Separator for electrochemical device and electrochemical device including the same

Abstract

The present disclosure relates to a separator for an electrochemical device, and an electrochemical device including the same, and more specifically, to a separator for an electrochemical device including a boron nitride-based compound in a coating layer, thereby adsorbing transition metal ions eluted from an electrode into an electrolyte liquid and improving heat resistance of the separator, and an electrochemical device comprising the separator.

Description

Technical Field

[0001] This disclosure claims the priority and benefit of Korean Patent Application No. 10-2023-0103351, filed with the Korean Intellectual Property Office on August 8, 2023, the entire content of which is incorporated herein by reference. This disclosure relates to a separator for an electrochemical device and an electrochemical device including the separator. In particular, this disclosure relates to a separator for an electrochemical device including a boron nitride-based compound in a coating, thereby adsorbing transition metal ions eluted from an electrode into an electrolyte liquid and improving the heat resistance of the separator, and an electrochemical device including the separator. Background Art

[0002] Among the components of an electrochemical device, the separator includes a polymer substrate having a porous structure, which is located between a positive electrode and a negative electrode, separates the positive electrode and the negative electrode, and serves to prevent an electrical short circuit between the two electrodes and allow an electrolyte and ions to pass through. The separator itself does not participate in an electrochemical reaction. However, physical properties such as the wettability, porosity, and degree of thermal shrinkage of the electrolyte liquid affect the performance and safety of the electrochemical device.

[0003] Therefore, in order to enhance the physical properties of the separator, a coating is added to the porous polymer substrate, and various methods of changing the coating properties by adding various materials to the coating have been attempted. For example, an inorganic substance can be added to the coating to improve the mechanical strength of the separator, or an inorganic substance or hydrate can be added to the coating to improve the flame retardancy and heat resistance of the polymer substrate.

[0004] The separator can be attached to the electrode by a lamination process, and in order to ensure the adhesion strength between the electrode and the separator, an adhesive resin can be added to the slurry of the coating for the separator.

[0005] Meanwhile, the separator has a problem that its breakdown voltage decreases as it becomes thinner, and there are problems such as a decrease in battery performance due to dendrites formed on the electrode and a short circuit occurring in the battery.

[0006] Therefore, research on a separator that can ensure battery performance, improve battery safety, and prevent dendrite formation is required. Summary of the Invention

[0007] Technical Problem

[0008] This disclosure aims to provide a separator for an electrochemical device and an electrochemical device including the separator, which can ensure the heat resistance of the separator by adding a boron nitride-based compound to the coating included in the separator and adjusting its content, and can adsorb transition metal ions eluted from the electrode.

[0009] However, the problems to be solved by the present disclosure are not limited to the above problems, and those skilled in the art will clearly understand other problems not mentioned through the following description.

[0010] Technical solution

[0011] One embodiment of the present disclosure provides a separator for an electrochemical device, the separator comprising: a porous polymer substrate; and a coating disposed on at least one surface of the porous polymer substrate and containing a boron nitride-based compound, polymer binder particles, and inorganic particles, wherein the content of the inorganic particles is 80 parts by weight or more relative to 100 parts by weight of the coating.

[0012] According to one embodiment of the present disclosure, the content of the boron nitride-based compound in the coating may be 0.1 part by weight or more and 20 parts by weight or less relative to 100 parts by weight of the coating.

[0013] According to one embodiment of the present disclosure, the boron nitride-based compound may be boron nitride nanotubes.

[0014] According to one embodiment of the present disclosure, the average outer diameter of the boron nitride-based compound may be 10 nm or more and 100 nm or less.

[0015] According to one embodiment of the present disclosure, the average length of the boron nitride-based compound may be 1 μm or more and 50 μm or less.

[0016] According to one embodiment of the present disclosure, the aspect ratio of the boron nitride-based compound may be 10 to 5,000.

[0017] According to one embodiment of the present disclosure, the density of the boron nitride-based compound may be 1.0 g / cm 3 or more and 5.0 g / cm 3 or less.

[0018] According to one embodiment of the present disclosure, the specific surface area of the boron nitride-based compound may be 20 m 2 / g or more and 55 m 2 / g or less.

[0019] According to one embodiment of the present disclosure, in the separator for an electrochemical device, the inorganic particles are one selected from boehmite, alumina, and combinations thereof.

[0020] One embodiment of the present disclosure provides an electrochemical device, comprising: a positive electrode; a negative electrode; and the separator interposed between the positive electrode and the negative electrode.

[0021] Beneficial effects

[0022] A separator for an electrochemical device according to an embodiment of the present disclosure can minimize dendrites formed on an electrode by adsorbing transition metal ions eluted from the electrode by utilizing the polarity of a compound generated by the electronegativity difference between nitrogen and boron in a boron nitride-based compound and the specific surface area of the boron nitride-based compound.

[0023] A separator for an electrochemical device according to an embodiment of the present disclosure can improve the heat resistance of the separator by utilizing the heat resistance of a boron nitride-based compound.

[0024] An electrochemical device according to an embodiment of the present disclosure minimizes dendrites formed on an electrode, thereby achieving battery safety and improving battery performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Figs. 1a and 1b are schematic views of a separator for an electrochemical device according to an embodiment of the present disclosure. Specifically, Figure 1 Fig. 1a is a schematic view of a separator for an electrochemical device having a coating on one surface, and Figure 1 Fig. 1b is a schematic view of a separator for an electrochemical device having coatings on both surfaces.

[0026] Figure 2 is a schematic view of an electrochemical device according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0027] In this specification, a description of a certain part "including" certain components means that it may further include other components and does not exclude other components, unless specifically stated to the contrary.

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

[0029] In this specification, a description of being "on" a certain component means that another component may be further placed thereon and does not exclude placing another component therebetween, unless specifically stated to the contrary.

[0030] In this specification, the property of "having pores" means that an object includes a plurality of pores interconnected by a pore structure through which a gaseous and / or liquid fluid can flow from one side of the object to the other side.

[0031] In this specification, the separator has a porous property including a plurality of pores and functions 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 an electrochemical device.

[0032] In the following, the present disclosure will be described in more detail.

[0033] One embodiment of the present disclosure provides a separator 100 for an electrochemical device, the separator including: a porous polymer substrate 110; and a coating 130 disposed on at least one surface of the porous polymer substrate 110 and containing a boron nitride-based compound 131, polymer binder particles 133, and inorganic particles 135, wherein the content of the inorganic particles 135 is 80 parts by weight or more relative to 100 parts by weight of the coating 130.

[0034] The separator 100 for an electrochemical device according to one embodiment of the present disclosure can adsorb transition metal ions eluted from an electrode by utilizing the polarity of the compound generated by the electronegativity difference between nitrogen and boron in the boron nitride-based compound 131 and the specific surface area of the boron nitride-based compound 131, thereby minimizing dendrites formed on the electrode. In addition, the separator 100 for an electrochemical device according to one embodiment of the present disclosure can improve the heat resistance of the separator by utilizing the excellent heat resistance of the boron nitride-based compound 131.

