Negative active material for rechargeable lithium battery and rechargeable lithium battery including the same

Abstract

Disclosed are a negative electrode active material for a rechargeable lithium battery and a rechargeable lithium battery including the same, and the negative electrode active material includes: a silicon primary particle core having a particle size of micrometers; a particle layer formed by aggregating silicon oxide primary particles having a particle size of 10 nm or less on the surface of the core, the particle layer including pores; and a carbon material filled in the pores of the particle layer.

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. Rechargeable lithium batteries use an organic electrolyte solution and thus have a discharge voltage that is two or more times that of a conventional battery using an alkaline aqueous solution, and therefore have a high energy density.

[0003] As the positive electrode active material for a rechargeable lithium battery, a lithium-transition metal oxide having a structure capable of intercalating lithium ions, such as LiCoO 2 , LiMn 2 O 4 , and LiNi 1-x Co x O 2 (0 < x < 1), etc., has 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, etc., have been mainly used.

[0005] The above information disclosed in this background art section is only for enhancing the understanding of the background art of the present invention, and thus it may contain information that does not constitute 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 that exhibits excellent capacity and 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, which includes: a silicon primary particle core having a particle size in microns; a particle layer formed by aggregating silica primary particles having a particle size of about 10 nm or less on the surface of the silicon primary particle core and including pores; and a carbon-based material filled in the pores.

[0009] The silicon primary particle core may have a particle size of about 1 μm to about 20 μm.

[0010] The silica primary particles may have a particle size of about 1 nm to about 10 nm.

[0011] The particle layer may have a thickness of about 60 nm to about 500 nm.

[0012] The particle layer may be continuously located in the form of a layer on the surface of the silicon primary particle core.

[0013] The amount of the carbon-based material may be about 1 wt % to about 5 wt % based on 100 wt % in total of the negative active material.

[0014] The carbon-based material may be amorphous carbon.

[0015] Another embodiment provides a rechargeable lithium battery including: a negative electrode including a negative active material; a positive electrode; and an electrolyte.

[0016] Other implementations are included in the detailed description below.

[0017] A negative active material for a rechargeable lithium battery according to one embodiment may provide a rechargeable lithium battery exhibiting excellent capacity and good cycle-life characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a schematic diagram showing the structure of a negative electrode active material according to one embodiment.

[0019] Figure 2 To show more clearly Figure 1 The diagram shows the structure of the particle layer in the negative electrode active material.

[0020] Figure 3 is a schematic diagram showing the structure of a rechargeable lithium battery according to one embodiment.

[0021] Figure 4 This is a 150,000-fold TEM photograph of the negative electrode active material according to Example 1.

[0022] Figure 5 This is a 50,000-fold TEM photograph of the negative electrode active material according to Example 1. DETAILED DESCRIPTION

[0023] Hereinafter, embodiments are described in detail. However, these embodiments are exemplary and do not limit the present invention, and the present invention is defined by the scope of the claims described above.

[0024] One embodiment provides a negative active material for a rechargeable lithium battery, which includes a silicon primary particle core and a particle layer of silicon oxide primary particles having a particle size of about 10 nm or less. The silicon particle core may have a particle size of microns, and the particle layer may include pores and amorphous carbon may be filled in the pores. Figure 1 The structure of the negative electrode active material is schematically shown. Figure 1, a negative active material 1 according to one embodiment includes silicon primary particle cores 3 and a particle layer 9 formed on the surface of the silicon primary particle core 3. The particle layer 9 may be formed by aggregating silicon oxide primary particles 5, and may include pores in which a carbon-based material 7 is filled. Figure 1 It is shown that the silicon oxide primary particles 5 are aggregated so as to exist in the form of a layer. Figure 2 It can be seen that the particle layer 9 is formed by aggregating the silicon oxide primary particles 5 and the carbon-based material 7 is filled in the spaces (pores) existing between the silicon oxide primary particles 5 resulting from the aggregation of the silicon oxide primary particles 5 .

[0025] In one embodiment, the core indicates an area located inside the active substance, and when it is described in more detail, the core is an area surrounded by a granular layer, so that it indicates an area that is not substantially exposed to the outside. Therefore, the area located on the surface portion (outside) of the active substance is considered to be a granular layer, and the area located inside the granular layer is considered to be a core.

[0026] The silicon primary particle core may have a particle size of micrometers and may have a particle size of about 1 μm to about 20 μm. The silicon particles constituting the core may be macroscopic particles having a size of micrometers and may be single particles, that is, primary particles, not aggregated particles.

[0027] The size of the silicon primary particle core may be an average particle size, and in this case, the size indicates "D50", which is a particle diameter corresponding to 50% of the minimum particle size when the total number of particles is 100% in a distribution curve accumulated from the minimum particle size to the maximum particle size.

