Separation Membrane for Electrochemical Element and Electrochemical Element Containing the Same

Abstract

The present invention relates to a separation membrane for an electrochemical element and an electrochemical element including the same. In the separation membrane for an electrochemical element provided in a negative electrode containing a silicon (Si)-based active material, the separation membrane includes a porous polymer substrate; a first coating layer provided on at least one surface of the porous polymer substrate and containing a first polymer resin; and a second coating layer provided on the first coating layer and containing a second polymer resin and inorganic particles, and the solubility of the first polymer resin in the electrolytic solution is greater than the solubility of the second polymer resin in the electrolytic solution. The present invention relates to a separation membrane for an electrochemical element.

Description

Technical Field

[0001] This application claims priority based on Korean Patent Application No. 10-2023-0058002, filed with the Korean Intellectual Property Office on May 3, 2023, the contents of which are incorporated herein by reference in their entirety.

[0002] The present invention relates to a separator for an electrochemical device and an electrochemical device including the same.

Background Art

[0003] In secondary batteries, such as lithium secondary batteries, whose range of use is increasingly expanding in electric vehicles and the like, electricity is generally generated by a chemical reaction of lithium ions moving between a positive electrode material and a negative electrode material. Here, if the positive electrode material determines the capacity and voltage of the entire battery, the negative electrode material serves to store and release lithium ions coming out of the positive electrode.

[0004] On the other hand, if the positive electrode and the negative electrode are materials representing the performance of the battery, the separator can be said to be a core material related to the safety of the battery. Briefly speaking, the separator is a thin film of an insulating material and serves to separate the positive electrode and the negative electrode so that they do not come into contact inside the battery. In addition, although invisible to our eyes, the separator has very fine pores, and through these pores, lithium ions play a role in moving between the positive electrode and the negative electrode. The separator also sometimes serves to block the movement of lithium ions by closing pores and the like located on the surface of the separator (shut-down) when the internal temperature of the battery rises above a certain level, thereby preventing the occurrence of an internal short circuit (electric shortage).

[0005] For these reasons, film substrates based on polymer resins having a large number of pores are widely used as separators for electrochemical devices. Usually, an electrode assembly is manufactured by a lamination process of joining a separator and an electrode with heat and pressure, and the higher the heat and pressure applied in this process, the higher the bonding strength between the electrode and the separator.

Summary of the Invention

Problems to be Solved by the Invention

[0006] The technical problem to be achieved by the present invention is to adjust the solubility of the first polymer resin in the first coating layer and the second polymer resin in the second coating layer in the electrolyte in the separation membrane for an electrochemical element provided in a negative electrode containing a silicon (Si)-based active material, and to improve the problem that the pores in the porous polymer substrate are closed, and to provide a separation membrane for an electrochemical element and an electrochemical element including the same.

Means for Solving the Problems

[0007] One embodiment of the present invention is a separation membrane for an electrochemical element provided in a negative electrode containing a silicon (Si)-based active material, wherein the separation membrane for an electrochemical element includes a porous polymer substrate; a first coating layer provided on at least one surface of the porous polymer substrate and containing a first polymer resin; and a second coating layer provided on the first coating layer and containing a second polymer resin and inorganic particles, and the solubility of the first polymer resin in the electrolyte is greater than the solubility of the second polymer resin in the electrolyte, and provides a separation membrane for an electrochemical element.

[0008] According to one embodiment of the present invention, the solubility index of the first polymer resin is about 17 MPa 1 / 2 or more and 27 MPa 1 / 2 or less.

[0009] According to one embodiment of the present invention, the solubility index of the second polymer resin is less than about 17 MPa 1 / 2 or more than 27 MPa 1 / 2 or more.

[0010] According to one embodiment of the present invention, the first polymer resin may include one selected from the group consisting of polystyrene, poly ethyl acrylate, poly methyl acrylate, poly styrene sulfide, poly ethylene terephthalate, poly vinyl chloride (PVC), poly vinyl pyrrolidone (PVP), poly vinyl acetate (PVAc), polyacrylonitrile (PAN), polylactic acid (PLA), polyacrylic acid (PAA), and combinations thereof.

[0011] According to one embodiment of the present invention, the second polymer resin may include one selected from the group consisting of PVDF-HFP copolymer, PVDF-CTFE copolymer, PVDF-HFP-CTFE terpolymer, cyanoethyl polyvinyl alcohol, and combinations thereof.

[0012] According to one embodiment of the present invention, the separation membrane has a large number of pores, the polydispersity index (PDI) of the porous polymer substrate is about 2.5 or more and 10 or less, and the average pore diameter of the porous polymer substrate may be about 20 nm or more and 80 nm or less.

[0013] According to one embodiment of the present invention, the content of the silicon (Si)-based active material in the negative electrode may be about 50% by weight or more.

[0014] According to one embodiment of the present invention, the hardness of the negative electrode may be about 50 MPa or more and 350 MPa or less.

[0015] One embodiment of the present invention provides an electrochemical device, which includes a positive electrode, a negative electrode, and an electrolyte solution, and further includes a separator interposed between the positive electrode and the negative electrode. The separator is a separator for an electrochemical device having the above-described characteristics.

[0016] According to one embodiment of the present invention, the solubility index of the electrolyte solution is about 17 MPa 1 / 2 or more and 27 MPa 1 / 2 or less.

[0017] According to one embodiment of the present invention, the electrolyte solution may include one selected from the group consisting of propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), and combinations thereof.

[0018] According to one embodiment of the present invention, the electrolyte solution may be used by mixing diethyl carbonate (DEC) and fluoroethylene carbonate (FEC).

[0019] According to one embodiment of the present invention, the content ratio of diethyl carbonate (DEC) to fluoroethylene carbonate (FEC) in the electrolyte solution may be about 10:90 to 99:1.

[0020] According to another embodiment of the present invention, a method for manufacturing a separator for an electrochemical device is provided, which coats a porous polymer substrate with a first polymer resin and a second polymer resin having different solubilities in an electrolyte solution and is provided on a negative electrode containing a silicon (Si)-based active material.

[0021] The solubility of the first polymer resin in the electrolyte may be greater than the solubility of the second polymer resin in the electrolyte.

[0022] The separation membrane may include a porous polymer substrate; a first coating layer provided on at least one surface of the porous polymer substrate and containing a first polymer resin; and a second coating layer provided on the first coating layer and containing a second polymer resin and inorganic particles.

[0023] The solubility index of the first polymer resin is about 17 MPa 1 / 2 or more and 27 MPa 1 / 2 or less.

[0024] The first polymer resin may include one selected from the group consisting of polystyrene, poly ethyl acrylate, poly methyl acrylate, poly styrene sulfide, poly ethylene terephthalate, poly vinyl chloride (PVC), poly vinyl pyrrolidone (PVP), poly vinyl acetate (PVAc), polyacrylonitrile (PAN), polylactic acid (PLA), polyacrylic acid (PAA), and combinations thereof.

[0025] The second polymer resin may be selected from the group consisting of a PVDF-HFP copolymer, a PVDF-CTFE copolymer, a PVDF-HFP-CTFE terpolymer, cyanoethyl polyvinyl alcohol, and combinations thereof.

Advantages of the Invention

[0026] The separation membrane for an electrochemical element according to an embodiment of the present invention adjusts the solubility of the first polymer resin in the first coating layer and the second polymer resin in the second coating layer contained in the coating layer, and even when a negative electrode containing a silicon (Si)-based active material is applied, deformation of pores in the porous polymer base material can be prevented.

