Self-supporting separator for electrochemical device and electrochemical device comprising same

Abstract

The present invention relates to a self-supporting separator for an electrochemical device and an electrochemical device comprising the same. In a self-supporting separator for an electrochemical device including a negative electrode containing a silicon-based active material, the surface roughness (Sa) of the separator is adjusted by adjusting the content of inorganic particles and the average particle diameter, thereby improving compression resistance and energy density and exhibiting longer lifespan characteristics.

Description

Technical Field

[0001] The present disclosure claims the benefit of Korean Patent Application No. 10-2023-0058001 filed on May 3, 2023, in the Korean Intellectual Property Office, and Korean Patent Application No. 10-2024-0057294 filed on April 30, 2024, in the Korean Intellectual Property Office, and is incorporated in its entirety into the present disclosure.

[0002] The present disclosure relates to a self-supporting diaphragm for an electrochemical device and an electrochemical device comprising the same, and specifically to a self-supporting diaphragm for an electrochemical device and an electrochemical device comprising the self-supporting diaphragm, wherein the electrochemical device is provided with a negative electrode containing a silicon-based active material, and the surface roughness Sa of the diaphragm is adjusted by adjusting the content and average particle size of inorganic particles in the self-supporting diaphragm, thereby improving compression resistance, improving energy density, and exhibiting high electrochemical device life characteristics. Background Art

[0003] Among the components of an electrochemical device, a separator includes a polymer substrate having a porous structure located between the positive electrode and the negative electrode, and plays the role of separating the positive electrode and the negative electrode, preventing electrical short circuits between the two electrodes, and allowing electrolytes and ions to pass through. The separator itself does not participate in the electrochemical reaction, but physical properties such as wettability to the electrolyte, degree of porosity, and thermal shrinkage affect the performance and safety of the electrochemical device.

[0004] Therefore, in order to enhance the physical properties of the separator, various methods of adding a coating to the porous polymer substrate and adding various materials to the coating to change the physical properties of the coating have been tried. For example, inorganic substances may be added to the coating to improve the mechanical strength of the separator, or inorganic substances or hydrates may be added to the coating to improve the flame retardancy and heat resistance of the polymer substrate.

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

[0006] On the other hand, since polyolefin-based resins widely used as porous polymer substrates for electrochemical devices shrink when exposed to high temperatures, there are problems such as contact between the positive and negative electrodes causing an electrical short circuit between the two electrodes, resulting in heat generation, and thermal runaway due to decomposition reactions of the electrolyte and active materials.

[0007] Therefore, there is a need to develop self-supporting separators that can improve the energy density and lifespan characteristics of electrochemical devices. Summary of the invention

[0008] Technical issues

[0009] The technical problem to be solved by the present disclosure is to provide a self-supporting diaphragm for an electrochemical device and an electrochemical device comprising the same, wherein the electrochemical device is provided with a negative electrode containing a silicon-based active material, and the surface roughness Sa of the diaphragm is adjusted by adjusting the content of inorganic particles in the self-supporting diaphragm, thereby improving compression resistance, and being able to improve the energy density and life characteristics of the electrochemical device.

[0010] However, the problems to be solved by the present disclosure 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 following description.

[0011] Technical Solution

[0012] One embodiment of the present disclosure is a self-supporting diaphragm for an electrochemical device, wherein the electrochemical device is provided with a negative electrode containing a silicon-based active material, the self-supporting diaphragm comprises inorganic particles and a polymer binder disposed on a portion or all of the surface of the inorganic particles, and contains pores, the content of the inorganic particles is greater than 70 parts by weight based on 100 parts by weight of the diaphragm, and the surface roughness Sa of the diaphragm is greater than 600 nm and less than 1100 nm.

[0013] According to one embodiment of the present disclosure, the average particle size D of the inorganic particles is 50 It can be greater than or equal to 40 nm and less than or equal to 300 nm.

[0014] According to one embodiment of the present disclosure, the content of the silicon-based active material in the negative electrode may be 50 wt % or more.

[0015] According to one embodiment of the present disclosure, the hardness of the negative electrode may be 50 MPa or more and 350 MPa or less.

[0016] According to one embodiment of the present disclosure, the polymer binder may be included in an amount of 30 parts by weight or less based on 100 parts by weight of the separator.

[0017] According to one embodiment of the present disclosure, the polymer binder may be an acrylic binder, a polyvinylidene binder, or a combination thereof.

[0018] According to one embodiment of the present disclosure, the thickness of the separator may be 10 μm or more and 30 μm or less.

[0019] According to one embodiment of the present disclosure, the air permeability change rate of the separator according to the following formula 1 may be 10% or less:

[0020] [Formula 1]

[0021] Permeability change rate (%) = {(permeability of the diaphragm after pressure is applied - permeability of the diaphragm before pressure is applied) / permeability of the diaphragm before pressure is applied} × 100.

[0022] One embodiment of the present disclosure provides an electrochemical device including: a positive electrode; a negative electrode containing a silicon-based active material; and a separator interposed between the positive electrode and the negative electrode containing the silicon-based active material.

[0023] According to one embodiment of the present disclosure, the driving voltage range of the electrochemical device may be 2.5V to 4.2V.

[0024] Beneficial Effects

[0025] A self-supporting separator for an electrochemical device according to one embodiment of the present disclosure may have improved compression resistance.

[0026] An electrochemical device including a self-supporting separator for an electrochemical device according to one embodiment of the present disclosure can improve energy density and life characteristics by utilizing a lower limit voltage. DETAILED DESCRIPTION

[0027] In the present specification, when a part “includes” a certain constituent element, it does not mean that other constituent elements are excluded, but the part may further include other constituent elements unless explicitly stated otherwise.

[0028] In the present specification, "A and / or B" means "A and B, or A or B".