[0028] When no definition is otherwise provided, such a particle diameter D50 indicates an average particle diameter D50 of about 50% by volume of the cumulative volume in a particle distribution.

[0029] The average particle diameter D50 can be measured by a general technique well known to those skilled in the relevant art (e.g., using a particle size analyzer, transmission electron microscopy (TEM) photography, or scanning electron microscopy photography). Another method can be performed by measuring the particle size using a measuring device with dynamic light scattering, analyzing the data to count the number of particles relative to each particle size, and then calculating to obtain the average particle diameter D50.

[0030] When the particle size of the silicon primary particle core is in the micrometer range, and more specifically, in the above range, the high capacity of silicon can be utilized, and the cycle life improvement effect can be appropriately obtained.

[0031] If the silicon primary particle core is very small and has a nanometer size, and more specifically, less than 1 μm, the irreversible capacity increases so that the effect of high capacity cannot be obtained. Alternatively, if the silicon primary particle core is larger than a micrometer size, and more specifically, larger than 20 μm, the effect of improving the cycle life is not exhibited.

[0032] A granular layer may form on the surface of the core.

[0033] The particle layer may be continuously located on the surface of the core in the form of a layer, and according to one embodiment, the particle layer may be formed by substantially completely covering the surface of the core. When the particle layer is continuously located on the surface of the core in the form of a layer to substantially completely cover the surface of the core, side reactions with the electrolyte may be prevented to improve the cycle life characteristics. If the particle layer is not formed to completely cover the surface of the core and is not continuously located on the surface of the core to partially expose the surface of the core, side reactions with the electrolyte may occur to deteriorate the cycle life characteristics.

[0034] The particle layer can be formed by aggregating small-sized silicon oxide primary particles having a particle size of about 10 nm or less, and can include pores. The size of the silicon oxide primary particles can be about 10 nm or less, or about 1 nm to about 10 nm. When the size of the silicon oxide primary particles is about 10 nm or less, and in particular, about 1 nm to about 10 nm, a thick oxide layer can be formed to improve cycle life and provide a path through lithium ions, thereby having a high capacity. If the size of the silicon oxide primary particles is greater than 10 nm, the path through lithium ions will be blocked, and thus high capacity will not occur.

[0035] The silicon oxide primary particle refers to a single particle having a small-sized particle size of about 10 nm or less.

[0036] The silicon oxide primary particles may aggregate to form a particle layer. When explained in more detail, a plurality of silicon oxide primary particles may aggregate to form a particle layer, and herein, the silicon oxide primary particles may aggregate to form a slightly loose particle layer so as to form spaces (pores) between the silicon oxide primary particles, rather than a substantially dense particle layer.

[0037] Thus, since the particle layer includes pores, the penetration of lithium ions can occur appropriately. If the particle layer does not include pores, that is, is a dense layer without pores, the penetration of lithium ions will rarely occur, so that the silicon primary particle core will not participate in the charge and discharge reaction.

[0038] In addition, the hole formed in the particle layer may have a diameter smaller than the thickness of the particle layer so as not to penetrate the particle layer. If the hole is formed in the form of a permeable hole sufficient to penetrate the particle layer, the path of electrons and ions in the permeable particle layer is insufficient to increase resistance.

[0039] The carbon material may be filled in the pores of the particle layer. When the carbon material is filled in the pores of the particle layer, the carbon material may prevent the electrolyte from penetrating through the pores, so that the degradation of the cycle life characteristics due to the penetration of the electrolyte may be suppressed. Since the carbon material does not suppress the penetration of lithium ions, the penetration effect of lithium ions due to the pores may be maintained and only the impregnation of the electrolyte may be suppressed. The carbon material may be amorphous carbon or crystalline carbon, but may be appropriately amorphous because the desired structure of the active material may be more easily maintained and the effect of filling the carbon material may be further increased.

[0040] In one embodiment, the carbon-based material may be positioned by filling pores present in the particle layer. If the carbon-based material is present in a layer separate from the particle layer, electrons and ions may not penetrate the pores in the particle layer.

[0041] The particle layer may have a thickness of about 60 nm to about 500 nm, or about 61 nm to about 460 nm. Since the particle layer includes pores, as described above, even if the particle layer is about 60 nm to about 500 nm thick, lithium ions can be effectively infiltrated so that the cycle life characteristics can be effectively improved. In addition, the carbon-based material filled in the pores can inhibit the penetration of the electrolyte, so that the deterioration of the cycle life characteristics due to the penetration of the electrolyte can be suppressed, and the effect of improving the cycle life characteristics due to the penetration of lithium ions can be well maintained.