[0027] The electrochemical element according to an embodiment of the present invention includes a second coating layer containing a second polymer resin and inorganic particles on a first coating layer containing a first polymer resin, and even when a negative electrode containing a silicon (Si)-based active material is applied, deformation of pores in the porous polymer base material can be prevented, and the compression resistance and heat resistance are improved simultaneously.

Brief Description of the Drawings

[0028]

Figure 1

[0029] In a part of the attached drawings, the same drawing reference numerals are given to corresponding components. Those skilled in the art will understand that this figure simply and clearly illustrates the elements, etc., and is not necessarily drawn to scale. For example, for the purpose of assisting the understanding of various embodiments, the dimensions of some of the elements, etc. shown in the figure may be exaggerated compared to other elements, etc. Also, elements, etc. of known technologies that are useful or essential in commercially feasible embodiments may often not be depicted so as not to impede the gist of various embodiments of the present invention.

Modes for Carrying Out the Invention

[0030] In this specification, when a certain part "includes" a certain component, this means that, unless otherwise stated to the contrary, it does not exclude other components, but may further include other components.

[0031] In this specification, "A and / or B" means "A and B, or A or B".

[0032] As used herein, when a component is described as being "above" another component, this does not exclude the possibility that other components may be disposed therebetween, but rather means that other components may further be disposed, unless otherwise stated to the contrary.

[0033] As used herein, the characteristic of "having pores" means that the object contains a plurality of pores, and a fluid in the gas phase and / or liquid phase can pass from one side surface to the other side surface of the object through a structure in which the pores are interconnected with each other.

[0034] As used herein, "about", "substantially", and "approximately" are used in the context of inherent manufacturing and material tolerances and are used to mean a range of values or degrees close thereto, and are used to prevent an infringer from improperly using the disclosed content that refers to an exact or absolute numerical value provided to assist in understanding the present invention.

[0035] In the case of a lithium secondary battery, graphite is widely used as the material of the negative electrode material. However, in order to improve the energy density of the lithium secondary battery, the use range of a silicon (Si)-based negative electrode material as the negative electrode material is expanding. For example, since the silicon negative electrode material has an energy density about 10 times higher than that of the graphite negative electrode material, when the silicon negative electrode material is applied, there are advantageous aspects for improving the battery performance, such as increasing the battery capacity and shortening the charging speed.

[0036] On the other hand, in the manufacturing process of a secondary battery, the separator and the electrode may undergo a lamination process in which a relatively high temperature and pressure are applied. At this time, when applying a silicon negative electrode material, since its hardness is higher than that of a general graphite-based negative electrode material, when the silicon negative electrode material comes into contact with the separator in the lamination process, the pores of the separator may be deformed. Therefore, when applying a silicon negative electrode material with high hardness as the electrode assembly, the separator must ensure compression resistance, insulation, and heat resistance such that the pores are not deformed even when the separator comes into contact with the silicon negative electrode material under the high pressure and heat of the lamination process.

[0037] For example, recently, for the purpose of improving productivity, as the speed of the process increases, the time for applying heat to the separation membrane becomes shorter, and the adhesive force is ensured by increasing the pressure to ensure the adhesive force. However, in such a process, deformation of the separation membrane due to high pressure is a concern. Furthermore, in the lamination process, a large decrease in the thickness of the polymer film substrate appears, and accordingly, the pores of the separation membrane may be significantly damaged. As a result, there are problems such as a decrease not only in the performance of the battery but also in the breakdown voltage of the separation membrane.

[0038] In particular, when applying a silicon-based negative electrode active material such as Si, SiO, or Si alloy as the negative electrode active material of a lithium secondary battery, since the volume expansion of the negative electrode is large, the compressive deformation of the separation membrane due to the increase in the internal pressure of the cell during charge / discharge becomes even more severe. In addition, the silicon-based negative electrode active material has a larger particle size, roughness, and hardness than the graphite negative electrode active material, and may cause local damage to the separation membrane during lamination with the separation membrane. Therefore, the present invention provides a separation membrane with improved pressure resistance, insulation, and heat resistance in which pores are not deformed when applying a silicon-based negative electrode active material. In the present specification, the separation membrane has a porous property including a large number of pores, and serves as an ion-conducting barrier that blocks electrical contact between the negative electrode and the positive electrode in an electrochemical element and allows ions to pass through.

[0039] Hereinafter, the present invention will be described in more detail with reference to FIG. 1.

[0040]

[0041] ​​One embodiment of the present invention relates to a separator (100) for an electrochemical device provided in a negative electrode (200) containing a silicon (Si)-based active material. The separator (100) includes a porous polymer substrate (110); a first coating layer (131) provided on at least one surface of the porous polymer substrate (110) and containing a first polymer resin; and a second coating layer (133) provided on the first coating layer (131) and containing a second polymer resin and inorganic particles. The solubility of the first polymer resin contained in the first coating layer (131) in the electrolyte is greater than the solubility of the second polymer resin contained in the second coating layer (133) in the electrolyte. The separator (100) for an electrochemical device is included.

[0042] The separator for an electrochemical device according to one embodiment of the present invention adjusts the solubility of the first polymer resin of the first coating layer and the second polymer resin of the second coating layer contained in the coating layer, and even when a negative electrode containing a silicon (Si)-based active material is applied, deformation of pores in the porous polymer substrate can be prevented.

[0043] FIG. 1 is a schematic view of a separator for an electrochemical device and a negative electrode according to one embodiment of the present invention. Referring to FIG. 1, a separator for an electrochemical device and a negative electrode, which are one embodiment of the present invention, will be described.

[0044] According to one embodiment of the present invention, the silicon (Si)-based negative electrode active material essentially contains an Si-based compound, and the Si-based compound reversibly occludes and releases lithium by a formation reaction of a compound with lithium. Since the theoretical maximum capacity is about 4200 mAh / g (9366 mAh / cc, specific gravity 2.23), which is very large compared to carbon-based materials, it is used as a high-capacity negative electrode material.

[0045] According to one embodiment of the present invention, the Si-based compound is an Si / C composite, SiO2, SiO x (0 < x < 2), SiO doped with a metal x (0 < x < 2), pure Si (pure It can be any one or a mixture of two or more selected from the group consisting of silicon (Si), silicon (Si) nanostructures, and Si alloys (Si-alloy). Specifically, it can be SiO x It can be a silicon-based oxide of (0 < x < 2). For example, it can be 0.1 ≦ x ≦ 1.2, or x = 1.

[0046] The Si / C composite can be, for example, a structure in which a carbon substance is coated on the surface of particles or a structure in which carbon is atomically dispersed inside silicon particles by performing heat treatment (firing) in a state where carbon is bonded to silicon or silicon oxide particles. However, as long as carbon and silicon substances form a composite, it is possible without limitation.

[0047] In addition, the metal-doped SiO x (0 < x < 2) can be a structure doped with one or more metals selected from the group consisting of Li, Mg, Al, Ca, and Ti.

[0048] As described above, when SiO x is doped, it is more preferable to reduce the irreversible SiO2 phase of the SiO x material or convert it into an electrochemically inactive metal-silicate phase to increase the initial efficiency of the SiO x material.

[0049] The Si alloy (Si-alloy) is alloyed with Si and one or more metals selected from the group consisting of Zn, Al, Mn, Ti, Fe, and Sn, and examples include solid solutions, intermetallic compounds, eutectic alloys, etc. with these, but are not limited thereto.

[0050] The negative electrode may further contain other negative electrode active materials such as graphite in addition to the silicon (Si)-based negative electrode active material.

