Self-supporting separator for electrochemical element and electrochemical element including the same

Abstract

The present invention relates to a self-supporting separator for an electrochemical device and an electrochemical device including the same. The present invention relates to a self-supporting separator for an electrochemical device including a negative electrode containing a silicon-based active material, and to an electrochemical device including the same, which has improved compression resistance, improved energy density, and exhibits long life characteristics by adjusting the surface roughness (Sa) of the self-supporting separator through adjustment of the content and average particle size of inorganic particles.

Description

[Technical Field]

[0001] This application claims the benefit of the filing dates of Patent Application No. 10-2023-0058001 filed with the Korean Intellectual Property Office on May 3, 2023, and Patent Application No. 10-2024-0057294 filed with the Korean Intellectual Property Office on April 30, 2024, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a self-supporting separator for an electrochemical device and an electrochemical device including the same. Specifically, the present invention relates to a self-supporting separator for an electrochemical device having a negative electrode containing a silicon-based active material, in which the content and average particle size of inorganic particles are adjusted to control the surface roughness (Sa) of the separator, thereby improving compression resistance, thereby improving energy density and exhibiting long life characteristics of the electrochemical device, and an electrochemical device including the same. [Background technology]

[0003] Among the components of an electrochemical device, the separator is disposed between the positive and negative electrodes and contains a polymer matrix with a porous structure. It serves to separate the positive and negative electrodes, prevent electrical shorts between the two electrodes, and allow the electrolyte and ions to pass through. Although the separator itself does not participate in the electrochemical reaction, its physical properties, such as wettability with the electrolyte, degree of porosity, and thermal shrinkage, affect the performance and safety of the electrochemical device.

[0004] Therefore, various methods have been attempted to add a coating layer to a porous polymer substrate to enhance the physical properties of the separator, and to modify the physical properties of the coating layer by adding various substances to the coating layer. For example, an inorganic substance may be added to the coating layer to improve the mechanical strength of the separator, or an inorganic substance or hydrate may be added to the coating layer to improve the flame retardancy and heat resistance of the polymer substrate.

[0005] The separator may be attached to the electrode through a lamination process, and a polymer binder may be added to the coating layer composition of the separator to ensure adhesion between the electrode and the separator.

[0006] On the other hand, polyolefin resins, which are often used as porous polymer substrates for electrochemical elements, have the problem of shrinking when exposed to high temperatures, causing the positive and negative electrodes to come into contact, resulting in an electrical short circuit between the two electrodes, generating heat and causing thermal runaway due to a decomposition reaction between the electrolyte and active material.

[0007] Therefore, there has been a need for research into a self-supporting separator that can improve the energy density and life characteristics of electrochemical devices. Summary of the Invention [Problem to be solved by the invention]

[0008] The technical problem to be solved by the present invention is to provide a self-standing separator for an electrochemical device having a negative electrode containing a silicon-based active material, which can improve compression resistance by adjusting the content of inorganic particles to adjust the surface roughness (Sa) of the separator, thereby improving the energy density and life characteristics of the electrochemical device, and an electrochemical device including the same.

[0009] However, the problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0010] One embodiment of the present invention provides a self-supporting separator for an electrochemical device having a negative electrode containing a silicon-based active material, the self-supporting separator comprising inorganic particles and a polymer binder provided on all or part of the surface of the inorganic particles, the self-supporting separator comprising pores, the content of the inorganic particles being 70 parts by weight or more per 100 parts by weight of the self-supporting separator, and the surface roughness (Sa) of the self-supporting separator being 600 nm or more and 1100 nm or less.

[0011] According to one embodiment of the present invention, the inorganic particles may have an average particle size (D50) of 40 nm or more and 300 nm or less.

[0012] According to one embodiment of the present invention, the content of the silicon-based active material in the negative electrode may be 50% by weight or more.

[0013] According to one embodiment of the present invention, the hardness of the negative electrode may be 50 MPa or more and 350 MPa or less.

[0014] According to one embodiment of the present invention, the content of the polymer binder may be 30 parts by weight or less based on 100 parts by weight of the self-supporting separator.

[0015] According to one embodiment of the present invention, the polymer binder may be an acrylic binder, a polyvinylidene binder, or a combination thereof.

[0016] According to one embodiment of the present invention, the thickness of the self-supporting separator may be 10 μm or more and 30 μm or less.

[0017] According to one embodiment of the present invention, the self-supporting separator may have an air permeability change rate of 10% or less according to the following formula 1: [Formula 1] Air permeability change rate (%) = {(Air permeability of separation membrane after pressure application - Air permeability of separation membrane before pressure application) / Air permeability of separation membrane before pressure application} x 100

[0018] One embodiment of the present invention provides an electrochemical device comprising: a positive electrode; a negative electrode containing a silicon-based active material; and the above-described free-standing separator interposed between the positive electrode and the negative electrode containing the silicon-based active material.

[0019] According to one embodiment of the present invention, the driving voltage range of the electrochemical device may be 2.5V to 4.2V. [Effects of the Invention]

[0020] A self-supporting separator for an electrochemical device according to an embodiment of the present invention may have improved compression resistance.

[0021] An electrochemical device including a self-supporting separator for an electrochemical device according to an embodiment of the present invention can improve energy density and life characteristics by utilizing a lower limit voltage. DETAILED DESCRIPTION OF THE INVENTION

[0022] In this specification, when a part is said to "comprise" a certain component, this does not mean that it excludes other components, but that it may further include other components, unless otherwise specified.

