Separator and secondary battery comprising same

Abstract

The present disclosure relates to a separator and a secondary battery including the same, the separator including a porous substrate and an inorganic particle layer including inorganic particles on at least one surface of the porous substrate, the inorganic particle layer having a surface roughness (Ra) of 100 nm to 160 nm. The separator according to one embodiment of the present invention has the aforementioned surface roughness, and thus can improve the heat resistance, charge / discharge characteristics, and life characteristics of a battery.

Description

Technical Field

[0001] The present disclosure relates to a separator and a secondary battery including the same. Background Art

[0002] Among electrochemical components, battery separators are crucial for improving battery stability, lifespan, and performance. The separator's primary function is to provide a pathway for ion movement within the battery and prevent physical contact between the negative and positive electrodes. Improving separator properties can lead to the production of superior battery performance.

[0003] To improve the properties of battery separators, multilayer separators are formed by laminating porous polymers such as polyolefins and polypropylene, or separators with a porous polymer base and a coating formed by mixing binders and inorganic particles have been developed. Compared to single-layer separators, multilayer separators or coatings mixed with binders can improve various separator properties, but they may increase separator thickness and have low permeability, reduced wettability, and poor impregnation, which may lead to a decrease in battery performance. To address this issue, research is underway to produce separators with various properties suitable for battery separators, thin thickness, and sufficient mechanical and chemical stability to improve battery performance. Summary of the Invention

[0004] Technical issues

[0005] An object of one embodiment is to provide a separator having excellent heat resistance, charge and discharge characteristics, and life characteristics.

[0006] Another embodiment provides a secondary battery comprising the separator.

[0007] Technical Solution

[0008] One implementation example provides a membrane including a porous substrate and an inorganic particle layer, wherein the inorganic particle layer is located on at least one side of the porous substrate and contains inorganic particles, and the surface roughness (Ra) of the inorganic particle layer is 100 nm to 160 nm.

[0009] Another embodiment provides a secondary battery including the separator of the one embodiment.

[0010] Effects of the Invention

[0011] The present disclosure relates to a separator comprising a porous substrate and an inorganic particle layer comprising inorganic particles on at least one side of the porous substrate, wherein the inorganic particle layer has a surface roughness (Ra) of 100 nm to 160 nm. The separator of one embodiment having such a surface roughness can improve the heat resistance, charge-discharge characteristics, and lifespan of a battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The structure of a diaphragm according to one embodiment is schematically illustrated.

[0013] Description of reference numerals:

[0014] 100: Diaphragm

[0015] 10: Porous substrate

[0016] 20: Inorganic particle layer DETAILED DESCRIPTION

[0017] The embodiments described in this specification may be modified into various other forms, and therefore, the technology of one implementation example is not limited to the embodiments described below. In addition, throughout this specification, unless otherwise specified, the phrases "comprising, including, containing," "having," "containing," or "having" a component indicate that other components may also be included, rather than excluding other components, and do not exclude elements, materials, or processes not further listed.

[0018] Numerical ranges used in this specification include lower and upper limits, all values ​​within the range, increments logically derived from the form and magnitude of the defined range, all values ​​defined in pairs, and all possible combinations of upper and lower limits of numerical ranges defined in different ways. For example, if the content of a component is defined as 10% to 80% or 20% to 50%, it should be interpreted that the numerical range of 10% to 50% or 50% to 80% is also included in this specification. Unless otherwise specified in this specification, values ​​outside the numerical range that may occur due to experimental error or rounding are also included in the defined numerical range.

[0019] Hereinafter, unless otherwise defined herein, "about" may be considered to be a value within 30%, 25%, 20%, 15%, 10%, 5%, 3%, 2%, 1% or 0.5% of a given value.

[0020] Hereinafter, unless otherwise defined in the present specification, "(meth)acrylic acid" means acrylic acid and / or methacrylic acid.

[0021] Unless otherwise defined in this specification, the average particle size of inorganic particles refers to D 50 value.

[0022] Unless otherwise defined in this specification, when a layer, membrane, film, region, plate or the like is described as being “on” or “over” another part, this includes not only the case where it is “directly above” the other part, but also the case where there are other parts between the two parts.

[0023] Unless otherwise defined in this specification, "polymer" refers to a molecule of relatively high molecular weight, the structure of which may include multiple repetitions of units derived from molecules of low molecular weight. In one embodiment, the polymer may be an alternating copolymer, a block copolymer, a random copolymer, a graft copolymer, a gradient copolymer, a branched copolymer, a crosslinked copolymer, or a copolymer comprising all of these (e.g., a polymer comprising more than one monomer). In another embodiment, the polymer may be a homopolymer (e.g., a polymer comprising one monomer).

[0024] An implementation example provides a diaphragm that has high heat resistance and can suppress the degradation of battery performance during the charge and discharge process. Specifically, the diaphragm 100 according to an implementation example is characterized in that it includes a porous substrate 10 and an inorganic particle layer 20 located on at least one side of the porous substrate and containing inorganic particles. In this case, the surface roughness (Ra) of the inorganic particle layer is 100nm to 160nm. For the first time, it was recognized that the inorganic particle layer included in the diaphragm according to an implementation example satisfies the surface roughness (Ra) of 100nm to 160nm, so that during the charge and discharge process of the battery, lithium ions can move evenly, and at the same time, the side reaction problem caused by moisture can be effectively suppressed, thereby making an invention.

