Negative active material for rechargeable lithium battery and rechargeable lithium battery

Abstract

Disclosed are a negative active material for a rechargeable lithium battery and a rechargeable lithium battery. The negative active material for a rechargeable lithium battery includes a composite and second amorphous carbon surrounding a surface of the composite. The composite includes a mixture of silicon particles, metal particles, and first amorphous carbon.

Description

Technical Field

[0001] The present disclosure relates to a negative electrode active material for a rechargeable lithium battery and a rechargeable lithium battery. Background Art

[0002] Recently, rechargeable lithium batteries have attracted attention as power sources for small portable electronic devices. Since rechargeable lithium batteries use an organic electrolyte solution, the discharge voltage of a rechargeable lithium battery is two or more times that of a conventional battery using an alkaline aqueous solution, and thus a rechargeable lithium battery has a high energy density.

[0003] For the positive electrode active material of a rechargeable lithium battery, lithium-transition metal oxides such as LiCoO2, LiMn2O4, LiNi 1-x Co x O2 (0 < x < 1), etc., having a structure capable of intercalating lithium ions have been used.

[0004] As the negative electrode active material, various carbon-based negative electrode active materials such as artificial graphite, natural graphite, and hard carbon have been mainly used. However, such carbon-based negative electrode active materials have a low capacity of about 360 mAh / g, and thus silicon-based negative electrode active materials having a capacity of 2500 mAh / g or more, which is four or more times that of the carbon-based negative electrode active material, have been actively studied. However, compared with the carbon-based negative electrode active material (specifically, graphite), silicon has a severe volume expansion (300% relative to graphite) that occurs during charging and discharging, which causes a serious side reaction with the electrolyte, thereby consuming the electrolyte solution, resulting in deterioration of the cycle life characteristics.

[0005] The above information disclosed in this background art section is only for enhancing the understanding of the background of the invention, and thus it may include information that does not form the prior art known to those of ordinary skill in the art in the country. Summary of the Invention

[0006] One embodiment provides a negative electrode active material for a rechargeable lithium battery, which exhibits excellent initial efficiency and stable cycle life characteristics.

[0007] Another embodiment provides a rechargeable lithium battery including the negative electrode active material.

[0008] One embodiment provides a negative electrode active material for a rechargeable lithium battery, the negative electrode active material including: a composite including silicon particles, metal particles, and first amorphous carbon; and second amorphous carbon surrounding the surface of the composite.

[0009] The metal particles may be positioned on the surface of the silicon particles.In one embodiment, the composite may include the metal particles positioned on the surface of the silicon particles and a first amorphous carbon surrounding the silicon particles and the metal particles.

[0010] The metal particles may be Ni, Ti, Sn or a combination thereof.

[0011] The silicon particles may have a rod-like shape, a flake-like shape, or a spherical shape. In one embodiment, if the silicon particles have a rod-like shape or a flake-like shape, the silicon particles may have an aspect ratio of about 5 to about 20. Alternatively, if the silicon particles have a spherical shape, the silicon particles may have a particle diameter of about 5 nm to about 300 nm.

[0012] The metal particles may have a spherical shape. In one embodiment, if the metal particles have a spherical shape, the metal particles may have a particle diameter of about 1 nm to about 20 nm.

[0013] The second amorphous carbon may be continuously positioned on the surface of the composite in the form of a layer.

[0014] Another embodiment provides a rechargeable lithium battery, the rechargeable lithium battery including: a negative electrode including the negative active material; a positive electrode; and an electrolyte.

[0015] Other embodiments are included in the detailed description below.

[0016] The negative active material for a rechargeable lithium battery according to one embodiment may provide a rechargeable lithium battery exhibiting excellent initial efficiency and cycle-life characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 FIG2 is a schematic diagram showing the structure of a negative electrode active material according to one embodiment.

[0018] Figure 2 The process for preparing a negative active material according to an embodiment is schematically shown.

[0019] Figure 3 is a schematic diagram illustrating the structure of a rechargeable lithium battery according to one embodiment.

[0020] Figure 4 TEM photographs showing the structure at each step during the preparation of the negative active material according to Example 1.

[0021] Figure 5 is a graph showing the impedance of half cells according to Examples 1 and 2 and Comparative Example 1.

[0022] Figure 6is a graph showing impedances of half cells according to Example 1 and Comparative Examples 2 to 4.

[0023] Figure 7 is a graph showing the strength of the negative electrodes according to Example 1 and Comparative Examples 2 and 3. DETAILED DESCRIPTION

[0024] Hereinafter, embodiments are described in detail. However, these embodiments are exemplary and do not limit the present invention, which is defined by the scope of the claims.

[0025] According to one embodiment, a negative active material for a rechargeable lithium battery includes a composite comprising silicon particles, metal particles, and a first amorphous carbon; and a second amorphous carbon surrounding a surface of the composite. The composite may include a mixture of the silicon particles, the metal particles, and the first amorphous carbon.

[0026] In one embodiment, the first amorphous carbon may be hard carbon derived from a compound selected from tannic acid, gallic acid, dopamine, pyrogallol acid, or a combination thereof, and the second amorphous carbon may be soft carbon derived from a pitch selected from petroleum pitch, coal pitch, or a combination thereof. Alternatively, the first amorphous carbon and the second amorphous carbon may be ultimately prepared amorphous carbons having similar physical properties, regardless of whether the amorphous carbons are prepared from the compound or pitch.

[0027] In one embodiment, the metal particles may be positioned on the surface of the silicon particles, the metal particles may be positioned in direct contact with the surface of the silicon particles, for example, may be supported on the surface of the silicon particles, or the metal particles may be positioned within a predetermined distance from the surface of the silicon particles.

