Composite separator and electrochemical element containing the same

Abstract

The present invention provides a composite separator having excellent heat resistance and adhesive strength simultaneously, a method for manufacturing the same, and an electrochemical element containing the composite separator. [Solution] A composite separator is provided comprising a porous substrate and a ceramic layer formed on one or both sides of the substrate, the ceramic layer containing inorganic particles and a binder, wherein the binder contains carboxymethylcellulose having a weight-average molecular weight of 180,000 to 280,000 g / mol and a degree of substitution of 0.6 to 1.2.

Description

Technical Field

[0001] The present disclosure relates to a separator and an electrochemical device including the same.

Background Art

[0002] Recently, as electrochemical devices are gradually increasing in capacity and output, the need to ensure heat resistance and safety has been growing, and in particular, the required performance for separators, which act as very important elements for this purpose, has been becoming more advanced.

[0003] For example, as a method for ensuring the heat resistance and safety of a separator, a composite separator in which a coating layer containing inorganic particles such as alumina (Al2O3), silica (SiO2), zirconia (ZrO2), etc. and a binder is introduced on a porous substrate has become an important technology. However, recently, due to the high capacity and high output characteristics of electrochemical devices, research has been conducted in the direction of thinning the separator, and the binder applied to the conventional composite separator cannot have sufficient adhesion to both the substrate and the inorganic particles, and there is a problem that the mechanical strength and / or heat resistance decreases as the thickness of the inorganic particle coating layer becomes thinner.

[0004] [[ID=十九]] Although research to solve this problem has continued, in the case of a binder material with improved heat resistance, the adhesion is somewhat insufficient, or when trying to improve the adhesion of the separator, there are limits in that characteristics such as air permeability and interfacial resistance deteriorate and the device performance decreases.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] One aspect of the present invention relates to a composite separator including a porous substrate and a ceramic layer formed on one or both surfaces of the porous substrate, wherein inorganic particles are connected and fixed by a binder, and pores are formed between the inorganic particles, and provides a composite separator having excellent heat resistance and adhesion at the same time.

[0007] Another aspect of the present invention provides an electrochemical device excellent in battery performance and safety by employing the composite separator.

Means for Solving the Problems

[0008] One aspect of the present invention includes a porous substrate and a ceramic layer formed on one or both surfaces of the substrate, the ceramic layer including inorganic particles and a binder, the binder including carboxymethyl cellulose having a weight average molecular weight of 180,000 to 280,000 g / mol and a degree of substitution of 0.6 to 1.2, and provides a composite separator.

[0009] The carboxymethyl cellulose may have a weight average molecular weight of 200,000 to 250,000 g / mol. [[ID=ID=18]]

[0010] The carboxymethyl cellulose may have a degree of substitution of 0.7 to 1.0.

[0011] The ceramic layer may include 0.1 to 10 parts by weight of a binder with respect to 100 parts by weight of the inorganic particles.

[0012] The binder may include 70% by weight or more of carboxymethyl cellulose with respect to the total weight of the binder, or may be composed of carboxymethyl cellulose.

[0013] The inorganic particles may be one or more selected from boehmite, BaSO4, CeO2, MgO, CaO, ZnO, Al2O3, TiO2, BaTiO3, HfO2, SrTiO3, SnO2, NiO, ZrO2, Y2O3, and SiC.

[0014] The average particle size of the inorganic particles may be 0.1 μm to 1.0 μm.

[0015] The porous substrate may be treated with a hydrophilic surface treatment.

[0016] The total thickness of the ceramic layer may be 0.5 μm to 10 μm.

[0017] The composite separator in one state may be left at 150°C for 60 minutes, and the measured thermal shrinkage rates in both the MD and TD directions may be 4% or less.

[0018] In the case of the composite separator made in one form, when the degree of foreign matter adhesion to the surface of the cardboard is evaluated after the cardboard test, the ratio of the area occupied by the attached foreign matter to the area of ​​the cardboard may be 5% or less. [Cardboard Test] A 2cm x 10cm black cardboard and a rubber pad are placed sequentially on the ceramic layer of a 5cm x 10cm composite separator test piece. A force of 10N is applied to the rubber pad using a press device, and the cardboard is horizontally removed at a speed of 0.1m / s to a depth of 60mm. The degree to which foreign matter adheres to the surface of the cardboard is then tested.

[0019] A further embodiment of the present invention provides a method for producing a composite separator, comprising the steps of applying a ceramic layer-forming composition containing a binder and inorganic particles to one or both sides of a porous substrate, drying it, wherein the binder contains carboxymethylcellulose having a weight-average molecular weight of 180,000 to 280,000 g / mol and a degree of substitution of 0.6 to 1.2.

[0020] A further embodiment of the present invention provides an electrochemical element comprising a positive electrode, a negative electrode, and a composite separator, wherein the composite separator comprises a porous substrate and a ceramic layer formed on one or both sides of the substrate, comprising inorganic particles and a binder, the binder comprising carboxymethylcellulose having a weight-average molecular weight of 180,000 to 280,000 g / mol and a degree of substitution of 0.6 to 1.2. [Effects of the Invention]

[0021] A uniform composite separator can satisfy all requirements for outstanding mechanical and thermal stability and ionic conductivity. Specifically, a uniform composite separator includes a ceramic layer in which a porous substrate and inorganic particles are bound and fixed by a binder, and pores are formed between the inorganic particles. The adhesion between the inorganic particles and between the inorganic particles and the substrate is excellent, and the desorption phenomenon of the inorganic particles and the shrinkage phenomenon at high temperatures can be effectively suppressed.