[0023] In this specification, "A and / or B" means "A and B, or A or B."

[0024] In this specification, when a component is said to be "provided on" another component, this does not exclude other components from being disposed therebetween, unless otherwise specified, and means that other components may also be disposed thereon.

[0025] As used herein, the characteristic of "having pores" means that an object contains a plurality of pores, and the pores are interconnected to allow gas and / or liquid fluids to pass from one side of the object to the other side.

[0026] In this specification, the separator has a porous property including a large number of pores and serves as a porous ion-conducting barrier that allows ions to pass through while blocking electrical contact between the negative electrode and the positive electrode in the electrochemical device.

[0027] In this specification, the term "self-supporting separator for an electrochemical device" refers to a separator for an electrochemical device that includes inorganic particles and a polymer binder and is not provided with a porous polymer substrate.

[0028] The present invention will be described in further detail below.

[0029] One embodiment of the present invention provides a self-supporting separator for an electrochemical device including a negative electrode containing a silicon-based active material, the self-supporting separator comprising inorganic particles and a polymer binder provided on all or part of the surface of the inorganic particles, the self-supporting separator comprising pores, the content of the inorganic particles being 70 parts by weight or more per 100 parts by weight of the self-supporting separator, and the surface roughness (Sa) of the self-supporting separator being 600 nm or more and 1100 nm or less.

[0030] A self-supporting separator for an electrochemical device according to an embodiment of the present invention may have improved compression resistance. Furthermore, when the separator for an electrochemical device according to an embodiment of the present invention is applied to an electrochemical device including a negative electrode containing a silicon-based active material, the energy density and life characteristics of the electrochemical device may be improved. That is, among negative electrode active materials used in the negative electrode of an electrochemical device, silicon-based active materials have a capacity about 10 times higher than carbon-based active materials, and therefore have the advantage of being able to achieve high energy density even in a thin electrode due to their high capacity.

[0031] According to one embodiment of the present invention, a self-supporting separator for an electrochemical device does not include a porous polymer substrate. By not including a porous polymer substrate in the self-supporting separator, the heat resistance of the separator can be improved and the separator can be prevented from shrinking at high temperatures, which can cause an electrical short circuit in the electrodes.

[0032] According to one embodiment of the present invention, the separator includes inorganic particles and a polymer binder. As described above, the separator includes inorganic particles and a polymer binder, which improves the heat resistance of the separator and prevents the separator from shrinking at high temperatures, which can cause an electrical short circuit in the electrodes. Furthermore, pores can be formed inside the separator.

[0033] According to one embodiment of the present invention, the separator contains inorganic particles. Non-limiting examples of inorganic particles include BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT, 0 <x<1、0<y<1)、Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3 (PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, Mg(OH)2, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, SiC, Al(OH)3, TiO2, aluminum peroxide, zinc tin hydroxide (ZnSn(OH)6), tin-zinc oxide (Zn2SnO4, ZnSnO3), antimony trioxide (Sb2O3), antimony tetroxide (Sb2O4), antimony pentoxide (Sb2O5), zeolite A, zeolite X, zeolite Y, γ-AlO(OH), etc., and the separator may contain one or more of these inorganic particles. As described above, the inclusion of the inorganic particles in the separator can improve the heat resistance of the separator.

[0034] According to one embodiment of the present invention, the separator includes a polymer binder provided on all or part of the surface of the inorganic particles. As described above, by providing the polymer binder on all or part of the surface of the inorganic particles, the inorganic particles are densely stacked, thereby improving the compression resistance of the separator.

[0035] According to one embodiment of the present invention, the separator includes pores. Specifically, the separator may include a plurality of pores. More specifically, the separator may be a porous separator including a plurality of pores therein. As described above, the separator includes pores, which allows lithium ions to pass through and current to flow while physically isolating the anode and cathode.

[0036] According to one embodiment of the present invention, the separator may be formed by binding inorganic particles with a polymer binder and accumulating them in a layer. The pores within the separator may be due to interstitial volume, which is the void space between the inorganic particles. Specifically, as described below, the structure and size of the pores may vary depending on the content and average particle size of the inorganic particles. Furthermore, the difference in the structure and size of the pores may prevent transition metals leached from the positive electrode from migrating to the opposite side of the negative electrode.

[0037] According to one embodiment of the present invention, the content of the inorganic particles is 70 parts by weight or more per 100 parts by weight of the separation membrane. Specifically, the content may be 70 parts by weight or more but less than 100 parts by weight, 75 parts by weight or more but less than 95 parts by weight, or 80 parts by weight or more but less than 90 parts by weight per 100 parts by weight of the separation membrane. By adjusting the content of the inorganic particles within the above ranges, the heat resistance and compression resistance of the separation membrane can be improved, and the separation membrane can be manufactured into a free-standing separation membrane.

[0038] According to one embodiment of the present invention, the surface roughness (Sa) of the separator is 600 nm to 1100 nm. Specifically, the surface roughness (Sa) of the separator may be 650 nm to 1050 nm, 700 nm to 1000 nm, 750 nm to 950 nm, or 750 nm to 900 nm. Herein, the surface roughness (Sa) may be defined as the arithmetic average of the differences between the center line and the perpendicular direction of each portion randomly sampled from the surface of the separator facing the electrode, with the long axis of the separator as the center line. By adjusting the surface roughness of the separator within the above range, the compression resistance of the separator can be improved without causing aggregation of the inorganic particles and polymer binder.

