Battery cell

Abstract

A battery cell is provided, the battery cell including an electrode assembly received in a battery case and including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the separator includes a porous polymer substrate, a first organic / inorganic porous coating layer formed on at least one surface of the porous polymer substrate, and a second organic / inorganic porous coating layer formed on the first organic / inorganic porous coating layer, the first organic / inorganic porous coating layer including first inorganic particles and a first binder polymer, the second organic / inorganic porous coating layer including second inorganic particles and a second binder polymer, the second organic / inorganic porous coating layer facing the positive electrode, and the second binder polymer having a higher weight average molecular weight than the first binder polymer. The battery cell shows increased adhesion between the positive electrode and the separator. Accordingly, overcharge safety can be enhanced without any additional device.

Description

Technical Field

[0001] This application claims priority to Korean Patent Application No. 10-2020-0088490, filed in Korea on July 16, 2020, the disclosure of which is incorporated herein by reference.

[0002] This disclosure relates to a battery cell and a method of manufacturing the same. Background Technology

[0003] Energy storage technology has recently received increasing attention. Efforts to develop electrochemical devices are increasingly being realized, as applications of energy storage technology have expanded to power mobile phones, cameras, and laptops, and even electric vehicles. In this context, electrochemical devices have garnered the most attention. Among these electrochemical devices, the development of rechargeable secondary batteries has been a focus. Recently, active research has been conducted on designing novel electrodes and batteries to improve capacity density and specific energy in the development of these batteries.

[0004] Among commercially available rechargeable batteries, lithium-ion batteries, developed in the early 1990s, have attracted considerable attention due to their higher operating voltage and significantly higher energy density compared to conventional batteries such as Ni-MH, Ni-Cd, and lead-sulfuric acid batteries that utilize aqueous electrolytes.

[0005] Although these electrochemical devices have been manufactured by many companies, their safety characteristics have shown varying degrees of inconsistency. It is crucial to evaluate and ensure the safety of these electrochemical devices.

[0006] Meanwhile, "overcharging" refers to the act of continuing to charge a battery cell beyond its cutoff voltage (e.g., 4.2 to 4.3V), resulting in exceeding the cell's normal capacity. In this case, side reactions occur in the electrodes, electrolyte, or similar components within the cell, and the internal temperature of the cell rises, causing the separators to contract and creating an internal short circuit. Due to the momentary short circuit that occurs under these conditions, the cell temperature rises rapidly and reacts with flammable gases within the cell, potentially leading to an explosion. This rapid rise in cell temperature is further amplified by the low thermal conductivity of lithium-ion cells.

[0007] According to relevant technologies, attempts have been made to address the aforementioned problems by inserting pads or foils with excellent thermal conductivity onto the surface of the battery cell. In this way, the rapid temperature rise has been reduced by improving heat dissipation capacity (the ability to release heat). However, this method currently cannot meet the high energy density requirements of automotive battery cells. This is because the energy density per unit volume decreases when pads or foils are inserted.

[0008] In these cases, there is a need for a cell that provides enhanced heat dissipation characteristics while maintaining an energy density equal to that of conventional cells. Summary of the Invention

[0009] Technical issues

[0010] This disclosure relates to providing a separator that can enhance overcharge safety without any additional devices.

[0011] This disclosure also relates to providing a battery cell that has improved safety by improving the heat dissipation characteristics of the cell, while maintaining conventional energy density.

[0012] Technical solution

[0013] In one aspect of this disclosure, a battery cell is provided according to any of the following embodiments.

[0014] According to a first embodiment, a battery cell is provided, the battery cell including an electrode assembly housed in a battery casing and including a positive electrode, a negative electrode, and a separator inserted between the positive electrode and the negative electrode.

[0015] The separator comprises a porous polymer substrate, a first organic / inorganic porous coating formed on at least one surface of the porous polymer substrate, and a second organic / inorganic porous coating formed on the first organic / inorganic porous coating.

[0016] The first organic / inorganic porous coating comprises first inorganic particles and a first binder polymer.

[0017] The second organic / inorganic porous coating comprises second inorganic particles and a second binder polymer.

[0018] The second organic / inorganic porous coating faces the positive electrode, and

[0019] The weight-average molecular weight of the second adhesive polymer is higher than that of the first adhesive polymer.

[0020] According to the second embodiment, a battery cell as defined in the first embodiment is provided.

[0021] The second adhesive polymer has a weight-average molecular weight of 800,000 to 1,500,000.

[0022] According to the third embodiment, a battery cell as defined in the first or second embodiment is provided.

[0023] The first adhesive polymer has a weight-average molecular weight of 300,000 to 600,000.

[0024] According to the fourth embodiment, a battery cell as defined in any of the first to third embodiments is provided.

[0025] The thickness of the first organic / inorganic porous coating is greater than the thickness of the second organic / inorganic porous coating.

[0026] According to the fifth embodiment, a battery cell as defined in the fourth embodiment is provided.

[0027] The ratio of the thickness of the first organic / inorganic porous coating to the thickness of the second organic / inorganic porous coating is 6:4 to 9:1.

[0028] According to the sixth embodiment, a battery cell as defined in any of the first to fifth embodiments is provided.

[0029] The first adhesive polymer and the second adhesive polymer are each independently selected from polyvinylidene fluoride (PVDF), hexafluoropropylene (HFP), polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. The group consisting of acetatepropionate, cyanoethylpullulan, cyanoethylpolyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxyl methyl cellulose, acrylonitrile-styrene-butadiene copolymer, and polyimide, or a mixture of two or more thereof.

[0030] According to the seventh embodiment, a battery cell as defined in any of the first to sixth embodiments is provided.

[0031] The adhesion between the separator and the positive electrode is 40 gf / 25 mm or greater.

[0032] According to the eighth embodiment, a battery cell as defined in any of the first to seventh embodiments is provided.