[0035] Figure 1 Figs. 1a and 1b are schematic views of a separator 100 for an electrochemical device according to one embodiment of the present disclosure. Specifically, Figure 1 Fig. 1a is a schematic view of a separator 100 for an electrochemical device having a coating 130 disposed on one surface, Figure 1 Fig. 1b is a schematic view of a separator 100 for an electrochemical device having coatings disposed on both surfaces. The separator 100 for an electrochemical device according to one embodiment of the present disclosure will be specifically described with reference to Figure 1 Figs. 1a and 1b.

[0036] According to one embodiment of the present disclosure, the separator 100 for an electrochemical device includes a porous polymer substrate 110. As described above, the separator 100 for an electrochemical device allows lithium ions to pass through while blocking electrical contact by including the porous polymer substrate 110, and can achieve a shutdown function at an appropriate temperature.

[0037] According to one embodiment of the present disclosure, the porous polymer substrate 110 can be prepared using a polyolefin-based resin as a base resin. Examples of the polyolefin-based resin may include polyethylene, polypropylene, polyisopentene, etc., and the polyolefin-based resin may include one or more types thereof. The porous separator, i.e., the separator having a plurality of pores, prepared using such a polyolefin-based resin as a base resin can provide a shutdown function at an appropriate temperature.

[0038] According to one embodiment of the present disclosure, the weight average molecular weight of the polyolefin-based resin may be 500,000 or greater and 2,000,000 or less. By adjusting the weight average molecular weight of the polyolefin-based resin within the above range, the compressive strength of the separator can be improved. In addition, when different types of polyolefin-based resins are used after mixing or a separator having a multilayer structure formed of different types of polyolefin-based resins is formed, the weight average molecular weight of the polyolefin-based substrate material can be calculated by adding the weight average molecular weights of each polyolefin resin according to the content ratio.

[0039] In the present specification, 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.

[0040] - Column: PL Olexis (Polymer Laboratories)

[0041] - Solvent: TCB (trichlorobenzene)

[0042] - Flow rate: 1.0 ml / min

[0043] - Sample concentration: 1.0 mg / ml

[0044] - Injection volume: 200 μl

[0045] - Column temperature: 160 °C

[0046] - Detector: Agilent high temperature RI detector

[0047] - Standard: Polystyrene (corrected with a third-order function)

[0048] According to one embodiment of the present disclosure, the porous polymer substrate 110 can be prepared using the following method (wet method): wherein a polyolefin-based resin and a plasticizer (diluent) are mixed at a high temperature to form a single phase, the polymer material and the plasticizer are phase-separated during cooling, and then the plasticizer is extracted to form pores, and stretching and heat setting treatments are performed. In addition, the porous polymer substrate using the polyolefin-based resin may be provided with a core formed of a mixture of polyethylene and polypropylene, and polyethylene skin portions laminated on both surfaces of the core.

[0049] According to one embodiment of the present disclosure, those skilled in the art can easily prepare the average pore diameter and the maximum pore diameter of the separator 100 within the scope of the present disclosure by adjusting the mixing ratio of the plasticizer, the stretching ratio, the heat setting treatment temperature, etc.

[0050] According to an embodiment of the present disclosure, the thickness of the porous polymer substrate 110 may be 1 μm or more and 50 μm or less. Specifically, the thickness of the porous polymer substrate 110 may be 2 μm or more and 45 μm or less, 3 μm or more and 40 μm or less, 4 μm or more and 35 μm or less, 5 μm or more and 30 μm or less, 6 μm or more and 25 μm or less, 7 μm or more and 20 μm or less, or 8 μm or more and 15 μm or less. By adjusting the thickness of the porous polymer substrate 110 within the above range, the energy density of the battery can be increased.

[0051] According to an embodiment of the present disclosure, the porosity of the porous polymer substrate 110 may be 10 vol% or more and 90 vol% or less. Specifically, the porosity of the porous polymer substrate 110 may be 10 vol% or more and 90 vol% or less, 20 vol% or more and 80 vol% or less, 30 vol% or more and 70 vol% or less, or 40 vol% or more and 60 vol% or less. By adjusting the porosity of the porous polymer substrate 110 within the above range, the separator permeability of lithium ions can be controlled.

[0052] According to an embodiment of the present disclosure, the coating 130 is provided on at least one surface of the porous polymer substrate 110. Specifically, the separator 100 for an electrochemical device includes the coating 130 provided on one surface or both surfaces of the porous polymer substrate 110. By the separator 100 for an electrochemical device including the coating 130 provided on at least one surface of the porous polymer substrate 110 as described above, the heat resistance of the separator is improved, the mechanical properties are improved, and the occurrence of electrode electrical short circuit caused by the shrinkage of the separator at high temperature can be prevented.

[0053] According to an embodiment of the present disclosure, the separator 100 for an electrochemical device includes the coating 130, and the coating 130 includes a boron nitride-based compound 131, polymer binder particles 133, and inorganic particles 135. By the coating 130 including the boron nitride-based compound 131, polymer binder particles 133, and inorganic particles 135 as described above, the heat resistance of the separator 100 is improved, the mechanical properties are improved, the occurrence of electrode electrical short circuit caused by the shrinkage of the separator 100 at high temperature is prevented, and pores can be formed in the coating 130. In addition, the heat resistance of the separator 100 is improved, and transition metal ions eluted from the electrode can be adsorbed.

[0054] According to one embodiment of the present disclosure, the coating 130 may uniformly contain a boron nitride-based compound 131, polymer binder particles 133, and inorganic particles 135. Specifically, the boron nitride-based compound 131, polymer binder particles 133, and inorganic particles 135 are uniformly dispersed in a coating slurry for forming the coating, and as the coating slurry is coated and the dispersion medium or solvent is removed, the boron nitride-based compound 131, polymer binder particles 133, and inorganic particles 135 may be distributed in a uniform content. Each content (by weight) of the boron nitride-based compound 131, polymer binder particles 133, and inorganic particles 135 is uniform in the coating, and even if there are some differences, the differences may be about 5%. By uniformly containing the boron nitride-based compound 131, polymer binder particles 133, and inorganic particles 135 in the coating 130 as described above, the compressive strength of the separator can be improved.

[0055] According to one embodiment of the present disclosure, the content of the inorganic particles 135 in the coating 130 may be 80 parts by weight or more relative to 100 parts by weight of the coating 130. Specifically, the content of the inorganic particles 135 in the coating 130 may be 81 parts by weight or more and less than 100 parts by weight, 82 parts by weight or more and 99 parts by weight or less, 83 parts by weight or more and 98 parts by weight or less, 84 parts by weight or more and 97 parts by weight or less, 85 parts by weight or more and 96 parts by weight or less, 86 parts by weight or more and 95 parts by weight or less, 87 parts by weight or more and 94 parts by weight or less, 88 parts by weight or more and 93 parts by weight or less, 89 parts by weight or more and 92 parts by weight or less, or 90 parts by weight or more and 91 parts by weight or less relative to 100 parts by weight of the coating 130. By adjusting the content of the inorganic particles 135 contained in the coating 130 within the above range, the polymer binder particles and the inorganic particles can be uniformly distributed in the coating, and the compressive strength and heat resistance of the coating can be improved.

