Separator for electrochemical device and electrochemical device including the same

Abstract

The present invention relates to a separator for an electrochemical device and an electrochemical device including the same, and more particularly to a separator for an electrochemical device that can reduce the weight of the separator by including cellulose nanocrystals in a porous polymer substrate, thereby improving the energy density and rigidity of the battery, and an electrochemical device including the same.

Description

[Technical Field]

[0001] This invention claims the benefit of the filing date of Korean Patent Application No. 10-2023-0043721, filed with the Korean Intellectual Property Office on April 3, 2023, the entire contents of which are incorporated herein by reference. The present invention relates to a separator for an electrochemical device and an electrochemical device including the same, and more particularly to a separator for an electrochemical device including the same, which can reduce the weight of the separator by including cellulose nanocrystals in a porous polymer substrate, thereby improving the energy density and rigidity of the battery. [Background technology]

[0002] Among the components of an electrochemical device, the separator is disposed between the positive and negative electrodes and contains a polymer matrix with a porous structure. It serves to separate the positive and negative electrodes, prevent electrical shorts between the two electrodes, and allow electrolytes and ions to pass through. Although the separator itself does not participate in the electrochemical reaction, its physical properties, such as wettability with the electrolyte, degree of porosity, and thermal shrinkage, affect the performance and safety of the electrochemical device.

[0003] Therefore, various methods have been attempted to add a coating layer to a porous polymer substrate to enhance the physical properties of the separator, and to change the physical properties of the coating layer by adding various substances to the coating layer. For example, an inorganic substance may be added to the coating layer to improve the mechanical strength of the separator, or an inorganic substance or hydrate may be added to the coating layer to improve the flame retardancy and heat resistance of the polymer substrate.

[0004] The separator may be attached to the electrode through a lamination process, and a polymer binder may be added to the coating layer composition of the separator to ensure adhesion between the electrode and the separator.

[0005] Meanwhile, inorganic materials contained in the coating layer are generally metal oxides or metal hydroxides such as alumina and boehmite, but these inorganic materials have high density, making it difficult to reduce the weight of the separator.Furthermore, the inorganic materials in the coating layer have problems such as poor binding properties.

[0006] Therefore, there has been a need for research into separators that are lighter in weight, more rigid, and have excellent mechanical properties in order to improve the energy density of batteries. Summary of the Invention [Problem to be solved by the invention]

[0007] The technical problem to be solved by the present invention is to provide a separator for an electrochemical device, which has low density to reduce the weight of the separator, but can improve mechanical properties and rigidity, and which includes a porous polymer substrate containing cellulose nanocrystals to improve the energy density of a battery and the strength of the separator, and an electrochemical device including the same.

[0008] However, the problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0009] One embodiment of the present invention provides a separator for an electrochemical device, comprising a porous polymer substrate containing cellulose nanocrystals.

[0010] According to one embodiment of the present invention, the cellulose nanocrystals may be provided in the pores of the porous polymer substrate.

[0011] According to one embodiment of the present invention, the density of the cellulose nanocrystals is 0.1 g / m 3 More than 2.0g / m 3 It can be the following:

[0012] According to one embodiment of the present invention, the Young's modulus of the cellulose nanocrystals may be 50 GPa or more and 80 GPa or less.

[0013] According to one embodiment of the present invention, the diameter of the cellulose nanocrystals may be 30 nm or less.

[0014] According to one embodiment of the present invention, the length of the cellulose nanocrystals may be 600 nm or less.

[0015] According to one embodiment of the present invention, the aspect ratio of the cellulose nanocrystals may be 50 or more and 300 or less.

[0016] According to one embodiment of the present invention, the porous polymer substrate may be a nonwoven fabric.

[0017] According to one embodiment of the present invention, the pore diameter of the porous polymer substrate may be 1 μm or more and 20 μm or less.

[0018] According to one embodiment of the present invention, the porosity of the porous polymer substrate may be 30% by volume or more and 80% by volume or less.

[0019] One embodiment of the present invention provides an electrochemical device comprising: a positive electrode; a negative electrode; and the separator for an electrochemical device interposed between the positive electrode and the negative electrode. [Effects of the Invention]

[0020] The separator for an electrochemical device according to an embodiment of the present invention can achieve high strength due to the high Young's modulus of the cellulose nanocrystals.

[0021] The separator for an electrochemical device according to one embodiment of the present invention can improve the wettability of the separator to an electrolyte through a large number of hydroxyl groups in the cellulose nanocrystals, thereby improving the ionic conductivity of the battery.

[0022] A separator for an electrochemical device according to one embodiment of the present invention exhibits strong binding properties even when the binder content in the coating layer is reduced due to strong hydrogen bonds between cellulose nanocrystals, thereby improving the coating stability of the separator.

[0023] An electrochemical device according to an embodiment of the present invention can improve energy density and ionic conductivity. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a schematic diagram of a porous polymeric substrate according to one embodiment of the present invention. [Figure 2] 1 is a schematic diagram of a separator for an electrochemical element according to one embodiment of the present invention. [Figure 3] 1 is a photograph showing an enlarged view of the surface of Example 1 according to an embodiment of the present invention. [Figure 4] 1 is an enlarged photograph of a cross section of Example 1 according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] In this specification, when a part is said to "comprise" a certain component, this does not mean that it excludes other components, but that it may further include other components, unless otherwise specified.

[0026] In this specification, "A and / or B" means "A and B, or A or B."

[0027] In this specification, when a component is said to be "located on" another component, unless otherwise specified, this does not exclude other components from being located therebetween, but rather means that other components may be further located therein.