[0033] The first adhesive polymer may be the same as or different from the second adhesive polymer.

[0034] According to the ninth embodiment, a battery cell as defined in any of the first to eighth embodiments is provided.

[0035] The first inorganic particle may be the same as or different from the second inorganic particle.

[0036] Beneficial effects

[0037] According to embodiments of this disclosure, a battery cell with increased adhesion between the positive electrode and the separator is provided.

[0038] According to embodiments of this disclosure, heat release at high temperatures that occurs when the battery cell is overcharged is reduced, thereby enhancing overcharge safety without any additional devices.

[0039] According to embodiments of this disclosure, the heat dissipation characteristics of the battery cell can be increased, thereby enhancing the overcharge safety of the battery cell without any additional devices. Simultaneously, the heat dissipation characteristics of the battery cell can be improved while maintaining conventional energy density, thus improving the safety of the battery cell. Attached Figure Description

[0040] Figure 1 This is a schematic diagram illustrating the partition based on the comparative example.

[0041] Figure 2 This is a schematic diagram illustrating a partition according to an embodiment of the present disclosure. Detailed Implementation

[0042] In the following description, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Before the description, it should be understood that the terminology used in the specification and appended claims should not be construed as limited to its common or dictionary meaning, but rather should be interpreted based on its meaning and concept in relation to the technical aspects of the present disclosure, on the principle that the inventors are allowed to appropriately define the terminology for the best interpretation. Therefore, the descriptions presented herein are merely preferred examples for illustrative purposes and are not intended to limit the scope of the present disclosure; thus, it should be understood that other equivalents and modifications may be made thereto without departing from the scope of the present disclosure.

[0043] Throughout the specification, the statement "a portion includes an element" does not exclude the presence of any other elements, but rather implies that the portion may further include other elements.

[0044] As used herein, the terms “approximately,” “substantially,” or similar, when implying an acceptable degree of preparation and material error unique to the claimed meaning, are used to mean from or to the claimed value and to prevent unintentional infringers from improperly using the claimed disclosure, including accurate or absolute values ​​provided to aid in understanding this disclosure.

[0045] As used in this article, the expression "A and / or B" means "A, B, or both of them".

[0046] The specific terms used in the following description are for illustrative purposes and are not intended to be limiting. Terms such as “right,” “left,” “top surface,” and “bottom surface” indicate directions in the accompanying drawings in which they are mentioned. Terms such as “inward” and “outward” indicate directions toward and away from the geometric center of the respective device, system, and its components, respectively. “Front,” “back,” “top,” and “bottom,” as well as related words and expressions, indicate positions and points in the accompanying drawings in which they are mentioned and should not be limiting. These terms include the words listed above, their derivatives, and words with similar meanings.

[0047] When a battery cell burns due to overcharging, its internal temperature rises through side reactions in the components that make up the cell, caused by the overcharging current. As a result, the separators contract, leading to an internal short circuit. Due to this transient short circuit, the cell temperature rises rapidly and reacts with flammable gases within the cell, potentially causing an explosion. This rapid temperature rise is further amplified by the low thermal conductivity of lithium-ion cells.

[0048] According to relevant technologies, attempts have been made to address the aforementioned problems by inserting pads or foils with excellent thermal conductivity onto the surface of the battery cell. In this way, the rapid temperature rise has been reduced by improving heat dissipation capacity (the ability to release heat). However, this method currently cannot meet the high energy density requirements of automotive battery cells. This is because the energy density per unit volume decreases when pads or foils are inserted.

[0049] The inventors of this disclosure have conducted in-depth research to achieve the aforementioned objectives and have discovered that the portion with the highest heat resistance among the heat-resistant components of a battery cell is the positive electrode / separator interface. The inventors of this disclosure have also discovered the need to enhance the adhesion between the positive electrode and the separator to reduce heat resistance at the interface.

[0050] In one aspect of this disclosure, a battery cell is provided, the battery cell including an electrode assembly housed in a battery casing and including a positive electrode, a negative electrode, and a separator inserted between the positive electrode and the negative electrode.

[0051] The separator comprises a porous polymer substrate, a first organic / inorganic porous coating formed on at least one surface of the porous polymer substrate, and a second organic / inorganic porous coating formed on the first organic / inorganic porous coating.

[0052] The first organic / inorganic porous coating comprises first inorganic particles and a first binder polymer.

[0053] The second organic / inorganic porous coating comprises second inorganic particles and a second binder polymer.

[0054] The second organic / inorganic porous coating faces the positive electrode, and

[0055] The weight-average molecular weight of the second adhesive polymer is higher than that of the first adhesive polymer.

[0056] The battery cell according to embodiments of this disclosure includes a porous coating having two layers. Specifically, the separator inserted into the battery cell includes a porous polymer substrate with multiple pores, a first organic / inorganic porous coating, and a second organic / inorganic porous coating.

[0057] According to this disclosure, the porous polymer substrate is a porous membrane that provides channels for lithium-ion transport while electrically insulating the positive and negative electrodes from each other to prevent short circuits. Any material can be used without particular limitation, as long as it is a material conventionally used as a separator in electrochemical devices.

[0058] In particular, the porous polymer substrate can be a porous polymer film substrate or a porous polymer nonwoven mesh substrate.

[0059] The porous polymer membrane substrate can be a porous polymer membrane comprising polyolefins such as polyethylene and polypropylene. This polyolefin porous polymer membrane substrate achieves a shut-off function at temperatures ranging from 80°C to 150°C.

[0060] In this document, polyolefin-based porous polymer membranes may be formed from polymers, either alone or in combination of two or more of them, including polyolefin polymers such as polyethylene, polypropylene, polybutene, or polypentene, which contain high-density polyethylene, linear low-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene.