[0042] If the particle layer is thinner than the above range, it is difficult to suppress the volume change of the silicon primary particle core during charge and discharge. If the particle layer is thicker than the above range, it is difficult to penetrate lithium ions during charge and discharge to reduce initial efficiency and increase irreversible capacity.

[0043] The thickness of the particle layer can be confirmed by measurement by TEM. For example, when the negative electrode active material is measured by TEM, the area where the shadow changes is used as a reference, the inside is considered to be the silicon primary particle core and the outside is considered to be the particle layer, wherein the thickness from the area where the shadow changes to the outermost part of the particle can be determined as the thickness of the particle layer. Alternatively, by performing TEM-EDS (Energy Dispersive Spectrometer) analysis, the thickness from the inflection point where the amount of oxygen changes to the outermost part can be considered to be the thickness of the particle layer. For example, by performing TEM-EDS analysis, the distance from the outermost part to the inflection point where the amount of oxygen surprisingly changes from about 53wt% to 0wt% (based on the total weight of the active material) can be considered to be the thickness of the particle layer. In addition, when measured by TEM, in the area where the shadow changes, and particularly in the area where the particle layer is found to be brighter, the size of the slightly dark area in the form of particles can be considered to be the size of silicon oxide.

[0044] As described above, a negative electrode active material including a silicon primary particle core having a particle size in microns, and a particle layer formed by aggregating silica primary particles having a particle size of about 10 nm or less on the surface of the core and including pores filled with a carbonaceous material therein, can exhibit a high capacity due to the silicon primary particle core, and can provide easy penetration of lithium ions through the pores of the particle layer, and the carbonaceous material filled in the pores can suppress the penetration of the electrolyte, so that the effect of improving the cycle life characteristics can be obtained. If the size of the core exceeds the micron range, and specifically exceeds about 1 μm to about 20 μm, the particle layer does not include pores; the particle layer includes pores but is not filled with a carbonaceous material, or the size of the silica primary particles is greater than 10 nm, and the desired excellent capacity and cycle life characteristics cannot be obtained.

[0045] The silica can be, for example, SiO x (0 < x ≤ 2 or 0 < x < 2).

[0046] Based on the total 100 wt% of the negative electrode active material, the amount of the carbonaceous material can be about 1 wt% to about 5 wt%. When the amount of the carbonaceous material is within the above range, the penetration of the electrolyte through the pores of the particle layer can be prevented and the capacity of the active material can be highly maintained.

[0047] Based on the total 100 wt% of the negative electrode active material, the amount of oxygen in the negative electrode active material can be about 5 wt% to about 20 wt%. When the amount of oxygen is within this range, the irreversible capacity can be low and excellent cycle life characteristics can be obtained. In one embodiment, the amount of oxygen can be confirmed by thermogravimetric analysis (TGA). Measuring the amount of oxygen by thermogravimetric analysis can be determined by the reduced amount of the negative electrode active material while increasing the temperature to about 1000 °C in an oxygen atmosphere.

[0048] The negative electrode active material according to one embodiment can be prepared by the following two methods.

[0049] The first method includes adding silicon primary particles to a solvent to prepare a liquid of the silicon primary particles and mixing beads with the liquid of the silicon primary particles. The silicon primary particles can be used in a micron size (for example, a particle size of about 1 μm to about 20 μm). The beads are used for easy distribution and can be zirconia beads. The solvent can be water.

[0050] While mixing the beads, silicon reacts with the solvent (especially water) to oxidize the silicon and dissolve it partially, thereby forming silica having a particle size of about 10 nm or less, and at least one silica particle aggregates on the surface of the silicon, so that the silica particles adhere to the silicon surface. The silica primary particles are loosely aggregated to adhere to the surface of the silicon primary particles, and thus, there can be spaces (pores) between the silica primary particles.

[0051] The mixing process may be performed for about 3 hours to about 8 hours. When the mixing process is performed within the above range, silicon oxide may be prepared in a desired amount. If the mixing process is performed for a time exceeding this range, oxidation of silicon may rarely occur.

[0052] Herein, the beads may be added in an amount of about 10 wt % to about 50 wt % based on 100 wt % of the silicon particles. When the beads are added in an amount within this range, they may be uniformly distributed in the solvent to uniformly prepare the oxide.

[0053] Thereafter, the mixed solution is spray-dried, and the dried product is mixed with a carbon precursor to coat the dried product with the carbon precursor, followed by heat treatment, thereby preparing a negative electrode active material.