[0028] Furthermore, the composite material may include metal particles positioned on the surface of the silicon particles and first amorphous carbon surrounding the silicon particles and the metal particles. As described above, regardless of the type of positioning of the metal particles on the surface of the silicon particles, when the metal particles are positioned on the surface of the silicon particles, the metal particles are included in the amorphous carbon surrounding the surface of the silicon particles. This improves the strength and conductivity of the composite material including the silicon particles and the first amorphous carbon, resulting in improved cycle life characteristics.

[0029] When the first amorphous carbon is included in the composite (specifically, the first amorphous carbon is included to surround the silicon particles and the metal particles), electrical conductivity may be improved and strength may be maintained.

[0030] The amount of the first amorphous carbon may be about 1 wt % to about 20 wt % based on 100 wt % of the total negative active material for a rechargeable lithium battery, or about 10 wt % to about 20 wt % based on 100 wt % of the total negative active material for a rechargeable lithium battery. When the amount of the first amorphous carbon is within the above range, it can well surround silicon particles and metal particles, and it allows the metal particles to be well distributed in the composite, thus further improving the effect of including the amorphous carbon.

[0031] The silicon particles may have a rod-like shape, a sheet-like shape, or a spherical shape. In one embodiment, if the silicon particles have a rod-like shape or a sheet-like shape, the silicon particles may have an aspect ratio (aspect ratio) (major axis / minor axis) of about 5 to about 20. When the aspect ratio of the silicon particles meets the above range, the long cycle life characteristics of the battery including the active material can be achieved, and the volume expansion of the active material during charge and discharge can be effectively suppressed. In addition, if the silicon particles have a rod-like shape or a sheet-like shape, the size can be about 5 nm to about 300 nm. When the size of the silicon particles is within the above range, the long cycle life characteristics of the battery including the active material can be provided, and the volume expansion of the active material during charge and discharge can be effectively suppressed.

[0032] When the silicon particles have a spherical shape, the silicon particles may have a particle diameter of about 5 nm to about 300 nm. When the particle diameter of the silicon particles is within the above range, a battery including the active material can be provided with long cycle life characteristics and the volume expansion of the active material during charge and discharge can be effectively suppressed.

[0033] Here, the particle diameter refers to the average particle diameter, which may be the particle diameter D50 measured by the cumulative volume. When no additional definition is provided, such particle diameter D50 means the average particle diameter D50 in which the cumulative volume is about 50% by volume in the particle distribution.

[0034] The average particle diameter D50 can be measured by a general technique known to those skilled in the art, for example, using a particle size analyzer, transmission electron microscopy, or scanning electron microscopy. Another method can be performed by measuring it using a measurement device with dynamic light scattering, analyzing the data to count the number of particles for each particle size, and then calculating to obtain the average particle diameter D50.

[0035] The amount of the silicon particles may be about 20 wt% to about 80 wt% or about 40 wt% to about 70 wt% based on 100 wt% of the total weight of the negative active material for a rechargeable lithium battery. When the amount of the silicon particles is within this range, the capacity of the battery including the negative active material may be improved and a long cycle life may be exhibited.

[0036] The metal particles may be Ni, Ti, Sn, or a combination thereof. Such metal particles may have a spherical shape, and the particle diameter may be from about 1 nm to about 20 nm, and in one embodiment, from about 1 nm to about 10 nm. When the particle diameter of the metal particles is within the above range, the resistance of the negative electrode active material may be reduced, and the rate performance of a battery including the active material may be improved.

[0037] The amount of the metal particles may be about 2 wt% to about 32 wt% based on the total weight (100 wt%) of the negative active material for a rechargeable lithium battery. According to one embodiment, the amount of the metal particles may be about 2 wt% to about 10 wt% based on the total weight (100 wt%) of the negative active material for a rechargeable lithium battery. When the amount of the metal particles is within the above range, the resistance of the active material can be reduced and a high capacity can be exhibited.

[0038] The second amorphous carbon may be located continuously as a layer type on the surface of the composite, or may be located discontinuously as an island type on the surface of the composite.

[0039] The amount of the second amorphous carbon may be about 5 wt % to about 40 wt % based on 100 wt % of the total weight of the negative electrode active material for a rechargeable lithium battery, or about 10 wt % to about 30 wt % based on 100 wt % of the total weight of the negative electrode active material for a rechargeable lithium battery. When the amount of the second amorphous carbon is within the above range, a long cycle life characteristic may be exhibited, and the irreversible capacity of a battery including the active material during charge and discharge may be reduced.

[0040] Figure 1 Schematically shows the structure of a negative active material for a rechargeable lithium battery according to one embodiment. Figure 1 As shown in FIG, the negative electrode active material 1 includes a composite and a second amorphous carbon 9 surrounding the composite, and the composite includes silicon particles 3, metal particles 5, and first amorphous carbon 7. The composite includes silicon particles 3, metal particles 5 positioned on the surface of the silicon particles 3, and the first amorphous carbon 7 surrounding the silicon particles 3 and the metal particles 5. Figure 1 As shown in FIG, the second amorphous carbon 9a may be filled between the composites. Figure 1The metal particles 5 positioned on the surface of the silicon particles 3 are shown as an example, but are not limited thereto. As described, the metal particles and the silicon particles may also be positioned within a predetermined distance in a region where the metal particles and the silicon particles are surrounded by the first amorphous carbon. In addition, Figure 1 An example is shown in which the second amorphous carbon is continuously located on the surface of the composite as a layer type, but alternatively, it may be discontinuously located on the surface of the composite as an island type.

[0041] The following will be based on Figure 2 The preparation of a negative electrode active material according to one embodiment is shown.