[0025] The effect described above is achieved by adjusting the surface roughness (Ra) of the inorganic particle layer to 100 nm to 160 nm, and is not solely affected by the components of the separator or any specific factors during the separator manufacturing process. As confirmed in one embodiment, this effect can be achieved in a variety of ways, including various factors such as the average particle size of the inorganic material, the solid content of the slurry, and the coating speed. Therefore, there is no limitation on how the surface roughness (Ra) of the inorganic particle layer is achieved.

[0026] Therefore, regardless of the average particle size or distribution or combination of the inorganic matter, regardless of the manufacturing conditions of the diaphragm, that is, the content and type of binder, dispersant, lubricant, slurry solid content, rotation speed and / or bead size during slurry preparation, whether a smoothing bar is used, drying temperature, regardless of the porous substrate, regardless of the type of electrolyte of the battery, as long as the surface roughness (Ra) of the inorganic particle layer of the one implementation example is met, the heat resistance of the diaphragm is excellent, and the life characteristics and charge and discharge characteristics of the battery manufactured using the diaphragm are excellent.

[0027] In one embodiment, the surface roughness (Ra) of the diaphragm may be 100 nm to 160 nm, 110 nm to 150 nm, 120 nm to 140 nm, or an average of about 130 nm. In one embodiment, the surface roughness (Ra) value of the diaphragm may be the surface roughness value of the fresh diaphragm before cyclic driving.

[0028] In one embodiment, the inorganic particles included in the inorganic particle layer are not particularly limited in type as long as they are electrochemically stable, known inorganic particles. For example, the inorganic particles may include at least one of boehmite, CeO2, MgO, CaO, ZnO, Al2O3, TiO2, BaTiO3, HfO2, SrTiO3, SnO2, NiO, ZrO2, Y2O3, and / or SiC.

[0029] In one embodiment, the average particle size (D 50 ) As long as the surface roughness range of the diaphragm according to an implementation example can be met, it can be appropriately selected according to the experimental conditions and purpose, and is not necessarily limited to a specific range. For example, the average particle size of the inorganic particles can be 0.01 μm to 10.0 μm, 0.01 μm to 5.0 μm, 0.1 μm to 3.0 μm, 0.05 μm to 2.0 μm, or 0.1 μm to 1.0 μm. The average particle size (D) of the inorganic particles was measured using a particle size analyzer (Microtrac, Microtrac S3500) according to ISO standard specifications (ISO13320-1). 50 ).

[0030] Alternatively, the inorganic particles may be mixed with one, two, three or more inorganic particles having different average particle sizes. For example, a first inorganic particle having an average particle size of 0.1 μm to 0.6 μm, 0.1 μm to 0.5 μm or about 0.3 μm; a second inorganic particle having an average particle size of 0.3 μm to 1.0 μm, 0.5 μm to 1.0 μm or about 0.7 μm; and any one or more of a third inorganic particle having an average particle size of 1.0 μm to 3.0 μm, 1.0 μm to 2.0 μm or about 1.6 μm may be mixed for use. For example, the inorganic particles may include first inorganic particles and second inorganic particles, or include first inorganic particles and third inorganic particles. In this case, the first inorganic particles, the second inorganic particles and the third inorganic particles may be the same inorganic particles or different inorganic particles.

[0031] In one embodiment, when using inorganic particles having two different average particle sizes, the weight ratio thereof is not particularly limited, but, for example, can be mixed according to 20:80 to 80:20, 30:70 to 70:30, 50:50 to 80:20, 70:30 or 50:50. For example, the inorganic particles may include the first inorganic particles and the second inorganic particles in a weight ratio of 30:70 to 80:20, 50:50 to 80:20, 60:40 to 80:20 or about 70:30. Alternatively, the inorganic particles may include the first inorganic particles and the third inorganic particles in a weight ratio of 30:70 to 70:30, 40:60 to 60:40 or about 50:50. However, this is only an example, and therefore the inorganic particles should not be mixed according to the above weight ratios. In this case, the first inorganic particles, the second inorganic particles and the third inorganic particles can be the same inorganic particles or different inorganic particles.

[0032] In one embodiment, the inorganic particle layer may further include an adhesive. For the adhesive, an adhesive known to those skilled in the art of the art disclosed in this application may be appropriately selected according to the purpose and circumstances. In one embodiment, the adhesive may include a polymer, for example, it may include any one or more of the group consisting of ester polymers, amide polymers, imide polymers, acrylic polymers, acrylamide polymers, vinyl alcohol polymers, fluorine polymers and / or vinyl pyrrolidone polymers. In one embodiment, the adhesive may include an acrylamide polymer. Or for example, the adhesive may include a polymer made of any one or more monomers in (meth) acrylamide monomers, hydroxyl-containing (meth) acrylic monomers and / or multifunctional (meth) acrylamide monomers, as long as the inorganic particles formed on the surface of the porous substrate layer of the secondary battery separator are connected to each other by an adhesive to form an inorganic particle layer of pores, the material is not limited.

[0033] In one embodiment, the content of the binder can be appropriately adjusted according to the situation and purpose within the range of 100 nm to 160 nm in the surface roughness (Ra) of the inorganic particle layer. For example, relative to 100 parts by weight of the inorganic particles, the content of the binder can be 0.1 to 20.0 parts by weight, 0.1 to 15.0 parts by weight, 1.0 to 10.0 parts by weight, 1.0 to 5.0 parts by weight, or about 3.0 parts by weight.