[0061] In addition, porous polymer membrane substrates can be obtained by molding various polymers other than polyolefins, such as polyesters, into a membrane shape. Furthermore, porous polymer membrane substrates can have a stacked structure of two or more membrane layers, wherein each membrane layer can be formed by a polymer, including the polymers mentioned above such as polyolefins or polyesters, alone or in combination of two or more of them.

[0062] In addition to the polyolefins mentioned above, porous polymer membrane substrates and porous polymer nonwoven substrates can also be formed from polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, or polyethylene naphthalene, either alone or in combination.

[0063] There are no particular limitations on the thickness of the porous polymer substrate, and the porous polymer film substrate has a thickness of 1 μm to 100 μm, particularly 5 μm to 50 μm. Since batteries have recently offered high output / high capacity, it is advantageous to use thin films as porous polymer substrates. The pores present in the porous polymer substrate can have diameters of 10 nm to 100 nm, 10 nm to 70 nm, 10 nm to 50 nm, or 10 nm to 35 nm, and porosity of 5% to 90%, preferably 20% to 80%. However, according to this disclosure, these numerical ranges can be easily changed depending on the specific embodiment or as necessary.

[0064] The pores in a porous polymer substrate can include various types of pore structures. A substrate falls within the scope of this disclosure when either the average pore size measured using a porosimeter or the average pore size observed using a field emission scanning electron microscope (FE-SEM) meets the ranges defined above.

[0065] In this paper, in the case of dry separators with uniaxial tension as commonly known, the median pore size, measured by FE-SEM in the transverse (TD) direction rather than the longitudinal (MD) direction, is taken as the standard pore size. In the case of other porous polymer substrates with network structures (e.g., wet polyethylene (PE) separators), the pore size measured by a porosimeter is taken as the standard pore size.

[0066] A first organic / inorganic porous coating is applied to at least one region selected from at least one surface and pore of a porous polymer substrate, and includes first inorganic particles and a first adhesive polymer. The first adhesive polymer is partially or wholly disposed on the first inorganic particles, such that the first inorganic particles are interconnected and fixed.

[0067] A second organic / inorganic porous coating is applied over the first organic / inorganic porous coating and comprises second inorganic particles and a second adhesive polymer. The second adhesive polymer is partially or wholly disposed on the second inorganic particles, such that the second inorganic particles are interconnected and fixed.

[0068] Here, the second organic / inorganic porous coating faces the positive electrode, and the second binder polymer has a higher weight-average molecular weight than the first binder polymer.

[0069] According to embodiments of this disclosure, a second organic / inorganic porous coating comprising a second binder polymer having a high weight-average molecular weight is oriented towards the positive electrode, and thus adhesion to the positive electrode can be increased. On the other hand, a first organic / inorganic porous coating comprising a first binder polymer having a low weight-average molecular weight is oriented towards a porous polymer substrate, and thus the separator can exhibit reduced resistance.

[0070] According to embodiments of this disclosure, the first adhesive polymer may have a weight-average molecular weight of 300,000 or greater, 330,000 or greater, 350,000 or greater, 400,000 or greater, or 540,000 or greater, and 600,000 or less, 580,000 or less, or 560,000 or less. For example, from the perspective of ensuring processability, heat resistance, and adhesion, the first adhesive polymer may have a weight-average molecular weight of 333,000 to 540,000.

[0071] According to embodiments of this disclosure, the second adhesive polymer may have a weight-average molecular weight of 800,000 or greater, 850,000 or greater, 910,000 or greater, 950,000 or greater, or 1,000,000 or greater, and 1,500,000 or less, 1,300,000 or less, or 1,200,000 or less. For example, from the perspective of ensuring processability combined with heat resistance and adhesion, the second adhesive polymer may have a weight-average molecular weight of 910,000 to 1,300,000.

[0072] Here, the weight-average molecular weight can be determined using gel permeation chromatography (GPC: gel permeation chromatography, PL GPC220, Agilent Technologies).

[0073] Specifically, the weight-average molecular weight can be determined under the following analytical conditions:

[0074] - Column: PL MiniMixed B x 2

[0075] Solvent: THF

[0076] - Flow rate: 0.3 mL / min

[0077] - Sample concentration: 2.0 mg / mL

[0078] Injection volume: 10μL

[0079] - Column temperature: 40℃

[0080] - Detector: Agilent RI detector

[0081] - Standard: Polystyrene (corrected using a third-order function)

[0082] -Data Processing: ChemStation

[0083] The first adhesive polymer and the second adhesive polymer can each be independently selected from polyvinylidene fluoride (PVDF), hexafluoropropylene (HFP), polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. The group consisting of acetatepropionate, cyanoethylpullulan, cyanoethylpolyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxyl methyl cellulose, acrylonitrile-styrene-butadiene copolymer, and polyimide, or a mixture of two or more thereof.

[0084] Here, the type of the first adhesive polymer can be the same as that of the second adhesive polymer.

[0085] The first inorganic particle may be the same as or different from the second inorganic particle.

[0086] According to this disclosure, there are no particular limitations on the inorganic particles, as long as they are electrochemically stable. That is, there are no particular limitations on the inorganic particles, as long as they are within the operating voltage range of the applicable electrochemical device (e.g., based on Li / Li). + It should not cause oxidation and / or reduction in the 0-5V range. In particular, when using inorganic particles with high dielectric constants, they help increase the degree of dissociation of electrolyte salts, especially lithium salts, in liquid electrolytes, and thus they can improve the ionic conductivity of the electrolyte.

[0087] For these reasons, inorganic particles may include inorganic particles with a dielectric constant of 5 or greater, inorganic particles capable of transporting lithium ions, and mixtures thereof.