[0051] The silicon (Si)-based negative electrode active material as described above is a negative electrode active material that is continuously being researched and developed considering factors such as capacity. When applied as a negative electrode active material of a lithium secondary battery, since the volume expansion of the negative electrode is large, there is a problem that the compression deformation of the separator due to the increase in pressure inside the cell during charge / discharge becomes even more severe. In addition, since the Si-based negative electrode active material has a larger particle size, roughness, and hardness compared to the graphite negative electrode active material, it may cause local damage to the separator during lamination with the separator. Therefore, it is necessary to apply a separator that can simultaneously ensure the compression resistance and heat resistance that prevent the pores of the separator from being deformed.

[0052] According to one embodiment of the present invention, the porous polymer substrate (110) of the separator can be manufactured from known polymers known to be usable as porous polymer substrates of lithium secondary batteries, such as polyolefin, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, etc., and can particularly be manufactured with a polyolefin as a base polymer. Examples of polyolefin include polyethylene, polypropylene, polypentene, etc., and one or more of these can be included.

[0053] The porous polymer substrate manufactured based on the polyolefin, for example, a polymer substrate having a large number of pores, is advantageous from the viewpoint of imparting a shutdown function at an appropriate temperature. In particular, when polyethylene and polypropylene are simultaneously included as the polyolefin, physical properties such as shutdown characteristics and mechanical strength can be improved simultaneously.

[0054] According to one embodiment of the present invention, the thickness of the porous polymer substrate can be about 1 μm to about 100 μm. For example, the thickness of the porous polymer substrate can be about 10 μm or more and 95 μm or less, 15 μm or more and 90 μm or less, 20 μm or more and 85 μm or less, 25 μm or more and 80 μm or less, 30 μm or more and 75 μm or less, 35 μm or more and 70 μm or less, 40 μm or more and 65 μm or less, 45 μm or more and 60 μm or less, 50 μm or more and 65 μm or less, or 55 μm or more and 60 μm or less. For example, it can be about 1 μm to 30 μm, or about 5 μm to 30 μm. By adjusting the thickness of the porous polymer substrate within the above-described range, the volume of the electrochemical element can be minimized, and the positive electrode and the negative electrode can be electrically insulated from each other.

[0055] According to one embodiment of the present invention, the porous polyolefin polymer substrate most commonly used as the porous polymer substrate can be manufactured as follows, but is not limited thereto.

[0056] The porous polyolefin polymer substrate can be manufactured by a method (dry method) in which a polyolefin polymer is melt-extruded and formed into a sheet shape, and then stretched to induce fine cracks (micro cracks) between lamellae, which are crystalline portions of the polymer, to form fine voids. Alternatively, the separation membrane can be manufactured by a method (wet method) in which a polyolefin polymer is kneaded with diluents at a high temperature to form a single phase, the polymer material and the diluent are phase-separated during the cooling process, the diluent is extracted to form pores, and then stretching and heat setting treatments are performed. crack) to form fine voids. Alternatively, the separation membrane can be manufactured by a method (wet method) in which a polyolefin polymer is kneaded with diluents at a high temperature to form a single phase, the polymer material and the diluent are phase-separated during the cooling process, the diluent is extracted to form pores, and then stretching and heat setting treatments are performed.

[0057] According to an embodiment of the present invention, the separation membrane for the electrochemical element includes a coating layer (130) provided on at least one surface of the porous polymer substrate. For example, the separation membrane for the electrochemical element includes a coating layer provided on one or both surfaces of the porous polymer substrate. As described above, by including a coating layer provided on at least one surface of the porous polymer substrate in the separation membrane for the electrochemical element, the heat resistance of the separation membrane can be improved, the mechanical properties can be improved, and it is possible to prevent the separation membrane from shrinking at high temperature and causing an electrical short circuit of the electrode.

[0058] According to an embodiment of the present invention, the separation membrane includes a first coating layer (131) containing a first polymer resin. For example, the first coating layer can be located on the porous polymer substrate. Thereby, when the first coating layer is coated on the porous polymer substrate, the first polymer resin may be located inside the pores in the porous polymer substrate and the pores may be closed. Thus, even when a negative electrode containing a relatively hard Si-based negative electrode active material is applied and the lamination process proceeds, the deformation phenomenon in which the pores become smaller or are closed by the first polymer resin located inside the pores can be improved. As described above, by including a first coating layer containing a first polymer resin in the separation membrane, it is possible to embody a separation membrane for an electrochemical element with improved compression resistance and heat resistance even when a Si-based negative electrode active material is applied.

[0059] According to an embodiment of the present invention, the separation membrane is provided on the first coating layer and includes a second coating layer (133) containing a second polymer resin and inorganic particles. For example, the second coating layer can be located on the first coating layer located on the porous polymer substrate. When the first polymer resin contained in the first coating layer is located in the pores in the porous polymer substrate and all or part of the first coating layer does not remain, the second coating layer can be located in contact with the porous polymer substrate. As described above, by including the separation membrane on the first coating layer and including a second coating layer containing a second polymer resin and inorganic particles, the heat resistance of the separation membrane is improved, the mechanical properties are improved, and it is possible to prevent the separation membrane from shrinking at high temperatures and causing an electrical short circuit of the electrode, and pores can be formed inside the coating layer.

[0060] According to an embodiment of the present invention, the first polymer resin and the second polymer resin can each be of a particulate type. As described above, by utilizing the fact that each of the first polymer resin and the second polymer resin is of a particulate type, pores can be formed in the coating layer.

[0061] According to an embodiment of the present invention, the first polymer resin and the second polymer resin can each be of a soluble type. The soluble polymer means a polymer that is dissolved by a solvent and does not represent a particulate type.

[0062] According to an embodiment of the present invention, the first coating layer may not contain inorganic particles.

[0063] According to an embodiment of the present invention, the second coating layer may include a plurality of pores. Here, the pores refer to the pores within the coating layer, and the positions where they are generated are different from those of the pores within the porous polymer substrate. For example, the coating layer may be a porous coating layer. For example, the coating layer may be a porous coating layer that includes a plurality of pores inside. As described above, by including a plurality of pores in the coating layer, while physically blocking the negative electrode and the positive electrode, lithium ions can pass through and an electric current can flow.

[0064] According to an embodiment of the present invention, the second coating layer can be formed by binding inorganic particles with second polymer resin particles. The pores inside the second coating layer may be due to the interstitial volume, which is the free space between the inorganic particles and the like.

[0065] According to an embodiment of the present invention, the inorganic particles included in the second coating layer are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are not particularly limited as long as oxidation and / or reduction reactions do not occur within the operating voltage range of the applied electrochemical device (for example, 0 to 5V based on Li / Li + reference). For example, when using inorganic particles with ion transfer ability, the ionic conductivity within the electrochemical device can be increased to improve performance. Also, when using inorganic particles with a high dielectric constant (hereinafter, "high-k inorganic particles") as the inorganic particles, it contributes to an increase in the dissociation degree of electrolyte salts, such as lithium salts, in the liquid electrolyte, and the ionic conductivity of the electrolyte solution can be improved. The inorganic particles may include high dielectric constant inorganic particles with a dielectric constant of about 5 or more or 10 or more, inorganic particles with lithium ion transfer ability, or a mixture thereof. For example, the inorganic particles may be BaSO4, BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y TiyO3 (PLZT, 0 < x < 1, 0 < y < 1), Pb(Mg 1 / 3Nb 2 / 3 ) It may be one selected from the group consisting of (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 oxides (Zn2SnO4, ZnSnO3), antimony trioxide (Sb2O3), antimony tetroxide (Sb2O4), antimony pentoxide (Sb2O5), boehmite (AlO(OH)), and combinations thereof, but this is merely illustrative and not limiting thereto.

