Secondary battery

Abstract

This specification relates to a secondary battery including a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode includes a negative electrode active material layer, and the negative electrode active material layer includes a SiO β (0 < β < 2) oxide and a carbon-based active material, the positive electrode includes a positive electrode active material layer, and the positive electrode active material layer includes small particle active materials with an average particle size (D 50 ) of 3 μm to 10 μm and large particle active materials with an average particle size (D 50 ) of 8 μm to 20 μm, and a secondary battery is provided in which the porosity of the positive electrode active material layer is 19% to 23%.

Description

Technical Field

[0001] The present invention relates to a secondary battery.

[0002] This application claims the benefit of the filing dates of Korean Patent Application No. 10-2022-0133985, filed with the Korean Intellectual Property Office on October 18, 2022, and Korean Patent Application No. 10-2023-0137406, filed with the Korean Intellectual Property Office on October 16, 2023, and all of its contents are incorporated herein.

Background Art

[0003] Secondary batteries with high adaptability according to product groups and having electrical characteristics such as high energy density are widely applied not only to portable devices but also to electric vehicles (EVs), hybrid electric vehicles (HEVs), etc. driven by an electric drive source.

[0004] Such secondary batteries have not only the primary advantage of significantly reducing the use of fossil fuels but also the advantage of generating no by-products from the use of energy, so they are environmentally friendly and are attracting attention as a new energy source for improving energy efficiency.

[0005] Generally, a secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. Also, an active material layer containing a positive electrode active material and a negative electrode active material may be formed on a current collector for the positive electrode and the negative electrode. Generally, LiCoO 2 , LiMn 2 O 4 and other lithium-containing metal oxides are used as the positive electrode active material, and carbon-based compounds, silicon-based compounds, mixtures thereof, etc. are used as the negative electrode active material.

[0006] In recent years, in order to develop a battery that can be rapidly charged and has a high energy density, a carbon-based compound such as graphite and a silicon-based compound are mixed and used in the negative electrode. However, when a silicon-based compound is included, electrode expansion / contraction due to the use of the silicon-based compound occurs at the end of discharge, and as a side reaction, the battery life is shortened and the normal temperature cycle characteristics deteriorate. There is a need to develop a battery to solve such problems.

Summary of the Invention

Problems to be Solved by the Invention

[0007] The present invention provides a secondary battery that improves the battery life and normal temperature cycle characteristics by reducing the intervention of a silicon-based compound (SiO β (0 < β < 2) oxide) at the end of discharge while including the SiO β (0 < β < 2) oxide in the negative electrode active material layer.

[0008] However, the technical problems to be solved by the present invention are not limited to the above-mentioned problems, and other problems not mentioned will be clearly understood by those skilled in the art from the description of the invention described below.

Means for Solving the Problems

[0009] One embodiment of the present invention is a secondary battery including a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode includes a negative electrode active material layer, the negative electrode active material layer includes a SiO β (0 < β < 2) oxide and a carbon-based active material, the positive electrode includes a positive electrode active material layer, the positive electrode active material layer includes a small particle active material having an average particle size (D 50 ) of 3 μm to 10 μm and a large particle active material having an average particle size (D 50 ) of 8 μm to 20 μm, and the porosity of the positive electrode active material layer is 19% to 23%.

Effects of the Invention

[0010] The secondary battery of the present invention has a SiO βWhile containing an oxide (0 < β < 2), the positive electrode active material layer includes a small particle active material with an average particle diameter (D 50 ) of 3 μm to 10 μm and a large particle active material with an average particle diameter (D 50 ) of 8 μm to 20 μm, thereby increasing the positive electrode resistance at the end of discharge. The voltage of the secondary battery is determined by the difference between the positive electrode voltage and the negative electrode voltage. By increasing the positive electrode resistance at the end of discharge, the positive electrode voltage rapidly decreases, and thereby the negative electrode voltage is induced to increase relatively less, reducing the depth of use of the silicon-based compound (SiO β (0 < β < 2) oxide), and a secondary battery with improved life and normal temperature cycle characteristics can be obtained.