[0029] In the present specification, when it is mentioned that a component is disposed “on” a component, unless explicitly stated otherwise, this means that other components may be disposed between them, and does not exclude that other components may be disposed.

[0030] In the present specification, the property of “containing pores” means that an object contains a plurality of pores so that a fluid in a gas phase and / or a liquid phase can flow from one side of the object to the other side due to a structure in which the pores are connected to each other.

[0031] In the present specification, the separator has a porous property including a large number of pores, and functions as an ion conductive barrier in an electrochemical device, which allows ions to pass therethrough while blocking electrical contact between a negative electrode and a positive electrode.

[0032] In the present specification, the “self-supporting separator for an electrochemical device” refers to a separator for an electrochemical device, which contains inorganic particles and a polymer binder but does not have a porous polymer substrate.

[0033] The present disclosure will be described in more detail below.

[0034] One embodiment of the present disclosure provides a self-supporting diaphragm for an electrochemical device, wherein the electrochemical device includes a negative electrode containing a silicon-based active material, wherein the self-supporting diaphragm for an electrochemical device includes inorganic particles and a polymer binder arranged on a part or all of the surface of the inorganic particles, and contains pores, based on 100 parts by weight of the diaphragm, the content of the inorganic particles is greater than 70 parts by weight, and the surface roughness Sa of the diaphragm is greater than 600 nm and less than 1100 nm.

[0035] A self-supporting diaphragm for an electrochemical device according to one embodiment of the present disclosure may have improved compression resistance. In addition, when a diaphragm for an electrochemical device according to one embodiment of the present disclosure is applied to an electrochemical device comprising a negative electrode containing a silicon-based active material, the energy density and life characteristics of the electrochemical device can be improved. That is, among the negative electrode active materials used for the negative electrode of an electrochemical device, the capacity of the silicon-based active material is about 10 times higher than that of the carbon-based active material, and due to such a high capacity, it has the advantage of being able to achieve high energy density even with a thin electrode.

[0036] According to one embodiment of the present disclosure, the self-supporting separator for an electrochemical device does not contain a porous polymer substrate. Since the self-supporting separator for an electrochemical device does not contain a porous polymer substrate, the heat resistance of the separator can be improved, and the separator can be prevented from shrinking at high temperatures and causing electrical short circuits in the electrodes.

[0037] According to one embodiment of the present disclosure, the separator contains inorganic particles and a polymer binder. As described above, since the separator contains the inorganic particles and the polymer binder, the heat resistance of the separator can be improved, and the separator can be prevented from shrinking at high temperatures and causing electrical short circuits in the electrodes. In addition, holes can be formed inside the separator.

[0038] According to one embodiment of the present disclosure, the separator contains inorganic particles. A non-limiting example of the inorganic particles may be BaTiO 3 、Pb(Zr,Ti)O 3 (PZT), Pb 1-x La x Zr 1-y Ti y O 3 (PLZT,0 <x<1,0<y<1)、Pb(Mg 1 / 3 Nb 2 / 3 ) 3 -PbTiO 3 (PMN-PT), hafnium dioxide (HfO 2)、SrTiO 3 SnO 2 、CeO 2 、MgO、Mg(OH) 2 、NiO、CaO、ZnO、ZrO 2 、SiO 2 , Y 2 O 3 、Al 2 O 3 、SiC、Al(OH) 3 、TiO 2 , aluminum peroxide, zinc tin hydroxide (ZnSn(OH) 6 ), tin zinc oxide (Zn 2 SnO 4 、ZnSnO 3 ), antimony trioxide (Sb 2 O 3 ), antimony tetroxide (Sb 2 O 4 ), antimony pentoxide (Sb 2 O 5 ), zeolite A, zeolite X, zeolite Y, γ-AlO(OH), etc., and may contain one or more of them. As described above, when the separator contains the inorganic particles, the heat resistance of the separator can be improved.

[0039] According to one embodiment of the present disclosure, the separator contains a polymer binder, and the polymer binder is disposed on a part or all of the surface of the inorganic particles. As described above, the separator may contain a polymer binder disposed on a part or all of the surface of the inorganic particles, thereby tightly stacking the inorganic particles, thereby improving the compression resistance of the separator.

[0040] According to one embodiment of the present disclosure, the separator contains pores. Specifically, it may contain a plurality of pores. More specifically, the separator may be a porous separator containing a plurality of pores therein. As described above, since the separator contains pores, lithium ions may be allowed to pass through while physically separating the negative electrode and the positive electrode, thereby allowing current to flow.

[0041] According to one embodiment of the present disclosure, the separator can be formed by bonding inorganic particles using a polymer binder and stacking them in layers. The pores inside the separator can be caused by the interstitial volume (i.e., the gaps between the inorganic particles). As described in detail below, depending on the content and average particle size of the inorganic particles, the structure and size of the pores may differ. In addition, depending on the difference in the structure and size of the pores, it is possible to prevent the transition metal dissolved from the positive electrode from moving to the negative electrode surface.

[0042] According to one embodiment of the present disclosure, based on 100 parts by weight of the diaphragm, the content of the inorganic particles is 70 parts by weight or more. Specifically, based on 100 parts by weight of the diaphragm, the content of the inorganic particles may be 70 parts by weight or more and less than 100 parts by weight, 75 parts by weight or more and 95 parts by weight or less, or 80 parts by weight or more and 90 parts by weight or less. By adjusting the content of the inorganic particles to within the above range, the heat resistance and compression resistance of the diaphragm can be improved, and the diaphragm can be prepared as a self-supporting diaphragm.