[0022] Furthermore, a composite separator made of a single material can achieve excellent adhesive strength and heat resistance even when the ceramic layer is formed to a very thin thickness, and an electrochemical element employing this can simultaneously satisfy safety, high capacity, and high output characteristics. [Brief explanation of the drawing]

[0023] [Figure 1] This is a diagram illustrating a cross-section of a composite separator according to one embodiment. [Modes for carrying out the invention]

[0024] Unless otherwise defined herein, all technical and scientific terms have the same meanings as those generally understood by those skilled in the art in which the present invention pertains. Terms used in this description are solely for the purpose of effectively describing specific examples and are not intended to limit the present invention.

[0025] As used herein, the singular form may also include the plural form unless otherwise indicated in the context.

[0026] Throughout this specification, the terms "includes," "companies," "contains," or "has" a component mean, unless otherwise specified, that it may include other components rather than excluding them, and do not exclude any other elements, materials, or processes not listed.

[0027] The numerical ranges used herein include lower and upper limits, all values ​​within those limits, increments logically derived from the form and width of the defined range, all double-limited values, and all possible combinations of upper and lower limits of numerical ranges limited to different forms. Unless otherwise specifically defined herein, values ​​outside the numerical range that may arise due to experimental error or rounding of values ​​are also included in the defined numerical range.

[0028] Unless otherwise defined herein, "about" may refer to values ​​up to 30%, 25%, 20%, 15%, 10%, or 5% of the specified value.

[0029] In this specification, "average particle size" is defined as "D 50 This means "D 50 " " refers to the particle size of inorganic particles corresponding to 50% of the cumulative fraction based on volume. The average particle size can be derived from the particle size distribution results obtained by sampling the inorganic particles to be measured in accordance with the ISO 13320-1 standard and analyzing them using the S3500 manufactured by MICROTRAC. Also, "D 90 " refers to the particle size that corresponds to 90% of the cumulative fraction by volume, and "D 10 " refers to the particle size of inorganic particles that corresponds to 10% of the cumulative fraction based on volume. 90 and D 10 D 50 It can be derived using the same method.

[0030] In this specification, carboxymethyl cellulose (CMC) means a cellulose derivative in which the hydroxyl group (-OH) of cellulose is substituted and etherified with -OCH2COOH and / or -OCH2COO - M + where M + is an alkali metal cation and may be selected from lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). In this specification, the "degree of substitution (DS)" of carboxymethyl cellulose means the number of the average substituents contained in one anhydroglucose unit of a cellulose molecule, and it can be measured by known or tolerated methods. For example, it can be measured according to ASTM D1439, or it can be calculated by 1 H-NMR or 13 13C-NMR analysis.

[0031] The degree of substitution (DS) of carboxymethyl cellulose (CMC) was measured using a titration method according to ASTM D1439. In the experiment, a magnetic stirrer, an aspirator, a dry oven, a 300 mL beaker, a pipette, a 250 mL Erlenmeyer flask, and a Petri dish were used. The reagents used were 80% ethanol, 100% ethanol, 0.1 N sodium hydroxide (NaOH) solution, phenolphthalein indicator, and 0.1 N sulfuric acid (H2SO4) solution.

[0032] Specifically, 150 mL of 80% ethanol was placed in a 300 mL beaker, followed by the addition of 10 mL of 1N nitric acid (HNO3). Approximately 1-2 g of CMC sample was added to this mixture and stirred for 1 hour to form CMC acid. After standing for approximately 10-20 minutes, the supernatant was removed (decanting).

[0033] Next, 150 mL of 80% ethanol was added again, and the mixture was stirred for 30-40 minutes, after which the supernatant was removed again. The precipitated CMC-acid was filtered using a suction filter, washed with 500 mL of 80% ethanol, and then washed once or twice more with 100% ethanol.

[0034] The central portion of the purified CMC acid was taken and transferred to a clean weighing dish, and dried in a drying oven for 20-30 minutes. After drying, approximately 0.2 ± 0.05 g of the sample was accurately weighed, and 25 mL of 0.1 N NaOH solution was added. This sample solution was transferred to a 250 mL Erlenmeyer flask, 100 mL of distilled water was added, and the mixture was stirred for 40-60 minutes until completely dissolved.

[0035] Next, 2-3 drops of phenolphthalein indicator were added, and the 0.1N H2SO4 solution was titrated while continuously stirring until the solution changed color from red to colorless.

[0036] The number of millimoles (A) of CMC-acid per gram of dried sample was calculated using the following formula.

[0037]

number

[0038] Next, the degree of substitution (DS) was calculated from A using the following formula.

[0039]

number

[0040] The following provides a detailed description of this disclosure. However, this is illustrative only, and the disclosure is not limited to the specific embodiments described herein.

[0041] This disclosure provides a composite separator that can simultaneously ensure excellent mechanical and thermal stability and ionic conductivity.

[0042] Specifically, a uniform composite separator comprises a porous substrate and a ceramic layer formed on one or both sides of the substrate, containing inorganic particles and a binder, wherein the binder may include carboxymethylcellulose having a weight-average molecular weight of 180,000 to 280,000 g / mol and a degree of substitution of 0.6 to 1.2.

