Secondary batteries

Abstract

The present invention relates to a secondary battery including a positive electrode, a negative electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte, wherein the positive electrode includes a positive electrode active material including lithium cobalt-based oxide particles and a metal doped or coated on the lithium cobalt-based oxide particles, the metal including aluminum (Al), magnesium (Mg), titanium (Ti), and zirconium (Zr), the metal including titanium (Ti) and zirconium (Zr) at 300 ppm to 1,500 ppm based on the weight of the positive electrode active material, and the metal including aluminum (Al) at 3,000 ppm to 7,000 ppm based on the weight of the positive electrode active material, and the negative electrode includes a carbon-based active material and a silicon-based active material.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0184260, filed December 21, 2021, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference. The present invention relates to a secondary battery, and more particularly to a lithium secondary battery. [Background technology]

[0002] In recent years, with the rapid spread of battery-powered electronic devices such as mobile phones, laptop computers, and electric vehicles, the demand for lithium secondary batteries that are small, lightweight, and have relatively high capacity has been rapidly increasing. In particular, the rapid development of portable electronic devices has led to a demand for the development of lithium secondary batteries that can be used at high voltages and have high energy density.

[0003] Generally, a lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte, etc. The positive electrode and the negative electrode may each have an active material layer containing a positive electrode active material or a negative electrode active material formed on a current collector. The positive electrode typically uses a lithium-containing metal oxide such as lithium cobalt oxide (LiCoO2) or lithium manganese oxide (LiMn2O4) as the positive electrode active material. Accordingly, the negative electrode typically uses a lithium-free carbon-based active material or a silicon-based active material as the negative electrode active material.

[0004] Among the lithium-containing metal oxides used as positive electrode active materials, lithium cobalt oxides have been attracting attention due to their high operating voltage and excellent capacity characteristics. However, they have problems such as poor thermal properties due to the destabilization of the crystal structure caused by lithium elimination, and structural instability under high voltage. In addition, when charging lithium cobalt oxides, the oxidation number of Co becomes 4. +When the lithium cobalt oxide is oxidized, it causes problems of deterioration of surface stability and shortened lifespan due to side reactions with the electrolyte. In particular, the need to develop secondary batteries with high energy densities of 800 Wh / L or more requires the expansion of the operating voltage range of lithium cobalt oxides, the increase of charging voltage, and the increase of rolling density, so there is a need to solve the above problems. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Chinese Patent Application Publication No. 103500827 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a secondary battery that has excellent rapid charging performance and life performance even at a high energy density, specifically, a high energy density of 800 Wh / L or more. [Means for solving the problem]

[0007] The present invention provides a secondary battery including a positive electrode, a negative electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte, wherein the positive electrode includes a positive electrode active material including lithium-cobalt-based oxide particles and a metal doped or coated on the lithium-cobalt-based oxide particles, the metal including aluminum (Al), magnesium (Mg), titanium (Ti), and zirconium (Zr), the metal including titanium (Ti) and zirconium (Zr) being 300 ppm to 1,500 ppm based on the weight of the positive electrode active material, and the metal including aluminum (Al) being 3,000 ppm to 7,000 ppm based on the weight of the positive electrode active material, and the negative electrode includes a carbon-based active material and a silicon-based active material. [Effects of the Invention]

[0008] The secondary battery of the present invention includes a positive electrode including a positive electrode active material containing lithium-cobalt-based oxide particles and specific amounts of metals doped or coated thereon, and a negative electrode including a carbon-based active material and a silicon-based active material. The metals included in the positive electrode active material include aluminum (Al), magnesium (Mg), titanium (Ti), and zirconium (Zr), and the metals include specific amounts of titanium (Ti) and zirconium (Zr) and specific amounts of aluminum (Al). The positive electrode includes the above-described positive electrode active material, which can provide high structural stability and lifespan characteristics. In particular, when the positive electrode is used with a negative electrode containing the carbon-based active material and a silicon-based active material, a secondary battery with excellent fast charging performance and lifespan can be realized, even at high energy densities, specifically, at energy densities of 800 Wh / L or more. DETAILED DESCRIPTION OF THE INVENTION

[0009] The terms and words used in this specification and claims are not to be construed as being limited to their ordinary or dictionary meanings, but are to be construed as having meanings and concepts that are consistent with the technical idea of ​​the present invention, in accordance with the principle that the inventor can appropriately define the concepts of terms in order to best explain his or her invention.

[0010] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless otherwise clearly indicated in the context.

[0011] It is to be understood that in this specification, the terms "comprises," "comprises," or "having" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but do not preclude the presence or possible addition of one or more other features, numbers, steps, components, or combinations thereof.

[0012] In this specification, the average particle size (D 50 The average particle size (D) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. 50 ) can be measured, for example, by using a laser diffraction method. The laser diffraction method is generally capable of measuring particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution. The present invention will be specifically described below.

[0013] <Secondary battery> The present invention relates to a secondary battery, and more particularly to a lithium secondary battery. Specifically, the secondary battery according to the present invention includes a positive electrode, a negative electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte. The positive electrode includes a positive electrode active material including lithium-cobalt-based oxide particles and a metal doped or coated on the lithium-cobalt-based oxide particles, and the metal includes aluminum (Al), magnesium (Mg), titanium (Ti), and zirconium (Zr). The metal includes titanium (Ti) and zirconium (Zr) in an amount of 300 ppm to 1,500 ppm based on the weight of the positive electrode active material, and the metal includes aluminum (Al) in an amount of 3,000 ppm to 7,000 ppm based on the weight of the positive electrode active material. The negative electrode includes a carbon-based active material and a silicon-based active material.

[0014] Conventionally, when lithium cobalt oxide (LiCoO2) is used as a positive electrode active material at high voltage, a large amount of lithium ions are released from the lithium cobalt oxide, causing defects in the crystal structure, which then becomes unstable and collapses, resulting in a decrease in reversibility. In addition, when lithium ions are released, the Co present on the surface of the lithium cobalt oxide becomes unstable. 3+ or Co 4+When ions are reduced by the electrolyte, oxygen is released from the crystalline structure, which can further accelerate the collapse of the structure. In particular, the need for the development of secondary batteries with high energy densities of 800 Wh / L or more requires the expansion of the operating voltage range of lithium cobalt-based oxides, the increase in charging voltage, and the increase in rolling density, so there is a need to further solve the above-mentioned problems.

[0015] To address these issues, the present invention provides a cathode active material comprising lithium-cobalt-based oxide particles and a metal doped or coated on the lithium-cobalt-based oxide particles, the metals being aluminum (Al), magnesium (Mg), titanium (Ti), and zirconium (Zr). The metals include titanium (Ti) and zirconium (Zr) in an amount of 300 ppm to 1,500 ppm by weight of the cathode active material, and aluminum (Al) in an amount of 3,000 ppm to 7,000 ppm by weight of the cathode active material. This significantly improves the structural stability of the cathode active material during use at high voltages and high energy densities. In particular, the present invention provides a secondary battery having a high energy density, specifically, a high energy density of 800 Wh / L or more, by using a negative electrode comprising a carbon-based active material and a silicon-based active material in addition to the above-described cathode. This significantly improves the rapid charging performance and lifespan of the secondary battery.

[0016] positive electrode The positive electrode according to the present invention includes a positive electrode active material including lithium-cobalt-based oxide particles and a metal doped or coated on the lithium-cobalt-based oxide particles, and the metal includes aluminum (Al), magnesium (Mg), titanium (Ti), and zirconium (Zr), and the metal includes titanium (Ti) and zirconium (Zr) in an amount of 300 ppm to 1,500 ppm based on the weight of the positive electrode active material, and the metal includes aluminum (Al) in an amount of 3,000 ppm to 7,000 ppm based on the weight of the positive electrode active material.