[0011] Specifically, in order to reduce the cracking of the active material while increasing the energy density and rolling density of the battery, a single particle nickel-based active material with a high nickel content is used in the positive electrode active material layer. In order to enable rapid charging, when the negative electrode active material layer contains a silicon-based compound such as SiO β (0 < β < 2) oxide, the negative electrode voltage rapidly rises at the end of discharge, and the use of the silicon-based compound (SiO β (0 < β < 2) oxide) contained in the negative electrode active material layer will excessively increase (increase in depth of use), resulting in a decrease in the life performance of the battery. To improve this, the positive electrode active material layer includes a small particle active material with an average particle diameter (D 50 ) of 3 μm to 10 μm and a large particle active material with an average particle diameter (D 50 ) of 8 μm to 20 μm, enabling rapid charging, improving the resistance of the positive electrode, reducing the depth of use of the silicon-based compound (SiO β (0 < β < 2) oxide) due to the voltage difference between the positive electrode and the negative electrode, and obtaining a secondary battery with improved normal temperature life.

Brief Description of the Drawings

[0012]

Figure 1

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Figure 3

Embodiments for Carrying Out the Invention

[0013] Hereinafter, the present invention will be described in detail. The following content is for helping the understanding of the present invention, and the scope of the invention rights is not defined or limited by this.

[0014] In this specification, when a certain part "includes" a certain component, this means that, unless otherwise stated to the contrary, it does not exclude other components, but may further include other components.

[0015] In this specification, when a certain member is located "above" another member, this includes not only the case where a certain member is in contact with another member, but also the case where another member exists between the two members.

[0016] The terms or words used in this specification are not construed as being limited to their ordinary or dictionary meanings. The inventor interprets them in accordance with the meaning and concept that conform to the technical idea of the present invention in accordance with the principle that the inventor can appropriately define the concept of the terms in order to explain his invention in the best way.

[0017] The singular expressions of the terms used in this specification include plural expressions unless the context clearly has a different meaning.

[0018] In this specification, the crystallinity of the structure contained in the active material of the positive electrode or the negative electrode can be confirmed by X-ray diffraction analysis. The X-ray diffraction analysis can be performed using an X-ray diffraction (XRD) analyzer (product name: D4-endavor, manufacturer: bruker). In addition to the said equipment, equipment used in the industry can also be appropriately adopted.

[0019] In this specification, the presence and content of elements in the active material of the positive electrode or negative electrode can be confirmed by ICP (Inductively Coupled Plasma) analysis, and the ICP analysis can be performed using an inductively coupled plasma optical emission spectrometer (ICPAES, Perkin-Elmer 7300).

[0020] In this specification, the "end of discharge" means a region where the SOC (states of charge) of the battery (Full cell) is 10% or less.

[0021] In this specification, "average particle diameter (D 50 )" can be defined as the particle diameter corresponding to 50% of the volume cumulative amount in the particle size distribution curve. The average particle diameter (D 50 ) can be measured using the laser diffraction method. For example, the method for measuring the average particle diameter (D 50 ) of the positive electrode active material is to disperse the particles of the positive electrode active material in a dispersion medium and then introduce them into a commercially available laser diffraction particle size measuring device (for example, LA-960 manufactured by HORIBA). After irradiating with ultrasonic waves of about 28 kHz at an output of 60 W, the average particle diameter (D 50 ) corresponding to 50% of the volume cumulative amount in the measuring device can be calculated.

[0022] In this specification, the "single particle" is a concept contrasted with the secondary particle state formed by the aggregation of dozens to hundreds of primary particles, and means a particle composed of 10 or fewer primary particles. Specifically, in the present invention, the single particle may be a single particle composed of one primary particle or may be in the form of a particle formed by the aggregation of a plurality of primary particles.

[0023] In this specification, the "primary particle" means the smallest unit of the particle recognized when observing the active material through a scanning electron microscope, and the "secondary particle" means a secondary structure formed by the aggregation of dozens to hundreds of primary particles.

[0024] In this specification, "particles" refer to grains in micrometers. When observed under magnification, they can be classified into "grains" with a crystal form in the order of dozens of nanometers. When observed under further magnification, it is possible to confirm separated regions in which atoms form a lattice structure in a certain direction, and these are called "crystallite grains". The size of the particles observed by XRD is defined as the crystallite size. The crystallite size can be quantitatively determined using XRD data through the Scherrer equation.