[0056] According to one embodiment of the present disclosure, the content of the boron nitride-based compound 131 in the coating 130 may be 0.1 part by weight or more and 20 parts by weight or less relative to 100 parts by weight of the coating 130. By adjusting the content of the boron nitride-based compound in the coating within the above range, the insulation and heat conduction performance of the separator are improved by utilizing the insulation performance of the boron nitride-based compound, and transition metal ions eluted from the electrode can be adsorbed by inducing the polarity of the compound caused by the electronegativity difference between nitrogen and boron in the boron nitride-based compound.

[0057] According to one embodiment of the present disclosure, boron nitride-based compounds may form a network in the coating. Specifically, the boron nitride-based compounds may be connected to each other to form a single network (mesh). By the boron nitride-based compounds that form a network in the coating as described above, the heat resistance of the boron nitride-based compounds can be uniformly exhibited throughout the coating.

[0058] According to one embodiment of the present disclosure, the boron nitride-based compound 131 may be a boron nitride nanotube (BNNT). By using the boron nitride nanotube as the boron nitride-based compound as described above, the insulation and heat conduction performance of the separator are improved by the insulating property of the boron nitride nanotube, and transition metal ions eluted from the electrode can be adsorbed by inducing the polarity of the compound caused by the electronegativity difference between nitrogen and boron in the boron nitride nanotube.

[0059] According to one embodiment of the present disclosure, the average outer diameter of the boron nitride-based compound 131 may be 10 nm or more and 100 nm or less. Specifically, the average outer diameter of the boron nitride-based compound 131 may be 20 nm or more and 90 nm or less, 30 nm or more and 80 nm or less, 40 nm or more and 70 nm or less, or 50 nm or more and 60 nm or less. By adjusting the average outer diameter of the boron nitride-based compound 131 within the above range, a uniform network is formed in the coating, thereby improving the thermal stability, mechanical strength, and electrical insulation of the separator.

[0060] According to one embodiment of the present disclosure, the average length of the boron nitride-based compound 131 may be 1 μm or more and 50 μm or less. Specifically, the average length of the boron nitride-based compound 131 may be 5 μm or more and 45 μm or less, 10 μm or more and 40 μm or less, 15 μm or more and 35 μm or less, or 20 μm or more and 30 μm or less. By adjusting the average length of the boron nitride-based compound 131 within the above range, a uniform network is formed in the coating, thereby improving the thermal stability, mechanical strength, and electrical insulation of the separator.

[0061] According to one embodiment of the present disclosure, the aspect ratio of the boron nitride-based compound 131 may be 10 or more and 5,000 or less. Specifically, the aspect ratio of the boron nitride-based compound 131 may be 500 or more and 4,500 or less, 1,000 or more and 4,000 or less, 1,500 or more and 3,500 or less, or 2,000 or more and 3,000 or less. By adjusting the aspect ratio of the boron nitride-based compound 131 to within the above range, a uniform network is formed in the coating, thereby improving the thermal stability and mechanical strength of the separator.

[0062] According to one embodiment of the present disclosure, the density of the boron nitride-based compound 131 can be 1.0 g / cm 3 or greater and 5.0 g / cm 3 or less. Specifically, the density of the boron nitride-based compound 131 can be 1.5 g / cm 3 or greater and 4.5 g / cm 3 or less, 2.0 g / cm 3 or greater and 4.0 g / cm 3 or less, or 2.5 g / cm 3 or greater and 3.5 g / cm 3 or less. By adjusting the density of the boron nitride-based compound 131 within the above range, the energy density of the electrochemical device can be increased while having the thermal stability and mechanical strength of the separator.

[0063] According to one embodiment of the present disclosure, the boron nitride-based compound 131 can have a specific surface area (BET) of 20 m 2 / g or greater and 55 m 2 / g or less. Specifically, the specific surface area of the boron nitride-based compound 131 can be 21 m 2 / g or greater and 54 m 2 / g or less, 22 m 2 / g or greater and 53 m 2 / g or less, 23 m 2 / g or greater and 52 m 2 / g or less, 24 m 2 / g or greater and 51 m 2 / g or less, 25 m 2 / g or greater and 50 m 2 / g or less, 26 m 2 / g or greater and 49 m 2 / g or less, 27 m 2 / g or greater and 48 m 2 / g or less, 28 m 2 / g or greater and 47 m 2 / g or less, 29 m 2 / g or greater and 46 m 2 / g or less, 30 m 2 / g or greater and 45 m 2 / g or less, 31 m 2 / g or greater and 44 m 2 / g or less, 32 m 2 / g or greater and 43 m 2 / g or less, 33 m 2 / g or greater and 42 m 2 / g or less, 34m 2 / g or greater and 41m 2 / g or less, 35m 2 / g or greater and 40m 2 / g or less, 36m 2 / g or greater and 39m 2 / g or less, or 37m 2 / g or greater and 38m 2 / g or less. By adjusting the specific surface area of the boron nitride-based compound 131 within the above range, the energy density of the electrochemical device can be increased, while having the thermal stability and mechanical strength of the separator, and the adsorption efficiency of the transition metal can be improved.

[0064] In this specification, the "specific surface area" can be the BET surface area calculated when measuring the adsorption isotherm up to 1 bar at -196 °C using a BET specific surface area analyzer (BEL, Microtrac) and measuring the N2 adsorption isotherm using the Brunauer-Ennett-Teller (BET) model.

[0065] According to one embodiment of the present disclosure, the coating 130 may include a plurality of pores. Specifically, the coating may be a porous coating. More specifically, the coating may be a porous coating including a plurality of pores. Through the coating including a plurality of pores as described above, the separator can allow lithium ions to pass through and allow current to flow, while physically blocking the negative electrode and the positive electrode.

[0066] According to one embodiment of the present disclosure, the coating 130 may be formed of a boron nitride-based compound and inorganic particles 135, and the inorganic particles 135 are bound by polymer binder particles 133 and integrated in the coating. The pores in the coating 130 may be caused by the interstitial volume and the empty space between the boron nitride-based compound and the inorganic particles.

[0067] According to one embodiment of the present disclosure, the coating 130 may be formed to a thickness of 1 μm to 20 μm on any side of the porous polymer substrate 110. By adjusting the thickness of the coating 130 within the above range, the heat resistance or resistance of the separator can be controlled within an appropriate range.

[0068] In one embodiment of the present disclosure, a contact thickness measurement device may be used to measure the thickness of the porous polymer substrate, the coating, etc. As an example of the contact thickness measurement device, VL-50S-B manufactured by Mitutoyo Corporation may be used.