[0028] As used herein, the characteristic of "having pores" means that an object contains a plurality of pores, and the pores are interconnected to allow gas and / or liquid fluids to pass from one side of the object to the other side.

[0029] In this specification, the separator has a porous property including a large number of pores, and serves as a porous ion-conducting barrier that allows ions to pass through while blocking electrical contact between the negative electrode and the positive electrode in the electrochemical device.

[0030] The present invention will be described in further detail below.

[0031] One embodiment of the present disclosure provides a separator 100 for an electrochemical device, which includes a porous polymer substrate 110 containing cellulose nanocrystals (CNC) 113 .

[0032] The separator for an electrochemical device according to one embodiment of the present invention can achieve high strength due to the high Young's modulus of the cellulose nanocrystals. Furthermore, the separator for an electrochemical device according to one embodiment of the present invention can improve the wettability of the separator to the electrolyte through the numerous hydroxyl groups of the cellulose nanocrystals, thereby improving the ionic conductivity of the battery. Furthermore, the separator for an electrochemical device according to one embodiment of the present invention can improve the coating stability of the separator by exhibiting strong binding properties even when the binder content in the coating layer is reduced due to the strong hydrogen bonds between the cellulose nanocrystals.

[0033] 1 is a schematic view of a porous polymer substrate 110 according to one embodiment of the present invention. A separator 100 for an electrochemical device according to one embodiment of the present invention will be described in detail with reference to FIG.

[0034] One embodiment of the present invention relates to a separator for an electrochemical device, which can be used as a separator itself or as a component of a separator. Therefore, in the separator according to one embodiment of the present invention, other layers may be additionally disposed on at least one surface of the separator substrate, depending on the material or function. In one embodiment of the present invention, the separator may have a coating layer containing inorganic particles and / or a polymer binder, i.e., an organic / inorganic composite coating layer, formed on at least one surface or both opposing surfaces of the porous substrate.

[0035] According to one embodiment of the present invention, the separator 100 for an electrochemical device includes a porous polymer substrate 110. As described above, the separator 100 for an electrochemical device includes the porous polymer substrate 110, which allows lithium ions to pass through while blocking electrical contact, and can implement a shutdown function at an appropriate temperature.

[0036] According to one embodiment of the present invention, the porous polymer substrate 110 includes cellulose nanocrystals (CNC) 113. As described above, the porous polymer substrate 110 includes cellulose nanocrystals (CNC) 113, which ensures the rigidity of the separator and improves the wettability of the separator, thereby improving the ionic conductivity of the separator.

[0037] According to one embodiment of the present invention, the cellulose nanocrystals may have a crystalline structure. As described above, the crystalline structure of the cellulose nanocrystals can ensure the rigidity of the separator. In this specification, the crystalline structure can be confirmed using an X-ray diffraction method. More specifically, X-rays are irradiated onto a crystal to cause partial diffraction, and the diffraction angle and intensity of the diffracted X-rays are analyzed to measure the inherent values ​​of the material structure and determine whether the material has a crystalline structure.

[0038] According to one embodiment of the present invention, the cellulose nanocrystals may be derived from cellulose containing crystalline and amorphous regions, and the crystalline regions may refer to regions containing only the crystalline structure.

[0039] According to one embodiment of the present invention, the cellulose may be composed of alternating crystalline and amorphous regions.

[0040] According to one embodiment of the present invention, the cellulose nanocrystals may be formed by treating cellulose containing crystalline and amorphous regions with an acid to remove the amorphous regions. Specifically, the cellulose nanocrystals may be the crystalline regions of the cellulose. As described above, the rigidity of the separation membrane can be ensured by selecting the crystalline regions of the cellulose for the cellulose nanocrystals.

[0041] According to one embodiment of the present invention, the acid may be hydrochloric acid, sulfuric acid, phosphoric acid, hydrobromic acid, nitric acid, or the like.

[0042] According to one embodiment of the present invention, the concentration of the acid may be 50% by weight or more and 70% by weight.

[0043] According to one embodiment of the present invention, the acid treatment may be carried out at a temperature of 40°C or higher and 50°C or lower.

[0044] As used herein, the cellulose nanocrystals may refer to cellulose crystallites, cellulose nanowhiskers, or nanocrystalline cellulose.

[0045] According to one embodiment of the present invention, the cellulose nanocrystals 113 may be provided in the pores 111 of the porous polymer substrate 110. Specifically, the cellulose nanocrystals 113 may not be contained in the porous polymer substrate 110 itself, but may be disposed or dispersed within the pores 111 formed within the porous polymer substrate 110. As described above, providing the cellulose nanocrystals 113 in the pores 111 of the porous polymer substrate 110 ensures the rigidity of the separator, reduces the weight of the separator, and improves the energy density of the battery. Furthermore, the wettability of the separator may be improved, thereby improving ionic conductivity.

[0046] According to one embodiment of the present invention, the density of the cellulose nanocrystals 113 is 0.1 g / m 3 More than 2.0g / m 3 Specifically, the density of the cellulose nanocrystals 113 may be 0.2 g / m or less. 3 More than 1.9g / m 3 Below 0.3g / m 3 More than 1.8g / m 3 Below, 0.4g / m 3 More than 1.7g / m 3 Below 0.5g / m 3 More than 1.6g / m 3 Below, 0.6g / m 3 More than 1.5g / m 3 Below, 0.7g / m 3 More than 1.4g / m 3 Below, 0.8g / m 3 More than 1.3g / m 3 Below, 0.9g / m 3 More than 1.2g / m 3 or less than 1.0 g / m 3 More than 1.1g / m 3 By adjusting the density of the cellulose nanocrystals 113 within the above range, the weight of the separator can be reduced and the energy density of the battery can be improved.