[0025] The secondary battery of the present invention is a secondary battery including a positive electrode, a negative electrode, a separator, and an electrolyte. The negative electrode includes a negative electrode active material layer, and the negative electrode active material layer includes SiO β (0 < β < 2) oxide and a carbon-based active material. The positive electrode includes a positive electrode active material layer, and the positive electrode active material layer includes small particle active materials with an average particle size (D 50 ) of 3 μm to 10 μm and large particle active materials with an average particle size (D 50 ) of 8 μm to 20 μm.

[0026] In this specification, when the negative electrode active material layer contains SiO β (0 < β < 2) oxide, at the end of discharge, the negative electrode resistance rapidly increases, and the positive electrode resistance using a positive electrode material with low resistance characteristics rapidly decreases. Therefore, the difference between the negative electrode resistance and the positive electrode resistance becomes very large. As a result, the degradation of the negative electrode progresses rapidly, the life of the battery becomes short, and there is a problem that the normal temperature cycle characteristics deteriorate. To solve this problem, small particle active materials with an average particle size (D 50 ) of 3 μm to 10 μm and large particle active materials with an average particle size (D 50 ) of 8 μm to 20 μm are included in the positive electrode active material layer to reduce the rapid decrease in the positive electrode resistance, and a battery with improved life and normal temperature cycle characteristics can be obtained.

[0027] <Positive Electrode> The positive electrode of the present invention includes a positive electrode active material layer, and the positive electrode active material layer includes small particle active materials with an average particle size (D 50 ) of 3 μm to 10 μm and large particle active materials with an average particle size (D 50) contains large particle active material with a size of 8 μm to 20 μm, and the porosity of the positive electrode active material layer is 19% to 23%.

[0028] According to another embodiment of the present invention, the positive electrode active material layer has an average particle size (D 50 ) of small particle active material of 3 μm to 7 μm and an average particle size (D 50 ) of large particle active material of 8 μm to 20 μm, and the porosity of the positive electrode active material layer is 19% to 23%.

[0029] According to one embodiment of the present invention, the small particle active material and the large particle active material each contain 80 mol% or more of nickel based on the total number of moles of transition metals excluding lithium.

[0030] In one embodiment of the present invention, the weight ratio of the small particle active material to the large particle active material (weight of small particle active material: weight of large particle active material) is 2:8 to 8:2. When the content of the large particle active material satisfies the above range, it has the effect of increasing the positive electrode resistance at the end of discharge. When it is outside the above range, there is a problem that it is difficult to adjust the porosity within an appropriate range due to cracking of the large particles.

[0031] According to one embodiment of the present invention, the small particle active material is in the form of single particles.

[0032] According to another embodiment of the present invention, the small particle active material is in the form of single particles in which one or more primary particles are aggregated.

[0033] In one embodiment of the present invention, the large particle active material is in the form of secondary particles.

[0034] The small particle active material and the large particle active material may each independently contain a lithium composite metal oxide containing one or more metals such as cobalt, manganese, nickel or aluminum and lithium. More specifically, a lithium-nickel-manganese-cobalt-based oxide (for example, Li(Ni p Co q Mn r1 )O 2(Here, 0 < p < 1, 0 < q < 1, 0 < r1 < 1, and p + q + r1 = 1) or Li(Ni p1 Co q1 Mn r2 )O 4 (Here, 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, and p1 + q1 + r2 = 2), etc.), lithium-nickel-cobalt-transition metal (M) oxides (e.g., Li(Ni p2 Co q2 Mn r3 M S2 )O 2 (Here, M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and p2, q2, r3, and s2 are the atomic fractions of the respective independent elements, where 0 < p2 < 1, 0 < q2 < 1, 0 ≤ r3 < 1, 0 < s2 < 1, and p2 + q2 + r3 + s2 = 1), etc.), and any one or two or more of these compounds may be included, but are not limited thereto.

[0035] In addition to the aforementioned positive electrode active material layer, the positive electrode may further include a positive electrode current collector. At this time, the positive electrode active material layer is formed on at least one surface of the positive electrode current collector.

[0036] In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those surface-treated with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel can be used. Further, the positive electrode current collector may usually have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive force of the positive electrode active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and non-woven fabrics.

[0037] The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the aforementioned positive electrode active material.

[0038] At this time, the positive electrode conductive material is used to impart conductivity to the electrode, and in the configured battery, it can be used without particular limitation as long as it has electron conductivity without causing a chemical change. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Among these, one kind alone or a mixture of two or more kinds may be used.