[0043] A composite separator in a single state, by applying carboxymethylcellulose that satisfies the aforementioned combination of weight-average molecular weight and degree of substitution as a binder, exhibits excellent adhesion between inorganic particles and between inorganic particles and the substrate, as well as superior heat resistance. Furthermore, even when the ceramic layer of the composite separator in a single state is formed to a very thin thickness, outstanding adhesion and heat resistance can be achieved, and electrochemical elements employing this separator can simultaneously satisfy safety, high capacity, and high output characteristics.

[0044] In one embodiment, the carboxymethylcellulose may have a weight-average molecular weight of 180,000 to 280,000 g / mol, 180,000 to 260,000 g / mol, or 180,000 to 250,000 g / mol, or 190,000 to 250,000 g / mol, or 200,000 to 250,000 g / mol, and may include all possible combinations of the upper and lower limits of the numerical range. The weight-average molecular weight may refer to the weight-average molecular weight calculated using a molecular weight calibration curve utilizing polysaccharide standard samples measured by the GPC method. A sample of carboxymethylcellulose dissolved in a standard substance at approximately 0.1% w / v was injected into a GPC instrument and measured.

[0045] Furthermore, the carboxymethylcellulose may have a degree of substitution of 0.6 to 1.2, or 0.6 to 1.1, 0.6 to 1.0, or 0.7 to 1.2, or 0.7 to 1.1, or 0.7 to 1.0, or 0.8 to 1.2, or 0.8 to 1.1, or 0.8 to 1.0, or 0.9 to 1.2, or 0.9 to 1.1, or 0.9 to 1.0, and may include all possible combinations of the upper and lower limits of the numerical range. By using carboxymethylcellulose that satisfies the combination of weight-average molecular weight and degree of substitution range, when the ceramic layer is formed and applied to the surface of the porous substrate using a coating slurry, the coating properties are excellent, and even if the thickness of the ceramic layer in the composite separator containing it is thin, the heat resistance is excellent, and the adhesion between inorganic particles or between the ceramic layer and the porous substrate is improved, thus making the effect of simultaneously improving heat resistance and adhesion even more excellent.

[0046] In one embodiment, the type of inorganic particle can be any type commonly used in the art, and as a non-limiting example, it may be one or more selected from metal oxides, metal hydrates, metal carbides, metal nitrides, and metal carbonitrides such as boehmite, BaSO4, CeO2, MgO, CaO, ZnO, Al2O3, TiO2, BaTiO3, HfO2, SrTiO3, SnO2, NiO, ZrO2, Y2O3, and SiC.

[0047] In one embodiment, the average particle size (D) of the inorganic particles 50 ) may be, for example, 0.1 μm to 10.0 μm, or 0.1 μm to 5.0 μm, or 0.1 μm to 3.0 μm, or 0.1 μm to 2.0 μm, or 0.1 μm to 1.0 μm, or 0.1 μm to 0.5 μm, or include, but is not limited to, all possible combinations of the upper and lower limits of these numerical ranges.

[0048] In one embodiment, the ceramic layer may contain inorganic particles in an amount of 90-99.9% by weight, 92-99.5% by weight, or 92-99% by weight relative to the total weight of the ceramic layer. Compared to the inorganic particle content of conventional coating layers formed by linking inorganic particles containing a binder, a higher amount can be included, and despite this, it is possible to form a coating layer (ceramic layer) with excellent heat resistance and numerical stability, and with a thinner thickness.

[0049] In one embodiment, the ceramic layer may use a binder of 10 parts by weight or less, 8 parts by weight or less, 5 parts by weight or less, 3 parts by weight or less, 2 parts by weight or less, or 1 part by weight or less per 100 parts by weight of the inorganic particles, or 0.1 parts by weight or more, 0.5 parts by weight or more, 1 part by weight or more, or 2 parts by weight or more, specifically 0.1 to 5 parts by weight, or 1 to 5 parts by weight, or 1 to 3 parts by weight, or a content between these numerical ranges, and the binder may use carboxymethylcellulose at a concentration of 70% by weight or more, or 80% by weight or more, or 90% by weight or more, or 95% by weight or more, or 100% by weight relative to the total weight of the binder. Preferably, carboxymethylcellulose alone (100% by weight) may be used, and this is more preferable.

[0050] By using carboxymethylcellulose that satisfies the above-mentioned combination of weight-average molecular weight and degree of substitution range, the composite separator in one form can simultaneously satisfy excellent adhesion between inorganic particles and between inorganic particles and the substrate, as well as heat resistance, even when carboxymethylcellulose is used alone as the binder for the ceramic layer.

[0051] Furthermore, in one embodiment, when carboxymethylcellulose having a weight-average molecular weight of 180,000 to 280,000 g / mol and a degree of carboxymethyl substitution of 0.6 to 1.2 is selected as the main component of the binder, it may also further contain a conventional binder used in the present art. For example, polyvinylidene fluoride (PVdF), hexafluoropropylene (HFP), polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-cotrichloroethylene, polymethyl methacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. propionate), cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethylcellulose, pullulan, cyanoethylsucrose, carboxyl methylcellulose, styrene-butadiene rubberOne or more materials selected from rubber, acrylonitrile-styrene-butadiene copolymer, and polyimide may be used, and any other polymer used in this field as a separator or electrode active material may be used without limitation.