[0039] According to one embodiment of the present invention, the surface roughness (Sa) of a separation membrane can be measured using an Optical Profiler NV 2700 from Nanosystem. The upper surface of the separation membrane is set on the sample stage as the measurement surface, and the average value can be calculated for four different measurement areas. The measurement instrument settings are as follows: Cutoff: 0.8mm, Scan speed: 0.1mm / s, Magnification: 500x.

[0040] According to one embodiment of the present invention, the inorganic particles may have an average particle size (D50) of 40 to 300 nm. Specifically, the average particle size (D50) of the inorganic particles may be 50 to 290 nm, 60 to 280 nm, 70 to 270 nm, 80 to 260 nm, 90 to 250 nm, 100 to 240 nm, 110 to 230 nm, 120 to 220 nm, 130 to 210 nm, 140 to 200 nm, 150 to 190 nm, or 160 to 180 nm. By adjusting the average particle size (D50) of the inorganic particles within the above range, the phase separation rate and efficiency between the polymer binder and the inorganic particles can be improved in a separation membrane slurry, which is an emulsion of the polymer binder dispersed in water. Furthermore, if the particle size is less than 40 nm, the dispersibility of the inorganic particles in the slurry prepared for producing the separation membrane may decrease, and if the particle size is more than 300 nm, the compression resistance of the resulting separation membrane may decrease.

[0041] In this specification, the "D50 particle size" means the particle size at the 50% point of the cumulative distribution of the number of particles according to the particle size. The particle size can be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac S3500). When the particles pass through the laser beam, the difference in the diffraction pattern according to the particle size is measured to calculate the particle size distribution. The D50 particle size can be measured by calculating the particle diameter at the point where the cumulative distribution of the number of particles according to the particle size in the measuring device reaches 50%.

[0042] According to an embodiment of the present invention, the inorganic particles that can be used for the separation membrane may be electrochemically stable. That is, the inorganic particles that can be used in an embodiment of the present invention may be those in which oxidation and / or reduction reactions do not occur within the operating voltage range of the applied electrochemical device (for example, 0 V to 5 V based on Li / Li + ).

[0043] According to an embodiment of the present invention, the negative electrode contains a silicon-based active material. Specifically, the negative electrode may contain a silicon-based compound as the silicon-based active material. Non-limiting examples of the silicon-based compound include Si, SiO x (0 < x < 2), Si-Y (Y is an alkali metal, alkaline earth metal, group 13 element, group 14 element, transition metal, rare earth element, or a combination thereof, and is not Si) alloy, and Si-C composite, etc., and may include one or more of these. Specifically, when the negative electrode contains a silicon-based negative electrode active material, the energy density and rapid charging performance can be improved.

[0044] According to one embodiment of the present invention, the content of the silicon-based active material in the negative electrode may be 50 wt% or more. Specifically, the content of the silicon-based active material in the negative electrode may be 50 wt% or more but less than 100 wt%, 55 wt% or more but less than 95 wt%, 60 wt% or more but less than 90 wt%, 65 wt% or more but less than 85 wt%, or 70 wt% or more but less than 80 wt%. By adjusting the content of the silicon-based active material within the above range, the hardness of the negative electrode can be maintained within a certain range and pore deformation of the separator can be prevented.

[0045] According to one embodiment of the present invention, the hardness of the negative electrode may be 50 MPa to 350 MPa. Specifically, the hardness of the negative electrode may be 75 MPa to 325 MPa, 100 MPa to 300 MPa, 125 MPa to 275 MPa, 150 MPa to 250 MPa, or 175 MPa to 225 MPa. Adjusting the hardness of the negative electrode within the above range can prevent deformation of the pores of the separator during the assembly process of the electrochemical device.

[0046] According to one embodiment of the present invention, the hardness of the negative electrode can be measured using a microindenter. The microindenter can be an indentation device manufactured by Anton Paar. The electrode was indented to a depth of 5 μm, and the hardness was measured by loading / unloading at a rate of 2 N per minute at five points per indentation depth.

[0047] According to one embodiment of the present invention, the content of the polymer binder may be 30 parts by weight or less per 100 parts by weight of the separator. Specifically, the content of the polymer binder may be more than 0 parts by weight and less than 30 parts by weight, 5 parts by weight to 25 parts by weight, or 10 parts by weight to 20 parts by weight per 100 parts by weight of the separator. By adjusting the content of the polymer binder within the above range, the porosity of the separator can be maintained, and the adhesive strength can be maintained even when the coating layer is wetted by the electrolyte after activation of the battery.

[0048] According to one embodiment of the present invention, the polymer binder may be particulate or non-particulate. Specifically, as described below, the polymer binder may be one that does not dissolve in a dispersion medium or solvent and maintains its particulate shape, or the polymer binder may not dissolve in a dispersion medium or solvent and maintain its particulate shape. As described above, by selecting a particulate or non-particulate polymer binder, the mechanical properties and porosity of the separator can be adjusted.

[0049] According to one embodiment of the present invention, the average particle size (D50) of the particulate polymer binder is 1.0 μm or less. Specifically, the average particle size (D50) of the first polymer binder particles may be 0.10 μm to 0.90 μm, 0.15 μm to 0.85 μm, 0.20 μm to 0.70 μm, 0.25 μm to 0.65 μm, or 0.30 μm to 0.50 μm. By adjusting the average particle size (D50) of the particulate polymer binder within the above range, the phase separation rate and efficiency between the particulate polymer binder and the inorganic particles can be improved in a coating layer slurry, which is an emulsion of the particulate polymer binder dispersed in water.

