Patent Application
20250158229
This application claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2023-0157974, filed on Nov. 15, 2023, the disclosure of which is incorporated herein by reference in its entirety.
Embodiments of the present disclosure generally relate generally to a separator and an electrochemical device including the same. More specifically, the embodiments of the present disclosure relate to an improved separator that improves the safety, and performance characteristics of an electrochemical device such as a secondary battery.
Recently, as the demand for eco-friendly energy increases, research on electrochemical devices is in progress in various fields including electronic devices, such as mobile phones and PCs, and electric vehicles.
An insulating separator is typically interposed between a positive electrode and a negative electrode in an electrochemical device such as a secondary battery. Research in reducing the thickness of the separator is under way for increasing the capacity and output characteristics of the electrochemical device. However, generally when the separator thickness is reduced, its mechanical strength and/or heat resistance may also be decreased which presents a safety problem during a manufacturing process and use of a battery. As an example, a short circuit between electrodes due to damage or deformation of the separator caused by a temperature rise in the battery may occur, resulting in an increased risk of overheating or fire of the battery.
Therefore, development of a separator which is thin and has improved mechanical strength and heat resistance is needed. In addition, development of a separator having high permeability for improving capacity and output is needed.
An embodiment of the present disclosure is directed to providing a separator for an electrochemical device with improved safety and performance characteristics.
An embodiment of the present disclosure is directed to providing a separator having excellent heat resistance and adhesion even at a small thickness, and an electrochemical device including the separator.
Another embodiment of the present disclosure is directed to providing a separator having improved mechanical strength and permeability even at a small thickness, and an electrochemical device including the separator.
Still another embodiment of the present disclosure is directed to providing an electrochemical device having excellent resistance properties and thermal safety.
The separator is designed to extend battery capacity and performance characteristics in high energy applications, including electric vehicles, thereby supporting reduced reliance in carbon-based fuels by enabling broader adoption of electric-powered transportation.
In an embodiment, the electrochemical device may be a secondary battery such as a lithium secondary battery which exhibits improved safety, capacity, and performance characteristics. The inventive lithium secondary battery can play a significant role in mitigating climate change by enabling cleaner, more efficient energy storage solutions that support renewable energy integration, reduce reliance on fossil fuels, and promote sustainable technologies.
For example, the inventive separator may be widely applied to a green technology field such as electric vehicles, battery charging stations, and other solar power generations and wind power generations using batteries. In addition, the inventive separator may be used in eco-friendly electric vehicles, hybrid vehicles, and the like for suppressing air pollution and greenhouse gas emissions from conventional carbon fuel power sources and, thus it is expected to significantly contribute in reducing and mitigating climate change.
According to an embodiment of the present disclosure, a separator is provided which includes a porous substrate; and an inorganic particle layer which is formed on at least one surface of the porous substrate and includes a binder and inorganic particles, wherein the separator has a peak shown in a range of 1082.5 to 1086.5 cm−1 in a spectrum by Fourier-transform infrared spectroscopy (FT-IR), and has a saturated moisture content measured by a Karl Fischer method of 350 to 1000 ppm.
In an embodiment, the saturated moisture content may be 450 to 1000 ppm.
In an embodiment, the porous substrate may have an average thickness of 5 to 15 μm, and a ratio between the average thickness of the porous substrate and an average thickness of the separator may be 0.7 or more.
In an embodiment, a total thickness of the inorganic particle layer formed on the porous substrate may be 3.2 μm or less.
In an embodiment, the binder may include a polyacrylamide-based resin.
In an embodiment, the polyacrylamide-based resin may be a copolymer including a unit derived from a (meth)acrylamide-based monomer and a unit derived from a comonomer.
In an embodiment, the polyacrylamide-based resin may include a structural unit derived from the (meth)acrylamide-based monomer and a structural unit derived from a (meth)acryl-based monomer containing a hydroxyl group.
In an embodiment, the polyacrylamide-based resin may have a weight average molecular weight of 100,000 to 2,000,000 g/mol.
In an embodiment, the binder may further include one or two or more additional binders selected from the group consisting of polyvinyl alcohol, polyvinylidene fluoride, carboxymethyl cellulose, styrene butadiene rubber, polyacrylic acid, polyethylene glycol, polyacrylonitrile, polyvinylpyrrolidone, and copolymers thereof.
In an embodiment, a content of the additional binder may be 0.1 to 30 wt % of the total content of the binder.
In an embodiment, the inorganic particles may have a BET specific surface area of 3 to 7 m2/g.
In an embodiment, the inorganic particles may have an average particle diameter (D50) of 0.5 to 1.5 μm.
In an embodiment, the inorganic particles may include one or two or more selected from the group consisting of metal hydroxides, metal oxides, metal nitrides, and metal carbides.
In an embodiment, heat shrinkage rates in the machine direction and the transverse direction which are measured after leaving the separator at 130° C. for 60 minutes may be 5% or less.
In an embodiment, the inorganic particle layer may have a weight ratio between the inorganic particles and the binder of 50:50 to 99.9:0.1.
In an embodiment, the inorganic particle layer may be formed at 0.5 to 10 g/m2.
In another embodiment, an electrochemical device includes the separator described above.
In an embodiment, the separator may be used in a renewable energy storage system for storing energy generated from a renewable source including, for example, at least one of a solar, and wind power generation system. The renewable energy storage system may comprise a plurality of secondary batteries employing the inventive separator. The secondary batteries may be lithium batteries.
The renewable energy storage system may be coupled to a power grid. During a first time period, the renewable energy storage system may store renewable energy generated from one or more renewable energy sources which are operatively coupled with the renewable energy storage system. The first time period may be a period when, for example, excess renewable energy is generated. The system may then supply the stored energy during a second time period, e.g., a time period when solar and/or wind energy are not generated, or when demand from a power grid is increased.