[0052] In one embodiment, after leaving the composite separator at 150°C for 60 minutes, the measured thermal shrinkage rates in the MD direction and TD direction may both be 5% or less, specifically 4% or less, 3% or less, or 2.5% or less.

[0053] Furthermore, in one embodiment, when the degree of foreign matter adhesion to the surface of the cardboard is evaluated after the composite separator has undergone a cardboard test, the ratio of the area occupied by the adhered foreign matter to the area of ​​the cardboard may be 5% or less, specifically less than 5%, less than 4%, less than 3%, less than 2%, or less than 1.5%.

[0054] The cardboard test method involves placing a 2cm x 10cm black cardboard and a rubber pad sequentially on the upper surface of the ceramic layer of a 5cm x 10cm composite separator test piece, applying a force of 10N to the rubber pad using a press device, horizontally removing the cardboard at a speed of 0.1m / s, and testing the extent of foreign matter adhering to the surface of the cardboard by evaluating the area. The foreign matter may be a component of the ceramic layer, such as inorganic particles, a binder, or a combination thereof.

[0055] When evaluating adhesive strength using the cardboard test method described above, it is possible to measure not only the adhesive strength between the substrate and the ceramic layer interface, but also the adhesive strength between inorganic particles within the ceramic layer. Based on the results of the adhesive strength test, the degree of thermal shrinkage can be predicted more accurately than with the conventional peel test. In other words, if the ratio of the area occupied by the attached foreign matter calculated by the cardboard test is less than 5%, less than 4%, less than 3%, less than 2%, or less than 1.5%, it may mean that the adhesive strength between inorganic particles and between inorganic particles and the substrate is excellent, and that the thermal shrinkage phenomenon can be effectively suppressed.

[0056] For example, in conventional composite separators, methods such as peeling tests used to evaluate the adhesive strength of the inorganic particle coating layer evaluate the adhesive strength between the substrate and the inorganic particle coating layer. However, the adhesive strength between inorganic particles is difficult to predict, and there is a disadvantage in that the thermal shrinkage characteristics of the separator cannot be accurately predicted from the evaluation value.

[0057] In one embodiment, the porous substrate is not limited as long as it is commonly used in the art, and may be, for example, a woven fabric, a nonwoven fabric, or a porous film. Specifically, the porous substrate may be a polyolefin such as polyethylene or polypropylene, a polyester such as polyethylene terephthalate or polybutylene terephthalate, a polyacetal, a polyamide, a polyimide, a polycarbonate, a polyetheretherketone, a polyaryletherketone, a polyetherimide, a polyamideimide, a polybenzimidazole, a polyethersulfone, a polyphenylene oxide, a cyclic olefin copolymer, a polyphenylene sulfide, a polyethylene naphthalate, a glass fiber, Teflon®, and / or polytetrafluoroethylene, and two or more of these may be used. Among the porous substrates, the porous film is manufactured by dry and wet methods and is known in the art, so it will not be described further.

[0058] In one embodiment, the porous substrate may have a porosity of 20-60%, 30-60%, 30-50%, or 35-45%, but is not limited thereto.

[0059] In one embodiment, the porous substrate may be subjected to a hydrophilic surface treatment to introduce polar functional groups, such as carboxyl groups, aldehyde groups, and hydroxyl groups. The hydrophilic surface treatment may, for example, be corona discharge treatment or plasma discharge treatment, but is not particularly limited.

[0060] In one embodiment, the thickness of the porous substrate is not particularly limited and may be, for example, 1 μm to 100 μm, 1 μm to 50 μm, 1 μm to 30 μm, 5 μm to 20 μm, or any value between the above numbers.

[0061] In one embodiment, the ceramic layer may be coated on one or both sides of the porous substrate. When the ceramic layer is coated on both sides of the porous substrate, the thicknesses of the ceramic layers coated on one side and the other side may be the same or different. Although not particularly limited, the total thickness of the ceramic layer in one embodiment may be, for example, 0.1 μm to 10.0 μm, 0.5 μm to 10.0 μm, or 1 μm to 10 μm, or 1 μm to 8 μm, or 1 μm to 5 μm, or about 1.5 μm to 5 μm, or 2 μm to 5 μm, or 2 μm to 4 μm, or a value between the above numbers. In one embodiment, the composite separator can achieve excellent adhesion and heat resistance even when the ceramic layer is formed to a very thin thickness, and the electrochemical element employing it can simultaneously satisfy safety, high capacity, and high output characteristics.

[0062] A further embodiment of the present invention provides a method for producing the composite separator, the method comprising the steps of applying a ceramic layer-forming composition containing a binder and inorganic particles to at least one surface of a porous substrate, drying it, and forming a ceramic layer, wherein the binder may contain carboxymethylcellulose having a weight-average molecular weight of 180,000 to 280,000 g / mol and a degree of substitution of 0.6 to 1.2.

[0063] The porous substrate, binder, and inorganic particles are as described above, and a detailed explanation is omitted.

[0064] The ceramic layer forming composition may be manufactured by dispersing a binder and inorganic particles, or by dispersing aggregated inorganic particles using a ball mill.