[0050] According to one embodiment of the present invention, the polymeric binder can be an acrylic binder, a polyvinylidene binder, or a combination thereof.

[0051] According to one embodiment of the present invention, the polymer binder may include two or more polymer binders. As described above, by including two or more polymer binders, the adhesive strength between inorganic materials in the coating layer can be improved, the porosity of the coating layer can be improved, and the dry adhesive strength before the electrolyte solution is injected and the wet adhesive strength after the electrolyte solution is injected can be improved simultaneously.

[0052] According to one embodiment of the present invention, the polymer binder may include an acrylic binder, which may maintain the porosity of the separator, improve the adhesive strength between the electrode and the separator during the lamination process of the battery, thereby improving the ease of battery fabrication and stably implementing the stacking process.

[0053] According to one embodiment of the present invention, the acrylic binder is a polymer containing a carboxylic acid ester as a repeating unit, and is preferably a (meth)acrylic acid ester or an acrylic-styrene copolymer.

[0054] According to one embodiment of the present invention, specific examples of the (meth)acrylic acid ester include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, n-amyl (meth)acrylate, i-amyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, nonyl (meth)acrylate, and methyl (meth)acrylate. Examples of suitable acrylates include decyl (meth)acrylate, hydroxymethyl (meth)acrylate, hydroxyethyl (meth)acrylate, ethylene glycol (meth)acrylate, ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, allyl (meth)acrylate, and ethylene di(meth)acrylate, and the acrylate may be one or more selected from these. Among these, the acrylate may be one or more selected from methyl (meth)acrylate, ethyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate, and methyl (meth)acrylate is particularly preferred.

[0055] According to one embodiment of the present invention, the acrylic-styrene copolymer may contain an acrylic binder, and the acrylic binder may be a polyacrylate. For example, the binder may be one or more selected from the group consisting of styrene-butadiene rubber, nitrile-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, and acrylate-based polymers, and more particularly, may be a copolymer containing acrylate.

[0056] According to one embodiment of the present invention, the polymer binder may include a polyvinylidene-based binder. Specifically, according to one embodiment of the present invention, the polyvinylidene-based binder may be a copolymer of polyvinylidene fluoride and hexafluoropropylene. As described above, by selecting the polymer binder from a polyvinylidene-based binder, the porosity of the separator can be maintained and the adhesive strength can be maintained even when the coating layer is wetted by the electrolyte after activation of the battery. Furthermore, the rigidity of the battery can be improved and bending of the separator can be prevented.

[0057] According to one embodiment of the present invention, the polyvinylidene-based binder may be a water-based binder. Specifically, by selecting the polyvinylidene-based binder from water-based binders, it is possible to minimize pollutants emitted during the separator manufacturing process and reduce the battery manufacturing cost.

[0058] According to one embodiment of the present invention, the thickness of the separator may be, but is not limited to, 10 μm to 30 μm. Specifically, the thickness of the separator may be 12 μm to 28 μm, 14 μm to 26 μm, 16 μm to 24 μm, or 18 μm to 22 μm. The thickness can be adjusted to an appropriate range by those skilled in the art in consideration of heat resistance and electrical resistance. As described above, the inorganic particles constituting the separator form a dense layered structure and the average particle size (D50) of the inorganic particles is 300 nm or less, so the thickness of the separator can be adjusted to an appropriate range within the above range.

[0059] According to one embodiment of the present invention, the thickness of the separator can be measured using a contact-type thickness gauge, such as Mitutoyo's VL-50S-B.

[0060] According to one embodiment of the present invention, a separator may have improved compression resistance. Specifically, the compression resistance of the separator can be improved by adjusting the content and average particle size (D50) of inorganic particles contained in the separator. Furthermore, a separator with improved compression resistance can improve the performance of an electrochemical device by suppressing deformation of the separator's pores when a silicon-based negative electrode active material with a large volume expansion rate during charge and discharge is used as the negative electrode.

[0061] According to one embodiment of the present invention, the separator may have an air permeability change rate of 10% or less. Specifically, the air permeability change rate may be greater than 0% and less than 10%, 1% to 9%, 2% to 8%, 3% to 7%, or 4% to 6%. As described above, by adjusting the content and average particle size (D50) of the inorganic particles contained in the separator to improve compression resistance, the change in pore size may not be significant even after the lamination process, and the air permeability change rate of the separator may be reduced.

[0062] In this specification, the term "rate of change in air permeability" may refer to a value indicating the rate of change in air permeability measured before and after a separator is subjected to a lamination process.

[0063] According to one embodiment of the present invention, the porosity of the separator may be 30% by volume or more. Specifically, the porosity of the separator may be 30% by volume to 70% by volume, 32% by volume to 68% by volume, 34% by volume to 66% by volume, 36% by volume to 64% by volume, 38% by volume to 62% by volume, 40% by volume to 60% by volume, 42% by volume to 58% by volume, 44% by volume to 56% by volume, 46% by volume to 54% by volume, or 48% by volume to 52% by volume. Adjusting the porosity of the separator within the above ranges can maintain ion mobility in the separator and prevent an increase in the resistance of the separator. Specifically, a porosity of 70% by volume or less can ensure mechanical properties that can withstand the pressing process for bonding to an electrode. This is also suitable for ensuring adhesive strength without an excessively high surface opening ratio. On the other hand, a porosity of 30% by volume or more is advantageous in terms of ion permeability.

