negative electrode active material, the amount of magnesium silicate is 0.01wt% to 0.6wt%.

4. The negative electrode active material for a rechargeable lithium battery according to claim 1, wherein, Carbon includes amorphous carbon.

5. The negative electrode active material for a rechargeable lithium battery according to claim 4, wherein, Amorphous carbon includes soft carbon, hard carbon, or combinations thereof.

6. The negative electrode active material for a rechargeable lithium battery according to claim 1, wherein, The amount of carbon is between 5 wt% and 45 wt%, based on the total weight of the negative electrode active material.

7. The negative electrode active material for a rechargeable lithium battery according to claim 1, wherein, The porous silicon-carbon composite includes pores, with carbon covering the outer walls of the pores, silicon, and magnesium silicate.

8. The negative electrode active material for a rechargeable lithium battery according to claim 7, wherein, The pores have an average size of 50 nm or greater.

9. The negative electrode active material for a rechargeable lithium battery according to claim 8, wherein, The pores have an average size ranging from 50 nm to 500 nm.

10. The negative electrode active material for a rechargeable lithium battery according to claim 1, wherein, The negative electrode active material is prepared through the following steps: Magnesium silicide is subjected to a single heat treatment to prepare the heating product; Etching heated products to prepare porous silicon; A mixture is prepared by mixing porous silicon with an amorphous carbon precursor; and The mixture is subjected to a second heat treatment.

11. The negative electrode active material for a rechargeable lithium battery according to claim 10, wherein, Perform a heat treatment in air atmosphere.

12. The negative electrode active material for a rechargeable lithium battery according to claim 10, wherein, A heat treatment is performed at 600℃ to 700℃ for 5 to 30 hours.

13. The negative electrode active material for a rechargeable lithium battery according to claim 10, wherein, Etching is performed using acid.

14. The negative electrode active material for a rechargeable lithium battery according to claim 13, wherein, The acid is hydrochloric acid.

15. The negative electrode active material for a rechargeable lithium battery according to claim 10, wherein, The mixing ratio of porous silicon and amorphous carbon precursors is 95:5 to 55:45 by weight.

16. The negative electrode active material for a rechargeable lithium battery according to claim 10, wherein, A secondary heat treatment is performed at 800℃ to 1200℃.

17. A rechargeable lithium battery, said rechargeable lithium battery comprising: The negative electrode comprises the negative electrode active material according to any one of claims 1 to 16; Positive electrode, including positive electrode active material; as well as Non-aqueous electrolyte.

18. The rechargeable lithium battery according to claim 17, wherein, The negative electrode comprises a negative electrode active material as the first negative electrode active material and crystalline carbon as the second negative electrode active material.

19. The rechargeable lithium battery according to claim 18, wherein, The mixing ratio of the first negative electrode active material and the second negative electrode active material by weight is 1:99 to 40:60.

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