[0039] In addition, the positive electrode binder plays a role in improving the adhesion between the positive electrode active material particles and the adhesive force between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVdF), vinylidene fluoride - hexafluoropropylene copolymer (PVdF - coHFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene polymer (EPDM), sulfonated EPDM, styrene - butadiene rubber (SBR), fluororubber, or various copolymers thereof. Among these, one kind alone or a mixture of two or more kinds may be used.

[0040] The positive electrode active material layer may be formed by applying a positive electrode slurry containing a binder and / or a conductive material together with the aforementioned small particle active material and large particle active material onto at least one surface of the positive electrode current collector, followed by drying and rolling.

[0041] The positive electrode slurry according to an embodiment of the present invention may further contain a solvent for forming the positive electrode slurry. Specifically, the solvent for forming the positive electrode slurry may contain N-methylpyrrolidone (NMP) or the like from the aspect of facilitating the dispersion of components.

[0042] In one embodiment of the present invention, the solid content weight of the positive electrode slurry may be 20 parts by weight to 85 parts by weight, specifically 30 parts by weight to 80 parts by weight, based on 100 parts by weight of the total positive electrode slurry.

[0043] According to an embodiment of the present invention, the porosity of the positive electrode is 19% to 23%. When the porosity of the positive electrode is less than 19%, side reactions due to cracking of the positive electrode active material may occur, and the packing density is too high to make sufficient contact with the electrolyte, which may reduce the output characteristics and cycle characteristics of the battery. Conversely, when the porosity of the positive electrode exceeds 23%, there is a problem that the energy density of the battery becomes low. The porosity of the positive electrode can be adjusted by, in addition to the particle size of the positive electrode active material described above, the presence or absence of surface modification of the positive electrode active material, the types of binder and solvent, rolling temperature and pressure, and the like.

[0044] The porosity can be calculated by (1 - (rolling density / true density of the electrode)) × 100 (%). At this time, the rolling density can be calculated as follows.

[0045] Rolling density: After electrode rolling, the weight of the electrode excluding the foil (g) / the volume of the electrode excluding the foil (sample area × electrode layer thickness, cm 3 )

[0046] Here, since the rolling density is the density in the state before the electrode is put into the battery and activated (charged or discharged) after electrode rolling, it has the same meaning as the density of the active material layer of the electrode used in the production of the electrode assembly or the density of the active material layer of the electrode contained in the battery.

[0047] The electrode volume excluding the foil means the total volume including pores inside the electrode and is calculated by the product of the unit area of the sample and the thickness of the electrode layer after roll press.

[0048] The true density of the electrode is the intrinsic density of the electrode active material and can be measured by XRD Rietveld refinement.

[0049] <Negative electrode> The negative electrode according to an embodiment of the present invention includes a negative electrode active material layer, and the negative electrode active material layer contains SiO β (0 < β < 2) oxides and carbon-based active materials.

[0050] The negative electrode may further include a negative electrode current collector in addition to the negative electrode active material layer described above. At this time, the negative electrode active material layer is formed on at least one surface of the negative electrode current collector. The negative electrode active material layer contains SiO β (0 < β < 2) oxides and carbon-based active materials. Further, the negative electrode active material layer may further include a binder and / or a conductive material.

[0051] According to an embodiment of the present invention, the carbon-based active material may be artificial graphite, natural graphite, carbon black, or the like.

[0052] According to an embodiment of the present invention, the carbon-based active material can be used without particular limitation, and typical examples thereof include crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite and artificial graphite. Examples of the amorphous carbon include soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, and calcined coke. The graphite may be natural graphite, artificial graphite, or a mixture thereof. With respect to 100 parts by weight of the total negative electrode active material contained in the negative electrode active material layer, the carbon-based active material may be contained in an amount of 60 parts by weight or more and 99 parts by weight or less.

[0053] According to one embodiment of the present invention, the negative electrode active material layer may contain an active material containing SiO β (0 < β < 2) oxide and a carbon-based active material, and the active material containing SiO β (0 < β < 2) oxide may be silicon-based composite particles containing SiO β (0 < β < 2) and pores.

[0054] The SiO β (0 < β < 2) corresponds to a matrix within the silicon-based composite particles. The SiO β (0 < β < 2) may be in a form containing Si and SiO 2 , and the Si may form a phase. That is, the β corresponds to the number ratio of O to Si contained in the SiO β (0 < β < 2). When the silicon-based composite particles contain the SiO β (0 < β < 2), the discharge capacity of the secondary battery can be improved.