[0042] First, silicon particles can be prepared. The silicon particles can be nanoparticles, and in one embodiment, can be nanoparticles having a particle diameter of about 10 nm to about 200 nm. Such silicon nanoparticles can be obtained by conventional nanoparticle preparation such as top-down techniques (e.g., pulverization) or bottom-up techniques (e.g., chemical vapor deposition (CVD)) in which silicon organic gases such as SiH4 are used to agglomerate atoms. The pulverization can be ball milling.

[0043] The silicon particles may have a rod-like shape, a plate-like shape, or a spherical shape.

[0044] Silicon particles, a first amorphous carbon precursor, and a metal compound are mixed to prepare a mixture. The first amorphous carbon precursor may be tannic acid, gallic acid, dopamine, pyrogallic acid, or a combination thereof. The metal compound may be a compound including Ni, Ti, Sn, or a combination thereof, and the compound may be a chloride, hydroxide, or nitride.

[0045] During the mixing, a bonding layer of the metal in the metal compound and the first amorphous carbon may be formed.

[0046] The mixing ratio of the silicon particles, the first amorphous carbon precursor, and the metal compound may be about 50:30:50 to about 50:30:28 by weight. When the mixing ratio of the silicon particles, the first amorphous carbon precursor, and the metal compound is within the above range, side reactants such as Ni2Si that may be generated due to the reaction between the silicon particles and the metal compound can be effectively prevented.

[0047] The mixing can be performed by a wet process using a solvent or a dry process without a solvent. The solvent can be isopropyl alcohol, ethanol, propanol, butanol, or a combination thereof.

[0048] The resulting mixture can be subjected to a hydrothermal reaction. The hydrothermal reaction can be carried out at about 80°C to about 150°C. In addition, the hydrothermal reaction can be carried out by inserting a microwave reactor of an autoclave type and injecting microwave electromagnetic waves (e.g., ultra-high frequency (UHF) waves), but the heat source for reduction is not limited to microwave electromagnetic waves. The microwave electromagnetic waves can be injected in a range of about 300W to about 1600W, and the hydrothermal reaction can be optimally controlled to a temperature range of about 80°C to about 150°C (e.g., about 100°C to about 120°C).

[0049] According to the hydrothermal reaction, the first amorphous carbon reacts with the metal compound to produce a reaction product. Thereafter, the reaction product is spray-dried to produce a reaction dried product. The spray drying can be performed at about 80°C to about 170°C or at about 120°C to about 150°C. When spray drying is performed within this temperature range, the solvent can be efficiently dried, and a dense spray-dried product can be produced.

[0050] The obtained spray-dried product may first be subjected to a first heat treatment to prepare a composite. The first heat treatment may be performed at about 300°C to about 600°C or at about 400°C to about 500°C. When the first heat treatment is performed within the temperature range, it is beneficial to remove organic materials and produce metals. The first heat treatment may be performed under an inert atmosphere, wherein the inert atmosphere may be a mixed atmosphere of argon (Ar) gas and H2 gas or an N2 gas atmosphere. According to the first heat treatment, the first amorphous carbon precursor is converted into a first amorphous carbon that can be included in the composite as the first amorphous carbon.

[0051] The prepared composite can be mixed with a second amorphous carbon, and the resulting mixture can then be subjected to a secondary heat treatment to prepare a negative electrode active material. The second amorphous carbon precursor can be petroleum pitch, coal tar, or a combination thereof. The mixing ratio of the composite and the second amorphous carbon precursor can be about 60wt%:40wt% to about 90wt%:10wt%, or can be about 80wt%:20wt% to about 90wt%:10wt%. When the mixing ratio of the composite and the second amorphous carbon is within the range, high capacity and long cycle life characteristics can be obtained.

[0052] The secondary heat treatment may be performed at about 600°C to about 1100°C or at about 900°C to about 1000°C. When the secondary heat treatment is performed within the temperature range, the resistance of the active material can be effectively reduced, and the charge and discharge efficiency can be improved. According to the secondary heat treatment, the second amorphous carbon precursor is converted into the second amorphous carbon that can be present on the surface of the composite as the second amorphous carbon.

[0053] According to one embodiment, there is provided a rechargeable lithium battery including a negative electrode, a positive electrode, and an electrolyte.

[0054] The negative electrode may include a current collector and a negative active material layer formed on the current collector, and the negative active material includes the negative active material according to one embodiment.

[0055] The negative electrode active material layer may further include a carbon-based negative electrode active material. Examples of carbon-based negative electrode active materials may include crystalline carbon, amorphous carbon, or a combination thereof. Crystalline carbon may be natural graphite or artificial graphite such as those having an amorphous shape, a plate shape, a flake shape, a spherical shape, or a fiber shape. Amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbide, sintered coke, or the like.

[0056] In the negative electrode active material layer, the negative electrode active material may be included in an amount of 95 wt % to 99 wt % based on the total weight of the negative electrode active material layer. If the negative electrode active material layer includes both the negative electrode active materials according to one embodiment (i.e., silicon-based negative electrode active materials and carbon-based negative electrode active materials), the mixing ratio of the silicon-based negative electrode active material to the carbon-based negative electrode active material may be about 20:80 to 10:90 by weight. When the mixing ratio of the silicon-based negative electrode active material to the carbon-based negative electrode active material is within the range, long cycle life characteristics and volume expansion suppression may be obtained.

[0057] The negative electrode active material layer may include a binder and may optionally include a conductive material. In the negative electrode active material layer, the amount of the binder may be from about 1 wt % to about 5 wt % based on the total weight of the negative electrode active material layer. When the negative electrode active material layer further includes a conductive material, the negative electrode active material layer includes from about 90 wt % to about 98 wt % of the negative electrode active material, from about 1 wt % to about 5 wt % of the binder, and from about 1 wt % to about 5 wt % of the conductive material.

[0058] The binder allows the negative active material particles to adhere well to each other and also allows the negative active material to adhere to the current collector. The binder may include a non-water-soluble binder, a water-soluble binder, or a combination thereof.