[0054] Spray drying can be performed at about 150° C. to about 200° C. Drying can volatilize water and thus can prepare a product in which silicon oxide adheres to the surface of silicon. If spray drying is performed at a temperature lower than the above range, water will not volatilize and will remain. If spray drying is performed at a temperature higher than the above range, silicon reacts with oxygen in the air to increase the degree of oxidation. As a drying process, spray drying is desirable because it has the advantages of removing water and maintaining oxidation. If the drying process is performed by natural drying in which the mixed solution is dried as it is, or by thermal drying, it is undesirable that silicon particles will aggregate.

[0055] In addition, since the heat treatment is performed after the carbon precursor is applied, the carbon precursor can be converted into a carbon-based material. The carbon precursor can be an amorphous carbon precursor, and the amorphous carbon precursor can be petroleum coke, coal coke, petroleum pitch, coal pitch, green coke or a combination thereof. Amorphous carbon can be soft carbon or hard carbon.

[0056] The heat treatment may be performed at about 900° C. to about 950° C. In particular, when the heat treatment is performed at the above temperature, the carbon precursor may be converted into amorphous carbon in the carbon-based material. If the heat treatment is performed at a temperature higher than 950° C., silicon may react with carbon to prepare undesirable silicon carbide. If the heat treatment is performed at a temperature lower than the above range, the irreversible capacity of the carbon-based material may increase.

[0057] In coating the dried product with the amorphous carbon precursor, the amount of amorphous carbon may be appropriately controlled until the amount of amorphous carbon in the final product may be about 1 wt % to about 5 wt % (based on a total of 100 wt % of the negative electrode active material). For example, the dried product and the amorphous carbon precursor may be mixed at a weight ratio of about 99:1 to 95:5.

[0058] The second method for preparing the negative active material includes mixing large silicon particles having a micron particle size (e.g., about 10 μm to about 20 μm), small silicon oxide particles having a nanometer particle size (e.g., about 10 nm or less), and an amorphous carbon precursor, and sintering the resulting mixture. The sintering process may be performed at about 900° C. to about 950° C. The sintering process may be performed under a nitrogen atmosphere.

[0059] According to one embodiment, a rechargeable lithium battery including a negative electrode, a positive electrode, and an electrolyte is provided.

[0060] The negative electrode may include a current collector and a negative active material layer formed on the current collector, and the negative active material layer includes the negative active material according to one embodiment.

[0061] The negative electrode active material layer may further include a carbon-based negative electrode active material.

[0062] Examples of carbon-based negative electrode active materials may be crystalline carbon, amorphous carbon, or a combination thereof. Crystalline carbon may be natural graphite or artificial graphite, such as having no specific shape, a flake shape, a scale shape, a spherical shape, or a fiber shape, and amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbide, or sintered coke, etc.

[0063] In the negative electrode active material layer, the content of the negative electrode active material may be 95wt% to 99wt% based on the total weight of the negative electrode active material layer. If the negative electrode active material layer includes two negative electrode active materials according to one embodiment, that is, a silicon-based negative electrode active material (i.e., a negative electrode active material for a rechargeable lithium battery according to an embodiment of the present invention) and a carbon-based negative electrode active material, the mixing ratio of the silicon-based negative electrode active material to the carbon-based negative electrode active material may be about 5:95 to about 50:50 by weight ratio. When the mixing ratio of the silicon-based negative electrode active material and the carbon-based negative electrode active material is within this range, the expansion of the negative electrode can be suppressed during charging and discharging and a higher capacity can be achieved.

[0064] The amount of oxygen in the negative active material layer may be about 0.5 wt % to about 10 wt % based on 100 wt % of the total negative active material layer. When the amount of oxygen in the negative active material is within the above range, irreversible capacity may be effectively suppressed and cycle life characteristics may be well maintained.

[0065] The negative electrode active material layer may include a binder and may further optionally include a conductive material. In the negative electrode active material layer, the amount of the binder may be about 1wt% to about 5wt% 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 about 90wt% to about 98wt% of the negative electrode active material, about 1wt% to about 5wt% of the binder, and about 1wt% to about 5wt% of the conductive material.

[0066] 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.

[0067] 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, or a combination thereof.

[0068] 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.

[0069] When a water-soluble binder is used as a negative electrode binder, a cellulose compound may be further used as a thickener to provide viscosity. The cellulose compound includes one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose and alkali metal salts thereof. The alkali metal may be Na, K or Li. Based on 100 parts by weight of the negative electrode active material, the content of the thickener may be 0.1 parts by weight to 3 parts by weight.

[0070] 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, and carbon fiber, etc.; metal-based materials including metal powders or metal fibers of copper, nickel, aluminum, and silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0071] 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.

[0072] The negative electrode may 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 may be water.

[0073] Such negative electrode preparation is well known in the relevant art, and thus a detailed description will not be explained in the specification.

[0074] The positive electrode may include a positive electrode collector and a positive electrode active material layer formed on the positive electrode collector.