[0034] In one embodiment, the weight average molecular weight (Mw) of the adhesive (or the polymer contained in the adhesive) can be 10000 g / mol to 2000000 g / mol, 50000 g / mol to 2000000 g / mol, 50000 g / mol to 1000000 g / mol, 50000 g / mol to 500000 g / mol, 50000 g / mol to 300000 g / mol, 100000 g / mol to 300000 g / mol or about 150000 g / mol, but this is only an example, as long as the surface roughness range of the diaphragm according to the present application can be met, it can be appropriately selected according to experimental conditions. The weight average molecular weight can be measured by gel permeation chromatography (GPC). The weight-average molecular weight can be measured by GPC (Tosoh Corporation, EcoSEC HLC-8320GPC Refractive Index detector) using two columns, TSKgel GMPWxl and TSKgel G2500PWxl (7.8×300 mm), as TSKgel guard PWx, GPC columns, 0.1 M NaNO3 aqueous solution as the developing solvent, polyethylene glycol as the standard, and analysis at a flow rate of 1 mL / min at 40°C.

[0035] In one embodiment, the porous substrate is not limited as long as it is commonly used in the field, and can be, for example, a woven fabric, a non-woven fabric, or a porous film. Specifically, the porous substrate can be made of polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyetheretherketone, polyaryletherketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cycloolefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, and / or polytetrafluoroethylene, or any two or more thereof.

[0036] In one embodiment, the thickness of the porous substrate is not particularly limited, and for example, may be 1 μm to 100 μm, 1 μm to 50 μm, 1 μm to 30 μm, 5 μm to 20 μm, or about 9 μm.

[0037] In one embodiment, the thickness of the inorganic particle layer formed on either side of the porous substrate can be, for example, 0.1 μm to 10.0 μm, 0.1 μm to 5.0 μm, 0.5 μm to 3.0 μm, 1.0 μm to 2.0 μm, or about 1.5 μm. If the inorganic particle layer is formed on both sides of the porous substrate, its thickness can be 0.2 μm to 15.0 μm, 0.3 μm to 10.0 μm, 1.0 μm to 8.0 μm, 2.0 μm to 5.0 μm, or about 3.0 μm.

[0038] In one embodiment, the coating density of the inorganic particle layer can be 0.8 g / (m 2 ·μm) or more, in this case, the upper limit can be 3.0g / (m 2 Specifically, the coating density can be 1.0 g / (m 2 ·μm) to 3.0g / (m 2 ·μm)、1.0g / (m 2 ·μm) to 2.0g / (m 2 ·μm)、1.0g / (m 2 ·μm) to 1.5g / (m 2 ·μm)、1.1g / (m 2 ·μm) to 1.4g / (m 2 ·μm) or 1.1g / (m 2 ·μm) to 1.3g / (m 2 The coating density is defined as the inorganic particle layer per unit area (m 2 The value obtained by dividing the weight (g) of the inorganic particle layer by the thickness (μm) of the inorganic particle layer.

[0039] In one embodiment, after the separator is placed at 150° C. for 60 minutes, both the machine direction (MD) shrinkage and the transverse direction (TD) shrinkage may be 5.0% or less. In this case, the lower limit may be 5.0%. Specifically, the shrinkage may be 0.5% to 5.0%, 1.0% to 4.0%, or 1.0% to 3.0%.

[0040] In one embodiment, the air permeability (Gurley air permeability) of the separator measured according to ASTM D726 may be 150 s / 100 cc to 190 s / 100 cc, 160 s / 100 cc to 175 s / 100 cc, or 160 s / 100 cc to 170 s / 100 cc.

[0041] In one embodiment, the membrane is dried at 80°C for 12 hours in a drying room with a dew point of -40°C or less, placed in a drying room for 30 minutes, and then heated at 150°C. The moisture content measured can be 300ppm to 1000ppm, 550ppm to 800ppm, 550ppm to 700ppm, or 580ppm to 680ppm. In one embodiment, the moisture content can be measured by the following method. In order to determine the moisture content, the membrane is first dried. Drying is carried out in a drying room with a dew point of -40°C and dried in a convection oven at 80°C for 12 hours. Then, the membrane is taken out of the oven and stored in a drying room for 30 minutes. Afterwards, 0.3g of the dried membrane is collected, and the amount of moisture produced is measured while the sample is heated at 150°C according to the Karl Fischer moisture determination method using a moisture meter (Metrohm, 917 Coulometer).

[0042] According to one embodiment, the thermal shrinkage of the diaphragm having a surface roughness (Ra) of 100 nm to 160 nm is low, the filling density and air permeability of the inorganic matter are at the most suitable level for achieving diaphragm performance and battery performance, and the moisture content is low. As a result, the charge and discharge performance and life characteristics of the battery are excellently achieved. On the other hand, when the surface roughness (Ra) of the diaphragm is higher than 160 nm, the inorganic matter is not well filled, so the air permeability, moisture content, and initial resistance are low, but the lithium ions cannot move evenly during the charge and discharge process of the battery, so the performance may be degraded. Moreover, when the surface roughness (Ra) of the diaphragm is lower than 100 nm, the inorganic matter is too densely filled, and the air permeability, moisture content, and initial resistance are high, so the performance may be degraded due to the side reaction problem caused by moisture during the charge and discharge process of the battery.