[0088] Inorganic particles with a dielectric constant of 5 or greater can be selected from Al2O3, SiO2, ZrO2, AlO(OH), Al(OH)3, TiO2, BaTiO3, Pb(Zr) x Ti 1-x O3(PZT, where 0 < x < 1), Pb 1-x La x Zr 1-y Ti y O3(PLZT, where 0 < x < 1, 0 < y < 1), (1-x)Pb(Mg) 1 / 3 Nb 2 / 3 It is at least one of the group consisting of O3-xPbTiO3 (PMN-PT, where 0 < x < 1), hafnium oxide (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, and SiC.

[0089] Inorganic particles capable of transporting lithium ions can be selected from lithium phosphate (Li3PO4), lithium titanium phosphate (Li... x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0<x<2, 0<y<1, 0<z<3), (LiAlTiP) x O y Base glass (1 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), lithium germanium thiophosphate (Li x Ge y P z S w 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride (Lix N y , 0 < x < 4, 0 < y < 2), SiS2-based glass (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4), and P2S5-based glass (Li x P y S z At least one of the groups consisting of (0 < x < 3, 0 < y < 3, 0 < z < 7).

[0090] Although there is no particular limitation on the average particle diameter of inorganic particles, the inorganic particles are preferably 0.001 μm to 10 μm, more preferably 10 nm to 2 μm, and most preferably 50 nm to 150 nm in order to form a porous coating with uniform thickness and provide suitable porosity.

[0091] Here, the first organic / inorganic porous coating and the second organic / inorganic porous coating may further include other additives in addition to inorganic particles and binder polymers.

[0092] Simultaneously, the first organic / inorganic porous coating can have a greater thickness than the second organic / inorganic porous coating. For example, the ratio of the thickness of the first organic / inorganic porous coating to the thickness of the second organic / inorganic porous coating can be 6:4 to 9:1, 6:4 to 8:2, or 6:4 to 7:3. When the thickness of the second organic / inorganic porous coating is less than the thickness of the first organic / inorganic porous coating as described above, it is easier to advantageously reduce the resistance of the cell.

[0093] For example, the first organic / inorganic porous coating may have a thickness of 1 μm to 10 μm, while the second organic / inorganic porous coating may have a thickness of 0.5 μm to 10 μm. Here, although there is no particular limitation on the porosity of each porous coating, it is preferably 35% to 65%.

[0094] Figure 1 This is a schematic diagram illustrating the partition based on the comparative example. Figure 2 This is a schematic diagram illustrating a partition according to an embodiment of the present disclosure. For example... Figure 1 As shown, when the separator comprises a porous polymer substrate 10 and a single porous coating 20, a large amount of binder polymer with higher molecular weight cannot be used in the porous coating because the cell resistance increases. As a result, there is a problem that the adhesion between the positive electrode and the separator may not be improved. In contrast, as... Figure 2As shown, when the separator comprises a porous polymer substrate 30, a first organic / inorganic porous coating 40, and a second organic / inorganic porous coating 50, the first organic / inorganic porous coating facing the porous polymer substrate uses a binder polymer with a low weight-average molecular weight and exhibiting low resistance to reduce cell resistance. Furthermore, the second organic / inorganic porous coating facing the positive electrode uses a binder polymer with a high weight-average molecular weight to enhance adhesion between the separator and the positive electrode. As a result, the heat dissipation characteristics of the cell can be advantageously enhanced.

[0095] In another aspect of this disclosure, a method for manufacturing a separator for a lithium secondary battery is provided.

[0096] Specifically, a method for manufacturing a battery cell is provided, the battery cell comprising an electrode assembly housed in a battery casing and including a positive electrode, a negative electrode, and a separator inserted between the positive electrode and the negative electrode, comprising the following steps:

[0097] The first inorganic particles are added to a first adhesive solution containing a first adhesive polymer dissolved in a first solvent and stirred to form a slurry for a first organic / inorganic porous coating comprising the first inorganic particles dispersed therein.

[0098] The second inorganic particles are added to a second adhesive solution containing a second adhesive polymer dissolved in a second solvent and stirred to form a slurry for a second organic / inorganic porous coating comprising the second inorganic particles dispersed therein.

[0099] A slurry for a first organic / inorganic porous coating is applied to at least one surface of a porous polymer substrate and then dried to form a first organic / inorganic porous coating in at least one region selected from at least one surface and pore of the porous polymer substrate; and

[0100] A slurry for the second organic / inorganic porous coating is applied onto the first organic / inorganic porous coating and then dried to form the second organic / inorganic porous coating.

[0101] The second organic / inorganic porous coating faces the positive electrode, and

[0102] The weight-average molecular weight of the second adhesive polymer is higher than that of the first adhesive polymer.

[0103] First, the first inorganic particles are added to a first adhesive solution containing a first adhesive polymer dissolved in a first solvent and stirred to form a slurry for a first organic / inorganic porous coating comprising the first inorganic particles dispersed therein.

[0104] The first adhesive polymer may be the same as that described above with reference to the separator for secondary batteries.

[0105] The first solvent preferably has a solubility parameter similar to that of the first adhesive polymer to be used and a low boiling point. This is because such a solvent allows for homogeneous mixing and can subsequently be easily removed. Non-limiting examples of the first solvent may include any one of the group consisting of acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), and cyclohexane, or mixtures of two or more of these.

[0106] First inorganic particles are added to a first adhesive polymer solution to form a slurry for a first organic / inorganic porous coating containing the first inorganic particles dispersed therein.

[0107] The first inorganic particle may be the same as that described above with reference to the separator used in secondary batteries.

[0108] The content of the first solvent can be approximately 40% to 95% by weight, or approximately 60% to 90% by weight, of the total weight of the slurry used for the first organic / inorganic porous coating. When the content of the first solvent meets the above-defined range, it is easier to ensure the wettability of the slurry used for the first organic / inorganic porous coating on the porous polymer substrate during subsequent coating processes, while also helping to maintain the pore structure of the porous polymer substrate.

[0109] The first inorganic particles may be added after they have been pre-crushed to a predetermined average particle diameter. Alternatively, the first inorganic particles may be added to a first binder polymer solution, then crushed and dispersed, while controlling them to have a predetermined average particle diameter using a ball milling process or the like.