[0075] The positive electrode active material may include a compound that reversibly intercalates and deintercalates lithium ions (lithiated intercalation compound). Specifically, it may include one or more composite oxides of a metal 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 D 2 (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 E 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 T 2 (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0≤α<2); Li a Ni 1-b-c Mn 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 Mnb 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 Nor 1-b-c Mn b X c O 2-α T 2 (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0≤α≤2);Li a Nor b E c G d O 2 (0.90≤a≤1.8,0≤b≤0.9,0≤c≤0.5,0.001≤d≤0.1);Li a Nor b Co c Mn d G e O 2 (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 O 2 (0.90≤a≤1.8,0.001≤b≤0.1);Li a CoG b O 2 (0.90≤a≤1.8,0.001≤b≤0.1);Li a Mn 1-b G b O 2 (0.90≤a≤1.8,0.001≤b≤0.1);Li a Mn 2 G b O 4 (0.90≤a≤1.8,0.001≤b≤0.1);Li a Mn 1-g G g MONTH 4 (0.90≤a≤1.8,0≤g≤0.5);QO 2 ;QS 2 ;LiQS 2 ;V 2 O 5 ;LiV 2 O 5 ;LiZO 2 ;LiLevel 4 ;The(3-f) J 2 (PO 4 ) 3 (0≤f≤2);Li (3-f) Fe 2 (PO 4 ) 3 (0≤f≤2); and Li a FePO 4 (0.90≤a≤1.8).

[0076] 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.

[0077] The compound may have a coating on the surface, or may be mixed with another compound having a coating. The coating may include at least one coating element compound selected from an oxide of the coating element, a hydroxide of the coating element, an oxyhydroxide of the coating element, an oxycarbonate of the coating element, and a hydroxycarbonate of the coating element. The compound for the coating may be amorphous or crystalline. The coating element included in the coating may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. The coating may be provided by using these elements in the compound in a method that has no adverse effect on the properties of the positive active material. For example, the method may include any coating method, such as spraying and dipping, etc., but because it is well known in the relevant art, it is not explained in more detail.

[0078] 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.

[0079] In one embodiment, the positive active material layer may further include a binder and a conductive material. Herein, the binder and the conductive material may each be present in an amount of about 1 wt % to about 5 wt % based on the total amount of the positive active material layer.

[0080] The binder improves the bonding properties of the positive electrode active material particles to each other and to the current collector. Examples of the binder may include 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, but are not limited thereto.

[0081] A conductive material is included to provide electrode conductivity. Any conductive material can be used as the conductive material unless it causes a chemical change in the battery. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fiber, etc.; metal-based materials including metal powders or metal fibers of copper, nickel, aluminum, and silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0082] The current collector may be aluminum foil, nickel foil, or a combination thereof, but is not limited thereto.

[0083] The positive electrode can be prepared by mixing a positive active material, a binder and an optional conductive material in a solvent to prepare an active material composition, and coating the active material composition on a current collector. Such positive electrode preparation is well known in the relevant art, and a detailed description is not explained in the specification. The solvent may be N-methylpyrrolidone, but is not limited thereto.

[0084] The electrolyte may include a non-aqueous organic solvent and a lithium salt.

[0085] The nonaqueous organic solvent serves as a medium for transporting ions participating in the electrochemical reaction of the battery.

[0086] 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.

[0087] Carbonate solvents may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC) and 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, decalactone, valerolactone, mevalonolactone and caprolactone, etc. Ether solvents may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran and tetrahydrofuran, etc. Ketone solvents may include cyclohexanone, etc. Alcohol solvents may include ethanol and 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), etc., dioxolanes such as 1,3-dioxolane, etc., and cyclopentane, etc.

[0088] 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.

[0089] The carbonate-based solvent may desirably be 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 at a volume ratio of 1:1 to 1:9, so that the performance of the electrolyte may be improved.

[0090] 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.

[0091] Herein, when cyclic carbonate and linear carbonate or cyclic carbonate and propionate solvent are mixed, they can be mixed in a volume ratio of about 1:1 to about 1:9, so that the performance of the electrolyte solution can be improved. In addition, when cyclic carbonate, linear carbonate and propionate solvent are mixed, 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 property.

[0092] The non-aqueous organic solvent may further include an aromatic hydrocarbon organic solvent in addition to the carbonate-based solvent. Herein, the carbonate-based solvent and the aromatic hydrocarbon organic solvent may be mixed in a volume ratio of about 1:1 to about 30:1.

[0093] The aromatic hydrocarbon organic solvent may be an aromatic hydrocarbon compound of Chemical Formula 1.