[0043] According to one embodiment of the present disclosure, the surface roughness Sa of the diaphragm is greater than 600nm and less than 1100nm. Specifically, the surface roughness Sa of the diaphragm may be greater than 650nm and less than 1050nm, greater than 700nm and less than 1000nm, greater than 750nm and less than 950nm, or greater than 750nm and less than 900nm. In this specification, the surface roughness Sa may be defined as the value obtained by taking the long axis of the diaphragm as the center line and performing arithmetic averaging of the differences between the center line of each part randomly extracted from the surface facing the electrode of the diaphragm and the vertical direction. By adjusting the surface roughness of the diaphragm to the above range, the inorganic particles and the polymer binder do not agglomerate, and the compression resistance of the diaphragm can be improved.

[0044] According to one embodiment of the present disclosure, the surface roughness Sa of the diaphragm can be measured using an optical profiler (Optical Profiler) NV 2700 of Nanosystem. The upper surface of the diaphragm is set on a sample stage and used as a measurement surface, and the average value of four different measurement areas can be calculated. The setting conditions of the measurement device are as follows.

[0045] Cut-off: 0.8 mm, scanning speed: 0.1 mm / sec, magnification: 500x.

[0046] According to one embodiment of the present disclosure, the average particle size D of the inorganic particles is 50 The average particle size D of the inorganic particles can be greater than 40 nm and less than 300 nm. 50The average particle size D of the inorganic particles may be 50 nm to 290 nm, 60 nm to 280 nm, 70 nm to 270 nm, 80 nm to 260 nm, 90 nm to 250 nm, 100 nm to 240 nm, 110 nm to 230 nm, 120 nm to 220 nm, 130 nm to 210 nm, 140 nm to 200 nm, 150 nm to 190 nm, or 160 nm to 180 nm. 50 Adjusting to the above range can improve the phase separation speed and phase separation efficiency between the polymer binder and the inorganic particles in the slurry for the separator, wherein the slurry is an emulsion containing a polymer binder dispersed in water. In addition, if the average particle size D 50 If the average particle size D is less than 40 nm, the dispersibility of the inorganic particles in the slurry prepared for preparing the diaphragm may be reduced. 50 If the thickness exceeds 300 nm, the compression resistance of the formed separator may be reduced.

[0047] In this manual, "D 50 The particle size “particle size” refers to 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 a laser diffraction method. Specifically, by dispersing the measurement target powder in a dispersion medium and then introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500), when the particles pass through a laser beam, the particle size distribution is calculated by measuring the difference in the diffraction pattern according to the particle size. The D 50 The particle size can be measured by calculating the particle size at the point where the cumulative distribution of the number of particles according to the particle size in the measuring device reaches 50%.

[0048] According to one embodiment of the present disclosure, the inorganic particles that can be used in the separator can be electrochemically stable. That is, the inorganic particles that can be used in one embodiment of the present disclosure can be in the operating voltage range of the applied electrochemical device (for example, in terms of Li / Li + As a benchmark, those inorganic particles that do not undergo oxidation and / or reduction reactions within the range of 0V to 5V).

[0049] According to one embodiment of the present disclosure, 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 may be Si, SiO x(0 < x < 2), Si-Y (where 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, Si-C composite material, etc., and may include one or more of them. Specifically, when the silicon-based anode active material is contained in the anode, the energy density and fast charging performance can be improved.

[0050] According to an embodiment of the present disclosure, the content of the silicon-based active material in the anode may be 50 wt% or more. Specifically, the content of the silicon-based active material in the anode may be 50 wt% or more and less than 100 wt%, 55 wt% or more and 95 wt% or less, 60 wt% or more and 90 wt% or less, 65 wt% or more and 85 wt% or less, or 70 wt% or more and 80 wt% or less. By adjusting the content of the silicon-based active material to the above range, the hardness of the anode can be maintained within a certain range, thereby preventing the pores of the separator from deforming.

[0051] According to an embodiment of the present disclosure, the hardness of the anode may be 50 MPa or more and 350 MPa or less. Specifically, the hardness of the anode may be 75 MPa or more and 325 MPa or less, 100 MPa or more and 300 MPa or less, 125 MPa or more and 275 MPa or less, 150 MPa or more and 250 MPa or less, or 175 MPa or more and 225 MPa or less. By adjusting the hardness of the anode to the above range, the pores of the separator can be prevented from deforming during the assembly process of the electrochemical device.

[0052] According to an embodiment of the present disclosure, the hardness of the anode can be measured by applying a micro-indentation tester. The micro-indentation tester can use the indentation equipment of Anton Paar. Press into the electrode until a depth of 5 μm, and measure the hardness by loading / unloading 5 points at each indentation depth at a rate of 2 N per minute.

[0053] According to an embodiment of the present disclosure, based on 100 parts by weight of the separator, the content of the polymer binder may be 30 parts by weight or less. Specifically, based on 100 parts by weight of the separator, the content of the polymer binder may be greater than 0 parts by weight and 30 parts by weight or less, 5 parts by weight or more and 25 parts by weight or less, or 10 parts by weight or more and 20 parts by weight or less. By adjusting the content of the polymer binder to the above range, the porosity of the separator can be maintained, and the adhesion can be maintained even when the coating is wetted by the electrolyte after battery activation.

[0054] According to one embodiment of the present disclosure, the polymer binder may be a particle type or a non-particle type. Specifically, as will be described below, the polymer binder may maintain a particle shape without being dissolved by a dispersion medium or a solvent, or the polymer binder may be dissolved by a dispersion medium or a solvent without maintaining a particle shape. As described above, by selecting a particle type or a non-particle type polymer binder, the mechanical properties and porosity of the diaphragm can be adjusted.

[0055] According to one embodiment of the present disclosure, the average particle size D of the particle-type polymer binder is 50 Specifically, the average particle size D of the polymer binder particles is 50 The average particle size D of the particle-type polymer binder 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. 50 The above range can be adjusted to improve the phase separation rate and phase separation efficiency between the particle type polymer binder and the inorganic particles in the coating slurry (ie, the emulsion containing the particle type polymer binder dispersed in water).