[0110] The weight ratio of the first inorganic particles to the first binder polymer can be from 90:10 to 50:50. When the weight ratio of the first inorganic particles to the total content of the first binder polymer meets the above-defined range, it is easier to prevent the problem of reduced pore size and porosity of the resulting first porous coating caused by an increase in the content of the first binder polymer. It is also easier to solve the problem of reduced peel resistance of the resulting first porous coating caused by a decrease in the content of the first binder polymer.

[0111] The first inorganic particles can be dispersed using methods commonly known to those skilled in the art. For example, a ball mill, bead mill, disperser, mixer, or similar method can be used. In particular, a ball mill or bead mill process is preferred. Here, the dispersion time can vary with the particle volume, but can suitably be from 1 hour to 20 hours. Furthermore, the particle size of the pulverized first inorganic particles can be controlled by the size of the beads used in the ball mill or bead mill, or by the ball milling (bead milling) time.

[0112] The second binder polymer may be the same as or different from the first binder polymer, and independently, the second solvent may be the same as or different from the first solvent. Second inorganic particles are added to the second binder polymer solution to form a slurry for a second organic / inorganic porous coating containing the second inorganic particles dispersed therein. The second inorganic particles may be the same as those described above with reference to separators for secondary batteries.

[0113] The second solvent preferably has a solubility parameter similar to that of the second adhesive polymer to be used and a low boiling point. This is because such a solvent allows for homogeneous mixing and can subsequently be easily removed. Non-limiting examples of the second solvent may include any one of the group consisting of acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), and cyclohexane, or mixtures of two or more of these.

[0114] The second inorganic particles are added to the second binder polymer solution to form a slurry for a second organic / inorganic porous coating containing the second inorganic particles dispersed therein.

[0115] The second adhesive polymer may be the same as that described above with reference to the separator for secondary batteries.

[0116] The content of the second solvent can be about 40% to 95% by weight, or about 60% to 90% by weight, of the slurry used for the second organic / inorganic porous coating. When the content of the second solvent meets the above-defined range, it is easier to prevent mixing of the first organic / inorganic porous coating with the second organic / inorganic porous coating before subsequent drying. Therefore, it can promote the formation of stable interface states.

[0117] The second inorganic particles can be added after they have been pre-crushed to a predetermined average particle diameter. Alternatively, the second inorganic particles can be added to the second binder polymer solution, then crushed and dispersed, while controlling them to have a predetermined average particle diameter using a ball milling process or the like.

[0118] The weight ratio of the second inorganic particles to the second binder polymer can be from 90:10 to 50:50. When the weight ratio of the second inorganic particles to the total content of the second binder polymer meets the above-defined range, the problem of reduced pore size and porosity of the resulting second porous coating due to increased content of the second binder polymer can be prevented. It also more easily solves the problem of reduced peel resistance of the resulting second porous coating due to decreased content of the second binder polymer.

[0119] The second inorganic particles can be dispersed using methods commonly known to those skilled in the art. For example, a ball mill, bead mill, disperser, mixer, or similar method can be used. In particular, a ball mill or bead mill process is preferred. Here, the dispersion time can vary with the particle volume, but can suitably be from 1 hour to 20 hours. Furthermore, the particle size of the pulverized second inorganic particles can be controlled by the size of the beads used in the ball mill or bead mill, or by the ball milling (bead milling) time.

[0120] Next, the slurry for the first organic / inorganic porous coating formed above is applied to at least one surface of a porous polymer substrate. Then, the porous polymer substrate coated with the slurry for the first organic / inorganic porous coating is dried to remove the first solvent from the slurry for the first organic / inorganic porous coating. Once the first solvent is removed, the first organic / inorganic porous coating is formed on at least one region selected from at least one surface and pore of the porous polymer substrate.

[0121] The porous polymer substrate can be the same as that described above with reference to the separator. The porous polymer substrate can be obtained by forming pores from the substrate material mentioned above by conventional methods known to those skilled in the art, such as wet processes using solvents, diluents, or pore-forming agents, or dry processes based on stretching processes, as methods to ensure excellent air permeability and porosity.

[0122] A slurry for a first organic / inorganic porous coating, comprising first inorganic particles dispersed therein, can be applied to a porous polymer substrate using conventional coating processes known to those skilled in the art. Specific examples of coating processes may include dip coating, slot die coating, roll coating, comma coating, or combinations thereof. Furthermore, the first organic / inorganic porous coating may be formed on both surfaces of the porous polymer substrate or selectively formed only on one surface. Due to the characteristics of the porous polymer substrate, the first organic / inorganic porous coating formed as described above by the coating method exists not only on the surface of the porous polymer substrate but also within it.

[0123] Next, the slurry for the second organic / inorganic porous coating formed above is applied to the first organic / inorganic porous coating formed above. Then, the first organic / inorganic porous coating coated with the slurry for the second organic / inorganic porous coating is dried to remove the second solvent from the slurry for the second organic / inorganic porous coating, thereby forming the second organic / inorganic porous coating on the first organic / inorganic porous coating.

[0124] The slurry for the second organic / inorganic porous coating, including the second inorganic particles dispersed therein, can be applied onto the first organic / inorganic porous coating by conventional coating processes known to those skilled in the art, as previously mentioned with reference to the first organic / inorganic porous coating.

[0125] Apart from the separator, the positive electrode, negative electrode, and electrolyte are known to those skilled in the art and are commercially available or can be easily prepared by processes and / or methods known to those skilled in the art.

[0126] In organic / inorganic porous coatings, inorganic particles can be bonded together by a binder polymer, while they stack up and come into contact with each other, thereby forming an interstitial volume between the inorganic particles, and the interstitial volume between the inorganic particles becomes an empty space to form pores.