In another embodiment the inventive separator may be used in a plurality of secondary batteries used for powering an electric vehicle. Because of the greater capacity, improved performance and safety characteristics the separator is expected to lead to broader adoption of electric vehicles and replacement of combustion engine vehicles, thus making significant contributions to reducing future carbon fuel emissions.
According to an embodiment of the present disclosure, a separator comprise a porous substrate comprising a polyolefin polymer material with a porosity of 20 to 60%; and an inorganic particle layer formed on both surfaces of the porous substrate, the inorganic particle layer comprising a binder and inorganic particles, wherein the binder includes a polyacrylamide-based resin, wherein the inorganic particles have a BET specific surface area of 3 to 7 m2/g, an average particle diameter (D50) of 0.5 to 1.5 μm, and include one or two or more selected from the group consisting of metal hydroxides, metal oxides, metal nitrides, and metal carbides, wherein the separator has a peak shown in a range of 1082.5 to 1086.5 cm−1 in a spectrum by Fourier-transform infrared spectroscopy (FT-IR), and has a saturated moisture content measured by a Karl Fischer method of 350 to 1000 ppm.
These and other features and aspects of the embodiments of the present disclosure will become apparent to the skilled person having ordinary skill in the art from the following detailed description, the drawings, and the claims.
Hereinafter, the embodiments of the present disclosure will be described in detail. However, it is noted that the described embodiments are only illustrative and the embodiments are not limited to the described embodiments only.
In addition, it is noted that a singular form used in the specification and claims appended thereto may be intended to include a plural form also, unless otherwise indicated in the context.
In addition, it is noted that a numerical range used in the present specification includes all values within the range including the lower limit and the upper limit, increments logically derived in a form and span of a defined range, all double limited values, and all possible combinations of the upper limit and the lower limit in the numerical range defined in different forms. Unless otherwise defined in the present specification, values which may be outside a numerical range due to experimental error or rounding of a value are also included in the defined numerical range.
Furthermore, throughout the specification, unless explicitly described to the contrary, the transitional phrase “comprising” any constituent elements will be understood to allow further inclusion of other constituent elements rather than exclusion of other constituent elements.
In the present specification, it will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” or “above” another element, it can be directly on the other element or intervening elements may also be present.
In the present specification, “average particle diameter” refers to “D50”, and “D50” refers to a particle diameter of an inorganic particle corresponding to 50% in terms of a volume-based integrated fraction. The average particle diameter may be derived from particle size distribution results obtained by collecting a sample of inorganic particles to be measured in accordance with the standard of ISO 13320-1 and performing analysis using S3500 available from MICROTRAC. In addition, “D90” refers to a particle diameter of a particle corresponding to 90% in the volume-based integrated fraction, and “D10” refers to a particle diameter of an inorganic particle corresponding to 10% in a volume-based integrated fraction. D90 and D10 may be derived in the same manner as D50.
An embodiment of the present disclosure provides a separator including a porous substrate, and an inorganic particle layer which is formed on at least one surface of the porous substrate and includes a binder and inorganic particles. The separator has a peak shown in a range of 1082.5 to 1086.5 cm−1 (hereinafter, referred to as a first peak) in a spectrum by Fourier-transform infrared spectroscopy (FT-IR), and has a saturated moisture content measured by a Karl Fischer method of 350 to 1000 ppm.
It has been found, rather unexpectedly, that a separator which has a peak shown in a range of 1082.5 to 1086.5 cm−1 in a spectrum by Fourier-transform infrared spectroscopy (FT-IR) and also has a saturated moisture content measured by a Karl Fischer method of 350 to 1000 ppm has excellent heat resistance and adhesion and excellent permeability even at a small thickness.
In addition, an electrochemical device according to an embodiment may have both excellent resistance properties and thermal safety by including the separator which satisfies both the first peak in the specific range shown in the FT-IR spectrum and the saturated moisture content in the specific range. Specifically, since the electrochemical device according to an embodiment may show significantly low discharge resistance after 600 cycles, it may have improved charge and discharge performance.
When an increase rate of moisture content of the separator is high, a moisture content remaining in a battery is increased even after battery assembly, and the increase in moisture content as such may be a cause of decreasing a battery capacity by causing electrolyte decomposition. Conventionally, to lower the moisture content in the battery, a high-priced packaging material such as aluminum should be used. However, the present inventive separator according may have a low increase rate of moisture content after storage, by satisfying both the first peak in the specific range shown in the FT-IR spectrum and the saturated moisture content in the specific range. Accordingly, since the embodiment has a low moisture content remaining in the battery, a battery having excellent performance may be provided even when a packaging material of polyethylene is utilized instead of an aluminum material. That is, according to the embodiments of the present disclosure, battery costs may be reduced while battery performance is improved.
In an embodiment, though the separator has a very thin inorganic particle layer so that the average thickness of the porous substrate is 15 μm or less and the thickness of the porous substrate is 0.7 times or more of the entire thickness of the separator, it may have excellent mechanical properties, electrical properties, and thermal properties described later. Manufacture of the separator having the above properties may be achieved by adjusting one or more selected from the thickness of each layer, the size of inorganic particles, the type of binder, the type of binder which is additionally used, surface properties of the porous substrate, the surface of inorganic particles, and the saturated moisture content of the separator, however, it is noted that the means are not particularly limited as long as the above properties are achieved.
In an embodiment, the separator having the first peak in the specific range shown in the FT-IR spectrum and the saturated moisture content in the specific range may be manufactured using inorganic particles having a certain specific surface area. For example, the separator according to an embodiment may have a BET specific surface area of the inorganic particles included of 3 m2/g or more, 4 m2/g or more and 7 m2/g or less, 6 m2/g or less, or a value between the numerical values. Specifically, 3 to 7 m2/g or 4 to 6 m2/g.
In an embodiment, the separator as described above may be manufactured by adjusting a thickness ratio of the porous substrate and the separator included to a specific value. For example, the ratio between the average thickness of the porous substrate and the average thickness of the separator may be 0.7 or more, 0.75 or more, 0.77 or more and 0.99 or less, 0.9 or less, 0.85 or less, or a value between the numerical values. Specifically, 0.7 to 0.99, 0.75 to 0.9, or 0.77 to 0.85.