[0017] The positive electrode active material includes lithium-cobalt-based oxide particles. Compared to other positive electrode active materials, such as lithium-nickel-cobalt-manganese-based oxides, the lithium-cobalt-based oxide particles exhibit stability in a higher voltage range, for example, at charging voltages of 4.4 V or higher. However, structural stability may still be reduced during use at high voltages. However, as described below, the positive electrode active material according to the present invention exhibits excellent stability during use at high voltages and high energy densities due to the metal doped or coated in a specific amount on the lithium-cobalt-based oxide particles.

[0018] The lithium cobalt-based oxide particles may include a compound represented by the following Chemical Formula 1:

[0019] [Chemical formula 1] Li 1+x Co 1-x O2 In the above Chemical Formula 1, 0≦x≦0.2.

[0020] The lithium cobalt-based oxide particles are doped or coated with the metal, which includes aluminum (Al), magnesium (Mg), titanium (Ti), and zirconium (Zr). The metals include titanium (Ti) and zirconium (Zr) in an amount of 300 ppm to 1,500 ppm based on the weight of the positive electrode active material.

[0021] The positive electrode active material includes titanium (Ti) and zirconium (Zr) doped or coated on lithium-cobalt-based oxide particles in the above-mentioned amounts, thereby improving durability and reducing resistance. This prevents structural collapse of the positive electrode active material during high-voltage use of the secondary battery, as described below, thereby enabling the realization of a secondary battery with improved fast charging performance and lifespan. Specifically, titanium (Ti) is used together with aluminum (Al) and magnesium (Mg), which can improve rate characteristics by reducing resistance. Furthermore, zirconium (Zr), when used together with aluminum (Al) and magnesium (Mg), can form a structure capable of trapping lithium at high voltages, thereby suppressing structural changes in the lithium-cobalt-based oxide particles and improving structural stability.

[0022] If the metal contains titanium (Ti) and zirconium (Zr) in an amount less than 300 ppm by weight of the positive electrode active material, it may be difficult to achieve the aforementioned effects of improving the structural stability and resistance of the positive electrode active material. Also, if the metal contains titanium (Ti) and zirconium (Zr) in an amount more than 1,500 ppm by weight of the positive electrode active material, the metal may excessively dope or coat the positive electrode active material, resulting in an increase in resistance.

[0023] Furthermore, when the metal contains only titanium out of titanium (Ti) and zirconium (Zr), the structural stability of the positive electrode active material is reduced, resulting in a problem of reduced long-term life characteristics.When the metal contains only zirconium out of titanium (Ti) and zirconium (Zr), the resistance of the surface of the active material is increased, resulting in a problem of reduced cell rate characteristics.

[0024] The metals in the positive electrode active material may include titanium (Ti) and zirconium (Zr) in an amount of 500 ppm to 1,200 ppm, specifically 700 ppm to 1,100 ppm, based on the weight of the positive electrode active material. When the amount is within this range, the aforementioned structural stability and resistance improvement effects are further enhanced, and the rapid charge performance and life performance when used at a high voltage in a high-energy-density secondary battery can be further improved.

[0025] The titanium (Ti) may be contained in the metal at a concentration of, based on the positive electrode active material, specifically, 250 ppm to 1,000 ppm, more specifically, 400 ppm to 800 ppm, and even more specifically, 600 ppm to 700 ppm, and the zirconium (Zr) may be contained in the metal at a concentration of, based on the positive electrode active material, specifically, 40 ppm to 500 ppm, more specifically, 45 ppm to 450 ppm, and even more specifically, 100 ppm to 300 ppm. When titanium (Ti) and zirconium (Zr) are used in the above ranges, they are preferred in that they do not reduce initial efficiency even at high voltages and can suppress structural changes in the positive electrode active material, thereby improving cell life.

[0026] In the positive electrode active material, the weight ratio of the titanium (Ti) to the zirconium (Zr) may be 0.5:1 to 18:1, specifically 3:1 to 10:1, and more specifically 3.5:1 to 4:1. When the weight ratio is within the above range, the resistance of the surface of the active material can be maintained low, thereby improving the rate characteristics of the cell, and the crystalline structure of the positive electrode active material can be well maintained, which is preferable in terms of improving long-term life performance.

[0027] The aluminum (Al) is doped or coated on the positive electrode active material to further improve the structural stability of the positive electrode active material and enhance the life characteristics.

[0028] The metal contains aluminum (Al) in an amount of 3,000 ppm to 7,000 ppm by weight of the positive electrode active material. If the metal contains aluminum (Al) in an amount less than 3,000 ppm by weight of the positive electrode active material, it is difficult to improve stability at high voltage and cobalt dissolution increases. Also, if the metal contains aluminum (Al) in an amount more than 7,000 ppm by weight of the positive electrode active material, aluminum is excessively doped or coated on the positive electrode active material, increasing resistance and reducing life performance, and increasing cobalt dissolution. Specifically, the metal may contain 4,000 ppm to 4,800 ppm of aluminum (Al) based on the total weight of the positive electrode active material.

[0029] The weight ratio of the aluminum (Al) to the total weight of the titanium (Ti) and zirconium (Zr) may be 4 to 8, specifically 4.5 to 6.5. When it is in the above range, the structural stability of the positive electrode active material, the control of Co elution, and the effect of extending the life of the lithium secondary battery can be improved in a balanced manner.

[0030] When magnesium (Mg) is doped or coated on a positive electrode active material, it can improve the structural stability of the positive electrode active material due to its wide band gap and facilitate the movement of lithium and electrons on the surface or inside of the positive electrode active material.

[0031] The metal may contain 800 ppm to 2,000 ppm, specifically 1,000 ppm to 1,700 ppm of magnesium (Mg) based on the total weight of the positive electrode active material.

[0032] The weight ratio of the magnesium (Mg) to the total weight of the titanium (Ti) and zirconium (Zr) may be 1.2 to 4.5, specifically 1.5 to 2.0. When the weight ratio is within this range, the structural stability of the positive electrode active material, smooth lithium migration in the positive electrode active material, and the effect of extending the life of the lithium secondary battery can be improved in a balanced manner.

[0033] The content of the metal doped or coated on the lithium cobalt-based oxide particles can be measured using an inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0034] The positive electrode active material may be composed of a plurality of particles, and the plurality of particles may have a bimodal structure of large particles and small particles. When the positive electrode active material has a bimodal structure, the packing of the positive electrode active material in the positive electrode is improved, thereby enabling the realization of a positive electrode with high energy density.

[0035] When the positive electrode active material has a bimodal structure, the average particle size (D 50 ) may be 10 μm to 25 μm, specifically 12 μm to 18 μm, and the average particle size (D 50 ) may be 1 μm to 7 μm, specifically 2 μm to 6 μm. When it is in the above range, it is preferable in that a high energy density of the positive electrode can be realized.

[0036] When the positive electrode active material has a bimodal structure, the weight ratio of the large particles to the small particles may be 1:1 to 15:1, specifically 2:1 to 5:1. When the weight ratio is within this range, dispersibility can be improved during preparation of a positive electrode slurry for manufacturing a positive electrode, and the rate characteristics of the cell can be further improved during preparation of a high-loading positive electrode.

[0037] The method for producing the positive electrode active material is not particularly limited as long as it is possible to realize a positive electrode active material having the above-described characteristics. For example, the positive electrode active material may be produced by a method including the following steps.

[0038] (a) dry-mixing a cobaltate, a lithium precursor, and metal precursors including aluminum (Al), magnesium (Mg), titanium (Ti), and zirconium (Zr) to form a mixture; and (b) heat treating the mixture at a temperature of 900°C or higher;

[0039] The cobaltate may be at least one selected from the group consisting of Co3O4, CoCO3, Co(NO3)2, and Co(OH)2, and specifically may be at least one selected from Co3O4 and Co(OH)2.