[0055] The silicon-based composite particles may further contain at least one of an Mg compound and an Li compound. The Mg compound and the Li compound can correspond to a matrix within the silicon-based composite particles.

[0056] The Mg compound and / or the Li compound may be present inside and / or on the surface of the SiO β (0 < β < 2). The initial efficiency of the battery can be improved by the Mg compound and / or the Li compound.

[0057] The Mg compound may contain at least one selected from the group consisting of Mg silicate, Mg silicide, and Mg oxide. The Mg silicate may contain at least one of Mg 2 SiO 4 and MgSiO 3 . The Mg silicide is Mg 2It may contain Si. The Mg oxide may contain MgO.

[0058] In one embodiment of the present specification, the Mg element is the SiO β (0 < β < 2) It may be contained in an amount of 0.1% by weight to 20% by weight, based on 100% by weight of the total active material including the oxide, and may be contained in an amount of 0.1% by weight to 10% by weight. Specifically, the Mg element may be contained in an amount of 0.5% by weight to 8% by weight or 0.8% by weight to 4% by weight. When the above range is satisfied, the Mg compound can be contained in an appropriate content in the active material containing the SiO β (0 < β < 2) oxide, so that the volume change of the silicon-based active material during charging and discharging of the battery can be easily suppressed, and the discharge capacity and initial efficiency of the battery can be improved.

[0059] The Li compound may contain at least one selected from the group consisting of Li silicate, Li silicide, and Li oxide. The Li silicate may contain at least one of Li 2 SiO 3 , Li 4 SiO 4 , and Li 2 Si 2 O 5 The Li silicide may contain Li 7 Si 2 The Li oxide may contain Li 2 O.

[0060] In one embodiment of the present invention, the Li compound may contain the form of lithium silicate. The lithium silicate is represented by Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and can be classified into crystalline lithium silicate and amorphous lithium silicate. The crystalline lithium silicate is Li 2 SiO 3 , Li 4 SiO 4 and Li 2 Si 2O 5 It can exist in the form of at least one lithium silicate selected from the group consisting of, and the amorphous lithium silicate is Li a Si b O c (2 ≦ a ≦ 4, 0 < b ≦ 2, 2 ≦ c ≦ 5), and is not limited to the above form.

[0061] In one embodiment of the present specification, the Li element may be contained in an amount of 0.1 wt% to 20 wt%, or may be contained in an amount of 0.1 wt% to 10 wt%, based on 100 wt% of the total active material including the SiO β (0 < β < 2) oxide. Specifically, the Li element may be contained in an amount of 0.5 wt% to 8 wt%, and more specifically, may be contained in an amount of 0.5 wt% to 4 wt%. When the above range is satisfied, the Li compound can be contained in an appropriate content in the silicon-based active material, the change in the volume of the negative electrode active material during charging and discharging of the battery can be easily suppressed, and the discharge capacity and initial efficiency of the battery can be improved.

[0062] The content of the Mg element or Li element can be confirmed by ICP analysis. After accurately sampling a certain amount (about 0.01 g) of the negative electrode active material for the ICP analysis, it is transferred to a platinum crucible, nitric acid, hydrofluoric acid, and sulfuric acid are added, and it is completely decomposed on a hot plate. Then, using an inductively coupled plasma atomic emission spectrometer (ICPAES, Perkin-Elmer 7300), the intensity of a standard solution (5 mg / kg) prepared using a standard solution at the specific wavelength of the Mg element or Li element is measured to create a calibration curve. Then, the pretreated sample solution and the matrix sample are introduced into the instrument, the intensity of each is measured to calculate the actual intensity, the concentration of each component is calculated by comparing with the created calibration curve, and then it is converted so that the total sum becomes the theoretical value, and the Mg element or Li element content of the active material including the SiO β (0 < β < 2) oxide can be analyzed.

[0063] In one embodiment of the present specification, a carbon layer may be provided on the surface and / or inside the pores of the silicon-based composite particles. The carbon layer imparts conductivity to the silicon-based composite particles, and the initial efficiency, life characteristics, and battery capacity characteristics of a secondary battery including a negative electrode active material containing the silicon-based composite particles can be improved. The total weight of the carbon layer may be included in an amount of 5% to 40% based on 100% by weight of the silicon-based composite particles in total.

