Secondary batteries

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 date 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, the entire contents of which are incorporated herein by reference. [Background technology]

[0003] Secondary batteries, which are highly adaptable to various product groups and have electrical properties such as high energy density, are widely used not only in portable devices but also in electric vehicles (EVs) and hybrid electric vehicles (HEVs), which are powered by electrical sources.

[0004] Such secondary batteries not only have the primary advantage of dramatically reducing the use of fossil fuels, but also have the advantage of not producing any by-products from energy use, making them environmentally friendly and drawing 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. The positive electrode and the negative electrode may each have an active material layer formed on a current collector, the active material layer including a positive electrode active material and a negative electrode active material. Generally, the positive electrode uses a lithium-containing metal oxide such as LiCoO2 or LiMn2O4 as the positive electrode active material, while the negative electrode uses a carbon-based compound, a silicon-based compound, or a mixture thereof as the negative electrode active material.

[0006] In recent years, in order to develop batteries that are capable of rapid charging and have high energy density, carbon-based compounds such as graphite have been mixed with silicon-based compounds in the anode. However, when silicon-based compounds are used, the electrode expands / contracts due to the use of silicon-based compounds at the end of discharge, resulting in side reactions that shorten the battery's lifespan and reduce room temperature cycle characteristics. Therefore, there is a need to develop a battery that solves these problems. Summary of the Invention [Problem to be solved by the invention]

[0007] In the present invention, the negative electrode active material layer contains SiO β (0<β<2) oxides, but silicon-based compounds (SiO β By reducing the involvement of (0<β<2) oxides, a secondary battery with improved battery life and room temperature cycle characteristics is provided.

[0008] However, the technical problems that the present invention aims to solve 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 problem]

[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, and the negative electrode active material layer is made of SiO β (0<β<2) oxide and a carbon-based active material, and the positive electrode includes a positive electrode active material layer, and the positive electrode active material layer has an average particle diameter (D 50 ) of 3 μm to 10 μm and small particle active material with an average particle size (D 50 ) contains large particle active material 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 negative electrode active material layer containing SiO β(0<β<2) oxides are contained in the positive electrode active material layer, but the average particle size (D 50 ) of 3 μm to 10 μm and small particle active material with an average particle size (D 50 The positive electrode resistance at the end of discharge can be increased by including a large particle active material of 8 μm to 20 μm. The voltage of a 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 decreases rapidly, and this leads to a relatively small increase in the negative electrode voltage. β By reducing the depth of use of the (0<β<2) oxide, a secondary battery with improved life and room temperature cycle characteristics can be obtained.

[0011] Specifically, to increase the energy density and rolling density of the battery while reducing cracking of the active material, a single-particle nickel-based active material with a high nickel content is used in the positive electrode active material layer, and SiO is used in the negative electrode active material layer to enable rapid charging. β When silicon-based compounds such as (0<β<2) oxides are included, the negative electrode voltage rises sharply at the end of discharge. β This results in an excessive increase in the amount of (0<β<2) oxides (increased depth of use), which leads to a decrease in the battery life performance. 50 ) of 3 μm to 10 μm and small particle active material with an average particle size (D 50 ) contains large particles of active material of 8μm to 20μm, enabling rapid charging, and the resistance of the positive electrode is improved, and the voltage difference between the positive electrode and the negative electrode is reduced by the silicon-based compound (SiO β By reducing the depth of use of the (0<β<2) oxide, a secondary battery with improved room temperature life can be obtained. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a graph showing the cycle life characteristics of the lithium secondary batteries manufactured in Example 1 and Comparative Example 1, which were charged at 0.33 C and discharged at 0.5 C at room temperature. [Figure 2]FIG. 10 is a diagram showing voltage curves during discharge of the three-electrode system secondary batteries manufactured in Example 2 and Comparative Example 2. [Figure 3] FIG. 2 is a graph showing the results of measuring the cycle life characteristics of the lithium secondary batteries produced in Example 1 and Comparative Examples 1 and 3. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below. The following description is provided to aid in understanding the present invention, and is not intended to limit or define the scope of the invention.

[0014] In this specification, when a part is said to "comprise" a certain component, this means that it may further include other components, rather than excluding other components, unless specifically stated to the contrary.

[0015] In this specification, when a member is said to be located "on" another member, this includes not only when the member is in contact with the other member, but also when there is another member between the two members.

[0016] The terms or words used in this specification should not be construed as being limited to their ordinary or dictionary meanings, but should be construed in a meaning and concept that is consistent with the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to best explain his / her invention.