[0056] According to one embodiment of the present disclosure, the polymer adhesive may be an acrylic adhesive, a polyvinylene adhesive, or a combination thereof.

[0057] According to one embodiment of the present disclosure, the polymer binder may include two or more polymer binders. As described above, the polymer binder may include two or more polymer binders, thereby improving the adhesion between inorganic substances in the coating, improving the porosity of the coating, and simultaneously improving the dry adhesion in the state before the electrolyte is injected and the wet adhesion after the electrolyte is injected.

[0058] According to one embodiment of the present disclosure, the polymer binder may include an acrylic binder. The porosity of the separator can be maintained and the adhesion between the electrode and the separator can be improved in a battery lamination process, thereby improving the ease of battery manufacturing and stably performing a stacking process.

[0059] According to one embodiment of the present disclosure, the acrylic adhesive is a polymer containing carboxylic acid ester as a repeating unit, and preferably may be (meth)acrylate or acrylic-styrene copolymer.

[0060] According to one embodiment of the present disclosure, specific examples of the (meth)acrylate may include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, nonyl (meth)acrylate, 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, ethylene di(meth)acrylate, and the like, and the (meth)acrylate may be one or more selected from them. Among them, at least one selected from methyl (meth)acrylate, ethyl (meth)acrylate and 2-ethylhexyl (meth)acrylate is preferred, and methyl (meth)acrylate is particularly preferred.

[0061] According to one embodiment of the present disclosure, the acrylic-styrene copolymer may include an acrylic adhesive, and the acrylic adhesive may be a polyacrylate adhesive. For example, the adhesive may be one or more selected from the group consisting of styrene-butadiene rubber, nitrile rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, and acrylate polymers, and specifically, may be a copolymer containing acrylate.

[0062] According to one embodiment of the present disclosure, the polymer binder may include a polyvinylidene-based binder. Specifically, according to one embodiment of the present disclosure, the polyvinylidene-based binder may be a copolymer of polyvinylidene fluoride and hexafluoropropylene. As described above, a polyvinylidene-based binder may be selected as the polymer binder so as to maintain the porosity of the separator and maintain adhesion even when the coating is wetted by the electrolyte after battery activation. In addition, the rigidity of the battery can be improved, and the bending of the separator can be prevented.

[0063] According to one embodiment of the present disclosure, the polyvinylene-based adhesive may be an aqueous adhesive. Specifically, the polyvinylene-based adhesive may be selected as an aqueous adhesive, thereby reducing the manufacturing cost of the battery by minimizing pollutants discharged from the separator preparation process.

[0064] According to one embodiment of the present disclosure, the thickness of the diaphragm may be greater than 10 μm and less than 30 μm, but is not particularly limited thereto. Specifically, the thickness of the diaphragm may be greater than 12 μm and less than 28 μm, greater than 14 μm and less than 26 μm, greater than 16 μm and less than 24 μm, or greater than 18 μm and less than 22 μm. The thickness may be adjusted to an appropriate range by a person skilled in the art from the perspective of heat resistance or resistance. As described above, since the inorganic particles constituting the diaphragm form a dense stacking structure, and the average particle size D of the inorganic particles 50 The thickness of the separator can be adjusted to a suitable range within the above range because the thickness of the separator is 300 nm or less.

[0065] According to one embodiment of the present disclosure, a contact thickness gauge may be used to measure the thickness of the diaphragm, such as VL-50S-B manufactured by Mitutoyo.

[0066] According to one embodiment of the present disclosure, the separator may have improved compression resistance. Specifically, the content and average particle size D of the inorganic particles contained in the separator may be adjusted. 50 In addition, when a silicon-based negative electrode active material having a large volume expansion rate during charge and discharge is used as the negative electrode, the separator having improved compression resistance can improve the performance of the electrochemical device by suppressing deformation of the pores of the separator.

[0067] According to one embodiment of the present disclosure, the air permeability change rate of the separator may be 10% or less. Specifically, the air permeability change rate of the separator may be greater than 0% and less than 10%, greater than 1% and less than 9%, greater than 2% and less than 8%, greater than 3% and less than 7%, or greater than 4% and less than 6%. As described above, by adjusting the content and average particle size D of the inorganic particles contained in the separator, 50 The compression resistance is improved, and even after the lamination process, the pores do not change significantly, so the air permeability change rate of the separator can be shown to be low.

[0068] In the present specification, “air permeability change rate” may refer to a change rate obtained by measuring the air permeability of a separator before and after a lamination process.

[0069] According to one embodiment of the present disclosure, the porosity of the diaphragm may be 30% by volume or more. Specifically, the porosity of the diaphragm may be 30% by volume or more and 70% by volume or less, 32% by volume or more and 68% by volume or less, 34% by volume or more and 66% by volume or less, 36% by volume or more and 64% by volume or less, 38% by volume or more and 62% by volume or less, 40% by volume or more and 60% by volume or less, 42% by volume or more and 58% by volume or less, 44% by volume or more and 56% by volume or less, 46% by volume or more and 54% by volume or less, or 48% by volume or more and 52% by volume or less. The porosity of the diaphragm may be adjusted within the above range to maintain the movement of ions in the diaphragm and prevent the increase in the resistance of the diaphragm. Specifically, if the porosity is 70% or less, it is possible to ensure that the mechanical properties of the pressing process of bonding the diaphragm to the electrode can be ensured, and in addition, the surface opening rate will not become too high, which is suitable for ensuring adhesion. On the other hand, if the porosity is 30% or more, it is advantageous from the viewpoint of ion permeability.

[0070] In the present specification, "porosity" refers to the ratio of the volume occupied by pores to the entire volume, with volume % as its unit, and is used interchangeably with terms such as void ratio and porosity.

[0071] In this specification, the porosity corresponds to a value obtained by subtracting a volume converted from the weight and density of each component of the separator from a volume calculated from the thickness, width, and length of the separator.