[0043] When a secondary battery manufactured using a diaphragm according to an embodiment is charged and discharged for 600 cycles, the rate of change of the surface roughness (Ra) of the diaphragm may be less than 30%, less than 20% or less than 15%, and may be 1% to 20%, 5% to 20%, 5% to 15%, 10% to 15% or 10% to 13%. In this case, the rate of change is an absolute value, and the absolute value is calculated by {│(surface roughness (Ra) after 600 cycles)-(initial surface roughness (Ra))│} / (initial surface roughness (Ra)). When the surface roughness (Ra) value of the diaphragm according to an embodiment meets the requirement of 100nm to 160nm and the change value after 600 cycles of battery charge and discharge meets the requirement of less than 30%, better battery performance can be achieved.

[0044] According to one embodiment, a diaphragm having a surface roughness (Ra) of 100 nm to 160 nm can be manufactured by the steps of preparing a composition for forming an inorganic particle layer containing inorganic particles; and forming an inorganic particle layer by coating (or applying) the composition for forming an inorganic particle layer on at least one side of a porous substrate and then drying it.

[0045] In one embodiment, the solvent used in the composition for forming the inorganic particle layer is not particularly limited. In the case where the composition includes a binder, a solvent that is easy to dissolve or disperse the binder can be selected. For example, water, acetone, ethanol, tetrahydrofuran, methylene chloride (methylene chloride), trifluoromethane (fluoroform), cyclohexane, dimethylformamide and / or N-methyl-2-pyrrolidone can be used.

[0046] In one embodiment, the composition for forming the inorganic particle layer may be a slurry. For example, the solid content of the slurry may be 15 wt % to 40 wt %, 20 wt % to 40 wt %, or 20 wt % to 35 wt %.

[0047] In one embodiment, the method of applying or coating the composition for forming an inorganic particle layer onto a porous substrate is not particularly limited, and for example, roll coating, spin coating, dip coating, bar coating, die coating, slit coating or inkjet printing can be used.

[0048] In one embodiment, the drying can be performed by drying with warm air, hot air, low-humidity air, vacuum drying, or irradiation with far infrared rays or electron beams. The drying temperature is not particularly limited and can be appropriately adjusted according to the experimental environment or purpose. For example, it can be 30° C. to 120° C., 30° C. to 100° C., 30° C. to 50° C., or about 45° C.

[0049] As described above, the surface roughness (Ra) of the diaphragm according to one embodiment can be achieved in a variety of ways, and can thus be adjusted by the size of the inorganic particles, the distribution of the inorganic particles, the type and content of the adhesive, the solid content of the slurry, the slurry preparation conditions, the slurry viscosity, the drying conditions (temperature, speed), the coating speed, the leveling method using a smoothing rod, etc.

[0050] Another implementation example provides a secondary battery including the separator according to one of the above embodiments.

[0051] In one embodiment, the capacity change rate of the secondary battery after 100 charge and discharge cycles may be less than 20%, less than 10%, less than 9%, less than 8%, or less than 7%, and may be between 2% and 10%, between 3% and 8%, or between 4% and 5%. In this case, the capacity change rate is an absolute value, which is calculated by {|(capacity after 100 cycles)-(initial capacity)|} / (initial capacity).

[0052] Hereinafter, the components of the secondary battery according to the present disclosure will be further described.

[0053] [positive electrode]

[0054] The positive electrode may include a positive electrode current collector and a positive electrode mixture layer disposed on at least one surface of the positive electrode current collector.

[0055] (Positive electrode current collector)

[0056] The positive electrode current collector may comprise stainless steel, nickel, aluminum, titanium, or alloys thereof. Alternatively, the positive electrode current collector may comprise aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. The positive electrode current collector may be, for example, 10 μm to 50 μm, but is not limited thereto.

[0057] (Cathode Material)

[0058] The positive electrode mixture layer may include a positive electrode active material. The positive electrode active material may include a compound capable of reversibly intercalating and deintercalating lithium ions.

[0059] According to an exemplary embodiment, any conventionally used positive electrode active material may be used without limitation. For example, the positive electrode active material may include lithium nickel metal oxide. The lithium nickel metal oxide may further include at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0060] The positive electrode active material may further include a coating element or a doping element. For example, an element substantially identical to or similar to the auxiliary element may be used as the coating element or doping element. For example, a single element or a combination of two or more of the above elements may be used as the coating element or doping element.

[0061] The positive active material may include a nickel-cobalt-manganese (NCM)-based lithium oxide. In this case, an NCM-based lithium oxide with an increased nickel content may be used.

[0062] The Ni content of the NCM-based lithium oxide (e.g., the mole fraction of nickel in the total moles of nickel, cobalt, and manganese) may be greater than 0.6, greater than 0.7, or greater than 0.8. In some embodiments, the Ni content may be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95.

[0063] In some embodiments, the positive electrode active material may also include a lithium cobalt oxide-based active material, a lithium manganese oxide-based active material, a lithium nickel oxide-based active material, or a lithium iron phosphate (LFP)-based active material (eg, LiFePO 4 ).