[0047] According to one embodiment of the present invention, the Young's modulus of the cellulose nanocrystals 113 may be 50 GPa to 80 GPa. Specifically, the Young's modulus of the cellulose nanocrystals 113 may be 51 GPa to 79 GPa, 52 GPa to 78 GPa, 53 GPa to 77 GPa, 54 GPa to 76 GPa, 55 GPa to 75 GPa, 56 GPa to 74 GPa, 57 GPa to 73 GPa, 58 GPa to 72 GPa, 59 GPa to 71 GPa, 60 GPa to 70 GPa, 61 GPa to 69 GPa, 62 GPa to 68 GPa, 63 GPa to 67 GPa, or 64 GPa to 66 GPa. Adjusting the Young's modulus of the cellulose nanocrystals 113 within the above ranges improves the stability of the separation membrane and ensures its rigidity.

[0048] According to one embodiment of the present invention, the diameter of the cellulose nanocrystals 113 may be 30 nm or less. Specifically, the diameter of the cellulose nanocrystals 113 may be greater than 0 nm, 30 nm or less, 1 nm to 29 nm, 2 nm to 28 nm, 3 nm to 27 nm, 4 nm to 26 nm, 5 nm to 25 nm, 6 nm to 24 nm, 7 nm to 23 nm, 8 nm to 22 nm, 9 nm to 21 nm, 10 nm to 20 nm, 11 nm to 19 nm, 12 nm to 18 nm, 13 nm to 17 nm, or 14 nm to 16 nm. Adjusting the diameter of the cellulose nanocrystals 113 within the above-described ranges facilitates the placement of the cellulose nanocrystals in the pores of the porous polymer substrate, thereby improving the dispersibility of the cellulose nanocrystals in the pores of the porous polymer substrate.

[0049] According to one embodiment of the present invention, the length of the cellulose nanocrystals 113 may be 600 nm or less. Specifically, the length of the cellulose nanocrystals 113 may be 100 nm to 600 nm, 150 nm to 550 nm, 200 nm to 500 nm, 250 nm to 450 nm, or 300 nm to 400 nm. By adjusting the length of the cellulose nanocrystals 113 within the above-mentioned ranges, the cellulose nanocrystals can be easily arranged in the pores of the porous polymer substrate, and the dispersibility of the cellulose nanocrystals in the pores of the porous polymer substrate can be improved.

[0050] According to one embodiment of the present invention, the aspect ratio of the cellulose nanocrystals 113 may be 50 or more and 300 or less. That is, the cellulose nanocrystals may have a high aspect ratio, similar to that of fibers. Specifically, the aspect ratio of the cellulose nanocrystals 113 may be 60 or more and 290 or less, 70 or more and 280 or less, 80 or more and 260 or less, 90 or more and 250 or less, 100 or more and 240 or less, 110 or more and 230 or less, 120 or more and 220 or less, 130 or more and 210 or less, 140 or more and 200 or less, 150 or more and 190 or less, or 160 or more and 180 or less. Adjusting the aspect ratio of the cellulose nanocrystals 113 within the above-described ranges facilitates the placement of the cellulose nanocrystals in the pores of the porous polymer substrate, thereby improving the dispersibility of the cellulose nanocrystals in the pores of the porous polymer substrate.

[0051] In this specification, the aspect ratio may refer to the ratio (L / D) of the length (L) of a fibrous filler to the diameter (D) of its cross section (cross section perpendicular to the longitudinal direction). The length and diameter may be measured by taking a magnified image of the measurement target substance.

[0052] According to one embodiment of the present invention, the diameter of the pores 111 of the porous polymer substrate 110 may be from 1 μm to 20 μm. Specifically, the diameter of the pores 111 of the porous polymer substrate 110 may be from 2 μm to 19 μm, from 3 μm to 18 μm, from 4 μm to 17 μm, from 5 μm to 16 μm, from 6 μm to 15 μm, from 7 μm to 14 μm, from 8 μm to 13 μm, or from 9 μm to 12 μm. The pore size may be an average size. By adjusting the pore diameter of the porous polymer substrate within the above range, the content of the cellulose nanocrystals in the pores of the porous polymer substrate can be increased, thereby improving the rigidity of the separator. By adjusting the pore size within the above range, the degree of lithium ion mobility through the separator can be adjusted, thereby improving electrical performance. In this specification, the pore size can be calculated from the pore size distribution measured using a capillary flow porometer. For example, a separator to be measured is first wetted with a wetting agent such as Galwick solution, and then air pressure is gradually increased on one side of the substrate. When the applied air pressure exceeds the capillary attraction of the wetting agent present in the pores, the wetting agent blocking the pores is expelled. The pore size and distribution can be measured based on the pressure and flow rate at the moment of expulsion, and the average pore size and maximum size can be determined from the measured air pressure and flow rate.

[0053] According to one embodiment of the present invention, the porosity of the porous polymer substrate 110 may be 30 to 80 vol%. Specifically, the porosity of the porous polymer substrate 110 may be 30 to 80 vol%, 32 to 78 vol%, 34 to 76 vol%, 36 to 74 vol%, 38 to 72 vol%, 40 to 70 vol%, 42 to 68 vol%, 44 to 66 vol%, 46 to 64 vol%, or 48 to 62 vol%. Adjusting the porosity of the porous polymer substrate 110 within the above ranges increases the amount of cellulose nanocrystals in the pores of the porous polymer substrate, thereby improving the rigidity of the separator.

[0054] In the present specification, the term "porosity" refers to the ratio of the volume occupied by pores to the total volume, and is expressed in volume %. The term "porosity" may be used interchangeably with terms such as void ratio and porosity.