[0069] According to one embodiment of the present disclosure, the polymer binder particles 133 may be an acryloyl binder, a polyvinylidene binder, or a combination thereof. The combination of the acryloyl binder and the polyvinylidene binder may be a mixture of the acryloyl binder and the polyvinylidene binder, a copolymer including acryloyl repeating units and polyvinylidene repeating units, or a hybrid product of the acryloyl binder and the polyvinylidene binder. In addition, the polyvinylidene binder may be a copolymer of polyvinylidene fluoride (PVdF) and hexafluoropropylene (HFP). By selecting the polymer binder particles from the above, the porosity of the separator can be maintained, the battery can be easily manufactured by increasing the adhesion strength between the electrode and the separator during the lamination process of the battery, and the stacking process can be stably performed. In addition, even after the battery is activated and the coating is wetted by the electrolyte liquid, the porosity of the separator can be maintained and the adhesion strength can be maintained. In addition, the stiffness of the battery is increased and the bending of the separator can be prevented.

[0070] According to one embodiment of the present disclosure, the acryloyl binder is a polymer including a carboxylate ester as a repeating unit, and may preferably be a (meth)acrylate or an acryloyl-styrene copolymer.

[0071] According to one embodiment of the present disclosure, specific examples of the (meth)acrylate may include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, hydroxymethyl (meth)acrylate, hydroxyethyl (meth)acrylate, ethylene glycol (meth)acrylate, ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, allyl (meth)acrylate, ethylene di(meth)acrylate, etc., and may be one or more types selected from these. Among them, one or more selected from methyl (meth)acrylate, ethyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate are preferred, and methyl (meth)acrylate is particularly preferred.

[0072] According to an embodiment of the present disclosure, the acryloyl-styrene copolymer may include an acryloyl binder, and the acryloyl binder may be a polyacrylate-based. For example, the acryloyl binder may be one or more types selected from the group consisting of styrene-butyl acrylate, styrenebutadiene rubber, nitril-butadienerubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, and acrylate-based polymers. Specifically, it may be a copolymer including acrylate.

[0073] According to an embodiment of the present disclosure, the glass transition temperature (Tg) of the polymer binder particles 133 may be 20 °C or higher and 60 °C or lower. Specifically, the glass transition temperature (Tg) of the polymer binder particles may be 22 °C or higher and 58 °C or lower, 24 °C or higher and 56 °C or lower, 26 °C or higher and 54 °C or lower, 28 °C or higher and 52 °C or lower, 30 °C or higher and 50 °C or lower, 32 °C or higher and 48 °C or lower, 34 °C or higher and 46 °C or lower, 36 °C or higher and 44 °C or lower, or 38 °C or higher and 42 °C or lower. By adjusting the glass transition temperature (Tg) of the polymer binder particles within the above range, the viscosity of the slurry for preparing the coating can be controlled, and the convenience of battery manufacturing can be improved.

[0074] According to an embodiment of the present disclosure, the average diameter (D 50 ) of the polymer binder particles 133 is not particularly limited, but is preferably in the range of 0.1 μm or more and 1 μm or less to form a coating 130 having a uniform thickness and appropriate porosity. Specifically, the average diameter (D 50 ) of the polymer binder particles 135 may be 0.2 μm or more and 0.9 μm or less, 0.3 μm or more and 0.8 μm or less, 0.4 μm or more and 0.7 μm or less, or 0.5 μm or more and 0.6 μm or less. By adjusting the average diameter (D 50 ) of the polymer binder particles 133 within the above range, the dispersibility of the slurry prepared for preparing the coating can be improved, and the thickness of the formed coating can be reduced.

[0075] According to one embodiment of the present disclosure, the polyvinylidene fluoride binder may be a polyvinylidene fluoride binder having a hexafluoropropylene (HFP) content of 1 wt% or more and 50 wt% or less. Specifically, the polyvinylidene fluoride binder may have a hexafluoropropylene (HFP) content of 1 wt% or more and 50 wt% or less, 2 wt% or more and 45 wt% or less, 3 wt% or more and 40 wt% or less, 4 wt% or more and 35 wt% or less, 5 wt% or more and 30 wt% or less, 7 wt% or more and 25 wt% or less, or 10 wt% or more and 20 wt% or less. By selecting a polyvinylidene fluoride binder having a hexafluoropropylene content of 1 wt% or more and 50 wt% or less as the polyvinylidene binder, the porosity of the separator can be maintained, and the adhesive strength can be maintained even when the coating is wetted by the electrolyte liquid after the battery is activated. In this specification, the degree of substitution of the polyvinylidene fluoride binder may refer to the weight ratio including hexafluoropropylene.

[0076] According to one embodiment of the present disclosure, the content of the polymer binder particles 133 may be 20 parts by weight or less relative to 100 parts by weight of the coating 130. Specifically, the content of the polymer binder particles 133 may be greater than 0 parts by weight and 20 parts by weight or less, 1 part by weight or more and 19 parts by weight or less, 2 parts by weight or more and 18 parts by weight or less, 3 parts by weight or more and 17 parts by weight or less, 4 parts by weight or more and 16 parts by weight or less, 5 parts by weight or more and 15 parts by weight or less, 6 parts by weight or more and 14 parts by weight or less, 7 parts by weight or more and 13 parts by weight or less, 8 parts by weight or more and 12 parts by weight or less, 9 parts by weight or more and 11 parts by weight or less, or 10 parts by weight or more and 11 parts by weight or less. By adjusting the content of the polymer binder particles 133 within the above range, the assembly readiness during the electrode assembly process can be improved, and the heat resistance of the coating can be improved.

[0077] According to one embodiment of the present disclosure, when the acryloyl binder and the polyvinylidene fluoride binder in the composite coating 130 are combined, the weight ratio may be 9:1 to 1:9. Specifically, when the acryloyl binder and the polyvinylidene fluoride binder in the composite coating 130 are combined, the weight ratio may be 8:1 to 1:8, 7:1 to 1:7, 6:1 to 1:6, 5:1 to 1:5, 4:1 to 1:4, 3:1 to 1:3, or 2:1 to 1:2. By adjusting the weight ratio between the acryloyl binder and the polyvinylidene fluoride binder within the above range, the wet adhesive strength and the dry adhesive strength of the separator for the electrochemical device can be improved simultaneously.

[0078] According to one embodiment of the present disclosure, the inorganic particles 135 that can be used for the coating 130 can be electrochemically stable substances. Specifically, the inorganic particles that can be used in one embodiment of the present disclosure can be substances that do not undergo oxidation and / or reduction reactions within the operating voltage range of the applied electrochemical device (e.g., 0 V to 5 V based on Li / Li + ).

[0079] According to one embodiment of the present disclosure, the inorganic particles 135 can 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), hafnium dioxide (HfO2), SrTiO3, SnO2, CeO2, MgO, Mg(OH)2, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, SiC, Al(OH)3, TiO2, aluminum peroxide, zinc stannate hydroxide (ZnSn(OH)6), zinc tin oxide (Zn2SnO4, ZnSnO3), antimony trioxide (Sb2O3), antimony tetroxide (Sb2O4), antimony pentoxide (Sb2O), boehmite, etc. The inorganic particles can include one, two, or more of them. Specifically, the inorganic particles 135 are preferably selected from one of boehmite, alumina, and combinations thereof. By selecting one of boehmite, alumina, and combinations thereof as the inorganic particles as described above, the heat resistance of the separator can be improved.