[0040] The lithium precursor may be at least one selected from the group consisting of Li2CO3, LiOH, LiNO3, CH3COOLi, and Li2(COO)2, and specifically may be at least one selected from LiOH and Li2CO3.

[0041] The metal precursor includes aluminum (Al), magnesium (Mg), titanium (Ti), and zirconium (Zr). Specifically, the metal precursor may be at least one selected from the group consisting of metals, metal oxides, and metal salts including aluminum (Al), magnesium (Mg), titanium (Ti), and zirconium (Zr).

[0042] The heat treatment may be performed at a temperature of 900° C. or higher, specifically 900° C. to 1,200° C., and more specifically 1,000° C. to 1,100° C. The heat treatment may be performed for 4 hours to 20 hours, and specifically 5 hours to 15 hours.

[0043] The input or mixing ratio of the cobaltate, lithium precursor, and metal precursor including aluminum (Al), magnesium (Mg), titanium (Ti), and zirconium (Zr) may be adjusted in consideration of the content of each component of the positive electrode active material.

[0044] In addition to steps (a) and (b), the method for producing a positive electrode active material further includes (c) increasing the average particle size (D 50 For example, the step (c) may further include a step of adjusting the average particle diameter (D 50) and realize a positive electrode active material with a bimodal structure.

[0045] The positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. The positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity. Specifically, the positive electrode current collector may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, and an aluminum-cadmium alloy, and may specifically include aluminum. The positive electrode current collector may generally have a thickness of 3 to 500 μm.

[0046] The positive electrode current collector may have a surface with fine irregularities to enhance the bonding strength of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, a sheet, a foil, a mesh, a porous material, a foam, or a nonwoven fabric.

[0047] The positive electrode active material layer may be disposed on the positive electrode current collector, specifically, on one or both surfaces of the positive electrode current collector. The positive electrode active material layer may contain the positive electrode active material described above.

[0048] The positive electrode active material may be contained in the positive electrode active material layer in an amount of 80% by weight to 99% by weight, preferably 92% by weight to 98% by weight, in consideration of the positive electrode active material being able to exhibit sufficient capacity.

[0049] The positive electrode active material layer may further include a positive electrode binder and a positive electrode conductive material in addition to the positive electrode active material. The positive electrode binder is a component that aids in binding the active material and conductive material, etc., and in binding them to the current collector, and specifically may include at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, and preferably may include polyvinylidene fluoride.

[0050] In order to ensure sufficient binding strength between components such as the positive electrode active material, the positive electrode binder may be contained in the positive electrode active material layer in an amount of 0.1 wt % to 10 wt %, preferably 0.1 wt % to 3 wt %, more specifically 0.5 wt % to 2.5 wt %.

[0051] The positive electrode conductive material may be used to supplement and improve the conductivity of a secondary battery, and is not particularly limited as long as it does not induce chemical changes and is conductive. Specifically, the conductive material may include at least one selected from the group consisting of graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; carbon nanotubes such as single-walled carbon nanotubes and multi-walled carbon nanotubes; fluorocarbons; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives. Specifically, in terms of improving conductivity, the conductive material may include carbon black and carbon nanotubes, more specifically, carbon black and multi-walled carbon nanotubes.

[0052] In order to ensure sufficient electrical conductivity, the positive electrode conductive material may be contained in the positive electrode active material layer in an amount of 0.1 wt % to 10 wt %, specifically 0.1 wt % to 3.0 wt %, and more specifically 0.5 wt % to 2.5 wt %. The thickness of the positive electrode active material layer may be 30 μm to 400 μm, preferably 50 μm to 200 μm.

[0053] The loading of the positive electrode is 3.5mAh / cm 2 ~7.5mAh / cm 2 , specifically 4.5mAh / cm 2 ~6.5mAh / cm 2 , more specifically 4.7mAh / cm 2 ~5.0mAh / cm 2 may be.

[0054] The electrode density of the positive electrode may be 3.6 g / cc to 4.5 g / cc, specifically 4.0 g / cc to 4.3 g / cc. According to the present invention, excellent rapid charge performance and life performance can be exhibited even at high electrode density and energy density. Because the positive electrode active material according to the present invention contains lithium-cobalt-based oxide particles, there is less risk of cracking of the active material during rolling compared to other positive electrode active materials (e.g., lithium nickel-cobalt manganese oxide particles), making it possible to achieve a high level of electrode density. Thus, by using a positive electrode having the above-described characteristics, the secondary battery of the present invention can significantly improve its excellent rapid charge performance and life performance even at high energy densities (e.g., 800 Wh / L or more).

[0055] The positive electrode may be fabricated by coating a positive electrode slurry containing a positive electrode active material, and optionally a positive electrode binder, a positive electrode conductive material, and a solvent for forming the positive electrode slurry, on the positive electrode current collector, followed by drying and rolling.

[0056] The solvent for forming the positive electrode slurry may include an organic solvent such as NMP (N-methyl-2-pyrrolidone), and may be used in an amount that provides a preferred viscosity when containing the positive electrode active material, and optionally a positive electrode binder and a positive electrode conductive material, etc. For example, the solvent for forming the positive electrode slurry may be included in the positive electrode slurry so that the concentration of solids including the positive electrode active material, and optionally a positive electrode binder and a positive electrode conductive material is 50 wt % to 95 wt %, preferably 70 wt % to 90 wt %.

[0057] negative electrode The negative electrode according to the present invention may be disposed opposite the positive electrode. The negative electrode according to the present invention is characterized by containing a carbon-based active material and a silicon-based active material.

[0058] The anode according to the present invention can have a high energy density while being thin by using a silicon-based active material with high capacity characteristics together with a carbon-based active material. In particular, when the anode according to the present invention is used together with the above-described positive electrode, the lithium intercalation rate can be significantly improved, thereby realizing a secondary battery with improved fast charging performance and life performance. If only a carbon-based active material is used as the anode active material, it is difficult to ensure a high capacity per volume compared to when a carbon-based active material and a silicon-based active material are used in combination. To achieve high capacity, the thickness of the anode must be increased, and the increased thickness of the anode inevitably slows the lithium intercalation rate from the positive electrode, preventing improved fast charging performance.

[0059] The carbon-based active material may include at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon, and specifically may include at least one selected from the group consisting of artificial graphite and natural graphite.

[0060] The average particle size (D 50It may be 5 μm to 35 μm, preferably 10 μm to 20 μm, in terms of achieving structural stability during charge and discharge and reducing side reactions with the electrolyte.

[0061] The silicon-based active material may contain a silicon-based compound represented by SiO x (0 ≦ x < 2). The silicon-based compound may be represented by the chemical formula SiO x (0 ≦ x < 2), and specifically, it may be represented by the chemical formula SiO x (0 < x < 2). On the other hand, in the case of SiO2 (when x = 2), since it does not react with lithium ions and cannot store lithium, x is preferably within the above range. Specifically, the silicon-based compound may be represented by the chemical formula SiO x (0.5 ≦ x ≦ 1.5).

[0062] More specifically, the silicon-based active material may contain a silicon-based compound represented by SiO x (0 ≦ x < 2), and a metal doped into the silicon-based compound. Generally, in the case of a silicon-based active material, due to the presence of irreversible sites in the silicon-based active material, there is a problem that a part of the lithium that has moved to the negative electrode during the initial charge undergoes an irreversible reaction and does not return to the positive electrode during discharge. To prevent such a problem, the metal may be doped into the silicon-based compound to reduce the irreversible phase of the silicon-based compound and may be introduced to improve efficiency.