[0055] In this specification, the porosity corresponds to a value obtained by subtracting the weight and density of each component of the porous polymer substrate 110 from the volume calculated based on the thickness, width, and length of the coating layer 130.

[0056] According to one embodiment of the present invention, the porous polymer substrate 110 may be a nonwoven fabric. Specifically, the nonwoven fabric may refer to a material having high porosity. As described above, by selecting the porous polymer substrate 110 from a nonwoven fabric, the content of the cellulose nanocrystals 113 in the pores 111 within the porous polymer substrate 110 can be increased, thereby improving the rigidity of the separator.

[0057] According to one embodiment of the present invention, the porous polymer substrate 110 may be manufactured using a polyolefin-based resin as a base resin. Examples of polyolefin-based resins include polyethylene, polypropylene, and polypentene, and the porous polymer substrate 110 may include at least one of these. A porous separator having a large number of pores manufactured using such a polyolefin-based resin as a base resin may be provided with a shutdown function at an appropriate temperature.

[0058] According to one embodiment of the present invention, the porous polymer substrate 110 may be manufactured using polyethylene terephthalate (PET) resin as a base resin. A separator having porosity, i.e., a large number of pores, manufactured using such polyethylene terephthalate (PET) resin as a base resin may be provided with a shutdown function at an appropriate temperature.

[0059] According to one embodiment of the present invention, the weight-average molecular weight of the polyolefin-based resin or the polyethylene terephthalate-based resin may be from 30,000 to 1,500,000. Adjusting the weight-average molecular weight of the polyolefin-based resin within the above range can improve the compression resistance of the separation membrane. Furthermore, when different polyolefin-based resins or polyethylene terephthalate-based resins are mixed and used, or when a separation membrane is formed with a multi-layer structure made of different polyolefin-based resins or polyethylene terephthalate-based resins, the weight-average molecular weight of the polyolefin-based resin or the polyethylene terephthalate-based resin can be calculated by adding the weight-average molecular weights corresponding to the content ratio of each polyolefin-based resin or the polyethylene terephthalate-based resin.

[0060] In the present invention, the weight average molecular weight (Mw) can be measured by gel permeation chromatography (GPC, PL GPC220, Agilent Technologies), and the measurement conditions can be set as follows:

[0061] Column: PL Olexis (Polymer Laboratories) -Solvent: TCB (Trichlorobenzene) -Flow rate: 1.0ml / min -Sample concentration: 1.0mg / ml -Injection volume: 200μl -Column temperature: 160℃ -Detector: Agilent High Temperature RI detector -Standard: Polystyrene (corrected by a cubic function)

[0062] In addition to the polyolefin-based resin or the polyethylene terephthalate-based resin, other resin components may be further mixed as needed, and in addition to the resin components, for example, filler particles may be included. The filler particles may be introduced for the purpose of acting as a pressure barrier to prevent excessive reduction in the thickness, pore size, and porosity of the separator substrate due to the high pressure applied in the lamination process described below. The filler particles may include organic fillers or inorganic fillers having a predetermined particle size, and are not limited to a specific component as long as they have strength equal to or greater than that of the polyolefin-based resin or the polyethylene terephthalate-based resin.

[0063] According to one embodiment of the present invention, the porous polymer substrate 110 may be manufactured by a method (wet method) in which a polyolefin resin or a polyethylene terephthalate resin is mixed with a plasticizer (diluents) at a high temperature to form a single phase, and then the polymer material and the plasticizer are phase-separated during a cooling process, and the plasticizer is extracted to form pores, followed by stretching and heat setting.

[0064] According to one embodiment of the present invention, the average pore size and maximum pore size of the separator 100 or the porous polymer substrate 110 can be easily prepared by a person skilled in the art to meet the scope of the present invention by adjusting the mixing ratio of the plasticizer, the stretching ratio, the heat setting temperature, etc.

[0065] According to one embodiment of the present invention, the pore size of the separator 100 may be from 1 μm to 100 μm. The pore size may be an average size. By adjusting the pore size within the above range, the degree of lithium ion movement through the separator can be adjusted, thereby improving electrical performance.

[0066] The pore size can be calculated from the pore size distribution measured using a capillary flow porometer. For example, the separation membrane to be measured is first wetted with a wetting agent such as Galwick solution, and then the air pressure on one side of the substrate is gradually increased. When the applied air pressure exceeds the capillary attraction of the wetting agent present in the pores, the wetting agent blocking the pores is expelled. The pore size and distribution can be measured based on the pressure and flow rate at the moment of expulsion, and the average pore size and maximum size can be determined from this.

[0067] According to one embodiment of the present invention, the porous polymer substrate 110 may have a thickness of 5 μm to 30 μm.

[0068] 2 is a schematic diagram of a separator for an electrochemical device according to one embodiment of the present invention, and the separator according to one embodiment of the present invention will be described in detail with reference to FIG.

[0069] According to an embodiment of the present invention, the separator 100 for an electrochemical device may further include a coating layer 130 formed on at least one surface of the porous polymer substrate 110 .

[0070] According to one embodiment of the present invention, the coating layer 130 includes a polymer binder 131 and inorganic particles 133 and has porous properties.

[0071] According to one embodiment of the present invention, the polymer binder 131 and the inorganic particles 133 in the coating layer 130 may be contained in a weight ratio of 1:99 to 30:70. The ratio may be appropriately adjusted within the above range, and the polymer binder may be 1 wt% or more, 5 wt% or more, or 10 wt% or more, and the inorganic particles may be 80 wt% or more, 85 wt% or more, 90 wt% or more, or 95 wt% or more, relative to a total of 100 wt% of the polymer binder 131 and the inorganic particles 133.