[0080] According to one embodiment of the present disclosure, the average diameter (D 50 ) of the inorganic particles 135 is not particularly limited, but is preferably in the range of 0.3 μm or more and 1 μm or less to form a coating 130 having a uniform thickness and appropriate porosity. Specifically, the average diameter (D 50 ) of the inorganic particles 135 can be 0.2 μm or more and 0.9 μm or less, 0.3 μm or more and 0.8 μm or less, 0.4 μm or more and 0.7 μm or less, or 0.5 μm or more and 0.6 μm or less. Specifically, when the average diameter is less than 0.3 μm, the dispersibility of the inorganic particles in the slurry prepared for coating may decrease, and when the average diameter is greater than 1 μm, the thickness of the formed coating may increase.

[0081] In this specification, "D 50"Particle size" refers to the particle size at the 50% point in the cumulative distribution of the number of particles depending on the particle size. The particle size can be measured using the 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 measuring device (such as Microtrac S3500), and when the particles pass through the laser beam, the difference in the diffraction pattern depending on the particle size is measured to calculate the particle size distribution. D 50 The particle size can be measured by calculating the particle size at the 50% point in the cumulative distribution of the number of particles depending on the particle size in the measuring device.

[0082] According to one embodiment of the present disclosure, the porosity of the coating 130 can be 30% by volume or more. Specifically, the porosity of the coating 130 can be 30% by volume or more and 70% by volume or less, 32% by volume or more and 68% by volume or less, 34% by volume or more and 66% by volume or less, 36% by volume or more and 64% by volume or less, 38% by volume or more and 62% by volume or less, 40% by volume or more and 60% by volume or less, 42% by volume or more and 58% by volume or less, 44% by volume or more and 56% by volume or less, 46% by volume or more and 54% by volume or less, or 48% by volume or more and 52% by volume or less. By adjusting the porosity of the coating 130 within the above range, the migration of ions in the separator is maintained, and an increase in the resistance of the separator can be prevented. Specifically, when the porosity is 70% by volume or less, the dynamic performance capable of withstanding the pressing process of adhesion to the electrode can be ensured, and since the surface opening ratio does not increase too much, it is also suitable for ensuring the adhesion strength. At the same time, a porosity of 30% by volume or more is advantageous in terms of ion permeability.

[0083] In this specification, "porosity" refers to the ratio of the volume occupied by pores to the total volume. Volume % is used as its unit, and porosity can be used interchangeably with terms such as void ratio.

[0084] In this specification, the porosity can correspond to the value obtained by subtracting the volume converted from the weight and density of each component of the porous polymer substrate 100 and / or the coating 130 from the volume calculated from the thickness, width, and length of the porous polymer substrate 110 and / or the coating 130.

[0085] In one embodiment of the present disclosure, the porosity and pore size of the porous polymer substrate 110 and / or the coating 130 can be measured by the BET 6-point method using the nitrogen adsorption flow method, which uses a scanning electron microscope (SEM) image, a mercury porosimeter, a capillary flow porometer, or a porosimetry analyzer (Porosimetry analyzer, Bell Japan Inc, Belsorp-II mini). Here, it may be advantageous to use a capillary flow porometer.

[0086] According to one embodiment of the present disclosure, the polyvinylidene binder may be an aqueous binder. Specifically, by selecting an aqueous binder as the polyvinylidene binder, the pollutants emitted during the separator manufacturing process can be minimized, thereby reducing the battery manufacturing cost.

[0087] According to one embodiment of the present disclosure, the separator may further include an adhesive layer on the coating. By further including the adhesive layer as described above, the adhesion strength between the coating and the electrode described later can be improved.

[0088] According to one embodiment of the present disclosure, the adhesive layer may include a polymer binder.

[0089] According to one embodiment of the present disclosure, the polymer binder may be in the form of particles or a solution.

[0090] According to one embodiment of the present disclosure, the polymer binder in the adhesive layer may be an acryloyl binder, a polyvinylidene binder, or a combination thereof. The combination of the acryloyl binder and the polyvinylidene binder may be a mixture of the acryloyl binder and the polyvinylidene binder, a copolymer containing acryloyl repeating units and polyvinylidene repeating units, or a hybrid product of the acryloyl binder and the polyvinylidene binder. In addition, the polyvinylidene binder may be a copolymer of polyvinylidene fluoride (PVdF) and hexafluoropropylene (HFP). By selecting the polymer binder from the above polymer binders, the adhesion strength between the coating and the electrode can be improved, and the stacking process can be carried out stably. In addition, even after the battery is activated and the coating is wetted with the electrolyte liquid, the porosity of the separator can be maintained, and the adhesion strength can be maintained. In addition, the stiffness of the battery is increased, and the bending of the separator can be prevented. In addition, the description of the polymer binder overlaps with the description provided in the polymer binder particles of the coating above, so it is not included.

[0091] According to an embodiment of the present disclosure, the separator may have a polymer binder disposed on the coating. Specifically, the separator may have a polymer binder that is partially disposed on the coating rather than provided as a single layer. The polymer binder may be in the form of particles or in a dissolved form. When the polymer binder on the coating is in the form of particles, the polymer binder may be partially disposed on the coating while maintaining its particle shape. When the polymer binder is in a dissolved form, a layer may be formed on a part of the coating while providing the polymer binder. By disposing a separator having a polymer binder on the coating as described above, the adhesion strength to the electrode can be ensured, and the porosity of the coating can be ensured.

[0092] An embodiment of the present disclosure provides a method for manufacturing a separator for an electrochemical device, the method including: mixing a slurry for a coating 130 that includes a boron nitride-based compound 131, polymer binder particles 133, and inorganic particles 135 (S10); coating the slurry for the coating on at least one surface of a porous polymer substrate 110 (S30); and providing the coating 130 by drying the slurry for the coating (S50).

[0093] The method for manufacturing a separator for an electrochemical device according to an embodiment of the present disclosure can improve the heat resistance of the separator.

[0094] According to an embodiment of the present disclosure, the method for manufacturing a separator 100 for an electrochemical device includes mixing a slurry for a coating that includes a boron nitride-based compound 131, polymer binder particles 133, and inorganic particles 135 (S10). By including the mixing of the slurry for the coating that includes the boron nitride-based compound 131, polymer binder particles 133, and inorganic particles 135 as described above (S10), a coating can be easily formed on the separator.

[0095] According to an embodiment of the present disclosure, the slurry for the coating may be provided by preparing a polymer emulsion by dispersing polymer binder particles 133 in an appropriate dispersion medium, water. As described above, by preparing a polymer emulsion by dispersing polymer binder particles 133 in water as an appropriate dispersion medium for the slurry for the coating, contaminants generated during the manufacturing process can be minimized. In the present specification, the dispersion medium may be a solvent during the process of preparing the slurry.