[0094] [Chemical formula 1]

[0095]

[0096] In Chemical Formula 1, R 1 To R 6 are the same or different and are selected from hydrogen, halogen, C1 to C10 alkyl, haloalkyl, and combinations thereof.

[0097] 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, 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.

[0098] The electrolyte may further include vinylene carbonate or an ethylene carbonate-based compound represented by Chemical Formula 2 as an additive for improving a cycle life of the battery.

[0099] [Chemical formula 2]

[0100]

[0101] In chemical formula 2, R 7 and R 8 are the same or different and are selected from hydrogen, halogen, cyano (CN), nitro (NO 2 ) and a fluorinated C1 to C5 alkyl group, provided that R 7 and R 8 At least one of them is halogen, cyano (CN), nitro (NO 2 ) or a fluorinated C1 to C5 alkyl group, and R 7 and R 8 Not all are hydrogen.

[0102] 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 the additive for improving the cycle life may be used within an appropriate range.

[0103] The electrolyte may further include vinyl ethylene carbonate, propane sultone, succinonitrile, or a combination thereof, and the amount thereof may be appropriately controlled.

[0104] 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 the lithium salt include those selected from LiPF 6 , LiBF 4 、LiSbF 6 、LiAsF 6 、LiN(SO 2 C 2 F 5 ) 2 、Li(CF 3 SO 2 ) 2 N、LiN(SO 3 C 2 F 5 ) 2 、Li(FSO 2 ) 2 N (Lithium bis(fluorosulfonyl)imide: LiFSI), LiC 4 F 9 SO 3 、LiClO 4 、LiAlO 2 、LiAlCl 4 、LiPO 2 F 2 、LiN(C x F 2x+1 SO 2 )(C y F 2y+1 SO 2 (wherein x and y are natural numbers, for example, integers from 0 to 20), lithium difluoro(bisoxalato)phosphate, LiCl, LiI, LiB(C 2 O 4 ) 2 At least one supporting salt of lithium bis(oxalate)borate: LiBOB) and lithium difluoro(oxalate)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.

[0105] Depending on the type of lithium secondary battery, a separator may be disposed between the positive electrode and the negative electrode. Such separators may include polyethylene, polypropylene, polyvinylidene fluoride, and multilayers thereof, such as polyethylene / polypropylene double-layer separators, polyethylene / polypropylene / polyethylene three-layer separators, and polypropylene / polyethylene / polypropylene three-layer separators.

[0106] Figure 3 2 is an exploded perspective view of a lithium secondary battery according to an embodiment. The lithium secondary battery according to an embodiment is illustrated as a prismatic battery, but is not limited thereto and may include batteries of various shapes such as a cylindrical or pouch type battery.

[0107] See also Figure 3 , the lithium secondary battery 100 according to the embodiment includes: an electrode assembly 40 manufactured by winding a separator 30 interposed between a positive electrode 10 and a negative electrode 20; and a case 50 accommodating the electrode assembly 40. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte solution (not shown).

[0108] Hereinafter, examples of the present invention and comparative examples are described. However, these examples are not to be construed in any sense as limiting the scope of the present invention.

[0109] (Example 1)

[0110] 50wt% of silicon primary particles are added to water to prepare a liquid of silicon primary particles, and zirconium oxide beads are added to the liquid of silicon primary particles and mixed for 3 hours. During mixing, silicon oxide primary particles are prepared and a plurality of silicon oxide primary particles are aggregated and adhered to the surface of the silicon primary particles, thereby obtaining a product. Herein, based on 100wt% of silicon particles, the addition amount of zirconium oxide beads is 30wt%, and in the product, the size of the silicon oxide primary particles is 10nm.

[0111] Thereafter, the mixed solution including the product was spray dried at 200°C. The dried product was mixed with petroleum asphalt in a weight ratio of 97:3 to coat the dried product with petroleum asphalt, and heat treated at 950°C to prepare a negative electrode active material. The resulting negative electrode active material includes a particle layer formed by aggregating silicon oxide primary particles having a size of 10nm on the surface of silicon primary particles having a particle size of 5μm, and includes pores filled with amorphous carbon. Herein, the thickness of the particle layer is 61nm, and the amount of amorphous carbon is 3wt% of the total 100wt% of the negative electrode active material. In the resulting negative electrode active material, the amount of oxygen is 5wt% based on a total of 100wt% of the negative electrode active material.

[0112] 97.5 wt % of the negative electrode active material, 1.5 wt % of a styrene-butadiene rubber binder, and 1 wt % of carboxymethyl cellulose as an agent for increasing viscosity were mixed in a water solvent to prepare a negative electrode active material slurry.

[0113] The produced negative electrode active material slurry was coated on a Cu current collector, dried, and pressed to produce a negative electrode including a negative electrode active material layer formed on the current collector. In the negative electrode, the amount of oxygen included in the negative electrode active material layer was 1 wt % based on 100 wt % of the total negative electrode active material layer.