[0063] The metal may be doped into the silicon-based compound. Specifically, the metal may be doped into the silicon-based compound and may be located inside, on the surface, or both inside and on the surface of the silicon-based compound. The metal may be doped into the silicon-based compound to form silicon oxide and metal silicate contained in the first silicon-based compound.

[0064] The metal may include at least one metal selected from the group consisting of Li, Mg, Ca, and Al. Specifically, at least one metal selected from the group consisting of Li and Mg, more specifically Mg, may be included in order to achieve excellent effects such as control of volume expansion of silicon-based oxide particles, prevention of damage, and improvement of initial efficiency.

[0065] The weight of the metal may be 1 wt% to 30 wt%, specifically 5 wt% to 20 wt%, based on the total weight of the silicon-based compound and the metal. When the weight is within this range, the irreversible capacity of the first silicon-based active material can be sufficiently eliminated while preventing a decrease in capacity due to excessive metal doping. The metal content can be measured using an inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0066] The silicon-based active material may further include a carbon coating layer disposed on the surface thereof, which may function as a protective layer to suppress volume expansion of the silicon-based active material and prevent side reactions with the electrolyte.

[0067] The carbon coating layer may be contained in the silicon-based active material in an amount of 0.1 wt % to 10 wt %, preferably 3 wt % to 7 wt %, which is preferable in that the carbon coating layer can effectively control the volume expansion of the silicon-based active material while preventing side reactions with the electrolyte.

[0068] The carbon coating layer may be an amorphous carbon coating layer. Specifically, the carbon coating layer may be formed by chemical vapor deposition (CVD) using at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene.

[0069] The average particle size (D 50) may be 1 μm to 15 μm, more preferably 2 μm to 8 μm, in order to achieve structural stability of the active material during charge and discharge, to prevent the problem of an excessively large particle size resulting in an increased level of volume expansion / contraction, and to prevent the problem of an excessively small particle size resulting in a decrease in initial efficiency.

[0070] The weight ratio of the carbon-based active material to the silicon-based active material may be 83:17 to 99:1, specifically 88:12 to 93:7. When the weight ratio is within this range, the negative electrode can have sufficient capacity while reducing the effect of volume expansion of the silicon-based active material, thereby enabling a high-loading negative electrode to be realized.

[0071] The negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity. Specifically, the negative electrode current collector may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, and an aluminum-cadmium alloy, and may specifically include copper. The negative electrode current collector may generally have a thickness of 3 to 500 μm.

[0072] The negative electrode current collector may have a surface with fine irregularities to enhance the bonding strength of the negative electrode active material. For example, the negative electrode current collector may be used in various forms such as a film, a sheet, a foil, a mesh, a porous material, a foam, or a nonwoven fabric.

[0073] The negative electrode active material layer may be formed on at least one surface of the negative electrode current collector. Specifically, the negative electrode active material layer may be formed on one or both surfaces of the negative electrode current collector.

[0074] The negative electrode active material layer includes the carbon-based active material and the silicon-based active material described above.

[0075] The carbon-based active material may be contained in the negative electrode active material layer in an amount of 65% to 98% by weight, specifically 80% to 95% by weight. The silicon-based active material may be included in the negative electrode active material layer in an amount of 1 wt % to 20 wt %, specifically 3 wt % to 15 wt %, to ensure sufficient capacity of the negative electrode while reducing the effect of the silicon-based active material on volume expansion.

[0076] The negative electrode active material layer may further include a negative electrode binder and a negative electrode conductive material in addition to the carbon-based active material and the silicon-based active material. The negative electrode binder may include at least one selected from the group consisting of polyvinylidene fluoride (PVdF), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber, acrylic rubber, butyl rubber, fluororubber, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyethylene glycol (PEG), polyacrylonitrile (PAN), and polyacrylamide (PAM), in terms of further improving electrode adhesive strength and providing sufficient resistance to volume expansion / contraction of the active material. Specifically, the negative electrode binder may include styrene butadiene rubber (SBR).

[0077] The negative electrode binder may be present in the negative electrode active material layer in an amount of 0.1 to 10% by weight, specifically 2 to 8% by weight, in the above range, which is preferable because it improves adhesive strength, controls the thickness expansion of the negative electrode, and enables the realization of a negative electrode with excellent capacity.

[0078] The negative electrode conductive material may be used to improve the conductivity of the negative electrode active material layer, and is preferably conductive without inducing chemical changes. Specifically, the negative electrode conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, conductive fiber, single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives. Preferably, the negative electrode conductive material may include at least one selected from single-walled carbon nanotubes and multi-walled carbon nanotubes, more specifically, single-walled carbon nanotubes, in consideration of maintaining the conductive network of the silicon-based active material.

[0079] The conductive material may be contained in the negative electrode active material layer in an amount of 0.001 wt % to 10 wt %, specifically 0.01 wt % to 1 wt %, which is preferable in that the volume expansion due to charge and discharge can be controlled while preventing the conductive network from being broken due to the volume expansion of the negative electrode active material.

[0080] The negative electrode active material layer may further include a thickener, and the thickener may include carboxymethyl cellulose (CMC). The thickener may be contained in the negative electrode active material layer in an amount of 0.5 wt % to 5 wt %, but is not limited thereto.

[0081] The loading amount of the negative electrode active material layer was 4 mAh / cm 2 ~8mAh / cm 2 , specifically 4.0mAh / cm 2 ~7.5mAh / cm 2 , more specifically 4mAh / cm 2 ~7mAh / cm 2According to the present invention, even in the case of a high loading negative electrode as described above, it is possible to have excellent levels of rapid charging performance and life performance.

[0082] The electrode density of the negative electrode active material layer may be 1.4 to 2.0 g / cc, specifically 1.5 g / cc to 1.9 g / cc, and more specifically 1.6 g / cc to 1.8 g / cc. According to the present invention, excellent rapid charging performance and life performance can be exhibited even at high electrode density and energy density.

[0083] The thickness of the negative electrode active material layer may be 20 μm to 200 μm, specifically 30 μm to 90 μm. The negative electrode according to the present invention can achieve a thin negative electrode with high energy density by using a carbon-based active material and a silicon-based active material, and can smoothly intercalate lithium ions from the positive electrode, thereby improving rapid charging performance.

[0084] The negative electrode active material layer can be prepared by adding the carbon-based active material and the silicon-based active material, and optionally a negative electrode binder, a negative electrode conductive material, and / or a thickener to a solvent (e.g., water) to prepare a negative electrode slurry, and then coating, rolling, and drying the negative electrode slurry on the negative electrode current collector.

[0085] The negative electrode active material layer may have a double layer structure, specifically, the negative electrode active material layer may include a first negative electrode active material layer disposed on the negative electrode current collector and a second negative electrode active material layer disposed on the first negative electrode active material layer.

[0086] Specifically, the carbon-based active material may include a first carbon-based active material and a second carbon-based active material, and the silicon-based active material may include a first silicon-based active material and a second silicon-based active material. Also, the first negative electrode active material layer may include the first carbon-based active material and the first silicon-based active material, and the second negative electrode active material layer may include the second carbon-based active material and the second silicon-based active material.

[0087] In this specification, the terms "first carbon-based active material" and "second carbon-based active material" and "first silicon-based active material" and "second silicon-based active material" are terms used to describe the locations where the carbon-based active material and silicon-based active material are contained, respectively, and the above-mentioned descriptions of the carbon-based active material and silicon-based active material may be similarly applied.