[0066] According to one embodiment of the present invention, there is no limitation on the size of the inorganic particles, but for the formation of a coating layer with a uniform thickness and an appropriate porosity, it can be about 40 nm or more and 3 μm or less. For example, it can be about 40 nm or more and 2.5 μm or less, 40 nm or more and 2 μm or less, 40 nm or more and 1.5 μm or less, or 40 nm or more and 1.0 μm or less. When the size of the inorganic particles satisfies the above range, the dispersibility can be maintained, it is easy to adjust the physical properties of the separation membrane, the phenomenon of increasing the thickness of the coating layer can be avoided, the mechanical physical properties can be improved, and the probability of internal short circuit occurring during charging / discharging of the battery due to an overly large pore size is low.

[0067] According to one embodiment of the present invention, the thickness of the coating layer may be formed to be about 1 μm or more and 10 μm or less with respect to any one of the porous polymer substrates. For example, it can be about 1 μm or more and 9 μm or less, 2 μm or more and 8 μm or less, 3 μm or more and 7 μm or less, 3 μm or more and 6 μm or less, or 3 μm or more and 5 μm or less. According to one example, it can be coated on both sides by 4 μm each with respect to any one of the porous polymer substrates.

[0068] According to one embodiment of the present invention, the thickness of the polymer substrate and / or the coating layer, etc. can be measured by applying a contact thickness measuring instrument. For example, VL-50S-B of Mitutoyo Corporation can be used as the contact thickness measuring instrument.

[0069] According to one embodiment of the present invention, the solubility of the first polymer resin in the electrolyte is greater than the solubility of the second polymer resin in the electrolyte.

[0070] For example, the first polymer resin is a polymer resin that is injected into the interior of a battery case having an electrode assembly and is dissolved by an electrolyte that impregnates the electrode assembly, and means a polymer resin that is finally eluted from a lithium secondary battery product by the electrolyte. The polymer solution coated on the porous polymer substrate is produced by dissolving a first polymer resin having solubility in an electrolyte in a solvent. Any liquid that can dissolve the first polymer resin can be used as the solvent, but it is easy to penetrate into the pores of the porous polymer substrate by using a solvent having an affinity with the polymer component of the porous polymer substrate.

[0071] Further, the second polymer resin is a polymer resin that is injected into the interior of a battery case having an electrode assembly and is not dissolved or only a very small amount is dissolved by an electrolyte that impregnates the electrode assembly, and means a polymer resin that is not finally eluted in a large amount from a lithium secondary battery product by the electrolyte. That is, since the second polymer resin does not have to be eluted in the electrolyte, it must be interpreted as meaning a polymer resin that swells but is not dissolved by the electrolyte.

[0072] As described above, by adjusting the solubility of the first polymer resin in the electrolyte to be greater than the solubility of the second polymer resin in the electrolyte, even when a negative electrode containing a silicon (Si)-based active material is applied, deformation of the pores in the porous polymer substrate can be prevented, and compression resistance and heat resistance can be improved.

[0073] According to one embodiment of the present invention, the solubility index of the first polymer resin can be about 17 MPa 1 / 2 or more and 27 MPa 1 / 2 or less. For example, about 18 MPa 1 / 2 or more and 26 MPa 1 / 2 or less, 19 MPa1 / 2 Above 25 MPa 1 / 2 Below, 20 MPa 1 / 2 Above 24 MPa 1 / 2 Below, or 21 MPa 1 / 2 Above 23 MPa 1 / 2 It may be below. By adjusting the solubility index of the first polymer resin, it is possible to increase the solubility in the electrolyte and realize a separation membrane for an electrochemical element with improved compressive resistance.

[0074] According to one embodiment of the present invention, the solubility index of the second polymer resin is less than 17 MPa 1 / 2 Or may exceed 27 MPa 1 / 2 By adjusting the solubility index of the second polymer resin, since the difference in the solubility index with the electrolyte is relatively large, the particle phase can be maintained even under the electrolyte, and it is prevented from eluting into the electrolyte. The heat resistance of the separation membrane made of the second polymer resin and inorganic particles is improved, the mechanical properties are improved, and it is prevented that the separation membrane shrinks at a relatively high temperature and an electrical short circuit occurs between the electrodes, and pores can be formed inside the coating layer.

[0075] According to one embodiment of the present invention, the difference between the solubility index of the first polymer resin and the solubility index of the second polymer resin can be about 3 or more and 100 or less. For example, it can be about 5 or more and 100 or less, or about 7 or more and 100 or less.

[0076] According to one embodiment of the present invention, the solubility index of the electrolyte can be represented by the Hansen Solubility parameter (HSP). That is, each substance has a unique solubility factor value, and substances with similar solubility factor values are likely to dissolve or mix with each other.

[0077] The Hansen Solubility Parameter was proposed by Dr. C. Hansen, and the degree of bonding in a substance is considered by subdividing it into the following three factors. (1) Solubility factor (δD) generated by non-polar dispersion bonds (2) Solubility parameter (δP) generated by polar bonding due to permanent dipoles (3) Solubility parameter (δH) generated by hydrogen bonding In this way, HSP can accurately and systematically evaluate the solubility and miscibility of substances. HSP = (δD, δP, δH), (J / cm 3 ) 1 / 2 (1) δTot = (δD 2 + δP 2 + δH 2 ) 1 / 2 , (J / cm 3 ) 1 / 2 (2) HSP is a vector with magnitude and direction in a space consisting of three elements, and δTot represents the magnitude of the HSP vector. The basic unit representing HSP is (J / cm 3 ) 1 / 2 . This HSP value can be calculated using the program HSPiP (Hansen Solubility Parameters in Practice) developed by the Dr. Hansen group that proposed HSP. As described above, if the HSP values of two substances are similar, they are likely to dissolve in each other. However, since HSP is a vector, in order to determine that they are similar to each other, all three HSP components and the magnitude of HSP of each substance must be similar. All substances have HSP, and using this, through comparative analysis of the differences in similarity, it is possible to predict whether substances of interest will dissolve in each other.

[0078] According to an embodiment of the present invention, the first polymer resin may include one selected from the group consisting of polystyrene, poly ethyl acrylate, poly methyl acrylate, poly styrene sulfide, poly ethylene terephthalate, poly vinyl chloride (PVC), poly vinyl pyrrolidone (PVP), poly vinyl acetate (PVAc), polyacrylonitrile (PAN), polylactic acid (PLA), polyacrylic acid (PAA), and combinations thereof. It may be polyacrylic acid (PAA). As described above, by selecting the first polymer resin from the listed group, a first coating layer eluted into the electrolytic solution is formed, and even when a negative electrode containing a silicon (Si)-based active material is applied, deformation of pores in the porous polymer substrate can be prevented and compressibility resistance can be improved. Acid) and combinations thereof. It may be polyacrylic acid (PAA). As described above, by selecting the first polymer resin from the listed group, a first coating layer eluted into the electrolytic solution is formed, and even when a negative electrode containing a silicon (Si)-based active material is applied, deformation of pores in the porous polymer substrate can be prevented and compressibility resistance can be improved.

[0079] According to one embodiment of the present invention, the second polymer resin may include one selected from the group consisting of a PVDF-HFP copolymer (polyvinylidenefluoride hexafluoropropylene copolymer), a PVDF-CTFE copolymer (vinylidenefluoride-chlorotrifluoroethylene copolymer), a PVDF-HFPCTFE terpolymer (vinylidenefluoride-hexafluoropropylene-chlorotrifluoroethylene terpolymer), cyanoethyl polyvinyl alcohol, and combinations thereof. For example, it may be a PVDF-HFP copolymer and / or a PVDF-CTFE copolymer. As described above, by selecting the second polymer resin from the listed group, a second coating layer containing the second polymer resin that is not eluted into the electrolytic solution can be formed, and even when a negative electrode containing a silicon (Si)-based active material is applied, deformation of the pores in the porous polymer substrate can be prevented, and the compression resistance and heat resistance can be improved simultaneously.