[0127] In other words, the adhesive polymer can attach inorganic particles to each other, allowing them to maintain their bonded state, thus connecting and fixing the inorganic particles together. Furthermore, the pores in the organic / inorganic porous coating can be those formed by interstitial volumes between the inorganic particles, which become vacant spaces. These spaces can be defined by inorganic particles that are substantially facing each other in a closely packed or densely packed structure.

[0128] Drying can be carried out in a drying chamber, where the conditions are not particularly limited due to the use of non-solvents.

[0129] However, since the partition is dried under humidified conditions according to embodiments of this disclosure, the adhesive polymer can be primarily distributed on the surface of the organic / inorganic porous coating. The drying step can be performed at a relative humidity of 30% or greater, 35% or greater, or 40% or greater, and 80% or less, 75% or less, or 70% or less. For example, the drying step can be performed at a relative humidity of 40% to 80%. Alternatively, the drying step can be performed at temperatures of 20°C to 120°C, 20°C to 100°C, or 20°C to 70°C for 0.1 minutes to 2 minutes.

[0130] In another aspect of this disclosure, an electrochemical device is provided, including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the separator is the separator described above according to the embodiments of this disclosure.

[0131] According to embodiments of this disclosure, the adhesion between the separator and the positive electrode in the electrochemical device can be 40 gf / 25 mm or greater.

[0132] Electrochemical devices include any device that performs an electrochemical reaction, and specific examples include all types of primary cells, secondary cells, fuel cells, solar cells, or capacitors such as supercapacitors. In particular, lithium secondary cells, including lithium metal secondary cells, lithium-ion secondary cells, lithium polymer secondary cells, or lithium-ion polymer batteries, are preferred among secondary cells.

[0133] There are no particular limitations on the positive and negative electrodes used in conjunction with the separator according to this disclosure, and they can be obtained by incorporating electrode active materials into the electrode current collector using methods generally known in the art. Non-limiting examples of positive electrode active materials include conventional positive electrode active materials that can be used as positive electrodes in conventional electrochemical devices. In particular, NCM-based materials, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or lithium composite oxides containing combinations thereof are preferred. Non-limiting examples of negative electrode active materials include conventional negative electrode active materials that can be used as negative electrodes in conventional electrochemical devices. In particular, materials such as lithium metal or lithium alloys (which are lithium-intercalated), carbonaceous materials, petroleum coke, activated carbon, graphite, or other carbonaceous materials are preferred. Non-limiting examples of positive electrode current collectors may include foils made of aluminum, nickel, or combinations thereof. Non-limiting examples of negative electrode current collectors may include foils made of copper, gold, nickel, copper alloys, or combinations thereof.

[0134] The electrolyte that can be used in the electrochemical device according to this disclosure is having A + B - Salts of structure, in which A + Including, for example, Li + Na + K + alkali metal cations such as B, or combinations thereof, - Including PF6 - BF4 - Cl - ,Br - I - ClO4 - AsF6 - CH3CO2 - CF3SO3 - N(CF3SO2)2 - C(CF2SO2)3 - Anions such as 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 mixtures thereof, are present. However, this disclosure is not limited thereto.

[0135] Depending on the manufacturing process of the final product and the desired properties of the final product, electrolyte injection can be performed at an appropriate step during the process used to manufacture the battery. That is, electrolyte injection can be performed before battery assembly or as a final step in battery assembly.

[0136] The embodiments will then be described in more detail so that this disclosure can be readily understood. However, the following embodiments may be embodied in many different forms and should not be construed as limited to the exemplary implementations set forth herein. Rather, these exemplary implementations are provided so that this disclosure will be thorough and complete, and will fully convey the scope of this disclosure to those skilled in the art.

[0137] Example 1

[0138] Manufacturing of partitions

[0139] First, polyvinylidene fluoride (PVDF) with a weight-average molecular weight of 330,000 (Kureha Co., PVDF) was introduced as the first binder polymer into N-methyl-2-pyrrolidone as the first solvent and dissolved therein at 50°C for approximately 4 hours to prepare a first binder polymer solution. Next, aluminum hydroxide (Al(OH)3, particle size (D50): 60 nm) was introduced as the first inorganic particles into the first binder polymer solution. Here, the weight ratio of the first inorganic particles to the first binder polymer was controlled at 80:20 to prepare a slurry for forming a first organic / inorganic porous coating. Here, the solids content (solvent-free slurry) was 18 parts by weight based on 100 parts by weight of the slurry for forming the first organic / inorganic porous coating.

[0140] Then, polyvinylidene fluoride (PVDF) with a weight-average molecular weight of 910,000 was introduced as a second binder polymer into N-methyl-2-pyrrolidone as a second solvent and dissolved therein at 50°C for about 4 hours to prepare a second binder polymer solution. Next, aluminum hydroxide (Al(OH)3, particle size (D50): 60 nm) was introduced as a second inorganic particle into the second binder polymer solution. Here, the weight ratio of the second inorganic particle to the second binder polymer was controlled at 80:20 to prepare a slurry for forming a second organic / inorganic porous coating. Here, the solids content (solvent-free slurry) was 18 parts by weight based on 100 parts by weight of the slurry for forming the second organic / inorganic porous coating.

[0141] Subsequently, the slurry for forming the first organic / inorganic porous coating was applied to both surfaces of a 9 μm thick polyethylene porous membrane (porosity: 45%) at 23°C using an dip coating process, and dried at 110°C at 45% relative humidity to form a first organic / inorganic porous coating with a thickness of 2.1 μm on each surface of the porous membrane.

[0142] Finally, the slurry for forming the second organic / inorganic porous coating was applied to both surfaces of the first organic / inorganic porous coating at 23°C and a rate of 5 m / min via an dip-coating process, and dried at 110°C at 45% relative humidity to form a second organic / inorganic porous coating with a thickness of 0.9 μm on each surface of the first organic / inorganic porous coating. Here, the ratio of the thickness of the first organic / inorganic porous coating to the thickness of the second organic / inorganic porous coating is 7:3.