[0064] In one embodiment of the present specification, the carbon layer may include at least one of amorphous carbon and crystalline carbon.

[0065] Also, according to one embodiment of the present invention, the SiO β (0 < β < 2) oxide is included in an amount of 1 part by weight to 15 parts by weight, preferably 1 part by weight to 10 parts by weight, more preferably 5 parts by weight to 10 parts by weight based on 100 parts by weight of the negative electrode active material. When the content of the SiO β (0 < β < 2) oxide satisfies the above range, it has an improved effect in terms of energy density and cell resistance, has less volume expansion during charge / discharge, and also has an excellent effect in terms of life.

[0066] The negative electrode active material layer may be formed by applying a negative electrode slurry containing a binder and / or a conductive material together with the SiO β (0 < β < 2) oxide and a carbon-based active material onto at least one surface of a negative electrode current collector, followed by drying and rolling.

[0067] According to one embodiment of the present specification, the negative electrode slurry may further include an additional negative electrode active material in addition to the aforementioned SiO β (0 < β < 2) oxide and the carbon-based active material.

[0068] The negative current collector only needs to have conductivity without inducing chemical changes in the battery, and is not particularly limited. For example, as the current collector, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel can be used. Specifically, transition metals that can well adsorb carbon such as copper and nickel can be used as the current collector. The thickness of the current collector can be 6 μm to 20 μm, but the thickness of the current collector is not limited thereto.

[0069] The binder may include at least one selected from the group consisting of polyvinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene - propylene - diene monomer (EPDM), sulfonated EPDM, styrene - butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which their hydrogens are substituted with Li, Na, or Ca, etc., and may also include various copolymers thereof.

[0070] The conductive material is not particularly limited as long as it has conductivity without inducing chemical changes in the battery. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; fluorocarbon powder; metal powders such as aluminum and nickel powders; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives can be used.

[0071] The negative electrode slurry may further contain a thickening agent such as Na-CMC (Sodium carboxymethyl cellulose), Li-CMC (Carboxymethyl cellulose lithium), CNF (Cellulose nano fiber).

[0072] The negative electrode slurry according to an embodiment of the present invention may further contain a solvent for forming the negative electrode slurry. Specifically, the solvent for forming the negative electrode slurry is at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol in terms of facilitating the dispersion of components, and specifically, may contain distilled water.

[0073] In one embodiment of the present invention, the solid content weight of the negative electrode slurry may be 20 to 75 parts by weight, specifically 30 to 70 parts by weight based on 100 parts by weight of the total negative electrode slurry.

[0074] <Secondary battery> The secondary battery according to an embodiment of the present invention may include a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. Since the positive electrode and the negative electrode have been described above, specific descriptions are omitted.

[0075] The separation membrane is used to separate the negative electrode and the positive electrode and provide a migration path for lithium ions. Generally, any material that can be used as a separation membrane in a secondary battery can be used without particular limitation. In particular, it is preferably low in resistance to the ion migration of the electrolyte while being excellent in the ability to hold the electrolyte solution in a moist state. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as a homopolymer of ethylene, a homopolymer of propylene, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof may be used. Further, a normal porous nonwoven fabric, for example, a nonwoven fabric made of high-melting glass fibers, polyethylene terephthalate fibers, etc. may be used. Further, in order to ensure heat resistance or mechanical strength, a coated separation membrane containing a ceramic component or a polymer substance can also be used, and it may be selectively used in a single-layer or multilayer structure.

[0076] Examples of the electrolyte include, but are not limited to, 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 the manufacture of lithium secondary batteries.

[0077] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0078] Examples of the non-aqueous organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate, etc. may be used.

[0079] In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, are high-viscosity organic solvents and have a high dielectric constant, which can dissociate lithium salts well, so they are preferably used. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constant such as dimethyl carbonate and diethyl carbonate in an appropriate ratio and used, an electrolyte having high electrical conductivity can be produced and can be more preferably used.