[0080] According to one embodiment of the present invention, generally used acrylic polymers have a relatively high relative affinity for electrolytic solutions and swell a lot under electrolytic solutions even when crosslinked. Therefore, when used alone, acrylic polymers can swell and dissolve under electrolytic solutions. On the other hand, in the case of PVDF-based polymers with a large difference from the solubility index of electrolytic solutions, it is advantageous to maintain the particle phase even under electrolytic solutions, and they do not dissolve even when swelling under electrolytic solutions, and the compression resistance and heat resistance according to the present invention can be improved.

[0081] According to an embodiment of the present invention, the separation membrane has a large number of pores, the polydispersity index (PDI) of the porous polymer substrate is about 2.5 or more and 10 or less, and the average pore size of the pores of the porous polymer substrate can be 20 nm or more and 80 nm or less. The polydispersity index of the porous polymer substrate is low, and the average pore size of the pores of the porous polymer substrate is small. When this range is satisfied simultaneously, the compressibility resistance can be improved. For example, the polydispersity index (PDI) of the porous polymer substrate can be about 3.0 or more and 9.5 or less, 3.5 or more and 9.0 or less, 4.0 or more and 8.5 or less, 4.5 or more and 8.0 or less, 5.0 or more and 7.5 or less, 5.5 or more and 7.0 or less, or 6.0 or more and 6.5 or less. If the polydispersity index is less than 2.5, there is a problem that the processability deteriorates and the film uniformity is poor, and if it exceeds 10, there is a problem that the compressibility resistance decreases.

[0082] Furthermore, for example, the average pore size of the pores of the porous polymer substrate can be about 25 nm or more and 75 nm or less, 30 nm or more and 70 nm or less, 35 nm or more and 65 nm or less, 40 nm or more and 60 nm or less, or 45 nm or more and 55 nm or less. If the average pore size is less than 20 nm, there is a problem that the air permeability decreases and a phenomenon occurs in which by-products close small pores during charging / discharging of the battery. If it exceeds about 80 nm, the thickness of the separation membrane is not uniform, thickness deformation is caused, and there is a problem that the compressibility resistance decreases due to local thickness deformation.

[0083] According to an embodiment of the present invention, the average pore size of the pores of the porous polymer substrate can be calculated from the pore size distribution measured using the Capillary flow Porometer method. For example, first, after wetting the separation membrane to be measured with a wetting agent such as galwick solution, the air pressure on one side of the substrate is gradually increased. At this time, when the applied air pressure becomes larger than the capillary attraction of the wetting agent present in the pores, the wetting agent closing the pores is pushed out, and the size and distribution of the pores are measured based on the pressure and flow rate at the moment of extrusion, and the size of the average pore diameter can be confirmed from these.

[0084] According to an embodiment of the present invention, the content of the silicon (Si)-based active material in the negative electrode can be about 50% by weight or more. For example, it can be about 50% by weight or more and less than 100% by weight, 55% by weight or more and 95% by weight or less, 60% by weight or more and 90% by weight or less, 65% by weight or more and 85% by weight or less, 60% by weight or more and 80% by weight or less, or 65% by weight or more and 75% by weight or less. As described above, by adjusting the content of the silicon (Si)-based active material in the negative electrode, the energy density of the battery can be improved compared to the case where a graphite-based negative electrode active material is applied alone.

[0085] According to an embodiment of the present invention, the hardness of the negative electrode can be about 50 MPa or more and 350 MPa or less. For example, it can be about 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. When deviating from the above range, the pores of the separator are more likely to be deformed compared to the case where a graphite-based negative electrode active material is applied, and the energy density of the battery may decrease.

[0086] According to an embodiment of the present invention, the hardness refers to the indentation hardness (H IT ) measured by a nanoindenter.

[0087] The indentation is one of the analysis techniques for the mechanical properties of materials. It is an experimental method in which diamond indenters of various shapes are pressed into a material, and then the indentation mark and the load during indentation are compared and analyzed. The indentation test is not only a measurement technique for the fracture toughness and hardness of materials, but recently, many studies have been conducted in various directions, and it is also used as a research technique for analyzing the carbon behavior of materials, the residual stress state, the adhesion test of thin films, fracture characteristics, and phase transformation analysis. In particular, when performing indentation on fine materials such as electrodes as in the present invention, nano-indentation in which a load of N or less units is applied using an indenter can be applied.

[0088] The hardness is obtained by continuously measuring the load from the indenter and the depth of indentation when the indenter is pressed into the surface of the electrode active material layer during loading and unloading, and calculating from the obtained load-depth of indentation curve. For example, the hardness is calculated by the formula (Pmax) / A from the maximum load (Pmax) and the contact projected area A of the indenter when the maximum load (Pmax) is applied and the indenter is pressed in.

[0089] The hardness is an index that can represent the physical properties of the electrode active material layer. A large hardness means that the degree of deformation of the electrode active material layer against an external force is small. That is, the larger the hardness, the stronger the particles constituting the electrode active material layer are bonded to each other, which means that the resistance to indentation is large. On the other hand, the smaller the hardness, the weaker the particles constituting the electrode active material layer are bonded to each other, which means that the resistance to indentation is small.

[0090] According to one embodiment of the present invention, since the Si-based negative electrode active material has a higher hardness than the graphite negative electrode active material, there is a problem that the pores of the separator are likely to be deformed in the electrode assembly process.

[0091] According to an embodiment of the present invention, the method of forming the coating layer is as follows, for example. First, a binder resin is dissolved in a suitable organic solvent to produce a polymer solution. For example, as the solvent, the solubility index is similar to the binder polymer to be used, and the boiling point is low. This is to facilitate uniform mixing and subsequent removal of the solvent. Non-limiting examples of solvents that can be used include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), cyclohexane, water, or a mixture thereof. Next, inorganic particles are added to and dispersed in the produced polymer solution to produce a porous polymer substrate (110). In the present invention, the content ratio of the inorganic particles to the binder is appropriately adjusted in consideration of the thickness, pore size, and porosity of the coating layer of the present invention finally produced. Next, a first polymer substance and a second polymer substance for producing slurries for the first coating layer and the second coating layer are respectively selected. Then, the solubility of the selected first polymer substance in the electrolyte and the solubility of the second polymer substance in the electrolyte are compared.

[0092] As a result of comparison, if it is determined that the solubility of the first polymer substance in the electrolyte solution is greater than the solubility of the second polymer substance in the electrolyte solution, the selected first polymer substance is applied to produce a slurry for the first coating layer. Thereafter, the slurry for the first coating layer containing the first polymer substance is applied to at least one side surface of the prepared porous polymer substrate (110) and dried to form a first coating layer (131) on the porous polymer substrate (110). If, in step S140, it is determined that the solubility of the first polymer substance in the electrolyte solution is smaller than the solubility of the second polymer substance in the electrolyte solution, the process returns to the previous step and the selection of the first polymer substance and the second polymer substance is repeated. Next, the selected second polymer substance is applied to produce a slurry for the second coating layer, and the produced slurry for the second coating is applied onto the first coating layer and dried to form a second coating layer.