[0143] Battery cell manufacturing

[0144] First, LiNi, as the positive electrode active material 0.6 Co 0.2 Mn 0.2 O2, carbon black, and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 96:2:2. The resulting mixture was then introduced into N-methyl-2-pyrrolidone (NMP) and mixed with NMP to prepare a positive electrode slurry. The resulting positive electrode slurry was coated onto aluminum foil (thickness: 20 μm) to achieve a capacity of 3.28 mAh / g to obtain the positive electrode.

[0145] First, artificial graphite as the negative electrode active material, Denka black as the conductive material, and polyvinylidene fluoride (PVDF) as the binder are mixed in a weight ratio of 75:5:15. The resulting mixture is then added to N-methylpyrrolidone as a solvent to prepare the negative electrode slurry.

[0146] The negative electrode slurry was coated onto the copper current collector to a capacity of 3.8 mAh / cm³. 2 The loading is then adjusted, followed by drying to obtain the negative electrode.

[0147] The separator obtained as described above is inserted between the positive and negative electrodes in such a way that the second organic / inorganic porous coating can face the positive electrode, and a non-aqueous electrolyte (1M LiPF6, ethylene carbonate (EC) / propylene carbonate (PC) / diethyl carbonate (DEC) = 3:3:4, volume ratio) is injected therein to obtain a battery cell.

[0148] Comparative Example 1

[0149] Manufacturing of partitions

[0150] First, polyvinylidene fluoride (PVDF) with a weight-average molecular weight of 330,000 (Kureha Co., PVDF) was introduced as a binder polymer into N-methyl-2-pyrrolidone as a solvent and dissolved therein at 50°C for approximately 4 hours to prepare a binder polymer solution. Next, aluminum hydroxide (Al(OH)3, particle size (D50): 60 nm) was introduced as inorganic particles into the binder polymer solution. Here, the weight ratio of inorganic particles to binder polymer was controlled at 80:20 to prepare a slurry for forming an organic / inorganic porous coating. Here, the solids content (solvent-free slurry) was 18 parts by weight based on 100 parts by weight of the slurry.

[0151] Then, the slurry for forming the organic / inorganic porous coating is applied to both surfaces of a 9 μm thick polyethylene porous membrane (porosity: 45%) by an dip coating process and dried at 23°C at 45% relative humidity to form an organic / inorganic porous coating with a thickness of 3 μm on each surface of the porous membrane.

[0152] Battery cell manufacturing

[0153] The battery cell was obtained in the same manner as in Example 1, except that the separator obtained in this example was used.

[0154] Comparative Example 2

[0155] Manufacturing of partitions

[0156] The separator was obtained in the same manner as in Comparative Example 1, except that polyvinylidene fluoride (PVDF) with a weight average molecular weight of 910,000 was used as the adhesive polymer.

[0157] Battery cell manufacturing

[0158] The battery cell was obtained in the same manner as in Example 1, except that the separator obtained in this example was used.

[0159] Comparative Example 3

[0160] Manufacturing of partitions

[0161] First, polyvinylidene fluoride (PVDF) with a weight-average molecular weight of 910,000 (Kureha Co., PVDF) was introduced as the first binder polymer into N-methyl-2-pyrrolidone as the first solvent and dissolved therein at 50°C for approximately 4 hours to prepare a first binder polymer solution. Next, aluminum hydroxide (Al(OH)3, particle size (D50): 60 nm) was introduced as the first inorganic particles into the first binder polymer solution. Here, the weight ratio of the first inorganic particles to the first binder polymer was controlled at 80:20 to prepare a slurry for forming a first organic / inorganic porous coating. Here, the solids content (solvent-free slurry) was 18 parts by weight based on 100 parts by weight of the slurry for forming the first organic / inorganic porous coating.

[0162] Then, polyvinylidene fluoride (PVDF) with a weight-average molecular weight of 330,000 was introduced as a second binder polymer into N-methyl-2-pyrrolidone as a second solvent and dissolved therein at 50°C for about 4 hours to prepare a second binder polymer solution. Next, aluminum hydroxide (Al(OH)3, particle size (D50): 60 nm) was introduced as a second inorganic particle into the second binder polymer solution. Here, the weight ratio of the second inorganic particle to the second binder polymer was controlled at 80:20 to prepare a slurry for forming a second organic / inorganic porous coating. Here, the solids content (solvent-free slurry) was 15 parts by weight based on 100 parts by weight of the slurry for forming the second organic / inorganic porous coating.

[0163] Subsequently, the slurry for forming the first organic / inorganic porous coating was applied to both surfaces of a 9 μm thick polyethylene porous membrane (porosity: 45%) by an dip coating process and dried at 23°C at 45% relative humidity to form a first organic / inorganic porous coating with a thickness of 2.1 μm on each surface of the porous membrane.

[0164] Finally, the slurry for forming the second organic / inorganic porous coating is applied to both surfaces of the first organic / inorganic porous coating via an dip coating process and dried at 23°C with a relative humidity of 45% to form a second organic / inorganic porous coating with a thickness of 0.9 μm on each surface of the first organic / inorganic porous coating. Here, the ratio of the thickness of the first organic / inorganic porous coating to the thickness of the second organic / inorganic porous coating is 7:3.

[0165] Battery cell manufacturing

[0166] The battery cell was obtained in the same manner as in Example 1, except that the separator obtained in this example was used.

[0167] Test Example: Evaluation of the Physical Properties of Battery Cells

[0168] The thickness of the porous coating, the adhesion between the positive electrode and the separator, overcharge safety, and pulse resistance were evaluated for the respective battery cells of Example 1 and Comparative Examples 1 to 3. The results are shown in Table 1 below.