[0064] (Manufacturing Method of Positive Electrode)

[0065] For example, the positive electrode slurry can be prepared by mixing the positive electrode active material in a solvent. The positive electrode mixture layer can be manufactured by coating the positive electrode slurry on the positive electrode current collector, drying and rolling. The coating process can be carried out by gravure coating, slit die coating, multi-layer simultaneous die coating, stamping, doctor blade coating, dip coating, bar coating, casting and other processes, but is not limited thereto. The positive electrode mixture layer may further include a binder and may optionally include a conductive material, a thickener and the like.

[0066] (Cathode Solvent)

[0067] Non-limiting examples of the solvent used to prepare the positive electrode mixture include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, and the like.

[0068] (Positive electrode binder)

[0069] The binder may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-hexafluoropropylene (PVDF), polyacrylonitrile, polymethyl methacrylate, acrylonitrile-butadiene rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. In one embodiment, a PVDF series binder can be used as a positive electrode binder.

[0070] (Positive electrode conductive material)

[0071] The conductive material may be added to improve the conductivity of the positive electrode mixture layer and / or the mobility of lithium ions or electrons. For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), and carbon fiber, and / or metal-based conductive materials such as perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3, but is not limited thereto.

[0072] (Positive electrode thickener / dispersant)

[0073] As needed, the positive electrode mixture may further include a thickener and / or a dispersant, etc. As an example, the positive electrode mixture may include a thickener such as carboxymethyl cellulose (CMC).

[0074] [negative electrode]

[0075] The negative electrode may include a negative electrode current collector and a negative electrode mixture layer disposed on at least one surface of the negative electrode current collector.

[0076] (Negative electrode current collector)

[0077] Non-limiting examples of the negative electrode current collector include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, and a polymer substrate coated with a conductive metal. The negative electrode current collector may be, for example, 10 to 50 μm, but is not limited thereto.

[0078] (Anode material)

[0079] The negative electrode mixture layer may include a negative electrode active material. The negative electrode active material may be a material capable of adsorbing and desorbing lithium ions. For example, the negative electrode active material may include carbon materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fibers; lithium metal; lithium alloys; silicon (Si)-containing materials; or tin (Sn)-containing materials.

[0080] Examples of the amorphous carbon include hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), and mesophase pitch-based carbon fibers (MPCF).

[0081] Examples of the crystalline carbon include graphite-based carbon such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, and graphitized MPCF.

[0082] The lithium metal may be, for example, pure lithium metal or lithium metal with a protective layer formed thereon for suppressing dendrite growth or the like. In one embodiment, the lithium metal-containing layer deposited or coated on the negative electrode current collector may be used as the negative electrode active material layer. In one embodiment, the lithium thin film layer may also be used as the negative electrode active material layer.

[0083] Examples of the elements contained in the lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, etc.

[0084] The silicon-containing material may provide further enhanced capacitance characteristics. The silicon-containing material may include silicon (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, and metal-doped SiO x (0 < x < 2) may include metal silicates.

[0085] (Method for manufacturing the negative electrode)

[0086] For example, the negative electrode paste may be prepared by mixing the negative electrode active material in a solvent. After coating / depositing the negative electrode paste on the negative electrode current collector, drying and calendering are performed to manufacture the negative electrode mixture layer. The coating process may be carried out by processes such as gravure coating, slot die coating, multi-layer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, casting, etc., but is not limited thereto. The negative electrode mixture layer may further contain an adhesive, and may also optionally contain a conductive material, a thickener, etc.

[0087] In some embodiments, the negative electrode may also include a negative electrode active material layer in the form of lithium metal formed by a deposition / coating process.

[0088] (Negative electrode solvent)

[0089] Non-limiting examples of the solvent for the negative electrode mixture include water, pure water, deionized water, distilled water, ethanol, isopropyl alcohol, methanol, acetone, n-propanol, tert-butanol, etc.

[0090] (Negative electrode adhesive / conductive material / thickener)

[0091] The above substances that can be used in manufacturing the positive electrode may be used as the adhesive, conductive material, and thickener. <�

[0092] In some embodiments, styrene-butadiene rubber (SBR)-based binders, carboxymethyl cellulose (CMC), polyacrylic acid-based binders, poly(3,4-ethylenedioxythiophene) (PEDOT)-based binders, etc. can be used as the negative electrode binder.

[0093] [Electrode assembly]

[0094] According to exemplary embodiments, the positive electrode, the negative electrode, and the separator may be repeatedly arranged to form an electrode assembly. In some embodiments, the electrode assembly may be in a winding, stacking, z-folding, or stack-folding configuration.

[0095] [Electrolytes]

[0096] The electrode assembly may be housed in a housing together with an electrolyte to define a lithium secondary battery. According to an exemplary embodiment, a non-aqueous electrolyte may be used as the electrolyte.

[0097] (lithium salt / organic solvent)

[0098] The non-aqueous electrolyte includes a lithium salt as an electrolyte and an organic solvent. + X - Indicates that, as the negative ion of the lithium salt (X - ), can be an example of 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 - wait.