In an embodiment, the separator as described above may be manufactured using the binder included in the separator as a specific resin. For example, the binder may include a polyacrylamide-based resin. In an embodiment, a polyacrylamide-based resin including a structural unit derived from a (meth)acrylamide-based monomer and a structural unit derived from a (meth)acryl-based monomer containing a hydroxyl group may be used.
According to an embodiment, the separator as described above may be manufactured by using a specific additional binder with the polyacrylamide-based resin described above as a binder. For example, the specific additional binder may be one or two or more selected from the group consisting of polyvinyl alcohol (PVA), polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyvinylpyrrolidone (PVP), and copolymers thereof.
According to another embodiment, the separator as described above may be manufactured by using the polyacrylamide-based resin described above as the binder and using the porous substrate including a polar functional group on the surface. A non-limiting example of the polar functional group may include a carboxyl group, an aldehyde group, a hydroxyl group, and the like, however, it is noted that the polar functional group is not particularly limited. For example, the polar functional group may be introduced by a hydrophilic surface treatment. The hydrophilic surface treatment may be performed by including, according to an example, one or more of a corona discharge treatment and a plasma discharge treatment.
The separator which has the first peak in the specific range shown in the FT-IR spectrum and the saturated moisture content in the specific range as described above may be obtained by adjusting one or a combination of two or more selected from the thickness and the thickness ratio of each layer, the size of the inorganic particles, the type of binder, the type of an additionally used binder, the surface properties of the porous substrate, and the surface area of the inorganic particles of the separator. However, as long as the separator satisfies the first peak shown in the FT-IR spectrum and the saturated moisture content in the specific range, it is included in the range of the present disclosure, and the means are not particularly limited as long as they are satisfied.
Hereinafter, the separator will be described in more detail.
In an embodiment, the first peak has the highest intensity in a range of 1082.5 to 1086.5 cm−1. Specifically, it may be a peak having the highest intensity in a range of 1083 to 1086.5 cm−1 or in a range of 1083.5 to 1086 cm−1.
In an embodiment, the separator may further have a second peak shown in a range of 1140 to 1160 cm−1 in the FT-IR spectrum. The second peak has the highest intensity in the range described above. Specifically, it may be a peak having the highest intensity in a range of 1145 to 1155 cm−1.
In an embodiment, the separator may further have a third peak shown in a range of 2910 to 2930 cm−1 in the FT-IR spectrum. In an embodiment, the third peak has the highest intensity in the range described above. Specifically, it may be a peak having the highest intensity in a range of 2915 to 2925 cm−1 or in a range of 2915 to 2920 cm−1.
In an embodiment, the separator may further have a fourth peak shown in a range of 3090 to 3100 cm−1 in the FT-IR spectrum. The fourth peak has the highest intensity in the range described above. Specifically, it may be a peak having the highest intensity in a range of 3092 to 3098 cm−1.
In an embodiment, the separator may further have a fifth peak shown in a range of 3270 to 3295 cm−1 in the FT-IR spectrum. In an embodiment, the fifth peak has the highest intensity in the range described above. Specifically, it may be a peak having the highest intensity in a range of 3275 to 3290 cm−1 or in a range of 3275 to 3285 cm−1.
In an embodiment, the FT-IR spectrum of the separator may be measured using a FT-IR instrument equipped with a mercury cadmium telluride (MCT) detector. Specifically, it may be measured in a transmission mode by scanning 5 to 200 times at a resolution of 4 cm−2 in a range of 4000 to 675 cm−1.
In an embodiment, the separator may have a Gurley permeability of 250 sec/100 cc or less, 230 sec/100 cc or less, 200 sec/100 cc or less, 180 sec/100 cc or less, 10 sec/100 cc or more, 50 sec/100 cc or more, 90 sec/100 cc or more, 100 sec/100 cc or more, or a value between the numerical values. Specifically, the Gurley permeability may be 10 to 250 sec/100 cc, 50 to 200 sec/100 cc, 90 to 230 sec/100 cc, or 100 to 180 sec/100 cc. Since the gas Gurley permeability range described above is satisfied, ion conductivity may be excellent, and charge and discharge properties of the electrochemical device may be improved due to low internal resistance of the electrochemical device.
In an embodiment, the separator may have a puncture strength of 0.3 N/μm or more, 0.32 N/μm or more, 0.35 N/μm or more and 1.0 N/μm or less, 0.8 N/μm or less, 0.5 N/μm or less, or a value between the numerical values. Specifically, the puncture strength may be 0.3 to 1.0 N/μm, 0.32 to 0.8 N/μm, or 0.35 N/μm to 0.5 N/μm.
In an embodiment, the separator may have a tensile strength in the machine direction (MD) of 1500 to 2500 kgf/cm2 or 1500 to 2000 kgf/cm2.
In an embodiment, the separator may have a tensile strength in the transverse direction (TD) of 1500 kgf/cm2 or more, 1600 kgf/cm2 or more, 1700 kgf/cm2 or more and 2500 kgf/cm2 or less, 2000 kgf/cm2 or less, or a value between the numerical values. Specifically, the tensile strength in the transverse direction may be 1500 to 2500 kgf/cm2, 1600 to 2000 kgf/cm2, or 1700 to 2000 kgf/cm2.
Since the puncture strength and the tensile strength in the ranges described above are satisfied, resistance to external stress occurring during manufacture of an electrochemical device and a dendrite occurring during charge and discharge of an electrochemical device is excellent, and safety of the electrochemical device may be secured.