[0096] According to an embodiment of the present disclosure, the boron nitride-based compound 131 and the inorganic particles 135 may be added and dispersed in the polymer emulsion. The content ratios among the boron nitride-based compound, the inorganic particles, and the polymer binder particles are as described above, and are appropriately controlled in consideration of the thickness, pore diameter, and porosity of the finally prepared coating according to an embodiment of the present disclosure.

[0097] According to one embodiment of the present disclosure, the boron nitride-based compound 131, the polymer binder particles 133, and the inorganic particles 135 may be dispersed in a dispersion medium water to prepare a slurry for coating. Specifically, without preparing the polymer emulsion as described above, the boron nitride-based compound 131, the polymer binder particles 133, and the inorganic particles 135 may be directly dispersed in a dispersion medium water to prepare a slurry for coating.

[0098] According to one embodiment of the present disclosure, the slurry for coating may have a solid content of 10 wt% or more and 50 wt% or less. Specifically, the slurry for coating may have a solid content of 15 wt% or more and 40 wt% or less, 20 wt% or more and 35 wt% or less, or 15 wt% or more and 40 wt% or less. By adjusting the solid content of the slurry for coating within the above range, the processability of the coating preparation process can be improved.

[0099] According to one embodiment of the present disclosure, a method for manufacturing a separator 100 for an electrochemical device includes coating a slurry for coating on at least one surface of a porous polymer substrate 110 (S30). By including a coating of the slurry for coating on at least one surface of the porous polymer substrate 110 as described above, the coating 130 can be formed by a single coating, and the inorganic particles, the polymer binder particles, and the boron nitride-based compound are distributed in the slurry for coating at a uniform concentration. As a result, a uniform coating can be formed.

[0100] According to one embodiment of the present disclosure, the method of coating the slurry for coating on the surface of the porous polymer substrate 110 is not particularly limited to any one method, and a commonly used method known in the art may be used. For example, various methods such as dip coating, die coating, roll coating, comma coating, or a hybrid method thereof may be used.

[0101] According to one embodiment of the present disclosure, a method for manufacturing a separator 100 for an electrochemical device includes providing a coating 130 by drying the slurry for coating (S50). By providing the coating 130 by drying the slurry for coating as described above (S50), damage to the coating can be minimized, and the dispersion medium contained in the slurry can be easily removed.

[0102] According to one embodiment of the present disclosure, the temperature of the drying process may be 25 °C or higher and 75 °C or lower. Specifically, the temperature of the drying process may be 30 °C or higher and 70 °C or lower, 35 °C or higher and 65 °C or lower, 40 °C or higher and 60 °C or lower, or 45 °C or higher and 55 °C or lower. By adjusting the temperature of the drying process within the above range, denaturation of the porous polymer substrate can be prevented, and the dispersion medium can be effectively removed.

[0103] According to one embodiment of the present disclosure, the drying process appropriately sets time conditions to minimize the occurrence of surface defects in the coating 130. For drying, drying aids such as a drying furnace or hot air can be used within an appropriate range.

[0104] According to one embodiment of the present disclosure, the method may further include forming an adhesive layer by coating a slurry for the adhesive layer containing a polymer binder on the coating. By further including forming an adhesive layer by coating a slurry for the adhesive layer containing a polymer binder on the coating as described above, the adhesion strength between the separator and the electrode can be improved, the adhesion strength can be maintained during the lamination process with the electrode, and the stiffness can be improved or bending of the pouch-type battery can be prevented by maintaining the adhesion strength after activating the battery.

[0105] According to one embodiment of the present disclosure, the dispersion medium or solvent of the slurry for the adhesive layer may be water. By selecting the dispersion medium or solvent of the slurry for the adhesive layer as described above, environmental pollution caused by the dispersion medium or solution can be prevented.

[0106] According to one embodiment of the present disclosure, the method may further include drying the coated adhesive layer.

[0107] According to one embodiment of the present disclosure, the separator 100 is interposed between the positive electrode 300 and the negative electrode 500, and an electrochemical device 1000 is manufactured using a lamination process in which heat and / or pressure is applied thereto for bonding. In one embodiment of the present disclosure, the lamination process may be performed using a roll press device including a pair of pressure rollers. In other words, the negative electrode 500, the separator 100, and the positive electrode 300 are sequentially laminated and inserted between the pressure rollers to achieve interlayer bonding. Here, the lamination process may be performed using a hot pressing method.

[0108] One embodiment of the present disclosure provides an electrochemical device 1000, including: a positive electrode 300; a negative electrode 500; and a separator 100 interposed between the positive electrode 300 and the negative electrode 500.

[0109] The electrochemical device 1000 according to an embodiment of the present disclosure minimizes dendrites formed on the electrodes, thereby achieving battery safety and improving battery performance.

[0110] Figure 2 is a schematic diagram of the electrochemical device 1000 according to an embodiment of the present disclosure. Reference will be made to Figure 2 Specifically describe the electrochemical device 1000 according to an embodiment of the present disclosure.

[0111] In an embodiment of the present disclosure, an electrochemical device is a device that converts chemical energy into electrical energy through an electrochemical reaction, and is a concept including a primary battery and a secondary battery. In this specification, a secondary battery can be charged and discharged, and refers to a lithium secondary battery, a nickel-cadmium battery, a nickel-metal hydride battery, etc. A lithium secondary battery uses lithium ions as an ion conductor, and examples thereof may include a non-aqueous electrolyte secondary battery containing a liquid electrolyte, an all-solid-state battery including a solid electrolyte, a lithium polymer battery including a gel polymer electrolyte, a lithium metal battery using lithium metal as a negative electrode, etc., but are not limited thereto.

[0112] In an embodiment of the present disclosure, the electrochemical device may have a cylindrical shape. Specifically, the electrochemical device may have an electrode assembly including a positive electrode, a separator, and a negative electrode embedded in a cylindrical metal casing. More specifically, the electrochemical device having a cylindrical shape can be manufactured by storing a jelly-roll type electrode assembly in a cylindrical metal casing, injecting an electrolyte liquid into the cylindrical metal casing, and then bonding a cap formed with electrode terminals to the open top of the metal casing. By manufacturing the electrochemical device in the above-described cylindrical shape, the capacity can be increased, and the structural safety can be improved.

[0113] According to an embodiment of the present disclosure, the positive electrode is provided with a positive electrode current collector and a positive electrode active material layer on at least one side surface of the current collector, and the positive electrode active material includes a positive electrode active material, a conductor, and an adhesive resin. The positive electrode active material may include a layered compound or a compound substituted by one or more transition metals, such as lithium manganese composite oxides (LiMn2O4, LiMnO2, etc.), lithium cobalt oxide (LiCoO2), or lithium nickel oxide (LiNiO2); lithium manganese oxides, such as the chemical formula Li 1+x Mn 2-x O4 (where x is from 0 to 0.33), LiMnO3, LiMn2O3, or LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides, such as LiV3O8, LiV3O4, V2O5, or Cu2V2O7; represented by the chemical formula LiNi 1-x M xNi-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3); lithium manganese composite oxide represented by the chemical formula LiMn 1- x M x O2 (where M = Co, Ni, Fe, Cr, Zn or Ta, x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); LiMn2O4, in which some Li in the chemical formula is replaced by alkaline earth metal ions; disulfide compounds; Fe2(MoO4)3 or a mixture of two or more types thereof.