[0114] (Example 2)

[0115] 50wt% of silicon primary particles are added to water to prepare a liquid of silicon primary particles, and zirconium oxide beads are added to the liquid of silicon primary particles and mixed for 8 hours. During mixing, silicon oxide primary particles are prepared and a plurality of silicon oxide primary particles are aggregated and adhered to the surface of the silicon primary particles, thereby obtaining a product. Herein, based on 100wt% of silicon particles, the addition amount of zirconium oxide beads is 30wt%, and in the product, the size of the silicon oxide primary particles is 10nm.

[0116] Thereafter, the mixed solution including the product is spray dried at 200°C. The dried product is mixed with petroleum asphalt in a weight ratio of 97:3 to coat the dried product with petroleum asphalt and heat treated at 950°C to prepare a negative electrode active material. The resulting negative electrode active material includes a particle layer formed by aggregating silicon oxide primary particles having a particle size of 10nm on the surface of silicon primary particles having a particle size of 5μm, and includes pores filled with amorphous carbon. Herein, the thickness of the particle layer is 463nm, and the amount of amorphous carbon is 3wt% of the total 100wt% of the negative electrode active material. In the resulting negative electrode active material, the amount of oxygen is 20wt% based on the total 100wt% of the negative electrode active material.

[0117] A negative electrode was prepared by the same process as in Example 1 using the negative active material.

[0118] (Reference Example 1)

[0119] 50wt% of silicon primary particles are added to water to prepare a liquid of silicon primary particles, and zirconium oxide beads are added to the liquid of silicon primary particles and mixed for 1 hour. During mixing, silicon oxide primary particles are prepared and a plurality of silicon oxide primary particles are aggregated and adhered to the surface of the silicon primary particles, thereby obtaining a product. Herein, based on 100wt% of silicon particles, the addition amount of zirconium oxide beads is 30wt%, and in the product, the size of the silicon oxide primary particles is 10nm.

[0120] Thereafter, the mixed solution including the product is spray dried at 200°C. The dried product is mixed with petroleum asphalt in a weight ratio of 97:3 to coat the dried product with petroleum asphalt and heat treated at 950°C to prepare a negative electrode active material. The resulting negative electrode active material includes a particle layer formed by aggregating silicon oxide primary particles having a particle size of 10nm on the surface of silicon primary particles having a particle size of 5μm, and includes pores filled with amorphous carbon. Herein, the thickness of the particle layer is 39nm, and the amount of amorphous carbon is 3wt% of the total 100wt% of the negative electrode active material. In the resulting negative electrode active material, the amount of oxygen is 2wt% based on the total 100wt% of the negative electrode active material.

[0121] Using the negative electrode active material, a negative electrode was prepared by the same process as in Example 1. In the obtained negative electrode active material layer, the amount of oxygen was 0.2 wt % based on 100 wt % in total of the negative electrode active material layer.

[0122] (Comparative Example 1)

[0123] 50wt% of silicon primary particles are added to water to prepare a liquid of silicon primary particles, and zirconium oxide beads are added to the liquid of silicon primary particles and mixed for 8 hours. During mixing, silicon oxide primary particles are prepared and a plurality of silicon oxide primary particles are aggregated and adhered to the surface of the silicon primary particles, thereby obtaining a product. Herein, based on 100wt% of silicon particles, the addition amount of zirconium oxide beads is 30wt%, and in the product, the size of the silicon oxide primary particles is 10nm.

[0124] Thereafter, the mixed solution including the product was spray dried at 200°C, and the dried product was heat treated at 950°C to prepare a negative electrode active material. The resulting negative electrode active material includes a particle layer formed by aggregating silicon oxide primary particles having a particle size of 10nm on the surface of silicon primary particles having a particle size of 5μm, and includes pores filled with amorphous carbon. Herein, the thickness of the particle layer is 463nm. In the resulting negative electrode active material, the amount of oxygen is 20wt% based on a total of 100wt% of the negative electrode active material.

[0125] Using the negative electrode active material, a negative electrode was prepared by the same process as in Example 1. In the obtained negative electrode active material layer, the amount of oxygen was 4 wt % based on 100 wt % in total of the negative electrode active material layer.

[0126] (Comparative Example 2)

[0127] A negative active material was prepared by the same procedure as in Example 1, except that silicon primary particles having a particle size of 100 nm were used.

[0128] 97.5 wt % of the negative electrode active material, 1.5 wt % of a styrene-butadiene rubber binder, and 1 wt % of carboxymethyl cellulose as an agent for increasing viscosity were mixed in a water solvent to prepare a negative electrode active material slurry.