[0072] According to one embodiment of the present invention, the coating layer 130 may be formed by binding inorganic particles 133 with a polymer binder 131 and accumulating them on the coating layer side. The pores inside the coating layer 130 may be due to interstitial volumes, which are empty spaces between the inorganic particles.

[0073] In one embodiment of the present invention, the porosity of the coating layer 130 may be 30% to 70% by volume. A porosity of 70% by volume or less ensures mechanical properties that can withstand the pressing process for bonding to the electrode, and is suitable for ensuring adhesive strength without increasing the surface opening ratio too much. On the other hand, a porosity of 30% by volume or more is advantageous from the viewpoint of ion permeability.

[0074] In the present specification, the term "porosity" refers to the ratio of the volume occupied by pores to the total volume, and is expressed in volume %. The term "porosity" may be used interchangeably with terms such as void ratio and porosity.

[0075] In this specification, the porosity corresponds to a value obtained by subtracting the volume converted into the weight and density of each component of the coating layer 130 from the volume calculated from the thickness, width, and length of the coating layer 130.

[0076] In one embodiment of the present invention, the porosity and pore size of the coating layer 130 can be measured using a scanning electron microscope (SEM) image, a mercury porosimeter, a capillary flow porometer, or a porosimetry analyzer (Belsorp-II mini, Bell Japan Inc.) by a nitrogen gas adsorption flow method using a BET 6-point method. In this case, it may be advantageous to use a capillary flow porosimeter.

[0077] According to one embodiment of the present invention, the coating layer 130 may have a thickness of 1 μm to 20 μm on any one side of the porous polymer substrate 110, but is not limited thereto. The thickness can be adjusted to an appropriate range by those skilled in the art in consideration of heat resistance and electrical resistance.

[0078] According to one embodiment of the present invention, the thickness of the porous polymer substrate 110 and / or the coating layer 130 may be measured using a contact-type thickness gauge, such as Mitutoyo's VL-50S-B.

[0079] According to one embodiment of the present invention, the polymer binder 131 usable in the coating layer 130 is polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyethylene The polymer resin may be any one selected from the group consisting of polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, and carboxyl methyl cellulose, or a mixture of two or more of these polymer resins, but is not limited thereto.

[0080] In one embodiment of the present invention, the inorganic particles 133 that can be used in the coating layer 130 are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles 133 that can be used in one embodiment of the present invention are those that can be used within the operating voltage range (e.g., Li / Li) of the applied electrochemical device. + There are no particular limitations as long as oxidation and / or reduction reactions do not occur at a voltage (0 V to 5 V relative to the reference voltage).

[0081] According to one embodiment of the present invention, non-limiting examples of the inorganic particles 133 include BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT, 0 <x<1、0<y<1)、Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3 (PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, Mg(OH)2, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, SiC, Al(OH)3, TiO2, aluminum peroxide, zinc tin hydroxide (ZnSn(OH)6), tin-zinc oxide (Zn2SnO4, ZnSnO3), antimony trioxide (Sb2O3), antimony tetroxide (Sb2O4), antimony pentoxide (Sb2O5), etc., and one or more of these may be included.

[0082] According to one embodiment of the present invention, the average diameter (D 50 Although there are no particular limitations on the thickness of the coating layer 130, it is preferably in the range of 0.3 μm to 1 μm inclusive in order to form a coating layer 130 of uniform thickness and to have an appropriate porosity. Specifically, if the thickness is less than 0.3 μm, the dispersibility of inorganic particles in the slurry prepared for producing the coating layer may decrease, and if the thickness is more than 1 μm, the thickness of the formed coating layer may increase.

[0083] As used herein, the term "D50 particle size" refers to the particle size at 50% of the cumulative distribution of particle numbers according to particle size. The particle size can be measured using a laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500). The particle size distribution is calculated by measuring the difference in the diffraction pattern according to particle size as the particles pass through a laser beam. The D50 particle size can be measured by calculating the particle diameter at 50% of the cumulative distribution of particle numbers according to particle size measured by the analyzer.

[0084] According to one embodiment of the present invention, the coating layer 130 may be formed, for example, as follows. First, a polymer binder 131 is dissolved in an appropriate organic solvent to prepare a polymer solution. The solvent preferably has a solubility index similar to that of the polymer binder to be used and a low boiling point. This facilitates uniform mixing and subsequent solvent removal. Non-limiting examples of usable solvents include acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), cyclohexane, water, or a mixture thereof.

[0085] Next, inorganic particles 133 are added and dispersed in the prepared polymer solution. According to one embodiment of the present invention, the content ratio of the inorganic particles 133 to the polymer binder 131 is as described above, and is appropriately adjusted in consideration of the thickness, pore size, and porosity of the coating layer of the present invention to be finally prepared.

[0086] Next, the inorganic particle slurry prepared as described above is coated on at least one surface of the prepared separator substrate and dried. The method for coating the slurry on the surface of the porous polymer substrate is not limited to any particular method, and any conventional method known in the art can be used. For example, various methods such as dip coating, die coating, roll coating, comma coating, or a combination thereof can be used.

[0087] The drying process is performed by appropriately setting temperature and time conditions to minimize the occurrence of surface defects on the coating layer 130. The drying process may be performed using auxiliary drying devices such as a drying oven or hot air within an appropriate range.

[0088] When the separator 100 includes the coating layer 130, damage caused by pressure of the inorganic particles 133 on the surface of the porous polymer substrate 110 facing the coating layer 130 during the lamination process can be reduced.