[0114] According to an embodiment of the present disclosure, the negative electrode is provided with a negative electrode current collector and a negative electrode active material layer on at least one side surface of the current collector. The negative electrode active material layer includes a negative electrode active material, a conductor, and an adhesive resin. The negative electrode may include one type selected from lithium metal oxides; carbon, such as non-graphitizable carbon or graphite-based carbon; metal composite oxides, such as 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, G; Me’: Al, B, P, Si, elements of Groups 1, 2 and 3 of the periodic table, halogens; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8); 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 substrates; and titanium oxide, or a mixture of two or more thereof, as the negative electrode active material.

[0115] According to one embodiment of the present disclosure, the conductor may be, for example, any one selected from the group consisting of graphite, carbon black, carbon fiber or metal fiber, metal powder, conductive whisker, conductive metal oxide, activated carbon, and polyphenylene derivative, or a mixture of two or more of these conductive materials. More specifically, the conductor may be one type 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.

[0116] According to one embodiment of the present disclosure, the current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes to the corresponding battery. For example, stainless steel, copper, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel whose surface is treated with carbon, nickel, titanium, silver, etc. may be used.

[0117] According to one embodiment of the present disclosure, as the binder resin, polymers commonly used in electrodes in the art can be used. Non-limiting examples of such binder resins may include polyvinylidene fluoride-co-hexafluoropropylene copolymer, polyvinylidene fluoride-cotrichloroethylene, polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetatebutyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxyl methyl cellulose, etc., but are not limited thereto.

[0118] According to one embodiment of the present disclosure, the positive electrode paste for preparing the positive electrode active material layer may include a dispersant, and the dispersant may be a pyrrolidone-based compound. Specifically, the dispersant may be N-methylpyrrolidone (ADC-01, LG Chem).

[0119] According to one embodiment of the present disclosure, the content of the dispersant included in the positive electrode paste may be greater than 0 parts by weight and 0.5 parts by weight or less relative to 100 parts by weight of the positive electrode paste. Specifically, the content of the dispersant included in the positive electrode paste may be greater than 0.05 parts by weight and 0.4 parts by weight or less relative to 100 parts by weight of the positive electrode paste.

[0120] According to one embodiment of the present disclosure, the negative electrode paste 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 Chemical CO., Ltd. in Japan).

[0121] According to one embodiment of the present disclosure, the content of the dispersant included in the negative electrode paste may be greater than 0 parts by weight and 0.5 parts by weight or less relative to 100 parts by weight of the negative electrode paste. Specifically, the content of the dispersant included in the negative electrode paste may be greater than 0.05 parts by weight and 0.4 parts by weight or less relative to 100 parts by weight of the negative electrode paste.

[0122] According to one embodiment of the present disclosure, the electrochemical device manufactured as described above may be inserted into a suitable housing, and an electrolyte liquid may be injected therein to manufacture a battery.

[0123] According to one embodiment of the present disclosure, the electrolyte liquid is obtained by dissolving or dissociating a salt having a structure such as A + B - 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, where A + includes ions composed of alkali metal cations such as Li + , Na + or K or a combination thereof +, and B - includes anions such as PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2- or C(CF2SO2)3 - or an ion composed of a combination thereof. However, the electrolyte liquid is not limited thereto.

[0124] One embodiment of the present disclosure provides a battery module, which includes a battery with an electrochemical device as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source. Specific examples of the device may include power tools powered by an electric motor; motor vehicles, including electric vehicles (EV), hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), etc.; electric two-wheel bicycles, including electric bikes (E-bike) and electric scooters (E-scooter); electric golf carts; systems for electric power storage, etc., but not limited thereto.

[0125] Mode of implementing the invention

[0126] Hereinafter, the present disclosure will be described in detail with reference to embodiments to specifically describe the present disclosure. However, the embodiments according to the present disclosure can be modified into various different forms, and the scope of the present disclosure is not to be construed as limited to the embodiments described below. The embodiments of this specification are provided to more comprehensively describe the present disclosure to those with average knowledge in the art.

[0127] <Example 1>

[0128] Extrude a polyethylene resin (weight average molecular weight 900,000), and use the wet method to prepare a porous polymer substrate (total thickness about 9 μm, porosity 40% by volume).

[0129] Introduce boron nitride nanotubes (average outer diameter: 50 nm, length: 25 μm, aspect ratio: 100, density 3.0 g / cm 3 , specific surface area (BET): 40 m 2 / g), which are boron nitride-based compounds, styrene-butyl acrylate (glass transition temperature 40 °C) as polymer binder particles (which is an acryloyl binder with a particle size of 500 nm), and boehmite (particle size: 500 nm) as inorganic particles into water and disperse them therein to prepare a slurry for coating (solid concentration 20% by weight). The weight ratio of the boron nitride-based compound, polymer binder particles, and inorganic particles used is 2:5:93.

[0130] The slurry for coating was applied to both surfaces of the porous polymer substrate by the bar coating method using a doctor blade, and dried with hot air at 50 °C to form a coating with a thickness of 1.5 μm on each of the two surfaces, resulting in the production of a separator with a total thickness of 12 μm.

[0131] <Example 2>

[0132] A separator was manufactured in the same manner as in Example 1, except that the weight ratio of the boron nitride-based compound, polymer binder particles, and inorganic particles used was 0.05:4.95:95.

[0133] <Comparative Example 1>

[0134] A separator was manufactured in the same manner as in Example 1, except that the weight ratio of the boron nitride-based compound, polymer binder particles, and inorganic particles used was 0:5:95.

[0135] <Comparative Example 2>

[0136] A separator was manufactured in the same manner as in Example 1, except that the weight ratio of the boron nitride-based compound, polymer binder particles, and inorganic particles used was 25:5:70.

[0137] <Manufacture of Electrochemical Device>

[0138] 1) Preparation of Positive Electrode

[0139] The positive electrode active material (LiNi 0.8 Mn 0.1 Co 0.1 O2), conductor (carbon black), dispersant (N-methylpyrrolidone, ADC-01, LG Chem.), and binder resin (mixture of PVDF-HFP and PVDF) were mixed with water at a weight ratio of 97.5:0.7:0.14:1.66 to prepare a slurry for the positive electrode active material layer with a concentration of 50 wt% of the components other than water. Then, the slurry was applied to the surface of an aluminum film (thickness 10 μm) and dried to prepare a positive electrode with a positive electrode active material layer (thickness 120 μm).