[0059] The non-water-soluble binder may be polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an ethylene oxide-containing polymer, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, lithium polyacrylate, or a combination thereof.

[0060] The water-soluble binder can be styrene-butadiene rubber, acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluororubber, ethylene propylene copolymer, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene propylene diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol or a combination thereof.

[0061] When a water-soluble binder is used as a negative electrode binder, a cellulose compound may also be used as a thickener to provide viscosity. Cellulose compounds include one or more of carboxymethyl cellulose, hydroxypropyl methylcellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal may be Na, K, or Li. The thickener may be included in an amount of 0.1 to 3 parts by weight based on 100 parts by weight of the negative electrode active material.

[0062] A conductive material is included to provide electrode conductivity, and any conductive material can be used as the conductive material unless it causes a chemical change. Examples of the conductive material include: carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, Denka black, carbon fiber, etc.; metal-based materials including metal powder or metal fiber of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0063] The current collector may include one selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof, but is not limited thereto.

[0064] The negative electrode can be prepared by mixing a negative active material, a binder, and an optional conductive material in a solvent to prepare an active material composition and coating the composition on a current collector. The solvent can be water.

[0065] Such negative electrode preparation is well known in the related art, and thus a detailed description will not be shown in the specification.

[0066] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector.

[0067] The positive electrode active material may include a compound that allows lithium ions to be reversibly intercalated and deintercalated (lithiated intercalation compound). Specifically, it may include one or more composite oxides of metals selected from cobalt, manganese, nickel, and combinations thereof and lithium. A more specific example may be a compound represented by one of the following chemical formulas: Li a A 1-b X b D2(0.90≤a≤1.8, 0≤b≤0.5); Li a A 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a E 1-b X b O 2-c D c(0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05);Li a HAVE BEEN 2-b X b O 4-c D c (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05);Li a Ni 1-b-c Co b X c D α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0≤α≤2);Li a Ni 1-b- c Co b X c O 2-α T α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0≤α<2);Li a Ni 1-b-c Co b X c O 2-α T2(0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0≤α<2);Li a Ni 1-b-c Mr b X c D α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0≤α≤2);Li a Ni 1-b-c Mr b X c O 2-α T α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0≤α≤2);Li a Ni 1-b-c Mr b X c O 2-α T2(0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0≤α≤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 eO2 (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 Mn 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 Mn 1-g G g PO4(0.90≤a≤1.8, 0≤g≤0.5); QO2; QS2; LiQS2; V2O5; LiV2O5; LiZO2; LiNiVO4; Li (3-f) J2PO 43 (0≤f≤2);Li (3-f) Fe2PO 43 (0≤f≤2); and Li a FePO4(0.90≤a≤1.8).

[0068] In the chemical formula, 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 is 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.

[0069] 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 an oxide of a coating element, a hydroxide of a coating element, an oxyhydroxide of a coating element, an oxycarbonate of a coating element, and a hydroxycarbonate of a coating element. The compound used for the coating layer may be amorphous or crystalline. The coating elements included in the coating layer may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. The coating layer may be provided 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 relevant art, it is not described in more detail.

[0070] In the positive electrode, the amount of the positive active material may be 90 wt % to 98 wt % based on the total weight of the positive active material layer.

[0071] In one embodiment, the positive active material layer may further include a binder and a conductive material, and the binder and the conductive material may be each included in an amount of about 1 wt % to about 5 wt % based on the total weight of the positive active material layer.

[0072] The binder improves the bonding between the positive electrode active material particles and between the positive electrode active material particles and the current collector. Examples of the binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, and nylon.

[0073] A conductive material is included to provide electrode conductivity. Any conductive material can be used as the conductive material unless it causes chemical changes in the battery. Examples of the conductive material include: carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.; metal-based materials including metal powders or metal fibers such as copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0074] The current collector may be aluminum foil, nickel foil, or a combination thereof, but is not limited thereto.

[0075] The positive electrode can be prepared by mixing a positive electrode active material, a binder, and an optional conductive material in a solvent to prepare an active material composition, and then coating the active material composition on a current collector. Such positive electrode preparation is well known in the relevant art and is not described in detail in this specification. The solvent can be N-methylpyrrolidone, but is not limited thereto.

[0076] The electrolyte may include a non-aqueous organic solvent and a lithium salt.

[0077] The non-aqueous organic solvent serves as a medium for transporting ions participating in the electrochemical reaction of the battery.

[0078] The non-aqueous organic solvent may include a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent, or an aprotic solvent.

[0079] Carbonate solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethyl methyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Ester solvents may include methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerolactone, mevalonolactone, caprolactone, etc. Ether solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. Ketone solvents may include cyclohexanone, etc. Alcohol solvents may include ethanol, isopropanol, etc., and aprotic solvents may include nitriles such as R-CN (wherein R is a hydrocarbon group having a C2 to C20 linear, branched or cyclic structure, and may include a double bond, an aromatic ring or an ether bond), dioxolanes such as 1,3-dioxolane, and cyclopentane, etc.

[0080] The non-aqueous organic solvent may be used alone or in a mixture. When the organic solvent is used in a mixture, the mixing ratio may be controlled according to the desired battery performance.

[0081] The carbonate-based solvent may be preferably a mixture of a cyclic carbonate and a chain carbonate. In this case, the cyclic carbonate and the chain carbonate may be mixed and used in a volume ratio of 1:1 to 1:9, so that the performance of the electrolyte may be improved.

[0082] When the non-aqueous organic solvent is used as a mixture, a mixed solvent of a cyclic carbonate and a chain carbonate; a mixed solvent of a cyclic carbonate and a propionate solvent; or a mixed solvent of a cyclic carbonate, a chain carbonate, and a propionate solvent can be used. The propionate solvent can be methyl propionate, ethyl propionate, propyl propionate, or a combination thereof.