[0088] The first negative electrode active material layer may contain the first carbon-based active material and the first silicon-based active material in a weight ratio of 83:17 to 99:1, specifically 88:12 to 93:7. The second negative electrode active material layer may contain the second carbon-based active material and the second silicon-based active material in a weight ratio of 83:17 to 99:1, specifically 88:12 to 93:7. When the ratios are within the above ranges, sufficient capacity of the negative electrode can be ensured while reducing the effect of volume expansion of the silicon-based active material, thereby enabling a high-loading negative electrode.

[0089] The first carbon-based active material may be contained in the first negative electrode active material layer in an amount of 65% to 98% by weight, specifically 80% to 95% by weight, and the second carbon-based active material may be contained in the second negative electrode active material layer in an amount of 65% to 98% by weight, specifically 80% to 95% by weight.

[0090] The first silicon-based active material may be contained in the first negative electrode active material layer in an amount of 1 wt % to 20 wt %, specifically 3 wt % to 15 wt %, and the second silicon-based active material may be contained in the second negative electrode active material layer in an amount of 1 wt % to 20 wt %, specifically 3 wt % to 15 wt %.

[0091] When the negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer, and the negative electrode active material layer includes the above-described negative electrode binder, negative electrode conductive material, and / or thickener, the negative electrode binder may include a first negative electrode binder and a second negative electrode binder, the negative electrode conductive material may include a first negative electrode conductive material and a second negative electrode conductive material, and the thickener may include a first thickener and a second thickener. In this case, the first negative electrode active material layer may further include the first negative electrode binder, the first negative electrode conductive material, and / or the first thickener in addition to the first carbon-based active material and the first silicon-based active material. The second negative electrode active material layer may include the second negative electrode binder, the second negative electrode conductive material, and / or the second thickener in addition to the second carbon-based active material and the second silicon-based active material.

[0092] In this specification, the terms "first negative electrode binder" and "second negative electrode binder", "first negative electrode conductive material" and "second negative electrode conductive material", and "first thickener" and "second thickener" are terms used to describe the locations where the negative electrode binder, negative electrode conductive material, and thickener are contained, and the above descriptions regarding the negative electrode binder, negative electrode conductive material, and thickener may also be applied.

[0093] The first negative electrode binder may be present in the first negative electrode active material layer at 0.1 wt % to 10 wt %, specifically 2 wt % to 8 wt %, and the second negative electrode binder may be present in the second negative electrode active material layer at 0.1 wt % to 10 wt %, specifically 2 wt % to 8 wt %.

[0094] The first conductive material may be contained in the first negative electrode active material layer in an amount of 0.001 wt % to 10 wt %, specifically 0.01 wt % to 1 wt %, and the second conductive material may be contained in the second negative electrode active material layer in an amount of 0.001 wt % to 10 wt %, specifically 0.01 wt % to 1 wt %.

[0095] The first thickener may be contained in the first negative electrode active material layer in an amount of 0.5% by weight to 5% by weight, and the second thickener may be contained in the second negative electrode active material layer in an amount of 0.5% by weight to 5% by weight.

[0096] When the negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer, and the first negative electrode active material layer and the second negative electrode active material layer include a first negative electrode binder and a second negative electrode binder, respectively, the weight percentage of the first negative electrode binder relative to the total weight of the first negative electrode active material layer may be greater than the weight percentage of the second negative electrode binder relative to the total weight of the second negative electrode active material layer. This is preferable in that the binder is unevenly distributed in the upper portion of the negative electrode active material layer, preventing a binder deficiency in the lower portion of the negative electrode active material layer, thereby achieving a uniform binder distribution throughout the negative electrode active material layer.

[0097] Specifically, the ratio of the weight percentage of the first negative electrode binder to the total weight of the first negative electrode active material layer to the weight percentage of the second negative electrode binder to the total weight of the second negative electrode active material layer may be 1.5:1 to 2.5:1.

[0098] The ratio of the thickness of the first negative electrode active material layer to the thickness of the second negative electrode active material layer may be 1:0.5 to 1:2, specifically 1:0.8 to 1:1.3, which is preferable in that the overall charge / discharge performance, adhesive strength, and thickness expansion control effect of the negative electrode can be simultaneously improved.

[0099] The ratio of the loading amount of the first negative electrode active material layer to the loading amount of the second negative electrode active material layer may be 1:0.5 to 1:2, specifically 1:0.8 to 1:1.3, which is preferable in that the overall charge / discharge performance, adhesive strength, and thickness expansion control effect of the negative electrode can be simultaneously improved.

[0100] When the negative electrode active material layer includes the first negative electrode active material layer and the second negative electrode active material layer, the method for producing the negative electrode is not particularly limited as long as it is possible to realize the first negative electrode active material layer and the second negative electrode active material layer having the above-mentioned characteristics. For example, the negative electrode according to the present invention can be produced by dispersing a first carbon-based active material, a first silicon-based active material, a first binder, a first conductive material, and / or a thickener in a solvent (e.g., water) to produce a slurry for the first negative electrode active material layer, dispersing the second carbon-based active material, the second silicon-based active material, a second binder, and / or a second conductive material in a solvent (e.g., water) to produce a slurry for the second negative electrode active material layer, and then applying the resulting slurry to a negative electrode current collector. More specifically, the anode according to the present invention can be manufactured by applying the slurry for the first anode active material layer prepared above to a anode current collector, rolling and drying the slurry, and then applying the slurry for the second anode active material layer prepared above onto the first anode active material layer, rolling and drying the slurry, to form a second anode active material layer. Alternatively, the anode according to the present invention can be manufactured by applying the slurry for the first anode active material layer to a anode current collector, and substantially simultaneously applying the slurry for the second anode active material layer onto the slurry for the first anode active material layer to be applied, and then rolling and drying the slurry.

[0101] Separator The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in lithium secondary batteries can be used without particular limitations. It is particularly preferable that the separator exhibits low resistance to electrolyte ion migration and has excellent electrolyte humidifying ability. Specifically, a porous polymer film, such as a porous polymer film made from a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material may be used, and may be selectively used as a single-layer or multi-layer structure.

[0102] electrolyte Furthermore, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing secondary batteries, but are not limited to these.

[0103] Specifically, the electrolyte may include an organic solvent and a lithium salt. The lithium salt may be any compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The lithium salt is preferably used at a concentration in the range of 0.1M to 2.0M. When the lithium salt concentration is within this range, the electrolyte has suitable conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0104] The organic solvent may include at least one selected from linear carbonates, cyclic carbonates, linear esters, cyclic esters, ethers, glymes, and nitriles.

[0105] The linear carbonate may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate.

[0106] The cyclic carbonate may include at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, and 2,3-pentylene carbonate.

[0107] Specific examples of the linear ester include, but are not limited to, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0108] Specific examples of the cyclic ester include, but are not limited to, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0109] Specific examples of the ether include, but are not limited to, dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, 1,3-dioxolane (DOL), and 2,2-bis(trifluoromethyl)-1,3-dioxolane (TFDOL).

[0110] Specific examples of the glyme include, but are not limited to, dimethoxyethane (glyme, DME), diethoxyethane, diglyme, triglyme, and tetraglyme (TEGDME).

[0111] Specific examples of the nitrile include, but are not limited to, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0112] More specifically, the organic solvent may include a cyclic carbonate, a linear ester, and a halogen-containing cyclic carbonate. In this case, the cyclic carbonate has the effect of improving high dielectric constant and ionic conductivity, while the linear ester has the effect of realizing suitable viscosity, improving electrolyte impregnation, and reducing the degree of reductive decomposition at high voltage. This is preferable in terms of improving stability and life performance at high voltage. In particular, the halogen-containing cyclic carbonate is preferable because it can form a stable SEI layer (Solid Electrolyte Interface layer) on the negative electrode of the present invention using a silicon-based active material.