[0140] 2) Preparation of Negative Electrode

[0141] Graphite (a mixture of natural graphite and artificial graphite), a conductor (carbon black), a dispersant (polyvinylpyrrolidone, Junsei Chemical CO., Ltd. of Japan), and a binder resin (a mixture of PVDF-HFP and PVDF) were mixed with water at a weight ratio of 97.5:0.7:0.14:1.66 to prepare a slurry for the negative electrode active material layer, where the concentration of the components other than water was 50 wt%. Then, the slurry was coated on the surface of a copper film (thickness 10 μm) and dried to prepare a negative electrode having a negative electrode active material layer (thickness 120 μm).

[0142] <Experimental Example 1: Air Permeability>

[0143] For each of the separators in Examples 1 and 2 and Comparative Examples 1 and 2, the air permeability was measured using the method of ASTM D-2873. Specifically, according to the Gurley (JIS Gurley) measurement method of Japanese Industrial Standards, the air permeability was measured using a Gurley-type air permeability tester (No. 158) manufactured by Toyo Seiki Seisaku-Sho, Ltd. The air permeability value is expressed as the time (seconds) required for 100 ml of air to pass through the cross-section of 1 in of the separator at a pressure of 12.2 in H2O, that is, the air penetration time. 2 of the separator.

[0144] <Experimental Example 2: Measurement of Dry Heat Shrinkage Rate>

[0145] The separators in Examples 1 and 2 and Comparative Examples 1 and 2 were each cut into a size of 50 mm x 50 mm, placed between A4 papers, and introduced into a convection oven at 150 °C for 30 minutes. Then, the dry heat shrinkage rates in the machine direction (MD) and the transverse direction (TD) were measured.

[0146] The dry heat shrinkage rate (%) was calculated using the following mathematical equation 1.

[0147] [Mathematical Equation 1]

[0148] Dry heat shrinkage rate (%) = (Initial length - Length after heat treatment) / (Initial length) x 100

[0149] <Experimental Example 3: Measurement of Damp Heat Shrinkage Rate>

[0150] The separators in Examples 1 and 2 and Comparative Examples 1 and 2 were each cut into a size of 50 mm x 50 mm, then introduced into a bag together with the electrolyte liquid, and the bag was sealed. After heat treatment at 135 °C for 30 minutes, the dimensional change was observed.

[0151] The electrolyte liquid was prepared by dissolving lithium hexafluorophosphate (LiPF6) with a concentration of 1.0 M in an organic solvent formed by ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) (mixing volume ratio of EC / EMC / DEC = 3:4:3).

[0152] The damp heat shrinkage rate was calculated using the following Mathematical Equation 2.

[0153] [Mathematical Equation 2]

[0154] Damp heat shrinkage rate (%) = (Initial length - Length after heat treatment) / (Initial length) x 100

[0155] <Experimental Example 4: Measurement of Peel Strength>

[0156] To evaluate the adhesion strength between the porous polymer substrate and the coating in the separators of each of Examples 1 and 2 and Comparative Examples 1 and 2, the peel strength was measured according to the following method.

[0157] First, the separator was cut into a size of 15 mm x 100 mm. A double-sided tape was attached to a glass plate, and the cut separator was attached to the tape such that the coated surface of the cut separator adhered to the tape.

[0158] After that, the end of the adhered separator was mounted on a UTM device (LLOYD Instrument LF Plus), and then a force was applied at a measurement rate of 300 mm / min and an angle of 180° to measure the force required to peel the porous polymer substrate and the coating. In addition, during the manufacturing process of the separators in each of Examples 1 and 2 and Comparative Examples 1 and 2, the surface first coated with the slurry for the coating was set as Surface A, and the surface of the second-coated slurry was set as Surface B, and the peel strength of each of Surface A and Surface B was measured.

[0159] <Experimental Example 5: Measurement of Breakdown Voltage>

[0160] For each of the separators in Examples 1 and 2 and Comparative Examples 1 and 2, a sample cut into a size of 5 cm x 5 cm was placed between aluminum clamps (upper clamp diameter 30 mm, lower clamp 50 mm x 100 mm), and the voltage at the failure condition (>0.5 mA, 3 seconds) was measured using a high-voltage tester. Here, the measurement conditions were set to direct current (DC), a current of 0.5 mA, and a voltage increase of 100 V / s (up to 3 kV). The measured value was expressed as the average of 30 samples.

[0161] [Table 1]

[0162]

[0163]

[0164] Referring to Table 1, it was confirmed that Example 1 including BNNT as a boron nitride-based compound had a reduced dry heat shrinkage rate and a reduced hydrothermal shrinkage rate while achieving a gas permeability and a peel strength similar to those of the conventional separator, and the breakdown voltage was increased.

[0165] In contrast, it was confirmed that in Comparative Example 1 not including BNNT and Example 2 including a small amount of BNNT, the dry heat shrinkage rate and the hydrothermal shrinkage rate increased rapidly, the heat resistance was reduced, and the breakdown voltage was decreased. Further, it was confirmed that Comparative Example 2 including an excessive amount of BNNT had a reduced dry heat shrinkage rate and a reduced hydrothermal shrinkage rate; however, the breakdown voltage increased rapidly along with the reduction of the peel strength.

[0166] Therefore, by including a boron nitride-based compound in the coating of the separator, which is an embodiment of the present disclosure, the heat resistance can be improved.

[0167] [Reference Signs]

[0168] 100: Separator for an electrochemical device

[0169] 110: Porous polymer substrate

[0170] 130: Coating

[0171] 130a: A part

[0172] 130b: Another part

[0173] 131: Boron nitride-based compound

[0174] 133: Polymer binder particles

[0175] 135: Inorganic particles

[0176] 300: Positive electrode

[0177] 500: Negative electrode

[0178] 1000: Electrochemical device

Claims

1. A separator for an electrochemical device, the separator comprising: a porous polymer substrate; and a coating disposed on at least one surface of the porous polymer substrate and comprising a boron nitride-based compound, polymer binder particles, and inorganic particles, wherein the content of the inorganic particles is 80 parts by weight or more relative to 100 parts by weight of the coating.

2. The separator according to claim 1, wherein the content of the boron nitride-based compound in the coating is 0.1 part by weight or more and 20 parts by weight or less relative to 100 parts by weight of the coating.

3. The separator according to claim 1, wherein the boron nitride-based compound is a boron nitride nanotube.

4. The separator according to claim 1, wherein the average outer diameter of the boron nitride-based compound is 10 nm or more and 100 nm or less.

5. The separator according to claim 1, wherein the average length of the boron nitride-based compound is 1 μm or more and 50 μm or less.

6. The separator according to claim 1, wherein the aspect ratio of the boron nitride-based compound is 10 to 5,000.

7. The partition according to claim 1, wherein the density of the boron nitride-based compound is 1.0 g / cm 3 or greater and 5.0 g / cm 3 or less.

8. The partition according to claim 1, wherein the specific surface area of the boron nitride-based compound is 20 m 2 / g or more and 55 m 2 / g or less.

9. The separator according to claim 1, wherein the inorganic particle is one selected from boehmite, alumina, and combinations thereof.

10. An electrochemical device, comprising: a positive electrode; a negative electrode; and the separator according to any one of claims 1 to 9 interposed between the positive electrode and the negative electrode.

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