[0064] As used herein, the term "porosity" refers to the ratio of the volume occupied by pores to the total volume, and is expressed in units of volume %. It may be used interchangeably with terms such as void ratio and porosity.

[0065] In this specification, the porosity corresponds to a value obtained by subtracting the weight and density of each component of the separator from the volume calculated from the thickness, width, and length of the separator.

[0066] In one embodiment of the present invention, the porosity and pore size of the separation membrane can be measured by a BET 6-point method using a scanning electron microscope (SEM) image, a mercury porosimeter, a capillary flow porometer, or a porosimetry analyzer (Belsorp-II mini, Bell Japan Inc.) via a nitrogen gas adsorption flow method. In this case, it may be advantageous to use a capillary flow porosimeter.

[0067] According to one embodiment of the present invention, a method for forming a separator is as follows: First, a polymer binder is dissolved in a suitable solvent or dispersed in a dispersion medium to prepare a polymer solution or emulsion. Non-limiting examples of usable solvents or dispersion mediums include N-methyl-2-pyrrolidone (NMP), acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, cyclohexane, water, or a mixture thereof.

[0068] Next, the inorganic particles are dispersed in a suitable solvent to prepare an inorganic slurry. Usable solvents include propylene carbonate (PC), ethylene carbonate (EC), N-methyl-2-pyrrolidone (NMP), and mixtures thereof. According to one embodiment of the present invention, the content ratio of the inorganic particles to the polymer binder is as described above and is appropriately adjusted taking into account the thickness, pore size, and porosity of the separator of the present invention to be finally produced.

[0069] Next, the inorganic slurry prepared as described above is applied to at least one side of the prepared PET release film and dried. The method for applying the inorganic slurry to the surface of the PET release film is not limited to any particular method, and any conventional method known in the art can be used. For example, various methods can be used, such as dip coating, die coating, roll coating, comma coating, or a combination thereof.

[0070] In the drying process, the temperature and time conditions are appropriately set to minimize the occurrence of surface defects on the separation membrane. In the drying process, auxiliary drying devices such as a drying oven or hot air can be used within an appropriate range.

[0071] After the drying process, the PET release film is removed to produce a separator.

[0072] According to one embodiment of the present invention, the separator is interposed between the anode and cathode and fabricated into an electrochemical device through a lamination process in which heat and / or pressure are applied to bond them together. In one embodiment of the present invention, the lamination process can be performed using a roll press device including a pair of pressure rollers. That is, the anode, separator, and cathode can be stacked in this order and then inserted between the pressure rollers to achieve interlayer bonding. The lamination process can be performed using a hot press method.

[0073] One embodiment of the present invention provides an electrochemical device comprising: a positive electrode; a negative electrode containing a silicon-based active material; and the separator interposed between the positive electrode and the negative electrode containing the silicon-based active material.

[0074] An electrochemical device according to one embodiment of the present invention includes inorganic particles and a polymer binder provided on all or part of the surface of the inorganic particles, the inorganic particles having pores and a surface roughness (Sa) of 600 nm to 1100 nm, and a separator without a porous polymer substrate, thereby improving heat resistance and compression resistance, and thereby improving the energy density and life characteristics of the battery.

[0075] According to one embodiment of the present invention, the operating voltage range of the electrochemical device may be 2.5 V to 4.2 V. Specifically, by including a separator with improved compression resistance, the lower limit voltage of a battery including a negative electrode containing a silicon-based active material can be utilized.

[0076] In the present invention, an electrochemical device is a device that converts chemical energy into electrical energy through an electrochemical reaction, and is a concept that encompasses primary batteries and secondary batteries. In this specification, secondary batteries refer to lithium secondary batteries, nickel-cadmium batteries, nickel-metal hydride batteries, etc., which can be charged and discharged. Lithium secondary batteries use lithium ions as an ion conductor, and examples include non-aqueous electrolyte secondary batteries containing a liquid electrolyte, all-solid-state batteries containing a solid electrolyte, lithium polymer batteries containing a gel polymer electrolyte, and lithium metal batteries using lithium metal as the anode, but are not limited thereto.

[0077] According to one embodiment of the present invention, the positive electrode has a positive electrode current collector and a positive electrode active material layer containing a positive electrode active material, a conductive material, and a binder resin on at least one surface of the positive electrode current collector. The positive electrode active material includes layered compounds such as lithium manganese composite oxides (LiMn2O4, LiMnO2, etc.), lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), and compounds substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x O4 (where x is 0 to 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x M x O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3), Ni-site type lithium nickel oxides represented by; chemical formula LiMn 1-x MxO2 (where M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1), or lithium manganese composite oxides represented by Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with alkaline earth metal ions; disulfide compounds; one or a mixture of two or more of Fe2(MoO4)3 may be included.

[0078] According to one embodiment of the present invention, the negative electrode has a negative electrode current collector and a negative electrode active material layer containing a negative electrode active material, a conductive material, and a binder resin on at least one surface of the negative electrode current collector. The negative electrode active material may include one or more silicon-based negative electrode active materials selected from the group consisting of Si, SiO x (0 < x < 2), Si-Y alloys, and Si-C composites. Further, as the negative electrode active material, the negative electrode includes carbon such as lithium metal oxide, graphitized carbon, graphite-based carbon; LixFe2O3 (0 ≦ x ≦ 1), Li x WO2 (0 ≦ x ≦ 1), Sn x Me 1-x Me’ y O z(Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8), etc. metal composite oxides; lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials; and may further contain one or more mixtures selected from titanium oxides.