[0017] As used herein, the singular expression of a term includes the plural expression unless the context clearly dictates otherwise.

[0018] In this specification, the crystallinity of the structure contained in the positive or negative electrode active material can be confirmed by X-ray diffraction analysis. X-ray diffraction analysis can be performed using an X-ray diffraction (XRD) analysis device (product name: D4-Endavor, manufacturer: Bruker), and in addition to the above device, any device used in the art can be appropriately adopted.

[0019] In this specification, the presence or absence of elements and the content of elements in the active material of the positive 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 term "end of discharge" refers to a region where the SOC (states of charge) of a full cell is 10% or less.

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

[0022] In this specification, the term "single particle" is a concept that contrasts with secondary particles formed by aggregation of tens to hundreds of primary particles, and refers to a particle consisting of 10 or less primary particles. Specifically, in the present invention, the single particle may be a single particle consisting of one primary particle, or may be in the form of a particle formed by aggregation of multiple primary particles.

[0023] In this specification, the term "primary particle" refers to the smallest particle unit that can be recognized when observing an active material through a scanning electron microscope, and the term "secondary particle" refers to a secondary structure formed by aggregation of several tens to several hundreds of primary particles.

[0024] In this specification, "particle" refers to a particle measured in micrometers, which, when observed under magnification, can be divided into "grains" with crystalline forms measured in units of several tens of nanometers. Further magnification reveals separate regions in which atoms form a lattice structure in a specific direction, which are called "crystal grains." The size of particles observed by XRD is defined as the crystal grain size. Crystal grain size can be quantitatively determined using the Scherrer equation from XRD data.

[0025] The secondary battery 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, and the negative electrode active material layer is made of 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 has an average particle size (D 50 ) of 3 μm to 10 μm and small particle active material with an average particle size (D 50 ) contains large particles of active material of 8 μm to 20 μm.

[0026] In this specification, the negative electrode active material layer is SiO β When a battery contains a (0<β<2) oxide, the negative electrode resistance rises sharply at the end of discharge, while the positive electrode resistance drops sharply when a low-resistance positive electrode material is used. This results in a large difference between the negative and positive electrode resistances. This causes rapid degradation of the negative electrode, shortens the battery life, and reduces the room-temperature cycle characteristics. To solve this problem, the positive electrode active material layer is made of an average particle size (D 50 ) of 3 μm to 10 μm and small particle active material with an average particle size (D 50 ) contains large particle active material with a particle size of 8 μm to 20 μm, it is possible to reduce the sudden decrease in the positive electrode resistance and obtain a battery with improved life and room temperature cycle characteristics.

[0027] <Positive electrode> The positive electrode of the present invention includes a positive electrode active material layer, and the positive electrode active material layer has an average particle diameter (D 50 ) of 3 μm to 10 μm and small particle active material with an average particle size (D 50) contains large particle active material 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 3 μm to 7 μm and small particle active material with an average particle size (D 50 ) contains 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 relative to 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 the small particle active material:weight of the large particle active material) is 2:8 to 8:2. When the content of the large particle active material is within this range, the positive electrode resistance at the end of discharge is increased, but when it is outside this range, 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 a single particle.

[0032] According to another embodiment of the present invention, the small particle active material is in the form of a single particle formed by agglomeration of one or more primary particles.

[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 comprise a lithium composite metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. More specifically, a lithium-nickel-manganese-cobalt-based oxide (e.g., Li(Ni p Co q Mn r1)O2 (where 0 < p < 1, 0 < q < 1, 0 < r1 < 1, p + q + r1 = 1) or Li(Ni p1 Co q1 Mn r2 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r2 < 2, p1 + q1 + r2 = 2), etc.), lithium-nickel-cobalt-transition metal (M) oxides (e.g., Li(Ni p2 Co q2 Mn r3 M S2 )O2 (where 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, 0 < p2 < 1, 0 < q2 < 1, 0 ≤ r3 < 1, 0 < s2 < 1, and p2 + q2 + r3 + s2 = 1), etc.), etc. Examples include, but are not limited to, any one or two or more of these compounds.

[0035] In addition to the above-described positive electrode active material layer, the positive electrode may further include a positive electrode current collector. In this case, 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 can 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, non-woven fabrics, etc.

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

[0038] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without any particular limitation as long as it has electronic conductivity without undergoing chemical changes in the battery that is constructed. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives, and the like, and these may be used alone or in combination of two or more.

[0039] The positive electrode binder serves to improve adhesion between particles of the positive electrode active material and 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, and various copolymers thereof. These may be used alone or in combination.