[0080] As the metal salt, a lithium salt can be used. The lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte. For example, as the anion of the lithium salt, F - , Cl - , I - , NO 3 - , N(CN) 2 - , BF 4 - , ClO 4 - , PF 6 - , (CF 3 ) 2 PF 4 - , (CF 3 )3 PF 3 - ,(CF 3 ) 4 PF 2 - ,(CF 3 ) 5 PF - ,(CF 3 ) 6 P - ,CF 3 SO 3 - ,CF 3 CF 2 SO 3 - ,(CF 3 SO 2 ) 2 N - ,(FSO 2 ) 2 N - ,CF 3 CF 2 (CF 3 ) 2 CO - ,(CF 3 SO 2 ) 2 CH - ,(SF 5 ) 3 C - ,(CF 3 SO 2 ) 3 C - ,CF 3 (CF 2 ) 7 SO 3 - ,CF 3 CO 2 - ,CH 3 CO 2 - ,SCN - and (CF 3 CF 2 SO 2 ) 2 N - One or more selected from the group consisting of can be used.

[0081] In addition to the electrolyte constituent components, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, triamide hexaline, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride for the purpose of improving the life characteristics of the battery, suppressing the reduction of the battery capacity, and improving the discharge capacity of the battery.

[0082] According to another embodiment of the present invention, there are provided a battery module including the secondary battery as a unit cell and a battery pack including the same. Since the battery module and the battery pack include the secondary battery having a high capacity, high life characteristics, and cycle characteristics, they can be used as a power source for medium to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0083] Hereinafter, preferred examples are presented to assist in understanding the present invention. However, it is obvious to those skilled in the art that the examples are illustrative of the description and various changes and modifications are possible within the scope of the description and the scope of the technical idea. It is natural that such variations and modifications belong to the scope of the appended claims.

[0084] <Cell Fabrication> Example 1. As the positive electrode active material, an NCMA (nickel-cobalt-manganese-aluminum) large particle positive electrode material with an average particle size (D 50 ) of 10 μm and an Ni content of 87 mol% and an average particle size (D 50) was mixed with a single - particle NCM cathode material with a Ni content of 86 mol% and a particle size of 5 μm at a weight ratio of 5:5. As a conductive material, CNT (carbon nanotube) was used, acrylate as a dispersant, and PVdF as a binder were added to N - methylpyrrolidone (NMP) as a solvent at a weight ratio of 97:1:0.4:1.6 to prepare a cathode slurry.

[0085] Next, using a slot die, the cathode slurry was coated / dried on one side of an aluminum current collector with a thickness of 12 μm, and then rolled by a roll - press method to produce a cathode with a porosity of 22% and a thickness of 125.6 μm.

[0086] As a negative - electrode active material, a mixture of artificial graphite, natural graphite, and SiO (70 wt%:22 wt%:8 wt%) was used. As a conductive material, carbon black and CNT were used, SBR as a binder, and CMC as a thickener were added to distilled water as a solvent at a weight ratio of 95:1:2:3 to produce a negative - electrode slurry. The negative - electrode slurry was coated on a copper current collector with a thickness of 6 μm, and dried and rolled under the same conditions as the cathode to produce a negative electrode.

[0087] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a composition of 30:70 (volume ratio). As additives, tetravinylsilane, ethylene sulfate, 1,3 - propenesultone, lithium difluorophosphate, LiBF 4 were mixed, and a non - aqueous electrolyte in which 1.0 M of LiPF 6 was dissolved was produced.

[0088] After interposing a separation membrane for stability enhancement (SRS (Safety Reinforced Separator), 12 μm) between the cathode and the negative electrode, the electrolyte was injected to manufacture a lithium secondary battery.

[0089] Example 2. The cathode of Example 1 was punched out to a size of 3 cm×4 cm, and the negative electrode was punched out to a size of 3.1 cm×4.1 cm to form a cathode and a negative electrode. Between them, the separation membrane - LTO (Li4 Ti 5 O 12 ) After interposing a wire-separation membrane, a diluted electrolyte solution was injected to manufacture a lithium secondary battery having a three-electrode system. The LTO wire was manufactured by coating a slurry prepared by adding LTO as an active material, carbon black as a conductive material, and PVdF as a binder in a weight ratio of 38.2:2.7:59.1 to NMP as a solvent onto a copper wire and then drying at 130°C, and was utilized as a reference electrode.

[0090] Comparative Example 1. A lithium secondary battery with a cathode porosity of 22% was manufactured in the same manner as in Example 1, except that an NCM single-particle cathode material with an average particle size (D 50 ) of 5 μm and an Ni content of 86% was used as the cathode material.