[0079] According to an embodiment of the present invention, the conductive material can be, for example, any one selected from the group consisting of graphite, carbon black, carbon fiber or metal fiber, metal powder, conductive whisker, conductive metal oxide, activated carbon, and polyphenylene derivative, or a mixture of two or more of these conductive materials. More specifically, it can be one or a mixture of two or more of these conductive materials selected from the group consisting of natural graphite, artificial graphite, super-p, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide.

[0080] According to an embodiment of the present invention, the current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery. For example, stainless steel, copper, 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.

[0081] According to one embodiment of the present invention, the binder resin may be a polymer that is commonly used in electrodes in the industry. Non-limiting examples of such binder resins include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyethylhexyl acrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. Examples of suitable cellulose acetates include, but are not limited to, cyanoethyl acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, and carboxyl methyl cellulose.

[0082] According to one embodiment of the present invention, the positive electrode slurry for preparing the positive electrode active material layer may include a dispersant, and the dispersant may be a pyrrolidone-based compound, specifically, N-methylpyrrolidone (ADC-01, LG Chemical Co., Ltd.).

[0083] According to one embodiment of the present invention, the content of the dispersant in the positive electrode slurry may be more than 0 parts by weight and not more than 0.5 parts by weight per 100 parts by weight of the positive electrode slurry. Specifically, the content of the dispersant in the positive electrode slurry may be more than 0.05 parts by weight and not more than 0.4 parts by weight per 100 parts by weight of the positive electrode slurry.

[0084] According to one embodiment of the present invention, the negative electrode slurry for manufacturing the negative electrode active material layer may contain a dispersant, and the dispersant may be a CMC dispersion (SWCNT, Ocsial, Tuball dispersion).

[0085] According to one embodiment of the present invention, the content of the dispersant in the negative electrode slurry may be more than 0 part by weight and not more than 1.0 part by weight per 100 parts by weight of the negative electrode slurry. Specifically, the content of the dispersant in the negative electrode slurry may be 0.1 parts by weight to 0.9 parts by weight, 0.2 parts by weight to 0.8 parts by weight, 0.3 parts by weight to 0.7 parts by weight, or 0.4 parts by weight to 0.6 parts by weight per 100 parts by weight of the negative electrode slurry.

[0086] According to one embodiment of the present invention, the electrochemical device prepared as described above can be placed in a suitable case and filled with an electrolyte to fabricate a battery.

[0087] According to one embodiment of the present invention, the electrolyte is + B - A salt having the structure: + Li + , Na + , K. + or a combination thereof, - is PF6 - , BF4- , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2) 2- , C(CF2SO2) 3- or a salt containing an anion such as, or a combination thereof, dissolved or dissociated in an organic solvent such as, but not limited to, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma butyrolactone (γ-butyrolactone), or a mixture thereof.

[0088] One embodiment of the present invention provides a battery module including a battery containing the electrochemical device as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source. Specific examples of the devices include, but are not limited to, power tools powered by a battery-like motor, electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters, electric golf carts, and power storage systems. [Example]

[0089] Hereinafter, the present invention will be described in detail with reference to examples. However, the examples of the present invention can be modified into various different forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples in this specification are provided to more completely explain the present invention to those skilled in the art.

[0090] Example 1 <Separation membrane manufacturing> As inorganic particles, boehmite with an average particle size (D50) of 60 nm (Sasol, Disperal 60) and boehmite with an average particle size (D50) of 80 nm (Sasol, Disperal 80) were added to a solvent, propylene carbonate (PC), in a weight ratio of 3:2 and dispersed to prepare an oil-based slurry.

[0091] A polymer binder solution prepared by dispersing PVDF (Solvay, Solef5140-02) in NMP solvent was added to the oil-based slurry in a weight ratio and stirred at 3000 rpm for 45 minutes to prepare an inorganic slurry.

[0092] The inorganic slurry was then applied to one side of a PET release film using a doctor blade by bar coating, and dried with air at 50°C using a heat gun. The weight ratio of inorganic particles to polymer binder was 73:27.

[0093] Then, the PET release film was removed to prepare a separator having a total thickness of 14.7 μm and a surface roughness (Sa) of 750 nm.

[0094] An electrochemical device including the prepared separator was manufactured, and an experiment was carried out with the driving voltage range of 2.5V to 4.2V.

[0095] <Manufacturing of electrochemical elements> 1) Manufacturing of the positive electrode Cathode active material (LiNi 0.8 Mn 0.1 Co 0.1 O2), conductive material (carbon black), dispersant (N-methylpyrrolidone, ADC-01, LG Chemicals), and binder resin (a mixture of PVDF-HFP and PVDF) were mixed with water in a weight ratio of 97.5:0.7:0.14:1.66 to prepare a slurry for the positive electrode active material layer, with the remaining components (excluding water) at a concentration of 50 wt%. Next, this slurry was applied to the surface of an aluminum thin film (10 μm thick) and dried to prepare a positive electrode having a positive electrode active material layer (120 μm thick).