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

[0041] The cathode slurry according to an embodiment of the present invention may further include a solvent for forming the cathode slurry. Specifically, the solvent for forming the cathode slurry may include methylpyrrolidone (NMP) to facilitate 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 a total of 100 parts by weight of the positive electrode slurry.

[0043] According to one embodiment of the present invention, the porosity of the positive electrode is 19% to 23%. If the porosity of the positive electrode is less than 19%, side reactions may occur due to cracking of the positive electrode active material, and the packing density may be too high to allow sufficient contact with the electrolyte, resulting in a decrease in the output characteristics and cycle characteristics of the battery. Conversely, if the porosity of the positive electrode exceeds 23%, the energy density of the battery may be reduced. The porosity of the positive electrode can be adjusted by the particle size of the positive electrode active material, whether or not the positive electrode active material is surface-modified, the type of binder and solvent, the rolling temperature and pressure, etc.

[0044] The porosity can be calculated by (1-(rolled density / true electrode density)) x 100 (%). In this case, the rolled 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, the rolling density is the density of the electrode after rolling and before it is inserted into a battery and activated (charged or discharged), and therefore has the same meaning as the density of the active material layer of the electrode used to prepare 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 the pores inside the electrode, and is calculated as the product of the unit area of ​​the sample and the thickness of the electrode layer after roll pressing.

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

[0049] <Negative electrode> According to one embodiment of the present invention, there is provided a negative electrode comprising a negative electrode active material layer, the negative electrode active material layer comprising SiO β (0<β<2) Includes 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, and in this case, the negative electrode active material layer is formed on at least one surface of the negative electrode current collector. β (0<β<2) The negative electrode active material layer may further include a binder and / or a conductive material.

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

[0052] According to one embodiment of the present invention, the carbon-based active material may be used without any particular limitation. Representative examples thereof include crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite and artificial graphite. Examples of 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. The carbon-based active material may be included in an amount of 60 to 99 parts by weight based on 100 parts by weight of the total negative electrode active material contained in the negative electrode active material layer.

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

[0054] The SiO β (0<β<2) corresponds to the matrix in the silicon-based composite particles. β (0<β<2) may be in a form containing Si and SiO2, and the Si may form a phase. That is, the β is the SiO β The ratio of the number of O to Si falls within the range of (0<β<2). β When (0<β<2) is included, the discharge capacity of the secondary battery can be improved.

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

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

[0057] The Mg compound may include at least one selected from the group consisting of Mg silicate, Mg silicide, and Mg oxide. The Mg silicate may include at least one of Mg2SiO4 and MgSiO3. The Mg silicide may include Mg2Si. The Mg oxide may include MgO.

[0058] In one embodiment of the present specification, the Mg element is in the SiO β (0 < β < 2) oxide, and may be contained in an amount of 0.1% to 20% by weight, or may be contained in an amount of 0.1% to 10% by weight, based on 100% by weight of the total active material including the oxide. Specifically, the Mg element may be contained in an amount of 0.5% to 8% by weight or 0.8% to 4% by weight. When the above range is satisfied, the Mg compound can be contained in an appropriate content within the active material including the SiO β (0 < β < 2) oxide. Therefore, 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 include at least one selected from the group consisting of Li silicate, Li silicide, and Li oxide. The Li silicate may include at least one of Li2SiO3, Li4SiO4, and Li2Si2O5. The Li silicide may include Li7Si2. The Li oxide may include Li2O.

[0060] In one embodiment of the present invention, the Li compound may include a lithium silicate form. 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 can exist in the form of at least one lithium silicate selected from the group consisting of Li2SiO3, Li4SiO4, and Li2Si2O5 within the silicon-based composite particles. The amorphous lithium silicate may be in the form of 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 is in the SiO βThe (0<β<2) oxide-containing active material may contain 0.1 wt % to 20 wt %, or 0.1 wt % to 10 wt %, based on a total of 100 wt % of the active material. Specifically, the Li element may be contained in an amount of 0.5 wt % to 8 wt %, or more specifically, 0.5 wt % to 4 wt %. When this range is satisfied, the Li compound can be contained in the silicon-based active material in an appropriate amount, which can easily suppress volumetric changes in the negative electrode active material during battery charge and discharge, thereby improving the battery's discharge capacity and initial efficiency.