[0089] According to one embodiment of the present invention, the separator 100 is interposed between the anode and cathode and fabricated into an electrochemical device through a lamination process in which heat and / or pressure are applied to bond them together. In one embodiment of the present invention, the lamination process can be performed using a roll press device including a pair of pressure rollers. That is, the anode, separator, and cathode are sequentially stacked and then inserted between the pressure rollers to achieve interlayer bonding. In this case, the lamination process can be performed using a hot press method.

[0090] One embodiment of the present invention provides an electrochemical device including a positive electrode; a negative electrode; and the separator 100 interposed between the positive electrode and the negative electrode.

[0091] An electrochemical device according to an embodiment of the present invention can improve energy density and ionic conductivity.

[0092] In the present invention, the electrochemical device is a device that converts chemical energy into electrical energy through an electrochemical reaction, and is a type of device that includes a primary battery and a secondary battery. In this specification, the secondary battery is a battery that can be charged and discharged, and refers to a lithium secondary battery, a nickel-cadmium battery, a nickel-metal hydride battery, etc. The lithium secondary battery uses lithium ions as an ion conductor, and examples thereof include, but are not limited to, 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.

[0093] According to one embodiment of the present invention, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer on at least one surface of the current collector, the positive electrode active material layer comprising a positive electrode active material, a conductive material, and a binder resin. The positive electrode active material may be a layered compound such as lithium manganese composite oxide (LiMn2O4, LiMnO2, etc.), lithium cobalt oxide (LiCoO2), or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; 1+x Mn 2-x Lithium manganese oxides such as LiMnO4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, and Cu2V2O7; and the chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by the chemical formula LiMnO2 (where M=Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x=0.01 to 0.3) 1-x M xO2 (where M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 - 0.1), or a lithium manganese composite oxide represented by Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); LiMn2O4 in which a part of Li in the chemical formula is substituted with an alkaline earth metal ion; a disulfide compound; It can contain one or a mixture of two or more of Fe2(MoO4)3.

[0094] According to one embodiment of the present invention, the negative electrode has a negative electrode current collector and a negative electrode active material layer containing a negative electrode active material, a conductive material, and a binder resin on at least one surface of the current collector. As the negative electrode active material, the negative electrode contains carbon such as lithium metal oxide, graphitized carbon, and graphite-based carbon; Li x Fe2O3 (0 ≤ x ≤ 1), Li x WO2 (0 ≤ x ≤ 1), Sn x Me 1-x Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8), etc. metal composite oxides; lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials; It can contain one or a mixture of two or more selected from titanium oxides.

[0095] According to one embodiment of the present invention, the conductive material may be, for example, any one selected from the group consisting of graphite, carbon black, carbon or metal fiber, metal powder, conductive whisker, conductive metal oxide, activated carbon, and polyphenylene derivatives, or a mixture of two or more of these conductive materials. More specifically, the conductive material may be any 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, Denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide, or a mixture of two or more of these conductive materials.

[0096] According to one embodiment of the present invention, the current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery. For example, stainless steel, copper, aluminum, nickel, titanium, baked carbon, or aluminum and stainless steel whose surfaces have been surface-treated with carbon, nickel, titanium, silver, or the like can be used.

[0097] According to one embodiment of the present invention, the binder resin may be a polymer commonly used in electrodes in the art. Non-limiting examples of such binder resins include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyethylhexyl acrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, ethylene-vinyl acetate copolymer, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. Examples of suitable cellulose acetates include, but are not limited to, cyanoethyl acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, and carboxyl methyl cellulose.

[0098] In the present invention, the positive electrode slurry for preparing the positive electrode active material layer may include a dispersant, and the dispersant may be a pyrrolidone-based compound, specifically, N-methylpyrrolidone (ADC-01, LG Chemicals).

[0099] According to one embodiment of the present invention, the content of the dispersant in the positive electrode slurry may be more than 0 parts by weight and not more than 0.5 parts by weight, relative to 100 parts by weight of the positive electrode slurry. Specifically, the content of the dispersant in the positive electrode slurry may be more than 0.05 parts by weight and not more than 0.4 parts by weight, relative to 100 parts by weight of the positive electrode slurry.

[0100] According to an embodiment of the present invention, the negative electrode slurry for preparing the negative electrode active material layer may include a dispersant, and the dispersant may be a polypyrrolidone-based compound. Specifically, the dispersant may be polyvinylpyrrolidone (manufactured by Junsei Corporation).

[0101] According to one embodiment of the present invention, the content of the dispersant in the negative electrode slurry may be more than 0 parts by weight and not more than 0.5 parts by weight, relative to 100 parts by weight of the negative electrode slurry. Specifically, the content of the dispersant in the negative electrode slurry may be more than 0.05 parts by weight and not more than 0.4 parts by weight, relative to 100 parts by weight of the negative electrode slurry.

[0102] According to one embodiment of the present invention, the electrochemical device prepared as described above can be placed in a suitable case and filled with an electrolyte to fabricate a battery.

[0103] According to one embodiment of the present invention, the electrolyte is A + B - A salt having the structure: + Li + , Na + , K. + or a combination thereof, - is PF6 -, BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 - or a salt containing an anion such as, or a combination thereof, dissolved or dissociated in an organic solvent such as, but not limited to, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma butyrolactone (γ-butyrolactone), or a mixture thereof.

[0104] One embodiment of the present invention provides a battery module including a battery containing the electrochemical device as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source. Specific examples of the device include, but are not limited to, power tools powered by a battery motor; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric two-wheeled vehicles, including electric bicycles (E-bikes) and electric scooters; electric golf carts; and power storage systems. [Example]

[0105] Hereinafter, the present invention will be described in detail with reference to examples. However, the examples of the present invention can be modified in various different forms, and the scope of the present invention should not be construed as being limited to the examples described below. The examples in this specification are provided to more completely explain the present invention to those skilled in the art.