[0083] Here, when mixing cyclic carbonate and chain carbonate or mixing cyclic carbonate and propionate solvent, they can be mixed in a volume ratio of about 1:1 to about 1:9, thereby improving the performance of the electrolyte solution. In addition, when mixing cyclic carbonate, chain carbonate and propionate solvent, they can be mixed in a volume ratio of about 1:1:1 to about 3:3:4. The mixing ratio of the solvent can be appropriately adjusted according to the desired properties.

[0084] In addition to the carbonate-based solvent, the non-aqueous organic solvent may further include an aromatic hydrocarbon-based organic solvent. Here, the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent may be mixed in a volume ratio of about 1:1 to about 30:1.

[0085] The aromatic hydrocarbon organic solvent may be an aromatic hydrocarbon compound of Chemical Formula 1.

[0086]

Chemical Formula 1

[0087]

[0088] In Chemical Formula 1, R1 to R6 are the same or different and are selected from hydrogen, halogen, C1 to C10 alkyl, halogenated alkyl, and combinations thereof.

[0089] Specific examples of aromatic hydrocarbon organic solvents can 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, fluoroform, 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.

[0090] The electrolyte may further include vinylene carbonate or an ethylene carbonate-based compound represented by Chemical Formula 2 as an additive for improving the cycle life of the battery.

[0091]

Chemical Formula 2

[0092]

[0093] In Chemical Formula 2, R7 and R8 are the same or different and are selected from hydrogen, halogen, cyano (CN), nitro (NO2) and fluorinated C1-C5 alkyl, with the proviso that at least one of R7 and R8 is halogen, cyano (CN), nitro (NO2) or fluorinated C1 to C5 alkyl, and both R7 and R8 are not hydrogen.

[0094] Examples of ethylene carbonate compounds may include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or fluoroethylene carbonate. The amount of the additive for improving cycle life may be used within an appropriate range.

[0095] The electrolyte may further include vinyl ethylene carbonate, propane sultone, succinonitrile, or a combination thereof, and the amount thereof may be appropriately controlled.

[0096] The lithium salt dissolved in the organic solvent supplies lithium ions in the battery, enables the basic operation of the rechargeable lithium battery, and improves the transport of lithium ions between the positive electrode and the negative electrode. Examples of lithium salts include those selected from LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide LiFSI), LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (wherein, x and y are natural numbers, such as integers from 0 to 20), at least one supporting salt selected from the group consisting of lithium difluoro(bisoxalato)phosphate, LiCl, LiI, LiB(C2O4)2 (lithium bis(oxalato)borate: LiBOB), and lithium difluoro(oxalato)borate (LiDFOB). The lithium salt may be used in a concentration range of 0.1 M to 2.0 M. When the lithium salt is included in the above concentration range, the electrolyte may have excellent performance and lithium ion mobility due to optimal electrolyte conductivity and viscosity.

[0097] Depending on the type of lithium secondary battery, a separator may be provided between the positive electrode and the negative electrode. Such separators may include polyethylene, polypropylene, polyvinylidene fluoride, and multilayers thereof, such as a polyethylene / polypropylene double-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator.

[0098] Figure 3is an exploded perspective view of a lithium secondary battery according to an embodiment. The lithium secondary 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 a cylindrical or pouch-shaped battery.

[0099] Reference Figure 3 The lithium secondary battery 100 according to the embodiment includes an electrode assembly 40 and a case 50 accommodating the electrode assembly 40. The electrode assembly 40 is manufactured by winding a separator 30 interposed between a positive electrode 10 and a negative electrode 20. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte solution (not shown).

[0100] Hereinafter, examples and comparative examples of the present invention are described. However, these examples are not to be construed as limiting the scope of the invention in any sense.

[0101] (Example 1)

[0102] The Si particles were pulverized by ball milling to prepare Si particles having a size of 100 nm and a flake shape.

[0103] The prepared Si particles, tannic acid and Ni chloride (NiCl2) were added to an isopropyl alcohol solvent at a weight ratio of 50:30:28, mixed and dispersed to prepare a mixture. Regarding the mixture, a 75,000x TEM photograph is shown in FIG. Figure 4 A 150,000-fold magnified TEM photograph of part a is shown in FIG. Figure 4 In a1. Figure 4 In a, the MPN layer represents the bonding layer of Ni and tannic acid.

[0104] The prepared mixture was added to a microwave reactor of autoclave type, and 1500W ultrahigh frequency was injected thereto to perform a hydrothermal reaction at 100°C. The obtained hydrothermal reaction product was spray-dried at 120°C using a spray dryer. Regarding the spray-dried product, a 300,000x TEM photograph is shown in Figure 4 b, and a 600,000-fold magnified photograph of part b is shown in Figure 4 In b1. Figure 4 In b, Si NPs represents Si nanoparticles, and p-MPN layer represents polymerized MPN.

[0105] The spray-dried product was added to a furnace in a mixed atmosphere of Ar and H2 (3:1 volume ratio) and subjected to a heat treatment at 450°C to prepare a composite. TEM images of the prepared composite are shown in Figure 4 c (500,000 times), and a 1500,000 times magnified photograph of part c is shown in Figure 480 wt% of the prepared composite was mixed with 20 wt% of petroleum asphalt, and the resulting mixture was subjected to a secondary heat treatment at 900° C. to prepare a negative electrode active material.