[0062] The Mg or Li element content can be confirmed by ICP analysis. For the ICP analysis, a fixed amount (approximately 0.01 g) of the negative electrode active material is accurately taken and transferred to a platinum crucible. Nitric acid, hydrofluoric acid, and sulfuric acid are added and the mixture is completely decomposed on a hot plate. Then, an inductively coupled plasma emission spectroscope (ICPAES, Perkin-Elmer 7300) is used to measure the intensity of a standard solution prepared using a standard solution (5 mg / kg) at the wavelength specific to Mg or Li element, and a reference calibration curve is created. The pretreated sample solution and the base sample are then introduced into the instrument, and their respective intensities are measured to calculate the actual intensities. The concentrations of each component are calculated relative to the created calibration curve, and the SiO was prepared by converting the total to the theoretical value. β The Mg element or Li element content of the active material containing the (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 may impart conductivity to the silicon-based composite particles, thereby improving 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. The total weight of the carbon layer may be 5 wt % to 40 wt % based on 100 wt % of the silicon-based composite particles.

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

[0065] According to one embodiment of the present invention, the SiO β The (0<β<2) oxide is contained in an amount of 1 to 15 parts by weight, preferably 1 to 10 parts by weight, and more preferably 5 to 10 parts by weight, based on 100 parts by weight of the negative electrode active material. β (0<β<2) When the oxide content is within this range, the energy density and cell resistance are improved, and the volume expansion that occurs during charge / discharge is small, resulting in an excellent lifespan.

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

[0067] According to one embodiment of the present specification, the negative electrode slurry contains the above-mentioned SiO β In addition to the (0<β<2) oxide and the carbon-based active material, an additional negative electrode active material may be further included.

[0068] The negative electrode current collector is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. For example, the current collector can be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like. Specifically, transition metals that adsorb carbon well, 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 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 hydrogen is substituted with Li, Na, Ca, or the like, or may include various copolymers thereof.

[0070] The conductive material is not particularly limited as long as it does not induce chemical changes in the battery and has conductivity. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; fluorocarbon powder; metal powder such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used.

[0071] The negative electrode slurry may further include a thickener such as sodium carboxymethyl cellulose (Na-CMC), carboxymethyl cellulose lithium (Li-CMC), or cellulose nanofiber (CNF).

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

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

[0074] <Secondary battery> A 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, detailed description thereof will be omitted.

[0075] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without limitation. It is particularly preferable that the separator has low resistance to electrolyte ion movement and excellent electrolyte humidification capability. 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, can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material can also be used, and it can be used in a single-layer or multi-layer 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 manufacturing lithium secondary batteries.

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

[0078] Examples of the non-aqueous organic solvent that may be used 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, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

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

[0080] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, the anion of the lithium salt may be F - , Cl - , I - , NO3 -, N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more selected from the group consisting of:

[0081] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving the discharge capacity of the battery.

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

[0083] In the following, preferred embodiments are presented to aid in understanding the present invention, but these embodiments are merely illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the present invention and the technical spirit of the present invention. Such changes and modifications are naturally intended to fall within the scope of the appended claims.

[0084] <Cel production> Example 1 The average particle size (D 50 ) of 10 μm and NCMA (nickel-cobalt-manganese-aluminum) large particle cathode material with 87 mol% Ni content and average particle size (D 50 The cathode material was made by mixing NCM single particle cathode material with a Ni content of 86 mol% and a diameter of 5 μm in a weight ratio of 5:5, and CNT (carbon nanotube) as a conductive material, acrylate as a dispersant, and PVdF as a binder in a weight ratio of 97:1:0.4:1.6 to methylpyrrolidone (NMP) as a solvent to prepare a cathode slurry.

[0085] Next, the positive electrode slurry was coated on one side of an aluminum current collector having a thickness of 12 μm using a slot die, dried, and then rolled using a roll press method to prepare a positive electrode having a porosity of 22% and a thickness of 125.6 μm.

[0086] A negative electrode slurry was prepared by adding a mixture of artificial graphite, natural graphite, and SiO (70 wt%:22 wt%:8 wt%) as the negative electrode active material, carbon black and CNT as the conductive material, SBR as the binder, and CMC as the thickener in a weight ratio of 95:1:2:3 to distilled water as the solvent. The negative electrode slurry was coated onto a 6 μm thick copper current collector, and then dried and rolled under the same conditions as the positive electrode to prepare the negative electrode.

[0087] A non-aqueous electrolyte was prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a 30:70 (volume ratio) organic solvent with additives such as tetravinylsilane, ethylene sulfate, 1,3-propene sultone, lithium difluorophosphate, and LiBF4, and dissolving 1.0 M LiPF6.