In an embodiment, the saturated moisture content is measured after leaving the separator in a thermo-hygrostat set to 40° C. and a relative humidity of 90% for 24 hours, and may be 350 ppm or more, 450 ppm or more, 500 ppm or more, 550 ppm or more, 600 ppm or more and 1000 ppm or less, 900 ppm or less, 800 ppm or less, 750 ppm or less, 700 or less, 670 or less, or a value between the numerical values. Specifically, the saturated moisture content may be 350 to 1000 ppm, 450 to 1000 ppm, 500 to 900 ppm, 550 to 800 ppm, or 600 to 750 ppm.
In an embodiment, the average thickness (t1) of the porous substrate may be 5 to 15 μm. Further, in an embodiment a ratio (t1/t2) between the average thickness of the porous substrate and the average thickness (t2) of the separator may be 0.7 or more. The separator according to an embodiment may implement the Gurley permeability, the puncture strength, the tensile strength, and the saturated moisture content in the ranges described above even under the thickness conditions described above simultaneously. Accordingly, a separator for a secondary battery may be thinned, and is appropriate for being applied to a high capacity/high output battery.
In an embodiment, the average thickness of the porous substrate is not necessarily limited thereto, however, it is noted that it may be 5 μm or more, 8 μm or more and 15 μm or less, 12 μm or less, or a value between the numerical values. Specifically, the average thickness of the porous substrate may be 5 to 15 μm or 8 to 12 μm.
In an embodiment, a ratio between the average thickness of the porous substrate and an average thickness of the separator may be 0.7 or more, 0.75 or more, 0.77 or more and 0.99 or less, 0.9 or less, 0.85 or less, or a value between the numerical values. Specifically, a ratio between the average thickness of the porous substrate and the average thickness of the separator may be 0.7 to 0.99, 0.75 to 0.9, or 0.77 to 0.85.
In an embodiment, the average thickness of the separator is not necessarily limited thereto, however, it is noted that it may be 7 μm or more, 10 μm or more, 12 μm or more and 20 μm or less, 15 μm or less, or a value between the numerical values. Specifically, the average thickness of the separator may be 7 to 20 μm, 10 to 15 μm, or 12 to 15 μm.
In an embodiment, the inorganic particle layer may be coated on one or both surfaces of the porous substrate, and when both surfaces of the porous substrate are coated with the inorganic particle layer, the thicknesses of the inorganic particle layers coated on one surface and the other surface may be the same as or different from each other.
In an embodiment, the total thickness of the inorganic particle layer formed on the porous substrate is not necessarily limited thereto, however, it is noted that it may be 4 μm or less, 3.5 μm or less and 1 μm or more, 1.5 μm or more, or a value between the numerical values. Preferably, the total thickness of the inorganic particle layer may be 3.2 μm or less. Specifically, the total thickness of the inorganic particle layer may be 1 to 4 μm, 1.5 to 3.5 μm, 1 to 3.2 μm, or 1.5 to 3.2 μm.
In an embodiment, the binder may include a polyacrylamide-based resin.
In an embodiment, the polyacrylamide-based resin may be polyacrylamide or a copolymer including the same. In an embodiment, the copolymer may be a block copolymer or a random copolymer, however, it is noted that the copolymer described in an embodiment refers to a random copolymer which is polymerized by mixing two or more monomers together.
In an embodiment, the polyacrylamide-based resin may be a copolymer including a unit derived from a (meth)acrylamide-based monomer and a unit derived from a comonomer. Preferably, the polyacrylamide-based resin may include a structural unit derived from the (meth)acrylamide-based monomer and a structural unit derived from a (meth)acryl-based monomer containing a hydroxyl group.
Since the separator according to an embodiment includes the above copolymer rather than a homopolymer derived from an acrylamide-based monomer, mechanical strength, gas permeability, heat resistance, and adhesion may be further improved. In addition, since the electrochemical device includes the separator, it may have better resistance properties and heat stability.
The unit derived from the (meth)acrylamide-based monomer of the polyacrylamide-based resin may be represented by the following Chemical Formula 1:
wherein R1 is hydrogen or a C1 to C6 alkyl group.
The unit derived from the hydroxyl group-containing (meth)acryl-based monomer of the polyacrylamide-based resin may be represented by the following Chemical Formula 2:
wherein R2 is hydrogen or a C1 to C6 alkyl group. In addition, L1 is a linear or branched C1 to C6 alkylene group, preferably C1 to C3 alkylene group, or more preferably C2 ethylene group.
In the polyacrylamide-based resin according to an embodiment the (meth)acrylamide-based monomer may be included at 65 to 98 mol %, 70 to 97 mol %, or 75 to 95 mol %. The (meth)acryl-based monomer containing a hydroxyl group may be included at 2 to 35 mol %, 3 to 30 mol %, or 5 to 25 mol %. When the polyacrylamide-based resin is prepared within the content range, sufficient adhesive strength may be obtained, and a more significant effect may be obtained at a shrinkage rate at a high temperature.
In an embodiment, the polyacrylamide-based resin may have a weight average molecular weight in terms of polyethylene glycol of 100,000 g/mol or more, 200,000 g/mol or more and 2,000,000 g/mol or less, 1,000,000 g/mol or less, 500,000 g/mol or less, or a value between the numerical values as measured using gel permeation chromatography. Specifically, the polyacrylamide-based resin may have a weight average molecular weight of 100,000 to 2,000,000 g/mol, 200,000 to 1,000,000 g/mol, or 200,000 to 500,000 g/mol. According to an embodiment, when the weight average molecular weight of the polyacrylamide-based resin satisfies the above range, heat resistance and adhesion may be further improved.
In an embodiment, the binder may further include one or two or more additional binders selected from the group consisting of polyvinyl alcohol (PVA), polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyvinylpyrrolidone (PVP), copolymers thereof.
Since the separator according to an embodiment uses the additional binder described above with the polyacrylamide-based resin as a binder, mechanical strength, gas permeability, heat resistance, and adhesion may be further improved. In addition, since improvement of the physical properties as described above may be achieved without pretreatment such as corona discharge treatment on the porous substrate, time and material costs in terms of process may be reduced.