[0065] The ceramic layer forming composition further comprises a solvent, which may be, but is not limited to, water, lower alcohols such as ethanol, methanol, and propanol, solvents such as dimethylformamide, acetone, tetrahydrofuran, diethyl ether, methylene chloride, N-methyl-2-pyrrolidone, hexane, and cyclohexane, or mixtures thereof.

[0066] In one embodiment, the solid content of the ceramic layer-forming composition is not particularly limited, but may be, for example, 1 to 50% by weight, 5 to 30% by weight, or 10 to 30% by weight, but is not limited thereto. Furthermore, the ceramic layer-forming composition may have a viscosity of 800 to 5,000 mPa·s, or 800 to 4,000 mPa·s, or 800 to 3,000 mPa·s, or 1,000 to 3,000 mPa·s, based on a solid content of 25% by weight, which can facilitate the formation of the ceramic layer and improve the heat resistance and adhesive strength of the separator.

[0067] In one embodiment, the method for applying or coating the ceramic layer-forming composition onto a porous substrate is not particularly limited, but examples include roll coating, spin coating, dip coating, bar coating, die coating, slit coating, or inkjet printing.

[0068] In one embodiment, the drying can be carried out by drying with warm air, hot air, low-humidity air, vacuum drying, or irradiation by far-infrared rays or electron beams. The drying temperature is not particularly limited and may be adjusted as appropriate depending on the experimental environment and purpose, for example, it may be 30°C to 120°C, 30°C to 100°C, 50°C to 80°C, or 50°C to 70°C. The drying time is not particularly limited but may be 30 seconds to 300 seconds, 60 seconds to 300 seconds, 100 seconds to 300 seconds, 150 seconds to 250 seconds, or about 180 seconds.

[0069] A further embodiment of the present invention provides an electrochemical element comprising a composite separator according to the above embodiment, wherein the electrochemical element may, for example, be a lithium secondary battery.

[0070] Specifically, the electrochemical element in one state includes a positive electrode, a negative electrode, and a composite separator, the composite separator includes a porous substrate and a ceramic layer formed on one or both sides of the substrate, the ceramic layer containing inorganic particles and a binder, the binder may include carboxymethylcellulose having a weight-average molecular weight of 180,000 to 280,000 g / mol and a degree of substitution of 0.6 to 1.2.

[0071] The following explanation will describe electrochemical elements in a single state, using lithium secondary batteries as an example. It goes without saying that, except for composite separators in a single state, these can be manufactured using conventional manufacturing methods and materials in the art, resulting in structures well known in the art.

[0072] As an example, the lithium secondary battery can be manufactured using a common method in which the negative electrode, composite separator, and positive electrode are arranged in order and assembled, and then the electrolyte is injected to complete the battery.

[0073] [Positive electrode] The positive electrode may include a positive electrode current collector and a positive electrode mixture layer on at least one surface of the positive electrode current collector. The positive electrode may be manufactured by applying a positive electrode material slurry to one or both surfaces of the positive electrode current collector, drying and rolling it to form a positive electrode mixture layer. The positive electrode material slurry may contain a positive electrode active material and a binder, and may further contain conductive materials, thickeners, etc., as needed.

[0074] The positive electrode current collector may include stainless steel, nickel, aluminum, titanium, or alloys thereof, and may also include aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. The thickness of the positive electrode current collector may be, for example, 10 μm to 50 μm, but is not limited thereto.

[0075] The positive electrode active material can be used without limitation as long as it is a compound that is commonly used in the art as a compound capable of reversibly intercalating and deintercalating lithium ions. Non-limiting examples include composite oxides of lithium with metals selected from cobalt (Co), manganese (Mn), nickel (Ni), iron (Fe), niobium (Nb), magnesium (Mg), copper (Cu), zinc (Zn), molybdenum (Mo), tantalum (Ta), tungsten (W), aluminum (Al), and combinations thereof.

[0076] In one embodiment, the positive electrode active material may be a lithium-nickel composite oxide, and the lithium-nickel composite oxide may further contain one or more selected from cobalt, manganese, and aluminum.

[0077] In one embodiment, the positive electrode active material may include a lithium nickel-cobalt-manganese (NCM) composite oxide, and the composition of the metal is not particularly limited, but a high-Ni composition with a high nickel content may be used, and the Ni content of the NCM lithium oxide (for example, the mole fraction of nickel in the total number of moles of nickel, cobalt, and manganese) may be 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the Ni content may be 0.8~0.95, 0.82~0.95, 0.83~0.95, 0.84~0.95, 0.85~0.95, or 0.88~0.95. The NCM composite oxide is, as an example, LiNi 0.33 Co 0.33 Mn 0.33 O2, LiLiLi 0.4 Co 0.2 Mn 0.4 O2, LiLiLi 0.5 Co 0.2 Mn 0.3 O2, LiLiLi 0.6 Co 0.2 Mn 0.2 O2, LiLiLi 0.7 Co 0.15 Mn 0.15 O2, LiLiLi 0.8 Co 0.1 Mn 0.1 While O2 is one example, it is not the only option.

[0078] In one embodiment, the positive electrode active material may be, for example, a lithium cobalt oxide system, a lithium manganese oxide system, a lithium nickel oxide system, a lithium iron phosphate system (LFP, e.g., LiFePO4), a lithium manganese phosphate system (e.g., LiMnPO4), a lithium cobalt phosphate system (e.g., LiCoPO4), a lithium iron pyrophosphate system (e.g., Li2FeP2O7), or the like.