[0106] Example 1 As a porous polymer substrate, a nonwoven fabric (total thickness 14 μm, pore size: 10 μm or more, porosity 40% by volume) made of polyethylene terephthalate (PET, weight average molecular weight 50,000) was prepared.

[0107] Then, cellulose nanocrystals (diameter: 10 nm, length: 200 nm, density: 1.5 g / cm) were prepared. 3 A dispersion was prepared by adding and dispersing a polymer (Young's modulus: 70 GPa, manufactured by MAINE) to water.

[0108] After the porous polymer substrate was immersed in the dispersion, it was dried with air at 50°C using a heat gun, and the loading amount of the cellulose nanocrystals in the porous polymer substrate was 9.7 g / m 2 A separation membrane having a thickness of 15 μm was manufactured in this manner. FIG. 3 is a photograph showing a magnified view of the surface of Example 1 according to one embodiment of the present invention. FIG. 4 is a photograph showing a magnified view of the cross section of Example 1 according to one embodiment of the present invention. Referring to FIGS. 3 and 4, it was confirmed that the cellulose nanocrystals were arranged in the pores and that the cellulose nanocrystals were stacked in the planar direction on the surface of the porous polymer substrate to form a densely packed structure.

[0109] <Comparative Example 1> In Example 1, Al2O3 (density: 3.95 g / cm3) was used instead of cellulose nanocrystals. 3 The porous polymer substrate was loaded with Al2O3 at a loading of 25.2 g / m2.2 A separation membrane having a thickness of 15 μm was produced in the same manner as in Example 1.

[0110] <Comparative Example 2> In Example 1, Al(OH)3 (density: 2.42 g / cm3) was used instead of cellulose nanocrystals. 3 The porous polymer substrate was loaded with Al(OH)3 at a loading of 15.6 g / m2. 2 A separation membrane having a thickness of 15 μm was produced in the same manner as in Example 1.

[0111] <Comparative Example 3> In Example 1, SiO2 (density: 2.65 g / cm3) was used instead of cellulose nanocrystals. 3 The porous polymer substrate was loaded with Al(OH)3 at a loading amount of 17.1 g / m2. 2 A separation membrane having a thickness of 15 μm was produced in the same manner as in Example 1.

[0112] <Comparative Example 4> In Example 1, a porous polymer substrate (total thickness 9 μm, pore size: 100 nm or less, porosity: 40% by volume) was prepared by extruding polyethylene resin (weight average molecular weight 900,000) and using a wet method.

[0113] The acrylic binder styrene-butyl acrylate with a particle size of 500 nm, a PVdF / HFP copolymer with a degree of substitution (weight ratio of HFP in PVdF polymer) of 20 wt% with a particle size of 500 nm, and cellulose nanocrystals (diameter: 10 nm, length: 200 nm, density: 1.5 g / cm) were used. 3 A slurry for the coating layer was prepared by dispersing polymer binder particles (Maine, Young's modulus: 70 GPa) in water. The weight ratio of the polymer binder particles to the inorganic particles was 25:75.

[0114] The slurry for the coating layer was applied to both sides of the surface of the porous polymer substrate by a bar coating method using a doctor blade, and then dried with air at 50°C using a heat gun, resulting in a loading amount of the cellulose nanocrystals on the porous polymer substrate of 8.5 g / m. 2 Thus, a separation membrane having a thickness of 10 μm was produced.

[0115] <Manufacturing of electrochemical elements> 1) Manufacturing of the positive electrode Cathode active material (LiNi 0.8 Mn 0.1 CO 0.1 O2), conductive material (carbon black), dispersant (N-methylpyrrolidone, ADC-01, LG Chemicals), and binder resin (a mixture of PVDF-HFP and PVDF) were mixed with water in a weight ratio of 97.5:0.7:0.14:1.66 to prepare a slurry for the positive electrode active material layer, with the remaining components (excluding water) being 50 wt%. The slurry was then applied to the surface of an aluminum thin film (10 μm thick) and dried to prepare a positive electrode having a positive electrode active material layer (120 μm thick).

[0116] 2) Manufacturing of negative electrodes Graphite (a blend of natural and artificial graphite), conductive material (carbon black), dispersant (Polyvinylpyrrolidone, Junsei), and binder resin (a blend of PVDF-HFP and PVDF) were mixed with water in a weight ratio of 97.5:0.7:0.14:1.66 to prepare a slurry for the negative electrode active material layer, with the remaining components (excluding water) at a concentration of 50 wt%. The slurry was then applied to the surface of a copper thin film (10 μm thick) and dried to prepare a negative electrode having a negative electrode active material layer (120 μm thick).

[0117] 3) Lamination process The prepared negative and positive electrodes were stacked with the separators of the Examples and Comparative Examples interposed therebetween, and a lamination process was performed to obtain an electrode assembly using a hot press at 70°C and 5.2 MPa for 10 seconds.

[0118] <Experimental Example 1: Air permeability of separation membrane> The air permeability (air permeability time, Gurley) of the separation membranes of the examples and comparative examples was measured according to the ASTM D-2873 method. The Gurley value was measured using a Gurley type densometer (No. 158) manufactured by Toyoseiki Co., Ltd., in accordance with the JIS Gurley measurement method. The air permeability value was measured by passing 100 ml of air through 1 in of the separation membrane under a pressure of 12.2 inH2O. 2 The time (seconds) required for the air to pass through the cross section of the sample was expressed as the aeration time.

[0119] <Experimental Example 2: Heat shrinkage rate of separator> The separators of the Examples and Comparative Examples were cut to a size of 50 mm x 50 mm, placed between sheets of A4 paper, and placed in a convection oven at 120°C for 1 hour, after which the thermal shrinkage was measured.