[0113] When the organic solvent contains a cyclic carbonate, a linear ester, and a halogen-containing cyclic carbonate, the cyclic carbonate may include at least one halogen-free cyclic carbonate selected from ethylene carbonate and propylene carbonate, the linear ester may include at least one ethyl propionate and propyl propionate, and the halogen-containing cyclic carbonate may include at least one fluoroethylene carbonate and difluoroethylene carbonate.

[0114] When the organic solvent contains a cyclic carbonate, a linear ester, and a halogen-containing cyclic carbonate, the cyclic carbonate may be contained in the organic solvent at 10% by weight to 50% by weight, specifically 15% by weight to 30% by weight, the linear ester may be contained in the organic solvent at 30% by weight to 80% by weight, specifically 40% by weight to 70% by weight, and the halogen-containing cyclic carbonate may be contained in the organic solvent at 5% by weight to 30% by weight, specifically 10% by weight to 25% by weight.

[0115] The electrolyte may further contain an additive in addition to the lithium salt and the organic solvent. The additive may include at least one selected from the group consisting of vinyl ethylene carbonate, propane sultone, LiBF (lithium tetrafluoroborate), LiODFB (lithium difluoro(oxalato)borate), 1,3,6-HTCN (hexane tri-cyanide), and NaO (sodium superoxide), specifically, fluoroethylene carbonate, difluoroethylene carbonate, vinyl ethylene carbonate, propane sultone, LiBF (lithium tetrafluoroborate), LiODFB (lithium difluoro(oxalato)borate), 1,3,6-HTCN (hexane tri-cyanide), succinonitrile, 1,4-dicyano-2-butyne, adiponitrile, lithium difluorophosphate (LiPOF), and NaO (sodium superoxide). The other additives may be contained in the electrolyte in an amount of 0.1 wt % to 20 wt %, specifically 1 wt % to 10 wt %, but are not limited thereto.

[0116] The secondary battery according to the present invention can have excellent rapid charging performance and lifespan performance when used at a high voltage as a high energy density secondary battery by combining a positive electrode having excellent structural stability and resistance improvement effect with a negative electrode having a thin thickness and high energy density.

[0117] Specifically, the energy density of the secondary battery according to the present invention may be 800 Wh / L or more. The energy density can be calculated by charging the secondary battery at 0.7 C to 4.5 V in a constant current / constant voltage (CC / CV) mode, and then discharging at 0.2 C to 3.0 V in a constant current (CC) mode, using the following formula 1:

[0118] [Formula 1] Energy density (Wh / L) = {Discharge capacity in the first cycle (Ah) × Average voltage (V)} / (Volume of the secondary battery when charging is completed in the first cycle (L))

[0119] In Equation 1, the average voltage was calculated by multiplying the voltage, current, and discharge duration at the end of the discharge to obtain Wh (Watt-hour), and dividing the result by the discharge capacity in the first cycle.

[0120] In the secondary battery of the present invention, the N / P ratio calculated by the following formula 2 may be 1.0 to 1.5, preferably 1.0 to 1.2.

[0121] [Formula 2] N / P ratio={(discharge capacity per unit area of ​​the negative electrode) / (discharge capacity per unit area of ​​the positive electrode)}.

[0122] Specifically, the discharge capacity per unit area of ​​the negative electrode can be determined by the following method. First, a negative electrode sample similar to the negative electrode used is prepared. A coin-shaped half-cell is fabricated including the negative electrode sample, a lithium metal counter electrode facing the negative electrode, a separator interposed between the negative electrode and the lithium metal counter electrode, and an electrolyte, and the discharge capacity is determined. The discharge capacity per unit area of ​​the negative electrode can be determined by dividing the discharge capacity by the area of ​​the negative electrode sample.

[0123] The discharge capacity per unit area of ​​the positive electrode can be determined by the following method. First, a positive electrode sample similar to the positive electrode used is prepared. A coin-shaped half-cell is manufactured including the positive electrode sample, a lithium metal counter electrode facing the positive electrode, a separator interposed between the negative electrode and the lithium metal counter electrode, and an electrolyte, and the discharge capacity is determined. The discharge capacity per unit area of ​​the positive electrode can be determined by dividing the discharge capacity by the area of ​​the positive electrode sample.

[0124] The secondary battery may further include a battery case that accommodates the negative electrode, the positive electrode, the separator, and the electrolyte. The secondary battery can be manufactured by a conventional method for manufacturing a secondary battery, by placing an electrode assembly, in which a separator is interposed between the negative electrode and the positive electrode, inside the battery case and injecting an electrolyte solution.

[0125] <Battery system> The present invention also provides a battery system including the above-described secondary battery. Specifically, the battery system includes the above-mentioned secondary battery and a control unit capable of setting a voltage range for charging and discharging the secondary battery. The secondary battery has been described above.

[0126] The control unit is not particularly limited as long as it can control the voltage range during charging and discharging of the secondary battery, and may be, for example, an electrochemical charger / discharger. Specifically, the control unit may be built into a BMS (Battery Management System) included in the battery pack.

[0127] The voltage range set by the control unit may be set to satisfy the following formula 3.

[0128] [Formula 3] 0.60≦(V max -X) / Y≦0.67

[0129] In the above formula 3, V max is the maximum voltage set by the control unit, and Y is the voltage V max -V min / 1.47, where V min is the minimum voltage set by the control unit, and X is V max and V min is the average voltage when the secondary battery is charged and discharged.

[0130] In the formula 3, the V max may be 4.4V to 4.6V, specifically 4.40V to 4.55V, and minAccording to the present invention, the secondary battery can exhibit a long life even when used at a high voltage. max , V min It is possible to realize a battery system with excellent life performance in this environment.

[0131] The present invention may be embodied in various different forms and should not be construed as limited to the embodiments set forth herein, although the present invention may be embodied in various different forms and should not be construed as limited to the embodiments set forth herein.

[0132] Example Example 1: Manufacturing of secondary battery 1. Manufacturing the negative electrode (1) Preparation of carbon-based and silicon-based active materials As a carbon-based active material, artificial graphite (average particle size (D 50 ): 18 μm) was prepared. The carbon-based active material was used as a first carbon-based active material and a second carbon-based active material, which will be described later.

[0133] As a silicon-based active material, a silicon-based active material was prepared in which Mg was doped into SiO and the surface had a carbon coating layer. 50 The thickness of the silicon-based active material was 8.5 μm, the carbon coating layer was contained in the silicon-based active material at 4 wt %, and Mg was doped into the silicon-based active material at 9 wt %. The silicon-based active material was used as a first silicon-based active material and a second silicon-based active material, which will be described later.

[0134] <Preparation of Slurry for First Negative Electrode Active Material Layer> The first carbon-based active material, the first silicon-based active material, styrene butadiene rubber (SBR) as a first negative electrode binder, carboxymethyl cellulose (CMC) as a first thickener, and single-walled carbon nanotubes (SWCNTs) as a first negative electrode conductive material were mixed in a weight ratio of 85.2:9.5:4.0:1.0:0.3, and the mixture was added to water as a solvent to prepare a slurry for a first negative electrode active material layer.

[0135] <Preparation of Slurry for Second Negative Electrode Active Material Layer> The second carbon-based active material, the second silicon-based active material, styrene butadiene rubber (SBR) as a second negative electrode binder, carboxymethyl cellulose (CMC) as a second thickener, and single-walled carbon nanotubes (SWCNTs) as a second negative electrode conductive material were mixed in a weight ratio of 87.0:9.7:2.0:1.0:0.3, and the mixture was added to water as a solvent to prepare a slurry for a second negative electrode active material layer.