[0106] The prepared negative electrode active material includes a composite and a second amorphous carbon surrounding the composite, and the composite includes silicon particles, nickel particles positioned on the surface of the silicon particles, and a first amorphous carbon surrounding the nickel particles. The first amorphous carbon is hard carbon, and the second amorphous carbon is soft carbon. The silicon particles have a size of 100 nm, a flaky shape, and an aspect ratio (major axis / minor axis) of 5. In addition, the nickel particles have a spherical shape and an average particle diameter D50 of 10 nm. The first amorphous carbon and the second amorphous carbon are completely surrounded on the surface of the nickel particles and the composite, respectively.

[0107] In the negative electrode active material, based on the total weight of the negative electrode active material 100wt%, the amount of silicon particles is 60wt%; based on the total weight of the negative electrode active material 100wt%, the amount of the first amorphous carbon is 10wt%; based on the total weight of the negative electrode active material 100wt%, the amount of nickel particles is 15wt%; based on the total weight of the negative electrode active material 100wt%, the amount of the second amorphous carbon is 15wt%.

[0108] 85 wt% of the negative active material, 5 wt% of carbon black (trademark: Super-P) conductive material, and 10 wt% of lithium polyacrylate binder were mixed in an N-methylpyrrolidone solvent to prepare a negative active material slurry. The negative active material slurry was coated on a Cu current collector, dried, and pressed to prepare a negative electrode including a negative active material layer formed on the current collector.

[0109] A coin-type half-cell was fabricated using a negative electrode, a lithium metal counter electrode, and an electrolyte. As the electrolyte, 1.5 M LiPF6 dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate (20:40:40 by volume) was used.

[0110] (Example 2)

[0111] A negative active material was prepared by the same procedure as in Example 1, except that the mixing ratio of the prepared Si particles, tannic acid, and Ni chloride was changed to 50:30:50 by weight. Using the negative active material, a negative electrode was prepared.

[0112] In the negative electrode active material, the amount of silicon particles is 50wt% based on the total weight of the negative electrode active material 100wt%; the amount of the first amorphous carbon is 10wt% based on the total weight of the negative electrode active material 100wt%; the amount of nickel particles is 25wt% based on the total weight of the negative electrode active material 100wt%; and the amount of the second amorphous carbon is 15wt% based on the total weight of the negative electrode active material 100wt%.

[0113] A coin-type half-cell was manufactured through the same steps as in Example 1 using the negative electrode.

[0114] (Example 3)

[0115] A negative electrode active material was prepared by the same procedure as in Example 1, except that Sn chloride (SnCl 2 ) was used instead of Ni chloride. Using the negative electrode active material, a negative electrode was prepared.

[0116] (Comparative Example 1)

[0117] The Si particles were crushed to prepare spherical Si particles having a size of 100 nm. An amorphous carbon layer was formed on the surface of the prepared Si particles using chemical vapor deposition using an acetylene source to prepare a negative electrode active material. A negative electrode was prepared using the negative electrode active material.

[0118] A negative electrode was prepared by the same steps as in Example 1 using the negative active material.

[0119] (Comparative Example 2)

[0120] Si particles were crushed to prepare spherical Si particles with a size of 50 nm. The prepared Si particles were mixed with dopamine at a weight ratio of 1:2, and the mixture was heat-treated at 900°C under a nitrogen atmosphere to prepare a negative electrode active material including a Si core and an amorphous carbon layer formed on the core. The amorphous carbon layer is hard carbon doped with nitrogen. Using the negative electrode active material, a negative electrode was prepared by the same steps as in Example 1.

[0121] A coin-type half-cell was manufactured through the same steps as in Example 1 using the negative electrode.

[0122] (Comparative Example 3)

[0123] Si particles were crushed to produce spherical Si particles with a size of 50 nm. The prepared Si particles were mixed with petroleum pitch at a weight ratio of 1:2, and the mixture was heat-treated at 900°C under a nitrogen atmosphere to produce a negative electrode active material comprising a Si core and an amorphous carbon layer formed on the core. The amorphous carbon layer is hard carbon. Using the negative electrode active material, a negative electrode was produced using the same procedures as in Example 1.

[0124] A coin-type half-cell was manufactured through the same steps as in Example 1 using the negative electrode.

[0125] (Comparative Example 4)

[0126] The Si particles were crushed to prepare Si particles having a size of 50 nm and a spherical shape. The prepared Si particles, tannic acid, and reduced graphene oxide were mixed in a weight ratio of 1:0.2:0.5, and the mixture was heat-treated at 900° C. under a N2 atmosphere to prepare a negative electrode active material including a Si core and a coating layer formed on the core. The coating layer included a mixture of hard carbon and reduced graphene oxide. Using the negative electrode active material, a negative electrode was prepared by the same steps as in Example 1.

[0127] A coin-type half-cell was manufactured through the same steps as in Example 1 using the negative electrode.

[0128] (Example 4)

[0129] 97 wt% of a mixture of the negative active material according to Example 1 and artificial graphite (mixing ratio: 9:91 by weight) was mixed in an aqueous solvent with 1.5 wt% of styrene-butadiene as a binder and 1.5 wt% of carboxymethyl cellulose as a viscosity-enhancing agent to prepare a negative active material slurry. The negative active material slurry was coated on a Cu current collector, dried, and pressed to prepare a negative electrode.

[0130] A coin-type half-cell was fabricated using a negative electrode, a lithium metal counter electrode, and an electrolyte. As the electrolyte, 1.5 M LiPF6 dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate (20:40:40 by volume) was used.

[0131] (Example 5)

[0132] 97 wt% of a mixture of the negative active material according to Example 2 and artificial graphite (mixing ratio: 13:87 weight ratio) was mixed in an aqueous solvent with 1.5 wt% of styrene-butadiene as a binder and 1.5 wt% of carboxymethyl cellulose as a viscosity-enhancing agent to prepare a negative active material slurry. The negative active material slurry was coated on a Cu current collector, dried, and pressed to prepare a negative electrode.