[0072] In one embodiment of the present disclosure, the porosity and pore size of the separator can be measured by a nitrogen adsorption distribution method using a BET six-point method using a scanning electron microscope (SEM) image, a mercury porosimeter, a capillary flow porosimeter, or a porosity analyzer (Belsorp-II mini of Bell Japan Inc.). At this time, the use of a capillary flow porosimeter may be advantageous.

[0073] According to one embodiment of the present disclosure, the method for forming the diaphragm is, for example, as follows. First, the polymer binder is dissolved in a suitable solvent, or dispersed in a dispersion medium to prepare a polymer solution or a polymer emulsion. Non-limiting examples of usable solvents or dispersion media include N-methyl-2-pyrrolidone (NMP), acetone, tetrahydrofuran, dichloromethane, chloroform, dimethylformamide, cyclohexane, water, or a mixture thereof.

[0074] Next, the inorganic particles are dispersed in a suitable solvent to prepare an inorganic slurry. Available solvents include propylene carbonate (PC), ethylene carbonate (EC), N-methyl-2-pyrrolidone (NMP), or a mixture thereof. According to one embodiment of the present disclosure, the content ratio of the inorganic particles to the polymer binder is as described above, and the thickness, pore size and porosity of the diaphragm of the present disclosure finally prepared are appropriately adjusted in consideration.

[0075] Next, the inorganic slurry prepared above is applied to at least one side of the prepared PET release film and dried. The method of applying the inorganic slurry to the surface of the PET release film is not particularly limited to any one method, and conventional methods known in the art can be used. For example, various methods such as dip coating, die coating, roller coating, comma coating, or a combination thereof can be used.

[0076] In the drying process, temperature and time conditions are appropriately set to minimize the occurrence of surface defects of the separator. For the drying, drying auxiliary equipment such as a drying furnace or hot air may be used within an appropriate range.

[0077] After the drying process, the PET release film may be removed to prepare the separator.

[0078] According to one embodiment of the present disclosure, the separator is inserted between the negative electrode and the positive electrode, and an electrochemical device is prepared by a lamination process in which heat and / or pressure are applied to combine them. In one embodiment of the present disclosure, the lamination process can be performed by a rolling device including a pair of pressing rollers. That is, interlayer bonding can be achieved by stacking the negative electrode, the separator, and the positive electrode in sequence and placing them between the pressing rollers. At this time, the lamination process can be performed using a hot pressing method.

[0079] One embodiment of the present disclosure provides an electrochemical device including: a positive electrode; a negative electrode containing a silicon-based active material; and a separator interposed between the positive electrode and the negative electrode containing the silicon-based active material.

[0080] An electrochemical device according to one embodiment of the present disclosure includes a separator, which includes inorganic particles and a polymer binder arranged on a part or all of the surface of the inorganic particles, contains pores, has a surface roughness Sa of greater than 600nm and less than 1100nm, and does not contain a porous polymer substrate, thereby being able to improve heat resistance and compression resistance, and being able to improve the energy density and life characteristics of the battery.

[0081] According to one embodiment of the present disclosure, the driving voltage of the electrochemical device may range from 2.5 V to 4.2 V. Specifically, by including a separator having improved compression resistance, the electrochemical device can utilize the lower limit voltage of a battery including a negative electrode containing a silicon-based active material.

[0082] In the present disclosure, the electrochemical device is a device that converts chemical energy into electrical energy through an electrochemical reaction, and is a concept covering primary batteries and secondary batteries. In this specification, the secondary battery can be charged and discharged, and refers to a lithium secondary battery, a nickel-cadmium battery, a nickel-hydrogen battery, etc. The lithium secondary battery uses lithium ions as an ion conductor, and examples thereof may include a non-aqueous electrolyte secondary battery containing a liquid electrolyte, an all-solid-state battery containing a solid electrolyte, a lithium polymer battery containing a gel polymer electrolyte, and a lithium metal battery using lithium metal as a negative electrode, but is not limited thereto.

[0083] According to one embodiment of the present disclosure, the positive electrode comprises 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 current collector. The positive electrode active material may include one or a mixture of two or more of the following: a layered compound, such as a lithium manganese composite oxide (LiMn 2 O 4 、LiMnO 2 etc.), lithium cobalt oxide (LiCoO 2 ), or lithium nickel oxide (LiNiO 2 ), or a compound replaced by one or more transition metals; 1+x Mn 2-x O 4 (wherein x is 0 to 0.33) represented by lithium manganese oxide, such as LiMnO 3 、LiMn 2 O 3 、LiMnO 2 etc.; Lithium copper oxide (Li 2 CuO 2 ); Vanadium oxides, such as LiV 3 O 8 , LiV 3 O 4 、V 2 O 5 , Cu 2 V 2 O 7 Etc.; by formula LiNi 1-x M x O 2Ni-site type lithium nickel oxide represented by (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3); lithium manganese composite oxide represented by the formula LiMn 1-x M x O 2 (where M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1) or Li 2 Mn 3 MO 8 (where M = Fe, Co, Ni, Cu or Zn); LiMn 2 O 4 in which a part of Li is replaced by an alkaline earth metal ion; disulfide compound; and Fe 2 (MoO 4 ) 3 .

[0084] According to one embodiment of the present disclosure, the negative electrode includes 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 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 alloy, and Si-C composite. In addition, the negative electrode may further contain a mixture of one or two or more selected from the following materials as the negative electrode active material: lithium metal oxide; carbon, such as non-graphitizable carbon and graphite-based carbon; metal composite oxide, such as Li x Fe 2 O 3 (0 ≤ x ≤ 1), Li x WO 2 (0 ≤ x ≤ 1), or Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb or Ge; Me': Al, B, P, Si, elements of Group 1, Group 2 or Group 3 of the periodic table, or halogen; 0 < x ≤ 1; 1 ≤ y ≤ 3; and 1 ≤ z ≤ 8); lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxide, such as SnO, SnO 2 , PbO, PbO 2 , Pb 2 O 3 , Pb 3 O 4 , Sb 2 O 3 , Sb 2 O 4 , Sb 2 O5 、GeO、GeO 2 、Bi 2 O 3 、Bi 2 O 4 and Bi 2 O 5 ; conductive polymers, such as polyacetylene; Li-Co-Ni based materials; and titanium oxide.