[0136] <Formation of First and Second Negative Electrode Active Material Layers> The slurry for the first negative electrode active material layer prepared above was applied to a copper foil (thickness: 6 μm) as a negative electrode current collector, and substantially simultaneously, the slurry for the second negative electrode active material layer prepared above was applied onto the applied slurry for the first negative electrode active material layer, followed by roll pressing and drying in a vacuum oven at 130°C for 10 hours to prepare a negative electrode in which the negative electrode current collector, the first negative electrode active material layer, and the second negative electrode active material layer were sequentially stacked.

[0137] The weight ratio of the first negative electrode binder in the first negative electrode active material layer (4 wt %, based on 100 wt % of the first negative electrode active material layer) to the weight ratio of the second negative electrode binder in the second negative electrode active material layer (2 wt %, based on 100 wt % of the second negative electrode active material layer) was approximately 2:1.

[0138] The total weight of the first negative electrode binder and the second negative electrode binder was 3 wt % based on the total weight of the first negative electrode active material layer and the second negative electrode active material layer.

[0139] The loading capacity of the first negative electrode active material layer is 2.55 mAh / cm 2 The loading of the second negative electrode active material layer is 2.55 mAh / cm 2 The sum of the loading amounts of the first negative electrode active material layer and the second negative electrode active material layer is 5.1 mAh / cm 2 It was.

[0140] The first negative electrode active material layer had a thickness of 31.75 μm, the second negative electrode active material layer had a thickness of 31.75 μm, and the sum of the thicknesses of the first negative electrode active material layer and the second negative electrode active material layer was 63.5 μm. The electrode density of the first negative electrode active material layer and the second negative electrode active material layer was 1.7 g / cc.

[0141] 2. Fabrication of the cathode Co3O4 80.270 g as cobaltate, Li2CO3 36.940 g as lithium precursor, TiO2 0.051 g, ZrO2 0.050 g, Al2O3 0.590 g, and MgO 0.177 g as metal precursors were dry mixed and then heat-treated in a furnace at 1,050 °C for 10 hours to obtain large particles (average particle size (D)) in which 437 ppm of Ti, 423 ppm of Zr, 1,500 ppm of Mg, and 4,500 ppm of Al were doped or coated on the lithium cobalt oxide particles. 50 The metal content was measured by ICP-AES (instrument name: AVIO500, manufacturer: Perkin Elmer).

[0142] In addition, the average particle size (D 50 Small particles similar to the large particles were prepared, except that the particle diameter was adjusted to 3 μm. The large particles and the small particles were mixed in a weight ratio of 3:1 to form a positive electrode active material.

[0143] The positive electrode active material, a mixture of carbon black and multi-walled carbon nanotubes as conductive materials in a weight ratio of 1:0.5, and polyvinylidene fluoride (PVdF) as a binder in a weight ratio of 96:1.5:1.5 were added to N-methyl-2-pyrrolidone (NMP) as a solvent for forming a positive electrode slurry to prepare a positive electrode slurry.

[0144] The positive electrode slurry was applied to an aluminum current collector (thickness: 10 μm) as a positive electrode current collector at 4.85 mAh / cm 2The coated film was rolled and dried in a vacuum oven at 130°C for 10 hours to form a positive electrode active material layer (thickness: 63.5 μm) and fabricate a positive electrode (thickness: 73.5 μm). The electrode density of the positive electrode was 4.15 g / cc.

[0145] 3. Secondary battery manufacturing A polyethylene separator was interposed between the negative electrode and positive electrode produced as described above, and an electrolyte was injected to produce a secondary battery of Example 1. The electrolyte used was an organic solvent made by mixing fluoroethylene carbonate (FEC), ethylene carbonate (EC), and ethylene propionate (EP) in a volume ratio of 20:20:60, to which 3 wt % vinylene carbonate was added, and LiPF6 was added as a lithium salt at a concentration of 1 mol / L. The N / P ratio of the secondary battery of Example 1 was 1.05.

[0146] 4. Energy Density Measurement The energy density of the secondary battery of Example 1 was measured as follows. First, the secondary battery was charged and discharged once under the following conditions.

[0147] <Charge and discharge conditions> Charging: CC / CV mode charging at 0.7C up to 4.5V (0.05C current cutoff) Discharge: CC mode discharge at 0.2C to 3.0V

[0148] The energy density was calculated using the following formula 1. [Formula 1] Energy density (Wh / L) = {Discharge capacity in the first cycle (Ah) × Average voltage (V)} / (Volume of the secondary battery when charging is completed in the first cycle (L))

[0149] In Equation 1, the average voltage was calculated by multiplying the voltage, current, and discharge duration at the time when the minimum voltage was reached and discharge was terminated to obtain Wh (Watt-hour), and then dividing the result by the discharge capacity in the first cycle. The energy density of the secondary battery of Example 1 calculated above was 810 Wh / L.

[0150] Example 2: Manufacturing of secondary battery A positive electrode active material was prepared in the same manner as in Example 1, except that the metal contents of the large particles and the small particles were adjusted to Ti 752 ppm, Zr 48 ppm, Mg 1,500 ppm, and Al 4,500 ppm, respectively.

[0151] A secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode active material prepared above was used. The N / P ratio of the secondary battery was 1.05, and the energy density was 810 Wh / L.

[0152] Example 3: Production of secondary battery A positive electrode active material was prepared in the same manner as in Example 1, except that the metal contents of the large particles and the small particles were adjusted to Ti 653 ppm, Zr 171 ppm, Mg 1,500 ppm, and Al 4,500 ppm, respectively.

[0153] A secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode active material prepared above was used. The N / P ratio of the secondary battery was 1.05, and the energy density was 810 Wh / L.

[0154] Comparative Example 1: Manufacturing of secondary battery A positive electrode active material was prepared in the same manner as in Example 1, except that Ti and Zr were not used as the metals contained in the large particles and the small particles, and the metal contents of the large particles and the small particles were adjusted to 1,500 ppm Mg and 4,500 ppm Al, respectively.

[0155] A secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode active material prepared above was used. The N / P ratio of the secondary battery was 1.05, and the energy density was 810 Wh / L.

[0156] Comparative Example 2: Manufacturing of secondary battery A positive electrode active material was prepared in the same manner as in Example 1, except that Zr was not used as the metal contained in the large particles and the small particles, and the metal contents of the large particles and the small particles were adjusted to Ti 800 ppm, Mg 1,500 ppm, and Al 4,500 ppm, respectively.

[0157] A secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode active material prepared above was used. The N / P ratio of the secondary battery was 1.05, and the energy density was 810 Wh / L.

[0158] Comparative Example 3: Manufacture of secondary battery A positive electrode active material was prepared in the same manner as in Example 1, except that Ti was not used as the metal contained in the large particles and the small particles, and the metal contents of the large particles and the small particles were adjusted to Zr 800 ppm, Mg 1,500 ppm, and Al 4,500 ppm, respectively.

[0159] A secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode active material prepared above was used. The N / P ratio of the secondary battery was 1.05, and the energy density was 810 Wh / L.

[0160] Comparative Example 4: Production of secondary battery A positive electrode active material was prepared in the same manner as in Example 1, except that the metal contents of the large particles and the small particles were adjusted to Ti 239 ppm, Zr 57 ppm, Mg 1,500 ppm, and Al 4,500 ppm, respectively.

[0161] A secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode active material prepared above was used. The N / P ratio of the secondary battery was 1.05, and the energy density was 810 Wh / L.

[0162] Comparative Example 5: Production of secondary battery A positive electrode active material was prepared in the same manner as in Example 1, except that the metal contents of the large particles and the small particles were adjusted to Ti 1,275 ppm, Zr 250 ppm, Mg 1,500 ppm, and Al 4,500 ppm, respectively.

[0163] A secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode active material prepared above was used. The N / P ratio of the secondary battery was 1.05, and the energy density was 810 Wh / L.