[0120] At this time, the heat shrinkage rate (%) was calculated as [(initial area - area after heat treatment at 150°C for 30 minutes) / (initial area)] x 100.

[0121] <Experimental Example 3: Tensile Strength> Test pieces each having a size of 100 mm x 15 mm were prepared for the separation membranes of the Examples and Comparative Examples.

[0122] The test specimen was exposed to 180°C for 1 minute, and then pulled at a rate of 50 mm / min at 25°C according to ASTM D882 using a Universal Testing Systems (Instron® 3345). The strength at which the test specimen broke was defined as the tensile strength.

[0123] <Experimental Example 4: Density of separation membrane> The separation membranes of the examples and comparative examples were cut into a size of 50 mm x 50 mm, and the volume and mass were measured at 25°C and 1 atmosphere to calculate the density.

[0124] <Experimental Example 5: Thickness Change Rate> The initial thickness of the porous polymer substrates of the Examples and Comparative Examples was measured using a contact thickness gauge, as well as the thickness after pressing at 70°C under a pressure of 5 MPa. Measurements were taken at 5 mm intervals over a distance of 30 cm along the TD direction of the porous substrate. The measurement along the TD direction was taken five times at different MD positions, and the arithmetic mean was used to determine the thickness of the porous substrate. The thickness change rate (%) of each porous polymer substrate was calculated using the following Equation 1:

[0125] [Formula 1] Thickness change rate (%) = [(initial thickness - thickness after pressing) / initial thickness] x 100

[0126] <Experimental Example 6: Resistance of separation membrane> Coin cells were fabricated using the separators of the examples and comparative examples, and the coin cells were left at room temperature for one day, after which the resistance of the separator was measured by an impedance measurement method. The coin cells were fabricated as follows.

[0127] Artificial graphite as a negative electrode active material, carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed in a weight ratio of 75:5:20, and N-methylpyrrolidone (NMP) as a solvent was added to prepare a negative electrode slurry.

[0128] The negative electrode slurry was charged to 3.8 mAh / cm 2 The resulting mixture was coated on a copper current collector in a loading amount of 0.1g and dried to prepare a negative electrode.

[0129] A cathode active material slurry was prepared by adding LiCoO2 as a cathode active material, Denka black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder in a weight ratio of 85:5:10 to N-methylpyrrolidone (NMP) as a solvent. The cathode active material slurry was coated on a sheet-shaped aluminum current collector and dried, resulting in a cathode loading capacity of 3.3 mAh / cm. 2 The positive electrode active material layer was formed so as to have the following structure.

[0130] The separators of the Examples and Comparative Examples were interposed between the negative electrode and the positive electrode prepared as above, and a non-aqueous electrolyte (1ML iPF 6、 A coin cell was fabricated by injecting ethylene carbonate (EC) / propylene carbonate (PC) / diethyl carbonate (DEC) (volume ratio = 3:3:4).

[0131] [Table 1]

[0132] Referring to Table 1, it was confirmed that in Example 1, which is one embodiment of the present invention, the cellulose nanocrystals are contained in the pores of the porous polymer substrate, thereby reducing the resistance and density of the separator, and maintaining the tensile strength at a level equivalent to that of the Comparative Example.

[0133] In contrast, it was confirmed that the density of the separator increased sharply and the resistance increased in Comparative Examples 1 to 3 due to the inclusion of aluminum oxide, aluminum hydroxide, and silicon dioxide, respectively.In Comparative Example 4, the cellulose nanocrystals were included in a separate coating layer, and it was confirmed that the thermal shrinkage rate and thickness change rate increased, resulting in a decrease in heat resistance.

[0134] According to one embodiment of the present invention, cellulose nanocrystals are contained in the pores of the porous polymer substrate, which is a nonwoven fabric, thereby improving the mechanical properties of the separation membrane and increasing the ionic conductivity. [Explanation of symbols]

[0135] 100: Separation membrane for electrochemical elements 110: Porous polymer base material 111: Stoma 113: Cellulose nanocrystals 130: Coating layer 131: Polymer binder 133: Inorganic particles

Claims

1. A separator for an electrochemical device, comprising a porous polymer substrate containing cellulose nanocrystals.

2. The separator for an electrochemical device according to claim 1 , wherein the cellulose nanocrystals are provided in pores of the porous polymer substrate.

3. The density of the cellulose nanocrystals is 0.1 g / m ３ 2.0g / m or more ３ The separator for electrochemical elements according to claim 1, wherein:

4. 2. The separator for an electrochemical device according to claim 1, wherein the cellulose nanocrystal has a Young's modulus of 50 GPa or more and 80 GPa or less.

5. The separator for an electrochemical device according to claim 1 , wherein the cellulose nanocrystals have a diameter of 30 nm or less.

6. The separator for an electrochemical device according to claim 1 , wherein the cellulose nanocrystals have a length of 600 nm or less.

7. 2. The separator for an electrochemical device according to claim 1, wherein the cellulose nanocrystals have an aspect ratio of 50 or more and 300 or less.

8. The separator for an electrochemical device according to claim 1 , wherein the porous polymer substrate is a nonwoven fabric.

9. 2. The separator for an electrochemical device according to claim 1, wherein the pore diameter of the porous polymer substrate is 1 μm or more and 20 μm or less.

10. 2. The separator for an electrochemical device according to claim 1, wherein the porosity of the porous polymer substrate is 30% by volume or more and 80% by volume or less.

11. An electrochemical device comprising: a positive electrode; a negative electrode; and the separator for an electrochemical device according to claim 1 interposed between the positive electrode and the negative electrode.

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