[0085] According to one embodiment of the present disclosure, the conductive material may be any one selected from the group consisting of, for example, graphite, carbon black, carbon fiber or metal fiber, metal powder, conductive whisker, conductive metal oxide, activated carbon, polyphenylene derivatives, or a mixture of two or more conductive materials. More specifically, the conductive material may be one selected from the group consisting of natural graphite, artificial graphite, super-p, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, Danka black, aluminum powder, nickel powder, zinc oxide, potassium titanate and titanium oxide, or a mixture of two or more conductive materials.

[0086] According to one embodiment of the present disclosure, there is no particular limitation on the current collector as long as it has high conductivity and does not cause chemical changes in the corresponding battery. For example, stainless steel, copper, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used.

[0087] According to one embodiment of the present disclosure, a polymer commonly used in electrodes in the art can be used as the binder resin. Non-limiting examples of such binder resins may include polyvinylidene fluoride-to-hexafluoropropylene, polyvinylidene fluoride-to-trichloroethylene, polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl acetate, poly(ethylene-to-vinyl acetate) copolymer, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, etc., but are not limited thereto.

[0088] According to one embodiment of the present disclosure, the positive electrode slurry used to prepare the positive electrode active material layer may contain a dispersant, and the dispersant may be a pyrrolidone-based compound, specifically, N-methylpyrrolidone (ADC-01, LG Chemical Company).

[0089] According to one embodiment of the present disclosure, based on 100 parts by weight of the positive electrode slurry, the content of the dispersant contained in the positive electrode slurry may be greater than 0 parts by weight and less than 0.5 parts by weight. Specifically, based on 100 parts by weight of the positive electrode slurry, the content of the dispersant contained in the positive electrode slurry may be greater than 0.05 parts by weight and less than 0.4 parts by weight.

[0090] According to one embodiment of the present disclosure, the negative electrode slurry for preparing the negative electrode active material layer may contain a dispersant, and the dispersant may be a CMC dispersant (SWCNT, OCSiAl, Tuball dispersant).

[0091] According to one embodiment of the present disclosure, based on 100 parts by weight of the negative electrode slurry, the content of the dispersant contained in the negative electrode slurry may be greater than 0 parts by weight and less than 1.0 parts by weight. Specifically, based on 100 parts by weight of the negative electrode slurry, the content of the dispersant contained in the negative electrode slurry may be greater than 0.1 parts by weight and less than 0.9 parts by weight, greater than 0.2 parts by weight and less than 0.8 parts by weight, greater than 0.3 parts by weight and less than 0.7 parts by weight, or greater than 0.4 parts by weight and less than 0.6 parts by weight.

[0092] According to one embodiment of the present disclosure, a battery may be manufactured by housing the electrochemical device prepared as described above in a suitable housing and injecting an electrolyte.

[0093] According to one embodiment of the present disclosure, the electrolyte may be a solid having a structure such as A which is dissolved or dissociated in an organic solvent. + B - The electrolyte is obtained from a salt of the structure, wherein A + including alkali metal cations (such as Li + 、Na + and K + ) or a combination thereof; and B - Including by such as PF 6 - , BF 4 - , Cl - Br - ,I - , ClO 4 - , AsF 6 - , CH 3 CO 2 - CF 3 SO 3 - 、N(CF 3 SO2 ) 2- and C(CF 2 SO 2 ) 3- anions or their combinations; the organic solvent is composed of 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), γ-butyrolactone (gamma-butyrolactone), or a mixture thereof, but is not limited thereto.

[0094] One embodiment of the present disclosure provides a battery module, the 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 device may include an electric tool driven by the power of a battery motor; an electric vehicle, including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid vehicle (PHEV), etc.; an electric two-wheeled vehicle, including an electric bicycle (E-bike) and an electric scooter (E-scooter); an electric golf cart; a power storage system, etc., but are not limited thereto.

[0095] Mode for Carrying Out the Invention

[0096] The present disclosure will be described in detail below with reference to the embodiments to specifically explain the present disclosure. However, the embodiments according to the present disclosure can be modified into various other forms, and the scope of the present disclosure should not be interpreted as being limited to the embodiments described below. The embodiments of this specification are provided to more completely explain the present disclosure to those skilled in the art.

[0097] <Example 1>

[0098] <Preparation of Separator>

[0099] The average particle size D of the inorganic particles 50 The boehmite (Sasol's Disperal 60) with an average particle size of 60 nm 50 Boehmite (Disperal 80 from Sasol) having a size of 80 nm was added to propylene carbonate (PC) as a solvent at a weight ratio of 3:2 and dispersed therein to prepare an oil-based slurry.

[0100] A polymer binder solution prepared by dispersing PVDF (Solef 5140-02 from Solvay) as a polymer binder in an NMP solvent was added to the oil-based slurry according to a weight ratio, and the mixture was stirred at 3000 rpm for 45 minutes to prepare an inorganic slurry.

[0101] Then, the inorganic slurry was applied to one surface of a PET release film by bar coating using a doctor blade, and dried using a hot air gun with wind at 50° C. The weight ratio of the inorganic particles to the polymer binder was 73:27.

[0102] Subsequently, the PET release film was removed, thereby preparing a separator having a total thickness of 14.7 μm and a surface roughness Sa of 750 nm.