[0096] 2) Manufacturing of negative electrodes Silicon particles (Elkem, M702), PAM binder (Arakawa, BUH0452), conductive material (Imerys, SFG-6L), conductive material (SWCNT, Ocsial, Tuball dispersion), and CMC dispersant (SWCNT, Ocsial, Tuball dispersion) were mixed with water in a weight ratio of 80:9.4:9.6:0.4:0.6 to prepare a slurry for the negative electrode active material layer, with the remaining components (excluding water) at a concentration of 25 wt%. The slurry was then applied to the surface of a copper thin film (8 μm thick) and dried to produce a negative electrode loading of 8 mAh / cm. 2 A negative electrode having the following composition was produced.

[0097] 3) Lamination process The separators of the Examples and Comparative Examples were interposed between the negative and positive electrodes, and a lamination process was performed to obtain an electrode assembly using a hot press at 70°C and 5.2 MPa for 10 seconds.

[0098] <Example 2> A separator was prepared in the same manner as in Example 1, except that the weight ratio of inorganic particles to polymer binder was 75:25, the surface roughness (Sa) was 600 nm, and the thickness was 14.8 μm.

[0099] An electrochemical device including the prepared separator was manufactured, and an experiment was carried out with the driving voltage range of 2.5V to 4.2V.

[0100] Example 3 In Example 1, a separation membrane was manufactured in the same manner as in Example 1, except that the inorganic particles used were a mixture of boehmite (Sasol, Disperal 60) with an average particle size (D50) of 60 nm and boehmite (Sasol, Disperal 80) with an average particle size (D50) of 80 nm in a weight ratio of 9:1, the weight ratio of the inorganic particles to the polymer binder was 70:30, the surface roughness (Sa) was 1100 nm, and the thickness was 14.9 μm.

[0101] An electrochemical device including the prepared separator was manufactured, and an experiment was carried out with the driving voltage range of 2.5V to 4.2V.

[0102] <Comparative Example 1> A separation membrane was manufactured in the same manner as in Example 1, except that inorganic particles having an average particle size (D50) of 500 nm were added instead of boehmite (Sasol, Disperal 80) having an average particle size (D50) of 80 nm, and the surface roughness (Sa) was 300 nm and the thickness was 14.6 μm.

[0103] An electrochemical device including the prepared separator was manufactured, and an experiment was carried out with the driving voltage range of 2.5V to 4.2V.

[0104] <Comparative Example 2> In Example 1, a 7 μm-thick polyolefin substrate was used, and both sides of the polyolefin substrate were coated with the inorganic slurry of Example 1. A separator was manufactured in the same manner as in Example 1, except that the weight ratio of the inorganic particles to the polymer binder was 50:50, the surface roughness (Sa) was 450 nm, and the thickness was 14.8 μm.

[0105] An electrochemical device including the prepared separator was manufactured, and an experiment was carried out with the driving voltage range of 2.5V to 4.2V.

[0106] <Comparative Example 3> In Example 1, a 7 μm thick polyolefin substrate was used, and inorganic particles with an average particle size (D50) of 500 nm were added to both sides of the polyolefin substrate instead of the boehmite (Sasol, Disperal 80) with an average particle size (D50) of 80 nm used in Example 1. The weight ratio of the inorganic particles to the polymer binder was 50:50, the surface roughness (Sa) was 300 nm, and the thickness was 15.0 μm. A separation membrane was manufactured in the same manner as in Example 1.

[0107] An electrochemical device including the prepared separator was manufactured, and an experiment was carried out with the driving voltage range of 2.5V to 4.2V.

[0108] <Comparative Example 4> In Example 1, a 7 μm-thick polyolefin substrate was used, and both sides of the polyolefin substrate were coated with the inorganic slurry of Example 1. A separator was prepared in the same manner as in Example 1, except that the weight ratio of inorganic particles to polymer binder was 50:50, the surface roughness (Sa) was 450 nm, and the thickness was 14.7 μm.

[0109] An electrochemical device including the prepared separator was manufactured, and an experiment was carried out with the driving voltage range of 3.0V to 4.2V.

[0110] <Comparative Example 5> In Example 1, a 7 μm-thick polyolefin substrate was used, and both sides of the polyolefin substrate were coated with the inorganic slurry of Comparative Example 1, in which inorganic particles with an average particle size (D50) of 500 nm were applied. A separator was manufactured in the same manner as in Example 1, except that the weight ratio of the inorganic particles to the polymer binder was 50:50, the surface roughness (Sa) was 300 nm, and the thickness was 14.9 μm.

[0111] An electrochemical device including the prepared separator was manufactured, and an experiment was carried out with the driving voltage range of 3.0V to 4.2V.

[0112] <Comparative Example 6> A separator was prepared in the same manner as in Example 1, except that inorganic particles with an average particle size (D50) of 60 nm were added, the weight ratio of inorganic particles to polymer binder was 65:35, the surface roughness (Sa) was 1200 nm, and the thickness was 15.0 μm.

[0113] An electrochemical device including the prepared separator was manufactured, and an experiment was carried out with the driving voltage range of 2.5V to 4.2V.

[0114] <Experimental Example 1: Rate of change in air permeability of separation membrane> The air permeability (air permeability time, Gurley) of the separation membranes of the Examples and Comparative Examples was measured according to the ASTM D-2873 method. The Gurley value was measured using a Gurley-type Densometer (No. 158) manufactured by Toyo Seiki Co., Ltd. in accordance with the JIS Gurley measurement method. The air permeability refers to the time it takes for 100 cc of air to permeate through an object being measured for air permeability time, such as a separation membrane, and can be measured in units of seconds / 100 cc. The air permeability change rate was measured by measuring the air permeability of the separation membranes of the Examples and Comparative Examples before and after the lamination process, and the change rate was expressed as the rate of change.