In an embodiment, a content of the additional binder may be 0.1 wt % or more, 1 wt % or more, 5 wt % or more and 30 wt % or less, 20 wt % or less, or 15 wt % or less of the total content of the binder. Otherwise, the content may be a value between the numerical values. Specifically, the content of the additional binder may be 0.1 to 30 wt %, 1 to 20 wt %, or 5 to 15 wt %, however, it is noted that it is not necessarily limited thereto.
In an embodiment, a degree of saponification when the additional binder is polyvinyl alcohol may be 80 to 95 mol %, specifically 85 to 90 mol %, however, it is noted that it is not particularly limited thereto.
In an embodiment, the additional binder may have a weight average molecular weight of 10,000 to 100,000 g/mol, specifically 30,000 to 70,000 g/mol, however, it is noted that it is not particularly limited thereto.
The separator according to an embodiment may have excellent heat resistance even at a small thickness. In an embodiment, heat shrinkage rates in the machine direction and in the transverse direction which are measured after leaving the separator at 130° C. for 60 minutes may be 5% or less, preferably 4% or less, more preferably 3% or less, 2% or less, or 1.5% or less, or 1.2% or less, 1.1% or less in each direction.
In an embodiment, the porous substrate may be a polyolefin-based porous substrate such as polyethylene, polypropylene, or copolymers thereof, however, it is noted that it is not thereto, and all porous substrates known as a porous substrate of a separator of an electrochemical device may be used. In an embodiment, the porous substrate may be manufactured into a film or sheet, however, it is noted that it is not particularly limited.
In an embodiment, the porous substrate may have a porosity of 20 to 60%, specifically 30 to 60%, however, it is noted that is not limited thereto. Porosity refers to the fraction of the substrate's volume that is occupied by pores, i.e., empty spaces, and it is expressed as a volume percent.
In an embodiment, the inorganic particle layer may include a binder and inorganic particles, and may be a porous inorganic particle layer in which the inorganic particles are connected and fixed by the binder to form pores. In an embodiment, the inorganic particle layer is provided on at least one surface of the porous substrate, may occupy an area fraction of 60% or more, 70% or more, 80% or more, or 90% or more, based on an overall surface of the porous substrate, and preferably, may be formed on the area of the porous substrate of 100%.
In an embodiment, the inorganic particles are not limited as long as they are inorganic particles used in the art. As a non-limiting example, the inorganic particle particles may include one or two or more selected from the group consisting of metal hydroxides, metal oxides, metal nitrides, and metal carbides. For example, the inorganic particles may include one or two or more selected from the group consisting of magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), alumina (Al2O3), boehmite (γ-AlO(OH)), aluminum hydroxide (Al(OH)3), silica (SiO2), silicon carbide (SiC), calcium oxide (CaO), titanium dioxide (TiO2), strontium titanate (SrTiO3), zinc oxide (ZnO), yttrium oxide (Y2O3), zirconium oxide (ZrO2), tin oxide (SnO2), and cerium oxide (CeO2). In terms of stability of a battery, the inorganic particles may be preferably one or two or more metal hydroxide particles selected from the group consisting of boehmite, aluminum hydroxide (Al(OH)3), and magnesium hydroxide (Mg(OH)2).
In an embodiment, the shape of the inorganic particles is not limited, and may be spherical, oval, needle-shaped, and the like.
In an embodiment, the inorganic particles may have a BET specific surface area of 3 m2/g or more, 4 m2/g or more and 7 m2/g or less, 6 m2/g or less, or a value between the numerical values. Specifically, the inorganic particles may have the BET specific surface area of 3 to 7 m2/g or 4 to 6 m2/g. Embodiments of the present disclosure may provide a separator satisfying the physical properties to be implemented disclosed in the present disclosure simultaneously, when the specific surface area in the above described range is satisfied. Herein, the BET specific surface area of the inorganic particles may be measured by the method of ASTM C1069.
In an embodiment, the inorganic particles may have an average particle diameter (D50) of 0.5 μm or more, 0.6 μm or more and 1.5 μm or less, 1.0 μm or less, or a value between the numerical values. Specifically, the inorganic particles may have the D50 of 0.5 to 1.5 μm or 0.6 to 1.0 μm, however, it is noted that it may be changed as long as it is not out of the range of the present disclosure.
In an embodiment, the inorganic particle layer may have a weight ratio between the inorganic particles and the binder of 50:50 to 99.9:0.1, 60:40 to 98:2, or 80:20 to 98:2, however, it is noted that it is not particularly limited thereto.
In an embodiment, the inorganic particle layer may be formed at 0.5 to 10 g/m2, specifically 1 to 5 g/m2, and more specifically 2.5 to 4 g/m2, however, it is noted that it is not particularly limited thereto.
Hereinafter, a method for manufacturing a separator of the present disclosure will be described.
The method for manufacturing the separator satisfying the physical properties described above simultaneously may include a first process of preparing a coating slurry including a binder and inorganic particles; and a second process of applying the coating slurry on at least one surface of a porous substrate to form an inorganic particle layer.
Since the description of each of the porous substrate, the inorganic particle layer, the inorganic particles, and the binder is as described above, a detailed description thereof may be omitted.
Any common method known in the art may be applied without limitation to the method for preparing a coating slurry in the first process, and though it is not particularly limited, according to a non-limiting example, the inorganic particles may be dispersed by stirring to prepare a slurry, and the agglomerated inorganic particles may be dispersed using a ball mill.
The coating slurry includes inorganic particles, a binder, and a solvent, and the solvent may be water, lower alcohols such as ethanol, methanol, and propanol, solvents such as dimethylformamide, acetone, tetrahydrofuran, diethyl ether, methylene chloride, DMF, N-ethyl-2-pyrrolidone, hexane, and cyclohexane, or a mixture thereof, however, it is noted that it is not necessarily limited thereto.