[0099] The organic solvent may include an organic compound that has sufficient solubility for the lithium salt and additives and is non-reactive within the battery. For example, the organic solvent may include at least one of a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, an alcohol solvent, and an aprotic solvent. As the organic solvent, for example, propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methylpropyl carbonate, ethylpropyl carbonate, dipropyl carbonate, vinylene carbonate, methylacetate (MA), ethyl acetate (EA), n-propylacetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), fluoroethyl acetate (FEA), difluoroethyl acetate (DFEA), trifluoroethyl acetate (TFEA), dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DME), dimethylether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), 2-methyltetrahydrofuran, ethanol, isopropyl alcohol, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, γ-butyrolactone, and propylene sulfite. These can be used alone or in combination of two or more.

[0100] (additive)

[0101] The non-aqueous electrolyte may further include additives. For example, the additives may include cyclic carbonate compounds, fluorine-substituted carbonate compounds, sultone compounds, cyclic sulfate compounds, cyclic sulfite compounds, phosphate compounds, and borate compounds. The cyclic carbonate compounds may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), etc. The fluorine-substituted cyclic carbonate compounds may include fluoroethylene carbonate (FEC), etc. The sultone compounds may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, etc. The cyclic sulfate compounds may include 1,2-ethylene sulfate, 1,2-propylene sulfate, etc. The cyclic sulfite compound may include ethylene sulfite, butylene sulfite, etc. The phosphate compound may include lithium difluoro bis-oxalato phosphate, lithium difluoro phosphate, etc. The borate compound may include lithium bis(oxalate)borate, etc.

[0102] The following will describe embodiments and experimental examples in detail. However, since the embodiments and experimental examples described below only illustrate a part of one implementation, the technology described in this specification should not be interpreted as being limited thereto.

[0103] <Experimental Methods>

[0104] 1. Determination of surface roughness (Ra)

[0105] The fabricated membrane was cut into 1 cm squares and fixed to a glass slide using double-sided tape. The roughness was measured using atomic force microscopy (Bruker, Icon). The measurement mode was tapping mode, using a TESPA-V2 tip, a scan speed of 1.0 Hz, and a resolution of 256.

[0106] 2. Determination of coating density

[0107] The weight per unit area (g / m 2 ) divided by the thickness of the inorganic particle layer (μm) to calculate (unit: g / (m 2 ·μm)).

[0108] 3. Determination of air permeability

[0109] Air permeability (Gurley air permeability) was measured using a Densometer (Toyoseiki Ltd.) according to ASTM D726, and the time required for 100 cc of air to pass through 1 square inch of the membrane was recorded in seconds.

[0110] 4. Determination of thermal shrinkage

[0111] The manufactured separator was cut into 10 cm squares and marked in the machine direction (MD) and transverse direction (TD). The sample was placed in the center, five sheets of paper were placed above and below the sample, and the four sides of the paper were wrapped with tape. The paper-wrapped sample was placed in a hot air drying oven at 150°C for 60 minutes. The sample was then removed, and the separator was measured with a camera. The shrinkage in the machine direction (MD) was calculated using the following formula 1, and the shrinkage in the transverse direction (TD) was calculated using the following formula 2.

[0112] [Mathematical formula 1]

[0113] Machine direction (MD) shrinkage (%) = (machine direction length before heating - machine direction length after heating) × 100 / machine direction length before heating

[0114] [Mathematical formula 2]

[0115] Transverse direction (TD) shrinkage (%) = (transverse length before heating - transverse length after heating) × 100 / transverse length before heating

[0116] 5. Determination of moisture content

[0117] To determine moisture content, the membrane was first dried in a drying room with a dew point of -40°C and then in a convection oven at 80°C for 12 hours. The membrane was then removed from the oven and stored in the drying room for 30 minutes. Afterwards, 0.3 g of the dried membrane was sampled and the amount of moisture generated was measured using a moisture analyzer (Metrohm 917 Coulometer) using the Karl Fischer method while heating the sample at 150°C.

[0118] 6. Determination of initial and 100-cycle driving performance

[0119] The secondary battery resistance (DC-IR) was evaluated using the J-pulse (Japan Electric Vehicle Association Standards, JEVSD 713) method, which evaluates 10-second charge and discharge characteristics at 0.25C, 0.5C, 1.0C, 1.5C, 2.0C, and 2.5C. The initial resistance value was calculated by averaging the impedance of three batteries using this method.

[0120] For DC-IR and capacity after 100 cycles, from 2.7V (constant current) to 4.3V (constant current constant voltage), the first cycle was charged and discharged at 0.1C, the second cycle was charged and discharged at 0.2C, and then from the third cycle onwards, the charge and discharge was carried out at 0.5C. After 100 cycles, the DC-IR after 100 cycles (100 cycles) was measured using the J pulse method in the same way as the initial resistance, and the capacity at this time was measured.

[0121] 7. Determination of surface roughness after 600 driving cycles

[0122] After 600 cycles in the same manner as in item 6 above, the battery was discharged three times until the voltage reached 2.7 V, and the bag was then removed. The battery was then washed with dimethyl carbonate and dried thoroughly in an 80°C oven for one week. Surface roughness was then measured in the same manner as in item 1.

[0123] 8. Determination of thickness

[0124] Thickness of separator: After laminating 10 separators, the thickness was measured at 5 random points in the width direction using a thickness gauge produced by Mitutoyo. The average thickness of the 10 separators was calculated and divided by 10 to obtain the average thickness of the entire separator.