[0133] A coin-type half-cell was manufactured through the same steps as in Example 4 using the negative electrode, the lithium metal counter electrode, and the electrolyte.

[0134] (Example 6)

[0135] 97 wt% of a mixture of the negative active material and artificial graphite according to Example 3 (mixing ratio: 7:93 weight ratio) was mixed in an aqueous solvent with 1.5 wt% of styrene-butadiene as a binder and 1.5 wt% of carboxymethyl cellulose as a viscosity-enhancing agent to prepare a negative active material slurry. The negative active material slurry was coated on a Cu current collector, dried, and pressed to prepare a negative electrode.

[0136] A coin-type half-cell was manufactured through the same steps as in Example 4 using the negative electrode, the lithium metal counter electrode, and the electrolyte.

[0137] (Comparative Example 5)

[0138] 97 wt% of a mixture of the negative active material and artificial graphite according to Comparative Example 1 (mixing ratio: 9:91 by weight) was mixed in an aqueous solvent with 1.5 wt% of styrene-butadiene as a binder and 1.5 wt% of carboxymethyl cellulose as a viscosity-enhancing agent to prepare a negative active material slurry. The negative active material slurry was coated on a Cu current collector, dried, and pressed to prepare a negative electrode.

[0139] A coin-type half-cell was manufactured through the same steps as in Example 4 using the negative electrode, the lithium metal counter electrode, and the electrolyte.

[0140] (Comparative Example 6)

[0141] 97 wt% of the negative active material according to Comparative Example 2, 1.5 wt% of styrene-butadiene as a binder, and 1.5 wt% of carboxymethyl cellulose as a viscosity-enhancing agent were mixed in an aqueous solvent to prepare a negative active material slurry. The negative active material slurry was coated on a Cu current collector, dried, and pressed to prepare a negative electrode.

[0142] A coin-type half-cell was manufactured through the same steps as in Example 4 using the negative electrode, the lithium metal counter electrode, and the electrolyte.

[0143] (Comparative Example 7)

[0144] 97 wt% of the negative active material according to Comparative Example 3, 1.5 wt% of styrene-butadiene as a binder, and 1.5 wt% of carboxymethyl cellulose as a viscosity-enhancing agent were mixed in an aqueous solvent to prepare a negative active material slurry. The negative active material slurry was coated on a Cu current collector, dried, and pressed to prepare a negative electrode.

[0145] A coin-type half-cell was manufactured through the same steps as in Example 4 using the negative electrode, the lithium metal counter electrode, and the electrolyte.

[0146] (Comparative Example 8)

[0147] 97 wt% of the negative active material according to Comparative Example 4, 1.5 wt% of styrene-butadiene as a binder, and 1.5 wt% of carboxymethyl cellulose as a viscosity-enhancing agent were mixed in an aqueous solvent to prepare a negative active material slurry. The negative active material slurry was coated on a Cu current collector, dried, and pressed to prepare a negative electrode.

[0148] A coin-type half-cell was manufactured through the same steps as in Example 4 using the negative electrode, the lithium metal counter electrode, and the electrolyte.

[0149] 1) Impedance measurement (Electrochemical impedance spectroscopy: EIS)

[0150] The half-cell was charged and discharged at 0.7C, 4.4V cut-off and SOC100 to measure the impedance according to the EIS (electrochemical impedance spectroscopy) method. Among these results, the results according to Examples 1 and 2 and Comparative Example 1 are shown in FIG. Figure 5 The results of Example 1 and Comparative Examples 2 to 4 show that Figure 6 middle.

[0151] like Figure 5 As shown in , the impedance of the half-cells according to Examples 1 and 2 is smaller than the impedance of the half-cell according to Comparative Example 1. Specifically, as Figure 6 As shown in , the impedance of the half-cell using the negative electrode according to Example 1 is significantly smaller than the impedance of the half-cells according to Comparative Examples 2 to 4.

[0152] 2) Hardness measurement

[0153] The strength of the negative electrodes according to Example 1 and Comparative Examples 2 and 3 was measured by applying a force of 30 kgf using a nanoindentation measuring device (available from Rockwell Automation, Inc., product name: VH3300). The measured strength is the indentation hardness. The results are shown in FIG. Figure 7 middle.

[0154] like Figure 7 As shown in , the hardness of the negative electrode according to Example 1 is significantly higher than the hardness of the negative electrodes according to Comparative Examples 2 and 3.

[0155] 3) Evaluation of half-cell charge and discharge efficiency and cycle life characteristics

[0156] The half-cells according to Examples 1 to 3 and Comparative Examples 1 to 4 were charged and discharged once at 0.5 C, and the charge and discharge capacities were measured. The results are shown in Table 1. Furthermore, the charge and discharge efficiency, which is the ratio of the first discharge capacity to the first charge capacity, was measured. The results are shown in Table 1.

[0157] Table 1

[0158] Charging capacity (mAh / g) Discharge capacity (mAh / g) Charge and discharge efficiency (%) Example 1 2414 2100 87 Example 2 1867 1550 83 Example 3 3023 2600 86 Comparative Example 1 2716 2200 81 Comparative Example 2 2308 1800 78 Comparative Example 3 1975 1600 81 Comparative Example 4 2400 1800 75

[0159] As can be seen from Table 1, the half-cells using the negative active materials according to Examples 1 to 3 exhibited excellent charge and discharge efficiency compared to Comparative Examples 1 to 4.

[0160] The half-cells according to Examples 4 to 6 and Comparative Examples 5 to 8 were charged and discharged 100 times at 0.5C, and the ratio of the 100th discharge capacity to the 1st discharge capacity was measured. The results are shown in Table 2 as capacity retention. Furthermore, the charge and discharge efficiency, which is the ratio of the first discharge capacity to the first charge capacity, was measured. The results are shown in Table 2.