In an embodiment, a solid content of the coating slurry is not particularly limited, however, it may be, for example, 1 to 50 wt %, 5 to 30 wt %, or 10 to 30 wt %.
In an embodiment, the coating slurry may include 50 to 99.9 wt % of the inorganic particles and 0.1 to 50 wt % of the binder, and more specifically, 60 to 98 wt % of the inorganic particles and 2 to 40 wt % of the binder, and more specifically, 80 to 98 wt % of the inorganic particles and 2 to 20 wt % of the binder, based on the total weight of the solid content. However, it is noted that the coating slurry may not be limited in this way.
Any common method known in the art may be applied to the method for applying the coating slurry in the second process without limitation, and according to a non-limiting example, roll coating, spin coating, dip coating, bar coating, die coating, slit coating, inkjet printing, and a combination of these methods may be applied. The applied slurry may be dried and formed into an inorganic particle layer. Drying for forming the inorganic particle layer is not particularly limited, however, it is noted that it may be performed at 100° C. or lower or 30 to 60° C.
In a specific embodiment, after performing drying for forming the inorganic particle layer, a process of aging the porous substrate having the inorganic particle layer formed thereon may not be further included. The aging may be performed at 50 to 150° C. or 60 to 120° C., and an aging time may be 2 hours to 24 hours or 10 to 20 hours. More specifically, the aging may be performed in a temperature range of 70 to 120° C. for 10 to 15 hours. According to an embodiment, since a separator satisfying the physical properties as described above simultaneously may be manufactured without performing the aging process, time and material costs in terms of process may be reduced.
The embodiments of the present disclosure may provide a separator comprise a porous substrate comprising a polyolefin polymer material with a porosity of 20 to 60%; and an inorganic particle layer formed on both surfaces of the porous substrate, the inorganic particle layer comprising a binder and inorganic particles, wherein the binder includes a polyacrylamide-based resin, wherein the inorganic particles have a BET specific surface area of 3 to 7 m2/g, an average particle diameter (D50) of 0.5 to 1.5 μm, and include one or two or more selected from the group consisting of metal hydroxides, metal oxides, metal nitrides, and metal carbides, wherein the separator has a peak shown in a range of 1082.5 to 1086.5 cm−1 in a spectrum by Fourier-transform infrared spectroscopy (FT-IR), and has a saturated moisture content measured by a Karl Fischer method of 350 to 1000 ppm.
An embodiment of the present disclosure may provide an electrochemical device such as, for example, a secondary battery, including the inventive separator according to an embodiment described above. Since the electrochemical device includes the separator as described above, electrical resistance is reduced, and thus, the electrochemical device may have significantly improved life characteristics and excellent thermal stability at a high temperature.
The electrochemical device may be any known energy storage device, and though it is not particularly limited, as a non-limiting example, it may be a secondary battery such as lithium secondary battery. Since the lithium secondary battery is well known and its configuration is also known, it will not be described in detail in the present disclosure.
The lithium secondary battery according to an embodiment may include the separator described above between a positive electrode and a negative electrode. Any suitable positive electrode and negative electrode may be used without limitation, including those commonly used in the lithium secondary battery.
When the separator according to an embodiment is used in a secondary battery, the manufacturing method follows a common manufacturing method in which a negative electrode, a separator, and a positive electrode are arranged and assembled, and an electrolyte solution is injected thereto to complete the manufacture, and thus, the manufacturing method will not be described any more in detail.
Hereinafter, the embodiments of the present disclosure will be further described with reference to specific experimental examples. It is apparent to those skilled in the art that the examples and the comparative examples included in the experimental examples only illustrate embodiments of the present invention and do not limit the appended claims. Various modifications and alterations of the embodiments may be made within the range of the scope of the present disclosure as defined in the appended claims.
First, the methods used for measuring physical properties of the separator and a method for evaluating characteristics of the secondary battery will be described.
A separator was cut into a size of 1 cmxl cm to prepare a measurement sample, and measurement was performed using an FT-IR instrument (available from Thermo Scientific, Nicolet iN10 Infrared Microscope) equipped with a mercury cadmium telluride (MCT) detector under the following conditions:
The separators were overlapped in 10 layers, each thickness was measured at 5 random points in the transverse direction with a thickness meter available from Mitutoyo and combined, the thicknesses were divided by 5 to derive an average thickness of the 10 layer separator, and the value was divided by 10 again to derive an overall average thickness of a single separator.
The average thickness of the porous substrate was determined by overlapping only the porous substrates in 10 layers, measuring each thickness at 5 random points in the transverse direction with a thickness meter available from Mitutoyo and combining them, dividing the thicknesses by 5 to derive an average thickness of the 10 layer separator, and dividing the value by 10 again to derive an average thickness of the porous substrate. After the inorganic particle layer was formed, the inorganic particle layer was detached, dried sufficiently, and the average thickness of the porous substrate from which the inorganic particle layer was detached was derived as described above.
The Gurley permeability was measured according to the standard of ASTM D726, using Densometer available from Toyoseiki. A time in seconds it took for 100 cc of air to pass a separator having an area of 1 in2 was recorded and compared.
Puncture strength (N/μm)
The puncture strength was measured by attaching a pin tip having a diameter of 1.0 mm and a radius of curvature of 0.5 mm to the Universal Test Machine (UTM) 3345 available from INSTRON and pressing the separator at a speed of 120 mm/min. At this time, the load (N) when the separator was broken was divided by the thickness (μm) of the separator to calculate the puncture strength.
Tensile Strength (kgf/cm2)
The tensile strength was measured at room temperature (25° C.) as a strength when a separator was broken by pulling the separator in the transverse direction and in the machine direction, respectively at a speed of 100 mm/min using a Universal Test Machine (UTM) 3345 available from INSTRON in accordance with ASTM D882.