[0125] Thickness of porous film: Regarding the average thickness of the porous film, after stacking 10 layers of porous films, the thickness was measured at any five points in the width direction using a thickness meter from Mitutoyo. The average thickness of the 10 layers of porous films was then derived and divided by 10 to obtain the average thickness of a single porous film.

[0126] The thickness of the inorganic particle layer is determined by subtracting the average thickness of the individual porous thin films from the overall average thickness of the individual separators obtained in the above manner.

[0127] 9. Determination of weight average molecular weight

[0128] The weight-average molecular weight was determined using GPC (Tosoh EcoSEC HLC-8320GPC Reflective Index detector). The GPC columns used were TSKgel guard PWx, two TSKgel GMPWxl, and TSKgel G2500PWxl (7.8 x 300 mm). A 0.1 M NaNO3 aqueous solution was used as the developing solvent. Polyethylene glycol was used as the standard substance. The analysis was performed at 40°C and a flow rate of 1 mL / min.

[0129] <Example 1>

[0130] Diaphragm manufacturing

[0131] Add the average particle size (D 50 ) were 300 nm and 700 nm, respectively, and 0.7 parts by weight of a dispersant, BYK-2018 (BYK GmbH), was added to 100 parts by weight of the boehmite, followed by stirring for 30 minutes to prepare an aqueous dispersion having a solid content of 45% by weight. The aqueous dispersion was then further stirred at 250 rpm for 3 minutes using a planetary mixer (bead size: 0.65 nm). Next, 3 parts by weight of polyacrylamide (Mw: 150,000 g / mol, Sigma Aldrich Inc.) was added to 100 parts by weight of the boehmite, followed by water, to prepare an aqueous slurry having a solid content of 32% by weight.

[0132] The aqueous slurry was applied to both sides of a 9-μm-thick porous polyolefin membrane (ENPASS, SK Innovation, average pore size: 40 nm) at a speed of 10 m / min, forming an approximately 1.5-μm-thick inorganic particle layer on each side. To flatten the inorganic particle layer, the membrane was passed through a non-patterned smoothing rod and then placed in a hot air dryer at 45°C to produce the separator.

[0133] Battery manufacturing

[0134] Positive electrode production: 92% by weight of lithium cobalt composite oxide (LiCoO2) as the positive electrode active material, 4% by weight of carbon black as the conductive material, and 4% by weight of polyvinylidene fluoride (PVdF) as the binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent to prepare a positive electrode mixture slurry. The prepared slurry was coated onto a 30μm thick aluminum (Al) film and dried at 120°C. A 140μm thick positive electrode was then produced by roll-pressing.

[0135] Negative electrode preparation: Graphite carbon, PVdF as a binder, and carbon black as a conductive agent were added to NMP as a solvent at 96 wt%, 3 wt%, and 1 wt%, respectively, to prepare a negative electrode mixture slurry. The prepared slurry was coated on a 20 μm thick copper film (thin film) and dried at 120°C. A 150 μm thick negative electrode was produced by roll-pressing.

[0136] The prepared separators were stacked between the positive and negative electrodes to form pouch-type cells. A 1M electrolyte solution of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / dimethyl carbonate (DMC) in a volume ratio of 3:5:2, containing lithium hexafluorophosphate (LiPF6), was injected into each cell to produce a lithium secondary battery. This resulted in a pouch-type lithium-ion secondary battery with a capacity of 80 mAh.

[0137] <Example 2>

[0138] In addition to using the average particle size (D 50 ) were used as boehmite, respectively, with a diameter of 300 nm and a diameter of 1600 nm, and a battery was manufactured in the same manner as in Example 1, except that the rotation speed was 150 rpm.

[0139] <Example 3>

[0140] A battery was manufactured in the same manner as in Example 1, except that the final solid content of the aqueous slurry was adjusted to 22 wt % in the manufacture of the separator in Example 1.

[0141] <Example 4>

[0142] A battery was manufactured in the same manner as in Example 2, except that the final solid content of the aqueous slurry was adjusted to 39 wt % in the manufacture of the separator in Example 2.

[0143] <Example 5>

[0144] A battery was manufactured in the same manner as in Example 1, except that the rotation speed was 200 rpm and the drying temperature of the hot air dryer was adjusted to 40°C.

[0145] Comparative Example 1

[0146] A battery was manufactured in the same manner as in Example 1, except that the final solid content of the aqueous slurry was adjusted to 39% by weight, the slurry was applied at a speed of 20 m / min, and no smoothing bar was used.

[0147] Comparative Example 2

[0148] A battery was manufactured in the same manner as in Example 2, except that the final solid content of the aqueous slurry was adjusted to 39% by weight, the slurry was applied at a speed of 20 m / min, and no smoothing bar was used.

[0149] Comparative Example 3

[0150] The battery was manufactured in the same manner as in Example 1, except that a rotation speed of 300 rpm was used in the manufacture of the diaphragm of Example 1, the final solid content of the aqueous slurry was adjusted to 22% by weight, the slurry was applied at a speed of 5 m per minute, and a 35°C hot air dryer was used as the dryer.

[0151] Comparative Example 4

[0152] The battery was manufactured in the same manner as in Example 2, except that a rotation speed of 300 rpm was used in the manufacture of the diaphragm of Example 2, the final solid content of the aqueous slurry was adjusted to 22 wt %, the slurry was applied at a speed of 5 m per minute, and a 35°C hot air dryer was used as the dryer.