[0079] The positive electrode binder is not particularly limited as long as it is commonly used in the art, and may include a non-aqueous binder and / or an aqueous binder, or a rubber binder and / or a fluorine-based binder. For example, it may be one or more selected from acrylic polymers such as polyacrylate, polymethacrylate, polybutyl acrylate, and polyacrylonitrile; fluorine-based polymers such as polyvinylidene fluoride, polyhexafluoropropylene, polyvinylidene fluoride-hexafluoropropylene, and polyvinylidene fluoride-trichloroethylene; polyvinyl acetate, polyethylene oxide, cellulose, modified cellulose, polyamide, polyacrylamide, rubber, elastomer, etc., but is not limited thereto.

[0080] The conductive material may be added to enhance the conductivity and / or the mobility of lithium ions or electrons in the positive electrode mixture layer. For example, the conductive material may be a linear conductive material and / or a point conductive material, and may include, but is not limited to, carbon-based conductive materials such as graphite, carbon black, acetylene black, Ketjenblack, graphene, carbon nanotubes, VGCF (vapor-grown carbon fiber), carbon fiber, and / or metallic conductive materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3, which are perovskite materials. As used herein, the term "point conductive material" may mean a conductive material in a general spherical or particulate form.

[0081] [Negative electrode] The negative electrode may include a negative electrode current collector and a negative electrode mixture layer on at least one surface of the negative electrode current collector. The negative electrode may be manufactured by applying a negative electrode material slurry to one or both surfaces of the negative electrode current collector, drying and rolling it to form a negative electrode mixture layer. The negative electrode material slurry may contain a negative electrode active material and a binder, and may further contain conductive materials, thickeners, etc., as needed.

[0082] The negative electrode current collector may include a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a polymer substrate coated with a conductive metal, and the like. The thickness of the negative electrode current collector may be, for example, 10 μm to 50 μm, but is not limited thereto.

[0083] The negative electrode active material can be used without limitation as long as it is a material that can adsorb and desorb lithium ions and is commonly used in the art. As a non-limiting example, carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers; lithium metal; lithium alloys; silicon (Si)-containing substances or tin (Sn)-containing substances can be used.

[0084] Examples of the amorphous carbon include hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers (MPCF), etc. Examples of the crystalline carbon include graphite-based carbons such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF.

[0085] Examples of the elements contained in the lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium.

[0086] The silicon-containing substance can provide better capacity characteristics. The silicon-containing substance may include Si, SiO x (0 < x ≤ 2), metal-doped SiO x (0 < x ≤ 2), silicon-carbon composites, etc. The metal may include lithium and / or magnesium. Metal-doped SiO x (0 < x ≤ 2) may include metal silicates. The binder, conductive material, and thickening agent of the negative electrode may be the above-mentioned substances that can be used during the manufacture of the positive electrode.

[0087] The negative electrode binder is not particularly limited as long as it is commonly used in the art, and can be rubber binders such as styrene-butadiene rubber (SBR) binders, carboxymethylcellulose (CMC), polyacrylic acid, polyethylene dioxythiophene (poly(3,4-ethylenedioxythiophene), or PEDOT) binders.

[0088] [Electrolyte] In one embodiment, the electrolyte may be a non-aqueous electrolyte, and the non-aqueous electrolyte may contain a lithium salt, which is the electrolyte, and an organic solvent.

[0089] The lithium salt is, for example, Li + X - The anion of the lithium salt (X) is represented as - ) and F - Cl - , Br - , I - NO3 - , N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 - CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN -, and (CF3CF2SO2)2N - These are some examples.

[0090] The organic solvent may contain organic compounds that sufficiently dissolve the lithium salt and additives and are not reactive within the battery. The organic solvent may include, for example, at least one of carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, and aprotic solvents. The organic solvent may be one or more selected from, for example, propylene carbonate, ethylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, vinylene carbonate, methyl acetate, ethyl acetate, n-propyl acetate, 1,1-dimethylethyl acetate, methyl propionate, ethyl propionate, fluoroethyl acetate, difluoroethyl acetate, trifluoroethyl acetate, dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, ethanol, isopropyl alcohol, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, γ-butyrolactone, and propylene sulfide.

[0091] The embodiments described above will be explained in more detail below with reference to the examples. However, the following examples are for illustrative purposes only and do not limit the scope of the rights.

[0092] The physical properties of the examples were measured as follows.

[0093] 1) Viscosity The kinematic viscosity of a ceramic layer-forming composition (25% solids by weight) was measured at a temperature of 25°C and a shear rate of 1 (1 / s) using a rotary rheometer (TA Corporation, Discovery HR-20) and a 60 mm diameter flat plate (TA Corporation, HA Aluminum, 60 mm Plate) spindle. The sample was loaded onto the instrument plate, and the spindle was set to a gap of 250 μm. The kinematic viscosity was measured while increasing the shear rate from 1 (1 / s) to 10,000 (1 / s).

[0094] 2) Thickness After stacking 10 layers of composite separators, the thickness was measured at room temperature and pressure using a Mitutoyo (ID-C112X) to derive the average thickness of the 10 layers of composite separators, and this average was then divided by 10 to obtain the thickness of the composite separators. The total thickness of the ceramic layer was obtained by subtracting the thickness of the porous substrate (9 μm) from the thickness of the composite separators.