A separator was cut into a square shape with a side of 10 cm and a transverse direction (TD) and a machine direction (MD) were indicated. A sample was placed in the center, 5 sheets of paper were placed on and under the sample, respectively, and the four sides of the paper were wrapped with tape. The sample wrapped in paper was allowed to stand in a hot air drying oven at 130° C. for 60 minutes. Thereafter, the sample was taken out, the separator was measured with a camera, and shrinkage rates in the machine direction (MD) and in the transverse direction (TD) were calculated using the following equations:
MD Heat shrinkage rate (%)=[(length in MD before heating−length in MD after heating)/length in MD before heating]×100
TD Heat shrinkage rate (%)=[(length in TD before heating−length in TD after heating)/length in TD before heating]×100
Saturated Moisture Content (ppm)
For measuring the saturated moisture content of the separator, a Karl Fischer method was used. A Karl Fischer titrator available from Metrohm was used as measuring equipment, and measuring conditions were a separator sample weight of 0.3 g, an oven temperature of 150° C., and a measurement time of 600 seconds.
Specifically, the manufactured separator was left for 24 hours in a thermo-hygrostat set to 40° C. and a relative humidity of 90%, and then the saturated moisture content was measured under the conditions described above.
A separator was cut into a size of 50 mm wide×50 mm long and placed so that the inorganic particle layer was on top. A piece of black drawing paper (20 mm wide×150 mm long×0.25 mm thick) having a coefficient of dynamic fraction of 0.15 was placed thereon, a pressing device was used to apply a certain pressure (200 g/cm2), the black drawing paper was forcibly pulled to the side, and a degree of inorganic substance adhered on the surface was confirmed and determined as A/B/C/D/F depending on the adhesion degree, referring to the following grades:
Each battery manufactured according to the examples and the comparative examples was charged at a constant current-constant voltage (CC-CV) of 4.2 V using a charge/discharge cycle device, and then was discharged. Specifically, each battery was charged at constant current with a 0.5 C rate at 25° C. until the voltage reached 4.2 V, and charged at constant voltage until the current was 0.01 C while maintaining 4.2 V. Subsequently, a cycle of discharging at a constant current of 0.5 C until the voltage reached 3.0 V during discharging was repeated 600 times. When a state of charge (SoC) at the 600th charge/discharge cycle was 60%, direct current internal resistance (DC-IR) was measured during discharging by a J-pulse method to derive a resistance value.
At this time, when an increase in resistance of each battery manufactured according to the examples and the comparative examples was less than 5% based on the resistance value of Example 1, it was marked as “low”, when the increase was 5% or more, it was marked as “middle”, and when the increase was 10% or more, it was marked as “high”.
96.5 wt % of boehmite (D10: 0.45 μm, D50: 0.71 μm, D90: 1.57 μm, BET specific surface area: 5 m2/g) as inorganic particles, and 3.0 wt % of a polyacrylamide-based resin (Mw=300,000 g/mol, acrylamide: 2-hydroxyethyl methacrylate=90 mol %: 10 mol %) and 0.5 wt % of polyvinyl alcohol (degree of saponification: 88 mol %, Mw: 50,000 g/mol) as a binder, based on the total weight of the solid, were added to water, and then stirring was performed to prepare a coating slurry having a solid content concentration of 28 wt %.
A polyethylene porous film (porosity: 42%, Gurley permeability: 128 sec/100 cc, tensile strength in MD: 2,317 kgf/cm2, tensile strength in TD: 2,514 kgf/cm2) having an average thickness of 10 μm was used as a porous substrate. The coating slurry prepared above was applied by coating on both surfaces of the porous substrate and then dried, thereby manufacturing a separator having an inorganic particle layer having an average thickness of 1.35 μm formed on both surfaces, respectively, of the porous substrate. The physical properties of the separator are listed in the following Table 1, and the FT-IR spectrum measurement results of the separator are shown in Table 3,
94 wt % of LiCoO2 as a positive electrode active material, 2.5 wt % of polyvinylidene fluoride as a fusing agent, and 3.5 wt % of carbon black as a conductive agent were added to N-methyl-2-pyrrolidone (NMP) as a solvent, and stirring was performed to prepare a uniform positive electrode slurry. The slurry prepared above was coated on an aluminum foil having a thickness of 30 μm, dried, and pressed to manufacture a positive electrode having a total thickness of 150 μm. 95 wt % of artificial graphite as a negative electrode active material, 3 wt % of acryl-based latex having Tg of −52° C. as a fusing agent, and 2 wt % of carboxymethyl cellulose (CMC) as a thickener were added to water as a solvent, and stirring was performed to prepare a uniform negative electrode slurry. The slurry prepared above was coated on a copper foil having a thickness of 20 μm, dried, and pressed to manufacture a negative electrode having a total thickness of 150 μm. A pouch type battery was assembled by stacking the separator manufactured above between the positive electrode and the negative electrode, and in order to fuse the positive electrode, the negative electrode, and the separator together, the assembled battery was heat-fused at 80° C., 1 MPa with a heat press machine. Thereafter, an electrolyte in which 1 M lithium hexafluorophosphate (LiPF6) was dissolved in a solution including ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) at a volume ratio of 30:50:20 was injected, and the battery was sealed to manufacture a secondary battery having a capacity of 2 Ah. The resistance properties of the secondary battery are listed in the following Table 1.
The process was performed in the same manner as in Example 1, except that 3.5 wt % of a polyacrylamide resin was used instead of using polyvinyl alcohol as the binder and the porous substrate which was pretreated by the following method was used. The pretreated porous substrate was manufactured by treating both surfaces of a polyethylene porous film (porosity: 42%, Gurley permeability: 128 sec/100 cc, tensile strength in MD: 2,317 kgf/cm2, tensile strength in TD: 2,514 kgf/cm2) having an average thickness of 10 μm with corona discharge. At this time, the corona discharge treatment was performed at a power density of 2 W/mm and a rate of 3 to 20 mpm (meter per minute).
The characteristics of the manufactured separator and secondary battery are listed in the following Tables 1 and 3.