[0088] A safety reinforced separator (SRS, 12 μm) was interposed between the positive electrode and the negative electrode, and the electrolyte was injected to prepare a lithium secondary battery.

[0089] Example 2. The positive electrode of Example 1 was punched out to a size of 3 cm x 4 cm, and the negative electrode was punched out to a size of 3.1 cm x 4.1 cm to form a positive electrode and a negative electrode. The separator of Example 1 - LTO (Li4Ti5O 12 A lithium secondary battery with a three-electrode system was fabricated by inserting a wire-separator and injecting a diluted electrolyte. The LTO wire was used as a reference electrode. It was fabricated by coating a copper wire with a slurry prepared by adding LTO as an active material, carbon black as a conductive material, and PVdF as a binder to NMP as a solvent in a weight ratio of 38.2:2.7:59.1, and then drying at 130°C.

[0090] Comparative Example 1 As a cathode material, the average particle size (D 50A lithium secondary battery having a positive electrode porosity of 22% was manufactured in the same manner as in Example 1, except that a NCM monoparticle positive electrode material having a diameter of 5 μm and a Ni content of 86% was used.

[0091] Comparative Example 2 As a cathode material, the average particle size (D 50 A lithium secondary battery having a positive electrode porosity of 22% was manufactured in the same manner as in Example 2, except that a NCM monoparticle positive electrode material having a diameter of 5 μm and a Ni content of 86% was used.

[0092] Comparative Example 3. A cathode material having the same composition as in Example 1 was rolled in a rolling process to increase the thickness of the electrode to 132.2 μm, which was larger than that in Example 1, to produce a cathode material with a porosity of 26%. A lithium secondary battery was manufactured using the same method as in Example 1.

[0093] FIG. 1 shows the cycle life characteristics of the lithium secondary batteries prepared in Example 1 and Comparative Example 1, measured by charging at 0.33 C and discharging at 0.5 C at room temperature. Charge was performed in CC mode, then switched to CV mode with a cutoff of 4.2 V at 0.05 C. Discharge was performed in CC mode with a cutoff of 2.8 V. It can be seen from FIG. 1 that the lithium secondary battery prepared in Example 1 has improved life characteristics compared to the lithium secondary battery prepared in Comparative Example 1. In FIG. 1, Blended cathode 5:5 represents Example 1, and Single crystaline cathode 100% represents Comparative Example 1.

[0094] FIG. 2 shows voltage curves during discharge for the three-electrode system secondary batteries manufactured in Example 2 and Comparative Example 2. In FIG. 2, the first line from the left indicates the secondary battery voltage, the second line indicates the positive electrode voltage, and the third line indicates the negative electrode voltage. Discharge was performed in CC mode at 0.33 C to 2.5 V, based on the secondary battery voltage. From the positive electrode voltage curves in FIG. 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 identical, it can be seen that the positive electrode of Example 2 has a relatively high resistance at the end of discharge. Since the voltage of a secondary battery is determined by the voltage difference between the positive and negative electrodes, it can be seen that the voltage drop of the positive electrode in Example 2 suppresses the rise in the negative electrode voltage at the end of discharge. This suggests that the silicon-based compound (SiO β 2, Blended cathode 5:5 represents Example 2, and Single crystalline cathode 100% represents Comparative Example 2.

[0095] Figure 3 shows the cycle life characteristics of the lithium secondary batteries prepared in Example 1 and Comparative Examples 1 and 3, measured by charging at 0.33 C and discharging at 0.5 C at room temperature. Charging was performed in CC mode, then switched to CV mode with a cutoff at 4.2 V and 0.05 C. Discharging was performed in CC mode with a cutoff at 2.5 V. It can be seen from Figure 3 that the lithium secondary battery prepared in Comparative Example 3 had inferior life characteristics compared to the lithium secondary battery prepared in Example 1.

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

Claims

1. 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, The negative electrode active material layer is made of 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 has an average particle size (D ５０ ) is 3 μm to 10 μm and the average particle size (D ５０ ) contains large particle active material of 8 μm to 20 μm, The positive electrode active material layer has a porosity of 19% to 23%.

2. 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 relative to the total number of moles of transition metals excluding lithium.

3. The secondary battery according to claim 1 , wherein the small particle active material is in a single particle form.

4. The SiO β 2. The secondary battery according to claim 1, wherein the (0<β<2) oxide is contained in an amount of 1 to 15 parts by weight based on 100 parts by weight of the negative electrode active material of the negative electrode active material layer.

5. 2. 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 the small particle active material:weight of the large particle active material) is 2:8 to 8:2.

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