[0103] An electrochemical device including the separator prepared above was fabricated to conduct experiments within a driving voltage range of 2.5V to 4.2V.

[0104] <Manufacturing of Electrochemical Device>

[0105] 1) Preparation of positive electrode

[0106] The positive electrode active material (LiNi 0.8 Mn 0.1 Co 0.1 O 2 ), a conductive material (carbon black), a dispersant (N-methylpyrrolidone, ADC-01, LG Chemical Company), and a 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 a positive electrode active material layer having a concentration of 50% by weight of the remaining components except water. Next, the slurry was applied to the surface of an aluminum film (thickness of 10 μm) and dried to prepare a positive electrode having a positive electrode active material layer (thickness of 120 μm).

[0107] 2) Preparation of negative electrode

[0108] Silicon particles (M702 from Elkem), PAM-based binder (BUH0452 from Arakawa), conductive material (SFG-6L from Imerys), conductive material (SWCNT, OCSiAl, Tuball dispersant) and CMC dispersant (SWCNT, OCSiAl, Tuball dispersant) were mixed with water at a weight ratio of 80:9.4:9.6:0.4:0.6 to prepare a slurry for a negative electrode active material layer having a concentration of 25 wt % of the remaining components except water. Next, the slurry was applied to the surface of a copper thin film (thickness 8 μm) and dried to prepare a negative electrode with a negative electrode loading of 8 mAh / cm2 of the negative electrode.

[0109] 3) Lamination process

[0110] An electrode assembly was obtained by interposing the separator of Example 1 between the prepared negative electrode and positive electrode and stacking and performing a lamination process The lamination process was performed using a hot press under the conditions of 70° C. and 5.2 MPa for 10 seconds.

[0111] <Example 2>

[0112] A separator was prepared in the same manner as in Example 1, except that the weight ratio of the inorganic particles to the polymer binder in Example 1 was set to 75:25, the surface roughness Sa was 600 nm, and the thickness was 14.8 μm.

[0113] An electrochemical device including the separator prepared above was fabricated to conduct experiments within a driving voltage range of 2.5V to 4.2V.

[0114] <Example 3>

[0115] The diaphragm was prepared in the same manner as in Example 1, except that the average particle size D of the inorganic particles in Example 1 was 50 The boehmite (Sasol's Disperal 60) with an average particle size of 60 nm 50 The weight ratio of boehmite (Disperal 80 from Sasol) with a particle size of 80 nm was set to 9:1, and the weight ratio of the inorganic particles to the polymer binder was set to 70:30. The surface roughness Sa was 1100 nm and the thickness was 14.9 μm.

[0116] An electrochemical device including the separator prepared above was fabricated to conduct experiments within a driving voltage range of 2.5V to 4.2V.

[0117] <Comparative Example 1>

[0118] The separator was prepared in the same manner as in Example 1, except that a particle with an average particle size D was added to the separator. 50 The average particle size D of the inorganic particles is 500 nm. 50 The molten metal is boehmite with a thickness of 80 nm (Disperal 80 from Sasol), and has a surface roughness Sa of 300 nm and a thickness of 14.6 μm.

[0119] An electrochemical device including the separator prepared above was fabricated to conduct experiments within a driving voltage range of 2.5V to 4.2V.

[0120] <Comparative Example 2>

[0121] A diaphragm was prepared in the same manner as in Example 1, except that a polyolefin substrate with a thickness of 7 μm was used in Example 1, the inorganic slurry of Example 1 was applied on both surfaces of the polyolefin substrate, the weight ratio of the inorganic particles to the polymer binder was set to 50:50, the surface roughness Sa was 450 nm, and the thickness was 14.8 μm.

[0122] An electrochemical device including the separator prepared above was fabricated to conduct experiments within a driving voltage range of 2.5V to 4.2V.

[0123] <Comparative Example 3>

[0124] The separator was prepared in the same manner as in Example 1, except that a polyolefin substrate having a thickness of 7 μm was used in Example 1, and particles having an average particle size of D were added to both surfaces of the polyolefin substrate. 50 The average particle size D of boehmite is 500 nm. 50 The boehmite is 80 nm (Disperal 80 from Sasol), the weight ratio of the inorganic particles to the polymer binder is 50:50, the surface roughness Sa is 300 nm, and the thickness is 15.0 μm.

[0125] An electrochemical device including the separator prepared above was fabricated to conduct experiments within a driving voltage range of 2.5V to 4.2V.

[0126] <Comparative Example 4>

[0127] A diaphragm is prepared in the same manner as in Example 1, except that in Example 1, a polyolefin substrate with a thickness of 7 μm is used, the inorganic slurry of Example 1 is applied to both surfaces of the polyolefin substrate, and the weight ratio of the inorganic particles to the polymer binder is set to 50:50, the surface roughness Sa is 450 nm, and the thickness is 14.7 μm.

[0128] An electrochemical device including the separator prepared above was fabricated to conduct experiments within a driving voltage range of 3.0V to 4.2V.

[0129] <Comparative Example 5>

[0130] The separator was prepared in the same manner as in Example 1, except that a polyolefin substrate having a thickness of 7 μm was used in Example 1, and a polyolefin substrate having an average particle size D 50The inorganic slurry of Comparative Example 1 having inorganic particles of 500 nm was coated on both surfaces of the polyolefin substrate, and the weight ratio of the inorganic particles to the polymer binder was set to 50:50, the surface roughness Sa was 300 nm, and the thickness was 14.9 μm.

[0131] An electrochemical device including the separator prepared above was fabricated to conduct experiments within a driving voltage range of 3.0V to 4.2V.

[0132] <Comparative Example 6>

[0133] The separator was prepared in the same manner as in Example 1, except that a particle with an average particle size D was added to the separator. 50 The inorganic particles are 60 nm in diameter, the weight ratio of the inorganic particles to the polymer binder is set to 65:35, the surface roughness Sa is 1200 nm, and the thickness is 15.0 μm.