[0093] The first coating layer and the second coating layer can be manufactured so as to be separated from each other by the method described above. However, the first coating layer and the second coating layer are not separated from each other and can be formed, for example, by coating them simultaneously to form a coating layer. Further, the order of the manufacturing processes described above is not limited to the described order and can be appropriately modified. For example, the process of selecting the first polymer substance and the second polymer substance and comparing their solubilities in the electrolyte solution may also be performed before the production of the porous polymer solution, and the production of the slurries for the first coating layer and the second coating layer to which these first and second polymer substances are applied can also be performed before the production of the porous polymer solution. Also, the slurry for the first coating layer and the slurry for the second coating layer are not limited by the order of the processes and can be independently produced at the same time or at different times from each other.

[0094] According to an embodiment of the present invention, the method of applying the slurry to the surface of the separation membrane substrate is not particularly limited to any one of the methods described above. For example, various methods such as dip coating, die coating, roll coating, comma coating, or a mixed method thereof can be used.

[0095] According to one embodiment of the present invention, in the drying step, the temperature and time conditions are appropriately set so as to minimize the generation of surface defects in the organic / inorganic composite coating layer. For the drying, drying auxiliary devices such as a drying oven or a hot air blower can be used within an appropriate range.

[0096] According to one embodiment of the present invention, the manufactured separator is interposed between a negative electrode containing a Si-based negative electrode active material and a positive electrode, and is manufactured into an electrode assembly by a lamination step of applying heat and / or pressure to bind them. The lamination step can be performed by a roll press device including a pair of pressure rollers. That is, the negative electrode, the separator, and the positive electrode are sequentially laminated, and this is introduced between the pressure rollers to achieve binding between the layers. At this time, the lamination step can be performed by a hot pressing method.

[0097] One embodiment of the present invention includes an electrochemical device including a positive electrode, a negative electrode, an electrolytic solution, and a separator interposed between the positive electrode and the negative electrode.

[0098] The electrochemical device according to one embodiment of the present invention includes a second coating layer containing a second polymer resin and inorganic particles on a first coating layer containing a first polymer resin, and even when a negative electrode containing a silicon (Si)-based active material is applied, it prevents deformation of pores in the porous polymer base material, and simultaneously improves compression resistance and heat resistance.

[0099] According to one embodiment of the present invention, the negative electrode includes a negative electrode current collector and a negative electrode active material layer containing a Si-based negative electrode active material, a binder resin, and optionally a conductive material on at least one surface of the current collector. As the negative electrode active material, a silicon (Si)-based negative electrode active material can be used alone, or selectively used in combination with a carbon-based negative electrode active material such as graphite. The silicon (Si)-based negative electrode active material can be the same as those described above.

[0100] According to one embodiment of the present invention, the content of the silicon (Si)-based negative electrode active material can be about 50% by weight or more. For example, it can be 50% by weight or more and less than 100% by weight, 55% by weight or more and 95% by weight or less, 60% by weight or more and 90% by weight or less, 65% by weight or more and 85% by weight or less, 60% by weight or more and 80% by weight or less, or 65% by weight or more and 75% by weight or less. As described above, by adjusting the content of the silicon (Si)-based active material in the negative electrode, the energy density of the battery can be improved compared to when a graphite-based negative electrode active material is applied alone.

[0101] According to one embodiment of the present invention, the positive electrode includes 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 includes layered compounds such as lithium manganese composite oxides (LiMn2O4, LiMnO2, etc.), lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals; the 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; the 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 this; the chemical formula LiMn 1-x M x O2 (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 a 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. For example, it can be LiNi 0.8 Mn 0.1 Co 0.1 O2.

[0102] According to one 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. Further, for example, it can be one selected from the group consisting of natural graphite, artificial graphite, super-p, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide, or a mixture of two or more of these conductive materials.

[0103] According to one embodiment of the present invention, as the binder resin, a polymer resin commonly used for electrodes in the art can be used.Non-limiting examples of the binder resin include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyetylexyl acrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetatepropionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose (CMC), polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyethylene glycol (PEG), polyacrylonitrile (PAN), and polyacryl amide (PAM), etc., but are not limited thereto.

[0104] The electrode assembly prepared as described above can be placed in a suitable case and an electrolytic solution can be injected to manufacture a battery.

[0105] According to one embodiment of the present invention, the solubility index of the electrolytic solution is about 17 MPa 1 / 2 or more and 27 MPa 1 / 2 or less. For example, about 18 MPa 1 / 2 or more and 26 MPa 1 / 2 or less, 19 MPa 1 / 2 or more and 25 MPa 1 / 2 or less, 20 MPa 1 / 2 or more and 24 MPa 1 / 2 or less, or 21 MPa 1 / 2 or more and 23 MPa 1 / 2 or less. When the range of the solubility index of the electrolytic solution is satisfied, after impregnating a first polymer resin having a solubility index similar to the solubility index and then eluting it, even if a negative electrode containing a silicon (Si)-based active material is applied, deformation of pores in the porous polymer substrate can be prevented, and compressibility resistance and heat resistance can be improved simultaneously. That is, the smaller the difference between the solubility index of the electrolytic solution and the solubility index of the first polymer resin, the more excellent the solubility can be. Therefore, the solubility index of the electrolytic solution can be similar to or the same as the solubility index of the first polymer resin.

[0106] According to one embodiment of the present invention, the electrolytic solution is a salt having a structure such as A + B - , where A + is an ion composed of an alkali metal cation such as Li + , Na + , K + or a combination thereof, and B - is PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , NCF3SO2)2 - , CCF2SO2)3- There are salts containing anions such as or ions composed of these combinations dissolved or dissociated in an organic solvent 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), gamma-butyrolactone (γ-butyrolactone) or a mixture thereof. For example, according to one embodiment of the present invention, the electrolyte may contain one selected from the group consisting of propylene carbonate (PC, propylene carbonate), dimethyl carbonate (DMC, dimethyl carbonate), diethyl carbonate (DEC, Diethyl carbonate), fluoroethylene carbonate (FEC, Fluoro-ethylene carbonate) and combinations thereof.

[0107] According to one embodiment of the present invention, the electrolyte may be a mixture of diethyl carbonate (DEC, Diethyl carbonate) and fluoroethylene carbonate (FEC, Fluoro-ethylene carbonate) for use.

[0108] According to one embodiment of the present invention, the electrolyte may have a content ratio of propylene carbonate (PC, propylene carbonate) to dimethyl carbonate (DMC, dimethyl Carbonate) of about 10:90 to 99:1. For example, it may be about 20:80 to 98:2, 30:70 to 97:3, 40:60 to 96:4, 50:50 to 95:5, 60:40 to 94:6, 70:30 to 93:7, 80:20 to 92:8, or about 90:10.

[0109] According to one embodiment of the present invention, there is provided a battery module including a battery including the electrode assembly 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 include a power tool powered by a battery-powered motor; an electric vehicle such as an Electric Vehicle (EV), a Hybrid Electric Vehicle (HEV), a Plug-in Hybrid Electric Vehicle (PHEV); an electric two-wheeler 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. Electric Vehicle, HEV), Plug-in Hybrid Electric Vehicle (PHEV), etc.; electric two-wheelers including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf carts; power storage systems, etc., but are not limited thereto.

Example

[0110] Hereinafter, in order to specifically describe the present invention, examples will be given and described in detail. However, the examples according to the present invention may be deformed into various other forms, and the scope of the present invention is not construed as being limited to the examples described later. The examples in this specification are provided to more fully explain the present invention to those with average knowledge in the industry. <Example> As the porous polymer substrate, the SV9 of Shanghai Energy Co., Ltd. (thickness 9 μm, porosity 46%, basis weight 4.9 g / m 2 , gurley value 70 sec / 100 cc) separation membrane raw material was used.