A separator and a secondary battery were manufactured in the same manner as in Example 1, except that when the coating slurry was prepared, boehmite (D10: 0.56 μm, D50: 0.85 μm, D90: 1.93 μm, BET specific surface area: 4 m2/g) was used as the inorganic particles. The characteristics of the separator and the secondary battery are listed in the following Tables 1 and 3.
A separator and a secondary battery were manufactured in the same manner as in Example 1, except that when the coating slurry was prepared, boehmite (D10: 0.38 μm, D50: 0.67 μm, D90: 1.52 μm, BET specific surface area: 6 m2/g) was used as the inorganic particles. The characteristics of the separator and the secondary battery are listed in the following Tables 1 and 3.
A separator and a secondary battery were manufactured in the same manner as in Example 1, except that polyacrylamide having a weight average molecular weight of 200,000 g/mol was used instead of the polyacrylamide-based resin of Example 1. The characteristics of the separator and the secondary battery are listed in the following Tables 1 and 3.
A separator and a secondary battery were manufactured in the same manner as in Example 2, except that when the separator was manufactured, the inorganic particle layer was formed at an average thickness of 2 μm on both surfaces of a polyethylene porous film (porosity: 40%, Gurley permeability: 152 sec/100 cc, tensile strength in MD: 2,242 kgf/cm2, tensile strength in TD: 1,864 kgf/cm2) having an average thickness of 9 μm, respectively. The characteristics of the separator and the secondary battery are listed in the following Tables 2 and 3.
A separator and a secondary battery were manufactured in the same manner as in Example 2, except that when the coating slurry was prepared, boehmite (D10: 0.16 μm, D50: 0.31 μm, D90: 0.75 μm, BET specific surface area: 20 m2/g) was used as the inorganic particles. The characteristics of the separator and the secondary battery are shown in Tables 2 and 3 and
A separator and a secondary battery were manufactured in the same manner as in Example 2, except that when the coating slurry was prepared, boehmite (D10: 0.79 μm, D50: 1.64 μm, D90: 2.85 μm, BET specific surface area: 2.5 m2/g) was used as the inorganic particles. The characteristics of the separator and the secondary battery are shown in Tables 2 and 3, and
A separator and a secondary battery were manufactured in the same manner as in Example 2, except that when the coating slurry was prepared, boehmite (D10: 0.31 μm, D50: 0.58 μm, D90: 1.28 μm, BET specific surface area: 8 m2/g) was used as the inorganic particles. The characteristics of the separator and the secondary battery are shown in Tables 2 and 3, and
Referring to Tables 1 and 2, the separators of Examples 1 to 5 had excellent heat resistance even at a small thickness with a heat shrinkage rate of 5% or less. The separators of Examples 1 to 5 also had excellent adhesive strength property with no adhesion (“A”) in the adhesive strength test. In addition, it was confirmed that the discharge resistance of the battery to which the separators were applied after 600 cycles was low.
Specifically, referring to Table 3, the separators of the examples which had the peak shown in the range of 1082.5 to 1086.5 cm−1 in the FT-IR spectrum and also satisfied the saturated moisture content of 350 to 1000 ppm were all excellent in terms of heat resistance, adhesion, and battery resistance properties, unlike the separators of Comparative Examples 2 and 4 which did not have the peak and the saturated moisture content in the range described above or the separator of Comparative Example 1 which did not have the saturated moisture content in the range described above.
In particular, since Examples 1 to 4 used the polyacrylamide-based resin prepared by further including the hydroxyl group-containing (meth)acrylate-based monomer other than the (meth)acrylamide-based monomer as the binder, they were confirmed to have better heat resistance than Example 5 using the (meth)acrylamide-based monomer alone.
In addition, since Example 1 further included polyvinyl alcohol as the binder, it was confirmed to have better heat resistance than Example 2, even without pretreatment on the porous substrate.
However, since the separator of Comparative Example 1 had a t1/t2 value of less than 0.75, it did not satisfy the saturated moisture content range to be implemented in the present disclosure, and thus, the discharge resistance of the battery to which the separator was applied after 600 cycles was confirmed to be significantly higher than the examples.
In addition, the separator of Comparative Example 2 used the inorganic particles having a BET specific surface area of 20 m2/g, and as a result, it did not satisfy the peak in the specific range shown in the FT-IR spectrum and the saturated moisture content in the specific range which are to be implemented in the present disclosure, and thus, the discharge resistance of the battery to which the separator was applied after 600 cycles was confirmed to be significantly higher than the examples.
In addition, the separator of Comparative Example 3 used the inorganic particles having a BET specific surface area of 2.5 m2/g, and as a result, it did not satisfy the peak in the specific range shown in the FT-IR spectrum and the saturated moisture content in the specific range which are to be implemented in the present disclosure, and thus, was confirmed to have significantly reduced heat resistance and adhesive strength at a small thickness. In addition, the discharge resistance of the battery to which the separator was applied after 600 cycles was confirmed to be significantly higher than the example.
In addition, the separator of Comparative Example 4 used the inorganic particles having a BET specific surface area of 8 m2/g, and as a result, it did not satisfy the peak in the specific range shown in the FT-IR spectrum and the saturated moisture content in the specific range which are to be implemented in the present disclosure, and thus, the discharge resistance of the battery to which the separator was applied after 600 cycles was confirmed to be higher than Example.
The separator according to the present disclosure may have excellent heat resistance and adhesion properties even at a small thickness.
In addition, the separator according to the present disclosure may have excellent mechanical strength and permeability properties even at a small thickness.
In addition, since the present disclosure includes the separator according to various embodiments, an electrochemical device having excellent resistance properties and thermal safety may be provided.
The above description provides various example embodiments of the technical concepts of the present disclosure. Other embodiments and constitutions may be further envisioned by those with ordinary skill in the art after having read the present disclosure without departing from the scope of the present disclosure. Furthermore, the embodiments may be combined to form additional embodiments.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2023-0157974 | Nov 2023 | KR | national |