[0129] The produced negative electrode active material slurry was coated on a Cu current collector, dried, and pressed to produce a negative electrode including a negative electrode active material layer formed on the current collector. In the negative electrode, the amount of oxygen included in the negative electrode active material layer was 1 wt % based on 100 wt % of the total negative electrode active material layer.

[0130] *TEM Photo

[0131] The surface of the negative electrode active material of Example 1 was photographed at 150,000 times TEM and 50,000 times TEM. The results are shown in Figure 4 (Magnification: 150,000x) and Figure 5 (Magnification: 50,000 times).

[0132] like Figure 4 , there are regions where the shading of the particles changes, and in these regions, the darker black indicates the silicon primary particle core portion and the lighter region indicates the particle layer portion having a thickness of 61 nm. It can be seen that the size of the silicon oxide primary particle is 10 nm.

[0133] In addition, if Figure 5 It is shown in Figure 2 that all surfaces of the silicon primary particles are covered with a layer of silicon oxide particles.

[0134] * Manufacturing of single battery

[0135] Each of the negative electrodes according to Examples 1 and 2, Comparative Examples 1 and 2, and Reference Example 1 was used according to a general method, having LiNi 0.88 Co 0.06 Al 0.06 O 2 A positive electrode of a positive active material and an electrolyte are used to manufacture a rechargeable lithium battery. As the electrolyte, 1.0 M LiPF added to 100% by volume is used. 6 10% by volume of fluoroethylene carbonate (dissolved in a mixed solvent of ethylene carbonate, diethyl carbonate and dimethyl carbonate (3 / 5 / 2 by volume)).

[0136] *Capacity measurement

[0137] The single cell was charged and discharged once at 0.2C formation to measure the formation charge and discharge capacity. From these results, the capacity per weight was obtained. The results of Examples 1 and 2, Comparative Example 1, and Reference Example 1 are shown in Table 1.

[0138] *Measurement of capacity retention

[0139] The single cell was charged and discharged 500 times at 1 C and the 1st discharge capacity and the 500th discharge capacity were measured. From these results, the ratio of the 500th discharge capacity to the 1st discharge capacity was calculated. The results are shown in Table 1.

[0140] Table 1

[0141]

[0142] As shown in Table 1, the single cells of Examples 1 and 2 using negative electrode active materials in which the size of the silicon primary particle core is micrometers (5 μm), the size of the silicon oxide primary particles is 10 nm, and the thickness of the particle layer is 61 nm and 463 nm, respectively, exhibit excellent capacity and capacity retention. While the single cell of Reference Example 1 using a very thin negative electrode active material in which the thickness of the particle layer is 39 nm exhibits good capacity, the capacity retention is very low at 16%, which makes it impossible to use in practice. The single cell of Comparative Example 1, which does not use amorphous carbon, exhibits a slightly lower capacity and an equally low capacity retention of 23%.

[0143] *Measurement of initial efficiency

[0144] The cells according to Example 1 and Comparative Example 2 were charged and discharged once at 0.2C formation to measure the formation charge and discharge capacity. From these results, the initial efficiency was obtained. The result of Example 1 was 85%, while the result of Comparative Example 2 suddenly decreased, that is, 70%.

[0145] While the present invention has been described in conjunction with what are presently considered to be practicable exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but 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, include: Silicon primary particle cores consisting of silicon and having a particle size in the micrometer range, wherein the silicon primary particle cores have a particle size of 1 μm to 20 μm; an outermost particle layer formed by aggregating silicon oxide primary particles having a particle size of 10 nm or less on the surface of the silicon primary particle core, the particle layer including pores; and The carbon material filled in the pores of the particle layer, Wherein, based on 100 wt % of the total negative electrode active material, the amount of the carbon-based material is 1 wt % to 5 wt %. 2 . The negative active material for a rechargeable lithium battery as claimed in claim 1 , wherein the silicon oxide primary particles have a particle size of 1 nm to 10 nm. 3 . The negative active material for a rechargeable lithium battery as claimed in claim 1 , wherein the particle layer has a thickness of 60 nm to 500 nm. 4 . The negative active material for a rechargeable lithium battery as claimed in claim 1 , wherein the particle layer is continuously located on the surface of the silicon primary particle core in the form of a layer. 5 . The negative active material for a rechargeable lithium battery as claimed in claim 1 , wherein the carbon-based material is amorphous carbon.

6. A rechargeable lithium battery, include: A negative electrode, the negative electrode comprising a negative electrode active material as claimed in any one of claims 1 to 5; Positive electrode; and Electrolytes. 7 . The rechargeable lithium battery of claim 6 , wherein the negative electrode further comprises a carbon-based negative active material.

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