[0111] On the other hand, Poly acrylic acid (PAA, Dow Co., CK-702) was used as the first polymer resin having electrolyte solubility, and the first polymer resin was completely dissolved in water as a solvent at a concentration of 10% by weight to prepare a polymer solution. The solubility index of the electrolyte of the first polymer resin is 22.4 MPa 1 / 2 is.

[0112] The prepared polymer solution was dip-coated onto a porous polyethylene polymer base stock and dried at 65 °C to form a polymer coating layer.

[0113] Next, PVDF-HFP (Solvay, solef 21510, 15 wt% HFP) and PVDF-CTFE (Solvay, solef 32008) as the second polymer resins are dissolved in the solvent acetone. And a slurry in which Cyano resin (Miwon Trading, CYR-301) as a dispersant is dissolved in the solvent acetone is prepared. The solubility parameters of 21510 and 32008 which are the second polymer resins are 13.5 MPa 1 / 2 , 15.1 MPa 1 / 2 respectively.

[0114] As inorganic particles, Al2O3 with an average particle size of about 500 nm and Boehmite particles with an average particle size of 300 nm are prepared. The weight ratio of the final slurry is set to Al2O3:Boehmite:21510:32008:CYR-301 = 66.3:11.7:15.5:4.5:2.0 and added to the solvent acetone at a weight ratio of 15%, and these components are uniformly mixed to produce a slurry.

[0115] The prepared slurry was coated on both sides with a thickness of 8 μm on the above-mentioned polymer coating layer and dried at 45 °C to form an outer coating layer. Manufacture of the positive electrode The positive electrode active material (LiNi 0.8 Mn 0.1 Co 0.1 O2), a conductive material (carbon black), a dispersant, and a binder resin (a mixture of PVDF-HFP and PVDF) are mixed with water at a weight ratio of 97.5:0.7:0.14:1.66, and a slurry for a positive electrode active material layer with a concentration of 50 wt% of the remaining components excluding water is prepared. Next, the slurry was applied to the surface of an aluminum thin film (thickness 10 μm) and dried to manufacture a positive electrode having a positive electrode active material layer (thickness 120 μm). Manufacture of the negative electrode Silicon particles (Elkem, M702), PAM-based 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 at 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 a concentration of 25 wt% of the remaining components excluding water. Next, the slurry was applied to the surface of a copper thin film (thickness 8 μm) and dried to produce a negative electrode with a negative electrode loading of 8 mAh / cm 2 The hardness of the negative electrode was measured to be 80 Mpa. Lamination process A separator of the example and the comparative example was interposed between the produced negative electrode and the positive electrode and laminated, and a lamination process was performed to obtain an electrode assembly. The lamination process was carried out for 10 seconds under the conditions of 70 °C and 5.2 MPa using hot pressing. Electrolyte injection process The electrode assembly obtained in the lamination process was inserted into a pouch exterior material, and LiPF6 was added to a solvent mixed with a composition of DEC / FEC = 90 / 10 (vol.%) An electrolyte in which 0.5 M and 1.0 M of LiFSI were dissolved was injected to manufacture a lithium secondary battery. <Comparative Example 1> Except for those in which the separator raw material was not coated with a solution of the first polymer resin, it was manufactured in the same manner as in the example. <Comparative Example 2> The separator raw material is not coated with a solution of the first polymer resin. And as the second polymer resin, a slurry in which PVDF (Solvay, KF9700) with a solubility in the electrolyte of 17 MPa 1 / 2 or more was dissolved in acetone was prepared. The solubility index of PVDF, which is the second polymer resin, is 19.2 MPa 1 / 2 And as a dispersant, a slurry in which Cyano resin (Miwon Trading, CYR-301) was dissolved in the solvent acetone was prepared.

[0116] Prepare Al2O3 with an average particle size of about 500 nm and Boehmite particles with an average particle size of 300 nm as inorganic particles. Add these components to acetone solvent at a weight ratio of 15% with the weight ratio of the final slurry being Al2O3:Boehmite:PVDF:CYR-301 = 66.3:11.7:20:2.0, and mix these components uniformly to produce a slurry.

[0117] Coat both sides of the prepared slurry with 8 μm coating and dry it at 45 °C to form an outer coating layer. <Comparative Example 3> As a porous polymer substrate, use the separation membrane original film of SV9 from Shanghai Energy Co., Ltd. (thickness; 9 μm, porosity; 46%, basis weight; 4.9 g / m 2 , gurley value; 70 sec / 100 cc). On the other hand, use Poly acrylic acid (PAA, Dow Co., CK-702) as the first polymer resin with electrolyte solubility, and completely dissolve the first polymer resin in water as the solvent at a concentration of 10 wt% to prepare a polymer solution. The solubility index of the first polymer resin in the electrolyte is 22.4 MPa 1 / 2 is.

[0118] As the second polymer resin, prepare a slurry in which PVDF (Solvay Co., KF9700) with a solubility in the electrolyte of 17 MPa 1 / 2 or more is dissolved in acetone. The solubility index of PVDF, which is the second polymer resin, is 19.2 MPa 1 / 2 is. Then, prepare a slurry in which Cyano resin (Miwon Trading Co., CYR-301) is dissolved in acetone solvent as a dispersant.

[0119] Prepare Al2O3 with an average particle size of about 500 nm and Boehmite particles with an average particle size of 300 nm as inorganic particles. Add these components to acetone solvent at a weight ratio of 15% with the weight ratio of the final slurry being Al2O3:Boehmite:PVDF:CYR-301 = 66.3:11.7:20:2.0, and mix these components uniformly to produce a slurry.

[0120] The prepared slurry was coated on both sides with a thickness of 8 μm on the above-mentioned polymer coating layer and dried at 45 °C to form an outer coating layer. <Comparative Example 4> As the first polymer resin having no electrolyte solubility, Poly acrylamide (PAM, Sungang Co., MP15) was used, and the first polymer resin was completely dissolved in water as a solvent at a concentration of 10% by weight to prepare a polymer solution. The solubility index of the electrolyte of the first polymer resin is 13.5 MPa 1 / 2 And the first polymer resin is coated on the same porous polymer substrate as in the examples.

[0121] Next, PVDF-HFP (Solvay, solef 21510, HFP 15 wt%) and PVDF-CTFE (Solvay, solef 32008) are dissolved in the solvent acetone as the second polymer resin. And a slurry in which Cyano resin (Miwon Trading Co., CYR-301) is dissolved in the solvent acetone is prepared as a dispersant. The solubility indices of 21510 and 32008, which are the second polymer resins, are 13.5 MPa 1 / 2 , 15.1 MPa 1 / 2 respectively.

[0122] As inorganic particles, Al2O3 with an average particle size of about 500 nm and Boehmite particles with an average particle size of 300 nm are prepared. The weight ratio of the final slurry is Al2O3: Boehmite: 21510: 32008: CYR-301 = 66.3: 11.7: 15.5: 4.5: 2.0 and added to the solvent acetone at a weight ratio of 15%, and these components are uniformly mixed to produce a slurry.

[0123] The prepared slurry was coated on both sides with a thickness of 8 μm on the above-mentioned polymer coating layer and dried at 45 °C to form an outer coating layer. <Comparative Example 5> As the first polymer resin having no electrolyte solubility, Poly acrylamide (PAM, Sungang Co., MP15) was used, and the first polymer resin was completely dissolved in water as a solvent at a concentration of 10% by weight to prepare a polymer solution. The solubility index of the first polymer resin in the electrolyte is 13.5 MPa 1 / 2 It is. Then, the first polymer resin is coated on the same porous polymer substrate as in the example.