[0169] [Table 1]

[0170]

[0171] As can be seen from Table 1, in the case of Example 1, the second binder polymer used in the second organic / inorganic porous coating has a higher weight-average molecular weight than the first binder polymer, and thus can improve the adhesion between the positive electrode and the separator.

[0172] In contrast, when only a binder polymer with a low weight-average molecular weight was used in Comparative Example 1, the battery cell failed the safety test and exhibited poor adhesion between the positive electrode and the separator. In the case of Comparative Example 2, the use of only a binder polymer with a high weight-average molecular weight resulted in an excessive increase in resistance.

[0173] In Comparative Example 3, a binder polymer with a low weight-average molecular weight was used in the second organic / inorganic porous coating, while a binder polymer with a high weight-average molecular weight was used in the first organic / inorganic porous coating. In this case, unlike in Example 1, the interfacial adhesion between the positive electrode and the separator was significantly reduced. Therefore, the battery exhibited poor exothermic characteristics, leading to the cell's own explosion.

[0174] Test methods

[0175] 1) Determination of the weight-average molecular weight of the adhesive polymer

[0176] The weight-average molecular weight of the binder polymer used in the organic / inorganic porous coating of the separator in the battery cells of Examples 1 and Comparative Examples 1 to 3 was determined by gel permeation chromatography (GPC, PL GPC220, Agilent Technologies) under the following conditions:

[0177] - Column: PL MiniMixed B x 2

[0178] Solvent: THF

[0179] - Flow rate: 0.3 mL / min

[0180] - Sample concentration: 2.0 mg / mL

[0181] Injection volume: 10μL

[0182] - Column temperature: 40℃

[0183] - Detector: Agilent RI detector

[0184] - Standard: Polystyrene (corrected using a third-order function)

[0185] -Data Processing: ChemStation

[0186] 2) Thickness measurement

[0187] The thickness of each organic / inorganic porous coating was determined using a thickness gauge (VL-50S-B, available from Mitutoyo Co.).

[0188] 3) Determination of the adhesion (laminar strength) between the positive electrode and the separator.

[0189] In the battery cells according to Example 1 and Comparative Examples 1 to 3 respectively, the adhesion (laminar strength) between the positive electrode and the separator was measured as follows:

[0190] The positive electrode was cut into 25mm × 100mm dimensions. The separators were also cut into 25mm × 100mm dimensions. The prepared separators were stacked with the positive electrode, and the resulting stack was inserted between 100μm thick PET films and adhered using a flatbed press. Here, the flatbed press was heated and pressurized at 80°C for 1 second at a pressure of 1000kgf. The adhered separators and positive electrodes were attached to a glass slide using double-sided adhesive tape. The ends of the adhesive surfaces of the separators (10mm or less from the ends of the adhesive surfaces) were peeled off and attached to the 25mm × 100mm PET films using single-sided adhesive tape, allowing them to be joined longitudinally. The glass slide was then mounted to the lower fixture of a UTM instrument (LLOYD Instrument LF Plus), and the PET film adhered to the separators was mounted to the upper fixture of the UTM instrument. Force was then applied at 180° and a rate of 100mm / min. The force required to separate the positive electrode from the outermost porous coating (second organic / inorganic porous coating or organic / inorganic porous coating) facing the positive electrode is measured.

[0191] 4) Evaluation of overcharge safety

[0192] The battery cells of Examples 1 and 1 to 3 were fully charged to 0.3C / 4.2V. An overcharge test was performed to check whether an explosion occurred when the battery cell was charged to 8.4V at 1C at room temperature.

[0193] 5) Measurement of pulse resistance

[0194] The battery cells of Examples 1 and 1 to 3 were charged / discharged once at 0.33C / 25°C to 4.2–2.5V and set to SOC (State of Charge) 50, and then discharged at a rate of 2.5C for 30 seconds. Cell voltage curves were then plotted, and resistance was calculated by subtracting OCV (Open Circuit Voltage) from the voltage and dividing the result by the current.

[0195] (For example, the pulse resistance can be calculated using the formula (4.2V - 3.6V) / 1A = 0.6 ohms)

Claims

1. A battery cell, the battery cell comprising an electrode assembly housed in a battery casing and including a positive electrode, a negative electrode, and a separator inserted between the positive electrode and the negative electrode. The separator comprises a porous polymer substrate, a first organic / inorganic porous coating formed on at least one surface of the porous polymer substrate, and a second organic / inorganic porous coating formed on the first organic / inorganic porous coating. The first organic / inorganic porous coating comprises first inorganic particles and a first binder polymer. The second organic / inorganic porous coating comprises second inorganic particles and a second binder polymer. The second organic / inorganic porous coating faces the positive electrode, and The weight-average molecular weight of the second adhesive polymer is higher than that of the first adhesive polymer. The second adhesive polymer has a weight-average molecular weight of 800,000 to 1,500,000, and the first adhesive polymer has a weight-average molecular weight of 300,000 to 600,000. The first adhesive polymer is of the same type as the second adhesive polymer.

2. The battery cell according to claim 1, wherein the thickness of the first organic / inorganic porous coating is greater than the thickness of the second organic / inorganic porous coating.

3. The battery cell according to claim 1, wherein the ratio of the thickness of the first organic / inorganic porous coating to the thickness of the second organic / inorganic porous coating is 6:4 to 9:

1.

4. The battery cell according to claim 1, wherein the first adhesive polymer and the second adhesive polymer are each independently selected from the group consisting of polyvinylidene fluoride (PVDF), hexafluoropropylene (HFP), polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, acrylonitrile-styrene-butadiene copolymer, and polyimide, or a mixture of two or more thereof.

5. The battery cell according to claim 1, wherein the adhesion between the separator and the positive electrode is 40gf / 25mm or greater.

6. The battery cell according to claim 1, wherein the first inorganic particle is the same as or different from the second inorganic particle.

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