[0115] <Experimental Example 2: Performance maintenance rate of electrochemical element>

[0116] To evaluate the lifespan of the electrochemical devices prepared using the separators of the Examples and Comparative Examples, each electrochemical device was charged to 4.2 V at 1.0 C and discharged to 2.5 V or 3.0 V at 0.5 C for 100 cycles, and the initial capacity and remaining capacity were measured and the rate of change was shown.

[0117] [Table 1] Referring to Table 1, it was confirmed that the separator of Example 1 according to an embodiment of the present invention had the lowest rate of change in air permeability before and after the lamination process, and also had the best performance maintenance rate of the electrochemical device even when the driving voltage of the electrochemical device was used in the range of 2.5 V to 4.2 V.

[0118] Furthermore, in Examples 1 to 3, the rate of change in air permeability before and after the lamination process was maintained low when the surface roughness (Sa) was in the range of 600 nm to 1100 nm, and it was confirmed that the performance retention rate of the electrochemical element was excellent even when the driving voltage range of the electrochemical element was used from 2.5 V to 4.2 V.

[0119] In contrast, it was confirmed that Comparative Example 1 had an inferior rate of change in air permeability to Example 1, and also had a reduced performance retention rate when the same driving voltage range of the electrochemical device as in Examples 1 to 3 was applied. This is thought to be due to the fact that as the size of the inorganic material applied to the separation membrane increased, the size of the pores in the separation membrane increased and the pore distribution became wider, resulting in a decrease in compression resistance.

[0120] Comparative Examples 2 and 3 are separators prepared by coating both sides of a 7 μm-thick polyolefin substrate with the inorganic slurries of Example 1 and Comparative Example 1, respectively. When a polyolefin substrate, which is softer and less hard than inorganic materials, was used as a separator, the rate of change in air permeability before and after the lamination process tended to increase sharply. As a result, when the voltage driving range of the prepared electrochemical device was evaluated in the same manner as in Example 1, it was confirmed that the performance retention rate of the electrochemical device decreased sharply.

[0121] Comparative Examples 4 and 5 were conducted using the same separator as Comparative Examples 2 and 3, but with the voltage driving range of the electrochemical device changed to 3.0 V to 4.2 V. Therefore, it was confirmed that the rate of change in air permeability before and after the separator lamination process was the same as in Comparative Examples 2 and 3. When the voltage driving range of the electrochemical device was changed to a narrower range (3.0 V to 4.2 V) than in Comparative Examples 2 and 3 (2.5 V to 4.2 V), the performance retention rate of the electrochemical device was slightly improved, but the level was not as high as in Example 1.

[0122] It was confirmed that Comparative Example 6 had a lower rate of change in air permeability than Example 1, and also had a lower performance retention rate when the same driving voltage range of the electrochemical device was applied. This is believed to be because as the size of the inorganic material applied to the separator decreased, the roughness of the separator surface increased, resulting in a decrease in compression resistance.

[0123] In one embodiment of the present invention, the self-supporting separator for an electrochemical device can be expected to have improved compression resistance, improved energy density, excellent performance retention rate, and improved lifespan characteristics by adjusting the surface roughness (Sa) of the separator through adjusting the content and average particle size of inorganic particles.

Claims

1. A self-supporting separator for an electrochemical device having a negative electrode containing a silicon-based active material, The present invention includes inorganic particles and a polymer binder provided on a part or all of the surfaces of the inorganic particles, Contains pores, The content of the inorganic particles is 70 parts by weight or more relative to 100 parts by weight of the self-supporting separation membrane, The self-supporting separation membrane has a surface roughness (Sa) of 600 nm or more and 1100 nm or less.

2. The self-supporting separation membrane according to claim 1 , wherein the inorganic particles have an average particle size (D50) of 40 nm or more and 300 nm or less.

3. The self-supporting separator according to claim 1 , wherein the content of the silicon-based active material in the negative electrode is 50% by weight or more.

4. The self-supporting separator according to claim 1 , wherein the hardness of the negative electrode is 50 MPa to 350 MPa.

5. The self-supporting separation membrane according to claim 1 , wherein the content of the polymer binder is 30 parts by weight or less based on 100 parts by weight of the self-supporting separation membrane.

6. The self-supporting separator according to claim 1 , wherein the polymer binder is an acrylic binder, a polyvinylidene binder, or a combination thereof.

7. The self-supporting separation membrane according to claim 1 , wherein the thickness of the self-supporting separation membrane is 10 μm or more and 30 μm or less.

8. The self-supporting separation membrane according to claim 1, wherein the self-supporting separation membrane has an air permeability change rate according to the following formula 1 of 10% or less: [Formula 1] Air permeability change rate (%)={(air permeability of separation membrane after pressure application−air permeability of separation membrane before pressure application) / air permeability of separation membrane before pressure application}×100.

9. An electrochemical device comprising: a positive electrode; a negative electrode containing a silicon-based active material; and the self-supporting separator according to any one of claims 1 to 8 interposed between the positive electrode and the negative electrode containing the silicon-based active material.

10. 10. The electrochemical device according to claim 9, wherein the driving voltage range of the electrochemical device is 2.5 V to 4.2 V.

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