[0164] Comparative Example 6: Production of secondary battery 1. Manufacturing the negative electrode Artificial graphite as a carbon-based active material (average particle size (D 50 ):18 μm), styrene butadiene rubber (SBR) as a negative electrode binder, carboxymethyl cellulose (CMC) as a thickener, and single-walled carbon nanotubes (SWCNT) as a negative electrode conductive material were mixed in a weight ratio of 96.3:2.0:1.5:0.2 and added to water as a solvent to produce a slurry for the negative electrode active material layer.

[0165] The slurry for the negative electrode active material layer prepared above was applied to a copper foil (thickness: 6 μm) as a negative electrode current collector, rolled, and dried in a vacuum oven at 130°C for 10 hours to form a negative electrode active material layer, which was used as a negative electrode.

[0166] The loading of the negative electrode active material layer is 5.17mAh / cm 2 The thickness of the negative electrode active material layer was 87 μm, and the electrode density of the negative electrode active material layer was 1.8 g / cc.

[0167] 2. Fabrication of the cathode A positive electrode similar to that produced in Example 3 was prepared.

[0168] 3. Secondary battery manufacturing A secondary battery was produced in the same manner as in Example 3, except that the negative electrode and positive electrode prepared above were used. The N / P ratio of the secondary battery was 1.05, and the energy density was 810 Wh / L.

[0169] Comparative Example 7: Production of secondary battery A positive electrode active material was prepared in the same manner as in Example 1, except that the metal contents of the large particles and the small particles were adjusted to Ti 653 ppm, Zr 171 ppm, Mg 1,500 ppm, and Al 2,800 ppm, respectively.

[0170] A secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode active material prepared above was used. The N / P ratio of the secondary battery was 1.05, and the energy density was 810 Wh / L.

[0171] Comparative Example 8: Production of secondary battery A positive electrode active material was prepared in the same manner as in Example 1, except that the metal contents of the large particles and the small particles were adjusted to Ti 653 ppm, Zr 171 ppm, Mg 1,500 ppm, and Al 7,600 ppm, respectively.

[0172] A secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode active material prepared above was used. The N / P ratio of the secondary battery was 1.05, and the energy density was 810 Wh / L.

[0173] [Table 1]

[0174] Experimental example Experimental example 1: Evaluation of room temperature rapid charging performance The secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 8 were evaluated for cycle capacity retention using an electrochemical charger / discharger.

[0175] The cycle capacity retention rate was measured at a temperature of 25°C under the following charge and discharge conditions. Charging conditions: CC / CV mode, 0.7C, 4.5V, 0.05C cutoff Discharge conditions: CC mode, 0.2C, 3.2V cutoff

[0176] The capacity retention rate was calculated as follows. Capacity retention rate (%) = {(discharge capacity at Nth cycle) / (discharge capacity at first cycle)} × 100 (In the above formula, N is an integer of 1 or more.) The capacity retention rate (%) at the 500th cycle is shown in Table 2 below.

[0177] Experimental example 2: Evaluation of high-temperature fast charging performance The secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 8 were evaluated for cycle capacity retention using an electrochemical charger / discharger.

[0178] The cycle capacity retention rate was measured at a temperature of 45°C under the following charge and discharge conditions. Charging conditions: CC / CV mode, 0.7C, 4.5V, 0.05C cutoff Discharge conditions: CC mode, 0.2C, 3.2V cutoff

[0179] The capacity retention rate was calculated as follows. Capacity retention rate (%) = {(discharge capacity at Nth cycle) / (discharge capacity at first cycle)} × 100 (In the above formula, N is an integer of 1 or more.) The capacity retention rate (%) at the 500th cycle is shown in Table 2 below.

[0180] Experimental Example 3: Measurement of Co elution amount In Experimental Example 2, 500 charge / discharge cycles were completed, and the negative electrodes were separated from the secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 8. The separated negative electrodes were washed with dimethyl carbonate (DMC), and the negative electrodes were scraped with a spatula to obtain 100 mg of negative electrode active material. 100 mg of the obtained negative electrode active material was placed in a centrifuge tube, and 1 mL of hydrochloric acid and 0.5 mL of hydrogen peroxide were added to the centrifuge tube. The mixture was dissolved at 100°C for 3 hours to prepare an analytical sample. The analytical sample was analyzed using ICP-OES (instrument name: AVIO 500, manufacturer: Perkin Elmer) to analyze the amount of Co elution. The weight of Co relative to the weight of the negative electrode active material (unit: mg / kg) is shown in Table 2 below.

[0181] [Table 2]

[0182] Referring to Table 2, it can be seen that the secondary batteries of Examples 1 to 3 including the anode and cathode having the characteristics of the present invention have significantly improved rapid charge performance and life performance at room temperature and high temperature, and have a significantly reduced amount of Co elution, compared to Comparative Examples 1 to 8.

Claims

1. a positive electrode, a negative electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte; The positive electrode includes a positive electrode active material including lithium cobalt-based oxide particles and a metal doped or coated on the lithium cobalt-based oxide particles, the metals include aluminum (Al), magnesium (Mg), titanium (Ti), and zirconium (Zr); The metals include titanium (Ti) and zirconium (Zr) in an amount of 300 ppm to 1,500 ppm based on the weight of the positive electrode active material; The metal contains aluminum (Al) in an amount of 3,000 ppm to 7,000 ppm based on the weight of the positive electrode active material, the negative electrode includes a carbon-based active material and a silicon-based active material, A secondary battery, wherein the weight ratio of the aluminum (Al) to the total weight of the titanium (Ti) and the zirconium (Zr) is 4.5 to 6.

5.

2. 2. The secondary battery according to claim 1, wherein the energy density of the secondary battery is 800 Wh / L or more.

3. 3. The secondary battery according to claim 1, wherein the weight ratio of the carbon-based active material to the silicon-based active material is 83:17 to 99:

1.

4. 3. The secondary battery according to claim 1, wherein the carbon-based active material comprises at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon.

5. 3. The secondary battery according to claim 1, wherein the silicon-based active material includes a silicon-based compound represented by SiOx (0≦x<2).

6. the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, The secondary battery according to claim 1 , wherein the negative electrode active material layer contains the carbon-based active material and the silicon-based active material.

7. the positive electrode active material is composed of a plurality of particles, The secondary battery according to claim 1 , wherein the plurality of particles have a bimodal structure of large particles and small particles.

8. The large particles have an average particle size (D50) of 10 μm to 25 μm, 8. The secondary battery according to claim 7, wherein the small particles have an average particle size (D50) of 1 μm to 7 μm.

9. 3. The secondary battery according to claim 1, wherein a weight ratio of the titanium (Ti) to the zirconium (Zr) is 0.5:1 to 18:

1.

10. 3. The secondary battery according to claim 1, wherein the metal contains magnesium (Mg) in an amount of 800 ppm to 2,000 ppm based on the weight of the positive electrode active material.

11. The loading of the positive electrode is 3.5 mAh / cm ２ ~7.5mAh / cm ２ The secondary battery according to claim 1 or 2,

12. The loading capacity of the negative electrode is 4 mAh / cm ２ ~8mAh / cm ２ The secondary battery according to claim 1 or 2,

13. the electrolyte comprises a lithium salt and an organic solvent; The secondary battery according to claim 1 , wherein the organic solvent includes a cyclic carbonate, a linear ester, and a halogen-containing cyclic carbonate.

14. 14. The secondary battery according to claim 13, wherein the organic solvent contains 10% by weight to 50% by weight of the cyclic carbonate, 30% by weight to 80% by weight of the linear ester, and 5% by weight to 30% by weight of the halogen-containing cyclic carbonate.

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