[0124] As the second polymer resin, a slurry in which PVDF (Solvay Co., KF9700) with a solubility in the electrolyte of 17 MPa 1 / 2 or more is dissolved in acetone is prepared. The solubility index of PVDF, which is the second polymer resin, is 19.2 MPa 1 / 2 It is. Then, as a dispersant, Cyano resin (Miwon Trading Co., CYR-301) is prepared as a slurry dissolved in the solvent acetone.

[0125] As inorganic particles, Al2O3 with an average particle size of about 500 nm and Boehmite particles with an average particle size of 300 nm are prepared. The weight ratio of the final slurry is Al2O3: Boehmite:PVDF:CYR-301 = 66.3:11.7:20:2.0 and added to acetone as a solvent at 15% by weight, and these components are uniformly mixed to produce a slurry. The prepared slurry is coated on both sides with 8 μm on the above-mentioned polymer coating layer and dried at 45 °C to form an outer coating layer. [Experimental Example] [PDI Measurement] PDI = (weight average molecular weight) / (number average molecular weight) At this time, the values of the weight average molecular weight and the number average molecular weight were the values derived by cutting the separation membrane into a predetermined size and performing GPC (Gel Permeation Chromatography) analysis. [Measurement of the Average Particle Size of Pores] The particle size was measured by pore size distribution using a Capillary flow porometer (CFP method). [Thickness reduction rate after hot pressing] The separation membranes of the examples and comparative examples manufactured above were pressurized using hot pressing to deform the thickness, and then the thickness was measured. The thickness reduction rate was calculated using the following formula. The pressurization was carried out under the conditions of 70 °C, 5.2 MPa, and 10 Sec. The thickness was measured using a thickness measuring instrument (Mitutoyo, VL-50S): Thickness reduction ratio = {(thickness of the separation membrane before hot pressing - thickness of the separation membrane after hot pressing) / thickness of the separation membrane before hot pressing} × 100 [Measurement experiment of wet heat shrinkage rate] The separation membrane was cut into 5 × 5 cm and prepared. After injecting 1 g of PC solution into the pouch and sealing it, a sample was prepared. After leaving the sample at a temperature of 135 °C for 30 minutes, the shrinkage rate of the separation membrane was measured.

[0126] The shrinkage rate is the result of calculating the increase or decrease rate of the distance (marking distance) between any two points respectively from the MD direction and TD direction of the separation membrane according to the following (Formula 1). (Formula 1) Shrinkage rate (%) = {(B - A) / A} × 100 In the above formula, A is the marking distance in the initial state before being left at a high temperature, and B is the marking distance in the final state after being left at a high temperature. [Measurement of capacity retention rate after 500 cycles at 25 °C, 1C / 1C] For the battery manufactured by the method described above, before charging / discharging at 25 °C, charging / discharging was repeated in the range of 2.5 V to 4.25 V at a rate of 1C respectively, and the ratio of the discharge capacity after 500 cycles was derived by calculation.

[0127]

Table 1

[0128] Compared with Comparative Example 1, in the case of Comparative Example 2, since the solubility index of the coating layer is relatively similar to that of the electrolytic solution, it was confirmed that the retention rate of the cell capacity was slightly improved.

[0129] Comparative Example 3 is a separation membrane in which the difference in solubility between the first polymer resin and the second polymer resin is reduced compared with the Example. Due to the characteristic of being excessively dissolved in the electrolytic solution compared with the Example, the ionic conductivity of the electrolytic solution is inferior, and the retention rate of the long-term cell capacity tends to be inferior.

[0130] In the case of Comparative Example 4, it is a separation membrane coated with a polymer or the like in which both the first polymer resin and the second polymer resin are not dissolved in the electrolytic solution. As a result, it was confirmed that the retention rate of the cell capacity is the worst compared with the Example and Comparative Examples 3 and 5.

[0131] In the case of Comparative Example 5, the first polymer resin coated on the base material is not dissolved in the electrolytic solution, and the second polymer resin applied to the coating layer has a characteristic of being relatively dissolved in the electrolytic solution. However, the reason why the retention rate of the cell capacity is inferior compared with the Example is that the solubility index of the second polymer resin applied to the coating layer is lower than the solubility index of the first polymer resin coated on the original reaction of the Example, so it is confirmed that the characteristic of being dissolved in the electrolytic solution is inferior.

[0132] Although the preferred embodiments of the present invention have been described above with reference to the examples, those skilled in the art or those having ordinary knowledge in the technical field can understand that the present invention can be variously modified and changed without departing from the spirit and technical field of the present invention described in the claims to be described later. Therefore, the technical scope of the present invention should not be limited to the content described in the detailed description of the specification, but should be determined by the claims.

Description of Reference Numerals

[0133] 100: Separation membrane 110: Porous polymer base material 130: Coating layer 131: First coating layer 133: Second coating layer 200: Negative electrode

Claims

1. A separator for an electrochemical device provided in a negative electrode containing a silicon (Si)-based active material, The separator for an electrochemical device includes a porous polymer substrate; a first coating layer provided on at least one surface of the porous polymer substrate and including a first polymer resin; and a second coating layer provided on the first coating layer and including a second polymer resin and inorganic particles. A separator for an electrochemical device, wherein the solubility of the first polymer resin in an electrolyte solution is greater than the solubility of the second polymer resin in the electrolyte solution.

2. The solubility index of the first polymer resin is 17 MPa. １ / ２ 27MPa or more １ / ２ The separator for electrochemical elements according to claim 1 , wherein:

3. The solubility index of the second polymer resin is 17 MPa. １ / ２ or less than 27 MPa １ / ２ The separator for electrochemical elements according to claim 1 , wherein the molecular weight is greater than 1000.

4. The first polymer resin is polystyrene, polyethyl acrylate, polymethyl acrylate, or the like.

2. The separator for an electrochemical device according to claim 1, comprising one selected from the group consisting of polyvinyl chloride (PVC), polyvinyl pyrrolidone (PVP), polyvinyl acetate (PVAc), polyacrylonitrile (PAN), polylactic acid (PLA), polyacrylic acid (PAA), and combinations thereof.

5. 2. The separator for an electrochemical device according to claim 1, wherein the second polymer resin comprises one selected from the group consisting of PVDF-HFP copolymer, PVDF-CTFE copolymer, PVDF-HFP-CTFE terpolymer, cyanoethyl polyvinyl alcohol, and combinations thereof.

6. The separation membrane has pores, The polydispersity index (PDI) of the porous polymer substrate is 2.5 to 10, 2. The separator for an electrochemical device according to claim 1, wherein the average pore size of the porous polymer substrate is 20 nm or more and 80 nm or less.

7. 2. The separator for an electrochemical device according to claim 1, wherein the content of the silicon (Si)-based active material in the negative electrode is 50 wt % or more.

8. 2. The separator for an electrochemical device according to claim 1, wherein the negative electrode has a hardness of 50 MPa to 350 MPa.

9. An electrochemical device, comprising: The battery includes a positive electrode, a negative electrode, and an electrolyte, and further includes a separator interposed between the positive electrode and the negative electrode; An electrochemical element, wherein the separator is the separator for electrochemical elements according to claim 1 .

10. The solubility index of the electrolyte is 17 MPa. １ / ２ 27MPa or more １ / ２ 10. The electrochemical device according to claim 9, wherein:

11. 10. The electrochemical device according to claim 9, wherein the electrolyte solution comprises one selected from the group consisting of propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), and combinations thereof.

12. 12. The electrochemical device according to claim 11, wherein the electrolyte is a mixture of diethyl carbonate (DEC) and fluoroethylene carbonate (FEC).

13. 13. The electrochemical device according to claim 12, wherein the electrolyte contains diethyl carbonate (DEC) and fluoroethylene carbonate (FEC) in a ratio of 10:90 to 99:1.

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