[0161] Table 2

[0162]

[0163] As shown in Table 2, the half-cells using the negative active materials according to Examples 4 to 6 exhibited good charge and discharge efficiency compared to Comparative Examples 5 to 8, and in particular, exhibited unexpectedly excellent capacity retention compared to Comparative Examples 5 to 8.

[0164] (Example 7)

[0165] 98 wt% of a mixture of the negative active material and artificial graphite according to Example 1 (mixing ratio: 9:91 by weight) was mixed in an aqueous solvent with 1 wt% of styrene-butadiene as a binder and 1 wt% of carboxymethyl cellulose as a viscosity-enhancing agent to prepare a negative active material slurry. The negative active material slurry was coated on a Cu current collector, dried, and pressed to prepare a negative electrode.

[0166] A positive electrode slurry was prepared by mixing 96 wt% of LiCoO2 positive active material, 2 wt% of polyvinylidene fluoride binder, and 2 wt% of Ketjen Black conductive material in N-methylpyrrolidone solvent. The positive electrode slurry was coated on an Al current collector, dried, and pressed to prepare a positive electrode.

[0167] A rechargeable lithium battery was fabricated using the negative electrode, the positive electrode, and the electrolyte. As the electrolyte, 1.5 M LiPF 6 dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate (20:40:40 by volume) was used.

[0168] (Example 8)

[0169] 97 wt% of a mixture of the negative active material according to Example 3 and artificial graphite (mixing ratio: 15:85 weight ratio) was mixed in an aqueous solvent with 1.5 wt% of styrene-butadiene as a binder and 1.5 wt% of carboxymethyl cellulose as a viscosity-enhancing agent to prepare a negative active material slurry. The negative active material slurry was coated on a Cu current collector, dried, and pressed to prepare a negative electrode.

[0170] A rechargeable lithium battery was manufactured through the same steps as in Example 7 except that a negative electrode was used.

[0171] (Comparative Example 9)

[0172] 97 wt% of a mixture of the negative active material and artificial graphite according to Comparative Example 1 (mixing ratio: 13:87 by weight) was mixed in an aqueous solvent with 1.5 wt% of styrene-butadiene as a binder and 1.5 wt% of carboxymethyl cellulose as a viscosity-enhancing agent to prepare a negative active material slurry. The negative active material slurry was coated on a Cu current collector, dried, and pressed to prepare a negative electrode.

[0173] A rechargeable lithium battery was manufactured through the same steps as in Example 7 except that a negative electrode was used.

[0174] 4) Evaluation of cycle life characteristics of rechargeable lithium batteries

[0175] The rechargeable lithium batteries according to Examples 7 and 8 and Comparative Example 9 were charged and discharged 100 times at 0.5C, and the ratio of the 100th discharge capacity to the 1st discharge capacity was measured. The results are shown in Table 3 as the capacity retention rate. In addition, the charge and discharge efficiency, which is the ratio of the first discharge capacity to the first charge capacity, was measured. The results are shown in Table 3.

[0176] Table 3

[0177] Initial efficiency (%) Capacity retention rate (%) Example 7 88 60 Example 8 88 56 Comparative Example 9 85 48

[0178] As can be seen from Table 3, the initial efficiencies of the batteries according to Examples 7 and 8 are slightly higher than that of the battery of Comparative Example 9, and the capacity retention rates according to Examples 7 and 8 are unexpectedly higher than that of Comparative Example 9.

[0179] While the invention has been described in connection with what are presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A negative electrode active material for a rechargeable lithium battery, the negative electrode active material comprising: a composite comprising silicon particles, metal particles, and first amorphous carbon; as well as The second amorphous carbon surrounds the composite. Among them, the first amorphous carbon surrounds the silicon particles and the metal particles. wherein the metal particles are positioned on the surface of the silicon particles and are included in the first amorphous carbon surrounding the surface of the silicon particles, The composite has a core-shell structure, in which the silicon particles constitute the core of the core-shell structure, and the metal particles and the first amorphous carbon constitute the shell of the core-shell structure. The composite is prepared by a method comprising the following steps: mixing silicon particles, a first amorphous carbon precursor, and a compound of the metal in the metal particles to prepare a mixture; subjecting the mixture to a hydrothermal reaction to produce a reaction product; spray-drying the reaction product to produce a spray-dried product; and The spray-dried product is subjected to a first heat treatment to prepare a composite, and The hydrothermal reaction is carried out by inserting a microwave reactor of the autoclave type and injecting microwave electromagnetic waves.

2. The negative electrode active material for a rechargeable lithium battery according to claim 1, wherein The metal particles are Ni, Ti, Sn or a combination thereof.

3. The negative electrode active material for a rechargeable lithium battery according to claim 1, wherein The silicon particles have a rod-like shape, a plate-like shape, or a spherical shape.

4. The negative electrode active material for a rechargeable lithium battery according to claim 1, wherein The silicon particles have a rod-like shape or a plate-like shape, and The silicon particles have an aspect ratio of 5 to 20.

5. The negative electrode active material for a rechargeable lithium battery according to claim 1, wherein The silicon particles have a spherical shape, and The silicon particles have a particle diameter of 5 nm to 300 nm.

6. The negative electrode active material for a rechargeable lithium battery according to claim 1, wherein The metal particles have a spherical shape.

7. The negative electrode active material for a rechargeable lithium battery according to claim 1, wherein The metal particles have a particle diameter of 1 nm to 20 nm.

8. The negative electrode active material for a rechargeable lithium battery according to claim 1, wherein The second amorphous carbon is continuously located as a layer type on the surface of the composite.

9. A rechargeable lithium battery, comprising: A negative electrode comprising a negative electrode active material according to any one of claims 1 to 8; positive electrode; as well as electrolytes.

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