[0153] Comparative Example 5

[0154] The battery was manufactured in the same manner as in Example 1, except that a rotation speed of 350 rpm was used in the manufacture of the diaphragm in Example 1, the final solid content of the aqueous slurry was adjusted to 39% by weight, the slurry was applied at a speed of 5 m per minute, and a 35°C hot air dryer was used as the dryer.

[0155] Comparative Example 6

[0156] A battery was manufactured in the same manner as in Example 2, except that the final solid content of the aqueous slurry was adjusted to 39% by weight, the slurry was applied at a speed of 20 m / min, and a 45°C hot air dryer was used as the dryer.

[0157] The surface roughness and physical properties of the separators produced in the examples and comparative examples were measured and are shown in Table 1 below.

[0158]

Table 1

[0159]

[0160] The performance of the batteries manufactured in the examples and comparative examples was evaluated and is shown in Tables 2 and 3 below.

[0161]

Table 2

[0162]

[0163] It can be confirmed from Table 2 that the separators of the embodiments having a surface roughness of 100 nm to 160 nm exhibit an increase in battery resistance and a decrease in capacity of less than 15% even after 100 cycles of driving. On the contrary, in the case of separators having a surface roughness value higher than 160 nm (Comparative Example 1, Comparative Example 2, Comparative Example 6) or lower than 100 nm (Comparative Example 3, Comparative Example 4, Comparative Example 5), the battery resistance increased by more than 14% and the capacity decreased by more than 10% after 100 cycles of driving.

[0164] Specifically, the separators of Comparative Examples 1, 2, and 6 have high surface roughness, resulting in an insufficiently dense packing of inorganic particles. Consequently, the separators have low air permeability and moisture content, resulting in a low initial resistance of the battery. However, the battery performance deteriorates due to the inability of lithium ions to move evenly during charge and discharge. The separators of Comparative Examples 3, 4, and 5 have low surface roughness, resulting in a relatively dense packing of inorganic particles. Consequently, the separators have high air permeability and moisture content, resulting in a high initial resistance of the battery. Side reactions caused by moisture during charge and discharge cause the battery performance to deteriorate. Conversely, the separators of Examples having a surface roughness within the range of 100 nm to 160 nm have excellent heat resistance, and batteries manufactured using these separators have high output performance and discharge efficiency, while also improving battery life.

[0165]

Table 3

[0166]

[0167] It can be confirmed from Table 3 that the diaphragm according to the embodiment still has a surface roughness change rate significantly lower than that of the comparative example after 600 cycles of charge and discharge. Therefore, it can be seen that the surface properties of the diaphragm are still maintained even after the battery is driven for a long time, and therefore the life characteristics are excellent.

[0168] Although an implementation example has been described in detail above through embodiments and experimental examples, the scope of an implementation example is not limited to the specific embodiments and should be interpreted according to the appended claims.

Claims

1. A diaphragm, comprising: Porous substrate; as well as The inorganic particle layer is located on at least one side of the porous substrate and comprises inorganic particles. The surface roughness Ra of the inorganic particle layer is 100 nm to 160 nm.

2. The diaphragm according to claim 1, wherein the inorganic particles include one or more selected from the group consisting of boehmite, CeO2, MgO, CaO, ZnO, Al2O3, TiO2, BaTiO3, HfO2, SrTiO3, SnO2, NiO, ZrO2, Y2O3 and SiC. The separator according to claim 1 , wherein the inorganic particle layer further comprises a binder. 4 . The separator according to claim 3 , wherein the binder comprises at least one selected from the group consisting of ester polymers, amide polymers, imide polymers, acrylic polymers, acrylamide polymers, vinyl alcohol polymers, fluorine polymers and vinyl pyrrolidone polymers. 5 . The separator according to claim 3 , comprising 0.1 to 20.0 parts by weight of the binder relative to 100 parts by weight of the inorganic particles. The separator according to claim 3 , wherein the binder has a weight average molecular weight of 10,000 g / mol to 2,000,000 g / mol.

7. The separator according to claim 1, wherein the inorganic particles have different average particle sizes D 50 One or more inorganic particles.

8. The separator according to claim 1, wherein the inorganic particles have an average particle size D 50 Inorganic particles of 0.05 μm to 2.0 μm. 9 . The separator according to claim 1 , wherein the inorganic particle layer has a thickness of 0.1 μm to 10.0 μm.

10. The separator according to claim 1, wherein the coating density of the inorganic particle layer is 0.8 g / (m 2 ·μm) or more. The separator according to claim 1 , wherein after the separator is left at 150° C. for 60 minutes, both the shrinkage in the machine direction (MD) and the shrinkage in the transverse direction (TD) are 5.0% or less. The separator according to claim 1, wherein the separator has a moisture content of 300 ppm to 1000 ppm when the separator is dried at 80°C for 12 hours in a drying room having a dew point of -40°C or less, left in the drying room for 30 minutes, and then heated at 150°C. 13 . The separator according to claim 1 , wherein a rate of change in surface roughness Ra of the separator is 30% or less when a secondary battery manufactured using the separator is charged and discharged for 600 cycles. 14 . A secondary battery comprising the separator according to claim 1 . 15 . The secondary battery according to claim 14 , wherein the capacity change rate of the secondary battery after 100 cycles of charge and discharge is 20% or less.

Images