[0095] 3) Adhesive strength [Cardboard Test] A composite separator was cut to a size of 5 cm x 10 cm to prepare a test specimen. A 2 cm x 10 cm black cardboard and a rubber pad were placed sequentially on the ceramic layer of the composite separator test specimen. While applying a force of 10 N to the rubber pad using a press device, the cardboard was horizontally removed at a speed of 0.1 m / s to a length of 60 mm. The adhesive strength was evaluated according to the degree to which foreign matter adhered to the surface of the cardboard. The foreign matter may be a component of the ceramic layer, such as inorganic particles, a binder, or a combination thereof.

[0096] [Evaluation of the degree of foreign matter adhesion] After the cardboard test, the surface of the cardboard was photographed with an optical camera to create an image, and the area of ​​the attached foreign matter was measured. Specifically, indirect lighting was set up with an LED lamp in the visible light range at a 60° gradient, and the cardboard was photographed with a 640M pixel optical camera at a height of 40 cm above the sample (cardboard). After loading the captured cardboard image into the ImageJ program, the crop function was used to select and cut out only the area that passed through the separator and rubber pad. The image file format of the cut-out area was then converted to an 8-bit image, and the brightness and contrast of the image were adjusted by applying a Sharpen filter to facilitate the distinction between the cardboard and the white foreign matter. A threshold was applied to the image to convert it to a binary image, and the Analyze Particles function was executed to calculate the ratio of the area occupied by the white foreign matter to the total area, and the adhesive strength was evaluated according to the following criteria.

[0097] A: <1.5% B: 1.5%~5% C:>5%

[0098] 4) Thermal shrinkage rate The thermal shrinkage rate of the composite separator was measured according to the ASTM D1204 standard, using the following method. A grid of 10cm squares with 2cm intervals was marked on the composite separator test specimen. One side of this square represented the transverse direction (TD), and the other side represented the machine direction (MD). The test specimen was positioned in the center, and five sheets of paper were placed above and below it. The four sides of the paper were wrapped with tape, and the paper-wrapped test specimen was placed in a 150°C hot air drying oven for 60 minutes. After that, the test specimen was removed, the separator was observed with a camera, and the shrinkage rates in the machine direction (MD) and the transverse direction (TD) were calculated and recorded in Table 1 below.

[0099] MD heat shrinkage rate (%) = (length of MD before heating - length of MD after heating) / length of MD before heating × 100 TD thermal shrinkage rate (%) = (TD length before heating - TD length after heating) / TD length before heating × 100

[0100] [Example 1] Average particle size in water (D 50 A slurry with a solid content of 45% by weight was prepared by mixing 100 parts by weight of 0.3 μm boehmite with 2 parts by weight of the dispersant 1,2-benzoisothiazolin-3-one (DIO2). A carboxymethyl cellulose (CMC) with a degree of substitution of 0.9 and a weight-average molecular weight of 250,000 g / mol was mixed with the prepared slurry so that the ratio was 3 parts by weight of CMC to 100 parts by weight of boehmite, and the mixture was diluted with water to a solid content of 25% by weight to prepare a composition for forming a ceramic layer.

[0101] Both sides of a 9μm thick polyethylene film (porosity 35%~45%, SKIET) were treated with corona discharge (power density 2W / m²). 2 Surface polar groups were introduced by ) and the corona surface treatment was carried out at a speed of 5 mpm (meter per minute). The ceramic layer forming composition was applied to both sides of the corona surface treated polyethylene film using a bar coating method and dried at 50°C to produce a composite separator in which ceramic layers of the same thickness were formed on both sides.

[0102] [Examples 2 and 3] The procedure was carried out in the same manner as in Example 1, except that the thickness of the ceramic layer was changed as shown in Table 1 below.

[0103] [Example 4] The procedure was carried out in the same manner as in Example 1, except that a CMC with a degree of substitution of 1.0 and a weight-average molecular weight of 200,000 g / mol was used.

[0104] [Example 5] The procedure was carried out in the same manner as in Example 1, except that a CMC with a degree of substitution of 0.7 and a weight-average molecular weight of 240,000 g / mol was used.

[0105] [Example 6] The procedure was carried out in the same manner as in Example 1, except that a CMC with a degree of substitution of 0.7 and a weight-average molecular weight of 210,000 g / mol was used.

[0106] [Comparative Example 1] The procedure was carried out in the same manner as in Example 1, except that a CMC with a degree of substitution of 0.9 and a weight-average molecular weight of 60,000 g / mol was used.

[0107] [Comparative Example 2] The procedure was carried out in the same manner as in Example 1, except that a CMC with a degree of substitution of 0.9 and a weight-average molecular weight of 150,000 g / mol was used.

[0108] [Comparative Example 3] The procedure was carried out in the same manner as in Example 1, except that a CMC with a degree of substitution of 0.9 and a weight-average molecular weight of 300,000 g / mol was used.

[0109] [Comparative Example 4] The procedure was carried out in the same manner as in Example 1, except that a CMC with a degree of substitution of 0.5 and a weight-average molecular weight of 230,000 g / mol was used.

[0110] [Comparative Example 5] The procedure was carried out in the same manner as in Example 1, except that a CMC with a degree of substitution of 1.3 and a weight-average molecular weight of 190,000 g / mol was used.