[0091] Comparative Example 2. A lithium secondary battery with a cathode porosity of 22% was manufactured in the same manner as in Example 2, except that an NCM single-particle cathode material with an average particle size (D 50 ) of 5 μm and an Ni content of 86% was used as the cathode material.

[0092] Comparative Example 3. For a cathode material having the same composition as in Example 1, after rolling in a rolling process, the thickness of the electrode was increased to 132.2 μm compared to Example 1 to manufacture a cathode material with a porosity of 26%, and a lithium secondary battery was manufactured in the same manner as in Example 1.

[0093] Figure 1 is a graph showing the cycle life characteristics measured at room temperature with a 0.33C charge and 0.5C discharge in the lithium secondary batteries manufactured in Example 1 and Comparative Example 1. During charging, it starts in the CC mode and then changes to CV and is set to be cut off at 4.2V and 0.05C. During discharging, it is set to be cut off at 2.8V in the CC mode. In Figure 1, it can be confirmed that the life characteristics of the lithium secondary battery manufactured in Example 1 are improved compared to the lithium secondary battery manufactured in Comparative Example 1. In Figure 1, Blended cathode5:5 shows the graph of Example 1, and Single crystaline cathode100% shows the graph of Comparative Example 1.

[0094] Figure 2 is a graph showing the voltage curves in the discharge situation of the three - electrode system secondary batteries manufactured in Example 2 and Comparative Example 2. In Figure 2, the first from the left shows the voltage of the secondary battery, the second shows the voltage of the positive electrode, and the third shows the voltage of the negative electrode. The discharge was carried out at 0.33C in the CC mode until the secondary battery voltage reached 2.5V. From the positive - electrode voltage curve in Figure 2, it can be seen that the voltage of Example 2 drops more rapidly than that of Comparative Example 2 at the end of discharge. Since the negative electrodes of Example 2 and Comparative Example 2 are the same, it can be understood that the positive electrode of Example 2 has a relatively high resistance at the end of discharge. Since the voltage of the secondary battery is determined by the voltage difference between the positive and negative electrodes, in Example 2, due to the voltage drop of the positive electrode, it can be seen that the increase in the negative - electrode voltage at the end of discharge is suppressed, and from this, it can be seen that the depth of use of the silicon - based compound (SiO β (0 < β < 2) oxide) decreases. In Figure 2, Blended cathode5:5 shows the graph of Example 2, and Single crystaline cathode100% shows the graph of Comparative Example 2.

[0095] Figure 3 is a graph showing the cycle life characteristics measured at room temperature with 0.33C charge and 0.5C discharge in the lithium secondary batteries manufactured in Example 1, Comparative Example 1, and Comparative Example 3. During charging, it starts in the CC mode and then changes to CV and is set to cut off at 4.2V and 0.05C. During discharging, it is set to cut off at 2.5V in the CC mode. From Figure 3, it was confirmed that the lithium secondary battery manufactured in Comparative Example 3 has inferior life characteristics compared to the lithium secondary battery manufactured in Example 1.

[0096] In Figure 3, the graph of Blended cathode 5:5 p22% shows Example 1, Single crystaline cathode 100% shows Comparative Example 1, and Blended cathode 5:5 p26% shows Comparative Example 3.

Claims

**Claim 1** A secondary battery including a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the negative electrode includes a negative electrode active material layer, The negative electrode active material layer contains SiO β oxide (0 < β < 2) and a carbon-based active material, the positive electrode includes a positive electrode active material layer, The positive electrode active material layer has a small particle active material with an average particle diameter (D ５０ ) of 3 μm to 10 μm and a large particle active material with an average particle diameter (D ５０ ) of 8 μm to 20 μm, and and the porosity of the positive electrode active material layer is 19% to 23%. The secondary battery. **Claim 2** The secondary battery according to claim 1, wherein the small particle active material and the large particle active material each contain 80 mol% or more of nickel with respect to the total number of moles of transition metals excluding lithium. **Claim 3** The secondary battery according to claim 1, wherein the small particle active material is in a single particle state. **Claim 4** The SiO β (0 < β < 2) oxide is included in an amount of 1 part by weight to 15 parts by weight based on 100 parts by weight of the negative electrode active material of the negative electrode active material layer, and the secondary battery according to claim 1. **Claim 5** The secondary battery according to claim 1, wherein the weight ratio of the small particle active material to the large particle active material (weight of small particle active material: weight of large particle active material) is 2:8 to 8:2.

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