[0134] An electrochemical device including the separator prepared above was fabricated to conduct experiments within a driving voltage range of 2.5V to 4.2V.

[0135] <Experimental Example 1: Change Rate of Air Permeability of Separator>

[0136] The air permeability (air permeability time, Gurley) of the diaphragms of the examples and comparative examples was measured by the ASTM D-2873 method. The Gurley value was measured using a Gurley type air permeometer (No. 158) of Toyo Seiki Co., Ltd. in accordance with the JIS Gurley measurement method of the Japanese Industrial Standard. Air permeability refers to the time it takes for 100cc of air to pass through the air permeability measurement object (such as a diaphragm), and seconds / 100cc can be used as its unit. The air permeability change rate is expressed by measuring the air permeability of the diaphragms of the examples and comparative examples before and after the lamination process.

[0137] <Experimental Example 2: Performance Retention Rate of Electrochemical Device>

[0138] In order to evaluate the life of the electrochemical devices manufactured including the separators of the embodiments 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, the process was performed 100 cycles, and the initial capacity and the remaining capacity were measured to show their change rates.

[0139]

[0140] Referring to Table 1, it is confirmed that the separator of Example 1 according to one embodiment of the present disclosure has the lowest air permeability change rate after compression resistance, and the performance retention rate of the electrochemical device is the best even when the electrochemical device is used up to the driving voltage range of 2.5V to 4.2V.

[0141] In addition, through the above-mentioned Examples 1 to 3, it was confirmed that within the range of surface roughness Sa of 600nm to 1100nm, the air permeability change rate after compression resistance remained low, and even when the electrochemical device was used in a driving voltage range of up to 2.5V to 4.2V, the performance retention rate of the electrochemical device was excellent.

[0142] In contrast, it was confirmed that the air permeability change rate of Comparative Example 1 was inferior to that of Example 1, and the performance retention rate also decreased when the same electrochemical device driving voltage range as Examples 1 to 3 was applied. This is considered to be because as the size of the inorganic substance applied to the separator increases, the pore size of the separator increases and the distribution of the pores becomes wider, resulting in poor compression resistance.

[0143] Comparative Examples 2 and 3 are diaphragms prepared by applying the inorganic slurry of Example 1 and Comparative Example 1 to both surfaces of a 7 μm thick polyolefin substrate, respectively. When a polyolefin substrate having a low hardness and being soft compared to an inorganic substance is applied to a diaphragm, the rate of change of air permeability after compression resistance shows a trend of rapid increase. Therefore, when the driving voltage range of the manufactured electrochemical device is evaluated in the same manner as in Example 1, it is confirmed that the performance retention rate of the electrochemical device decreases rapidly.

[0144] Comparative Examples 4 and 5 are the same separators as Comparative Examples 2 and 3, and the experiment was performed by changing the driving voltage range of the electrochemical device to 3.0 V to 4.2 V. Thus, it was confirmed that the air permeability change rate after compression resistance of the separator was the same as that of Comparative Examples 2 and 3. Although it was confirmed that the performance retention rate of the electrochemical device was slightly improved when the driving voltage range of the electrochemical device was changed to a narrower range (3.0 V to 4.2 V) than Comparative Examples 2 and 3 (2.5 V to 4.2 V), it was confirmed that it did not reach the level of Example 1.

[0145] It was confirmed that the air permeability change rate of Comparative Example 6 was inferior to that of Example 1, and the performance retention rate also decreased when the same driving voltage range of the electrochemical device was applied. This was confirmed to be due to the increase in surface roughness of the diaphragm as the size of the inorganic material applied to the diaphragm decreased, resulting in poor compression resistance.

[0146] According to one embodiment of the present disclosure, the self-supporting separator for an electrochemical device can adjust the surface roughness Sa of the separator by adjusting the content and average particle size of inorganic particles, thereby improving compression resistance and energy density, and has excellent electrochemical device performance retention rate, thereby expecting improvement in life characteristics.

Claims

1. A self-supporting diaphragm for an electrochemical device, the electrochemical device being provided with a negative electrode containing a silicon-based active material, The self-supporting membrane comprises inorganic particles and a polymer binder disposed on a part or all of the surface of the inorganic particles, and contains pores. Based on 100 parts by weight of the separator, the content of the inorganic particles is 70 parts by weight or more, and The separator has a surface roughness Sa of 600 nm or more and 1100 nm or less.

2. The self-supporting separator for an electrochemical device according to claim 1, wherein The average particle size D of the inorganic particles 50 It is greater than or equal to 40 nm and less than or equal to 300 nm.

3. The self-supporting separator for an electrochemical device according to claim 1, wherein: The content of the silicon-based active material in the negative electrode is 50 wt % or more. 4 . The self-supporting separator for an electrochemical device according to claim 1 , wherein the hardness of the negative electrode is 50 MPa or more and 350 MPa or less. 5 . The self-supporting separator for an electrochemical device 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 separator. 6 . The self-supporting separator for an electrochemical device according to claim 1 , wherein the polymer binder is an acrylic binder, a polyvinylene binder, or a combination thereof. 7 . The self-supporting separator for an electrochemical device according to claim 1 , wherein the thickness of the separator is 10 μm or more and 30 μm or less.

8. The self-supporting separator for an electrochemical device according to claim 1, wherein the separator has an air permeability change rate of 10% or less according to the following formula 1: [Formula 1] Permeability change rate (%) = {(permeability of the diaphragm after pressure is applied - permeability of the diaphragm before pressure is applied) / permeability of the diaphragm before pressure is applied} × 100. 9 . An electrochemical device comprising: a positive electrode; a negative electrode containing a silicon-based active material; and the separator according to claim 1 interposed between the positive electrode and the negative electrode containing the silicon-based active material.

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

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