[0111] [Comparative Example 6] The procedure was carried out in the same manner as in Example 1, except that cellulose nanofiber (CNF) was used instead of carboxymethylcellulose.

[0112] [Table 1]

[0113] Referring to Table 1, it can be seen that the composite separator according to one embodiment of the present invention contains carboxymethylcellulose as a binder that simultaneously satisfies a weight-average molecular weight of 180,000 to 280,000 g / mol and a degree of substitution of 0.6 to 1.2, resulting in excellent adhesion not only between the interface between the substrate and the ceramic film layer, but also between inorganic particles within the ceramic layer, excellent heat resistance, and effective suppression of thermal shrinkage. An electrochemical element employing the composite separator according to one embodiment can ensure heat resistance and safety, and can be advantageous for increasing capacity and output.

[0114] On the other hand, in the case of the composite separators of Comparative Examples 1 to 5, which contained carboxymethylcellulose that deviated from the weight-average molecular weight and / or degree of substitution range, it was confirmed that the ceramic layer coating itself was impossible, or that the adhesive strength and thermal shrinkage rate were significantly reduced. In the case of the composite separator of Comparative Example 6, which used cellulose nanofiber instead of CMC, it was confirmed that both the adhesive strength and thermal shrinkage rate were significantly reduced.

[0115] The composite separator disclosed herein is widely applicable in green technology fields such as electric vehicles, battery charging stands, and other battery-powered solar and wind power generation. Furthermore, the separator disclosed herein can be used in eco-friendly electric vehicles, hybrid vehicles, and other applications that reduce air pollution and greenhouse gas emissions to prevent climate change.

[0116] Although this disclosure has been described through specific matters and limited embodiments, these are provided to facilitate a more general understanding of the disclosure, and the disclosure is not limited to the embodiments described above. Various modifications and variations can be made from such descriptions by a person with ordinary skill in the art to which the disclosure pertains.

[0117] Therefore, this disclosure should not be limited to the embodiments described above, and it can be said that not only the claims described later, but also all variations that are equivalent or comparable to the claims described herein, fall within the scope of this disclosure.

Claims

1. A composite separator comprising a porous substrate and a ceramic layer formed on one or both sides of the substrate, the ceramic layer containing inorganic particles and a binder, The binder is a composite separator comprising carboxymethylcellulose having a weight-average molecular weight of 180,000 to 280,000 g / mol and a degree of substitution of 0.6 to 1.

2.

2. The composite separator according to claim 1, wherein the carboxymethylcellulose has a weight-average molecular weight of 200,000 to 250,000 g / mol.

3. The composite separator according to claim 1, wherein the carboxymethylcellulose has a degree of substitution of 0.7 to 1.

0.

4. The composite separator according to claim 1, comprising 0.1 to 10 parts by weight of a binder per 100 parts by weight of the inorganic particles.

5. The composite separator according to claim 1, wherein the binder contains 70% by weight or more of carboxymethylcellulose based on the total weight of the binder.

6. The composite separator according to claim 1, wherein the binder is composed of carboxymethylcellulose.

7. The inorganic particles are boehmite, BaSO ４ , CeO ２ , MgO, CaO, ZnO, Al ２ O ３ , TiO ２ , BaTiO ３ , HfO ２ , SrTiO ３ , SnO ２ , NiO, ZrO ２ , Y ２ O ３ ; and are one or more selected from SiC. The composite separator according to claim 1.

8. The composite separator according to claim 1, wherein the average particle size of the inorganic particles is 0.1 μm to 1.0 μm.

9. The composite separator according to claim 1, wherein the porous substrate is subjected to a hydrophilic surface treatment.

10. The composite separator according to claim 1, wherein the total thickness of the ceramic layer is 0.5 μm to 10 μm.

11. The composite separator according to claim 1, wherein the thermal shrinkage rates in the MD direction and TD direction, measured after leaving the composite separator at 150°C for 60 minutes, are both 4% or less.

12. The composite separator according to claim 1, wherein, after a cardboard test, when the degree of foreign matter adhesion to the surface of the cardboard is evaluated, the ratio of the area occupied by the foreign matter to the area of ​​the cardboard is 5% or less. [Cardboard Test] A 2cm x 10cm black cardboard and a rubber pad are placed sequentially on the ceramic layer of a 5cm x 10cm composite separator test piece. A force of 10N is applied to the rubber pad using a press device, and the cardboard is horizontally removed at a speed of 0.1m / s. The degree to which foreign matter adheres to the surface of the cardboard is then tested.

13. The process includes the step of applying a ceramic layer-forming composition containing a binder and inorganic particles to one or both sides of a porous substrate, drying it, and forming a ceramic layer. A method for producing a composite separator, wherein the binder comprises carboxymethylcellulose having a weight-average molecular weight of 180,000 to 280,000 g / mol and a degree of substitution of 0.6 to 1.

2.

14. An electrochemical element comprising a positive electrode, a negative electrode, and a composite separator, The composite separator is an electrochemical element comprising a porous substrate and a ceramic layer formed on one or both sides of the substrate, comprising inorganic particles and a binder, wherein the binder comprises carboxymethylcellulose having a weight-average molecular weight of 180,000 to 280,000 g / mol and a degree of substitution of 0.6 to 1.2.

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